Topochemical Reaction Research Articles

Three-way competition in a topochemical reaction: permutative azide–alkyne cycloaddition reactions leading to a vast library of products in the crystal

Crystals of 5-azido-3-O-propargyl-1,2-O-isopropylidene-α-d-ribofuranose undergo topochemical azide–alkyne cycloaddition reaction in three different pathways leading to a library of products.

Synthesis of nickel nanopowders in water/ethylene glycol solutions. The influence of the solution composition on the particles’ size

Air stable nickel nanopowders have been synthesized via the reduction of as-prepared Ni(OH) 2 by hydrazine in water/ethylene glycol solutions under heterogeneous nucleation conditions at70 °C. The resulting product is a powder of black color; yield of product in all cases exceeded 95%. The influence of the water/ethylene glycol ratio on the reaction proceeding and the size and size distribution of obtained nickel nanoparticles have been investigated. Using the method of electron microscopy it was found that the obtained nickel particles are mainly globular. It was established that the mean diameter and polydispersity of the particles practically do not change in the range of ethylene glycol concentrations of 33–89 % by volume and are equal to 140±50 nm and increase drammatically when the concentration of ethylene glycol is reduced by less than 10 % by volume and the obtained particles are agglomerates of irregular shape with an average diameter of 500 nm and high polydispersity. Using the powder diffraction method it was found that the obtained products do not contain nickel oxide or hydroxide. Using Scherrer equation the average crystallites sizes for some nickel samples have been calculated. It was found that the sizes of crystallites of obtained nickel nanopowders increase from 20 to 33 nm with a decreasein the ethylene glycol concentration in the reaction mixture. It was determined that the regulation of the composition of the solvent can be used to obtain nickel nanopowders with predicted sizes and polydispersity of particles. Based on the comparison of the values of the induction period times and the average diameters of the resulting nickel particles, it was found that ethylene glycol is not only a particles stabilizer, but also participates in the topochemical reaction of reduction of nickel hydroxide with hydrazine. Keywords: nickel nanopowders, heterogeneous nucleation, ethylene glycol, hydrazine.

Whether do nano-particles act as nucleation sites for C-S-H gel growth during cement hydration?

In this study, three modelling experiments were designed to investigate whether nano-particles incorporated in the cement paste act as nucleation sites for CSH gel growth during cement hydration. The nano-particles with (nano-SiO2) and without (nano-TiO2) pozzolanic reactivity were used. In the first experiment, both the cement and nano-particles were dispersed in water to prepare dilute cement paste, in which the cement and nano-particles can contact each other. In the second one, the cement particles were laid inside a filter paper funnel and immersed in tap and ultrapure water with nano-particles dispersed, in order to separate the cement particles with nano-particles by using the filter paper. In the third one, large clinker particle was embedded in resin, surface-polished and then exposed upside down in ultrapure water with and without nano-particles dispersed. After hydration for 7 days, the hydration products in the paste or the nano-particle dispersion were observed by using TEM and the hydrated surface of the embedded clinkers were detected by using SEM. Based on the experimental results and the detailed discussions by using the classic nucleation theory, it was found that there may have no nucleus function of the nano-particles for the CSH gel precipitation during cement hydration, at least in the hydrating system with nano-silica and nano-TiO2 addition. It was proposed to more reasonably explain the observations in the three modelling experiments by using the topochemical reaction instead of the through-solution mechanism for the CSH gel formation.

Promoted Hydride/Oxide Exchange in SrTiO3 by Introduction of Anion Vacancy via Aliovalent Cation Substitution.

We investigated topochemical anion exchange reactions for a ScIII-substituted SrTiIVO3 perovskite, Sr(Ti1-yScy)O3-y/2□y/2 (y ≤ 0.1), using CaH2. It was found that the initial introduction of a small amount of anion vacancies (y/2) is crucial to enhance the anion (H-/O2-) exchangeability. For example, hydride reduction of Sr(Ti0.95Sc0.05)O2.975 yielded the oxyhydride SrTi0.95Sc0.05O2.56H0.41 in which the hydride concentration is increased by 33% with respect to pristine SrTiO3 (leading to SrTiO2.76H0.24). This observation highlights the importance of anion vacancies to improve anion (H-/O2-) diffusion, which is a well-known strategy for improving oxide anion conductivity, and suggests that such a vacancy-assisted reaction could be applied to other anion exchange reactions (e.g., F-/O2- and N3-/O2-) to extend the solubility range.

