Adsorption Behavior Of Cationic And Anionic Dyes By Biochar Derived From Traditional Chinese Medicine Residues Prepared Via Vacuum Pyrolysis

Dyes can be used in different fields,and wastewater containing dyes will harm the environment and human health,so it should be treated in some ways before discharging.The method of adsorption is simple,low-cost,and suitable for the removal of most dyes.It is important to find an adsorbent that is low-cost and has a stable source.With the rapid development of Traditional Chinese medicine industry and the gradual industrialization,a large amount of the Traditional Chinese medicine residue has been produced,which,if improperly disposed of,will harm the environment.In this study,Traditional Chinese medicine residue-derived biochar（TCMDBC）was prepared via the um pyrolysis method,and it was used to remove anion and cation dyes in water.The best preparation conditions of TCMDBC were pyrolysis temperature 900℃for 4h.The results showed that the specific surface area of TCMDBC was 808.6 m²/g,and the TCMDBC can remove methylene blue and reactive blue 19 efficiently,and the maximum were 192.31 and85.47 mg/g,respectively.Langmuir model could better fit the isotherm data,and the correlation coefficient was above 0.992.The pseudo-second model fitted the dynamic data best,comparing other models,and the correlation coefficient was above 0.994.Thermodynamic analysis showed that the adsorption of both dyes by TCMDBC was spontaneous and endothermic.To improve the adsorption capacity of MB by TCMDBC,acid-modified biochar was prepared in this experiment,The optimal preparation conditions of ATCMDBC explored were modified with 40%sulfuric acid at 60℃for 6h.The maximum was 370.37mg/g.Batch experiments determined that the Langmuir model could better fit the dye adsorption isotherms process（R²>0.975）and the Pseudo second-order model could describe the adsorption kinetic experimental data best（R²>0.999）.The intra-particle diffusion model showed that the adsorption process involved film diffusion and intra-particle diffusion,and the Boyd model showed that membrane diffusion was the main rate-limiting step.X-ray fluorescence spectroscopy（XRF）analysis showed that the content of metal compounds in ATCMDBC decreased significantly.Brunauer–Emmett–Teller（BET）showed that the specific surface area of ATCMDBC increased to 1110.3 m²/g,Fourier Transform Infrared spectroscope（FTIR）analysis showed that the carboxyl group in ATCMDBC was formed.The adsorption mechanism of ATCMDBC for MB included pore filling,cation exchange and hydrogen bonding.The results of dynamic adsorption showed that with the decrease of the flow rate,the adsorption capacity increased,and the time of penetration was longer.The dynamic data fitted well with both Thomas and Y-N models.To improve the adsorption capacity of RB19 by TCMDBC,Mg（OH）₂ modified biochar（MTCMDBC）was prepared in this experiment.Batch experiments determined that the Langmuir model could better fit the dye adsorption isotherms process（R²>0.990）and the Pseudo second-order model could describe the adsorption kinetic experimental data best（R²>0.995）.The intra-particle diffusion model showed that the adsorption process involved film diffusion and intra-particle diffusion.FTIR analysis showed that a new peak of hydroxyl was added to MTCMDBC.The adsorption mechanism of MTCMDBC to RB19 included pore filling,electrostatic interaction and hydrogen bonding.The results of dynamic adsorption showed that with the decrease of the flow rate,the adsorption capacity increased,and the time of penetration was longer.The dynamic data fitted well with both Thomas and Y-N models.