Fabrication of bulk macroporous zirconia by combining sol–gel with calcination processes

Macroporous yttria-stablized tetragonal zirconia has been synthesized combining the sol–gel with Pechini method. Polyacetylacetonatozirconium (PAZ) served as the zirconium precursor while polyvinyl alcohol (PVA) was used as pore template. The thermal behaviors of xerogel and porous zirconia were determined by thermogravimetric/differential thermal analysis (TG/DTA). FT-IR, FE-SEM, and XRD analysis indicated that the organic components of xerogel have been completely removed and porous zirconia was formed after annealing at 600 °C for 2 h in air. The skeleton is composed of zirconia particles with diameter of about 60 nm and the pore diameter is about 68 nm. The surface area and pore volume of the bulk macroporous yttria-stablized tetragonal zirconia are 9.4 m²/g and 0.016 cm³/g, respectively, evaluated from nitrogen adsorption/desorption measurements.     

Electrosynthesis of thin sol–gel films at a three-phase junction

Thin, functionalised silica films of between 4 and 15 nm thickness were prepared by sol–gel processing at an electrode organic phase aqueous phase junction by slow withdrawal of a conducting support through the liquid–liquid interface. Protons were electrogenerated in the aqueous phase and catalysed the hydrolysis of the sol–gel precursor in the organic phase. The film was characterised using atomic force microscopy, scanning electron microscopy, ellipsometry, infrared spectroscopy, voltammetry and scanning electrochemical microscopy. The thickness, electrodeposited on gold, was determined to be less than 10 nm and the density of imidazolium functional groups was estimated to be 1.2 molecules nm⁻². The film obtained on ITO is approximately twice thicker compared to the gold support.     

Electrochemically assisted deposition of sol–gel bio-composite with co-immobilized dehydrogenase and diaphorase

We report here that the electrochemically assisted deposition (EAD) of silica thin films can be a good strategy to co-encapsulate d-sorbitol dehydrogenase (DSDH) and diaphorase in an active form. This is achieved via the electrolysis of a hydrolyzed sol containing the biomolecules to initiate the poly-condensation of silica precursors upon electrochemically induced pH increase at the electrode/solution interface. DSDH was found to be very sensitive to the silica gel environment and the addition of a positively-charged polyelectrolyte was necessary to ensure effective operational behavior of the biomolecules. The composition of the sol and the conditions for electrolysis have been optimized with respect to the intensity of the electrochemical response to d-sorbitol oxidation. The K_m of DSDH in the electrodeposited film was in the range of 3 mM, slightly better than the value determined biochemically in solution (6.5 mM). The co-immobilization of DSDH and diaphorase in this way led on the one hand to the possible reduction of NAD⁺ to NADH (simultaneously to d-sorbitol oxidation) and on the other hand to the safe re-oxidation of the co-factor using a mediator (ferrocenedimethanol) as electron relay. The bioelectrocatalytic response looks promising for electro-enzymatic applications. To support this idea, the EAD of sol–gel bio-composite has been extended to macroporous electrodes displaying a much bigger electroactive surface area.     

Preparation and characterization of sol–gel derived UV-curable organo-silica–titania hybrid coatings

In this work, UV-curable organic–inorganic hybrid coatings based on cycloaliphatic epoxyacrylate were prepared by sol–gel technique. Acid catalyzed solutions of tetraethylorthosilane (TEOS) containing Ti:acac complex were used as an inorganic precursors. UV-curable, transparent hybrid coating materials were applied on plexiglass substrates and their coating performance was investigated by the analyses of various tests such as hardness, gloss, cross-cut adhesion tests, stress–strain test and optical transmission. The mechanical measurements showed that, the tensile properties of coatings underwent an abrupt change from a brittle to a tough material when the inorganic part was incorporated into the cycloaliphatic epoxy acrylate based organic network. UV–vis transmission spectroscopy results indicated that the hybrid materials with high titanium content have good transparences. The thermal behaviour of the coatings was also evaluated. It is observed that the thermal stability of the hybrids is enhanced with incorporation of sol–gel precursor.     

