Sol-gel Films Research Articles

Investigation of a low-stress and low-contamination clamping method for large-aperture optics.

Motivated by the need to decrease initial contact seal stress on Nd:glass coated with SiO2 sol-gel film and effectively control the surface contaminants from film debris induced by stress in the assembly process, a novel vacuum clamping method is studied to achieve the purpose of low stress and low contamination. In this article, theoretical analyses, numerical simulations, and field experiments are used to verify the feasibility of this method. Mechanical simulation results indicate that under the same radial compression conditions, the higher the hollowness of the O-ring rubber, the less the contact stress on Nd:glass. In addition, microstructures of the SiO2 sol-gel film are observed by scanning electron microscopy, and the damage mechanism is analyzed in order to optimize assembly stress. By optimizing the distribution of hollowness, the honeycomb structure is proved to have lower contact stress due to its larger deformation. Finally, experimental results verify that the low-stress vacuum clamping method can meet the strict surface cleanliness requirements of Nd:glass. This study also provides a promising method for clean assembly of other large-aperture optics.

Sputtered vs. sol-gel TiO2-doped films: Characterization and assessment of aqueous bisphenol A oxidation under UV and visible light radiation

In this work, TiO2 thin films were deposited onto soda lime glass substrate by two different techniques: sol-gel (SG) and sputtering (SP). The photocatalytic film performance was assessed in a batch recycle reactor testing the photocatalytic degradation of aqueous solutions of bisphenol A (BPA). The use of supported catalysts in batch recycle reactor systems for the photocatalytic degradation of organic pollutants in waste water can be an alternative to nowadays more used slurry batch reactor systems and powdered catalysts, since it is more economically sustainable and not requiring the removal of catalyst particles after waste water treatment. The best photocatalytic activities were achieved with SG films due to their porosity, which allows BPA molecule to better access the catalytic site than in case of SP films. Raman spectroscopy also showed that SP films have more oxygen vacancies, which may end up acting as charge recombination centers. Doping of TiO2 thin films, either with N or Cu, enabled us to trigger the catalytic activity of films also under UV-free visible light radiation. Regardless the order of stacking in the double-layered films, the latter did not result in an increased catalytic activity towards the photodegradation of BPA.

Enhanced Antibacterial Capability and Corrosion Resistance of Ti6Al4V Implant Coated with ZrO2/Organosilica Nanocomposite Sol-Gel Films

Ti6Al4V is one of the most commonly used biomaterials in orthopedic applications due to its interesting mechanical properties, corrosion resistance and reasonable biocompatibility, which derive from a compact, thin, and chemically stable oxide film that spontaneously develops on these materials surface able to minimize ion release. Despite these advantages, a post-operative serious and unresolved problem leading to the failure of the implant is the appearance of implant-associated infections. For this reason, the ability to control microbial adhesion is of importance in healthcare, particularly in modern surgery where postoperative implant associated infections are still an unresolved and serious complication. As a proof of concept, we have assessed the antibacterial behaviour of Ti6Al4V surfaces modified by organic-inorganic hybrid sol-gel films with different loading of ZrO2 nanoparticles. The starting organosilica sol was prepared using a mixture of γ-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethyl orthosilicate (TMOS). Tetrabutoxyzirconium (TBZ) was used as precursor of ZrO2 nanoparticles. Sol-gel films with variable contents of TBZ (0.2—1.0 wt.%) have been tested. The thermal stability of the resulting sol-gel films was studied by using thermal analysis (TG/DTG). Structural characterization of the films was carried out using Attenuated Total Reflectance Fourier transformer Infrared spectroscopy (ATR-FTIR). Surface morphology and composition of coated samples have been analized by Optical and Scanning Electron Microscopy coupled with Energy Dispersive X-ray (OM and SEM/EDX) both before and after the corrosion tests were carried out. The evaluation of the barrier properties on the films and corrosion behaviour of the Ti6Al4V were carried out using Global and Local Electrochemical Impedance Spectroscopy (EIS/LEIS) during immersion in a simulated body fluid (SBF). Regarding bacterial adhesion, two representative strains of the vast majority of nosocomial infections related to orthopedic implants, i.e., Staphylococcus aureus and Staphylococcus epidermidis, were used. Optical and scanning electron microscopies observations have shown the formation of a uniform, homogeneous, crack free and highly adherent protective film on the Ti6Al4V substrates. The electrochemical studies and bacterial adhesion assessments have shown that the incorporation of ZrO2 in MAPTMS/TMOS matrix of the sol-gel films enhance their corrosion protection behaviour and antibacterial capability. Studies on the optimization of the sol-gel formulation to obtain the films with the best antibacterial capability without compromising their good corrosion resistance using different ZrO2 doses are in progress. Acknowledgments The authors would like to acknowledge financial support from the Ministry of Economy of Spain (MAT2015-65445-C2-1-R and MAT2015-63974-C4-3 Projects). M-ERA.NET PCIN-2016-146; Spanish “Junta de Extremadura” and FEDER for the projects IB16117, TE-0016-18 and GR15089

