Kinetics and mechanistic studies of chlorine dioxide reactions in aqueous solution, and, Kinetics of halites reactions with aqueous bromine chloride

Chlorine dioxide is a strong oxidizing agent and a powerful disinfectant. The kinetics and mechanisms of several reactions involving chlorine dioxide in aqueous solution are determined. The self-decomposition of ClO2 is accelerated in the presence of hydroxide, carbonate, and phosphate. Three pathways are responsible for ClO2 decay, all of which are base-assisted electron-transfer reactions. The reaction of HO2− with ClO2 is fast (1.6 × 105 M −1s−1) and buffers do not affect the rate of the reaction. The relative rates of sulfur-containing species with ClO 2 are cysteine \u3e sulfite \u3e\u3e cystine. Aqueous Iron(II) reaction with ClO2 is rapid, a study of the subsequent Cl(III)/Fe2+ reaction is completed and an overall mechanism for the five-electron reduction of ClO2 to Cl− is outlined. Bromine chloride is involved in ozone depletion in the troposphere during the polar sunrise in the Arctic. Aqueous bromine chloride reacts with halites through BrOXO intermediates (X = Br or Cl). The reaction of ClO2 − with BrCl to give ClO2 is 27.4 times faster the BrCl/BrO2 reaction. The BrCl/BrO2 reaction forms chloride and the carcinogen bromate. Both reactions proceed by Br+-transfer mechanisms

Thermogravimetric kinetics study of scrap tires pyrolysis using silica embedded with NiO and/or MgO nanocataly

In this study, a set of three new silica-based embedded with NiO and/or MgO nanocatalysts (SBNs) have been prepared and tested for the pyrolysis of scrap tires (STs). The intent is to identify and optimize the best nanocatalyst that decreases the operating temperature and speeds up the pyrolysis reaction rate. The influence of the three prepared SBNs nanocatalysts on STs was scrutinized using thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). The kinetic triplets were estimated utilizing the isoconversional method of the Ozawa–Flynn–Wall (OFW) corrected model. Experimental TGA and FT-IR results showed a thermal decomposition of all volatile organic additives alongside the polyvinyl compounds at a lower temperature in the presence of these SBNs. However, a competitive decomposition behavior appeared for each SBN nanocatalysts. The kinetic triplets’ findings showed different effective activation energy trends at two different conversion regions (low and high conversions), suggesting different reaction mechanisms confirmed by the reaction kinetic models. Interestingly, NiO-MgO-SBNs showed the highest reaction rate for this thermo-pyrolysis of STs, which could be because of synergetic interaction between NiO and MgO nanoparticles. Moreover, the results of the change in Gibbs free energy of activation (ΔG‡) indicated the promising catalytic activity for those SBNs by promoting the spontaneity of pyrolysis reaction. These proof-of-concept findings could promote the futuristic use of NiO-MgO-SBNs at the industrial level toward sustainable ST pyrolysis.The authors thankfully acknowledge Deanship of Scientific Research in An-Najah National University, Nablus, Palestine for providing financial support to this study via Project Number (ANNU-1819-Sc008). The technical assistance provided by Mr. Nafith Dwikat and by the faculty of Science at An-Najah National University (ANNU), Nablus, Palestine is also highly appreciated.Scopu

Influence of Stacking Morphology and Edge Nitrogen Doping on the Dielectric Performance of Graphene–Polymer Nanocomposites

We demonstrate that functional groups obtained by varying the preparation route of reduced graphene oxide (rGO) highly influence filler morphology and the overall dielectric performance of rGO-relaxor ferroelectric polymer nanocomposite. Specifically, we show that nitrogen-doping by hydrazine along the edges of reduced graphene oxide embedded in poly­(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) results in a dielectric permittivity above 10 000 while maintaining a dielectric loss below 2. This is one of the best-reported dielectric constant/dielectric loss performance values. In contrast, rGO produced by the hydrothermal reduction route shows a much lower enhancement, reaching a maximum dielectric permittivity of 900. Furthermore, functional derivatives present in rGO are found to strongly affect the quality of dispersion and the resultant percolation threshold at low loading levels. However, high leakage currents and lowered breakdown voltages offset the advantages of increased capacitance in these ultrahigh-k systems, resulting in no significant improvement in stored energy density

