A green and efficient CuS/oxalic acid-modified Ocimum tenuiflorum biosorbent (OT-(Cu-Ox)) was synthesized and evaluated for the removal of methylene blue (MB) from aqueous solutions. Surface modification significantly enhanced the Brunauer–Emmett–Teller (BET) surface area from 6.49 to 160.09 m2 g−1, increased pore volume, and enhanced active functional groups. Adsorption performance was strongly influenced by pH, contact time, adsorbent dosage, initial concentration, and temperature. Maximum removal efficiency of 94.73% was achieved at pH 8–12 with an optimal dosage of 0.02 g. The point of zero charge) pHpzc( was determined to be 7.3, indicating enhanced electrostatic attraction at alkaline pH. Kinetic data were best fitted by the pseudo-second-order model (R2 ≥ 0.995), suggesting chemisorption. Langmuir isotherm showed excellent correlation with a maximum adsorption capacity of 666.67 mg/g at 27 °C. Thermodynamic analysis revealed negative ΔG° (− 11.18 to − 2.61 kJ mol−1) and ΔH° (− 84.60 to − 51.14 kJ mol−1), confirming spontaneous and exothermic adsorption. The results demonstrate that OT-(Cu-Ox) is a high-performance, sustainable biosorbent for treating dye-contaminated wastewater.
Bani‐Atta et al. (Mon,) studied this question.