Botryoidal nanolignin channel stabilized ultrasmall PdNP incorporating with filter membrane for enhanced removal of Cr(VI) via synergetic filtration and catalysis

[Display omitted] •The Pd@LNP/FP composite filter membrane provided a filtration and catalysis strategy.•The controllable synthesis of ultrasmall PdNP was achieved by botryoidal nanolignin.•The PdNP was with an ultrasmall diameter of 1.8 ± 0.27 nm and abundant active sites.•Botryoidal nanolignin channel created a microenvironment for H* generation.•The Pd@LNP/FP composite membrane possessed high efficiency for Cr(VI) removal. Catalytic membrane technology, as a combination of membrane separation and catalysis, is a high-efficiency and feasible route for wastewater remediation. The controllable synthesis of ultrasmall metal nanoparticles on the membrane to maximize the size effect is a challenging task yet. Herein, the filter paper-based botryoidal nanolignin channel stabilized ultrasmall PdNP membrane (Pd@LNP/FP) was prepared by chemical crosslinking of epichlorohydrin (EPI), the nanolignin (LNP) serves as both reducing and capping agent for the in-situ synthesis of ultrasmall PdNP with enhanced active sites. The mean size of PdNP was effectively tuned from 1.76 to 2.09 nm by varying the LNP loading amount of composite membranes. The botryoidal LNP supported on FP also provides the nanoscale channel to keep reactants on active sites of ultrasmall PdNP to improve the catalytic performance of Pd@LNPE/FP. The complete removal of hazardous Cr(VI) required only 2.5 min using Pd@LNPE/FP membrane, the pseudo-first-order rate constant (k) is 1.2725 min−1, much higher than that of the Pd@LNPp/FP membrane prepared by physical composite (0.2885 min−1). Moreover, the rapid filtration-catalysis removal of Cr(VI) can be achieved by twice filtration, demonstrating the high efficiency and feasibility of Pd@LNPE/FP via synergetic filtration enrichment and catalysis reduction.