Tetragonal Zirconia Nanoparticles Research Articles

Insight into continuous growth mechanisms of ZrO2-Al2O3 composite PEO coatings with superior cavitation erosion resistance

The ZrO2-Al2O3 composite coatings were fabricated on TiB2/2024Al composite by the plasma electrolytic oxidation (PEO) treatment with either monoclinic (m-ZrO2) or tetragonal zirconia (t-ZrO2) nanoparticles (NPs) addition. Such PEO coatings showed a double layer morphology due to the limited physical motion ability of ZrO2 colloidal particles into coatings. t-ZrO2 remained as the main phase in ZrO2-Al2O3 PEO composite coatings whether t-ZrO2 or m-ZrO2 NPs were added. Based on the microstructure analyses by focus ion beam plus scanning electron microscopy and transmission electron microscopy, ZrO2 showed netlike morphology in the outer layer with NPs partially melted at the mesh boundary and lines-like morphology fully melted at the inner mesh in the coating. A prominent morphological transition of ZrO2 was clearly observed at the interface between outer layer and inner layer. Therefore, the continuous growth mechanisms of ZrO2-Al2O3 composite PEO coatings were proposed in terms of morphological evolution process. Furthermore, electrochemical measurements and cavitation erosion tests were conducted to study the comprehensive surface properties (corrosion and impact resistance) of ZrO2-Al2O3 composite coatings. As a result, the ZrO2-Al2O3 composite PEO coatings with m-ZrO2 addition exhibited the greatly reduced corrosion rate, and superior cavitation erosion resistance. Accordingly, the underlying mechanisms for these improved properties were intensively discussed.

Preparation of nanometer zirconia by hydrothermal method: Influence of temperature and mechanism

Monoclinic (m-ZrO2) and tetragonal zirconia (t-ZrO2) nanoparticles with average grain size of 22.8 nm were synthesized by hydrothermal method using zirconium oxychloride octahydrate (ZrOCl2·8H2O), urea (CO(NH2)2) and deionized water as zirconium source, precipitant, and solvent, respectively. The effects of CO(NH2)2 hydrolysis rate, hydrothermal temperature, and time on the crystal structure, morphology, and grain size were studied. The structure, morphology, grain size, and crystal phase of zirconium oxide (ZrO2) were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Thermogravimetry (TG-DTA), and Fourier Transform Infrared spectroscopy (FT-IR). The results show that the formation mechanisms of different crystal forms can be controlled by the average pH value. The hydrolysis rate of CO(NH2)2 was relatively slow at 120 °C, resulting in a slower rate of OH− production. The lower average pH value favors the formation of m-ZrO2 through the dissolution precipitation mechanism. With the increase of crystallization temperature, the hydrolysis rate of CO(NH2)2 is accelerated, and the average pH value of the solution is increased, which is conducive to the structural rearrangement of [Zr(OH)8(H2O)16]8+ precursor to form tetragonal phase. In addition, the number of defect sites is directly proportional to the crystallization temperature. Extension of crystallization time helps the generation of ZrO2 crystals by polycondensation and directional growth.

Modified carbon paste ion selective electrode for determining Cr(iii) ions in aqueous solutions and some real samples using tetragonal zirconia nanoparticles.

