Efficient Activation Of Peroxydisulfate By Bean Dregs Derived Biochar For Bisphenol A Removal

The pyrrolic N doped in the carbon matrix is the catalytic active site for the metal-free activation of persulfates.Compared with traditional metal-based catalysts,N-doped biochar can also effectively activate persulfates to degrade organic pollutants.Different from the radical mechanism,N-doped biochar can activate persulfates to produce ¹O₂ or degrade pollutants through the electron-transfer mechanism.In addition,compared with the radical mechanism,nonradical mechanisms are more selective and have stronger anti-interference ability.Herein,a series of N-doped biochars were prepared by using waste bean dregs as the precursor and the catalytic properties of the biochars were investigated.The conclusions are as follows:（1）SEM,TEM and BET characterization results showed that the biochar prepared at high temperature（900℃）had ultrahigh specific surface area(3194.9 m² g^-1),large pore volume(2.30 cm³ g^-1)and pore size（3.31 nm）.XPS and Raman analysis results showed that with the increase of pyrolysis temperature,more defective sites were created.However,the content of N in catalysts decreased,which might be caused by the loss of N under high temperature.In addition,almost all N species were converted to pyrrolic N in BDK900,which could function as the potential active sites in biochar.（2）The adsorption performance of biochar for BPA was evaluated by a series of adsorption experiments.The results showed that BPA molecules could be rapidly adsorbed by biochar,and the adsorption equilibrium could be achieved within 100 min.High correlation coefficients（R²>0.99）were got by fitting with the pseudo first-order kinetic model,which indicated that the adsorption process was much likely to be physisorption.In addition,the adsorption isotherms were well fitted with Langmuir equation rather than Freundlich equation,which suggested that the adsorption process was a monolayer adsorption.（3）The catalytic performance of biochar was evaluated by the degradation experiment of BPA.The results showed that BDK900 could efficiently activate PDS to degrade BPA,while biochar prepared at other temperatures had lower catalytic activity.In addition,the ability of biochar to activate other oxidants was also explored,and the results showed that both peroxymonosulfate（PMS）and hydrogen peroxide（H₂O₂）could hardly be activated by biochar.（4）The stability of the reaction system was investigated by exploring the influence of different environmental factors（p H,temperature,inorganic anion,biochar and PDS dosage）on the reaction system.In addition,considering the potential application of the BDK900/PDS process in the treatment of BPA-contained wastewater,a biochar packed column was prepared to test the stability of the biochar in a continuous flow reaction.The results showed that with the increase of biochar dosage,PDS dosage and temperature,the removal rate of BPA increased.However,inorganic anions and natural organic matter would inhibit the degradation of BPA.It is worth noting that the BDK900/PDS system can achieve more than70%of BPA removal rate in river water and wastewater effluents.In addition,the column experiment results also showed that BDK900 had excellent stability.（5）The mechanism of activation of PDS by biochar was revealed by DFT calculation,quenching experiment and ESR test.The results showed that the pyrrolic N in biochar could effectively promote the decomposition of PDS to produce active species.Surface-bound radicals and electron transfer mechanism played vital roles in PDS/BDK900/BPA system.This study will shed new light on the rational design of N-rich biochar and develop a low-cost technology toward remediation of BPA-contaminated wastewater.