Physicochemical properties of mesoporous acid activated materials from Lemna minor for Bezaktiv Red S-MAX dye removal

Lemna minor, a cheap and easily accessible substance, was utilized to create activated carbon through acid activation [with H₃PO₄ (ALM-P) and citric acid (ALM-C)]. Brunauer–Emmett–Teller (BET) analysis reveals that the L. minor activated materials (LACs) had a surface area of 208.54 m² g⁻¹ and 216.11 m² g⁻¹ after H₃PO₄ and citric acid activation, respectively. The presence of rich hydroxyl, carboxyl, amide, and phosphate functional groups on the surface of LACs is revealed by Fourier transform infrared spectroscopy (FTIR). This enables easy Bezaktiv dye, type Red S-MAX (BRSM), binding to the surface through strong chemisorptive bonds or ion exchange. With a maximal mono-layer adsorption capacity (q_m) of 16.86 and 7.69 mg g⁻¹ at 25 °C, the pseudo-second-order model and Langmuir isotherm provided a good description of the kinetic and equilibrium data. The adsorption was caused in part by the intra-particle diffusion mechanism. With negative ΔG° and positive ΔH° values, the adsorption process was spontaneous and endothermic. Under optimum conditions of pH 3.0 and 25 °C, the maximum % removal for BRSM (90 mg L⁻¹) was reported to be 77.65% within 90 min. These indicated that dye-contaminated water might be treated with the inexpensive LACs as a possible adsorbent.