Lower-temperature preparation of SiC ceramic membrane using zeolite residue as sintering aid for oil-in-water separation

Advanced Low-Cost Natural Materials for High-Performance Oil-Water Filtration Membranes: Achievements, Challenges, and Future Directions

The development of affordable ceramic membranes is essential for reducing expenses and optimizing the treatment of oily wastewater. There is an urgent demand for membranes that are not only affordable and easy to operate but also stable and capable of managing high fluxes to address the increasing volumes of oily wastewater. The significant production demands associated with many commercially available ceramic membranes, primarily due to the use of specialised raw materials and intricate processing methods, limiting their suitability for many wastewater treatment applications. Consequently, there is a rising interest in creating innovative ceramic membranes using affordable materials and simpler production techniques. This study reviewed the oil-water ceramic membranes utilizing affordable natural ceramic materials aimed at improving membrane performance. It focused on reviewing the environmentally friendly and economically viable membranes derived from natural ceramic resources as an alternative to conventional synthetic membranes. These natural ceramic materials possess crucial properties like hydrophilicity and oleophobicity, which are vital for effective oil-water separation. The ceramic membranes were reviewed for their filtration performance and advantages. It was reported that these natural ceramic material-based membranes demonstrate superior separation efficiency, and strong mechanical stability, making them promising candidates for sustainable water treatment.

Pervaporation Separation of Isopropanol/Water Using Zeolite Nanosheets: A Molecular Simulation Study

Reducing greenhouse gas emissions plays a crucial role in slowing down the rise of the global temperature. One of the viable options is to employ renewable energy sources such as alcohols that can be produced from biomass. Specifically, one of the most common alcohols is isopropanol (IPA). Energy-intensive distillation processes are however involved in its production because of the rather low product concentration from fermentation. Membrane technologies, specifically pervaporation (PV), represent a promising alternative to the IPA/water separation. Particularly, employing zeolite nanosheets as PV membranes may provide great opportunities to extract IPA owing to their ultrathin and hydrophobic nature. By employing molecular dynamics simulations, this study conducts a systematic study on a diverse set of nanosheet candidates with the aim of exploring their potential and identifying top-performing structures. The best candidate among structures studied herein is predicted to offer an exceptional IPA/water selectivity of more than 400 with an unprecedentedly large flux. Structure-property-performance relationships have also been established to offer insights into the rational design of PV membranes with improved performance.

Investigating the Corrosion Resistance of Different SiC Crystal Types: From Energy Sectors to Advanced Applications

Silicon carbide, as a third-generation semiconductor material, plays a pivotal role in various advanced technological applications. Its exceptional stability under extreme conditions has garnered a significant amount of attention. These superior characteristics make silicon carbide an ideal candidate material for high-frequency, high-power electronic devices and applications in harsh environments. In particular, corrosion resistance in natural or artificially acidic and alkaline environments limits the practical application of many other materials. In fields such as chemical engineering, energy conversion, and environmental engineering, materials often face severe chemical erosion, necessitating materials with excellent chemical stability as foundational materials, carriers, or reaction media. Silicon carbide exhibits outstanding performance under these conditions, demonstrating significant resistance to corrosive substances such as hydrochloric acid, sulfuric acid, nitric acid, and alkaline substances such as potassium hydroxide and sodium hydroxide. Despite the well-known chemical stability of silicon carbide, the stability conditions of its different types (such as 3C-, 4H-, and 6H-SiC polycrystals) in acidic and alkaline environments, as well as the specific corrosion mechanisms and differences, warrant further investigation. This Review not only delves deeply into the detailed studies related to this topic but also highlights the current applications of different silicon carbide polycrystals in chemical reaction systems, energy conversion equipment, and recycling processes. Through a comprehensive analysis, this Review aims to bridge research gaps, offering a comparative analysis of the advantages and disadvantages between different polymorphs. It provides material scientists, engineers, and developers with a thorough understanding of silicon carbide's behavior in various chemical environments. This work will propel the research and development of silicon carbide materials under extreme conditions, especially in areas where chemical stability is crucial for device performance and durability. It lays a solid foundation for ultra-high-power, high-integration, high-reliability module architectures, supercomputing chips, and highly safe long-life batteries.

