| Biochar,a porous carbonaceous by-product generated from biomass through pyrolysis/carbonization under anoxic and anaerobic condition,has attracted more attention due to its application either in soil or in wastewater treatment recently.In this work,beta-cyclodextrin-chitosan modified walnut shell biochars(β-CCWB)were synthesized as a low-cost adsorbent for the removal of heavy metal Cr(VI)from aqueous solution.The removal efficiency of Cr(VI)by β-CCWB(about 93%)was higher than that by the pristine biochar(about 27%).Characteristic analysis including aperture(BET),Scanning electron microscopy(SEM),Fourier infrared spectrum(FT-IR)and X-ray photoelectron spectroscopy(XPS),which indicated that amino and carboxyl groups were the major functional groups for Cr(VI)sorption,and implied that the electrostatic attraction of Cr(VI)to positively charged biochar surface,reduction of Cr(VI)to Cr(III)ion and the complexation between Cr(III)ion and β-CCWB functional groups were responsible for Cr(VI)removal mechanism in this research.Batch sorption experiments were carried out to investigate the adsorption characteristic of β-CCWB.Experimental data fitted pseudo-second order equation and Freundlich isotherm model,and the optimum adsorption of the modified biochar was observed at pH 2.0 with the adsorption capacity of 206 mg g-1.Thermodynamic analysis showed that the adsorption process was spontaneous and endothermic.Furthermore,we investigated the effect of the presence of NaCl(background ionic strength)to Cr(VI)adsorption,the adsorption capacity reduced 24%at high NaCl concentration(1.0 mol L-1).We also found the adsorbed β-CCWB could be effectively regenerated by 0.5 mol L-1 NaOH solutions.In a word,the environmentally friendly and low-cost β-CCWB has bifuctional roles of adsorption and reduction to heavy metal Cr(VI),and could be applied as a potential effective adsorbent to remediate Cr(VI)contamination from wastewater. |
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