Tetragonal ZrO2 Nanoparticles Research Articles

Effect of applied stress on microstructural evolution during the sintering of nanocrystalline tetragonal zirconia below 1000 °C

Microstructural evolution during the sintering of tetragonal ZrO2 nanoparticles was investigated using stress-free sintering and sinter forging. The green body prepared via gel casting had a densely packed structure with a narrow pore size distribution. Special attention was paid to the evolution of pore structures in the initial and intermediate stages of sintering. Pore coarsening, which is considered an important issue in the nanoceramics densification, was not remarkable in sinter forging. The accelerated densification rate, coupled with the retention of finer pore size than that in stress-free sintering throughout densification, lowered the sintering temperature requirement. This temperature reduction effectively inhibited grain growth, allowing samples prepared via pressure-assisted sintering to maintain a nanometric structure.

Structure-reactivity relations in Cu/ZrO2 catalysed glycerol dehydration to acetol in continuous flow system

The selective dehydration of glycerol to hydroxyacetone (acetol) was studied in a continuous flow fixed-bed reactor with CuO supported on monoclinic (m-) or tetragonal (t-) ZrO2 nanoparticles. Catalysts were characterised...

Stabilizing tetragonal ZrO2 nanocrystallites in solvothermal synthesis.

Phase-pure tetragonal ZrO2 nanoparticles have been prepared under simple solvothermal synthesis conditions using different types of alcohols as solvents and studied using in situ X-ray scattering. The variation of tetragonal/monoclinic phase ratios within the produced powders was directly correlated with the amount of in situ generated water from solvent dehydration during the syntheses. By controlling the dehydration kinetics, either choosing primary alcohols of varying thermal stability or by changing synthesis temperatures, it is possible to selectively tune this tetragonal/monoclinic phase ratio.

Plasmonic effect on the emission intensity of Ce3+ ions doped zirconia-silicate glass

Ce3+:SiO2-ZrO2 samples doped with and without plasmonic nanoparticles of copper were prepared by the easy and economic non-hydrolytic sol–gel method. Structural, morphological, and optical studies were done on the samples after being dried at room temperature and annealed at 800 °C. Fourier transform infrared (FTIR) spectra confirms the formation of the host glass SiO2-ZrO2 from the asymmetric stretching of Si-O-Zr bond. Tetragonal ZrO2 and plasmonic copper nanoparticles formation was affirmed from the X-ray diffraction (XRD) spectra. Transmission electron microscopy (TEM) confirms the formation of plasmonic nanoparticles of copper. UV/Visible spectra show an absorption around 330 nm. The photoluminescence (PL) spectra show emission centered around 469 nm; an enhancement in the PL intensity occurred due to the localized surface plasmon resonance (LSPR) effect of the plasmonic nanoparticles of copper.

Impact of doping ZrO2 with Sn on CO2 hydrogenation over dispersed Ru

Thermocatalytic CO2 hydrogenation is a scalable route to renewable fuels and chemicals that can also mitigate climate change. Here, we demonstrate how subtle changes in a mixed phase zirconia support induce large changes in catalyst activity and selectivity. Ru/SnxZr1-xO2 catalysts were prepared using co-precipitated Sn-doped ZrO2. Ru/ZrO2 and Ru/Sn0.01Zr0.99O2 both comprised tetragonal (t-) and monoclinic (m-) ZrO2 nanoparticles decorated by RuO2·H2O clusters. Ru/Sn0.2Zr0.8O2 exhibited similar textural properties and metal speciation, however, X-ray diffraction evidenced new crystalline phases wherein Sn atoms substituted for Zr. Operando XRD evidenced minimal perturbation of ZrO2 and Sn-doped ZrO2 phases, despite which 20 atom% Sn switched product selectivity from 99% CH4 for Ru/ZrO2 to 67% CO for Ru/Sn0.2Zr0.8O2, due to increased support CO2 adsorption capacity/strength. Operando infrared spectroscopy identify linear surface CO* as a catalytic spectator with (bi)carbonate a precursor to reactive HCOO*/carboxylate intermediates to methane. Sn0.2Zr0.8O2 promotes CO2/(bi)carbonate/formate decomposition, favouring a reverse water gas shift pathway.

