AFM characterisation of sol‐gel TiO2 films deposited on stainless steel

One‐layer, two‐layer and three‐layer titania films on AISI 304 stainless steel were deposited by sol‐gel process and dip‐coating method. Two sols were prepared by using titanium isopropoxide as a precursor, propanol as a solvent, nitric acid as a catalyst and acetylacetone for peptization. Both of the prepared sols contained the same amount of mentioned components, the only difference was in the addition of polyethylene glycol (PEG) as templating reagent to one of the sols. After calcination at 550°C, deposited films on the stainless steel substrate were characterized by atomic force microscope (AFM). Influence of layer number as well as addition of polyethylene glycol on morphology of titania films was analysed and discussed. Generally, by increasing the number of layers and by addition of polyethylene glycol, roughness parameters increase by changing surface topography. The surface topography analysis is very important when choosing the adequate industrial application of prepared layers.     

Efficient Metal‐Free Electrocatalysts from N‐Doped Carbon Nanomaterials: Mono‐Doping and Co‐Doping

N‐doped carbon nanomaterials have rapidly grown as the most important metal‐free catalysts in a wide range of chemical and electrochemical reactions. This current report summarizes the latest advances in N‐doped carbon electrocatalysts prepared by N mono‐doping and co‐doping with other heteroatoms. The structure–performance relationship of these materials is subsequently rationalized and perspectives on developing more efficient and sustainable electrocatalysts from carbon nanomaterials are also suggested.     

Sulfur and Nitrogen Co‐Doped Graphene for Metal‐Free Catalytic Oxidation Reactions

Sulfur and nitrogen co‐doped reduced graphene oxide (rGO) is synthesized by a facile method and demonstrated remarkably enhanced activities in metal‐free activation of peroxymonosulfate (PMS) for catalytic oxidation of phenol. Based on first‐order kinetic model, S–N co‐doped rGO (SNG) presents an apparent reaction rate constant of 0.043 ± 0.002 min^?1, which is 86.6, 22.8, 19.7, and 4.5‐fold as high as that over graphene oxide (GO), rGO, S‐doped rGO (S‐rGO), and N‐doped rGO (N‐rGO), respectively. A variety of characterization techniques and density functional theory calculations are employed to investigate the synergistic effect of sulfur and nitrogen co‐doping. Co‐doping of rGO at an optimal sulfur loading can effectively break the inertness of carbon systems, activate the sp²‐hybridized carbon lattice and facilitate the electron transfer from covalent graphene sheets for PMS activation. Moreover, both electron paramagnetic resonance (EPR) spectroscopy and classical quenching tests are employed to investigate the generation and evolution of reactive radicals on the SNG sample for phenol catalytic oxidation. This study presents a novel metal‐free catalyst for green remediation of organic pollutants in water.     

二氧化钛薄膜材料的制备及其性能研究

采用溶胶-凝胶法,以钛酸丁酯[Ti(OC4O9)]4为原料,乙醇为溶剂,冰醋酸为抑制剂,制备了二氧化钛薄膜,同时以硝酸镧和硝酸镍为掺杂物制备了单掺、共掺的二氧化钛薄膜,研究了其可见光吸收性能和光催化降解性能。实验表明,掺杂后的二氧化钛薄膜在可见光区仍有明显吸收,掺镧的二氧化钛薄膜对亚甲基蓝降解效果较好,光催化降解率达到76.54%。     

Synthesis of organic-inorganic hybrid sols with nano silica particles and organoalkoxysilanes for transparent and high-thermal-resistance coating films using sol-gel reaction

