Facile preparation of superhydrophilic/underwater superoleophobic cellulose membrane with CaCO3 particles for oil/water separation

A low-cost, easily fabricated sodium alginate-nanoparticle coated paper membrane with superb oil-fouling resistance for efficient oil-in-water emulsion separation

The treatment of kitchen oily wastewater has often been neglected, despite its significant annual discharge and associated environmental risks. This study addresses the issue by developing a novel composite paper membrane, using A4 paper as a substrate coated with a simple and durable hydrogel composite of nanoparticles (SiO2 or TiO2) and sodium alginate. The optimal membrane preparation conditions were determined to be 0.6 wt% sodium alginate and 0.1 wt% nanoparticles, ensuring a stable and effective coating. Oil-in-water emulsions can be effectively separated by the resultant membrane, which exhibits superhydrophilic and underwater superoleophobic properties, with a water contact angle in air close to 14° and an oil contact angle in water close to 150°. According to experimental findings, adding nanoparticles improved the composite membrane's surface roughness and selective wettability. The membrane demonstrated outstanding oil removal efficiency for five types of oil-water emulsions (>95 %) and exhibited excellent reusability (over 15 cycles), without causing significant environmental concerns after prolonged use. This study introduces an inexpensive and eco-friendly hydrogel composite membrane that is easy to fabricate and demonstrates excellent emulsion separation capabilities, regeneration performance, and practical application potential. It is positioned as a viable material for treating oily wastewater because of these qualities.

Transparent Superhydrophilic Coating with Robust and Persistent Anti-Oil-Fouling Properties for Efficient Long-Term Oil/Water Emulsion Separation

Porous membranes with superhydrophilicity and underwater superoleophobicity have attracted considerable attention for efficient oil/water emulsion separation. However, such membranes fail to remediate severe oil contamination in long-term applications and exhibit a serious water flux decline. Herein, a universal combination strategy integrating the high coverage of a mussel-inspired sticky interlayer and a double rigid cellulose nanofiber-amorphous calcium carbonate (CNF-ACC) composite outer layer is proposed to prepare a superhydrophilic coating surface with superior anti-oil-fouling properties on diverse substrates. The introduction of the mussel-inspired interlayer not only provides a stable and complete coverage interface but also offers an anchor to fix the outstanding hydration of the outer CNF-ACC composite layer. The high-coverage and double rigid superior hydration CNF-ACC layer provides excellent anti-oil-fouling characteristics, irrespective of the type of oil, under various conditions, such as water-prewetted or oil-fouled environments. Owing to its superior anti-oil-fouling property, the coating-modified membrane shows efficient and long-term separation of diverse oil/water emulsions without significant flux decline and with a flux recovery ratio of nearly 100%. In addition, this coating exhibits antifogging and high transparency, which may show promising applications in diverse optical devices.

Superhydrophobic and environmentally friendly bovine bone biomass based cellulose membrane for oil-water separation

With the development of superhydrophobic materials for oil-water separation, there is an urgent need to develop environmentally friendly, low-cost, and novel hydrophobic materials. In this paper, based on bovine bone biomass raw materials, bone ash particles are obtained by calcination and grinding, and then bovine bone ash/cotton fabric cellulose membranes are prepared by vacuum filtration and impregnation methods. The pore size of the membrane is regulated and the hydrophobicity of the material is enhanced by constructing the surface microstructures. Results indicate that the membranes possess good hydrophobicity with a contact angle of 161° and the flux can reach 53,635.2 L/m2h for light oil. The separation efficiencies for petroleum ether, cyclohexane, kerosene, and dichloromethane all reach >99 %. In addition, the separation efficiency of the cellulose membrane is still >99 % in the 40-day separation test and always exceeds 90 % for 30 cycling test, indicating that it has good stability and recoverability. Interestingly, the cellulose membrane is prepared from biodegradable and renewable raw materials, which reduces environmental pollution and effectively utilize natural resources.

Construction of biodegradable superhydrophilic/underwater superoleophobic materials with CNF (cellulose nanofiber) fence-like attached on the surface for efficient oil/water emulsion separation

Superhydrophilic/underwater superoleophobic materials for the separation of oil-water emulsions by filtration have received much attention in order to solve the pollution problem of oil-water emulsion. In this paper, a fence-like structure on the surface of CNF/KGM (Konjac Glucomannan) materials by a simple method using CNF instead of metal nanowires was successfully developed based on the hydrogen bonding of KGM and CNF. The resulted organic CNF/KGM materials surface has outstanding superhydrophilic (WCA = 0°) in air and superoleophobicity (OCA≥151°) in water, which could separate oil-water mixtures with high separation efficiency above 99.14 % under the pressure of the emulsion itself. The material shows good mechanical properties because of the addition of CNF and has outstanding anti-fouling property and reusability. More importantly, the material can be completely biodegraded after buried in soil for 4 weeks since both of KGM and CNF are organic substances. Therefore, it may have a broad application prospect in the separation of oil-water emulsion because of its outstanding separation properties, simply preparation method and biodegradability.

