A Rapid Solar Reduction Method to TiO 2 /MoO 2 /Graphene Nanocomposites for Photocatalytic Water Splitting
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A Rapid Solar Reduction Method to TiO2/MoO2/Graphene Nanocomposites for Photocatalytic Water Splitting Jyothirmayee Aravind.S.S, Kandalam Ramanujachary, Timothy D.Vaden and Amos Mugweru Department of Chemistry and Biochemistry, Rowan University, Glassboro, NJ 08028, U.S.A.
ABSTRACT Semiconductor photocatalysis has emerged as an interesting area of research since the discovery of Honda-Fujishima effect. In this study, TiO2/MoO2/graphene composites have been prepared by a solar radiation-assisted co-reduction method, wherein ammonium tetrathiomolybdate salt and graphite oxide are reduced to MoO2 and graphene respectively along with TiO2. The method involved the utilization of focused pulses of natural sunlight using a simple convex lens, thereby eliminating the need for harmful reducing agents. The compound was characterized by XRD and SEM for phase identification and morphology. The TiO2/MoO2/graphene composite exhibits superior photocatalytic water splitting activity without using a co-catalyst. In addition, we demonstrate the electrocatalytic hydrogen production using this earth abundant catalyst, which shows high current density (60 mA/cm2) and low Tafel slope (47 mV/dec). The hydrogen evolved during photocatalysis was detected by gas chromatography. INTRODUCTION Solar radiation in the UV, visible and IR regions contains huge amount of energy capable of contributing in a large amount to our electrical and chemical needs. A material contribution to the energy supply might be capturing, conversion and storage of solar radiation. The most attractive method for this solar conversion and storage is in the form of the energy carrier, hydrogen. The most promising method for production of hydrogen using renewable energy source is based on water decomposition using photo catalytic technology using sunlight [1,2]. This process also known as artificial photosynthesis utilizes inorganic semiconductors to catalyze water splitting reaction:
1 H 2O (l ) → O2 ( g ) + H 2 ( g ) 2
(1)
Titanium dioxide (TiO2) has been investigated vigorously as a semiconductor photocatalyst mainly due to its superior characteristics such as non-toxicity, easy availability, and good stability [3,4]. The recombination of photogenerated electrons and holes is one of the major issues in photocatalysis. Of the several methods reported, preparation of TiO2 based composites to improve the efficiency of TiO2 photocatalysis is remarkable via retarding the charge recombination [5]. Combination of TiO2 with noble metal Au [6] as well as other semiconductors such as MoO3, SnO2 and WO3 is reported with significant improvement in photocatalytic efficiency [7-9]. TiO2 loaded on reduced graphene oxide (RGO) under UV
irradiation is reported to accelerate the electron transfer from TiO2 to RGO resulting in improved photocatalytic behavior [10]. In the present study, we report the preparation of TiO2/MoO2/graphene composite by an eco-friendly solar irradiation technique and further demonstrate its hydrogen generation under UV irradiation. EXPERIMENT TiO2 (anatas
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