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Abstract
Photocatalytic activity of Zinc stannate (Zn2SnO4) ZTO described in our previous work [1, 2] depict that ZTO nanoparticles have comparable photocatalytic activity to other photocatalyst such as Zinc Oxide (ZnO) nanoparticles and Titanium dioxide (TiO2) nanoparticles. The aim of this work is to explore the effect of annealing i.e. high temperature behavior on size, morphology and photocatalytic activity of room temperature synthesized nanoparticles.
It has been reported that annealing at high temperature results in alterations in surface states of semiconductor [3, 4]. These surface alterations can impact the dye adsorption on surface of catalyst. Room temperature synthesized samples were annealed to study the annealing effect at different temperatures on the photocatalytic efficiency of ZTO. Annealing was carried out at two different temperatures i.e. at 250oC and 400oC.
Scanning electron micrograph (SEM) of annealed particles was carried out in order to observe morphological changes before and after annealing at two different temperatures. SEM micrographs obtained for above samples revealed that annealed samples did not result in any morphological changes in the length or diameter of ZTO nanoparticles.
Optical absorption spectra of Methylene Blue (MB) adsorption on surface of ZTO nanoparticles annealed at 250oC and 400oC for period of one hour was calculated which perceived that the amount of MB adsorbed is higher for the ZTO samples without annealing as compared to samples annealed at different temperatures i.e. at 250 °C and at 400 °C.
UV/Vis optical absorption spectra of annealed ZTO samples was used to study the effect of annealing on native defects. It was observed that the absorption peak is at about 270 nm in all the cases i.e. annealed and without annealed samples which illustrate that the ZTO nanoparticles preserve uniform size after annealing at different temperatures.
Photocatalytic activity of annealed samples and without annealing was observed for the degradation of methylene blue and corresponding reaction rate constant k values were calculated.
From reaction rate constant k values it is evident that annealing didn’t result in improvement of photocatalytic activity as samples without annealing showed higher photocatalytic activity then sample annealed at 400oC.
This can be attributed to removal of surface defects due to annealing and subsequent reduction in photocatalytic activity.
References:
- Najam Khan, M., et al., Visible light photocatalysis of mixed phase zinc stannate/zinc oxide nanostructures precipitated at room temperature in aqueous media. Ceramics International, 40(6):8743–8752.
- Baruah, S., Dutta Zinc stannate nanostructures: Hydrothermal growth. Science and Technology of Advanced Materials, 2011. 12(1): p. 013004.
- Sun, R.-D., et al., Photoinduced Surface Wettability Conversion of ZnO and TiO2 Thin Films. The Journal of Physical Chemistry B, 2001. 105(10): p. 1984-1990.
- Chung, J., J. Lee, and S. Lim, Annealing effects of ZnO nanorods on dye-sensitized solar cell efficiency. Physica B: Condensed Matter, 2010. 405(11): p. 2593-2598.
