Bleaching effectiveness and cytotoxicity of new experimental formulation of niobium-based bleaching gel.

OBJECTIVES: The development of new bleaching agents with minimum concentration of hydrogen peroxide (HP), without adverse effects, and with bleaching effectiveness, has great clinical relevance. The aim of this study was to evaluate the bleaching efficacy and cytotoxicity of a new niobium-based bleaching gel, compared to already available HP-based gels. MATERIALS AND METHODS: For the bleaching efficacy analysis, 40 bovine incisors were randomly divided into 4 groups according to the established bleaching protocol: control, untreated; 35HP, 35% HP bleaching gel; 6HP, 6% HP bleaching gel; NbHP, niobium gel associated with 3% HP gel. The color variation was measured in a spectrophotometer and the values of ΔL, Δa, Δb, and ΔE obtained. For the cell viability assay by MTT, MC3T3 cells were exposed to bleaching gel extracts (1:500, 1:250, 1:125 dilutions; immediately and 24 h). Statistical tests were performed (P < 0.05). RESULTS: The color alteration for all bleaching gels was significant compared to control (P < 0.05), but the NbHP gel showed a significant ΔE than other gels, with expressive color alteration at 14 days (P < 0.05). The 35HP showed high cytotoxicity regarding control and the most groups in all periods and extracts analyzed (P < 0.05), while the NbHP showed greater cell viability than control in the immediate period, dilution of the 1:500 and superior to 6HP in the most extracts at 24 h. CONCLUSION: The new experimental niobium-based gel has bleaching efficacy similar to that of gels with a high concentration of HP, and it has high cytocompatibility. CLINICAL RELEVANCE: The use of this new generation of niobium-based whitening gel associated with a low concentration of hydrogen peroxide represents the possibility of a tooth whitening with lower dentin sensitivity.

Effect of pH, ionic strength, and temperature on the adsorption behavior of Acid Blue 113 onto mesoporous carbon.

Mesoporous carbon (MC) derived from cassava starch was used to remove Acid Blue 113 azo dye from aqueous solutions. The influence of temperature, pH, ionic strength, and the adsorbent dose was investigated in a set of batch experiments. Experimental data showed that Acid Blue 113 adsorption was higher in the acid pH range than in the alkaline one, that dye adsorption increases when the ionic strength and temperature increase, and that adsorption results presented a good correlation with the Langmuir isotherm model. The adsorption capacity of MC was 295 mg g-1, at pH = 7.0 and 298 K, respectively. Zeta potential (ζ) showed the compression of the diffuse double layer of adsorbent with an increase in temperature and ionic strength, promoting the decrease of electrostatic repulsion between the negatively charged surface of the carbon particles and the anionic dye. Thermodynamic results demonstrate that the adsorption process was spontaneous and endothermic. Moreover, for the first time, this work has demonstrated that the pH, temperature, and ionic strength of the aqueous medium are also able to change the surface charge of carbon-based adsorbents and surely influence the adsorption capacity. Finally, the regeneration of the adsorbent by the photo-Fenton reaction regenerated the adsorption capacity of the adsorbent without generating secondary pollution to the environment.

Use of iron ore tailing from tailing dam as catalyst in a fenton-like process for methylene blue oxidation in continuous flow mode.

The global demand for iron ore with high iron contents to supply the steel industry is associated, in most countries, with the generation of tailings from mineral processing. The chemical compositions of iron ore tailings (basically Fe2O3 and SiO2) make them an excellent candidate as a catalyst for advanced oxidation processes (AOPs), especially the Fenton process and its derivatives. Therefore, this paper aimed to transform iron ore tailings from tailing dams into catalysts able to activate H2O2 for the purpose of treating, in a continuous flow, effluents contaminated with organic dyes, employing methylene blue as a model molecule. The mineralogical characteristics of in natura tailings, such as the associations between iron oxides and quartz and the particle sizes of iron oxides, are favourable points for their transformation into catalysts by Fenton-like processes. Different pellet geometries and binding agents were evaluated to optimize the dye removal. Pellet pretreatment in a CH4 atmosphere at 550 °C for 2 h with 10% bentonite as a binding agent (RCSP sample) resulted in the removal of approximately 80% of dye. Kinetic removal data show the good stability of the catalyst in the flow system. Significant catalytic activity loss was not observed after four runs, and data from TG-MS indicate that there is a synergetic mechanism between the adsorption, radical attack and desorption processes of the substrate on the catalyst surface.