A comprehensive review on state-of-the-art antifouling super(wetting and anti-wetting) membranes for oily wastewater treatment

One of the most dangerous types of pollution to the environment is oily wastewater, which is produced from a number of industrial sources and can cause damage to the environment, people, and creatures. To overcome this issue, membrane technology as an advanced method has been considered for treating oily wastewater due to its stability, high removal efficiency, and simplicity in scaling up. Membrane fouling, or the accumulation of oil droplets at or within the membrane pores, compromises the efficiency of membrane separation and water flux. In the last decade, the fabrication of membranes with specific wettability to reduce fouling has received much consideration. The purpose of this article is to offer a literature overview of all fabricated anti-fouling super(wetting and anti-wetting) membranes for applicable membrane processes for the separation of immiscible and emulsified oil/water mixtures. In this review, we first explain membrane fouling and discuss methods for preventing it. Afterwards, in all membrane separation processes, including pressure-driven, gravity-driven, and thermal-driven, membranes based on the form and density of oil are categorized as oil-removing or water-removing with special wettability, and then their wettability modification with different materials is particularly discussed. Finally, the prospect of anti-fouling membrane fabrication in the future is presented.

Rationally designed calcium carbonate multifunctional trap for contaminants adsorption

Adsorption technology has been widely developed to control environmental pollution, which plays an important role in the sustainable development of modern society. Calcium carbonate (CaCO3) is characterized by its flexible pore design and functional group modification, which meet the high capacity and targeting requirements of adsorption. Therefore, its charm of "small materials for great use" makes it a suitable candidate for adsorption. Firstly, we comprehensively review the research progress of controlled synthesis and surface modification of CaCO3, and its application for adsorbing contaminants from water and air. Then, we systematically examine the structure-effect relationship between CaCO3 adsorbents and contaminants, while also intrinsic mechanism of remarkable capacity and targeted adsorption. Finally, from the perspective of material design and engineering application, we offer insightful discussion on the prospects and challenges of calcium carbonate adsorbents, providing a valuable reference for the further research in this field.

Efficient oil-water emulsion treatment via novel composite membranes fabricated by CaCO3-based biomineralization and TA-Ti(IV) coating strategy

Continuous increasing discharge of industrial oily wastewater and frequent occurrence of oil spill accidents have taken heavy tolls on global environment and human health. Organic-inorganic modifications can fabricate superhydrophilic/submerged superoleophobic membranes for efficient oil-water separation/treatment though they still suffer from complex operation, non-environmental friendliness, expensive cost or uneven distribution. Herein, a new strategy regarding tannic acid (TA)-Ti(IV) coating and CaCO₃-based biomineralization through simple inkjet printing processes was proposed to modify polyvinylidene fluoride (PVDF) membrane, endowing the membrane with high hydrophilicity (water contact angle (WCA) decreased from 86.01° to 14.94°) and underwater superoleophobicity (underwater contact angle (UOCA) > 155°). The optimized TA-Ti(IV)-CaCO₃ modified membrane possessed perfect water permeation to various oil/water emulsions (e.g., 355.7 L·m^-2·h^-1 for gasoline emulsion) under gravity with superior separation efficiency (>98.8 %), leading the way in oil/water emulsion separation performance of PVDF membranes modified with polyphenolic surfaces to our knowledge. Moreover, the modified membrane displayed rather high flux recovery after eight cycles of filtration while maintaining the original excellent separation efficiency. The modification process proposed in this study is almost independent of the nature of the substrate, and meets the demand for simple, inexpensive, rapid preparation of highly hydrophilic antifouling membranes, showing abroad application prospect for oil-water emulsion separation/treatment.

Recent progress and future directions of membranes green polymers for oily wastewater treatment

The preparation, modification and application of green polymers such as poly-lactic acid (PLA), chitosan (CS), and cellulose acetate (CA) for oily wastewater treatment is summed up in this review. Due to the low environmental pollution, good chemical resistivity, high hydrophobicity, and good capacity for water-oil emulsion separation of the presented polymers, it then highlights the various membrane production methods and their role in producing effective membranes, with a focus on recent advances in improving membrane properties through the addition of various Nano materials. As a result, the hydrophilic/hydrophobic properties that are critical in the oil separation mechanism are highlighted. Finally, it looks at the predictions and challenges in oil/water separation and recovery. These ideas are discussed with a focus on modern production methods and oil separation proficiency.

