Hexadecyltrimethylammonium bromide-modified zeolite@carbon composite: transforming waste-derived materials into herbicide adsorbents

Abstract Industrial by-products (e.g., fly ash) are increasingly utilized to develop novel materials for environmental applications. The growing interest arises from their potential to enhance the sustainability and cost-effectiveness of adsorbents for water treatment. This research examined the adsorption performance of a fly ash-based zeolite@carbon composite modified with 0.05 and 0.1 mol L −1 hexadecyltrimethylammonium bromide, targeting the removal of 2,4-dichlorophenoxyacetic acid from aqueous solutions. Comprehensive characterization of the samples with X-ray fluorescence, elemental analysis, X-ray diffraction, low-temperature nitrogen adsorption/desorption, point of zero charge determination, Fourier transform infrared spectroscopy, and scanning electron microscopy was performed. It was followed by the assessment of how solution pH, adsorbent-adsorbate contact time, and initial pesticide concentration influence their sorption capacities. Functionalized composites displayed significantly improved adsorption performance compared to pure material. Zeolite@carbon composite modified with 0.05 mol L −1 hexadecyltrimethylammonium bromide achieved the highest sorption capacity (28 mg g −1 ) since the modification with 0.1 mol L −1 concentration promoted the coating of the composite’s surface, hindering the access of herbicide to active sites. The adsorption of 2,4-dichlorophenoxyacetic acid followed pseudo-second-order kinetics and fit the Langmuir model. Regeneration studies showed that the materials’ adsorption efficiency decreases considerably after the third cycle. These findings demonstrate that the analyzed samples are effective and low-cost adsorbents with the potential for use in water purification processes.