CaO-doped tetragonal ZrO2 nanoparticles as an effective adsorbent for the removal of organic dye waste

In this work, we show the promise and potential of CaO-doped tetragonal ZrO2 nanoparticles as a brilliant adsorbent for toxic azo dye (e.g., Congo red). Contrary to past works, where zirconia has mostly been used as a member to form composite for such adsorption experiments, we show that the system (i.e., doped-ZrO2) alone is capable to portray maximum adsorption capacity up to 186 mg/g for Congo red. High surface area (113 m2/gm) of the synthesized zirconia nanoparticles ensured a rapid removal of the dyes (>85% in just five minutes). The adsorption followed a pseudo-second order kinetic model and fitted closely with the Langmuir isotherm model. Adsorption mechanism reveals the efficacy of the dopant (i.e., CaO) which enabled a chemical interaction (via ion-exchange between the Ca2+ ion of dopant and Na+ ions in the dye molecules) that eventually holds all the success for the adsorption phenomena. To prove the environmental remediation of CaO-ZrO2 as a dye adsorbent in a more practical way, these dye adsorption studies were also carried out in real water. The popular market composition (i.e., yttria-stabilized ZrO2) was also compared and showed modest/little adsorption.

Microstructure and Piezoelectric Properties of Lead Zirconate Titanate Nanocomposites Reinforced with In-Situ Formed ZrO2 Nanoparticles.

Lead zirconate titanate (PZT)-based ceramics are used in numerous advanced applications, including sensors, displays, actuators, resonators, chips; however, the poor mechanical characteristics of these materials severely limits their utility in composite materials. To address this issue, we herein fabricate transgranular type PZT ceramic nanocomposites by a novel method. Thermodynamically metastable single perovskite-type Pb0.99(Zr0.52+xTi0.48)0.98Nb0.02O3+1.96x powders are prepared from a citrate precursor before both monoclinic and tetragonal ZrO2 nanoparticles ranging from 20 to 80 nm are precipitated in situ at a sintering temperature of 1260 °C. The effects of ZrO2 content on the microstructure, dielectric, and piezoelectric properties are investigated and the mechanism, by which ZrO2 toughened PZT is analyzed in detail. The ZrO2 nanoparticles underwent a tetragonal to monoclinic phase transition upon cooling. The fracture mode changed from intergranular to transgranular with increasing ZrO2 content. The incorporation of ZrO2 nanoparticles improved the mechanical and piezoelectric properties. The optimized piezoelectric properties (εT33/ε0 = 1398, tan δ = 0.024 d33 = 354 pC N−1, kp = 0.66 Qm = 78) are obtained when x = 0.02. Tc initially increased and subsequently decreased with increasing ZrO2 content. The highest Tc = (387 °C) and lowest εT33/ε0 was obtained at x = 0.01.

Enhancing corrosion and mechanical properties of 304 stainless steel by depositing and annealing Zr75Cu25 thin-film metallic glass

Zr75Cu25/S-phase composite films were prepared on 304ss by magnetron sputtering and subsequently oxygen-annealed for improved corrosion and mechanical properties. It was discovered that tetragonal ZrO2 nanoparticles nucleated on the film surface after annealing and Cu atoms segregated at the surfaces as well, when the annealing temperature was increased. The amorphous/crystalline microstructural features of the films were established by transmission electron microscopy and grazing incidence X-ray diffraction. Nanoindentation tests on Zr75Cu25 thin film metallic glasses (TFMGs) were conducted and their corrosion properties in 3.5 wt% NaCl solution examined by potentiostatic polarization and electrochemical impedance spectroscopy. The Zr75Cu25 TFMGs in annealed conditions indicated a superior hardness and Young modulus values. Similarly, the Zr75Cu25 TFMGs, exhibited a better corrosion resistance value as compared with the performance of the 304ss substrate. Potentially, candidate Zr75Cu25 film-based coating materials can be synthesized at the annealing temperature of 350 °C to optimize the performance characteristics of 304ss.

