Synthesis of High-Entropy Perovskite Hydroxides as Bifunctional Electrocatalysts for Oxygen Evolution Reaction and Oxygen Reduction Reaction.

Oxygen reduction reaction (ORR) and oxygen evolutionc reaction (OER) are important chemical reactions for a rechargeable lithium-oxygen battery (LOB). Recently, high-entropy alloys and oxides have attracted much attention because they showed good electrocatalytic performance for oxygen evolution reaction (OER) and/or oxygen reduction reaction (ORR). In this study, we aimed to synthesize and characterize CoSn(OH)6 and two types of high-entropy perovskite hydroxides, that is, (Co0.2Cu0.2Fe0.2Mn0.2Mg0.2)Sn(OH)6 (CCFMMSOH) and (Co0.2Cu0.2Fe0.2Mn0.2Ni0.2)Sn(OH)6 (CCFMNSOH). TEM observation and XRD measurements revealed that the high-entropy hydroxides CCFMMSOH and CCFMNSOH had cubic crystals with sides of approximately 150-200 nm and crystal structures similar to those of perovskite-type CSOH. LSV measurement results showed that the high-entropy hydroxides CCFMMSOH and CCFMNSOH showed bifunctional catalytic functions for the ORR and OER. CCFMNSOH showed better catalytic performance than CCFMMSOH.

Reduced graphene oxide/zinc oxide composite as an electrochemical sensor for acetylcholine detection.

Acetylcholine (ACh) plays a pivotal role as a neurotransmitter, influencing nerve cell communication and overall nervous system health. Imbalances in ACh levels are linked to neurodegenerative diseases, such as Alzheimer's and Parkinson's. This study focused on developing electrochemical sensors for ACh detection, utilizing graphene oxide (GO) and a composite of reduced graphene oxide and zinc oxide (rGO/ZnO). The synthesis involved modified Hummers' and hydrothermal methods, unveiling the formation of rGO through deoxygenation and the integration of nano-sized ZnO particles onto rGO, as demonstrated by XPS and TEM. EIS analysis also revealed the enhancement of electron transfer efficiency in rGO/ZnO. Cyclic voltammograms of the electrode, comprising the rGO/ZnO composite in ACh solutions, demonstrated prominent oxidation and reduction reactions. Notably, the composite exhibited promise for ACh detection due to its sensitivity, low detection threshold, reusability, and selectivity against interfering compounds, specifically glutamate and gamma-aminobutyric acid. The unique properties of rGO, such as high specific surface area and electron mobility, coupled with ZnO's stability and catalytic efficiency, contributed to the composite's potential in electrochemical sensor applications. This research, emphasizing the synthesis, fabrication, and characterization of the rGO/ZnO composite, established itself as a reliable platform for detecting the acetylcholine neurotransmitter.

Solution-Plasma Synthesis and Characterization of Transition Metals and N-Containing Carbon-Carbon Nanotube Composites.

Lithium-air batteries (LABs) have a theoretically high energy density. However, LABs have some issues, such as low energy efficiency, short life cycle, and high overpotential in charge-discharge cycles. To solve these issues electrocatalytic materials were developed for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which significantly affect battery performance. In this study, we aimed to synthesize electrocatalytic N-doped carbon-based composite materials with solution plasma (SP) using Co or Ni as electrodes from organic solvents containing cup-stacked carbon nanotubes (CSCNTs), iron (II) phthalocyanine (FePc), and N-nethyl-2-pyrrolidinone (NMP). The synthesized N-doped carbon-based composite materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). TEM observation and XPS measurements revealed that the synthesized carbon materials contained elemental N, Fe, and electrode-derived Co or Ni, leading to the successful synthesis of N-doped carbon-based composite materials. The electrocatalytic activity for ORR of the synthesized carbon-based composite materials was also evaluated using electrochemical measurements. The electrochemical measurements demonstrated that the electrocatalytic performance for ORR of N-doped carbon-based composite material including Fe and Co showed superiority to that of N-doped carbon-based composite material including Fe and Ni. The difference in the electrocatalytic performance for ORR is discussed regarding the difference in the specific surface area and the presence ratio of chemical bonding species.

