Thermochemical treatment of mixed mandarin peel and algae via microwave and H3PO4 activation: process optimization and adsorption mechanism for methylene blue dye

Herein, blended mandarin (Citrus reticulata) peel (MP) and algae (AG) biomass were thermochemically treated (TCTMPAG) to yield a cost-effective and renewable adsorbent for removal of methylene blue (MB), a known toxic cationic dye. The preparation included microwave irradiation, in conjunction with H3PO4 activation at 800 W for 15 min in a nitrogen atmosphere. The adsorption characteristics of TCTMPAG were studied by assessing its capacity to remove methylene blue (MB) dye from aqueous media. The Box-Behnken design (BBD) was used to optimize key adsorption factors, namely A: TCTMPAG dosage (0.02-0.12 g/0.1 L), B: pH (4-10), and C: contact period (30-420) min. The BBD model determined that the highest elimination of MB (98.4%) occurred for a TCTMPAG dosage of 0.12 g/0.1L, pH 10, and a contact time of 225 min. The MB dye adsorption rate profile conformed to a pseudo-second-order (PSO) model, while the Langmuir and Temkin model adequately represented the equilibrium adsorption profile (R2 = 0.97). The highest adsorption capacity (qmax) of TCTMPAG for MB dye was determined to be 48.5 mg/g. Various contributions to the adsorption mechanism include various contributions such as electrostatic forces, H-bonding, pore filling, and pi-pi stacking onto the TCTMPAG adsorbent surface.