Rate and Voltage Dependence of the Electrode-Electrolyte Interface in Ni Containing Lithium-Ion Cathode Materials

Performance, safety, lifetime, and cost of lithium-ion batteries (LIB) are strongly influenced by the active materials used. As a result, cell chemistries are selected with the end goal in mind. For applications requiring superior power and safety, cells containing LiFePO4 cathodes and graphite anodes with an organic liquid electrolyte are frequently used. The major drawback of LIB cells designed for high-power is a relatively low energy density compared to high-energy cells, which conversely have poor rate capability. While graphite anodes remain a constant in most commercial LIB, recent research has identified cathode materials which would potentially mitigate the tradeoff between power, energy, and safety. In particular, spinel structured “LNMO” (LiNi0.5Mn1.5O4) and layered nickel-rich “NCM” compounds (LiNixMnyCozO2, X ≥ 0.5) have reportedly high energy densities relative to LiFePO4 while maintaining good power capability and thermal stability (1) (2). While LNMO and NCM compounds have similar composition and produce Ni4+ when fully charged, several reports have highlighted variations in surface chemistry resulting from electrolyte-electrode interactions as a function of cathode stoichiometry (3; 4; 5). One issue known to influence the surface chemistry and associated cycling stability of transition metal oxide cathode materials is the upper voltage cutoff needed to extract lithium during charge. Layered compounds can typically be reversibly delithiated within a voltage range of 4.2 to 4.6 V vs. Li/Li+ depending on the specific stoichiometry, while the spinel must be charged in excess of 4.8 V vs. Li/Li+, which historically has been a major hurdle to application. These upper voltage cutoff are already within the range of expected electrolyte oxidation, which is exacerbated by over potentials produced when charging at high current densities which further increase the upper voltage cutoff required to fully delithiate the cathode. This presentation will focus on analysis of the electrode-electrolyte interface, which is known to be a critical indicator of cell safety and lifetime, as a function of high-rate cycling and upper voltage cutoff. Composite cathodes containing spinel LNMO and layered NCM523 were cycled in a conventional lithium-ion electrolyte at various rates of charge and discharge, then disassembled in an inert atmosphere for analysis by X-ray Photoelectron Spectroscopy (XPS). Capacity and electrochemical impedance measurements were correlated with XPS analysis. Our results indicated that even when cycled in identical electrolytes spinel and layered compounds have notably different responses to an increased charge rate, specifically high rate charging (5C rate) is actually found to benefit LNMO, leading to lower impedance rise and associated formation of LiF, while the opposite is true for NCM523. One complicating factor in the XPS analysis of composite electrode is the presence of inactive components, specifically the binder and conductive additive. Both of these compounds dilute the overall signal detected from the active material, and some reports suggest may even contribute to the specific surface chemistry observed. To remove these effects, sol-gel films of identical composition to the composite electrode active materials were also synthesized and subjected to electrochemical cycling in the same electrolyte. [1] Review-Li-Rich Layered Oxide Cathodes for Next-Generation Li-Ion Batteries: Chances and Challenges. Rozier, P and Tarascon, JM. 14, 2015, Journal of the Electrochemical Society, Vol. 162, pp. A2490-A2499. [2] Spinel LiNi0.5Mn1.5O4 and its derivates as cathodes for high-voltage Li-ion batteries. Liu, G Q, Wen, L and Liu, Y M. 2010, Journal of Solid State Electrochemistry, Vol. 14, pp. 2191-2202. [3] Coupled LiPF6 Decomposition and Carbonate Dehydrogenation Enhanced by Highly Covalent Metal Oxides in High-Energy Li-Ion Batteries. Yu, Y, et al. 2018, Journal of Physical Chemistry C, Vol. 122, pp. 27368-27382. [4] XPS Studies of Surface Chemistry Changes of LiNi0.5Mn0.5O2 Electrodes during High-Voltage Cycling. Quinlan, RA, et al. 4, 2013, Journal of the Electrochemical Society, Vol. 160, pp. A669-A677. [5] Probing the Electrode-Electrolyte Interface in Cycled LiNi0.5Mn1.5O4 by XPS Using Mg and Synchrotron X-rays. Mansour, AN, et al. 14, 2016, Journal of the Electrochemical Society, Vol. 163, pp. A2911-A2918.

