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This work investigated the performances of ZIF-8 membranes coated on a low-cost ceramic hollow fiber (CHF) support developed from quarry dust (QD). The ceramic hollow fiber (CHF) was first fabricated using phase inversion and sintering techniques. The effects of the bore fluid flow rate (6–10 ml·min− 1) and sintering temperature (1050–1150 °C) on the morphology and mechanical strength of the final CHF were systematically evaluated. A larger finger-like macrovoid structure was observed when a longer air gap distance was used. A higher sintering temperature enhances the mechanical properties of CHFs due to pore densification, but it also leads to a less porous CHF, which can affect their permeation flux. The relatively low sintering temperature needed for QD-based CHF (< 1150 °C) leads to a reduction in energy consumption, which is economically attractive for future commercialization. By controlling the ZIF-8 loading (0.4–1.6 wt%) in the coating solution, a uniform and well-coated ZIF-8 selective layer was coated to form a quarry dust ceramic hollow fiber membrane (QD-CHFM). A single gas permeation study was conducted at 2–6 bar, and it was observed that the permeability of gases was greater when the ZIF-8 loading was lower, particularly for CO2(1.19 × 10− 4cm3(STP)·cm·cm− 2·s− 1·cm− 1·Hg− 1). A further increase in the ZIF-8 concentration in the coating solution caused agglomeration, which simultaneously increased the path tortuosity. Therefore, the gas diffusion rate across the membrane decreased. The performances of ZIF-8/QD-CHFM were observed to be similar to those of other ceramic membranes available in the literature. This work indicated that ZIF-8 loading could significantly affect gas separation performance. In addition, reutilizing QDs as a raw material for ceramic membrane fabrication can help reduce disposal issues and reduce the overall cost of ceramic membranes for future development.

Recently, a thermally-driven membrane process known as membrane distillation (MD) has emerged as an alternative to the high-pressure membrane process for contaminants removal from water. The driving force for MD is a vapor pressure gradient produced by a temperature differential across a hydrophobic porous membrane, which results in the transfer of water vapor from hot to cold side. However, the feasibility of MD for industry adoption is hampered by several issues such as temperature polarisation effects, low permeate flux, membrane wetting, and fouling. The membrane properties are known to have a significant role in controlling the final performances of MD. This review first looks into the feature of ideal MD membrane properties. Then, the use of graphene-based materials for the development of high performances MD membrane is discussed. Besides enhancing the water permeability and selectivity of MD, the incorporation of graphene offers additional properties such as anti-fouling, antibacterial, and photodegradation. The future direction of using graphene-based photothermal material in MD for heat generation under solar irradiation is also reviewed. It is found that the localised heating at membrane surfaces by photothermal material can minimise temperature polarisation effects and subsequently enhance the driving force for effective vapour transport. Thus, a more energy-efficient MD system can be developed.

Discharging of coloured dyes into wastewater has become one of the crucial issues around the world. Among various established alternatives to treat dye-contaminated water, photocatalytic degradation is a promising method to remove various dyes from water and wastewater due to their excellent photocatalytic activity and minimal final by-products. Nowadays, an immense number of photocatalysts have been synthesized and modified to achieve efficient treatment of photocatalytic degradation on dyes. On top of that, criteria include appropriate band gap energy of photo-catalysts, applicability for solar light irradiation, good stability, and maximum recyclability have become the main prioritized. Herein, this review summarised the progress of emerging photocatalysts, graphene oxide, graphitic carbon nitride (g-C3N4) and molybdenum disulfide (MoS2) in treating dyes. Furthermore, the performance of photocatalyst, the type of dyes treated, and significant findings from the treatment was also discussed. Finally, the future trends and challenges in applying photocatalysts to treat dyes in wastewater are comprehensively deliberated.

This paper discusses the response surface methodology (RSM) study on a recent direct contact membrane distillation (DCMD) system. The DCMD system is reviewed due to its myriad attention on desalination process, especially on water treatment of high salinity and reclamation of industrial process water. The fundamental of DCMD, as well as the mass and heat transfer principles for modelling the system, are firstly explained and compared with previous studies. Then, the researcher highlighted the parameters involved in the modelling of DCMD process, such as feed temperature, velocity, and concentration, simultaneously with common membrane properties in mass and heat transfer models. The correlation of these frequently studied parameters with the conventional model was included and summarised. Subsequently, RSM was performed for the model development of the DCMD system, which included common design matrix applications, such as Box–Behnken, central composite design, and full factorial design. Finally, this work reviews the most recent application for the DCMD modelling of the model, comparing its experimental number runs, independent input number, model levels, and accuracy for optimising the DCMD process using RSM.

