Organosilica Hollow Nanospheres Research Articles

Self‐Organization of Ionic Liquid‐Modified Organosilica Hollow Nanospheres and Heteropolyacids: Efficient Preparation of 5‐HMF Under Mild Conditions

AbstractAs a biomass‐derived platform molecule, 5‐hydroxymethylfurfural (5‐HMF) is a highly desirable feedstock for manufacturing of high value‐added chemicals ranging from starting materials for polyesters to biofuels. In this work, we reported the fabrication of a series of multicomponent solid acid catalysts based on heteropolyacids immobilized ILs‐modified organosilica hollow nanospheres (denoted as PW12‐ILs‐Cn‐HNS), in which PW12 (PW12=H3PW12O40 ⋅ xH2O) provides Brønsted acid site, ILs show strong electrostatic interactions with PW12, Cn (Cn=alkyl chain) is attached for hydrophobicity and HNS represents organosilica hollow nanospheres. When applied for catalytic dehydration of fructose to 5‐HMF, the PW12‐ILs‐C4‐HNS catalyst with 15.2 % PW12 loading exhibited the best dehydration activity to 5‐HMF with 93.7 % yield in DMSO at 100 °C in 2 h. Compared with 2D hexagonal and 3D interconnected structures, the excellent porosity properties of hollow nanospherical structure can provide a high population of the PW12 sites and enough confined nanospace for the dehydration of fructose. Moreover, the PW12‐ILs‐Cn‐HNS catalyst showed excellent stability over six catalytic cycles without obvious loss of activity. Most importantly, careful identification of the observed intermediates revealed crucial information for the dehydration process of fructose to 5‐HMF. As such, the proposed heterogeneous catalysts show great potential in biomass conversion processes.

A cationic surfactant-induced selective etching strategy for the synthesis of organosilica hollow nanospheres

The simple and effective synthesis of well-defined organosilica hollow nanospheres (OHNSs) for fundamental research and practical applications is still a significant challenge. In this work, a facile “cationic surfactant-induced selective etching” strategy was developed for the fabrication of hollow thiocyanatopropyl silsesquioxanes (thiocyanatopropyl-SQ), mercaptopropyl silsesquioxane (mercaptopropyl-SQ) from cyanoethyl-SQ@thiocyanatopropyl-SQ and cyanoethyl-SQ@mercaptopropyl-SQ, respectively. The experiments demonstrated that cetyltrimethylammonium bromide (CTAB) had remarkable influence on the formation of hollow structure and could accelerate the etching process significantly. A formation mechanism initiated by the adsorption of cationic surfactant followed by the etching of inner core with NH3·H2O was proposed. Hollow thiocyanatopropyl-SQ and mercaptopropyl-SQ with various shell thickness could be prepared by manipulating the amount of CTAB. And large-scale OHNSs were obtained at appropriate concentration of CTAB through this strategy. Moreover, this strategy might be further extended to fabricate OHNSs with other worthy functional groups.

Upgrading of pyrolysis biofuel via esterification of acetic acid with benzyl alcohol catalyzed by Brønsted acidic ionic liquid functionalized ethyl-bridged organosilica hollow nanospheres

Catalytic esterification of acetic acid with high boiling point benzyl alcohol is a primary goal to decrease oxygen content and acidity of crude pyrolysis biofuels before their further refining steps; meanwhile, the produced benzyl acetate is a value-added chemical building. In the search for efficient and recyclable solid acids for the above process, Brønsted acidic ionic liquid functionalized ethyl-bridged organosilica hollow nanospheres, [C3Im][SO3CF3]-Si(Et)Si HNSs (C3 = PrSO3H, Im = imidazolium cation), are demonstrated via co-condensation route followed by quaternary ammonization and anion exchange. The [C3Im][SO3CF3]-Si(Et)Si HNSs with nanometer size, hollow interior, opening and permeable thin shell as well as large BET surface area are successfully applied in esterification of acetic acid with benzyl alcohol in toluene as a simulated pyrolysis biofuel, and influence of reaction temperature, benzyl alcohol-to-acetic acid molar ratio and water content on the catalytic activity and selectivity are evaluated. The [C3Im][SO3CF3]-Si(Et)Si HNSs exhibit significantly high catalytic activity and selectivity in target reaction, outperforming Amberlyst-15 resin and HY zeolite; moreover, morphological characteristics, textural properties and surface hydrophobicity impact the esterification activity. The [C3Im][SO3CF3]-Si(Et)Si HNSs also exhibit good catalytic stability and reusability, and leaching of acid sites as well as changes of chemical structure and morphology of the nanohybrids are hardly observed after the reaction.

