Self-cleaning Efficiency Research Articles

A durable self-cleaning superhydrophobic coating fabricated using the preset grid-spraying method

Herein, a new durable superhydrophobic coating was prepared using the preset grid-spraying method which was low cost and simple. To achieve the regular continuous grid structure which had protection and support function to the coatings, the sieve mesh was preset on the substrate with hot pressing process. After spraying the superhydrophobic coating on the substrate of the preset mesh followed by curing, a superhydrophobic coating was obtained. The surface morphology of the superhydrophobic coating prepared using the preset grid-spraying method was primarily composed of the regular grid structure and island-like structure with the micro-nano scale rough structure on them. Compared with the superhydrophobic coating prepared with the traditional spraying method, the mechanical stability of the superhydrophobic coating, which was prepared using the preset grid-spraying method, was considerably higher along with good hydrophobic properties. The superhydrophobic coating demonstrated superhydrophobic properties after 170 cycles of the sandpaper abrasion test, which was about 300% higher than the traditional superhydrophobic coating. Furthermore, the superhydrophobic coating prepared using the preset grid-spraying method had excellent self-cleaning performance and weather resistance. Self-cleaning efficiencies of this superhydrophobic coatings on kaolin and sand were 99.2% and 98.9%, respectively. Even after 170 cycles of the sandpaper abrasion test, the self-cleaning efficiency of superhydrophobic coatings on kaolin and sand remained over 85% and 90%, respectively. The coated surface still showed superhydrophobic properties after 30 days of the outdoor placement experiment. Showing excellent comprehensive properties and low cost, the superhydrophobic coating prepared using the preset grid-spraying method had a board application prospect.

Photoactive self-cleaning zinc oxychloride coatings

Zinc oxychloride cement (ZOC) is considered a promising quick-drying material for fabricating photoactive coatings composed of three components: zinc oxide (ZnO), zinc chloride (ZnCl2), and water. However, its massive application has not been implemented due to the lack of research about its stability and mechanical performance. Thus, this article aims to provide insights about the self-cleaning photoactivity of ZOC coatings incorporated with titanium dioxide (TiO2) nanoparticles to boost the photocatalytic performance. Two stoichiometries of ZnO:ZnCl:H2O (112 and 415) were studied to investigate the influence of the molar ratio of the components on the physical and chemical properties. According to these results, no significant differences were observed in the physical and chemical properties between the two stoichiometries studied; however, the mechanical properties were affected. The coatings crystallized as simonkolleite Zn5(OH)8Cl2·H2O with a laminar hexagonal morphology, show high surface area, and absorbs light in the UVA region. The self-cleaning activity was evaluated using four model pollutants: Rhodamine B, Methylene blue, Orange G, and Carbon under accelerated weathering conditions. All the coatings were photoactive to decompose the pollutants from their surface and the addition of TiO2 nanoparticles did not significantly enhance the self-cleaning efficiency, but it improves the mechanical performance of the coatings. These results could be associated with the fact that TiO2 works as filler for voids in the coatings without affecting its settings. The stability of the coatings was confirmed after the exposure to accelerated weathering at high humidity conditions, which places them as an attractive, low-cost, and easy to apply self-cleaning material.

Multienzyme Immobilization on PVDF Membrane via One-Step Mussel-Inspired Method: Enhancing Fouling Resistance and Self-Cleaning Efficiency.

Immobilizing different enzymes on membranes can result in biocatalytic active membranes with a self-cleaning capacity toward a complex mixture of foulants. The membrane modification can reduce fouling and enhance filtration performance. Protease, lipase, and amylase were immobilized on poly(vinylidene fluoride) (PVDF) microfiltration membranes using a polydopamine coating in a one-step method. The concentrations of polydopamine precursor and enzymes were optimized during the immobilization. The higher hydrolytic activities were obtained using 0.2 mg/mL of dopamine hydrochloride and 4 mg/mL of enzymes: 0.90 mgstarch/min·cm2 for amylase, 10.16 nmoltyrosine/min·cm2 for protease, and 20.48 µmolp-nitrophenol/min·cm2 for lipase. Filtration tests using a protein, lipid, and carbohydrate mixture showed that the modified membrane retained 41%, 29%, and 28% of its initial water permeance (1808 ± 39 L/m2·h·bar) after three consecutive filtration cycles, respectively. In contrast, the pristine membrane (initial water permeance of 2016 ± 40 L/m2·h·bar) retained only 23%, 12%, and 8%. Filtrations of milk powder solution were also performed to simulate dairy industry wastewater: the modified membrane maintained 28%, 26%, and 26% of its initial water permeance after three consecutive filtration cycles, respectively, and the pristine membrane retained 34%, 21%, and 7%. The modified membrane showed increased fouling resistance against a mixture of foulants and presented a similar water permeance after three cycles of simulated dairy wastewater filtration. Membrane fouling is reduced by the immobilized enzymes through two mechanisms: increased membrane hydrophilicity (evidenced by the reduced water contact angle after modification) and the enzymatic hydrolysis of foulants as they accumulate on the membrane surface.