Unveiling the structural transitions during activation of a CO2 methanation catalyst Ru0/ZrO2 synthesised from a MOF precursor

Carbon Capture, Utilisation and Storage (CCUS) technologies are utilised to minimise net CO2 emissions and hence mitigate the impact of anthropogenic emissions on the global climate. One example of CO2 utilisation is the production of carbon-neutral methane fuel via catalytic CO2 reduction with H2 (methanation). Thermal activation of a metal impregnated metal-organic framework (MOF), 1 wt%Ru/UiO-66 in the presence of H2 and CO2 provides in situ synthesis of a highly active methanation catalyst: H2 promotes the formation of Ru0 nanoparticles, and CO2 behaves as a mild oxidant to remove framework carbon and promote ZrO2 crystallisation. The nature of the active MOF-derived Ru0/ZrO2 catalyst was studied by PXRD, TEM, and XAS, and the evolution of the parent 1 wt%Ru/UiO-66 during thermal activation monitored in operando by synchrotron PXRD. The Ru impregnated Zr-based MOF collapses on heating in H2 and CO2 to form an amorphous C and Zr containing phase that subsequently crystallises as tetragonal (t-) ZrO2 nanoparticles. These t-ZrO2 nanoparticles undergo a subsequent phase transition to the more stable monoclinic (m-) ZrO2 polymorph. In situ activation of Ru/UiO-66 generates a highly active catalyst for CO2 methanation by transforming the MOF precursor into a (carbon-free) crystalline t-ZrO2 support that stabilises highly dispersed metallic Ru nanoparticles. This insight may guide the rational design of future MOF-derived catalysts.

UiO-66 derived zirconia/porous carbon nanocomposites for efficient removal of carbamazepine and adsorption mechanism

Nanoarchitecture design of metal oxides/porous carbon nanocomposites from metal-organic frameworks is attracting considerable attention. Herein, UiO-66 was used as precursor and template to fabricate zirconia/porous carbon nanocomposites with tunable specific surface area and pore volume by a two-step calcination. The results showed that the tetragonal ZrO2 nanoparticles in carbon matrix gradually grow up and transform into monoclinic ZrO2 and ZrO as well as escape from the porous carbon nanocubes resulting in the increase of their specific surface area and pore volume with the increase of calcination temperature. The as-prepared nanocomposites at 1200 °C (ZPCNCs-12) exhibited a high specific surface area up to 468.9 m2 g−1, and excellent adsorption performance with high adsorption capacity (190 mg g−1), fast adsorption equilibrium (60 min) and recyclability for the removal of carbamazepine from water in a wide pH range of 2–12. FTIR spectra suggested that the adsorption of carbamazepine on ZPCNCs-12 was physical, and XPS results further confirmed that the adsorption was mainly dominated by the π-π electron donor-acceptor interaction between carbamazepine molecule and carbon nanocubes. It indicates that the two-step calcination of metal-organic frameworks is an effective approach to fabricate highly efficient sorbent for the removal of organic pollutants from water.

Template-free synthesis of tetragonal Co-doped ZrO2 nanoparticles for applications in electrochemical energy storage and water treatment

Template-free synthesis of pure and Co-doped ZrO2 tetragonal structured nanoparticles was achieved by the hydrothermal method and their photocatalytic, photoelectrocatalytic, and electrochemical energy storage supercapacitive properties were investigated for the first time. XRD revealed tetragonal crystal structure, while BET surface analysis suggested that Co-doped ZrO2 has higher surface area (186.4 m2g−1) than that of the undoped sample (99.5 m2g−1). The band gap value was reduced from 4.95 to 2.12 eV due to incorporation of cobalt. Under visible-light illumination, photocatalytic and photoelectrocatalytic activities for methyl orange (MO) dye degradation were evaluated. The working electrodes have been prepared with 85 wt% active material (pure and doped ZrO2), 10 wt% active carbon black, and 5 wt% polyvinylidene difluoride (PVDF) in order to perform the supercapacitive properties. The Co-doped ZrO2 material exhibited 93.7% and 27.4% MO dye degradation within 100 min with the highest specific capacitance value of 2151.2 Fg-1.

