Papers by Keyword: Carbonate Ion

Abstract: Carbonate is a common pollutant in water and wastewater. A study to understand its influence on the photodegradation rates is necessary especially when TiO₂/UV technique is emerging as an advanced technology for pollution abatement. In the present investigation, we report surface modification of titanium dioxide using carbonate ions, characterization of carbonate modified titanium dioxide (CMT) and photocatalytic application of carbonate modified TiO₂. Titanium dioxide from two different sources namely BDH, Mumbai and Degussa AG, Germany was used as photocatalyst. The CMT catalysts were characterized using potentiometry, FT-IR and XPS. Approximately, 18.9 mg CO₃/g CMT(BDH) and 8.13 mg CO₃/g CMT(Degussa) was found loaded as determined by potentiometry. The C 1s and O 1s binding energies observed at 289.2 and 531.3 eV, respectively were attributed to surface carbonate species. The adsorption and photodegradation of Acid Blue I dye examined using neat TiO₂ as well as CMT catalysts revealed that carbonate inhibits catalytic activity for color and Chemical Oxygen Demand (COD) removal. The photo degradation rate constant (k, s^-1) decreases gradually with increasing concentration of carbonate. Thus, in the absence of carbonate k_dye is 5.45 × 10^-4 s^-1 (R² = 0.97) and k_COD is 3.50 × 10^-5 s^-1 (R² = 0.97). At 100 mg/L CO₃^2-, k_dye is 0.16 × 10^-4 s^-1 (R² = 0.96) and k_COD is 2.66 × 10^-5 s^-1 (R² = 0.98). In addition, the carbonate spiking studies revealed the onset of inhibition soon after the addition of carbonate into reacting suspensions of TiO₂. The results suggest that carbonate inhibits catalytic activity through formation of strong surface complex under suitable pH by displacing OH₂⁺ and OH groups from TiO₂ surface. This results not only in fewer (OH)_surface groups available for h⁺ trapping for oxidation into OH radicals but also in non-availability of adsorption sites for the dye molecules. A pretreatment to remove carbonate from (waste) water appears necessary prior to application of TiO₂/UV technique

Abstract: We demonstrate that the formation of carbonate-like moiety in SiO₂ could be the origin of negative fixed charge in SiC thermal wet oxidation, based on first-principles calculations. We find that negative CO₃ ion appears in SiO₂ due to not only the existence of residual C atoms that are expected to be emitted from the SiC/SiO₂ interface, but also a large enough number of incorporated H atoms during wet oxidation.

Abstract: Effect of heat-treatment temperature on the osteoconductivity of the apatite derived from bovine trabecular bone was investigated. Three different heat-treatment temperatures (600, 800 and 1000 oC) were adopted in the experiment and their effects on the physical properties of apatite granules, which could affect on the osteoconductivity, were evaluated. The content of carbonate ions in the apatite structure was assessed by FT-IR and its crystallinity was evaluated by X-ray diffractometry. The microstructure was assessed by field emission electron microscopy. Apatite granules heat-treated at 600 oC and 1000 oC were implanted into the calvaria of New Zealand White rabbit for 4 weeks, respectively, and the undecalcified ground histologic specimens stained with multiple staining method was observed. As increasing the heat-treatment temperature, the crystal size and crystallinity of the apatite increased while the content of carbonate ions decreased. The apatite granules heat-treated at 600 oC showed much better osteoconductivity comparing to that heat-treated at 1000 oC. The results were explained in terms of the physical properties of apatite which could affect to the osteoconductivity.

Abstract: Protein loading on apatite hydrogel cake and its solubility was studied. A mixture of di-sodium hydrogen phosphate dodeca-hydrate and calcium chloride di-hydrate was dissolved in water, and kept at room temperature for 2 weeks in air or N2 atmosphere to make apatite hydrogel. The obtained apatite hydrogel contains carbonate ions, and its carbonate content strongly affect the aggregation of particles. With maturation period, the particle size of apatite hydrogel decreased in air, but increased in N2 atmosphere. The quantity of loaded Cytochrome C in apatite hydrogel formed in air was 0.490 wt%, while that in apatite hydrogel formed under N2 atmosphere was 0.305 wt%. But the quantity of loaded albumin in apatite hydrogel formed in air was less than that in apatite hydrogel formed under N2 atmosphere. The difference may be due to the relationship between isoelectric point of protein and apatite hydrogel. The apatite hydrogel containing protein was dried for 4 days in air at 40 % of relative humidity to make cakes, and the cakes were immersed in pure water or PBS solution. The dried specimen slowly dissolves in aqueous solution, and the decrease in weight of apatite cake prepared from hydrogel formed in air was larger than that from hydrogel formed under N2 atmosphere compared to the dissolved apatite, the released protein was less, which may be associated with recrystallization of the apatite hydrogel.