Fabrication of 3D biomimetic composite coating with broadband antireflection, superhydrophilicity, and double p-n heterojunctions

The traditional single material with two-dimensional （2D） biomimetic moth-eye structures is limited by its narrowband antireflection and single functional capability. To overcome these disadvantages, we exploited wet etching and hydrothermal synthesis coupled with chemical oxidation for fabricating a three- dimensional （3D） biomimetic moth-eye coating with ternary materials （polypyrrole nanoparticles, TiO2 nanorods, and Si micropyramids, i.e., PPy/TiOa/Si-p）. This coating reduced the reflectivity to 〈4% at wavelengths ranging from 200 to 2,300 nm and exhibited remarkable superhydrophilidty with a low water contact angle of 1.8°. Moreover, the composite coating had double p-n heterojunctions, allowing the high-efficiency separation of photogenerated carriers. The photo- current density of PPy/TiO2/Si-p was more than three times higher than that of TiO2/Si-p at a positive potential of 1.5 V. The proposed method provides a means to enhance solar energy conversion.

A facile method to fabricate surfaces showing superhydrophilicity in air and superhydrophobicity in oil

The changes of the wettability of the solid surfaces have attracted massive attention due to their important practical implications in numerous fields. As a new subject, the research on the wettability under the different environments is still in its early stage. So the fundamental research must be performed for the practical applications under different environments. However, it is seldom that the comprehensive wettability of a surface in air, in water and in oil has been reported. In this paper, the authors investigated the wettability of the stainless steel mesh coated with polyurethane in the above three different environments. The surface of the uncoated mesh was found to be hydrophobic in air, but the surface of the coated mesh was superhydrophilic in air. More interestingly, the surfaces of the coated meshes were superoleophilic in water and superhydrophobic in oil. Due to the coated meshes with these wettabilities were fabricated via a facile two-step method, the presented method may be adopted for large-scale industrial production, in various fields, such as icing prevention or the oil-field industry.

Reversible wettability between superhydrophobicity and superhydrophilicity of Ag surface

We present a facile one-step method to fabricate superhydrophobic Ag surface by electrodeposition without using any low surface energy reagent. The water contact angle of the prepared surface is 167.1° and the sliding angle is only 0.5° after heat treatment. It is demonstrated by the field emission scanning electron microscopy(FESEM),X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) analyses that the dendrites of rough micro-nanostructure combined with the spontaneously adsorbed hydrocarbon make the surface exhibit superhydrophobicity.However, the superhydrophobic Ag surface becomes superhydrophilic when the surface is irradiated by UV light for several hours. It recovers superhydrophobicity after further heat treatment and can successfully implement the reversible wettability transition between superhydrophobicity and superhydrophilicity for several cycles.

Spider-capture-silk mimicking fibers with high-performance fog collection derived from superhydrophilicity and volume-swelling of gelatin knots

Spider-capture-silk(SCS)can directionally capture and transport water from humid air relying on the unique geometrical structure.Although there have been adequate reports on the fabrication of artificial SCSs from petroleum-based materials,it remains a big challenge to innovate bio-based SCS mimicking fibers with high-performance fog collection ability and efficiency simultaneously.Herein,we report an eco-friendly and economical fiber system for water collection by coating gelatin on degummed silk.Compared to the previously reported fibers with the best fog collection ability(~13.10μL),Gelatin on silk fiber 10(GSF10)can collect larger water droplet(~16.70μL in 330 s)with~98%less mass.Meanwhile,the water collection efficiency of GSF10 demonstrates~72%and~48%enhancement to the existing best water collection polymer coated SCS fibers and spidroin eMaSp2 coated degummed silk respectively in terms of volume-to-TCL(vapor-liquid-solid three-phase contact line)index.The simultaneous function of superhydro-philicity,surface energy gradient,and~65%water-induced volume swelling of the gelatin knots are the key factors in advancing the water collection performance.Abundant availability of feedstocks and~75%improved space utiliza-tion guarantee the scalability and practical application of such bio-based fiber.