Design of Pt/t-ZrO2/g-C3N4 efficient photocatalyst for the hydrogen evolution reaction

Photocatalytic efficiency of graphitic carbon nitride (g–C3N4) has been hindered by fast carrier recombination and high reaction energy barriers, which can be improved by combining a semiconductor with a large work function. Based on this strategy, we synthesized a novel Pt/t–ZrO2/g–C3N4 composite by integrating g–C3N4 with tetragonal ZrO2 and Pt nanoparticles. Results of experimental measurements and density functional theory simulation demonstrate that the carrier lifetime, transferability and energy barriers of catalysts depend on their work function. The optimal composite exhibits an extraordinary catalytic ability for hydrogen generation of 722.5 μmol(gh)−1 and solar–to–hydrogen energy conversion efficiency of 0.215% under visible–light irradiation, and high catalytic stability. The modification strategy could be applied to designing various different high–efficient catalysts by selecting semiconductors with suitable work functions.

Synthesis and structural, optical, photocatalytic, and electrochemical properties of undoped and yttrium-doped tetragonal ZrO2 nanoparticles

Template-free undoped and yttrium-doped tetragonal ZrO2 nanoparticles were successfully synthesized using a hydrothermal technique, and their structural, morphological, optical, and electrochemical properties were characterized. The photocatalytic activity for the dye degradation of the Rhodamine B (RhB) was also studied under UV light irradiation. The tetragonal crystal phase of the nanoparticles was confirmed by XRD analysis. The observed peak shift in XRD patterns confirmed the incorporation of dopant into host lattice. The Yttrium-doped ZrO2 nanoparticles showed a higher specific surface area and smaller optical band gap (191.5 m2/g and 3.66 eV) than the pristine ZrO2 nanoparticles (108.6 m2/g and 4.94 eV). The yttrium-doped ZrO2 nanoparticles exhibited greater photocatalytic activity (~98%) than the pure ZrO2 nanoparticles within 40 min, due to their high specific surface area and reduced photogenerated charge carrier recombination rate. The Nyquist plot of yttrium-doped sample exhibited lower charge transfer resistance than that of the undoped sample. The photocurrent of the doped sample (28.6 mA/cm2) was ~9 times higher than that of pristine ZrO2 sample (3.2 mA/cm2). The doped sample showed stable and higher photocurrent density up to 520 s under light illumination.

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.

Reactant effect on visible-light driven photocatalytic performance of sol–gel derived tetragonal ZrO2 nanoparticles

Tetragonal ZrO2 (t-ZrO2) nanocrystals were prepared through sol–gel process and the influence of zirconium starting reactants on visible-light photocatalytic performance for degrading tetracycline hydrochloride was discussed. The t-ZrO2 powders synthesized by using zirconium n-propoxide show low specific surface area of ∼20m2/g. Those synthesized by zirconium oxychloride exhibit high specific surface area of ∼76m2/g, along with a great deal of oxygen vacancies, which shows highly visible-light photocatalytic performance. Accordingly, the apparent quantum efficiency of the t-ZrO2 catalyst synthesized by zirconium oxychloride is seven times as much as that synthesized by zirconium n-propoxide. Furthermore, their photocatalytic mechanism was discussed.

