Conventional Synthetic Techniques Research Articles

Shape-controllable preparation of covalent organic frameworks and their application in efficient removal of aromatic organic pollutants

Covalent organic frameworks (COFs), as well-ordered porous materials, have garnered considerable attention in the adsorption of environmental contaminants due to their long-range ordered crystal structure, great specific surface area, etc. In this work, alcoholic solvents were used as the reaction media to successfully synthesize three COFs with regular crystalline structures under nearly ambient conditions, whereas conventional synthetic techniques have not been documented for the synthesis of TAPB-TFPT COFs. Inspired by the excellent physical and chemical properties of the generated rod-like TAPB-DHTP COFs, which can be served as an ideal solid adsorbent for aromatic organic pollutant adsorption and removal. It is worth mentioning that TAPB-DHTP COFs showed fast adsorption kinetic rates (within 40 min) and high adsorption capacities (288 mg/g, 87.7 mg/g and 105 mg/g) for naphthalene, 2-naphthol and 2-naphthylamine, superior to most reported adsorbents. The effective removal of aromatic organic pollutants is ascribed to numerous non-covalent interactions between targets and TAPB-DHTP COFs, including π-π interactions and hydrogen bonding. Thus, this research might present a promising route to the green preparation of COFs and their prospective application in environmental restoration.

Unravelling the Influence of Binder Typology during the Additive Manufacturing of Hybrid Multi-Channel Cylinders for Catalytic Purposes

In this work, a 3D printing methodology based on the robocasting of catalytic ink pastes was applied to obtain structured matrix-like cylinders as innovative materials for an effective utilization of carbon dioxide. The influence of three different binders (i.e., PEI, HPMC and MC) on the physio-chemical, mechanical and catalytic properties of multi-channel monoliths was studied against a reference binder-free powdered system in order to envisage the effectiveness of the printing procedure in realizing hybrid advanced materials at a higher control and reproducibility than from traditional preparation techniques. In terms of textural and structural properties, the micro-extruded 3D cylinders only evidenced a slight difference in terms of relative crystallinity, with minor effects on the surface area exposure in relation to the specific binder used during the direct ink writing process. More importantly, the typology of binder significantly affected the rheological properties of the catalytic ink, with the need of a controlled viscosity to ensure a suitable thixotropic behaviour of the extrudable pastes, finally determining an optimal mechanical resistance of the final 3D monolith. The experimental validation of the hybrid multi-channel cylinders under conditions of CO2 hydrogenation demonstrated the great potential of additive manufacturing in the realization of catalyst architectures characterized by unique features and fidelity scarcely reproducible via conventional synthetic techniques.

Controlled Sequence Photoresists from Polypeptoids

Low stochastics, high sensitivity photoresists remain a goal for lithography. Here we present a study of a polymer system, polypeptoids, using a synthetic strategy borrowed from the biomedical community to make improvements to these resist characteristics through control of polymer sequence. We describe peptoid polymers that possess identical molecular size, composition and sequence with higher molecular uniformity than possible by conventional synthetic techniques. We report the results of exposure of these materials to DUV radiation and the chemical changes that occur. In addition, we highlight unexpected observations of the role of sequence on lithographic performance.

Combustion synthesis of high-entropy carbide nanoparticles for tetracycline degradation via persulfate activation

The development of high-entropy carbide nanoparticles merits untold scientific and technological potential, yet their synthesis remains a challenge using conventional synthetic techniques. Herein we present a facile, rapid and low-cost route for the combustion synthesis of (Ta0.25Nb0.25−Zr0.25Ti0.25)C high-entropy carbide (HEC-1) nanoparticles by self-propagating reaction of metal oxides, carbon and Mg mixture precursors in NaF salt media for the first time. The combustion synthesis possibility of HEC-1 is first analyzed theoretically from thermodynamic aspects, and then the ultrafine HEC-1 nanoparticles (average particle size: ∼19 nm) are synthesized successfully by the combustion synthesis technique at combustion temperature of ∼1487 K, duration of 63 s, and heating rate of ∼68 K s−1. The as-synthesized HEC-1 nanoparticles possess high compositional uniformity and low oxygen impurity content of 2.98 wt%. To prove their utility, the as-synthesized HEC-1 nanoparticles are utilized as an effective persulfate activation catalyst for the degradation of tetracycline pollutant in groundwater or wastewater and a removal efficiency of ∼65.5% for tetracycline is obtained after 10 h.