Organic-inorganic hybrid sols were synthesized from nano silica particles dispersed in water and from organoalkoxysilanes, using the sol-gel reaction. This work focuses on the effects of the three multifunctional organoalkoxysilanes dimethyldimethoxysilane (DMDMS), methyltrimethoxysilane (MTMS), and tetramethoxysilane (TMOS) to form a transparent and high-thermal-resistance coating film. The stability of the hybrid sol was evaluated as a function of the reaction time for 10 d through the variation of the viscosity. The viscosity of the silica/DMDMS and silica/MTMS sol was slightly increased for 10 d. The multifunctional organoalkoxysilanes formed dense silica networks through hydrolysis and condensation reaction, which enhanced the thermal resistance of the coating films. No thermal degradation of the silica/DMDMS sample occurred up to 600 degrees C, and none of the silica/MTMS and silica/TMOS samples occurred either up to 700 degrees C. The organic-inorganic hybrid sols were coated on the glass substrate using a spin-coating procedure. The organic-inorganic hybrid sols formed flat coating films without cracks. The transmittance of the hybrid sol coating films using MTMS and DMDMS was shown to be over 90%. The transmittance of the silica/TMOS sol coating film reacted for 10 d abruptly decreased due to faster gelation. The silica/DMDMS and silica/MTMS hybrid sols formed smooth coating films while the surface roughness of the silica/TMOS coating film markedly increased when the hybrid sol reacted for 10 d. The increase of the surface roughness of the silica/TMOS coating film can be attributed to the degradation of the stability of the hybrid sol and to the loss of transmittance of the coating film. It was confirmed in this study that the use of organic-inorganic hybrid sol can yield transparent and high-thermal-resistance coating films.     

Surface structure of the TiO2 thin film photocatalyst

Control of the surface structure of titanium dioxide thin film photocatalysts was successfully carried out by a polymer-doped dip-coating process. The thin films prepared were either transparent or opaque, depending on the molecular weight of the polymer doped. All the thin film photocatalysts had anatase form with similar crystallinity. The surface of the transparent thin films looked plain consisting of uniformly aggregated nanometer-size TiO2 particles, while the opaque thin films were formed of cubic crystalline TiO2 at the micrometer level. Both the transparent and opaque films showed catalytic activity for the elimination of NOx in air. The specific surface area and photocatalytic activity of the transparent thin film was almost the same as that of the opaque one. The activity of the thin films was almost equal to the commercial photocatalyst P25. Decrease in the film thickness led to a decrease of the elimination of NO in air by the thin films. The thin films were porous and the surface area was dependent on the film thickness. Adsorbed NO was photooxidized to NO2 by the thin films, while the NO2 formed was re-photooxidized to HNO3 before the desorption of NO2 from the film surface.     

Funktionelle Beschichtungen auf Basis anorganischer Nanosole

Functional coatings on basis of inorganic nanosols The controlled hydrolysis of silicon or metal alkoxides produces nanoparticulate oxide sols which condense to thin transparent gel films on any substrates after coating and drying (so‐called “sol‐gel process”). The co‐hydrolysis and co‐condensation of different alkoxides (chemical modification) as well as the embedding of different additives (physical modification) offers almost unlimited possibilities to vary the properties of nanosols and, therefore, also of the resulting coatings, and to adapt them to the purpose intended. By coating of flexible substrates like textiles, papers or polymer foils it is possible to combine the material protecting functions of the inorganic oxide layer with new functional qualities, e. g. modification of surface energy and charge, alteration of the optical properties, realization of biocompatible and bioactive properties.     

Role of iron and chromium in the photocatalytic activity of titanium dioxide films on stainless steel

Photocatalytically active titanium dioxide films have been formed on stainless steel grids via sol–gel process followed by heat treatment in the temperature range of 450–550°C. During UV irradiation of the films in an aqueous solution of the Rhodamine B dye and in distilled water we have detected iron and chromium dissolution from uncoated grid regions and the deposition of iron and chromium compounds onto the titanium dioxide surface. The deposition rate of these compounds increases with annealing temperature, which leads to a decrease in the photocatalytic activity of the films.     

