Synthesis and characterization of Co-containing SBA-15 catalysts

Two Co-SBA-15 catalysts were synthesized and characterized by thermogravimetry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, porosity, UV–visible diffuse reflectance and temperature programmed reduction with H₂. The first catalyst was prepared synthesizing SBA-15 and then adding Co ions by impregnation (Co_imprSBA-15). The second catalyst was prepared using a more complex procedure of immobilization of cobalt ions in the presence of pyridine and H₂O₂ on –COOH groups anchored to the SBA-15 structure [Co-SBA-15(COOH)]. These COOH groups were created starting from cyano groups introduced during the synthesis of the periodic mesoporous materials as 4-triethoxysilylbutyronitrile. Characterization of the samples indicates that in both cases the typical 2D periodical hexagonal structure of SBA-15 was obtained, but with less ordered packing in the second case. The cobalt is highly dispersed in the SBA-15 (up to 9% w/w) and is present mainly as Co²⁺ ions in highly distorted tetrahedral or square pyramidal coordination. Some coordinatively unsaturated Co(II) Lewis acid centers are present in Co_imprSBA-15, while in Co-SBA-15(COOH) coordination of pyridine to cobalt tentatively may induce the formation of Co³⁺ ions, although in both catalysts the dominant species are Co²⁺ ions in a very close environment.     

Sulfonic acid functionalised SBA-15 as catalysts for Beckmann rearrangement and esterification reaction

Hybrid inorganic–organic solid acid materials SBA-15–Ph–SO₃H were synthesized by the directly co-condensation method under the acid medium. The resulting materials perform well both in the liquid phase Beckmann rearrangement (The yield is 32.3%) and esterification reaction (The yield is 95.5%). And more, the catalysts show the different catalytic performance in these two reactions.     

Phase transition of mesoporous SiO<Subscript>2</Subscript> impregnated with an organic templating agent by post-synthetic microwave heating

Mesoporous silica SBA-15 samples were subjected to microwave heating for 10–40 min at 393 and 443 K after dry-impregnation with TPAOH (tetrapropylammonium hydroxide) to prepare a mesoporous material with zeolytically ordered pore walls. Physicochemical properties of the materials prepared were characterized by XRD, N₂ adsorption at 77 K, SEM, TEM, UV–vis and FT-IR spectroscopies. These investigations revealed that selective transformation of amorphous pore walls of SBA-15 to crystalline zeolytic phase is difficult to be achieved and a mixed phase of mesoporous silica/zeolite composite material was obtained, instead. Microwave heating time, temperature, TPAOH concentration, and hydrothermal stability of the mesoporous host materials tested (MCM-41, HMS, and SBA-15) were important factors to maintain the mesopore structure of the host materials during the post-synthetic microwave heating treatment.     

Preparation, Characterization and Catalytic Activity of Palladium Nanoparticles Encapsulated in SBA-15

A simple adsorption method was studied for the preparation of SBA-15-encapsulated palladium nanoparticles. This method employed the SBA-15 with organic template removed by ethanol extraction for the adsorption of cationic Pd precursors in alkaline solution followed by calcination and H₂ reduction. The pH of the solution was found to be a critical factor in determining the palladium content and the ordered mesoporous structure. Our characterizations revealed that the Pd nanoparticles prepared by this method were located inside the mesoporous channels and were quite uniform in size (mostly 3–4 nm). The SBA-15-encapsulated uniform Pd nanoparticles were efficient catalysts for solvent-free aerobic oxidation of alcohols.     

Inorganic–organic hybrid materials based on functionalized silica and carbon: A comprehensive understanding toward the structural property and catalytic activity difference over mesoporous silica and carbon supports

Inorganic–organic hybrid materials based on functionalized silica and carbon were synthesized by anchoring molybdovanadophosphoric acid (H₅[PMo₁₀V₂O₄₀] · 32.5H₂O) onto amine-functionalized SBA-15, ethane-bridged SBA-15 and mesoporous carbon, respectively. Small angle X-ray diffraction, N₂ sorption analysis, HRTEM, SEM, FT-IR, CP-MAS NMR were used to diagnose the mesoporous structure of inorganic–organic hybrid materials. The structural integrity of molybdovanadophosphoric acid has been found to be retained after immobilization over mesoporous materials. These inorganic–organic hybrid materials were tested in the environmentally friendly oxidation of 2-methylnaphthalene (2MN) with 30% aqueous hydrogen peroxide. Molybdovanadophosphoric acid containing mesoporous organosilica hybrid material (ethane-bridged SBA-15) exhibited higher catalytic activities in the oxidation of 2MN to give a clean product 2-methy-1,4-naphthoquinone (menadione vitamin K3 precursor), because of the improved hydrophobicity of the material. The correlation between structural properties and catalytic activities of these hybrid materials has been well addressed in our present studies.     

