Green synthesis of Fe and Fe/Pd bimetallic nanoparticles in membranes for reductive degradation of chlorinated organics

Membranes containing reactive nanoparticles (Fe and Fe/Pd) immobilized in a polymer film (polyacrylic acid, PAA-coated polyvinylidene fluoride, PVDF membrane) are prepared by a new method. In the present work a biodegradable, non-toxic-" green" reducing agent, green tea extract was used for nanoparticle (NP) synthesis, instead of the well-known sodium borohydride. Green tea extract contains a number of polyphenols that can act as both chelating/reducing and capping agents for the nanoparticles. Therefore, the particles are protected from oxidation and aggregation, which increases their stability and longevity. The membrane supported NPs were successfully used for the degradation of a common and highly important pollutant, trichloroethylene (TCE). The rate of TCE degradation was found to increase linearly with the amount of Fe immobilized on the membrane, the surface normalized rate constant (k_SA) being 0.005L/m²h. The addition of a second catalytic metal, Pd, to form bimetallic Fe/Pd increased the k_SA value to 0.008L/m²h. For comparison purposes, Fe and Fe/Pd nanoparticles were synthesized in membranes using sodium borohydride as a reducing agent. Although the initial k_SA values for this case (for Fe) are one order of magnitude higher than the tea extract synthesized NPs, the rapid oxidation reduced their reactivity to less than 20% within 4 cycles. For the green tea extract NPs, the initial reactivity in the membrane domain was preserved even after 3 months of repeated use. The reactivity of TCE was verified with "real" water system.