Reaction Of Precursor Research Articles

Characterization of cyclic dust growth in a low-pressure, radio-frequency driven argon-hexamethyldisiloxane plasma

In a dusty plasma, nanometer-sized solid dust particles can be grown by the polymerization of plasma species from a reactive precursor gas. This type of plasma can be found in large-scale astrophysical objects, as well as in semiconductor manufacturing and material processing. In a laboratory environment, the plasma parameters can be carefully controlled and the dynamics of dust growth as well as the interaction between the plasma and the dust can be studied. In this work, we investigate the cyclic growth of dust particles in a low-pressure, radio-frequency driven argon-hexamethyldisiloxane plasma using a multitude of diagnostics in a time-synchronized fashion. The combination of microwave cavity resonance spectroscopy, plasma impedance measurements, laser light scattering, laser light extinction measurements and optical emission spectroscopy offers a broad view on the temporal behavior of the plasma in concert with the plasma-grown dust particles. We have studied the variation of several discharge parameters such as plasma power and hexamethyldisiloxane content. Therefore, this multi-diagnostic approach contributes to the fundamental understanding of the mechanisms behind dust growth in low-pressure plasmas.

P-Chiral Phosphine Sulfide Synthesis by Combination of Enzymatic Desymmetrization and Successive Deformylative P–C Cross-Couplings

AbstractA process for the synthesis of P-chiral triarylphosphine sulfides via sequential Pd-catalyzed stereospecific P–C coupling reactions of P-chiral precursors prepared by enzymatic desymmetrization was developed. Three independent aryl substituents could be introduced onto the P atom by the sequential P–C couplings under mild conditions while retaining the high enantiopurity.

Chemical vapor deposition from metal (Cr, Mo, W) carbonyls in a conical spouted bed vacuum reactor with a downflow reactant feeding

A vacuum set-up with a conical spouted bed reactor for LPCVD of coatings onto powders, where a volatile solid substance is used as a CVD precursor (reactant), is developed. Structurally, the reactor is a cone with a vertical axis, fluidizing gas is supplied through the bottom branch, and reactant vapor is supplied from the evaporator through a thermostated nozzle into the top of the spouted particle bed (substrate powder). Examples given include the deposition of chromium, molybdenum, and tungsten coatings from carbonyls Cr(CO)6, Mo(CO)6, and W(CO)6 onto diamond powders with grain sizes from 150 to 500 μm, when coatings up to 1 μm thick were obtained at the reactor efficiency (the degree of the reactant conversion to the coating) within 42–77 %. In addition to the set-up design and process parameters, the saturated vapor pressure of carbonyls, chemical reactions during the deposition from carbonyls, and fluidized bed hydrodynamics are discussed.

Towards Selective Removal of Bromide from Drinking Water Resources using Electrochemical Desalination

Disinfection of drinking water is crucial in water treatment as it suppresses waterborne pathogenic diseases. However, as an unintended consequence, disinfection generates disinfection byproducts (DBP). DBPs are cytotoxic, carcinogenic, and nephrotoxic especially when they are brominated. Brominated DBP formation is governed by the interaction of reactive precursors such as natural organic matter (NOM), and Brˉ with oxidants that are added as disinfectants (e.g., chlorine, chloramines, ozone). Historically, the main strategy to control the formation of DBP was to remove NOM from water by coagulation, adsorption, bio-filtration, pre-oxidation, or membrane separation; however, processes that remove NOM do not necessarily remove Brˉ. Herein, we investigated the utilization of combined capacitive and faradaic ion removal in a flow cell to remove Brˉ as well as Clˉ concurrently with more selectivity towards the former. The effectiveness of the proposed technique was evaluated by determining the maximum salt adsorption capacity and measuring the specific ion concentration with ion chromatography. In a binary equimolar mixture of Brˉ and Clˉ, Brˉ was more selectively adsorbed over Clˉ at 1.2 V applied potential due to the contribution of bromine gas evolution to the capacitive deionization.

