This review is focused on the strategies and designs of magnetic nanostructured catalysts showing the enhanced and sustainable catalytic performances for the heterogeneous reduction of nitoaromatics. ...Magnetic catalysts have the benefits of easy recovery and reuse after the completion of the reactions and green chemical processes. Magnetic separation, among the various procedures for removing catalysts, not only obviates the requirement of catalyst filtration or centrifugation after the completion of reactions, but also provides a practical technique for recycling the magnetized nanostructured catalysts. Consequently, discussions will address the methodologies and exemplars for the reusable magnetic composite catalysts. Because the synthesis of ideal magnetic nanostructured catalysts is of primary importance in the development of high-quality sustainable processes, the designs, preparation methods and recyclability of various recoverable magnetic nanostructured catalysts are emphasized. The representative methods and strategies for the synthesis of durable and reusable magnetic nanostructured catalysts are highlighted. The advantages, disadvantages, recyclability and the efficiency of the introduced heterogeneous systems have been explored in the reduction of nitrobenzene derivatives.
Display omitted
•Advances in oxidations by polymer-supported palladium nanoparticles and complexes, are described.•Synthetic methods are highlighted for attaining the polymer-supported palladium ...catalysts.•Catalytic oxidation of alcohols, olefins, alkenes, carbon monoxide, etc. are presented.•Future challenges and opportunities on oxidation reactions using Pd catalysts, are discussed.
This review describes the recent advances in the fabrication, characterization and applications of palladium nanoparticles (Pd NPs)/complexes supported on polymers. Nanostructured materials and NPs of various natures, shapes and sizes in combination with polymers, provide unique physicochemical properties and significant potential applications. An overview in catalysis encompassing the preparation of polymer-supported Pd nanocatalysts and Pd complexes for the oxidation of alcohols, olefins, alkenes, carbon monoxide, etc. is presented. Heterogeneous oxidation catalysis, a vital tool in chemical synthesis and transformations, includes the development of various synthetic strategies for the fabrication of Pd-based catalysts; eminent role played by polymer supports in the morphological and structural properties of the ensuing catalysts, is highlighted.
Neuro-transmitters have been considered to be essential biochemical molecules, which monitor physiological and behavioral function in the peripheral and central nervous systems. Thus, it is of high ...pharmaceutical and biological significance to analyze neuro-transmitters in the biological samples. So far, researchers have devised a lot of techniques for assaying these samples. It has been found that electro-chemical sensors possess features of robustness, selectivity, and sensitivity as well as real-time measurement. Graphene quantum dots (GQDs) and carbon QDs (CQDs) are considered some of the most promising carbon-based nanomaterials at the forefront of this research area. This is due to their characteristics including lower toxicity, higher solubility in various solvents, great electronic features, strong chemical inertness, high specific surface areas, plenty of edge sites for functionalization, and versatility, in addition to their ability to be modified
via
absorbent surface chemicals and the addition of modifiers or nano-materials. Hence in the present review, the synthesis methods of GQDs and CQDs has been summarized and their characterization methods also been analyzed. The applications of carbon-based QDs (GQDs and CQDs) in biological and sensing areas, such as biological imaging, drug/gene delivery, antibacterial and antioxidant activity, photoluminescence sensors, electrochemiluminescence sensors and electrochemical sensors, have also been discussed. This study then covers sensing features of key neurotransmitters, including dopamine, tyrosine, epinephrine, norepinephrine, serotonin and acetylcholine. Hence, issues and challenges of the GQDs and CQDs were analyzed for their further development.
Carbon and graphene quantum dots for biological and sensing applications of neurotransmitters.
