Self-cleaning Performance Research Articles

Durable daytime radiative cooling achieved by super-slippery coatings containing polydimethylsiloxane brushes

Radiative cooling technology is an effective method for mitigating global warming and the urban heat island effect. It achieves cooling through self-radiation and reflection solar energy without consuming energy. However, preparing a long-lasting and durable radiative cooling material remains a challenge. Here, we prepared a super-slippery radiative cooling (SSRC) coating with self-cleaning capability and mechanical stability for future large-scale and long-lasting applications of radiative cooling. The coating containing epoxy, polydimethylsiloxane (PDMS) brushes, and TiO2 exhibit high solar reflectance and infrared emissivity. Especially, the surface microstructures of the coatings enhance the emissivity in the atmospheric window. The high solar reflectivity (90 %) and infrared emissivity (93 %) of the SSRC coatings ensure effective cooling, with coatings on metal surfaces cooling down to an average of 10.4 °C outdoors. For the fruit preservation, the SSRC coating can even extend the shelf life of fruits by up to 10 days. More importantly, due to the low surface energy and high mobility of PDMS brushes, the coating exhibits excellent super-slippery and self-cleaning performances. Water and oil can easily slide on the surface of the SSRC coating. This approach prevents the coverage of contaminants, which is crucial for using radiative cooling coatings outdoors. Furthermore, the SSRC coating exhibits exceptional mechanical stability and can maintain a consistently low coefficient of friction during a 5-hour tribological test. After being impacted with water and sand outdoors for a long time, the coating retains its cooling and self-cleaning properties. Such durable and self-cleaning radiative cooling coating has potential for future applications in thermal management.

Excellent self-cleaning surface achieved through the synergistic effect of superhydrophilicity and photocatalysis of PVDF-TiO2-HAP coating

With the increasing demand for living environment, high-performance self-cleaning coatings have become an urgent need in the development of new building industry. Herein, a TiO2-HAP-PVDF self-cleaning coating was successfully developed using a facile precursor mixing method, where porous hydroxyapatite (HAP) was used to facilitate the adsorption of pollutants, TiO2 served as photocatalyst to decompose pollutants, and polyvinylidene fluoride (PVDF) served as adhesive to combine TiO2 with HAP. Owing to the synergistic effect of superhydrophilicity and photocatalysis, the TiO2-HAP-PVDF coating displays outstanding self-cleaning performance. Furthermore, the as-fabricated coating attached to aluminum veneer not only resists mechanical abrasion such as rainwater, sand flow and sandpaper, but also exhibits good stability in the extremely temperatures from -196 to 150 °C, as well as in strong acid and alkaline solutions, and even presents satisfactory performance after 8000 hours of outdoor service test. These merits open exciting possibilities for the industrial application of self-cleaning coating.

Facile sol-gel synthesis of highly durable anti-reflection films with enhanced self-cleaning performance for perovskite solar cells

Facile sol-gel synthesis of highly durable anti-reflection films with enhanced self-cleaning performance for perovskite solar cells

Scalable multifunctional MOFs-textiles via diazonium chemistry

Cellulose fiber-based textiles are ubiquitous in daily life for their processability, biodegradability, and outstanding flexibility. Integrating cellulose textiles with functional coating materials can unlock their potential functionalities to engage diverse applications. Metal-organic frameworks (MOFs) are ideal candidate materials for such integration, thanks to their unique merits, such as large specific surface area, tunable pore size, and species diversity. However, achieving scalable fabrication of MOFs-textiles with high mechanical durability remains challenging. Here, we report a facile and scalable strategy for direct MOF growth on cotton fibers grafted via the diazonium chemistry. The as-prepared ZIF-67-Cotton textile (ZIF-67-CT) exhibits excellent ultraviolet (UV) resistance and organic contamination degradation via the peroxymonosulfate activation. The ZIF-67-CT is also used to encapsulate essential oils such as carvacrol to enable antibacterial activity against E. coli and S. aureus. Additionally, by directly tethering a hydrophobic molecular layer onto the MOF-coated surface, superhydrophobic ZIF-67-CT is achieved with excellent self-cleaning, antifouling, and oil-water separation performances. More importantly, the reported strategy is generic and applicable to other MOFs and cellulose fiber-based materials, and various large-scale multi-functional MOFs-textiles can be successfully manufactured, resulting in vast applications in wastewater purification, fragrance industry, and outdoor gears.

