Modified spent tea ( <i>Camellia sinensis</i> L.) leaves/crosslinked chitosan‐citric acid composite for organic dye removal: Characterization, adsorption optimization, and economic analysis

Abstract The utilization of sustainable biomaterials derived from chitosan biopolymers and waste biomass presents a highly promising approach for dye wastewater treatment. In the present work, a sustainable biomaterial derived from modified spent tea ( Camellia sinensis L.) leaves with sulfuric (H 2 SO 4 ) acid and crosslinked chitosan‐citric acid was prepared for efficient organic dye (safranin O, SO) adsorption. The modeling and optimization of the adsorption factors, including A: adsorbent dose (0.03–0.09 g), B: pH (4–10), and C: time (10–50 min), were achieved via Box–Behnken Design (BBD). The BET analysis revealed that modified spent tea leaves/crosslinked chitosan‐citric acid (CHT‐CT/STL‐SA) has a surface area of 369.59 m 2 /g, a pore volume of 0.3235 cm 3 /g, and a mean pore width of 3.50 nm, confirming its mesoporous nature. The findings of the BBD model illustrated that the ideal adsorption parameters for maximum SO dye removal (95.58%) were as follows: adsorbent dosage = 0.044 g, pH ~ 9, and contact time = 13 min. The adsorption data of SO uptake by CHT‐CT/STL‐SA illustrated agreement with pseudo‐first‐order and Langmuir models. The CHT‐CT/STL‐SA has a high ability to uptake SO, with an adsorption ability of 559.46 mg g −1 for CHT‐CT/STL‐SA. This work promotes the development of alternative adsorbents for the rapid and highly efficient treatment of water‐having organic dyes. The present research meets several of the sustainable development goals (SDGs), including clean water and sanitation (SDG6), responsible consumption and production (SDG12), climate action (SDG13), and life below water (SDG14).