The Mechanisms Of Modified Reed Biochar-mediated Redox Reactions For Water Ecological Remediation

Biochar,come from incomplete combustion of biomass,widely used in carbon sequestration and soil reclamation.By adsorption and partition,biochar could block the contaminants from soil-water interface or extract from water.Reed is widely used in phytoremediation,and the addition of Reed derived biochar can promote its remediation efficiency,as well as improving the economic benefit and resource/energy recycle efficiency.However,the degradation or transformation of contaminants could not be achieved by the adsorption.And the migration/desorption caused by natural weathering,may lead to secondary pollution or polluted diffusion.The involvement of redox reactions would give rise to the stability and degradation of contaminants.The heterogeneous physic-chemical reactions of oxidizing or reductant may lead to the transformation of biochar structure.However,due to the lack of corresponding study,the application of biochar-mediated redox reactions is limited.Based on the electron donor?core-shelled nano zero-valent iron,nZVI-BCs?or electron acceptor?graphitic nitrogen-persulfate,N-BCs/PDS?,the study aims to probe the synergy mechanims of Reed-driven biochar towards redox reactions.Based on dosage and preparation temperature effect,the study probed the evolution mechanims of reed biochar structure by nZVI and N/PDS involving.The results showed that,400⁶00°C biochars were comprised of amorphous carbon and C-O/C-OOH;the surface is electronegative at pH>2.The specific surface area?SSA?of 700⁹00°C biochars decreased(from 181.2 to 95.2 m² g^-1),which were composed of amorphous-aromatic clusters,C=C/C=O,and the boundary defects.nZVI?20¹00 nm?regulated the biochar structure through nZVI dosage,during which C-O binded with Fe⁰ and the core-shell formed through coordination?C-O-Fe?.nZVI improved the aromaticity and stability,and reduced SSA and electronegativity of biochar.Besides,the graphitized nitrogen?N?improved SSA(95.2⁴96.7 m² g^-1)of biochar.The preparation temperature exhibited major influence on the structure of graphitized nitrogen?N?and biochar surface structure,forming aromatic and boundary defect structure.Moreover,PDS interacted with C=O,C=C,and C-N in biochar,forming Mⁿ⁺-O-O-SO₃ metastable active structure.The results demonstrated,nZVI-biochar exhibited selectivity adsorption towards high-valent heavy metals,which Cr?VI?was completely reduced to Cr?III??>99%?.Biochar promoted the reduction rate of nZVI significantly,indicating that the C-O-Fe and C=C/C=O acted as electron transfers further accelating the reaction process.The nZVI concentration and pH value affected the reduction reaction.The reduction reaction of nZVI mediated by biochar was less affected by anions,but affected more by organics.The N-biochar owned a high adsorption capacity for organic contaminants.Moreover,PDS reduced the concentration of organics on the surface of N-biochar significantly.For example,orange G?OG?and phenol?PN?first increased to 0.023 and 0.076 mg g^-1 and then decreased to 0,indicating that an adsorption mediated oxidation reaction took place on the surface of N-biochar/PDS.N increased the oxidation rate of PDS-biochar significantly?6.5 times?.Compared to commercial materials?such as CNT and rGO?,biochar exhibited the prior mediation efficiency.And bisphenol A?BPA?and sulfamethonidazole?SMX?degradation rates by N-biochar were highly-efficiency.The results showed that the C-O structure of biochar acted as adsorption sites for Langmuir homogeneous adsorption,further mediated Cr?VI?reduction by nZVI on the surface.Moreover,the C-O-Fe and C=C formed between nZVI and biochar accelated electron transfer and reduced the activation energy of the reaction(⁸.84kJ mol^-1).Cr?VI?was reduced to form Fe-O-Cr³⁺in the pore structure at the edge.The reaction orders of adsorption and reduction were 0.52 and 1.67 respectively.The adsorption rate was faster(k_d1=2.437 min^0.5),while the reduction as rate-limiting step occurred in the molecular diffusion stage with slower rate(k_d2=0.325).The graphitic?>700°C?N-biochar,as the preparation temperature improved,exhibited higher adsorption capacity.The above theoretical adsorption quantities of N-BCs and different organics(Qe,mmol g^-1)showed a good linear positive correlation with their oxidation rates(k_obs),with R² of 0.753 and 0.835,respectively.The linear equations were k_obs=0.223Qe-0.001 and k_obs=0.215Qe-0.012,respectively.Moreover,N-biochar presented low impedance,which generated the current detected in the volt-ampere curve during oxidation reaction.The results indicated the oxidation reaction was a surface-adsorption mediated electron transfer process,which was different from the free radical reaction mediated by PFRs in the literature.And the C=O structure also led to the production of ¹O₂.The orders of adsorption and oxidation were 3.63 and 0.45,respectively,in which the adsorption is the rate-limiting step.According to the normalization,SSA of biochar was the major factor affecting adsorption,while oxidative degradation mainly depended on electron transfer rate.