FABRICATION OF MIXED MATRIX MEMBRANE USING HETEROATOM-ENRICHED NANOPOROUS MATERIALS UTILIZED FOR ADSORPTIVE REMOVAL OF Hg(II), Pb(II), AND U(VI) IONS

Abstract

The profligate increase in the world’s population and an ever growing industrialization led to the contamination of aquatic environment to their peak. According to Leonardo da Vinci “Water is the driving force of all the nature”. It is even popularly told that “The third world war would be fought for water only”. Approximately half of the world's population currently resides in regions that experience acute water stress. This is anticipated to get worsen in the time to come as a result of the society's unbridled materialism. Hence, the importance of clean water remains a top priority. In last few decades, a lot of efforts have been made to reduce the water pollution and clean the water bodies in order to provide safe usable water. Among the plethora of pollutants, the heavy metal ions are recognized as one of the major cause of concern. The removal of heavy metal ions from water bodies is the foremost solution to the problem. For the selective and efficient removal of heavy metal ions from aqueous solution, the synthesis of metal-free heteroatoms enriched nanoporous materials have been carried out by using quick and facile microwave-assisted synthesis method. The adsorbents (CTHM-2, NPNM and NENP) have been synthesized with high specific surface area and utilized as an adsorbent for the removal of Hg(II), Pb(II) and U(VI) via batch mode adsorption and membrane filtration method. The synthesized adsorbents used to fabricate the membrane and used as mixed matrix membrane for the large scale wastewater treatment. The CTHM-2 has been synthesized within 60 min in microwave-assisted method via polycondensation reaction and possesses SABET of 95 m2 g-1. The CTHM-2 having high heteroatom content (S of 46.5 wt.% and N of 21.9 wt.%) used as an efficient adsorbent for the removal of Hg(II) and U(VI) by both batch and membrane filtration method. The CTHM-2 shows high selectivity towards Hg(II) ion and exhibit 774 mg g-1 adsorption capacity at 298 K. The CTHM-2 used as mixed matrix membrane (MMM-2) and can able to treat 5 L of Hg(II) contaminated water for 8 h within the permissible limit (<1 ppb) by WHO. Moreover, the CTHM-2 is also used as an efficient adsorbent for the removal of U(VI) from aqueous solution as well as simulated seawater condition by using both the methods. For U(VI), it exhibits 580 mg g-1 adsorption capacity in batch mode and is able to treat 5 L of U(VI) contaminated water for 5 h within the permissible limit of drinking water (<15 ppb by WHO). Additionally, the CTHM-2 and MMM-2 could be further used to remove uranium ions from the simulated seawater with the adsorption capacities of 53 and 167 mg g-1, respectively. Furthermore, NPNM and NENP used as adsorbents for the efficient removal of Pb(II) ion from aqueous solution. NPNM and NENP exhibits specific surface area (SABET) of 450 and 700 m2 g-1, respectively. The NPNM adsorbent shows rapid and selective removal of Pb(II) ion within 15 min only from aqueous solution and final concentration reached below the permissible limit (by WHO) of <15 ppb. The NPNM based MMM also exhibits high removal efficiency and can treat 5 L of Pb(II) contaminated water for 7 h with 10.1 L m-2 h-1 flux and 2 bar transmembrane pressure and provide safe drinking water <10 ppb by WHO and USEPA. Moreover, the NENP used to fabricate mixed matrix membrane (N-MMM) and the experiments have been performed by using cross-flow membrane setup which can treat large scale Pb(II) contaminated wastewater. The N-MMM with the flux of 16.2 L m-2 h-1, can treat 5 L of Pb(II) contaminated water and provide safe drinking water for 300 min within the permissible limit at 2 bar transmembrane pressure (TMP). The N-MMM has shown good retention ability of 46% for 4 consecutive cycles.