Bio-catalytic degradation of recalcitrant micropollutants with enzymes such as laccase provides an environmentally attractive alternative to the conventional filtration and adsorption processes. ...However, enzyme loss and denaturation remain key challenges for their potential use in water treatment applications. In this work, laccase immobilization on TiO2 nanoparticles and TiO2 blended polyethersulfone (PES) membranes were investigated due to TiO2's chemical stability, ease of functionalization, and architecture. Different surface modification and functionalization strategies on support materials were compared based on enzyme loading, apparent activity, activity recovery, and stability. When coupling agent 3-aminopropyltriethoxysilane (APTES) and cross-linker glutaraldehyde (GLU) were applied sequentially, effective coupling of laccase was achieved based on 2,2′-azino-bis-(3-ethyl benzothiazoline-6-sulfonic acid) (ABTS) assays. TiO2 functionalized PES membrane showed better enzyme immobilization efficiency than the non-functionalized membrane. Optimal performance was observed for PES membrane containing 4wt% TiO2, where TiO2 not only provided the enzyme coupling sites but also affected the membrane surface morphology and hydrophilicity to favor the enzyme immobilization. These bio-catalytic membranes also displayed good enzyme stability, tolerance to wider pH range and vigorous filtration conditions required for water treatment applications. Kinetic study also indicated that the enzyme affinity to assay substrate was maintained after immobilization when compared with packed bed and batch reactors.
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•Laccase is immobilized on TiO2 nanoparticles and TiO2 functionalized membranes.•TiO2 loading has significant effect on bio-catalytic membrane performance.•Bio-catalytic membrane stability is mainly determined by immobilization technique.•Laccase on membrane has higher affinity to ABTS than batch and packed bed reactors.
Superhydrophobic membrane for the application in membrane distillation was generated by creating a hierarchical structure with multilevel roughness via depositing TiO2 nanoparticles on microporous ...PVDF membranes by means of a low temperature hydrothermal (LTH) process. The TiO2 coated membranes were then fluorosilanized using a low surface energy material H, 1H, 2H, 2H-perfluorododecyltrichlorosilane. A variety of techniques such as capillary flow porometry, TEM, SEM, XPS, KI test, liquid entry pressure (LEP) measurement and contact angle goniometry were applied to explore the effects of surface modification on the surface chemistry, structure and performance of the membranes. The anti-fouling performance of virgin and modified membranes were examined in a direct contact membrane distillation (DCMD) process using sodium chloride and humic acid solution as a model feed. Results showed that the modification was mechanically and thermally robust and photoactive. The liquid entry pressure (LEP) and water contact angle were increased from 120kPa and 125° to 190kPa and 166°, respectively. The fluorosilanization of TiO2 nanocomposite PVDF membranes did not compromise the mean pore size. It was also appeared that the TiO2 coating not only contributes in engineering the hierarchical structure but also provides sites (OH functional groups) for the hydrolyzed silane coupling agent to be anchored forming a robust uniform water repellent film. The filtration results also showed that the pure water flux of the modified membrane was lower than that of the virgin membrane particularly at higher temperatures. However, the sodium chloride DCMD test showed that the permeate conductivity of the virgin membrane was increased sharply whereas it was not changed for the modified membrane over the period of the experiment. A 20h fouling DCMD experiment with humic acid did not show a reduction in flux for virgin and modified membranes. However, a substantial reduction in flux was observed with the addition of 3.775mM CaCl2 into the solution due to the formation of complexes with humic acid and consequent particles coagulation and precipitation on the membrane surface. Although both virgin and modified membranes showed similar fouling behaviors, a significantly higher flux recovery was found for modified membrane compared to the virgin membrane.
► A superhydrophobic PVDF membrane with water contact angle of 163° was prepared. ► Super-hydrophobicity is a result of multi-level roughness and low surface energy. ► Titania coating provides hierarchical structure and site for functionalization. ► Significant increase in flux recovery for modified membrane was obtained.
Zero liquid discharge after treatment of industrial wastewater is a major goal to avoid environmental pollution. For that, membrane distillation appears as an advanced technique to generate pure ...water and to concentrate recyclable matter. Here, we review membrane distillation with focus on the industry of the traditional Chinese medicine. Membrane distillation has been successfully applied to concentrate fruit juice and herbal bioactive compounds in food and medicine, and to manage brine from gas, oil and desalination industries. Membrane distillation holds many advantages including energy conservation and better rejection of bioactive compounds by comparison with distillation and reverse osmosis. The recent synthesis of superhydrophobic or omniphobic membranes, such as the Janus membrane, allows to decrease wetting and fouling.