Polyphenol mediated α-FeOOH/g-C3N4 heterojunction membrane for fast purification of surfactant-stabilized O/W emulsions with super-wetting and Photo-Fenton self-cleaning functions

In the practical purification of oily wastewater, the application of polymer-based membrane is greatly restricted due to the oil adhesion and complicated fouling problems. Herein, to conquer the aforementioned challenges, we prepared the polyphenol mediated Photo-Fenton self-cleaning and superhydrophilic/underwater superoleophobic α-FeOOH/g-C3N4@PVDF composite membrane via simple vacuum-assisted self-assembly technology. The g-C3N4 nanosheets modified by tannic acid were introduced into the surface of PVDF ultrafiltration membrane, in which the intercalation structure was regulated by the random interpenetration of α-FeOOH nanorods. The abundant hydroxyl and amino groups and the rough micro-nano structure formed by intercalation structure were favorable for the superhydrophilic feature (WCA = 0°, UOCA>150°), thus resulting in ultra-low oil adhesion. Specially, the intercalation structure improved the water permeation channel, further promoting the water/oil separation flux. Therefore, the composite membrane exhibited superior separation flux (452.35–650.21 L m−2 h−1) and separation efficiency (>99.06 %) for various surfactant-stabilized emulsions. Moreover, thanks to the Photo-Fenton reaction, the composite membrane showed excellent degradation efficiency on simulated pollutants (various dyes) within 60 min (MeB: 95.55 %, CR: 90.83 %, MO: 98.90 %, CV: 95.11 %), showing satisfactory photocatalytic self-cleaning performance. This work provides a strategy for the potential application of polymer-based membranes in the treatment of complex surfactant-stabilized emulsion wastewater from petrochemical industry.

A Sunlight-Driven Self-Cleaning CuCo-MOF Composite Membrane for Highly Efficient Emulsion Separation and Water Purification.

The fouling phenomenon of membranes has hindered the rapid development of separation technology in wastewater treatment. The integration of materials into membranes with both excellent separation performance and self-cleaning properties still pose challenges. Here, a self-assembled composite membrane with solar-driven self-cleaning performance is reported for the treatment of complex oil-water emulsions. The mechanical robustness of the composite membrane is enhanced by the electrostatic attraction between chitosan and metal-organic frameworks (MOF) CuCo-HHTP as well as the crosslinking effect of glutaraldehyde. Molecular dynamics (MD) simulations also revealed the hydrogen bonding interaction between chitosan and CuCo-HHTP. The composite membrane of CuCo-HHTP-5@CS/MPVDF exhibits a high flux ranging from 700.6 to 2350.6 L∙m-2∙h-1∙bar-1 and excellent separation efficiency (>99.0%) for various oil-water emulsions, including crude oil, kerosene, and other light oils. The addition of CuCo-HHTP shows remarkable photothermal effects, thus demonstrating excellent solar-driven self-cleaning capability and antibacterial performance (with an efficiency of ≈100%). Furthermore, CuCo-HHTP-5@CS/MPVDF can activate peroxomonosulfate (PMS) under sunlight, quickly removing oil-fouling and dyes. Density functional theory (DFT) calculations indicate that the bimetallic sites of Cu and Co in CuCo-HHTP effectively promoted the activation of PMS. This study provides distinctive insights into the multifaceted applications of MOFs-derived photothermal anti-fouling composite membranes.

Liquid gated membrane with self-cleaning properties for controllable removal and multi-component separation of organic/bacterial contaminants

Membrane technology plays an important role in sustainable water treatment; however, the non-adjustable pores make it difficult to achieve precise molecular separation, and membrane fouling remains a challenge in membrane processes. Herein, a smart liquid gated membrane (LGM) was prepared by filling different lubricants in the micropores of PET track-etched membrane that was pre-treated with nano roughening and fluorination. When the pressure exceeds a critical breakthrough pressure, the liquid lined pores are formed, and higher gating liquid/water interfacial tension requires higher pressure to break through the gate. The effective pore size of LGM increases with increasing pressure. When the pressure is removed, the liquid refilling that leads to pore-closing is promoted by lower lubricant viscosity and larger effective pore size. Through the tunable permeability, controllable removal and multi-component separation of organic/bacterial contaminants can be achieved. The maximum rejection for protein approaches 94 %; as the pressure increases, three components are separated in the order of pectin, soy protein isolate and Staphylococcus aureus with maximum separation coefficient of 56.7. Due to the stable lubricant lining, LGM shows excellent self-cleaning performance with much higher flux recovery rate than the non-lubricated membranes. This liquid gated membrane has great application prospects in size-fractionated separation and product recovery.

