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GreenChemistryCutting-edge research for a greener sustainable futurewww.rsc.org/greenchem
ISSN 1463-9262
CRITICAL REVIEWG. Chatel et al.Heterogeneous catalytic oxidation for lignin valorization into valuable chemicals: what results? What limitations? What trends?
Volume 18 Number 7 7 April 2016 Pages 1821–2242
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Shenashen, H. Yamaguchi, A. S. Alamoudi and S. El-Safty, Green Chem., 2018, DOI:
10.1039/C7GC03673F.
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Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
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Extraction and recovery of Co2+
ions from spent lithium-ion
batteries using hierarchal mesosponge γ-Al2O3 monolith
extractors
H. Gomaaa, M. A. Shenashen
a, ⃰, H. Yamaguchi
a, A. S. Alamoudi
b, S. A. El-Safty
a, c, ⃰
Visual extraction, detection, and recovery of Co2+
ions from spent lithium-ion batteries (SLIBs) via a one-step process
become a new attractive simple route for management of urban electronic wastes (e-wastes), which in turn lead to exploit
of the accumulated e-waste ideally and protect the green environment. The Co2+
ion-capture system was achieved by
selective binding with synthesized chelating agents, namely, (E)-4-((2-mercaptophenyl)diazenyl)-2-nitrosonaphthalen-1-ol
(MPDN) and (E)-5-((1,3,4-thiadiazol-2-yl)diazenyl)benzene-1,3-diol (TDDB), at controlled pH solution. The dense dressing
assembly of MPDN and TDDB into microscopic, mesospongy γ-Al2O3 monoliths enabled the design of solid/sponge Co2+
ion
extractor (IE) from SLIB leach liquor. Our recycling process of Co2+
ions from SLIBs showed evidence of (i) Co2+
ion waste
management, (ii) low-cost collection/recovery of Co2+
ions, (iii) sensitive and selective extraction of ultra-trace Co2+
ion,
and (iv) reduction of e-waste volume through multiple reusability or recyclability. Furthermore, our sponge IE design with
large surface area-to-volume ratios, macro/mesopores, and grooves along the micrometric, hierarchal monolith structures
results in a facile, naked eye monitoring of the ultra-trace Co2+
ion collection/binding to a detection limit of approximately
3.05 × 10−8
M during multifunction extraction steps from SLIBs. Our result also showed evidence of the extraction of Co2+
ions (196 mg/g) from SLIBs by a one-step process. This finding provides a basis for the control of multifunction processes
(i.e., extraction, detection, and recovery) and the high performance for selective extraction and recovery of Co2+
ions from
SLIBs in a one-step process.
Introduction
To date, given the rareness and high cost of metal sources in the
industrial sustainability, global attention is devoted to electronic
waste (e-waste) recycling as an alternative sustainable source. E-
waste is expected to increase by 33% (~72 million ton/year)
worldwide by the end of 2017; this waste includes laptops, digital
cameras, watches, cellular telephones, leisure apparatus,
pacemakers, etc.1-3
The USA alone produces approximately 400
million e-waste items annually. The European Union and Japan
wastes are about 8.9 and 4 million tons, respectively. In addition to
other gross domestic products, a total of 1.5 million tons of illegal e-
waste enter China each year. In India, the e-waste increases by 25%
annually. Developing countries are also producing large quantities
of e-wastes due to expansion in complex uses and electronic
devices. 1-3
In the past, e-waste is destroyed by milling and burial or
incineration; nevertheless, recently, the reuse of these wastes is
considered because of its economic value and the high costs of
disposal.4 Furthermore, e-waste accumulation may lead to adverse
effects on the surrounding environment and bio-systems due to
their toxic ingredients. Therefore, innovative ways to exploit these
wastes properly through recycling and extraction of their main
components should be determined.
The increasing use of electronic devices worldwide results in large
quantities of spent batteries due to number of charging and
discharging processes.5
Lithium-ion batteries (LIBs) are used to
produce power for many electronic devices, such as portable
electronics, electric vehicles, and other modern appliances; the first
LIB was marketed by Sony Corporation in Japan in 1991. 6
Approximately 500 million cells are produced worldwide in 2000,
which causes 200–500 million tons of spent LIB wastes annually. 6
The global annual production of LIBs increases by 800% between
2000 and 2010, and it is expected to increase by 2025. According to
the United Nations Environment Programme report in 2011, only
less than 1% of spent LIB (SLIB) from diverse applications is
recycled. 7
Recycling of SLIBs is a significant process to reduce the
environmental pollution and recover precious metals, such as
cobalt.8
Cobalt (Co2+
) is an important element in various industrial
applications.8 Cobalt ions can be used in LIBs as a positive
electrode,9
in magnet and alloy manufacturing,10, 11
and in
electroplating.12
Cobalt-60 is used in food preservation.13
Co2+
is
present in LIBs in a mass ratio of 5%–15%; thus, LIB is considered an
important secondary source of cobalt.14
Therefore, the present
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work aims to selectively detect and efficiently extract/recover Co2+
from SLIBs.
Many methods have been developed to extract or separate cobalt
from SLIBs;15
these methods include hydrometallurgical,16
biohydrometallurgical,17
and pyrometallurgical processes.18
Given
the high cost, slow operation, toxic gas production, and inefficiency
of biohydrometallurgical and pyrometallurgical methodologies, the
hydrometallurgical process is the most remarkable and most
suitable method. In this process, SLIB recycling requires two main
stages to recover the metal contents of SLIBs; these stages are
mechanical processes (crushing and grinding) and dissolution
processes under thermal treatment at high temperature (i.e., acid
or alkaline leaching).19, 20
Several techniques have been utilized to
detect, determine, and recognize the Co2+
content quantitatively
even at considerably low concentrations; these techniques include
inductively coupled plasma-atomic emission spectroscopy,
inductively coupled plasma-optical emission spectrometry,
inductively coupled plasma mass spectrometry (ICP-MS), graphite-
furnace atomic absorption spectrometry, and electrochemical,
potentiometric, and spectrophotometric techniques.21-27
Among
these techniques, spectrophotometric quantitative detection of
Co2+
is the most preferred due to its fast metal detection, low cost,
and simple methodology. Thus, UV-Vis detection of Co2+
ion is
becoming popular worldwide due to accurate and rapid detection,
selective determination, and highly sensitive determination of ultra-
trace concentrations.28, 29
A wide variety of physical and chemical methods, such as chemical
precipitation, ion exchange, electrochemical treatment, and reverse
osmosis, is used to remove and extract Co2+
ions from its solutions
(i.e., an aqueous solution or leach liquor).30-33
However, optical
adsorption process remains the most remarkable among these
methods due to its fast adsorption response (time-dependent
process), simple process, follow-up interaction, naked eye
observation of colour change with concentration change, suitability
in low target concentrations (i.e., sensitive process), high efficiency
in the presence of other competitive ions, high adsorption capacity,
large-scale applicability, and the possibility of recycling spent
adsorbents for consecutive times.34
Currently, several chemical optical adsorbents or extractors have
been synthesized as a new technology for many actual applications,
such as recognition, determination, and removal of metals in water
purification and e-waste management fields.35
Optical adsorbents
are still used for specific sensing, extraction, and recovery
applications for a wide range of metals.36
The most remarkable
feature of optical adsorbent or extractor approach is the qualitative
and semi-quantitative detection of target metals without using any
complicated spectroscopic instrumentation or methodology.37
Optical extractors consist of two main parts, namely, solid
carrier/substrate/platform material and organic chromophore as a
selective chelating agent, namely as indicator/ligand/probe.38
Recently, a wide range of carriers, such as metal oxides, is
developed in mesoscale architectures (2 nm < pore size < 50 nm)
and high surface area; these carriers exhibit controllable mesopore
size, shape, and surface charge, which made them promising
materials for different applications, such as separations, sensing,
extraction, and electronic systems.39-41
Mesoporous materials
facilitate material diffusion and enhance the amount of accessible
active sites.
Among metal oxides, alumina γ-Al2O3 is intensively applied in
various industries because of its favorable characteristics, such as
thermal stability, moderate Lewis acidity, and economic cost. In
addition, porous γ-Al2O3 monoliths provide a remarkably strong,
open, and tunable periodic scaffold on the nanometer scale.42, 43
Therefore, high-order mesoporous γ-Al2O3 monoliths with uniform
pore size, monodisperse porosity, and microsized particles display
promising potentials as a new class of carrier materials. The
preparation of highly stable and efficient extractors is highly
required in successful application fields.
Additionally, chromophore receptors, such as azo dyes, have been
synthesized and applied to form considerably stable complexes with
transition metal ions. Therefore, different trapped ligands on a
variety of solid matrices are successfully utilized for the removal or
extraction with a low detection limit of Co2+
ions.44
The –N=N–, –
OH, –N=O, and –SH functional groups of chromophore receptors
also play key roles in the adsorption or extraction selectivity.45
In
this report, we discuss the grafting techniques used in fabrication of
chemical optical extractors for colorimetric and visual extraction,
detection, and recovery of cobalt ions at low concentrations. These
techniques are commonly used methods to control the
immobilization of the chromogenic receptors onto solid materials.
In the present study, the (E)-4-((2-mercaptophenyl)diazenyl)-2-
nitrosonaphthalen-1-ol (MPDN) and (E)-5-((1,3,4-thiadiazol-2-
yl)diazenyl)benzene-1,3-diol (TDDB) chelating agents were
synthesized. These agents were subsequently attached to the
micro-structured mesospongy γ-Al2O3 monoliths by direct
immobilization process to produce a pair of selective, sensitive, and
efficient Co2+
ion extractors (IEs). IEs were used to extract or collect
Co2+
ions rapidly from SLIB solution even at low concentrations. Our
strategy depended on the naked eye monitoring of the colour
change of extractors. Several remarkable parameters affecting
extraction behavior, such as pH, limit of detection (LOD), contact
time, initial Co2+
concentration, and interfering ions, were
systematically investigated. The wasted IEs can be recycled using
HCl and reused for several uptake–elution cycles without losing its
functionality or platform surface features. These IEs are promising
materials in terms of cost effectiveness and suitability for large-
scale recycling of SLIBs. Therefore, our IEs are highly applicable to
the environmental clean-up of precious cobalt metal and
administration of urban e-wastes.
Experimental
Materials
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All chemicals were used without further purification. Aluminum
isopropoxide (AIP) ≥ 98%, cetyltrimethylammonium bromide
(CTAB), 2-amino-1,3,4-thiadiazole and NaNO2 were obtained from
Sigma Aldrich, Company Ltd., USA. Ethanol 99.5%, phosphoric acid
85% and HCl 37% were procured from Nacalai Tesque, INC., Japan.
