Soon Huat Tan

The growing demand for high-performance air filtration materials, coupled with increasing concerns over plastic waste accumulation, has accelerated interest in sustainable filtration technologies. Recycled polyethylene terephthalate (r-PET) has emerged as a promising feedstock for electrospun nanofibrous membranes due to the abundance, low cost, and sustainability of this plastic waste feedstock. The filtration performance of r-PET membranes has been demonstrated to be comparable to that of conventional virgin polymer filters. This review critically examines recent developments in electrospun r-PET nanofibrous membranes for air filtration applications, with particular emphasis on the role of membrane morphology in governing filtration performance. Unlike previous reviews that primarily summarize electrospinning techniques or recycled polymer applications, this review critically evaluates how membrane morphology—including fiber diameter, pore architecture, bead-on-string structures, and multilayer configurations—governs filtration performance in electrospun r-PET membranes. Evidence suggests that rational morphological engineering plays a more decisive role than polymer chemistry in overcoming the conventional filtration efficiency–pressure drop trade-off. Finally, future research opportunities in scalable manufacturing, environmentally benign processing, and artificial intelligence-assisted membrane design are discussed to support the development of next-generation sustainable air filtration media.

Visible-light dye photodegradation is often constrained by band-structure limitations, weak interfacial coupling, and slow charge transport, which collectively accelerate electron–hole recombination and limit durability. To address these bottlenecks, a polypyrrole–titanium dioxide–carbon nanotube (PPy–TiO₂–CNT) heterojunction was designed in which PPy serves as a visible-light photosensitizer, TiO₂ provides a stable oxidative scaffold and electron-accepting phase, and CNTs create conductive pathways that strengthen interfacial coupling and accelerate electron extraction and transfer. Unlike previously reported binary PPy–oxide or PPy/CNT systems, the present work develops a continuously coupled ternary PPy–TiO₂–CNT interface that integrates visible-light sensitization, oxide redox functionality, and CNT-mediated electron conduction within a single heterojunction while also linking the material design to an LC–MS-verified degradation pathway. The synthesized PPy–TiO₂–CNT heterojunction nanocomposite was evaluated by systematic screening of key operating variables (pH 3–11; 5–50 mg L^–1; 0.10–1.00 mg mL^–1). Under optimal conditions, the nanocomposite achieved a rate constant of 0.053 min^–1 and 99.4% MB removal under visible light, while retaining 92.3% activity after five cycles. The targeted bottlenecks were addressed experimentally by (i) extended visible absorption and an apparent optical gap of ≈2.10 eV (DRS/Tauc) to enhance photon harvesting, (ii) strong PL quenching, which provides evidence of suppressed radiative recombination, and (iii) the smallest Nyquist semicircle (lowest Rct) to confirm accelerated interfacial charge transfer. These characterization results collectively indicate improved interfacial charge separation and transport, which is reflected in the favorable quantitative performance of the optimized CTP-3 sample, namely an apparent optical gap of ≈2.10 eV, a rate constant of 0.053 min^–1, 99.4% MB removal, and 92.3% retained activity after five cycles. Under visible irradiation, PPy acts as the primary photoactive component (HOMO → LUMO), while the CNT network promotes electron extraction and delivery to interfacial O₂, supporting a reactive oxygen species (ROS) sequence from superoxide (^•O₂^–) to hydroxyl radical (^•OH) that oxidizes MB. Liquid chromatography–mass spectrometry reveals sequential N-demethylation, aromatic oxidation, and ring opening toward mineralization. Overall, the continuously coupled PPy–TiO₂–CNT interface mitigates recombination and transport limitations while maintaining durability, establishing a reproducible route to mechanism-guided materials-process codesign for efficient visible-light photocatalysis.

