Surface modification with phosphoric acid of SiO2/Nb2O5 prepared by the sol-gel method: structural-textural and acid sites studies and an ion exchange model

Design and Development of Tantalum and Strontium Ion Doped Hydroxyapatite Composite Coating on Titanium Substrate: Structural and Human Osteoblast-like Cell Viability Studies

In order to reduce the loosening of dental implants, surface modification with hydroxyapatite (HA) coating has shown promising results. Therefore, in this present study, the sol-gel technique has been employed to form a tantalum and strontium ion-doped hybrid HA layer coating onto the titanium (Ti)-alloy substrate. In this study, the surface modification was completed by using 3% tantalum pent oxide (Ta₂O₅), 3% strontium (Sr), and a combination of 1.5% Ta₂O₅ and 1.5% Sr as additives, along with HA gel by spin coating technique. These additives played a prominent role in producing a porous structure layer coating and further cell growth. The MG63 cell culture assay results indicated that due to the incorporation of strontium ions along with tantalum embedded in HA, cell proliferation increased significantly after a 48 h study. Therefore, the present results, including microstructure, crystal structure, binding energy, and cell proliferation, showed that the additives 1.5% Ta₂O₅ and 1.5% Sr embedded in HA on the Ti-substrate had an optimized porous coating structure, which will enhance bone in-growth in surface-modified Ti-implants. This material had a proper porous morphology with a roughness profile, which may be suitable for tissue in-growth between a surface-modified textured implant and bone interface and could be applicable for dental implants.

Phosphate doping as a promising approach to improve reactivity of Nb2O5 in catalytic activation of hydrogen peroxide and removal of methylene blue via adsorption and oxidative degradation

This study is devoted to the evaluation of the influence of phosphate dopants on the reactivity of Nb₂O₅-based nanomaterials in the combined catalytic activation of H₂O₂ and the elimination of methylene blue (MB) from an aqueous solution via adsorption and chemical degradation. For this purpose, several niobia-based catalysts doped with various amounts of phosphate were prepared by a facile hydrothermal method and subsequent calcination. Phosphate doping was shown to strongly enhance the ability of Nb₂O₅ to activate H₂O₂, as well as to adsorb and degrade MB. The most pronounced differences in the reactivity of the parent Nb₂O₅ and phosphate-doped samples were observed under strongly acidic conditions (pH ~ 2.4), at which the most active modified catalysts (Nb/P molar ratio = 5/1) was approximately 6 times more efficient in the removal of MB. The observed enhancement of reactivity was attributed to the increased generation of singlet oxygen ¹O₂, which was identified as the main oxidizing agent responsible for efficient degradation of MB. To our knowledge, it is the first report revealing that phosphate doping of Nb₂O₅ resulted in an improved activity of niobia in the adsorption and degradation of organic pollutants.

Mesoporous Nb2O5/SiO2 material obtained by sol-gel method and applied as adsorbent of crystal violet dye

In this work, SiO₂/Nb₂O₅ (SiNb) material was prepared using sol-gel method and employed as adsorbent for removal of crystal violet dye (CV). The material was characterized using nitrogen adsorption-desorption isotherms, FTIR spectroscopy, pH_pzc, and SEM-EDS. The analysis of N₂ isotherms revealed the presence of micro- and mesopores in the SiNb sample with specific surface area as high as 747 m² g^-1. For the CV adsorption process, variations of several parameters such as of pH, temperature, contact time, and concentration of dye of the process were evaluated. The optimum initial pH of the CV dye solution was 7.0. The adsorption kinetic and equilibrium data for CV adsorption were suitably represented by the general-order and Liu models, respectively. The maximum adsorption capacity of the CV dye by SiNb was achieved at 303 K, which attained 116 mg g^-1 at this temperaure. Dye effluents were simulated and used to check the applicability of the SiNb material for treatment of effluents - the material showed very good efficiency for decolorization of dye effluents.

SiO2/SnO2/Sb2O5 microporous ceramic material for immobilization of Meldola's blue: application as an electrochemical sensor for NADH

The mixed oxide SiO(2)/SnO(2), containing 25 wt% of SnO(2), determined by X-ray fluorescence, was prepared by the sol-gel method and the porous matrix obtained was then grafted with Sb (V), resulting the solid designated as (SiSnSb). XPS indicated 0.7% of Sb atoms on the surface. Sb grafted on the surface contains Brønsted acid centers (SbOH groups) that can immobilize Meldola's blue (MB(+)) cationic dye onto the surface by an ion exchange reaction, resulting the solid designated as (SiSnSb/MB). In the present case a surface concentration of MB(+)=2.5×10(-11) mol cm(2) on the surface was obtained. A homogeneous mixture of the SiSnSb/MB with ultra pure graphite (99.99%) was pressed in disk format and used to fabricate a working electrode that displayed an excellent specific electrocatalytic response to NADH oxidation, with a formal potential of -0.05 V at pH 7.3. The electrochemical properties of the resulting electrode were investigated thoroughly with cyclic voltammetric and chronoamperometry techniques. The proposed sensor showed a good linear response range for NADH concentrations between 8×10(-5) and 9.0×10(-4) mol L(-1), with a detection limit of 1.5×10(-7) mol L(-1). The presence of dopamine and ascorbic acid did not show any interference in the detection of NADH on this modified electrode surface.

Simulation of adsorption equilibria on hybrid materials: Binding of metal chlorides with 3-n-propylpyridinium silsesquioxane chloride ion exchanger

The quantitative description of cooperativity effects at binding of low-molecular reagents with active reactive centers of hybrid materials requires the elaboration of convenient and reliable meaningful models and calculation procedures. The model of fixed polydentate centers was analyzed as a prospective tool for simulation of adsorption equilibria. The model was shown to be flexible and adaptive. At the theoretic foundations, it is equivalent or more general as compared with another approaches. The procedure for constructing the models fitting the experimental data within their errors and the corresponding calculation tools were discussed. The special attention was paid to the problem of simultaneous determination of sorption capacities and equilibrium constants. To overcome this difficulty the strategy involving the fuzzy sets theory was proposed. The elaborated methods were used to characterize a new material, 3-n-propylpyridinium silsesquioxane chloride ion exchanger. Adsorption of Fe(III), Cu(II), Zn(II), Cd(II), and Hg(II) chlorides by the material from ethanol solutions was studied at 298 K. The material was found to possess a high affinity to metal chlorides. The sorption capacities of the material and the constants of adsorption equilibria were determined. The material demonstrates the following order of affinity: FeCl(3) > CuCl(2), HgCl(2) > CdCl(2) > ZnCl(2). On the base of simulation, the negative cooperativity in the case of the CuCl(2) adsorption was concluded, while adsorption of other chlorides is accompanied by the positive cooperativity.

The Li+, Na+ and K+ ion exchange reaction process on the surface of mixed oxide SiO2/TiO2/Sb2O5 surface prepared by the sol-gel processing method

The porous mixed oxide SiO2/TiO2/Sb2O5 obtained by the sol-gel processing method presented a good ion exchange property and a high exchange capacity towards the Li+, Na+ and K+ ions. In the H+/M+ ion exchange process, the H+ / Na+ could be described as presenting an ideal character. The ion exchange equilibria of Li+ and K+ were quantitatively described with the help of the model of fixed tetradentate centers. The results of simulation evidence that for the H+ / Li+ exchange the usual situation takes place: the affinity of the material to the Li+ ions is decreased with increasing the degree of ion exchange. On the contrary, for K+ the effects of positive cooperativity, that facilitate the H+ / K+ exchange, were revealed.