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Thermodynamic stabled CO2 molecules can be biocatalytically reduced to methanol via three cascade dehydrogenases (formate, formaldehyde and alcohol) with the aid of cofactor as the electron donor. In this study, Alcohol dehydrogenase (EC 1.1.1.1), the third step of the cascade enzymatic reaction which catalyzed formaldehyde (CHOH) to methanol (CH3OH) will be immobilized in an ultrafiltration membrane. The enzyme will be immobilized in the support layer of a poly(ether)sulfone (PES) membrane via a technique called fouling induced enzyme immobilization. The objective of this study is to evaluate the effect of varying pH (acid (pH 5), neutral (pH 7) and alkaline (pH 9)) of the feed solution during immobilization process of ADH in the membrane in terms of permeate flux, observed rejection, enzyme loading and fouling mechanism. The experiment was conducted in a pressure driven, dead-end stirred filtration cell. Reaction conversion and biocatalytic productivity will be also evaluated. The results showed that permeate flux for acid solution were the lowest during immobilization. High concentration polarization and fouling resistance cause lower observed rejection for pH 7 and 9. Enzyme loading for pH 5 give 73.8% loading rate which is the highest compared to 62.4% at pH 7 and 70.1% at pH 9. Meanwhile, the conversion rate during the reaction shows that reaction on fouled membrane showed more than 90% conversion for pH 5 and 7. The fouling model predicted that irreversible fouling occurs during enzyme immobilization at pH 7 with standard blocking mechanism while reversible fouling occurs at pH 5 and 9 with intermediate and complete blocking, respectively. [ABSTRACT FROM AUTHOR]

Combination of the reaction simultaneously with separation inside a single process unit or commonly known as reactive separation technology is widely studied nowadays as it would give mutual benefits for both enzymatic catalysis and membrane separation process. Alcohol dehydrogenase (ADH) at 0.10 g/L (dissolved in 0.10 M Tris-HCl buffer) was immobilized on commercially available PES and PVDF membrane at pH 7 and TMP 2 bar by reverse filtration method. Then the immobilized enzyme was subjected to the biocatalytic conversion of formaldehyde to methanol. The immobilization process successfully immobilized 87.67% and 70.94% of ADH enzyme in/on the PVDF and PES membrane, respectively. The subsequent reaction was able to convert formaldehyde to methanol as high as 90% conversion and a high biocatalytic productivity of 460 µmol CH3OH/mgenzyme·h for PVDF membranes. Enzyme relative activity could be retained for at least seven consecutive cycles. This study suggested that immobilization of ADH on the polymer membrane can increase enzyme loading and also retain its activity for a simultaneous conversion and separation of formaldehyde to methanol. [ABSTRACT FROM AUTHOR]

A designed biocatalytic cascade system based on reverse enzymatic catalysis by formate dehydrogenase (EC 1.2.1.2), formaldehyde dehydrogenase (EC 1.2.1.46), and alcohol dehydrogenase (EC 1.1.1.1) can convert carbon dioxide (CO 2 ) to methanol (CH 3 OH) via formation of formic acid (CHOOH) and formaldehyde (CHOH) during equimolar cofactor oxidation of NADH to NAD + . This reaction is appealing because it represents a double gain: (1) reduction of CO 2 and (2) an alternative to fossil fuel based production of CH 3 OH. The present review evaluates the efficiency of different immobilized enzyme systems and reaction designs that have been explored for optimizing this sequential enzymatic conversion of CO 2 to CH 3 OH, including multilayer microcapsules, bead scaffolds, cationic nanofibers, and membrane systems. The recent progress within efficient cofactor regeneration, protein engineering of the enzymes for robustness, and advanced uses of membrane systems for enzyme reuse and product separation are assessed for large scale implementation of this biocatalytic reaction cascade. Industrial realization of enzymatic CO 2 to CH 3 OH conversion including the option for reaping of formaldehyde and formate during the reaction warrants innovative development. There is a particular need for development of i) better enzymes; ii) improved understanding of enzyme structure function aspects of reverse catalysis by dehydrogenases, iii) quantitative kinetic models of the enzymatic cascade reaction during simultaneous cofactor regeneration, iv) robust systems for regeneration of reducing equivalents. [ABSTRACT FROM AUTHOR]

