Sulphur functionalized materials for Hg(II) adsorption: A review

Water is a scarce commodity and access to safe drinking water is a challenge due to increased release of inadequately treated effluent containing toxic heavy metals into the water systems. Due to widespread mercury contamination via anthropogenic activities such as artisanal gold mining and its high toxicity, it is necessary to remove mercury from water to protect both human and aquatic life. Currently, significant efforts are being made to develop materials with large and tailorable surfaces capable of selective and efficient adsorption of Hg(II). The high affinity of mercury towards sulphur is crucial in developing methods for the functionalization of various materials with sulphur for Hg(II) abatement. The technique of adsorption is favourable for mercury removal from water over other conventional techniques such as ion exchange, solvent extraction, membrane separation, precipitation, etc. The adsorption process offers design and operational dexterity whereas the latter techniques have several disadvantages such as huge energy consumption, high initial capital costs, sludge generation etc. In this review, recent trends in Hg(II) uptake by sulphur functionalized materials via adsorption are discussed. A variety of materials such as metal oxides, carbon nanotubes, metal organic frameworks, mesoporous silica, that provide a platform for sulphurization via various innovative methods are discussed. The physical adsorbent characteristics, adsorbent capabilities, role of sulphur in Hg(II) uptake and the adsorption process mechanisms are comprehensively highlighted. Conclusively, this review paper outlines the commercial viability and future perspectives and trends of sulphur functionalized adsorbents for Hg(II) uptake.