Tetragonal zirconia (t-ZrO2) nanoparticles (ionophore) are used in newly designed and improved ion selective electrodes for chromium ion detection as an alternative, low-cost, high-precision, and selectivity method. Tetragonal zirconia nanoparticles were synthesized using a modified co-precipitation technique and calcined at 1000 °C for an hour. The phase composition, surface area, microstructure, pore size and particle size of synthesized t-ZrO2 nanoparticles were examined using the X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), transmission electron microscope (TEM) and scanning electron microscopy (SEM) attached with an EDAX unit, respectively. Results from XRD showed that the t-zirconia was synthesized and have nanocrystallites size about 20.2 nm. The nano size of t-ZrO2 was confirmed by the SEM and TEM (the particle size between 26.48 and 40.4 nm), the mesoporous character (average pore size about 4.868 nm) and large surface area (76.2802 m2 g-1) was confirmed by BET analysis. The paste composition with 67.3 : 30.5 : 2.7 (wt%) graphite, t-ZrO2, and TCP, respectively, exhibited the best results. With a detection limit of 1.0 × 10-8 mol L-1, the electrode displayed a good Nernstian slope of 19.50 ± 0.10 mV decade-1 over the concentration range from 1.0 × 10-2 to 1.0 × 10-8 mol L-1 of Cr(iii) ions. The built-in sensor displayed a quick response time (7 s), was highly thermally stable in the range of 10 to 60 °C without departing from Nernstian behaviour and could be used for about 60 days in the pH range of 2.0 to 6.0. The electrode demonstrated excellent selectivity for the Cr(iii) ion towards a variety of metal ions. For chromium ion determination, numerous spiked real samples, including honey, water, tea, coffee, milk, cheese, and cosmetics, were used. Validation methods were used, and the results showed that there is no significant difference between the two methods (ICP and ISE) at a 95% confidence level. In several real water samples, the estimated limits of detection, limits of quantification, percent recovery, standard deviation, and relative standard deviation showed the effectiveness of the proposed electrode in the potentiometric detection of Cr(iii) ions.

Do smaller oxide particles sinter worse? Paradoxes of the initial stages of sintering of zirconia nanoparticles

The effect of particle size on the dominant densification mechanism at the initial stage of sintering of tetragonal zirconia nanoparticles was investigated. It has been found that a decrease in the particle size of zirconia leads to a change in the diffusion mechanism. The volume diffusion mechanism identified by the value of densification parameter n = 0.5 was dominant in zirconia nanoparticles with the average particle size 32 and 26.2 nm. The grain-boundary diffusion mechanism (n = 0.3) dominated during the sintering zirconia nanoparticles with the average particle size 21.7 nm. It was established that the change in densification parameter n from 0.5 to 0.3 caused by the increase in the value of particle surface to volume ratio due to the particles size decrease from 32 to 21 nm. A further decrease in the particle size to 17–12 nm led to a decrease in the densification parameter n to 0.17–0.11, respectively. This may be due to an increase in the influence of the particle surface on the sintering process (large values of particle surface to volume ratio) and, accordingly, the action of the surface diffusion mechanism.

Site‐Engineered Tetragonal ZrO2 Nanoparticles: A Promising Oxygen Reduction Catalyst with High Activity and Chemical Stability in Alkaline Medium

AbstractPractical implementation of anion exchange membrane fuel cells mainly relies on the choice of highly active and stable oxygen reduction reaction (ORR) catalysts. Transition metal oxides based on Group 4 and 5 are well known for their chemical stability and corrosion‐resistance and they are earth‐abundant too. Among them, zirconia (ZrO2) has exceptional chemical stability, but its poor conductivity and less active sites hinder the application of zirconia‐based materials toward ORR. In order to bring out the best activity from ZrO2, careful site engineering without losing the phase purity and chemical stability is essential. In this context, nitrogen doping on tetragonal zirconia (t‐ZrO2) as a viable method to obtain a highly active ORR catalyst is adopted. The temperature for the phase pure synthesis of t‐ZrO2 is optimized by crystallographic study. The nitrogen doping in the zirconia lattice is confirmed by various microscopy and spectroscopy analysis. The N doped tetragonal zirconia nanoparticles on N doped carbon (N:ZrO2–NC) show much improved ORR activity than pristine zirconia counterparts in terms of onset potential, current density, and 4e_ selectivity in alkaline medium. The ORR activity of N:ZrO2‐NC is approaching the one of Pt/C with excellent chemical and electrochemical stability.

