ZrO2 Surface Research Articles

Fractal Dimension of the Fracture Surface of Porous ZrO2–MgO Composite

Fractal Dimension of the Fracture Surface of Porous ZrO2–MgO Composite

Influence of Strain on Acid–Basic Properties of Oxide Surfaces

The surface of oxide nanostructures (nanoparticles, nanowires, and epitaxial thin films) can be significantly strained compared to the regular crystallographic surfaces. In this work, using density functional theory methods, we studied the dependence of properties of MgO(100), CaO(100), SrO(100), BaO(100), anatase TiO2(101), and tetragonal ZrO2(101) surfaces (band gap, work function) on external tensile and compressive strain from +4 to −4%. To probe the acid sites, the adsorption of CO as a probe molecule was investigated. In most cases, tensile strain favors the adsorption of CO, while compressive strain weakens it. To also probe the anionic basic sites, we used H2O as a probe molecule. On most surfaces, two competing adsorption modes (molecular and dissociative) are present. Applying strain has a different effect on the adsorption modes. On t-ZrO2, we can invert the stability order of molecular and dissociative adsorption by applying 1.4% biaxial tensile strain. We described the dependency of different properties on strain with a simple empirical model with only three fitting parameters. This allows for a precise interpolation of our data and gives the opportunity to predict surface properties of strained surfaces.

Influence of pH on the structural, spectral, optical, morphological and photocatalytic properties of ZrO2 nanoparticles synthesized by sol–gel technique

In the present work, ZrO2 nanoparticles are synthesized with different pH (3 to 8) by the sol–gel technique. From X-ray diffraction analysis, the synthesized particles show a tetragonal crystal structure, and the average crystallite size is found to vary from 7.35 to 4.7 nm as the pH increases from 3 to 8. From the FTIR analysis, the peak observed at 621 cm−1 is ascribed to Zr–O vibrations in the nano-tetragonal ZrO2. The bandgap values are found to increase from 2.0 to 2.9 eV with an increase in pH. From the PL analysis, the observed peaks show a large band and considerable red shift in the band maximum compared to the bandgap of bulk ZrO2. This strongly expresses that the fluorescence involves extrinsic states. From the morphological analysis, the synthesized nanoparticles are found to be spherical in shape and EDS results confirm the presence of Zr and O. The photocatalytic analysis carried out using Alizarin yellow dye, shows that the degradation efficiency is 84.04% for ZrO2 (S3-pH 6). This is attributed to the excess –OH group present on the surface of ZrO2.

Characterization of Acid and Basic Sites on Zirconia Surfaces and Nanoparticles by Adsorbed Probe Molecules: A Theoretical Study

Acid and basic sites on monoclinic and tetragonal zirconia were investigated at the DFT level by computing IR and NMR properties of adsorbed probe molecules. Regular and stepped ZrO2 surfaces as well as stoichiometric zirconia nanoparticles have been considered. Acidity and basicity were probed by the adsorption of carbon monoxide and pyrrole, respectively. CO adsorption shows a positive shift of the C–O stretching frequency in IR spectra while the C atom of CO is shielded and 13C chemical shifts moves to higher field as a function of the strength of the acid site. For the study of basic sites we used a pyrrole molecule, but the interaction between the pyrrole ring and the surface leads to adsorption modes that cannot be used to titrate the surface basicity. On the other hand, at high coverage the molecule assumes an upright position and the formation of a hydrogen bond of the pyrrole NH group with the oxygen atoms of the surfaces provides a proxy of the basic properties of these sites. In particular, we focus on changes of the N–H IR frequency, 1H, 15N, and 17O NMR chemical shifts and their correlations with the surface basicity. Among the correlations found, that between the N–H stretching frequency of adsorbed pyrrole and the 17O NMR chemical shift of the O ion where the molecule is bound show a nice linear correlation. These two properties can provide useful information about the basic character of various O sites on the surface of zirconia.Graphic

Surface Modification of ZrO2 Nanoparticles and Its Effects on the Properties of Dental Resin Composites.