O-aminothiophenol, 2-nitroso-1-naphthol, and NaOH from Wako
Pure Chemicals, Osaka, Japan. Where, resorcinol >99.0% was
purchased Tokyo Chemical Industry, Co. LTD., Japan (TCI).
Instrumentation
The absorbance spectrum of the IE materials was measured before
and after adsorption by UV-Vis spectrophotometer (Shimadzu 3700,
Japan). The Co2+
ions concentration was determined by using ICP-
MS (ICP-MS, Perkin Elmer, Elan-6000). Shape and surface topologies
of γ-Al2O3 monoliths and IE samples were studied using scanning
electron microscope FE-SEM (JEOL Model 6500) at 20kV. Small-
Angle and Wide-Angle X-ray diffraction (SA/WA-XRD) was applied
using a 18kW diffractometer (Bruker D8 Advance) to investigate the
phase and crystal structure of γ-Al2O3 monoliths. The porous
structure and specific surface area of the samples were measured
by N2 adsorption-desorption isotherms at 77° K using a BELSORP36
analyzer (BEL Co., Ltd., Japan). Scanning TEM-energy dispersive X-
ray spectroscopy (STEM-EDS) characterization was carried out using
a JEOL JEM model 2100F microscope. 27
Al magic-angle spinning
nuclear magnetic resonance (27
Al MAS-NMR) analysis of γ-Al2O3 and
IEs were investigated using a Bruker AMX-500 spectrometer. HNMR
and FT-IR analysis of prepared chromophores were conducted using
ECS-400 (JEOL Ltd. Japan) and IR Tracer-100 (Shimadzu Corporation,
Japan), respectively. Thermal stability of used material was
investigated using a simultaneous DTA–TG Apparatus TG-60
(Shimadzu Corporation, Japan).
Fabrication of hierarchical mesospongy γ-Al2O3 in monolith-
shaped rocks
The tunable micrometric, mesospongy γ-Al2O3 monolith was formed
through soft templating-assisted synthesis using CTAB as a cationic
surfactant (Scheme 1A). CTAB (0.75 g) was dissolved in a mixture of
2 g of Milli-Q H2O and 10 g of ethanol under continuous stirring at
room temperature for 0.5 h. AIP precursor (7.5 g) was added to the
previous solution, until a homogeneous sol-gel was obtained. The
pH of the final product was adjusted to 1.3 by adding a few drops of
concentrated H3PO4. The isopropanol produced from the AIP
hydrolysis was removed by using a diaphragm vacuum pump
connected to a rotary evaporator at 45°C for 1 h. To complete the
drying process, the resulting optical gel-like carrier material was
dried at 60°C overnight. The as-made solid was calcined at 550 °C in
open air for 5 h to remove the organic moieties or templates and
produce mesospongy γ-Al2O3 monolith scaffold. The
carrier/platform material was crushed to fine powder and stored
for further use in IE manufacturing. The architectural and surface
characteristics of the as-synthesized platform were analyzed using
FE-SEM, HRTEM, XRD, 27
AlNMR, and N2 adsorption isotherm. The
acidic properties of the mesoporous γ-Al2O3 platform provide
positive attributes in creating IEs, thereby enabling easy, intense,
and strong interaction with MPDN and TDDB ligands inside/outside
the mesopores. Moreover, the atomic structural configuration of γ-
Al2O3 platform shows a face-centered cubic Fm-3m crystalline
geometry (Scheme 1B). The crystalline matrices of alumina surface-
coverage domains exhibit that the [O2−
] and [Al3+
] distributions
provide partially negative active sites to form hydrogen bonds with
the hydroxyl groups of MPDN and TDDB chromophores.
Scheme 1
Synthesis and characterization of MPDN and TDDB
Azo dyes of MPDN and TDDB were fabricated by the standard
coupling of diazonium salt of o-aminothiophenol and 2-amino-
1,3,4-thiadiazole with 2-nitroso-1-naphthol and resorcinol,
respectively under freezing temperature (see Electronic
Supplementary Information ESI). The final dye-products were
investigated by 1H-NMR and FT-IR spectroscopies. The
1H-NMR
spectrum of MPDN (at 400 MHz and using CDCl3 as solvent) shows
the corresponded proton peaks as follow: at δ 3.42ppm (H, thiol
group (HS-ph)), δ 5.3ppm (H, phenolic group (HO-ph)), around δ
7.5~7.8ppm (multiplet H, aromatic ring of thiophenol), δ 8.2ppm
(2H, naphthalene). On the other hand, the 1H-NMR spectrum of
TDDB shows the following peaks, δ 5.3ppm (H, equivalent phenolic
proton, Ar-OH), δ 6.2~6.42ppm (H, equivalent aromatic proton), δ
8.3ppm (H, heterocyclic proton). Meanwhile, the FT-IR spectra
confirm disappear of –NH2 peaks because of the azo-dye formation.
FT-IR spectrum of MPDN shows the following peaks: at 3062cm-1
(aromatic C-H, stretch), 1582cm-1
(stretching N=N), 2627cm-1
(stretching, aromatic S-H), 1127-1318cm-1
(stretching C-N), 651cm-1
(stretching C-S), and 1318-1582cm-1
(stretching N=O) and 1039cm-1
(-C-O stretch). While, the FT-IR spectrum of TDDB shows strong
peaks at 3250cm-1
(phenolic, O-H stretching), 3093cm-1
(aromatic C-
H stretching), 1670cm-1
(stretching C=C), 1070cm-1
(stretching C-O),
682-696cm-1
(stretching C-S) and 1551cm-1
(stretching N=N).
Design of mesostructured IEs by direct grafting technique
To obtain the studied IEs, the solid carrier monoliths were well
crushed to fine powder with a mortar to obtain the desired surfaces
for the homogeneity of material sensing and facilitate the analysis
process. Approximately 10 mg of the prepared chelating agents
(MPDN and TDDB) were dissolved well in 100 mL of absolute
ethanol. In a direct grafting procedure, 1 g of ground γ-Al2O3 solid
was added to the ethanolic solution of MPDN and TDDB probes
under continuous stirring for 12 h at room temperature. The
ethanol was removed by a gentle vacuum connected to a rotary
evaporator at 35±1°C temperature. The resulting solid IE monoliths
were thoroughly washed with Milli-Q H2O until no elution of the
chromophore colour was observed. The IEs were dried at 65 °C for 2
h to produce IE-1 and IE-2. The obtained IEs were ground to a fine
powder prior to the Co2+
extraction operation (see Scheme 2). The
acidic characteristic of γ-Al2O3 framework resulted in the strong
binding of ligands, which increased the stability of IEs during the
uptake-elution processes. The immobilized amounts (Qe, ~0.14
mmol/g) of MPDN and TDDB into mesoporous γ-Al2O3 scaffold can
be determined using the following equation:
Q� = �C� − C� V w� �1
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Where Cb and Ca (mmol/L) are the concentrations of MPDN and
TDDB before and after immobilization process, respectively, V is the
volume of ligand solutions (L), and w is the weight of the γ-Al2O3
scaffold (g). The good dressing assembly of ligands inside the
mesoscale pores of γ-Al2O3 improved the interaction/adsorption of
targeted ions. Despite the repeated embedding of chromophores
along γ-Al2O3 pores, γ-Al2O3 preserved their architectural texture.
SLIB remediation stages
The spent and scraped LIBs were remediated in two main stages in
accordance to the method used by H. Zou et al.,46
as shown in
Scheme S1. In the first stage, the scraped SLIBs were collected from
the urban e-waste, crushed to extract the black internal contents,
and ground to obtain a leachable fine powder. SLIB fine powder (1
g) was leached through refluxing with 50 mL of sulfuric acid (H2SO4,
4M) and hydrogen peroxide (H2O2, 30wt%) at 70°C-80°C under
constant stirring for 3 h. The residual solid waste was filtered and
washed with 50 mL of Milli-Q H2O; this stage is called leaching
process. In the second stage, the Fe3+
ion content was separated by
adding NaOH solution until pH ≥ 5, where Fe3+
ions precipitated as
brown Fe(OH)3 precipitates, which presented a considerably low
solubility constant, and other metals remained in the solution. The
final obtained solution was subjected to the following
extraction/adsorption process.
Batch extraction, detection, and recovery of Co2+
ions
In a typical Co2+
ion batch extraction experiment, 20 mg of the
optical IE-1 and IE-2 were stirred with 20 mL of Co2+
ion solution at
the appropriate pH values of 5 and 4 at room temperature, thereby
enabling the accuracy control and sensing efficiency of the IEs
towards Co2+
ion. The clear change in the IE colour as a result of the
formation of [Co2+
/IE]n+
complexes was observed by the naked eye,
as shown in Scheme 2. A blank sample was also prepared by the
same procedure without cobalt for comparison. After the
equilibrium stage, the optical IEs were filtered at room temperature
using a nitrocellulose filter membrane (0.45 μm, Ireland) under mild
vacuum at a pressure of 0.02 MPa to facilitate the colorimetric
analysis. UV-Vis spectrophotometer measurements obtained the
absorbance intensities and visual colours of the blank and
[Co2+
/IE]n+
samples, which provided evidence for the direct
proportionality of absorbance intensities with the concentration of
Co2+
ions. The LOD of the IEs for Co2+
ion-sensing was determined as
follows: 47
�LOD = 3S�S �2
Where Sd and S are the standard deviation and slope of the
calibration graph, respectively. The optical IE-1 and IE-2 were
filtered, and the filtrate was analyzed using ICP-MS to determine
the remaining Co2+
ion concentration after the complete ion-
sensing process. The adsorption capacity and uptake efficiency of
Co2+
ions were determined by measuring a wide-range
concentrations of standard Co2+
ion solutions and estimated using
the following equations: 48, 49
q� = �C� − C� V m� �3
Uptake% = �C� − C�C� ! × 100�4
Where qe is the adsorption capacity (mg/g) of applied IE extractors,
Co and Ce are the concentrations of Co2+
ions before and after
adsorption (mg/L), respectively, V is the volume of the applied Co2+
ion solution (L), and m is the mass of used IEs (g). The effects of pH,
contact time, initial concentration of Co2+
ions, and coexisting ions
were examined to assess the optimal extraction conditions. The
adsorbed Co2+
ions can be released/desorbed/eluted using suitable
stripping agent, such as HCl, to enable the recycling of the
consumed IEs and consequently decrease the extraction cost and
produce pure cobalt. All the experiments were conducted using the
prepared IEs, a standard solution of Co2+
ions or simulated
solutions, and real solutions of SLIBs as a secondary source of
cobalt. E-wasted LIBs were collected from the urban mine, crushed,
and leached using H2SO4 and H2O2 through hydrometallurgy process
to produce a leach liquor, which contained Co2+
ions and other
competitive ions. The practical implementations or actual
extraction processes of Co2+
ions (i.e., from the leach liquor) were
performed at the optimum adsorption conditions.