Valence electronic engineering of superhydrophilic Dy-evoked Ni-MOF outperforming RuO_(2) for highly efficient electrocatalytic oxygen evolution

Tackling the problem of poor conductivity and catalytic stability of pristine metal-organic frameworks(MOFs) is crucial to improve their oxygen evolution reaction(OER) performance.Herein,we introduce a novel strategy of dysprosium(Dy) doping,using the unique 4f orbitals of this rare earth element to enhance electrocatalytic activity of MOFs.Our method involves constructing Dy-doped Ni-MOF(Dy@Ni-MOF) nanoneedles on carbon cloth via a Dy-induced valence electronic perturbation approach.Experiments and density functional theory(DFT) calculations reveal that Dy doping can effectively modify the electronic structure of the Ni active centers and foster a strong electronic interaction between Ni and Dy.The resulting benefits include a reduced work function and a closer proximity of the d-band center to the Fermi level,which is conducive to improving electrical conductivity and promoting the adsorption of oxygen-containing intermediates.Furthermore,the Dy@Ni-MOF achieves superhydrophilicity,ensuring effective electrolyte contact and thus accelerating reaction kinetics,Ex-situ and in-situ analysis results manifest Dy_(2)O_(3)/NiOOH as the actual active species.Therefore,Dy@Ni-MOF shows impressive OER performance,significantly surpassing Ni-MOF.Besides,the overall water splitting device with Dy@NiMOF as an anode delivers a low cell voltage of 1.51 V at 10 mA cm^(-2) and demonstrates long-term stability for 100 h,positioning it as a promising substitute for precious metal catalysts.

Transparent and anti-fogging AlPO_(4)-5 films constructed by oblique oriented nano-flake crystals

In the present work,transparent and anti-fogging AlPO_(4)-5 films were prepared on glass substrates using a novel developed process.The process entails a simple in-situ sol–gel followed by vapor phase transport.The in-situ sol–gel process was implemented by coating the precursor sols for the synthesis of AlPO4-5 on the glass substrates successively using the spin-coating method.The films and powders scribed from the films were characterized by X-Ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),scanning electron microscope(SEM),atomic force microscope(AFM),X-ray photoelectron spectroscopy and transmission electron microscope(TEM).The unique films were composed of oblique oriented nanoflake AlPO_(4)-5 crystals with the thickness of about 20 nm.The formation of nano-flake crystals can be ascribed to the high concentration of the precursors,resulting in the formation of a supersaturation system.The obtained films showed high antifogging performance due to the superhydrophilicity with a water contact angle of lower than 1.0°.The silicone oil contact angle was also low about 8.2°.In addition,heteroatom-substituted AlPO_(4)-5 films showing different colors can be obtained easily by simply adding transition metal ions in the phosphate acid solution during the preparation that can extend the application of the method for different coating demand.

Superhydrophilic–superhydrophobic patterned surfaces:From simplified fabrication to emerging applications

Superhydrophilic–superhydrophobic patterned surfaces constitute a branch of surface chemistry involving the two extreme states of superhydrophilicity and superhydrophobicity combined on the same surface in precise patterns.Such surfaces have many advantages,including controllable wettability,enrichment ability,accessibility,and the ability to manipulate and pattern water droplets,and they offer new functionalities and possibilities for a wide variety of emerging applications,such as microarrays,biomedical assays,microfluidics,and environmental protection.This review presents the basic theory,simplified fabrication,and emerging applications of superhydrophilic–superhydrophobic patterned surfaces.First,the fundamental theories of wettability that explain the spreading of a droplet on a solid surface are described.Then,the fabrication methods for preparing superhydrophilic–superhydrophobic patterned surfaces are introduced,and the emerging applications of such surfaces that are currently being explored are highlighted.Finally,the remaining challenges of constructing such surfaces and future applications that would benefit from their use are discussed.

