Synthesis And Photocatalytic Activity Of Cu₂O And Ag₃PO₄ With Different Shaped Nano- And Microstructrues

With the rapid development of the social economics and improvement of the living standard, the environmental pollution becomes increasing seriously. Therefore, environmental problems need to be solved as soon as possible,for example, haze weather and polluted water from industry and life. The research results have demonstrated that photocatalysis is a simple, efficient and cheap technique. Copper and silver are categorized asⅠB in the periodic table of chemical elements. And Cu₂ O and Ag₃PO₄ can be used as catalyst because that they can absorb visible light. The purpose of this work aims at the synthesis, growth mechanism and photocatalytic activity of Cu₂ O and Ag₃PO₄ crystals with different structures and sizes, so that catalyst with high photocatalytic activity can be found and evidences for basic research are able to be provided.1) Cu₂ O nanocrystals with average particle sizes ranging from 25 to 155 nm were synthesized by a simple solvothermal method and the relevant photocatalytic activity has been researched. The results suggested that samples with smaller sizes had better photocatalytic activity. The hierarchical nanoclusters（NCs） with an average size of 25 nm exhibited the best photocatalytic ability among the as-prepared samples. And NCs are made up of many ultrafine grains with the sizes of 2⁷ nm. It could degradate the MO solution（100 m L, 10 mg/L） completely in 12 minutes with a dosage of 10 mg because such a structure facilitated the generating and transferring of the carriers. Thus it is concluded that the photocatalytic activity of Cu₂ O nanocrystal can be enhanced by just decreasing their particle size.2) Cu₂ O crystals with different morphologies（solid and porous） and sizes（from dozens of nm to hundreds of nm） were synthesized controllably through a facile solvothermal route. The experimental results can be concluded as follows:（1） The aggregation of thin crystallites occurred in both the low and high PVP concentration, but sample with high size uniformity and good dispersal could be synthesized with suitable dosage.（2） When Ac- ions were used, NCs with an average size of 25 nm converted into porous sub-microspheres with an average size of 282 nm gradually along with the amount of DMF varying from 30 to 60 and 90 m L.（3） While NO3- ions were used instead of Ac- ions, the porous Cu₂ O nanospheres（NSs） had no changes in shape, but with decrease in sizes.（4） Porous Cu₂ O NSs with an average size of 72 nm exhibited better adsorption ability towards methyl orange compared with activated carbon.3) The self-assembly of three types of 3D Cu₂ O nanocrystals was discussed and can be summarized as several steps:（i） Formation of 0D Cu₂ O nanodots with size of 1-7 nm;（ii） Aggregation of 0D nanodots to 2D nanosheets（quasi-spherical and bookmark-like） via OA;（iii） Formation of 3D structures（NCs or NSs） via self-assembly of 2D units; and（iv） Aging of porous Cu₂ O NSs via Ostwald ripening.4) Cu₂ O octahedral, cuprous oxide cubes and other samples with different morphologies were synthesized by using hydrazine hydrate and ascorbic acid as reducing agents, respectively. The results have demonstrated that the amount of PVP, reaction time and so on have influences on the final morphologies of the crystals. Furthermore, the photocatalytic activity of Cu₂ O cubes is much better than that of the octahedral because that the particle sizes of the former are bigger than the later.5) The influences of PH values on the morphologies of Ag₃PO₄ crystals were researched. The results suggested that Ag₃PO₄ crystals couldn’t be obtained with p H value lower than 5 while Ag₃PO₄ quasi-spheres evolved into polyhedral along with the p H value inceasing from 5.5 to 10. The experimental results also revealed that particles with larger spaces between each other exhibited higher photocatalytic activity. Moreover, compared with Cu₂ O crystals, the photocatalytic ability of Ag₃PO₄ crystals is better with the similar particle sizes.6) The photocatalytic processes of Cu₂ O cubes and Ag₃PO₄ crystals were studied under three different intensities of visible irradiation. The results suggested that the photocatalytic rate became rapid both with the two sample as catalysts when the luminous power increased. It is because that photogenerated electron/hole pairs are more in stronger irradiation. Furthermore, with the same increment of luminous power,the increase in degradation rate of Ag₃PO₄ crystals is faster compared with Cu₂ O, which can be attributed to higher quantum yield of the former.