Silicate glass matrix@Cu2O/Cu2V2O7 p-n heterojunction for enhanced visible light photo-degradation of sulfamethoxazole: High charge separation and interfacial transfer

Focusing on the treatment of pharmaceuticals contaminated water by advanced oxidation processes, a novel three dimensional silicate glass matrix (3-DG) coupled Cu₂O/Cu₂V₂O₇ p-n heterojunction was constructed by in-situ hydrothermal technique. The optimal Cu₂O/Cu₂V₂O₇ with 30 wt % Cu₂V₂O₇ (CV-30) degrades 90.1 % sulfamethoxazole (SMX) in 60 min and nearly 100 % removal in 45 min via coupling with 3-DG. Under natural sunlight ∼ 80 % SMX removal was observed. The internal electric field of the p-n junction facilitates the electron flow via the interface. 3-D silicate glass increases the visible light absorption dramatically via internal reflection which facilitates higher exposure for the junction and shortens the diffusion length of charge carriers. The effect of reaction parameters suggests that HCO₃^- and CO₃^2- ions substantially escalate the SMX removal rate. Scavenging experiments and ESR probe suggest O₂^- as the main active species followed by OH radicals. The degradation products were detected by LC-MS analysis and a degradation mechanism was also predicted. The photocatalytic mechanism was explained in terms of the electron transfer facilitated by conventional transfer and Z-scheme. This strategy to construct such highly visible and solar active p-n heterojunctions will pave way for future opportunities for the degradation of recalcitrant pharmaceutical pollutants.

Silica Glass Toughened by Consolidation of Glassy Nanoparticles

The brittleness of oxide glasses has dramatically restricted their practical applications as structural materials despite very high theoretical strength. Herein, using molecular dynamics simulations, we show that silica glass prepared by consolidating glassy nanoparticles exhibit remarkable tensile ductility. Because of dangling bonds at surfaces and high contact stresses, the pressure applied for consolidating glassy nanoparticles to achieve ductility is significantly lower than that required to toughen bulk glass via permanent densification. We have identified 5-fold silicon, with a higher propensity to carry out local shear deformation than 4-fold silicon, as the structural origin for the observed tensile ductility. Interestingly, the work hardening effect has been, for the first time, observed in thus-prepared silica glass, with its strength increasing from 4 GPa to ∼7 GPa upon cold work. This is due to stress-assisted relaxation of 5-fold silicon to 4-fold during cold work, analogous to transformation hardening.

Using fractal geometry to examine failed implants and prostheses

OBJECTIVE

To develop a novel protocol that is precise and accurate for analyzing the fracture surfaces of ceramic specimens using fractal geometry and to demonstrate its use on both clinically retrieved specimens and standard test specimens.

METHODS

A MathCAD script was written to transfer data from atomic force microscope scans to the FRACTALS software of John Russ. This software provided six algorithms for analyzing surfaces, so an experiment was conducted to determine which algorithm provided the most precision in fractal dimensional increment (D*) values and to calibrate that algorithm on surfaces generated with known D* values. Physical specimens were then tested using the chosen algorithm. These included pure silica glass fractured in deionized water versus nominally identical specimens fractured in saliva. Light body polyvinysiloxane was used to make impressions of Y-TZP fracture surfaces, and replicas were casted using a low-viscosity, low-shrinkage epoxy. Clinically failed Y-TZP dental implants were also examined. In addition, the fracture toughness and D* values of four ceramic materials (silicon nitride, silica glass, Y-TZP, and lithium disilicate glass-ceramic) were tested using standard geometry flexure beam specimens (ISO 6872).

RESULTS

The Minkowksi Cover algorithm was the most precise algorithm, and it had a negative bias that was corrected. There was no difference in D* based on water vs. saliva environment (p>0.05), and D* values from the deionized water group had lower standard deviation. The mean D* value obtained from the epoxy replicas 2.247 (0.007) was the same as that obtained from the original Y-TZP specimens 2.245 (0.002) (p=0.43, paired t-test). All scanned areas of the dental implants were fractal in nature, and there was no difference in fractal dimension between the locations near the failure origin and those far from the origin (on the compression curl) (p=0.74, repeated measures ANOVA). There was little scatter in the data collected using the revised protocol on ISO 6872 specimens, and the regression models succeeded in passing through the origin while achieving a good fit to the data (R2=0.99 and 0.95).

SIGNIFICANCE

The new protocol proved to be a powerful tool in analyzing fracture surfaces of dental ceramic materials.