Biodegradation of gelatin stabilized tetragonal zirconia synthesized by microwave assisted sol-gel method

The purpose of current work of is to organize stabilized tetragonal zirconia (t-ZrO2) nano-particles with microwave abetted sol-gel technique. To increase the stability and shrink the crystal size, both microwave (MW) and gelatin components are used as structure guiding methods. Gelatin was used with the aim of bone implantations, as raw materials used in gelatin production are cattle bones. It contains purified collagen protein (a main protein that in the extracellular matrix found in the body's various connective tissues) that also helps in implantations and repairing. Moreover, MW heating provides a uniform heating and control of microstructures. Zirconium oxychloride was used as precursor of zirconium Effect of gelatin contents (1g, 2g, 3g, 4g and 5g) was observed. X-ray diffraction (XRD) analysis attributes the presence of phase pure t-ZrO2 at low gelatin content 3g with crystallite size ∼6.68296 nm. Formation of phase pure t-ZrO2 without post heat treatment is due to sufficient amount of gelatin to coat the zirconia crystals. Relatively higher x-ray density has been observed in case of phase pure t-ZrO2 at 5g of gelatin content. Value of the hardness is increasing from 1263 to 1443 HV with gelatin content due to phase strengthening. Raman shift presents characteristic peak at 148 cm−1 of tetragonal zirconia. Phase fraction calculated from Raman spectra is in good agreement with XRD data. At 3g of gelatin content porous structure has been observed in scanning electron microscope images. This porosity decreases with gelatin content and the distribution of particles is more uniform, and dispersion is better. The porosity of the samples decreases and reaching a minimum value at 5g of gelatin content, at which the sample was the densest. The size of nanoparticles is in the range of 500–600 nm. Optimized t-ZrO2 is soaked in stimulated body fluid (SBF) for 1, 2, 4, 8, 12, 18 and 24 weeks. Slight variation in weight and hardness has been observed even after 24 weeks of soaking.

Effect of tetragonal zirconia nanoparticle content on enamel strength

The fracture failure of enamel is caused by hole-type flaws and cracks generally present in enamel. In this study, the effect of tetragonal zirconia nanoparticles (nano-t-ZrO2) on enamel strength was investigated. The addition of nano-t-ZrO2 improved the surface morphology and reduced the porosity of the enamel as determined by morphological and porosity distribution analyses. The strain on the enamel surface was recorded using a strain gauge attached to the enamel surface. The crack initiation force and strain were measured using the strain gauge, and the crack propagation diagrams at various stages of the tensile process were recorded. The relationship between the crack initiation energy and nano-t-ZrO2 content was found to be non-linear. Nano-t-ZrO2 affected the strength of the enamel. Moreover, the tensile force required for the appearance of cracks first increased and then decreased with an increase in the nano-t-ZrO2 content. The addition of nano-t-ZrO2 to the enamel matrix suppressed the formation of stress concentration regions and decreased the brittleness of the enamel. At a nano-t-ZrO2 content of more than 5 wt%, the ZrO2 particles agglomerated.

Superelasticity and shape memory effect in zirconia nanoparticles

Superelasticity and shape memory effect are two key properties of zirconia-based ceramics which are mediated by the reversible tetragonal to monoclinic phase transformation. Although experimental studies discovered that the shape memory behavior of ceramics can be improved by reducing the grain boundary density, degradation in shape memory response still happens after a few cycles of loading–unloading–heating–cooling. In this work, superelastic and shape memory properties of single crystalline and polycrystalline yttria stabilized tetragonal zirconia (YSTZ) nanoparticles are studied by atomistic simulations. Fully recoverable superelastic strain (8.3%) is observed in a single crystalline nanoparticle by merely removing the compressive load. However, the shape memory behavior degrades with the increase of loading–unloading–heating–cooling cycles. In other words, a higher temperature is required for an additional strain recovery, but certain residual displacement may still remain after few cyclic loadings. Amorphous phase formation and its accumulation around the applied load contact area, as well as an increase in surface roughness are responsible for the observed degradation of shape memory response. In a polycrystalline YSTZ nanoparticle, besides the regular reverse transformation at the end of cyclic loading, most amorphous phase transfers back to the original tetragonal structure. However, a small amount of monoclinic phase is restrained by the permanent amorphous phase and grain boundaries at the end of cyclic loading, causing degradation of shape memory behavior.

