Two-step Solid-state Chemical Synthesis Of Perovskite MSnO₃?Ca,Sr,Ba? Nanomaterials And Their Photocatalytic Properties

Semiconductor-based photocatalytic technology has attract attention for wastewater treatment and clean energy production,due to its low energy consumption,simple process,complete degradation of pollutants and free from secondary pollution.As novel and lucrative photocatalytic materials,perovskite materials possess the highly stable octahedral crystal structure,flexible structure and composition,unique electronic/band structure,have been expected to be an efficient visible light photocatalys.In this thesis,perovskite photocatalytic nanomaterials was fabricated through a simply synthetic approach.Firstly,the precursor of hydroxide?MSn?OH?₆?M=Ca,Sr,Ba??was obtained by a one-step room-temperature solid-state route with different kinds of solid inorganic salts as raw materials,and then the perovskite-type oxide?MSnO₃?M=Ca,Sr,Ba??nanomaterial was obtained by heating treatment of hydroxide.The growth mechanism of rod-like structure under different temperature conditions was discussed,and the structure-activity relationship between the morphology,crystal surface,energy band and the photocatalytic performance of the perovskite oxide were studied.Subsquentily,the N doped perovskite oxide nanomaterials were also fabricated by a two-step solid-state chemical reaction,which could evidently improve the light absorption efficiency,utilization efficiency of pure perovskite oxide.Thus,a highly efficient and stable perovskite photocatalyst was obtained.This paper is of guiding significance for the subsequent development,design and practical application of perovskite semiconductor materials.The detailed work is summarized as follows:?1?Perovskite SrSnO₃ nanomaterials with different morphologies?nanoparticle,nanorod,flower-like nanoribbon?were obtained by a two-step solid-state chemical method that was regulated by the reaction materials,calcination temperature and holding time.SrSnO₃ nanomaterials with different morphologies are ascribed to the highly sensitivity to calcination temperature.At a lower temperature,only{001}crystal planes existed on the surface of both granular and rod-shaped products.While the thermal condition of final product is up to a relatively higher temperature,the high-index facet{111}will be exposed that had a negative influence in the photocatalytic activity.The photodecomposition rate of MB by SrSnO₃ nanorods with{001}reached 75%,about 10%higher than that of nanoribbons exposed on{111}.Only SrSnO₃ with exposed{001}facets exhibited a better photodegradation of MB activity and stability due to lower photoinduced carrier recombination rate,narrower band gap and shorter charge transfer distance.?2?In order to further study the photocatalytic properties of alkaline earth metal-group perovskite tin-based oxides,MSnO₃?M=Ca,Ba?nanomaterials were successfully prepared by a two-step solid-state route of alkaline earth metal nitrate with tin chloride and sodium hydroxide.The amount of sodium hydroxide is different during the preparation of CaSnO₃ and BaSnO₃,the size of CaSnO₃ and BaSnO₃nanoparticles is different.The band gap of as-prepared CaSnO₃ and BaSnO₃ in our case were calculated to be about 4.16 eV and 3.01 eV,respectively.The photocatalytic degradation of MB with perovskite CaSnO₃ and BaSnO₃ photocatalysts was investigated under UV light.There was high photocatalytic degradation for MB and almost no obvious decline after 5 runs,demonstrating its high photocatalytic activity and outstanding stability.?3?Since the absorption rate of pristine perovskite materials is low in the photodegradation of macromolecular organic pollutants,an easy-to-manipulate two-step solid-state synthetic method was adopted to incorporate N element into MSnO₃?M=Ca,Sr,Ba?,separately.The addition of non-metallic element N could broden the adsorbtion range.The effects of doping N on the crystal phase,microstructure and morphology of the samples have been investigated.Different from MSn?OH?₆?M=Ca,Ba?,the addition of urea had little effect on the phase structure of SrSn?OH?₆,whereas it pulverized its morphology and transforms it from nanorods to discrete nanoparticles.Compared with CaSnO₃-N and BaSnO₃-N,the photocatalytic degradation efficiency of SrSnO₃-N is most significantly improved,which may due to the increased surface area,reduced particle size and decreased band gap.The reaction kinetic constant of SSO-700-N₁ for photodegradating MB under UV light was 0.040min^-1,which was about 10,5 and 3 times as much as that of the bare SrSnO₃(0.004min^-1),CaSnO₃(0.008 min^-1)and BaSnO₃(0.012 min^-1).