Selective catalytic oxidation of formaldehyde on single V- and Cr-atom decorated magnetic C4N3 substrate: A first principles study

Formaldehyde (HCHO) is the most common indoor hazardous pollutant and has attracted great concern because its long-term exposure has adverse health effects on humans. Retention and catalytic oxidation of highly hazardous HCHO is an efficient and environmentally friendly method to use for air remediation, but a major obstacle to this procedure is the lack of an appropriate catalyst. Herein, two-dimensional magnetic C4N3 material with a 3d-transition metal as activate sites was systemically investigated in HCHO oxidation using density functional theory calculations. The results show that V-C4N3 and Cr-C4N3 have high structural stability and shallow activation barriers for O2 decomposition; these characteristics provide the necessary precursors for the subsequent oxidation reaction. Moreover, the V-C4N3 and Cr-C4N3 catalysts have unique selective adsorption and catalysis toward HCHO in a mixture of some typical in-door volatile organic compounds (VOCs) and air. The corresponding dynamic barrier for each reaction step was investigated and the mechanism involved in HCHO oxidation was revealed in detail. Aggregation of metal atoms in the V-C4N3 and Cr-C4N3 catalysts is prevented by enormous diffusion resistance, and this is further confirmed by AIMD simulations. These results provide insightful guidance for developing advanced magnetic catalysts for HCHO oxidation to improve the remediation of air contaminants.

Dynamically Cross-Linked Waterborne Polyurethanes: Transalkylation Exchange of C–N Bonds Toward High Performance and Reprocessable Thermosets

Thermosetting waterborne polyurethanes (WPUs) have received wide attention because of their excellent chemical resistance, mechanical properties, and low water absorption. However, their permanent network structure hinders their reprocessing applications, making it vital to prepare reprocessable thermosetting WPUs to minimize plastic pollution. Herein, for the first time, the cross-linked WPUs with excellent reprocessability were designed and synthesized by introducing covalent adaptable networks (CANs) in the form of quaternary ammonium alkyl chains. Our methodology combined CO2-triggered WPUs (CO2-triggered WPUs) with 1,6-diiodohexane. After the CO2 evaporated during film formation, the CO2-triggered WPUs left tertiary amine groups as reaction precursors, which could cross-link into a WPU CAN with 1,6-diiodohexane. All cross-linked WPUs possessed classic vitrimer performance including stress relaxation and malleability, as confirmed by stress-relaxation and hot-press tests. The results showed that cross-linked WPUs had excellent reprocessability and high mechanical properties, and the recovery ratios of the mechanical properties for the recycled samples were over 80% and the tensile strength was more than 17 MPa. More importantly, the cross-linked WPUs’ antibacterial rates of Staphylococcus aureus and Escherichia coli were 94.3 and 89.5%, respectively. This research offers a new method to synthesize high-performance WPUs via facile quaternary ammonium reversible cross-linking and demonstrates that WPU CANs have great potential as sustainable materials.

On-Surface Synthesis of Unsaturated Hydrocarbon Chains through C-S Activation.

We use an on‐surface synthesis approach to drive the homocoupling reaction of a simple dithiophenyl‐functionalized precursor on Cu(111). The C−S activation reaction is initiated at low annealing temperature and yields unsaturated hydrocarbon chains interconnected in a fully conjugated reticulated network. High‐resolution atomic force microscopy imaging reveals the opening of the thiophenyl rings and the presence of trans‐ and cis‐oligoacetylene chains as well as pentalene units. The chemical transformations were studied by C 1s and S 2p core level photoemission spectroscopy and supported by theoretical calculations. At higher annealing temperature, additional cyclization reactions take place, leading to the formation of small graphene flakes.

