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(2016) 2013–2020

Ceramics International 42

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Photocatalytic properties of Bi2O3 powders obtainedby an ultrasound-assisted precipitation method

D. Sánchez-Martínezn, I. Juárez-Ramírez, Leticia M. Torres-Martínez, I. de León-Abarte

Universidad Autónoma de Nuevo León, Facultad de Ingeniería Civil-Departamento de Ecomateriales y Energía, Cd. Universitaria, C.P. 66455 San Nicolás de losGarza, N.L., México

Received 29 July 2015; received in revised form 2 October 2015; accepted 2 October 2015Available online 14 October 2015

Abstract

Bi2O3 nanoplates were synthesized by an ultrasound-assisted precipitation method in aqueous solution with different times of exposure toultrasound radiation. The formation of Bi2O3 oxide with a monoclinic structure was confirmed by X-ray powder diffraction (XRD), which wasalso used to determine the crystallite size and lattice strain. The characterization of Bi2O3 samples was complemented with scanning electronmicroscopy (SEM), which revealed the morphology of the particles as irregular, ovoid and rectangular nanoplates as a function of the time ofexposure to ultrasound radiation. Infrared spectroscopy (FT-IR) was used to confirm the elimination of the bismuth nitrate used in the synthesis.The specific surface area was determined by the BET method. Diffuse reflectance spectroscopy (DRS) was used to determine the band-gapenergy (Eg) of the Bi2O3 samples. The photocatalytic activity of Bi2O3 samples was evaluated with respect to the degradation reactions ofrhodamine B (rhB), indigo carmine (IC) and tetracycline hydrochloride (TC) in aqueous solution under Xe lamp irradiation. The highestphotocatalytic activity was identified for the sample exposed to 2 h ultrasound radiation, i.e., the sample that presented the highest crystallinity,smaller particle size and a more homogeneous morphology. The mineralization degree of organic dyes and antibiotic by Bi2O3 was determined bythe total organic carbon analysis (TOC), reaching percentages of 40% for rhB, 13% for IC and 72% for TC after 24 h of Xe lamp irradiation.& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Keywords: Bi2O3; Ultrasound-assisted precipitation synthesis; Organic pollutants; Photocatalysis

1. Introduction

The environmental pollution caused by human activities hascontinued to increase, which has necessitated the implementa-tion of sustainable processes. Heterogeneous photocatalysis,which is a clean, green and sustainable technology for theelimination of organic pollutants present in water as dyes,medicine and pesticides, has been introduced [1]. This technol-ogy uses a material semiconductor called a photocatalyst for thedegradation of organic contaminants active under irradiationwith UV and visible light. Recently, the development ofmaterial photocatalyst have been oriented toward the use ofthe solar radiation, including simple oxides, such as Bi2O3 [2],

10.1016/j.ceramint.2015.10.00715 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

g author.42 4400x5143; fax: þ52 81 1442 4443.ss: dansanm@gmail.com (D. Sánchez-Martínez).

CuO [3], ZnO [4] and WO3 [5], and some mixed oxides such asBi2MoO6 [6], BiVO4 [7] and Bi2WO6 [8]. Bi2O3 has attractedthe most attention because it has the advantages of beingeconomically and environmentally viable for use as a photo-catalyst in the remediation of contaminated water [4,9]. Bi2O3 isactive under irradiation with visible light due to having an Eg ofapproximately 2.7–2.8 eV [9,10]. This oxide presents thepolymorphism phenomenon with the phase α-Bi2O3 being morestable at ambient temperature [11]. There are few studies in theliterature about the use of Bi2O3 as a photocatalyst in thedegradation of organic compounds, such as dyes, and even lessfor the degradation of antibiotics. Bi2O3 has been regularly usedwhen doped or mixed with other oxides. Therefore, Bi2O3 is agood candidate to further explore the degradation of organicpollutants in aqueous media. The synthesis of Bi2O3 hasattracted special attention, and researchers have attempted toprepare it through various methods, including precipitation [12],

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Inte

nsity

(a.u

.)

Wavelength (nm)

a) Xe lamp

b) Xe lamp inside the reactor

c) solar spectrum

Fig. 1. Emission spectrum of: (a) Xe lamp, (b) Xe lamp inside the reactorand (c) solar spectrum.

