Immobilisation of palladium nanostructures in polyethersulfone beads: recyclable catalyst for chromium(VI) remediation

Abstract

Environmental contextChromium, a carcinogenic metal present in the wastewater of several industries, is currently removed by treatment with large amounts of chemicals and expensive nano-catalysts. We have immobilised a nano-catalyst in tiny polymeric balls that are highly efficient at capturing chromium, and are easy to isolate for multiple reuse. Using our methodology, consumption of chemicals for removing chromium from wastewater is reduced by 97%. AbstractWe have synthesised and immobilised palladium nanostructures in porous polyethersulfone beads for the first time and demonstrated their catalytic application for the reductive transformation of toxic CrVI to nontoxic CrIII by formic acid at 25°C. The reduction of CrVI using palladium-polyethersulfone composite beads (Pd-PES), with a minimal Pd loading of 0.4 wt%, is found to be 98% with excellent operational stability retained up to 100 consecutive reaction cycles. Pseudo-first-order rate constant kapp for the 1st and 100th catalytic cycles is 0.167 and 0.158min−1 respectively. Pd-PES beads having a diameter of 2mm are easy to isolate post reduction by simple mesh filtration and can be re-used consecutively without any treatment. Owing to the high catalytic stability of the Pd nanostructures inside the beads, and the good mechanical and thermal stability of polyethersulfone, these beads can withstand rigorous treatment like mechanical stirring and elevated temperature, which renders them as highly reusable and as promising metal-polymer composite for practical application in CrVI remediation. For large scale application of this catalyst, we have demonstrated a methodology which reduces the consumption of formic acid by 98% in chromium remediation technology.