A Hydrogel-coated Wood Membrane with Intelligent Oil Pollution Detection for Emulsion Separation.

Considering the potential threats posed by oily wastewater to the ecosystem, it is urgently in demand to develop efficient, eco-friendly, and intelligent oil/water separation materials to enhance the safety of the water environment. Herein, an intelligent hydrogel-coated wood (PPT/PPy@DW) membrane with self-healing, self-cleaning, and oil pollution detection performances is fabricated for the controllable separation of oil-in-water (O/W) emulsions and water-in-oil (W/O) emulsions. The PPT/PPy@DW is prepared by loading polypyrrole (PPy) particles on the delignified wood (DW) membranes, further modifying the hydrogel layer as an oil-repellent barrier. The layered porous structure and selective wettability endow PPT/PPy@DW with great separation performance for various O/W emulsions (≥98.69% for separation efficiency and ≈1000Lm-2h-1bar-1 for permeance). Notably, the oil pollution degree of PPT/PPy@DW can be monitored in real-time based on the changed voltage generated during O/W emulsion separation, and the oil-polluted PPT/PPy@DW can be self-cleaned by soaking in water to recover its separation performance. The high affinity of PPT/PPy@DW for water makes it effective in trapping water from the mixed surfactant-stabilized W/O emulsions. The prepared eco-friendly and low-cost multifunctional hydrogel wood membrane shows promising potential in on-demand oil/water separation and provides new ideas for the functional improvement of new biomass oil/water separation membrane materials.

Fabrication of CNTs/MMT/PPS composite hydrophobic coatings on metal with enhanced anticorrosive and self-cleaning performance

Although much work has been reported on anticorrosive coatings at this stage, most materials are confronted with a variety of harsh environments in practical applications, posing extreme challenges to the various properties of the coatings. In this study, carbon nanotube/montmorillonite/polyphenylene sulfide (CNTs/MMT/PPS) composite coatings were prepared by air spraying method. CNTs-MMT composite fillers with nanostructures were prepared by the amide reaction of 3-aminopropyltriethoxysilane (APTES) modified MMT and carboxylated CNTs. The particle size distribution test demonstrated that the amidated CNTs-MMT exhibited superior dispersion performance compared to CNTs and MMT alone, resulted in a more homogeneous and dense coating. The coatings obtained by combining the low surface energy of polytetrafluoroethylene (PTFE) exhibits hydrophobicity and has excellent self-cleaning properties. The electrochemical corrosion current density of the composite coating was three orders of magnitude lower than that of bare iron, and the corrosion efficiency was 99.43 %, demonstrating excellent corrosion resistance. The thermogravimetric test results showed that the CNTs/MMT/PPS composite coatings displayed excellent thermal stability up to 530 °C. Therefore, the CNTs/MMT/PPS composite coating possesses significant advantages in the field of anti-corrosion due to its enhanced durability, heat resistance, and corrosion resistance.

Membrane hybrid system assembled with MXene@h-BN for efficient typical pharmaceuticals removal and self-cleaning: Synergetic effect on adsorption-photocatalytic process

