Synthesis of hydrochar supported zero-valent iron composites through hydrothermal carbonization of granatum and zero-valent iron: potential applications for Pb2+ removal

In the present investigation, a one-step synthesis of hydrochar (HC) supported zero-valent iron (ZVI) was performed through hydrothermal carbonization (HTC) of granatum and ZVI. According to XRD, XPS, and FTIR data, ZVI was evenly distributed on the surface of the hydrochar. In addition, the external ZVI oxide layer and the functional groups present in the hydrochar remained on the surface of the HC/ZVI composites after HTC treatment. The surface area of the HC/ZVI composites was between 31.11 and 44.16 m2/g. These numbers were higher than those obtained for hydrochar (20.36 m2/g) and ZVI (12.14 m2/g) separately. The Pb2+ adsorption capacity of hydrochar and ZVI was 28.64 and 192.44 mg/g, respectively (25 °C, pH = 6.05, Pb2+ concentration of 200 mg/L with 0.05 g HC and 0.01 g ZVI). In addition, the adsorption capacity of the composites was between 49.63 and 88.09 mg/g. The data obtained for Pb2+ removal by the samples used in this experiments fitted well the pseudo-second-order kinetics and Langmuir isotherm models. Therefore, hydrochar may represent a promising supporting material for the synthesis of ZVI composites.