Stabilization of Silica Gel against Hydrolysis by Doping with F^(-) or Zr(Ⅳ)

Silica gel (SG) was synthesized via acidification of sodium silicate solution then doped with Fˉ or Zr(IV) in molar ratios of F/Si 3/100, and Zr/Si 0.75/100 and 3.75/100 and sintered at 500°C, 800°C and 1000°C. The samples were investigated by X-ray diffractometry, infrared absorption and Raman spectra, surface area measurement, and inductively coupled plasma-optical emission spectrometry-monitored silica hydrolysis. All samples are mesoporous with BET surface areas 181.5 - 523.9 m2·gˉ1. The surface area of the silica samples decreases as the sintering temperature increases. The hydrolysis process of silica decreases as the sintering temperature increases and as the surface area decreases. The pH and the type of buffer solution affect the hydrolysis of silica samples due to a SN2 reaction mechanism favored in basic media using ammonia buffer. Zr(IV) increases the stability of silica samples against the hydrolysis as confirmed by the structural investigation, surface area and silica hydrolysis. Fˉ observably decreases the silica hydrolysis process when presenting on the surface of SG.

Hierarchical assemblies of molecular frameworks—MOF-on-MOF epitaxial heterostructures

Functional,porous metal-organic frameworks(MOFs)have attracted much attention as a very flexible class of crystalline,porous materials.For more advanced applications that exploit photophysical properties,the fabrication of hierarchical assemblies,including the creation of MOF/MOF heterointerfaces,is important.For the manufacturing of superstructures with length scales well beyond that of the MOF pore size,layer-by-layer(Ibl)methods are particularly attractive.These allow the isoreticular approach to be extended to superstructures with micrometer length scales,a range that is not accessible using conventional MOF design.The Ibl approach further substantially extends the compositional diversity in MOFs.At the same time,the favorable elastic properties of MOFs allow for heteroepitaxial growth,even in the case of lattice misfits as large as 20%.While the MOF-on-MOF approach to designing multicomponent superstructures with synergistic multifunctionality can also be realized with sophisticated solvothermal synthesis schemes,the Ibl(or liquid-phase epitaxy)approach carries substantial advantages,in particular when it comes to the integration of such MOF superstructures into optical or electronic devices.While the structure vertical to the substrate can be adjusted using the Ibl method,photolithographic methods can be used for lateral structuring.In this review,we will discuss the Ibl liquid-phase epitaxy approach to growing surface-anchored MOF thins films(SURMOFs)as well as other relevant one-pot synthesis methods for constructing such hierarchically designed structures and their emerging applications.

Continuous size fractionation of magnetic nanoparticles by using simulated moving bed chromatography

The size fractionation of magnetic nanoparticles is a technical problem,which until today can only be solved with great effort.Nevertheless,there is an important demand for nanoparticles with sharp size distributions,for example for medical technology or sensor technology.Using magnetic chromatography,we show a promising method for fractionation of magnetic nanoparticles with respect to their size and/or magnetic properties.This was achieved by passing magnetic nanoparticles through a packed bed of fine steel spheres with which they interact magnetically because single domain ferro-/ferrimagnetic nanoparticles show a spontaneous magnetization.Since the strength of this interaction is related to particle size,the principle is suitable for size fractionation.This concept was transferred into a continuous process in this work using a so-called simulated moving bed chromatography.Applying a suspension of magnetic nanoparticles within a size range from 20 to 120 nm,the process showed a separation sharpness of up to 0.52 with recovery rates of 100%.The continuous feed stream of magnetic nanoparticles could be fractionated with a space-time-yield of up to 5 mg/(L∙min).Due to the easy scalability of continuous chromatography,the process is a promising approach for the efficient fractionation of industrially relevant amounts of magnetic nanoparticles.

