The Removal Effect Mechanisem Of Per-and Polyfluoroalkyl Substances By Modified Biochar In Water

Per-and polyfluoroalkyl substances（PFASs）are a large group of synthetic aliphatic compounds.The hydrogen atoms on the carbon chains are completely or partially replaced by fluorine atoms,which have strong stability and have been widely used in industrial production such as medical equipment,pesticides,and textiles.Owing to the insufficient understanding,a variety of ecological environment media are polluted by PFASs.The hazards of PFASs mainly include environmental toxicity,animal toxicity and human toxicity,which may lead to serious consequences if not disposed in time.Therefore,different methods were used to modify biochar to prepare adsorbents and catalysts respectively,in order to achieve the purpose of efficient treatment of PFASs pollution in water environment in this paper.The main conclusions are as follows:（1）Sludge biochar（H-SL and Me BC-8）with good adsorption capacity and catalytic degradation ability were prepared by acid modification and metal modification,respectively.H-SL had loose structure,rough surface,rich pore structure,many oxygen-containing functional groups and hydrophobicity.Me BC-8 had abundant unpaired electrons,and had excellent persulfate activation ability after the introduction of iron-manganese bimetallic.The active Fe⁰ and Fe²⁺in Me BC-8 account for42.0%of the relative content,and the main components Mn²⁺and Mn³⁺that can promote the reduction of Fe³⁺account for 69.9%of the relative content,which endows Me BC-8 with better catalytic ability.（2）The theoretical maximum adsorption capacity of H-SL for PFOS and PFOA was 72.17 and 45.88 mg·g^-1,respectively.The adsorption process was a heterogeneous physical adsorption and chemical adsorption process.The main mechanisms of the adsorption process were electrostatic interaction,hydrogen bonding and hydrophobic interaction.The electrostatic interaction played the main role.In addition,different functional groups had different adsorption energies for PFASs,and the adsorption energy of C=O group is the highest.（3）When the dosage was 0.1 g·L^-1,the initial concentration of PFOS was 1 mg·L^-1,and the persulfate concentration was 5 m M,Me BC-8 could achieve more than 90%degradation rate and more than 5%defluorination rate in 30 min.Under acidic and neutral conditions,Me BC-8 activated persulfate system had good degradation ability for PFOS.Me BC-8 degraded PFOS by generating·OH and·SO₄^-.The main processes were as follows:（1）Fe⁰ as an electron donor directly catalyzed PDS to generate·SO₄^-.（2）Fe²⁺and Mn³⁺acted as electron donors to promote the cleavage of O-O bond in persulfate.The first generated·SO₄^-would react with water to generate·OH,and then combined with Fe²⁺and Mn³⁺to form metastable iron-manganese intermediates.Under the induction of surface carbon-oxygen functional groups,they would react with HSO₅^-to generate·SO₄^-and·OH.（3）As the main electron donor-acceptor,Mn³⁺regulated the electron density between iron and manganese,which promoted the conversion of high-valence iron to low-valence iron,and ensured the catalytic activity.（4）Fe⁰could also be used as an electron donor to reduce Fe³⁺to Fe²⁺to ensure catalytic activity.