Highly Stable Amide-Functionalized Zirconium-Organic Frameworks: Synthesis, Structure, and Methane Storage Capacity

With the development of crystalline porous materials toward methane storage, the stability issue of metal–organic framework (MOF) materials has caused great concern despite high working capacity. Considering the high stability of zirconium-based MOFs and effective functions of amide groups toward gas adsorption, herein, a series of UiO-66 type of Zr-MOFs, namely, Zr-fcu-H/F/CH3/OH, were successfully designed and synthesized by virtue of amide-functionalized dicarboxylate ligands bearing distinct side groups (i.e., −H, −F, −CH3, and −OH) and ZrCl4 in the presence of trifluoroacetic acid as the modulator. Single-crystal X-ray diffraction and topology analyses reveal that these compounds are archetypal fcu MOFs encompassing octahedral and tetrahedral cages, respectively. The N2 sorption isotherms and acid–base stability tests demonstrate that the materials possess not only relatively high surface areas, pore volumes, and appropriate pore sizes but also great hydrolytic stabilities ranging pH = 3–11. Furthermore, the volumetric methane storage working capacities of Zr-fcu-H, Zr-fcu-F, Zr-fcu-CH3, and Zr-fcu-OH at 298/273 K and 80 bar are 187/217, 175/193, 167/187, and 154/171 cm3 (STP) cm–3, respectively, which indicate that the zirconium-based crystalline porous materials are capable of storing relatively high amounts of methane

Correlation coefficients of air pollutants across 25 districts.

<p>Abbreviations: PM₁₀, particles with aerodynamic diameter 10 µm or less; SO₂, sulfur dioxide; NO₂, nitrogen dioxide; CO, carbon monoxide; O₃, ozone.</p><p>*<i>p</i><0.05.</p

Adjusted OR and 95% CIs of respiratory diseases with respect to ambient air pollutants (2006–2008) among children with allergic predisposition (n = 4135)^†.

†<p>Models were adjusted for the variables with asterisks in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022470#pone-0022470-t004" target="_blank">table 4</a>.</p>‡<p>OR were scaled to the interquartile range for each pollutant (31 µg/m³ for PM₁₀, 21 µg/m³ for SO₂, 10 µg/m³ for NO₂, 1001 µg/m³ for CO, and 23 µg/m³ for O₃).</p

Adjusted odds ratios (OR) for personal and household covariates associated with respiratory morbidity.

<p>*<i>p</i><0.15;</p><p>**<i>p</i><0.05.</p><p>Items with asterisks are included in the final adjustment model for this measurement. These items are adjusted for each other; remaining variables are adjusted only for the footnoted items, as well as for districts.</p

Adjusted OR and 95% CIs of respiratory diseases with respect to ambient air pollutants (2006–2008) among children without allergic predisposition (n = 26004)^†.

†<p>Models were adjusted for the variables with asterisks in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022470#pone-0022470-t004" target="_blank">table 4</a>.</p>‡<p>OR were scaled to the interquartile range for each pollutant (31 µg/m³ for PM₁₀, 21 µg/m³ for SO₂, 10 µg/m³ for NO₂, 1001 µg/m³ for CO, and 23 µg/m³ for O₃).</p

Predictive Equations Using Regression Analysis for the Developed and other Reference Equations Based on the Training Subset.

<p>Predictive Equations Using Regression Analysis for the Developed and other Reference Equations Based on the Training Subset.</p

Pearson's correlation coefficients between spirometric parameters and height, weight, age in the training subset^*.

*<p><i>P</i><0.001 for all correlation coefficients. FVC, forced vital capacity; FEV1, forced expiratory volume in one second; PEF, peak expiratory flow; MMEF, maximal mid-expiratory flow.</p

Difference Between Measured and Predicted Values Based on the Validation Subset.

*<p>Data are presented as mean of difference (predicted-measured) ±95% CI (confidence interval) of difference, and <i>P</i> value.</p

The frequency and percentage for age stratified by gender.

<p>The frequency and percentage for age stratified by gender.</p