Publications

This work describes the fabrication and evaluation of fluoropolymer surface coating on polymer fibre core prepared from polymethyl methacrylate (PMMA) using ultraviolet (UV) photopolymerisation curing method. The curing condition has a significant influence on the coating adhesion on the core. The focus of this study was to evaluate an effective and simple process for polymer optical fabrication using UV curing with dip-coating method. The coating performance was evaluated through surface morphology analysis and physical properties. FESEM–EDX images indicate that the fluoropolymer coating formed a compact structure with a cladding thickness of 67.63 μm for the highest UV irradiation strength. FTIR analysis revealed the presence of fluorine elements on coated fibre with EDX surface mapping of fluorine dispersion. The performance of the fibre was studied and compared with commercially available polymer optical fibre in terms of fibre spectral fluorescence properties and light attenuation. The dip-coating photopolymerisation method was effective in forming the cladding for step-index polymer fibre with similar spectral excitation wavelength recorded at 620 to 630 nm with the lowest power loss at −13.40 dBm.

Background Antibiotic resistances (ARs) in water are a major concern in the aquatic environment, as they are present at very low concentration ranging from ng/L to µg/L. It is necessary to design a photocatalyst with highly efficient ARs degradation utilizing solar energy. Method nanocomposite photocatalyst of CeO2 with carboxylated graphene oxide (cGO) were constructed via carboxylation and hydrothermal processes. The ciprofloxacin (CPX) photodegradation of the CeO2@cGO photocatalysts compared with pure CeO2 was performed under UV and visible light. cGO was employed as support for CeO2 with carboxyl anchoring sites as well as electron sink to prevent rapid charge recombination during photocatalytic reaction. Significant findings FTIR and XRD results show the interaction between cGO's carboxyl groups and CeO2, forming anchoring sites. XPS reveals an increased Ce3+/Ce4+ ratio (0.14) with cGO, creating oxygen vacancies that enhance photocatalytic activity. The CeO2@cGO nanocomposite exhibits a narrower band gap energy (from 3.17 eV to 2.76 eV), improving visible light absorption. In adsorption alone, CeO2@cGO achieves the highest capacity (12.1 mg/g). CPX degradation with 50% CeO2@cGO under UV light reaches 99.23%, compared to 74.67% for pure CeO2. Enhanced charge transfer, electron-hole pair separation, and electrostatic interaction contribute to this improvement. CeO2@cGO demonstrates excellent regeneration capacity and stability, maintaining 93% performance after five cycles. These findings pave the way for advanced photocatalysts for efficient pollutant removal from wastewater.

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.

Methylene blue is a refractory pollutant commonly present in textile wastewater. This study tests the feasibility of TiO2/graphene oxide (GO) composite in enhancing photocatalytic degradation of MB in synthetic wastewater with respect to scientific and engineering aspects. To enhance its removal, we vary the composition of the composite based on the TiO2 weight. Under UV–vis irradiation, the effects of photocatalyst's dose, pH, and reaction time on MB removal by the composites are evaluated under optimum conditions, while any changes in their physico-chemical properties before and after treatment are analyzed by using TEM, SEM, XRD, FTIR and BET. The photodegradation pathways of the target pollutant by the composite and its removal mechanisms are also elaborated. It is found that the same composite with a 1:2 wt ratio of GO/TiO2 has the largest surface area of 104.51 m2/g. Under optimum reactions (0.2 g/L of dose, pH 10, and 5 mg/L of pollutant's concentration), an almost complete MB removal could be attained within 4 h. This result is higher than that of the TiO2 alone (30%) under the same conditions. Since the treated effluents could meet the strict discharge standard limit of ≤0.2 μg/L set by China's regulation, subsequent biological treatments are unnecessary for completing biodegradation of remaining oxidation by-products in the wastewater effluents.

Asymmetric pore configuration of dual-layer hollow fibre catalyst membrane of NiO-YSZ (inner layer)/La0.7Sr0.3Co0.2Fe0.8O3-δ-YSZ (outer layer) has been studied from its morphology and oxygen transport point of view. The membrane was synthesized by phase inversion method and co-extruded using water as the external coagulant and water, ethanol and NMP mixture as the internal coagulant (bore liquid mixture), followed by sintering at 1300 °C for 8h. Volume ratio of water:ethanol:NMP was 4:1:5. The resulted dual-layer membrane has non-sandwich like pore configuration. SEM images of the membrane showed finger-like pores on the internal side and sponge-like pores on the external side. Bending strength of the membrane was 9.76 MPa and nitrogen permeability (gas tightness) was 1.36 x 10−4 mol.m−2.s−2. Pa−1. The oxygen permeability of the membrane at 600, 700 and 800 °C was 2.78 x 10-8, 2.84 x 10−8 and 3.10 x 10-8 mol.s−1.cm-2, respectively, which is about two order of magnitude lower than oxygen permeability of other reported perovskite-based membranes.