D. Sánchez-Martínez et al. / Ceramics International 42 (2016) 2013–20202014

refluxing [13], urea [14], citrate [15], sonochemical [16],electrospinning [17] and hydrothermal [18]. The precipitationmethod is the simplest to obtain Bi2O3 with good crystallinitybut with the disadvantage of obtained particle size andmorphology being highly variable. However, this variabilitycan be controlled and improved with the assistance of othermethods, such as ultrasound. This combination of synthesismethods potentiates the preparation of materials because it ispossible to exploit the advantages of both methods to achievesynergy that minimizes the disadvantages of the individualmethods, thus obtaining materials with unique properties.

Therefore, in this work, Bi2O3 nanoplates were successfullyprepared by ultrasound-assisted precipitation in aqueous solutionwith different times of exposure to ultrasound radiation. Thesamples were characterized, and their photocatalytic propertieswere evaluated in the degradation of two dyes and an antibiotic:rhodamine B (rhB, CAS 81-88-9), indigo carmine (IC, CAS 860-22-0) and tetracycline hydrochloride (TC, CAS 64-75-5) underXe lamp irradiation as a simulated sunlight source.

2. Experimental

2.1. Synthesis of Bi2O3

Bi2O3 powders were synthesized by ultrasound-assistedprecipitation in aqueous solution with different times ofexposure to ultrasound radiation. The Bi2O3 samples wereprepared by the following procedure: 6.25 g (0.0129 mol) ofbismuth(III) nitrate pentahydrate (BiN3O9 � 5H2O, Z98% pur-ity, Sigma-Aldrich) was dissolved in 100 mL of a nitric acidsolution (10% v/v, HNO3) under continuous stirring at 80 1C inan electric oven. Then, the pH of the solution was adjusted to 11with a 2 M NaOH solution, causing the formation of a whiteprecipitate. The precipitated was maintained without stirring inan ultrasonic bath (42 kHz þ /� 6%, 100 W) for 1, 2 or 3 h.The precipitate was then washed several times with distilledwater to neutralize the pH of the solution and was dried in air at80 1C for 24 h. Finally, the material was thermally treated at500 1C for 4 h from room temperature to the specified tempera-ture at a heating rate of 10 1C min�1 to obtain Bi2O3. Forcomparative purposes, commercial Bi2O3 was used (99.9%purity, 10 mm, Sigma-Aldrich).

2.2. Characterization of the samples

Structural characterization of the Bi2O3 samples was per-formed by X-ray powder diffraction (XRD) analysis using aBRUKER D8 ADVANCED diffractometer with CuKα radia-tion (λ¼1.5418 Å) equipped with a high-speed Vantec detector.X-ray diffraction data were collected in the 2θ range of 10–701with a scan rate of 0.051 and 0.5 s�1. To estimate the crystallitesize and lattice strain behavior, the Bi2O3 samples werefollowed by means of the half-width of the strongest line ofthe XRD pattern of oxide. Using these data, the crystallite sizeof the particles of the samples was calculated through theScherrer equation [19,20], as follows: L¼kλ/βcos(θ); where L isthe crystallite size, k is the Scherrer constant, usually taken as

0.89, λ is the wavelength of the X-ray radiation (1.5418 Å), β isthe full width at half-maximum (FWHM) of the diffraction peakmeasured at 2θ and θ is the diffraction angle. The lattice strainof the samples was calculated by the following equation: ε¼β/4tan(θ) [20]; where ε is the lattice strain, and β and θ are thesame values used to determine the crystallite size. Infraredspectroscopy (NICOLET 380 FT-IR) was used to confirm theelimination of the bismuth nitrate used in the synthesis. Themorphology and particle size were investigated by scanningelectron microscopy using JEOL Instruments model JSM 6490.The band-gap energy (Eg) was determined by means of the

UV–vis diffuse reflectance absorption spectra of the Bi2O3samples, which were taken using a Cary 500 UV–vis NIRspectrophotometer equipped with an integrating sphere. The Egvalue was calculated for direct transition from the UV–visspectrum by extrapolating a straight line to the slope of the x-axis using the following equation: Eg¼1240/λg, where λg isthe wavelength (nm) of the exciting light, and Eg is the band-gap energy [19]. The BET surface area of the Bi2O3 sampleswas determined by adsorption–desorption N2 isotherms using aBELSORP-mini II surface area and pore size analyzer. Theisotherms were evaluated at �196 1C after degassing thesamples by thermal treatment at 150 1C for 12 h.