Development of Hydrophobic Coal-Fly-Ash-Based Ceramic Membrane for Vacuum Membrane Distillation

Membrane distillation is an emerging separation technology with a high separation factor in water desalination. Ceramic membranes are increasingly used in membrane distillation because of high thermal and chemical stabilities. Coal fly ash is a promising ceramic membrane material with low thermal conductivity. In this study, three hydrophobic coal-fly-ash-based ceramic membranes were prepared for saline water desalination. The performances of different membranes in membrane distillation were compared. The effects of membrane pore size on permeate flux and salt rejection were researched. The coal-fly-ash-based membrane showed both a higher permeate flux and a higher salt rejection than the alumina membrane. As a result, using coal fly ash as the material for membrane fabrication can effectively increase the performance when applied to MD. Increasing the membrane pore size improved the permeate flux, but reduced the salt rejection. When the mean pore size increased from 0.15 μm to 1.57 μm, the water flux rose from 5.15 L·m^-2·h^-1 to 19.72 L·m^-2·h^-1, but the initial salt rejection was reduced from 99.95% to 99.87%. The hydrophobic coal-fly-ash-based membrane with a mean pore size of 0.18 μm exhibited a water flux of 9.54 L·m^-2·h^-1 and a salt rejection of higher than 98.36% in membrane distillation.

Ag-CuO-Decorated Ceramic Membranes for Effective Treatment of Oily Wastewater

Although ultrafiltration is a reliable method for separating oily wastewater, the process is limited by problems of low flux and membrane fouling. In this study, for the first time, commercial TiO₂/ZrO₂ ceramic membranes modified with silver-functionalized copper oxide (Ag-CuO) nanoparticles are reported for the improved separation performance of emulsified oil. Ag-CuO nanoparticles were synthesized via hydrothermal technique and dip-coated onto commercial membranes at varying concentrations (0.1, 0.5, and 1.0 wt.%). The prepared membranes were further examined to understand the improvements in oil-water separation due to Ag-CuO coating. All modified ceramic membranes exhibited higher hydrophilicity and decreased porosity. Additionally, the permeate flux, oil rejection, and antifouling performance of the Ag-CuO-coated membranes were more significantly improved than the pristine commercial membrane. The 0.5 wt.% modified membrane exhibited a 30% higher water flux (303.63 L m^-2 h^-1) and better oil rejection efficiency (97.8%) for oil/water separation among the modified membranes. After several separation cycles, the 0.5 wt.% Ag-CuO-modified membranes showed a constant permeate flux with an excellent oil rejection of >95% compared with the unmodified membrane. Moreover, the corrosion resistance of the coated membrane against acid, alkali, actual seawater, and oily wastewater was remarkable. Thus, the Ag-CuO-modified ceramic membranes are promising for oil separation applications due to their high flux, enhanced oil rejection, better antifouling characteristics, and good stability.

Development of advanced oil/water separation technologies to enhance the effectiveness of mechanical oil recovery operations at sea: Potential and challenges

Mechanical oil recovery (i.e., booming and skimming) is the most common tool for oil spill response. The recovered fluid generated from skimming processes may contain a considerable proportion of water (10 % ~ 70 %). As a result of regulatory prohibition on the discharge of contaminated waters at sea, vessels and/or storage barges must make frequent trips to shore for oil-water waste disposal. This practice can be time- consuming thus reduces the overall efficiency and capacity of oil recovery. One potential solution is on-site oil-water separation and disposal of water fraction at sea. However, currently available decanting processes may have limited oil/water separation capabilities, especially in the presence of oil-water emulsion, which is inevitable in mechanical oil recovery. The decanted water may not meet the discharge standards and cause severe ecotoxicological impacts. This paper therefore comprehensively reviews the principles and progress in oil/water separation, demulsification, and on-site treatment technologies, investigates their applicability on decanting at sea, and discusses the ecotoxicity of decanted water in the marine environment. The outputs provide the fundamental and practical knowledge on decanting and help enhance response effectiveness and consequently reducing the environmental impacts of oil spills.

Silicon carbide microfiltration membranes for oil-water separation: Pore structure-dependent wettability matters

Both the pore size and surface properties of silicon carbide (SiC) membranes are demonstrated to significantly affect their separation efficiency when used for oily water treatment. However, the potential influences of open porosity together with the pore size of SiC membranes on their surface properties and oil-water separation performance have rarely been investigated. In this work, porous SiC ceramic membranes with tunable open porosity and pore size were purposely prepared and selected to systematically study the effect of pore structure-dependent wettability on the oil-water separation performance. The measured pure water flux of selected membranes as a function of open porosity (34-48%) and pore size (0.43-0.67 μm) was well-fitted by using a modified H-P equation. Interestingly, the hydrophilicity of SiC membranes was improved with the increase in open porosity and pore size, as evidenced by the gradually decreased dynamic water contact angle and underwater adhesion of oil droplets. Further, the open porosity of SiC membranes was found to contribute more to the improved surface wettability. As a result, the stable flux of SiC membranes in oil-in-water (O/W) emulsions was increased by 24% with the increased open porosity while the oil rejection rate remained above 90%. This work quantitatively reveals the contributions of the pore structure to the surface wettability of ceramic membranes, and thus provides an effective pathway to improve their performance in oil-water separation.

