Adsorption refers to a process wherein a species is concentrated on a solid surface from its liquid or gaseous surroundings. More precisely, adsorption is a physical/chemical separation process by which certain solute components of a fluid phase are attracted to the surface of a solid adsorbent and forms surface complex via physical or chemical bonds, and hence removing the said solute component from the fluid phase [54, 55]. Adsorption process usually occurs at interfacial layers which are regarded as two regions: the surface layer of the adsorbent (often simply called the adsorbent surface) and the adsorption space, in which the enrichment of the adsorptive can occur . In general, adsorption processes may be classified into two groups: physical sorption and chemical sorption; depending on the nature of forces and bond formation are involved. Depending on the nature of the interactions ionic species and molecular species carrying different functional groups may be held to the surface through electrostatic attraction to sites of opposite charge at the surface or physiosorbed due to action of Van der Waals forces or chemisorbed involving strong adsorbate-adsorbent bonding which may lead to attachment of adsorbate molecules at specific functional group on adsorbent surface . The main physical forces controlling adsorption are Van der Waals forces, hydrogen bonds, polarity, dipole-dipole П-П interaction, etc. .
Adsorption is one of the effective separation techniques for the removal of inorganic/organics from its aqueous phase. Adsorption has been found to be superior to other techniques for water re-use in terms of initial cost, flexibility and simplicity of design, ease of operation and insensitivity to toxic pollutants . Adsorption also does not result in the formation of harmful substances . Therefore considerable attention has been paid to adsorption technologies as efficient and versatile methods of removing dyes from wastewater effluents.