Residual stress induced wetting variation on electric brush-plated Cu film

Nanocrystalline Cu film with a mirror surface finishing is prepared by the electric brush-plating technique. The as- prepared Cu film exhibits a superhydrophilic behavior with an apparent water contact angle smaller than 10°. A subsequent increase in the water contact angle and a final wetting transition from inherent hydrophilicity with water contact angle smaller than 90° to apparent hydrophobicity with water contact angle larger than 90° are observed when the Cu film is subjected to natural aging. Analysis based on the measurement of hardness with nanoindentation and the theory of the bond-order-length-strength correlation reveals that this wetting variation on the Cu film is attributed to the relaxation of residual stress generated during brush-plating deposition and a surface hydrophobization role associated with the broken bond polarization induced by surface nanostructure.

Ambient Fast Synthesis of Superaerophobic/Superhydrophilic Electrode for Superior Electrocatalytic Water Oxidation

Developing cost-effective and facile methods to synthesize efficient and stable electrocatalysts for large-scale water splitting is highly desirable but remains a significant challenge.In this study,a facile ambient temperature synthesis of hierarchical nickel-iron(oxy)hydroxides nanosheets on iron foam(FF-FN)with both superhydrophilicity and superaerophobicity is reported.Specifically,the as-fabricated FF-FN electrode demonstrates extraordinary oxygen evolution reaction(OER)activity with an ultralow overpotential of 195 mV at 10 mA cm^(-2)and a small Tafel slope of 34 mV dec^(-1)in alkaline media.Further theoretical investigation indicates that the involved lattice oxygen in nickel-iron-based-oxyhydroxide during electrochemical self-reconstruction can significantly reduce the OER reaction overpotential via the dominated lattice oxygen mechanism.The rechargeable Zn-air battery assembled by directly using the as-prepared FF-FN as cathode displays remarkable cycling performance.It is believed that this work affords an economical approach to steer commercial Fe foam into robust electrocatalysts for sustainable energy conversion and storage systems.

Bioinspired superwetting surfaces for fog harvesting fabricated by picosecond laser direct ablation

Fog harvesting has been considered as a promising method for solving water crisis in underdeveloped regions.To mimic and optimize the alleged natural fog harvesting ability of the stenocara beetle,hybrid superhydrophobic(hydrophobic,superhydrophilic)/hydrophilic patterns are processed on stainless steel via picosecond laser direct writing.Basically,after laser processing,the surfaces of stainless steel change from hydrophilic to superhydrophilic.Then,after chemical and heat treatment,the superhydrophilic surfaces become superhydrophobic with ultra-low adhesion,and superhydrophobic(hydrophobic)with ultra-high adhesion,respectively.This work systematically examines the fog harvesting ability of picosecond laser treated surfaces(LTS),pristine surfaces(PS),laser and chemical treated surfaces(LCTS),laser and heat-treated surfaces(LHTS).Compared with the PS,the as-prepared surfaces enhanced the fog harvesting efficiency by 50%.This work provides a fast and simple method to fog collectors,which offer a great opportunity to develop water harvesters for real world applications.

Hierarchically wood-derived integrated electrode with tunable superhydrophilic/superaerophobic surface for efficient urea electrolysis

Conferring surfaces with superhydrophilic/superaerophobic characteristics is desirable for synthesizing efficient gas reaction catalysts.However,complicated procedures,high costs,and poor interfaces hinder commercialization.Here,an integrated electrode with tunable wettability derived from a hierarchically porous wood scaffold was well designed for urea oxidation reaction(UOR).Interestingly,the outer surface of the wood lumen was optimized to the preferred wettability via stoichiometry to promote electrolyte permeation and gas escape.This catalyst exhibits outstanding activity and durability for UOR in alkaline media,requiring only a potential of 1.36 V(vs.RHE)to deliver 10 m A cm^(-2)and maintain its activity without significant decay for 60 h.These experiments and theoretical calculations demonstrate that the nickel(oxy)hydroxide layer formed through surface reconstruction of nickel nanoparticles improves the active sites and intrinsic activity.Moreover,the superwetting properties of the electrode promote mass transfer by guaranteeing substantial contact with the electrolyte and accelerating the separation of gaseous products during electrocatalysis.These findings provide the understanding needed to manipulate the surface wettability through rational design and fabrication of efficient electrocatalysts for gas-evolving processes.

