Recent advances in adsorptive removal of heavy metal and metalloid ions by metal oxide-based nanomaterials

• Science of interface between the inorganic pollutants in water and the adsorbent materials is discussed. • Adsorptive removal of heavy metal and metalloid ions for water purification. • A wide range of nanostructured metal oxides and their composites are reviewed as adsorbents. • Surface chemistry, structural, and morphological features of nanostructured materials are discussed. The science of interface between the inorganic pollutants (heavy metal and metalloid ions) and the adsorbents is gaining increasing interest for wastewater remediation applications to mitigate the emerging issue of water scarcity. Over the recent past, metal oxides and their composites have shown immense interest as novel adsorbents. The ample surface active sites, tunable surface chemistry, ease to synthesize and functionalization, high accessible surface area, economic viability, and good recyclability make the metal oxide-based nanomaterials potential adsorbents for fast and effective removal of a wide range of heavy metal and metalloid ions. The present article critically reviews the recent developments in surface chemistry and structural engineering of variable metal oxides and their composites for the adsorptive removal of arsenic, chromium, lead, cadmium, and mercury-based ions from the contaminated water. The various parameters like pH, coexisting ions, concentration and types of pollutants, temperature, etc., which govern the interfacial chemistry and interaction pathways, are discussed to understand the adsorption process. The technical challenges and futuristic directions are emphasized to improve the adsorption performance and the reusability of metal oxides-based nanomaterials, including their indulgence at an industrial scale to mark their commercial viability for real-time applications, a motive towards water security.