Guojun Zhang

For the biofuel production industry, the implementation of membrane-based processes has great potential for significantly reducing energy consumption relative to thermodynamic separation methods such as distillation. However, to achieve this goal, the key issue is developing new membrane materials with higher selectivity, permeability and stability than available at present. Here, we report composite materials consisting of crystalline porous polymers of hydrazone-linked covalent organic-frameworks (COFs) dispersed within commercial polydimethylsiloxane. The resultant COF-based membrane shows ultra-high selectivity for n-butanol over water with improved permeate flux, due to the increased preferential pathways for n-butanol and hindrance to water diffusion from COFs in the selective layer. By coupling the COF-based membrane with a commercial dehydration membrane, a 5 wt% feed solution could be first concentrated and then directly purified to over 99.2 wt% n-butanol. The developed ultra-high selectivity COF-based membranes could provide a possible non-distillation way for biobutanol production in the future.

The key to improve nanofiltration membrane permeance is reducing its thickness, while maintaining high rejection. Herein, a 25 nm thick ultrathin polyamide layer was prepared by a micro-phase diffusion-controlled interfacial polymerization (MDC-IP) of poly(ethyleneimine) and trimesoyl chloride, which is much thinner than the conventional interfacial polymerization (CIP) polyamide layer. A new formation mechanism for such an ultrathin layer is presented, which included a micro-phase interfacial reaction and eliminated loose layers due to the confinement of micro-phase diffusion and the termination of stepwise diffusion. Moreover, the polyamide layer was post-crosslinked to form a stable dual-crosslinked interwoven structure. Such a membrane showed an ultrahigh permeance of 1246 kg/(m2 h MPa), which was 23 times that of CIP membranes. MDC-IP could efficiently control the micro-interface between two immiscible phases, which provided a facile way to regulate the membrane at nano-scale.

The hierarchical-structured superhydrophilic poly(ethylenimine)/poly(acrylic acid) (PEI/PAA)calcium silicate hydrate (CSH) multilayered membranes (PEI/PAA-CSH)_n were prepared as aqueous nanofiltration (NF) membrane, and then they were transformed into superhydrophobic organic solvent nanofiltration (OSN) membranes by one-step modification of trimethylperfluorinatedsilane (PFTS). Investigation on surface structures and properties of these multilayered membranes (PEI/PAA-CSH)_n indicated that the hierarchical-structured (PEI/PAA-CSH)_n multilayered membrane produced by in situ incorporation of CSH aggregates into PEI/PAA multilayers facilitated its one-step transformation from superhydrophilicity into superhydrophobicity. Both of the superwetting membranes showed better nanofiltration performances for retention of dyes of water and ethanol solution, respectively. Moreover, the long-term performance and antifouling behaviors, investigated by retention of methyl blue (MB), bovine serum albumin (BSA), and humic acid (HA) aqueous water solution and nonaqueous ethanol solution indicated that both of the superhydrophilic and superhydrophobic membrane showed higher stability and excellent antifouling property.

Removal of natural organic matter (NOM) from drinking water by membrane technology is attracting increasing attention. However, the fouling of the membrane by NOM is one of the biggest obstacles restricting its widespread application. Therefore an anti-NOM fouling polyelectrolyte complex (PEC) membrane was obtained by creating a negatively charged multilayer on a polyacrylonitrile (PAN) supporting membrane using a layer-by-layer assembly method. To improve the stability of the PEC membrane, the electrostatically assembled (poly(ethyleneimine)/poly(sodium 4-styrenesulfonate))_n/PAN membranes were crosslinked by glutaraldehyde. It was found that the zeta potential of the membrane surface decreased after chemical crosslinking, which further improved the electrostatic repulsion to NOM and thus improved the anti-NOM fouling property. Results of a 30 day nanofiltration operation showed the crosslinked membrane had good stability and gave a higher rejection of NOM; the permeance of the crosslinked membrane was double that of the uncrosslinked membrane.

Inspired by the complementary roles of surface energy and roughness on natural nonwetting surfaces, a superhydrophobic surface has been successfully designed and prepared by self-assembled monolayer modification on a hierarchical ZIF-8/polymer hybrid membrane. The as-prepared membrane exhibited the best overall performance for n-butanol pervaporation.

