Structure Of ZrO2 Research Articles

A comparative study on antibacterial properties of EuO, CuO, and ZnO dopped ZrO2 sol-gel coatings

ZnO, CuO, and EuO doped ZrO2 films were prepared using a sol-gel dip coating technique, and the effects of the doping on the film thickness, crystallite size, surface roughness, band gap energy, adhesion strength, and antibacterial properties of the coatings were investigated. It was found that the addition of small amounts of ZnO and EuO can significantly improve the uniforminty of the sol-gel coating, while the greater the difference in the coefficients of thermal expansion (CTEs) of the coating and the substrate, the higher the probability of developing surface microcracks. The XRD patterns of the coatings synthesized based on ZrO2 as well as EuO, ZnO, and CuO dopants showed that the ZrO2 structure was tetragonal for all of the compounds. In addition, it was revealed that with an increase in the calcination temperature, the crystallite sizes of the coatings containing ZrO2 and ZnO increased, and in contrast, the crystallite sizes of ZrO2:ZnO, ZrO2:ZnO,CuO and ZrO2:ZnO,EuO compounds decreased. The evaluation of the reflectance of visible light functions showed that adding 30 % ZnO led to a decrease in the band gap energy from 3.19 eV for ZnO2 to 3.01 eV for ZrO2 + 30 % ZnO. Moreover, the lowest band gap energy (2.81 eV) was achieved for the compound containing EuO. Finally, it was concluded that the ZrO2:ZnO,EuO sol-gel coating with the least band gap energy shows better antibacterial activity.

Comparison of the structure and physicochemical properties of ZrO2 based crystals partially stabilized with Y2O3, Gd2O3 and Sm2O3

The phase composition, density, microhardness and fracture toughness of (ZrO2)1-x(R2O3)х crystals (where R = Y, Sm and Gd) for x = 0.02–0.04 have been compared. The crystals have been grown using directional melt crystallization in a cold crucible. The phase composition of the crystals has been studied using X-ray diffraction and Raman spectroscopy. The microhardness and fracture toughness of the crystals have been evaluated by means of indentation. At stabilizing oxide concentrations of ≥ 2.8 mol.% for Y2O3 and Gd2O3 and ≥ 3.7 mol.% for Sm2O3 the crystals have densities close to the theoretical ones and contain two tetragonal phases. At lower stabilizing oxide concentrations the crystals contain the monoclinic phase. The fracture toughness of the tetragonal crystals increases with the ionic radius of the stabilizer. The highest fracture toughness values achieved when stabilized by a specific oxide are 11.0, 13.0 and 14.3 MPa·m1/2 for the 2.8YSZ, 2.8GdSZ and 3.7SmSZ crystals, respectively. The fracture toughness proves to depend on the crystallographic orientation of the crystals. The results of this work can be used in the design and fabrication of various structural components and devices.

Effects of ZrO2 crystalline phase on oxygen vacancy of GaZr oxides and their properties for CO2 hydrogenation to light olefins

A bifunctional catalyst, comprising GaZr oxide and SAPO-34 zeolite, manifests enhanced catalytic activity in CO2 hydrogenation to light olefins; nonetheless, the comprehensive analysis of the pivotal role played by the underlying structure of ZrO2 in Ga-Zr oxide has not been investigated. Herein, different crystalline structures of ZrO2 were prepared by the co-precipitation method and adopted as a support to deposit Ga to obtain ZrO2 with different ratios of monoclinic ZrO2 (m-ZrO2) to tetragonal ZrO2 (t-ZrO2) in GaZr oxides for CO2 hydrogenation to light olefins. Various characterizations demonstrated that the interface between Ga and the mixed phase of (m-t) ZrO2 produces more oxygen vacancies which favors the adsorption and activation of CO2, and the larger specific surface area and stronger H2 adsorption and dissociation capacity promote CO2 conversion. Interestingly, the GaZr oxide with high m-ZrO2 content exhibits superior catalytic activity than the GaZr oxide with high content of t-ZrO2. The highest light olefins yield (9.0%) and selectivity (77.9%) (CO free) with 27.9% CO2 conversion was achieved. In-situ DRIFT spectra further elaborated that the GaZr oxides with different ZrO2 crystalline phases follow the same reaction pathway to hydrogenate CO2 first to HCOO* and then to CH3O* on GaZr oxide surface. While compared with sole ZrO2, the introduction of Ga significantly promotes the hydrogenation of HCOO* to CH3O*, acting as a crucial reaction intermediate that subsequently diffuses into SAPO-34 pores to enhance the desired light olefins selectivity.