Effect of cobalt doping on the structural and optical properties of TiO2 films prepared by sol-gel process

Pure and cobalt doped titanium dioxide thin films have been prepared on glass and Si (100) substrates by sol-gel spin coating method. The structural and optical properties of the films as a function of cobalt concentration (up to 15 wt.%) have been systematically studied by Rutherford backscattering spectroscopy, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, optical spectroscopy and spectroscopic ellipsometry methods. Rutherford backscattering studies show the presence of cobalt dopant in the films is almost equal to the precursor stoichiometry. Grazing incidence X-ray diffraction and Raman spectroscopy studies confirm the amorphous phase of the as-deposited films and crystalline anatase phase for the films annealed at 600 °C. The optical spectroscopy measurements show that the films are fully transparent in the visible region and there is a band gap narrowing upon increasing cobalt dopant concentration. The refractive index, band gap (E_g) and thickness of the films were determined from spectroscopic ellipsometry measurements. The refractive index of the films was found to increase from 2.2 to 2.7 with the increase in cobalt concentration with a simultaneous decrease of band gap from 3.1 to 2.8, which is favorable for photocatalytic applications. The packing density of the films was calculated by Clausius-Mossotti relation and is found to increase with cobalt concentration.     

Controlled adsorption of titanium(IV) oxide particles on electroplated zinc coatings to improve the corrosion resistance of chromium(VI)‐free conversion layers

Adsorption of nano‐scaled titanium(IV) oxide particles on electroplated zinc is performed by a simple dip‐coating technique in an aqueous titanium(IV) oxide suspension prepared with a stirred media mill. X‐ray photoelectron spectroscopy, scanning electron microscopy and X‐ray fluorescence spectroscopy are carried out to investigate the composition of the zinc surface and the thickness and porosity of the adsorbed titania films. The zinc surface formed during the electrodeposition process is of oxyhydroxide nature and the thickness of the adsorbed titania particle layer is controlled by the pH value and the solid concentration of the suspension. In the range of 10 wt.%–30 wt.% titanium(IV) oxide, a linear dependence between the titania film thickness and the solid content of titania particles in the suspension is found. Highest film thicknesses are obtained in alkaline media (pH≥9). At 13.5 wt.% titania particles and pH values below pH = 2.4, the titania particle film is not closely packed and the zinc layer underneath is still visible in electron microscopy, which is a prerequisite for imbedding these particles by a thin second zinc layer for formation of a robust chromium(VI)‐free passivation layer containing the titania particles.     

Hydroxyapatite coating by dipping method,and bone bonding strength

Hydroxyapatite (HA) was coated onto titanium rods by a dip coating method using HA sol. The HA sols were prepared by dispersing HA crystals less than 100 nm length in distilled water or physiological salt solution using an ultrasonic homogenizer. The surface of the HA coating was homogeneous as determined by scanning electron microscopy (SEM). After implantation of uncoated and HA dip coated titanium rods in dog femurs, new bone formation was observed only around the coated material. The bone bonding strength to HA coated rods was 1.0, 1.5, 2.0 and 2.5 Mpa after 1,2,3 and 4 weeks implantation, respectively, as determined by pull-out testing. These values were over twice that of the uncoated titanium rods at 1–4 weeks after implantation. The dip coated titanium exhibited superior biocompatibility to the uncoated implant and may be of great value for bone repacement applications.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September.     

Development and characterization of sol‐gel composite coatings on aluminum alloys for corrosion protection

