article · Bulletin of the National Research Centre/Bulletin of the National Research Center
Agricultural waste from Dodonaea viscosa tree branches can be converted into a low-cost magnetised activated carbon to remove toxic hexavalent chromium from water. Material characterisation showed a porous structure with a surface area of nearly 410 square metres per gram, functional hydroxyl and carboxyl groups, and iron oxide nanoparticles on the carbon surface. In laboratory tests on synthetic aqueous solutions, the material reached a maximum removal efficiency of 97.1 per cent within 60 minutes at pH 4. The adsorption process proved spontaneous, endothermic, and governed primarily by chemisorption, achieving a maximum capacity of 15.89 milligrams per gram at 60 degrees Celsius. Operating effectively at pH 4 offers an advantage over conventional adsorbents that require highly acidic and costly conditions, presenting a viable laboratory-proven method for water decontamination.
Hexavalent chromium is a hazardous water pollutant, yet many existing cleanup methods require extreme acidity that is expensive and impractical to maintain at scale. By using common agricultural waste to create an effective magnetic adsorbent that functions at milder pH levels, this approach demonstrates a potentially cheaper, more practical pathway for treating contaminated water.
This technology could enable low-cost wastewater treatment systems for industrial operators needing to remove toxic hexavalent chromium, such as metal finishing or chemical facilities. Because testing was conducted strictly on synthetic solutions under controlled laboratory conditions, the material is at an early research stage. Practical commercialisation would require testing on real industrial effluents, life-cycle cost analysis, and evaluation of magnetic recovery and regeneration processes at scale.
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Abstract In this study, we prepared a low-cost adsorbent, magnetised activated carbon (MAC), from agricultural waste (Dodonaea Viscosa tree branches) and used it to adsorb hexavalent chromium (Cr (VI)) from aqueous solutions. The study includes a framework for material characterisation by (XRD, FTIR, SEM and BET). The major operating factors were tested, such as solution pH, adsorbent dose, initial Cr (VI) concentration, contact time and temperature, using a two-factor study method to determine optimal conditions. Adsorption isotherm models, kinetic investigations, and thermodynamic analyses were used to examine the adsorption performance and the processes involved. The FTIR spectra showed the presence of hydroxyl and carboxyl groups, and the XRD confirmed the formation of Fe 3 O 4 on the surface of the activated carbon. SEM images showed a rough heterogeneous morphology; BET analysis showed a porous structure with a surface area of 409.584 m 2 /g and a total pore volume of 0.55764 cc/g. The maximum removal efficiency (97.1%) was achieved at pH 4 and 60 min, with the optimum adsorbent dose, and the adsorption capacity increased at higher temperatures. Kinetic analysis indicated that the pseudo-second-order model best fit the adsorption data, suggesting that chemisorption was the main process. The Langmuir isotherm fitted well with the equilibrium data, with the maximum adsorption capacity of 15.89 mg/g at 60 °C with an adsorbent dose (1 g/L), indicating monolayer adsorption on a homogeneous surface. Thermodynamic data (ΔG, ΔH, ΔS) indicated that the process was spontaneous and endothermic, with increased adsorption at higher temperatures. The results showed that the prepared magnetic adsorbent performed well in Cr (VI) removal under controlled laboratory conditions. In contrast to prior studies, adsorbents efficiently remove Cr (VI) at low pH (1–2), but these conditions are impractical and expensive. In addition, the influence of surface functional groups on adsorption is poorly understood. Moreover, the adsorption mechanism remains unclear because the kinetic and thermodynamic analyses are incomplete.
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DOI: 10.1186/s42269-026-01486-9
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