Size-Dependent Graphene Support for Decorating Gold Nanoparticles as a Catalyst for Hydrogen Evolution Reaction with Machine Learning-Assisted Prediction.

Size-dependent two-dimensional (2D) materials (e.g., graphene) have been recently used to improve their performance in various applications such as membrane filtration, energy storage, and electrocatalysts. It has also been demonstrated that 2D nanosheets can be one of the promising support materials for decorating nanoparticles (NPs). However, the optimum nanosheet size (lateral length and thickness) for supporting NPs has not yet been explored to enhance their catalytic performance. Herein, we elucidate the mechanism behind size-dependent graphene (GP) as a support due to which gold nanoparticles (AuNPs) are used as an active catalyst for the hydrogen evolution reaction (HER). Surprisingly, the decoration of AuNPs increased with the increasing nanosheet size, counter to what is widely reported in the literature (high surface area for smaller nanosheet size). We found that a large graphene nanosheet (lGP; ∼800 nm) used as the AuNP support (lGP/AuNPs) exhibited superior performance for the HER with long-term stability. The lGP/AuNPs with a suitable content of AuNPs provides a low overpotential and a small Tafel slope, being lower than that of other reported carbon-based HER electrocatalysts. This results from highly exposed active sites of well-dispersed AuNPs on lGP giving high conductivity. The laminar structure of the stacked graphene nanosheets and the high wettability of the lGP/AuNPs electrode surface also play crucial roles in enhancing electrolytes for penetration in the electrode, suggesting a highly electrochemical surface area. Moreover, machine learning (Random Forest) was also used to reveal the essential features of the advanced catalytic material design for catalyst-based applications.

Introducing micropores into carbon nanoparticles synthesized via a solution plasma process by thermal treatment and their charge storage properties in supercapacitors.

Carbon materials synthesized via a solution plasma process (SPP) have recently shown great potential for various applications. However, they mainly possess a meso-macroporous structure with a lack of micropores, which limits their applications for supercapacitors. Herein, carbon nanoparticles (CNPs) were synthesized from benzene via SPP and then subjected to thermal treatment at different temperatures (400, 600, 800, and 1000 °C) in an argon environment. The CNPs exhibited an amorphous phase and were more graphitized at high treatment temperatures. A small content of tungsten carbide particles was also observed, which were encapsulated in CNPs. An increase in treatment temperature led to an increase in the specific surface area of CNPs from 184 to 260 m2 g-1 through the development of micropores, while their meso-macropore structure remained unchanged. The oxygen content of CNPs decreased from 14.72 to 1.20 atom% as the treatment temperature increased due to the degradation of oxygen functionality. The charge storage properties of CNPs were evaluated for supercapacitor applications by electrochemical measurements using a three-electrode system in 1 M H2SO4 electrolyte. The CNPs treated at low temperatures exhibited an electric double layer and pseudocapacitive behavior due to the presence of quinone groups on the carbon surface. With increasing treatment temperature, the electric double layer behavior became more dominant, while pseudocapacitive behavior was suppressed due to the quinone degradation. Regarding cycling stability, the CNPs treated at high temperatures (with a lack of oxygen functionality) were more stable than those treated at low temperatures. This work highlights a way of introducing micropores into CNPs derived from SPP via thermal treatment, which could be helpful for controlling and adjusting their pore structure for supercapacitor applications.

Sugar molasses as a sustainable precursor for the synthesis of graphene sand composite adsorbent for tetracycline and methylene blue removal.

