| Photocatalytic hydrogen-production technology is one of the most effective means to solve the energy crisis and alleviate environmental pollution problems.Among various photocatalysts,titanium dioxide（Ti O2）has been widely used in photocatalytic H2-generation area due to its inexpensive,stable physical and chemical properties and suitable conduction band position（-0.29 V）.However,the easily recombined photogenerated carriers and limited surface-active sites of pure Ti O2lead to extremely low H2-production rate.Appropriate cocatalysts can accelerate the transport and separation of photogenerated electrons and provide a large number of H2-evolution active sites,thereby enhancing the H2-evolution performance of Ti O2.In recent years,molybdenum carbide has attracted increasing attention in the field of catalytic hydrogen production owing to its good electrical conductivity,high chemical stability,and platinum-like d-band density of states.As for molybdenum carbide,its activity as a cocatalyst is largely influenced by its conductivity,the bond energy of Mo-H and the number of active sites exposed on its surface.Therefore,it is necessary to optimize the electrical conductivity,the bond strength of Mo-H and active contres of molybdenum carbide based cocatalysts to further improve the photocatalytic H2-production activity of Ti O2.To improve the conductivity of molybdenum carbide and regulate its active site,in this dissertation,the hetero-phase WC-Mo2C@C and the double hetero-phase Mo S2-Mo C@r GO modified Ti O2composite photocatalysts are designed.The photocatalytic performance and mechanism of the photocatalysts are explored.The research contents are as follows:In chapter 2,to address the issue of the limited conductivity(102S cm-1)and strong Mo-H bond of traditional hexagonal Mo2C,the hetero-phase WC-Mo2C@C was constructed by introducing high conductive WC(105S cm-1)with high electrical conductivity into Mo2C for the weakened Mo-H bond to optimize the H2-evolution performance of Ti O2.The carbon-coated WC-Mo2C heterojunction nanoparticles（WC-Mo2C@C）was obtained by one-step calcination of a controllable ratio of ammonium molybdate and ammonium metatungstate,which were decorated on Ti O2to form the WC-Mo2C@C/Ti O2composite photocatalysts by ultrasonic-assisted method.The photocatalytic results demonstrated that the WC-Mo2C@C/Ti O2（5 wt%）sample displayed the highest H2-production performance(903μmol h-1g-1),which was 90.3,3.6 and 2.5 times higher than that of pure Ti O2,Mo2C@C/Ti O2and WC@C/Ti O2,respectively.Based on the experimental and DFT calculations results,the mechanism of the hetero-phase WC-Mo2C@C modified Ti O2photocatalyst for boosting photocatalytic performances was proposed.The introduction of high-conductive WC both enhanced the conductivity and weaken the bond strength of Mo2C,and the Mo sites at the interface of the hetero-phase WC-Mo2C@C has a more ideal H-adsorption free energy(ΔGH*),which can act as H2-evolution active sites to accelerate the H2-production reaction of Ti O2.In chapter 3,in view of the limited conductivity(2.04×103S cm-1)and insufficient active sites of cubic Mo C,the double hetero-phase Mo S2-Mo C@r GO nanoparticles were prepared by introducing graphene(106S cm-1)and the unsaturated S to enhance the photocatalytic H2-production performance of Ti O2.Herein,the double hetero-phase Mo S2-Mo C@r GO nanoparticles were generated on the graphene by one-step calcination,and modified on Ti O2to synthesize the Mo S2-Mo C@r GO/Ti O2composite photocatalysts.The results showed that the highest H2-evolution activity of Mo S2-Mo C@r GO/Ti O2composite photocatalysts reached up to 575μmol h-1g-1,which was 58,3.6 and 2.1 times than that of the pure Ti O2,Mo C@r GO/Ti O2and Mo S2@r GO/Ti O2samples,respectively.Based on the above experimental results,the mechanism of the boosted Mo S2-Mo C@r GO/Ti O2photocatalytic performance was proposed.The external graphene can promote the transfer of photogenerated electrons to the inner hetero-phase Mo S2-Mo C,and then the Mo sites and exposed edge S sites can serve as reaction centers to improve the hydrogen-evolution reaction. |
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