Adsorption of Cr (VI) and Textile Dyes on to Mesoporous Silica, Titanate Nanotubes, and Layered Double Hydroxides
Acharya, R; Naik, B; Parida, KM
Wastewater treatment from hazardous pollutants is a promising topic and gaining considerable attention worldwide. The removal of chromium (VI) and noxious textile dyes to get clean drinking water is a concerning issue. Effluents contain ing Cr (VI) species from various industrial processes such as leather tanning, electroplating, metal finishing, etc. are being discharged into the natural water ecosystems. Contamination of Cr (VI) also occurs from accidental leakage and improper disposal at mining sites. Being cytotoxic, mutagenic, and carcinogenic, it poses threat to both aquatic life and downstream users when its concentration exceeds permissible limits. Dyes are also considered to be toxic or carcinogenic. Due to the complex aromatic structure and synthetic origin of dyes, these possess high chemical stability and low biodegradability in water. It causes major prob lems in discharge of large quantities of these organic compounds in wastewater and becomes potentially harmful to the environment. Thus, treatment of indus trial wastewater containing Cr (VI) and dyes has become an important and urgent environmental issue. Several techniques such as ion exchange, reverse osmosis, chemical precipi tation, electrochemical reduction, solvent extraction, adsorption, photocatalysis, etc. have been developed to remove Cr (VI) and dyes from water. However, high efficiency, simple operation, avoidance of the formation of secondary pollutants, and low energy consumption are some of the advantages that make adsorption an effective and promising technique for the removal of these pollutants from contaminated water bodies. Nanomaterials are being used as potential adsorbents in wastewater treatment due to their large surface area, enough active surface sites, and high adsorption capacity. Silica-based nanomaterials, graphene-based nano materials, titanate nanotubes, ferrites, layer double hydroxides, etc. have recently been successfully applied for the removal of Cr (VI) and dyes. In this chapter, we have discussed the adsorption behavior of silica-based nanomaterials, titanate nanotubes, and layer double hydroxides in terms of isotherm models, kinetics, and thermodynamics of adsorption. Maximum adsorption capacities obtained under optimum adsorption conditions such as adsorbent dose, concentration of Cr (VI)/ dye solution, pH, and temperature are presented in tables. Mechanisms of adsorp tion are explained in different schemes. © 2018 Scrivener Publishing LLC. All rights reserved.