A Novel Aluminum-Based Metal-Organic Framework with Uniform Micropores for Trace BTEX Adsorption.

Metal-organic frameworks (MOFs) are potential porous adsorbents for benzene, toluene, ethylbenzene and xylene (BTEX). A novel MOF, using low toxic aluminum (Al) as the metal, named as ZJU-620(Al), with uniform micropore size of 8.37±0.73 Šand specific surface area of 1347 m2 g-1 , was synthesized. It is constructed by one-dimensional rod-shaped AlO6 clusters, formate ligands and 4,4',4''-(2,4,6-trimethylbenzene-1,3,5-triyl) tribenzoic ligands. ZJU-620(Al) exhibits excellent chemical-thermal stability and adsorption for trace BTEX, e.g., benzene adsorption of 3.80 mmol g-1 at P/P0 =0.01 and 298 K, which is the largest one reported. Using Grand Canonical Monte Carlo simulations and Single-crystal X-ray diffraction analyses, it was observed that the excellent adsorption could be attributed to the high affinity of BTEX molecules in ZJU-620(Al) micropores because the kinetic diameters of BTEX are close up to the pore size of ZJU-620(Al).

Green synthesis of a superhydrophobic porous organic polymer for the removal of volatile organic compounds at high humidity.

Superhydrophobic porous organic polymers are potential sorbents for volatile organic compounds (VOCs) pollution control by suppressing the competition of water molecules on their surfaces. However, the synthesis of superhydrophobic reagents usually requires large amounts of organic solvents and a long reaction time (≥ 24 h). Herein, a green mechanochemical method was developed to synthesize a superhydrophobic polymer (MSHMP-1) with the advantages of using a small amount of organic solvents (5 mL/g) and a short reaction time (2 h). Meanwhile, MSHMP-1 with a water contact angle (WCA) of 162° exhibited a dramatically rich pore structure as revealed by its specific surface area (SSA) of 1780 m2/g. The decrease in the adsorption of benzene on MSHMP-1 due to the competition of water molecules, even at relative humidity of 90 %, was nonsignificant (<10 %), indicating the great application potential of MSHMP-1 in hydrophobic adsorption. Moreover, the adsorption capacity of MSHMP-1 was maintained after at least five adsorption-desorption cycles. Therefore, MSHMP-1 can be a remarkable adsorbent for the removal of hazardous VOCs, especially at high humidity levels.

Simultaneous adsorption of fulvic acid and organic contaminants by KOH activated mesoporous biochar with large surface area.

Returning carbon materials from biomass to soil is a potential technology to retard organic contaminants or dissolved organic matter (DOM) in soil by adsorption, as well as to store carbon in soil for carbon sequestration. However, DOM was widely reported to inhibit adsorption of organic contaminants on carbon materials by competition and by enhancing contaminants' solubility. In this study, a KOH activated carbon material (KAC), pyrolyzed from bamboo chips, with high surface area (3108 m2/g), micropores volumes (0.964 cm3/g), mesopores volumes (1.284 cm3/g), was observed that it can adsorb fulvic acid (FA) and organic contaminants (e.g., nitrobenzene, phenols, and anilines) simultaneously with weak competition and high adsorption capacity. With 50 mg TOC/L FA, for example, the average competition suppressing rate (ΔKf/Kf-m) of organic contaminants on KAC was lower than 5%, the adsorption for organic contaminants and FA were higher than 1100 mg/g and 90 mg TOC/g, respectively. The weak competition on KAC could be attributed to the low micropore blockage (<35%) and the weak adsorption sites competition on mesopores of KAC, as well as the minimal solubility enhancement of organic contaminants by FA because most FA is adsorbed on KAC but is not dissolved in the solution. In addition, adsorption of organic contaminants with high hydrogen-bonding donor ability (αm) and adsorption affinity was less suppressed by FA because of the heterogeneous nature of hydrophilic sites on KAC's surface. Therefore, KAC could be a potential carbon material to be produced to implement to soil for carbon storage and simultaneous retarding organic contaminants and DOM.

Double-walled Al-based MOF with large microporous specific surface area for trace benzene adsorption.

Double-walled metal-organic frameworks (MOFs), synthesized using Zn and Co, are potential porous materials for trace benzene adsorption. Aluminum is with low-toxicity and abundance in nature, in comparison with Zn and Co. Therefore, a double-walled Al-based MOF, named as ZJU-520(Al), with large microporous specific surface area of 2235 m2 g-1, pore size distribution in the range of 9.26-12.99 Å and excellent chemical stability, was synthesized. ZJU-520(Al) is consisted by helical chain of AlO6 clusters and 4,6-Di(4-carboxyphenyl)pyrimidine ligands. Trace benzene adsorption of ZJU-520(Al) is up to 5.98 mmol g-1 at 298 K and P/P0 = 0.01. Adsorbed benzene molecules are trapped on two types of sites. One (site I) is near the AlO6 clusters, another (site II) is near the N atom of ligands, using Grand Canonical Monte Carlo simulations. ZJU-520(Al) can effectively separate trace benzene from mixed vapor flow of benzene and cyclohexane, due to the adsorption affinity of benzene higher than that of cyclohexane. Therefore, ZJU-520(Al) is a potential adsorbent for trace benzene adsorption and benzene/cyclohexane separation.

Methyl-Functionalized Al-Based MOF ZJU-620(Al): A Potential Physisorbent for Carbon Dioxide Capture.

Developing Al-based metal-organic frameworks (MOFs) with moisture-resistance ability is a challenge for carbon dioxide (CO2) capture. Methyl-functionalized Al-based MOF ZJU-620(Al), with excellent chemical-thermal stability and specific surface area of 1347 m2/g, observed here, is a potential adsorbent for CO2 capture with good recyclability and large capacity up to 4.25 mmol/g at 298 K and 1 atm. CO2 molecules are largely trapped on two types of sites. One (site I) is near the AlO6 clusters, and another (site II) is between two parallel benzene rings with a distance of 6.64 Å. ZJU-620(Al) can be used for CO2/N2 (15/85) separation with the excellent selectivity up to 107.20 at 273 K and 31.93 at 298 K, and the separation factor of 13.68. It is also with excellent moisture-resistance ability due to 5% breakthrough time (outlet concentration reached the 5% of inlet concentration) without reduction at 80% relative humidity than under dry conditions. Water molecules occupy a small amount of CO2 adsorption site I, but they almost do not occupy the CO2 adsorption site II due to hydrophobic methyl-functional ligands. Moreover, CO2 can be adsorbed on the ZJU-620(Al) surface through C═O···H binding of water molecules with high affinity. Thus, ZJU-620(Al) is a candidate adsorbent for CO2 capture and separation especially under humidity conditions.