Preparation And Studies On Photocatalytic Activities Of Peony-like InOOH And FeTaMoO₇/InOOH Heterojunction Catalysts

In recent years,photocatalysis technology has attracted much attention from scientists because of its properties of high-efficiency,simple operation and no secondary pollution.As a wide-band gap n-type semiconductor,InOOH has high redox characteristics and is gradually applied in the field of photocatalysis.In this study,InOOH was selected as the research object,and the photocatalytic activity and stability of InOOH were improved by morphology controlling and heterojunction building.In terms of morphology control,glycerin was a regulation solvent during solvothermal process,and the peony-like InOOH was achieved by adjusting the ratio of glycerol.At the same time,this paper expounded the influence of glycerol on the structure and morphology of InOOH and selected the optimum preparation conditions for synthesizing the peony-like InOOH.Subsequently,the photocatalytic activity of InOOH with different morphologies on norfloxacin were discussed.In addition,the degradation pathways and mechanisms were investigated detailedly.As for heterojunction building,a p-n heterojunction structure was constructed by combining the new p-type multi-metal oxide FeTaMoO₇ with peony-like InOOH in this paper.The effects of the introduction of heterojunction on the physical and chemical properties of InOOH and the photocatalytic activities of norfloxacin and rhodamine B were investigated.The main conclusions of this paper are as follows:1.A new morphology InOOH catalytic material with peony-like morphology was successfully obtained by glycerol assisted solvothermal method,and the glycerol played a crucial role in the structure and morphology of InOOH.By discussing the solvothermal reaction factors,the optimum preparation conditions of peony-like InOOH were selected as the glycerol proportion of 25%,reaction temperature of 200℃and reaction time of 12 h.The shape of the synthesized InOOH was peony-like morphology with average particle size of 2–5μm approximately,which was assembled with nanosheet.The Mott-Schottky curve proved that InOOH was an n-type semiconductor with a conduction band potential of-0.47 V,a valence band potential of3.18 V and a band gap of 3.65 e V（versus standard hydrogen electrode potential）.2.Peony-like InOOH possessed an excellent photocatalytic activity for degrading norfloxacin.The degradation rate of norfloxacin reached up to 98.84%within 180 min of UV-light irradiation,and its first order rate constant was 4.8 times or 1.7 times than that of reported hexagram-like InOOH or reported InOOH nanosheet,respectively.The synthesized peony-like InOOH owned better light absorption capacity,higher separation rate and lower recombination rate of photogenerated electrons and holes,which were the main reasons for the improvement of photocatalytic activity.After four photoreaction cycles,the peony-like InOOH samples still maintained high photocatalytic activity,and its phase structure,specific surface area,morphology and surface chemical composition were in good states.Eleven possible degradation intermediates of norfloxacin were detected by mass spectrometry,and four possible photocatalytic degradation pathways were proposed.Path I was decarboxylation,defluorination and demethylation.Path II was mainly the opening of quinolone moieties.Path III was mainly the destruction of piperazine ring.Path IV was the opening of the benzene ring.The active species involved in photocatalytic degradation process included h⁺,·OH radicals and·O₂^-radicals,and·O₂^-radicals were main active species.3.A new multi-metal oxide FeTaMoO₇ was prepared by solid phase sintering method for the first time,and then FeTaMoO₇/InOOH heterojunction catalysts with different proportions were synthesized by solvothermal method.The prepared FeTaMoO₇ was a tetragonal crystal structure with a good crystallinity and a space group of P42/mnm.The lattice parameters are a=0.4666 nm,b=0.4666 nm,c=0.3032 nm,respectively.The morphology of FeTaMoO₇/InOOH heterojunction catalysts were affected by FeTaMoO₇ contents.With the increasing of the ratio of FeTaMoO₇,the peony-like shape of the heterojunction catalyst was gradually changed into ball-like shape,and the particle diameter showed a trend of decreasing.The band gaps of 5wt%FeTaMoO₇/InOOH,10wt%FeTaMoO₇/InOOH and 20wt%FeTaMoO₇/InOOH were3.61 e V,3.33 e V and 3.45 e V,respectively.Mott-Schottky curves showed that FeTaMoO₇ was a p-type semiconductor material and FeTaMoO₇/InOOH composite successfully constructed p-n heterojunction.4.The photocatalytic performances of FeTaMoO₇/InOOH heterojunction catalysts were obviously better than that of peony-like InOOH and FeTaMoO₇ single catalysts.10wt%FeTaMoO₇/InOOH heterojunction catalysts showed the best photocatalytic activities for degrading norfloxacin and rhodamine B within 180 min of UV-light irradiation.Their degradation rates were 99.98%and 88.01%,respectively.The rate constant of norfloxacin was 4.3 times or 1.5 times than that of FeTaMoO₇ or InOOH,respectively.The rate constant of rhodamine B was 11.3 times or 3.6 times than that of FeTaMoO₇ or InOOH,respectively.The presence of FeTaMoO₇ could improve the light absorption capacity,enhance the separation rate and reduce the recombination rate of photogenerated electrons and holes of heterojunction catalysts,which were the main reasons for the improvement of photocatalytic activity.The main active species of heterojunction catalysts were·O₂^-radicals in the photodegradation process.