Sol–gel synthesis of macro–mesoporous titania monoliths and their applications to chromatographic separation media for organophosphate compounds

Photocatalytic degradation-based ambient mass spectrometry imaging for enhancing detection coverage of poorly-ionizable lipidomes

Localization of lipidomes and tracking their spatial changes in tissues by mass spectrometry imaging (MSI) plays an important role in unveiling the mechanisms of living processes, diseases and therapeutic treatments. However, it is always challenging to achieve direct MSI of poorly-ionizable lipids, such as glycolipids and glycerolipids, due to the strong ion suppression and isobaric peaks interference from high-abundance phosphatidylcholines (PCs) in tissues. Here we developed a photocatalytic degradation-based ambient liquid extraction MSI method to largely enhance the detection coverage of poorly-ionizable lipids by rapid online removal of PCs in MSI. Phospholipids were found to be selectively photodegraded on TiO2 surface in acidic conditions in the presence of water under UV irradiation, while other poorly-ionizable lipids remained. Sulfate ion could largely improve the degradation efficiencies. Anatase nanoparticles-embedded TiO2 monolith was in-situ synthesized in the capillary of ambient liquid extraction system, and rapid online photodegradation of PCs was achieved during MSI with efficiency >80 %, largely reducing ion suppression. The pathway analysis showed that PC was oxidatively degraded starting from hydroxylation of C=C bonds. With intense UV irradiation, PCs were completely degraded into small molecules<200 Da without interference on the detection of endogenous lipids. With the new MSI method, detection coverage to cerebrosides, ceramides and diglycerides was enhanced by 2-9 times comparing with traditional MSI. Clearer localizations were observed for poorly-ionizable lipids via the new method than traditional method. Thus, this work provided a complementary MSI method for traditional MSI to address the issues on direct imaging of poorly ionizable lipids in ambient conditions.

Review of recent advances in development and applications of organic-silica hybrid monoliths

Organic-silica hybrid monoliths attracted attention as an alternative to extensively researched organic polymer-based and silica-based counterparts. The development and applications of these materials as extraction and separation media in capillary liquid chromatography and capillary electrochromatography were previously reviewed in several manuscripts. In this review, we will concentrate on work published since mid-2016 focusing on advances in their development using sol-gel chemistry of tetra- and trialkoxysilanes and subsequent surface modification with organic monomers, and "one-pot" strategy incorporating sol-gel chemistry of alkoxysilanes and free-radical polymerization, ring-opening polymerization, or thiol-based click polymerization with organic monomers. Approaches adapted to the preparation of hybrid monoliths made with polyhedral oligomeric silsesquioxanes will be covered as well.

Photocatalytic reactive liquid microjunction surface sampling-mass spectrometry for rapid and selective in-situ analysis of alpha-unsubstituted amine metabolites or drugs in brain tissue

In in-situ mass spectrometry (MS), different on-tissue derivatization methods have been developed to enhance the signals of poorly ionizable primary amines. However, those chemical derivatization methods are laborious and time-consuming, and are usually limited to detection of high-abundance amino acids which suppress the reaction of low-abundance monoamine neurotransmitters and drugs. Herein, A rapid and selective photocatalytic derivatization technique for alpha-unsubstituted primary amine was developed with 5-hydroxyindole as derivatization reagent and TiO₂ as photocatalyst, and was introduced into liquid microjunction surface sampling (LMJSS)-MS system as online derivatization. The results showed that the photocatalytic derivatization method largely enhanced the signals of primary amines by 5-300 fold, and were selective to alpha-unsubstituted primary amines. Thus, the suppression effects from high-abundance amino acids to the reaction of monoamine neurotransmitters and benzylamine drugs proved to be largely reduced in the new method (matrix effect>50%) comparing with those in chemical derivatization method (matrix effect<10%). In addition, the optimal pH of the derivatization reaction was measured to be 7, which indicates the mild and physiologically compatible reaction conditions. By in-situ synthesis of TiO₂ monolith in the transfer capillary of the LMJSS-MS system, rapid on-line photocatalytic derivatization was achieved and completed in 5 s during the transfer of sampling extract from the flow-probe to the MS inlet. With the new photocatalytic reactive LMJSS-MS method, detection limits of three primary amines on glass slides were in the range of 0.031-0.17 ng/mm² with acceptable linearity (r=0.9815-0.9998) and relatively high repeatability (relative standard deviations <22.1%). Finally, endogenous tyramine, serotonin, two dipeptides and one doped benzylamine drug were identified and in-situ analyzed in the mouse cerebrum by the new method with largely enhanced signals comparing with LMJSS-MS without online derivatization. The new method provides a more selective, rapid and automated way to analyze alpha-unsubstituted amine metabolites and drugs in-situ comparing with traditional methods.

