Fang Na Gu

One‐Pot Synthesis of Potassium‐Functionalized Mesoporous γ‐Alumina: A Solid Superbase

The synthesis of mesoporous superbases is a challenge for chemists owing to their wide range of potential applications in green chemistry and the difficulties inherent in their preparation. Mesoporous superbasic materials are extremely desirable for use in environmentally benign and economical chemical processes as they can catalyze diverse reactions under mild conditions, therefore many attempts have been made to prepare mesoporous solid bases, for example, by incorporating nitrogen-containing species into mesoporous silica and by grafting organic bases onto mesoporous silica. Owing to the reaction of these strongly basic species with silica, however, most of the solid bases reported to date are relatively weak, which suggests that it is difficult to generate superbasicity on mesoporous silica. In contrast to silica, alumina, especially that of the g-type, is a well-known support for a variety of solid strong bases, which means that the occurrence of mesoporous aluminas affords a good opportunity to prepare mesoporous superbasic materials. Unfortunately, the stability of mesoporous aluminas is relatively poor and structural damage occurs to a greater or lesser extent even if postsynthesis modification is performed carefully. This drawback hinders the application of mesoporous aluminas in preparing solid superbases and other functional materials. Herein we report a new strategy for the one-pot synthesis of potassium-functionalized mesoporous g-alumina that involves the use of K2CO3 to adjust the pH value of the reaction system such that the base precursor KNO3 is produced in situ by hydrolysis of Al(NO3)3. KNO3 is decomposed to the strongly basic species K2O on the g-Al2O3 that is also formed in situ during the same calcination process. This strategy allows the synthesis and modification of mesoporous alumina in a one-pot process, avoids post-treatment framework damage, and saves time and energy. The basic materials obtained exhibit a well-defined mesoporous structure and superbasicity and are active in 1-hexene isomerization, which means that they are valuable candidates for selective adsorption and catalysis involving strong solid bases. The synthetic process is shown schematically in Figure S1 in the Supporting Information. KNO3-coated mesoporous boehmite (AlOOH) with a K/Al atomic ratio (n) of between 0 and 0.27 (Table 1) is obtained initially (denoted as MA-B (n=

New Attempt at Directly Generating Superbasicity on Mesoporous Silica SBA-15

Direct generation of superbasicity on mesoporous silica SBA-15 was realized by tailoring the host-guest interaction, and calcium species were selected as the guest in modifying SBA-15. The results show that calcium species could be homogeneously distributed on the surface of SBA-15. Because of the host-guest interaction, the decomposition of the supported calcium nitrate was apparently easier than the bulk one. Surprisingly, the calcium nitrates modified SBA-15 (CaNS) samples exhibited superbasicity with good preservation of the mesostructure after activation, differing from the potassium nitrate loaded SBA-15 samples that displayed weak basicity with collapsed mesostructure. The present superbasic CaNS materials also possess good water resistance and high surface areas, up to 429 m(2) g(-1), which is promising for their potential applications in adsorption and catalysis. Further investigation concerning the roles played by the guest in basicity formation on SBA-15 was conducted. The samples modified by Group 2 metal nitrates showed strong basicity with base strength (H-) of 22.5-27.0 and good preservation of mesostructure. In contrast, loading Group 1 metal nitrates on SBA-15 produced samples with weak basicity ( H-=9.3-15.0) and collapsed mesostructure after activation. Such differences can be related to the interaction between the resulting metal oxide and the silica support, as well as the mobility of the cations in the metal oxide.

One-pot synthesis of the amine-modified meso-structured monolith CO2 adsorbent

A new attempt to synthesize the amine-modified meso-structured monolith CO2 adsorbent in a one-pot process is reported here for the first time, in which tetraethylenepentamine (TEPA) is utilized not only as the modifier coating onto the resulting monolith, but also the additive controlling the generation of micropores in the silica wall. The amount of TEPA has multiple influences on the synthesis, affecting hydrolysis-condensation of the silicate precursor, impacting the textural properties of the silica skeleton and determining the final CO2 adsorption ability. Apart from the advantage of saving time and energy in their synthesis, these resulting TEPA containing monoliths possess a considerable mechanistic strength bearing the pressure of 64 N cm−2, and exhibiting a high capacity up to 171 mg g−1 in CO2 adsorption.

Capturing 1,3-butadiene by the highly ordered Al-containing SBA-15.

This investigation examined the instantaneous adsorption of 1,3-butadiene by aluminum-modified mesoporous silica SBA-15 at ambient temperature. To efficiently trap the 1,3-butadiene pollutant in environment, alumina was incorporated in SBA-15 through various pathways such as one-pot synthesis, solid state grinding and impregnation, and the property-function relation of resulting composites were characterized with XRD, N(2) adsorption-desorption, FTIR and NH(3)-TPD techniques. Adsorption of N-nitrosopyrrolidine (NPYR) was employed for the first time to reveal the difference between the mesoporous silica with the same Al-content but prepared with different methods, providing a potential method for the delicate characterization. Modification with alumina significantly increased the capability of SBA-15 to adsorb 1,3-butadiene, and the one-pot synthesized sample exhibited a higher activity than the post-modified samples, resulting from the formation of Brønsted acidic sites and reservation of silianol groups on SBA-15 host.

One-pot synthesis of novel ferric cubic mesoporous silica (Im3m symmetry) and its highly efficient adsorption performance

A novel facile route, denoted here as I0HO∼COO−S+, was reported to synthesize cubic Im3m mesoporous silicas and metal substituted analogues for the first time by utilizing commercial conventional cationic surfactant cetyltrimethylammonium bromide (CTAB) to direct the mesostructures along with citric acid as the acid media to give a weak acidic condition. This weak acidic system favors not only the fine phase control but also the optimal incorporation of ferric ions, providing a skilful way to prepare the mesoporous composites with a surprising adsorption capability. UV-vis DRS and ESR spectra indicated that the majority of the metal ions inserted into the siliceous framework within the tetrahedral coordination environment. Owing to the controllable incorporation of ferric species that form a monolayer on the channel wall plus the three-dimensional cage-like mesostructure that generates a fine geometric confinement towards the adsorbate, the mesoporous composite overruns zeolite NaY in the instantaneous adsorption of volatile nitrosamines and 1,3-butadiene for the first time.

Zeolite multifunctional materials as the menthol carrier and nitrosamines trapper

The attempt of utilizing zeolite as the multifunctional additive to carry given guest and to trap nitrosamines in smoke was reported for the first time. After the menthol was adsorbed by zeolite, the composite was added onto tobacco rod. The release of menthol took place when the hot coal of the burning cigarette approached the zeolite. At the same time, the zeolite reduced the nitrosamines level of cigarette smoke. The thermal release of menthol from zeolite was measured by a temperature programmed desorption (TPD) method. Most zeolites studied in this work showed a main desorption peak below 500 K with the exception of NaY, which displayed two desorption peaks around 545 and 650 K. In addition, the zeolite additives reduced about 30% of nitrosamines in the side stream smoke.