Plasma Surface Modification of 3Y-TZP at Low and Atmospheric Pressures with Different Treatment Times.

The efficiency of plasma surface modifications depends on the operating conditions. This study investigated the effect of chamber pressure and plasma exposure time on the surface properties of 3Y-TZP with N2/Ar gas. Plate-shaped zirconia specimens were randomly divided into two categories: vacuum plasma and atmospheric plasma. Each group was subdivided into five subgroups according to the treatment time: 1, 5, 10, 15, and 20 min. Following the plasma treatments, we characterized the surface properties, including wettability, chemical composition, crystal structure, surface morphology, and zeta potential. These were analyzed through various techniques, such as contact angle measurement, XPS, XRD, SEM, FIB, CLSM, and electrokinetic measurements. The atmospheric plasma treatments increased zirconia's electron donation (γ-) capacity, while the vacuum plasma treatments decreased γ- parameter with increasing times. The highest concentration of the basic hydroxyl OH(b) groups was identified after a 5 min exposure to atmospheric plasmas. With longer exposure times, the vacuum plasmas induce electrical damage. Both plasma systems increased the zeta potential of 3Y-TZP, showing positive values in a vacuum. In the atmosphere, the zeta potential rapidly increased after 1 min. Atmospheric plasma treatments would be beneficial for the adsorption of oxygen and nitrogen from ambient air and the generation of various active species on the zirconia surface.

Effect of the Plasma Gas Type on the Surface Characteristics of 3Y-TZP Ceramic.

Plasma surface treatment can be an attractive strategy for modifying the chemically inert nature of zirconia to improve its clinical performance. This study aimed to clarify the effect of plasma gas compositions on the physicochemical surface modifications of 3 mol% yttria-stabilized zirconia (3Y-TZP). The cold, atmospheric plasma discharges were carried out by using four different plasma gases, which are He/O2, N2/Ar, N2, and Ar from an application distance of 10 mm for 60 s. Static contact angles were measured to define the surface free energy. Changes in elemental composition, surface crystallinity, and surface topography were assessed with X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM), respectively. A significant decrease in water contact angle was observed in all plasma groups with the lowest value of 69° in the N2/Ar group. CLSM and SEM investigations exhibited no morphological changes in all plasma groups. XPS revealed that a reduction in the surface C content along with an increase in O content was pronounced in the case of N2/Ar compared to others, which was responsible for high hydrophilicity of the surface. XRD showed that the changes in crystallite size and microstrain due to oxygen atom displacements were observed in the N2/Ar group. The N2/Ar plasma treatment may contribute to enhancing the bioactivity as well as the bonding performance of 3Y-TZP by controlling the plasma-generated nitrogen functionalities.

Engineering defects and photocatalytic activity of TiO2 nanoparticles by thermal treatments in NH3 and subsequent surface chemical etchings.

TiO2 nanoparticles with N dopants were prepared by thermal treatments in NH3 and their surface defects were controlled by post chemical etching in HF to find out the influence of the N dopants on photoactivity. The effect of N-doping is found to enhance the photoactivity of TiO2, but is strongly dependent on the degree of N-doping and the detailed distribution of nitrogen species within the TiO2 nanoparticles. In particular, the N-rich layers formed near the surface are found to contribute to the enhanced photoactivity due to the reduced band gap. But, the increase in the N concentration may induce defects that act as recombination centers and reduce the photoactivity. Subsequent chemical etching in HF confirms the existence of the substitutional N species near the surface from the observation of paramagnetic N species. But, prolonged HF treatments are found to decrease the photoactivity primarily due to the removal of the N-rich surface layers that are responsible for the enhanced photoactivity. Our results show that the photoactivity of N-doped TiO2 is strongly influenced by the type and the density of the N dopants induced by the N doping.

The effect of oxygen vacancies on the binding interactions of NH3 with rutile TiO2(110)-1 × 1.