Spark plasma sintering was applied on ZrB2–25 vol% SiC composites doped with 2, 4 and 6 wt% vanadium at 1900 °C for 7 min under 40 MPa pressure. A comprehensive microstructure-mechanical properties ...correlation study was carried out on the obtained near-fully dense composites. The composite samples were microstructurally studied via scanning electron microscopy and energy dispersive spectroscopy. Phase analysis and mechanical investigations were carried out by X-ray diffraction spectrometry and Vickers indentation method, respectively. The results indicated that vanadium not only promotes reactive sintering mechanism, but also increases the fracture toughness via transformation toughening mechanism, majorly due to the in-situ synthesized reinforcement phases such as VB2. It was also found that besides the reinforcing effect of VB2, the obtained indentation fracture toughness may not follow a distinct trend, particularly due to internal microcracking of VB2, derived by its volume changes. Although increasing the vanadium content from 2 to 4 wt% resulted in enhanced hardness (from 22.1 to 22.9 GPa) and fracture toughness (from 4.0 to 4.5 MPa m1/2), further vanadium addition up to 6 wt% worsened the hardness. Based on microstructural and phase analyses, such a decreased hardness was attributed to the increased volume fraction of low-melting point reactive sintering byproducts, particularly SiO2 and VSi2.
•Fully-dense ZrB2–SiC composites were achieved using vanadium additive.•The best mechanical and microstructural behavior were obtained by 4 wt% vanadium.•Contradictory toughening behavior of in-situ synthesized VB2 was scrutinized.
This research presents the influence of Al addition on microstructure and mechanical behavior of ZrB2–SiC ultra-high temperature ceramic matrix composite (UHTCMC) fabricated by spark plasma sintering ...(SPS). A 2.5 wt% Al-doped ZrB2–20 vol% SiC UHTCMC was produced by SPS method at 1900 °C under a pressure of 40 MPa for 7 min. The microstructural and phase analysis of the composite showed that aluminum-containing compounds were formed in-situ during the SPS as a result of chemical reactions between Al and surface oxide films of the raw materials (i.e. ZrO2 and SiO2 on the surfaces of ZrB2 and SiC particles, respectively). The Al dopant was completely consumed and converted to the intermetallic Al3Zr and Al4Si compounds as well as Al2O3 and Al2SiO5. A relative density of 99.8%, a hardness (HV5) of 21.5 GPa and a fracture toughness (indentation method) of 6.3 MPa m1/2 were estimated for the Al-doped ZrB2–SiC composite. Crack bridging, branching, and deflection were identified as the main toughening mechanisms.
Abstract
Plasmonic AgPd alloy nanoparticles (AgPd
NPs
) decorated on single-layer carbon nitride (AgPd
NPs
/SLCN) for the designing of the Mott-Schottky junction were constructed with the ...ultrasonically assisted hydrothermal method and used toward photo evolution H
2
from formic acid (FA) at near room temperature (30 °C). The Pd atom contains active sites that are synergistically boosted by the localized surface plasmon resonance (LSPR) effect of Ag atoms, leading to considerably enhanced photocatalytic properties. The photoactive AgPd
NPs
/SLCN obtained supreme catalytic activity to produce 50 mL of gas (H
2
+ CO
2
) with the initial turnover frequency of 224 h
-1
under light irradiation. The catalyst showed stable catalytic performance during successive cycles.
Scientists have categorized conductive polymers as materials having strongly reversible redox behavior and uncommon combined features of plastics and metal. Because of their multifunctional ...characteristics,
e.g.
, simplistic synthesis, acceptable environmental stability, beneficial optical, electronic, and mechanical features, researchers have largely considered them for diverse applications. Therefore, their capability of catalyzing several electrode reactions has been introduced as one of their significant features. A thin layer of the conducting polymer deposited on the substrate electrode surface can augment the electrode process kinetics of several solution species. Such electrocatalytic procedures with modified conducting polymer electrodes can create beneficial utilization in diverse fields of applied electrochemistry. This review article explores typical recent applications of conductive polymers (2016-2020) as active electrode materials for energy storage applications, electrochemical sensing, and conversion fields such as electrochemical supercapacitors, lithium-ion batteries, fuel cells, and solar cells.
Scientists have categorized conductive polymers as materials having strongly reversible redox behavior and uncommon combined features of plastics and metal.