Highly Efficient Near-IR Photoluminescence of Er Immobilized in Mesoporous SBA-15

SiO₂ mesoporous molecular sieve SBA-15 with the incorporation of erbium ions is studied as a novel type of nanoscopic composite photoluminescent material in this paper. To enhance the photoluminescence efficiency, two schemes have been used for the incorporation of Er³⁺ where (1) Er³⁺ is ligated with bis-(perfluoromethylsulfonyl)-aminate (PMS) forming Er(PMS)_x-SBA-15 and (2) Yb³⁺ is codoped with Er³⁺ forming Yb-Er-SBA-15. As high as 11.17 × 10⁻²¹cm² of fluorescent cross section at 1534 nm and 88 nm of “effective bandwidth” have been gained. It is a 29.3% boost in fluorescent cross section compared to what has been obtained in conventional silica. The upconversion coefficient in Yb-Er-SBA-15 is relatively small compared to that in other ordinary glass hosts. The increased fluorescent cross section and lowered upconversion coefficient could benefit for the high-gain optical amplifier. Finally, the Judd–Ofelt theory has also been used for the analyses of the optical spectra of Er(PMS)_x-SBA-15.     

Functionalized Mesoporous SBA-15 with CeF<Subscript>3</Subscript>: Eu<Superscript>3+</Superscript> Nanoparticle by Three Different Methods: Synthesis,Characterization, and Photoluminescence

Luminescence functionalization of the ordered mesoporous SBA-15 silica is realized by depositing a CeF₃: Eu³⁺ phosphor layer on its surface (denoted as CeF₃: Eu³⁺/SBA-15/IS, CeF₃: Eu³⁺/SBA-15/SI and CeF₃: Eu³⁺/SBA-15/SS) using three different methods, which are reaction in situ (I-S), solution impregnation (S-I) and solid phase grinding synthesis (S-S), respectively. The structure, morphology, porosity, and optical properties of the materials are well characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, N₂ adsorption, and photoluminescence spectra. These materials all have high surface area, uniformity in the mesostructure and crystallinity. As expected, the pore volume, surface area, and pore size of SBA-15 decrease in sequence after deposition of the CeF₃: Eu³⁺ nanophosphors. Furthermore, the efficient energy transfer in mesoporous material mainly occurs between the Ce³⁺ and the central Eu³⁺ ion. They show the characteristic emission of Ce³⁺ 5d → 4f (200–320 nm) and Eu^{3+ 5}D₀ → ⁷F _J (J = 1–4, with ⁵D₀ → ⁷F₁ orange emission at 588 nm as the strongest one) transitions, respectively. In addition, for comparison, the mesoporous material CeF₃: Eu³⁺/SBA-15/SS exhibits the characteristic emission of Eu³⁺ ion under UV irradiation with higher luminescence intensity than the other materials.     

Platinum incorporated into the SBA-15 mesostructure via deposition-precipitation method: Pt nanoparticle size estimation and catalytic testing

We report the use of the deposition precipitation (DP) method for the functionalization of mesoporous silica SBA-15 with Pt. [Pt(NH₃)₄](OH)₂ was used as a platinum precursor. Experiments were performed at 90 °C, and urea was used to control the pH during precipitation. From the obtained pH profiles, an interaction between the support and the precipitating species is suggested. A general formula of the species is proposed to be [Pt^II(OH)_n] _s ^II-n . By Transmission electron microscopy (TEM) it is shown that the majority of Pt nanoparticles on SBA-15 reside in the range between 2 and 4 nm. However, particles in the range of 15 nm were also detected, which indicates that the precipitation does not occur exclusively within the channels of the SBA-15. The obtained material is compared to a reference catalyst, Pt/SBA-15, prepared by a conventional wet impregnation method. Here, larger Pt nanoparticles (4–6 nm) were detected. The catalysts were found to exhibit comparable activity in toluene hydrogenation in terms of turnover frequency based on CO chemisorption.     

