Modified zeolitic imidazolate framework-8 as solid-phase microextraction Arrow coating for sampling of amines in wastewater and food samples followed by gas chromatography-mass spectrometry

In this study, a novel solid phase microextration (SPME) Arrow was prepared for the sampling of volatile low molecular weight alkylamines (trimethylamine (TMA) and triethylamine (TEA)) in wastewater, salmon and mushroom samples before gas chromatographic separation with mass spectrometer as detector. Acidified zeolitic imidazolate framework-8 (A-ZIF-8) was utilized as adsorbent and poly(vinyl chloride) (PVC) as the adhesive. The custom SPME Arrow was fabricated via a physical adhesion: (1) ZIF-8 particles were suspended in a mixture of tetrahydrofuran (THF) and PVC to form a homogeneous suspension, (2) a non-coated stainless steel SPME Arrow was dipped in the ZIF-8/PVC suspension for several times to obtain a uniform and thick coating, (3) the pore size of ZIF-8 was modified by headspace exposure to hydrochloric acid in order to increase the extraction efficiency for amines. The effect of ZIF-8 concentration in PVC solution, dipping cycles and aging temperature on extraction efficiency was investigated. In addition, sampling parameters such as NaCI concentration, sample volume, extraction time, potassium hydroxide concentration, desorption temperature and desorption time were optimized. The Arrow-to-Arrow reproducibilities (RSDs) for five ZIF-8 coated Arrows were 15.6% and 13.3% for TMA and TEA, respectively. The extraction with A-ZIF-8/PVC Arrow was highly reproducible for at least 130 cycles without noticeable decrease of performance (RSD < 12.5%). Headspace SPME of 7.5 mL sample solution with the fabricated ZIF-8 coated Arrow achieved linear ranges of 1-200 ngmL(-1) for both TMA and TEA. The limit of quantitation (LOQ) was 1 ng mL(-1) for both TMA and TEA. The method was successfully applied to the determination of TMA and TEA in wastewater, salmon and mushroom samples giving satisfactory selectivity towards the studied amines.Peer reviewe

Metal oxides prepared through the nanocasting approach-mechanistic study, surface interactions and applications in separation

Mesoporous metal oxides are nowadays widely used in various technological applications, for instance in catalysis, biomolecular separations and drug delivery. A popular technique used to synthesize mesoporous metal oxides is the nanocasting process. Mesoporous metal oxide replicas are obtained from the impregnation of a porous template with a metal oxide precursor followed by thermal treatment and removal of the template by etching in NaOH or HF solutions. In a similar manner to the traditional casting wherein the product inherits the features of the mold, the metal oxide replicas are supposed to have an inverse structure of the starting porous template. This is however not the case, as broken or deformed particles and other structural defects have all been experienced during nanocasting experiments. Although the nanocasting technique is widely used, not all the processing steps are well understood. Questions over the fidelity of replication and morphology control are yet to be adequately answered. This work therefore attempts to answer some of these questions by elucidating the nanocasting process, pin pointing the crucial steps involved and how to harness this knowledge in making wholesome replicas which are a true replication of the starting templates. The rich surface chemistry of mesoporous metal oxides is an important reason why they are widely used in applications such as catalysis, biomolecular separation, etc. At times the surface is modified or functionalized with organic species for stability or for a particular application. In this work, nanocast metal oxides (TiO2, ZrO2 and SnO2) and SiO2 were modified with amino-containing molecules using four different approaches, namely (a) covalent bonding of 3-aminopropyltriethoxysilane (APTES), (b) adsorption of 2-aminoethyl dihydrogen phosphate (AEDP), (c) surface polymerization of aziridine and (d) adsorption of poly(ethylenimine) (PEI) through electrostatic interactions. Afterwards, the hydrolytic stability of each functionalization was investigated at pH 2 and 10 by zeta potential measurements. The modifications were successful except for the AEDP approach which was unable to produce efficient amino-modification on any of the metal oxides used. The APTES, aziridine and PEI amino-modifications were fairly stable at pH 10 for all the metal oxides tested while only AZ and PEI modified-SnO2 were stable at pH 2 after 40 h. Furthermore, the functionalized metal oxides (SiO2, Mn2O3, ZrO2 and SnO2) were packed into columns for capillary liquid chromatography (CLC) and capillary electrochromatography (CEC). Among the functionalized metal oxides, aziridinefunctionalized SiO2, (SiO2-AZ) showed good chemical stability, and was the most useful packing material in both CLC and CEC. Lastly, nanocast metal oxides were synthesized for phosphopeptide enrichment which is a technique used to enrich phosphorylated proteins in biological samples prior to mass spectrometry analysis. By using the nanocasting technique to prepare the metal oxides, the surface area was controlled within a range of 42-75 m2/g thereby enabling an objective comparison of the metal oxides. The binding characteristics of these metal oxides were compared by using samples with different levels of complexity such as synthetic peptides and cell lysates. The results show that nanocast TiO2, ZrO2, Fe2O3 and In2O3 have comparable binding characteristics. Furthermore, In2O3 which is a novel material in phosphopeptide enrichment applications performed comparably with standard TiO2 which is the benchmark for such phosphopeptide enrichment procedures. The performance of the metal oxides was explained by ranking the metal oxides according to their isoelectric points and acidity. Overall, the clarification of the nanocasting process provided in this work will aid the synthesis of metal oxides with true fidelity of replication. Also, the different applications of the metal oxides based on their surface interactions and binding characteristics show the versatility of metal oxide materials. Some of these results can form the basis from which further applications and protocols can be developed