Surface-Oriented Assembly of Cyclodextrin Metal-Organic Framework Film for Enhanced Peptide-Enantiomers Sensing

Oriented metal-organic framework(MOF)films are attracting great attention due to their fascinating physicochemical properties and unique functionalities.Here,we report an[110]-oriented biomolecularγ-cyclodextrin(γCD)MOF film with arrayed CD channels running perpendicular to the substrate surface.This sophisticated architecturewas realized by combining liquid phase epitaxial layer-by-layer(lbl)methods with aγCD-based thiol self-assembled monolayer(SAM)functionalized surface.This first demonstration of the lbl method for MOF growth from aqueous conditions yielded oriented,highly homogeneous,and chiralγCD-SURMOFs(surfacecoordinated MOFs)with tunable thickness.Using a quartz crystal microbalance(QCM)to monitor adsorption of biomolecules,we demonstrated thatγCD-SURMOF provides highly-efficient recognition of tripeptide enantiomers(Tyr-(L-Ala)-Phe vs Tyr-(D-Ala)-Phe),clearly outperformingγCD(SH)_(8) SAMs as well as polycrystalline,mixed-orientationsγCDMOF film.The presence of well-alignedγCD-channels enables highly efficient transport channels with large adsorption capacity and fast loading,along with high enantioselectivity.In addition,the fast and highly specific loading rates allow for the realization of highly specific sensors for biomolecules with short response times.

Polymeric photonic molecule super-mode lasers on silicon

Optically coupled microcavities have emerged as photonic structures with promising properties for investigation of fundamental science as well as for applications.We report on the fabrication and spatially resolved spectroscopy of on-chip photonic molecule(PM)lasers consisting of two coupled,dye-doped polymeric microdisks on a silicon substrate.We investigate the fundamental lasing properties with focus on the spatial distribution of modes,the coupling dependent suppression of lasing modes,and in particular the application-oriented operation of these devices in aqueous environments.By depositing an additional polymer layer onto the lithographically structured cavities made of dye-doped poly(methyl methacrylate),coupling-gap widths below 150 nm with aspect ratios of the micro-/nanostructure exceeding 9:1 are achieved.This enables strong optical coupling at visible wavelengths despite relatively small resonator radii of 25 μm.The lasing properties of dye-doped PMs are investigated using spatially resolved micro-photoluminescence(μ-PL)spectroscopy.This technique allows for the direct imaging of whispering-gallery modes(WGMs)in the photonics molecules.For subwavelength coupling gaps,we observe lasing from delocalized eigenstates of the PMs(termed in the following as super-modes).Using size-mismatched cavities,the lasing mode suppression for different coupling-gap widths is investigated.We further demonstrate single-mode lasing operation in aqueous environments with PMs,which are realized on a low-cost,polymer-on-silicon platform.

Laser-induced hierarchical carbon patterns on polyimide substrates for flexible urea sensors

Thermochemical decomposition of organic materials under heat-treatment in the absence of oxygen,known as the pyrolysis process,is often employed to convert micro and nano patterned polymers into carbon structures,which are subsequently used as device components.Pyrolysis is performed at≥900℃,which entails substrate materials with a high thermal stability that excludes flexible,polymeric substrates.We use optimized laser radiation to pattern graphitic carbon structures onto commercially available polyimide(Kapton)sheets in the micrometer to millimeter scale by inducing a localized,rapid pyrolysis,for the fabrication of flexible devices.Resulting laser carbon films are electrically conductive and exhibit a high-surface area with a hierarchical porosity distribution along their cross-section.The material is obtained using various combinations of laser parameters and pyrolysis environment(oxygen-containing and inert).Extensive characterization of laser carbon is performed to understand the correlation between the material properties and laser parameters,primarily fluence and power.A photothermal carbonization mechanism based on the plume formation is proposed.Further,laser carbon is used for the fabrication of enzymatic,pH-based urea sensors using two approaches:(i)direct urease enzyme immobilization onto carbon and(ii)electrodeposition of an intermediate chitosan layer prior to urease immobilization.This flexible sensor is tested for quantitative urea detection down to 10^(−4) M concentrations,while a qualitative,color-indicative test is performed on a folded sensor placed inside a tube to demonstrate its compatibility with catheters.Laser carbon is suitable for a variety of other flexible electronics and sensors,can be conveniently integrated with an external circuitry,heating elements,and with other microfabrication techniques such as fluidic platforms.