Effect of the addition of thermally activated hydrotalcite on the protective features of sol–gel coatings applied on AA2024 aluminium alloys

The present work assesses the effect of the thermal activation of hydrotalcite particles when they are added to a hybrid sol–gel film to improve its corrosion properties. Although previous studies have demonstrated the anti-corrosion properties of as-synthesised hydrotalcite particles incorporated into sol–gel coatings, their inhibitive action has not been well-established. Some hypotheses suggest that it should be related to their anion exchange capacity, which increases when the hydrotalcite is thermally activated.Several techniques were used to characterise the uncalcined and calcined hydrotalcite: X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric and differential scanning calorimetry techniques. To analyse the inhibition action, hybrid sol–gel coatings were doped with 10 wt% of CHT. Accelerated tests and electrochemical impedance spectroscopy were used for performance evaluation between the sol–gel coatings doped with calcined and uncalcined HT.The results obtained indicate the superior behaviour of samples doped with calcined HT at longer immersion times, which suggests better inhibition action.     

The effect of linker of electrodes prepared from sol–gel ionic liquid precursor and carbon nanoparticles on dioxygen electroreduction bioelectrocatalysis

The effect of linker of three-dimensional, hydrophilic-carbon-nanoparticle film-electrodes prepared by layer-by-layer method on redox probe accumulation and bioelectrocatalytic dioxygen reduction was studied and compared for two different electrode scaffolds. The linker in both of these scaffolds was based on the same ionic liquid sol–gel precursor, 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium bis(trifluoromethyl-sulfonyl)imide. The first electrode type was prepared by alternative immersion of tin doped indium oxide substrate in an aqueous suspension of carbon nanoparticles modified with phenyl sulphonic groups and a sol composed of ionic liquid sol–gel precursor and tetramethoxysilane. For the second electrode type sol was replaced by a methanolic suspension of silicate submicroparticles with appended imidazolium functional groups. In both films 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) anions accumulate irreversibly. In the case of the first electrode electrostatic attraction plays the more important role in comparison to the case of the second where stable adsorption of the redox probe takes place. After adsorption of bilirubin oxidase, electrodes obtained from sol and carbon nanoparticles exhibit modest bioelectrocatalytic activity towards dioxygen reduction at pH 4.8, however those obtained from oppositely charged particles are much more efficient. The magnitude of the associated catalytic current in both cases depends on the number of immersion and withdrawal steps. Interestingly, mediatorless catalysis at electrodes obtained from oppositely charged particles is more efficient than mediated catalysis.     

Preparation and photocatalytic properties of macroporous honeycomb alumina ceramics used for water purification

In this work, porous alumina ceramics with highly ordered capillaries were successfully fabricated by ionotropic gelation process of alginate/alumina suspensions. By varying the initial solid loading (10–30 wt%) of slurries, the porosity of alumina ceramics ranged from 60.4% to 79.5% with controlled pore size (180–315 μm). Due to the well-crosslinked macroporous structure and large specific surface areas, the porous ceramics were utilized as the photocatalyst supports of TiO₂ catalysts whose photocatalytic activity was characterized by degrading methyl blue under UV irradiation. TiO₂ coatings prepared by sol–gel method demonstrated excellent adhesion to the substrates. When the solid loading of supports reached 15 wt%, the TiO₂ coatings showed the highest photocatalytic efficiency of 79.52%. Besides, TiO₂ films possessed nearly the same photocatalytic activity as titania/water suspension. Thus, the honeycomb ceramic prepared by self-organization process holds promise for use as photocatalyst supports in water purification without recycling process of powders.     

Preparation and characterization of polyimide/Al2O3 hybrid films by sol–gel process

A sol–gel process has been developed to prepare polyimide (PI)/Al₂O₃ hybrid films with different contents of Al₂O₃ based on pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline (ODA) as monomers. FESEM and TEM images indicated that Al₂O₃ particles are relatively well dispersed in the polyimide matrix after ultrasonic treatment of the sol from aluminum isopropoxide and thermal imidization of the gel film. The dimensional stability, thermal stability, mechanical properties of hybrid PI films were improved obviously by an addition of adequate Al₂O₃ content, whereas, dielectric property and the elongation at break decreased with the increase of Al₂O₃ content. Surprisingly, the corona‐resistance property of hybrid film was improved greatly with increasing Al₂O₃ content within certain range as compared with pure PI film. Especially, the hybrid film with 15 wt % of Al₂O₃ content exhibited obviously enhanced corona‐resistance property, which was explained by the formation of compact Al₂O₃ network in hybrid film. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Corrosion protection performance of novel hybrid polyaniline/sol–gel coatings on an aluminium 2024 alloy in neutral, alkaline and acidic solutions