Membrane filtration is regarded as one of the promising technologies for water treatment. However, insufficient micropollutants removal and membrane fouling still limited the further application. Herein, this study engineered a novel membrane hybrid system integrating typical pharmaceuticals removal and membrane self-cleaning by assembled layered MXene and hexagonal boron nitride (h-BN). By doping a small amount of MXene into h-BN (mass ratio of 1 to 10), the synergetic process of adsorption and photocatalytic degradation were achieved. Based on experimental and density functional theory (DFT) calculation results, the chemisorption-photodegradation performance of the membrane hybrid system assembled with 1/10 MXene@h-BN was significantly enhanced due to the termination group and conductive property of MXene. In addition, trimethoprim (TMP) degradation by the above membrane followed the Langmuir–Hinshelwood model, indicating pollutants removal initiated not only on the membrane surface but also in the bulk solution under simulated solar irradiation. This phenomenon was attributed to the generation of •OH and 1O2 by forming Ohmic contact with altered internal band structure. The durability and practical experiments with secondary effluent from local wastewater treatment were also tested. The exceptional self-cleaning performance of the membrane hybrid system assembled with 1/10 MXene@h-BN was demonstrated by lower membrane fouling and maintaining durability even after five cycles. Furthermore, the performance (both pollutants removal and flux) of the modified membrane for secondary effluent treatment was also considerable, validating its potential for practical application. Owing to the excellent features, the membrane assembled with MXene@h-BN is anticipated to be an ideal candidate for advanced wastewater treatment.

Investigation of photocatalytic and visible light self-cleaning performance of 2D/2D g-C3N4-ZrO2 based PES/PDA membranes for organic contaminants degradation

This study fabricated a novel photocatalytic, self-cleaning membrane by depositing a 2D-2D g-C3N4/ZrO2 photocatalyst on polydopamine-coated polyethersulfone. The morphologies and surface chemistry of the membranes were studied through FESEM-EDX, AFM, and XPS. The results showed the satisfactory binding stability of the photocatalyst on the polyethersulfone/polydopamine. Also, depositing of the photocatalyst on the polyethersulfone/polydopamine strongly enhanced hydrophilicity. The optimized photocatalytic membrane (39.68 Lm2h) had a substantially higher water flux than polyethersulfone (13.61 Lm2h) and polyethersulfone/polydopamine (19.42 Lm2h). The photocatalytic membranes showed high dye removal and protein rejection rates. The flux recovery ratio was 83.32 % after 30 min of visible-light exposure. The conversion of irreversible contaminants into reversible ones under visible-light demonstrated the self-cleaning nature of the membrane. In addition, the photocatalytic membrane showed substantial stability in the vibration and shear force tests. Therefore, the polyethersulfone/polydopamine/(g-C3N4/ZrO2) membrane is a promising candidate for removing organic contaminants from water due to high rejection, water flux rate, and satisfactory stability. This study not only proposed an efficient methodology to fabricate a novel photocatalytic self-cleaning membrane with high stability but also provided further insights into the effects of the 2D structure of photocatalyst on the flux and photocatalytic degradation performance of such membranes.

Biomimetic Slippery Surface with Exclusive Liquid-Repellent and Self-Cleaning Properties for Antifouling.

The nature always offers amazing inspiration, where it is highly desirable to endow coatings on marine equipment with powerful functions. An excellent example is slippery zone of Nepenthes pitcher, which possesses novel liquid-repellent and self-cleaning performance. Therefore, this study presents an efficient fabrication method to prepare a novel coating. The coatings were fabricated by designing biomimetic textures extracted from the lunate bodies of slippery zone on polydimethylsiloxane (PDMS) and then grafting Dictyophora indusiata polysaccharide (DIP) modifier. The as-prepared slippery coatings exhibited outstanding antifouling properties against kinds of daily life pollutants such as Chlorella and coffee. This synergistic strategy was proposed combined with environmentally friendly modifier grafting and heterogeneous microstructure on the surface to broaden new probabilities for manufacturing slippery coatings with incredible protective functionality.

In-situ preparation of titanic-based superhydrophilic self-cleaning glaze via a simple one-time firing route

The cleaning of traditional ceramics consumes much water and detergents. It is valuable to consider how to endow the ceramics with self-cleaning character. In this paper, titanic-based-crystallites (CaTi(SiO5) or TiO2) superhydrophilic glazes with superior self-cleaning properties were in situ prepared by a simple one-time firing method. There is no any extra treatment involved in the preparation process. It was found that the precipitation of titanic-based crystallites in the glaze could be adjusted by controlling the cooling system. The transformation mechanism of the phase was analyzed based on the phase separation state. Stress conditions of a dirt cell on surfaces with different roughness were discussed. The correlation between geometric structure and self-cleaning performance demonstrated that the multi-level structure is vital for self-cleaning performance. The self-cleaning mechanism of the superhydrophilic glaze was proposed. The titanic-based crystallite glazes possess superhydrophilic characteristics (<8.0 °), high hardness (642.44–707.85 kgf·mm−2), and excellent self-cleaning performance to oily ink stamps and relatively good performance to human fecal simulacrum, the miso sauce, due to the multi-level structure with nano-scale surface roughness, showing a good application potential on the self-cleaning domain, i.e. glass and traditional ceramic, etc.

