Cadmium removal from acidic wastewater using coconut–rice husk‐activated carbon: Adsorption behavior and fluorescence‐assisted monitoring

Activated carbon derived from a coconut husk–rice husk composite was investigated for Cd 2+ removal using a laser‐induced fluorescence (LIF) technique. The material was prepared through carbonization followed by chemical activation. It was subsequently characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray photoelectron spectroscopy, and Brunauer–Emmett–Teller (BET) analysis. The adsorbent exhibited a porous structure with oxygen‐containing surface functional groups and a BET surface area of approximately 196 m 2 g −1 . Adsorption experiments were conducted under acidic conditions (pH 1–4) with initial Cd 2+ concentrations of 25–75 mg L −1 and adsorbent dosages of 0.2–1.2 g. Rapid Cd 2+ uptake was observed, and selected samples were validated using ICP‐OES to confirm fluorescence measurements. The highest experimental adsorption capacity was 22.5 mg g −1 at an initial concentration of 75 mg L −1 . Adsorption kinetics followed the pseudo‐second‐order model ( R 2 >0.98), while equilibrium data were best described by the Freundlich isotherm ( R 2 ≥0.99, n = 1.7–2.2, KF = 9.9–19.0). The Langmuir model predicted a theoretical monolayer capacity of 31.76 mg g −1 . The results are relevant to acidic industrial effluents such as electroplating and battery wastewater.