Selective Adsorption of Cr(VI) Ions and Organic Dyes by a Magnetic Mesoporous Organo-Silicate Composite: Thermodynamic Insights

Water pollution has emerged as a critical threat to modern ecosystems. According to the United Nations Environment Program, approximately 80% of wastewater produced by human activity is discharged into the environment without treatment. This wastewater often carries a wide range of pollutants, from human and agricultural waste to industrial byproducts. Once these contaminants enter rivers, lakes, and oceans, they can cause severe ecological damage, including large-scale die-offs of aquatic life [1]. The few organisms that survive are often weakened, afflicted with diseases, or burdened with genetic mutations that can jeopardize future generations. These realities underscore the urgent need for cost-effective and efficient technologies capable of removing persistent pollutants—such as heavy metals and synthetic dyes—from contaminated water. One promising approach is the use of adsorbent materials, which bind pollutants and allow for their easier removal via conventional filtration methods [2–15]. However, most conventional adsorbents are expensive to produce and have low adsorption capacities, limiting their widespread use. Magnetic Mesoporous Organo-Silicate (MMOS) composites present a potential solution to these challenges, offering a combination of affordability, high adsorption performance, and reusability. In this study, the adsorption behavior of Cr(VI) ions, Congo Red (CR), and methylene blue (MB) dyes onto a Magnetic Mesoporous Organo-Silicate (MMOS) composite was investigated. The adsorption of Cr(VI) and MB was found to be spontaneous and exothermic, occurring with moderate to low energy barriers. Positive entropy changes for these adsorbates indicate increased randomness at the solid–liquid interface, further supporting the thermodynamic favorability of the process. In contrast, CR adsorption was non-spontaneous and endothermic, exhibiting highly unfavorable thermodynamic parameters, as reflected by positive ΔG values and a large negative activation energy. These results highlight the composite’s selective adsorption capabilities, with markedly superior performance for Cr(VI) and MB compared to CR. References Bishop, B.E., Savitzky, B.A. and Abdel-Fattah, T., Ecotoxicology and Environmental Safety, 73(4), pp.565-571 (2010). A Elmekawy, Q Quach, TM Abdel-Fattah, Nanomaterials 14 (13), 1143 (2024) SELME Mahmoud, TM Abdel-Fattah, ME Mahmoud, E Díaz, Environmental Nanotechnology, Monitoring & Management 22, 100977 (2024) SELME Mahmoud, D Ursueguia, ME Mahmoud, TM Abdel-Fattah, E Díaz, Biomass Conversion and Biorefinery, 1-1 (2023) A Elmekawy, Q Quach, TM Abdel-Fattah, Scientific Reports 13 (1), 12845 (2023) Omar H. Elsayed-Ali, Hani E. Elsayed-Ali and Tarek M. Abdel-Fattah, Journal of Hazardous Materials, 185 (2-3), 1550-1557 (2011) Alya Elsayed-Ali, Tarek Abdel-Fattah, Hani Elsayled-Ali, Hani, Journal of Chemical Education, 88(8), 1126-1129 (2011). TM Abdel-Fattah, ME Mahmoud, Chemical engineering journal 172 (1), 177-183 (2011) TM Abdel-Fattah, ME Mahmoud, MM Osmam, SB Ahmed, Journal of Environmental Science and health, part A 49 (9), 1064-1076 (2014) ME Mahmoud, TM Abdel-Fattah, MM Osman, SB Ahmed, Journal of Environmental Science and Health, Part A 47 (1), 130-141 (2012) TM Abdel-Fattah, B Bishop, Journal of Environmental Science and Health, Part A 39 (11-12), 2855-2866 (2004) ME Mahmoud, MM Osman, SB Ahmed, TM Abdel-Fattah, The Scientific World Journal 2012 (2012) ME Mahmoud, SS Haggag, TM Abdel-Fattah, Polyhedron 26 (14), 3956-3962 (2007) ME Mahmoud, AA Yakout, MT Abed El Aziz, MM Osman, TM Abdel-Fattah, Journal of Environmental Science and Health, Part A 50 (10), 1072-1081 (2015) H Namkoong, E Biehler, G Namkoong, TM Abdel-Fattah, ACS omega 7 (44), 39931-39937 (2022)