Efficient and low-cost mesoporous magnetic carbon composites derived from date palm stones for environmental remediation of hexavalent chromium

Abstract

This study was performed to achieve two important scientifically challenging goals, environmental remediation of toxic heavy metals and utilization of agricultural lignocellulosic wastes. In this work, a series of mesoporous magnetic carbon (MMC) adsorbents were synthesized by carbothermic reduction at different temperatures employing date palm (Phoenix dactylifera L.) stones as the carbon source. The synthesized adsorbents were characterized by different technquies and the results confirmed the presence of zero-valent iron (ZVI) nanoparticles and other iron oxides as products of the carbothermal reduction. The nature of phases present, crystallite size and the surface properties were found to be dependent on the calcination temperature. The adsorbent MMC700 exhibited the smallest (ZVI) crystallite size 36 nm and the largest S_BET 341 m²/g. All adsorbents showed mesoporous structure with mesopore average diameter lower than 6 nm. The performance was evaluated in the removal process of toxic Cr(VI) in an aqueous medium, and the optimum conditions of the process were reported. The removal process was dependant of solution pH where best results was achieved at pH = 2. Complete removal of chromium was achieved in less than 5 min by MMC700. The results were better fitted with pseudo-second-order kinetics and followed the Freundlich model isotherm. The maximum adsorption capacity was found to be 265.25 mg/g for MMC700, suggesting its application as an efficient, low-cost, and easily separable adsorbent for the toxic Cr(VI) removal process. The prepared adsorbents exhibited superior performance in the removal process compared to other agricultural wastes or biomass - derived adsorbents reported in literature.