Synthesis, characterization and adsorption capacity of magnetic carbon composites activated by CO2: implication for the catalytic mechanisms of iron salts

Magnetic carbon composites (MCs) have received great interest in areas such as environmental remediation, catalyst supports and carriers for drug delivery systems. In order to improve the porosity of the MCs, the catalytic mechanism of iron salts during CO2 activation of hydrochar was systematically investigated using a suite of methods including Mossbauer spectroscopy, on-line pyrolysis gases and porosity analysis. Fe3O4 and superparamagnetic alpha-Fe2O3(s), pyrolysis products of iron salts, were found to promote the reaction between carbon and CO2 gas, leading to a decrease in the activation temperature that is required for optimal porosity. However, the reduction reaction between iron oxide and carbon was completely inhibited by CO2 gas. FeCl3 enhanced the thermal cracking of hydrochar and increased the porosity of the MCs in terms of an improvement of the amount of H-2, namely the pore-creating effect. However, other iron salts showed adverse effects, due to their inhibition effects on the thermal cracking of hydrochar. The MCs with excellent porosities showed high adsorption capacities for pharmaceuticals and personal care products (PPCPs), and were negatively correlated with the melting points of the PPCPs. The findings from this work can guide the production of novel MCs for maximum removal performance of organic pollutants from the environment.