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.

Worldwide, a considerable amount of oily wastewater is generated, with oil droplets from 2 to 200 nm that are difficult to separate because of their size and colloidal stability. This study presents a novel approach for effectively separating microemulsions via cubic silicon carbide (3C-SiC)-coated alumina (Al ₂O ₃) membranes fabricated based on low pressure chemical vapor deposition (LPCVD). SiC was deposited at a relatively low temperature at 860 °C on 100 nm Al ₂O ₃ membranes using two precursors: SiH ₂Cl ₂ and C ₂H ₂. With the increase in deposition time, up to 25 min, the pore size decreased from 41 nm to 33 nm, which is a smaller pore size of a SiC membrane than previously used for oil/water separation. The polycrystalline 3C-SiC-coated membranes showed improved hydrophilicity (water contact angle of 15°) and highly negatively charged surfaces (−65 mV). Microemulsion filtration experiments were carried out at a constant permeate flux (80 Lm ⁻² h ⁻¹) for six cycles with varying deposition time, pH, surfactant types, and pore sizes. The fouling of the SiC-coated membrane was, compared to the Al ₂O ₃ membrane, effectively mitigated due to the enhanced electrostatic repulsion and hydrophilicity. Surfactant adsorption mainly occurred when the surface charge of the microemulsion and the membranes were opposite. Therefore, the surface charge of the alumina membrane changed from positive to negative when soaked in negatively charged microemulsions, whereas SiC-coated membranes remained negatively charged regardless of surfactant type. The membrane fouling was alleviated when the membrane and oil droplets had the same charge. Lastly, the 62 nm SiC-coated membrane with 20 min coating time was the best choice for the filtration of the microemulsion, because of the high rejection of the oil droplets and low fouling tendency.