Degradation Of 2, 4 Dichlorophenol In Water Using Nano-Fe⁰/TiO₂

The nano-TiO₂ has a good application prospect because of its high activity,stability in acid or alkaline solution,low cost and other advanstages.A novel photocatalyst TiO₂ loaded with Fe⁰ was prepared and studied in degrading 2,4 Dicholorophenol(2,4-DCP) in this paper. The analysis results from X-ray diffraction(XRD),X-ray photoelectron emission spectroscopy(XPS) and UV-Vis absorption spectrometer and catalytic property studies indicated that the dopant Fe⁰ have a significant influence on optical absorbancy,and catalytic activity and other characteristics of the photocatalysts.The Fe⁰/TiO₂ catalyst has a stronger absorbance under visible light with respect to the pure TiO₂.The photocatalytic activity of the Fe⁰/TiO₂ was evaluated in the 2,4-DCP degradation in aqueous solution under mainly UV illumination and visible light illumination,and the main research conclusions are as follows:(1) A series of nanoscale Fe⁰/TiO₂ composites prepared via combined sol-gel technique, chemical reduction and impregnation method were used in the degradation of 2,4-dichlorophenol(2,4-DCP),and the optimal Fe addition level is 1wt%.The factors influencing the degradation rate were investigated and optimized.The increase of 2,4-DCP initial concentration led to a decrease of dechlorination ratio,but an increase of dechlorination by-products,acidic conditions and dissolved oxygen were beneficial to the photo degradation. The mineralization and reaction kinetics analysis indicated that TOC removal was matched with degradation results,at the end of the reaction,Cl^- was released more than 97%,while TOC had 21%leftover.Different degradation styles(Fe⁰/N₂,Fe⁰/air,TiO₂/UV,Fe⁰-TiO₂/Vis, Fe⁰-TiO₂/UV) were used to removal 2,4-DCP,and the results indicated that the synthesized Fe⁰/TiO₂ under UV illumination achieved high degree of 2,4-DCP degradation and TOC removal.The reason is attributed to the cycle of Fe between different valence states that enhances the photocatalytic dengradation activity of the composite catalyst.Further the possible degradation mechanisms and process included adsorption,dechlorination, hydroxylation and cleavage of the benzene ring.The main products were CO₂ and chloride ion.(2) In order to improve the easy recovery and reuse rate of catalyst,a composite membrane combining Fe⁰ and photocatalyst was prepared by combining sol-gel technique, dip-coating and chemical reduction impregnation method.The photocatalytic activity of the Fe⁰/TiO₂/ACF composite membrane was evaluated in the 2,4-DCP degradation in aqueous solution under UV illumination with the optimal Fe addition level at 1wt%.The factors influencing the degradation rate were investigated and optimized:The presence of a small quantity of ACF on Fe⁰/TiO₂ catalysts could help the degradation of intermediate products from degrading 2,4-DCP and decrease the remaining TOC level significantly,from 45%to 74%.Increase the initial 2,4-DCP concentration from 10-30ppm to 50-100ppm,the percentage of degraded 2,4-DCP dropped from close to 100%to a decreased level at around 62%,but led to an increase of dechlorination by-products.Acidic conditions were beneficial to the photo degradation.The mineralization and reaction kinetics were analyzed,the 2,4-DCP degradation and its dechlorination are faster than its mineralization.More than 95%Cl^- was released, while TOC had 26%leftover.A two-stage first-order degradation kinetic is obviously observed in the dynamic curves.The stability and long-term performance of Fe⁰/TiO₂/ACF composite membrane was investigated,the removal efficiency of 2,4-DCP was kept more than 90%after seven cycles by the synthesized composite membrane,the XKD patterns showed that there is no significant changes in the intensity and patterns,characteristic peaks at the 20 of 44.64°for Fe⁰ were observed on both of the pre- and post-reaction catalysts,the composite membrane water permeation flux was not affected compared with the original substrate base membrane.Furthermore,the possible mechanisms and process included adsorption,dechlorination,hydroxylation and cleavage of the benzene ring.The main products were CO₂ and chloride ion.