Guangxi Dong

Challenges and opportunities for mixed-matrix membranes for gas separation

Mixed-Matrix Membranes (MMMs) combining the benefits of both polymeric and inorganic materials have become a focus for the next-generation gas separation membranes. In this review, major challenges surrounding MMMs and the strategies to tackle these challenges are given in detail. The selection criteria of polymeric and inorganic materials are discussed in terms of their physical and chemical compatibility as well as large scale fabrication issues. Major models for separation performance prediction of MMMs are reviewed in terms of their interrelations and limitations. A discussion is provided regarding the future direction of MMMs.

Hybrid membrane with TiO2 based bio-catalytic nanoparticle suspension system for the degradation of bisphenol-A

The removal of micropollutant in wastewater treatment has become a key environmental challenge for many industrialized countries. One approach is to use enzymes such as laccase for the degradation of micropollutants such as bisphenol-A. In this work, laccase was covalently immobilized on APTES modified TiO2 nanoparticles, and the effects of particle modification on the bio-catalytic performance were examined and optimized. These bio-catalytic particles were then suspended in a hybrid membrane reactor for BPA removal with good BPA degradation efficiency observed. Substantial improvement in laccase stability was achieved in the hybrid system compared with free laccase under simulated harsh industrial wastewater treatment conditions (such as a wide range of pH and presence of inhibitors). Kinetic study provided insight of the effect of immobilization on the bio-degradation reaction.

Biocatalytic Janus membranes for CO2 removal utilizing carbonic anhydrase

A novel hydrophilic–superhydrophobic biocatalytic membrane was developed for CO2 capture with a gas–liquid membrane contactor. This “Janus” membrane contains a layer of hydrophilic carbon nanotubes (CNTs) coated on a fluorosilane treated superhydrophobic membrane support. Carbonic anhydrase (CA) was then immobilized on the hydrophilic CNT side, which was located at the CO2–solvent interface within a gas–liquid membrane contactor, whilst the superhydrophobic porous side of the membrane was oriented towards the gas phase. This “Janus” configuration ensured that the immobilized CA remained hydrated, and minimized the CO2 diffusion length in the solvent. The CNT coating layer showed good integrity and adhesion to the membrane, and the effect of superhydrophobic treatment on the porous structure of the membrane was negligible. The p-NPA assay results revealed that up to 30% CA activity was retained after immobilization. Further, the CO2 hydration test confirmed that the immobilized CA possessed significantly improved catalytic efficiency when compared with the equal amount of free CA. Effective regeneration of the enzyme coating was demonstrated over five cycles. The novel “Janus” membrane developed in this study exhibits great potential to be used as an immobilization support for a wide variety of enzymes not only CA for CO2 capture but also other types of enzymes in different applications.

Preparation of titania based biocatalytic nanoparticles and membranes for CO2 conversion

A biomimetic route for CO2 conversion catalyzed by carbonic anhydrase (CA) is an attractive option for carbon capture and storage due to the high efficiency and specificity of CA in CO2 hydration. The preparation of TiO2 based biocatalytic nanoparticles and membranes via CA immobilization facilitates the reuse of the enzyme and could be potentially integrated in a gas–liquid membrane contactor for highly efficient CO2 capture. In this work, different immobilization protocols were compared based on CA loading, activity and stability. For biocatalytic nanoparticles, over 80% activity recovery corresponding to 163 mg g−1 support was achieved. Repeated reuse and recovery of the biocatalytic nanoparticles over twenty cycles showed only modest loss in activity. For the biocatalytic membranes, the nanostructure of the titania coating and the pH values during immobilization were examined to optimize the biocatalytic performance. Biocatalytic membranes prepared at pH 6 with two cycles of sol–gel coating were able to immobilize a 700 μg CA per cm2 nominal membrane area. The CO2 hydration efficiency of the biocatalytic nanoparticles and membranes was examined, and only marginal loss of catalytic efficiency was observed when compared with their free CA counterpart, indicating good potential for application of such biocatalytic nanoparticles and membranes for CO2 conversion.

Microporous polymeric membranes inspired by adsorbent for gas separation

Material research related to membrane has become a trending topic for gas purification with a strong focus on delivering better separation performance. This review conveys that this criterion alone is inadequate when holistically evaluating new materials for gas separation, so a broader set of criteria is needed. Consideration of additional criteria will focus material research on new formulations with a higher likelihood of commercialization. Through a comprehensive evaluation of most emerging organic materials against those criteria, we demonstrate that, the use of organic microporous materials that mimic the gas sieving functionality of adsorbent materials presents an ultimate solution for membrane gas separation. By plotting gas permeation performances by these emerging polymer materials against their structural properties, we reveal that, polymeric membranes exhibit a strong correlation between gas permeability and BET surface area. This implies a significant role for BET surface area in mass transfer. By identifying the architectural design pathway for these polymer materials to meet proposed criteria, this review provides guidance for polymer research into membrane gas separation technology, as well as other applications such as energy storage and heterogeneous catalysis.

1.8 Thermally Rearranged Polymeric Membranes: Materials and Applications

Thermally rearranged (TR) polymers are microporous with high fractional free volume and narrow cavity size distribution. As a result, they exhibit excellent gas permeability and selectivity, exceeding the Robeson upper bound. This article provides a detailed discussion on the influence of TR polymer types on free volume topology. General principles are offered for TR polymer design, including the choice of monomers and synthesis routes, and their relationships with the polymer free volume topology and eventually the gas permeation properties. Other aspects including characterization techniques and industrial-scale implementation and applications are also provided.