Seed crystal of modified potassium sodium niobate prepared by simple molten salt synthesis

AbstractRecently, an interesting phenomenon has been reported in (K,Na)NbO3 (KNN)‐based ceramics. That is the growth of huge grains (10‐30 mm) which is a kind of abnormal grain growth (AGG). It was also interesting that the huge grains showed the stack of plate‐type grains. Using one of those compositions, therefore, seed plates were synthesized by not topochemical reaction but simple molten salt synthesis (SMSS) which was a simple‐and‐cheap process. The calcined K0.4925Na0.4925Ba0.0165Nb0.998O3.004 (KNBN) powders and KF powders were heat‐treated at 1050°C‐1150°C. The seed crystals showed the (100)C‐oriented structure. The size of seed plates was smaller than 500 μm and one layer of a thin plate‐type grain might show the thickness of 50 nm. They might be useful as the seeds at RTGG or TGG process.

Synthesis of Ba0.6Sr0.4TiO3 platelet crystals based on Bi4Ti3O12 precursor by topochemical microcrystal conversion

A-site complex perovskite Ba0.6Sr0.4TiO3 (BST) platelet microcrystals were successfully synthesized using a two-step Molten Salt Synthesis (MSS) method based on Bi4Ti3O12 platelet precursor. During the synthesis process, the calcination temperature and the soaking time strongly influence on the morphology and particle size of BST. The optimal temperature for calcination is 740 °C. In addition, the increasing edge length with 5 μm–11.5 μm and thickness with less than 0.25 μm of BST platelets are obtained under the condition of rising soaking time from 5 h to 20 h, which can be used for preparing highly textured ceramics and microwave devices. Finally, the mechanism of topochemical microcrystal conversion reaction between BaCO3-SrCO3 mixture and Bi4Ti3O12 was discussed.

Optical properties of conjugated polymer: review of its change mechanism for ionizing radiation sensor

A review on the change mechanism of conjugated polymer upon radiation exposure is presented. The change mechanism is mainly focused on the polymer's optical properties instead of its electrical properties. This research explores the effect of ionizing radiation on the optical change of conjugated polymer. This study also reviewed the possibility of using conjugated polymer as a radiation sensor vis‐à‐vis radiation type and the optical response. From material point of view, topochemical reaction, conjugation length and the degree of anisotropy of the conjugated polymer itself were identified as factors affecting the polymer's optical properties. These factors are tunable to meet a required optical degree, thus making the observation using the optical properties of a conjugated polymer possible for a radiation sensing tool. Based on the review, alteration of the factors and its mechanism of change occurs at macromolecular level. Therefore, a material at its smallest size down to a single molecule could be possible for the indication of radiation. Thus, radiation sensor made of nano or micro colloidal conjugated polymer deserves attention for future development. Copyright © 2017 John Wiley & Sons, Ltd.

Topochemical Reaction of Exfoliated Layered Cobalt(II) Hydroxide for the Synthesis of Ultrapure Co3O4 as an Oxygen Reduction Catalyst

The liquid exfoliation of hydrotalcite‐like α‐Co(OH)2 in formamide produced a new pink β‐form of Co(OH)2 nanosheets [Ex‐NS‐Co(OH)2] with unique nanoscopic properties: a larger surface area of active hydroxides and a much narrower oxidation–reduction potential for the Co2+ ions in the hydroxide layer than those of the bulk α‐Co(OH)2. These unprecedented properties of Ex‐NS‐Co(OH)2 were applied to the topochemical synthesis of crystalline Co3O4 nanocubes (NCs) with clear edges and no impurity phases from an aqueous solution of Co2+ ions at 70 °C. A Co3O4 NC/C catalyst exhibited good catalytic activity for the oxygen reduction reaction (ORR) and higher stability under a continuous electrochemical operation than that of commercial Pt/C.