Comparison of Different Amino-Functionalization Procedures on a Selection of Metal Oxide Microparticles: Degree of Modification and Hydrolytic Stability

Amino-modified metal oxide materials are essential in a wide range of applications, including chromatography, ion adsorption, and as biomaterials. The aim of this study is to compare different functionalization techniques on a selection of metal oxides (SiO₂, TiO₂, ZrO₂, and SnO₂) in order to determine which combination has the optimal properties for a certain application. We have used the nanocasting approach to synthesize micrometer-sized TiO₂, ZrO₂, and SnO₂ particles, which have similar morphologies and porosities as the starting mesoporous SiO₂ microparticles (Lichroprep Si 60). These metal oxides were subsequently functionalized by four different approaches, (a) covalent bonding of 3-aminopropyltriethoxysilane (APTES), (b) adsorption of 2-aminoethyl dihydrogen phosphate (AEDP), (c) surface polymerization of aziridine (AZ), and (d) electrostatic interaction of poly­(ethylenimine) (PEI), to produce a high surface coverage of amino groups on their surfaces. Scanning electron microscopy, nitrogen physisorption, and X-ray diffraction were used to characterize the unmodified metal oxide particles, while thermogravimetric analysis, ninhydrin adsorption, and ζ potential titrations were applied to gain insight into the successfulness of the various surface modifications. Finally, the hydrolytic stability at pH 2 and 10 was investigated by ζ potential measurements. Unfortunately, the AEDP approach was not able to produce efficient amino-modification on any of the tested metal oxide surfaces. On the other hand, modifications with APTES, aziridine, and PEI appeared to give fairly stable amino-functionalizations at high pH values for all metal oxides, while these modifications were easily detached at pH 2, with the exception of SnO₂, where the AZ and PEI samples were stable up to 40 h. The results are expected to give valuable insights into the possibility of replacing amino-modified silica with more hydrolytically stable metal oxides in various application fields, for example, chromatography and drug delivery

Independent Fine-Tuning of the Intrawall Porosity and Primary Mesoporosity of SBA-15

We present a study in which the intrawall porosity and primary mesoporosity. of SBA-15 are independently controlled by modifying the strength of the molecular interaction that governs the formation of the material. The interactions are targeted at specific times during the process of formation, which results in selective tuning of the porosity, while other characteristics of the SBA-15 material are retained. We show that the intrawall porosity can be considerably reduced by addition of NaI, but not NaCl, and that the shape of the primary mesopores can be influenced by a decrease in temperature, while while the two-dimensional hexagonal structure and the particle morphology and size remain unchanged. The timing of the "tuning event" is imperative. We show that a decrease in intrawall porosity by addition of NaI is generic to Pluronic-based mesoporous silica syntheses. This work demonstrates that the material characteristic of mesoporous silica is not necessarily restricted by the initial synthesis conditions as the material properties can be tuned by "actions" taken upon the ongoing synthesis. The triblock copolymer Pluronic P104 was used as a structure director and tetramethyl orthosilicate as a silica source. The materials have been characterized primarily with nitrogen sorption and small angle X-ray diffraction

Detailed Study of the Nanocasting Process by in Situ X‑ray Scattering and Diffraction

The nanocasting method is a valuable tool for producing metal oxides with a well-defined nanostructure. However, the precise details on how the metal oxide is developed inside the mesoporous silica template remain unclear. In this study, we clarify how nickel nitrate species are evolving to nickel oxide and how they are redistributed inside mesoporous SBA-15 particles as a function of heating temperature and surrounding gas atmosphere by a combination of in situ small-angle X-ray scattering, X-ray diffraction and thermogravimetric techniques as well as ex situ transmission electron microscopy and nitrogen physisorption measurements. The SBA-15 template was initially impregnated with Ni­(NO₃)₂·6H₂O using the wet infiltration method. The results indicate an initial redistribution of the nickel nitrate salt located outside the pore system into the mesopores due to dissolution, while at temperatures of 110–150 °C (depending on which type of gas flow is used) the mobility of the salt is lost due to drying of the salt. Above 220 °C, the nickel nitrate decomposes, possibly via nickel hydroxynitrate, to NiO, forming nanoparticles inside the pore channels. The results shed light on the events occurring during the nanocasting process and can be used for further optimization of the fidelity of replication

Removal of Intrawall Pores in SBA-15 by Selective Modification

Removal of Intrawall Pores in SBA-15 by Selective Modificatio

Surface-initiated RAFT polymerization from vapor-based polymer coatings

Surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization was used to synthesize poly(methyl methacrylate) (PMMA) and poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammoniumhydroxide (PMEDSAH) brushes grafted from reactive poly[p-xylylene] surfaces. The synthetic approach involved functionalization of substrates via chemical vapor deposition polymerization of an electron-deficient alkynyl-functionalized [2.2]paracyclophane derivative. An azide-functionalized RAFT agent was anchored to the resulting poly[(p-xylylene-4-methyl propiolate)-co-p-xylylene] films via copper-free click-chemistry. Subsequent SI-RAFT polymerization yielded PMMA and PMEDSAH films with narrow dispersity which was further tuned by varying the concentration of a sacrificial RAFT agent in solution. Polymer dispersity was determined by size exclusion chromatography to be in the range of 1.2–1.4 for both polymers. This work provides a novel surface modification strategy to decorate a wide range of different substrates with polymer brushes, thereby eliminating the need for cumbersome modification protocols, which so far had to be established for each substrate material independently