Microwave assisted hydrothermal preparation of rice straw hydrochars for adsorption of organics and heavy metals

A series of rice straw hydrochars were produced through a microwave-assisted hydrothermal treatment method, characterized and used for the adsorption of three organics and two heavy metals from aqueous solutions. The hydrochars have carbon contents from 37.44% to 43.31%, are rich in oxygen containing functional groups, and the equilibrium of hydrothermal carbonization reactions could be reached rapidly in microwave environment. The hydrochars can effectively adsorb the model pollutants, the maximum adsorption capacities of Congo red, berberine hydrochloride and 2-naphthol at 298 K and initial concentration of 0.5 mg/mL were 222.1, 174.0 and 48.7 mg/g, respectively, and those of Zn²⁺ and Cu²⁺ were 112.8 and 144.9 mg/g, respectively. Adsorption thermodynamic parameters were calculated. These results suggest that microwave-assisted hydrothermal treatment is an effective method for the rapid production of hydrochars, and rice straw hydrochars are promising adsorbents for the removal of water pollutants such as organics and heavy metals.