Continuous and complete conversion of high concentration p ‐nitrophenol in a flow‐through membrane reactor

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

We developed a novel method to fabricate copper nanorods in situ in a poly(ether sulfone) (15 wt %) casting solution by a sonochemical reduction of Cu2+ ions with NaBH4. The main twist is the addition of ethanol to remove excess NaBH4 through Cu(0) catalyzed ethanolysis. This enabled the direct use of the resulting copper-containing casting dispersions for membrane preparation by liquid nonsolvent-induced phase separation and led to full utilization of the copper source, generating zero metal waste. We characterized the copper nanorods as presented in the membranes via scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV/vis spectroscopy. We could demonstrate that the rapid immobilization from reducing conditions led to the membrane incorporation of copper nanorods in a state of high reactivity, which also promoted the complete oxidation to CuO after fabrication. We further observed a large aspect ratio and crystal straining of the nanorods, likely resulting from growth around the matrix polymer. The entanglement with poly(ether sulfone) further facilitated a selective presentation at the pore surface of the final CuO-decorated membranes. The membranes also exhibit high water permeances of up to 2800 L/m2hbar. Our catalytic membranes achieved exceptionally high activities in the aqueous flow-through reduction of p-nitrophenol (p-NP), with turnover frequencies of up to 115 h-1, even surpassing those of other state-of-the-art catalytic membranes that incorporate Pd or Ag. Additionally, we demonstrated that catalytic hydrolysis of the reducing agent in water can lead to hydrogen gas formation and blocking of active sites during continuous catalytic p-NP hydrogenation. We illustrated that the accompanying conversion loss can be mitigated by facilitated gas transport in the water-filled pores, which is dependent on the orientation of the pore size gradient and the flow direction.

3D printing of recombinant Escherichia coli/Au nanocomposites as agitating paddles towards robust catalytic reduction of 4-nitrophenol

Three-dimensional (3D) printing technology has received remarkable attention in manufacturing catalysts with tailored shapes and high precision, particularly facilitating catalyst recovery, maximizing heat/mass transfer, as well as enhancing catalytic performance. Herein, an engineered recombinant Escherichia coli strain (denoted as e-E. coli) with overexpressing metallothionein (a metal-binding protein) was explored to synthesize Au nanoparticles serving as both reducing and stabilizing agents. Then, the mixed inks containing e-E. coli/Au composite and biocompatible polymers (sodium alginate and gelatin) were extruded based on a direct ink writing method followed by chemical crosslinking to form robust 3D grids with square symmetry. To boost the mass transfer and minimize pressure drop, the monolith catalysts were assembled into agitating paddles and used for liquid-phase batch reactions (volume: 1 L). As such, the reaction solutions were mixed internally via the powered "catalytic paddles" with high mechanical strength, excellent reactivity, and easy recyclability, which could be reused at least 7 cycles without performance loss. Our work provides a novel strategy for the fabrication of supported Au catalysts, and the proof-of-concept "catalytic paddles" by 3D printing technology can be applied to other industrial solution-based reactions.

Fabrication and catalytic application of tandem reactor module using Au nanoparticles-coated glass beads as packing materials

A tandem reactor module using Au nanoparticles (NPs)-coated glass beads as packing materials is designed and fabricated for the catalytic reduction of 4-NP. Au NPs-coated glass beads are firstly prepared...

Functional catalytic membrane development: A review of catalyst coating techniques

Catalytic membranes combine catalytic activity with conventional filtration membranes, thus enabling diverse attractive benefits into the conventional membrane filtration processes, such as easy catalyst reuse, antifouling, anti-microbial, and enhancing process efficiency. Up to date, tremendous progresses have been made on functional catalytic membrane preparation and applications, which significantly advances the competitiveness of membrane technologies in process industries. The present article provides a critical and holistic overview of the current state of knowledge on existing catalyst coating techniques for functional catalytic membrane development. Based on coating mechanisms, the techniques are generally categorized into physical and chemical surface coating routes. For each technique, we first introduce fundamental principle, followed by a critical discussion of their applications with representative case studies. Advantages and drawbacks are also emphasized for different surface coating technologies. Finally, future perspectives are highlighted to provide deep insights into their future developments.