Study on Preparation Technology of Novel Fluorosilicone Rubber Composite Insulator

Abstract Currently, commonly used external insulation materials for power products lack operational stability compared to high-temperature vulcanized silicone rubber. The excellent hydrophobicity of PTFE provides a direction for further enhancing high-temperature vulcanized silicone rubber. By utilizing fluorinated occupation directional design technology and improving the dispersion degree of the dispersed phase, we have successfully prepared high-temperature vulcanized fluorine silicone rubber. After testing its flammability and other aspects, the prepared material achieved HC1-level hydrophobicity, surpassing conventional silicone rubber insulators in terms of self-cleaning performance.

Carbonation of photocatalytic aluminosilicate cement composites: Evolution of self-cleaning and radiative cooling properties

This study aims to understand the impact of carbonation on the photocatalytic self-cleaning and radiative cooling properties of autoclaved cement composites. The composites are prepared with varying silica contents and sources, with and without alumina addition under autoclave conditions. The phase composition, microstructure, optical properties, and photocatalytic self-cleaning performance are systematically characterized and analyzed. Outdoor measurements are conducted to validate the cooling performance of the material under ambient conditions. Cracking behaviors during autoclave/carbonation treatments and the performance degradation in functionalities upon carbonation are observed. The cement/nanosilica/alumina ternary system demonstrates the best overall performance, considering productibility during autoclave curing, effectiveness, and carbonation durability of functionalities. C-A-S-H minerals, mainly Al-Foshagite, in this system, serve as precursors for the generation of γ-Al2O3 upon carbonation, mitigating the deterioration of photocatalytic properties. The findings are expected to provide new insights for the development and engineering practice of functional cementitious materials for durable cooling applications.

Design and preparation of durable intelligent haze removal and self-cleaning protective coatings

Conventional superhydrophobic coatings lose effectiveness over due to degradation from ultraviolet (UV) radiation, contaminants, and abrasion. Moreover, external cleaning methods are often needed to maintain self-cleaning performance in the presence of oils and organic contaminants. This study develops an organic-inorganic hybrid coating comprising polymethylhydrosiloxane (PMHS)-modified diatomaceous earth (DE) loaded with titanium dioxide (TiO2) on a room-temperature vulcanized rubber (RTV) substrate. The PMHS-DE-TiO2 coating achieves a synergistic effect, combining superhydrophobicity and photocatalysis. Notably, it exhibits a water contact angle (WCA) of 162.2°, a sliding angle (SA) of 5°, and achieves complete degradation of methylene blue (MB). It maintains hydrophobicity, integrity and functionality under UV radiation, prolonged abrasion, and acidic/alkaline salt solution immersion. The coating also degrades NO at 73.09 % maximum rate. Integration with a negative air ion generator further harnesses the timely superhydrophobic self-cleaning and photocatalysis to significantly enhance dust and fog removal efficiency beyond conventional commercial ion generators. Aligning with green low-carbon principles, this multifunctional coating provides an innovative solution for environmentally-friendly construction materials suitable for long-lasting exterior and interior usage. It resists pollution while mitigating airborne hazards, meeting growing demands for healthy buildings.

Superior droplet bouncing, anti-icing/anti-frosting and self-cleaning performance of an outstanding superhydrophobic PTFE coating

The prevention of ice/frosting formation is crucial in cold region for various applications. Superhydrophobic coatings are known for their excellent anti-icing/anti-frosting properties. In this study, a durable superhydrophobic PTFE coating on a stainless steel surface was fabricated with a high water contact angle of 171.4° and a low rolling angle of 1.1°. The freezing of water droplets on the coating exhibits a significantly prolonged duration of 809 s at −10 °C, representing a 25-fold increase compared to the uncoated stainless steel surface. The ice adhesion strength is reduced by 83.7%, making ice easier to remove. Anti-frosting tests show that a thinner and lower-density layer of frost formed on the PTFE coating due to its micro-nano hierarchical structure. Furthermore, the superhydrophobic PTFE coating demonstrates excellent mechanical stability, droplet bouncing dynamics and self-cleaning properties. It is anticipated that this durable superhydrophobic PTFE coating will be a candidate for anti-icing/anti-frosting and self-cleaning applications

