The present study shows that the H₂SO₄-modified coconut husk derived activated carbon powder (CHACP) can be used as a potential adsorbent for the removal of crystal violet (CV, basic dye) from aqueous solutions. Experiments were carried out as a function of contact time, concentration, pH, mass dosage, and temperature, the equilibrium was attained in 60 min. The amount of dye uptake (mg/g) was found to increase with increase in dye concentration, pH, temperature, and contact time. The kinetics of CV on to the adsorbent can be described well by pseudo-second order > Elovich > pseudo-first order > intra-particle diffusion equation. The applicability of the isotherm’s model for the present data follows the order: Freundlich > Temkin > Langmuir. Based on the calculated thermodynamic parameters such as enthalpy (ΔH°), entropy (ΔS°), activation energy (E_a), sticking probability (S^*), and Gibbs free energy changes (ΔG°), it is noticeable that the sorption of CV dye onto CHACP was a spontaneous and endothermic process. The morphological and chemical characteristics of the adsorbent were established by scanning electron microscopy and Fourier transform infrared spectroscopy.

Coffee residue, a low-cost agricultural byproduct, was tested as a precursor for the production of porous carbons in a chemical scheme using phosphoric acid. The raw material was impregnated and then paralyzed respectively at 600 and 700°C for 1h. The resulting products were characterized by adsorption of phenol at room temperature. The impregnation ratios have shown a strong influence on the capacity adsorption and surface area. The adsorption equilibrium was reached after forty minutes. The appropriate isotherms of adsorption involved in this study were developed according to Langmuir and Freundlich models