New insight into sequential of silica-zirconia precursors in stabilizing silica-doped tetragonal zirconia nanoparticles for enhanced photoactivity

Silica-doped tetragonal zirconia nanoparticles (SiO2-ZrO2) catalysts were synthesized with the addition of ZrO2 prior to SiO2 by the microwave-assisted method and compared with a different sequence of ZrO2 and SiO2 (ZrO2-SiO2). The catalysts were characterized by X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, Fourier-transform infrared, electron spin resonance, ultraviolet–visible diffuse reflectance spectroscopy and photoluminescence analyses. The catalyst phase was pure tetragonal ZrO2 (t-ZrO2) with nano in size (9–10 nm). The sequential of SiO2 and ZrO2 precursors significantly affected the catalyst framework and led to a different number of pore volume and defect sites, including oxygen vacancies (OV), metal defects site (MDS) and Si-O-Zr bonds, which altered their behaviour towards t-ZrO2 stabilization and applications. It was found that the synergistic effect between nanocrystals and the appropriate amount of defect sites influenced the stabilization of t-ZrO2. The catalytic activity towards photodegradation of 2-chlorophenol (2-CP) are in the following order: SiO2-ZrO2 (92%) > ZrO2-SiO2 (59%) > ZrO2 (50%) > SiO2 (20%). The highest photoactivity of SiO2-ZrO2 is due to the large pore volume, which offered good surface contact with light. Besides, the higher crystallinity, Si-O-Zr bonds, and OV and MDS also could contribute to the excellent performance in 2-CP degradation. The abovementioned properties provided good electron-hole pair mobility and electron trapping for enhanced photoactivity.

Fabrication and characterization of polymer-infiltrated ceramic network materials based on nano-tetragonal zirconia

Fabrication and characterization of polymer infiltrated ceramic networks (PICNs) were undertaken for use in dentistry. Calcia-stabilized tetragonal zirconia (7-tCSZ) nanoparticles were synthesized via a modified co-precipitation. The composition and particle size of the prepared nanoparticles were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Densification parameters of porous ceramic samples, with varying amounts of 7-tCSZ, 0, 5, 10, and 15 wt.%, and PICN materials were examined using the Archimedes principle. The flexural strength and elastic modulus of PICNs were measured using a three-point bending strength test. The microhardness and fracture toughness were determined using Vickers microhardness and V-notched bars tests, respectively. The microstructure was investigated for selected materials before and after polymer infiltration using scanning electron microscopy (SEM). The results revealed that the samples with 10 and 15 wt.% of nano-tetragonal zirconia showed the highest elastic modulus (8.24 GPa) and fracture toughness (1.82 MPa m1/2), respectively, which is attributed to transformation toughening of zirconia. The flexural strength and microhardness of PICNs were in the range 66.14–71.72 MPa, 0.18–0.19 GPa, respectively, whilst the brittleness index was maximally 0.21 μm−½, which is significantly below the ultimate brittleness index (4.3 μm−1/2) allowing machinability. Conclusively, the inclusion of nanometric zirconia posed a dramatic enhancement of the mechanical properties without affecting the machinability of these biomimetic materials, making them similar to natural dentin in terms of the elastic modulus and fracture toughness along with ease of machinability, which renders them promising as indirect dental restorative materials.

Rapid synthesis of tetragonal zirconia nanoparticles by microwave-solvothermal route and its photocatalytic activity towards organic dyes and hexavalent chromium in single and binary component systems

