| Metal-organic frameworks?MOFs?,a family of crystalline porous materials with high surface area,well-designed structure and morphology,show great potential as templates/precursors for the in situ synthesis cocatalysts or heterostructures by calcination,phosphidation or sulfurization,which were used for modified carbon nitride?g-C3N4?to enhancing photocatalytic H2 evolution.The structure and composition of the composite photocatalyst were characterized.And the hydrogen evolution properties of g-C3N4 modified by different cocatalysts were investigated.The main research contents are summarized as follows:?1?The CN/FeNiP polyhedron derived from in situ phosphidation of NH2-MIL-101?Fe?/Ni?OH?2 was used as high-efficiency cocatalyst for enhancing photocatalytic H2 evolution of EY-sensitized g-C3N4.The enhanced photocatalytic activity can be attributed to the efficient spatial separation of photo-induced electrons from excited EY and g-C3N4 to CN/Fe2P and Ni2P owing to their good interface,staggered band energy between g-C3N4,CN/Fe2P and Ni2P,more surface active sites presented on CN/Fe2P and promoted H+reduction reactions on Ni-Fe phosphides.The highest evolution rate observed over CN/FeNi7.47P/g-C3N4 was 13.81 mmol g-11 h-1under 1.0 mmol L-11 of Eosin Y?EY?-sensitization,which was higher than that of g-C3N4(1.33 mmol g-11 h-1)and CN/FeP/g-C3N4(2.73 mmol g-11 h-1).The apparent quantum yield at 420 nm reached 45.8%.And it has high cycle stability in photocatalytic H2 evolution from the water splitting.?2?Ni2P/Ni nanoparticles?NPs?encapsulated in carbon/g-C3N4 hybrids derived from in situ pyrolysis and phosphidation of Ni-MOF/g-C3N4 precursor were used as photocatalysts for H2-evolution under visible-light irradiation.This enhanced photocatalytic activity can be attributed to an efficient and rapid separation of the photo-generated charges from excited EY and g-C3N4 to Ni2P/Ni with carbon as an electron transport bridge,intimate contact of each components,staggered band alignment among g-C3N4,Ni and Ni2P.As the result,The highest H2-evolution rate over optimized Ni2P/Ni@C/g-C3N4-550 was 18.04 mmol g-11 h-11 with 1.0 mmol L-11 of EY-sensitization?compared to 0.21 mmol g-11 h-11 without EY-sensitization?,13 times higher than that of pristine g-C3N4(1.33 mmol g-11 h-1).The apparent quantum efficiency at 420 nm was 58.1%.At the same time,It has high cycle stability in photocatalytic H2 evolution from the water splitting.?3?The C-doped Ni3S4/Ni2P?C@Ni3S4/Ni2P?hybrid cocatalyst produced by in situ sulfuration and phosphidation of Ni-MOF was decorated on g-C3N4 and subsequently used for photocatalytic H2 evolution under visible-light irradiation.This enhanced photocatalytic activity can be attributed to the staggered band alignment among EY*,g-C3N4,Ni3S4 and Ni2P NPs and the electronic interactions and synergism between Ni2P and Ni3S4.As the result,the optimized g-C3N4/C@Ni3S4/Ni2P-30composite showed the highest H2 evolution rate(14.49 mmol g-11 h-1)with 1.0 mmol L-11 of EY-sensitization,which is higher than g-C3N4/C@Ni3S4(11.25 mmol g-11 h-1).?4?The Fe2O3@FeP hybrid material was prepared by calcination and phosphidation of a g-C3N4/Fe-MOF.The as-prepared Fe2O3@Fe P was used as both heterojunction and cocatalyst material to enhance the photocatalytic H2 evolution performance of g-C3N4 by water splitting under visible-light irradiation.The improved photocatalytic activity of this composite can be ascribed to efficient electron-hole separation by the formation of a type-II heterojunction with Fe2O3 and the loading of an electron collector such as FeP,as well as the accelerated H+reductive reaction resulting from the FeP cocatalyst.The results show that an optimized g-C3N4/Fe2O3@FeP-60 catalyst with a H2 evolution rate were 12.03 mmol g–1 h–11 with1.0 mmol L-11 of EY-sensitization?compared to 1.48 mmol g-11 h-11 without EY-sensitization?,higher than Fe2O3/g-C3N4(7.64 mmol g–1 h–1).?5?The MMT/g-C3N4/NiCoP hybrid catalyst produced by calcination andphosphidation which used NiNiCoP as a cocatalyst to decorate g-C3N4 simultaneously hybridized with MMT for H2 production from water splitting.The remarkably improved photocatalytic activity can be ascribed to the increased dispersion of g-C3N4layers,staggered conduction band potentials between g-C3N4 and NiCoP,as well as the electrostatic repulsion originated from negatively charged MMT.The highest hydrogen-evolution rate from water splitting under visible-light irradiation observed over MMT/g-C3N4/15%NiCoP was 12.50 mmol g-11 h-11 under 1.0 mmol L-11 of EY-sensitization at p H of 11,which was higher than that of MMT/g-C3N4(0.48 mmol g-11 h-1)and g-C3N4/15%NiCoP(7.69 mmol g-11 h-1). |
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