Scheme 2
Results and discussion Characterization of hierarchical mesoporous γ-Al2O3 monolithic
rocks and IEs
Herein, the microscopic mesospongy γ-Al2O3 monolith particles
were synthesized through direct soft templating and stirring-
assisted approach using CTAB as a cationic surfactant. The
mesostructured γ-Al2O3 monolith was formed using the quaternary
emulsion composition of AIP, CTAB, ethanol, and H2O acidified with
H3PO4 at pH 1.3 in the mass ratio of 1:0.1:0.26:1.3. The current
approach controlled the creation and expansion of new tunable
pores that resemble worm’s channels to produce mesostructured
architectures using CTAB. Quaternary emulsion phases were utilized
for engineering surveillance of pore arrangements, as proven by SA-
XRD, N2-adsorption isotherm, and HRTEM. The cage-shaped
mesoporous feature of the γ-Al2O3 monolith is a considerably
desired trait in chromophore trapping. Consequently, ions were
targeted into the interfaced cavities. The mesoporous γ-Al2O3
monolith was used as a solid support platform to create optical
chemical adsorbents for the detection, capture, and extraction of
Co2+
ions from SLIBs. Despite the vigorous stirring conditions, the
mesostructured alumina monolith maintained the microsized
morphology with the surface pore matrices, which resulted in the
structural stability during cobalt extraction processes.
Figure 1 shows the real and synthetic sample images (Fig. 1A-a, B-
a, and C-a) and FE-SEM micrographs of calcined, hierarchal
mesoporous sponge γ-Al2O3 monolithic rocks (Fig. 1A),
solid/mesosponge MPDN-γ-Al2O3 ion-extractor (IE-1) and Co2+
-
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ion-IE-1 samples (Fig. 1B&C, respectively). Fig. 1A-a, B-a, and C-c
shows evidence of the colour changes (white-to-yellow-to-reddish)
of the synthetic γ-Al2O3 sample with MPDN modification/dressing
and during the extraction/sensing/trapping of Co2+
ions using IE-1,
respectively.
Figure 1Ab-c shows FE-SEM micrographs of solid γ-Al2O3 in
micrometer-sized non-uniform/irregularly shaped rocks in a range
of 25–150 μm with a smooth surface. The outer side
microarchitectures of γ-Al2O3 surface contain small pores/holes in
nanoscale (100-120 nm). These holes are scattered along the top
surface of the γ-Al2O3 monolith to yield a sponge-like shape (as
shown in Fig. 1A-b&A-c). The distance between every two holes is
estimated at approximately tens of nanometers. These neat holes
help in facilitating the diffusion/mass transfer of chromophores and
cobalt ions along carrier’s pores. The upper view of γ-Al2O3 surface
shows evident lines, such as ridges; these ridges may refer to the
overlapping of hierarchical plate sheets during the formation of the
microsized alumina architectures (as shown in Fig. 1A-b, insert). FE-
SEM images of IE-1 (Figure 1B-b, and B-c) show the same
architecture specification of γ-Al2O3 carriers. The images shows the
existence of nanocaves-like grooves, which suggested that
(i) the suitable accommodation of chromophores during the
chemical immobilization process,
(ii) the interior decoration into cage porous frameworks, and
(iii) a formation of layered-probe dressing along the exterior
surface of mesoporous γ-Al2O3 (see Fig. 1B-b&c).
In the same context, Figure 1C-a displays the change in the IE-1
colour from yellow to reddish colour, thereby indicating the
chemical capture/trapping of Co2+
ions at the active sites of IE-1.
Figure 1C-b shows the retention of microarchitectures of IE-1,
despite the severe chemical capture/trapping/extraction process of
Co2+
ions under pH conditions.
Fig. 1C-c shows the SEM-EDX profile of monolithic Co2+
-ion-IE-1
sample, where the elemental content of Al, O, C and Co are 55.23,
42.31, 2.23 and 0.23 %. Furthermore, SEM-EDX profiles provided a
real evidence of the elemental composition of our IEs before and
after adsorption of Co2+
ions. As shown in Fig. S1, the EDX analysis
of γ-Al2O3 substrates showed the Al and O mass ratios of 58.9% and
41.1%, respectively, which are close to the theoretical values. The
high carbon content in the IE framework confirmed the grafting of
chromophores to solid carriers to produce the optical extractors IE1
and IE 2 (see Figs. S1B&C). Figures S1D&E provide evidence about
the adsorption of Co2+
ions and well-defined distribution along IE
monoliths, as shown in the elemental mapping of Al, O, C, and Co.
For example, monolithic Co2+
-ion-IE-1 sample contains 55.23%,
42.31%, 2.23%, and 0.23% of Al, O, C, and Co atoms, respectively.
Figure 1
The top view of FE-SEM clearly exhibits the formation of the spongy
γ-Al2O3 monolith-shaped rocks, as shown in Figs. 2A and 2B. The
microsized γ-Al2O3 framework shows sharp edges and nanorooms
along the surface, which are evident in the HRTEM analysis. Figs. 2C
and 2D show the HRTEM profiles of the γ-Al2O3 monolith, which
present the top-surface edge of the γ-Al2O3 architecture with a
downhill angle of less than 90°; the distance between the two rims
is approximately 110 nm. The end of the edge surfaces is tortuous,
and these sinuous edges enhance the flow of target ion solution
through the solid adsorbents. HRTEM nanographs show that the
worm-like mesopores (~14 nm) are diffused along the surface
regions of γ-Al2O3 domains, which agreed with the SA-XRD profiles.
Fig. 2E displays the electron diffraction profile of γ-Al2O3 monolith.
The profile clearly shows five luminous evident rings, which
correspond to the (220), (311), (400), (511), and (440) planes (from
the inside out). This result shows that the monolithic γ-Al2O3
framework is composed of polycrystalline cubic Fm-3m alumina,
thereby indicating that the γ-Al2O3 crystal grows around the
mesoscale pockets like worm channels; this growth presents the
mesostructured features of γ-Al2O3 carriers. STEM-energy
dispersive spectroscopy (STEM-EDS) mapping profiles provide
evidence of the uniformly distributed Al and O along the
mesosponge surface of the γ-Al2O3 monolith, that is, 58.3% and
41.7%, respectively, and the [Al]:[O] ratio is 1:0.71 (Figs. 2F–2H).
These values are largely close to the EDX mapping values that were
estimated using FE-SEM. The SEM-EDS mapping of solid IE-1, IE-2,
Co2+
-ion-IE-1, and Co2+
-ion-IE-2 samples is shown in Fig. S1.
Figure 2
N2 adsorption–desorption analysis was performed to determine the
specific surface area and porosity of γ-Al2O3 monolith before and
after immobilization of the organic chromophore and after cobalt
trapping.50
Fig. 3A illustrates N2 adsorption–desorption isotherms
with type IV of adsorption behaviour and sharp inflection in
adsorption–desorption isotherms (H2-type hysteresis loops), which
confirmed the mesoporosity of spongy γ-Al2O3 with a typical and
uniform mesocage structure with cramped inlet/nozzle. The
obtained findings can be attributed to the stepwise capillary
condensation of adsorbed species through a tight area of tubular
pores, depending on the amount of CTAB. Evidently, γ-Al2O3 shows
a high BET surface area of 419.8 m2/g, total pore volume
1.3115cm3/g, and pore size of 13.91 nm according to the NLDFT
pore size distributions (Fig. 3B and Table S1). Moreover, the high
surface area and large pore size of this material are remarkably
advantageous in the fabrication of nanocollectors that recognize
and capture ultra-trace amounts of Co2+
ions. The decreases in the
surface area from 419 m2/g to ~ 395 and 399.6 m
2/g, the pore
volume from 1.31 cm3/g to 0.9586 and 0.9598 cm
3/g, and pore size
from 13.9 mm to 12.1 and 12.2 nm for IE-1 and IE-2, respectively,
provide further evidence that a large quantity of chromophores
settled inside the interior mesocavities without blocking/damaging
the cage window of mesopores. The large decreases in surface area,
pore volume and pore size values emphasize the trapping of Co2+
ions (see Table S1).
Figure 3
SA-XRD analysis confirmed the mesoporosity of the γ-Al2O3
monolith. Fig. 3C shows the SA-XRD patterns of as-synthesized γ-
Al2O3, IE-1, and Co2+
-ion-IE-1. All of the examined samples show a
highly acute diffraction peak (Bragg peaks) at ~1.5° (2Ɵ) that is
indexed to (100) reflection with d-values of 10.5, 10.1, and 8.9 nm
for γ-Al2O3, IE-1, and Co2+
-ion-IE-1, respectively. The (100) peak
refers to the highly ordered mesoporous cubic Fm-3m γ-Al2O3
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domains, with of the mesoporosity frameworks retained after CTAB
removal. The decreased Bragg reflection peak and d-values may be
due to the small deficiency of internal pore structure through filling
the pores with organic ligands and Co2+
ions (not a significant
change). The diffraction (100) peaks of IE-1 and Co2+
-ion-IE-1 shift to
angles higher than those of the γ-Al2O3 reflections, thereby
indicating the successful immobilization of chelating agents and
trapping of cobalt ions. Our findings indicated that the highly
intense Bragg peak proves the mesoporosity of γ-Al2O3 despite the
high stuffing level of ligands and cobalt ions inside pores. A typical
diffraction pattern of WA-XRD of calcined γ-Al2O3 monoliths shows
poor crystallinity properties with three main reflections at 2Ɵ of
30°, 46°, and 67°, which correspond to (220), (400), and (440) with
d-values of 2.85, 2.05, and 1.51 nm, respectively. These diffraction
peaks are assigned to the standard values of the γ-Al2O3 with a
cubic unit cell according to JCPDS 10-0425 card number (Fig. 3D).51,
52 In addition, the broad and weak peak lines suggest the poor
crystallinity of the γ-Al2O3 phase. The existence of boehmite crystal
phase during the synthesis procedures can be confirmed by the FT-
IR spectra and TG analysis. Furthermore, the WA-XRD results of IE-1
and Co2+
-ion-IE-1 samples showed the same reflection peaks with
an intensity that is less than that of γ-Al2O3; this result is attributed
to the successful immobilization of chelating agents and trapping of
Co2+
ions into the interior cavities of γ-Al2O3 without change in the
orientational framework of γ-Al2O3 mesopores. The stability and
durability of the mesopore matrices enhance the flow and the
uptake of targeted ions during the extraction process even after
multiple reuse cycles.
