In summary, “Solution Combustion Method” has been used for preparing ZnO particles doped with nitrogen as it is suggested by the Raman spectra. This fact could indicate that nitrogen has been successfully introduced to the crystalline lattice creating a new absorption band in the visible range and therefore decreasing the bandgap. Raman spectra has also verified that the highest amount of nitrogen included into the crystal lattice of the catalyst are shown generally in the catalysts prepared with the lowest ratio (Urea-Zinc Nitrate Hexahydrate) and calcination temperature. As further work, test of catalytic activity will be performed in the photocatalytic reaction system displayed in above.

Julio Núñez Casas, Víctor A. de la Peña O’Shea, Juan M. Coronado, David Serrano Granados

Thermochemical Processes Group, IMDEA Energy, c/Tulipán, s/n, E-28933 Móstoles (Madrid), Spain*email:julio.nunez@imdea.org

Synthesis and characterization of ZnO(1-x)Nx by a novel method and its potential application as photocatalyst

Morphological characterization by ESEM depicts agglomerates of micrometer-sized crystals for ZnNU1 catalysts serie with triangular and hexagonal-prism-shaped crystals with an edge average of 2-4 μm. The crystals show high uniformity and low surface defects. [4] For the groups ZnNU2 and ZnNU3 agglomerates without specific particle morphology were observed. This fact is attributed to the increasing exothermicity of the combustion reaction leading to smaller crystal size than for ZnNU1 group.

The XRD patterns of all of the catalysts prepared can be indexed as the wurtzite structure, showing minor differences with respect to the XRD pattern of ZnO

ZnNU1 550

ZnNU1 450

ZnNU1 400

ZnNU1350

2θ (º)30 40 50 60 70 80 90

Inte

nsi

ty (

u.a

)

Acta Crystallogr., Sec. B: Structural Science, 45, 34, (1989)

ZnO

ZnNU2 600

ZnNU2 500

ZnNU2 450

ZnNU2 400

2θ (º)30 40 50 60 70 80 90

Inte

nsi

ty (

u.a

)

ZnO

Acta Crystallogr., Sec. B: Structural Science, 45, 34, (1989)

Inte

nsi

ty (

u.a

)

ZnNU3 600

ZnNU3 500

ZnNU3 450

ZnNU3 400

2θ (º)30 40 50 60 70 80 90

Acta Crystallogr., Sec. B: Structural Science, 45, 34, (1989)

ZnO

Greenhouse gases such as CO2 are the primary cause of global warming. One of the most promising and challenging routes for the remediation of this problem is the valorization of CO2 by its photoreduction with water under sunlight radiation to obtain chemicals with potential applications as fuels. This kind of process requires semiconductor materials such as TiO2 and ZnO in order to separate the electron and the holes generated during the photoexcitation of the materials under a suitable wavelenght that will perform the photoreduction of CO2.

ZnO has been widely used as a photocatalyst, due to its high activity, lowcost and environmentally friendly properties. [1] However, the main disadvantage is that the photocatalytic activity of ZnO is limited to wavelengths in the UV region. Consequently , in order to use this photocatalyst under visible light is necessary to modify its optical absorption properties. A successful approach is to introduce non-metallic elements in the crystalline lattice of this material in order to reduce the band gap energy. [2] Doping of ZnO with N has been performed by mean of a facile procedure called “Solution Combustion Method”.

INTRODUCTIONINTRODUCTION

EXPERIMENTAL PROCEDUREEXPERIMENTAL PROCEDURE

RESULTS AND DISCUSSIONRESULTS AND DISCUSSION

2 μm

ZnNU1 450

20 μm

ZnNU3 450

20 μm

ZnNU2 450

1.N. Sobana, M. Swaminathan, Sep. Purif. Technol. 56 (2007) 101–107 2. M. Aresta and A. Dibenedetto, Dalton Transactions 28 (2007) 2975-2992 3. V. Houskova, V. Stengl, S. Bakardjieva, F. Oplustil, J. Phys. Chem. A. 111 (2007) 4215–4221. 4. X. Zhou, Z. Xie, Z. Jiang, Q. Kuang, and L. Zheng, Chem. Commun., (2005) 5572–5574. 5. A. Kaschner, U. Haboeck, M. Strassburg, M. Strassburg, G. Kacz-marczyk, A. Hoffmann, C. Thomsen, Appl. Phys. Lett. 80 (11) (2002) 1909– 1911

