Design,Preparation And Properties Of Three Typical Photocatalysts Based On Light Absorption Enhancement And Charge Carrier Regulation

As a green chemical technology,the photocatalytic process has widely applied in alleviating environmental pollution and energy crisis,which has attracted great attention of scientific researchers.In recent decades,two major problems which restrict the widespread promotion of photocatalytic technology have gradually emerged---insufficient light absorption efficiency and low separation capacity of photogenerated charge carriers.Based on these two bottlenecks,corresponding modification methods have been continuously proposed,such as ions doping,defect engineering,heterojunction construction,crystal facets control,co-catalyst loading,and so on.It is worth noting that the combination of various modification methods is expected to exhibit synergistic effects,which can drive much better photocatalytic activities under various conditions.Therefore,the design and characterization of modified photocatalysts,the influence of microstructure on light absorption efficiency and carrier separation efficiency,the synergistic strengthening mechanism in photocatalytic reaction process have been explored detailedly in this thesis.The specific results are as follows:（1）UV-Vis responsive CaSn（OH）₆/SnO₂ photocatalyst.In view of the disadvantage of low charge carrier separation efficiency,we have constructed the CaSn（OH）₆/SnO₂heterojunctions by a facile one-pot hydrothermal process via the variation of Ca/Sn molar ratios.The photocurrent and the photocatalytic degradation indicate that the type-II heterojunction greatly promotes the transfer of the photo-induced charge carriers between CaSn（OH）₆ and SnO₂,and the photocatalytic MB degradation efficiency of CaSn（OH）₆/SnO₂ composites exhibit 1.9 times than that of pure CaSn（OH）₆.Furthermore,the CaSn（OH）₆/SnO₂ can only absorb UV light to drive the photocatalytic activities,which still restricts its widely application.Therefore,we have synthesized various Fe³⁺-doped CaSn（OH）₆/SnO₂ photocatalysts.The doping of Fe³⁺not only extends the absorption region of CaSn（OH）₆/SnO₂ from UV to Vis,but also exhibits extremely promoted charge carriers separation and transfer process,and then improves the UV/Vis light-induced photocatalytic activities dramatically,proving that the synergistic effects between the heterostructure construction and ion doping play important roles in charge carrier excitation and transfer during the photocatalytic process.（2）UV-NIR responsive Ag₂S/TiO₂ photocatalyst.In this work,we have modified the traditional UV-induced TiO₂ photocatalyst with Ag₂S to construct the type-II heterojunction,and the Ag₂S/TiO₂ composites exhibit greatly improved photogenerated charge carrier separation efficiency and promoted photocatalytic activities under UV light irradiation.Meanwhile,the narrow band gap characteristic of Ag₂S enables the Ag₂S/TiO₂ composites to be excited by the NIR light directly,and the degradation rate of MO reaches 42%in 180min（NIR light）with the existence of Ag₂S/TiO₂ composites,which highly improves the utilization efficiency of sunlight.In order to further increase the charge separation capacity of Ag₂S/TiO₂ composites,RGO has been introduced to provide an electron transport pathway.Owing to the synergistic effect of the wide spectral response range,effective carrier separation and high specific surface area,the RGO/Ag₂S/TiO₂ heterostructure not only improves the photocatalytic activities of TiO₂under UV/Vis light irradiation,but also inhibits the photo-corrosion of Ag₂S and improves the photo-stability of RGO/Ag₂S/TiO₂ composites,which further provides strong evidence for the synergistic strengthening mechanism between narrow-band gap semiconductor compound and cocatalyst loading in promoting the photocatalytic activity.（3）UV-Vis-NIR responsive BiVO₄（040）/Ag₂O photocatalyst.Monoclinic scheelite BiVO₄ is getting more attentions in photocatalytic oxidation reactions because of the co-existence of{110}facet and{010}facet,which promotes the directional transfer of photogenerated charge carriers under the drive of internal electric field.This work is based on the crystal-face engineering and interfacial heterojunction modification.From the viewpoint of the UV/Vis light-induced photocatalytic activity,the selective deposition of Ag₂O on the BiVO₄（040）facet greatly optimizes the charge carrier separation and transfer.Moreover,the narrow band gap characteristic of Ag₂O spreads the light absorption region of BiVO₄ from UV/Vis to NIR,which significantly improves the sunlight utilization efficiency of BiVO₄.In these circumstances,the photocatalytic degradation and water splitting efficiencies of BiVO₄（040）/Ag₂O heterojunction have been facilitated vastly no matter under the irradiation of UV,Vis or NIR light.This result reveals the synergetic effect of rational heterojunctions construction and crystal facets regulation on the optimization of photo-induced charge carrier dynamics and thermodynamics in the photocatalytic reactions.