The Al coordination frameworks of mesosponge γ-Al2O3 monolith
were investigated using 27
Al MAS NMR, depending on the chemical
shift values. Fig. 4A illustrates the 27
Al NMR spectrum of γ-Al2O3,
where the obtained spectra show two featured coordination
environments at ~0 and ~56 ppm (δ), which correspond to
octahedral (Oh) and tetrahedral (Th) aluminum, respectively; this
result showed that the Al atom is surrounded with six and four O
atoms as AlO6 (AlVI
) and AlO4 (AlIV
), respectively.53, 54
Fig. 4A exhibits
that the formed γ-Al2O3 monolith consists of the equivalent ratio of
AlO6 and AlO4 (approximately 1:1), which indicated the same
intensity of AlO6 and AlO4 peaks. As demonstrated in Fig. 4B, the
functionalization of γ-Al2O3 by chromophores (ligand decoration)
highly decreases the AlO4 peak intensity compared with that in the
AlO6 peak (slight change ) , which suggested that the tetrahedrally
coordinated aluminum is more active than the octahedral
configuration. In the same context, trapping, capture, and
adsorption of Co2+
ion result in a considerable reducing effect in
AlO4 peak intensity, as shown in Fig. 4C. Therefore, interaction and
diffusion occur at the outer surface of the carrier and at the inner
wall surface.
Figure 4
The FT-IR spectra of calcined γ-Al2O3 are presented in Fig. S2. The
broad and strong peak at 3500 cm−1
and the weak one at 1600 cm−1
are strongly attributed to the stretching and bending of adsorbed
water of γ-Al2O3 powder, respectively. The small broad peak at
approximately 2050 and 1390 cm−1
can be assigned to the
vibrational overtones of the surface, namely, the –OH groups of
AlOOH and Al–OH, respectively. The small peak at ∼1500 cm−1
can
be assigned to the C–O asymmetric stretches due to the presence
of AIP as an initial precursor. The peaks in the range of 1000–400
cm−1
are attributed to the Al–O band stretching vibration of
boehmite or pseudoboehmite.55-57
The absorbance of γ-Al2O3
functional groups is more remarkable than that of the functional
groups of immobilized chromophores due to the majority of γ-Al2O3
compared with the considerably low concentration of
chromophores. Therefore, the peak intensities at 1390, 1510, 1640,
and 2350 cm−1
increase as a result of the immobilization process.
The thermal attributes of γ-Al2O3, IE-1, and IE-2 were investigated
to evaluate the durability of the carrier and extractors with
increased temperature, as shown in Fig. S3. The obtained TG profile
of γ-Al2O3 exhibits that γ-Al2O3 as solid carrier loses approximately
5% of its original weight in the range of 27°C–650°C due to the
evaporation of moisture and bound H2O and the remaining
surfactant. The weight losses of IE-1 and IE-2 are ~6% and ~6.5% in
27°C–650°C, respectively. The increased weight loss of IE-1 and IE-2
may be attributed to the removal of the immobilized organic
chelating agent MPDN and TDDB as carbon and nitrogen oxides.
Moreover, the removal of MPDN and TDDB largely occurs in the
range of 27°C–300°C. These results inspire us to regenerate the
solid carrier (i.e., γ-Al2O3) and remove the consumed chelating
agents after repeated use and loss of its effectiveness in the
extraction or trapping of Co2+
ions. The TG studies of γ-Al2O3 and
current extractors presented that the weight loss is diminutive,
which indicated that the used carrier is highly durable under high-
temperature conditions.
Visual detection/adsorption/extraction of Co2+
ions
a. Influences of pH and contact time on the optical
extraction behavior of Co2+
ions
pH plays a pivotal role in the optical monitoring, sensitivity,
selectivity, and rapid extraction of Co2+
ions among other coexisting
ions. Thus, the effect of medium pH to optimize the most
remarkable absorbance signals and obtain stable (target ion–IE)
complex should be studied. Here, pH controls the functionality of
the attached chromophore, thereby making it either neutral or
protonated functional group. A set of optical extraction assays was
conducted by stirring 20 mg of IE-1 and IE-2 with 20 mL of Co2+
solution (1 ppm) at a wide pH range of 1–10. The pH values were
adjusted by adding 5 mL of buffer solutions to the reaction vessel.
The colorimetric detection of Co2+
ions at low and high
concentrations was conducted using UV-Vis spectroscopy. Fig. 5A
indicates that the colorimetric measurements of Co2+
-ion-IE-1 and
Co2+
-ion-IE-1 solids can be carefully studied at the maximum
absorbance (λmax) peaks of 370 and 410 nm, respectively. The
obtained results in Figure S4A exhibited that the highest
absorbance signals (most remarkable signal response) can be
achieved at pH 5 and 4 for IE-1 and IE-2, respectively. The
remarkable changes in absorbance peak are attributed to the high
sensitivity and visual monitoring efficiency of Co2+
ions as a result of
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formation of [Co2+
/IE-1]n+
and [Co2+
/IE-2]n+
complexes. At low pH
values, the optical sensing of studied adsorbents toward Co2+
ions
decreases due to the high protonation of interaction medium,
thereby leading to intense competition with cobalt ions at the
active sites of IE’s surface. This concept inspires us to regenerate
the consumed IEs under acidic pH conditions. After pH 5 and 4, the
absorbance intensities of [Co2+
/IE-1]n+
and [Co2+
/IE-2]n+
complexes
tend to decrease slightly. This decrease in optical signals of IE-1 and
IE-2 may be due to the obstruction of some effective group
functionalities of the impregnated MPDN and TDDB chelating
agents, especially in the alkaline medium, which consequently
decreases the extraction efficiency. Thus, our findings indicated
that the optimum changes in the colour intensity of the [Co2+
/IE-1]n+
and [Co2+
/IE-2]n+
complexes are at pH 5 and 4, respectively. Scheme
2 shows the colour switching of IEs to another colour as a result of
[Co2+
/IE-1]n+
and [Co2+
/IE-2]n+
formation. Our findings indicated that
the mesosponge IEs offer the following advantages: (i) pH-
dependent controlled Co2+
-sensing process, (ii) naked eye
monitoring of the change in IE colour after trapping Co2+
ions, and
(iii) efficient adsorption of Co2+
ions from aqueous solutions.
The effect of contact time on the colorimetric determination of Co2+
ions (i.e., required time to obtain the most remarkable signals) was
also investigated because contact time is significant in the intensity
of the corresponding signals of complex colour as a result of the
binding of Co2+
ions with IEs during the formation of the [Co2+
/IEs]n+
complexes (Fig. S4B.) A series of batch contact tests was performed
through mixing 20 mg of the IE-1 and IE-2 with 20 mL of Co2+
solution (1 ppm) at pH 5 and 4 and room temperature under
continuous stirring for 1–40 min. These findings exhibited that the
most remarkable signal response of the [Co2+
/IEs]n+
complexes at a
specific pH can be achieved within 7–10 min when mixing began,
regardless of the volume of Co2+
ion solution. The absorbance
signals show a relative stability, which provides evidence of the
quick interaction between targeted cobalt and used IEs due to the
chemical bonding with the functional groups of the chromophore
probes. Consequently, the subsequent colorimetric measurements
of Co2+
concentration were conducted after the actual rejoinder
time (≥ 10 min) to guarantee access to the equilibrium state. These
findings are considered satisfying result at the actual extraction of
Co2+
from SLIBs. The analytical ICP-MS data (see Fig. S4C) show the
ability of our extractors to adsorb more than 98.5% and 99% of Co2+
ions within 15 min of contact using IE-1 and IE-2, respectively. This
result proved that the adsorption or extraction of cobalt ions is a
rapid and time-dependent process. Increasing the contact time
enhances the adsorption efficiency to >99% within 30 min, which is
considered a good result in the cobalt extraction and removal
applications. In general, the obtained findings agree with the results
of the spectrophotometric analysis.
b. [Co2+
/IE] complex formation mechanism
The trapping/adsorption of Co2+
ion was studied at pH 5 and 4 using
IE-1 and IE-2, respectively. The chromophoric MPDN and TDDB
ligands immobilized into the platform γ-Al2O3 mesopores show
three charged groups, namely, –SH, –N=N–, and –N=, which can be
neutral or protonated based on the pH of the interaction. The
electronic structures of MPDN and TDDB contain three types of
electron transition orbitals from bonding and nonbonding electron
orbitals to antibonding orbitals as n→ π*, π → π*, and n→ σ* due
to the presence of nonbonding lone pair electrons on the nitrogen
and sulfur atoms. Given the required high transition energy, n→ π*
and π → π* are considered the most common electron donors
during the complex formation, which explained the emergence of
two peaks in the wavelength (λ) range of 350–600 nm (n→ π*) and
200–400 nm (π → π*) (Fig. 5A). The MPDN and TDDB chelacng
agents contain two electron donor groups, and each group
contributes to a pair of free electrons to form coordination bond
with the targeted ion. The metal complexes are created due to the
electron deficiency in the d-orbitals (empty orbitals). Thus, Co2+
ions
can be highly associated with –SH, –N=N–, and –N= groups due to
the electronegativity and protonation of these groups at the
studied pH. Consequently, symmetrical five-membered rings in
octahedral [Co2+
/IEs]n+
complexes with high stability constants are
formed, and hence the colour changes (Scheme 2).
c. Detection boundaries and performance assessment of
prepared IEs
The use of mesosponge IEs causes the high adsorption ability due to
the high surface area, mesoporosity, and pore volume features. IEs
show remarkable results for simultaneous visual detection,
sensitivity monitoring, and simple extraction even at relatively low
Co2+
ion concentrations under the optimum adsorption/sensing
conditions (Fig. 5). The concentration-dependent batch experiments
were conducted to determine the minimum limits of cobalt ions
that can be detected/extracted, where 20 mg of IEs were stirred
with 20 mL of a wide range of Co2+
concentration at pH 5 and 4 and
room temperature for 30 min. Fig. 5B illustrates that the increase in
Co2+
ion concentration results in the increased absorbance intensity
and the colour visible to the naked eye due to the chemically
expanding interaction of Co2+
ions with the exterior/interior
decoration of mesoporous IEs with actively functional MPDN and
TDDB groups, leading to the formation of [Co2+
/IE-1]n+
and [Co2+
/IE-
2]n+
complexes, respectively. As shown in Figs. 5C and 5D, the UV-
Vis spectra of IE-1 and IE-2 show the emergence of new response
peaks at λmax of 370 and 410 nm, respectively, due to the formation
of [Co2+
/IE-1]n+
and [Co2+
/IE-2]n+
complexes. The increase in
absorbance intensity depends on the strength of the obtained
colour between the IEs and Co2+
ions. Figs. 5C and 5D also show the
gradually increased values of (A–Ao) with the increased Co2+
concentration (ppm), where A and Ao are the absorbance values of
[Co2+
/IEs]n+
samples and IEs blank, respectively. Accordingly, the
obtained results indicated that the IE-1 and IE-2 offer a one-step,
fast, and direct optical sensing/adsorption/extraction technique for
Co2+
ions. This finding proved that the optical IE monoliths are
highly efficient in the detection and extraction of Co2+
ions from
SLIB solutions at low and high concentrations.
