Cassia Fistula‐Derived Biochar Anchored Al ₂ O ₃ /CeO ₂ Nano‐Hybrid for Detoxification of Pb ² ⁺ and Sulfamethoxazole From Aqueous System: Adsorption and Degradation Mechanism

ABSTRACT The present study investigates the eco‐friendly synthesis of a Cassia fistula biochar (CFB)‐supported Al 2 O 3 /CeO 2 (AlC) nanocomposite. The synthesis utilizes Hibiscus rosa‐sinensis (HRS) leaf extract as a surface functionalization, enhancing metal–support interaction and improving surface reactivity. The synthesized CFB/AlC nanocomposite was characterized using Fourier‐transform infrared spectroscopy (FTIR), field emission scanning electron (FESEM) and high‐resolution transmission electron microscopy (HRTEM), photoluminescence (PL) spectra, UV‐vis, x‐ray diffraction (XRD), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) surface area analyzer, energy‐dispersive x‐ray (EDX) with elemental mapping, and x‐ray photoelectron spectroscopy (XPS). The synthesized CFB/AlC nanocomposite was investigated for its dual functionality in the adsorption and degradation of toxic Pb 2 + and sulfamethoxazole (SMX) contaminants from waste water. The BET analysis revealed a higher surface area for CFB/AlC (133.52 m 2 /g) over CFB (101.50 m 2 /g), which enhances its adsorption efficiency. XRD and HRTEM analysis confirmed the nano crystallinity of the CFB/AlC composite. Under optimized conditions, CFB/AlC exhibited improved adsorption efficiencies of 94.78% and 98.47% for Pb 2 + and SMX, respectively. Isotherm analysis indicated that the sorption process conformed to the Langmuir model with a higher value of regression coefficient ( R 2 = 0.99), which conferred the monolayer adsorption of Pb 2 + ions and SMX. The adsorption kinetics were best fitted to pseudo‐second‐order model, indicating a chemisorption‐dominated mechanism that proceeded spontaneously and feasibly. To validate the adsorption process, FTIR spectra were recorded for SMX and Pb 2 + ‐loaded CFB/AlC nanocomposites, while the sorption of Pb 2 + ions was further confirmed through EDX and elemental mapping analyses. Additionally, photocatalytic activity of CFB/AlC nanocomposite was enhanced by its narrow bandgap of 2.24 eV, resulting in 90.05% degradation of SMX under visible‐light irradiations. Desorption–adsorption studies were carried out over seven consecutive cycles demonstrated consistent and efficient adsorption, highlighting the excellent stability and reusability of CFB/AlC nanocomposite. Therefore, the CFB/AlC nanocomposite emerged as an efficient and sustainable composite for wastewater treatment, providing a promising solution for the remediation of noxious Pb 2 + ions and SMX from the aquatic environment.