Investigation On Preparation And Properties Of Composite Photocatalysts Based On G-C₃N₄

Graphitic carbon nitride(g-C3N4)photocatalyst has attracted widespread attention owing to its excellent photocatalytic activity for H2 production.However,g-C3N4 has some defects,such as low light utilization rate and high photoinduced electron hole recombination rate.Loading cocatalyst to construct g-C3N4-based photocatalysts and the corresponding synergy effects can inhibit the recombination of photogenerated electron and hole effectively,improving the property of producing H2.Based on MOFs as the source of metal elements,two kinds of efficient and stable g-C3N4-based photocatalysts,Co P/g-C3N4 and CoSe2/NiSe2/g-C3N4 were prepared.The main contents are as follows:(1)Through calcination method under high temperature,using melamine,ZIF-67 nanoparticles and sodium hypophosphite as precursors,Co P/ g-C3N4 photocatalyst was prepared.Fourier transform infrared(FT-IR),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)results confirmed that the basic skeleton of g-C3N4 was retained in Co P/ g-C3N4 photocatalyst after calcination and the introduction of the Co P particles was successful.Co P/g-C3N4 photocatalyst exhibits excellent performance for hydrogen production under visible light.Notably,when the ZIF-67 mixed in precursors was approximately ca.5 wt% from a rough calculation,a high photocatalytic hydrogen production rate of 201.5 ?mol·g-1·h-1 was obtained,almost 21 times that of bulk g-C3N4.The fluorescence intensity of PL spectra exhibited that the separation efficiency of photogenerated electrons and holes are greatly enhanced.EIS analysis results showed that Co P/g-C3N4 photocatalyst has a smaller radius of the Nyquist curve than that of g-C3N4,indicating that Co P/g-C3N4 photocatalyst has less resistance to electronic transmission process.Thus,the efficiency of photocatalytic hydrogen production can be enhanced because of more efficient electron transfer.(2)Using melamine to obtain g-C3N4.The obtained g-C3N4,Ni doped ZIF-67 nanoparticles and selenium powder as the precursors were mixed and reacted,CoSe2/ NiSe2/ g-C3N4 was prepared.Meanwhile,X-ray diffraction(XRD)and Xray photoelectron spectroscopy(XPS)results confirmed the successful introduction of the CoSe2 and NiSe2 particles.When mass percentage of Ni2+ doped ZIF-67 in the precursors is 5%,the maximum hydrogen production rate is up to 854.1 mol·g-1·h-1,which is 87 times the hydrogen production rate of g-C3N4 from hydrogen production experiment.The photocurrent response curve shows that fluorescence intensity of CoSe2/ NiSe2/ g-C3N4 was lower than that of g-C3N4,indicating that the photogenerated electrons can be transferred more efficiently.CoSe2 and NiSe2 as co-catalysts can improve the separation efficiency of photogenerated electron and hole.Then,photogenerated electron was transferred.Further,the photocatalytic hydrogen production performance was improved.