The sensitivity of the functionalized mesoporous IEs was estimated
through the calibration curve between the absorbance response of
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the IEs blank and Co2+
-ion-IEs samples at λmax of 370 and 410 nm as
a function of Co2+
ion concentration (Figs. S5A and S5B). The
linearity calibration curves of IE-1 and IE-2 show a linear correlation
at wide-range Co2+
ion concentrations, thereby indicating the
possibility of detection, adsorption, and extraction of ultra-trace
and high Co2+
ion concentrations. This observation is attributed to
the highly sensitive/sensing characteristic of the prepared optical
IEs. The accuracy of the calibration curves is considerably significant
to ensure the precision of Co2+
ion detection/extraction. Thus, many
quantitative measurements were performed using a wide range of
standard Co2+
ion concentrations under the optimum pH conditions.
The obtained data of calibration curves suggested that the standard
deviation of the Co2+
ion analysis using IE-1 and IE-2 is less than
0.5%, as shown in Fig. S5. The LOD values of Co2+
ions were
determined from the linear part of the calibration curve (Fig. S5
inserts), where the LOD values of IE-1 and IE-2 are 4.5 × 10−8
and
3.05 × 10−8
M (i.e., equivalent to 2.7 and 1.8 ppb or μg/L),
respectively. These findings demonstrated that our optical IEs can
be used effectively for the detection and extraction of ultra-trace
amounts of Co2+
ions from their sources.
Figure 5
Selective and visual detection/extraction/adsorption of Co2+
ions
In this section, we carried out a basic study of Co2+
ion-selectivity in
water at optimal pH condition using our IEs as an important
function of optical sensor functionalities, in which the selectivity,
sensitivity and visual detection were considered (see Figure 6). Our
study was carried out to evaluate the sensitive detection and
extraction of Co2+
ions in the presence of an equivalent amount of
other competitive cations. Target selectivity is a fundamental
property in the extraction of a Co2+
ion from SLIB wastes. Therefore,
a series of batch-contact tests was carried out as follows: 20 mg of
IE-1 and IE-2 were stirred for 30 min with 20 mL of Co2+
, Li+, Ca
2+,
Mg2+
, Al3+
, Pb2+
, Hg2+
, Cd2+
, Cu2+
, Ni2+
, Fe3+
, Mn2+
, Cr3+
, and Au3+
(1
ppm) separately at optimized pH conditions of Co2+
extraction. The
obtained spectrophotometric results showed that the difference
between the blank (i.e., IE-1 and IE-2) and the [Mx+
/IEs]n+
complexes
is negligible in terms of the visual absorbance intensities, as shown
in Fig. 6A and B. Interfering ions, such as Cu2+
and Ni2+
, show weak
signal responses in UV-Vis spectra upon interaction with the studied
IEs due to the rapprochement/similarity of the chemical and
physical properties of Cu2+
and Ni2+
with those of Co2+
.
Consequently, the extraction process and the IE efficiency are
adversely affected. This challenge can be overcome by using
suitable masking agent. Furthermore, the same experiments were
conducted in binary and mixture systems under the optimum
extraction conditions in the presence of one or more coexisting
cations with Co2+
ions at equivalent concentrations (G1 to G15), as
listed in Fig. 6. The UV-Vis colorimetric spectra indicated that the
existence of foreign ions exerts no significant effect on the visual
colour or the absorbance intensity of the [Co2+
/IEs]n+
complexes, as
illustrated in Fig. 6C.
Due to the SLIBs may contain numerous anionic ingredients. Thus,
our experiments must be conducted to evaluate the extraction of
Co2+
ions among other anionic interfering components. In batch
contact vessel containing 20 mg of applied IEs, 50 ppm of sodium
salt of Cl−, NO3
−, SO3
2−, SO4
2−, and HCO3
−; 75 ppm of PO4
3−, NO2
−, and
C6H5O73−
; and 100 ppm of C2O42−
, C2H3O2−, C4H4O6
2−, CO3
2−, HAsO4
2−,
and CTAB were added separately to 20 mL of 1 ppm Co2+
ion and
stirred for 30 min under optimum pH conditions. Figure S6 showed
that the optical signalling of IEs in the presence of interfering
anionic species. No remarkable influence on the optical signal of
Co2+
ion-IES, indicating the high performance/efficiency of cobalt
ions adsorption/extraction from their solutions into IEs surfaces.
Therefore, our findings indicated the effective feasibility of the
extraction process of Co2+
ions even with increased concentrations
of coexisting ions under the optimum extraction conditions from
SLIBs (see Scheme S1).
To obtain high accuracy, we evaluated the efficiency of the studied
IEs in the extraction/adsorption of Co2+
ions among other
competitive ions in water via ICP-MS analyses. The batch contact
experiments were performed under room temperature and at pH 5
and 4 for IE-1 and IE-2, respectively, in the presence of equivalent
concentrations of the competitive cations in binary and mixture
systems, as listed in Fig. 6D. The obtained results in Fig. 6D
demonstrated that more than 99% of the Co2+
content can be
adsorbed in the absence of other interfering ions. In the presence
of comparable concentrations of other completive cations, the
adsorption efficiency of our optical IEs decreases to 96%–98% due
to the competitive effect of the interfering ions at the
interior/exterior active sites of IEs. The existence of Cu2+
and Ni2+
results in the largest negative effect. Our findings indicated the
possible fast extraction of Co2+
from its ion solutions efficiently,
selectively, even at low concentrations through extraction/
adsorption process. The high adsorption efficiency may be due to
the IEs surface functionalities in terms of (i) meso-/macro-porous
cavities, (ii) effective surface coverages, (iii) high surface are-to-
pore volume ratio, and (iv) the abundance of active sites of our IE-1
and IE-2. These features enable the microsized IEs particles with
multidirectional monolithic hierarchy to adsorb/uptake a large
amount of Co2+
ions. Our findings exhibited that the selectivity of
IEs may be due to the higher thermodynamic binding stability of
Co2+
ions with the active groups of MPDN and TDDB chromophores
than those with other competitive ions under fixed pH conditions.
Figure 6
Adsorption isotherm study of Co2+
ion
The Co2+
ion removal/adsorption isotherms of applied IEs were
investigated under the optimum experimental conditions to
evaluate the relation of the optical IEs with an adsorbed Co2+
ion in
terms of the quantity of adsorbed target ions qm (mg/g) at 25°C ±
2°C, as shown in Fig. S7. Batch experiments were carried out by
stirring 20 mL of Co2+
ions (0.01–500 ppm) with 20 mg of IE-1 and
IE-2. Fig. S7A shows that with the increased amount of the
adsorbed Co2+
(qe, mg/g) according to the increased initial Co2+
concentration, a stable state is reached. After this steady state, the
used IEs cannot accommodate additional Co2+
ions because the
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maximum saturation capacity is reached, where the experimental
qm values of IE-1 and IE-2 are 141.3 and 193.5 mg/g, respectively.
The high saturation capacities may be due to the high surface area
and the mesoporosity features of used IEs, which consequently
increase the number of active sites and allow the good propagation
of Co2+
ions. Thus, many [Co2+
/IEs]n+
complexes are formed along
the macro/meso-grooves of the micrometric monolith surfaces of
IEs, indicating the visual detection/signalling, and removal of Co2+
ions from solution. Moreover, the high surface area is attributed to
the well-accumulated chromophores/chelating agents inside the IE
mesopores. The interaction between Co2+
ions with IEs and the
capacity of these IEs were evaluated at the equilibrium stage using
the linearized form of the Langmuir and Freundlich equations as
follows: 58, 59
%&'& = (
)*'+ + - ('+. C��5
ln q� = lnK3 + (4 ln C��6
Where qm and KL are the theoretical maximum capacity of IEs
(mg/g) and the sorption equilibrium constant, respectively, and KF
and n are the constants relative to the adsorption capacity of IEs
and sorption intensity, respectively. These constants were
estimated from the slopeand intercept of the linear relations by
plotting Ce/qe versus Ce and ln qe versus ln Ce, as illustrated in Table
1 and Figs. S7B&C. The adsorption isotherm of the current optical
IEs for adsorption/trapping of Co2+
ions indicated that the Langmuir
isotherm model more satisfactorily fits than the Freundlich
isotherm model according to the correlation coefficient (Fig. S7C)
(R2 = 0.995 and 0.996 for IE-1 and IE-2, respectively). Theoretical
data of Langmuir constants demonstrated that the qm values of IE-1
and IE-2 are 142.8 and 196.07 mg/g, respectively, which agree with
the experimental findings. Hence, our findings indicated that 1 g of
studied IEs can accommodate approximately 0.143 and 0.196 g of
Co2+
ions from the real solution of leached SLIBs. The obtained data
also showed that all KL and 1/n values are < 1, thereby indicating
the reversibility of the adsorption process. Furthermore, the
adsorption/trapping of Co2+
ion is a chemisorption process, which
suggested that the adsorbed Co2+
ions bind to the active sites or
functional groups of IEs through real chemical bonds.60
The high
adsorption capacity can qualify our IEs effective in the recyclability
of SLIBs and other urban e-wastes.
Adsorption kinetics of Co2+
ion
Evaluation of the kinetic adsorption mechanism of Co2+
ions is
significant for understanding the adsorption behavior based on the
alteration in the contact time. Therefore, a set of batch experiments
wascarried out at a contact time of 2.5–60 min by stirring 20 mg of
optical IE-1 and IE-2 with 20 mL of [2 ppm] Co2+
ions at pH 5 and 4
and at room temperature. Here, the adsorption kinetic models,
such as pseudo-first- and pseudo-second-order models, were
applied according to the following equations.61, 62
log�q� − q8 = log q� −- )9:.<=<. t (7)
8'> = (
)?'&? + - ('&. t (8)
Where k1 (min-1) and k2 (g/mg.min) are the pseudo-first- and
pseudo-second-order rate constants, respectively, and qt is the
adsorbed Co2+
amount (mg/g) at time t (min). The obtained data
indicated that the studied optical adsorption process is considerably
quick; more than 98% of Co2+
ions can be adsorbed within 15 min
(Fig. S8). Complete adsorption/extraction (>99%) can be achieved
quickly using both IE-1 and IE-2. The massiveness of active sites and
easy Co2+
ion diffusion accelerate the extraction process. Numerical
values of unknown parameters can be estimated from the plot of
log (qe–qt) and t/qt versus t, as summarized in Table 1 and Fig. S8.
