Hydrochar silicate composite sorbent via simple hydrothermal carbonization and its application to methylene blue removal

Hydrochar synthesized using hydrothermal carbonization of walnut biomass, is found to be rich in surface functional groups, having low surface area, high pore diameters, as a result poor adsorption capacity. The present work attempts to modify hydrochar, using silicate via a one-step hydrothermal route. The hydrochar silicate composite (HS) exhibited porosity with surface area of 106 m² g^-1 and excellent adsorption capabilities for methylene blue (MB) (434.78 mg g^-1) at 35 °C. The adsorption capacity of the HS was found to be superior as compared to hydrochar and silicate. The adsorption isotherms as well as the adsorption kinetic data of HS were well describied by the Langmuir adsorption model and the pseudo-second order kinetic model. The adsorption was physical and the adsorption mechanism was partly controlled by the intraparticle diffusion. The study identified HS to be a potential low cost adsorbent for liquid phase adsorption involving high molecular weight compounds.