Endowing dental resin composites (DRCs) with suitable radiopacity is necessary for clinical diagnosis during treatment of caries. To reach this effect, ZrO2 nanoparticles were introduced into the DRCs in this work after modification with two different methods, one modified with 3-methacryloxypropyltrimethoxysilane (ZrO2@γ-MPS) and the other coated with mesoporous SiO2 and then modified with γ-MPS (ZrO2@m-SiO2@γ-MPS). These ZrO2 nanoparticles were used as functional additives, and the SiO2 nanoparticles were used as the fundamental filler in the preparation of DRCs to study the effects of the surface modification of ZrO2 nanoparticles and the amount of particles added (0, 3, 5, and 7 wt %) on the properties of the DRCs. The DRC containing ZrO2@m-SiO2@γ-MPS showed a higher transmittance, which may be attributed to the fact that the SiO2 coating reduced the refractive index of the nanoparticles and thus decreased the scattering of light within the DRC. The silane polymer film on the surface of ZrO2@γ-MPS nanoparticles acted as a lubricant and decreased the viscosity of DRC, but the DRC containing ZrO2@m-SiO2@γ-MPS showed a higher viscosity due to the presence of a mesoporous structure. The radiopacity value of the DRCs containing the functional additives was close to 1 mm Al, much higher than that of the DRC filled with SiO2 nanoparticles alone (0.74 ± 0.07 mm Al), meeting the requirement of ISO 4049:2009. The surface modification of ZrO2 nanoparticles had no significant influence on the mechanical properties, radiopacity, and cytotoxicity of DRCs (p > 0.05). This study provides useful insight into the design and development of radiopaque DRCs with excellent physical and mechanical properties.

Effect of the combined zirconium dioxide surface treatment on the shear bond strength of a veneering ceramic to zirconium dioxide.

Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) is used as a core material in all-ceramic restorations. The delamination and chipping of a veneering ceramic are the most common complications in the case of zirconia-based restorations. The aim of the study was to investigate the effect of the combined treatment of the zirconium dioxide (ZrO2) surface (airborne-particle abrasion with liner application) on the shear bond strength (SBS) of a veneering ceramic. Thirty pre-sintered ZrO2 cuboidal specimens (VITA YZ® HT) were sub-divided into 3 groups: group C consisted of 10 specimens without treatment at the sintering stage; group SZ1 consisted of 10 specimens treated with airborne-particle abrasion (50-micrometer paricles of aluminum oxide - Al2O3; Korox® 50), and then coated with a 0.1-millimeter liner (IPS e.max® Ceram ZirLiner) after sintering; group SZ2 consisted of 10 specimens treated with airborne-particle abrasion (50-micrometer particles of Al2O3), and then coated with a 0.2-millimeter liner after sintering. Ceramic veneers (IPS e.max Ceram Dentin) were then applied using the layering technique. After that, the SBS tests were conducted. The results showed that the combined treatment of the ZrO2 surface significantly affected SBS (p < 0.01). The highest mean value was shown in group C (12.441 ±2.284 MPa), followed by group SZ2 (7.889 ±0.794 MPa), whereas the lowest mean value was observed in group SZ1 (5.580 ±0.843 MPa). The combined treatment of the pre-sintered ZrO2 surface significantly reduced the SBS of a veneering ceramic. However, the combined surface treatment with a liner thickness of 0.2 mm significantly enhanced the SBS of a veneering ceramic compared to the same combined treatment but with a liner thickness of 0.1 mm.

Ag/ZrO2 and Ag/Fe–ZrO2 catalysts for the low temperature total oxidation of toluene in the presence of water vapor

New mesoporous and well-structured Ag-based catalysts (xAg/ZrO2 and xAg/Fe–ZrO2 with x = 2 wt%) have been investigated in the total oxidation of toluene with water vapor. The results showed that the catalytic activity of systems increases, in the 350–550 °C temperature range, following this order: ZrO2 < Fe–ZrO2 < Ag/ZrO2 ≈ Ag/Fe–ZrO2. Nevertheless, it was revealed that Ag/Fe–ZrO2 is the most active solid for the low temperature total oxidation of toluene (< 350 °C). The highest low temperature activity of this new catalyst can be related to the presence of more reactive surface oxygen, new active redox and acidic sites at Ag/Fe–ZrO2 surface, most probably generated by the simultaneous presence of Ag and Fe species.