These findings showed that according to the R2 (>0.97) values, the
pseudo-second-order model is more suitable than the pseudo-first-
order model for the assessment of the optical extraction process of
Co2+
ions using the present IEs. The qe values of pseudo-second-
order model are fitted to the experimental data using 2 ppm as
initial Co2+
concentration (see Table 1). The qe values of pseudo-
first-order model also agree with the experimental saturation
capacity (qm, mg/g).
Table 1
Releasing of adsorbed Co2+
ions from IEs surfaces (i.e.,
recyclability)
In this study, one of the most significant steps in extraction process
is the success elution/releasing of adsorbed Co2+
ions from IEs
surfaces. We offer a comprehensive study to complete the
extraction cycle of Co2+
ions from the leach liquor of SLIBs and
reproduce the spent optical IEs. In this study, the recyclability of the
IEs has gained considerable attention in terms of reduced extraction
cost and the exploited time and effort in the replacement of used
extractors during each operation (see Figure 7-A and 7-C). Basically,
the mechanistic concept of the Co2+
ion-releasing from IEs surface
occurred through the decomplexation of Co2+
-to- ligand binding
events. We can emphasize the success releasing of Co2+
ion via
colorimetric measurements of solid Co2+
-ion-IE-1 sample using
UV-Vis spectroscopy, in which indicating the colour change of
the solid formed [Co2+
/IEs]n+
complexes at IEs surface to its original
colour of IEs visible to the naked eyes. Furthermore, we
quantitatively measured the released Co2+
ion in effluent
solution via ICP-MS analysis (Figure 7A&B).
The Co2+
ion-releasing process allows the recycling of used IEs for
further extraction process. Therefore, many stripping experiments
were performed through a liquid exchange process to elute/desorb
the adsorbed Co2+
ions from solid Co2+
-ion-IEs samples and
consequently obtain cobalt-free IEs in effluent solution, where the
applied IEs were liquidated and dried prior to further extraction
step. In each Co2+
ion-releasing experiment, 50 mg of dried Co2+
-
ion-IEs solids were stirred with 50 mL of [0.2 M] HCl solution. Figure
S9 shows the influences of HCl concentration (0.05–0.35 M) and
stripping time (5–60 min) on the elution process were examined.
Figure S9A presents that the elution % of adsorbed Co2+
ions
increases with the decreased pH of the elution process (i.e., with
increased HCl concentration), where elution % increases from ~30%
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to >99.5% for both IE-1 and IE-2 from 0.05 M to 0.2 M of HCl. At low
pH, the adsorbed Co2+
ions at Co2+
-ion-IEs surfaces may be
replaced with the strong competitive H+ ions, thereby causing the
easy release of cobalt ions (as a CoCl2) in solution. Moreover, the
effect of stripping/elution time was studied from 5 min to 60 min
using HCl (0.2 M) as eluent agent. As depicted in Fig. S9B, the
adsorbed Co2+
ions are completely released (>99.9%) from the
complexes within 30 min.
Our finding shows that a monoprotic acid, such as HCl, effectively
used as eluent or stripping agent to strongly bind with Co2+
ions and
released as CoCl2 in effluent solution, and then form Co2+
-free IEs
solids. IEs solids were subsequently filtered to further extraction
process (i.e., reused/cycles). The elution % of de-trapped/de-
adsorbed Co2+
ions from solid Co2+
-ion-IEs samples can be
calculated by using the following equation: Elution% = (CR/CA) × 100,
where CR and CA are the released and adsorbed Co2+
concentrations
(ppm), respectively (Figure 7A). After 10 cycles of the adsorption–
elution–regeneration processes (1st
round of IEs cycling), the
uptake/adsorption efficiencies of both current IE-1 and IE-2
decrease to 48% and 45% of their original efficiency, respectively
(Fig. 7A). In turn, the elution efficiency (i.e., collection of Co ion
from surface per each experiment) is still high; >99.5% of adsorbed
cobalt can be released even after 10 reuse/cycles, as exhibited in
Fig. 7A. It seems that the building of IEs onto acidic nature carriers
such as γ-Al2O3 may cause a strong linkage with the accumulated
ligands, which results in the retention of ligands during repeated
Co2+
ion adsorption–elution processes. The repeated use of IEs may
lead to the release or decomposition of impregnated chromophores
because of vigorous mechanical stirring during the repeated
operations, as evidenced from the colour response intensity (i.e.,
absorbance) by using UV-Vis spectroscopy. Consequently, the
functional groups and active sites at the IE surface decrease, which
minimizes the extraction efficiency.
Reusability and reproducibility of IEs recycling
To investigate the possibility of extending reusability and
reproducibility of IEs recycling, named as 1st
round IEs recycling
(Figure 7A) to be used for further rounds of recycling (i.e. dead-end
recycling process), see Figure 7B and 7C. To explore the dead-end
usage of IEs recycling, the 10 cycle regenerated IEs (after 1st
round
cycling) surfaces were re-activated to be ready for 2nd
round of
extraction cycling of Co2+
ions (i.e., for further 10 reuse/cycles
continuously), see Figure 7B. This study will open new avenue to
extract cobalt from urban e-waste (such as SLIBs) efficiently and
cost effectively.
As evidently from our experimental sets using UV-Vis. Spectroscopy
of the optimum corresponding absorbance signals of 10 cycling
reused-IEs, there is a significant decrease in chromophore-dressed-
surface functionality within 1st
round, 10 cycling. The decrease in
the potential of the chelating/capturing probes at IEs surfaces leads
to the reduction of cobalt extraction efficiency and thus increase
the required extraction time. For example, the adsorption
capacities of IE-1 and IE-2 decrease after 1st
round, 10 reuse/cycles
from 141 and 193 to 85 and 122 mg/g, respectively. The decrease of
the adsorption/extraction efficiency after 10 reuse/cycles may be
due to the potential influence of the eluent HCl agent on the 1st
round reused-IEs surfaces. Our finding indicated that the eluent
agent inhibits the active-surface-site binding of reused IEs. Thus,
the reactivation of active-surface-binding sites was considered to
any further extraction steps (i.e., 2nd
round of IEs recycling, Figure
7B). Here, we consider two methodology for reactivation of IEs
surfaces: (i) direct re-impregnation through the immobilization of
current chromophores (MPDN and TDDB) into the consumed IEs
after the 10th
cycle directly or (ii) calcination of the consumed IEs
after the 10th
cycle at 250°C–300°C under air atmosphere to remove
the residual organic chelating agent completely as carbon and
nitrogen oxides; consequently, pure mesoporous γ-Al2O3 is
produced as a white solid material with retained effective
functionality and original surface textures. The latter method shows
drawbacks in (i) high-capital cost, (ii) consumed time and
temperature, (iii) mounting poisonous gases, and (iv) prevention of
potential negative effect of calcination in green environment. On
the base of our eco-efficiency e-waste recycles, we considered the
former method of re-addressing of IEs surfaces is more convenient
(named as 2nd
round reused-IEs). We carried out the decoration of
process of MPDN and TDDB probes into reused IES-1 and IES-2,
respectively, as shown in experimental section of first preparation
of IEs. Then we carried out the cobalt uptake/elution processes
(i.e., the 2nd
round of IEs recycling for further 10 reuse/cycles),
Figure 7B. The obtained results (Figure 7B) showed that the uptake
efficiency of Co2+
ions using the re-produced IE-1 and IE-2 (2nd
round IEs recycling) decreases by 2-3% compared with the freshly-
prepared IEs in the 1st
round cycling (Figure 7A), as an axiomatic
result of the reproduction/reactivating of the surface sites of 1st
round reused IEs. By contrast, the elution efficiencies of adsorbed
Co2+
ions remain at ≥ 99%. The extraction process was repeated for
another 10 times of reuse/cycles process and the decrease of Co2+
ion uptake efficiency was observed. For example, at the 10th
cycle
of 2nd
round of reused IEs, the uptake efficiencies of IE-1 and IE-2
decrease to 45% and 43%, respectively (see Fig. 7B).
Significantly, the consumed IEs surfaces (2nd
round recycling) can be
re-activated through direct reimpregnation of MPDN and TDDB
colorants to produce 3rd
round reused IEs. For instance, Figure 7C
shows the representative design of dead-end re-cycling mechanism
of Co2+
ion-uptake/elution processes using IEs. The retention of the
sponge IE design with large surface area-to-volume ratios,
macro/mesopores, and grooves along the micrometric, hierarchal
monolith structures (Figure 7C) enables the reduction of the Co2+
ion extraction cost by recycling the spent extractors for several
reuse/cycle processes (i.e. dead-end recycling process) without
significant changes in the distinct IEs architecture. The design shows
evidence of the full ion-uptake/trapping/recovery into the interior
pores IEs.
Figure 7
Extraction/recovery of Co2+
ions from simulated and real leach
liquors of SLIBs
ICP-MS analysis of the SLIB solutions indicated that the internal
black powder mainly consists of Co2+
, Li+, Ni
2+, Cu
2+, Al
3+, Mn
2+, and
Fe3+
. Therefore, a set of batch experiments was conducted using
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simulated solution similar to the metal content of SLIB leach liquor;
20 mL of 2 ppm Co2+
, Li+, Ni
2+, Cu
2+, Al
3+, Mn
2+, and Fe
3+ ions were
stirred with 20 mg of solid IE-1 and IE-2 in two different beakers
under the optimum pH conditions with continuous stirring for 30
min (Scheme S1). To suppress the interfering cations, few drops of
citrate (0.1 M), thiosulfate (10 mM), and tartrate mixture solution
were added to the above solutions as concealing agents. The
obtained filtrate solution was analyzed by ICP-MS, as summarized in
Table 2. The obtained data showed that 95% and 96.6% of Co2+
ions
are extracted using the optical IE-1 and IE-2, respectively. In
addition, ≥ 99% of the adsorbed Co2+
can be released by using HCl
(0.2 M) as stripping agent. Our findings indicated that the optical IEs
are highly selective for Co2+
ions even in the presence of equal
concentrations of competing ions. These IES can also be recycled.
