Unraveling adsorption characteristics and removal mechanism of novel Zn/Fe-bimetal-loaded and starch-coated corn cobs biochar for Pb(II) and Cd(II) in wastewater

Abstract

Two functionalized biochar composites (ZF@CBC and SZF@CBC) were fabricated and applied for capturing Pb(II) and Cd(II) from wastewater. SZF@CBC were achieved by loading Zn/Fe nanoparticles (NPs) and coating starch onto corn cobs biochar (CBC) surface, while ZF@CBC was realized by loading Zn/Fe NPs onto CBC surface. The characterization analysis (SEM-EDS, XRD and FTIR) revealed that Zn/Fe NPs and starch were successfully introduced onto CBC surface. The adsorption data of Pb(II) and Cd(II) by ZF@CBC and SZF@CBC conformed to the model of pseudo second order kinetic and Langmuir isothermal and the capture Pb(II) and Cd(II) was a chemisorption process. The maximum sorption capacities of SZF@CBC for Pb(II) and Cd(II) reached 199.98 mg/g and 183.93 mg/g, which were 3.37 and 3.84 times high as that of CBC, respectively. Due to the presence of plentiful exposed adsorption sites (–OH, –COOH, Zn-O and Fe-O) on SZF@CBC surface, which endowed it to accelerate Pb(II) and Cd(II) adsorption. In addition, complexation, electrostatic attraction, ion exchange and physical adsorption took part in the adsorption process. Besides, SZF@CBC still exhibited very good removal capacity for Pb(II) and Cd(II) even in the coexistence of multiple interfering ions and maintained stable adsorption capacity after five consecutive cycles. Therefore, SZF@CBC could be used as an excellent adsorbent for decontaminating Pb(II) and Cd(II) from wastewater with multiple pollutants, and also could be used in resource utilization of biomass waste, which possessed potential applications prospects.