Tailored Alkali Resistance of DeNOx Catalysts by Improving Redox Properties and Activating Adsorbed Reactive Species

SummaryIt is still challenging to develop strongly alkali-resistant catalysts for selective catalytic reduction of NOx with NH3. It is generally believed that the maintenance of acidity is the most important factor because of neutral effects of alkali. This work discovers that the redox properties rather than acidity play decisive roles in improving alkali resistance of some specific catalyst systems. K-poisoned Fe-decorated SO42−-modified CeZr oxide (Fe/SO42−/CeZr) catalysts show decreased acidity but reserve the high redox properties. The higher reactivity of NHx species induced by K poisoning compensates for the decreased amount of adsorbed NHx, leading to a desired reaction efficiency between adsorbed NHx and nitrate species. This study provides a unique perspective in designing an alkali-resistant deNOx catalyst via improving redox properties and activating the reactivities of NHx species rather than routinely increasing acidic sites for NHx adsorption, which is of significance for academic interests and practical applications.

Controlled synthesis of ordered mesoporous TiO2–ZrO2 supported CeSn oxides catalyst for the elimination of 1,2-dichlorobenzene

Abstract Ordered mesoporous TiO2–ZrO2 materials were prepared by evaporation-induced self-assembly (EISA). The CeSn/TizZr10-zOx catalysts were prepared by impregnation method, and its catalytic performance was evaluated for the removal of 1,2-dichlorobenzene (o-DCB). The structure and properties of CeSn/TizZr10-zOx were characterized by N2 adsorption-desorption, XRD, Raman, SEM, TEM, XPS and temperature programmed techniques. The results showed that Ce and Sn oxides were highly dispersed on TiO2–ZrO2 surface. Ti–Zr mixed oxides not only contributed to the formation of ordered mesopores, but also to the formation of strong acid sites. When the molar ratio of Ti/Zr was 6:4, the catalyst exhibited the excellent catalytic activity and outstanding stability and repeatability for the o-DCB elimination reaction because of its superior chlorine resistance. Furthermore, the reaction mechanism of o-DCB catalytic oxidation reduction was proposed based on surface lattice oxygen.

Effect of powder pre-oxidation on the microstructure and ablation resistance of ZrB2–SiC coating

Abstract To further improve the densification and properties of ZrB2–SiC coating, the ZrB2–SiC powder was pre-oxidized at different temperatures before plasma spraying. And the ablation property of the obtained coatings were assessed using an oxyacetylene torch flame. A core-shell structure powder was obtained after the pre-oxidation treatment at 800 °C. And the oxidized shell was dense and integral with an uniform thickness. Compared with the IPS-coating, the porosity percent of the corresponding pre-oxidized coating showing a classical lamellar structure decreased from 12.7% to 8.8%. The pre-oxidized coating showed a dense ZrO2 surface with a honeycomb-structure after ablation at 1800 °C for 60s.

Transparent Zirconium-doped Hematite Nanocoral Photoanode via In-Situ Diluted Hydrothermal Approach for Efficient Solar Water Splitting

To tackle the problem of bulk recombination and to solve the holes diffusion issue in hematite, the shape-guiding and in situ doping is an effective strategy. Herein, we developed a novel strategy for designing and fabricating zirconium-doped transparent hematite (Zr-Fe2O3(I)) photoanode through an in situ hydrothermal method and stoichiometric iron and zirconium dilution. The concentration of ZrO(NO3)2 and FeCl3·6H2O in the precursor solution effectively influenced the transparency and morphology of zirconium-doped Fe2O3. The XPS and TEM analyses confirms the co-existence of Zr doping and surface modification of Fe2O3 nanocoral diffused ZrO2 after high temperature quenching. Synergism between the Zr doping and ZrO2 layer facilizes the charge transfer in Zr-Fe2O3 nanocoral (NC) photoanodes. Among the photoanodes prepared by variously diluted concentrations of the iron and zirconium precursor, the in situ 1/32 Zr-Fe2O3 nanocoral (NC) photoanode achieved an excellent photocurrent density of 1.55 mA cm2 at 1.23 V vs. RHE, which is about doubles than that of the conventional pristine Fe2O3 (P-Fe2O3) NR. Additionally, as result of in situ Zr doping, favorable nanocoral morphology and ZrO2 surface modification exhibits the decreased changer transfer resistance and increased incident photon to current efficiency (IPCE) of 1/32 Zr-Fe2O3 NC upto 21.9%. This in situ Zr-doping and nanocoral morphology 1/32 Zr-Fe2O3 fulfills the requirements of both high charge separation efficiency and improved water oxidation kinetics. A novel 1/32 Zr-Fe2O3 (I) NC photoanode exhibits O2 and H2 evolution up to 69 and 138 μmol during 5 h of overall pure water splitting. This novel in situ hydrothermal dilution approach is feasible for fabricating a transparent hematite photoanode with NC morphology for practical PEC water splitting.