Poly(ethylene oxide)- (PEO-) based block copolymer membranes have great potential for use in CO2 separation because of their excellent selectivity and moderate permeability. Whereas numerous studies ...have focused on the permeation performance of such membranes, the influence of the microphase-separated structures on the gas transport is not well understood. This study examined the phase structure of PEO–polyamide (PA) (commercial name, Pebax) block copolymer membranes by scanning probe microscopy (SPM) imaging and thermal analysis. The membranes with the irregular and more disordered phase-separated structure, such as Pebax-1074 membranes, that had longer PA chains and were made using a faster sol-to-gel transition process resulted in higher CO2 permeability than the membranes with the more ordered phase structure. The CO2 solubility coefficient profile as a function of pressure in the Pebax membranes with dual-mode sorption characteristics indicated the involvement of a glassy hard phase in CO2 transport, particularly at low pressure. The effects of temperature on gas transport and separation performance for a CO2/N2 gas mixture were also investigated.
CO₂ induced plasticization presents a great challenge for sustainable performance of polymeric gas separation membranes for natural gas purification application. Comprehensive understanding of this ...phenomenon would lead to the formulation of suitable strategies to suppress it. In this study, a nodule structure model based on nucleation and growth mechanism was used to link the membrane microscopic structure to CO₂ sorption which causes plasticization. This approach considers the dilation in Henry's sites is the major contributor to the plasticization compared to the Langmuir sites. In order to verify the proposed model, gas sorption tests were analysed for Matrimid hollow fiber membranes with different selectivities and the Henry's and Langmuir sorption isotherms were decoupled and compared. The modelling results suggest that more gas molecules were adsorbed into the Henry's sites than Langmuir sites at lower pressure range for hollow fibers with higher selectivity regardless of the types of the gases used. The modelling results also predicted that hollow fibers with lower selectivity should possess better plasticization resistance which was in agreement with the experimental plasticization observation. Competitive sorption for mixed-gas permeation was also investigated. The simulation study demonstrated that membranes with lower selectivity exhibited stronger competitive sorption than hollow fibers with higher selectivity; therefore plasticization phenomenon is more likely to be masked by competitive sorption for hollow fibers with lower selectivity. Furthermore, thermal annealing at both above and below the Matrimid's glass transition temperature was applied on hollow fiber membranes to evaluate its effect on plasticization suppression. Permeation test results indicated that the effect of thermal annealing above 250°C for more than 30min was sufficient to suppress plasticization. The dual-mode sites de-coupling technique was also performed on the thermally annealed membrane. The results suggest that the re-distribution of the Henry's and Langmuir sites due to thermal annealing could contribute to the suppression of plasticization. Other possible plasticization suppression mechanisms (cross-linking, crystallization and the formation of charge transfer complexes) were also explored using techniques including FT-IR, DSC, and dissolution tests.
Blending selected polymer materials in the membrane fabrication process has been widely investigated for dense film membrane in order to improve the membrane gas separation performance. However, such ...a strategy has not been fully explored on hollow fiber membrane, which is preferred in industry for gas separation. In this study, Matrimid® 5218 hollow fibers with 0–12wt% additive (PEG or PEO–PDMS copolymer) were fabricated via phase inversion technique. The effects of additives on the hollow fiber׳s gas transport properties were discussed in terms of the membrane morphology and surface composition, gas separation performance as well as plasticization and aging property. Both additives showed significant impact on the membrane structure, particularly influencing the skin layer of the hollow fiber. However, the copolymer also displayed surface aggregation behavior which resulted in the modification of skin layer composition. The increase in the concentration of PEG improved the CO2 permeance from 21GPU (without PEG) to 37GPU (with 12wt% PEG) and the hollow fibers with 12wt% PEO–PDMS copolymer displayed a doubled CO2/N2 selectivity compared to the fibers without the additive. Addition of PEG reduced the CO2 plasticization pressure while PEO–PDMS improved the plasticization resistance of hollow fibers.
•Asymmetric Matrimid® hollow fiber with PEG and PEO–PDMS additives fabricated.•Additives affected membrane morphology and skin layer thickness.•Surface segregation was detected for PEO–PDMS copolymer additives.•Addition of 12wt% PEG improved the CO2 permeance by 75% to 37GPU.•Fibers with 12wt% PEO–PDMS copolymer had double the CO2/N2 selectivity.
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•TiO2 based bio-catalytic nanoparticle was prepared and optimized.•APTES had significant impact on the bio-catalytic nanoparticle performance.•Hybrid membrane–nanoparticle suspension ...system could effectively degrade BPA.•The effect of operational parameters on the hybrid system BPA removal was studied.•The hybrid system could still preserve good BPA removal ratio under harsh conditions.
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.
Fringe projection is an important technology in three-dimensional measurement and target recognition. The measurement accuracy depends heavily on the calibration of the absolute phase and projector ...pixels. An easy-to-implement calibration method based on the Random Sample Consensus (RANSAC) algorithm is proposed to exterminate the phase error data and elevate the measurement accuracy in a fringe projection system. The reconstruction experiments of a double-sphere standard demonstrate that the uncertainties in radius and sphere-distance measurement are reduced to one thousandth of the measured value or even less, and the standard deviation in multiple measurements is restricted to within 50 μm. The measurement accuracy provided by the proposed RANSAC method can be improved by up to 44% compared with that provided by traditional least squared method (LSM). The proposed calibration method is easy and simple to implement, and it does not need additional hardware, but rather a calibration board.