Fully Superhydrophilic, Self-Floatable, and Multi-Contamination-Resistant Solar Steam Generator Inspired by Seaweed

Highly hydrophilic materials enable rapid water delivery and salt redissolution in solar-driven seawater desalination. However, the lack of independent floatability inhibits heat localization at the air/water interface. In nature, seaweeds with internal gas microvesicles can float near the sea surface to ensure photosynthesis. Here, we have developed a seaweed-inspired, independently floatable, but superhydrophilic (SIFS) solar evaporator. It needs no extra floatation support and can simultaneously achieve continuous water pumping and heat concentration. The evaporator resists salt accumulation, oil pollution, microbial corrosion, and protein adsorption. Densely packed hollow glass microbeads promote intrinsic floatability and heat insulation. Superhydrophilic zwitterionic sulfobetaine hydrogel provides a continuous water supply, redissolves the deposited salt, and endows the SIFS evaporator with excellent anti-fouling properties. With its unprecedented anti-contamination ability, this SIFS evaporator is expected to open a new avenue for designing floatable superhydrophilic materials and solving real-world issues of solar steam generation in complex environmental conditions.

High Osteoconductive Surface of Pure Titanium by Hydrothermal Treatment

Surface properties of Ti implants (especially surface hydrophilicity) influence biological responses at the interface between the bone tissue and the implant. However, only a little research reported the effect of surface hydrophilicity on osteoconductivity by in vivo test. We have investigated the surface characteristics and osteoconductivity of titanium implant produced by hydrothermal treatment using distilled water at temperature of 180°C for 3 h, and compared with as-polished and those of implants produced by anodizing in 0.1 M H2SO4 with applied voltage from 0 V to 100 V at 0.1 Vsˉ1 and anodizing followed by hydrothermal treatment. The relationship between hydrophilic surface and osteoconductivity in various surface modifications was examined by in vivo test. In order to maintain the hydrophilicity of the hydrothermal sample surface, it was kept in to the phosphate buffered saline solution (PBS) with 5 times concentration: 5PBS(-) in room temperature. The surface characteristics were evaluated by scanning electron microscopy, XRD, X-ray photoelectron spectroscopy, surface roughness and contact angle measurement using a 2 μL droplet of distilled water. In in vivo testing, the rod samples (Φ2 × 5 mm) were implanted in male rat’s tibiae for 14 days and the bone-implant contact ratio, RB-I, was used to evaluate the osteoconductivity in the cortical and cancellous bone parts, respectively. As a result, hydrothermal treatment without anodizing still produced a smooth surface like an initial surface roughness of as-polished samples, Ra/μm B-I = 50% in cortical bone part (about four times higher than as-polished Ti) were provided by only hydrothermal process without anodizing after immersing into 5PBS(-).

Osteoconductivity of Superhydrophilic Anodized TiO₂Coatings on Ti Treated with Hydrothermal Processes

Surface hydrophilicity is considered to have a strong influence on the biological reactions of bone-substituting materials. However, the influence of a hydrophilic surface on osteoconductivity is not completely clear, especially for superhydrophilic surfaces. In this study, we conferred superhydrophilic properties on anodized TiO2 coatings using a hydrothermal treatment, and developed a method to maintain this surface until implantation. The osteoconductivity of these coatings was evaluated with in vivo tests. A hydrothermal treatment made the surface of as-anodized samples more hydrophilic, up to a water contact angle of 13 (deg.). Storage in both air and distilled water increased the water contact angle after several days because of the adsorption of hydrocarbon. However, storage in phosphate buffered solution led to a reduction in the water contact angle, because of the adsorption of the inorganic ions in the solution, and the sample retained its high hydrophilicity for a long time. As the water contact angle decreased, the hard tissue formation ratio increased continuously up to 58%, which was about four times higher than the hard tissue formation ratio on as-polished Ti.