Rapid synthesis of La–Ce–silica mesoporous SBA-15-type material via microwave technique

La–Ce–silica mesoporous SBA-15-type material has been rapidly synthesized using microwave technique and characterized by XRD, FT-IR, DRS, and low temperature N₂ adsorption–desorption measurement. The results show the La and Ce were successfully incorporated into the framework of SBA-15 molecular sieve and the synthesized material not only retains the hexagonal order and physical properties of purely siliceous SBA-15 but also possesses high surface area and narrow pore-size distribution. Further, the obtained material La–Ce–SBA-15 was used as catalyst support to load active metal Pt for CO oxidation reaction. The results of experiment indicate that the catalytic activity of Pt/La–Ce–SBA-15 is higher than that of the Pt/SBA-15 and Pt/La/Ce/SBA-15.     

Structure and Luminescence Properties of Eu<Superscript>3+</Superscript>-Doped Cubic Mesoporous Silica Thin Films

Eu³⁺ ions-doped cubic mesoporous silica thin films with a thickness of about 205 nm were prepared on silicon and glass substrates using triblock copolymer as a structure-directing agent using sol–gel spin-coating and calcination processes. X-ray diffraction and transmission electron microscopy analysis show that the mesoporous silica thin films have a highly ordered body-centered cubic mesoporous structure. High Eu³⁺ ion loading and high temperature calcination do not destroy the ordered cubic mesoporous structure of the mesoporous silica thin films. Photoluminescence spectra show two characteristic emission peaks corresponding to the transitions of ⁵D₀-⁷F₁ and ⁵D₀-⁷F₂ of Eu³⁺ ions located in low symmetry sites in mesoporous silica thin films. With the Eu/Si molar ratio increasing to 3.41%, the luminescence intensity of the Eu³⁺ ions-doped mesoporous silica thin films increases linearly with increasing Eu³⁺ concentration.     

Immobilization of uranium in cristobalite ceramic through adsorption on mesoporous SBA-15 and further sintering process

The development of an adsorbent which can be easily transformed into stable ceramic waste forms through a simple route is necessary for the treatment of the radioactive wastewater. Herein, we report on the immobilization of uranium in cristobalite ceramic through adsorption on mesoporous SBA-15 and further sintering process. The mesoporous SBA-15 with short pore length was synthesized and employed to remove uranium from aqueous solution. Subsequently, the SBA-15 with adsorbed U (U/SBA-15) was solidified by sintering. The effects of sintering temperature and U content on the structure, densification and aqueous durability of the obtained cristobalite ceramic waste forms were investigated. The results indicate that the U/SBA-15 can be transformed into stable cristobalite ceramic after sintering at 1100–1400 °C for 6 h. Furthermore, all the obtained cristobalite ceramic waste forms exhibit good aqueous durability (∼10⁻⁴ g m^-2 d^-1). This work demonstrates a potential route and adsorbent to dispose the radioactive wastewater.     

In Situ Preparation of Functional Heterogeneous Organotin Catalyst Tethered on SBA-15

A stable heterogeneous organotin catalyst has been prepared by in situ tethering organotin compounds on SBA-15. This was verified by XRD, TEM, N₂ adsorption/desorption at −196 °C, FTIR and diffuse reflectance UV–vis spectral techniques. This material was much more active than the sample prepared by the grafting method for the direct synthesis of dimethyl carbonate (DMC) from methanol and CO₂ despite that its catalytic activity was dependent on the organotin amount. This could be attributed to the formation of organotin clusters with different structures and the larger surface area. After immobilization on the SBA-15 mesoporous material, the six-coordinated organotin clusters showed higher activity, compared to the tetrahedral Sn species. With increasing reaction temperature and CO₂ pressure, the catalytic activity considerably increased.     

Ordered Mesostructured CdS Nanowire Arrays with Rectifying Properties

Highly ordered mesoporous CdS nanowire arrays were synthesized by using mesoporous silica as hard template and cadmium xanthate (CdR₂) as a single precursor. Upon etching silica, mesoporous CdS nanowire arrays were produced with a yield as high as 93 wt%. The nanowire arrays were characterized by XRD, N₂ adsorption, TEM, and SEM. The results show that the CdS products replicated from the mesoporous silica SBA-15 hard template possess highly ordered hexagonal mesostructure and fiber-like morphology, analogous to the mother template. The current–voltage characteristics of CdS nanoarrays are strongly nonlinear and asymmetrical, showing rectifying diode-like behavior.     