A nano-liter droplet-based microfluidic reactor serves as continuous large-scale production of inorganic perovskite nanocrystals

Lead halide perovskite nanocrystals (NCs) exhibit high photoluminescence quantum yield (PLQY), high defect tolerance, narrow half peak width, and wide luminous gamut, making them the ideal optoelectronic materials in numerous fields. Nonetheless, their production still suffers from the limited productivity at the bench level. In this work, we fabricated CsPbX3 (X = Cl, Br, I) NCs within droplet-based micro-reactors, where both the nucleation and growth processes could be precisely controlled inside 130-nL microdroplets. This provides a new paradigm for the large-scale synthesis of perovskite NCs with high PLQY. Compared with other synthetic methods, this method can increase the concentration of reactant precursors by 3–116 times, while lowering the ligand to reactant ratio to 2%–50% of the commonly used hot-injection method. By modulating the reaction temperature and residence time, the structure-function relationship between the morphology of NCs and PL properties was extensively investigated. The microfluidic-based process allows the flexible adjustment in the proportion of PbX2 precursors to achieve the fabrication of perovskite NCs whose luminescence range covers the entire visible spectrum (406–677 nm) within one reaction. Finally, perovskite NCs with different halide ions were encapsulated in polymethyl methacrylate to prepare a colored light-emitting diode strip.

Thiophene α-Chain-End-Functionalized Oligo(2-methyl-2-oxazoline) as Precursor Amphiphilic Macromonomer for Grafted Conjugated Oligomers/Polymers and as a Multifunctional Material with Relevant Properties for Biomedical Applications.

Because the combination of π-conjugated polymers with biocompatible synthetic counterparts leads to the development of bio-relevant functional materials, this paper reports a new oligo(2-methyl-2-oxazoline) (OMeOx)-containing thiophene macromonomer, denoted Th-OMeOx. It can be used as a reactive precursor for synthesis of a polymerizable 2,2’-3-OMeOx-substituted bithiophene by Suzuki coupling. Also a grafted polythiophene amphiphile with OMeOx side chains was synthesized by its self-acid-assisted polymerization (SAAP) in bulk. The results showed that Th-OMeOx is not only a reactive intermediate but also a versatile functional material in itself. This is due to the presence of 2-bromo-substituted thiophene and ω-hydroxyl functional end-groups, and due to the multiple functionalities encoded in its structure (photosensitivity, water self-dispersibility, self-assembling capacity). Thus, analysis of its behavior in solvents of different selectivities revealed that Th-OMeOx forms self-assembled structures (micelles or vesicles) by “direct dissolution”.Unexpectedly, by exciting the Th-OMeOx micelles formed in water with λabs of the OMeOx repeating units, the intensity of fluorescence emission varied in a concentration-dependent manner.These self-assembled structures showed excitation-dependent luminescence as well. Attributed to the clusteroluminescence phenomenon due to the aggregation and through space interactions of electron-rich groups in non-conjugated, non-aromatic OMeOx, this behavior certifies that polypeptides mimic the character of Th-OMeOx as a non-conventional intrinsic luminescent material.

Silicon nanocrystals-embedded carbon nanofibers from hybrid polyacrylonitrile – TEOS precursor as high-performance lithium-ion battery anodes

The high capacity of silicon (Si) for lithium incorporation makes it a promising anode material for lithium-ion batteries; however, pulverization of Si due to huge volume changes during lithiation/delithiation leads to significant capacity loss during cycling. To address challenges in low cyclability, nanostructured Si in carbon nanocomposites offers an attractive solution. In this study, we report an efficient method for the synthesis of a nanocomposite containing Si nanoparticles homogeneously embedded in an electrically conductive carbon nanofiber (CNF) network. Electrospinning of polyacrylonitrile (PAN) solution containing hydrolyzed tetraethyoxysilane (TEOS), as a Si precursor, and subsequent carbonization of hybrid nanofibers yielded a composite of SiO2 ultrafine nano-domains in the carbon network (C-SiO2). Low temperature molten salt-assisted aluminothermic reduction of C-SiO2 nanofibers allowed us to produce a C-Si/SiOx nanocomposite without forming detrimental SiC, which is thermodynamically favorable at high temperatures in a system with a high interfacial surface area between the carbon and SiO2 phases. The nanocomposite C-Si/SiOx anodes showed a reversible capacity of 860 mAh g−1 at a current rate of 200 mA g−1, retaining a capacity of 680 mAh g−1 after 100 cycles. In addition, the nanocomposite anodes delivered a reversible capacity of 569 mAh g−1 at a current rate of 400 mA g−1 while maintaining 95% of maximum capacity after subsequent 100 cycles. This study demonstrates the capability of designing nanocomposite anodes from reaction precursors combined with low-temperature aluminothermic reduction to produce a capacity-retaining anode composite of Si nanocrystals uniformly dispersed in the carbon matrix.

