| Energy crisis and environmental issues are two most severe problems faced by all human beings on this planet.In order to solve these two problems,researchers are seeking for clean as well as sustainable alternative energies abundant other than fossil fuels.From this point of view,hydrogen is a good candidate,which could be generated from a clean process,such as photocatalytic water splitting using the endless solar energy.Consequently,the semiconductor photocatalyst is a key factor.Polymeric graphitic carbon nitride(g-C3N4),which could respond to visible light owing to its narrow band gap of 2.7 e V and suitable conduction band(CB)of-1.1 e V to reduce protons,seems to be a promising candidate photocatalyst for photocatalytic H2generation.However,pristine g-C3N4 exhibits a poor photocatalytic performance due to the fast recombination of photoexcited electrons/holes and its low specific surface area.This project aims at suppressing the charge carriers recombination and thus enhancing the photocatalytic activity of g-C3N4 by embedding r GO,FeOOH,phosphides,Mo S2 and MOFs onto the g-C3N4 nanosheets.Firstly,considering the use of earth abundant elements on earth,such as iron,the ternary Z-scheme g-C3N4/FeOOH heterostructure photocatalyst was designed and fabricated by hydrothermal treatment with r GO acting as transport channel for the photo-exited charge carriers.Due to the narrow bandgap and low oxygen evolution overpotential of FeOOH,the Z-scheme g-C3N4/r GO/FeOOH ternary heterojunction exhibited an excellent photocatalytic hydrogen production of 124.9 and 869.8?mol/h/g(244.9 and 107.4 times larger than that of the pristine g-C3N4)under the visible and UV-visible light irradiation,respectively.Secondly,to reduce the aggregation and increase the separation efficiency of charge carriers of g-C3N4,the bimetallic Zeolite-imidazole frameworks with controllable flat band position,band gap and hydrogen evolution reaction characteristic were introduced onto g-C3N4-Mo S2 nanosheet.The Zn M-ZIFs not only inhibited the aggregation of the g-C3N4-Mo S2 heterostructure,but also improved the separation and transport efficiency of charge carriers in g-C3N4-Mo S2.Furthermore,the g-C3N4-Mo S2 2D-2D surface heterostructure was introduced to facilitate the separation as well as utilization efficiency of the photo-exited charge carriers in the Zn M-ZIFs,Consequently the optimal g-C3N4-Mo S2-Zn Ni-ZIF exhibited extraordinary photocatalytic hydrogen evolution activity of 214.4,37.5,and 3.7 times larger than that of the pristine g-C3N4,g-C3N4-Zn Ni-ZIF and g-C3N4-Mo S2,respectively,and exhibited a H2-evolution performance of 77.8?mol/h/g under UV-vis light irradiation coupled with oxidation of H2O into H2O2.Moreover,a facile and green redox relay reaction method was developed for the synthesis of g-C3N4–PPy–FeP ternary heterostructures,with FeCl3 acting as both the oxidant to polymerize the Py monomer and the precursor of the nanosized FeP cocatalyst.The as-formed conductive PPy nanospheres performing as the support to well disperse g-C3N4,meanwhile confining the size of FeP.Highly conductive PPy acted as the‘‘highway''for the transport of the photo-generated charge carriers.Consequently,the prepared catalyst demonstrated a photocatalytic hydrogen evolution activity 6 and 20 times larger than that of g-C3N4 singly loaded separately with PPy or FeP,respectively,under visible light irradiationIt is anticipated that the prepared g-C3N4-based hetero-structural materials with enhanced hydrogen production performance could have potential applications relating to environmental remediation or energy conversion. |
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