Layer-by-layer self-assembled smart antibacterial coatings for surface management of orthokeratology lens

ABSTRACT Orthokeratology (OK) lenses are designed to reshape the cornea overnight, allowing users to see clearly during the day without glasses. However, prolonged wear increases the risk of microbial contamination and eye infections. Even with cleaning techniques, the surface of OK lenses can become contaminated due to residual bacterial debris. Therefore, developing self-cleaning antibacterial technology for OK lens surfaces is an urgent clinical challenge. Herein, we integrated the temperature responsiveness of PNIPAM molecular chains with the surface contact-killing mechanism of AMP into the surface of OK lenses for the first time, constructing an intelligent OK lens with synergistic antibacterial and self-cleaning properties. The modified OK lenses can achieve over 95% bacterial efficiency against Staphylococcus aureus and Pseudomonas aeruginosa. More importantly, in both worn and removed states, the modified OK lenses can achieve a surface bacterial debris self-cleaning efficiency of 50–75%. These research findings provide important references and insights for the future development of more efficient self-cleaning lens materials.

Advanced photocatalytic membrane GO-NiFe@SiO2/PVDF for efficient decontamination of synthetic dyes in batik wastewater with superior antifouling features

A novel composite membrane, GO-NiFe@SiO2/polyvinylidene fluoride (PVDF), was prepared via the sol-gel method for nanocomposite synthesis and phase inversion method for membrane fabrication. The investigation encompassed the structural features and properties of the nanocomposite membranes, including photocatalytic activity under UV type C, antifouling capability, and self-cleaning behavior. The degradation of dyes in real Batik wastewater followed pseudo-first-order kinetics, with the GO-NiFe@SiO2/PVDF 1 wt% nanocomposite membranes exhibiting a highest dyes removal efficiency up to 90.50 % within 8 h, compared to the pristine PVDF membrane (60.95 %). The XRD pattern analysis indicates that the incorporation of GO-NiFe@SiO2 into the PVDF membrane induced a transformation in the semi-crystalline phase of PVDF, shifting from the alpha-phase to the beta-phase, consequently facilitating the development of electrostatic charge on the membrane surface. The pore-size distribution analysis revealed that all prepared membranes fall within the range of nanofiltration and tight ultrafiltration (NF-TUF). Additionally, the photocatalytic membrane demonstrated enhanced permeation flux of 30.46 L.m−2.h−1 and flux recovery rate up to 92.57 % under simulated UV light irradiation, showcasing improved antifouling capability. Moreover, the membrane exhibited outstanding cycle test with 6 consecutive cleaning every 3 h, self-cleaning efficiency, with 61.32 % cleaning efficiency under UV irradiation. The incorporation of GO-NiFe@SiO2 enhanced the physicochemical properties of the photocatalytic membrane, including hydrophilicity, surface topologies, and mechanical strength, thereby improving photocatalytic anti-fouling performance and expanding the potential applications of membrane filtration technology.

Reticulated mesoporous TiO2 scaffold for self-cleaning surfaces

Interest in self-cleaning coatings is rising due to their potential to enhance comfort and quality of life in polluted urban environments, driving the search for materials with optimal physical properties. Convergent with this goal, this study investigates the wetting properties and photo-catalytic efficiency of reticulated TiO2 layers. It shows that these properties are significantly influenced by the topographical characteristics of the TiO2 surface, which can be precisely controlled through variations in pulverization pressure and low-temperature post-annealing treatments. Post-deposition annealing of the TiO2 layers achieves 100 % self-cleaning efficiency for both thick and thin films, with optical transmission ranging from approximately 60 %–80 % in the visible spectrum. Additionally, the TiO2 layers exhibited promising capabilities for eliminating pathogenic microorganisms and disinfecting surfaces. The underlying causal factors of these remarkable and technologically promising surface features are explored and discussed.

