Designed synthesis of mesoporous solids via nonionic-surfactant-templating approach

The continual needs for improved performances in applications derived by diversified compositions and mesostructures have pushed forward the development of mesoporous solids. The nonionic-surfactant-templating approach has been a critical route in this advancement. A large number of nonionic surfactants widely used in industries and featured with low cost, low toxicity, bio-degradation and ordered microdomains can be utilized as effective templates to the design and synthesis of abundant mesoporous solids. This feature article provides recent reports on the use of nonionic surfactant self-assembly as examples to fabricate high-quality ordered mesoporous solids which illustrates advances in synthesis and understanding of formation mechanisms. It includes the selection of surfactants, a summary of the effects of synthetic parameters, the current understanding of the synthetic pathways and related mechanisms with some emphasis on evaporation induced self-assembly (EISA), as well as the design and synthesis on the microscale (atomic and molecular compositions) and mesoscale (mesostructures). Preliminary applications of mesoporous solids particularly in optical devices, electrodes and biomaterials are also presented.     

DNA-conjugated polymers for self-assembled DNA chip fabrication.

We developed two DNA-conjugated polymers, one based on polyallylamine and the other on polyacrylic acid, for use in DNA chips. A 30-mer single-stranded DNA probe and thioctic acid were covalently attached to polyallylamine as sidechains. The same single-stranded DNA and 3-(pyridyldithio)propionyl hydrazide were covalently attached to polyacrylic acid as sidechains. Both DNA-conjugated polymers could be specifically immobilized onto a gold sensor substrate by a self-assembly technique. The interactions between fully matched DNA and each DNA-conjugated polymer were investigated by surface plasmon resonance. A gold surface modified with either DNA-conjugated polymer recognized fully matched DNA much better than unmatched DNA. The hybridization selectivity and efficiency of DNA-conjugated polyallylamine was optimized by adjusting the pH so as to reduce the effects of cationic polymer sidechains. The hybridization selectivity and efficiency of DNA-conjugated polymers were higher than those of a conventional immobilized thiol-based DNA. The coating of DNA-conjugated polymers reduced nonspecific adsorption of DNA by the gold substrate. DNA-conjugated polyacrylic acid was more selective toward fully matched DNA than was DNA-conjugated polyallylamine. Therefore, DNA-conjugated polymers show promise for application in novel DNA chips.     

Sonochemical fabrication of fluorinated mesoporous titanium dioxide microspheres

A sonochemical-hydrothermal method for preparing fluorinated mesoporous TiO₂ microspheres was developed. Formation of mesoporous TiO₂ and doping of fluorine was achieved by sonication and then hydrothermal treatment of a solution containing titanium isopropoxide, template, and sodium fluoride. The as-synthesized TiO₂ microspheres were characterized by X-ray diffraction (XRD), Fourier translation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, photoluminescence spectroscopy (PL), and BET surface areas. The P123 template was removed completely during the hydrothermal and washing steps, which was different from the conventional calcination treatment. The as- synthesized TiO₂ microspheres had good crystallinity and high stability. Results from the photocatalytic degradation of methylene blue (MB) showed that fluorination could remarkably improve the photocatalytic activity of titanium dioxide.     

Precise fabrication of point defects in self-assembled three-dimensional macroporous photonic crystals

We demonstrate a new and simple method of precisely fabricating defects in three-dimensional (3D) CdS macroporous photonic crystals (PCs) with a variable pressure scanning electron microscope. Well-defined point defects, not only vacancies but also an impurity (a reduced-size sphere), were directly fabricated by electron-beam irradiation under a gas atmosphere. This provides a convenient and straightforward method of introducing various designed defects into 3D PCs for photonic-band-gap-based applications.     

孔壁富含微孔有序介孔材料的设计合成及表征

通过调节水热处理溶液的酸度和温度,进而调控材料孔壁上硅羟基与模板剂的相互作用以及模板剂亲水嵌段嵌入到孔壁内的量,制备出了墙壁富含微孔的有序介孔材料SBA-15.氮气吸附测试表明,当水热处理溶液的pH值和温度分别为2.2和100℃时,经300℃焙烧脱除模板剂后的样品具有较高的微孔含量,其微孔体积为0.176cm3/g,占总孔体积的21.6%.     

FeOOH-loaded mesoporous silica nanoparticles as a theranostic platform with pH-responsive MRI contrast enhancement and drug release

The development of stimuli-responsive theranostic platforms is of great demand for efficient cancer treatment because they can enhance diagnostic specificity and sensitivity.In this work,we report a p H-responsive theranostic nanoplatform based on Fe OOH clusters loaded mesoporous silica nanoparticles(Fe@MSNs).The as-synthesized Fe@MSNs possess activatable T_1magnetic resonance imaging(MRI)performance that can respond to the acidic microenvironment of solid tumor to turn on T_1singals by releasing paramagnetic Fe~(3+)ions.The Fe@MSNs are biocompatible without appreciable cytotoxicity.Moreover,the unique mesoporous structure endows the Fe@MSNs with significant advantages to effectively deliver chemotherapeutic drug for inhibiting the growth of solid tumor.We believe that this novel p H-responsive theranostic nanoplatform holds great promise in cancer treatment.     