A series of NH(3) temperature-programmed desorption (TPD) spectra were taken after dosing NH(3) at 70 K on rutile TiO(2)(110)-1 × 1 surfaces with oxygen vacancy (V(O)) concentrations of ~0% (p-TiO(2)) and 5% (r-TiO(2)), respectively, to study the effect of V(O)s on the desorption energy of NH(3) as a function of coverage, θ. Our results show that in the zero coverage limit, the desorption energy of NH(3) on r-TiO(2) is 115 kJ mol(-1), which is 10 kJ mol(-1) less than that on p-TiO(2). The desorption energy from the Ti(4+) sites decreases with increasing θ due to repulsive NH(3)-NH(3) interactions and approaches ~55 kJ mol(-1) upon the saturation of Ti(4+) sites (θ = 1 monolayer, ML) on both p- and r-TiO(2). The absolute monolayer saturation coverage is determined to be about 10% smaller on r-TiO(2) than that on p-TiO(2). Additionally, the trailing edges of the NH(3) TPD spectra on the hydroxylated TiO(2)(110) (h-TiO(2)) appear to be the same as that on r-TiO(2) while those on oxidized TiO(2)(110) (o-TiO(2)) shift to higher temperatures. We present a detailed analysis of the results and reconcile the observed differences based on the repulsive adsorbate-adsorbate dipole interactions between neighboring NH(3) molecules and the surface charge associated with the presence of V(O)s.

Copper-Catalyzed Oxidative Cleavage of the C-C Bonds of ß-Alkoxy Alcohols and ß-1 Compounds.

Copper-catalyzed aerobic oxidation conditions were employed to promote the C-C bond cleavage of ß-alkoxy alcohols and ß-1 compounds (lignin model compounds). Besides these compounds, various 1,2 and 1,3-diols were successfully converted to aldehydes. We propose the Cu(I)-catalyzed mechanism explaining the C-C cleavage of these 1,2 and 1,3-dihydroxy compounds and ß-alkoxy alcohols based on XPS data. Although our reaction conditions do not include large excess of bases and elaborated ligand-modified catalysts, copper salts with/without Me-TBD show good catalytic activities for C-C bond cleavage of various lignin model compounds.

Catalytic dehydration of 2-propanol on (WO3)3 clusters on TiO2(110).

Our study of a (WO3)3/TiO2(110) model mixed oxide catalyst shows that this system is an extremely efficient for dehydration of alcohols, effectively lowering the energy barrier as much as possible for an endothermic reaction without yielding a significant concentration of other side products.

Photocurrent Enhancement by a Rapid Thermal Treatment of Nanodisk-Shaped SnS Photocathodes.

Photocathodes made from the earth-abundant, ecofriendly mineral tin monosulfide (SnS) can be promising candidates for p/n-type photoelectrochemical cells because they meet the strict requirements of energy band edges for each individual photoelectrode. Herein we fabricated SnS-based cell that exhibited a prolonged photocurrent for 3 h at -0.3 V vs the reversible hydrogen electrode (RHE) in a 0.1 M HCl electrolyte. An enhancement of the cathodic photocurrent from 2 to 6 mA cm-2 is observed through a rapid thermal treatment. Mott-Schottky analysis of SnS samples revealed an anodic shift of 0.7 V in the flat band potential under light illumination. Incident photon-to-current conversion efficiency (IPCE) analysis indicates that an efficient charge transfer appropriate for solar hydrogen generation occurs at the -0.3 V vs RHE potential. This work shows that SnS is a promising material for photocathode in PEC cells and its performance can be enhanced via simple postannealing.

Alcohol Dehydration on Monooxo W═O and Dioxo O═W═O Species.

The dehydration of 1-propanol on nanoporous WO3 films prepared via ballistic deposition at ∼20 K has been investigated using temperature-programmed desorption, infrared reflection absorption spectroscopy, and density functional theory. The as-deposited films are extremely efficient in 1-propanol dehydration to propene. This activity is correlated with the presence of dioxo O═W═O groups, whereas monooxo W═O species are shown to be inactive. Annealing of the films induces densification that results in the loss of catalytic activity due to the annihilation of O═W═O species.