Highly sensitive surface acoustic wave HCl gas sensors based on hydroxyl-rich sol-gel AlOxOHy films

Gas sensors detecting low HCl gas concentrations used for early detection and continuous monitoring of leakage is of great concern because HCl gas is extremely hazardous. In order to tackle the potential hazardous threats, surface acoustic wave HCl gas sensors based on hydroxyl-rich sol-gel AlOxOHy films are reported. The fabricated SAW sensors show negative frequency shifts with exposure to HCl gas. The negative frequency shift is found to be caused by the increasing weight of sensitive films induced by the adsorption of HCl assisted by the hydroxyl groups and H2O captured on the films. The sensing performance of sensors is highly dependent on the heat-treatment temperature and thickness of films, as well as the ambient humidity because these parameters are highly influential on the amount of hydroxyl groups, H2O on films and the pore volume of films. For a sensor with a 198-nm-thick film annealed at 300 °C, it shows a response of ~ -1.4 KHz to HCl at a low concentration level (0.05 ppm) in an environment with a temperature of 25 °C and a RH value of 40%.

Effect of Ultraviolet-Ozone Treatment on the Properties and Antibacterial Activity of Zinc Oxide Sol-Gel Film.

To combat infectious diseases, zinc oxide (ZnO) has been identified as an effective antibacterial agent; however, its performance can be adversely affected by harsh application environments. The ozone impact on ZnO antibacterial film needs to be evaluated prior to its application in an ozone disinfection system. In this study, ZnO films synthesized via sol-gel/spin-coating were subjected to ultraviolet–ozone (UVO) treatment for different periods. Surface investigations using scanning electron microscopy, ultraviolet–visible spectroscopy, and X-ray photoelectron spectroscopy revealed that the treatment-induced film changes. With longer UVO treatment, the surface porosity of the film gradually increased from 5% to 30%, causing the transmittance reduction and absorbance increase in visible-light range. Phase transformation of Zn(OH)2 to ZnO occurred during the first 10 min of UVO treatment, followed by oxygen uptake as a consequence of the reaction with reactive oxygen species generated during UVO treatment. However, despite these surface changes, the satisfactory antibacterial activity of the synthesized ZnO film against Staphylococcus aureus and Escherichia coli was sustained even after 120 min of UVO treatment. This indicates that the UVO-induced surface changes do not have a significant effect on the antibacterial performance and that the ZnO sol-gel film possesses good functional durability in ozone environments.

