Abstract
MoS2/C3N4 (MS-CN) composite photocatalysts have been synthesized by three different methods, i.e., in situ-photodeposition, sonochemical, and thermal decomposition. The crystal structure, optical properties, chemical composition, microstructure, and electron transfer properties were investigated by X-ray diffraction, UV-vis diffuse reflectance spectroyscopy, X-ray photoelectron spectroscopy, electron microscopy, photoluminescence, and in situ electron paramagnetic resonance spectroscopy. During photodeposition, the 2H MoS2 phase was formed upon reduction of [MoS4]2− by photogenerated conduction band electrons and then deposited on the surface of CN. A thin crystalline layer of 2H MoS2 formed an intimate interfacial contact with CN that favors charge separation and enhances the photocatalytic activity. The 2H MS-CN phase showed the highest photocatalytic H2 evolution rate (2342 μmol h−1 g−1, 25 mg catalyst/reaction) under UV-vis light irradiation in the presence of lactic acid as sacrificial reagent and Pt as cocatalyst.
Highlights
Increasing concerns about energy demand and environmental pollution have stimulated research to find and utilize renewable energy resources as an alternative to fossil fuels such as coal, petroleum and natural gas [1]
In our previous work we have shown that in situ-EPR spectroscopy is a unique method to analyze separation and transfer of photoexcited electrons in oxidic semiconductors [49] or carbon nitrides [15,28]
Pt/2H MS-C3 N4 (CN) (PD) showed the highest photocatalytic hydrogen production activity of all investigated MS-CN composites, and it is the only one in which deposition of MoS2 improves the performance of Pt/CN
Summary
Increasing concerns about energy demand and environmental pollution have stimulated research to find and utilize renewable energy resources as an alternative to fossil fuels such as coal, petroleum and natural gas [1]. Photocatalytic water reduction using sunlight is a method for the direct conversion of solar energy into hydrogen, which is a practical and storable energy carrier [2,3,4,5,6]. A newer generation of semiconducting materials, including metal-organic frameworks, polyoxometalates, conducting polymers and metal free semiconductors is being introduced as potential candidates for H2 production [9,10,11]. Many of these materials work efficiently only with UV light and/or need a cocatalyst to raise their limited light absorption capability and/or to suppress fast recombination of photogenerated electron hole pairs [12]. Composite photocatalysts based on carbon nitride are promising systems with facilitated separation of electron hole pairs and extended light absorption in the visible region [13,14,15]
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