Aqueous scavenging of polycyclic aromatic hydrocarbons using epichlorohydrin, 1,6-hexamethylene diisocyanate and 4,4-methylene diphenyl diisocyanate modified starch: Pollution remediation approach

Abstract

Cross linking of starch molecules with suitable reagents provides opportunity for incorporation of relevant functional groups, thereby tuning the adsorption properties of the starch polymer adsorbent towards target pollutants, as a function of the nature of the cross linking agent and the chemical identity of the pollutants. In this vein, this study assessed the applicability of epichlorohydrin cross-linked starch (EPIS), 1,6-hexamethylene diisocyanate cross-linked starch (HDIS), and 4,4-methylene diphenyl diisocyanate cross-linked starch (MDIS) polymer adsorbents for treatment of aqueous Polycyclic Aromatic Hydrocarbon (PAHs) pollution in environmental water samples. Cross-linking process led to improvement in surface characteristics, level of hydrophobicity, and incorporation of relevant functional groups. Adsorption capacities of the adsorbents were in the order of MDIS > HDIS > EPIS. PAHs molecules were adsorbed in multi-layer, in a flat-wise orientation, while external and internal diffusion dominated the adsorption kinetics. Adsorption mechanisms suggested that these adsorbents spontaneously adsorb PAHs molecules driven mainly by enthalpy change, and the adsorption process was attributed to physisorption involving hydrophobic, van der Waals and π–π interactions between adsorbent and adsorbates. The thermodynamic evaluation indicated that the adsorption process was majorly endothermic and spontaneous. Desorption studies indicated that the adsorbents can be efficiently regenerated. The adsorbents were effective in treating simulated and real environmental water samples, and hence, are promising cost-effective alternative for control of aqueous PAHs pollution. Keywords: Polycyclic Aromatic Hydrocarbons (PAHs), Cross-linked starch polymer, Adsorption mechanism, Adsorbent regeneration, Water remediation