AcknowledgmentsAcknowledgmentsReferencesReferences

CONCLUSIONCONCLUSION

Synthesis procedure: Solution Combustion MethodSynthesis procedure: Solution Combustion Method Table of the catalysts preparedTable of the catalysts prepared Further work: test catalyst activity Further work: test catalyst activity in a photoreactorin a photoreactor

hט

Fotocatalizador

Metal (Pt, Ag, Cu…)

OH-

CO2H2O

C1 (CH4, CH3OH…)

Photocatalyst

Precursors were placed in a 250 mL beaker

with 10 mL of distilled waterand the mixture was stirred vigorously for homogenizing

It was placed into a muffle at different temperatures

ranging from 350 to 600 °C

Resultant powders afterhomogenization

The material was ground for homogenization

The obtained material following calcination in

static air

Catalysts label Ratio reactives (Urea:Zn Nitrate)

Calcination temperature (0C)

Colour Bandgap (eV) Cell Volume (Å3)

ZnNU1 350 1 350 Pale orange 1.97 47,6459 ZnNU1 400 1 400 Pale orange 1.99 47,6562 ZnNU1 450 1 450 Pale orange 2.00 47,6379 ZnNU1 500 1 500 Pale orange 2.04 ZnNU1 550 1 550 Pale orange 2.03 47,6726 ZnNU2 400 2 400 Pale orange 1.96 ZnNU2 450 3 450 Pale orange 1.97 47,5041 ZnNU2 500 2 500 Pale orange 1.93 ZnNU2 600 3 600 Very pale orange 1.86 47,6632 ZnNU3 400 2 400 Very pale orange 2.00 47,6880 ZnNU3 450 3 450 Very pale orange 1.84 47,6797 ZnNU3 500 2 500 Very pale orange 1.85 47,6759 ZnNU3 600 3 600 Very pale orange 1.80 47,6316

Raman spectra of all the catalysts shows a sharp and strong peak observed at 437 cm-1 and two more peaks at 380 cm-1 and 415 cm-1 associated with the ZnO-wurtzite phase. Additional peaks with respect to pure ZnO are observed at 270, 507, 582, and 642 cm-1, that are attributed to the Zn-N stretching.[5].

ZnNU1 550

ZnNU1 450

ZnNU1 400

ZnNU1350

Raman Shift(cm-1)200 250 300 350 400 450 500 550 600 650 700

Inte

nsi

ty (

a.u

.)

ZnO

ZnNU2 600

ZnNU2 500

ZnNU2 450

ZnNU2 400

Raman Shift(cm-1)200 250 300 350 400 450 500 550 600 650 700

Inte

nsi

ty (

a.u

.)

ZnO

In

ten

sity

(a.

u.)

ZnNU3 600

ZnNU3 500

ZnNU3 450

ZnNU3 400

Raman Shift(cm-1)200 250 300 350 400 450 500 550 600 650 700

ZnO

Zn-OZn-N

UV-Vis spectrums of all the catalysts show a new absorption band between 450-600 nm reaching a maximum around 500 nm. When ratio Urea/Zn increases absortivity intensity decreases. Calculated bandgaps of the catalysts from absortivity show a general decrease respect to pure ZnO (3.3 eV)

300 400 500 600 700

Ab

sort

ivit

y (a

.u.)

Wavelenght (nm)

ZnNU1350 ZnNU1400 ZnNU1450 ZnNU1500 ZnNU1550 ZnO

300 400 500 600 700

Ab

sort

ivit

y (a

.u.)

Wavelenght (nm)

ZnNU2400 ZnNU2450 ZnNU2500 ZnNU2600 ZnO

300 400 500 600 700

Ab

sort

ivit

y (a

.u.)

Wavelenght (nm)

ZnNU3400 ZnNU3450 ZnNU3500 ZnNU3600 ZnO

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