Titanium Dioxide Arrays Composite Electrode: Preparation,Performance And Mechanism On Its Photoelectrocatalytic Water Purification

Photoelectrocatalysis(PEC)is an efficient water purification technology.Among them,the novel design and preparation of PEC materials is the key to water treatment.However,the interfacial reactions of electrode materials in traditional PEC systems still face challenges with high catalytic efficiency,low energy consumption,and cycle stability.The recent development of 1D and 2D nanostructured photo-electrocatalytic materials provided an opportunity to develop novel and high-efficiency photoelectrode materials.In view of the common coexistence of heavy metal ions and new-type organic and PPCPs contaminant in water,this thesis based on TiO₂ nanowire arrays(TNA)as electrode substrate materials designed and prepared various composite electrode materials and study their performances and mechanisms for the mixed pollution in water.In order to realize the rapid reduction transformation and simultaneous oxidative degradation of various heavy metal ions and organic pollutants in water by the PEC system,the main research results are as follows:(1)The oxygen vacancies(V_o)enriched on the surface of TiO₂ nanowire arrays(TiO₂NA)are regulated by N-modified C quantum dots(NCDs),and it is found that the introduction of NCDs can not only optimize the band gap structure of TiO₂ NA,but also can in situ stabilize the V_o layer of TiO₂ NA.The research results show that the optimized NCDs/TiO₂ NA-V_o photoanode possessed the high PEC activity and cycling stability of tetracycline(TC)after 8 cycles,and its degradation rate constant is 2 and 3 folds higher than that of TiO₂ NA-V_o and TiO₂ NA photoanodes,respectively.Electron spin resonance(ESR)and fluorescence(PL)spectroscopy confirmed the superior PEC activity of NCDs/TiO₂NA-V_o electrode driven by the visible light was contributed that the efficient stabilization of V_o layer in TiO₂ NA by NCDs helps to generate more·OH,O₂^·?and ~1O₂ radicals.(2)Pd nanoparticles were introduced onto the TiO₂ nanowire array(TNA)electrode grown with defective Mo S₂(DMS),which used as the photocathode to reduce Cr(VI)and oxidize BPA simultaneously.The TNA/DMS/Pd photocathode showed excellent PEC performances:95%of Cr(VI)was rapidly reduced to Cr(III)(10 min),and 97%of BPA was synchronously oxidized with 75%mineralization(30 min).Compared with the TNA and TNA/DMS photocathodes,the kinetic constants of Cr(VI)reduction increased 24 and 5 folds,and the kinetic constants of BPA oxidation increased 6 and 3 folds by the TNA/DMS/Pd photocathode,respectively.Various characterizations and experimental results revealed that the superior PEC activity of the TNA/DMS/Pd photocathode is mainly attributed to the construction of the interfacial heterojunction between TNA and DMS,which facilitates the separation and transfer of photogenerated carriers at the photocathode interface to provide extra photogenerated electrons decraese the overpotential of HER,thus creating a suitable microenvironment for H*formation.More importantly,the introduction of Pd nanoparticles stabilized the H*generated on the TNA/DMS photocathode interface,which can rapidly reduce the Cr(VI)and combine with dissolved oxygen in the PEC system to activate H₂O₂production,thus generating·OH to oxidize the BPA.The synchronous reduction and oxidation reactions pathways were therefore opened up by the efficient utilization of H*.(3)According to the result of first principle calculations,the behavior of H*could be regulated by incorporating oxygen atoms to generate a locally favorable electron-rich state of S atoms in the Sn S₂.Subsequently,by lowering the activation energy barrier of OOH*(a rate-determining step),the finely controlled H*led to a 12-fold decrease in the overpotential of H₂O₂ generation(H*–OOH*–H₂O₂–·OH).Based on this,a new H*–·OH redox pair suitable for a wide pH range(3–11)was constructed on a single Sn S_1.85O_0.15 AL@TNA photocathode interface.The experimental results showed that the Sn S_1.85O_0.15 AL@TNA photocathode exhibits?90%Cr(VI)reduction(within 10 min)and?70%mineralization efficiency for 4-nitrophenol(4-NP)oxidation.The removal efficiency was nearly 2 times and 3 folds higher than that without oxygen incorporation,respectively.ESR spectroscopy and radical quenching experiments confirmed that the H*and the derived·OH by the3-electron pathway were the main active species.Operando Raman revealed that the stable SnO₂ phase helps to constantly activate the generation of H*–·OH.