In this study the corrosion performance of a novel coating, consisting of a combination of silica sol–gel and conductive polymer, in 3.5% NaCl at different pH levels is presented. Electrochemical Impedance Spectroscopy showed the impedance of the coating remained stable for up to 24 months in neutral 3.5% NaCl solution. No corrosion or delamination was observed after 500 h in salt spray tests and Scanning Vibrating Electrode Technique tests showed the coating exhibited a “self healing” property. The surface morphology was characterised by Scanning Electron Microscopy and the mechanical properties, notably adhesion, were studied using pull off and cross cut techniques.     

Preparation and photocatalytic properties of RuO2/TiO2 composite nanotube arrays

RuO₂/TiO₂ composite nanotube arrays were prepared using an anodic oxidation method combined with dipping. The photocatalytic properties of RuO₂/TiO₂ nanotube arrays in methylene blue solution were investigated under visible light irradiation. The results showed that Ru existing in the form of RuO₂ was dispersed uniformly on the surface of TiO₂ nanotubes, and the RuO₂ did not change the crystal structure of TiO₂ nanotubes. The load of RuO₂ on TiO₂ had a little influence on the band-gap energy and the absorption band edge, but could increase the amount of Ti-OH functional groups on the surface of TiO₂ nanotubes. The RuO₂/TiO₂ nanotube arrays with the optimal photocatalytic activity were formed in the ruthenium chloride solution with a concentration of 0.0030 mol/L. The 2 h photocatalytic degradation rate of methylene blue increased from 38% for pure TiO₂ nanotubes to 69% for RuO₂/TiO₂ nanotube arrays. This work demonstrated that RuO₂/TiO₂ nanotube arrays showed an improved photocatalytic property over pure TiO₂ nanotubes due to the fact that RuO₂ could capture the photo-generated holes, which greatly decreased the recombination of the photo-generated electrons and holes, and hence lengthen the lifetime of photo-induced electrons and increased the amount of hydroxyl groups absorbed on the TiO₂ nanotubes surface.     

Preparation and characterization of composite membranes using blends of SPEEK/PBI with boron phosphate

In this contribution composite membranes have been prepared from acid-base polymer blend and solid inorganic proton conductive boron phosphate (BPO₄). The blends are composed of sulfonated polyether-ether ketone (SPEEK) as the acidic component and polybenzimidazole (PBI) as the basic component. The contents of solid BPO₄ in the composite membrane varied from 10 to 40 wt%. The conductivity of the composite membranes was measured by impedance spectroscopy at room temperature. The conductivity of the composite membranes was found to increase with the incorporation of boron phosphate particles into blend membranes. The highest conductivity of 6 mS/cm was found for composite membrane at room temperature. The membranes were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and FTIR which showed acid-base interaction in the blend membranes and also confirmed the presence of solid BPO₄ into the composite membranes. These membranes show good perspective in the membrane fuel cell applications.     

An electrochemical study of corrosion protection by in situ oxidative polymerization in phenylenediamine crosslinked sol–gel hybrid coatings

The three isomers of phenylenediamine have been used as crosslinking agents for epoxide decorated silica colloids generated by high water content sol–gel chemistry techniques. The resulting materials were used as corrosion protection thin films for aluminum alloys in corrosive environments. These hybrid epoxy-amine crosslinked sol–gel materials have demonstrated an order of magnitude improvement over similar materials crosslinked with aliphatic diamines along with novel electrochemical and coloration behavior. The processes behind these performance improvements are explored and two possibly complementary mechanisms are identified, namely exposure-triggered toughening of the materials through oxidative polymerization of the phenylenediamines and an increase in corrosion inhibition via the formation of electroactive phenylenediamine oligomers.     

TiO2涂层的溶胶—凝胶法制备及其光催化性能

用溶胶-凝胶法在釉面砖上制备了均匀的TiO_2涂层,讨论了影响TiO_2涂层质量的某些因素,用X射线光电子能谱仪研究了釉面涂层的化学组成.在紫外线及日光照射下,TiO_2涂层可以对敌敌畏光催化降解.     

