Platinum (Pt) is recognized as the most active material for the hydrogen evolution reaction in acidic media; however, its catalytic activity is often underestimated in proton exchange membrane water electrolysis (PEMWE) due to poor utilization of the cathode catalyst layer. In this study, we present the synthesis, characterization, and application of Pt nanoparticles with atomic precision on a microporous-layer-coated gas diffusion layer for PEMWE. The Pt nanoparticles were synthesized via atomic layer deposition, a technique that enables precise control over loading and particle size at the atomic scale. The resulting gas diffusion electrode with an exceptionally low platinum loading (1.08–5.40 μg cm^-2) demonstrated mass activity at least one order of magnitude higher than that of benchmark Pt. Furthermore, the electrode exhibited exceptional stability at a current density of 1 A cm^-2 over 200 hours. It also showed robust performance under dynamic operation, enduring 25,000 cycles of alternating cell voltages between 1.45 V and 2 V.

Membrane modification is commonly applied in water purification and wastewater treatment to reduce fouling of membranes. However, the influence of fouling test methods on evaluating pristine and modified membranes is often overlooked. This study investigates fouling behavior of alumina and SiC-deposited alumina membranes during oil-in-water emulsion filtration under both constant flux and constant transmembrane pressure conditions. Threshold flux was first determined using flux-stepping experiments, with the 90-min SiC-deposited membrane showing the highest value at 95 L m^{− 2} h^{− 1}. In single-cycle constant flux tests, fouling trends aligned with threshold flux data. However, when backwash was included, fouling characteristics shifted and depended on the permeate flux. Enhanced hydrophilicity and surface charge improved backwash efficiency in modified membranes. Yet, extensive modification negatively affected performance due to significant permeance loss (>57 %). Under constant pressure, fouling was dominated by internal pore blocking, and backwash efficiency was solely linked to membrane permeance, regardless of surface properties. Thus, constant flux filtration with backwash best reflects operational conditions and is recommended for evaluating membrane modifications.

Membrane technology presents an effective solution for treating oily wastewater, a significant environmental hazard stemming from industries such as food processing, metalworking, and oil extraction. Compared to polymeric membranes, ceramic ones exhibit superior mechanical, chemical, and thermal stability, enabling more effective oil removal and easier cleaning. Despite their advantages, membrane fouling remains a challenge, impacting the efficiency of oily wastewater treatment. This review explores oily wastewater characteristics and ceramic membrane applications in treatment processes. It examines the factors influencing ceramic membrane fouling, including wastewater properties (e.g., oil concentration, pH), membrane characteristics (e.g., surface hydrophilicity, charge), and operational parameters (e.g., cross-flow velocity, permeate flux). Strategies to mitigate fouling, such as pretreatment, backpulsing/backwashing for sustained operation, and chemical cleaning for fouling removal, are discussed. By using pretreatment, membrane fouling can be reduced. Backpulsing/backwashing is effective to maintain a long-term operation. Chemical cleaning is effective in removing irreversible fouling and restoring the performance of the ceramic membranes. Moreover, membrane modification techniques that enhance performance are highlighted. Ultimately, the review identifies that effective fouling control is crucial for optimizing ceramic membrane use in oily wastewater treatment, underscoring the need for ongoing research in this area.

Atomic layer deposition (ALD) is known for its unparalleled control over layer thickness and 3D conformality and could be the future technique of choice to tailor the pore size of ceramic nanofiltration membranes. However, a major challenge in tuning and functionalizing a multichannel ceramic membrane is posed by its large internal pore volume, which needs to be evacuated during ALD cycling. This may require significant energy and processing time. This study presents a new reactor design, operating at atmospheric pressure, that is able to deposit thin layers in the pores of ceramic membranes. In this design, the reactor wall is formed by the industrial tubular ceramic membrane itself, and carrier gas flows are employed to transport the precursor and co-reactant vapors to the reactive surface groups present on the membrane surface. The layer growth for atmospheric-pressure ALD in this case proceeds similarly to that for state-of-the-art vacuum-based ALD. Moreover, for membrane preparation, this new reactor design has three advantages: (i) monolayers are deposited only at the outer pore mouths rather than in the entire bulk of the porous membrane substrate, resulting in reduced flow resistances for liquid permeation; (ii) an in-line gas permeation method was developed to follow the layer growth in the pores during the deposition process, allowing more precise control over the finished membrane; and (iii) expensive vacuum components and cleanroom environment are eliminated. This opens up a new avenue for ceramic membrane development with nano-scale precision using ALD at atmospheric pressure.