Activated carbon prepared from coffee pulp: potential adsorbent of organic contaminants in aqueous solution.

The processing of coffee beans generates large amounts of solid and liquid residues. The solid residues (pulp, husk and parchment) represent a serious environmental problem and do not have an adequate disposal mechanism. In this work, activated carbons (ACs) for adsorption of organic compounds were prepared from coffee pulp by controlled temperature at different pulp/Na2HPO4 ratios (4:1, 2:1, 5:4 and 1:1). The N2 adsorption/desorption isotherms showed ACs with high quantities of mesopores and micropores and specific surface areas of 140, 150, 450 and 440 m(2)g(-1) for AC 4:1, AC 2:1, AC 5:4 and AC 1:1, respectively. The prepared material AC 5:4 showed a higher removal capacity of the organic contaminants methylene blue (MB), direct red (DR) and phenol than did a Merck AC. The maximum capacities for this AC are approximately 150, 120 and 120 mg g(-1) for MB, DR and phenol, respectively. Thus, a good adsorbent was obtained from coffee pulp, an abundant Brazilian residue.

Controlling the morphology and pore size of mesostructured silica nanoparticles: the role of the iron oxidation state.

We demonstrate morphology and pore size dependence of silica nanoparticles (SNPs) synthesized via control of the iron oxidation state. In the absence of any Fe species, only spherical SNPs are produced, whereas in the presence of Fe³âº and Fe²âº ions, SNPs with rod-like and nanosheet morphologies, respectively, are formed. The average pore size increases from 1.7 nm in the absence of iron to 3.2 and 5.9 nm as Fe³âº and Fe²âº, respectively, were used during the synthesis. Both samples of SNPs synthesized in the presence of Fe²âº and Fe³âº have 0.2 wt% of tetrahedral iron in the silica framework, whereas most of the iron is in the silica extraframework, as verified by Mössbauer spectroscopy, UV-vis diffuse reflectance, FTIR, XRD data and TPR analysis. These Fe²âº and Fe³âº cations play a fundamental role in controlling these properties because they change the curvature and the surface charge density of CTAB micelles, thus favoring the spherical to rod-like transition. The rod-like shape was retained in Fe-containing samples, whereas a nanosheet-like morphology was produced in Fe²âº-containing samples due to the breakage of silica walls during the thermal treatment to remove the template. The control of the textural properties is interesting to allow the fabrication of selective photocatalysts for oxidation of different organic substrates.

A friendly environmental material: iron oxide dispersed over activated carbon from coffee husk for organic pollutants removal.

A friendly environmental material for organic contaminants removal was prepared in this work: small particles of iron oxide dispersed over activated carbon from coffee waste for Fenton-like application. The materials were characterized by means of XRD, N2 physisorption, Mössbauer spectroscopy and H2 pulse titration. The composites showed very good catalytic performances for methylene blue organic dye oxidation. The small goethite particles are the predominant iron oxide phase in the composites. The apparent surface area is quite high and is not very affected after iron impregnation. ESI-MS studies revealed that the dye removal occurs through a Fenton-type system by the composite whereas for the activated carbon the dye removal occurs mainly via adsorption. The iron leaching from the catalysts was negligible, less than 0.5 ppm, which evidences the occurrence of a heterogenous oxidation process. The catalyst was very active for methylene blue oxidation and could be repeatedly used for at least 5 cycles. The catalyst was also active in the oxidation of other organic compounds, such as caffeine and atrazine.