Fabrication of superhydrophilic surface on copper substrate by electrochemical deposition and sintering process

Superhydrophilic surfaces were fabricated on copper substrates by an electrochemical deposition and sintering process. Superhydrophobic surfaces were prepared by constructing micro/nano-structure on copper substrates through an electrochemical deposition method. Conversion from superhydrophobic to superhydrophilic was obtained via a suitable sintering process. After reduction sintering, the contact angle of the superhydrophilic surfaces changed from 155° to 0°. The scanning electron microscope （SEM） images show that the morphology of superhydrophobic and superhydrophilic surfaces looks like corals and cells respectively. The chemical composition and crystal structure of these surfaces were examined using energy dispersive spectrometry （EDS） and X-ray diffraction （XRD）. The results show that the main components on superhydrophobic surfaces are Cu, Cu2O and CuO, while the superhydrophilic surfaces are composed of Cu merely. The crystal structure is more inerratic and the grain size becomes bigger after the sintering. The interracial strength of the superhydrophilic surfaces was investigated, showing that the interfacial strength between superhydrophilic layer and copper substrate is considerably high.

Wettability Control between Oleophobic/Superhydrophilic and Superoleophilic/Superhydrophobic Characteristics on the Modified Surface Treated with Fluoroalkyl End-Capped Oligomers/Micro-Sized Polystyrene Particle Composites

Fluoroalkyl end-capped vinyltrimethoxysilane-N,N-dimethylacrylamide cooligomer [RF-(CH2-CHSi(OMe)3)x-(CH2-CHC(=O)NMe2)y-RF;RF = CF(CF3)OC3F7: RF-(VM)x-(DMAA)y-RF] was synthesized by reaction of fluoroalkanoyl peroxide [RF-C(=O)O-O(O=)C-RF] with vinyltrimethoxysilane (VM) and N,N-dimethylacrylamide (DMAA). The modified glass surface treated with the cooligomeric nanoparticles [RF-(VM-SiO3/2)x-(DMAA)y-RF] prepared under the sol-gel reaction of the cooligomer under alkaline conditions was found to exhibit an oleophobic/superhydrophilic property, although the corresponding fluorinated homooligomeric nanoparticles [RF-(VM-SiO3/2)n-RF] afforded an oleophobic/hydrophobic property on the modified surface under similar conditions. RF-(VM-SiO3/2)n-RF/RF-(VM-SiO3/2)x-(DMAA)y-RF/PSt (micro-sized polystyrene particles) composites, which were prepared by the sol-gel reactions of the corresponding homooligomer and cooligomer in the presence of PSt particle under alkaline conditions, provided an oleophobic/superhydrophilic property on the modified surface. However, it was demonstrated that the surface wettability on the modified surface treated with the RF-(VM-SiO3/2)n-RF/RF-(VM-SiO3/2)x-(DMAA)y-RF/PSt composites changes dramatically from oleophobic/superhydrophilic to superoleophilic/superhydrophilic and superoleophilic/superhydrophobic characteristics, increasing with greater feed ratios (mg/mg) of the RF-(VM)n-RF homooligomer in homooligomer/cooligomer from 0 to 100 in the preparation of the composites. Such controlled surfac

Role of Multi-scale Hierarchical Structures in Regulating Wetting State and Wetting Properties of Structured Surfaces

Amplifying the intrinsic wettability of substrate material by changing the solid/liquid contact area is considered to be the main mechanism for controlling the wettability of rough or structured surfaces.Through theoretical analysis and experimental exploration,we have found that in addition to this wettability structure amplification effect,the surface structure also simultaneously controls surface wettability by regulating the wetting state via changing the threshold Young angles of the Cassie-Baxter and Wenzel wetting regions.This wetting state regulation effect provides us with an alternative strategy to overcome the inherent limitation in surface chemistry by tailoring surface structure.The wetting state regulation effect created by multi-scale hierarchical structures is quite significant and plays is a crucial role in promoting the superhydrophobicity,superhydrophilicity and the transition between these two extreme wetting properties,as well as stabilizing the Cassie-Baxter superhydrophobic state on the fabricated lotus-like hierarchically structured Cu surface and the natural lotus leaf.

