Enhanced removal capacities and mechanisms of Mn/Fe-loaded biochar composites functionalized with chitosan Schiff-base or hydroxyl toward Pb (II) and Cd(II) from aqueous solutions

The efficient capture of heavy metal ions from actual wastewater is a global challenge. To enhance Pb(II) and Cd (II) removal, novel biochar composites (MF@CBC, MF-S@CBC and MF-OH@CBC) were successfully fabricated by loading magnetic Mn-Fe binary oxides and functionalizing chitosan Schiff-base or hydroxyl on biochar in the study. The maximum adsorption capacities of MF-OH@CBC and MF-S@CBC toward Pb(II)/Cd(II) were 196.69/ 187.29 mg/g and 161.61/153.69 mg/g (pH = 5.0, adsorbent dosage = 0.5 g/L), which were 2.09/3.05 and 1.54/ 2.33 times higher than corn cob biochar (CBC), respectively. The adsorption processes were conformed to Langmuir isothermal model and pseudo second order model. The numerous functional groups presented on MF-OH@CBC resulting from loading Mn-Fe nanoparticle and hydroxylation might be the main reason for dominating adsorption of Pb(II)/Cd(II) by complex interaction (contribution rate (CR) = 45.66%/43.12%). And also, the negative charge on MF-OH@CBC might be another reason for enhancing adsorption of Pb(II)/Cd(II) by elec-trostatic interaction (CR = 23.11%/22.45%). Besides, ion exchange (CR = 17.95%/19.33%) and physical adsorption (CR = 13.28%/15.10%) could also contributed to Pb(II)/Cd(II) removal. In addition, MF-OH@CBC displayed favorable recycling ability and its adsorption capacity retained over 80% after five cycles. It also exhibited anti-interfering ability, the adsorption capacity for Pb(II)/Cd(II) in actual sewage was 85.27%/80.47%, respectively. The results indicated that MF-OH@CBC possessed good potential for eliminating Pb(II) and Cd(II) from the complex aqueous environment.

Automated summary

In this study, novel biochar composites were fabricated by loading magnetic Mn-Fe binary oxides and functionalizing chitosan on biochar, and their efficiency in removing heavy metal ions Pb(II) and Cd(II) from wastewater was demonstrated. The biochar composites showed higher adsorption capacities compared to corn cob biochar, and the adsorption mechanisms were attributed to complex interaction, electrostatic interaction, ion exchange, and physical adsorption. The composites also exhibited favorable recycling ability and anti-interfering ability.