Highly Efficient Photocatalytic Hydrogen on CoS/TiO2 Photocatalysts from Aqueous Methanol Solution

Yu Niu,Kai Yang,Renzhang Wang,Fuying Li,Peijing Xu,Qiyou Wu

doi:10.1155/2018/8143940

Abstract

The photocatalyzed water splitting reaction in aqueous methanol solution is an efficient preparation method for hydrogen and methanal under mild conditions. In this work, metal sulfide-loaded TiO2 photocatalysts for hydrogen and methanol production were synthesized by hydrothermal method (180°C/12 h) and characterized by X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The crystal structures of the samples are the typical anatase phase of TiO2 and exhibit a spherical morphology. When TiO2 was loaded with CoS, ZnS, and Bi2S3, respectively, the resulting catalysts showed photocatalytic activities for water decomposition to hydrogen in aqueous methanol solution under 300 W Xe lamp irradiation. Among the photocatalysts with various compositions, the 20 wt% CoS/TiO2 sample with a 2.1 eV band gap showed the maximum photocatalytic activity for the photocatalytic reaction, which indicated that CoS improved the separation ratio of photoexcited electrons and holes. The enhanced activity can be attributed to the intimate junctions that are formed between CoS and TiO2, which can reduce the electron-hole recombination. The production rate of hydrogen with 20 wt% CoS/TiO2 photocatalyst was about 5.6 mmol/g/h, which was 67 times higher than that of pure TiO2. The formation rate of HCHO was 1.9 mmol/g/h with 98.7% selectivity. Moreover, the CoS/TiO2 photocatalyst demonstrated good reusability and stability. In the present study, it is demonstrated that CoS can act as an effective cocatalyst to enhance the photocatalytic hydrogen and methanal production activity of TiO2. The highly improved performance of the CoS/TiO2 composite was mainly ascribed to the efficient charge separation.

Highlights

Photocatalytic water splitting into hydrogen, a renewable, clean-burning, and environmental-friendly fuel for future energy sources, is considered as one of the most significant and attractive solutions to solve the global energy and environmental problems [1,2,3]
A previous study found that adding methanol (CH3OH) to pure water can dramatically enhance H2 production, suggesting that CH3OH plays a crucial role in H2 production [4]
The results showed that CoS/TiO2 had the best photocatalytic activity in the H2 and HCHO production reactions under 300 W Xe lamp irradiation

Summary

Introduction

Photocatalytic water splitting into hydrogen, a renewable, clean-burning, and environmental-friendly fuel for future energy sources, is considered as one of the most significant and attractive solutions to solve the global energy and environmental problems [1,2,3]. Methanol is used as a raw material for the industrial production of methanol through an oxidation reaction using Ag, Cu, or V2O5 as catalysts. This process requires high temperatures of 700– 900 K and expensive catalysts. Photocatalytic production of both hydrogen and methanol from aqueous methanol solution using photocatalysts is an efficient approach to address the above problems. Our research is focused on the development of nontoxic, environmentally friendly, and inexpensive promoters, such as CoS, ZnS, and Bi2S3. CoS, ZnS, and Bi2S3 were investigated as cocatalysts for photocatalytic H2 and methanal production from methanol solution under 300 W Xe lamp irradiation. The stability and reusability of the catalyst were evaluated

Experimental

Results and Discussion

Conclusion