Adsorption and reductive degradation of Cr(VI) and TCE by a simply synthesized zero valent iron magnetic biochar

To address inorganic and organic contaminants in the environment, economic new adsorbents are required. Here we test magnetic biochar for efficient capture of the typical pollutants Cr(VI) and trichloroethylene (TCE) from solution. We used a simple synthesis using 2M FeCl3 solution and peanut hull biomass to prepare magnetic ZVI biochar at alternate pyrolysis temperatures between 650 and 800 degrees C. The physicochemical character of the biochars were assessed using X-ray diffraction (XRD) and the Brunauer-Emmett-Teller (BET) method for surface area. The magnetic ZVI biochars were highly effective in the removal of Cr(VI) and TCE. The most effective magnetic biochar produced at 800 degrees C was further examined using scanning electron microscopy (SEM), revealing a high and even loading of ZVI. After sorption the same magnetic biochar was examined by X-ray photoelectron spectroscopy (XPS) to ascertain the underlying mechanisms. The dependence of Cr(VI) capture on solution pH was also examined. Our interpretation suggests that when pH < pH(zpc) (2.5) electrostatic attraction and redox reactions dominated the adsorption of Cr(VI). When pH > pH(zpc) the removal process was controlled mainly by redox reaction and substitution of chromate anions for hydroxyl (-OH) groups. Capture of TCE in contrast involved hydrophobic partitioning, pore-filling and reductive degradation. Overall our results suggest that simple synthesis of magnetic ZVI biochar could offer an economic and effective option to address water contamination issues.