Surfactant-modified MFI-type nanozeolites: Super-adsorbents for nitrate removal from contaminated water

Three surfactant-modified zeolites with high external surface areas and small crystal sizes were synthesized and modified for the nitrate removal from contaminated water. ZSM-5 nanocrystals (NC), nanosheets (NS) and nanosponges (NSp) were synthesized by different processes in order to obtain nanocrystals and hierarchized zeolites with extended external surfaces. In order to obtain an anion exchanger system: Surfactant-Modified Nanozeolites (SMZN), the as-synthesized zeolites were modified with a cationic surfactant (HDTMA(+)Br(-): hexadecyltrimethylammonium bromide). MFI-type zeolites with low external surface area and large crystal size (ZSM-5 microcrystals) were synthesized and modified with the same cationic surfactant for comparison with the SMZ(N) through nitrate removal. N-2 adsorption/desorption, XRD, SEM, TEM, and TGA analyses were done on the raw and the calcined form of the synthesized zeolites in order to determine the textural and structural properties. For the three studied materials nitrate removal tests were carried out in a large initial nitrate concentration range [0.8-40,5] mmol.L-1. Nitrate isotherms fitted Langmuir isotherm model and the maximum removal capacities were found to be 810 ( +/- 50), 1941 ( +/- 100), 2125 ( +/- 100) mmol.Kg(-1) for SMZ(NC), SMZ(NS), and SMZ(NSp), respectively. SMZ(NSp) showed the highest nitrate adsorption capacities obtained till now with surfactant-modified zeolites (SMZ) materials. These systems were found to be ultra-fast adsorbent systems and the kinetics fitted the pseudo-second order model.