2.3. Photocatalytic tests

The photochemical reactor employed in this work consisted of aglass borosilicate beaker surrounded by a water jacket to maintainthe reaction temperature at 25 1C 71. A 35 W Xe lamp of6000 K with a luminous flux of 36,000 lux was used as asimulated sunlight source. The emission spectrum of the Xe lampwas measured by an Ocean Optics Jaz Spectrometer (see Fig. 1). Anegligible contribution of UV radiation was observed (o390 nm).The Bi2O3 photocatalytic activity was evaluated by the

degradation reactions of two dyes, rhodamine B (rhB, CAS 81-88-9) and indigo carmine (IC, CAS 860-22-0), and oneantibiotic, tetracycline hydrochloride (TC, 64-75-5), in aqu-eous solution. By taking into account the molar extinction

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*

*

JCPDS 00-071-0465

2 degree

BCOM

B1U

Inte

nsity

(a.u

.) B2U

B3U

θ

Fig. 2. X-ray powder diffraction patterns of Bi2O3 samples exposed for 1, 2 or3 h to ultrasound radiation calcined at 500 1C and the commercial oxide;* bismuth nitrate traces.

Table 1Structural and surface characterization of Bi2O3 samples prepared by ultra-sound-assisted precipitation with different times of exposure to ultrasoundradiation.

Sample Crystallite size (nm) Lattice strain (%) Eg (eV) BET (m2 g�1)

BCOM 35 0.412 2.7 0.2B1U 33 0.439 2.7 1.1B2U 39 0.372 2.7 0.4B3U 21 0.669 2.3 1.6

4000 3500 3000 2500 2000 1500 1000 500

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BCOM

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ance

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.)

Wavenumber (cm )

Fig. 3. FT-IR spectra of the Bi2O3 samples exposed for 1, 2 or 3 hto ultrasound radiation and the commercial oxide.

D. Sánchez-Martínez et al. / Ceramics International 42 (2016) 2013–2020 2015

coefficient of the dyes and the antibiotic, the initial concentra-tions were 5 mg L�1 for rhB, 30 mg L�1 for IC and 20 mgL�1 for TC. The photocatalytic tests were performed asfollows: 200 mL of organic compound solution containing200 mg of Bi2O3 powder was added to a glass beaker and thenplaced in an ultrasonic bath for 1 min to eliminate aggregates.The solution was then transferred to the photocatalytic reactor.The solution was kept in the dark for 1 h to ensure that theadsorption–desorption equilibrium of the organic compoundon the catalyst surface was reached. After this time, the lightsource was turned on. During the reaction, aliquots were takenfrom the reactor at different time intervals. The powders wereseparated by centrifugation, and the filtered solution wasanalyzed in a UV–vis spectrophotometer following the proce-dure established in a previous work [21]. Repeatability testswere performed to evaluate the stability of Bi2O3 oxide.

The mineralization degree of the organic compounds wasexamined by the analysis of the total organic carbon (TOC)content of the solutions at different irradiation times using aSHIMADZU TOC-VSCH analyzer. For these experiments,200 mL of the organic compound solution (20 mg L�1 forrhB, 30 mg L�1 for IC and 20 mg L�1 for TC) containing200 mg of photocatalyst was used.

3. Results and discussion

3.1. Structural characterization

The obtained powders of Bi2O3 with exposure for 1, 2 or 3 h toultrasound radiation were thermally treated at 500 1C. For com-parative purposes, commercial Bi2O3 was used (BCOM). Thematerials presented a light yellow tinge. The formation of theBi2O3 crystalline structure was followed by the X-ray diffractionpattern. Fig. 2 shows the X-ray diffraction patterns of the Bi2O3samples exposed for 1, 2 or 3 h to ultrasound radiation and heatedat 500 1C (hereafter identified as B1U, B2U and B3U, respec-tively). For all samples, the materials crystallized as the α-Bi2O3polymorph with a monoclinic structure, according the JCPDS cardno. 01-071-0465. All samples presented main diffraction peakslocated at 2θ¼24.51, 25.71, 26.91, 27.31, 281, 331, 33.21 and 46.31,which are typical of the α-Bi2O3 polymorph. However, samplesB1U and B3U had an additional reflection at 2θ¼30.71 thatcorresponded to bismuth nitrate traces, which in these samples wasnot fully decomposed. It is assumed that longer ultrasound reactiontime provokes the partial decomposition of the Bi2O3, therefore thefree bismuth react with the ions nitrate, forming bismuth nitrate.Table 1 shows the crystallite size and lattice strain of thesynthesized samples. The results revealed that the B2U samplehad a higher crystallite size value, which indicates growth of thecrystals and increasing crystallinity. This result was corroboratedby the XRD pattern, where the B2U sample presented morenarrow peaks of higher intensity and the formation of the purephase. When lattice strain decreases, the crystallinity of the samplesincreases [22], and sample B2U presented the lowest value oflattice strain.

