Effects Of Aged-biochar From Platanus Leaves On The Removal Behavior And Mechanism On Tetracycline In Waste Water

Tetracycline（TCs）is one of the antibiotics with the highest concentration and frequency detection in aquatic environments.However,its adsorption capacity on pristine biochar is limited.Aged-biochar can greatly improve the adsorption amount of TCs.The choice of modification method on biochar is crucial,which can determine the potential application of biochar.Hence,a single-step preparation method for producing aged biochar based on viatic Platanus orientalis Linn leaves was prepared.The biochar was then modified by chemical oxidation with varied solutions（HNO₃/H₂SO₄=1/3,K₂Cr₂O₇,KMn O₄,H₂O₂（30%）,and distilled water,described as ABC,MBC,PBC,WBC and HBC,respectively）using impregnation method.The pristine biochar（BC）and aged biochars were characterized by BET,scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy（FTIR）and Zeta potential analyzer to investigate the influence of aged modification on the biochars’morphology,surface area,pore size,chemical composition,functional groups and electric potential.The biochars were used to adsorb TCs in waste water.The adsorption kinetics,isotherms,and mechanisms of TCs on biochar were further studied.This research can provide a pathway for the utilization of biochar resources and the removal of TCs from aquatic environments.The results indicated that:（1）Effects of different aged treatments on physicochemical properties of biocharAfter oxidation modification,rough surface and pore structure can be seen in the MBC,ABC,PBC,WBC and HBC.In addition,the KMn O₄modification resulted in the adhesion or agglomeration,making the pore structure of MBC more developed.Meanwhile,the N₂adsorption–desorption curves of all these biochar were of the typical type IV,which was characterized by an obvious hysteresis loop at high pressure.The MBC owned the highest surface area,which reached to 41.6 m²·g^-1.Compared with BC,the surface area of WBC,ABC,HBC and PBC were significantly increased by 70.6%,12.1%,41.2%and 144.4%,respectively.In addition,the average pore size of MBC,WBC,PBC,HBC and ABC were reduced by 58.4%,39.5%,30.6%,27.2%and 17.8%,respectively,compared with BC.The oxidation modification process,except MBC,decreased the p H values,specific conductance（EC）and ash content.The element contents of all these biochar were in the sequence of C>O>H>N.however,aged biochar was less aromatic and more hydrophilic,polar compared with BC.The p H_zpcof BC was 2.1,while the p H_zpcof PBC is 3.3,and the p H_zpcof ABC,MBC,HBC and WBC were all less than 2.0.Biochar have vibration peaks at wavelengths 3434 cm^-1（-OH）,2925 cm^-1and 2850 cm^-1（-CH₃and-CH₂）,1616 cm^-1（C=C and C=O）,1438 cm^-1（-COOH）and 873 cm^-1（C-H）.Compared with BC,the MBC,HBC and PBC showed new functional groups of Mn-O,C-O-C and Si-O-Si.（2）Effects of different aged treatment biochar on TCs adsorptionThe adsorption capacity of TCs on biochar varied among BC and aged biochar.The MBC and ABC showed highest adsorption capacity at p H=2.0 while the optimal p H values for PBC,WBC and HBC were at 11.0.MBC,which showed the best adsorption effect of TCs at p H=2.0(43.7 mg·g^-1),decreased the TCs removal capacity with increased p H value.The optimal application rate of MBC is 1.0 g·L^-1at p H=2.0 with the maximum removal ratios of 88.1%.Furthermore,the increase of Na⁺,Ca²⁺and Na⁺/Ca²⁺contents（both existed at the same time）inhibited the adsorption of TCs by MBC,clearly showed an ion competition.However,HBC,PBC,ABC and WBC had a slight promotion effect on TCs adsorption.The highest desorption rates of TCs from BC,MBC,PBC,HBC,WBC and ABC were 5.5%,7.7%,8.4%,4.9%,5.2%and 9.8%,respectively.（3）Mechanism of the effect of different aged treatment biochar on TCs adsorptionThe mechanisms of TCs adsorption on biochar included pore-filling,electrostatic interaction,surface complex interaction,hydrogen bonding,pore diffusion,andπ-πinteraction.Meanwhile the accurate second-order kinetics model is better to fit the adsorption process of TCs by PBC,MBC,ABC and the WBC,indicating that complexation（including surface functional groups complexation andπ-πcoordination）and minerals precipitation played important roles in TCs removal process.The results also indicated that the higher adsorption capacity of TCs on this biochar was mainly attributed to the precipitation of TCs on the surface benefited from the higher alkaline earth metal content in the raw material.Overall,all these results showed that KMn O₄modified biochar has the potential to act as adsorbent for TCs removal in aquatic environment.