Biological and physicochemical implications of the aging process on titanium and zirconia implant material surfaces

Statement of problemChanges in physicochemical properties because of implant material aging and natural deterioration in the oral environment can facilitate microbial colonization and disturb the soft-tissue seal between the implant surfaces. PurposeThe purpose of this in vitro study was to investigate the effect of aging time on the physicochemical profile of titanium (Ti) and zirconia (ZrO2) implant materials. Further microbiology and cell analyses were used to provide insights into the physicochemical implications of biological behavior. Material and methodsDisk-shaped specimens of Ti and ZrO2 were submitted to roughness, morphology, and surface free energy (SFE) analyses before nonaging (NA) and after the aging process (A). To simulate natural aging, disks were subjected to low-temperature degradation (LTD) by using an autoclave at 134 ºC and 0.2 MPa pressure for 20 hours. The biological activities of the Ti and ZrO2 surfaces were determined by analyzing Candida albicans (C. albicans) biofilms and human gingival fibroblast (HGF) cell proliferation. For the microbiology assays, a variance analysis method (ANOVA) was used with the Tukey post hoc test. For the evaluation of cellular proliferation, the Kruskal-Wallis test followed by Dunn multiple comparisons were used. ResultsTi nonaging (TNA) and ZrO2 nonaging (ZNA) disks displayed hydrophilic and lipophilic properties, and this effect was sustained after the aging process. Low-temperature degradation resulted in a modest change in intermolecular interaction, with 1.06-fold for TA and 1.10-fold for ZA. No difference in biofilm formation was observed between NA and A disks of the same material. After 48 hours, the viability of the attached HGF cells was very similar to that in the NA and A groups, regardless of the tested material. ConclusionThe changes in the physicochemical properties of Ti and ZrO2 induced by the aging process do not interfere with C. albicans biofilm formation and HGF cell attachment, even after long-term exposure.

Enhanced Antimicrobial Activity of Biofunctionalized Zirconia Nanoparticles.

The effective interactions of nanomaterials with biological constituents play a significant role in enhancing their biomedicinal properties. These interactions can be efficiently enhanced by altering the surface properties of nanomaterials. In this study, we demonstrate the method of altering the surface properties of ZrO2 nanoparticles (NPs) to enhance their antimicrobial properties. To do this, the surfaces of the ZrO2 NPs prepared using a solvothermal method is functionalized with glutamic acid, which is an α-amino acid containing both COO– and NH4+ ions. The binding of glutamic acid (GA) on the surface of ZrO2 was confirmed by UV–visible and Fourier transform infrared spectroscopies, whereas the phase and morphology of resulting GA-functionalized ZrO2 (GA-ZrO2) was identified by X-ray diffraction and transmission electron microscopy. GA stabilization has altered the surface charges of the ZrO2, which enhanced the dispersion qualities of NPs in aqueous media. The as-prepared GA-ZrO2 NPs were evaluated for their antibacterial properties toward four strains of oral bacteria, namely, Rothia mucilaginosa, Rothia dentocariosa, Streptococcus mitis, and Streptococcus mutans. GA-ZrO2 exhibited increased antimicrobial activities compared with pristine ZrO2. This improved activity can be attributed to the alteration of surface charges of ZrO2 with GA. Consequently, the dispersion properties of GA-ZrO2 in the aqueous solution have increased considerably, which may have enhanced the interactions between the nanomaterial and bacteria.