A Foam-Core Meniscus Coating Process for Retrofit Anti-Reflective Coatings

Foam-core meniscus coating is being used to retrofit 100 nm-scale sol–gel anti-reflective coatings (ARCs) onto in-field solar panels through the deposition, evaporation, and curing of wet films. Advantages of this technique include the means to control fluid flow relative to substrate motion and the ability to conform to large, warped substrates. While simple in practice, no models exist for predicting critical outcomes such as film thickness. In this paper, preliminary experiments are used to identify important process parameters, and an analytical model is developed and validated for predicting the thickness of silica sol–gel films deposited on solar glass.

Unprecedentedly Tough, Folding‐Endurance, and Multifunctional Graphene‐Based Artificial Nacre with Predesigned 3D Nanofiber Network as Matrix

AbstractMimicking the hierarchical brick‐and‐mortar architecture of natural nacre provides great opportunities for the design and synthesis of multifunctional artificial materials. The crucial challenge to push nacre‐mimetic functional materials toward practical applications is to achieve ample ductility, toughness, and folding endurance with simultaneously maintaining high‐level functional properties. In this study, the microstructure of nacre‐mimetics is reformed through predesigning a 3D nanofiber network to replace conventional polymer matrices. A unique sol–gel–film transformation approach is developed to fabricate a graphene‐based artificial nacre containing a preforming 3D, interconnective, inhomogeneous poly(p‐phenylene benzobisoxazole) nanofiber network. The fabulous coupling of the extensive sliding of graphene nanoplatelets and intensive stretching of the 3D nanofiber network over a large scale enables the artificial nacre to display natural nacre‐like deformation behavior, achieving ultralarge strain‐to‐failure (close to 35%), unprecedented toughness (close to 50 MJ m−3), and fold endurance (no decrease in tensile properties after folding for 10 000 times or folding at increasing stress). The new levels of ductility, toughness, and folding endurance are integrated with outstanding thermal properties, including thermal conductivity (≈130 W m−1 K−1), thermal stability (520 °C) and nonflammability, rendering the lightweight nacre‐mimetics promising in flexible electronic devices, particularly for aerospace electronics.

Anticorrosive performance of AA6061 aluminium alloy treated with sol-gel coatings doped with mangrove bark tannins in 3.5 wt% NaCl

Two different tannin extracts (70% acetone and methanol) were isolated from mangrove bark. Isolated tannins were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, Folin-Ciocalteu method and antioxidant assay. The inhibitive effects of sol-gel coatings doped with mangrove bark tannin extracts (0, 10, 50 and 100 ppm) on the corrosion protection of aluminium alloy were evaluated via potentiodynamic polarization, electrochemical impedance spectroscopy, and electrochemical noise analyses. It was revealed that sol-gel coatings doped with tannin extracts yielded high percentage inhibition efficiencies (% IE) of more than 80% than that of in the absence of tannins where 70% acetone tannin extract doped sol-gel coated aluminium alloy offered % IE of 87.20%. Electrochemical noise analysis depicted that aluminium alloy coated with 70% acetone tannin extract doped sol-gel film experienced the least current noise fluctuation among all tested samples. SEM-EDX analyses verified that the developed sol-gel coatings were able to inhibit the local dissolution of aluminium alloy. The present study unveiled the potential of mangrove bark tannins in enhancing the anticorrosive performance of TEOS based sol-gel coatings over AA6061 Al alloy surface.

Design and Application of an Optical pH Sensor Based on Thionine Doped Modified Sol–Gel Film

An optical chemical sensor was constructed by incorporating the thionine (TN) dye molecules into a sol–gel silica matrix and it was used for determination the pH of the aqueous solutions. Entrapment of TN dye into the silica matrix was made via an acid-catalyzed sol–gel reaction of tetraethyl orthosilicate (TEOS) and the thionine molecules. The thionine molecules in the immobilized form, showed a different spectral behavior than its solution form. After optimizing the experimental conditions, the fabricated optical sensor showed a fast response to pH changes in the range of 11–13 with a response time about one minute. Also, the obtained results indicate that the proposed pH sensor, has a good reproducibility, reversibility, stability and low leaching and a long lifetime of over 7 months.