Wettability regulation from superhydrophilic to superhydrophobic via nanosecond laser ablation

Metal surfaces play a crucial role in numerous applications,from self-cleaning and anti-icing to anti-fogging and oil-water separation.The regulation of their wettability is essential to enhance their performance in these areas.This paper proposes a multi-state regulation method for metal surface wettability,leveraging nanosecond laser ablation.By creating non-uniform microstructures on a metal surface,the contact area between the solid and liquid phases can be increased,resulting in the attainment of superhydrophilic properties(contact angle(CA),ranging from 4.6°to 8.5°).Conversely,the construction of uniform microstructures leads to a decreased solid-liquid contact area,thereby rendering the metal surface hydrophilic(CA=12.2°–53°).Furthermore,through heat treatment on a surface with uniform microstructures,organic matter adsorption can be promoted while simultaneously reducing surface energy.This process results in the metal surface acquiring hydrophobic properties(CA=92.1°–133.5°),facilitated by the“air cushion effect.”Building on the hydrophobic surface,stearic acid modification can further reduce surface energy,ultimately bestowing the metal surface with superhydrophobic properties(CA=150.1°–152.7°,and sliding angle=3.8°).Performance testing has validated the durability and self-cleaning effectiveness of the fabricated superhydrophobic surface while also highlighting the excellent anti-fog performance of the superhydrophilic surface.These findings strongly indicate the immense potential of these surfaces in various engineering applications.

Superhydrophilic nickel hydroxide ultrathin nanosheets enable high-performance asymmetric supercapacitors

Superhydrophilic surfaces have been applied for supercapacitor;however,during energy storage reaction,how the wettability affects the process of electrochemical reaction specifically is still unclear.Herein,we demonstrate superhydrophilic surface for promotion of electrochemical reactions by liquid affinity and further explain the mechanism,where the transition of the wettability state caused by the change in surface free energy is the main reason for the obvious increase in specific capacitance.Through citric acid assistance strategy,an intrinsically hydrophobic Ni(OH)_(2)thick nanosheets(HNHTNs,16 nm)can be transitioned into superhydrophilic Ni(OH)_(2)ultrathin nanosheets(SNHUNs,6.8 nm),where the water contact angle was 0°and the surface free energy increased from 8.6to 65.8 mN·m^(-1),implying superhydrophilicity.Compared with HNHTNs,the specific capacitance of SNHUNs is doubled:from 1230 F·g^(-1)(HNHTNs)to 2350 F·g^(-1)(2A·g^(-1))and,even at 20 A·g^(-1),from 833 F·g^(-1)(HNHTNs)to 1670 F·g^(-1).The asymmetric capacitors assembled by SNHUNs and activated carbon show 52.44 Wh·kg^(-1)at 160W·kg^(-1)and excellent stability with~90%retention after5000 cycles(~80%retention after 9500 cycles).The promotion of electrochemical performances is ascribed to the change of surface wettability caused by surface free energy,which greatly increase affinity of electrode to the surrounding liquid environment to reduce the interface resistance and optimize the electron transport path.

An unusual superhydrophilic/superoleophobic sponge for oil-water separation

Development of porous materials with anti-fouling and remote controllability is highly desired for oil-water separation application yet still challenging. Herein, to address this challenge, a sponge with unusual superhydrophilicity/superoleophobicity and magnetic property was fabricated through a dip-coating process. To exploit its superhydrophilic/superoleophobic property, the obtained sponge was used as a reusable water sorbent scaffold to collect water from bulk oils without absorbing any oil. Owing to its magnetic property, the sponge was manipulated remotely by a magnet without touching it directly during the whole water collection process, which could potentially lower the cost of the water collection process. Apart from acting as a water-absorbing material, the sponge can also be used as affiliation material to separate water from oil-water mixture and oil in water emulsion selectively, when fixed into a cone funnel. This research provides a key addition to the field of oil-water separation materials.