Fig. 3 shows the FT-IR spectra of the Bi2O3 samplesexposed for 1, 2 or 3 h to ultrasound radiation and heated at

500 1C, as well as the commercial Bi2O3. The IR analysis wasperformed with the aim of identifying the impurities observedby XRD in the B1U and B3U samples, i.e., the presence ofnitrate traces. In this sense, Fig. 3 shows that only the B1U andB3U samples presented additional bands compared to com-mercial oxide. These bands were located at 1340 and1390 cm�1 and corresponded to N–O, which can be attributedto the NO�3 ion.

Fig. 4. SEM images of Bi2O3 particles synthesized by ultrasound-assisted precipitation with different times of exposure to ultrasound radiation: (a) 1 h, (b) 2 h,(c) 3 h and (d) commercial oxide.

D. Sánchez-Martínez et al. / Ceramics International 42 (2016) 2013–20202016

3.2. SEM morphology analysis

The morphology and particle size of the Bi2O3 samples wereanalyzed by SEM. Fig. 4 shows the SEM micrographs of thesamples obtained by ultrasound irradiation for 1, 2 or 3 h andcalcined at 500 1C, in addition to the commercial oxide. Whenthe oxide was exposed for 1 h to ultrasound radiation,agglomerated particles were observed with the morphologyof irregular nanoplates, with a thickness of approximately50 nm and a length of 0.5 mm (see Fig. 4a). On the other hand,the samples synthesized with 2 h of ultrasound radiationpresented a change in morphology to ovoid nanoplates, witha more homogeneous and smooth surface and a thickness ofapproximately 50 nm and length of 200 nm, as shown in Fig.4b. The samples obtained with 3 h in the ultrasonic bathpresented a similar morphology to those exposed for 1 h butwith a more defined shape and a larger particle size, i.e.,mainly rectangular nanoplates with a thickness of approxi-mately 80 nm and a length above 1 mm (see Fig. 4c). Thecommercial sample had particles with a rod shape with athickness of approximately 3 mm and a length of 5–10 mm, asshown in Fig. 4d, which is different from the samplessynthesized by ultrasound.

Therefore, we can conclude that with the increase ofexposure to the ultrasound radiation, the Bi2O3 samplespresented a similar morphology of nanoplates with a changeof shape in the following order: irregular to ovoid torectangular (see Fig. 5). The sample exposed for 2 h in theultrasonic bath had the smallest particle size and a morehomogeneous morphology.

3.3. Band-gap energy and BET surface area analysis

The optical properties of the Bi2O3 samples (B1U, B2U andB3U) and commercial oxide were analyzed using UV–visdiffuse reflectance spectroscopy. Table 1 shows the band-gapenergy (Eg) values of the samples. The Eg values were withinthe range reported in the literature (i.e., 2.3–2.7 eV [9,10]) andwere similar to the Eg value of commercial oxide.The specific surface areas of the Bi2O3 samples measured by

the BET method are also included in Table 1. All of thesynthesized samples had a higher surface area value thancommercial Bi2O3. The specific surface area value obtained forall samples was low, at 2 m2 g�1. All samples presented a typeII isotherm (i.e., typical behavior of a material that is notporous, according to the classification previously establish foradsorption–desorption isotherm [23]).Therefore, these experiments revealed that the textural

properties, such as the specific surface area of the Bi2O3samples, were not influenced by the varying of time exposurein an ultrasonic bath during the synthesis. A similar effect wasobserved in the optical properties. In contrast, significantdifferences were observed in the morphology properties withvarying exposure time to ultrasound radiation.