Synthesis and characterization of functionalized silicon phthalocyanines for fabrication of self-assembled monolayers

Novel octasubstituted phthalocyanine derivatives XYSiPc(OR)₈ (X=alkyl, Y=alkoxy, R=alkane or alkene) were synthesized by reaction of alkoxy-substituted diiminoisoindolines with XSiCl₃ followed by quenching with an alcohol YOH. Three synthetic routes for adding anchoring groups to the phthalocyanines were explored: variation of the axial groups X and Y, or incorporation of vinyl groups around the periphery of the phthalocyanine ring. The latter approach yielded silicon and copper phthalocyanines with eight terminal vinyl groups, which reacted cleanly with thioacetic acid/AIBN to give products with eight protected terminal thiols.     

Water-assisted fabrication of aligned microsized carbon tubes made of self-assembled multi-wall carbon nanotubes

Aligned micro-sized carbon tubes have been successfully synthesized on silicon substrate by pyrolysis of cyclohexane/ferrocene in the presence of water, a spectacular feature of which is that the multi-wall carbon nanotubes formed in situ act as the basic building blocks for the construction of micro-tubes via a "multi-scale" self-assembly process.     

Nanometer-thick conformal pore sealing of self-assembled mesoporous silica by plasma-assisted atomic layer deposition

On a porous substrate, regular atomic layer deposition (ALD) not only takes place on top of the substrate but also penetrates into the internal porosity. Here we report a plasma-assisted process in which the ALD precursors are chosen to be nonreactive unless triggered by plasma, so that ALD can be spatially defined by the supply of plasma irradiation. Since plasma cannot penetrate within the internal porosity, ALD has been successfully confined to the immediate surface. This not only gives a possible solution for sealing of porous low dielectric constant films with a conformal layer of nm-scale thickness but also enables us to progressively reduce the pore size of mesoporous materials in a sub-A/cycle fashion for membrane formation.     

A new route to self-assembled tin dioxide nanospheres: fabrication and characterization

Nearly monodispersed self-assembled tin dioxide (SnO2) nanospheres with intense photoluminescence (PL) were synthesized using a new wet chemistry technique. Instead of coprecipitating stannous salts, bulk tin (Sn) metal was oxidized at room temperature in a solution of hydrogen peroxide and deionized water containing polyvinylpyrrolidone (PVP) and ethylenediamine (EDA). SnO2 nanocrystals were produced with diameters of approximately 3.8 nm that spontaneously self-assembled into uniform SnO2 nanospheres with diameters of approximately 30 nm. Analysis was performed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-vis absorption spectroscopy, PL spectroscopy, and fluorescence lifetime measurements. The SnO2 nanospheres displayed room-temperature purple luminescence with an intense band at 394 nm (approximately 3.15 eV) and a high quantum yield of approximately 15%, likely as a result of emission from the surface states of SnO2/PVP complexes. The present study could open a new avenue to large-scale synthesis of self-assembled functional oxide nanostructures with technological applications as purple emitters, biological labels, gas sensors, lithium batteries, and dye-sensitized solar cells.     

One-step fabrication of ultralow dielectric polyimide films consisting of size-controlled mesoporous nanoparticles

Dielectric materials with ultralow dielectric constants (<2.0) are desiderated in the integrated circuits (ICs). In this work, we fabricated polyimide (PI) films consisting of mesoporous nanoparticles (MPNPs-PF) through a one-step solvent evaporation induced self-assembly method. Poly(amic acid) was selected as the polymer matrix; and the commercial triblock copolymer F127 was adopted as the mesoporous template as well as the nanoparticle morphology controller, respectively. After imidization and template removal, the dense films consisting of closed-packed PI nanoparticles with an average diameter less than 50 nm were obtained. Since the nanoparticles were fully composed of worm-like mesopores, the dielectric constant (k value) of the resultant porous PI films can reach as low as 1.92. When the reactive end-capper of maleic anhydride (MA) was blended into poly(amic acid), k value decreased even lower to 1.86. Meanwhile, the modulus of the resultant porous PI films was higher than 1 GPa.     

