Structural, optical, and mechanical properties of cobalt copper oxide coatings synthesized from low concentrations of sol–gel process

Thin films of CoxCuyOz have been coated on aluminum substrates via sol–gel route using low concentration of copper and cobalt precursors at annealing temperatures in range of 500–650 °C. The coatings were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis-NIR spectrophotometry, and nanoindentation. The XRD analysis in 2θ-range of 30°–42° revealed that the coatings exhibited low crystallinity of CoCu2O3, CoCuO2, and CuCoO2. The surface bonding structure analyzed using XPS indicated that the coating contained: Cu (tetrahedral Cu+ and octahedral Cu2+), Co (octahedral Co3+, tetrahedral Co2+, and mixed Co2+ and Co3+), and O (lattice, surface, and sub-surface oxygens). The optical properties characterized using UV-Vis-NIR showed that the reflectance spectra of coatings formed a spectrally solar selective absorber profile associated with the interference peaks and the absorption edges around wavelengths of below 1.2 μm. The maximum absorptance (α = 75.8%) was shown by coating synthesized at 500 °C. The mechanical properties of coatings showed that the increase of annealing temperature increased the coating's hardness (H) and the elastic modulus (E) due to the enhancement of the [CoCuO2/CuCoO2]:[CoCu2O3] oxide phases ratio, as the result, an excellent stability of the wear resistance (H/E) of around ∼0.035 was recorded

Experimental studies on vacancy induced ferromagnetism in undoped TiO2

Room temperature ferromagnetism is observed in undoped TiO2 films deposited on Si substrates using pulsed laser deposition (PLD). The ferromagnetic properties of the samples depend on the oxygen partial pressure during the PLD synthesis. The appearance of higher binding energy component (HBEC) in the oxygen 1s core peak from x-ray photoelectron spectroscopy (XPS) suggests the presence of oxygen vacancies in these samples. The amount of oxygen during the synthesis determines the vacancy concentration in the samples which is directly related to the magnetic behavior of the samples. The magnetic moment decreases with oxygen vacancy concentration in the samples. Valence band measurements were performed to study the electronic structure of both stoichometric and reduced TiO2. The analyses show the presence of Ti 3d band near the Fermi level in reduced TiO2 samples. These bands are otherwise empty in stoichiometric TiO2 and reside in the conduction band which makes them unobservable by XPS. The existence of this Ti 3d band near the Fermi level can possibly lead to Stoner splitting of the band.Comment: 20 pages, 9 figur

Ultrathin porous NiO nanoflake arrays on nickel foam as an advanced electrode for high performance asymmetric supercapacitors

Nickel oxide (NiO) is a promising electrochemical material owing to its high theoretical specific capacitance, environmentally benign nature, and low cost, and can be synthesized easily by various strategies. However, the poor cycling stability of NiO hinders its potential for next generation high performance energy storage applications. In this work, we demonstrate that two-dimensional (2D) NiO nanoflake arrays possess ultrathin thickness and abundant nanoscale pores vertically grown on the surface of three-dimensional nickel foam via a solvothermal reaction followed by sintering in air. Transmission electron microscopy shows that the 2D NiO nanoflakes are as thin as ∼7 nm and possess ample pores (<10 nm). The outstanding cycling stability is enabled by the unique porous structure, which not only reduces diffusion resistance of electrolytes in rapid redox reactions but also preserves mechanical integrity during prolonged charging/discharging. The 2D ultrathin porous NiO nanoflakes electrode exhibits remarkably high specific capacitance (2013.7 F g-1 at 1 A g-1 and 1465.6 F g-1 at 20 A g-1) and excellent cycling ability (100% capacitance retention over 5000 cycles). An asymmetric supercapacitor (ASC) operating at 1.5 V is assembled using ultrathin porous NiO nanoflakes and reduced graphene oxide (rGO) as positive and negative electrodes, respectively. The NiO//rGO ASC delivers a high specific capacitance of 145 F g-1 at 1 A g-1 with a high energy density of 45.3 W h kg-1 at a power density of 1081.9 W kg-1 and outstanding cyclic stability (91.1% capacitance retention after 5000 cycles). These promising results open up a pathway for developing advanced electrode materials for energy storage devices

Defective TiO2 Nanotube Arrays for Efficient PhotoelectrochemicalDegradation of Organic Pollutants