Conversion of Furfuryl Alcohol to Levulinic Acid in Aqueous Solution Catalyzed by Shell Thickness-Controlled Arenesulfonic Acid-Functionalized Ethyl-Bridged Organosilica Hollow Nanospheres

A series of arenesulfonic acid functionalized ethyl-bridged organosilica hollow nanospheres, ArSO3H-Et-HNS, with different shell thicknesses (2–6 nm) were successfully fabricated by P123 and/or F12...

Synthesis of multiple-shelled organosilica hollow nanospheres via a dual-template method by using compressed CO2

A facile and sustainable approach for preparation of multiple-shelled hollow periodic mesoporous organosilicas (PMOs) nanospheres with adjustable shells thickness has been established by a dual-template method without any other extra additions. Triblock copolymer Pluronic P123 and cationic and anionic mixed surfactant (CTAB/SDS) were employed as dual templates and 1,4-Bis(triethoxysilyl) benzene (BTEB) was used as the organicsilica precursor. In the synthesis, single and multiple-shelled hollow nanospheres were synthesized with different CO2 pressures. Moreover, the shell thickness of hollow PMOs nanospheres could be tuned simply by adjusting the CO2 pressure. TEM, SAXS, N2 adsorption-desorption, solid-state NMR, and FTIR were employed to character the structure and component of the prepared PMOs. For their unique multiple-shelled structure, the obtained PMOs nanospheres were used as the drug carrier to demonstrate the high uploading and controlled release of an anti-cancer drug doxorubicin. The versatility of this method was demonstrated with the preparation of hollow PMO nanospheres from other surfactants.

Arenesulfonic acid-functionalized alkyl-bridged organosilica hollow nanospheres for selective esterification of glycerol with lauric acid to glycerol mono- and dilaurate

A series of arenesulfonic acid-functionalized alkyl-bridged organosilica hollow nanospheres, Si(R)Si-ArSO3H-HNS, with different bridging alkyl groups such as ethyl, phenyl, or biphenyl in the silica/carbon framework were successfully fabricated by a P123-directed sol–gel co-condensation route and carefully adjusted the concentration of micelle-expanding agent and the acidity in the starting preparation system. The Si(R)Si-ArSO3H-HNS were applied in the synthesis of glycerol mono- and dilaurate from the esterification of glycerol with lauric acid, and the influence of glycerol-to-lauric acid molar ratio, structure of the bridging alkyl groups, and morphology of the nanohybrids on the catalytic activity were studied. The esterification activity of the Si(R)Si-ArSO3H-HNS outperformed commercial solid acid such as Amberlyst-15 or H-ZSM-5, regardless of the structure of the bridging alkyl groups; additionally, the biphenyl-bridged Si(Ph-Ph)Si-ArSO3H-HNS exhibited the highest esterification activity among various Si(R)Si-ArSO3H-HNS nanohybrids, attributing to the combination of advantages of strong Brønsted acidity, excellent porosity properties, hydrophobic surface, and unique hollow spherical nanostructure. Afterward, selective formation of glycerol mono- and dilaurate and possible esterification mechanism were studied. Finally, the reusability was studied and showed the Si(R)Si-ArSO3H-HNS can be reused three times without significant activity loss as well as structural and morphological changes.

Design of organosulfonic acid functionalized organosilica hollow nanospheres for efficient conversion of furfural alcohol to ethyl levulinate

One-step prepared organosulfonic acid-functionalized organosilica hollow nanospheres exhibited excellent catalytic activity and stability in direct synthesis of ethyl levulinate from ethanolysis of biomass-derived furfural alcohol.

Heteropoly acid and ZrO2 bifunctionalized organosilica hollow nanospheres for esterification and transesterification

H3PW12O40/ZrO2-Et-HNS materials with strong Brönsted and Lewis acidity, unique hollow nanospherical morphology and enhanced surface hydrophobicity exihibit excellent catalytic activity.