Macroporosity Control by Phase Separation in Sol-Gel Derived Monoliths and Microspheres

Macroporous and hierarchically macro/mesoporous materials (mostly monoliths and microspheres) have attracted much attention for a variety of applications, such as supporting or enabling materials in chromatography, energy storage and conversion, catalysis, biomedical devices, drug delivery systems, and environmental remediation. A well-succeeded method to obtain these tailored porous materials relies on the sol-gel technique, combined with phase separation by spinodal decomposition, and involves as well emulsification as a soft template, in the case of the synthesis of porous microspheres. Significant advancements have been witnessed, in terms of synthesis methodologies optimized either for the use of alkoxides or metal-salts and material design, including the grafting or immobilization of a specific species (or nanoparticles) to enable the most recent trends in technological applications, such as photocatalysis. In this context, the evolution, in terms of material composition and synthesis strategies, is discussed in a concerted fashion in this review, with the goal of inspiring new improvements and breakthroughs in the framework of porous materials.

Preparation of monolithic polymer-magnetite nanoparticle composites into poly(ethylene-co-tetrafluoroethylene) tubes for uses in micro-bore HPLC separation and extraction of phosphorylated compounds

This paper describes the fabrication of a novel microbore monolithic column modified with magnetite nanoparticles (MNPs) prepared in a poly(ethylene-co-tetrafluoroethylene) (EFTE) tubing, and its application as stationary phase for the chromatographic separation of phosphorylated compounds. In order to obtain the composite column, a two-step procedure was performed. The formation of a glycidyl methacrylate-based monolith inside the activated ETFE tube was firstly carried out. Then, two incorporation approaches of MNPs in monoliths were investigated. The generic polymer was modified with 3-aminopropyltrimethoxysilane (APTMS) to be subsequently attached to MNP surfaces. Alternatively, APTMS-coated MNPs were firstly prepared and subsequently used for attachment onto the monolith surface through reaction of epoxy groups present in the generic monolith. This last strategy gave a reproducible layer of MNPs coated onto the polymer monolith as well as robust and permeable chromatographic columns. The retention behaviour of this MNP-based composite monolithic column was studied by using small phosphorylated compounds (adenosine phosphates). It was found that the retention of model analytes was ruled by partitioning and adsorption HILIC mechanisms. The columns also exhibited satisfactory performance in the separation of these target compounds, showing good chromatographic behaviour after two months of continued use. These composite monolithic columns were also successfully applied to the extraction of a tryptic digest of β-casein.

Designed Fabrication of Polymer-Mediated MOF-Derived Magnetic Hollow Carbon Nanocages for Specific Isolation of Bovine Hemoglobin

It is highly required to develop well-designed separation materials for the specific isolation of certain proteins in proteomic research. Herein, the new type of metal-organic framework (MOF)-derived polymer-mediated magnetic hollow nanocages was fabricated via stress-induced orientation contraction, which was further applied for specific enrichment of proteins. The core-shell nanocomposites comprised of polymer-mediated ZIF-67 cores and polydopamine (PDA) shells, after annealing, generated magnetic hollow carbon nanocages with hierarchical pores and structures. Particularly, the magnetic carbonized PDA@F127/ZIF-67 hollow nanocages exhibited a remarkable adsorption capacity toward bovine hemoglobin (BHB) up to 834.3 mg g^-1, which was significantly greater than that of the directed carbonized ZIF-67 nanoparticles. The results also exhibited the notable specificity of the obtained nanocages on complex biosamples, including intact mixed proteins and fetal calf serum. The hierarchically hollow porous structure greatly improves the specific surface area and reduces the mass transfer resistance, leading to enhanced high adsorption for target protein BHB. This novel method will be promising for the applications in purification and enrichment of biomacromolecules for complex biosamples, which successfully solve the problem of low adsorption efficiency and tedious separating process of the previous MOF-derived materials.

