Peanut shell biochar for Rhodamine B removal: Efficiency, desorption, and reusability

A high-performance and affordable peanut shell-derived biochar was employed for the efficient removal of Rhodamine B (RhB) from aqueous solutions. The properties of peanut shell biochar (PSB) were investigated through Fourier transform infrared (FTIR) spectroscopy and Brunauer-Emmett-Teller surface area measurements. The FTIR analysis revealed numerous active sites and functional groups for the binding of dye molecules, while the BET surface area was determined to be 351.11 m²g^-1. Four different isotherms and kinetic models were applied to determine the equilibrium adsorption of RhB, and the results indicated that the Freundlich isotherm was the most appropriate model. A maximum dye removal rate of 94.0% occurred at a pH of 3 with an adsorbent dose of 0.325 g L^-1. The prepared adsorbent showed excellent sorbent behaviour and can be reused multiple times after regeneration, with the surface area decreasing from 351.11 m²g^-1 to 140.13 m²g^-1 after the third cycle. The negative Gibbs free energy ΔG^o at all applied temperatures suggested that spontaneous adsorption occurred and RhB adsorption on the PSB was found exothermic, as evidenced by the negative value of ΔH^o. The regenerated PSB can be utilized as an efficient, environmentally friendly, and cost-effective sorbent for the removal of dyes at temperatures lower than ambient temperature, providing both technical and financial advantages for sustainable environmental management.