Engineered Inorganic Adsorbents for Water Remediation: From Surface Modification to Selective Heavy-Metal Capture

Abstract

Inorganic adsorbent materials have become key tools in water purification and industrial wastewater treatment due to their chemical stability, low cost, and strong adsorption performance. This article reviews the adsorption behavior of major inorganic adsorbent groups—zeolites (clinoptilolite), metal oxide nanoparticles (Fe₂O₃ and MnO₂), and functionalized silica—focusing on their structural features, surface chemistry, and pollutant–surface interactions. The main adsorption mechanisms include ion exchange, electrostatic attraction, surface complexation, and, in the case of MnO₂, oxidation-related processes. Comparative analysis indicates that surface modification significantly improves selectivity and capacity, particularly for heavy metal ions such as Pb²⁺, Cd²⁺, and Cr species. Isotherm and kinetic interpretations suggest that modified oxides and amine-functionalized silica often follow Langmuir-type behavior with pseudo-second-order kinetics, supporting chemically controlled adsorption. Regeneration studies highlight that many inorganic adsorbents maintain practical efficiency over multiple cycles, strengthening their sustainability and real-world applicability. Overall, modified inorganic nanomaterials show strong potential for long-term use in pollutant removal, especially when designed for selectivity, reusability, and performance under realistic wastewater conditions.