In actual extraction process (see Scheme S1), the black powder of
SLIBs was leached using a mixture of H2SO4 and H2O2 solution.
Subsequently, the Fe3+
content was eliminated through
precipitation with NaOH. The metal content of the obtained
solution analyzed by ICP-MS is as follows: 1.75 ppm Co2+
, 418 ppm
Ni2+
, 362 ppm Mn2+
, 375 ppm Li+, 1 ppm Al
3+, and 3 ppm Fe
3+, as
listed in Table 2. To evaluate the optical extraction of a Co2+
ion
from the leach liquor of SLIBs, a series of batch contact experiments
was carried out under the optimum extraction conditions (pH 5 and
4 for IE-1 and IE-2, respectively, with continuous stirring for 3 h at
25°C±2°C). Further clarification about the real leaching and optically
tracked extraction is shown in Scheme S1. Optical-IEs (20 mg) were
mixed with 20 mL of the leach liquor in the presence of a mixture of
0.1 M citrate and 10 mM thiosulfate and tartrate solution as a
masking agent to avoid the negative effect of other ions. The
removal/adsorption efficiencies of Co2+
ions decrease at the first
cycle from 95% and 96.6% of the simulated solution to 87.5% and
89% in actual adsorption from leach liquor of SLIBs using IE-1 and
IE-2, respectively (Fig. 8 and Table 2). The decreased uptake may be
attributed to the high concentration of coexisting ions, such as Ni2+
,
Mn2+
, and Li+, which causes the strong competition at the active
sites of the IE surfaces. Furthermore, the adsorbed Co2+
ions can be
extracted/separated (~98%) using HCl (0.2 M) as stripping agents to
produce Co2+
-free IEs. The regenerated IEs extractors can be utilized
for several reuse/cycles through uptake–elution processes. Our
findings indicated that the current optical IEs can be successfully
applied in the extraction of ultra-trace and high concentrations of
Co2+
ions from SLIBs and other urban e-wastes as secondary sources
of cobalt.
Table 2
Figure 8
Conclusion
Laboratory-scale experiments were conducted for fast, selective,
and sensitive extraction, detection, and recovery of Co2+
ions from
SLIBs even at low concentration levels of approximately 3.05 × 10−8
M using effective and low-cost IEs. IEs were fabricated by
functionalization of mesospongy γ-Al2O3 monoliths using MPDN and
TDDB chelating agents. The use of mesosponge IE architecture
results in quick particle diffusion between pores, high adsorption
capacity, and cost-effective operation. The colour change of IEs with
increased cobalt ion concentration can be tracked visually. The key
experimental values, such as pH solution, contact time, Co2+
concentration, and coexisting matrices, are significant for the
efficient extraction of Co2+
ions. Our findings proved that the
extraction process of Co2+
ions is a pH- and time-dependent
process. Langmuir and pseudo-second-order models are the most
convenient models to describe the optical extraction mechanism of
Co2+
ions. In addition, the consumed IEs can be regenerated or
recycled using HCl (0.2 M) as a stripping agent to release or recover
the adsorbed Co2+
ions completely and produce IE-free-surfaces
with retained functionality for multiple usages (i.e.,>20
reuse/cycles). The obtained findings offer a simple, one-step,
efficient, and widely applicable technique to extract cobalt from e-
wastes. This technique can enable e-waste administration and
recycling to obtain precious metals, thereby reducing a large
amount of accumulated e-wastes.
Conflicts of interest
“There are no conflicts to declare”.
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ACS Appl. Mater. Interfaces, 2015, 7, 13217−13231. (b) I.
M. El-Sewify, M. A. Shenashen, A. Shahat, H. Yamaguchi,
M. M. Selim, M. M. Khalil, S. A. El-Safty, ChemistrySelect,
2017, 2, 11083–11090.
38 (a) E. A. Elshehy, S. A. El-Safty, M. A. Shenashena and M.
Khairy Sens. Actuator B-Chem., 2014, 203, 363–374. (b)
S. A. El-Safty, S. Abdellatef, M. Ismael, and A. Shahat, Adv
Healthc Mater., 2013, 2, 854–862. (c) M. A Shenashen, A.
Shahat and S. El-Safty, J. Hazard. Mater., 2013, 244–245,
726–735. (d) M. A. Shenashen, D. Hassen, S. A. El-Safty,
H. Isago, A. Elmarakbi and H. Yamaguchi, Chem. Eng. J.,
2017, 313, 83-98.
39 (a) M. Y. Emran, M. A. Shenashen, M. Mekawy, A. M.
Azzam, N. Akhtar, H. Gomaa, M. M. Selim, A. Faheem
and S. A. El-Safty, Sens. Actuator B-Chem., 2018, 259,
114–124. (b) M. S. Selim, A. Elmarakbi, A. M. Azzam, M.
A. Shenashen, A. M. EL-Saeed and S. A. El-Safty, Prog.
Org. Coat., 2018, 116, 21-34. (c) M. S. Selim, M. A.
Shenashen, A. Elmarakbi, A. M. ELSaeed, M. M. Selimd
and S. A. El-Safty, RSC Adv., 2017, 7, 21796–21808. (d) M.
A. Shenashen, D. Hassen, S. A. El-Safty, M. M. Selim, N.
Akhtar, A. Chatterjee and A. Elmarakbi, Adv. Mater.
Interfaces. 2016, 3, 1600743-1600755.
40 (a) S. A. El-Safty, M. Ismael, A. Shahat and M. A.
Shenashen, Environ Sci Pollut Res., 2013, 20, 3863–3876.
(b) S. A. El-Safty, M. A. Shenashen, M. Khairy, Talanta,
2012, 98, 69–78. (c) M. A. Shenashen, N. Akhtar, M. M.
Selim, W. M. Morsy, H. Yamaguchi, S. Kawada, A. A.
Alhamid, N. Ohashi, I. Ichinose, A. S. Alamoudi and S. A.
El-Safty, Chem Asian J., 2017, 12, 1952-1964.
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41 (a) M. Y. Emran, H. Khalifa, H. Gomaa, M. A. Shenashen,
N. Akhtar, M. Mekawy, A. Faheem and S. A. El-Safty,
Microchim. Acta, 2017, 184, 4553–4562. (b) N. Akhtar,
M. Y. Emran, M. A. Shenashen, H. Khalifa, T. Osaka, A.
Faheem, T. Homma, H. Kawarada, S. A. El-Safty, J. Mater.
Chem. B, 2017, 5, 7985-7996. (c) M. Y. Emran, M.
Mekawy, N. Akhtar, M. A. Shenashen, I. M. EL-Sewify, A.
Faheem and S. A. El-Safty, Biosens Bioelectron., 2018,
100, 122-131.
42 (a) A. Derbalah, S. A. El-Safty, M. A. Shenashen, and N. A.
Abdel-Ghany, Chempluschem., 2015, 80,1119–1126. (b)
M. S. Selim, M. A. Shenashen, N. A. Fatthallah, A.
Elmarakbi, and S. A. El-Safty, ChemistrySelect., 2017, 15,
9686 – 9695.
43 (a) S. A. El-Safty and T. Hanaoka, Chem. Mater., 2004, 16,
384–400. (b) M. Shenashen, A. Derbalah, A. Hamza, A.
Mohamed and S. El Safty, Pest Manag Sci., 2017, 73,
1121-1126.
44 M. Shamsipur, A. Avanes, M. K. Rofouei, H. Sharghi and
G. Aghapour, Talanta, 2001, 54, 863–869.
45 (a) W. Warkocki, S. A. El-Safty, M. A. Shenashen, E.
Elshehy, H. Yamaguchi and N. Akhtar. J. Mater. Chem. A,
2015, 3, 17578–17589. (b) S. A. El-Safty and M. A.
Shenashen, Sens. Actuator B-Chem., 2013, 183, 58-70.
46 H. Zou, E. Gratz, D. Apelian and Y. Wang, Green Chem.,
2013, 15, 1183–1191.
47 A. Shrivastava and V. B. Gupta, Chron. Young Sci., 2011,
2, 21-25.
48 S. A. Al-Jlil, Appl Water Sci., 2017, 7, 383–391
49 S. Hashemian, H. Saffari and S. Ragabion, Water Air Soil
Pollut., 2015, 226, 2212-2222.
50 (a) A. M. Azzam, M. A. Shenashen, M. M. Selim, A. S.
Alamoudi and S. A. El-Safty, ChemistrySelect, 2017, 2,
11431–11437. (b) X. Li, M. A. Shenashen, X. Wang, A. Ito,
A. Taniguchi and S. A. EI-Safty, Adv. Biosys., 2018, 2,
1700114-1700121. (c) X. Li, M. A. Shenashen, X. Wang, A.
Ito, A. Taniguchi and S. A. EI-Safty, Scientific Reports,
2017 7, 16749-16759.
51 (a) S. A. El-Safty , M. A. Shenashen , M. Ismael and M.
Khairy, Adv. Funct. Mater. 2012, 22, 3013–3021. (b) Y.
Jian-hong, S. You-yi, G. Jian-feng and X. Chun-yan, Trans.
Nonferrous Met. Soc. China, 2009, 19, 1237−1242.
52 (a) S. Liu, C. Chen, Q. Liu, Y. Zhuo, D. Yuan, Z. Dai and J.
Bao, RSC Adv., 2015, 5, 71728–71734. (b) S. A. El-Safty, A.
Shahat, M. Ismael, J. Hazard. Mater., 2012, 201–202, 23–
32.
53 (a) S. K. Lee and C. W. Ahn, Sci. Rep., 2014, 4, 4200-4205.
(b) S. A. El-Safty, M. Sakai, M. M. Selim and A. A.
Alhamide, RSC Adv., 2015, 5, 60307–60321.
54 (a) J. R. Houston, R. S. Maxwell and S. A. Carroll,
Geochem. Trans., 2009, 10, 1-14. (b) S. A. El-Safty, J
Porous Mater., 2011, 18, 259–287.
55 J. Yu, H. Bai, J. Wang, Z. Li, C. Jiao, Q. Liu, M. Zhanga and
L. Liu, New J. Chem., 2013, 37, 366-372.
56 L. Wei, F. Li, C. Liu, C. Liu, M. Chen and Q. Lan, Clean:Soil,
Air, Water, 2013, 41, 856–864.
57 Y. Wang, W. Li, X. Jiao and D. Chen, J. Mater. Chem. A,
2013, 1, 10720–10726.
58 (a) D. Zhang, Q. Chen, L. Hu, X. Chen and J. Wang, J.
Mater. Chem. B, 2015, 3, 4363-4369. (b) H. Gomaa, M.
Farid, M. A. Abd-Elraheem, T. A. S. El-Naser and I. H.