Sugar molasses from agricultural waste could be a sustainable carbon source for the synthesis of graphene adsorbent introduced in this work. The sugar molasses was successfully converted to graphene-like material and subsequently coated on the sand as graphene sand composite (GSC), as proven by XRD, XPS, Raman spectroscopy, and SEM with EDX mapping analyses. The adsorption performance of GSC was evaluated against the removal of Tetracycline (TC) and methylene blue (MB) pollutants from an aqueous solution in a fixed bed column continuous-flow adsorption setup. The effect of different process conditions: bed height (4-12 cm), influent flow rate (3-7 mL/min), and contaminants' concentration (50-150 ppm) was investigated. The results revealed that column performance was improved by increasing the bed depth and lowering the flow rate and concentration of the pollutants. The best removal efficiency was obtained when the bed height was 12 cm, the influent flow rate of 3 mL/min, and the pollutants' initial concentration was 50 mg/L. Thomas, Adams-Bohart, and Yoon-Nelson models were attempted to fit the breakthrough curves. Regeneration of the GSC indicated the decline of breakthrough time from 240-280 to 180 min, reflecting the decrease in adsorptive sites due to the incomplete regeneration process. Overall, sugar molasses was shown to be a low-cost precursor for synthesizing valuable graphene material in the form of GSC, which can reduce the problem for industrial waste management of sugar molasses, and the GSC could be used as an adsorbent for environmental application.

Porous Biochar Supported Transition Metal Phosphide Catalysts for Hydrocracking of Palm Oil to Bio-Jet Fuel.

The upgrading of plant-based oils to liquid transportation fuels through the hydrotreating process has become the most attractive and promising technical pathway for producing biofuels. This work produced bio-jet fuel (C9-C14 hydrocarbons) from palm olein oil through hydrocracking over varied metal phosphide supported on porous biochar catalysts. Relative metal phosphide catalysts were investigated for the highest performance for bio-jet fuel production. The palm oil's fiber-derived porous biochar (PFC) revealed its high potential as a catalyst supporter. A series of PFC-supported cobalt, nickel, iron, and molybdenum metal phosphides (Co-P/PFC, Ni-P/PFC, Fe-P/PFC, and Mo-P/PFC) catalysts with a metal-loading content of 10 wt.% were synthesized by wet-impregnation and a reduction process. The performance of the prepared catalysts was tested for palm oil hydrocracking in a trickle-bed continuous flow reactor under fixed conditions; a reaction temperature of 420 °C, LHSV of 1 h-1, and H2 pressure of 50 bar was found. The Fe-P/PFC catalyst represented the highest hydrocracking performance based on 100% conversion with 94.6% bio-jet selectivity due to its higher active phase dispersion along with high acidity, which is higher than other synthesized catalysts. Moreover, the Fe-P/PFC catalyst was found to be the most selective to C9 (35.4%) and C10 (37.6%) hydrocarbons.

Nitrogen-doped carbon derived from horse manure biomass as a catalyst for the oxygen reduction reaction.

A massive amount of animal biomass is generated daily from livestock farms, agriculture, and food industries, causing environmental and ecological problems. The conversion of animal biomass into value-added products has recently gained considerable interest in materials science research. Herein, horse manure (HM) was utilized as a precursor for synthesizing nitrogen-doped carbons (NCs) via hydrothermal ammonia treatment and the post pyrolysis process. The ammonia concentration varied between 0.5, 1.0, and 1.5 M in the hydrothermal process. From the comprehensive characterization results, horse manure-derived nitrogen-doped carbons (HMNCs) exhibited an amorphous phase and a hierarchical nanoporous structure. The specific surface area decreased from 170.1 to 66.6 m2 g-1 as the ammonia concentration increased due to micropore deterioration. The nitrogen content was 0.90 atom% even with no ammonia treatment, indicating self-nitrogen doping. With hydrothermal ammonia treatment, the nitrogen content slightly enhanced up to 1.54 atom%. The electrocatalytic activity for the oxygen reduction reaction (ORR) of HMNCs in an alkaline solution was found to be related to nitrogen doping content and porous structure. The ORR activity of HMNCs mainly proceeded via a combination of two- and four-electron pathways. Although the ORR activity of HMNCs was still not satisfactory and comparable to that of a commercial Pt/carbon catalyst, it showed better long-term durability. The results obtained in this work provide the potential utilization of HM as a precursor for ORR catalysts and other related applications.