Family of Single-Micelle-Templated Organosilica Hollow Nanospheres and Nanotubes Synthesized through Adjustment of Organosilica/Surfactant Ratio

A family of hollow organosilica nanospheres and nanotubes was synthesized at appropriately low organosilica-precursor/block-copolymer-surfactant ratios. In Pluronic F127 (EO106PO70EO106) block copolymer templated synthesis of ethylene-bridged organosilicas in the presence of a swelling agent, the lowering of the organosilica-precursor/surfactant ratio led to a change from highly ordered face-centered cubic structure of spherical mesopores to individual hollow spherical nanoparticles. It was hypothesized that at low ratios of organosilica precursor to PEO-PPO-PEO, the framework precursor is solubilized in the micelles and its concentration on their surface is not sufficient to induce appreciable cross-linking between the resulting nanoobjects and the consolidation into larger particles. The inner pore size of the nanospheres was adjusted by varying the micelle expander, allowing us to obtain pore diameters up to ∼20 nm. By employing low precursor/surfactant ratios, hollow spheres of methylene-, ethenylene-...

Hydrolysis controlled synthesis of amine-functionalized hollow ethane–silica nanospheres as adsorbents for CO 2 capture

Bifunctionalized organosilica hollow nanospheres with bridging ethane group and protruding amine group have been successfully synthesized through prehydrolysis strategy using 3-(aminopropyl)triethoxysilane (APTES) and 1,2-bis(trimethoxysilyl)ethane (BTME) as precursor and F127 (EO 106PO 70EO 106) as a single micelle template in a neutral medium. It was found that prehydrolysis of BTME could efficiently decrease the interruption of amine group on the assembly process and result in the formation of uniform hollow nanospheres with particle size in 15–18 nm. This general synthetic strategy has been extended to the preparation of functionalized hollow nanospheres with different functional groups, such as N-propyl-4,5-dihydroimidzole and di-propyl-amine group. These amine-functionalized hollow nanospheres are efficient adsorbents for CO 2. The controlling experiments suggest that both the hollow structure and amine group are responsible for obtaining high CO 2 adsorption capacity.

Periodic organosilica hollow nanospheres as anode materials for lithium ion rechargeable batteries

Polymeric micelles with core-shell-corona architecture have been found to be the efficient colloidal templates for synthesis of periodic organosilica hollow nanospheres over a broad pH range from acidic to alkaline media. In alkaline medium, poly (styrene-b-[3-(methacryloylamino)propyl] trimethylammonium chloride-b-ethylene oxide) (PS-PMAPTAC-PEO) micelles yield benzene-silica hollow nanospheres with molecular scale periodicity of benzene groups in the shell domain of hollow particles. Whereas, an acidic medium (pH 4) produces diverse hollow particles with benzene, ethylene, and a mixture of ethylene and dipropyldisulfide bridging functionalities using poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-PVP-PEO) micelles. These hollow particles were thoroughly characterized by powder X-ray diffraction (XRD), dynamic light scattering (DLS), thermogravimetric analysis (TG/DTA), Fourier transformation infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), magic angle spinning-nuclear magnetic resonance ((29)Si MAS NMR and (13)CP-MAS NMR), Raman spectroscopy, and nitrogen adsorption/desorption analyses. The benzene-silica hollow nanospheres with molecular scale periodicity in the shell domain exhibit higher cycling performance of up to 300 cycles in lithium ion rechargeable batteries compared with micron-sized dense benzene-silica particles.

A General pH‐Responsive Supramolecular Nanovalve Based on Mesoporous Organosilica Hollow Nanospheres

Smart release on demand: A general pH-responsive supramolecular nanovalve operating in aqueous media has been designed by using mesoporous organosilica hollow nanospheres as nanocontainers (see picture). The nanovalve is capable of storing guest molecules within the hollow core and mesopore shell and releasing them on demand by acid/base triggering of the capping molecule, demonstrating a delicate vehicle for controlled release.

Tunable Assembly of Organosilica Hollow Nanospheres

Hollow nanospheres with a particle size of less than 25 nm have been successfully fabricated using an ethylene-, phenylene-, and 1,4-diethylphenylene-bridging silane precursor with F127 as a soft template under an acidic medium. As the size and flexibility of the bridging organic group increases, it is more and more difficult for the formation of hollow nanospheres. The organic additive, 1,3,5-trimethylbenzene, could finely tune the particle size of the nanosphere from 12 to 25 nm. It was found that silane precursors with hydrophobicity and slow hydrolysis rate favor the formation of hollow nanospheres and hydrophilic silane precursors such as tetramethoxysilane induce the formation of mesostructured bulk materials. Under the current synthesis conditions, carefully tuning the interaction between templates and silica species, organosilica hollow nanospheres with controlled composition can be successfully obtained.