Substrate temperature-controlled precursor reaction mechanism of PEALD-deposited MoOx thin films

Substrate temperature-controlled precursor reaction mechanism of PEALD-deposited MoOx thin films

Facile fabrication of antibacterial and fire-safety multifunctional cotton fabric with a triazine-phosphonate N-halamine

Cotton fabric, a cellulose-based substance, is widely utilized in our daily lives, yet it is simple to breed microorganisms and cause fires, a problem that must be addressed immediately. The goal of this research was to create a multi-purpose cotton fabric with biocidal efficacy and flame retardacy to lift a hand against harmful microorganism and fire hazard. To achieve this target, the typical reactivity of cyanuric chloride was utilized, and a reactive triazine-phosphonate N-halamine precursor (TDAD) was designed and deposited onto cotton fabric through traditional method. After chlorination, TDAD-modified cotton fabric presented strongly bactericidal effect against both positive and negative bacteria, all of which could be inactivated within 1 min. In addition, the multi-purpose cotton fabric demonstrated satisfactory flame retardancy with 27.5 % of LOI value and successfully passed the flame test with self-extinguishing effect due to the joint effect of P and N elements. Furthermore, the multi-purpose coating displayed slight influence on the cytocompatibility, tensile strength and whiteness of cotton fabric. Consequently, this work offers an efficient mean to prepare multi-purpose cotton fabric with high 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.

Upcycling Polytetrahydrofuran to Polyester

Upcycling Polytetrahydrofuran to Polyester

Phase transition of SrCo0.9Fe0.1O3 electrocatalysts and their effects on oxygen evolution reaction

AbstractComplex metal oxide has emerged as an important class of electrocatalyst for oxygen evolution reaction (OER) because of its flexibility in the crystal phase and relative ease in the control of defect structures. While different crystalline phases and solid structures may be produced from the same reactant precursors, their phase transitions and OER performances are not well understood. In this work, we present the preparation of different phases of SrCo0.9Fe0.1O3‐δ (nominal ratio) solids using a sol–gel method and the structure–catalytic property relationship of both crystalline and amorphous structures formed at different temperatures. We observed as synthetic temperature increased, phase and composition transitions occurred from the amorphous phase to strontium carbonate and cobalt oxide, to oxygen‐deficient perovskite, and finally to perovskite. The OER activity depended highly on crystal structures. The oxygen‐deficient perovskite prepared at 750°C exhibited the highest catalytic activity, while the perovskite showed the lowest activity. X‐ray photoelectron spectroscopy analysis reveals the change of oxidation state occurred during the phase transition. This work provides a useful guideline for the design of OER electrocatalysts through controlling the crystal structures and defects in complex metal oxides, such as perovskite.

Analysis of carbazole alkaloids in Murraya koenigii by means of high performance liquid chromatography coupled to Tandem mass spectrometry with a predictive multi experiment approach