Zidan, Biol. Chem. Res., 2016, 3, 313-340.
59 (a) S. Siva, S. Sudharsan and R. Sayee Kannan, RSC Adv.,
2015, 5, 23340–23349. (b) A. M. Azzam, M. A.
Shenashen, M. M. Selim, H. Yamaguchi, I. M. ElSewify, S.
Kawada, A. A. Alhamid and S. A. El-Safty, J. Phys. Chem.
Solids, 2017, 109, 78-88.
60 L. Dolatyari, M. R. Yaftian and S. Rostamnia, J. Environ.
Manage., 2016, 169, 8-17.
61 (a) M. K. Sureshkumar, D. Das, M. B. Mallia and P. C.
Gupta, J. Hazard. Mater., 2010, 184, 65–72. (b) H. G.
Abdien, M. F. M. Cheira, M. A. Abd-Elraheem, T. A. S. El-
Naser and I. H. Zidan, Elixir Appl. Chem., 2016, 100,
43462-43469.
62 S. Mishra, J. Dwivedi, A. Kumar and N.
Sankararamakrishnan, RSC Adv., 2015, 5, 33023–33036.
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Scheme 1 (A) Systematic synthesis and (B) crystal structure/composition framework of micrometric sponge, mesoporous cage γ-Al2O3 carriers using CTAB as a directing agent and AIP as a precursor in an acidic condition. B) The crystal structures provide evidence of the formation of dense electron along the active Al and O species in the exterior/interior surfaces, leading to facile and
strong binding with target species during the extraction/detection/recovery process.
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Scheme 2 The systematic perspective of Co2+
ion-optical/adsorption/recovery process using IE- and IE-2 designs that were built by direct impregnation/dressing of organic chelating agents (such as MPDN and TDDB colourants) onto meso-γ-Al2O3 carriers,
respectively. Under the visualization protocol of our process, the IE-1 and IE-2 changed their original colour within the Co2+
trapping at pH 5 and 4, respectively.
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Fig. 1 Real and synthetic sample images (A-a, B-a, and C-c) and representative top-view FE-SEM micrographs of calcined, hierarchal mesoporous sponge γ-Al2O3 monolithic rocks (Fig. 1A), solid/mesosponge MPDN-γ-Al2O3 ion-extractor (IE-1) and
Co2+
-ion-IE-1 (Fig. 1B &C, respectively). Figure C-c shows the SEM-EDX of monolithic Co2+
-ion-IE-1 sample, proving that the elemental composition of IE-1 and the trapping of Co
2+ ions.
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Fig. 2 (A, B) Representative FE-SEM, (C, E) HRTEM and (E) electron diffraction mico-graphs of
mesoporous, micro-sponge γ-Al2O3 monoliths. Figs. F-H show the STEM-EDS mapping of γ-
Al2O3 monoliths with display the distribution map of aluminum (G) and oxygen (H).
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Fig. 3 (A) N2 adsorption-desorption isotherm profiles of calcined γ-Al2O3 (blue line), IE-1 (red line) and IE-1/Co2+
(green line) including the values of surface area (SBET, m2/g ), pore size (D, nm) and pore volume (Vp, cm
3/g). (B)
NLDFT profile to explain the pore size distribution of γ-Al2O3, IE-1 and IE-1/Co2+
. (C and D) SA/WA-XRD pattern of
γ-Al2O3, IE-1 and IE-1/Co2+
.
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Fig. 4 27
Al MAS NMR spectra of γ-Al2O3 (A), IE-1 (B) and IE-
1/Co2+
(C).
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Fig. 5 (A) Real UV/Vis spectra of IEs-1 and 2 in blank form (before adsorption/trapping Co
2+ ions) and [Co
2+/IE]
n+ form. Indicating the generate new
peak at wavelength λmax= 370 and 410 nm for IE-1 and 2 at pH 5 and 4, respectively.
(B) Colour-profile shows the increasing of [Co2+
-IE]n+
colour with increasing of Co2+
ion concentration under the optimum sensing conditions. (C and D) UV-Vis spectra show the gradual proportional change of absorbance intensity of IE-1 (C) and IE-2
(D) depending on Co2+
concentration at pH 5 and 4, respectively.
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Fig. 6 Representative selective-profile of [2ppm] Co2+
adsorption/extraction among other competitive cations
in water using IE-1 and IE-2 at the optimal detection/extraction/capture conditions: We added the
competitive ions to the IEs assays as we called single/individual ion-system (A), binary and mixture systems
G1-G15 (colorimetric study, at wavelength λmax= 370 and 410 nm) (B) and (ICP-data) (C) at pH 5 and 4,
respectively. Our UV-Vis spectroscopic study and ICP-MS analyses show the high selective-extraction of Co2+
ions. G1{Co2+
+Li+}, G2{Co
2++Ca
2+}, G3{Co
2++Mn
2+}, G4{Co
2++Cu
2+}, G5{Co
2++Ni
2+}, G6{Co
2++Al
3+}, G7{Co
2++Hg
2+},
G8{Co2+
+Pb2+
}, G9{Co2+
+Cr3+
+Au3+
}, G10{Co2+
+Hg2+
+Pb2+
}, G11{Co2+
+Cd2+
+Li+}, G12{Co
2++Al
3++Pb
2++Hg
2+},
G13{Co2+
+Cu2+
+Mn2+
+Li++Ca
2+}, G14{Co
2++Ni
2++Cu
2++Ca
2++Mn
2++} and
G15{Co2+
+Li++Mg
2++Ca
2++Pb
2++Hg
2++Cr
3+}.
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Table 1 shows the isotherm and kinetic models of Co2+
adsorption using optical-IEs 1 and 2 at pH 5 and 4, respectively.
Langmuir
isotherm
Freundlich
isotherm
pseudo
first-order
pseudo
second-order
IE-1
Experimental
qm (mg/g) 141.3
R2 0.9952 R
2 0.9313 R
2 0.501 R
2 0.994
qm 142.8 KF, mg/g 22.2 qe, mg/g 140.05 qe, mg/g 2.29
KL, L/mg 0.161 1/n 0.3611 K1, min-1
1.8X10-4
K2, g/mg.min 0.139
IE-2
Experimental
qm (mg/g) 193.5
R2 0.9969 R
2 0.8843 R
2 0.51 R
2 0.996
qm 196.07 KF, mg/g 29.2 qe, mg/g 192.2 qe, mg/g 2.27
KL, L/mg 0.183 1/n 0.3969 K1, min-1
2.6X10-5
K2, g/mg.min 0.15
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Fig. 7 (A & B) Uptake and elution efficiencies of Co2+
ions using IE-1 and IE-2 as a function of adsorption-releasing cycle
numbers. To evaluate reusability and reproducibility of IEs in the extraction process, we carried out a set of experimental assays based on monitoring the Co
2+ extraction efficiency under continuous IE regeneration protocol. In this regard, we
treated 1st
used-IEs after 10th
reuse/cycles (A) by re-addressing and activating their surfaces by decorated-probes (MPDN and TDDB) to develop and generate 2
nd used-IEs. Note: The 1
st and 2
nd used-IES re-cycling protocol showed the dead-end
regeneration/extraction of Co2+
ions. The elution efficiencies of adsorbed Co2+
ions are more than ≥99% of the adsorbed Co
2+ ions. (C) Representative scheme of dead-end re-cycling protocol of Co
2+ ion-uptake/elution processes using
mesoporous IEs. The scheme shows evidence of the full ion-uptake/trapping/recovery into the interior pores IEs.
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Table 2. ICP-MS analysis data of Co2+
ions before and after adsorption and after elution in the presence of other competitive ions using
optical-IEs 1 and 2
[Co2+
], ppm % [Competitive ions], ppm
Simulated-Extraction
Before adsorption 2.1± 0.004 -- Li
+ 2.05, Ni
2+ 1.98, Cu
2+ 2.0, Al
3+ 1.89, Mn
2+ 2.1, Fe
3+ 2.05, Ca
2+ 3, K
+ 10
After adsorption
IE-1
IE-2
0.105±0.006
0.07±0.005
95.0
96.6
Li+
2.01, Ni2+
1.95, Cu2+
1.98, Al3+
2.1, Mn2+
2.03, Fe3+
2.03, Ca2+
2.99, K+
9.99
Li+
1.98, Ni2+
1.93, Cu2+
1.95, Al3+
2.14, Mn2+
2.07, Fe3+
2.04, Ca2+
3, K+
9.98
After elution
IE-1
IE-2
1.98±0.001
2.01±0.002
99.2
99.0
Li+
0.04, Ni2+
0.032, Cu2+
0.02, Al3+
0.08, Mn2+
0.06, Fe3+
0.02, Ca2+
0, K+
0.003
Li+
0.06, Ni2+
0.046, Cu2+
0.048, Al3+
0.12, Mn2+
0.031, Fe3+
0.012, Ca2+
0, K+
0.01
Real-Extraction
Leach liquor
3.5±0.006
--
Li+
375, Ni2+
3.6, Cu2+
1.5, Al3+
1.0, Mn2+
362, Fe3+
0.3, Ca2+
4.9, K+
47.5
After adsorption
IE-1
IE-2
0.435±0.003
0.39±0.0015
87.5
89.0
Li+
360, Ni2+
3.4, Cu2+
1.4, Al3+
1.45, Mn2+
345, Fe3+
0.2, Ca2+
4.8, K+46.5
Li+
363, Ni2+
3.2, Cu2+
1.37, Al3+
1.5, Mn2+
350, Fe3+
0.25, Ca2+
4.8, K+47.3
After elution
IE-1
IE-2
3.0±0.0062
3.05±0.0025
97.8
98.0
Li+
3.2, Ni2+
0.08, Cu2+
0.08, Al3+
0.3, Mn2+
3.2, Fe3+
0.055, Ca2+
0.05, K+
0.1
Li+
4.5, Ni2+
0.15, Cu2+
0.09, Al3+
0.2, Mn2+
2.54, Fe3+
0.063, Ca2+
0.02, K+
0.05
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Fig. 8 Real applicability shows the high efficient extraction process of Co2+
ions from a real solution of SLIBs using IEs-1 (A) and
IE-2 (B) at pH 5 and 4, respectively. These figures show the concentration (in ppm) of Co2+
ions and other co-existing ions (Li+,
Ni2+
, Cu2+
, Al3+
, Mn2+
, Fe3+
, Ca2+
, and K+) in leach liquor, after adsorption and after elution.
Page 25 of 26 Green Chemistry
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ARTICLE Journal Name
26 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx
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Page 26 of 26Green Chemistry
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45:3
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View Article OnlineDOI: 10.1039/C7GC03673F
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