1. M. Dhanasekar, Dr. S. Venkataprasad Bhat*
VISIBLE LIGHT PHOTOCATALYTIC DEGRADATION OF ORGANIC POLLUTANT USING SURFACTANT FREE CZTS NANOPARTICLES
M. Dhanasekar, Dr. S. Venkataprasad Bhat*
SRM Research Institute, SRM University, Kattankulathur, Tamilnadu , India. * Corresponding author,
ABSTRACT
Synthesis of CZTS nanoparticles
Characterization
As a low cost, earth abundant and environment-friendly visible light absorber material,Cu2ZnSnS4(CZTS) has a great potential for both photovoltaic and photo catalytic applications. Here we report a systematic study on the photo catalytic activity of surfactant free CZTS nanoparticles during the degradation of an organic pollutant (RhB dye). The nanoparticles, synthesized by hydrothermal method are characterized by powder X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and UV-visible absorbance spectroscopy. Further, RhB dye was adsorbed over the CZTS nanoparticles followed by the studies on its degradation under visible light irradiation using a 150W tungsten lamp.
XRD Pattern of CZTS nanoparticles
SEM image of surfactant free CZTS nanoparticles
Agglomerated particles , ~ 100nm average size
CuCl2.2H2O, SnCl2.2H2O, ZnCl2
added with 80 ml deionized water
Crystalline CZTS , with no hint of secondary phase
Ultra Sonication for 5 min
Add Na2S.9H2O
Stirred for 10min
Brown colour precipitate obtained
transferred to teflon lined stainless steel auto clave
INTRODUCTION
Composition: nearly stoichiometric
Band gap is 1.5 eV
heated at 150 °C
for 24h
Photocatalytic degradation is a promising green route to convert organic pollutants from wastewater into harmless end products [1].
Semiconductor photocatalysis is an advanced technology that employs the electrons in the conduction band and holes in the valence band when photons excite the semiconductor. The organic pollutants can be removed via oxidization or reduction [2].
Nanoparticles play a significant role in the photocatalysis owing to their high surface to volume ratio [3].Using TiO2 nanoparticles is a promising route to degrade organic pollutants under UV light, but the current challenge is to identify an efficient visible light active material as the photocatalyst.
CZTS is an earth abundant, environmental friendly visible light absorber, extensively being used for solar cells owing to its optimal band gap and high absorption coefficient 10-4 cm-1 [5].
In this work,surfactant free nanoparticles of CZTS has been employed as photocatalysts for the degradation of a highly carcinogenic organic pollutant (RhB dye) under visible light.
Washed with water and ethanol five times
dried at 80 °C for over night
Black colour powder obtained
Hydrothermal method:
Priya Kush et al,J.Mat.Chem.A,2015, 3,
EDS spectrum of surfactant free CZTS nanoparticles
UV-DRS absorbance spectrum of CZTS nanoparticles. Inset : the plot of (αhν)2 versus photon energy.
Dye degradation studies
10 gm of the catalyst in a 100ml solution of Rhodamine B (RhB) (0.012mmol) as a reference dye.
Adsorption-desorption equilibrium was achieved after stirring for one hour in dark followed by light irradiation (Tungsten halogen lamp, 150 W) to start photo-catalytic dye degradation.
Degradation of the dye was observed as the decrease in its concentration, indicated by the absorbance value at 550 nm, using UV-visible spectroscopy.
EVB = 0.2eV
ECB = -1.3eV
CZTS
Eg = 1.5eV R O
UV-visible absorption spectra of RhB degradation
CONCLUSION
The electrons and holes migrate to the surface of the photocatalyst,
get trapped and undergo redox chemistry with the organic contaminant.
The resulting OH- radicals are strongly oxidative in nature
and can degrade the contaminant.
The surfactant free CZTS nanoparticles synthesized by hydrothermal method, show promising visible light photocatalytic activity (97% degradation of RhB dye in 2 hours).
RhB was degraded ~ 97% in 2 hours.
C/C0 versus irradiation time curves for photo-
degradation of RhB by using CZTS.
Photographic evidence of degradation of Rhodamine B at various time intervals.
( Initial)
1h Adsorption
30 min
(60 min)
(90 min)
(120min)
ACKNOWLEDGEMENT
References
Prof . D. Narayana Rao, The Director (Research), SRM University.
Prof. Dr. John Thiruvadigal , The Head, Department of Physics and Nanotechnology, SRM University.
Nanotechnology Research Centre, SRM University.
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[2] Xian Hou, Highly efficient photocatalysis of p-type Cu2ZnSnS4 under visible-light llumination, Mat. Res. Bull, 60,(2014)628–633.
[3] H. Jiang, J. Mater. Chem.A,22,( 2012)
[4] K. Woo,Energy Environ.Sci,5, (2012)
[5] K. Hironori, Thin Solid Films,426,(2005)480–481.