Removal of haloacetonitriles by adsorption on modified inorganic porous materials

Abstract

The main objective of this study was to investigate the removal of haloacetonitriles (HANs) in aqueous solution by adsorption on various surface-modified inorganic porous materials. Hexagonal mesoporous silicate (HMS) was synthesized and modified surface with various organic functional groups (amino-, mercapto- and octyl groups) to investigate the effect of surface functional group on adsorption efficiency and mechanism compared with powder activated carbon (PAC). In addition, HMS then modified by substitution of titanium in silicate structure to investigate the relationship between the porous structure and the resultant adsorption capacities, compared to the similar mesopore SBA-15. Zeolite NaY was used so as to investigate the effect of crystalline structure. The results indicated that the adsorption rate and capacity of HANs both significantly influenced by the different porous and crystalline structures as well as by the surface functional group of adsorbent. M-HMS provided higher adsorption capacity of HANs than the other organic-functionalized adsorbents and had a comparable the adsorption capacity to PAC. The different molecular structure of HANs obviously affected the adsorption capacity and selectivity over M-HMS whereas selective adsorption over PAC was not observed. Moreover, the effect of electrolyte in tap water and in the presence of co-existing DBPs (trihalomethanes and haloacetic acids) did not affect the selective adsorption of both adsorbents significantly. The adsorption mechanism is believed to occur via a more complex interplay between an ion-dipole electrostatic interaction and chemisorption. Adsorbent regeneration study by extraction method revealed an irreversible adsorption on adsorbent surface which confirmed the chemisorption mechanism. Furthermore, mesoporous silicate SBA-CHX was modified surface by polymerizable gemini surfactant (PG-SBA-CHX) adsorption to investigate the influence of adsolubilization on HAN adsorption efficiency. PG-SBA-CHX could efficiently adsorb the HANs especially hydrophobic HANs compared with unmodified adsorbent, however, hydrophilic HANs were the lower adsorption capacity. This indicated that the partition process (adsolubilization) plays crucial role on the adsorption related to hydrophilic / hydrophobicity of adsorbate.