Dual Cocatalyst-modified Photocatalyst Semiconduct Material Synergy Enhancing Catalytic Activity

The energy problem has become serious,and semiconductor photocatalysis is one of the effective technologies to revolve the above problem.Titanium dioxide,as a typical photocatalytic material,usually shows a low photocatalytic activity,causing limited applications due to the absence of surface catalytic activity sites and the rapid recombination of photogenerated carriers.In this study,to improve the photocatalytic hydrogen production performance,we focused on the following two works:one is the preparation and improved photocatalytic H₂-evolution performance of MoS_x-rGO/TiO₂ photocatalyst by a facile photoreduction method and the other is the preparation of MoS_x-MnO_x/TiO₂ and its photocatalytic H₂-evolution mechanism.The detail work is shown as follows:First,MoS_x-rGO/TiO₂ was synthesized by a facilely two-step photocatalytic reduction approach including reducing GO/TiO2 to rGO/TiO2 and then reducing ammonium tetrathiomolybdate??NH₄?₂MoS₄?to form amorphous MoS_x on the rGO surface.In the case,the rGO nanosheets as an electron mediator caused rapid transportation of photogenerated electrons from the conduction band?CB?of TiO₂,while amorphous MoS_x served as an effective active site for the following interfacial reduction reaction for H₂ evolution.The photocatalytic results indicated that the H₂-evolution rate of synthesized MoS_x-rGO/TiO₂ was 206.6?mol h^-1,which was obviously higher than that of TiO₂(6.9?mol h^-1),rGO/TiO₂(31.8?mol h^-1)and MoS_x/TiO₂(150.1?mol h^-1)by a factor of 30.9,6.3 and 1.4 times,respectively,due to the rapid interfacial charge transfer and interfacial catalytic reaction.Second,MoS_x-MnO_x/TiO₂ was synthesized by a facile two-step photocatalytic reduction approach.One step is to reduce KMnO₄ to be MnO_x on TiO₂ surface to form MnO_x/TiO₂,and the second step is reducing?NH₄?₂MoS₄ to be amorphous MoSx on TiO2 surface to obtain the MoSx-MnOx/TiO2 composite.The hydrogen-production result shows that the dual cocatalyst modification of MoS_x and MnO_x can greatly improve the photocatalytic H₂-evolution activity of TiO₂.The MoS_x-MnO_x/TiO₂?0.5 wt%,0.05 wt%?sample shows the highest H₂-evolution activity with a rate of 225.3?mol h^-1,which is clearly higher than that of TiO₂,MnOx/TiO2?0.05 wt%?and MoSx/TiO2?0.5 wt%?by a factor of 168.1,3.9 and 1.5.The enhanced H₂-evolution activity of MoS_x-MnO_x/TiO₂ can be attributed to the synergistic effect of MoS_x and MnO_x cocatalysts,namely,the MnO_x cocatalyst can promote the rapid capture and transportation of photogenerated holes,while the amorphous MoS_x cocatalyst can act as the H₂-evolution active sites to promote the interfacial H₂ production.