Abstract: In this work, fouling principles in force in ultrafiltration were deployed to understand the role of selected variables—applied pressure (1–3bar), enzyme concentration (0.05–0.2gL−1), pH (5–9) and membrane properties—on fouling-induced enzyme immobilization. The immobilization and subsequent enzymatic reaction efficiency were evaluated in terms of enzyme loading, conversion rate and biocatalytic stability. Alcohol dehydrogenase (ADH) was selected as a model enzyme. Lower pressure, higher enzyme concentration and lower pH resulted in higher irreversible fouling resistance and lower permeate flux. High pH during immobilization produced increased permeate flux but declines in conversion rates, likely because of the weak immobilization resulting from strong electrostatic repulsion between enzymes and membrane. The results showed that pore blocking as a fouling mechanism permitted a higher enzyme loading but generated more permeability loss, while cake layer formation increased enzyme stability but resulted in low loading rate. Low pH (near isoelectric point) favored hydrophobic and electrostatic adsorption of enzymes on the membrane, which reduced the enzyme stability. Neutral pH, however, promoted entrapment and hydrogen bonding of enzymes on the membrane, which improved the enzyme stability. This study suggests that a compromise between different fouling/immobilization mechanisms must be found in order to maximize the immobilization performance, both in terms of enzyme loading and also of enzyme activity. [Copyright &y& Elsevier]

Tapping into solar energy seems to be a viable and sustainable solution for the ongoing global challenges of water scarcity and clean energy shortage. However, the natural mechanism of solar energy-driven water evaporation is often compromised by low evaporation rate and water and solar absorption spectrum mismatch. Therefore, localized heating on the water vapor-liquid interface by light-absorbing materials, known as photothermal materials, has been proposed. This allows the harvesting of energy from the full solar spectrum and high efficiency of light-to-heat conversion. With the emerging advances of photothermal nanomaterials and the urgent demand for a green transition of water treatment technology, the establishment of a photothermal-driven membrane distillation system has been reinvigorated, as seen by the number of publications recently. The efficiency of light absorption and light-to-heat conversion of photothermal materials are critical factors in determining the membrane performances. This review aims to assess the state-of-the-art photothermal materials, including innovative modifications that have been made. The second part is devoted to the emerging aspects and new directions of using these photothermal materials for the development of photothermal membranes. Lastly, the prospects of photothermal membrane for clean water production in the near future are also discussed. [Display omitted] • There is an urgent demand for a green transition of water treatment process. • The state-of-the-art of photothermal materials is discussed. • The utilization of photothermal membrane for various applications is highlighted. • Photothermal membranes for water-energy-environment nexus • Prospect of photothermal membrane for water reclamation and purification [ABSTRACT FROM AUTHOR]

• Development of free-standing supported and nanocomposite GO membranes. • GO properties can be easily tailored to enhance membrane performance. • Membrane fabrication parameters can affect the membrane performance. • Fouling can be minimized due to hierarchical surface structure of GO membrane. Separation of oil in water emulsion remains as a critical issue due to the high volume of oily wastewater discharged by industrial processes. Membrane technology has a great industrial interest for this oil–water separation owing to its simple operational process and high separation efficiency. However, the hydrophobicity properties of membrane can aid the membrane fouling phenomenon and shorten the life of membranes. As a result, modification of membranes, particularly on hydrophilicity enhancement, is required to optimise the membrane performances. Over the years, graphene and its derivatives, particularly graphene oxide (GO) have gained great research interest in the field of membrane for water and wastewater treatment due to its ultimate thinness and unique layered structure. These features enhance the permeation fluxes, increase hydrophilic property, improve physicochemical properties and provides rich oxygen-containing groups for further modification, making it excellent for ionic/molecular separation. This review article discusses the recent progress of GO-based membranes through various configurations, i.e., free-standing, supported, and polymer nanocomposite for oil–water separation. The advancements of using GO for membrane morphology alteration, fouling mitigations as well as mechanical strength are discussed. The key issues for the development of high-performance GO membranes and prospects for imminent research are highlighted. [ABSTRACT FROM AUTHOR]