The Influence of Sodium Silicate Concentration and Impregnation Time on Biochar Activation for Water Adsorption

A composite desiccant for water vapor adsorption, based on biomass-derived activated carbon (biochar) impregnated with sodium silicate, is presented. Silica gel is introduced into the biochar pores to enhance the water vapor adsorption capacity. Characterization using nitrogen isothermal adsorption, SEM imaging, and Fourier Transform Infrared (FTIR) analysis reveals that impregnation decreases the specific surface area and pore volume while increasing the concentration and types of oxygen-containing functional groups on the surface. The water vapor adsorption analysis demonstrates that the composite, under optimal conditions (20 wt% Na2SiO3 and 60 hours of impregnation), exhibits an equilibrium adsorption capacity quadruple that of non-impregnated biochar. Nevertheless, exceeding the optimal Na2SiO3 concentration or impregnation duration diminishes adsorption capacity. Kinetic analysis employing pseudo-first-order (PFO) and pseudo-second-order (PSO) models revealed that non-impregnated biochar fitted both models almost equally, whereas Na2SiO3-impregnated biochar followed the PSO model, as evidenced by higher R2 values.