Surface Hydrophobization Via CTAB Functionalization as a Strategy for Enhancing Geopolymer Adsorption Capacity: Synthesis, Characterization, and Carbamazepine Removal Performance in Simulated Pharmaceutical Effluent"

Abstract

Pharmaceutical active compounds (PACs) in wastewater pose a persistent environmental and public health threat due to their resistance to conventional treatment processes. Among these, carbamazepine (CBZ), a widely prescribed anticonvulsant, is frequently detected in effluents and surface waters at concentrations that disrupt aquatic ecosystems and potentiate antibiotic resistance. This study reports the synthesis, characterization, and adsorption performance of a cetyltrimethylammonium bromide (CTAB)-modified clay geopolymer composite (CTAB-BclayGeo) designed for targeted CBZ removal from aqueous media compared to an unmodified Clay Geopolymer (B-clayGeo). The composite was synthesized by alkaline activation of clay in the presence of a set CTAB concentration, followed by curing under controlled conditions. Physicochemical characterization was conducted using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy with energy-dispersive X-ray analysis (SEM/EDS) and Brunauer–Emmett–Teller (BET) surface area analysis. CTAB modification significantly increased the specific surface area from 27.28 m²/g (unmodified) to 67.16 m²/g, introduced hydrophobic organo-functional sites on the geopolymer surface, and enhanced mesopore accessibility for organic contaminant uptake. Batch adsorption experiments demonstrated that CTAB-ClayGeo achieved a maximum CBZ removal efficiency of 69.16% under optimized conditions (pH 8, contact time 24hrs, adsorbent dose 0.1 g/L). Adsorption kinetics followed the pseudo-second-order model, and equilibrium data were best described by the Langmuir isotherm, with a maximum monolayer adsorption capacity (qmax) of 58.2 mg/g. The adsorption mechanism is attributed to hydrophobic partitioning, π–π electron donor–acceptor interactions, and electrostatic attraction between CBZ and the organo-modified geopolymer surface.