Application of novel sol–gel composites on magnesium alloy

Abstract Application of defect-free, adherent, and corrosion protective sol–gel film on the magnesium alloys is generally difficult. In this study, two novel sol–gel/conversion coating composites were successfully deposited on AM60B magnesium alloy in order to provide sufficient protection against the corrosion. The first composite (Ti–Zr/hybrid) was obtained via combination of a hybrid sol–gel film (synthesized by mixing tetraethoxysilane (TEOS), and 3-glycidyloxypropyl-trimethoxysilane (GPTMS)) as outer layer and Ti–Zr conversion coating as primer. Also, the second composite (Ti–Zr/PTMS) was applied in a similar manner by combination of phenyl-trimethoxysilane (PTMS) sol–gel film with the Ti–Zr conversion coating. The morphology and elemental composition of the Ti–Zr conversion film were assessed by the Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS), respectively. A cracky conversion film was applied on the alloy surface after immersion in the Ti–Zr conversion coating bath which was mainly composed of MgO, TiO2, ZrO2, and MgF2 compounds. Uniform, but not-adherent PTMS and hybrid sol–gel films (pure sol–gel films) with obvious defects were directly deposited onto the magnesium alloy without the Ti–Zr pretreatment which were morphologically characterized by the SEM. However, formation of relatively uniform and completely defect-free Ti–Zr/hybrid and Ti–Zr/PTMS composites after using the Ti–Zr conversion coating as pretreatment was revealed by the SEM observations. In addition, the defects of the Ti–Zr conversion coating were completely filled by the sol–gel layers. The Ti–Zr/PTMS and Ti–Zr/hybrid composite coatings were provided much better corrosion protection capacity than the pure PTMS and hybrid sol–gel films, respectively which was confirmed by the Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PDP) examinations in 0.05 M NaCl solution.

A study of variable range hopping conduction of a sol-gel ZnSnO thin film transistor using low temperature measurements

This paper investigates variable range hopping conduction of a zinc tin oxide (ZTO) thin-film transistor (TFT). The ZTO channel layer was fabricated using a sol-gel process. Existence of Zn2SnO4 and ZnSnO3 crystal phases in the ZTO film is observed in the X-ray diffraction pattern. Distinct lattice fringes with different orientations that are observed in the transmission electron microscopy image verify the polycrystalline structure of the ZTO layer. To study the hopping mechanism, electrical characteristics of the ZTO TFT were measured at low temperatures of 100–220 K. The activation energy (Ea) is 97 meV when the gate voltage is 0 V, and it exponentially decreases with increasing gate voltage. The Ea is 22 meV when the gate voltage increases to 30 V. A negative exponential relationship between the density of states and the Ea is found. Temperature and gate voltage dependence of the hopping distance and hopping energy are also explored.

