A review of hexavalent chromium removal from aqueous solutions by sorption technique using nanomaterials

Heavy metals contamination has become a global environmental problem owing to anthropogenic sources. They are considered a stern threat to humans, aquatic life, and harmful pollutants to water resources due to their toxicity and carcinogenicity. Nanomaterials (NMs) have been used extensively from the available diversity of sorbents for heavy metals removal from wastewater. This review looks at the results of research undertaken using various NMs in the sequestration of Cr (VI). NMs have shown to be efficient and effective for the treatment of wastewater polluted by Cr (VI) owing to their unique properties like surface effect and quantum effect. Besides their large surface area, they also show exclusive characteristics like higher capacity, higher specificity, higher affinity, self-assembly, great reactivity, and catalytic-potential, making them superior adsorbing materials than traditional materials for Cr (VI) removal. The functionalization of these NMs was discovered to enhance their characteristics, hence improving the sorption capacity of NMs for Cr (VI) sorption. From previous studies reported, synthesized NMs had high sorption capacity for Cr (VI) and high retention of the sorbate metals. The Cr (VI) sorption onto various NMs or its functionalized materials were observed to depend on the pH, quantity of sorbent, contact time and temperature. The Langmuir isotherm and pseudo-second-order kinetic models best depicted the equilibrium data of the sorption processes. The determined sorption capacity of the various NMs for Cr (VI) sorption determined from the Langmuir model ranged from 3.197 to 666.67 mg/g for carbon nano materials, 8.67-1052.63 mg/g for metal and metals oxide NMs and 59.17-854.7 mg/g for polymers composite.