New Approaches to EUV Photoresists: Studies of Polyacetals and Polypeptoids to Expand the Photopolymer Toolbox

Low stochastics, high sensitivity photoresists remain a goal for EUV lithography. Here we present studies of two polymer systems that attempt to make improvements to these resist characteristics using two different chemical approaches. In one system we work on scissionable poly(phthalaldehyde) modified to enable incorporation of photoactive units on each repeat unit of the polymer chain. In a second system we explore peptoid polymers that possess identical molecular size and composition with much higher molecular uniformity than possible by conventional synthetic techniques. We report the results of exposure of these materials to EUV exposures and the chemical changes that occur.

Insights into effects of O-incorporated Ag nanoparticles as wetting seeds toward improving Ag wetting on oxides

Ag wetting on oxides is essential for implementing exceptional layered Ag superstructures with simultaneous ultralow losses in electrical conductance and optical transmittance. This goal is difficult to achieve by conventional synthetic techniques involving the incorporation of heterogeneous transition metals or metalloids into Ag as wetting inducers as they cause detrimental optoelectrical changes. This study provides novel insights into the use of homogeneous Ag wetting seeds to improve the wetting of Ag on oxides. We investigated the effect of atomic O incorporation on the improvement of Ag wetting by monitoring its participation in and contribution to the Ag clustering and layering processes. Minimal incorporation of dissolved atomic O as a surfactant into the Ag nanoparticles transposed the nanoparticle evolution path from a complete to incomplete coalescence mode at significantly reduced thicknesses, which was attributed to a reduction in the nanoparticle free energy. The size and shape of the O-incorporated Ag nanoparticles were precisely controlled to accelerate the wetting transition of Ag on ZnO substrates by circumventing the transmutation effect of O. These results demonstrate a notable strategy for accomplishing a rapid Ag wetting transition toward a completely continuous layer with ultralow optoelectrical losses.

Boride-based electrocatalysts: Emerging candidates for water splitting

Electrocatalytic water splitting (EWS) is a promising route to produce hydrogen in a sustainable and environment-benign manner. To realize the large-scale hydrogen production, it is paramount to develop desirable electrocatalysts with engineered structure, high catalytic activity, facile accessibility, low cost, and good durability. Of late, boride-based materials, especially transition-metal borides (TMBs), are emerging as promising candidates for the EWS process. However, so far, little attempt has been made to provide a comprehensive summary on these findings. Herein, this review provides the up-to-date status on upgrading the catalytic performance of TMB-based nanomaterials by regulating the internal and external characteristics. The conventional synthetic techniques are first presented for the preparation of TMB-based catalysts. Afterwards, the advanced strategies are summarized to enhance the catalytic performance of TMBs, including morphology control, component regulation, phase engineering, surface oxidation and hybridization. Then, the design principles of TMB-based electrocatalysts for high-performance EWS are outlined. Lastly, the current challenges and future directions in the development of TMB-based materials are proposed. This review article is expected to envisage insights into the TMBs-based water splitting and to provide strategies for design of the next-generation TMB-based electrocatalysts.

Process intensification for scalable synthesis of ytterbium and erbium co-doped sodium yttrium fluoride upconversion nanodispersions

Rare-earth doped NaYF4 upconversion nanomaterials have found many applications from biosensing through photoelectric conversion to luminescent anti-counterfeiting. However, the scalable synthesis methods of ultrasmall NaYF4 nanoparticles are still challenging. Herein, We demonstrated that the intensified mixing of the precursor by a high-gravity rotating packed bed (RPB) reactor before the hydrothermal synthesis process enabled the preparation of ultrasmall NaYF4:Yb3+/Er3+ upconversion nanoparticles, with much smaller size, more uniform distributions and higher Er3+-doping level than those obtained in the stirred tank reactor (STR) route. In stark contrast to conventional synthetic techniques that require stringent control over several experimental variables for controlling morphologies and sizes, the process intensification approach presented here requires modification of only a single variable while enabling tremendous improvements to control the formation of NaYF4 based UCNPs with small feature size. The UCNPs dispersed well in various organic solvents (e.g. ethanol, acetone, toluene, cyclohexane, etc.), forming transparent nanodispersions with upconversion luminescence under 980 nm NIR light irradiation. The preliminary applications of NaYF4:Yb3+/Er3+ nanodispersions for upconversion luminescent transparent hybrid films and anti-counterfeiting were also demonstrated.