3.4. Evaluation of photocatalytic activity

The photocatalytic activity of Bi2O3 samples was evaluated forthe degradation reactions of rhB, IC and TC in water under a6000 K Xe lamp as the radiation source. Fig. 6 shows the temporal

1U-500°C

2U-500°C

3U-500°C

Aqueous media

BiN O ·5H O Precursor

Bi O nanoplates

Fig. 5. Schematic representation of the formation of Bi2O3 particles exposed for 1, 2 or 3 h to ultrasound radiation.

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C/C

orh

B

Time (minutes)

Without photocatalystBCOMB1UB2UB3U

Fig. 6. Photocatalytic degradation of rhB (5 mg L�1) under simulated sunlightirradiation by Bi2O3 synthesized under different experimental conditions; a Xelamp was used as a simulated sunlight source, pH 6.0. The concentration ofrhB was determined through its maximum absorption band (554 nm).

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Fig. 7. Photocatalytic degradation of IC (30 mg L�1) under simulated sunlightirradiation by Bi2O3 synthesized under different experimental conditions; a Xelamp was used as a simulated sunlight source, pH 6.0. The concentration of ICwas determined through its maximum absorption band (610 nm).

D. Sánchez-Martínez et al. / Ceramics International 42 (2016) 2013–2020 2017

degradation of rhodamine B (5 mg L�1) with different synthesizedBi2O3 samples used as photocatalysts. After 180 min of Xe lampirradiation, all of the samples bleached the rhB solution to a largedegree. The best photocatalytic activity was shown by the B2Usample, i.e., the sample that presented the highest crystallinity,smallest particle size and more homogeneous morphology. There-fore, the activity could be attributed to the high crystallinity of theB2U sample because high crystallinity results in a reduced numberof defects and prevents the recombination of electron–hole pairs. Inthe same way, other factors that favor the photocatalytic activity ofthe B2U sample include its smaller particle size and morehomogeneous morphology because minimizing the size of thephotocatalyst particles can maximize the number of active sites,causing an increase in photocatalytic performance.

Fig. 7 shows the photocatalytic activity of the Bi2O3 samples forthe degradation of IC (30 mg L�1) by Xe lamp irradiation. Allsynthesized samples presented better activity than the commercialoxide. After of 180 min of exposure to Xe lamp radiation, theB1U, B2U and B3U samples bleached the IC solution nearly100%. The sample that presented the best photocatalytic activity

was B2U, which is similar to the findings in the evolution of theconcentration of rhB. Therefore these results we can conclude thatin the degradation of indigo carmine and rhodamine B, the IC hasa discoloration less time because it suffers the attack by radicalsformed in the photocatalytic process breaking its chromophoregroup, which is responsible of its coloration [24]. Nevertheless,mineralization becomes slow in concordance with the proposedmechanism by Vautier et al. [25], where it is observed that aminogroups and nitro groups bonded to a benzene group, which may becompeting in the oxidation processes to transform an amino group,forming a nitro group. While in the case of the rhB a fully de-ethylated rhB molecule occurs causing that the color of the solutiondisappears, indicating that the chromophore structure of the dyewas destroyed [26,27], which occurs slowly.The evolution of the concentration of TC (20 mg L�1) in

presence of the Bi2O3 samples used as photocatalysts under Xelamp irradiation is shown in the Fig. 8. The synthesized samplespresented better activity than BCOM, with the exception of thesample B3U, with a percentage of degradation of approximately50% after of 180 min of exposure to the Xe lamp. For B1U andB2U, the percentages of degradation were similar at approximately

D. Sánchez-Martínez et al. / Ceramics International 42 (2016) 2013–20202018

65%. However, B2U had the best photocatalytic activity. On theother hand, it seems that the degradation reaction of TC stop at60 min, however degradation continues but it is more slowly asshown in Figs. 8 and 9c. This is due to intermediary products thatform the TC structure during its degradation, which become morecomplex [28]. Therefore, these experiments revealed that the

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C/C

oTC

Time (minutes)

Without photocatalystBCOMB1UB2UB3U

Fig. 8. Photocatalytic degradation of TC (20 mg L�1) under simulated sun-light irradiation by Bi2O3 synthesized under different experimental conditions;a Xe lamp was used as a simulated sunlight source, pH 6.0. The concentrationof TC was determined through its maximum absorption band (357 nm).