Oxygen vacancies (OVs) are one of the most critical factors that enhance the electrical and catalytic characteristics of metal oxide-based photo-electrodes. In this work, a simple procedure was applied to prepare reduced TiO 2 nanotube arrays (NTAs) (TiO 2−x) via a one-step reduction method using NaBH 4. A series of characterization techniques were used to study the structural, optical, and electronic properties of TiO 2−x NTAs. X-ray photoelectron spectroscopy confirmed the presence of defects in TiO 2−x NTAs. Photoacoustic measurements were used to estimate the electron-trap density in the NTAs. Photoelectrochemical studies show that the photocurrent density of TiO 2−x NTAs was nearly 3 times higher than that of pristine TiO 2. It was found that increasing OVs in TiO 2 affects the surface recombination centers, enhances electrical conductivity, and improves charge transport. For the first time, a TiO 2−x photoanode was used in the photo-electrochemical (PEC) degradation of a textile dye (basic blue 41, B41) and ibuprofen (IBF) pharmaceutical using in situ generated reactive chlorine species (RCS). Liquid chromatography coupled with mass spectrometry was used to study the mechanisms for the degradation of B41 and IBF. Phytotoxicity tests of B41 and IBF solutions were performed using Lepidium sativum L. to evaluate the potential acute toxicity before and after the PEC treatment. The present work provides efficient PEC degradation of the B41 dye and IBF in the presence of RCS without generating harmful products

Photoelectrochemical activation of peroxymonosulfate using Sn-doped ▫α−Fe2O3α-Fe_2O_3▫ thin film for degradation of anti-inflammatory pharmaceutical drug

Introduction of oxygen vacancies (OVs) has been investigated as a promising way to improve the electrical and catalytic characteristics of a hematite (α-Fe2O3) based photoelectrode. In this work, we develop a novel method for preparing porous Sn-doped α-Fe2O3 (Sn:Fe2O3) thin films with intrinsic OVs. The procedure included spin- coating an iron precursor onto a fluorine-doped tin oxide (FTO) substrate, followed by thermal treatment at elevated temperatures. The influence of Sn dopant on the optoelectronic properties of α-Fe2O3 was demonstrated by X-ray photoelectron spectroscopy and photoelectrochemical (PEC) measurements. The combined effect of OVs and Sn doping was found to play a synergistic role in reducing the charge recombination’s. The Sn:Fe2O3 photoanodes were used as a dual catalyst to oxidise water and break down an anti-inflammatory drug called 2-(4- isobutylphenyl)propanoic acid (IBPA). The Sn:Fe2O3 thin film with a 30-minute heat treatment time displayed the highest incident photon-to-current efficiency. For the first time, Sn:Fe2O3 thin films were utilised in the effective PEC degradation of IBPA employing peroxymonosulfate (PMS) under visible light illumination. The hydroxyl radicals (•OH), singlet oxygen (1O2), photogenerated holes (h+), and sulfate radicals (SO4 • ) were discovered to be the main reactive species during PEC degradation. IBPA degradation and the formation of new compounds were verified using liquid chromatography-mass spectrometry. The Lepidium sativum L phytotoxicity test reveals that PEC-treated wastewater with IBPA exhibits decreased toxicity

Novel Nanosized Spinel MnCoFeO₄ for Low-Temperature Hydrocarbon Oxidation

The present paper reports on MnCoFeO4 spinels with peculiar composition and their catalytic behavior in the reactions of complete oxidation of hydrocarbons. The samples were synthesized by solution combustion method with sucrose and citric acid as fuels. All samples were characterized by powder X-ray diffraction, N2-physisorption, scanning electron microscopy, thermal analysis, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy. The catalytic properties of the spinels with Mn:Co:Fe = 1:1:1 composition were studied in reactions of complete oxidation of methane, propane, butane, and propane in the presence of water as model pollutants. Both prepared catalysts are nanosized materials. The slight difference in the compositions, structure, and morphology is due to the type of fuel used in the synthesis reaction. The spinel, prepared with sucrose, shows a higher specific surface area, pore volume, higher amount of small particles fraction, higher thermal stability, and as a result, more exposed active sites on the sample surface that lead to higher catalytic activity in the studied oxidation reactions. After the catalytic tests, both samples do not undergo any substantial phase and morphological changes; thus, they could be applied in low-temperature hydrocarbon oxidation reactions