Preparation and properties of modified SiO2/epoxy resin superhydrophobic coating

In this study, a superhydrophobic coating with excellent mechanical durability, chemical stability, anti-icing property and self-cleaning property was developed based on epoxy resin integrated with modified SiO2 nanoparticles (m-SiO2 NPs). The surface morphology and roughness of the coating were finely controlled by changing the content of m-SiO2 NPs, with optimal hydrophobicity and self-cleaning efficiency observed at the m-SiO2 NPs incorporation of 30 wt%. Benefitting from the three-dimensional stable micro-nano structure on the coating surface, the coating exhibited durable hydrophobicity upon multiple tape-peeling damages and good resistance to both acidic and alkaline corrosive environments. Furthermore, the SiO2-EP coating showed a prominent anti-icing property which could delay the water freezing time from 96 s to 650 s. This coating underscored its potential for applications in environments prone to ice formation.

Nanosecond laser-assisted fabrication of Ti6Al4V surfaces with gradient wettability and robust cross-linked microstructures

Abstract Surfaces with gradient wettability outperform singular superhydrophobic surfaces in terms of self-cleaning efficiency, anti-contamination properties, and fluid manipulation. These attributes offer extensive application potential across various industrial and scientific domains. This study introduces and employs nanosecond pulsed laser ablation to create wettability gradient surfaces on Ti6Al4V alloys, featuring robust cross-linked frame microstructures. Experimental results demonstrate that by varying the ridge width (w), associated with the liquid-solid contact fraction, we can achieve varying wettability and mechanical durability in these cross-linked frame microstructures. Wettability tests indicate static contact angles ranging from 150.7° to 105.45°. Furthermore, the sandpaper linear abrasion test illustrates a decrease in material wear rate with an increase in w. Under similar test conditions, the proposed surfaces demonstrate superior mechanical durability compared to two other prevalent wettability surface structures. The proposed surfaces, efficiently and eco-friendly produced through nanosecond laser fabrication, hold tremendous potential for diverse applications.

Optimizing flow uniformity and velocity fields in aquaculture tanks by modifying water inlets and nozzles arrangement: A computational fluid dynamics study

Ensuring optimal conditions for fish, especially in terms of uniform velocity fields, is crucial for aquaculture systems to attain self-cleaning efficiency in rearing tanks and better fish behavior, which ultimately impacts their survival and growth. The current study presented a full-scale computational fluid dynamics (CFD) model of three types of circular, square and square arc angle tanks used in aquaculture farms to choose the most optimal tank based on the flow uniformity and velocity field. At the next step, the optimal arrangement of the inlet number, inlet location, inlet angle, as well as the number of nozzles on each inlet was reconfigured to create the most optimal tank. The simulations were done using the CFD software FLUENT distributed by the ANSYS Corporation. The software calculates velocities in the tanks by solving the Reynolds-averaged Navier-Stokes equations of continuity and momentum that govern the mean turbulent flow of water. The results illustrated circular and square arc angle tanks had significantly more uniform fluid velocity compared to the square tanks, which the square arc angle tank due to better flow velocity near the wall and space utilization was selected for further rearrangements. Additionally, the implementation of two entrance pipes near the corner of the two parallel walls with an entry angle of 0° in a square arc angle tank resulted in a more consistent water velocity. As the number of inlet nozzles increased to six, the water streamlines became more uniform, suggesting a more consistent water velocity throughout the tank. However, when the number of input nozzles increased to nine, the tension on the nozzle apertures were increased probably due to the decrease of distance between them. Findings of the present study concluded that two inlets in the corner with an entry angle of 0° and six nozzles on each inlet pipe could provide the optimum water velocity in the square arc angle tanks.

