Based on earlier results on the photocatalytic properties of MoS2, the 1T form of MoSe2, prepared by lithium intercalation and exfoliation of bulk MoSe2, has been employed for the visible-light induced generation of hydrogen. 1T-MoSe2 is found to be superior to both 2H and 1T MoS2 as well as 2H-MoSe2 in producing hydrogen from water, the yield being in the 60–75 mmol h−1 g−1 range with a turn over frequency of 15–19 h−1. First principles calculations reveal that 1T-MoSe2 has a lower work function than 2H-MoSe2 as well as 1T and 2H-MoS2, making it easier to transfer an electron from 1T-MoSe2 for the production of H2.

Prompted by the early results on the catalytic activity of LiMn 2 O 4 and related oxides in the photochemical oxidation of water, our detailed study of several manganese oxides has shown that trivalency of Mn is an important factor in determining the catalytic activity. Thus, Mn 2 O 3 , LaMnO 3 , and MgMn 2 O 4 are found to be very good catalysts with turnover frequencies of 5 × 10 −4 s −1 , 4.8 × 10 −4 s −1 , and 0.8 ×10 −4 s −1 , respectively. Among the cobalt oxides, Li 2 Co 2 O 4 and LaCoO 3 -especially the latter-exhibit excellent catalytic activity, with the turnover frequencies being 9 × 10 −4 s −1 and 1.4 × 10 −3 s −1 , respectively. The common feature among the catalytic Mn and Co oxides is not only that Mn and Co are in the trivalent state, but Co 3+ in the Co oxides is in the intermediate t 2g 5 e g 1 state whereas Mn 3+ is in the t 2g 3 e g 1 state. The presence of the e g 1 electron in these Mn and Co oxides is considered to play a crucial role in the photocatalytic properties of the oxides.artificial photosynthesis | water oxidation A ny strategy for solving the energy crisis would involve the generation of fuels through artificial photosynthesis, involving the sun as the only source of energy. To complete the solar cycle, water has to act as the source of electrons, either to generate liquid fuels by the reduction of CO 2 or to yield H 2 through a complete cycle of transfer of electrons. Oxidation of water, involving the transfer of four electrons, is energy-intensive. One of the challenges with artificial photosynthesis is the development of cost-effective catalysts made of abundant elements for the efficient oxidation of water to O 2 (1). RuO 2 and IrO 2 are widely used as oxygen evolution catalysts although their availability is limited and are expensive (2-5). Oxidation of water in plants occurs in Photosystem II making use of the Mn 4 O 5 Ca cluster (6, 7) present in the protein. The structure of the water oxidation complex involves a cubic cluster with four Mn atoms bridged via oxygen atoms (8,9 Results and DiscussionWe first studied the catalytic properties of the nanoparticles of the LiMn 2 O 4 spinel, with an average crystallite size of 57 nm [see Fig. S1 for an X-ray diffraction pattern and transmission electron microscope (TEM) image], prepared by the citrate sol-gel method from their corresponding metal precursors. Oxygen evolution was studied under visible light in a standard photoexcitation system consisting of Ru(bpy) 3 2+ as the photosensitizer and Na 2 S 2 O 8 as the sacrificial electron acceptor in a solution buffered at pH = 5.8. Oxygen evolved was quantified both by a Clark-type electrode and gas chromatography. We found reasonable catalytic activity with these nanoparticles as shown in Fig. 1A. Delithiation of LiMn 2 O 4 in dilute nitric acid resulted in a decrease of unit cell volume and an increase in surface area from 20 to 55 m 2 /g (Table S1). The average crystallite size of the delithiated sample (DlLiMn 2 O 4 ) was 46 nm. Delithiation seemed to result in a slight impr...

Solvothermally synthesized Ga2O3 nanoparticles are incorporated into liquid metal/metal oxide (LM/MO) frameworks in order to form enhanced photocatalytic systems. The LM/MO frameworks, both with and without incorporated Ga2O3 nanoparticles, show photocatalytic activity due to a plasmonic effect where performance is related to the loading of Ga2O3 nanoparticles. Optimum photocatalytic efficiency is obtained with 1 wt % incorporation of Ga2O3 nanoparticles. This can be attributed to the sub-bandgap states of LM/MO frameworks, contributing to pseudo-ohmic contacts which reduce the free carrier injection barrier to Ga2O3.

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Perovskite oxides of the Ln0.5 A0.5 MnO3 (Ln=lanthanide, A=Sr, Ca) family have been investigated for the thermochemical splitting of H2 O and CO2 to produce H2 and CO respectively. The amounts of O2 and CO produced strongly depend on the size of the rare earth ions and alkaline earth ions. The manganite with the smallest rare earth possessing the highest distortion and size disorder as well as the smallest tolerance factor, gives out the maximum amount of O2 , and, hence, the maximum amount of CO. Thus, the best results are found with Y0.5 Sr0.5 MnO3 , which possesses the highest distortion and size disorder. Y0.5 Sr0.5 MnO3 shows remarkable fuel production activity even at the reduction and oxidation temperatures as low as 1200 °C and 900 °C, respectively.