Temperature and electric current distributions in the spark plasma sintering process of a ZrB2 sample were simulated using finite element method. The main source of heating in spark plasma sintering ...is perceived as the Joule heating effect, which is a result of electric current distribution in the setup. Two sets of governing equations including the electric charge and energy conversion are utilized to obtain the temperature distribution. The acquired results for the sintering process were compared with Al2O3 sintered counterpart propounding two different mechanisms of heating proceeding. Al2O3 is an electrical insulator; therefore, the operating electric current concentrates in the graphite die close to the sample, whereas the ZrB2 is an electric conductor resulting in a more uniform current distribution. In the non–conductive sample, heat is generally generated in the graphite die and conducted to the sample. Both Joule heating effect and thermal conduction from the die to the sample are involved in the sintering of ZrB2. The temperature distribution in electric resistant materials is more uniform than electric conductor cases. This is attributed to the different dominant heating mechanism of materials.
In this study, heat treatment effects on adsorption capabilities of nanoporous carbon particles derived from the metal-organic framework (MOF) were investigated at different temperatures. The carbon ...nanoparticles were synthesized by one-step carbonization of the metal-organic framework crystals. The results showed that the MOF derived carbons at 1000 °C had an outstanding surface area and micropore volume (1337.9 m2·g−1, 0.72 cm3·g−1) compared to nanoparticles carbonized at 900 °C (1073.9 m2·g−1, 0.58 cm3·g−1) and 800 °C (480.32 m2·g−1, 0.25cm3·g−1). The acid treatment was applied on the 800 °C carbonized specimen due to its lower specific surface area than others, and an increase in its surface area and micropore volume (856.71 m2·g−1, 0.28 cm3·g−1) was observed. The heat treatment at 1000 °C had a significant impact on the adsorption capacity of synthesized MOF derived porous carbon for the removing of methylene blue (MB) (about 2724 mg·g−1) from wastewater. The physicochemical properties of the MOF derived carbon samples were characterized by X-ray diffraction (XRD), HR-TEM, N2 adsorption-desorption, FTIR, Raman Spectroscopy, TGA, and X-ray photoelectron spectroscopy (XPS) analyses. From the XPS results, the chemical environment of oxygen-containing functional groups (C−O and CO) changed by enhancing the temperature that provides sufficient reactive sites for the MB binding during the sorption process. Also, by investigation of the adsorption isotherms of Langmuir, Freundlich Dubinin-Radushkevich (D-R), and Temkin concluded that the D-R isotherm model fitted better with the experimental data than the others. The best kinetic model for the MB adsorption onto the synthesized MOF derived carbons was the pseudo-second-order model. Based on the thermodynamic calculations, the adsorption process is found to be spontaneous and endothermic.
Display omitted
•Porous carbons with surface area of 1338 m2g-1 were synthesized from a low-quality MOF by one-step pyrolyzing•The synthesized porous carbons have high adsorption capacity of about 2724 mg. g-1 for MB•The effects of heat treatment on the structure and performance of the synthesized adsorbents were examined•Kinetic and isotherm modeling were performed to predict the MB adsorption
Display omitted
•A novel NS-CN/FeOCl system was synthesized via the calcination-hydrothermal method.•The prepared samples were employed for nitrogen fixation under mild condition.•The ...NS-CN/FeOCl(20%) exhibits 3.4 times higher than the CN in the ammonia production.•The mechanism of N2 fixation was illustrated for a better understanding of the photoactivity.
Climate change, global warming, and population growth have led researchers to use eco-sociable procedures for the N2 reduction reaction. It has discovered that N2 molecule can be transformed into NH3 in ambient circumstances with nanocomposites upon visible irradiation. In this research paper, a new visible-light-driven photocatalyst was constructed, with various weight percents of FeOCl particles (10, 20, 30, and 40%) that have adhered on NS-CN. Subsequently, multiple features of the nanocomposites were assayed in detail. The results illustrated that the NS-CN/FeOCl (20%) system has remarkable photoactivity in the NH4+ production reaction in comparison with the NS-CN and CN, which showed 2.5 and 8.6 higher activity, respectively. The durability of NS-CN/FeOCl (20%) system, as a substantial factor, was assayed for 5 recycles. Moreover, the effect of electron quenchers, pH of media, and solvent was studied. At last, a feasible Z-scheme mechanism for the remarkable improvement of N2 fixation efficiency was offered.
PDF
