Junhui He

Self-cleaning antireflective coatings assembled from peculiar mesoporous silica nanoparticles.

Novel mesoporous silica nanoparticles of peculiar shapes were synthesized, from which hierarchically porous silica coatings were fabricated on glass substrates via layer-by-layer (LbL) assembly, followed by calcination. These porous silica coatings were highly transparent and superhydrophilic. The maximum transmittance reached as high as 94%, whereas that of the glass substrate is 91%. The time for a droplet to spread lower than 5 degrees decreased to as short as 0.25 s. After the coating surface was treated with a low surface energy material, the surface became superhydrophobic (water contract angle >150 degrees) with a very low sliding angle of <1 degree. Compared with MCM-41-type mesoporous silica nanoparticles, the coatings fabricated using the novel mesoporous silica nanoparticles possess much better self-cleaning property. We used scanning (SEM) and transmission (TEM) electron microscopy to observe the morphology and structure of nanoparticles and surfaces. Transmission spectra and their change with time were characterized by UV-vis spectrophotometer. We studied the surface wettability by a contact angle/interface system. The influence of mesopores on the transmittance and wetting properties of coatings was discussed on the basis of experimental observations.

Fabrication of highly transparent superhydrophobic coatings from hollow silica nanoparticles.

We herein report a simple and effective method to fabricate excellent transparent superhydrophobic coatings. 3-Aminopropytriethoxysilane (APTS)-modified hollow silica nanoparticle sols were dip-coated on slide glasses, followed by thermal annealing and chemical vapor deposition with 1H,1H,2H,2H-perfluorooctyltrimethoxysilane (POTS). The largest water contact angle (WCA) of coating reached as high as 156° with a sliding angle (SA) of ≤2° and a maximum transmittance of 83.7%. The highest transmittance of coated slide glass reached as high as 92% with a WCA of 146° and an SA of ≤6°. A coating simultaneously showing both good transparency (90.2%) and superhydrophobicity (WCA: 150°, SA: 4°) was achieved through regulating the concentration of APTS and the withdrawing speed of dip-coating. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) were used to observe the morphology and structure of nanoparticles and coating surfaces. Optical properties were characterized by a UV-visible spectrophotometer. Surface wettability was studied by a contact angle/interface system. The effects of APTS concentration and the withdrawing speed of dip-coating were also discussed on the basis of experimental observations.

Synthesis of Raspberry-Like SiO2–TiO2 Nanoparticles toward Antireflective and Self-Cleaning Coatings

Silica-titania core-shell nanoparticles of 30, 40, 50, 55, 75, and 110 nm were prepared from tetraethyl orthosilicate (TEOS) and tetraisopropyl titanate (TIPT). After calcination, the amorphous titania shell transformed into anatase nanoparticles, and the silica-titania core-shell nanoparticles became raspberry-like nanoparticles. These nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and UV-vis spectroscopy. Hierarchically structured antireflective and self-cleaning particulate coatings were fabricated on glass substrates via layer-by-layer (LbL) assembly using silica-titania core-shell nanoparticles and silica nanoparticles as building blocks followed by calcination. The maximum transmittance of coated glass substrates reached as high as ca. 97%, while that of the glass substrates is only ca. 91%. The morphologies of the coatings were observed by SEM and atom force microscopy (AFM). Such hierarchically structured raspberry-like SiO2-TiO2 nanoparticle coatings had superhydrophilic and antifogging properties. The coatings also showed photocatalytic activity toward organic pollutants and thus a self-cleaning property.

Facile Fabrication of Hierarchically Structured Silica Coatings from Hierarchically Mesoporous Silica Nanoparticles and Their Excellent Superhydrophilicity and Superhydrophobicity

Silica coatings with hierarchical structures were prepared on glass substrates via layer-by-layer assembly using hierarchically mesoporous silica nanoparticles as building block. These coatings demonstrated excellent superhydrophilic properties. After hydrophobic modification, the obtained coatings exhibited hydrophobic properties in the measurements of water contact angles by employing contact-mode and drip-mode, respectively. Water droplet of large volume (15 muL) had a smaller sliding angle than that of small volume (3 muL) when using the contact-mode due to the role of gravity despite the existence of large adhesive force between water droplet and the coating surface, while very small sliding angles were noted when using the drip-mode because of the existence of kinetic energy. The transmittance of fabricated coatings was enhanced and reduced, respectively, in the long and short wavelength ranges as compared with blank slide glass.

Fine tuning of the morphology of copper oxide nanostructures and their application in ambient degradation of methylene blue.

In this work, flower-like, boat-like, plate-like and ellipsoid-like copper oxide (CuO) nanostructures were fabricated by simple modulation of reaction conditions. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, nitrogen adsorption-desorption measurements and UV-visible diffuse reflectance spectra were employed to characterize the obtained CuO nanostructures. Reactants, hydrothermal temperature and time were found to largely affect the morphology and structure of CuO nanostructures. Flower-like and boat-like CuO nanostructures were successively fabricated by increasing hydrothermal time. Plate-like and ellipsoid-like CuO nanostructures were produced by modulating the use of polyethylene glycol (PEG) and NH(3)·H(2)O. The formation mechanisms were proposed based on the experimental results, which show that both PEG and NH(3)·H(2)O play an important role in the formation of the morphology and structure of CuO. The catalytic activity of the as-prepared CuO nanostructures was demonstrated by catalytic oxidation of methylene blue (MB) in presence of hydrogen peroxide (H(2)O(2)). The as-prepared CuO nanostructures all show good catalytic activity.

