Percentage Of Active Sites Research Articles

Adsorption effect of porous zirconia for carbon dioxide under the influence of various factors

Global warming and environmental deterioration have caused socially catastrophic events, arousing people’s interest in discovering the root causes of such events. Looking for an economically efficient and highly adsorbing carbon dioxide adsorbent has become one of the research priorities. Porous zirconia is an ideal candidate material for absorbing CO2 due to its distinctive acid-base property and a large number of active sites. The present study analyzed the effects of external factors (e.g., porous zirconia, including temperature, pH value, and humidity) and internal factors (e.g., crystal structure, lattice defects, and percentage of active sites in zirconia) on the adsorption performance of porous zirconia. Porous zirconia was found to have a high adsorption efficiency at pH 3∼6 under humid conditions. When the crystal structure of zirconia was tetragonal, monoclinic, or tetrahedral, the zirconia had a larger void volume and a larger number of active vacancies and oxygen vacancies. Modifying and increasing oxygen vacancies resulted in a larger number of active sites and a greater Gibbs free energy in the ZrO2 materials and their composites.

Cycloaddition of carbon dioxide for commercially-imperative cyclic carbonates using ionic liquid-functionalized porous amorphous silica

Ionic liquid functionalized mesoporous silicas (IFMSs) were prepared from the coupling of 1-(triethoxysilylpropyl)-3- n-alkylimidazolium halides with tetraethyl orthosilicate (TEOS) through template-free condensation under strong acidic conditions. Optimal synthesis conditions and maximum incorporation of the active sites were achieved through varying the parameters of the co-condensation method. The obtained amorphous silica having 0.20–0.93 mmol of RIm + X − groups showed a surface area between 477 and 672 m 2/g with pore sizes from 3.2 to 7.8 nm. The materials synthesized under various TEOS pre-hydrolysis had larger surface areas, pore volumes, and average pore diameters than those synthesized without pre-hydrolysis. FT-IR, TG/DTG (thermogravimetry/differential thermogravimetry), and solid-state NMR showed that all the immobilized ionic liquid (IIL) groups were incorporated without affecting the organic moieties. Chemical fixation of carbon dioxide was studied at various carbon dioxide pressures by correlating reactivity with various parameters such as surface area, pore volume, pore size, percentage of active sites, type of counter ion, and length of the organic moiety extending from the alkyl halide.

Radiographic and clinical responses to periodontal therapy.

Mechanical periodontal therapy is widely used for a variety of periodontal conditions. While the clinical efficacy of this treatment has been validated, the radiographic response has not been studied in depth. The purpose of the present study was to examine the clinical and radiographic response to mechanical periodontal therapy, and assess the factors associated with these changes. One hundred and eight patients, with established periodontitis, received oral hygiene instruction and mechanical periodontal therapy for a period of 4 to 5 weeks. Scheduled maintenance visits were performed at 3, 6, 9, and 15 months. Probing depth (PD) and attachment level (AL) measurements were performed at baseline, and at 3 and 15 months. Intraoral radiographs were taken at baseline and 12 to 15 months postsurgery using a Rinn alignment system. Alveolar crestal height (ACH) measurements were performed on a pair of digitized images of the previously taken radiographs. An overall mean of patients' changes for PD, AL, and ACH was initially computed. Active sites (gainers and losers) were determined using a threshold method, and expressed as patient's percentage of active sites (number of active sites of the total sites measured in each patient). Mean overall probing reduction and AL gain was 0.5 mm and 0.44 mm, respectively. Of all sites measured, 16.6% exhibited AL gain, while only 6.2% of all sites exhibited AL loss. Mean overall change in ACH was -0.07 mm, of which 11.8% of all sites exhibited ACH gain, while 15.1% exhibited loss beyond the threshold. Non-smokers presented no change in bone loss, while smokers continued to lose bone at an annual rate of 0.17 mm, despite treatment (P <0.005). Likewise, the average percent of sites per patients showing attachment gain beyond the threshold were much greater in non-smokers (13.9%) compared to 9.0% in smokers (P <0.01). Mean probing reduction was 50% greater among non-smokers (0.6 mm) when compared to smokers (0.4 mm), which was also statistically significant (P <0.05). A positive and significant correlation was established between the percentage of sites with AL gain and sites with ACH gain (Rho =0.40; P=0.0001). It is suggested that monitoring sites for AL and ACH gain expressed as changes beyond a selective threshold is an important outcome variable in treatment studies.

Quantitative Determination of Catalytic Surface Adsorption Sites by Fourier Transform Infrared Photoacoustic Spectroscopy

The use of Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) as a method for quantitative analysis of surface adsorption sites is demonstrated. Mid-IR information about the amount of adsorption is available with the sampling advantages of PAS: ability to analyze opaque materials with minimal sample preparation, qualitative information about both gas [CO(g)] phase and adsorbed [CO(ads)] species, a sealed sample environment for control of the gas phase in contact with the sample, and the ability to monitor in situ reaction kinetics. In this study a calibration curve is constructed for the amount of CO(g) in the sample cell with a silica internal reference. This calibration curve is utilized to calculate the amount of CO(ads) by subtraction on a catalytic surface where both CO(g) and CO(ads) exist at equilibrium. Using standard parameters from gas titration/volume uptake studies, the surface covered and the percentage of active sites on the surface are determined. This analysis combines the qualitative analytical capabilities of PAS with quantitative analysis, thus demonstrating another facet of the usefulness of FT-IR/PAS in addressing unusual problems.