A chromotropic acid modified SBA-15 as a highly sensitive fluorescent probe for determination of Fe<Superscript>3+</Superscript> and I<Superscript>−</Superscript> ions in water

A novel organic–inorganic hybrid nanomaterial (SBA-15-CA) was prepared by covalent immobilization of chromotropic acid onto the surface of mesoporous silica material SBA-15. Different techniques such as XRD, TEM, FT-IR, N₂ adsorption–desorption and TGA analyses were employed to characterize the grafting process. The data showed that the organic moiety (0.41 mmol g^?1) was successfully grafted to the SBA-15 and the primary hexagonally ordered mesoporous structure of SBA-15 was preserved after the grafting procedure. SBA-15-CA has been realized as a highly sensitive and selective fluorescent probe towards Fe³⁺ and I^? ions in aqueous media. SBA-15-CA exhibited a remarkable fluorescent quenching in the presence of Fe³⁺ ion over other competitive cations including Na⁺, Mg²⁺, Al³⁺, K⁺, Ca²⁺, Cr³⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺ as well as I^? ion among a series of anions including F^?, Cl^?, Br^?, CO₃^2?, HCO₃^?, CN^?, NO₃^?, NO₂^?, SCN^?, SO₄^2?, H₂PO₄^?, HPO₄^2?, and CH₃COO^?. A good linear response was observed between the concentration of the quenchers (Fe³⁺ and I^? ions) and fluorescence intensity of SBA-15-CA with detection limits of 1.5?×?10^?7 M for Fe³⁺ and 0.2?×?10^?7 M for I^?. Moreover, the effects of various pH values on the sensing ability of SBA-15-CA were investigated. Finally, the proposed method was successfully utilized for the determination of Fe³⁺ and I^? ions in river water, well water and tap water samples.     

Electrochemical behavior and simultaneous determination of dihydroxybenzene isomers at a functionalized SBA-15 mesoporous silica modified carbon paste electrode

The simultaneous voltammetric determination of dihydroxybenzene isomers was investigated using cyclic and differential pulse voltammetries at the amino-functionalized SBA-15 mesoporous silica-modified carbon paste electrode (NH₂-SBA15/CPE) in phosphate buffer solution (pH 6.0). The NH₂-SBA15/CPE showed a larger peak current and higher selectivity for the dihydroxybenzene isomers in comparison with the bare carbon paste electrode (CPE) and SBA-15 mesoporous silica-modified carbon paste electrode (SBA15/CPE). The oxidation peak potential difference between hydroquinone (HQ) and catechol (CC) was 115 mV and was 396 mV between catechol and resorcinol (RC). This indicated that catechol, resorcinol and hydroquinone could be identified entirely at the NH₂-SBA15/CPE. Under the optimized conditions, the amperometric currents were linear over ranges from the following: 0.8–160 μmol L⁻¹ for hydroquinone, 1.0–140 μmol L⁻¹ for catechol and 2.0–160 μmol L⁻¹ for resorcinol. The detection limits were 0.3, 0.5 and 0.8 μmol L⁻¹, respectively. The proposed electrode can be applied to the simultaneous determination of dihydroxybenzene isomers in mixtures without previous chemical or physical separations.     

Trypsin immobilization on mesoporous silica with or without thiol functionalization

The effects of pore size, structure, and surface functionalization of mesoporous silica on the catalytic activity of the supported enzyme, trypsin, were investigated. For this purpose, SBA-15 with 1-dimensional pore arrangement and cubic Ia3d mesoporous silica with 3-dimensional pores were prepared and tested as a support. Materials with varying pore diameters in the range 5–10 nm were synthesized using a non-ionic block copolymer by controlling the synthesis temperature. Thiol-group was introduced to the porous materials via siloxypropane tethering either by post synthesis grafting or by direct synthesis. These materials were characterized using XRD, SEM, TEM, N₂ adsorption, and elemental analysis. Trypsin-supported on the solids prepared was active and stable for hydrolysis of N-α-benzoyl-DL-arginine-4-nitroanilide (BAPNA). Without applying thiol-functionalization, cubic Ia3d mesoporous silica with ca. 5.4 nm average pore diameter was found to be superior to SBA-15 for trypsin immobilization and showed a better catalytic performance. However, enzyme immobilized on the 5% thiol-functionalized SBA-15 prepared by directly synthesis was found to be the most promising and was also found recyclable.     