Preparation and photocatalytic activity of g-C3N4/TiO2 heterojunctions under solar light illumination

The solar light sensitive g-C₃N₄/TiO₂ heterojunction photocatalysts containing 20, 50, 80, and 90 wt% graphitic carbon nitride (g-C₃N₄) were prepared by growing Titania (TiO₂) nanoparticles on the surfaces of g-C₃N₄ particles via one step hydrothermal process. The hydrothermal reactions were allowed to take place at 110 °C at autogenous pressure for 1 h. Raman spectroscopy analyses confirmed that an interface developed between the surfaces of TiO₂ and g-C₃N₄ nanoparticles. The photocatalyst containing 80 wt% g-C₃N₄ was subsequently heat treated 1 h at temperatures between 350 and 500 °C to improve the photocatalytic efficiency. Structural and optical properties of the prepared g-C₃N₄/TiO₂ heterojunction nanocomposites were compared with those of the pristine TiO₂ and pristine g-C₃N₄ powders. Photocatalytic activity of all the nanocomposites and the pristine TiO₂ and g-C₃N₄ powders were assessed by the Methylene Blue (MB) degradation test under solar light illumination. g-C₃N₄/TiO₂ heterojunction photocatalysts exhibited better photocatalytic activity for the degradation of MB than both pristine TiO₂ and g-C₃N₄. The photocatalytic efficiency of the g-C₃N₄/TiO₂ heterojunction photocatalyst heat treated at 400 °C for 1 h is 1.45 times better than that of the pristine TiO₂ powder, 2.20 times better than that of the pristine g-C₃N₄ powder, and 1.24 times better than that of the commercially available TiO₂ powder (Degussa P25). The improvement in photocatalytic efficiency was related to i) the generation of reactive oxidation species induced by photogenerated electrons, ii) the reduced recombination rate for electron-hole pairs, and iii) large specific surface area.     

A kinetic study of lithium transport in the sol–gel Cr0.11V2O5.16 mixed oxide

The kinetics of the electrochemical lithium insertion reaction in the sol–gel chromium–vanadium mixed oxide Cr_0.11V₂O_5.16 has been investigated using ac impedance spectroscopy. The chemical lithium diffusion coefficient is found to be in the range 10⁻⁸/10⁻¹² cm²/s depending the Li content over the wide Li composition range 0 < x < 2 in Li_xCr_0.11V₂O_5.16. The evolution of the cathode impedance is investigated as a function of the lithium content and cycles. The results are discussed in relation with the cycling properties of the electrode material and the unusual structural response of the sol–gel mixed oxide which consists of a single phase behaviour with a continuous cell volume expansion of 6–7% in the 0 < x < 2 range for Li_xCr_0.11V₂O_5.16. For x < 1, a comparison with available kinetic data for the parent oxide indicates a very close behaviour. Cr_0.11V₂O_5.16 is shown to be the best V₂O₅-based cathode material with an initial specific capacity of 280 mAh/g at C/10 rate and still 240 mAh/g after 50 cycles in the 3.8–2 V potential range. The present kinetic data seem to indicate its better cycling behaviour mainly originates from its specific structural response rather than from kinetic reasons.     

Preparation and characterization of alumina hollow fiber membranes

With the rapid development of membrane technology in water treatment, there is a growing demand for membrane products with high performance. The inorganic hollow fiber membranes are of great interest due to their high resistance to abrasion, chemical/thermal degradation, and higher surface area/volume ratio therefore they can be utilized in the fields of water treatment. In this study, the alumina (Al₂O₃) hollow fiber membranes were prepared by a combined phase-inversion and sintering method. The organic binder solution (dope) containing suspended Al₂O₃ powders was spun to a hollow fiber precursor, which was then sintered at elevated temperatures in order to obtain the Al₂O₃ hollow fiber membrane. The dope solution consisted of polyethersulfone (PES), Nmethyl-2-pyrrolidone (NMP) and polyvinylpyrrolidone (PVP), which were used as polymer binder, solvent and additive, respectively. The prepared Al₂O₃ hollow fiber membranes were characterized by a scanning electron microscope (SEM) and thermal gravimetric analysis (TG). The effects of the sintering temperature and Al₂O₃/PES ratios on the morphological structure, pure water flux, pore size and porosity of the membranes were also investigated extensively. The results showed that the pure water flux, maximum pore size and porosity of the prepared membranes decreased with the increase in Al₂O₃/PES ratios and sintering temperature. When the Al₂O₃/PES ratio reached 9, the pure water flux and maximum pore size were at 2547 L/m²·h and 1.4 μm, respectively. Under 1600dgC of sintering temperature, the pure water flux and maximum pore size reached 2398 L/(m²·h) and 2.3 μm, respectively. The results showed that the alumina hollow fiber membranes we prepared were suitable for the microfiltration process. The morphology investigation also revealed that the prepared Al₂O₃ hollow fiber membrane retained its’asymmetric structure even after the sintering process.     