Insight on Solution Plasma in Aqueous Solution and Their Application in Modification of Chitin and Chitosan.

Sustainability and environmental concerns have persuaded researchers to explore renewable materials, such as nature-derived polysaccharides, and add value by changing chemical structures with the aim to possess specific properties, like biological properties. Meanwhile, finding methods and strategies that can lower hazardous chemicals, simplify production steps, reduce time consumption, and acquire high-purified products is an important task that requires attention. To break through these issues, electrical discharging in aqueous solutions at atmospheric pressure and room temperature, referred to as the "solution plasma process", has been introduced as a novel process for modification of nature-derived polysaccharides like chitin and chitosan. This review reveals insight into the electrical discharge in aqueous solutions and scientific progress on their application in a modification of chitin and chitosan, including degradation and deacetylation. The influencing parameters in the plasma process are intensively explained in order to provide a guideline for the modification of not only chitin and chitosan but also other nature-derived polysaccharides, aiming to address economic aspects and environmental concerns.

Au nanoparticle-decorated TiO2 hollow fibers with enhanced visible-light photocatalytic activity toward dye degradation.

TiO2 hollow fibers (THF) were prepared by a template method using kapok as a biotemplate and subsequently decorated by plasmonic Au nanoparticles using a solution plasma process. The THF exhibited an anatase phase and a hollow structure with a mesoporous wall. Au nanoparticles with a diameter of about 5-10 nm were uniformly distributed on the THF surface. Au nanoparticles-decorated TiO2 hollow fibers (Au/THF) have enhanced photocatalytic activity toward methylene blue degradation under visible light-emitting diode (Vis-LED) as compared to pristine THF and P25. This could be attributed to combined effects including effective light-harvesting by a hollow structure, large surface area due to a mesoporous wall of THF, and visible-light absorption and efficient charge separation induced by Au nanoparticles. The Au/THF also showed good recyclability and separation ability.

Titanium dioxide and fluoropolymer-based coating for smart fabrics with antimicrobial and water-repellent properties.

In the coronavirus disease 2019 pandemic, protective clothing is required for medical staff at risk of infection. This study proposes functional smart fabrics with antimicrobial and water-repellent properties, using titanium dioxide (TiO2) and fluoropolymer-based precursors as coating materials. Experimental results indicated a uniform distribution of TiO2 particles with an average size below 200 nm throughout the fabric. A zone of inhibition test revealed that the fabric inhibited bacterial growth, specifically of Staphylococcus aureus and Klebsiella pneumoniae, before and after 10 wash cycles of the fabric. In wetting angle measurements, the contact angles of water droplets on the fabric ranged from 120° to 139°. A water repellency test confirmed that the coated fabrics retained their water-repellent property after 10 wash cycles.

Nitriding an Oxygen-Doped Nanocarbonaceous Sorbent Synthesized via Solution Plasma Process for Improving CO2 Adsorption Capacity.

The synthesis of carbon nanoparticles (Cn) and oxygen-doped nanocarbon (OCn) was successfully done through a one-step synthesis by the solution plasma process (SPP). The Cn and OCn were nitrogen-doped by nitridation under an ammonia atmosphere at 800 °C for 2 h to yield NCn and NOCn, respectively, for carbon dioxide (CO2) adsorption. The NOCn exhibited the highest specific surface area (~570 m2 g-1) and highest CO2 adsorption capacity (1.63 mmol g-1 at 25 °C) among the synthesized samples. The primary nitrogen species on the surface of NOCn were pyridinic-N and pyrrolic-N. The synergistic effect of microporosity and nitrogen functionality on the NOCn surface played an essential role in CO2 adsorption enhancement. From the thermodynamic viewpoint, the CO2 adsorption on NOCn was physisorption, exothermic, and spontaneous. The NOCn showed a more negative enthalpy of adsorption, indicating its stronger interaction for CO2 on the surface, and hence, the higher adsorption capacity. The CO2 adsorption on NOCn over the whole pressure range at 25-55 °C best fitted the Toth model, suggesting monolayer adsorption on the heterogeneous surface. In addition, NOCn expressed a higher selective CO2 adsorption than Cn and so was a good candidate for multicycle adsorption.