For several years, Cr^IV compounds were used as effective and inexpensive corrosion inhibitors. Studies showed that these materials were toxic and carcinogenic. This has led to extensive research to develop alternative inhibitors. Organo‐silicate hybrid coatings appeared as an effective technique for forming protective layers on different metal alloys. A silane film was obtained by dip coating of the sample in sol solution prepared from the hydrolysis of 3‐glycidoxypropyltrimethoxysilane (GPTM), tetraethylorthosilicate (TEOS) with acid as catalyst and water as solvent instead of VOC (volatile organic compound). The sol solution was aged at ambient temperature to to enhance the effectiveness of the solution for the hydrolysis process. The sample was cured at 150 °C to ensure cross‐linking of the film. The experiments have shown that heat treatment leads to increased density and corrosion resistance of the films. Organic and inorganic inhibitors were added in different concentrations to improve the protection and self‐healing properties of the coating even after long‐time immersion in corrosive solution. The protection performance of the film was evaluated by electrochemical impedance spectroscopy (EIS) in 0.5 M NaCl solution (pH value 7). The surface morphologies of the treated samples were investigated using SEM.     

Ergebnisse von Sol‐Gel‐Beschichtungen auf austenitischem CrNi‐Stahl

Results from sol‐gel coatings on austenitic CrNi steel Thin aliuminia films were applicated on austenitic CrNi steel by sol‐gel‐process and tested with several examinations. The phase transformation and the measuring of residual stresses in the coatings were investigated by X‐ray diffraction. This research was completed by wear tests.     

Titania powder modified sol-gel process for photocatalytic applications

Thick films of TiO₂ were prepared on glass and stainless steel substrates using an alkoxide sol-gel process modified by addition of Degussa P-25 powder. The prepared films were characterized by SEM, EDS, XRD and other methods. The TiO₂ films obtained from the powder modified sol were compared to films obtained from the alkoxide sol-gel without modification. The films obtained from the modified sol-gel were about ten times thicker for a single dip coating/heat treatment cycle than the films obtained from the sol without powder addition. The prepared thick films were smooth and free of macrocracking, fracture or flaking. The grain size of these films was uniform and in the range 100–150 nm and the films were a mixture of anatase and rutile TiO₂. The films obtained from the powder modified sol on the stainless steel substrate were also much harder compared to the films obtained from sols without modification and displayed excellent adhesion to the substrate.     

Hydroxyapatite/Bioactive Glass Films Produced by a Sol–Gel Method: In Vitro Behavior

Hydroxyapatite (HA) and HA/bioactive glass (49S) films were deposited on Si(100) substrates by a sol–gel dip‐coating method. The microstructure and in vitro bioactivity of the films were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X‐ray photoelectron spectroscopy (XPS). Polycrystalline HA and amorphous bioactive glass films were obtained after annealing at 600 and 400 °C, respectively. The crystallization temperature of HA was determined to be around 568 °C. The surfaces of the HA films were covered with an apatite layer consists of spherulites formed by nanosized needle‐like aggregates after the soaking in simulated body fluid (SBF) for 10 days, while amorphous HA/bioactive glass surface was covered with larger spherical crystallites. Both XPS and EDS results obtained from HA/bioactive glass film, after soaking in SBF, showed increasing P amounts on the surface at the expense of Si. The higher density of the newly formed layer on HA/bioactive glass surface than that of the HA surface after 10 days of soaking was evidence of increased reaction rate and apatite forming ability when bioactive glass layer is present on the HA films.     

Graphene‐Supported Mesoporous Carbons Prepared with Thermally Removable Templates as Efficient Catalysts for Oxygen Electroreduction

Graphene‐supported mesoporous carbons with rich nitrogen self‐doped active sites (N‐MC/rGO) are prepared by direct pyrolysis of a graphene‐oxide‐supported polymer composite embedded with massive, evenly distributed amorphous FeOOH that serve as efficient thermally removable templates. The resulting N‐MC/rGO catalysts exhibit high surface areas and apparent electrocatalytic activity for oxygen reduction reaction in alkaline media. Among the series, the sample prepared at 800 °C displays the best performance with a more positive onset potential, higher limiting currents, much higher stability, and stronger poison resistance than commercial Pt/C. This is ascribed to the synergetic functions of the highly conductive graphene support and the mesoporous N‐doped carbons that effectively impede the restacking of the graphene sheets and enhance the exposure of the rich nitrogen self‐doped active sites.     