Distributed Fiber Optic pH Sensor for the Application in the Wellbore

pH measurement is important in many applications such as environmental science, civil engineering, biotechnology, earth science, and marine sciences. In the wellbore, the pH of the cement pore solution is around 13 at early stage, and the wellbore cement is relatively stable and less permeable above pH 10.5. However, pH drops in the CO2/H2S containing environment making the cement more porous and permeable, which leads to higher risk of wellbore integrity failure. The lower pH also makes the casing steel more susceptible to corrosion. Therefore, real time monitoring of pH in the wellbore is crucial for corrosion detection and cement failure prediction. Wellbores are often at high temperature high pressure (HTHP) conditions (> 149 °C, >1400 psi). Conventionally, pH measurement is made by a glass electrode, which is fragile, prone to drifting, and suffers from alkali interference. Furthermore, it requires a reference electrode, which becomes less stable and less reliable in HTHP conditions, hence there are only limited options available for conventional pH sensors under wellbore conditions. In the contrast, fiber optic pH sensors can offer desirable advantages such as the elimination of electrical connections and wiring and the lack of need for a separate reference electrode, making them inherently more compatible with harsh environment applications. Importantly, they can also be used for remote, distributed, and continuous pH sensing in harsh environment to enable a map of pH throughout a region of interest. Therefore, fiber optic sensors have become a promising solution for pH monitoring in the wellbore. To enable distributed pH sensing with the optical fiber platform, an optical fiber must be integrated with a pH sensitive layer along the fiber, such that the optical properties can be locally altered due to the pH change of the surrounding solution and the change is monitored by a detector in either a transmission or reflection/backscatter configuration. Therefore, the development of a stable, selective, and sensitive pH sensing layer is the critical enabling technology. Sol-gel SiO2 film is one of the most widely used substrates to immobilize pH indicators, such as organic dyes, on the optical fiber surface for pH sensing. SiO2 film has high thermal stability and excellent mechanical strength, which satisfies the HTHP wellbore conditions. The SiO2 thin film can be prepared over a large area at a comparatively low cost. Most investigations use the sol-gel SiO2 film as the substrate for immobilizing pH indicators, but very few studies have reported that the film itself can be used as a pH sensing layer. Using only SiO2 film makes the pH sensor simple to fabricate and free of leaching or photobleaching which are often encountered by the entrapped dye indicators. However, the mechanistic details of the response require elucidation to understand the potential for a selective and sensitive response as a function of pH in the presence of other chemical analytes and variations in temperature and pressure. Here we report recent results on fiber optic pH sensors utilizing porous silica based films and discuss them in the context of fundamental mechanistic considerations as well as their relevance to harsh environment sensing applications. The SiO2 film is coated onto the optical fibers through a sol-gel dip-coating method. The dip-coated fibers are calcined at temperatures of 200-600oC afterwards to obtain a porous SiO2 film of a few hundred nanometers thick. The pH sensing performance is investigated in terms of light transmission to confirm sensitivity and reversibility, and the distributed pH monitoring capability is demonstrated using an optical backscatter reflectometer. The optical fiber coated with a silica-based sol-gel and calcined at 200 °C shows good sensitivity and reversibility in the pH range from 4 to 13, and the sensor is found to be more sensitive in the alkaline region, which indicates that the developed fiber optic pH sensor has potential application in the wellbore pH range.

Derivative chiral copper(Ⅱ) complexes as template of an electrochemical molecular imprinting sol-gel sensor for enantiorecognition of aspartic acid

In this work, we reported a novel electrochemical sensor for enantiorecognition of electrochemically inactive aspartic acid (Asp) enantiomers. By combining sol-gel processing with molecular imprinting technology, an enantioselective interface of molecularly imprinted sol-gel (MIS) films with imprinted cavities was prepared on the surface of a glassy carbon electrode (GCE). In order to obtain the electrochemical responses of electrochemically inactive Asp, the ternary derivative of L-aspartic, (l-aspartic acid)Cu2+(N-carbobenzoxy-l-aspartic acid), was used as the template for fabrication of MIS. The stripping currents of target molecules could be detected by square-wave stripping voltammetry due to the reduction of cupric ion on the modified electrode. The resulted sensor showed good adsorbability to L-Asp derivative, and the recognition efficiency was obtained as 2.1. Meanwhile, the L-Asp was quantitatively determined by the MIS sensor. As a result, the proposed electrochemical sensor could be regarded as a potential platform for enantiorecognition of electrochemically inactive chiral compounds.

