Hydrothermal Synthesis of High-Efficiency Carbon Sorbent Based on Renewable Resources

Abstract

A technique of synthesis of new sorption materials by hydrothermal carbonization of sunflower meal (HTS) with the addition of graphene oxide (GO) and subsequent carbonization (C) has been developed. To assess morphological and phase changes during carbonization, the materials have been characterized by scanning electron microscopy and IR spectroscopy. According to the results obtained, carbonization facilitates the development of latent porosity and reduces the amount of oxygen-containing and alkyl groups. Kinetic sorption studies have also been carried out by the example of extraction of Pb²⁺ ions and organic dye molecules (methylene blue (MB)). The experimental results show that the adsorption capacities of the HTS, HTS/C, HTS/GO, and HTS/GO/C composites were 82.9, 108.6, 168.9, and 148.3 mg/g, respectively, for extraction of Pb²⁺ ions and 1481.8, 1601.1, 1920.3, and 2283 mg/g, respectively, for extraction of MB molecules. It is established that, during the absorption of MB molecules, carbonization affects significantly the contact time. Carbonized samples exhibit high sorption activity, which results in the equilibrium contact time of 15 min (this value is 60 min for noncarbonized samples). The equilibrium time during the adsorption of Pb²⁺ ions is 60 min for all samples. The adsorption kinetics is described using the following models: the pseudo-first-order model, pseudo-second-order model, Elovich model, and intraparticle diffusion model. It is found that the adsorption process is limited by the chemical-exchange reaction and runs in a mixed-diffusion mode.