Performance And Mechanism Of 2,4-Dichlorophenol Removal In Water By Peroxymonosulfate Activation With Modified Porous Biochar

Chlorophenol compounds（CPs）are widely used in agriculture and industry,where they are often detected in the natural environment.Because they are difficult to biodegrade,highly toxic,carcinogenic,they pose a great threat to human health and the long-term stable development of ecosystems.2,4-dichlorophenol（2,4-DCP）is a typical chlorophenol compound with strong chemical stability,long half-life,and easy to exist for a long time in the aqueous environment.Therefore,there is an urgent need to develop an efficient,economical and environmentally friendly 2,4-DCP treatment technology.In this study,modified porous biochar was prepared by two-step KOH activation pyrolysis and used as a catalyst for peroxymonosulfate（PMS）for adsorption and oxidative degradation of 2,4-DCP.The physicochemical properties and structural characteristics of biochar were explored by a series of characterization methods.The adsorption and catalytic properties of modified porous biochar were evaluated by the adsorption and degradation effects of 2,4-DCP,and the influencing factors were experimentally explored.The main active sites were determined by the correlation analysis of the surface structure of biochar and the reaction rate constant(k_obs)such as specific surface area,pore volume and defect site,and the degradation mechanism of the HPC800/PMS system was determined by combining quenching experiments,electron paramagnetic resonance（EPR）,X-ray photoelectron spectroscopy（XPS）and electrochemical analysis,and the intermediate products were identified and possible degradation pathways were speculated.In addition,the detoxification performance and actual engineering availability of HPC800/PMS were explored through biotoxicity experiments and the construction of alginate hydrogel composite biochar catalytic material/PMS continuous flow bed reactor system.The main research results are as follows:（1）Hierarchical porous biochars（HPCs）were prepared by using KOH activation to regulate the specific surface area,porosity,defect structure and surface function of biochar,in which HPC800 had the largest specific surface area（1460.1567 m²/g）,rich microporous structure and high surface defect structure（I_D/I_G=1.20）.（2）HPC800 pre-adsorbed to achieve adsorption equilibrium for 30 min to remove31.17%of 2,4-DCP,and then immediately add PMS to initiate oxidative degradation reaction,and degrade 97.51%of 2,4-DCP within 90 min.The reaction rate constant(k_obs=0.03536 min^-1)of the HPC800/PMS system was 3.93 times that of the reaction rate constant(k_obs=0.00237 min^-1)of the original BC900/PMS system,and the system shows strong anti-interference ability for natural organic substances and inorganic anions,strong environmental temperature adaptability and wide p H working range.（3）Microporous specific surface area,microporous pore volume,micropore proportion and defect structure are linearly related to k_obs,the increase of microporous specific surface area provides more active sites for HPC800,the increase of microporous pore volume provides a larger space for electron transport for HPC800,and the defect structure is the main active site of the system.After quenching experiments,EPR and XPS analysis,the degradation mechanism of HPC800/PMS system was dominated by nonradical pathway（¹O₂,HPC800-PMS*metastable active species-mediated electron transfer）,radical pathway（O₂·-,SO₄·-and·OH）as auxiliary effects,and carbonyl group（C=O）was the main source of ¹O₂.（4）The solution treated by HPC800/PMS successfully eliminated the toxic effects of2,4-DCP and its intermediate products on plants,and the continuous flow bed reactor system of HPC800 calcium alginate composite hydrogel catalyst/PMS can realize the flow removal of organic pollutants,which proves that the system has broad prospects in the practical engineering application of water treatment.