Development of novel adsorbents for the removal of emerging contaminants from water

Abstract

Emerging contaminants (ECs) such as estrogen hormones, perfluoro compounds (PFCs), bisphenol-A (BPA), and 1,4-dioxane have been detected in natural water at many places. The existing conventional wastewater treatment systems are not designed for the removal of these contaminants. This critical issue leads to the need for the development of advanced and effective technologies.β-cyclodextrin (β-CD) is a glucose-based molecule which has high affinity for different organic contaminants by the formation of host/guest inclusion complexes. In this research, water soluble β-CD was reacted with certain crosslinking agents and copolymers to form water insoluble β-CD and to coat β-CD onto silica particles. The development of such novel hybrid adsorbents provides high binding capacity with organic contaminants along with high mechanical strength. Three different approaches were used to develop adsorbents by using two crosslinking agents (epichlorohydrin (EPI) and hexamethylene diisocyanate (HMDI), two copolymers (glycidoxypropyl trimethoxysilane and aminopropyl triethoxysilane) and three solvents (NaOH, dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO). The developed adsorbents were tested for the removal of ECs of interest (estrogens, PFCs, 1,4-dioxane, and BPA) under batch and column conditions from Milli-Q water. The adsorbent prepared by reacting β-CD with HMDI as crosslinking agent with the molar ratio of 1:8 showed best results in removing the target compounds. The adsorbent showed more than 95% removal of 17β-estradiol (in single component) and more than 90% of most of the estrogens (in multicomponent), more than 99% of PFOA, and a maximum of 90% removal in case of BPA. However, the developed adsorbent did not show any removal in case of 1,4-dioxane. The developed adsorbent showed a good regeneration capacity in removing PFOA over three successive cycles. The characterization of the adsorbents using FTIR, TGA, and TEM confirmed the coating of β-CD onto silica particles. The removal of ECs of interest was dependent on the nature of both adsorbents and adsorbates. The nature of adsorbent such as type of crossling agent, molar ratio between β-CD and crosslinking agents affect the removal of the contaminants. Similarly, the nature of adsorbates such as size, shape, and presence of functional groups affect the removal efficiency.