Concurrent clean water generation and contaminant degradation from organic wastewater remain a significant challenge. In this work, we developed a natural down fiber-doped titanium dioxide (DF-TiO₂)/down fiber carbon (DFC) hybrid hydrogel that integrates efficient solar-driven water evaporation with visible-light photocatalytic decontamination. Unlike conventional chemical doping, the incorporation of biomass-derived DF introduces C, N, and S elements into the TiO₂ lattice, narrowing the bandgap and suppressing electron–hole recombination, as confirmed by density functional theory calculations. By coupling DF-TiO₂ with DFC in a chitosan–poly(vinyl alcohol) hydrogel matrix, the resulting DF-TiO₂/DFC hybrid hydrogel possessed satisfactory mechanical properties, high light absorption capacity, sufficient water supply, and visible-light-driven catalytic activity. As a result, the DF-TiO₂/DFC hydrogel demonstrated an evaporation rate of 2.14 kg·m^–2·h^–1 and a concurrent methyl orange (MO) degradation efficiency of 93.1% after 5 h under 1 sun illumination. Furthermore, the hydrogel retained its evaporation performance after continuous 5 h of evaporation for various contaminants, including MO, rhodamine B, and tetracycline. Actual outdoor experiments demonstrated an evaporation rate of 2.25 kg·m^–2·h^–1 at 2:00 p.m. and a simultaneous MO degradation efficiency of 93.79% from 8:00 a.m. to 6:00 p.m. This approach provides new perspectives on the sustainable bio-doping of catalytic materials and their use in high-tech applications, such as advanced solar evaporation, photocatalytic hydrogen production, photocatalytic carbon dioxide reduction, and other related areas.

Solar-driven interfacial evaporation system has attracted intensive attention owing to its great potential in harnessing renewable solar energy to purify water. To further enhance the solar-driven interfacial evaporation system performance, solar absorber structure with high light-thermal energy conversion efficiency is especially critical. In this work, polyvinyl pyrrolidone/poly(vinylidene fluoride co hexa fluoropropylene)/CuO-nanorods (PVP/PVDF-HFP/CuO-nanorods) membrane was prepared sequentially by electrospinning, heating and hydrothermal processes. The flexible electrospun membrane was used as the photothermal layer in the solar-driven interfacial evaporation system. The evenly distributed CuO nanorods function as solar energy absorbers. The polystyrene foam was used as an insulating layer, and filter paper was inserted in the middle of the polystyrene foam to transport water to the photothermal layer. The designed evaporator was used for the solar evaporation using pure water. As a result, the evaporation rate was 1.11 kg/m2h and the light-thermal energy conversion rate was 75.36%. The outcome of this work provides the potential of solar-driven interfacial evaporation system for water desalination and wastewater purification.

In this study, the electrospinning process modifies the commercial polyester filter media to increase filtration efficiency. The polyethylene terephthalate (PET) solution produces electrospun fiber on commercial polyester filter media at various rotation speeds and durations. The PET concentration and electrospinning applied voltage were adjusted accordingly to obtain bead-free electrospun fibers. As a result, the modified filter media’s filtration efficiency is approximately two times higher than the commercial polyester filter media at 300 rpm and 5 hours of electrospinning duration. Furthermore, the efficiency of the single unit modified filter media is 53.76% with an airflow resistance of 39.2 Pa and quality factor of 0.01968 Pa⁻¹ which are comparable to the combination of two units’ air filters. Thus, replacing two units’ air filters having a primary and secondary filter with a single unit modified filter media is justifiable.

This study focuses on the development of an asymmetric membrane comprised of an electrospun carboxyl‐functionalised multi‐walled carbon nanotube (COOH‐MWCNT)/poly (vinyl alcohol) (PVA) composite nanofibre layer on a dense PVA separation layer (M_COOH‐MWCNT). The electrospun nanofibre layer in this study acts as a “pre‐selective layer” instead of its common function as a membrane support. In addition, COOH‐MWCNT, a hydrophilic filler is integrated in the nanofibres to further enhance the membrane pervaporation separation performance. Immense improvement was observed in the pervaporation performance of the resultant asymmetric membranes in the dehydration of aqueous 1,4‐dioxane solutions, owing to the presence of the electrospun composite nanofibres as a hydrophilic layer. The resultant asymmetric membrane showed an increase of nearly 80% in water permeation flux as compared to that of the dense PVA membrane alone, and the separation factor was improved from 392.65 to 605.35. The parameters estimated using Rautenbach model showed that the dehydration of aqueous 1,4‐dioxane solutions via pervaporation is dominantly governed by sorption process. The permeation flux, transport coefficient of water and 1,4‐dioxane of the electrospun asymmetric membrane showed a good agreement in between the experimental data and those predicted using Rautenbach model.