RESUMO
This study consists of the synthesis of zinc-doped Bi2WO6 obtained by the sonochemical method. The XRD results indicated that the samples showed an orthorhombic phase with the P21ab space group without the presence of secondary phases, demonstrating success in the doping process. The results of the photocatalytic tests under the photodegradation of methylene blue showed better performance for the pure sample with 80% degradation during 2 hours of exposure to radiation. The high rate of photogenerated charges accompanied by the low recombination rate of the pairs and e-/h+ were responsible for forming hydroxyl radicals, the predominant oxidative agent of the mechanism. The increase in Zn2+ concentration in the Bi2WO6 matrix promoted inhibition of the photocatalytic properties by the appearance of oxygen vacancies that acted as a charge recombination center. In contrast, photoluminescence was improved by doping with Zn2+. The Bi2WO6:8% Zn2+ sample showed the highest PL intensity. The characteristics of the emitted colors are modulated from the emission spectra and are quantified in terms of the photometric parameters: chromaticity coordinates (x, y), color reproduction index (CRI), luminous radiation efficiency (LER), and purity of color (%) of samples. The adjustment in the colors is promoted as a function of the increase in the Zn2+ concentration observing the transition from: yellow â orange â green. PL is favored by the effect of the dopant (Zn2+) in the matrix, which allows Bi2WO6:Zn2+ to be considered a promising candidate for applications in optical devices. In addition, Bi2WO6 constitutes a high performance photocatalyst for the degradation of methylene blue.
RESUMO
This study presents indium-doped calcium tungstate for the first time. The photocatalytic and photoluminescent properties of pure and In3+ doped samples were investigated. All pure and indium-doped calcium tungstate particles were synthesized for 30 minutes by two different methods: the sonochemical method (SM) and the microwave-assisted hydrothermal method. The nanoparticles were characterized by X-ray diffraction (XRD), field emission gun-scanning electron microscopy (SEM-FEG), UV-Visible spectroscopy, Brunauer-Emmett-Teller method, and zeta potential analysis. The diffractogram results confirmed the formation of scheelite crystalline structures without forming deleterious phases. The SEM-FEG images show the powder with irregular morphology and agglomerated as rods and kibes. For both methods, samples with 8% In3+ ions showed lower PL intensities with maximum peaks at 479 and 483 nm, suggesting lower e-/h+ pair recombination, which led these samples to present better photocatalytic performance. The photocatalytic activity was estimated from the degradation of the methylene blue (MB) dye under UV light and the sample stability was tested in 3 reuse cycles. The scavenger methodology indicated that h+ is the most active mechanism in the photocatalysis process. The degradation of the dye mixture (MB, MO, and RhB dyes) was also performed.
RESUMO
Correction for 'Synthesis and evaluation of photocatalytic and photoluminescent properties of Zn2+-doped Bi2WO6' by L. X. Lovisa, et al., Dalton Trans., 2022, https://doi.org/10.1039/d2dt03175b.
RESUMO
OBJECTIVES: The purpose of this study was to evaluate the shear bond strength of veneering feldspathic porcelain to zirconia substrates modified by CNC-milling process or by coating zirconia with a composite interlayer. METHODS: Four types of zirconia-porcelain interface configurations were tested: RZ - porcelain bonded to rough zirconia substrate (n=16); PZ - porcelain bonded to zirconia substrate with surface holes (n=16); RZI - application of a composite interlayer between the veneering porcelain and the rough zirconia substrate (n=16); PZI - application of a composite interlayer between the porcelain and the zirconia substrate treated by CNC-milling (n=16). The composite interlayer was composed of zirconia particles reinforced porcelain (30%, vol%). The mechanical properties of the ceramic composite have been determined. The shear bond strength test was performed at 0.5mm/min using a universal testing machine. The interfaces of fractured and untested specimens were examined by FEG-SEM/EDS. Data was analyzed with Shapiro-Wilk test to test the assumption of normality. The one-way ANOVA followed by Tukey HSD multiple comparison test was used to compare shear bond strength results (α=0.05). RESULTS: The shear bond strength of PZ (100±15MPa) and RZI (96±11MPa) specimens were higher than that recorded for RZ (control group) specimens (89±15MPa), although not significantly (p>0.05). The highest shear bond strength values were recorded for PZI specimens (138±19MPa), yielding a significant improvement of 55% relative to RZ specimens (p<0.05). SIGNIFICANCE: This study shows that it is possible to highly enhance the zirconia-porcelain bond strength - even by ~55% - by combining surface holes in zirconia frameworks and the application of a proper ceramic composite interlayer.