Composition-dependent structure and bandgaps in HfxZr1−xO2 thin films

ZrO2 as a wide-bandgap semiconductor with high dielectric constant and ferroelectric properties has been extensively studied. To explore the impact of chemical doping on the structure and optical performance of ZrO2, HfxZr1−xO2 (x = 0, 0.25, 0.5, 0.75, 1) thin films were prepared through pulsed laser deposition. X-ray diffraction reveals that the orthorhombic phase (o) (111) gradually transforms into the monoclinic phase (m) (−111) with the increase in Hf content from 0 to 1. Furthermore, optical property analysis demonstrates an increase in the optical bandgap from 5.17 to 5.68 eV with the increase in Hf doping content. Density functional theory calculations and x-ray photoelectron spectroscopy suggest that the widening of the bandgap in HZO films is associated with the hybridization of Zr 4d and Hf 5d orbitals.

Multi-functional nanoscale ZrO2 catalysts for sustainable water treatment

This study aimed to synthesize highly reactive ZrO2 nanoparticles using a straightforward sol-gel method for addressing water contamination from hazardous metal ions and organic dyes. Structural and photocatalytic properties were assessed using X-ray diffraction (XRD), Fourier transmission Infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), and UV–visible absorption spectroscopy. XRD analysis confirmed the tetragonal crystal structure of ZrO2. Photodegradation experiments using Eriochrome Black T (EBT) as a model dye revealed nearly 99% degradation under natural sunlight. Investigations into catalyst loading, dye concentration, pH, and irradiation source were conducted. Preliminary tests demonstrated the adsorbent's efficacy in removing Ca2+ ions. Further process optimizations could significantly enhance the potential of this innovative adsorbent for extracting metal ions from complex effluents.

Selective Upcycling of Polyethylene Terephthalate towards High-valued Oxygenated Chemical Methyl p-Methyl Benzoate using a Cu/ZrO2 Catalyst.

Upgrading of polyethylene terephthalate (PET) waste into valuable oxygenated molecules is a fascinating process, yet it remains challenging. Herein, we developed a two-step strategy involving methanolysis of PET to dimethyl terephthalate (DMT), followed by hydrogenation of DMT to produce the high-valued chemical methyl p-methyl benzoate (MMB) using a fixed-bed reactor and a Cu/ZrO2 catalyst. Interestingly, we discovered the phase structure of ZrO2 significantly regulates the selectivity of products. Cu supported on monoclinic ZrO2 (5 %Cu/m-ZrO2 ) exhibits an exceptional selectivity of 86 % for conversion of DMT to MMB, while Cu supported on tetragonal ZrO2 (5 %Cu/t-ZrO2 ) predominantly produces p-xylene (PX) with selectivity of 75 %. The superior selectivity of MMB over Cu/m-ZrO2 can be attributed to the weaker acid sites present on m-ZrO2 compared to t-ZrO2 . This weak acidity of m-ZrO2 leads to a moderate adsorption capability of MMB, and facilitating its desorption. Furthermore, DFT calculations reveal Cu/m-ZrO2 catalyst shows a higher effective energy barrier for cleavage of second C-O bond compared to Cu/t-ZrO2 catalyst; this distinction ensures the high selectivity of MMB. This catalyst not only presents an approach for upgrading of PET waste into fine chemicals but also offers a strategy for controlling the primary product in a multistep hydrogenation reaction.

