Ferrous sulfide and carboxyl-functionalized ferroferric oxide incorporated PVDF-based nanocomposite membranes for simultaneous removal of highly toxic heavy-metal ions from industrial ground water

The deterioration of the aquatic environment by the heavy metal ions contamination causes serious threat to environment and human beings. However, the treatment of complex industrial wastewater by simultaneous removal of multiple heavy metal ions via a one-step method is still extremely challenging. To this end, we synthesize ferrous sulfide (FeS) and carboxyl-functionalized ferroferric oxide (CFFO) nanoparticles, which were introduced into polyvinylidene fluoride (PVDF) matrix (individually/mixed together in an optimum ratio) through phase inversion technique. Three types of mixed matrix membranes (MMMs) were developed, viz. FeS/PVDF, CFFO/PVDF and FeS/CFFO/PVDF. The prepared membranes were characterized by SEM, TEM, AFM, FTIR, XRD, BET, and XPS techniques. The properties of the membranes were also examined for pure water flux, hydrophilicity, water uptake capacity, mechanical and thermal property, salt separation and simultaneous separation of toxic heavy metal ions such as lead, (Pb), cadmium (Cd), and chromium (Cr) from industrial ground water. The resultant membranes exhibited relatively high water flux (340-1266 L/m(2)h) than the unmodified PVDF membrane, due to changes in the porosity and hydrophilicity of the membranes. FeS/CFFO/PVDF membrane showed that it could effectively treat Pb, Cd, Cr and As contaminated industrial ground water, simultaneously with a high removal efficiency of about 88% for Cr(VI), 99% for Cd2+, 99% for Pb2+ and 95% for As in a single filtration process. In addition, the developed membranes conspicuously reduce their concentrations below the maximum contaminant level of WHO and BIS (India). The probable mechanism of separation of heavy metal ions through MMMs could be understood through FTIR and XPS techniques. The results of this study inferred that FeS/CFFO/PVDF membrane is a potential candidate for the simultaneous separation of Pb, Cd, Cr, and As.