Facile synthesis of Ag/ZrO2 nanocomposite as a recyclable catalyst for the treatment of environmental pollutants

A green and in-situ strategy is reported for the biosynthesis of Ag/ZrO2 nanocomposite using Ageratum conyzoides L. extract as both reducing and stabilizer agents. Immobilizing Ag NPs on the ZrO2 surface was verified using various instrumental analyses such as field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The catalytic activity of the as-prepared Ag/ZrO2 nanocomposite was investigated in the reduction of different pollutants such as 2,4-dinitrophenylhydrazine (2,4-DNPH), 4-nitrophenol (4-NP), nigrosin (NS) and congo red (CR) in the presence of NaBH4. Furthermore, the catalyst can be recovered and used in multiple runs without significant loss of catalytic activity. The advantages of using nano-biotechnology to synthesize heterogeneous catalysts present a noteworthy area for further research.

The role of oxygen vacancies in the CO2 methanation employing Ni/ZrO2 doped with Ca

The Ni/ZrO2 catalyst doped with Ca and Ni/ZrO2 were employed in the CO2 methanation, a reaction which will possibly be used for storing intermittent energy in the future. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS, reduction in situ), X-ray diffraction (XRD, reduction in situ and Rietveld refinement), electron paramagnetic resonance (EPR), temperature-programmed surface reaction, cyclohexane dehydrogenation model reaction, temperature-programmed desorption of CO2 and chemical analysis. The catalytic behavior of these catalysts in the CO2 methanation was analyzed employing a conventional catalytic test. Adding Ca to Ni/ZrO2, the metallic surface area did not change whereas the CO2 consumption rate almost tripled. The XRD, XPS and EPR analyses showed that Ca+2 but also some Ni2+ are on the ZrO2 surface lattice of the Ni/CaZrO2 catalyst. These cations form pairs which are composed of oxygen vacancies and coordinatively unsaturated sites (cus). By increasing the number of these pairs, the CO2 methanation rate increases. Moreover, the number of active sites of the CO2 methanation rate limiting step (CO and/or formate species decomposition, rls) is enhanced as well, showing that the rls occurs on the vacancies-cus sites pairs.

Zirconia (1 1 0) surface adsorption behavior – A density functional theory study

In order to determine the adsorption mechanism of molecules on zirconia and factors affecting it, the adsorption of a wide range of small molecules (He, H2, O2, N2, CO, NH3, H2O, H2CO), alkanes (CH4, C2H6, C3H8), and amino acids (glycine, alanine, proline, hydroxyproline, aspartic acid) were studied on the cubic ZrO2(1 1 0) surface by density functional theory method, along with the dispersion correction (DFT-D3). It was found that zirconium d orbitals, nonbonding electron pairs of the adsorbed atoms, and surface oxygen atoms play an important role in the adsorption mechanism. In addition, it was found that in the physical adsorption process, the interaction of atoms with the surface can be approximated by functional form of the 6-12 Lennard-Jones potential. Parameters and functional form of interaction potential help us establish a validated force field using high-level quantum mechanical calculations.

Promising zirconia-mixed Al-based nitrogen carriers for chemical looping of NH3: Reduced NH3 decomposition and improved NH3 yield

The chemical looping ammonia generation (CLAG) of N-sorption/desorption reactions via Al-based N-carriers for producing ammonia (NH3) (a non-carbon fuel) is thought to be an important alternative to the conventional Haber–Bosh NH3 synthesis technology. However, the low yield of NH3, because of significant NH3 decomposition at the required N-desorption temperature, inhibits the development of CLAG. Accordingly, ZrO2 mixed AlN was designed in this study to investigate the NH3 generation characteristics of AlN during the N-desorption process in a stationary bed reactor. The results showed that ZrO2 can improve the formation of NH3 because the molecular adsorption of NH3 occurred on the ZrO2 surface, thus preventing NH3 from decomposing. The ZrO2 loadings and steam concentrations in the atmosphere positively affect the yield and generation efficiency of NH3, while increasing the reaction temperature increased the NH3 yield from 1.2 to 3.3 mmol, but reduced the NH3 generation efficiency from 91.7% to 60.3%.