Selective Upcycling of Polyethylene Terephthalate towards High‐valued Oxygenated Chemical Methyl p‐Methyl Benzoate using a Cu/ZrO2 Catalyst

AbstractUpgrading of polyethylene terephthalate (PET) waste into valuable oxygenated molecules is a fascinating process, yet it remains challenging. Herein, we developed a two‐step strategy involving methanolysis of PET to dimethyl terephthalate (DMT), followed by hydrogenation of DMT to produce the high‐valued chemical methyl p‐methyl benzoate (MMB) using a fixed‐bed reactor and a Cu/ZrO2 catalyst. Interestingly, we discovered the phase structure of ZrO2 significantly regulates the selectivity of products. Cu supported on monoclinic ZrO2 (5 %Cu/m‐ZrO2) exhibits an exceptional selectivity of 86 % for conversion of DMT to MMB, while Cu supported on tetragonal ZrO2 (5 %Cu/t‐ZrO2) predominantly produces p‐xylene (PX) with selectivity of 75 %. The superior selectivity of MMB over Cu/m‐ZrO2 can be attributed to the weaker acid sites present on m‐ZrO2 compared to t‐ZrO2. This weak acidity of m‐ZrO2 leads to a moderate adsorption capability of MMB, and facilitating its desorption. Furthermore, DFT calculations reveal Cu/m‐ZrO2 catalyst shows a higher effective energy barrier for cleavage of second C−O bond compared to Cu/t‐ZrO2 catalyst; this distinction ensures the high selectivity of MMB. This catalyst not only presents an approach for upgrading of PET waste into fine chemicals but also offers a strategy for controlling the primary product in a multistep hydrogenation reaction.

Effect of different rare earth fluoride doping on microstructure and ablation properties of C/C–ZrC–SiC composites prepared by molten salt assisted reactive melt infiltration

The effect of doping with rare earth elements of different ionic radii on the ablation resistance of C/C–ZrC–SiC composites was investigated and the ablative behavior and ablation resistance of C/C–ZrC–SiC composites with the addition of different rare earth elements was tested. Although rare-earth doped stabilized zirconia has been used for a long time in the field of thermal barrier coatings, the existing techniques are usually coating modifications with rare-earth oxide or boride additions, it is difficult to prepare coatings that can be used on the surface of carbon matrix materials due to the large difference in the coefficients of thermal expansion. Therefore, this study attempts to introduce rare earth components into the interior of C/C–ZrC–SiC composites for matrix modification. The results show that the addition of rare earth elements enhances the ablation performance of the composites, but the mechanism of enhancement is different: rare earth ions with a smaller radius difference from Zr4+ ions stabilize the crystal structure of ZrO2 by forming replacement solid solutions and stabilize the surface oxide film structure by preventing the homogeneous multiphase transformation of the oxide to achieve higher ablation performance; whereas rare earth ions with a larger radius difference from Zr4+ ions cannot stabilize ZrO2 by replacement solid solutions, but instead form high viscosity, low volatility liquid phase oxides to heal the surface defects of the oxide film and reduce liquid phase dissipation to enhance ablation performance.

Synthesis and properties of zirconium-cerium composite via solid-state route

This study synthesized CeO2-doped ZrO2 nanoparticles using the solid-state reaction, employing varying quantities of 0.05mol.%, 0.15mol.%, and 0.25mol.% CeO2. The structures of CeO2-doped ZrO2 were investigated through XRD, revealing the presence of monoclinic ZrO2 in all samples, while the average size of the crystallite increased as the concentration of CeO2 doping increased. The optical band gap of CeO2-doped ZrO2 was determined using diffuse reflectance spectra, showing that the band gap decreased with increasing doping concentrations. The investigation focused on characterizing parameters such as dielectric constants, dielectric loss, and AC conductivity, emphasizing their frequency dependence at room temperature (RT). The dielectric constant and dielectric loss of Zr1-x CexO2 exhibited a significant drop as the frequency increased (Maxwell-Wagner polarization). Furthermore, the dielectric constant and dielectric loss factor in the lower frequency band exhibited an increase as the cerium content in ZrO2 increased. The incorporation of cerium significantly impacted the optical and electrical characteristics of composite ceramics consisting of CeO2 and ZrO2.

Synthesis and characterization of ZrO2-ZnO heterojunction composite for isopropanol detection.

We prepared ZrO2-ZnO heterojunction composites by a simple hydrothermal method as materials sensitive to isopropanol gas. The 5% ZrO2-ZnO sample presented a uniform rod-like structure. The optimum operating temperature, sensitivity and response/recovery times were measured to investigate the response of ZrO2-ZnO composites to isopropanol. The sensor based on 5% ZrO2-ZnO composites at an optimum temperature of 260 °C had a response to 100 ppm isopropanol of up to 172.46, which was about 3.6 times higher than that of pure ZnO. The sensor also exhibited fast response and recovery times of 5 s and 11 s, respectively. The gas-sensitive properties can be attributed to the rod-like structure, heterojunction structure and catalytic activity of ZrO2. These results would contribute in expanding the application of ZrO2 in gas sensors.

