Preparation And Photocatalytic Properties Of Metal Oxide Doped And Composited G-C₃N₄ Catalysts

With the progress of science and technology and the rapid development of social economy,the problems of energy consumption and environmental issues are becoming more and more serious.In particular,the problem of environmental pollution has attracted attention and attention,among which photocatalytic technology is regarded as a promising method to solve the energy crisis and environmental pollution.Graphitic carbon nitride?g-C₃N₄?has attracted the attention of researchers due to its suitable band location and easy access to raw materials.However,due to its disadvantages such as fast photogenerated electron-hole recombination rate,larger particle size and smaller specific surface,how to improve the photocatalytic performance of metal oxide composite g-C₃N₄ has become the focus of attention.In this work,Hollowed-out nanostructures?-Fe₂O₃?Fe₃O₄ doped g-C₃N₄ catalysts?forming defects?,Fe₃O₄composite g-C₃N₄ catalysts,?-Al₂O₃ doped catalysts?forming defects?and composite catalysts were successfully prepared by calcination of melamine metal nitrate supramolecular hydrogel precursors.The morphology,structure,composition and photoelectrochemical properties of the prepared catalyst were analyzed.The main elements of the work are as follows:?1?The hollow-out nanostructure?-Fe₂O₃ with different structures?from bulk particles to hollow-out nanobelts and to hollow-out 3D columns?were successfully prepared by one-step calcination supramolecular hydrogel?melamine ferric nitrate?precursor.The characterization results show that the hollow nanostructure with different morphology can be obtained by simply changing the content of iron ions in the precursor,and the particle size of the hollow structure remains unchanged?40-60nm?.The catalytic oxidation H₂O₂ degradation of rhodamine B?RhB?solution under visible light proved that the prepared catalyst had good photocatalytic activity.At the same time,it was found that the photocatalytic effect of different structures had no special change,mainly because the size of the basic nanoparticles of its structural composition was consistent.Based on the test of the cycle performance,it is found that the photocatalytic effect of hollowed-out sheet?-Fe₂O₃ is basically unchanged after four cycles,which indicates that the photocatalytic performance is stable.?2?Fe₃O₄ doped g-C₃N₄?defective?and Fe₃O₄@g-C₃N₄ composite catalysts were successfully prepared by calcining the molar ratio of iron nitrate to melamine in melamine supramolecular hydrogel precursors.The characterization results show that Fe₃O₄ at small proportions to form defects with g-C₃N₄ doping and at high iron content to form heterojunctions with g-C₃N₄ recombination.The RhB photocatalytic degradation results showed that the degradation rate of RhB by Fe₃O₄ doped catalyst?FGCN-1%?reached 97.4%within 15 min,and the degradation rate was 11.6 times that of pure g-C₃N₄.The degradation rate of FGCN-10%is about 3 times higher than that of pure g-C₃N_4,and it has outstanding magnetic recovery.No obvious deactivation is observed after five runs of the recycling experiments for FGCN-1%and FGCN-10% catalysts.Finally,a possible mechanism was proposed to explain the synthesis process of FGCN-x samples?from Fe₃O₄ doped g-C₃N₄ catalyst to Fe₃O₄@g-C₃N₄ composites?.?3?The?-Al₂O₃ doping?defect formation?g-C₃N₄ and?-Al₂O₃@g-C₃N₄?AGCN-x?were obtained after calcination by adjusting the molar ratio of aluminum nitrate to melamine in the precursor of melamine aluminum nitrate supramolecular hydrogel.The characterization results showed that?-Al₂O₃ doped and composite g-C₃N₄ catalysts were successfully prepared and AGCN-0.5%had a large surface area?2.5 times that of pure g-C₃N₄?.The results of RhB degradation showed that AGCN-0.5%catalyst had the best visible light degradation rate to RhB,which was 5.6 times higher than that of pure g-C₃N₄.Moreover,with the increase of the molar ratio of Al³⁺in the precursor,the photocatalytic degradation rate of?-Al₂O₃@g-C₃N₄ composite catalyst?AGCN-7%?was 4.7 times higher than that of pure g-C₃N₄.Moreover,the cycling performance of the two samples was excellent,and no obvious degradation ability was decreased in the five cycles.Then the degradation performance of methylene blue was also tested for pure g-C₃N₄,AGCN-0.5%and AGCN-7%catalysts under visible light.It was found that the degradation rate constant of AGCN-0.5%was 2.9 times that of pure g-C₃N₄and 2.5 times higher than that of pure g-C₃N₄.The above results show that?-Al₂O₃doping and recombination g-C₃N₄ form defects,which can effectively enhance the photocatalytic performance of the g-C₃N₄.