In this paper, tetragonal zirconia nanoparticles (ZrO2 NPs) were synthesized via rapid microwave mediated solvothermal method in just 10 min reaction time. A combination of X-ray diffraction, Raman, Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM) and XPS analysis confirmed the formation of single phase tetragonal ZrO2 with average crystallite size ∼ 10 nm. The band gap energy of the synthesized ZrO2 was measured to be 3.67 eV. The photocatalytic behaviour of synthesized ZrO2 NPs was examined for the degradation of two anionic dyes (Eosin Yellow and Bromophenol Blue) and the reduction of Cr(VI) under UV light irradiation. ZrO2 adsorbed and degraded both the dyes within 120 min. At 20 mg/L concentration, more than 96 % of Cr(VI) was reduced to Cr(III) within 60 min. Under the operating conditions, both the degradation of dyes and reduction of Cr(VI) followed pseudo first-order kinetics and rate constant values were inversely dependent on the initial dye concentration. The probable mechanism for the degradation has been proposed through advanced oxidation process. ZrO2 NPs was also found efficient for simultaneous remediation of dye and Cr(VI). The photoreduction of Cr(VI) to Cr(III) was further confirmed from XPS analysis of ZrO2 NPs after chromium reduction.

Zirconium metal organic framework for design of tetragonal rare earth-doped zirconia nanoparticles

Zirconium metal–organic frameworks ZrOBDC (where BDC=C6H4(COOH)2, terephthalic acid) doped and co-doped with rare earth ions Ln (ZrOBDC:Ln3+, where Ln3+ = Eu3+ and Tb3+ as well as Er3+ and Yb3+) were used as precursors for the design of tetragonal rare earth doped zirconia nanoparticles (t-ZrO2:Ln3+ NPs) through annealing process. Preparation, characterization and luminescence properties of ZrOBDC:Ln3+ and ZrO2:Ln3+ NPs were investigated. The as-obtained t-ZrO2:Ln3+ NPs have high purity with an average size of 20–30 nm. The luminescence spectra of ZrOBDC:Tb3+ and ZrOBDC:Eu3+ display strong green and red emission at around 544 and 611 nm which correspond to 5D4 → 7F5 and 5D0 → 7F2 transitions of Tb3+ and Eu3+ ions, respectively. The green and red up-conversion emissions of ZrO2:Er3+,Yb3+ NPs due to 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of the Er3+ ions are observed under 976 nm laser excitation.

Structure dependent dielectric response of spray coated nanostructured zirconia thin films

In this work the structural dependent dielectric property of ZrO2 nanoparticles and films prepared using these nanoparticles is studied. The tetragonal and monoclinic dominant zirconia nanoparticles were obtained through thermal treatment of PVP/CTAB capped hydrous amorphous zirconia (HAZ) at 500 °C. The grain (Rg) and grain boundary (Rgb) resistances of both types of nanoparticles along with films are estimated by fitting the respective complex impedance (Nyquist) plots with an equivalent electrical circuit. The nanostructured tetragonal dominant zirconia films are highly conductive as compared to monoclinic films due to large amount of Zr3+ ions present at tetragonal sites. Consequently the film exhibits a high dielectric constant at lower frequency range due to Maxwell-Wagner polarization. Moreover the EPR signals observed at 1.946 (g∣∣) and 1.967 (g⊥) reveals the presence of greater Zr3+ ions tetragonal films. The Rgb of monoclinic dominant film is increased by an order of 103 and consequently results in significant reduction of dielectric constant. Further the shift of loss tangent peak to higher frequency side of tetragonal dominant films endorses the higher mobility of charge carriers as that of monoclinic films. The enhancement of dielectric properties shows the potential application of tetragonal dominant ZrO2 films for future electronic devices.

17O Solid-State NMR Studies of ZrO2 Nanoparticles

17O solid-state NMR spectroscopy was applied to study the structure of monoclinic and tetragonal zirconia nanoparticles with the help of density functional theory calculations for spectral assignments. Although high-temperature 17O enrichment allows detection of oxygen ions in the “bulk” part of nanoparticles, selective NMR observation of surface oxygen species can be realized using 17O-labeled water to enrich surface oxygen sites at a relatively low temperature. The high-frequency 17O NMR resonances arising from low-coordinated oxygen ions on the surface of monoclinic and tetragonal zirconia nanoparticles were observed for the first time. The results are the basis for further understanding of structure–properties relations of zirconia nanomaterials.