Synthesis and Superconductivity of Layered Compounds with Orthogonal [Zr2N2] Network

Layered α-form ZrNX (X: Cl and Br) compounds with high quality were prepared by chemical vapor transport. The intercalation of alkali metal A (A: Li, Na, K, Rb) was carried out to realize electron doping into the orthogonal [Zr2N2] layers. The Rietveld refinement analysis reveals that the [Zr2N2] crystalline layers in the intercalation compounds shift mutually in the ab plane when compared with the hosts. Magnetic measurements show that the intercalation compounds AxZrNX are changed into superconductors with transition temperature Tc of up to 12 K. Upon the cointercalation of solvent molecules such as THF, Tc decreases to as low as 6.1 K with increasing the interlayer spacing d up to 14 A, which is similar to the d dependence of Tc recently found in electron-doped α-form TiNX series. We also succeeded in synthesizing another new polymorph of α-Zr2N2S by the topochemical reaction between α-form ZrNX and Na2S. α-Zr2N2S (space group: Immm, a = 4.1375(1) A, b = 3.5422(1) A, and c = 11.5204(3) A) has the same α-[Zr2N2] layers, whereas the interlayer spacing between two adjacent [Zr2N2] layers is effectively decreased by 1/3 when compared with the parent compounds of ZrNX.

수직배양된 고집적 CdTe-Si 나노구조체의 제조방법

Cadmium compounds with one dimension (1D) nanostructures have attracted attention for their excellent electrical and optical properties. In this study, vertically aligned CdTe-Si nanostructures with high density were synthesized by several simple chemical reactions. First, l D Te nanostructures were synthesized by silver assisted chemical Si wafer etching followed by a galvanic displacement reaction of the etched Si nanowires. Nanowire length was controlled from 1 to <TEX>$25{\mu}m$</TEX> by adjusting etching time. The Si nanowire galvanic displacement reaction in <TEX>$HTeO_2{^+}$</TEX> electrolyte created hybrid 1D Te-branched Si nanostructures. The sequential topochemical reaction resulted in <TEX>$Ag_2Te-Si$</TEX> nanostructures, and the cation exchange reaction with the hybrid 1D Te-branched Si nanostructures resulted in CdTe-Si nanostructures. Wet chemical processes including metal assisted etching, galvanic displacement, topochemical and cation exchange reactions are proposed as simple routes to fabricate large scale, vertically aligned CdTe-Si hybrid nanostructures with high density.

Morphology and dehydration mechanism of transition metal sulfate heptahydrates

Processes and thermodynamic parameters of dehydration of transition metal (Ni, Co, and Fe) sulfate heptahydrate crystals grown in aqueous solutions have been investigated by optical thermomicroscopy, X-ray analysis, and differential scanning calorimetry. Values of temperature and specific heat of the first stage of dehydration have been determined, as well as the conditions under which the process was reversible. The morphology of the common topochemical reaction, as well as the mechanism of this reaction, has been characterized. The dehydration process has been shown to depend on multiple physical parameters and to consist in the growth of non-oriented crystals of the new phase with concomitant exudation of the water of crystallization.

Molecular weaving via surface-templated epitaxy of crystalline coordination networks.

One of the dream reactions in polymer chemistry is the bottom-up, self-assembled synthesis of polymer fabrics, with interwoven, one-dimensional fibres of monomolecular thickness forming planar pieces of textiles. We have made a major step towards realizing this goal by assembling sophisticated, quadritopic linkers into surface-mounted metal-organic frameworks. By sandwiching these quadritopic linkers between sacrificial metal-organic framework thin films, we obtained multi-heteroepitaxial, crystalline systems. In a next step, Glaser–Hay coupling of triple bonds in the quadritopic linkers yields linear, interwoven polymer chains. X-ray diffraction studies revealed that this topochemical reaction leaves the MOF backbone completely intact. After removing the metal ions, the textile sheets can be transferred onto different supports and imaged using scanning electron microscopy and atomic-force microscopy. The individual polymer strands forming the two-dimensional textiles have lengths on the order of 200 nm, as evidenced by atomic-force microscopy images recorded from the disassembled textiles.