Low-temperature V-oxide film for a flexible electrochromic device: Comparison of its electrochromic, IR and Raman properties to those of a crystalline V2O5 film

Manufacturing of flexible electrochromic (EC) devices requires the use of low-temperature films for deposition on electronically conductive foils. With this aim, low-temperature V-oxide films were spin-coated from a dispersion prepared by milling of crystalline V2O5 powder in vanadium(V) tri-n-propoxide oxide/isopropanol sol as dispersant. TEM images showed that the milling procedure enables the introduction of some V2O5 nanocrystallites into the matrix of the V-oxide pigmented film prepared at 150 °C. The electrochromic properties were analyzed using in situ UV–visible absorbance spectroelectrochemistry. The low transmittance values of as-prepared pigmented films revealed the presence of a greater amount of reduced V4+ centers compared to the crystalline sol-gel V2O5 model films. Significant bleaching of pigmented V-oxide films occurred during subsequent 521 cycles in the safe potential range.Three different types of vibrational spectroscopies were applied to examine the powdered V-oxide film, and the results were compared to the band changes for the sol-gel crystalline V2O5 films. For initial films, the modes in the IR reflection-absorption spectra were systematically shifted to higher wavenumbers with regard to the modes in the IR absorbance spectra. Both IR techniques confirmed the reversible shift of the vanadyl V-OA band to lower frequencies and the disappearance of the bridging V-OB-V mode upon intercalation. Raman spectra showed the appearance of two vanadyl stretching modes at 986 and 961 cm−1 that occurred simultaneously with the decrease in the intensity of the bands in the 750–400 cm−1 spectral region. After the deintercalation, the Raman spectra of the low-temperature films showed broad bands that remained after the second bleaching. Finally, a flexible NiO1-x/ormolyte/V-oxide EC device was constructed. The device was composed of two different pigmented films and demonstrated the practical applicability of the low-temperature pigmented films.

Multienzyme, Multistep Biosensor Produced through Kinetic Doping.

The recently developed kinetic doping technique has shown promise in loading individual enzymes for use as a biosensor. In this study, the first example of kinetic doping to produce a biosensor loaded with more than one enzyme and using a multistep reaction pathway for detection is presented. Glucose oxidase (GOD) is shown to load both individually and together with horseradish peroxidase (HRP) with the tandem action of the two enzymes proving to be effective at detecting glucose in solution. Using a calculation based on known maximum loadings and experimentally determined activities, the final dual-enzyme thin films of known volume are shown to contain 1.8 ± 0.1 mmol/L of HRP and 0.22 ± 0.01 mmol/L of GOD, which represent 33 and 92% of loading efficiencies that each enzyme is known to be, respectively, capable of in a singularly loaded thin film. With the high loading afforded by the kinetic doping process under benign conditions, the thin films are able to load both enzymes all at once in an amount sufficient to function as an efficient biosensor. The most advantageous aspects of this process are its ease of production, involving only a few steps to produce highly loaded thin films that require no additional processing to function as intended, as well as the protein friendly environment that exists in the sol-gel film at the time of enzyme loading. This removes many typical restrictions on immobilizing protein and opens up a wider range of enzymes amenable to the process that enables the fabrication of more complex multistep biosensors utilizing a large array of proteins in the foreseeable future.

Studies on sol-gel dip-coated nanostructured ZnO thin films

Nanostructured ZnO thin films were prepared by sol-gel dip coating technique. Zinc acetate and ammonium hydroxide were used as precursors and ethanol was as solvent. Ammonium hydroxide (NH4OH) solution was added drop-wise under vigorous stirring to obtain the sol-gel of different pH (varying from 6.9 to 7.2). ZnO thin films were obtained by dipping the glass substrates for few seconds and then dried in air at room temperature. This process was repeated for different number of coats for the typical sol. Different numbers of coating cycle was employed to obtain the films with varying thicknesses. These films were annealed at 5000C and were characterized by x-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive analysis of x-rays (EDAX). ZnO thin films obtained from sol-gel dip-coating technique were observed to nanostructured. Average particle size was observed to be smaller than 50 nm. The most of the particles were observed to be spherical in shape. ZnO films were observed to be nonstoichiometric (Zinc deficient) in nature. The results were discussed and interpreted.