Murraya koenigii (M. koenigii) is recognized as one of the most significant Indian medicinal plants, due to its therapeutic properties. In fact, various biological activities, including anti-inflammatory and antifungal, are attributed to carbazole alkaloids (CAs) and their metabolites, but it is still difficult to achieve a full classification of these compounds because of their heterogeneous structures. For this reason, the development of new strategies for their identification is necessary. In this work, a reliable method, including the simultaneous quantification of three main CAs of Murraya (Mahanimbine, Koenimbine and Koenigicine) and a putative identification for other compounds belonging to the huge family of CAs, was developed by means of HPLC-MS/MS. Also, an efficient extraction procedure followed by a suitable clean-up step was presented, in order to obtain reliable recoveries (resulted from 60 to 85% for all the analytes). The analyses were performed by using predictive multi experiment approach based on information-dependent acquisition (IDA), coupling multiple reaction monitoring (MRM) and precursor ion (PI) as survey scans, and enhanced product ion scan (EPI) as dependent scan. Competitive Fragmentation Modeling-ID (CFM-ID) was used to predict MS/MS spectra from the chemical structures of the compounds in order to create a suitable MRM inclusion list. The obtained results showed that this method can simultaneously provide quantitative information for the target analytes (Mahanimbine (7.22–5.62 mg/kg), Koenimbine (1.26–1.62 mg/kg) and Koenigicine (0.44–1.77 mg/kg)) and a putative identification for several compounds belonging to different classes of CAs which are not included in the target list, thanks to PI survey scan.

An Updated Anthropogenic Emission Inventory of Reactive Chlorine Precursors in China

An Updated Anthropogenic Emission Inventory of Reactive Chlorine Precursors in China

Chemical reaction mechanism of plasma scrubber for by-product treatment in TiN-atomic layer deposition processes

In atomic layer deposition (ALD), unreacted precursors released from the process chamber can cause agglomeration of powders inside the fore line, exhaust line, and dry pump. Thus, it shortens the preventive maintenance cycle of dry pumps in a high-volume manufacturing environment. A plasma pretreatment system (PPS) is designed to facilitate formation of by-product powders prior to entering the mechanical pumps in ALD systems. In this paper, we present the optimal operating conditions of a PPS for achieving an optimal TiO2 substitution rate with a TiCl4 precursor. To expedite the chemical reactions of unreacted precursors with oxygen, we studied reaction simulation and computational fluid dynamics to optimize the flow of oxygen in the PPS. The results established the basis for the gas flow conditions of actual processes. Gas waste and NO x production can be reduced through optimizing the amount of O2 supply.

A Bi(OTf)3-Promoted Hydrosulfonylation of Alkenes with Sulfonyl Hydrazides: An Approach to Branched Sulfones.

The Bi(OTf)3-promoted hydrosulfonylation of alkenes with sulfonyl hydrazides to produce branched sulfones is reported, in which various branched sulfones (>40 examples) have been prepared in moderate to good yields. The gram-scale reaction and synthesis of the experimental inhibitor precursor showed the potential application. A preliminary mechanistic study revealed that double-bond migration to form the α,β-conjugated alkene is crucial for this transformation.

Synthesis and Structures of Benzyl‐ and Amido‐Substituted N‐Heterocyclic Palladium Carbene Complexes

AbstractThe benzyl‐ and amido‐substituted benzimidazolium ligand precursor [Bz‐BimH‐CH2CONH2]Br (1) was synthesized. Under different conditions, the reactions of this ligand precursor with PdBr2 produced palladium carbene complexes: Pd[(Bz‐Bim‐CH2CONH2)2Br2] (2), Pd(Bz‐Bim‐CH2CONH)2 (3), [Pd(Bz‐Bim‐CH2CONH2)(Py)Br2] (4), or [Pd(Bz‐Bim‐CH2CONH2)(CH3CN)Br2] (5). These complexes were characterized by NMR, IR, and single‐crystal X‐ray diffraction analyses. Complex 2 contains two trans rotamers in both the solution and solid state, and a crystal that possesses a trans‐anti conformation is confirmed through single‐crystal X‐ray diffraction analysis. Complex 3 contains two cis‐orientated bidentate carbene ligands, and complexes 4 and 5 are mono‐carbene complexes. The chelate rings in complex 3 rendered the methylene protons of the amido‐substituted diastereotopic, and a long range (six bond) through bond interaction between the carbonyl carbon and the methylene protons of the benzyl‐substituent was observed through the HMBC experiment. The catalytic activity studies indicated 4 and 5 are better catalysts in Suzuki‐Miyaura coupling reaction.