Superhydrophobic Materials for Self-cleaning Applications: A Review

Abstract: Since the discovery of the “lotus effect,” the superhydrophobic structure of the research is more and more profound. When the droplets fall on the surface, it will not occur as a wetting phenomenon. Making full use of this feature will achieve the self-cleaning effect of the object surface. In the dust filtration problem, it is possible to spray superhydrophobic materials on the surface of the equipment using superhydrophobic self-cleaning characteristics to change the filtering method and to improve the self-cleaning efficiency. This paper describes the methods of preparing superhydrophobic materials, self-cleaning methods, and the application of superhydrophobic materials in the field of self-cleaning. Based on the summary of patents and papers, this paper focuses on the filtration and self-cleaning effect of superhydrophobic materials on dust particles in humid environments. With a simple structure, high filtration efficiency, and long service life, the super sparse/hydrophilic hybrid mesh can work continuously without manual operation. It can effectively filter dust particles and improve air quality in humid environments. Coal powder condensation experiments in this paper proved that the application of superhydrophobic materials in the field of self-cleaning yielded significant results. When superhydrophobic materials are sprayed on copper-based filters, the hydrophilic line mixes with the hydrophobic region, greatly improving the self-cleaning efficiency.

TiO2 nanoparticle embedded PEEKWC/PEI cross-linked ultrafiltration membrane: Improvement in flux and anti-fouling properties

Based on the previous study, the properties, separation efficiencies, and anti-fouling performances of TiO2 nanoparticle embedded PEEKWC/PEI cross-linked ultrafiltration membrane made via non-solvent-induced phase separation were investigated. SEM, contact angle measurement, ATR-FTIR, and other methods were used to characterize the membranes, and then the pure water flux (PWF) and dye rejection were measured. The TiO2 nanoparticle embedded PEEKWC/PEI cross-linked ultrafiltration membranes were prepared by stepwise solution blending method. Compared to the pristine PEEKWC/PEI cross-linked ultrafiltration membrane, the anti-fouling and pure water flux performances were enhanced as the addition of TiO2 nanoparticles. The pure water flux of TiO2 nanoparticle embedded membranes was significantly increased and could even reach 3368.2 LMH at 5 bar much greater than that of the pristine PEEKWC/PEI ultrafiltration membrane (1423.8 LMH), remaining a retention rate for BBR higher than 98.5%. And the TiO2 nanoparticle embedded PEEKWC/PEI cross-linked ultrafiltration membranes exhibited a certain degree of increase of FRR (higher than 80%) after UV illumination. After a series of characterisation, the dye wastewater treatment property of membranes was assessed through filtration of Coomassie brilliant blue and Congo red solutions and researches were conducted on the anti-fouling capabilities of membranes. The TiO2 nanoparticle embedded PEEKWC/PEI cross-linked ultrafiltration membranes exhibited self-cleaning efficiency with lower irreversible fouling ratio. The pure water flux recovery ratio following dye fouling was higher after being exposed to UV irradiation, which could be attributed to the TiO2 nanoparticles' photocatalytic destruction of organic pollutants.

Ag/ZnO microcavities with high sensitivity and self-cleaning properties for fast repetitive SERS detection.

A SERS substrate with high sensitivity and reusability was proposed. The chip consists of multiple ZnO microcavities loaded with silver particles. Based on structural characteristics, this coupling between cavity modes and localized surface plasmon modes can highly localize the electric field, where experimental results revealed a detection limit of 10-11 M for R6G. In addition, during carrier control in semiconductors with localized electromagnetic fields, our substrate also exhibits high self-cleaning efficiency and in situ detection stability. Even in a dry environment, it exhibits excellent light-mediated cleaning ability across multiple reuse test cycles. The convenient, rinse-free substrate, with its cost-effective and sustainable features, shows great promise for the study on detection and degradation of active materials.

