G-C₃N₄ And Copolymerization Modified TiO₂ Nanowire Arrays For Improved Photoelectrochemical Activity

Due to the shortage of water resources and severe water pollution,it is urgent to solve water pollution in China.Developing efficient,low energy consumption and deep oxidation removal technology is of great significance.With the ability to degrade organic pollutants completely and mild reaction conditions,photocatalytic technology has been widely studied,showing great potential in environmeantal application.However,the efficiency of current photocatalyst is still low due to the low separation efficiency of charge carries and limited solar light response.Therefore,the design and development of efficient photocatalyst is of great importance and has attracted much attention in photocatalysis research area.In this thesis,two kinds of novel efficient photocatalysts on the basis of classical semiconductors TiO₂ were designed and prepared: visible light responsed g-C₃N₄/TiO₂,copolymerized g-C₃N₄/ TiO₂ core-shell nanowire arrays.Bisphenol A and methylene blue were used as model pollutant,and the photoelectrocatalytic activity of as-prepared samples were investigated.Based on the results of characterization and performance evaluation,the relationship between the catalyst structure and performances has been studied systematically.The main conclusions have been summarized as follows:?1?Rutile TiO₂ nanowire arrays are synthesized on carbon cloth by hydrothermal reactions.Deposition of g-C₃N₄ onto the TiO₂ nanowire arrays was conducted by a facile chemical vapor deposition process with melamine as a precursor.A series of batch experiments were carried out to investigate the degradation rate of photocatalysis,electrocatalysis and photoelectrocatalysis by TiO₂ nanowire and g-C₃N₄/TiO₂ core-shell nanowire.The study found that reaction rate constant of g-C₃N₄/TiO₂ is higher than TiO₂,which is attributed to the enhanced visible light response and the promoted separation of electrons and holes by heterojunction.With increases in the bias potential,the trend of photoelectrocatalytic activity of g-C₃N₄/TiO₂ is at first increased and then decreased.The degradation rate of g-C₃N₄/TiO₂ reached a maximum at 2 V,which can degrade 92% BPA after 4h reaction.Reaction products were identified by gas chromatography/mass spectrometry–mass spectrometry?GC/MS–MS?,and the possible pathways for BPA degradation by g-C₃N₄/TiO₂ were proposed,featuring a series of steps including dehydroxylation,cleavage of C–C bond,and oxidation.?2?Modified g-C₃N₄ was prepared by co-polymerization of dicyandiamide and 4,5-dicyano imidazole and the modification does not alter the bulk structure or the core chemical skeleton of g-C₃N₄ too much.With the best mass ratio?4,5-dicyano imidazole/dicyandiamide=0.05g/3g?in synthesis,94% MB removal was achieved on co-polymerization modified g-C₃N₄ under 4h reaction.Co-polymerization modified g-C₃N₄ was introduced onto Ti O₂ nanowire arrays by chemical vapor deposition process,then a novel and highly efficient N-CN-0.05/TiO₂ photocatalyst was achieved.The photocatalytic and photoelectrocatalytic activity of N-CN-0.05/TiO₂ are higher than those of g-C₃N₄/TiO₂ and TiO₂,which can be attributed to the following reasons: co-polymerization modified g-C₃N₄ can improve the visible light absorption of photocatalyst;the promoted separation of electrons and holes can be achieved by heterojunction.