Highly selective phosphorescent nanoprobes for sensing and bioimaging of homocysteine and cysteine

Most of reported fluorescent probes for mercapto amino acids are organic dyes. They often exhibit poor water-solubility and require the use of biologically toxic organic solvents in sensing and bioimaging. In the present study, a biocompatible phosphorescent nanoprobe by using mesoporous silica nanoparticles as carriers and an iridium(III) complex as signaling units was demonstrated. The nanoprobe exhibits a naked-eye double-signal response for the detection of homocysteine (Hcy) and cysteine (Cys) in pure phosphate buffer saline (PBS), which provides the advantage in effectively avoiding the interference from background signal of biological samples and environmental effects. In addition, the response mechanism, cytotoxicity and bioimaging were studied in detail. These results demonstrated that such a design strategy of phosphorescent nanoprobes is an effective way to develop excellent phosphorescent cellular probes for live cell applications.

In situ assembly of raspberry- and mulberry-like silica nanospheres toward antireflective and antifogging coatings.

Raspberry- and mulberry-like hierarchically structured silica particulate coatings were fabricated via facile in situ layer-by-layer assembly with monodisperse silica nanoparticles (NPs) of two different sizes followed by calcination. Raspberry-like and mulberry-like silica particulate coatings were achieved when the size ratio of two silica particles was 20/200 and 20/70 nm, respectively. The latter coating exhibited good antireflective property. Its maximum transmittance reached as high as 97%, whereas that of the glass substrate is only 91%. The morphologies of the coatings were observed by scanning electron microscopy and atom force microscopy. The surface properties of these coatings were investigated by measuring their water contact angles and the spreading time of water droplet. The results showed that such hierarchically structured coatings had superhydrophilic and antifogging properties.

CuO Nanostructures As Quartz Crystal Microbalance Sensing Layers for Detection of Trace Hydrogen Cyanide Gas

In this work, quartz crystal microbalance (QCM) sensors for detection of trace hydrogen cyanide (HCN) gas were developed based on nanostructural (flower-like, boat-like, ellipsoid-like, plate-like) CuO. Responses of all the sensors to HCN were found to be in an opposite direction as compared with other common volatile substances, offering excellent selectivity for HCN detection. The sensitivity of these sensors is dependent on the morphology of CuO nanostructures, among which the plate-like CuO has the highest sensitivity (2.26 Hz/μg). Comparison of the specific surface areas of CuO nanostructures shows that CuO of higher surface area (9.3 m(2)/g) is more sensitive than that of lower surface area (1.5 m(2)/g), indicating that the specific surface area of these CuO nanostructures plays an important role in the sensitivity of related sensors. On the basis of experimental results, a sensing mechanism was proposed in which a surface redox reaction occurs between CuO and Cu(2)O on the CuO nanostructures reversibly upon contact with HCN and air, respectively. The CuO-functionalized QCM sensors are considered to be a promising candidate for trace HCN gas detection in practical applications.

One-Step Hydrothermal Creation of Hierarchical Microstructures toward Superhydrophilic and Superhydrophobic Surfaces

This article describes a simple and convenient method to fabricate hierarchically structured coatings on glass substrates from soda lime glass by one-step hydrothermal method. The surfaces of the coatings are rough and are composed of flower-like particles assembled by nanoflakes or urchin-like particles constructed by nanowires. These rough surfaces exhibit superhydrophilicity, their water contact angles reaching 0 degrees in less than 40 ms. After surface modification by 1H,1H,2H,2H-perfluorooctyltriethoxysilane, the wetting properties of these coatings switch from superhydrophilicity to superhydrophobicity, with water contact angles as high as 160 degrees and slide angle as low as 1 degrees . The formation mechanism of the hierarchically structured coatings is discussed in detail on the basis of experimental results.

Hierarchically Structured Porous Films of Silica Hollow Spheres via Layer-by-Layer Assembly and Their Superhydrophilic and Antifogging Properties

Raspberrylike organic/inorganic composite spheres are prepared by stepwise electrostatic assembly of polyelectrolytes and silica nanoparticles onto monodisperse polystyrene spheres. Hierarchically structured porous films of silica hollow spheres are fabricated from these composite spheres by layer-by-layer assembly with polyelectrolytes followed by calcination. The morphologies of the raspberrylike organic/inorganic composite spheres and the derived hierarchically structured porous films are observed by scanning and transmission electron microscopy. The surface properties of these films are investigated by measuring their water contact angles, water-spreading speed, and antifogging properties. The results show that such hierarchically structured porous films of silica hollow spheres have unique superhydrophilic and antifogging properties. Finally, the formation mechanism of these nanostructures and property-structure relationships are discussed in detail on the basis of experimental observations.