Efficiency And Mechanism Of TiO₂ Ntas Photocatalytic Activation Of Peroxymonosulfate For Degradation Of Bisphenols In Water

Photocatalytic activated persulfate advanced oxidation technology has attracted more and more attention in recent years because of its advantages in solving energy crisis and water pollution control.This technology usually requires photoactivated catalysts or photosensitive compounds to activate persulfate to produce reactive oxygen species,and then achieve the degradation of organic pollutants in water.Previous studies mainly focused on the design of new photocatalytic materials,but there was a lack of systematic research on the degradation and t ransformation of pollutants in the system.Additionally,the problems of difficult separation and recovery of powder catalyst and metal ion loss in photocatalytic materials need to be further improved.Based on these,this thesis systematically studied and compared the removal efficiency,mechanism and oxidation pathways of three bisphenols by photocatalytic activation of peroxymonosulfate（PMS）using titanium dioxide nanotubes arrays（TiO₂NTAs）as photocatalyst.To further improve the photocatalytic activity of TiO₂NTAs,TiO₂NTAs pretreated with silane coupling agent（KH570）were modified with noble metal Ag.The efficiency and mechanism of PMS activation for bisphenol A（BPA）degradation under visible light were investigated.In addition,it was found in the experimental process that natural organic matter,humic acid（HA）could promote the activation of PMS under visible light,so the thesis also explored the mechanism of HA photocatalytic activation of PMS.TiO₂ NTAs were prepared by anodic oxidation using Ti plate as substrate,then TiO₂NTAs were employed to activate PMS in visible light to degrade BPA.The results showed that TiO₂NTAs could effectively activate PMS to degrade BPA under visible light,94.6%of BPA could be removed within 30 min,which was much higher than TiO₂NTAs photocatalytic system（20.1%）and PMS photocatalytic system（9.4%）.Meanwhile,TiO₂NTAs showed excellent stability.A series of studies have shown that PMS-TiO₂ complex with visible light response was formed on the surface of TiO₂NTAs,which can be excited by visible light to transfer electrons to the conduction band of TiO₂,and then activating PMS.SO₄^·-and·OH were the main radicals responsible for BPA degradation.HA and chloride ions（Cl^-）significantly enhanced the BPA degradation,while bicarbonate（HCO₃^-）and phosphate（H₂PO₄^-）exhibited an inhibition effect.Moreover,TiO₂NTAs/PMS photocatalytic system displayed an enhanced BPA degradation in tap water and purified water compared with deionized water.Three BPA substitutes,bisphenol F（BPF）,bisphenol AF（BPAF）and bisphenol S（BPS）,were degraded by photocatalytic activation of PMS using TiO ₂NTAs.The degradation rates of three bisphenols followed the order of BPS<BPAF<BPF,and the acid condition was conducive to three bisphenols degradation.SO₄^·-,·OH,h⁺and^·O₂^-all participated in three bisphenols degradation,among which SO₄^·-and^·O₂^-played a major role in the BPF degradation,while SO₄^·-and h⁺were the main active species in the degradation of BPAF and BPS.Since the main reactive species in three bisphenols degradation process are different,the influences of inorganic anions on three bisphenols degradation were also different.By analyzing the oxidation intermediates of the three bisphenols,it was found that there were some common degradation pathways including bond-cleavage and hydroxylation of benzene ring shared by three bisphenols.Besides,some specific degradation pathways were also identified,for example,the self-coupling was found in BPF and BPS degradation process,while the benzene ring splitting was occurred only in BPAF transformation process.TiO₂NTAs was prepared by anodic oxidation on Ti mesh substrate.Then TiO₂NTAs pretreated with silane coupling agent（KH570）was modified with noble metal Ag to further improve the photocatalytic activation of PMS.Taking BPA as the target pollutant,the photocatalytic performance of Ag/KH570/TiO ₂NTAs/PMS/photocatalytic system was evaluated,and it was found that BPA could be completely removed within 60 min,much higher than Ag/KH570/TiO₂NTAs/photocatalytic system（36.6%）and TiO₂NTAs/PMS/photocatalytic system（53.1%）.The excellent oxidation performance could be attributed to:（1）the introduction of KH570 made Ag evenly dispersed on TiO₂NTAs so as to make more effective use of visible light.Meanwhile,the Ag loss was greatly reduced,which made Ag/TiO₂NTAs exhibit excellent stability,（2）KH570 and a series of redox reactions make part of Ag⁺doped into TiO₂ and generate oxygen vacancies to further activate PMS.Both free radicals(SO₄^·-,·OH)and non-free radicals（h⁺,¹O₂）contributed to the degradation of BPA.The Ag/KH570/TiO₂NTAs/PMS/photocatalytic system showed excellent oxidation performance in a wide pH range and was less affected by water matrix.The mechanism of activation of PMS by HA under visible light was investigated,in this process,the concentration of HA was correspondingly reduced,and the structure of HA was also damaged.HA was divided into different molecular weight compounds to explore the activation mechanism of PMS.The results indicated that the aromatic constituents of HA made the dominant contribution to the generation of reactive species,in which the phenolic groups played the role of electron-donor,and the quinone moieties acted as the electron shuttles could accelerate the electron-transfer between HA and PMS.¹O₂,·OH and SO₄^·-all made contribution to BPA degradation,and ¹O₂ played the dominant role in this process.In addition,the HA/PMS photocatalytic system was less affected by water matrix.Since HA is widely distributed in nature,which can avoid the complex catalyst preparation process,it provides a possibility for the practical application of the system...