Adsorption, kinetic and mechanistic studies of Pb(II) and Cr(VI) ions using APTES functionalized magnetic biochar

Magnetic composite (Fe3O4@BC/APTES) functionalized with 3-aminopropyl triethoxysilane (APTES) was prepared by capping magnetite nanoparticles with biochar prepared from the root of C. odorata and used as adsorbent for the adsorption of Pb(II) and Cr(VI) from aqueous solution. 93.95% of Pb(II) and 52.8% of Cr(VI) were successfully adsorbed from aqueous solution by the adsorbent after 1 h at 20 degrees C. The Langmuir equation best described the adsorption data with maximum adsorption capacities of 64.92 mg/g (R-2 = 0.97) and 48.86 mg/g (R-2 = 0.92) for Pb(II) and Cr(VI) respectively. The adsorption process was investigated using the intra-particle diffusion model together with the pseudo first and second order kinetic equations. The composite was stable in an alkaline environment while 8.55% of iron was leached in an acidic medium after 1 h and the results shows Pb(II) adsorption was not affected by competing ions. Pb(II) was better adsorbed at alkaline pH as against acidic pH for Cr(VI). 88% of adsorbed Cr(VI) ion was effectively desorbed using 0.005 M HNO3 after 4 cycles. Thermodynamic parameter suggested that the sorption process was by physisorption and exothermically moderated. The composite was magnetic and easily recovered with a small bar magnet from aqueous solution after 20 s.