Low-temperature metastable tetragonal zirconia nanoparticles (NpMTZ) synthesized from local zircon by a modified sodium carbonate sintering method

The metastable tetragonal zirconia is an interesting material exhibiting a high surface area and photoluminescence properties. The present work studies the characteristics of the metastable tetragonal zirconia nanoparticles that were successfully prepared from local zircon without using a template by a modified sodium carbonate sintering method, followed by leaching, slow hydrolysis, and calcination at a low temperature. Zircon and alkaline were combined at a mole ratio of 1:2 and sintered at 1000 °C. The sintered material was washed with water to dissolve the silica and followed by leaching with sulfuric acid at pH 1–2 to dissolve the zirconia then followed by slow hydrolysis until pH 9 to precipitate zirconium hydroxide. The final product was evaluated including thermal behavior, phase transformation, chemical composition, infrared spectra, microstructure, and textural properties. Crystallization of zirconia occurred at 564.29 °C. Good crystallinity of the zirconia phase was obtained at 800 °C consisting of 80% tetragonal zirconia with a crystal size of 11 nm corresponding to its crystal plane of (101) and 20% monoclinic zirconia. At this temperature, zirconia attains 83.19% in purity, shows typical infrared spectrum, and consists of particles less than 40 nm in sizes that agglomerate, belongs to a mesoporous material exhibiting a high surface area of 46.990 m2/g. Increase in calcination temperature at 1050 °C transformed the tetragonal phase to the monoclinic phase of zirconia. Overall, the present work reveals a promising template-free method on the preparation of the metastable tetragonal zirconia nanoparticles from local zircon.

Synergistic effect of microwave rapid heating and weak mineralizer on silica-stabilized tetragonal zirconia nanoparticles for enhanced photoactivity of Bisphenol A

Silica-doped tetragonal mesoporous zirconia nanoparticles (SZ) were successfully synthesized with various concentrations of ammonia solution(NH4OH) using microwave-assisted method for photodegradation of Bisphenol A (BPA). The phase of SZ catalyst was pure mesoporous tetragonal ZrO2 with nano in size (5–10nm). The increasing concentration of NH4OH solution enhanced the hydrolysis and condensation process, as confirmed by formation of additional ZrOZr, SiOSi and SiOZr bonds. The formation of oxygen vacancy (Vo) and Zr3+ surface defects (ZSD) also increased proportionally with the concentration of NH4OH solution. Both properties and the SiOZr bond are supposed to play important roles in stabilizing the tetragonal phase of ZrO2. The Vo and ZSD also lowered the band-gap energy (from 4.35eV to 3.05eV) and act as electron acceptors. Catalytic testing showed that 8-SZ gave the highest initial rate (0.372× 10−3mMmin−1) of 10mgL−1 BPA at pH7 using 0.5gL−1 catalyst within 4h while under similar conditions, 5-SZ, 3-SZ, 0-SZ, ZrO2 and TiO2 only gave 0.263×10−3, 0.211×10−3, 0.145× 10−3, 0.026× 10−3 and 0.305×10−3mMmin−1, respectively. These results demonstrate that higher numbers of SiOZr, Vo, and ZSD seemed to be the main factors in the high photoactivity of SZ prepared in 8M NH4OH solution (8-SZ). A kinetic study demonstrated that the photodegradation followed the pseudo-first-order Langmuir-Hinshelwood model. The mechanism study using scavenging agents proved that photogenerated hole was the main active species, thus led more hydroxyl radicals formed to degrade the BPA. The 8-SZ also exhibited a great potential on degradation of various phenols and dyes in wastewater.

Synthesis and characterization of pure tetragonal ZrO2 nanoparticles with enhanced photocatalytic activity

Tetragonal zirconia (t-ZrO2) nanoparticles were successfully prepared by a hydrothermal method and characterized by various measurement techniques. The tetragonal crystalline structure of ZrO2 nanoparticles were confirmed by X-ray diffraction analysis. The binding energies of Zr and O were confirmed from the XPS spectrum. The band gap energy was estimated using optical absorption spectroscopy, found to be 4.8eV. The UV (360nm) and visible (403nm and 537nm) emissions were observed from PL spectrum. The thermal stability of the prepared ZrO2 nanoparticles was studied by TG-DTA analysis. The photocatalytic degradation of the as-prepared ZrO2 nanoparticles was studied under UV light irradiation using methyl orange (MO) as a model organic pollutant. Results showed that 99% degradation was achieved within 50min. Photoelectrochemical studies were also supported the photocatalytic activities.

