D. Lin, D. Wang, Q. Zhang, H. You, K. Shetty, L. Hu
NH3–N removal, polyhedral ologomeric silsesquioxane (POSS), modification, zeolite molecular sieves (ZMS), diffusion coefficient, energy of transition state
This research explored the utilization of a waste resource, rice hull ash (RHA), for the synthesis of the polyhedral ologomeric silsesquioxane (POSS) modifier for mesoporous zeolite molecular sieve (ZMS) to enhance NH4+ ion-exchange capacity in drinking water. In this study, RHA and [Me4N]OH were employed to produce [Me4N]8(OSiO1.5)8 (TMN-POSS) and further [HMe2]8(SiOSiO1.5)8 (OHS) as a precursor. The OHS, CH2=CHCOOCCH3CH3CH3, CH3OH and NaOH were selected to prepare POSS-COONa with carboxyl sodium terminal groups, ion-exchange active groups for NH3-N removal in water, using to modify the ZMS surface via a connection of the carboxyl and Si-OH. The characterization of the POSS and the modified ZMS structure by standard techniques (such as EIS MS, SEM, XRD, NSP, etc.) were provided and discussed. As results of the testing, the NH3-N ion-exchange capacity of the POSS modified ZMS increased (enhancement of 108.7%, 171.3% and 81.8% for water containing 2, 5 and 10 mg/L NH4+, respectively). This increase tendency was validated using a molecular dynamic simulation (MDS) program to calculate the diffusion coefficient (DC) of NH4+ in the original ZMS (obtaining higher DC) and the POSS-modified ZMS (obtaining lower DC), and to compare transition-state energy of the NH4+ ion exchange with Si-OH in the original ZMS (Ea=590.57 kJ•mol–1) and with -COONa in the POSS-modified ZMS (Ea=154.31 kJ•mol–1). A positive conclusion that the RHA-POSS-modified ZMS can be applied for the NH3-N removal in drinking water was concluded.