No abstract

Commercial multi-wall carbon nanotubes with different properties (2 samples from Sigma-Aldrich, SA1 and SA2; 1 sample from Nanocyl, NC; and 2 samples from Shenzhen Nanotech, SZ and LSZ) were tested as catalysts in wet peroxide oxidation. Phenol was selected as model compound since represents a class of noxious compounds for human health and for the environment and, due to this, phenol is typically considered in wastewater treatment studies. The experiments were carried out under the following intensified conditions: phenol concentration = 4.5 g L-1 , hydrogen peroxide concentration = 25 g L-1 , catalyst load = 2.5 g L-1 , pH = 3.5, T = 353 K and 24 h. The results demonstrated that phenol is poorly adsorbed in this type of carbon materials (11 % as maximum when using the NC sample). However, in the catalytic experiments, complete removal of phenol is achieved when using some of the carbon nanotubes (SA1, NC and SA2), together with a remarkable total organic carbon removal (77, 69 and 67 %, respectively). These materials have the most pronounced basic character, which is often considered benefic for oxidation reactions in advanced oxidation processes and may explain the higher performance of SA1, NC and SA2 regarding the other materials. Leaching of Fe species into the solution was also observed in all cases, SA1 leading to the highest concentration of Fe species leached (26 mg L-1), followed by SA2 (2 mg L-1) and NC (1 mg L-1). Considering the lower Fe leaching levels observed for SA2 and NC, these catalysts were then tested in consecutive reusability cycles. SA2 showed a superior performance than NC, however, temperature programmed desorption, as well as thermogravimetric analysis, suggested that the carbon material is oxidized by hydrogen peroxide at the employed conditions and/or that carboxylic acids are adsorbed on the catalyst surface after consecutive runs (mainly after the first use), slightly reducing the catalyst activity.

A thermally stable and non-porous carbon material (S BET = 10 m 2 g −1 and no micropores), with low ash content and basic character, was produced by partial carbonization of glycerol with sulphuric acid followed by calcination under inert atmosphere. Further thermal activation in air atmosphere at different temperatures (from 150 to 350 • C) leads to materials with less basic character and to a tremendous evolution of the porosity, mostly microporosity (S BET = 598 m 2 g −1 and V Mic = 0.24 cm 3 g −1 ). Experiments show that metal-free carbon materials synthesized by this approach can be highly active catalysts for the catalytic wet peroxide oxidation (CWPO) process when the surface chemistry and textural properties are adequately tuned. Effective catalytic degradation of 2-nitrophenol (80% conversion) was achieved with the material treated under air atmosphere at 300 • C, even when operating under a high pollutant/catalyst mass ratio, opening a window of opportunity for added-value crude glycerol-derived products. Furthermore, catalyst activity was effectively recovered by a simple oxidative thermal regeneration procedure.

This study showed an association between periodontitis severity and carotid atherosclerosis, suggesting that periodontal disease might be a risk indicator for atherosclerotic disease.

Bonding strategies within different brackets and dental materials are still a challenge concerning adhesion and dental surface damage. This study compared the shear and tensile bond strength of orthodontic ceramic and metallic brackets to enamel, acrylic, and ceramic surfaces after thermal cycling. Dental surfaces were divided into three groups: enamel, ceramic, and acrylic. Each group received stainless-steel and ceramic brackets. After thermal cycling, specimens were randomly divided into two subgroups considering tensile (TBS) or shear bond strength (SBS) test. After the mechanical testing, scanning electron and optical microscopy were performed, and the adhesive remnant index (ARI) was determined. The two-way ANOVA full factorial design was used to compare TBS, SBS, and ARI on the surface and bracket type (α = 0.05). There were significant differences in TBS, SBS, and ARI values per surface (p < 0.001 and p = 0.009) and type of bracket (p = 0.025 and p = 0.001). The highest mean SBS values were recorded for a ceramic bracket bonded to an acrylic surface (8.4 ± 2.3 MPa). For TBS, a ceramic bracket bonded to acrylic showed the worst performance (5.2 ± 1.8 MPa) and the highest values were found on a metallic bracket bonded to enamel. The adhesion of metallic or ceramic brackets is enough for clinical practice although the damage of the enamel surface after debonding is irreversible and harmful for the aesthetic outcome of the teeth.