Designing waste Bioresource-derived value-added Nanohybrids for efficient photocatalysis water treatment

Although photocatalysis with ultraviolet-visible (UV-vis) light has made considerable advances, it is limited by the low efficiency of UV-vis energy conversion. To overcome this problem, UV-vis light can be replaced with near-infrared (NIR) light. Herein, we coupled eggshell-derived CaCO₃ with a NIR-absorbing CuSe semiconductor and fabricated an insulator-based heterojunction structure. In application case studies of 4-nitrophenol (4-NP) and bacteria, the nanocomposites showed enhanced photocatalysis activity under NIR light induction. A first-principles calculation indicated that photoexcited electrons could transfer from the conduction band of CuSe to the conduction band of CaCO₃. The main reactive species generated by the photocatalysis were ·CO₃^-, and ·OH free radicals. The antibacterial mechanisms of photocatalysis on the cell permeability and DNA layers of the bacterial cells were also revealed. Besides providing novel perspectives and mechanistic understanding of the fabrication of NIR light-driven photocatalysts, this study demonstrates the valorization of eggshell bio-wastes in environmental remediation.

Calcium carbonate: controlled synthesis, surface functionalization, and nanostructured materials

Calcium carbonate (CaCO₃) is an important inorganic mineral in biological and geological systems. Traditionally, it is widely used in plastics, papermaking, ink, building materials, textiles, cosmetics, and food. Over the last decade, there has been rapid development in the controlled synthesis and surface modification of CaCO₃, the stabilization of amorphous CaCO₃ (ACC), and CaCO₃-based nanostructured materials. In this review, the controlled synthesis of CaCO₃ is first examined, including Ca²⁺-CO₃^2- systems, solid-liquid-gas carbonation, water-in-oil reverse emulsions, and biomineralization. Advancing insights into the nucleation and crystallization of CaCO₃ have led to the development of efficient routes towards the controlled synthesis of CaCO₃ with specific sizes, morphologies, and polymorphs. Recently-developed surface modification methods of CaCO₃ include organic and inorganic modifications, as well as intensified surface reactions. The resultant CaCO₃ can then be further engineered via template-induced biomineralization and layer-by-layer assembly into porous, hollow, or core-shell organic-inorganic nanocomposites. The introduction of CaCO₃ into nanostructured materials has led to a significant improvement in the mechanical, optical, magnetic, and catalytic properties of such materials, with the resultant CaCO₃-based nanostructured materials showing great potential for use in biomaterials and biomedicine, environmental remediation, and energy production and storage. The influences that the preparation conditions and additives have on ACC preparation and stabilization are also discussed. Studies indicate that ACC can be used to construct environmentally-friendly hybrid films, supramolecular hydrogels, and drug vehicles. Finally, the existing challenges and future directions of the controlled synthesis and functionalization of CaCO₃ and its expanding applications are highlighted.

A review on super-wettable porous membranes and materials based on bio-polymeric chitosan for oil-water separation

Appropriate surface wettability of membranes and materials are of an extreme importance for targeting separation of mixtures/emulsions such as oil from water or conversely water from oil. The development of super-wettable membranes and materials surfaces have shown remarkable potential for recovering water from oil-water emulsion while offering maximum resistance to fouling. The availability of clean and potable water has been regarded as an important global challenge for coming human generations. Oil and gas industry is continuously producing immense quantities of waste stream regarded as produced water which contains oil dispersed in water along with other several components. Treating such immense quantities of oily wastewater is of utmost need for recovering precious water for possible reuse or safe disposal. Various technologies have been developed for targeting the separation of oil-water emulsions or mixtures to harness useful potable water and oil as products. Membrane-based separations or use of porous materials such as mesh have been explored in literature for separation of oil-water mixtures/emulsions. Given the unique features of special hydrophilicity, ease of tunability, control of molecular weight, abundant availability, and potential for commercial scale up, chitosan has been extensively used for modifying membranes/meshes or preparing composites with other materials for oil-water separations. This review has described in detail the synthesis, methods of modification and application of chitosan-based super-wettable membranes/meshes and porous materials for oil-water separation. The special wettability features including super-hydrophobicity/superoleophilicity, super-oleophobicity/super-hydrophilicity and super-hydrophilicity/underwater super-oleophobicity of various chitosan-based membranes and materials have been discussed in detail in the review. The strategies for enhancing or developing special wettability for target specific applications have also been discussed. Finally, the challenges, their respective importance have been identified along with a discussion on possible solutions to these challenges.