Robust zirconia ceramic membrane with exceptional performance for purifying nano-emulsion oily wastewater

While membrane-based oil-water separation has been widely explored, using conventional membranes to treat oily wastewaters remains practically challenging especially when such wastewaters contain more stable nano-sized oil droplets and are of high oil content, and harsh chemical conditions. Herein, we report a novel protocol of efficiently separating both synthetic and real oil nano-emulsions via specially designed robust zirconia membranes. The best-performing zirconia membrane, fabricated at low sintering temperature, has relatively uniform sub-100 nm pores and is underwater superoleophobic. Such zirconia membranes possess not only outstanding separation performance under long-term operation but robust structural stability at harsh conditions. At different cross-flow velocities, a combined model of intermediate pore blocking and cake filtration dominated membrane fouling behavior. Specifically, at high pH value (especially > pH_(IEP)), membrane fouling was effectively mitigated due to a dominant role of electrostatic repulsion interaction at membrane-oil interface. Compared with conventional and commercial ceramic membranes, our zirconia membrane is the first reported in literature that can effectively reject nano-sized oil droplets (∼18 nm) with over 99% rejection. Moreover, the zirconia membrane has also been challenged with real degreasing wastewater with very high oil content (∼4284 mg L^-1) and pH (∼12.4) and delivered consistently high separation performance over many operation cycles.

Ceramic Processing of Silicon Carbide Membranes with the Aid of Aluminum Nitrate Nonahydrate: Preparation, Characterization, and Performance

The development of a low-cost and environmentally-friendly procedure for the fabrication of silicon carbide (SiC) membranes while achieving good membrane performance is an important goal, but still a big challenge. To address this challenge, herein, a colloidal coating suspension of sub-micron SiC powders was prepared in aqueous media by employing aluminum nitrate nonahydrate as a sintering additive and was used for the deposition of a novel SiC membrane layer onto a SiC tubular support by dip-coating. The sintering temperature influence on the structural morphology was studied. Adding aluminum nitrate nonahydrate reduced the sintering temperature of the as-prepared membrane compared to conventional SiC membrane synthesis. Surface morphology, pore size distribution, crystalline structure, and chemical and mechanical stability of the membrane were characterized. The membrane showed excellent corrosion resistance in acidic and basic medium for 30 days with no significant changes in membrane properties. The pure water permeance of the membrane was measured as 2252 L h-1 m-2 bar-1. Lastly, the final membrane with 0.35 µm mean pore size showed high removal of oil droplets (99.7%) in emulsified oil-in-water with outstanding permeability. Hence, the new SiC membrane is promising for several industrial applications in the field of wastewater treatment.

Recent developments in porous ceramic membranes for wastewater treatment and desalination: A review

The development of membrane technology has proved vital in providing a sustainable and affordable supply of clean water to address the ever-increasing demand. Though liquid separation applications have been still dominated by polymeric membranes, porous ceramic membranes have gained a commercial foothold in microfiltration (MF) and ultrafiltration (UF) applications due to their hydrophilic nature, lower fouling, ease of cleaning, reliable performance, robust performance with harsh feeds, relative insensitivity to temperature and pH, and stable long-term flux. The enrichment of research and development on porous ceramic membranes extends its focus into advanced membrane separation technologies. The latest emerging nanofiltration (NF) and membrane distillation (MD) applications have witnessed special interests in constructing porous membrane with hydrophilic/functional/hydrophobic properties. However, NF and MD are relatively new, and many shortcomings must be addressed to compete with their polymeric counterparts. For the last three years (2018-2020), state-of-the-art literature on porous ceramic membranes has been collected and critically reviewed. This review highlights the efficiency (permeability, selectivity, and antifouling) of hydrophilic porous ceramic membranes in a wide variety of wastewater treatment applications and hydrophobic porous ceramic membranes in membrane distillation-based desalination applications. A significant focus on pores characteristics, pore sieving phenomenon, nano functionalization, and synergic effect on fouling, the hydrophilic porous ceramic membrane has been discussed. In another part of this review, the role of surface hydrophobicity, water contact angle, liquid entry pressure (LEP), thermal properties, surface micro-roughness, etc., has been discussed for different types of hydrophobic porous ceramic membranes -(a) metal-based, (b) silica-based, (c) other ceramics. Also, this review highlights the potential benefits, drawbacks, and limitations of the porous membrane in applications. Moreover, the prospects are emphasized to overcome the challenges in the field.