Exploiting copper–silica–zirconia cooperative interactions for the stabilization of tetragonal zirconia catalysts and enhancement of the visible-light photodegradation of bisphenol A

Abstract Silica-doped tetragonal mesoporous zirconia nanoparticles, SiO2/ZrO2 (SZ), were successfully prepared by a simple microwave-assisted method, and the subsequent incorporation of copper (1–10 wt%) via an electrochemical method gave CuO/SiO2/ZrO2 (CSZ) catalysts. The SiO2 stabilized the ZrO2 completely in the tetragonal phase, but that the added copper occupied oxygen vacancies in the SZ lattice to perturb the catalysts and partially reintroduce the monoclinic phase. However, CuO enhanced the photoactivity of CSZ catalysts by lowering the band gap energy (from 4.35 eV to 2.70 eV) and acting as an electron trapper to suppress the recombination of electron–hole pairs. The activity of the catalysts in the photodegradation of bisphenol A was ranked in the following order: 5 CSZ (82%) > 1 CSZ (65%) > 10 CSZ (60%) > SZ (58%). The silica–copper–zirconia cooperative interactions affected the numbers of oxygen vacancies, defect sites, Zr–O–Si and Zr–O–Cu bonds, which consequently influenced the stabilization of ZrO2 as well as the photoactivity of each catalyst. A kinetic study demonstrated that the photodegradation followed the pseudo-first-order Langmuir–Hinshelwood model.

Electrospun zirconia-embedded carbon nanofibre for high-sensitive determination of methyl parathion

Carbon nanofibers embedded with ultrafine zirconia nanoparticles (ZrO2-CNFs) are fabricated via a new methodology. Polyvinylpyrrolidone (PVP) and polymethylmethacrylate (PMMA) binary polymers containing zirconium n-butoxide are first dissolved in dimethylformamide, and the resulting solution is electrospun and heat-treated. The tetragonal zirconia nanoparticles formed, with a size of 5±2nm in diameter, are uniformly distributed in the carbon nanofibres. Using Nafion as an additive, ZrO2-CNFs are drop-cast onto the glassy carbon electrode (ZrO2-CNF/GCE) and the modified electrode is then applied to detect methyl parathion (MP) using differential pulse voltammetry. Two linear relationships are found at the concentration ranges of 1×10−9–2×10−8g/L and 2×10−8–2×10−7g/L, with a detection limit of 3.4×10−10g/L (S/N>3). The electrospun-based ZrO2-CNF is a very promising coating material for electrochemical sensing of organophosphorus compounds.

Structural transformation of polymeric and cationic capped zirconia nanoparticles with temperature

The phase transformation mechanisms of zirconia nanocrystals obtained on thermal treatment of polyvinylpyrrolidone (PVP) and cetyltrimethylammoniumbromide (CTAB) capped hydrous amorphous zirconia (HAZ) on thermal treatment are investigated. In PVP assisted synthesis, tetragonal zirconia nanoparticles formation is the predominant one as compared to CTAB assisted synthesis. The decomposition of surfactants capped on HAZ with temperature (526°C for PVP and 466°C for CTAB) and subsequent interaction of the by-products with zirconia nanoparticles are responsible for tetragonal to monoclinic phase transformation. The decomposition temperature of capped surfactants is observed from thermogravimetric analysis (TGA) and subsequent interaction of by-products with zirconia nanoparticles at different temperatures is investigated from FTIR spectra. Further the structure of nanoparticles annealed at different temperatures is investigated using XRD, micro Raman and photoluminescence (PL) analysis.