A self-cleaning photocatalytic membrane loaded with Bi2O2CO3/In(OH)3 S-scheme heterojunction composites for removing tetracycline from aqueous solutions

Bi2O2CO3/In(OH)3 (BON) photocatalysts were synthesized by a one-pot method and loaded onto polyvinylidene fluoride (PVDF) membranes to obtain a Bi2O2CO3/In(OH)3/PVDF (BON-M) catalytic membrane system. The catalytic membranes demonstrated complete degradation of tetracycline within 40 min under visible light. They demonstrated robust photocatalytic activity across a broad pH range (5–11) and in the presence of coexisting ions. The membranes demonstrated excellent self-cleaning performance. Following exposure to light, the irreversible contamination decreased from 27.1% to 4.7% and the membrane’s permeability was almost completely restored. Moreover, the charge transfer mechanism at the S-scheme heterojunction interface of BON was demonstrated by Density functional theory and in-situ X-ray Photoelectron Spectroscopy characterisation, and the active sites involved in tetracycline’s degradation were identified. Meanwhile, the mechanism of the “anemone effect” of BON-M was demonstrated in conjunction with Electron paramagnetic resonance, and the intrinsic Some factors enhancing the membranes’ photocatalytic activity are specified.

Excellent hydrophobicity and high mobility of condensate droplets on hierarchical nanostructured surfaces: Insights from MD simulations

Comprehending the fundamental physical mechanisms behind condensation and the formation of suspended droplets on hierarchical structured surfaces is of paramount importance in the design of anti-frosting surfaces. In this study, we characterize the nucleation, growth and dynamic wetting behaviors of condensate droplets on hierarchical nanostructured surfaces by molecular dynamics simulation, and reveal that hierarchical structures facilitate the rapid formation and high mobility of suspended droplet during condensation. The mechanism underlying the formation of suspended droplets on hierarchical surfaces is unveiled, which can be attributed to the spontaneous dewetting transition induced by confined growth of individual droplets. Additionally, the impact of solid fraction and secondary structure distribution on condensation and dynamic wetting is systematically discussed. The results indicate that an increase in solid fraction or the number of secondary structures enhances the stability of suspended droplets and improves the droplet mobility. In particular, the presence of bottom secondary structures on sidewalls plays a crucial role in the formation of suspended droplets on hierarchical surface. It is expected that the above findings could provide valuable guidance for optimizing the design of functionalized surfaces with anti-frosting and self-cleaning performance.

Anti-fouling underwater superoleophobic membranes based on hierarchical double networks for high efficiency oil–water separation

Oil fouling is a key problem of superwettable oil–water separation membranes because the membranes are inevitably susceptible to varying degrees of oil contamination during the ongoing separation processes, which usually results in a severe impact on separation performance. Consequently, it is a great challenge to construct oil-removal membranes with superior resistance to oil contamination. Herein, we fabricated hierarchical double networks (HDT)-modified porous glass membrane with superhydrophilicity/underwater superoleophobicity. Firstly, a layer of silicone nanofilament (SNF) network bearing tremendous C = C double bonds were fabricated on a porous glass membrane surface by one-step chemical vapor deposition (CVD) using vinyltrichlorosilane (VTCS) as a precursor. Subsequently, the second network layer was constructed by copolymerization of the C = C double bonds on the SNF network and those in sulfobetaine-derived monomer (sulfobetaine methacrylate, SBMA), using N,N′-methylenebisacrylamide (MBA) as the cross-linkering agent. It was observed that the obtained HDT-modified glass membranes displayed excellent superhydrophilicity/underwater superoleophobicity accompanied with superior self-cleaning performance and oil-resistance properties. As a result, the HDT-modified membranes showed high separation flux and high efficiency for both oil/water mixtures (7500 L m−2h−1, above 99.98%) and surfactant-stabilized oil-in-water emulsions (1100 L m−2h−1, above 99.96%) with excellent cyclability. The outstanding advantages with characteristics of excellent oil resistance and superior separation performance enable the HDT-modified glass membrane promising applications in a wide range of industries related to oil–water separations.