Laser irradiation synthesis and photocatalytic properties of TiO2-SiO2 hybrid thin films

In this study, we introduce a noble method for the fabrication of highly crystalline hybrid TiO2-SiO2 thin films using laser irradiation under ambient conditions. Upon light absorption at the interface between TiO2 sol-gel film and Si wafer during the laser irradiation process, the TiO2 gel film coated on the Si wafer is transformed into anatase TiO2 film, and the surface of underlying Si wafer is oxidized to a 20.63 μm thick SiO2 film composed of nano-spheres with average diameter of 24.12 nm. The photocatalytic characteristics of the TiO2-SiO2 hybrid film on methylene blue and its discriminated morphologies are compared with those of a TiO2 film fabricated by conventional thermal annealing. The TiO2-SiO2 hybrid film shows enhanced super-hydrophilicity and superior photocatalytic characteristics, while thermally annealed 0.16 μm thick TiO2 films exhibit hydrophobic and low photocatalytic properties. The laser assisting process is promising for the fabrication of highly crystalline TiO2-SiO2 hybrid film with super-hydrophilic and photocatalytic characteristics.

Photocatalytic Degradation of Azithromycin by Nanostructured TiO₂ Film: Kinetics, Degradation Products, and Toxicity.

In this paper, nanostructured TiO2 film was prepared by the by sol-gel process and dip-coating technique with titanium tetraisopropoxide as a precursor. After heat treatment at 550 °C, the deposited film was characterized by means of micro-Raman spectroscopy and atomic force microscopy (AFM). It was found that the TiO2 film consisted of only the TiO2 anatase phase and showed a granular microstructure. Photocatalytic degradation of azithromycin by using sol-gel nanostructured TiO2 film was studied to define the most effective degradation process for potential use in wastewater treatment. Different factors were evaluated during photocatalysis, such as pH (3, 7, and 10), water matrix (ultrapure water and synthetic municipal waste water effluent), influence of another pharmaceutically active compound (sulfamethoxazole, one of the most often detected pharmaceutic compounds in waste waters), and radiation sources (low pressure ultraviolet (UV) mercury lamps with a UV-A and UV-C range; a light-emitting diode (LED) lamp with a radiation peak at 365 nm). The most effective degradation process was achieved with the UV-C irradiation source in matrices at pH 10. The water matrix had little effect on the photocatalytic degradation rates of azithromycin. The presence of sulfamethoxazole in the water matrix decreased the degradation rate of azithromycin, however, only in matrices with a pH level adjusted to 10. During the experiments, five azithromycin degradation products were identified and none of them showed toxic properties, suggesting effective removal of azithromycin. LED 365 nm as the irradiation source was not as effective as the UV-C lamp. Nevertheless, considering the cost, energy efficiency, and environmental aspects of the irradiation source, the LED lamp could be a “real-life” alternative.

Impact of Zr precursor on the electrochemical properties of V2O5 sol-gel films

In this work, we explore the impact of Zr precursor on the electrochemical and optical properties of V2O5 thin films. These films were synthesized by the combination of the sol-gel route with dip-coating deposition on the electron conducting (fluorine tin oxide; FTO) substrate. We used vanadium oxytriisopropoxide (V) - [OV(OC3H7)3] and zirconium isopropoxide (IV) - [Zr(OCH2CH2CH3)4] as precursors, isopropanol as solvent, and glacial acetic acid as a catalyst. After the deposition, the thin films were subjected to densification at 350°C for 30min. We characterized these films by electrochemical techniques (cyclic voltammetry, chronoamperometry and chronocoulometry) and we obtained the best result of the load density of 109mC·cm−2 for V2O5 sample prepared with 5mol% of Zr precursor; this sample also presented satisfactory responses of cyclic stability. We used atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) to obtain morphology and crystallinity of this film. Its optical properties, we studied by UV–vis spectroscopy and the transmittance results were of 82% for the discolored and 39% for colored states, both measured at 633nm. In summary, we show that V2O5:ZrO2 thin films have quite attractive properties for their application as a working electrode in electrochromic devices.