| Chlorophenols are widely used in industry and agriculture as fungicides,wood preservatives and used as raw materials for synthetic drug intermediates.Environmental toxicology studies have shown that the stable carbon-chlorine bonds and electron-rich chlorine atoms on the aromatic ring of chlorophenols result in the highly toxic,carcinogenic,teratogenic,mutagenicity and environmental persistence,which seriously threatens the ecosystem and human health.Chlorophenols have been listed or marked as high risk environmental pollutants with priority control level in the world.Therefore,the key to address the environmental issues of chlorophenols is developing effective treatment methods to selectively and primarily cleaving the carbon-chlorine bond.Semiconductor photocatalysis with mild reaction conditions,friendly environment and strong REDOX capacity,is expected to be a feasible technology for dechlorination conversion of chlorophenols.Bi2O3 is considered an ideal photocatalyst with potential attributing to its visible light response,tunable structure and low-cost features.However,Bi2O3 photocatalyst still has some key issues in the photocatalytic conversion of chlorophenols,such as inefficient utilization for photogenerated electron,unclear selective dechlorination and unrecyclable from water.Thus,the research objectives in this thesis are preparing recyclable and high performance Bi2O3 base photocatalysts.The strategies of constructing proper level energy photoelectron platforms,preparing micro-nano hierarchical structures and surface hydrotreating were developed to achieve the objectives.In addition,we have also verified the photocatalytic mechanism and chlorophenols conversion paths.This thesis consists of three main parts:?1?Studied the effect of coupling phosphate-bridged Sn O2 on phase-mixed Bi2O3for photocatalytic activities.?Bi O?2CO3 microspheres precursor was primarily prepared by using citric acid assisted hydrothermal method.Then,phase-mixed hierarchically structured Bi2O3 microspheres were successfully fabricated via calcining?Bi O?2CO3.The exceptional photocatalytic activity for degrading 2,4-dichlorophenol?2,4-DCP?on hierarchically structured phase-mixed Bi2O3is mainly attributed to the enhanced charge separation due to the close?/?phase-mixed heterojunction,and the large surface area.The photocatalytic activities are further enhanced by coupling nano-Sn O2on phase-mixed Bi2O3and introducing phosphate-bridge between them via wet chemical method.It is confirmed that the enhanced charge separation is attributed to the effective transfer of excited proper-energy-level electrons from Bi2O3 to Sn O2 platform,especially to the phosphate-bridged one accelerating the interfacial charge transfer as the“electrons transport channel”.In addition,base on the results of radical-trapping experiments,detected main intermediates and mineralized chloride amounts,it is verified that the photogenerated holes dominate the photocatalytic decomposition of2,4-DCP on Bi2O3-based nanocomposites with possible decomposition paths suggested.?2?Studied the effects of coupling Bi PO4 on?-Bi2O3for photocatalytic activities.Bi PO4/?-Bi2O3 composites with different mole ratios were obtained by calcining phosphate anchored?Bi O?2CO3 precursor microspheres.Notably,the mole ratio-optimized heterojunctional microsphere displayed highest photocatalytic activity.The kinetic constant?k?for 2-CP degradation is even 5-time enhancement compared to the stander classical Ti O2?P25?photocatalyst.The exceptional photoactivities were mainly attributed to the strong adsorption of 2-CP due to the complexation of Bi on Bi2O3 with empty orbitals and Cl of chlorophenols with lone-pair electrons for efficiently modulating holes,and to the prolonged charge lifetime by transferring the photogenerated proper-energy-level electrons of?-Bi2O3 to the in-situ nano-Bi PO4.Additionally,it is confirm that the selective adsorption mode of?-Bi2O3 on monochlorophenol?CPs?base on the interaction between Bi and Cl,and the induced subsequent h+dechlorination degradation process,revealing the efficient photocatalytic degradation process.Interestingly,the selective conversion of CPs into high value-added chemicals?4-acetyloxyphenol?,along with H2 production on O2-free condition was realized,which brings a new idea of dual-functional photocatalysis.In addition,it was found that the adsorption capacities of CPs on the composite followed the order of o-chlorophenol>m-chlorophenol>p-chlorophenol.It can be inferred that the phenolic hydroxyl group in chlorophenol might affect the selective adsorption of the composite surface.?3?Explored the effects of surface hydrotreating on Bi PO4/?-Bi2O3 composite for photocatalytic activities.A controlled hydrotreating method was used to calcine the Bi PO4/?-Bi2O3 composite to produce surface oxygen defects on?-Bi2O3 surface which further induced the fresh hydroxyl on?-Bi2O3.The results showed that Bi PO4 was not affected during this hydrogenation treatment.Basis on the interaction between Bi and Cl,forming hydrogen bonding interaction between the generated hydroxyl around the surface of Bi atoms and the phenolic hydroxyl of phenolic hydroxyl,will auxiliary strengthen the selective adsorption to CPs.It is demonstrated that introducing oxygen defects by hydrogenation treatment could improve the photocatalytic activity of Bi PO4/?-Bi2O3 composite,and the k of the optimized sample is 9-time higher than that of P25 Ti O2.Photocatalytic activity test and photochemical reaction pathway by using LC-MS/MS and ion chromatography showed that the CPs conversion pathway is not changed after surface hydrogenation treatment,however,the amount of main product4-acetyloxyphenol and produced H2 are significantly increased.It is further proved that the main adsorption mode based on the interaction between Bi and Cl is a prerequisite for realizing dual-functional photocatalytic process.This result provides a basic scientific idea for further investigating photocatalytic selective primary-dechlorination degradation and conversion. |
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