Towards a green climate: Production of slag–red brick waste-based geopolymer mingled with WO3 nanoparticles with bio-mechanical achievements

According to the sustainability concept, this work developed a green geopolymeric composite (Geo) prepared by mingling 50 wt%slag+ 50 wt%brick-waste (BW) as an alternative eco-friendly and low-cost cementitious material. The main target of this study is to fnd a solution to the problem of poor characteristics of binding materials containing high proportions of BW; most previous studies recommended using only 10–20 wt%BW. The compressive-strength results showed that replacing slag with 50 wt% BW reduced the strength from 47 to 24.6 MPa at normal curing conditions for 28-days, referring to the detrimental impact of BW on mechanical performance. In an endeavour to enhance the mechanical performance of this composite, different doses from laboratory-prepared tungsten oxide nanoparticles (0.25, 0.5, 1 wt%WO3-NPs) and hydrothermal curing at various steam-pressure/periods were used. From an economic point of view, hydrothermally treated Geo-paste modified with 0.25 wt%WO3-NPs at 3 bar/4hrs was selected as an ideal composition/curing-conditions; the compressive-strength reached 54.5 MPa exceeding the standard limit of Portland cement (42.5 MPa). This clearly shows the synergistic role of using WO3-NPs and hydrothermal curing to enhance the compressive-strength, which was confirmed using different analysis techniques. XRD, TGA/DTG and SEM/mapping proved that the catalytic performance of WO3-NPs/hydrothermal-curing participates in augmenting binding hydrates, creating a cubic-stable-phase of tricalcium-aluminate-hydrate (C3AH6) and different types of zeolitic-like structure (spherical Zeolite-NaP, rods analcime and stacked-plates cancrinite). To maximize the benefits of employing WO3-NPs in the developed composites, their anti-microbial activity was studied. The measured inhibition zone around specimens containing WO3-NPs proved that these composites have a superior self-cleaning efficiency against Candida albicans, Mucor circinelloides, Salmonella typhi and Staphylococcus aureus due to the WO3-NPs’ photocatalytic activity.

Preparation and Characterization of Modified ZrO2/SiO2/Silicone-Modified Acrylic Emulsion Superhydrophobic Coating.

Superhydrophobic coatings have increasingly become the focal point of research due to their distinctive properties like water resistance, wear resistance, and acid-base resilience. In pursuit of maximizing their efficiency, research has primarily revolved around refining the fabrication process and the composition of emulsion/nanoparticle coatings. We innovatively devised a superhydrophobic coating by employing a spraying technique. This involved integrating a γ-Methacryloyloxypropyltrimethoxysilane (KH570)-modified ZrO2/SiO2/silicone-modified acrylic emulsion. A comprehensive evaluation of this coating was undertaken using analytical instruments such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and confocal laser scanning microscopy (CLSM). The coating demonstrated exceptional performance across a range of tests, including wear, immersion, and anti-icing cleaning, showcasing notable wear resistance, sodium chloride corrosion resistance, self-cleaning efficiency, and thermal stability. In particular, one coating exhibited super-hydrophobic properties, with a high contact angle of 158.5 degrees and an impressively low rolling angle of 1.85 degrees. This remarkable combination of properties is attributed to the judicious selection of components, which significantly reinforced the mechanical strength of the coating. These enhancements make it highly suitable for industrial applications where self-cleaning, anti-icing, and anti-contamination capabilities are critical.

3D Xanthium-like of Ni-Co-Zn ternary alloys as superhydrophobic coatings toward porous Ti surface for its anti-icing performances

Super-hydrophobic surface has attracted great interests as functional coatings in spacecraft wings and wind-turbine fans. With the ever-increasing demands of durability and low cost, the scopes for industrial application of hydrophobic coatings have been restricted. Herein we proposed an innovative and simple approach for electroplating Ni0.12Co0.88-xZnx (x = 0–0.36) coatings toward porous Ti substrate. Featuring as 3D Xanthium-like spherical textures, the Ni-Co-Zn ternary alloy coatings were achieved by optimizing the Zn2+ concentration and complexing agent (Na3Cit) in bath. Results validated that its crystal size was refined into ∼300 nm, leading into pinning growth through hole-hole linked porous channel of Ti substrate to increase interfacial strength. Based on the wettability tests, it depicted the water-droplet contact angle (WCA) value of 126.3° attached with sliding angle (SA) of 17.5° for coating samples after being exposed in air for 14 days. Further studies of different ageing treatments on micro structural evolution and super-hydrophobic characteristics were well explored. Through artificial ageing at 200 °C, its attained super-hydrophobic surfaces shorted than 7 days, showing the maximal WCA value up to 153.2° and SA ≤ 7.8° for Ni0.12Co0.88-xZnx (x = 0.24) samples, which was mainly contributed to the self-assembly of multi-tentacles ZnO dendrites. Meanwhile the anti-icing behaviors were compared and featured as peach blossom at −10 °C for all the samples. The icing-delay time of water droplets on coating samples was >1425 s, which was 20 times longer than that of porous Ti substrate. Similarly, it was higher than 90 % for its self-cleaning efficiency based on salt pollutants. Besides the mechanical durability of tested samples against the abrasion-resistant tests and water impact-resistance tests were studied. Results implied that good durability was achieved for Ni-Co-Zn superhydrophobic coatings, but sanded surfaces within a serious decrease of WCA was obtained after a continuous testing for 30 min by abrasion-resistant tests because of the partial destruction of Xanthium-like spherical textures. With the respect to reconstructing of multi-tentacles ZnO dendrites onto the Ni-Co-Zn coatings in air, it was the bio-inspired strategies for self-healing super hydrophobic metal coatings used in warship surfaces, etc.