The most widely used method for the synthesis of graphene in large scale is through the thermal exfoliation and reduction process of graphene oxide (GO). Well know that the physicochemical properties of graphene greatly affected by the oxidation time employed in GO preparation. In this study, GO samples were prepared at different oxidation time through the Hummers' method. The formation of oxygen containing functional groups in GO and their influences onto its’ structure were analyzed and compared. XPS analysis and 13C NMR revealed the formation of carboxyl groups mainly formed at a longer oxidation time. XRD results obtained indicated that the oxidation time have no effect on the interlayer spacing (d) once it reached the optimal extent, however, the graphite stacking order was disrupted due to the insertion of oxygen-containing functional groups. The influence of oxidation time on the stability of GO dispersions was evaluated by zeta potential, which exhibited higher zeta potential and stability at longer oxidation time. This study demonstrates that the integrity and physicochemical properties of GO can be tuned and depend on the type of oxygen-containing functional groups generated at the basal or edge structure, which may foster a range of new applications.

In response to the ever-growing global water crisis, the use of innovative and sustainable solutions based on membrane technology particularly membrane distillation (MD) is essential. MD process uses a hydrophobic membrane to separate impurities from feed water by utilizing a temperature difference to create water vapor, leaving contaminants behind. It has become more favorable compared to pressure-driven processes as it operates at low temperatures and pressures. However, MD needs external energy for heating which can be expensive and consumes a lot of energy. Photothermal membrane distillation (PMD) is an advancement of MD where it uses renewable energy, which is solar energy, to increase the temperature at the membrane’s interface, eliminating the need for external power. This makes PMD more energy-efficient and eco-friendly compared to the MD. In this chapter, the fundamental of MD was first introduced, followed by a discussion on how MD employs hydrophobic membranes to create a temperature gradient, enabling selective separation. Then, the focus of this chapter shifts to PMD, an innovative approach that harnesses the power of renewable energy sources to heat the feed water. The principles behind photothermal energy conversion and its integration with MD technology were first reviewed. Then, numerous advantages offered by PMD over conventional MD, making it an attractive solution for addressing the pressing global challenges of water scarcity and wastewater treatment were highlighted. Lastly, the fabrication of membranes for PMD particularly in terms of incorporation of photothermal material into membrane matrix as well as surface modification was reviewed. Overall, this chapter aims to shed light on this cutting-edge technology's potential to revolutionize water treatment, offering sustainable, cost-effective, and environmentally friendly solutions in the face of growing water scarcity and environmental concerns.

This work focused on in situ growth of α-Fe2O3 on an asymmetric Al2O3/YSZ hollow fiber via hydrothermal route. An asymmetric Al2O3/YSZ hollow fiber composite was prepared using the dry–wet phase inversion method and sintering process. The pristine hollow fiber and hollow fiber with α-Fe2O3 were systematically characterized using FESEM. The separation performance of the membranes was determined using the fluxes of both pure water and synthetic oily wastewater and membrane rejection. The FESEM images show more α-Fe2O3 particles grew and deposited on the hollow fiber with at increasing iron (Fe) concentration. The flux of the hollow fiber with α-Fe2O3 was higher compared to that of the pristine hollow fiber (1003 and 1148–1370 L∙m−2∙h−1, respectively). As for oily wastewater separation, the flux declined when the Fe concentration was increased from 0.05 to 0.5 M. However, an improvement in oil rejection up to 95% was obtained. Under visible light assisted filtration, fluxes and rejections of oil emulsion increased, which indicates that the α-Fe2O3 growth on top of the hollow fiber is prone to activate the photocatalytic activity for self-cleaning properties. Hence, the α-Fe2O3 supported Al2O3/YSZ hollow fiber can act as both separation membrane and photocatalytic membrane.