Thiol-ene polymerization for hierarchically porous hybrid materials by adding degradable polycaprolactone for adsorption of bisphenol A

Hierarchically porous materials with multiple pore structures have the potential application in catalysis, separation or bioengineering. A concept was introduced to design and fabricate hierarchically porous hybrid materials (HPHMs) simultaneously containing mesopores and macropores. The proof-of-concept design was demonstrated by fabrication of several kinds of hybrid materials by adding degradable polycaprolactone (PCL) additive, which was simple and easy-operating. The specific surface areas of HPHMs prepared with polyhedral oligomeric vinylsilsesquioxanes (vinylPOSS) and 1,4-dithiothreitol (DTT) could reach 727 m²/g by adding 25% PCL additive, while the HPHMs were imperforate prior to degradation of PCL. The characterization further indicated that the macropores could be controlled by the amount of PCL additive. Moreover, the porous properties of HPHMs were influenced by the molecular weight of PCL. Other dithiols compounds were also successful in preparing HPHMs with high specific surface areas over 400 m²/g. Due to hydrophobic interaction and hydrogen bond interaction, the HPHM exhibited good adsorption ability for bisphenol A (BPA) in aqueous solution. Adsorption equilibrium could be achieved within 30 min, and the adsorption capacity was up to 157.4 mg/g. Meanwhile, the removal efficiency was found to be 95.37% for BPA.

Independent Tailoring of Macropore and Mesopore Space in TiO2 Monoliths

TiO₂ monoliths were synthesized by a partially hindered sol-gel process. Various synthesis parameters like precursor concentrations and gelation temperature were varied to investigate changes in the macroporosity (being in the range of micrometers) and to determine influences on the macropore formation mechanism. Ionic liquids (ILs) were used as templates to vary the mesopore size independently from the macropore size. Depending on the synthesis parameters, TiO₂ monoliths with exclusive mesoporosity or with hierarchical meso-/macropore structure were received, and the range of macropores can be shifted between 100 nm and 10 μm without influencing the mesopore diameter. Pore volumes up to 880 mm³/g were achieved, as determined by mercury intrusion porosimetry. The mesopores' diameter can be adjusted between 6 and 25 nm by adding different amounts of IL, and surface areas up to 260 m²/g and mesopore volumes of 0.5 cm³/g were obtained, based on N₂-physisorption measurements. The monoliths were cladded by polymer, allowing for studying the flow-through properties depending on the macropore size. This precise control for tailored macropores enables the design of optimized TiO₂ monoliths with respect to the desired application requirements.

Low-Temperature Continuous-Flow Dehydration of Xylose Over Water-Tolerant Niobia-Titania Heterogeneous Catalysts

The sustainable conversion of vegetable biomass-derived feeds to useful chemicals requires innovative routes meeting environmental and economical criteria. The approach herein pursued is the synthesis of water-tolerant, unconventional solid acid monolithic catalysts based on a mixed niobia-titania skeleton building up a hierarchical open-cell network of meso- and macropores, and tailored for use under continuous-flow conditions. The materials were characterized by spectroscopic, microscopy, and diffraction techniques, showing a reproducible isotropic structure and an increasing Lewis/Brønsted acid sites ratio with increasing Nb content. The catalytic dehydration reaction of xylose to furfural was investigated as a representative application. The efficiency of the catalyst was found to be dramatically affected by the niobia content in the titania lattice. The presence of as low as 2 wt % niobium resulted in the highest furfural yield at 140 °C under continuous-flow conditions, by using H₂ O/γ-valerolactone as a safe monophasic solvent system. The interception of a transient 2,5-anhydroxylose species suggested the dehydration process occurs via a cyclic intermediates mechanism. The catalytic activity and the formation of the anhydro intermediate were related to the Lewis acid sites (LAS)/Brønsted acid sites (BAS) ratio and indicated a significant contribution of xylose-xylulose isomerization. No significant catalyst deactivation was observed over 4 days usage.

