Highly Nickel Loaded Nanocomposite Membranes for Catalytic H₂ Production and Hydrogenation of <i>p</i>-Nitrophenol Using Ammonia Borane

Abstract

Herein, we successfully fabricated porous nanocomposite membranes decorated with high loadings of nickel nanoparticles (25–45 wt %) by using chelating additives (sodium dodecyl sulfate (SDS) and Fumion) for the film casting cum phase separation approach. These additives decreased the nickel agglomeration and promoted the presentation of particles at the pore surface of the final membranes, leading to increased water permeances (450 to 1200–2400 L/m2 hbar) and porosities (56% to 70–78%) in comparison to a nanocomposite membrane made without additives. The hydrophobic ionomer Fumion, incorporated into the polyethersulfone matrix during solidification, further allowed us to tune the membrane hydrophobicity. We discovered that the same nickel nanoparticles exhibited a 5× increased H2 generation rate during the catalytic hydrogen formation from ammonia borane when presented in a membrane with a higher water contact angle (85° compared to 60°). We could attribute this improvement to the lower capillary pressure in more hydrophobic pores, which facilitates the release of H2 bubbles. The nanocomposite membranes were further employed as flow-through reactors for the catalytic hydrogenation of p-nitrophenol (p-NP) in the presence of ammonia borane. Membranes with an additive-directed nickel nanoparticle presentation at the pore surface demonstrated 6 to 7× higher p-NP turnover frequencies (TOFs). We also observed that the formation of hydrogen gas from ammonia borane results in a permeance decrease during the flow-through p-NP conversion. However, this effect was mitigated in more hydrophilic membranes with an anisotropic pore structure.