Influence of co‐monomer structure on properties of co‐polyamide packaging films

In this work a series of co‐polyamides were prepared by random polymerization of ?‐caprolactam in presence of four different co‐monomers at a percentage of 5% w/w, with the aim of verifying their suitability as film‐forming materials. The effects of structural changes induced in the ?‐caprolactam homopolymer by co‐monomers were evaluated in both molten and solid states. Rheological tests in shear and elongational flow were performed to evaluate the processability of co‐polyamides. Cast films were obtained and their thermal, mechanical and transport properties were evaluated to establish the performances of the co‐polyamides in view of packaging applications. The results indicate that co‐polyamide films having a partially aromatic structure display the best mechanical performances and show a significant improvement in barrier properties to gases compared to the homopolymer. Copyright © 2002 John Wiley & Sons, Ltd.     

Fabrication of Flexible and Transparent Conductive Nanosheets by the UV‐Irradiation of Gold Nanoparticle Monolayers

Conductive films that are highly transparent and flexible are extremely attractive for emerging optoelectronic applications. Currently, indium‐doped tin oxide films are the most widely used transparent conductive films and much research effort is devoted to developing alternative transparent conductive materials to overcome their drawbacks. In this work, a novel and facile approach for fabricating transparent conductive Au nanosheets from Au nanoparticles (AuNPs) is proposed. Irradiating an AuNP monolayer at the air–water interface with UV light results in a nanosheet with ≈3.5 nm thickness and ≈80% transparency in the UV–visible region. Further, the so‐fabricated nanosheets are highly flexible and can maintain their electrical conductivity even when they are bent to a radius of curvature of 0.6 mm. Fourier‐transform infrared and X‐ray photoelectron spectroscopy characterizations reveal that the transformation of the monolayer of AuNPs into the nanosheet is induced by the photodecomposition and/or photodetachment of the dodecanethiol ligands capping the AuNPs. Further, the UV‐irradiation of a hybrid monolayer consisting of AuNPs and silica particles affords the patterning of Au nanosheets with periodic hole arrays.     

Significant Enhancement of Water Splitting Activity of N‐Carbon Electrocatalyst by Trace Level Co Doping

Replacement of precious metal electrocatalysts with highly active and cost efficient alternatives for complete water splitting at low voltage has attracted a growing attention in recent years. Here, this study reports a carbon‐based composite co‐doped with nitrogen and trace amount of metallic cobalt (1 at%) as a bifunctional electrocatalyst for water splitting at low overpotential and high current density. An excellent electrochemical activity of the newly developed electrocatalyst originates from its graphitic nanostructure and highly active Co‐N_x sites. In the case of carefully optimized sample of this electrocatalyst, 10 mA cm^?2 current density can be achieved for two half reactions in alkaline solutions—hydrogen evolution reaction and oxygen evolution reaction—at low overpotentials of 220 and 350 mV, respectively, which are smaller than those previously reported for nonprecious metal and metal‐free counterparts. Based on the spectroscopic and electrochemical investigations, the newly identified Co‐N_x sites in the carbon framework are responsible for high electrocatalytic activity of the Co,N‐doped carbon. This study indicates that a trace level of the introduced Co into N‐doped carbon can significantly enhance its electrocatalytic activity toward water splitting.     

掺银TiO2薄膜的亲水特性

采用溶胶—凝胶法及浸渍提拉法在普通的载玻片上制得含不同掺银量的TiO2薄膜，通过对薄膜及相应粉体的XRD、XPS及薄膜致密度的测量，分析了银的掺杂量对TiO2薄膜亲水特性的影响。结果表明：TiO2薄膜中银的掺杂量≤0．635mol％时有利于TiO2薄膜亲水性能的改善；表面羟基和表面桥氧的含量对TiO2薄膜的亲水性能均有直接影响。