Strain-induced skeletal rearrangement of a polycyclic aromatic hydrocarbon on a copper surface

Controlling the structural deformation of organic molecules can drive unique reactions that cannot be induced only by thermal, optical or electrochemical procedures. However, in conventional organic synthesis, including mechanochemical procedures, it is difficult to control skeletal rearrangement in polycyclic aromatic hydrocarbons (PAHs). Here, we demonstrate a reaction scheme for the skeletal rearrangement of PAHs on a metal surface using high-resolution noncontact atomic force microscopy. By a combination of organic synthesis and on-surface cyclodehydrogenation, we produce a well-designed PAH—diazuleno[1,2,3-cd:1′,2′,3′-fg]pyrene—adsorbed flatly onto Cu(001), in which two azuleno moieties are highly strained by their mutual proximity. This local strain drives the rearrangement of one of the azuleno moieties into a fulvaleno moiety, which has never been reported so far. Our proposed thermally driven, strain-induced synthesis on surfaces will pave the way for the production of a new class of nanocarbon materials that conventional synthetic techniques cannot attain.

Solvent‐free Synthesis, Characterization and Solvent‐Vapor Interaction of Zinc(II) and Copper(II) Coordination Polymers containing Nitrogen‐donor Ligands

Coordination polymers of [Zn(INA)2] (1) (INA = isonicotinate), [Cu2(mal)2(H2O)2(bipy)] (2) (mal = malonate, bipy = 4,4‐bipyridine), and [Zn2(OAC)4(bipy)2] (3) (OAC = acetate) were prepared using mechanochemical grinding and heating methods. The materials were characterized with elemental analysis, FT‐IR spectroscopy, TGA, SEM, EI‐MS, BET, and PXRD. Comparison of PXRD patterns of the materials with patterns simulated from single‐crystal X‐ray diffraction data allowed identification of the products. Compared to conventional synthetic techniques such as solvothermal/hydrothermal solvent‐based methods, solvent‐free method was found to be simple, highly efficient, and environmentally friendly especially for the preparation of these coordination polymers on a large scale. Solvent‐vapor interaction properties of 1, 2, and 3 were investigated by exposure of the compounds to water and methanol at room temperature.

Observation of Enhanced Hole Extraction in Br Concentration Gradient Perovskite Materials.

Enhancing hole extraction inside the perovskite layer is the key factor for boosting photovoltaic performance. Realization of halide concentration gradient perovskite materials has been expected to exhibit rapid hole extraction due to the precise bandgap tuning. Moreover, a formation of Br-rich region on the tri-iodide perovskite layer is expected to enhance moisture stability without a loss of current density. However, conventional synthetic techniques of perovskite materials such as the solution process have not achieved the realization of halide concentration gradient perovskite materials. In this report, we demonstrate the fabrication of Br concentration gradient mixed halide perovskite materials using a novel and facile halide conversion method based on vaporized hydrobromic acid. Accelerated hole extraction and enhanced lifetime due to Br gradient was verified by observing photoluminescence properties. Through the combination of secondary ion mass spectroscopy and transmission electron microscopy with energy-dispersive X-ray spectroscopy analysis, the diffusion behavior of Br ions in perovskite materials was investigated. The Br-gradient was found to be eventually converted into a homogeneous mixed halide layer after undergoing an intermixing process. Br-substituted perovskite solar cells exhibited a power conversion efficiency of 18.94% due to an increase in open circuit voltage from 1.08 to 1.11 V and an advance in fill-factor from 0.71 to 0.74. Long-term stability was also dramatically enhanced after the conversion process, i.e., the power conversion efficiency of the post-treated device has remained over 97% of the initial value under high humid conditions (40-90%) without any encapsulation for 4 weeks.

Visualization of Iron‐Binding Micelles in Acidic Recombinant Biomineralization Protein, MamC

Biological macromolecules are utilized in low‐temperature synthetic methods to exert precise control over nanoparticle nucleation and placement. They enable low‐temperature formation of a variety of functional nanostructured materials with properties often not achieved via conventional synthetic techniques. Here we report on the in situ visualization of a novel acidic bacterial recombinant protein, MamC, commonly present in the magnetosome membrane of several magnetotactic bacteria, including Magnetococcus marinus, strain MC‐1. Our findings provide an insight into the self‐assembly of MamC and point to formation of the extended protein surface, which is assumed to play an important role in the formation of biotemplated inorganic nanoparticles. The self‐organization of MamC is compared to the behavior of another acidic recombinant iron‐binding protein, Mms6.

