Sulphate (SO42­) is a model ion due to its negative charge and multivalent nature. Its rejection behavior serves as an indicator of the separation performance for other analogous ions in modified membranes. In literature the rejection of the SO42­ by negatively charged polymeric nanofiltration (NF) membranes has been studied extensively with rejection percentages of >90 %. Silicon carbide (SiC) membranes have gained attention for wastewater treatment due to their high hydrophilicity and negative charge. However, no negatively charged ceramic ultrafiltration (UF) membranes have been tested yet for SO42­ retention. In this study, a commercial alumina (Al2O3) UF membrane was converted into a highly negatively charged tight-UF membrane by coating it with SiC. This was achieved by depositing a 5 μm SiC coating in a single-step via low-pressure chemical vapor deposition (LP-CVD). LP-CVD facilitates the preparation of a SiC at much lower temperatures (700–900 °C) compared to the sol-gel methods (ca. 2100 °C), and it does not require multiple coating cycles and sintering steps to achieve the desired selective layer thickness. Subsequently, properties and performance of the as-prepared tight-UF membrane coated with SiC were evaluated. The SiC coated membrane had a highly negative charge of −70 mV at pH of 6, and a pure water permeability (PWP) of 26 L.m−2.h−1.bar−1. The SiC coated membrane furthermore demonstrated a SO42­ rejection of 79 % despite having a large pore size of 7 nm, in comparison with the pore sizes of below 1 nm of NF membranes. These results highlight the potential of singe-step LP-CVD modification of commercial UF ceramic membranes to produce highly negatively charged SiC coated UF membranes with a high SO42­ rejection, and without a large loss of PWP normally associated with NF membranes.

Stringent industrial wastewater discharge regulations and rising energy costs demand industries to shift to sustainable water treatment technologies. The conventional physical-chemical wastewater treatment processes struggle to separate inorganic ions and emulsions. While polymeric membranes have limited mechanical, thermal and chemical stability. Ceramic membranes, and in particular silicon carbide (SiC) membranes, have emerged as promising alternatives due to their mechanical strength, thermal resilience, resistance to fouling, low isoelectric point, and super hydrophilicity. However, fabricating both SiC membrane supports and the selective layers require sintering temperatures of ca. 2100°C, with consequent high energy consumption. Additionally, preparing a SiC selective layer requires multiple coating and sintering cycles, which hinder precise pore size control and economic feasibility. To address these limitations, this thesis explores low-pressure chemical vapor deposition (LPCVD) as a route to coat commercially available alumina (Al2O3) supports by SiC at moderate temperatures to replace full SiC membranes...

The growing global water crisis necessitates advanced wastewater treatment technologies capable of addressing complex contaminants. Adsorbents and membrane technologies provide viable solutions for wastewater treatment, and their performance can be significantly enhanced through surface modification by atomic layer deposition (ALD). ALD enables nanoscale engineering of materials, offering unprecedented control over surface chemistry, pore structure, and functional properties for improved wastewater treatment efficiency. This review critically examines the advancements in ALD-modified membranes and adsorbents for industrial wastewater treatment, highlighting how ALD enhances adsorption kinetics and selectivity in adsorbents, improves hydrophilicity and antifouling behavior in polymeric membranes, and enhances chemical and mechanical stability in ceramic membranes. Despite these advantages, challenges remain in adoption of ALD in wastewater treatment. Future research should focus on optimizing ALD process parameters and exploring synergies with emerging water purification strategies. The continued development of ALD presents a promising pathway towards more efficient and sustainable wastewater treatment solutions.

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.

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.

Sodium hypochlorite (NaClO) is widely used for the chemical cleaning of fouled ultrafiltration (UF) membranes. Various studies performed on polymeric membranes demonstrate that long-term (>100 h) exposure to NaClO deteriorates the physicochemical properties of the membranes, leading to reduced performance and service life. However, the effect of NaClO cleaning on ceramic membranes, particularly the number of cleaning cycles they can undergo to alleviate irreversible fouling, remains poorly understood. Silicon carbide (SiC) membranes have garnered widespread attention for water and wastewater treatment, but their chemical stability in NaClO has not been studied. Low-pressure chemical vapor deposition (LP-CVD) provides a simple and economical route to prepare/modify ceramic membranes. As such, LP-CVD facilitates the preparation of SiC membranes: (a) in a single step; and (b) at much lower temperatures (700–900 °C) in comparison with sol-gel methods (ca. 2000 °C). In this work, SiC ultrafiltration (UF) membranes were prepared via LP-CVD at two different deposition temperatures and pressures. Subsequently, their chemical stability in NaClO was investigated over 200 h of aging. Afterward, the properties and performance of as-prepared SiC UF membranes were evaluated before and after aging to determine the optimal deposition conditions. Our results indicate that the SiC UF membrane prepared via LP-CVD at 860 °C and 100 mTorr exhibited excellent resistance to NaClO aging, while the membrane prepared at 750 °C and 600 mTorr significantly deteriorated. These findings not only highlight a novel preparation route for SiC membranes in a single step via LP-CVD, but also provide new insights about the careful selection of LP-CVD conditions for SiC membranes to ensure their long-term performance and robustness under harsh chemical cleaning conditions.