Wood-based Biochar As An Activator Of Peroxydisulfate For Organic Contaminants Degradation

Biochar,prepared by heating the forest castoff with little oxygen atmosphere,not only has good adsorption capacity to the pollutant in waste water but also is an excellent activator of peroxydisulfate for contaminants degradation.In this study,the effects of pyrolysis temperature on wood-based biochar properties was investigated.What’s more,catalytic performance of biochars fabricated at different pyrolysis temperatures was explored and the underlying mechanisms involving the generation of radical from the biochars-activated PDS process were identified.In the first part,Wood-based biochars were fabricated at different pyrolysis temperatures of 400-700℃ and used to activate peroxydisulfate（PDS）for the degradation of clofibric acid（CA）.With the increase of pyrolysis temperature,biochar not only has higher degree of carbonization,larger specific surface area and smaller pore size,but also more abundant oxygen functional groups on the surface,aiding biochar have a good adsorption property and favorable catalytic performance.Biochar pyrolyzed at700℃（BC700）showed more excellent catalytic performance toward CA removal than other BCs with CA and TOC removal achieved 97.8%and 58.2%in a 60 min reaction,respectively.CA degradation remained efficient by BC700/PDS process in the initial p H value between 4.0 and 9.0.The effect of initial p H of CA solution（p H0）,catalyst loading,PDS dosage,initial CA concentration（C0）and some common substrates（e.g.Cl^–,HCO₃^–and humic acid）on on CA removal was examined.Radical quenching experiments and electron paramagnetic resonance spectra were applied to identify the reactive radicals generated in the BC700/PDS system.The role of persistent free radicals（PFRs）,oxygen functional groups andπ-π*transitions in aromatic rings of BC700 for the PDS activation was explored.The analysis of LC-MS spectra was conducted to follow the intermediate products formed in the BC700/PDS process and the plausible pathways were proposed.This study contributes to the development of green materials for sustainable remediation of organic contaminants in water and provides support for further studies.In the second part,BC700/PDS system was employed for efficient removal of Acid Orange 7（AO7）.The results demonstrate PDS could be efficiently activated by wood-based biochar,and AO7 was rapidly eliminated in a wide range of p H value（3.0–10.0）with AO7 removal achieved≥99.3%after 14 min reaction.Although 58.2%of AO7 can be adsorptive removed by BC700,the UV-visible spectra of methanol extraction from biochar after the biochar/PDS process demonstrated that AO7 in both aqueous and solid phases was totally oxidized.It is speculated that sulfate radicals(SO4^·-)and hydroxyl radicals（^·OH）were formed on the surface of biochar.Based on the results of X-ray photoelectron spectroscopy（XPS）,π-electron density and the oxygen functional groups（especially C?OH）on biochar surface were active centers for the catalytic reaction.The study also demonstrated that non-radical pathway didn’t exist in in the biochar/PDS process via electron paramagnetic resonance technique（EPR）and linear sweep voltammetry（LSV）method.Recycle experiments of biochar for 4 runs were carried out and the regeneration method of the catalyst was also studied.