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0306090120150180

Fig. 9. Variation of the UV–vis absorption spectra of: (a) rhodamine B, (b) indigophotocatalytic activity (B2U).

degradation of rhB, IC and TC is possible when Bi2O3 synthesizedby ultrasound-assisted precipitation is used as a photocatalyst, andB2U presented the best photocatalytic activity.Fig. 9 shows the UV–vis absorption spectra of rhB, IC and

TC solutions when being photodegraded by B2U. The UV–visabsorption spectra of the three pollutants decreased over thetime in the ultraviolet and visible regions. This decrease maybe indirectly caused by a direct attack on the aromatic rings ofits molecules [29], which leads to the breaking of the bondsand provokes the complete decomposition into small organic/inorganic molecules and/or ion products [30]. However,aromatic ring of the organic molecules remains even after4 h of reaction; this is due to the intermediary products that aregenerated during the degradation of the organic contaminants[25,27,28], which are difficult to decompose after this time.To determine if the mineralization of organic compounds by

Bi2O3 exposed under Xe lamp irradiation is feasible, total organiccarbon (TOC) content during the photocatalytic test for thedegradation reactions of rhB, IC and TC (see Fig. 10) wasperformed. For these experiments, the sample with the highestphotocatalytic activity (B2U) was used as the photocatalyst. After24 h under Xe lamp irradiation, the mineralization degree wasapproximately 40% for rhB, 13% for IC and 72% for TC.Therefore, Bi2O3 synthesized by ultrasound-assisted precipitation

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carmine and (c) tetracycline in presence of the sample that exhibited the best

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ICrhBTC

Fig. 10. Variation of the TOC during the mineralization of rhB, IC and TC byusing B2U catalyst under simulated sunlight irradiation; pH 6.0.

D. Sánchez-Martínez et al. / Ceramics International 42 (2016) 2013–2020 2019

method can be used as a photocatalyst to provoke a considerablemineralization degree of organic pollutants. These results wereassociated with the UV–vis absorption spectra previously explained,where it was observed that Bi2O3 is feasible for the partialdegradation of rhB, IC and almost the complete degradation ofTC. These results confirm that it is feasible to break the bonds oforganic compounds (rhB, IC and TC) during the photo-catalytic tests.

4. Conclusions

Bi2O3 powders with monoclinic structure were successfullysynthesized by ultrasound-assisted precipitation method withvaried times of exposure to ultrasound radiation. The largestcrystallite size and lowest lattice strain were obtained in theB2U sample, i.e., the sample with the highest crystallinity. TheBi2O3 samples exposed to ultrasound radiation (1, 2 or 3 h)presented a similar morphology of nanoplates in the followingorder: irregular to ovoid to rectangular, respectively. Thespecific surface area of the Bi2O3 samples was not influencedby the varying exposure time in the ultrasonic bath duringsynthesis. In contrast, significant differences were observed inthe morphology properties with varying exposure time. Thehighest photocatalytic activity was found for the B2U sample,i.e., the sample with the highest crystallinity, smallest particlesize and more homogeneous morphology. Therefore, thephotocatalytic activity of Bi2O3 was attributed to the crystal-linity, particle size and the morphology of rectangular nano-plates. After 24 h under Xe lamp irradiation, the mineralizationdegree of organic dyes and the antibiotic was: 40% for rhB,13% for IC and 72% for TC. These results indicate thepotential of Bi2O3 synthesized by ultrasound-assisted precipi-tation method as a good candidate for use as an effectivephotocatalyst in the removal of organic dyes and antibiotics.

Acknowledgments

The authors wish to thank to the Universidad Autónoma deNuevo León (UANL) for its invaluable support through the

project PAICYT 2015; CONACYT, for support of Project CB-2013-01 Clave: 220802 and SEP, for support of project PIFI2014 Apoyo al CA-UANL-244.

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Photocatalytic properties of Bi2O3 powders obtained by an ultrasound-assisted precipitation methodIntroductionExperimentalSynthesis of Bi2O3Characterization of the samplesPhotocatalytic tests

Results and discussionStructural characterizationSEM morphology analysisBand-gap energy and BET surface area analysisEvaluation of photocatalytic activity

ConclusionsAcknowledgmentsReferences