Growth mechanism of Al2O3 on surface of ZrO2 inclusions: experimental and first principles investigation

Zr has been widely used in high-quality steel due to its strong deoxidizing capacity and ability of improve performance of steel. ZrO2–Al2O3 inclusions with core-shell structure were observed in this study. The structure, electronic properties, and energy changes of ZrO2 and ZrO2–Al2O3 systems were studied based on first principles calculation. It indicates that ZrO2 can be used as the heterogeneous nucleation core of Al2O3. Al atoms were preferentially adsorbed on the bridge site of ZrO2 (001) and then form the ZrO2–Al2O3 interface. The template effect of ZrO2 was nine adsorption atomic layers, among which layers 1–5 was a coherent epitaxial layer, layers 5–9 was the transition layer, and the atomic ratio was 3:2. The growth mechanism of Al2O3 on ZrO2 surface was discussed. The results help understand the formation of inclusion at atomic scale and find ways to control the characteristics of inclusion in steel with Zr treatment.

Highly efficient ZrO2 photocatalysts in the presence of UV radiation synthesized in a very short time by plasma electrolytic oxidation of zirconium

We demonstrated in this paper that plasma electrolytic oxidation of zirconium in an alkaline electrolyte (10 g/L trisodium phosphate decahydrate) with the addition of NaAlO2 is a highly efficient method for obtaining ZrO2 coatings that are effective photocatalysts for the decomposition of organic pollutants under UV irradiation. ZrO2 coatings were formed by varying the PEO time from 60 s to 600 s, the NaAlO2 concentration up to 4 g/L, and characterized by SEM/EDS, XRD, XPS, DRS, and photoluminescence spectroscopy. Methyl orange decomposition was used to examine the photocatalytic activity (PA) of ZrO2 coatings. The PA of the formed PEO coatings is determined by the ratio of monoclinic and tetragonal ZrO2 phases, as well as the content of incorporated Al3+ in the crystal structure of ZrO2. Al3+ incorporated into ZrO2 coatings improves tetragonal phase stability by causing the formation of oxygen vacancies, which is crucial for enhancing their PA. Furthermore, the Al3+ dopant serves as a capture site for photo-induced electrons, inhibiting electron/hole recombination. The best PA was demonstrated by the ZrO2 coating formed after 60 s in an alkaline electrolyte with 4 g/L NaAlO2 addition, which contains the most tetragonal ZrO2 phases (around 51.3 %) and Al (around 3.14 at. %) of all formed ZrO2 coatings. After 8 h of irradiation, the PA of this coating was approximately 95 %.

CO2 hydrogenation to methanol over ceria-zirconia NiGa alloy catalysts

NiGa alloy particles supported on CeO2, ZrO2 and ZrO2-CeO2 solid solutions are prepared, characterized, and utilized for hydrogenation of CO2 into methanol. The nature of the support, including the Zr:Ce ratio, affects the catalyst structure and properties such as the ZrO2 crystalline phase, number of basic sites and concentration of oxygen vacancies. At high Zr:Ce ratios, the crystalline structure of ZrO2 has more influence on the catalytic activity than the oxygen vacancies introduced by the addition of CeO2, with the pure ZrO2 having the highest methanol selectivity of 53% with a CO2 conversion of 2.1% at 260 °C and 600 psi. In the equimolar and Ce-rich catalysts with a tetragonal ZrO2 crystalline phase, basic sites, and oxygen vacancies are the parameters most influencing the methanol production. The highest methanol productivity was obtained for the Zr5Ce5 supported catalyst, with a selectivity of 46.8% and a CO2 conversion of 2.7%. Overall, the space time yield of methanol is shown to correlate linearly with the concentration of moderate basic sites. The catalysts possess low activity relative to comparable systems utilizing metallic Cu phases, in part due to low NiGa dispersions achieved using the synthetic methods employed here.