Ceramic membranes have drawn increasing attention in oily wastewater treatment as an alternative to their traditional polymeric counterparts, yet persistent membrane fouling is still one of the largest challenges. Particularly, little is known about ceramic membrane fouling by oil-in-water (O/W) emulsions in constant flux filtration modes. In this study, the effects of emulsion chemistry (surfactant concentration, pH, salinity and Ca²⁺) and operation parameters (permeate flux and filtration time) were comparatively evaluated for alumina and silicon carbide (SiC) deposited ceramic membranes, with different physicochemical surface properties. The original membranes were made of 100% alumina, while the same membranes were also deposited with a SiC layer to change the surface charge and hydrophilicity. The SiC-deposited membrane showed a lower reversible and irreversible fouling when permeate flux was below 110 L m⁻² h⁻¹. In addition, it exhibited a higher permeance recovery after physical and chemical cleaning, as compared to the alumina membranes. Increasing sodium dodecyl sulfate (SDS) concentration in the feed decreased the fouling of both membranes, but to a higher extent in the alumina membranes. The fouling of both membranes could be reduced with increasing the pH of the emulsion due to the enhanced electrostatic repulsion between oil droplets and membrane surface. Because of the screening of surface charge in a high salinity solution (100 mM NaCl), only a small difference in irreversible fouling was observed for alumina and SiC-deposited membranes under these conditions. The presence of Ca²⁺ in the emulsion led to high irreversible fouling of both membranes, because of the compression of diffusion double layer and the interactions between Ca²⁺ and SDS. The low fouling tendency and/or high cleaning efficiency of the SiC-deposited membranes indicated their potential for oily wastewater treatment.

Highly efficient and economic treatment of wastewater sludges and wastewaters in one way is a challenging issue in the water treatment field. Herein we present a waste-to-resource strategy for rational fabrication of low–cost ceramic membranes, which simultaneously addresses the treatment of heavy metal-laden sludges and the separation of oil-in-water (O/W) emulsions. A thermal conversion mechanism is proposed for complicated reactions between simulated nickel-laden wastewater sludge and bauxite mineral. In addition to full stabilization and recycling of heavy metal wastewater sludges, rational tailoring of ceramic membrane structures can also be realized to achieve high water flux and favorable mechanical and surface properties. With rational structure design, the tailored spinel-based ceramic membranes exhibited high rejection and high flux (7473 LMH·bar⁻¹) simultaneously for separation of oily wastewater, outperforming other reported state-of-the-art ceramic membranes. The membrane fouling mechanism revealed the dominance of cake layer formation at low cross flow velocities, while a combined model of cake layer formation and pore blocking dominated membrane fouling at high cross-flow velocities. The proposed strategy can be potentially extended toward design of functional ceramic membranes derived from other heavy metal wastewater sludges and for other water treatment applications.

Silicon carbide (SiC) ceramic membranes are of particular significance for wastewater treatment due to their mechanical strength, chemical stability, and antifouling ability. Currently, the membranes are prepared by SiC-particle sintering at a high temperature. The production suffers from long production time and high costs. In this paper, we demonstrated a more economical way to produce SiC ultrafiltration membranes based on low-pressure chemical vapor deposition (LPCVD). SiC was deposited in the pores of alumina microfiltration supports using two precursors (SiH₂Cl₂ and C₂H₂/H₂) at a relatively low temperature of 750 °C. Different deposition times varying from 0 to 150 min were used to tune membrane pore size. The pure water permeance of the membranes only decreased from 350 Lm⁻²h⁻¹bar⁻¹ to 157 Lm⁻²h⁻¹bar⁻¹ when the deposition time was increased from 0 to 120 min due to the narrowing of membrane pore size from 71 to 47 nm. Increasing the deposition time from 120 to 150 min mainly resulted in the formation of a thin, dense layer on top of the support instead of in the pores. Oil-in-water emulsion filtration experiments illustrated that both the reversible and irreversible fouling of the SiC-deposited UF membrane was considerably lower as compared to the pristine alumina support. The unique feature that pore sizes decrease linearly as a function of SiC deposition time creates opportunities to produce low-fouling SiC membranes with tuned pore sizes on relatively cheap support.