Polydopamine-assisted immobilization of metallic nanoparticles confined regionally in bamboo microchannels as continuous-flow microreactors for enhanced catalysis

Abstract

In contrast to conventional plant-based microreactors where the nanocatalyst is anchored on the inner walls of microchannel structures, this study presents a bamboo-based flow microreactor in which the metallic nanocatalyst is immobilized within polydopamine (PDA) region-modified bamboo microchannels. This novel design facilitates a large surface area for nanocatalyst loading, enhances mass transfer, and reduces nanocatalyst leaching. Firstly, the hierarchical PDA architecture was fabricated on the wall surface of required bamboo microchannels through an ammoniation-induced self-assembly process to serve as a nanocatalyst support layer. The thickness of PDA architectures was modulated by adjusting the flow duration. Secondly, the metallic nanoparticles (NPs), including Pd, Au, and Ag, were effectively immobilized within the hierarchical PDA architectures as highly efficient catalysts using a flow-assisted method with minimal chemical usage and low catalyst loading (Pd content: 0.011 wt%). The catalytic performances of the proposed Pd-PDA/bamboo microreactor were evaluated for the continuous hydrogenation of nitroaromatics under flow conditions, encompassing variations in Pd content, nitroaromatic concentration, and liquid flow rate. The optimized Pd-PDA/bamboo microreactor exhibited high average conversion (>97 %) of nitroaromatics during 20 days of continuous operation without any noticeable deactivation or loss in activity due to its excellent stability resulting from firm immobilization of active metallic NPs within hierarchical PDA architectures. Additionally, this bamboo microreactor demonstrated potential applicability in environmental pollution treatment through azo dye hydrogenation.