Biosorption of Methylene Blue from Aqueous Solution Using Unmodified Rice Husk as Biomass

The discharge of synthetic dyes into aquatic environments poses serious environmental and health concerns due to their toxicity, persistence, and resistance to biodegradation. This study investigated the biosorption of methylene blue (MB) from aqueous solution using unmodified rice husk (URH) as low-cost and environmentally friendly adsorbed dye from aqueous solution was studied in this work. Batch adsorptions experiments were conducted to evaluate the effects of contact time, initial dye concentration, pH and temperature on adsorption performance. The unmodified rice husk biomass was characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The FTIR spectra showed shifting and disappearance of peaks after adsorption of MB dye for unmodified rice husk biomass. The SEM results showed a difference in the micrograph obtained before and after adsorption for unmodified rice husk biomass. Four adsorption isothermal models, the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) were used to describe the adsorption process of which data obtained best fit Langmuir for unmodified rice husk biomass indicating monolayer adsorption on homogeneous adsorption sites rice husk biomass, while adsorption kinetics were evaluated using pseudo-first-order, pseudo-second-order and intra particles diffusion models. Pseudo-second-order model best described the kinetics data with (R2 = 0.8845 for unmodified rice husk biomass at 25 mg/L initial dye concentration) due to higher linearity and higher R2 indicating chemisorption. The thermodynamic parameters obtained for unmodified rice husk biomass was negative change in Gibbs free energy which indicates spontaneity of the process, a positive change in enthalpy which suggests chemisorption and a positive change in entropy which indicates a high degree in randomness. The collective results suggest unmodified rice husk biomass can be employed as a promising and potential biosorbents for the removal of MB dye with 84.00 % removal for unmodified rice husk biomass.