Color Transition Properties of Water Dispersible Polydiacetylene Particles Conjugated with the Thermosensitive Polymer

An assembly of diacetylene molecules is necessary to progress a topochemical reaction as UV-irradiated polymerization. In this study, we attempt to regularly assemble 10, 12- pentacosadiynoic acid (PCDA) by freezing the solution, followed by lyophilization. Dried PCDA assembly was easily dispersed in aqueous solution by sonication. Irradiation of UV light can promote polymerization reaction of PCDA judging from a color change of the solution into blue. A color transition of the polyPCDA-dispersed solution from blue to red was observed at approximately 56°C due to distortion of its π-conjugated system. A color transition temperature could be controlled by hybridization with thermosensitive hydroxypropyl cellulose, of which lower critical solution temperature appears around 38-39°C. By synchronizing to coli-globule transition of HPC in aqueous media, blue-red transition response of water-dispersed polyPCDA could be induced by changing conformation of surrounded polymer.

Topochemical Azide-Alkyne Cycloaddition Reaction in Gels: Size-Tunable Synthesis of Triazole-Linked Polypeptides.

Though topochemical reactions are attractive, the difficulty associated with crystallization such as low yield, unsuitability for large-scale synthesis, etc. warranted the exploitation of other self-assembled media for topochemical reactions. We synthesized a dipeptide gelator decorated with azide and alkyne at its termini, N3-Ala-Val-NHCH2-C≡CH, which is designed to self-assemble through intermolecular hydrogen bonds to β-sheets thereby placing the azide and alkyne motifs in proximity. As anticipated, this peptide forms gels in organic solvents and water via hydrogen-bonded β-sheet assembly as evidenced from IR spectroscopy and PXRD profiling. The microscopic fibers present in organogel and hydrogel have different morphology as was evident from scanning electron microscopy (SEM) imaging of their xerogels, XGh (xerogel made from hydrogel) and XGo (xerogel made from organogel). Heating of xerogels at 80 °C resulted in the topochemical azide-alkyne cycloaddition (TAAC) polymerization to 1,4-triazole-linked oligopeptides. Under identical conditions, XGo produced larger oligopeptides, and XGh produced smaller peptides, as evidenced from MALDI-TOF spectrometry. We have also shown that degree of TAAC polymerization can be controlled by changing gel fiber thickness, which in turn can be controlled by concentration. SEM studies suggested the morphological intactness of the fibers even after the reaction, and their PXRD profiles revealed that both XGh and XGo undergo fiber-to-fiber oligomerization without losing their crystallinity. In contrast to crystals, the xerogels undergo TAAC polymerization in two distinct stages as shown by DSC analyses. Interestingly, XGh and XGo undergo spontaneous TAAC polymerization at room temperature; the latter shows faster kinetics. This is not only the first demonstration of the use of xerogels for thermally induced topochemical polymerization but also the first report on a spontaneous topochemical reaction in xerogels.

Topochemical build-up of BaTiO3nanorods using BaTi2O5as the template

One-dimensional BaTiO3 nanomaterials have important applications in nano-ferroelectric devices, and their high-quality synthesis is a hotspot in the field of chemistry of materials. In this work, single-crystalline perovskite BaTiO3 nanorods have been prepared by a two-step molten salt method. The conversion process and the topochemical mechanism were investigated based on XRD, DSC, SEM and TEM analysis. Firstly, one dimensional BaTi2O5 nanocrystallites have been synthesized in a molten environment and the self-polarization effect is responsible for the growth direction of [0 2 0]. Then, using these oriented BaTi2O5 monoclinic nanorods as templates, BaTiO3 perovskite nanorods have been further constructed through the topochemical reaction, in which all edge-sharing [TiO6] octahedra converted into corner-sharing modes to obtain the minimum energy state. One-dimensional morphology of BaTiO3 can only be obtained at a low calcination temperature, because at a high temperature, it will decompose into nanoparticles. This topological method is facile and can be developed to construct other orientated functional materials.

Light induced construction of porous covalent organic polymeric networks for significant enhancement of CO2 gas sorption

Porous covalent organic polymers were prepared from self-assembled fibers using a topochemical polymerization reaction and their four times higher CO2 sorption behaviour is demonstrated.