Systematic Search for Stabilizing Dopants in ZrO₂ and HfO₂ Using First-Principles Calculations

In this study, we performed a systematic search for dopants to stabilize the tetragonal structure of HfO2 and ZrO2 by using high-throughput first-principles calculations. By exhaustively exploring all possible impurity configurations for over 12,000 systems, we obtained the expected most stable doping status for various dopants at different doping levels. The stabilization effect of dopants are investigated and compared. The results show that Si or Ge significantly stabilize the tetragonal phase.

Silicon-induced optimization on phase structure and surface property of Pd/ZrO2 catalysts for enhanced methane combustion

Palladium-based catalysts are relatively active for eliminating anthropogenic methane emissions through catalytic combustion, while they tend to degrade under drastic conditions. Herein, the silicon promoter was rationally introduced into Pd/ZrO2 catalysts to tune the monoclinic (m-) and tetragonal (t-) phase ratio and boost the catalytic performance. The introduced Si–O–Zr structure in ZrO2 not only reduced the grain size, but also produced oxygen vacancies due to lattice distortion, which greatly improved the stability of t-ZrO2 in high-temperature (800 °C) calcined catalysts. However, the excessive Si-addition caused the blockage of oxygen vacancies by amorphous SiO2, facilitating the transformation from t-ZrO2 to m-ZrO2. In the Pd/0.05Si–ZrO2 catalyst with a relatively high t-ZrO2 ratio, the presence of abundant oxygen vacancies stimulated the formation of surface-active oxygen and Pd2+ species, improved the reducibility of PdO and the redox of Pd ↔ PdO, meanwhile depressed the accumulation of hydroxyls. These, coupled with the enhanced hydrophobicity by Si-modification, made Pd/0.05Si–ZrO2 exhibit superior catalytic activity, stability and water-resistance to catalysts with low t-ZrO2 ratio. The revealed Si-promotion effect could be generalized to design phase-regulated Pd-based catalysts with optimized surface property for catalytic oxidation reactions.

La-doped Ni/ZrO2 catalyst for the production of H2-rich gas by upgrading vapors coming from pyrolysis of biomass and co-pyrolysis of biomass with plastic

The main goal of this work was to develop efficient catalysts for the production of hydrogen-rich gas by upgrading vapors coming from the pyrolysis of biomass and co-pyrolysis of biomass with plastic. A series of nickel catalysts supported on zirconia modified by lanthanum was synthesized. The role of La and its optimal concentration have been studied. The activity of prepared materials was determined with the use of cellulose, poplar, and a mixture of poplar and low-density polyethylene. The analysis of the physicochemical properties of investigated catalysts showed that introducing lanthanum into the zirconia structure resulted in an increase in surface area, pore size, and pore volume. La contributed to the stabilization of tetragonal zirconia. Moreover, its incorporation into the ZrO2 structure led to the formation of stronger interactions between the active phase and support. This facilitated formation of smaller NiO crystallites on the surface of modified materials. It is worth noting that La doped catalysts were more resistant against coke deposition and their deactivation rate was lower than that noticed for parent Ni/ZrO2. It was demonstrated that the addition of polymer (LDPE) to biomass (poplar) resulted in a significant increase in the efficiency of hydrogen production. The highest hydrogen yield was obtained in the presence of the catalyst containing 8% of La.

Study of Structural and Optical Properties of Zirconium Oxide Nanoparticles

In present study Zirconium dioxide (ZrO2) nanoparticles (NPs) were synthesized by using the chemical method. For the synthesis of desired NPs, oleyl amine (OA) was used as a surfactant material. OA plays a crucial role in inhibiting the aggregation of ZrO2 nanocrystals. Particle surface stabilisation is facilitated by it. The average crystallite size estimated from X-ray diffraction (XRD) using Scherrer equation, to be 6.15nm. UV-vis absorption spectra in the wavelength range of 200-900 nm were obtained; energy band gap obtained approximately 2.52 eV in as prepared ZrO2 NPs. Using FT-IR, the functional group and band structure of ZrO2 were studied.