Preparation and characterization of nanofiltration composite membranes using polyacrylonitrile (PAN). II. Preparation and characterization of polyamide composite membranes

Polyamide (PA) composite membranes in which PA active layers were interconnected with support layers via the formation of ionic bonds were prepared by the interfacial polymerization of piperazine (PIP) with trimesoyl chloride (TMC) on the surfaces of microporous polyacrylonitrile (PAN) supports containing carboxylic acid groups. Formation of the ionic bonds through an acid‐base reaction between ? NH group of PIP and ? COOH of the support was studied using FTIR‐ATR spectroscopy. Variation of the surface morphologies of the composite membranes that was induced by the presence of the ionic bonds was observed with a FESEM and an AFM. Permeation tests with various feed solutions such as PEG 600, Na₂SO₄, MgSO₄, MgCl₂, and NaCl solutions were carried out to see how the characteristics of the PAN supports affected on the flux and rejection of the corresponding PA composite membranes. Chemical stabilities of the composite membranes with the ionic bonds were studied and compared with that of a conventional PA composite membrane, using alcohol solutions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2729–2736, 2001     

In situ immobilization of cobalt phthalocyanine on the mesoporous carbon ceramic SiO2/C prepared by the sol–gel process. Evaluation as an electrochemical sensor for oxalic acid

The mesoporous carbon ceramics SiO₂/20 wt% C (S_BET = 160 m² g⁻¹) and SiO₂/50 wt% C (S_BET = 170 m² g⁻¹), where C is graphite, were prepared by the sol–gel method. Scanning electron microscopy images and the respective element mapping showed that, within the magnification used, no phase segregation was detectable. The materials containing 20 and 50 wt% of C presented electric conductivities of 9.2 × 10⁻⁵ and 0.49 S cm⁻¹, respectively. These materials were used as matrices to support cobalt phthalocyanine (CoPc), prepared in situ on their surfaces, to assure homogeneous dispersion of the electroactive complex in the pores of both matrices. The surface densities of cobalt phthalocyanine on both matrix surfaces were 0.014 mol cm⁻² and 0.015 mol cm⁻² for materials containing 20 and 50 wt% of C, respectively. Pressed disk electrodes made with SiO₂/50 wt% C/CoPc and SiO₂/20 wt% C/CoPc were tested as sensors for oxalic acid. The electrode was chemically very stable and presented very high sensitivity for this analyte, with a limit of detection, LOD = 5.8 × 10⁻⁷ mol L⁻¹.     

Preparation and characterization of composite membranes of polysulfone and microcrystalline cellulose

Physical and chemical modifications of polymeric ultrafiltration membranes are necessary to improve their hydrophilic properties, strength, and other characteristics. Microcrystalline cellulose (MCC) was prepared from cellulose pulp by acid‐catalyzed hydrolysis in the presence of ultrasonic radiation, and the properties of MCC were evaluated. Through the addition of MCC to a polysulfone (PS) membrane solution, a casting solution of a PS/MCC blend was obtained. Subsequently, the ultrafiltration membrane from the blend was further developed in a phase‐inversion process comprising immersion and deposition. The capacity for ultrafiltration was better with increasing MCC content. When the ratio of MCC to PS was 0.3, the pure water flux of the composite membrane reached 234.2 L/m²/h, and the retention of a bovine serum albumin solution (1 g/L) was as high as 93.4%. The membranes were also observed with scanning electron microscopy and atomic force microscopy to study their microstructures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009