No abstract

Magnetic MCM-41 of large surface area (ca. 800 m2 g−1) and high magnetization (ca. 8.3 emu g−1) was prepared at a reasonable iron oxide nanoparticles loading of 10 wt % by a two-step synthesis process. The 8 nm iron oxide nanoparticles (i.e., 30 m2 g−1) were embedded in the MCM-41 with no observable effects on the particle morphology and pore symmetry, but a slight change (i.e., <20%) in the textural properties and surface chemistry was detected. Aminopropyls (2.7 mmol g−1) were grafted on the mesopore channels followed by the adsorption of 1.2 mmol g−1 Fe3+ to prepare selective adsorbents for arsenic(V) and chromium(VI) oxyanions. Detailed analyses indicated that the surface modifications of the magnetic and nonmagnetic MCM-41 by aminopropyls and Fe3+ yield similar site chemistry and accessibility. The Fe3+-magMCM-41 and Fe3+-MCM-41 displayed comparable adsorption capacity and selectivity. Both adsorbed only As(V) and Cr(VI) oxyanions (i.e., 1.0 and 2.0 mmol g−1, respectively), and none of the Cu(II). The magnetic adsorbent was easily dispersed in aqueous solution and can be removed by a magnet (1550 G) at a rate of 1 cm min−1 compared to 0.004 cm min−1 by gravity.

The sorption isotherms of CO 2 in wet ordered mesoporous silica KIT-6 with different amounts of pre-adsorbed water were firstly collected experimentally using a volumetric method in the temperature range of 275-281 K. The isotherms show an inflection point indicating CO 2 hydrates form in the pore spaces which is proofed by the enthalpy change calculated at the inflection pressure, and the quantity of water content shows considerable effect on the sorption capacity of CO 2 . The highest enhancement of sorption capacity in the presence of water is observed in wet KIT-6 sample with water loadings of 2.48, which is about 12.80 mmol/g and 1.86 times than that on dry sample. However, the saturation capacity is still far less than that what can be stored merely in the form of hydrates due to the low ratio of water utilization because of the large pore and the polar surface of KIT-6.

The anion effect was investigated for the copper adsorption on NH2-MCM-41 from Cu(NO3)2 and CuSO4 solutions. The copper adsorption was higher and faster in the presence of SO4 2− anion compared to NO3 −. The MCM-41 possesses well-ordered mesopores that are readily accessible and a uniform surface that is amenable to the attachment of the chemical moieties for creating tailored adsorption sites. The adsorption sites on NH2-MCM-41 were created by grafting aminopropyls on MCM-41, and the random deposition resulted in a site distribution best described by the Freundlich equation. The majority of the adsorption sites (i.e., up to 70%) are readily accessible to Cu2+ adsorption. The remaining sites were only accessible in the presence of SO4 2−. Evidence showed that the SO4 2− anion affects the adsorption by interacting with the dissolved copper to form [CuSO4]0 species, coadsorbing with Cu2+ to form stable complexes, and may even indirectly react with the weakly acidic silanol groups to liberate aminopropyls for more Cu2+ adsorption.

No abstract

No abstract

No abstract

Hierarchical SAPO-34 crystals were synthesized by a facile TEAOH etching post-treatment for the first time.