Highly efficient removal of crystal violet dye using citric acid-modified Lotus (Nelumbo nucifera) seed pod

In pursuit of sustainable wastewater treatment methods, lotus (Nelumbo nucifera) seed pods have been sequentially activated with a mild base and citric acid, for effectively removing crystal violet from contaminated water. Characterization techniques, including FTIR, FESEM, and BET analysis, have been used to assess the sample properties. Citric acid activation introduced COOH groups, as shown by FTIR, while FESEM revealed a highly porous structure conducive to increased dye adsorption. The pHzpc value 6.69 indicates the process is efficient in neutral pH conditions. The interaction mechanism aligns with the pseudo-second-order kinetic model (R² = 0.999) and Langmuir isotherm models. The uptake process is spontaneous (ΔG: –17.392 kJ/mol) and endothermic (ΔH: 21.076 kJ/mol). Notably, 92% of adsorption occurs within 20 min, reaching 99% after 45 min. The material can be regenerated with a 1:1 methanol/water solution with up to 75% efficiency and reused for four cycles. After the fourth cycle, the adsorption efficiency was found to be 72%. This method offers a promising long-term solution for water treatment, with an adsorption capacity of 90.89 mg/g under ambient conditions.