Study on the fabrication and photovoltaic property of TiO2 mesoporous microspheres

Titanium dioxide mesoporous microspheres with high surface area was successfully prepared by a facile one-step hydrothermal approach using polyethylene glycol (PEG, MW 200) as the soft template. Study shows that ∼15 nm TiO₂ nanoparticles was assembled into ∼1.1 μm mesoporous microspheres. The Brunauer-Emmett-Teller surface area of TiO₂ microsphere is up to 137 m²/g. TiO₂ mesoporous microspheres were fabricated onto the surface of fluorine-doped tin oxide glass and used as the photoanode of dye-sensitized solar cells, which exhibits an open circuit photovoltage of 0.80 V and an overall conversion efficiency of 6.6%. Owing to the enhanced dye loading and light-harvesting efficiency, a 26% improvement in the overall conversion efficiency was achieved when compared with the commercial Degussa P₂₅ nanoparticles.     

Facile fabrication of mesoporous manganese oxides as advanced electrode materials for supercapacitors

Mesoporous manganese oxides (MnO₂) were synthesized via a facile chemical deposition strategy. Three kinds of basic precipitants including sodium carbonate (Na₂CO₃), sodium bicarbonate (NaHCO₃), and sodium hydroxide (NaOH) were employed to adjust the microstructures and surface morphologies of MnO₂ materials. The obtained MnO₂ materials display different microstructures. Great differences are observed in their specific surface area and porosity properties. The microstructures and surface morphologies characteristics of MnO₂ materials largely determine their pseudocapacitive behavior for supercapacitors. The MnO₂ prepared with Na₂CO₃ precipitant exhibits the optimal microstructures and surface morphologies compared with the other two samples, contributing to their best electrochemical performances for supercapacitors when conducted either in the single electrode tests or in the capacitor measurements. The optimal MnO₂ electrode exhibits a high specific capacitance (173 F g^–1 at 0.25 A g^?1), high-rate capability (123 F g^?1 at 4 A g^?1), and excellent cyclic stability (no capacitance loss after 5,000 cycles at 1 A g^?1). The optimal activated carbon//MnO₂ hybrid capacitor exhibits a wide working voltage (1.8 V), high-power and high-energy densities (1,734 W kg^?1 and 20.9 Wh kg^?1), and excellent cycling behavior (93.8 % capacitance retention after 10,000 cycles at 1 A g^?1), indicating the promising applications of the easily fabricated mesoporous MnO₂ for supercapacitors.     

Voltammetric analysis of europium at screen-printed electrodes modified with salicylamide self-assembled on mesoporous silica

Mercury-free sensors for europium (Eu(3+)) assay based on the chemical modification of screen-printed carbon electrodes (SPCEs) with self-assembled salicylamide on mesoporous silica (Sal-SAMMS) have been developed. The preconcentration of Eu(3+) at SAMMS-based sensors utilizes the binding affinity of the salicylamide and Eu(3+), accomplished at open circuit potential without electrolyte and solution de-gassing. Optimal Eu detection was obtained after 3-5 min preconcentration in Eu solution (pH 2-6), electrolysis at -0.9 V for 60 s in a new medium (0.1-0.2 M NH(4)Cl, pH 3.5), followed by a square-wave voltammetric detection of Eu in the same electrolyte. Attributed to the strong covalent bonding of the functional groups on mesoporous silica and silane cross-linking, the SAMMS-modified SPCEs with a built-in 3-electrode system can be re-used for tens of measurements with minimal degradation, enabling the establishment of the calibration curve and lowering the costs. A linear calibration curve was found in the range of 75 to at least 500 ppb Eu(3+) after 5 min preconcentration. The experimental detection limit was 10 ppb after 10 min preconcentration, which can be improved with increased preconcentration time. Reproducibility (% RSD) of 100 ppb Eu(2+) was 10% for a single sensor and 10% for 5 sensors, which can be improved through the precision of sensor manufacturing, in which SAMMS modification can be made in-situ.     

A simple approach to sensor discovery and fabrication on self-assembled monolayers on glass

Self-assembled monolayers (SAMs) on glass were used as a platform to sequentially deposit fluorophores and small molecules for ion sensing. The preorganization provided by the surface avoids the need for complex receptor design, allowing for a combinatorial approach to sensing systems based on small molecules. The resulting libraries are easily measured and show varied responses to a series of both cations and anions. This technology is transferable from the macro- to the microscale both via microcontact printing (microCP), where the fluorophore is printed onto a glass surface, and via direct attachment of the fluorophore to microchannel walls. The ease of miniaturization of this technology may make the generation of a wide variety of simple yet efficient microarrays possible.     

Gold nanoparticles chemisorbed by a terphenyldithiol self-assembled monolayer for fabrication of a protein biosensor

In this study, improved detection of bovine serum albumin (BSA) was achieved by use of a fabricated surface plasmon resonance (SPR) biosensor. Terphenyldithiol (TPDT) was self-assembled on a gold substrate, then gold nanoparticles (Au-NPs) were chemisorbed on to the TPDT monolayer by strong bonding with the terminal thiol groups of the TPDT. The new sensor obtained was tested for immobilization of protein. The SPR results revealed much better detection of BSA by Au-NPs chemisorbed on the TPDT self-assembled monolayer (SAM) than by the bare SAM on the gold substrate.