Catalytic aerobic oxidation of ethylbenzene over Co/SBA-15

Co(II)O was highly dispersed in the mesopores of SBA-15 by alcoholic impregnation method and characterized by XRD, TEM, UV–VIS DRS, TPR, and XRF techniques. It was found that tetrahedral coordinated Co(II)O was stabilized by SBA-15 at low Co-loading. Co/SBA-15 showed much higher activity than Co(OAc)₂ or Co₃O₄ in the liquid-phase aerobic oxidation of ethylbenzene under solvent-free condition.     

介孔SBA-15有机化修饰对PMMA杂化材料力学性能的影响

采用硅烷偶联剂对SBA-15进行了有机化修饰(即:SBA-15-G),利用在位分散聚合法制备了SBA-15/PMMA和SBA-15-G/PMMA杂化材料,研究了SBA-15和SBA-15-G在PMMA基体中的介观有序性和分散性以及对杂化材料的力学性能的影响规律。结果表明有机化修饰使SBA-15孔容、孔径和比表面积减小,表面亲油性提高;SBA-15和SBA-15-G在基体中仍保持长程有序结构;有机化修饰改善了SBA-15在基体中的分散性和与基体的界面结合,显著增强了杂化材料的力学性能。当SBA-15-G为4%时,杂化材料的拉伸强度和模量分别提高了45%和40.4%,当SBA-15-G为2%时冲击强度达到最大,比基体提高了36.6%。,     

Application of Cs salt of 12-tungstophosphoric acid supported on SBA-15 mesoporous silica in NO x storage

Cs salt of 12-tungstophosphoric acid (HPW) was deposited simultaneously at the external surface of the SBA-15 silica microcrystals and inside its mesoporous channels at loading of 60 wt% and Cs/W ratio in the range between 0.9 and 2, followed by impregnation of 1 wt% Pt. The performance of the Pt/CsHPW/SBA-15 composite materials was tested in the NO _x storage. The optimal NO _x storage capacity and efficiency were achieved at Cs/W of 1.5. The dispersion of CsHPW on SBA-15 led to a significant decrease of its crystal size (5–13 nm) compared with bulk HPW and HPW supported on titania (28–29 nm). Pt/CsHPW/SBA-15 displayed lower NO _x absorption capacity but much higher absorption and desorption efficiency than the reference Pt/HPW and Pt/HPW/TiO₂ materials. Consequently, Pt/CsHPW/SBA-15 displayed a better performance in short lean (2 min)—rich (1 min) absorption-desorption cycles. The novel Pt/CsHPW/SBA-15 nanocomposites presents the basis for improved storage material for NO _x removal from lean exhaust gases in highly dynamic aftertreatment technologies.     

Binary and Ternary Heterometallic (La<Superscript>3+</Superscript>, Gd<Superscript>3+</Superscript>, Y<Superscript>3+</Superscript>)–Eu<Superscript>3+</Superscript> Functionalized SBA-15 Mesoporous Hybrids: Chemically Bonded Assembly and Photoluminescence

A novel kind of organic–inorganic monomer SUASi has been achieved by modifying 5-sulfosalicylic acid (SUA) with 3-aminopropyltrimethoxysilane (APS), subsequently binary and ternary Eu³⁺ mesoporous hybrid materials with 5-sulfosalicylic acid (SUA)-functionalized SBA-15 and 1,10-phenanthroline (phen) are synthesized by co-condensation of SUASi and TEOS in the presence of Eu³⁺ complex and Pluronic P123 as a template. Finally, luminescent hybrid mesoporous materials consisting of active rare earth ions (Eu³⁺)—inert rare earth ions (Y³⁺, La³⁺, Gd³⁺) complex covalently bonded to the mesoporous materials network have been obtained via this sol–gel approach. The physical characterization and photoluminescence of all these resulting materials are studied in detail. Especially the luminescent behavior has been studied with the different ratios of Eu³⁺–(Y³⁺, La³⁺, Gd³⁺), which suggests that the existence of inert rare earth ions can enhance the luminescence intensity of Eu³⁺. This may be due to the intramolecular energy transfer between Y³⁺, La³⁺, Gd³⁺, and Eu³⁺ through the covalently bonded mesoporous framework.