Modification of activated carbon-based adsorbent for removal of industrial dyes and heavy metals: A review

The resources of water are contaminated by discharging of various pollutants from sources including industrial and domestic zones. A variety of physical, chemical, and biological processes are implemented for treating pollutants. Adsorption is the most accustomed process due to its high efficiency, simple procedure, and cost-effectiveness. Adsorption is widely used for removing various pollutants from wastewater. This review focused on physical and chemical modified adsorption systems indicates the improvement in adsorption of industrial dyes and heavy metals from wastewater. Chemical modifications, comprise with the acid, base, and impregnation of metal ions, are broadly studied due to availability of reagents, easy in modification, and adjusting surface functional groups. Different activating agents are used to introduce the different surface functional groups, which also depend on the type of water to be treated. Literature shows the high adsorption ability of industrial dyes and heavy metals towards chemically modified activated carbon, especially with LiOH, KOH and H2SO4 which shows the improvement in oxygenated functional groups. The adsorption capacity increases up to 40 % after modification within an activation temperature of 75 to 900 ℃, and 60 to 240 min of activation time is beneficial and depends on the adsorbents used. The physical modification by microwave heating provides a quick thermal reaction with homogeneous structure from inside out and equal distribution of pore structure and texture. The modification cost also plays an essential role while selecting adsorbents. The physical and chemical modification significantly improves the pore volume and various functional groups, which are quick low-cost treatment processes. The physical and chemical activation cost with LiOH, KOH, and H2SO4 reagents found in USD 1.72 to 2.89 per kg of adsorbent is suitable for large-scale models.