Recycling Waste Soot from Merchant Ships to Produce Anode Materials for Rechargeable Lithium-Ion Batteries.

In this study, the waste soot generated by ships was recycled to produce an active material for use in lithium-ion batteries (LIBs). Soot collected from a ship was graphitized by a heat treatment process and used as an anode active material. It was confirmed that the graphitized soot was converted into a highly crystalline graphite, and was found to form carbon nano-onions with an average diameter of 70 nm. The graphitized soot showed a high discharge capacity and an excellent cycle life, with a reversible capacity of 260 mAhg-1 even after 150 cycles at a rate of 1 C. This study demonstrates that the annealed soot with a unique graphitic multilayer structure has an electrochemical performance that renders it suitable as a candidate for the production of low-cost anode materials for use in LIBs.

Fastest Formation Routes of Nanocarbons in Solution Plasma Processes.

Although solution-plasma processing enables room-temperature synthesis of nanocarbons, the underlying mechanisms are not well understood. We investigated the routes of solution-plasma-induced nanocarbon formation from hexane, hexadecane, cyclohexane, and benzene. The synthesis rate from benzene was the highest. However, the nanocarbons from linear molecules were more crystalline than those from ring molecules. Linear molecules decomposed into shorter olefins, whereas ring molecules were reconstructed in the plasma. In the saturated ring molecules, C-H dissociation proceeded, followed by conversion into unsaturated ring molecules. However, unsaturated ring molecules were directly polymerized through cation radicals, such as benzene radical cation, and were converted into two- and three-ring molecules at the plasma-solution interface. The nanocarbons from linear molecules were synthesized in plasma from small molecules such as C2 under heat; the obtained products were the same as those obtained via pyrolysis synthesis. Conversely, the nanocarbons obtained from ring molecules were directly synthesized through an intermediate, such as benzene radical cation, at the interface between plasma and solution, resulting in the same products as those obtained via polymerization. These two different reaction fields provide a reasonable explanation for the fastest synthesis rate observed in the case of benzene.

Effects of halogen doping on nanocarbon catalysts synthesized by a solution plasma process for the oxygen reduction reaction.

Halogen-doped carbon nanoparticles (CNPs) were synthesized by a simple one-step solution plasma process at room temperature using a mixture of benzene (C6H6) and organics containing halogen atoms as the precursors (i.e., hexafluorobenzene (C6F6), hexachlorobenzene (C6Cl6), and hexabromobenzene (C6Br6)). The experimental results demonstrated that halogen doping, especially F and Cl, could lead to more efficient removal of residual hydrogen compared to carbon synthesized with pure benzene. This phenomenon was related to the different binding energies between hydrogen and halogens to form hydrogen halides. Their crystallinity and morphology did not change and remained the same as non-doped carbon. The electrochemical evaluation of oxygen reduction reaction (ORR) activity in an alkaline solution revealed that halogen doping did not play a significant role in shifting the onset potential for the ORR, while a slight enhancement in diffusion limited current density was observed at high overpotentials. Moreover, the electron transfer number involved in the ORR process determined from the Koutecky-Levich plot at -0.6 V was found to increase for halogen-doped carbons in the following order: F-CNPs > Br-CNPs > Cl-CNPs > CNPs. The improved ORR performance of F-CNPs could reasonably be attributed to the synergistic effects of specific bonding states between the halogen and carbon, structural defects and surface functional groups. Our results confirmed the validity of using halogen doping to improve the ORR catalytic activity of CNPs.