In this work, inexpensive biochar derived from different feedstock was synthesized, characterized, and tested for Cr(VI) removal from synthetic wastewater. The physical properties of the sludge-based magnetic biochars (SSB) were analyzed using FT-IR, XRD, BET surface area, SEM-EDS, and XPS techniques. The effects of pyrolysis temperature (300–900 ℃), initial Cr(VI) concentration (2–30 mg/L), rotation speed (50–200 rpm), pH (3–11), and co-ions (Na+, Ca2+, Mg2+, K+, Cl−, HCO3 − and SO4 2−) on Cr(VI) removal by the SSB were determined in batch modes. It was found that the SSB had the highest Cr(VI) removal (43.7%), as compared to the other feedstock-derived biochars (p ≤ 0.05; Anova test). The characterization data indicated that with an increasing pyrolysis temperature from 300 to 900℃, the surface area, pore volume, and pore size decreased, while the Fe3O4 on SSB was gradually reduced to α-Fe0. With respect to Cr(VI) removal, under the optimized conditions of 900℃ of pyrolysis temperature, 2 mg/L of Cr(VI) concentration, 200 rpm of agitation speed, and pH 6.8, a complete Cr(VI) removal could be attained by the SSB900. Its treated effluents could comply with the required Cr(VI) discharge limit of <0.01 mg/L (GB3838-2002) mandated by local legislation. Therefore, further treatment was not required, avoiding additional cost. Coexisting ions experiments showed that all of them inhibited the Cr(VI) removal by the adsorbent after 1 h of reaction. The Cr(VI) removal followed the pseudo-second-order kinetics and the Langmuir isotherm model. The removal mechanism was based on the reduction of Cr(VI) by nZVI on the SSB900 and the Fe leakage might have facilitated the Cr(VI) removal. Overall, iron-enriched sewage sludge biochar is promising and cost-effective for treatment of low-level Cr(VI)-contaminated wastewater.

The development of wearable artificial kidney demands an efficient dialysate recovery, which relies upon the adsorption process. This study proposes a solution to solve the problem of competitive adsorption between the uremic toxins by employing two adsorptive components in a membrane separation process. Dual-layer hollow fiber (DLHF) membranes, which are composed of a polysulfone (PSf)/activated carbon (AC) inner layer and a PSf/poly(methyl methacrylate) (PMMA) outer layer, were prepared for co-adsorptive removal of creatinine and urea from aqueous solution. The DLHF membranes were characterized in terms of morphological, physicochemical, water transport, and creatinine adsorption properties. The membrane was then subjected to an ultrafiltration adsorption study for performance evaluation. The incorporation of AC in membrane, as confirmed by microscopic and surface analyses, has improved the pure water flux up to 25.2 L/(m2 h). A membrane with optimum AC loading (9 wt %) demonstrated the highest maximum creatinine adsorption capacity (86.2 mg/g) based on the Langmuir adsorption isotherm model. In the ultrafiltration adsorption experiment, the membrane removed creatinine and urea with a combined average percent removal of 29.3%. Moreover, the membrane exhibited creatinine and urea uptake recoveries of 98.8 and 81.2%, respectively. The combined action of PMMA and AC in the PSf DLHF membrane has made the adsorption of multiple uremic toxins possible during dialysate recovery.

This work investigates the performances of coconut shell waste-based activated carbon (CSWAC) adsorption in batch studies for removal of ammoniacal nitrogen (NH3–N) and refractory pollutants (as indicated by decreasing COD concentration) from landfill leachate. To valorize unused resources, coconut shell, recovered and recycled from agricultural waste, was converted into activated carbon, which can be used for leachate treatment. The ozonation of the CSWAC was conducted to enhance its removal performance for target pollutants. The adsorption mechanisms of refractory pollutants by the adsorbent are proposed. Perspectives on nutrient recovery technologies from landfill leachate from the view-points of downstream processing are presented. Their removal efficiencies for both recalcitrant compounds and ammoniacal nitrogen were compared to those of other techniques reported in previous work. It is found that the ozonated CSWAC substantially removed COD (i.e. 76%) as well as NH3–N (i.e. 75%), as compared to the CSWAC without pretreatment (i.e. COD: 44%; NH3–N: 51%) with NH3–N and COD concentrations of 2750 and 8500 mg/L, respectively. This reveals the need of ozonation for the adsorbent to improve its performance for the removal of COD and NH3–N at optimized reactions: 30 g/L of CSWAC, pH 8, 200 rpm of shaking speed and 20 min of reaction time. Nevertheless, treatment of the leachate samples using the ozonated CSWAC alone was still unable to result in treated effluents that could meet the COD and NH3–N discharge standards below 200 and 5 mg/L, respectively, set by legislative requirements. This reveals that another treatment is necessary to be undertaken to comply with the requirement of their effluent limit.