Multiple Functionalization of Mesoporous Silica in One‐Pot: Direct Synthesis of Aluminum‐Containing Plugged SBA‐15 from Aqueous Nitrate Solutions

Abstract

Aluminum‐containing plugged mesoporous silica has been successfully prepared in an aqueous solution that contains triblock copolymer templates, nitrates, and silica sources but without using mineral acid. The acidity of the solution can be finely tuned from pH 1.4 to 2.8 according to the amount of the introduced aluminum species which ranged from an Al/Si molar ratio of 0.25/1 to 4.0/1. The aluminum nitrate additive in the starting mixture, along with the weak acidity produced by the nitrates, contributes to the formation of plugged hexagonal structures and the introduction of different amounts of aluminum species into the mesostructure. Characterization by X‐ray diffraction, transmission electron microscopy, and N2 sorption measurements show that the Al‐containing plugged silicas possess well‐ordered hexagonal mesostructures with high surface areas (700–860 m2 g–1), large pore volume (0.77–1.05 cm3 g–1) and, more importantly, combined micropores and/or small mesopores in the cylindrical channels. Inductively coupled plasma–atomic emission spectrometry results show that 0.7–3.0 wt % aluminum can be introduced into the final samples. 27Al MAS NMR results display that about 43–60% aluminum species are incorporated into the skeleton of the Al‐containing silicas and the amount of the framework aluminum increases as the initial added nitrates rises. Scanning electron microscopy images reveal that the directly synthesized Al‐containing plugged silica has a similar morphology to that of traditional SBA‐15. Furthermore, the Al‐containing plugged samples have excellent performances in the adsorption and the catalytic decomposition of isopropyl alcohol and nitrosamine. Finally, the direct synthesis method is used to produce plugged mesoporous silicas that contain other metals such as chromium and copper, and the resultant samples also show good catalytic activities.

Characterization and adsorption behaviors of a novel synthesized mesoporous silica coated carbon composite

“…As a result, the transition process of micelles' 'sphere-to-rod' will take longer and plugs and/or constrictions are easily formed in the final mesopores if large amounts of salts existed in the reaction system. 21 In present study, the presence of plenty aluminum chloride leads to the generation of weak acidic reaction condition and the formation of constrictions/plugs in the mesopores. Furthermore, a distinctive limitless adsorption of SEG at high relative pressures can be observed, indicating the presence of macropores.…”

“…All SEG composites show a one-step capillary condensation, which indicates uniform mesopores, while a two-step capillary evaporation is observed in the desorption branches, which are typical characteristics for plugged mesoporous silica materials. 21 The special two-step branched desorption isotherm is inconspicuous in sample with rSiO 2 /C of 0.16 but obvious in other SEG composites. The plugs/constrictions in the SEG composites are related to the aluminum species and the weak acidities of the original reaction mixtures.…”

“…The plugs/constrictions in the SEG composites are related to the aluminum species and the weak acidities of the original reaction mixtures. 21 During the synthesis of mesoporous silica, the hydrolysis and condensation of siliceous source can be slowed under weak acidic conditions near the isoelectric point of silica. As a result, the transition process of micelles' 'sphere-to-rod' will take longer and plugs and/or constrictions are easily formed in the final mesopores if large amounts of salts existed in the reaction system.…”

“…are more homogeneous than heterogeneous, and the accessible sorption sites of SEG are probably identical and energetically equivalent to the MB molecules during the adsorption 21. The Langmuir constant K L and calculated monolayer capacity Q max of the SEG samples are also listed inTable 3.…”

Optimizing the matching between the acid and the base of cooperative catalysis to inhibit dehydration in the aldol condensation

“…In a typical synthesis, 2 g of Pluronic P123 [(EO) 20 (PO) 70 (EO) 20 , Aldrich] was first dissolved in 75 mL of H 2 O and then a calculated amount of Al(NO 3 ) 3 Á9H 2 O (e.g., 1.92 g for Al-0.25-SBA-15) was added and stirred for 0.5 h. After that, the mixture was heated to 318 K and 4.68 mL (0.02 mol) of TEOS was added. Then, the mixture was stirred under 318 K for 24 h, aged at 373 K for 24 h under static conditions, and then the product filtered, thoroughly washed, dried, and calcined as for the preparation of the Al-SBA-15 sample [20].…”