Resources, Environment and Sustainability 1 (2020) 0–8 Contents lists available at ScienceDirect Resources, Environment and Sustainability journal homepage: www.elsevier.com/locate/resenv A review on the influence of chemical modification on the performance of adsorbents Segun Michael Abegunde ∗ , Kayode Solomon Idowu, Olorunsola Morayo Adejuwon, Tinuade Adeyemi-Adejolu Department of Science Technology, Federal Polytechnic, Ado-Ekiti, Nigeria ARTICLE INFO Keywords: Adsorption Adsorbent Chemical modification Surface chemistry ABSTRACT Adsorption is one of the oldest and extensively studied techniques for water and wastewater treatment. As a surface phenomenon, adsorption efficiency relies heavily on the surface chemistry of the natural and modified material. The mode of surface modification and the nature of the precursor have significant impacts on surface functionalities. Chemical method of surface treatment is a technique that alters the structure and the surface properties of the precursor to enhance adsorption process. The present work intends to deliver precise knowledge on the choice and impacts of chemical modification on some known adsorbing materials. 1. Introduction Adsorption is a surface occurrence that involves the accumulation of atoms, molecules, or ions at the surface of a solid phase. It is a mass transfer process leading to the sorption of gases or solutes by solid or liquid surfaces (Crawford and Quinn, 2017). The substance adsorbed is an adsorbate, and the solid on which the material is accumulated is the adsorbent. Adsorption occurs due to surface energy created by an unbalanced force of attraction on the surface of the adsorbent (Artioli, 2008). The process of adsorption can be physical or chemical. Physical adsorption occurs when van der Waals and electrostatic forces are the cause of attraction between adsorbent and adsorbate molecules. Physical adsorption is exothermic in nature and reversible. On the other hand, chemical adsorption is the adsorption resulting from chemical bonding between adsorbate molecules and the adsorbent surface (Hu and Ke, 2020; Abegunde et al., 2020). It is endother- mic and irreversible. Adsorption, being a simple, non-toxic and eco- nomical technique has continued to maintain its popularity among the Researchers towards environmental sustainability (Olasehinde and Abegunde, 2020b; Zheng et al., 2013). Adsorption finds applications in separation and purification of materials, pollution control, indus- trial production process, refinery, mining and extraction. Adsorption technique has gained significant attention in water treatment, though various techniques for water purification and wastewater treatment had been reported. Presently, the adsorption technique is considered the most efficient, economical and selective treatment method for the decontamination of wastewater (Dana, 2017; Gayathri et al., 2019; Kyzas et al., 2019; Sharma et al., 2019; Sun et al., 2019). This method provides simplicity in design and operation in the complete recovery ∗ Corresponding author. E-mail address: abegunde_sm@fedpolyado.edu.ng (S.M. Abegunde). of dangerous pollutants from wastewater (Vijayakumar et al., 2012). Over the years, the adsorption process had recorded many successes in the treatment of water polluted by organic and inorganic pollu- tants. Adsorption of contaminants from aqueous solution employs a porous material with a large surface area and suitable surface chem- istry (Rashed, 2013; Wu and Tseng, 2008). Several precursors such as clay, silica gel, alumina, activated carbon, molecular sieve zeolites, synthetic resins and impregnated biomass industrial and agricultural waste (Lin and Juang, 2009; Shen et al., 2014; Wu et al., 2014; Krishna et al., 2001; Bilal et al., 2013; Ahmaruzzaman, 2008; Thakur and Semil, 2013) had been used. Optimum performance can be achieved during the process by the effective management of various experimen- tal conditions such as solution pH, initial concentration of adsorbate, the surrounding temperature, solid-phase dosage, and contact time, which are the primary determinants in adsorption technique (Vadivelan and Kumar, 2005). Many researchers have reported the significant improvements to surfaces of several materials commonly used as ad- sorbents after undergoing surface modification. The present work aims to summarise the effects of the chemical method of surface modification on the adsorption capacity of common materials used as an adsorbent for water and wastewater decontamination. 2. Adsorbent An adsorbent is a solid material that allows liquid or gaseous molecules to bind to its surface. Adsorbent’s performance depends on the chemical and physical properties of the adsorbent surface, as well as that of the soluble substances (Ip et al., 2009; Babel and Kurniawan, 2003). Characteristics of a suitable adsorbent material should include https://doi.org/10.1016/j.resenv.2020.100001 Received 30 July 2020; Received in revised form 21 August 2020; Accepted 25 August 2020 Available online 28 August 2020 2666-9161/© 2020 The Authors. Published by Elsevier B.V. on behalf of Nanjing Forestry University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).