Room-temperature growth of fluorapatite/CaCO3 heterogeneous structured composites inspired by human tooth

Organisms can synthesize heterogeneous structures with excellent mechanical properties through mineralization, the most typical of which are teeth. The tooth is an extraordinarily resilient bi-layered material that is composed of external enamel perpendicular to the tooth surface and internal dentin parallel to the tooth surface. The synthesis of enamel-like heterostructures with good mechanical properties remains an elusive challenge. In this study, we applied a biomimetic mineralization method to grow fluorapatite/CaCO₃ (FAP/CaCO₃) heterogeneous structured thin films that mimic their biogenic counterparts found in teeth through a three-step pathway: coating a polymer substrate, growing a layered calcite film, and mineralization of a fluorapatite columnar array on the calcite layer. The synthetic heterostructure composites combine well and exhibit good mechanical properties comparable to their biogenic counterparts. The FAP/CaCO₃ heterogeneous structured composite exhibits excellent mechanical properties, with a hardness and Young's modulus of 1.99 ± 0.02 GPa and 47.5 ± 0.6 GPa, respectively. This study provides a reasonable new idea for unique heterogeneous structured materials designed at room temperature.

Fluorapatite/CaCO₃ thin films were synthesized by mimicking their biogenic counterparts found in teeth using a biomimetic mineralization method. The synthetic heterostructure composites combine well and exhibit excellent mechanical properties.

Influence of Membrane Vibration on Particles Rejection Using a Slotted Pore Membrane Microfiltration

A new method is proposed to increase the rejection in microfiltration by applying membrane oscillation, using a new type of microfiltration membrane with slotted pores. The oscillations applied to the membrane surface result in reduced membrane fouling and increased separation efficiency. An exact mathematical solution of the flow in the surrounding solution outside the oscillating membrane is developed. The oscillation results in the appearance of a lift velocity, which moves oil particles away from the membrane. The latter results in both reduced membrane fouling and increased oil droplet rejection. This developed model was supported by the experimental results for oil water separation in the produced water treatment. It was proven that the oil droplet concentration was reduced notably in the permeate, due to the membrane oscillation, and that the applied shear rate caused by the membrane oscillation also reduced pore blockage. A four-times lower oil concentration was recorded in the permeate when the membrane vibration frequency was 25 Hz, compared to without membrane vibration. Newly generated microfiltration membranes with slotted pores were used in the experiments.

Cellulose-based special wetting materials for oil/water separation: A review

Oil spill accidents and oily wastewater discharged by petrochemical industries have severely wasted water resources and damaged the environment. The use of special wetting materials to separate oil and water is efficient and environment-friendly. Cellulose is the most abundant renewable resource and has natural advantages in removing pollutants from oily wastewater. The application and modification of cellulose as special wetting materials have attracted considerable research attention. Therefore, we summarized cellulose-based superlipophilic/superhydrophobic and superhydrophilic/superoleophobic materials exhibiting special wetting properties for oil/water separation. The treatment mechanism, preparation technology, treatment effect, and representative projects of oil-bearing wastewater are discussed. Moreover, cellulose-based intelligent-responsive materials for application to oil/water separation and the removal of other pollutants from oily wastewater have also been summarized. The prospects and potential challenges of all the materials have been highlighted.

Synthesis of Si-Based High-Efficiency and High-Durability Superhydrophilic-Underwater Superoleophobic Membrane of Oil-Water Separation

Oil pollution is caused by the frequent discharge of contaminated industrial wastewater and accidental oil spills and is a severe environmental and health concern. Therefore, efficient materials and processes for effective oil–water separation are being developed. Herein, SiO₂-Na₂SiO₃-coated stainless steel fibers (SSF) with underwater superoleophobic and low-adhesion properties were successfully prepared via a one-step hydrothermal process. The modified surfaces were characterized with scanning electron microscopy (SEM), and contact angle measurements to observe the surface morphology, confirm the successful incorporation of SiO₂, and evaluate the wettability, as well as with X-ray diffraction (XRD). The results revealed that SiO₂ nanoparticles were successfully grown on the stainless-steel fiber surface through the facile hydrothermal synthesis, and the formation of sodium silicate was detected with XRD. The SiO₂-Na₂SiO₃-coated SSF surface exhibited superior underwater superoleophobic properties (153–162°), super-hydrophilicity and high separation efficiency for dichloromethane–water, n-hexane–water, tetrachloromethane–water, paroline–water, and hexadecane–water mixtures. In addition, the as-prepared SiO₂-Na₂SiO₃-coated SSF demonstrated superior wear resistance, long-term stability, and re-usability. We suggest that the improved durability may be due to the presence of sodium silicate that enhanced the membrane strength. The SiO₂-Na₂SiO₃-coated SSF also exhibited desirable corrosion resistance in salty and acidic environments; however, further optimization is needed for their use in basic media. The current study presents a novel approach to fabricate high-performance oil–water separation membranes.