Alcohol-permselective membranes may play an increasingly important role in bioalcohol production. Developments for this membrane mostly involve hybrid membranes. Obtaining high compatibility and nanodispersion of inorganic nanoparticles in the polymer matrix is the key to fabricating hybrid membranes with high pervaporation performance. In this study, a homogeneous, nanodisperse ZIF-8/PDMS membrane was prepared by repeated immersion of a polysulfone supporting membrane in a dilute ZIF-8/PDMS suspension and subsequent removal of defects using a concentrated PDMS solution. To improve the nanoscale dispersion of ZIF-8, the nascent ZIF-8 suspension was directly dispersed in a PDMS solution without drying. This procedure avoids aggregation and redispersion of ZIF-8 nanoparticles after forming a powder. Analyses confirmed that the ZIF-8/PDMS dispersion effectively diminished aggregation between nanoparticles and led to the formation of a well-dispersed ZIF-8/PDMS membrane. A homogeneous and thin ZIF-8/PDMS permselective layer was obtained by adjusting the preparation conditions. The prepared ZIF-8/PDMS membrane exhibited a high separation factor (52.81) and high flux (2800.5 g m⁻² h⁻¹) in the separation of 5.0 wt% n-butanol–water solution at 80 °C. By comparing the powder-dispersed ZIF-8/PDMS hybrid membrane with the suspension-dispersed ZIF-8/PDMS membrane, we found that the latter showed much higher performance in butanol separation. Therefore, the nanodisperse ZIF-8/PDMS membrane has great potential applications for in situ recovery of biobutanol.

The ability to obtain a maximum loading of inorganic nanoparticles while maintaining uniform dispersion in the polymer is the key to the fabrication of mixed‐matrix membranes with high pervaporation performance in bioalcohol recovery from aqueous solution. Herein, we report the simultaneous spray self‐assembly of a zeolitic imidazolate framework (ZIF)–polymer suspension and a cross‐linker/catalyst solution as a method for the fabrication of a well‐dispersed ZIF‐8–PDMS nanohybrid membrane with an extremely high loading. The ZIF‐8–PDMS membrane showed excellent biobutanol‐permselective pervaporation performance. When the ZIF‐8 loading was increased to 40 wt %, the total flux and separation factor could reach 4846.2 g m⁻² h⁻¹ and 81.6, respectively, in the recovery of n‐butanol from 1.0 wt % aqueous solution (80 °C). This new method is expected to have serious implications for the preparation of defect‐free mixed‐matrix membranes for many applications.

The ability to obtain a maximum loading of inorganic nanoparticles while maintaining uniform dispersion in the polymer is the key to the fabrication of mixed‐matrix membranes with high pervaporation performance in bioalcohol recovery from aqueous solution. Herein, we report the simultaneous spray self‐assembly of a zeolitic imidazolate framework (ZIF)–polymer suspension and a cross‐linker/catalyst solution as a method for the fabrication of a well‐dispersed ZIF‐8–PDMS nanohybrid membrane with an extremely high loading. The ZIF‐8–PDMS membrane showed excellent biobutanol‐permselective pervaporation performance. When the ZIF‐8 loading was increased to 40 wt %, the total flux and separation factor could reach 4846.2 g m⁻² h⁻¹ and 81.6, respectively, in the recovery of n‐butanol from 1.0 wt % aqueous solution (80 °C). This new method is expected to have serious implications for the preparation of defect‐free mixed‐matrix membranes for many applications.

An automatically controlled spray-layer-by-layer (LbL) assembly method was used to build multilayers onto a tubular ceramic macroporous substrate. Poly(ethyleneimine) (PEI) and poly(acrylic acid) (PAA) were alternately sprayed onto a rotating tubular ceramic substrate. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analyses of different locations on the substrate confirmed that a fine coating formed on both the top surface and in the pores of the macroporous ceramic substrate. The substrate pretreatment using water filling greatly influenced the self-assembly process, slowing the penetration of the polyelectrolyte into the substrate pores, resulting in different multilayer morphologies. The effects of the substrate pretreatment, number of bilayers, and the addition of salt into the polyelectrolyte solution on the dye rejection performance were investigated. We found that the substrate pretreatment and the addition of NaCl to the polyelectrolyte solution could change the multilayer structure, in turn affecting the separation performance of the composite membranes. The composite membrane consisting of 5 layers of PEI/PAA had a flux of ∼10.0 kg m⁻² h⁻¹ and a rejection of >99%. Moreover, spray-LbL assembly using different polymer pairs such as poly(diallyldimethylammonium chloride)/poly(styrenesulfonate) (PDDA/PSS) and PEI/TiBisLac/PAA on vertically held tubular Al₂O₃ substrates was also explored. Using these materials led to the formation of different types of polymeric multilayers and in situ nanohybrid multilayers. Our study demonstrates that a multilayer membrane can be successfully prepared on a 3D support by an automated spray system, and can easily be used to rapidly coat large areas.