Lignocellulose Fiber- and Welded Fiber- Supports for Palladium-Based Catalytic Hydrogenation: A Natural Fiber Welding Application for Water Treatment

In our study, lignocellulose yarns were fabricated via natural fiber welding (NFW) into a robust, free-standing, sustainable catalyst for water treatment. First, a series of powder catalysts were created by loading monometallic palladium (Pd) and bimetallic palladium-copper (Pd-Cu) nanoparticles onto ball-milled yarn powders via incipient wetness (IW) followed by a gentle reduction method in hydrogen gas that preserved the natural fiber while reducing the metal ions to their zerovalent state. Material characterization revealed Pd preferentially reduced near the surface whereas Cu distributed more uniformly throughout the supports. Although no chemical bonding interactions were observed between the metals and their supports, small (5-10 nm), near-spherical crystalline nanoparticles were produced, and a Pd-Cu alloy formed on the surface of the supports. Catalytic performance was evaluated for each Pd-only and Pd-Cu powder catalyst via nitrite and nitrate reduction tests, respectively. Next, the optimized Pd-Cu linen powder catalyst was fiber-welded onto a macroporous linen yarn scaffold via NFW and its catalyst performance and reusability were evaluated. This fiber-welded catalyst reduced nitrate as effectively as the corresponding powder, and remained stable during five consecutive cycles of nitrate reduction tests. Although catalytic activity declined after the fiber-welded catalyst was left in air for several months, its reactivity could easily be regenerated by thermal treatment. Our research highlights how lignocellulose supported metal-based catalysts can be used for water purification, demonstrating a novel application of NFW for water treatment while presenting a sustainable approach to fabricate functional materials from natural fibers.