Self-cleaning SiO2/TiO2/PMMA nanocomposite films fabricated by spin coating technique: Effect of different spin speed and film layers

This research aims to develop the self-cleaning efficiency of silicon dioxide/titanium dioxide/methyl methacrylate (SiO2/TiO2/PMMA) nanocomposite films proved by optical and structural properties. The SiO2/TiO2/PMMA nanocomposite films were prepared by spin coating technique with the crucial parameters of spin speed and film layers. The ratio of SiO2:TiO2 in SiO2/TiO2 nanocomposite was conducted at 1:1 by sonochemical process and loading at 1 wt.% in PMMA matrix. Spin speed of SiO2/TiO2/PMMA nanocomposite films in coating process was conducted at 1000, 2000, and 3000 rpm with film growth at 2 layers. Meanwhile, the different film layers of the nanocomposite film were selected as other crucial parameter in spin coating technique and studied at 1, 2, and 3 layers with spin speed 2000 rpm. Surface morphologies, cross-section and element contents of SiO2/TiO2/PMMA nanocomposite films with different spinning speed and film layers were monitored by the photographs, field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Moreover, optical property in transmission mode of SiO2/TiO2/PMMA nanocomposite films was characterized by UV-VIS spectrophotometer. Furthermore, the contact angle measurement o f SiO2/TiO2/PMMA nanocomposite films can identify to hydrophilic properties on the film surface. Therefore, the improvement of self-cleaning property on SiO2/TiO2/PMMA nanocomposite film was occurred by the optimized conditions of spinning speed at 2000 rpm and film growth at 2 layers by spin coat technique.

Dimensionality effects of g-C3N4 from wettability to solar light assisted self-cleaning and electrocatalytic oxygen evolution reaction

Unique interfacial properties of 2D materials make them more functional than their bulk counterparts in a catalytic application. In the present study, bulk and 2D graphitic carbon nitride nanosheet (bulk g-C3N4 and 2D-g-C3N4 NS) coated cotton fabrics and nickel foam electrode interfaces have been applied for solar light-driven self-cleaning of methyl orange (MO) dye and electrocatalytic oxygen evolution reaction (OER), respectively. Compared to bulk, 2D-g-C3N4 coated interfaces show higher surface roughness (1.094 > 0.803) and enhanced hydrophilicity (θ ∼ 32° < 62° for cotton fabric and θ ∼ 25° < 54° for Ni foam substrate) due to oxygen defect induction as confirmed from morphological (HR-TEM and AFM) and interfacial (XPS) characterizations. The self-remediation efficiencies for blank and bulk/2D-g-C3N4 coated cotton fabrics are estimated through colorimetric absorbance and average intensity changes. The self-cleaning efficiency for 2D-g-C3N4 NS coated cotton fabric is 87%, whereas the blank and bulk-coated fabric show 31% and 52% efficiency. Liquid Chromatography-Mass Spectrometry (LC-MS) analysis determines the reaction intermediates for MO cleaning. 2D-g-C3N4 shows lower overpotential (108 mV) and onset potential (1.30 V) vs. RHE for 10 mA cm−2 OER current density in 0.1 M KOH. Also, the decreased charge transfer resistance (RCT = 12 Ω) and lower Tafel's slope (24 mV dec−1) of 2D-g-C3N4 make it the most efficient OER catalyst over bulk-g-C3N4 and state-of-the-art material RuO2. The pseudocapacitance behavior of OER governs the kinetics of electrode-electrolyte interaction through the electrical double layer (EDL) mechanism. The 2D electrocatalyst demonstrates long-term stability (retention ∼94%) and efficacy compared to commercial electrocatalysts.

