Recent Advances in Visible-Light Photocatalytic Asymmetric Synthesis Enabled by Chiral Lewis Acids
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In recent years, visible-light photocatalytic asymmetric synthesis has shown considerable potential in the mild and rapid construction of optically active organic molecules with structural diversity.Chiral Lewis acids (CLA), including chiral borane compounds, lanthanum complexes, first-row transition metal complexes, and chiral-at-iridium or rhodium complexes, have been established as one class of the most effective catalysts being capable of controlling the stereochemistry in photo-induced chemical transformations.The recent advances in this emerging field were presented by classifying the reactions into bifunctional CLA photocatalytic reactions and reactions enabled by dual catalysis with a CLA catalyst and an external photosensitizer, expecting that these studies will stimulate progress in organic synthesis, photocatalysis and asymmetric catalysis.Methyl orange
Zinc nitrate
p–n junction
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Silver-based photocatalytic semiconducting materials have drawn the attention of reseachers for their high visible photocatalytic activity. However, the silver-based photocatalytic semiconducting material exhibits light corrosion during the photocatalytic reaction, and the photocatalytic stability is poor. Therefore, improvingthe photocatalytic stability and inhibition of light corrosion of silver-based photocatalytic semiconductor materials have been the focus of attention. In this paper, according to the principle of photocatalysis and the principle of photo-corrosion, it is proposed to improve the photogenerated electrons and hole separation of photocatalytic semiconductor materials, to rapidly transfer photogenerated electrons, to inhibit photogenerated electrons and Ag + to prevent light corrosion, Stability of the catalyst. Ag2CO3 / GO composite photocatalytic materials were synthesized by precipitation method using polystyrene as photocatalyst. The characterization and photocatalytic performance tests showed that the graphene has a good auxiliary effect, which can promote the separation of photogenerated electrons and holes of Ag2CO3 and transfer the photogenerated electrons into O2 in H2O in time, thus suppressing the light of Ag2CO3 / GO photocatalytic materials Corrosion phenomenon, improve the photocatalytic performance. Ag2CO3 / GO-1.0 has the best catalytic activity for the catalytic activity and stability of Ag2CO3 / GO in the photocatalytic decomposition of methyl orange. Therefore, graphene as a photocatalytic auxiliaries can effectively improve the photocatalytic stability of silver-based photocatalytic materials and have some reference significance for improving the stability of other photocatalytic materials which are prone to light corrosion.
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This study prepared TiO2 film photocatalyst based on Ti plate using sol-gel method. XRD result demonstrated that the prepared photocatalyst mainly consisted of anatase crystals about 35.7nm on the average. SEM characterization result showed that the surface of the photocatalyst was very even and compact. And TiO2connected with the Ti plate closely and firmly. The photoelectrochemistry characteristic of the photocatalyst tested with electrochemistry method indicated that the prepared photocatalyst was n-type semiconductor and the extra electric field would promote the separation of photogenerated electron and hole in favor of the increase of the photocatalysis efficiency. The degradation experiments of benzamide by photocatalysis and electrically assisted photocatalysis (EAP) demonstrated that the extra electric field had the obvious assistant effect on photocatalysis and the benzamide degradation rate by EAP was much higher than that by photocatalysis. When the electrode potential of photocatalyst was -0.05V/SCE,the removal efficiency of benzamide could be 95% in 120min.
Benzamide
Degradation
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Redistribution
Settling
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The photocatalyst Ag3VO4 was prepared by the chemical precipitation method.The photocatalyst was characterized by X-ray powder diffraction(XRD),UV-Vis diffuse reflectance spectroscopy(UV-Vis) and Photoluminescence(PL) emission spectra.The photocatalytic activity of the photocatalyst was evaluated by photocatalytic reduction of Cr2O2-7 and photocatalytic oxidation of Methyl Orange(MO).The effect of different preparation conditions on the photocatalytic activity of Ag3VO4 was investigated.The results showed that the Ag3VO4 photocatalyst prepared in the presence of excess silver exhibited the excellent photocatalytic reduction activity of Cr2O2-7 and photocatalytic oxidation activity of Methyl Orange(MO) under visible light irradiation.And the photoabsorption wavelength range of the photocatalyst red shifts and the utilization of the total spectrum improves.As for the Ag3VO4 photocatalyst(Ag/V=6:1),the stability and cycling runs are studied.The possible mechanisms of influence on the photocatalytic activity of the Ag3VO4 photocatalyst were also discussed.
Methyl orange
Visible spectrum
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Fe3+ and Al 3+ co-doped TiO2(Fe3+/Al3+-TiO2)composite photocatalysts were prepared by the sol-gel method using Ti(OC4H9)4 as precursor and characterized by X-ray diffraction(XRD)and UV-Vis.The effect of calcination temperature and salts in photocatalytic system on the photocatalytic activity of Fe3+/Al3+-TiO2 were investigated by photocatalytic degradation of methyl orange irradiated by sunlight.The photocatalytic activity of Fe3+/Al3+-TiO2 was enhanced with increasing temperature.HCO3-and NO2-decreased its photocatalytic activity.
Methyl orange
Degradation
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In this paper, the present situation and progress on the area of semiconductor photocatalysis were reviewed briefly, including the mechanism of semiconductor photocatalysis, the improvement of photocatalyst and the coupling of the process of photocatalytic oxidation with other processes or techniques. The influence of sulfation and microwave heating method on the structure and photocatalytic properties of TiO 2 catalyst was discussed. The new processes with high efficiency for degradation of organic contaminants such as microwave-assisted photocatalysis and the coupling of thermal catalysis with photocatalysis were proposed.
Degradation
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Underlayer exposed ZnO:Al-TiO2 coupled films are prepared by different means.Surface morphology by SEM,microstructure by XRD,film thickness by surface profiler and photocatalysis are investigated.In order to explain the enhanced photocatalysis,reaction Ag++→Ag↓ is adopted to clarify the mechanism.It turns out that during the process of photocatalysis the exposed part of the underlayer releases e-and this suppresses recombination of light-induced charges,thus enhanced photocatalysis.
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