Tuning the crystalline and electronic structure of ZrO2 via oxygen vacancies and nano-structuring for polysulfides conversion in lithium-sulfur batteries

The recent emergence of tetragonal phases zirconium dioxide (ZrO2) with vacancies has generated significant interest as a highly efficient and stable electrocatalyst with potential applications in trapping polysulfides and facilitating rapid conversion in lithium-sulfur batteries (LSBs). However, the reduction of ZrO2 is challenging, even under strong reducing atmospheres at high temperatures and pressures. Consequently, the limited presence of oxygen vacancies results in insufficient active sites and reaction interfaces, thereby hindering practical implementation. Herein, we successfully introduced abundant oxygen vacancies into ZrO2 at the nanoscale with the help of carbon nanotubes (CNTs-OH) through hydrogen-etching at lower temperatures and pressures. The introduced oxygen vacancies on ZrO2−x/CNTs-OH can effectively rearrange charge distribution, enhance sulfiphilicity and increase active sites, contributing to high ionic and electronic transfer kinetics, strong binding energy and low redox barriers between polysulfides and ZrO2−x. These findings have been experimentally validated and supported by theory calculations. As a result, LSBs assembled with the ZrO2−x/CNTs-OH modified separators demonstrate excellent rate performance, superior cycling stability, and ultra-high sulfur utilization. Especially, at high sulfur loading of 6 mg cm−2, the area capacity is still up to 6.3 mA h cm−2. This work provides valuable insights into the structural and functional optimization of electrocatalysts for batteries.

Synthesis and Specific Properties of the Ceria and Ceria-Zirconia Nanocrystals and Their Aggregates Showing Outstanding Catalytic Activity in Redox Reactions—A Review

Non-stoichiometric CeO2−y, especially in the form of nanocrystal aggregates, exhibits exceptional catalytic activity in redox reactions. It significantly improves the activity of transition metals and their oxides dispersed on/or in it, also acting as an oxygen buffer. Particularly, active oxygen species (O2n−, O−) are generated at the M/CeO2−y nanoparticle interface, as well as in the surface layer of their solid-state solutions MxCe1−xO2−y. The crystal structure of CeO2, ZrO2 and (Ce, Zr)O2 and its defects are discussed in connection with the resulting specific catalytic activity. All the methods (simple precipitation and co-precipitation from mother liquors, sol–gel methods, precipitation from nanoemulsions, hydrothermal and solvothermal techniques, combustion and flame spray pyrolysis, precipitation using molecular and solid-state matrices, 3D printing and mechanochemical methods) used for the synthesis of these nanomaterials are comprehensively reviewed, describing the rules of individual procedures and preparation details. Methods of deposition of metal catalysts and their oxides on CeO2 nanoparticles, such as impregnation, washcoating and precipitation deposition, were also discussed. This review contains more than 160 references to representative papers wherein the reader can find further details on individual syntheses of effective ceria-based catalysts for redox reactions.

Phase equilibria in the ZrO2–HfO2–Nd2O3 system at 1500 °C and 1700 °C

The phase equilibria in the ZrO2–HfO2–Nd2O3 ternary system at 1500 °C and 1700 °C were studied over the whole concentration range by X-ray diffraction and microstructural analyses. Corresponding isothermal sections were constructed from the data obtained. It was found that solid solutions in this system are derived from a tetragonal (T) modification of ZrO2, a monoclinic (M) modification of HfO2, a hexagonal (A) modification of Nd2O3, a cubic phase with a fluorite (F) structure of ZrO2 (HfO2), and an ordered phase with a pyrochlore (Py) structure of Nd2Zr2O7 (Nd2Hf2O7). The phase boundaries and unit cell lattice parameters were determined. The solubility of Nd2O3 in M − HfO2 is pretty low and about less than 1 mol%, as confirmed by XRD and microstructural analyses. The ordered pyrochlore-type (Py) phase of Nd2Zr2O7 (Nd2Hf2O7) forms continuous series of solid solutions at 1500 °C and 1700 °C. The homogeneous region of these continuous series of solid solutions changes insignificantly with increasing temperature. The changes in the construction of the isothermal section of the ZrO2-HfO2-Nd2O3 phase diagram at 1500 °C compared to 1700 °C are associated with the thermal stability of cubic fluorite-type (F) solid solutions. Other phases in the ZrO2-HfO2-Nd2O3 ternary system are not detected at the studied temperatures.