Sol-gel synthesis of monolithic materials with hierarchical porosity

The development of synthetic routes to hierarchically organized porous materials containing multiple, discrete sets of pores having disparate length scales is of high interest for a wide range of applications. One possible route towards the formation of multilevel porous architectures relies on the processing of condensable, network forming precursors (sol-gel processes) in the presence of molecular porogens, lyotropic mesophases, supramolecular architectures, emulsions, organic polymers, or ice. In this review the focus is on sol-gel processing of inorganic and organic precursors with concurrently occurring microscopic and/or macroscopic phase separation for the formation of self-supporting monoliths. The potential and the limitations of the solution-based approaches is presented with special emphasis to recent examples of hierarchically organized silica, metal oxides and phosphates as well as carbon monoliths.

Facile Preparation of Titanium(IV)-Immobilized Hierarchically Porous Hybrid Monoliths

Hierarchically porous materials have become a key feature of biological materials and have been widely applied for adsorption or catalysis. Herein, we presented a new approach to directly prepare a phosphate-functionalized hierarchically porous hybrid monolith (HPHM), which simultaneously contained mesopores and macropores. The design was based on the copolymerization of polyhedral oligomeric vinylsilsesquioxanes (vinylPOSS) and vinylphosphonic acid (VPA) by adding degradable polycaprolactone (PCL) additive. The phosphate groups could be directly introduced into the hybrid monoliths. This approach was simple and time-saving, and overcame the defect of a rigorous, complex process for preparing traditional Ti⁴⁺-immobilized metal ion affinity chromatography (IMAC) materials. The specific surface area of an optimal hybrid monolith could reach 502 m²/g obtained by nitrogen adsorption/desorption measurements, which originated from the degradation of PCL. Meanwhile, the characterization of scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) also suggested that the macropores existed in the hybrid monoliths. The size of macropores could be controlled by the content of PCL in the polymerization mixture. The prepared Ti⁴⁺-IMAC HPHMs exhibited high adsorption capacity (63.6 mg/g for pyridocal 5'-phosphatemonohydrate), and excellent enrichment specificity (tryptic digest of β-casein/BSA at a molar ratio of 1:1000) and sensitivity (tryptic digest of 5 fmol of β-casein). Moreover, the Ti⁴⁺-IMAC HPHMs provided effective enrichment ability of low-abundance phosphopeptides from human serum and HeLa cell digests.

In situ preparation of oxygen-deficient TiO2 microspheres with modified {001} facets for enhanced photocatalytic activity

A facile in situ synthetic strategy has been developed to prepare highly active oxygen-deficient anatase TiO₂ microspheres single crystal with modified {001} faceted by simply controlling the hydrothermal reaction time.

Hierarchically porous materials: synthesis strategies and structure design

This review addresses recent advances in synthesis strategies of hierarchically porous materials and their structural design from micro-, meso- to macro-length scale.

High surface area hierarchical porous Al2O3 prepared by the integration of sol–gel transition and phase separation

Mechanism of gelation process and phase separation for production of hierarchical porous alumina with high surface area.

Applications of hierarchically structured porous materials from energy storage and conversion, catalysis, photocatalysis, adsorption, separation, and sensing to biomedicine

A comprehensive review of the recent progress in the applications of hierarchically structured porous materials is given.

Binder-Free TiO2 Monolith-Packed Pipette Tips for the Enrichment of Phosphorylated Peptides

A macroporous TiO2 monolith-entrapped pipette-tip was developed through a binder-free packing method for convenient phosphorylated peptide enrichment. A detection limit of 1 ng mL–1 for phosphorylated peptide is achieved, showing a better enrichment efficiency compared with the commercial pure TiO2-embedded NuTip.

Preparation of silver nanoparticles embedded hierarchically porous AlPO4 monoliths

Silver nanoparticles were homogenously embedded on the skeletons of hierarchically porous AlPO₄ by immersing the monoliths in a silver colloid.