In-water facile synthesis of poly-substituted 6-arylamino pyridines and 2-pyrrolidone derivatives using tetragonal nano-ZrO2as reusable catalyst

Green synthesis of functionalized 6-arylamino pyridines and 2-pyrrolidinone derivatives using tetragonal ZrO2nanoparticles as reusable catalyst in aqueous ethanol.

Hydrothermal synthesis and phase stability of Pb stabilized ZrO2 nanoparticles

The Pb doped metastable tetragonal ZrO2 (t-ZrO2:Pb) nanoparticles have been successfully synthesized by hydrothermal method. Pb ion doping has great effects on the phases, crystallite sizes and optical band gaps. Systematic structural characterization revealed that the introduction of Pb ion results in lattice expansion. The as-prepared t-ZrO2:Pb with ca 4–6 nm in size has high specific surface area (>150 m2/g) and narrow particle size distributions. The diffuse reflectance spectra investigated that the band gap shifts from ultraviolet (Eg = 5.19 eV) for pure ZrO2 to the visible region for t-ZrO2:Pb and the gap can be effectively adjusted with the content of Pb in nanocrystals. Through thermal treatment, Pb ion doped in ZrO2 crystals was excluded with increasing temperature. At 800 °C, the three t-ZrO2:Pb samples of ZPO-2, ZPO-3 and ZPO-4 still contained the pure tetragonal phase, in which Pb content were not reduced to zero, while the transformation from tetragonal to monoclinic phase occurred due to zero Pb content in ZPO-1. The reason to this transformation and stabilized mechanism of Pb ion in ZrO2 were discussed.

Sol–gel synthesis of tetragonal ZrO2 nanoparticles stabilized by crystallite size and oxygen vacancies

In this letter, we present a facile route to produce metastable tetragonal zirconia (ZrO2) nanoparticles via pH-controlled precipitation of dilute zirconyl nitrate dihydrate [ZrO(NO3)2·2H2O] solution in liquid NH3 under ambient conditions and calcination at 500 °C for 2 h. The phase pure tetragonal ZrO2 nanoparticles are obtained at pH 9. The effect of pH on metastable phase stabilization in precipitated ZrO2 nanoparticles is demonstrated with the help of XRD, SEM/EDX, and X-ray photoelectron spectroscopy techniques. The stability of tetragonal ZrO2 phase is attributed to the smaller crystallite size and greater oxygen deficiency in phase-pure tetragonal ZrO2.

Production of Al2O3‐Stabilized Tetragonal ZrO2 Nanoparticles for Thermal Barrier Coating

Al2O3‐stabilized tetragonal ZrO2 nanoparticles were obtained through hot‐air spray pyrolysis and characterized after postsynthesized treatments. The produced nanoparticles were 26 nm in size with surface area of 59 m2/g. A multilayer thermal barrier coating of nanostructured Al2O3‐ZrO2‐embedded silicate was applied to the mild steel (EN3) specimen using spin‐coating technique and characterized comprehensively employing X‐ray diffraction and scanning electron microscope. The Al2O3‐stabilized ZrO2 with silicate matrix facilitates the formation of zirconium silicate nanostructured surface‐protective coating on EN3 specimen. The Al2O3‐ZrO2/SiO2 matrix‐based hybrid inorganic coating shows effective thermal barrier for EN3 after firing at a high temperature of 600°C.

Controllable synthesis of metastable tetragonal zirconia nanocrystals using citric acid assisted sol–gel method

Metastable tetragonal ZrO2 nanoparticles and nanosheets were synthesized with citric acid assisted sol–gel method. In this approach, zirconium acetylacetonato, Zr(acac)2, citric acid (CA) and ethylene glycol (EG) were used as the source of Zr4+, the chelating, and solvent agent, respectively. The effects of heat treatment on zirconia phase evolution were investigated. We demonstrate that pure tetragonal nanocrystalline zirconia can be obtained with CA: EG mole ratio=5:1 and calcination temperature 490°C. The microstructure of the products was characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and Raman scattering. Finally, Photoluminescence (PL) of nanosheets and nanoparticles were also investigated.