Highly Nickel Loaded Nanocomposite Membranes for Catalytic H₂ Production and Hydrogenation of p-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.

Integrated In Situ Fabrication of CuO Nanorod-Decorated Polymer Membranes for the Catalytic Flow-Through Reduction of p-Nitrophenol

“…All three membranes also depict similar average contact angles. These values (71–73°) fit to a slight hydrophilization of the PES matrix by the incorporated copper (we determined 75° as the average for an analogously prepared base PES membrane in a previous study of our own) . However, for Cu_ BeforePES , we observed a significantly higher standard deviation of the contact angle (values between 65 and 84°).…”

“…For all membranes, we observed a drastic pressure increase at the beginning of the experiment (Figure c, orange). In our earlier studies, we could already demonstrate that such pressure increase results from the catalytic hydrolysis of the reducing agent and the accompanying gas formation inside the porous membranes. , After 30 min, the pressure remained almost constant for all membranes, indicating a steady state of catalytic gas formation and gas bubble release. Cu_ Pluronic achieved the lowest transmembrane pressure (∼0.12 bar) during the continuous p -NP reduction.…”

“…In this study, our aim was to develop a straightforward and efficient fabrication of copper-containing catalytic porous polymer membranes. After reviewing both the existing literature and our own contributions in this field, ,, we came to the conclusion that the existing methods for integrating metal nanomaterials into polymer membranes are particularly limited in terms of time and material efficiency. Both the prefabrication of nanomaterials and membrane coating strategies include a multitude of preparation steps and routinely use significantly more metal raw material than is incorporated into the final membranes.…”

“…This would directly result in incorporation at the pore surface after membrane solidification. For Cu_ BeforePES , the matrix polymer was only added to the casting dispersion after the copper reduction, and the formation of PES-copper clusters may be prevented by an ineffective interaction between already formed and hydrophilic Cu(0) nanorods and hydrophobic PES . The absence of any interaction as a directional driving force could then result in copper immobilization during membrane solidification that mirrors the preceding copper location in the casted polymer film.…”

“…The first involves adding a prefabricated metal catalyst powder to the casting solution, which is then taken up into the membrane matrix during solidification . However, challenges arise from the limited quality of the dispersion of the catalyst in the casting solution . Metal powders tend to strongly agglomerate during fabrication and isolation, and the redispersion process is often slow and incomplete. , The second approach consists of coating the metal catalyst onto a porous polymer membrane, either using preprepared nanomaterials or through in situ synthesis using the membrane as a support matrix .…”