In this work, the surface of a PVDF-based hollow fiber membrane was modified by coating MoS2-TiO2to improve the performance of membrane distillation (MD). The MoS2-TiO2was first synthesized at different ratios using a one-step hydrothermal process. Then, the PVDF-based hollow fiber membrane was spun at various air gaps and PES was also added as an additive. As 5M5T (50 wt% MoS2and 50 wt% TiO2) possessed better physicochemical properties and narrow band gap, the 5M5T was mixed with trichloro(octadecyl)silane in (OTS) at various loading to form a dip-coating solution. The PP20 membrane (PVDF + PES) spun at a 20 cm air gap was used as a support for MD due to its high porosity and low membrane thickness. It was observed that the contact angle of the MoS2-TiO2/PP20 membrane increased significantly to 136.8 ± 2.33° when the membrane was coated with 0.2% of 5M5T MoS2-TiO2. The MD performances were investigated via an in-house MD system. The results revealed that the performances of MoS2-TiO2/PP20 membranes were much higher than previously reported membranes due to their enhanced hydrophobicity and porosity properties. It was observed that a higher operating temperature could elevate the permeate flux up to 23.3 kg·m−2·h−1,but less than 0.1% changes in the rejection rate. The results obtained in this work suggest that the MoS2-TiO2coated on the PVDF-based membrane can overcomes the typical permeability/rejection rate trade-off effect, which can play a significant role in enhancing MD performances.

Hexavalent chromium, Cr(VI), is considered hazardous heavy metal in water bodies that can cause severe effects on human health and the environment. Over the years, myriad attention has been focused on developing photocatalysts to remove Cr(VI) from wastewater. However, broad bandgap energy and the high electron recombination rate of these conventional photocatalysts have limited their photocatalytic ability. Therefore, efficient photocatalytic materials for Cr(VI) removal in wastewater is strongly demanded. In this study, delaminated MXene was successfully synthesised and used to remove Cr(IV) from the aqueous solution. The synthesised delaminated MXene was characterised using XRD, EDX, FTIR, FESEM, nitrogen adsorption-desorption analysis, TGA, UV-Vis-NIR spectroscopy and XPS. Based on the results, the optimum operating conditions for Cr(VI) removal by the synthesised MXene was obtained at pH 4 with photocatalyst loading of 1.5 g/L and Cr(VI) initial concentration of 5 mg/L. The removal efficiency of Cr(VI) via adsorption-assisted photocatalysis over various concentrations was around 3.1–28.9% higher than adsorption, verifying a synergistic effect of adsorption and photocatalysis by the delaminated MXene. The isotherm of Cr(VI) adsorption was fitted by the Langmuir model (R2> 0.9848) and was found better than the Freundlich model (R2> 0.8824). Meanwhile, the time dependence of Cr(VI) adsorption was well fitted to the pseudo-second-order kinetic model with R2> 0.9999. In conclusion, the results obtained suggest that the delaminated MXene possesses excellent properties and the ability to remove Cr(VI) via adsorption-assisted photocatalysis and has great potential to be used for industrial wastewater applications.

A thin alginate layer induced on the surface of a commercial polysulfone membrane was used as a matrix for noncovalent immobilization of enzymes. Despite the expected decrease of flux across the membrane resulting from the coating, the initial hypothesis was that such a system should allow high immobilized enzyme loadings, which would benefit from the decreased flux in terms of increased enzyme/substrate contact time. The study was performed in a sequential fashion: first, the most suitable types of alginate able to induce a very thin, sustainable gel layer by pressure-driven membrane filtration were selected and evaluated. Then, an efficient method to make the gel layer adhere to the surface of the membrane was developed. Finally, and after confirming that the enzyme loading could remarkably be enhanced by using this method, several strategies to increase the permeate flux were evaluated. Alcohol dehydrogenase (EC 1.1.1.1), able to catalyze the conversion of formaldehyde into methanol, was selected as the model enzyme. An enzyme loading of 71.4% (44.8 μg/cm2) was attained under the optimal immobilization conditions, which resulted in a 40% conversion to methanol as compared to the control setup (without alginate) where only 10.8% (6.9 μg/cm2) enzyme was loaded, with less than 5% conversion. Such conversion increased to 60% when polyethylene glycol (PEG) was added during the construction of the gel layer, as a strategy to increase flux. No enzyme leakage was observed for both cases (with/without PEG addition). Modeling results showed that the dominant fouling mechanism during gel layer induction (involving enzyme entrapment) was cake layer formation in the initial and intermediate phases, while pore blocking was the dominant mechanism in the final phase. Such mechanisms had a direct consequence on the type of immobilization promoted in each phase. The results suggested that the strategy proposed could be efficiently used to enhance the enzyme loading on polymer membranes.