Nano-ZrO2 as hydrogenation phase in bi-functional catalyst for syngas aromatization

Oxide-zeolite bi-functional catalyst has shown promising potential in syngas aromatization. As hydrogenation phase in bi-functional catalyst, the preparation method of metal oxide will influence bi-functional catalyst properties. Herein, a series of nano-ZrO2 is successfully synthesized by using UiO-66 pyrolysis, hydrothermal, water/oil interface and sol-gel method. After thoroughly characterized through X-ray diffraction, transmission electron microscopy, N2 adsorption, pyridine-adsorbed infrared spectroscopy, temperature programmed desorption of NH3/CO/H2, X-ray photoelectron spectroscopy, electron paramagnetic resonance and temperature programmed reduction of H2. We find ZrO2 preparation method directly influences its surface oxygen vacancy content, inducing the variation of acid amount and acid distribution over ZrO2 surface. Combine the result of density functional theory calculation with catalyst evaluation, the oxygen vacancy determines ZrO2 catalytic properties. As the catalytic site, oxygen vacancy is responsible for CO activation, and beneficial for the intermediates CH3OH formation. In this case, using hydro-ZrO2 as hydrogenation phase, adjusting the zeolite acidity and the ratio between metal oxide and zeolite, the derived bi-functional catalyst shows 21.59% CO conversion under 1200 ml/(gcat·h), the aromatic selectivity reaches 95.13% in C5+. Furthermore, the catalyst shows excellent stability during a 120 h stability test.

Catalytic Reaction Mechanism of NO-CO on the ZrO2 (110) and (111) Surfaces.

Due to the large population of vehicles, significant amounts of carbon monoxide (CO), nitrogen oxides (NOx), and unburned hydrocarbons (HC) are emitted into the atmosphere, causing serious pollution to the environment. The use of catalysis prevents the exhaust from entering the atmosphere. To better understand the catalytic mechanism, it is necessary to establish a detailed chemical reaction mechanism. In this study, the adsorption behaviors of CO and NO, the reaction of NO reduction with CO on the ZrO2 (110) and (111) surfaces was performed through periodic density functional theory (DFT) calculations. The detailed mechanism for CO2 and N2 formation mainly involved two intermediates N2O complexes and NCO species. Moreover, the existence of oxygen vacancies was crucial for NO reduction reactions. From the calculated energy, it was found that the pathway involving NCO intermediate interaction occurring on the ZrO2 (110) surface was most favorable. Gas phase N2O formation and dissociation were also considered in this study. The results indicated the role of reaction intermediates NCO and N2O in catalytic reactions, which could solve the key scientific problems and disputes existing in the current experiments.

Graphene oxide-based experimental silane primers enhance shear bond strength between resin composite and zirconia.

Despite various mechanical and chemical surface-pretreatment methods, long-term bonding of resin composite to dental zirconia (ZrO2 ) remains a major concern. In this study, graphene oxide (GO) sheets were infused into two commercially available primers and the enclosed mould shear bond strength (EM-SBS) of resin composite to ZrO2 was evaluated. Twelve fully sintered ZrO2 blanks were pretreated and randomly allocated to four groups according to the primers used: RelyX (RX); GO blended RelyX (RXGO); Monobond-S (MB); and GO blended Monobond-S (MBGO). The resin composite stubs were bonded onto the pretreated ZrO2 surfaces and analysed at baseline and after storage in distilled water for 2 and 4months. The experimental primers blended with GO sheets influenced the surface morphology, visualized as increased surface roughness, and slightly increased the water contact angle measurements. Moreover, the infusion of primers with GO increased the mass fraction (wt%) of carbon and oxygen. The highest EM-SBS values were found for RXGO, with mean (SD) EM-SBS values of 26.4(3.7)MPa and 21.5(5.1)MPa after 2 and 4months of storage, respectively. Infusion of silane primers with nanometre- to micrometre-size GO sheets enhanced the SBS between resin composite and ZrO2 .