Heterocarbon nanosheets incorporating iron phthalocyanine for oxygen reduction reaction in both alkaline and acidic media.

Heterocarbon nanosheets incorporating iron phthalocyanine (FP-NCNs-SP) have been successfully synthesized by a facile one-pot solution plasma process at high repetition frequency. It was found that the Fe-N4 catalytic active sites could be preserved on the FP-NCNs-SP without degradation. The FP-NCNs-SP also possessed large surface area, good conductivity and high degree of graphitization. Electrochemical evaluations demonstrated that NCNs-SP had excellent electrocatalytic activity and selectivity toward oxygen reduction reaction (ORR) in alkaline medium through a direct four-electron pathway. Although the significant improvement in ORR activity was clearly observed in acidic medium, it was much poorer than in alkaline medium. We believe that the results presented in this work will shed light on the advanced synthesis and design of ORR electrocatalysts at room temperature with an abundance of catalytically active sites and high ORR performance.

Nitrogen-Doped Carbon Nanoparticle-Carbon Nanofiber Composite as an Efficient Metal-Free Cathode Catalyst for Oxygen Reduction Reaction.

Metal-free nitrogen-doped carbon materials are currently considered at the forefront of potential alternative cathode catalysts for the oxygen reduction reaction (ORR) in fuel cell technology. Despite numerous efforts in this area over the past decade, rational design and development of a new catalyst system based on nitrogen-doped carbon materials via an innovative approach still present intriguing challenges in ORR catalysis research. Herein, a new kind of nitrogen-doped carbon nanoparticle-carbon nanofiber (NCNP-CNF) composite with highly efficient and stable ORR catalytic activity has been developed via a new approach assisted by a solution plasma process. The integration of NCNPs and CNFs by the solution plasma process can lead to a unique morphological feature and modify physicochemical properties. The NCNP-CNF composite exhibits a significantly enhanced ORR activity through a dominant four-electron pathway in an alkaline solution. The enhancement in ORR activity of NCNP-CNF composite can be attributed to the synergistic effects of good electron transport from highly graphitized CNFs as well as abundance of exposed catalytic sites and meso/macroporosity from NCNPs. More importantly, NCNP-CNF composite reveals excellent long-term durability and high tolerance to methanol crossover compared with those of a commercial 20 wt % supported on Vulcan XC-72. We expect that NCNP-CNF composite prepared by this synthetic approach can be a promising metal-free cathode catalyst candidate for ORR in fuel cells and metal-air batteries.

Water-plasma-assisted synthesis of black titania spheres with efficient visible-light photocatalytic activity.

Black titania spheres (H-TiO2-x) were synthesized via a simple green method assisted by water plasma at a low temperature and atmospheric pressure. The in situ production of highly energetic hydroxyl and hydrogen species from water plasma are the prominent factors in the oxidation and hydrogenation reactions during the formation of H-TiO2-x, respectively. The visible-light photocatalytic activity toward the dye degradation of H-TiO2-x can be attributed to the synergistic effect of large-surface area, visible-light absorption and the existence of oxygen vacancies and Ti(3+) sites.

Nitrogen-doped carbon nanoparticles derived from acrylonitrile plasma for electrochemical oxygen reduction.

Nitrogen-doped carbon nanoparticles were synthesized via a solution plasma process, with acrylonitrile as a single-source precursor, followed by a post-thermal annealing process. The nitrogen-bonding states can be tuned by varying the annealing temperature. The best electrocatalytic activity for oxygen reduction reaction (ORR) in terms of both onset potential and limiting current density can be achieved for the catalyst annealed at an optimal temperature of 800 °C because of the high content of graphitic-N catalytic sites and a large specific surface area.