Zinc Oxide Nano‐ and Microfabrication from Coordination‐Polymer Templates

Hex nut: An emerging synthetic approach based on metal-organic coordination-polymer templates has been used to fabricate micro- and nanoscale crystals. By using a diverse range of molecular building blocks coupled with conventional synthetic techniques, it is possible to synthesize ZnO crystals with tailored sizes, shapes (such as hexagonal rings; see figure), and surface properties.

Molecular Minerals™: Lyophillic Colloids for Ceramists

This paper will focus on a novel class of inorganic compounds that we term as molecular minerals™ (MMs). MMs are clusters of ceramic fragments encapsulated with organic ligands. These compounds can be crystallized from solution as molecular single crystals and have well‐defined crystal structures that can be described with X‐ray diffraction methods. Most importantly, the ceramic clusters are perfectly monodisperse, and conventional synthetic techniques can be applied to facilitate control of size and composition. The organic encapsulate imparts solubility in organic solvents and polymers. More importantly, the solubility is thermodynamically driven to form a single‐phase system. Thus, unlike nanoparticles, the stability of clusters in solution is spontaneous rather than kinetically derived. A critical tool for creating MMs is a firm understanding of the fundamental issues governing cluster structure and stability. We have demonstrated a unique synthetic approach to these materials, capable of creating materials with oxo, sulfido, selenido, or tellurido ligands, whose ceramic fragment size can currently be varied from about 0.5 to 2 nm. Both homometallic and heterometallic lanthanide (Ln) complexes incorporating the group 12 metals Zn, Cd, and Hg have been prepared. Relative to prior work on metal organic or organometallic Ln complexes, MMs have unprecedented luminescent properties in terms of emission wavelength, emission intensity, and quantum efficiency. These materials match or exceed the luminescent properties of ceramics, glasses, and nanomaterials, while having the additional advantage of polymer solubility. Solubility facilitates the preparation of transparent molecular mineral nanocomposites that can be fabricated as bulk polymers, fibers, and films.

Synthetic receptors prepared by organized assembly of organic molecules.

Synthetic organic molecular approaches to prepare materials for fabricating molecular functional devices is one of the most attractive themes for chemists to pursue. Organized assemblies of organic molecules could be expected to exhibit new functionality in the resulting structure. However, the desirable functionality sometimes requires structure that is too complicated to synthesize by means of conventional synthetic techniques. In 1988, Lehn elucidated the concept of supramolecular chemistry in his Nobel lecture, which involved the construction of complicated molecules by self-assembling of small molecules with multiple weak-bond formation, allowing new functions to be induced. Considerable efforts have been made to develop supramolecular self-assembling systems. It appears that such systems have a great potential for the preparation of functional molecules in the field of molecular electronics and biosensor technology. In this article, we describe two topics with regard to self-assembly-induced molecular recognition systems including (1) metal ions-mediated supramolecular assembling of small molecules to form well-defined structures in aqueous solution and (2) molecular imprinting, the combined technique of self-assembling and cross-linked synthetic polymer synthesis to prepare synthetic receptors/enzymes. We present several examples and demonstrate the possibility of new frontier technologies of molecular architecture in designed chemistry, producing a new class of functional molecules.

REACTION OF p-HYDROXYCINNAMYL ALCOHOLS WITH TRANSITION METAL SALTS IV. TAILORED SYNTHESES OF β-O-4 TRIMERS1

Reaction of coniferyl alcohol or sinapyl alcohol with β-O-4 dimeric model compounds in the presence of manganese(III), copper(II), or vanadium(V) gave trimeric compounds that served as superior models for13C chemical shift assignments in natural and synthetic lignins. By appropriate choice of dimer and monomer, seven of the eight possible sequences of guaiacyl (G) and syringyl (S) units were prepared: GGG, GGS, GSG, GSS, SSS, SSG, and SGG. Preparaton of the missing sequence (SGS) by this method was not successful, so it was obtained by conventional synthetic techniques. Stereochemistry in the trimers was also controlled to some extent by utilizing dimers that were predominantly erythro (e) or threo (t), and by performing the oxidative coupling under conditions of high stereo-selectivity. The maximum number of geometric isomers in β-O-4 trimers is eight (one pair each of ee, et, te, tt). In this study the GGG and GGS trimers contained all eight isomers, the SGG trimer contained four isomers, and GSG, GSS, SSS, SSG, and SGS (synthetic) each contained only two isomers. The chemical shifts of the sidechain carbons in the trimers were compared with corresponding chemical shifts in natural lignins isolated from spruce (Picea mariana), birch (Betula papyrifera), and hickory (Carya ovata). The comparison indicated that GG and SG entities in lignin had e/t ratios ranging from 2/1 to 1/1, but GS and SS entities were predominantly e. This observation was consistent with the isomer composition of linkages formed by oxidative coupling of coniferyl alcohol or sinapyl alcohol with dimers.