Adsorption-Controlled Wettability and Self-Cleaning of TiO2.

Molecular adsorption on solids is inevitable and has significant influences on the wettability of materials, while the tuning mechanism of the wettability from molecular adsorption is yet to be understood. Using molecular dynamics (MD) simulations, we comprehensively studied the relation between the wettability of the TiO2 surface and the adsorption of water and carboxylic acid molecules. Our results reveal that the increasing amount of surface hydroxyl groups from the decomposition adsorption of H2O increases the hydrophilicity of TiO2, providing molecular-level evidence for the previously proposed mechanism of photo-induced hydrophilicity. By contrast, the surface wettability becomes tunable with water contact angles changing from 0 to ∼130° through length adjustment of the adsorbed carboxylic acids. The TiO2 surface is hydrophilic with the adsorption of short-alkyl-chain carboxylic acids (e.g., HCOOH) and becomes hydrophobic when longer-alkyl-chain carboxylic acids (H(CH2)nCOOH, n > 2) are present. Furthermore, long-alkyl-chain acids also increase surface oleophilicity, while the adsorption of HCOOH and CH3COOH significantly enhances the oleophobicity of TiO2. Water molecules can also more easily penetrate the space between oily contaminants and adsorbed short acid molecules, thereby further increasing its self-cleaning capacity. The present simulations not only reveal the mechanism of wettability caused by molecular adsorption but also provide a promising method to create materials with controllable wettability and high self-cleaning efficiency.

Exploring the self-cleaning and antimicrobial efficiency of the magnesium oxychloride cement composites

Composites of magnesium oxychloride cement (MOC) functionalized with TiO2 nanoparticles are proposed here as an alternative technology to maintain clean building surfaces from airborne pollutants and microorganisms. The MOC composites were characterized by different techniques such as XRD, FTIR, SEM, EDS, UV–Vis, compressive strength, and nanoindentation tests. According to the results, phase 3 (3 Mg(OH)2.MgCl2.8H2O) with needle-like morphology was the primary crystallized hydration product for the MOC composites. Also, the samples exhibited good mechanical properties and good light absorption, allowing them to activate under solar light irradiation. The self-cleaning efficiency of the MOC composites was evaluated by measuring the removal of three types of pollutants: methylene blue (MB), rhodamine B (RhB), and reactive black 5 (RB5), under two scenarios: natural sunlight and accelerated weathering conditions. The self-cleaning tests revealed outstanding efficiencies of the composites to remove MB (82%), RhB (88%), and RB5 (91%) under solar light and accelerated weathering tests. On the other hand, the antimicrobial activity was evaluated against E. coli (gram-negative) and S. aureus (gram-positive) under irradiation. The zone of inhibition (ZOI) showed diameters higher than 21 mm to E. coli for samples with 5% of TiO2 or superior, revealing a high microbial inhibition of the gram-negative bacteria. Also, the structural and morphological stability of the MOC composites was confirmed after several cycles for the accelerating weathering tests, demonstrating their potential to be used outdoors to reduce environmental pollution.

Enhanced self-cleaning performance of bio-inspired micropillar-arrayed surface by shear

Inspired by the sliding behavior of gecko feet during climbing, the contribution of the shear effect to the self-cleaning performance of a bio-inspired micropillar-arrayed surface is studied through a load-shear-pull contact process. It is found that self-cleaning efficiency can be enhanced significantly by shear. The efficiency also depends on microparticle size. For the case of relatively large and small microparticles, self-cleaning efficiency increases first and then almost keeps a constant with the increase of shear distance at different preloads. For medium microparticles, shear can effectively improve self-cleaning efficiency only when the preload is small. The mechanical mechanism under such enhancement is mainly due to the varying contact states between microparticles and micropillars with the shear distance. When the shear distance is large enough, the final self-cleaning efficiency is not sensitive to shear distance anymore because the contact state reaches dynamic equilibrium. Based on such a self-cleaning mechanism of large microparticles, a simple and effective manipulator that can efficiently transfer solid particles is further proposed.