Features of silicon– and titanium–polyethylene glycol precursors in sol–gel synthesis of new hydrogels

The formation of organic/inorganic hydrogels based on silicon and titanium polyethylene glycolates, new biocompatible water-soluble precursors in sol–gel processing, was investigated.

Synthesis of a SiO2/TiO2 hybrid boronate affinity monolithic column for specific capture of glycoproteins under neutral conditions

A unique boronate-functionalized SiO₂/TiO₂ hybrid monolithic column was synthesized by a facile approach. The monolith exhibited specific capacity to capture glycoproteins and antibodies in aqueous solution at neutral pH.

Preparation and photocatalytic activity of robust titania monoliths for water remediation

TiO(2) monoliths were prepared, characterized, and evaluated for photocatalytic performance. The TiO(2) monoliths were found to have an interconnected void lattice and a bimodal porous structure with macropores and mesopores after calcination at 500-700 °C. Monoliths calcined at 500 °C had high specific surface area (93.1 m(2)/g) and porosity (68%), which were maintained after calcination at 700-1100 °C (51-46%). The calcined monoliths had relatively high Vickers hardness (∼104) despite their porous structure. Monoliths calcined at 500 and 700 °C exhibited high performance for methylene blue decolorization because of their high specific surface area.

Mesostructured silica containing conjugated polymers formed within the channels of anodic alumina membranes from tetrahydrofuran-based solution

The synthesis of mesostructured silica from a tetrahydrofuran (THF)-based sol gel was carried out in the channels of an anodic alumina membrane (AAM) using the evaporation-induced self-assembly (EISA) method. Two different nonionic surfactants were used as structure-directing agents, the triblock copolymer Pluronic P123 and the oligomer surfactant Brij56. The effect of the relative humidity and surfactant concentration on the type of mesophase and orientation of the in-channel mesostructures was studied using transmission electron microscopy (TEM) and grazing incidence small angel X-ray scattering (GISAXS). The in-channel structures obtained in this study were primarily of the 2D hexagonal phase with a circular orientation in which the hexagonally packed cylinders form a spiral-like shape from the channel wall inward. In addition, a columnar orientation of the hexagonal phase, in which the axes of the hexagonally packed cylinders are oriented parallel to the channel axes, was also observed. Finally, the use of the THF-based synthesis allowed the in situ incorporation of the highly hydrophobic yellow-emitting conjugated polymer poly[9,9-dioctylfluorene-co-benzothiadiazole] into the in-channel mesostructure upon its formation. The conjugated polymer was well distributed within the mesostructure and maintained its optical properties.

Evolution of Mesopores in Monolithic Macroporous Ethylene-Bridged Polysilsesquioxane Gels Incorporated with Nonionic Surfactant

By combining the micellar templating in nanometer scale with the polymerization-induced phase separation in micrometer scale, ethylene-bridged polysilsesquioxane gels with hierarchical macropores and mesopores are prepared. The difference of mesopore structures depending on the method of the solvent removal has been observed by the X-ray diffraction and the nitrogen adsorption-desorption measurements. During the hydrothermal treatment under the basic condition, the reorganization of the polysilsesquioxane gel network occurred differently depending on the alkoxy group contained in the precursors. From29Si CP/MAS NMR measurements, it was revealed that the crosslinking density of the hydrothermally treated gels was increased so that the highly ordered mesostructure of the wet gel could be preserved even after the evaporative drying of solvent.

Hierarchically porous titania thin film prepared by controlled phase separation and surfactant templating

Poly(propylene glycol) (PPG) of moderately high molecular weight (M(n) = 3500 Da) exhibits amphibious behavior in aqueous solution in that it is hydrophilic at low temperature but hydrophobic at high temperature. This property is utilized to generate porous titania thin films with a hierarchical structure consisting of macroporous voids/cracks in films with mesoporous walls. The smaller mesopores result from the self-assembly of the Pluronic block copolymer P123 to form micellar templates in well-ordered arrays with hexagonal symmetry. The larger pores are generated from the phase separation of PPG during aging of the films. The PPG acts to a limited degree as a swelling agent for the P123 micelles, but because the films are aged at a low temperature where PPG is hydrophilic, much of the PPG remains in the polar titania phase. Upon heating, the PPG phase separates to form randomly dispersed, large pores throughout the film while retaining the ordered mesoporous P123-templated structure in the matrix of the material. TEM and SEM imaging confirm that calcined titania thin films have interconnected hierarchical porous structures consisting of ordered mesopores 4-12 nm in diameter and macroporous voids >100 nm in size. The density and size of the voids increase as more PPG is added to the films.