Microwave Preparation of Oxide Bronzes

Several vanadium, tungsten, and molybdenum oxide bronzes have been prepared using microwave irradiation. Metal oxides and alkali metal iodides were used as starting materials. Intermittent grinding and inert atmosphere were found to be necessary for the synthesis of most of the bronzes. The reaction temperatures are remarkably lower than those employed for conventional synthetic techniques and the microwave assisted reactions proceed at extremely fast rates. The microwave synthesized bronzes consist of particles having long, rectangular rod-like morphology.

A high-throughput search for electronic materials-thin-film dielectrics.

Parallel synthesis together with high-throughput screening was used to identify candidate materials for integrated circuit applications that demand a superior high permittivity dielectric thin film. Specifically, we developed a "continuous-composition spread" (CCS) technique to synthesize much of a pseudoternary oxide system in a single deposition and used this in conjunction with a high-throughput measurement protocol, thereby allowing each chemical system to be deposited and evaluated in about 24 h. This approach led to the identification of compositions in the Zr-Sn-Ti-O system with promising properties. The same technique was used to determine the optimum compositions as a function of processing parameters. Films with the composition Zr(.2)Sn(.2)Ti(.6)O(2) were then prepared using a conventional synthetic technique (on-axis sputtering) and were verified to have excellent properties. Thus, the CCS technique has demonstrated utility in rapidly identifying and developing a useful new material.

Synthesis of boron carbide via poly(vinylpentaborane) precursors

Limitations in traditional ceramic processing have encouraged interest in the development and utilization of polymer pyrolyses as low-temperature synthetic routes to nonoxide ceramic materials. Boron carbide is an example of a material where preparation from a polymer precursor might offer advantages over conventional synthetic techniques. Mixed B/sub 4/C-SiC ceramics have, in fact, been previously obtained from pyrolysis of poly(carboranesiloxane) polymers; however, a synthesis of pure B/sub 4/C from polymeric precursors has heretofore not been developed. They report here that 2-(H/sub 2/C=CH)-B/sub 5/H/sub 8/ will undergo thermal polymerization to vinylpentaborane oligomers and that these species can be converted to pure boron carbide (B/sub 4/C) in high ceramic yields under mild conditions.

Separation of photoredox products by local potential fields

Polyelectrolytes, ion exchangers and charged colloids can be used to control the rates of photo-induced chemical reactions. In particular, polyelectrolytes possess several additional features which make them attractive as suitable microassemblies in such systems. These include a well-defined structure whose properties of size, shape, charge density etc. may be modified by conventional synthetic techniques, the possibility of attaching specific molecular chromophores chemically to a polyelectrolyte such that they possess the desired properties ( e.g. light absorption, redox potential, solubility etc.) and their possible adsorption to colloidal catalysts and electrodes. Special emphasis on charge separation and the inhibition of photochemical back reactions by polyelectrolytes is therefore made. Charge separation effects are critically reviewed. Large effects on the quantum yields of photochemical electron transfer products are reported. The reactions of zwitterionic quenchers with excited photosensitizers in the presence of polyelectrolytes or charged colloids are also described in which there seems to be a lack of microenvironmental effect on the quantum yields of charge separation. The possible reasons for this are discussed. In general, back reactions are expected to be inhibited in the presence of polyelectrolytes when one of the reacting species lies in the polymer field and the other is an ion bearing the same charge as the polyion. However, the inhibition effect is usually found to be only of one or two orders of magnitude. On the basis of pulse radiolytic measurements of the rate of bimolecular reactions of polyelectrolyte radicals, it can be concluded that polyelectrolytes may lead to the inhibition of back reactions by up to five or six orders of magnitude if the two photochemical transient species are bound to different polyelectrolyte molecules carrying the same electric charge. A photochemical system which fulfils the conditions is described, and ways in which to apply such systems to the photochemical cleavage of water are discussed.