Oil industry waste based non-magnetic and magnetic hydrochar to sequester potentially toxic post-transition metal ions from water

Abstract

Solid waste conversion to value-added products is a stepping stone towards sustainable environment. Herein, sesame oil cake (SOC), an oil industry waste was utilized as a precursor to develop hydrochar (HC) samples by varying reaction temperature (150-250 degrees C) and time span (2-8 h), chemically treated with 10% H2O2 to optimize a sample with maximum yield and Pb(II) adsorption. Highest yield (29.2 %) and Pb(II) (24.57 mg/g at C-o: 15 mg/L) adsorption was observed on SOCHC@200 'C/6 h, magnetized (mSOCHC@200 degrees C/6 h) for comparative study. XRD displayed highly crystalline SOCHC@200 T/6 h and amorphous mSOCHC@200 degrees C/6 h, both having a characteristic cellulose peak at 14.9 degrees. mSOCHC@200 degrees C/6 h displayed superparamagnetic behavior with 11.2 emu/g saturation magnetization. IR spectra confirmed the development of samples rich in oxygen containing functionalities; an additional peak for iron oxides appeared at 586 cm(-1) in mSOCHC@200 degrees C/6 h spectrum. Four major peaks at 531.9, 399.9, 348.2 and 284.7 eV, assigned to O 1s, N 1s, Ca 2p and C 1s, respectively were observed during XPS analyses. An additional peak at 710.3 eV, ascribed to Fe 2p was observed in mSOCHC@ 200C/6 h XPS spectrum, while a peak at 143.2 eV for Pb 4f appeared in spectra of both Pb(II) saturated samples. pH dependent (maximum at similar to 6.7), exothermic Pb(II) adsorption was found. About 50-70% (at C-o: 25 mg/L) adsorption on both SOCHC@200 degrees C/6 h and mSOCHC@200 degrees C/6 h was accomplished in a minute, attaining equilibrium in 180 and 240 min, respectively. Error functions and superimposed q(e), (exp). and q(e), (caL) values supported Langmuir isotherm model applicability, with respective q(m) values of 304.9 and 361.7 mg/g at 25 degrees C for SOCHC@200 degrees C/6 h and mSOCHC@200 degrees C/6 h. Kinetic data was fitted to PSO model. Highest (between 92.2 and 88.9 %) amount of Pb(II) from SOCHC@200 degrees C/6 h and mSOCHC@200 degrees C/6 h was eluted by 0.01 M HCl.