Defect Engineering, Electronic Structure, and Catalytic Properties of Perovskite Oxide La0.5 Sr0.5 CoO3-δ.

The electronic structures of transition metal oxides play a crucial role in the physical and chemical properties of solid materials. Defect engineering is an efficient way to regulate the electronic structure and improve the performance of materials. Here, we develop a defect engineering route that is implemented by controlling the topochemical reactions between cobalt perovskite and urea to optimize the electronic structure of La0.5 Sr0.5 CoO3-δ (LSCO). Urea pyrolysis is able to increase the oxygen defect concentration and cause octahedral distortions. Furthermore, we can distinctly observe that the introduction of oxygen vacancies narrows the hybridization orbital between O 2p and Co 3d and optimizes the O p-band center near the Fermi level by X-ray absorption spectroscopy, which greatly improves the catalytic activity of CO oxidation and photocatalytic water splitting. These results highlight the relationship between oxygen defects, electronic structure, and catalytic activity of perovskite LSCO, and demonstrate a rational approach to defect design and reveal the importance of anion redox chemistry for the structures and properties of perovskite oxides.

Platinum clusters supported on/in Dion–Jacobson phase HLaNb2O7 by topochemical method

Platinum clusters were supported on/in HLaNb2O7 nanosheets by topochemical reaction strategy for the first time. The as-prepared samples were analyzed using ICP OES and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption isotherms and X-ray photoelectron spectroscopy. The results showed that HLaNb2O7 nanosheets were modified with platinum clusters with good monodispersity. The product was a mesoporous solid with broad pore size distribution and large surface area. The oxidation state of platinum was zero and the size of Pt clusters was only about 1–2 nm. This study provides a novel approach to support metal clusters on layered compounds.

Fabrication of Helical Nanoribbon Polydiacetylene via Supramolecular Gelation: Circularly Polarized Luminescence and Novel Diagnostic Chiroptical Signals for Sensing.

Four kinds of commercially available diacetylene (DA) monomers with different chain length, diacetylene positions were fabricated into the organogels via mixing with a chaperone gelator, an amphiphilic l-histidine ester derivative LHC18 that can help the nongelator to form gels. Upon photo irradiation with a 254 nm UV light, the white gels underwent topochemical reaction and turned into red or blue gels, depending on the DA monomer structures. Through the gel formation, the molecular chirality of LHC18 can be transferred to the polydiacetylene (PDA) and helical nanoribbon structures were obtained. The blue gels showed a clear response to stimuli such as pH variation, heating, mechanical force and organic solvents, and turned into red gels. Interestingly, the blue gel showed strong supramolecular chirality, which could be turned off or changed into red phase CD signals. Such changes in chiroptical signals depended on the external heating and various organic solvents. In the case of heating, the blue gel changed into red one, which showed both strong CD signals and circularly polarized luminescence. In the case of organic solvents, although all the tested solvents made the blue gel to red, only some of them could keep the CD signals, thus providing additional sensing capacity of the PDA system. So far, the blue-to-red color change and the "fluorescence on" was widely used as colorimetric and fluorogenic diagnostic signals for PDA, here we showed an additional chiroptical diagnostic signal for a more precise sensing by using the helical PDA.

Solid-State Photochemical Reaction of Multisubstituted Thymine Derivatives

Solid-state photochemical reactions in crystals, known as topochemical reactions, are solvent-free green chemical reactions that produce stereospecific molecules. The photoreaction of thymine is interesting because the dimeric photoproduct can form four types of stereoisomers and when the dimer is formed in DNA helices it can cause skin cancers. We investigated the photoreaction of five multisubstituted thymine derivatives in the solid-state, which were designed with crystal engineering concepts to promote π–π stacking of benzene rings in the crystal. Powder X-ray diffraction analysis revealed that a para-substituted bis-thymine derivative was aligned along the c axis in the crystal and was susceptible to topochemical reaction to form a polymer, as previously reported. Ortho- and meta-substituted bis-thymine derivatives and a tetrakis-substituted derivative were found to be topochemically unreactive using both gel permeation chromatography (GPC) and X-ray crystal structural analysis. The tris-substituted ...