Metal-Free, Single-Polymer Device Exhibits Resistive Memory Effect

All-polymer, write-once-read-many times resistive memory devices have been fabricated on flexible substrates using a single polymer, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). Spin-cast or inkjet-printed films of solvent-modified PEDOT:PSS are used as electrodes, while the unmodified or as-is PEDOT:PSS is used as the semiconducting active layer. The all-polymer devices exhibit an irreversible but stable transition from a low resistance state (ON) to a high resistance state (OFF) at low voltages caused by an electric-field-induced morphological rearrangement of PEDOT and PSS at the electrode interface. However, in the metal–PEDOT:PSS–metal devices, we have shown a metal filament formation switching the device from an initial high resistance state (OFF) to the low resistance state (ON). The all-PEDOT:PSS memory device has low write voltages (<3 V), high ON/OFF ratio (>10³), good retention characteristics (>10 000 s), and stability in ambient storage (>3 months)

Cryo-mediated exfoliation and fracturing of layered materials into 2D quantum dots

Atomically thin quantum dots from layered materials promise new science and applications, but their scalable synthesis and separation have been challenging. We demonstrate a universal approach for the preparation of quantum dots from a series of materials, such as graphite, MoS2, WS2, h-BN, TiS2, NbS2, Bi2Se3, MoTe2, Sb2Te3, etc., using a cryo-mediated liquid-phase exfoliation and fracturing process. The method relies on liquid nitrogen pretreatment of bulk layered materials before exfoliation and breakdown into atomically thin two-dimensional quantum dots of few-nanometer lateral dimensions, exhibiting size-confined optical properties. This process is efficient for a variety of common solvents with a wide range of surface tension parameters and eliminates the use of surfactants, resulting in pristine quantum dots without surfactant covering or chemical modification

A metal-free electrocatalyst for carbon dioxide reduction to multi-carbon hydrocarbons and oxygenates

Electroreduction of carbon dioxide into higher-energy liquid fuels and chemicals is a promising but challenging renewable energy conversion technology. Among the electrocatalysts screened so far for carbon dioxide reduction, which includes metals, alloys, organometallics, layered materials and carbon nanostructures, only copper exhibits selectivity towards formation of hydrocarbons and multi-carbon oxygenates at fairly high efficiencies, whereas most others favour production of carbon monoxide or formate. Here we report that nanometre-size N-doped graphene quantum dots (NGQDs) catalyse the electrochemical reduction of carbon dioxide into multi-carbon hydrocarbons and oxygenates at high Faradaic efficiencies, high current densities and low overpotentials. The NGQDs show a high total Faradaic efficiency of carbon dioxide reduction of up to 90%, with selectivity for ethylene and ethanol conversions reaching 45%. The C2 and C3 product distribution and production rate for NGQD-catalysed carbon dioxide reduction is comparable to those obtained with copper nanoparticle-based electrocatalysts

Anomalous Li Storage Capability in Atomically Thin Two-Dimensional Sheets of Nonlayered MoO₂

Since the first exfoliation and identification of graphene in 2004, research on layered ultrathin two-dimensional (2D) nanomaterials has achieved remarkable progress. Realizing the special importance of 2D geometry, we demonstrate that the controlled synthesis of nonlayered nanomaterials in 2D geometry can yield some unique properties that otherwise cannot be achieved in these nonlayered systems. Herein, we report a systematic study involving theoretical and experimental approaches to evaluate the Li-ion storage capability in 2D atomic sheets of nonlayered molybdenum dioxide (MoO₂). We develop a novel monomer-assisted reduction process to produce high quality 2D sheets of nonlayered MoO₂. When used as lithium-ion battery (LIB) anodes, these ultrathin 2D-MoO₂ electrodes demonstrate extraordinary reversible capacity, as high as 1516 mAh g^–1 after 100 cycles at the current rate of 100 mA g^–1 and 489 mAh g^–1 after 1050 cycles at 1000 mA g^–1. It is evident that these ultrathin 2D sheets did not follow the normal intercalation-cum-conversion mechanism when used as LIB anodes, which was observed for their bulk analogue. Our ex situ XPS and XRD studies reveal a Li-storage mechanism in these 2D-MoO₂ sheets consisting of an intercalation reaction and the formation of metallic Li phase. In addition, the 2D-MoO₂ based microsupercapacitors exhibit high areal capacitance (63.1 mF cm^–2 at 0.1 mA cm^–2), good rate performance (81% retention from 0.1 to 2 mA cm^–2), and superior cycle stability (86% retention after 10,000 cycles). We believe that our work identifies a new pathway to make 2D nanostructures from nonlayered compounds, which results in an extremely enhanced energy storage capability