In situ sol-gel preparation of porous alumina monoliths for chromatographic separations of adenosine phosphates

A method enabling the in situ preparation of porous alumina monoliths within 100 μm i.d. fused silica capillaries has been developed. These monoliths were prepared using the sol-gel process from a mixture consisting of an inorganic aluminum salt, a porogen, an epoxide, and a solvent. We investigated the effects of varying the preparation conditions on the physical characteristics of the monoliths with respect to their potential application in chromatographic separations. The best columns were obtained from a mixture of aluminum chloride hexahydrate, N,N-dimethylformamide, water, ethanol and propylene oxide. Adenosine phosphates were then separated in the optimized column with retention increasing according to number of phosphate functionalities.

Application of liquid phase deposited titania nanoparticles on silica spheres to phosphopeptide enrichment and high performance liquid chromatography packings

A novel core-shell composite (SiO(2)-nLPD), consisting of micrometer-sized silica spheres as a core and nanometer titania particles as a surface coating, was prepared by liquid phase deposition (LPD). Here, we show the resulting core-shell composite to have better efficient and selective enrichment for mono- and multi-phosphopeptides than commercially available TiO(2) spheres without any enhancer. The material exhibited favorable characteristics for HPLC, which include narrow pore size distribution, high surface area and pore volume. We also show that the core-shell composite can efficiently separate adenosine phosphate compounds due to the Lewis acid-base interaction between titania and phosphate group when used as HPLC packings. After coating the silica sphere with titania by LPD, the silanol of silica spheres will be shielded and that the stationary phase, C(18) bonded SiO(2)-3LPD, could be used under extreme pH condition.

Solid-solid interface formation in TiO2 nanoparticle networks

Aiming at a comparison of microstructure and paramagnetic properties of mesoporous TiO(2) nanoparticle networks, we subjected entirely different TiO(2-x) precursor structures to vacuum annealing. The transformation of an amorphous TiO(2-x) gel--obtained by sol-gel processing of an ethylene glycol-modified titanium precursor--into a network of interconnected anatase nanocrystals was explored by means of X-ray diffraction, nitrogen sorption, and electron microscopy. Crystalline junctions between the particles emerge from temperature treatment. This process of particle network formation is different from that related to the vapor phase grown anatase nanocrystals where particle-particle interface formation is induced by contact with water. It was found that, after annealing up to 873 K and controlled sample purification in oxygen atmosphere, both types of samples exhibit high concentrations of particle-particle interfaces and comparable properties in terms of surface area, porosity, and microstructure. With electron paramagnetic resonance (EPR) we observed on nonstoichiometric TiO(2-x) networks an identical type of subsurface defect which is related to the presence of solid-solid interfaces.

Capillary monolithic titania column for miniaturized liquid chromatography and extraction of organo-phosphorous compounds

A new sol-gel protocol was designed and optimized to produce titanium-dioxide-based columns within confined geometries such as monolithic capillary columns and porous-layer open-tubular columns. A surface pre-treatment of the capillary enabled an efficient anchorage of the monolith to the silica capillary wall during the synthesis. The monolith was further synthesized from a solution containing titanium n-propoxide, hydrochloric acid, N-methylformamide, water, and poly(ethylene oxide) as pore template. The chromatographic application of capillary titania-based columns was demonstrated with the separation of a set of phosphorylated nucleotides as probe molecules using aqueous normal-phase liquid chromatography conditions. Capillary titania monoliths offered a compromise between the high permeability and the important loading capacity needed to potentially achieve miniaturized sample preparations. The specificity of the miniaturized titania monolithic support is illustrated with the specific enrichment of 5'-adenosine mono-phosphate. The monolithic column offered a ten times higher loading capacity of 5'-adenosine mono-phosphate compared with that of the capillary titania porous-layer open-tubular geometry.