λ-MnO2 Thin Films with Sponge-Like Structures: Synthesis, Characterization and Physiochemical Applications

Manganese dioxide has acquired significant research attentiveness in many fields over the past years because of its exciting physicochemical features. The magnetized λ-MnO2 thin films with sponge-like structures (TSLs) were prepared by hydrothermal-soft chemical and delithiation-lithium manganese process. The XRD, XPS, EDX, FESEM, TEM, HR-TEM, and N2 adsorption-desorption techniques were used to characterize the as-prepared product’s structure composition, morphology, and surface area. The particle growth details of λ-MnO2 are postulated by the oxidation-ionic change-delithiation (OID) mechanism. The electrochemical property was analyzed by galvanostatic discharge-charging, electrochemical impedance spectrum (EIS), and cyclic voltammetry (CV). Special attention of λ-MnO2 S.L.s is given to their applications in the degradation of methyl orange (MO) from wastewater under O2 air bubble pump and cathodic substance in the lithium-ion battery. Due to the peculiarity crystal form and morphology face, the λ-MnO2 TSLs might be promisingly applied in the various physicochemical area.

Strengthened passivation and mechanism of 316L stainless steel in hot diluted sulfuric acid solution by connecting to Pd electrode

Purpose The purpose of this paper is to study the variations of composition and properties of the passive film on 316 L stainless steel surface in 80°C, 0.5 mol L-1 H2SO4 + 2 mg L-1 NaF solution, is helpful to understand the mechanisms of corrosion resistancethe of plated Pd on 316 L ss. Design/methodology/approach The variations of composition and properties of the passive film on 316 L stainless steel surface in 80°C, 0.5 mol L-1 H2SO4 + 2 mg L-1 NaF solution after connected to Pd electrode were studied with methods of potential monitor, X-ray photoelectron spectroscopy analysis and electrochemical impedance spectrum (EIS) measurement. Findings By connecting to a Pd electrode, the potential of the SS sample increased from the active region to the passive region. By connecting to the Pd electrode, the contents of Cr, Cr(OH)3 and Fe3O4 in passive film increased obviously. With increased Pd/SS area ratio, the Cr(OH)3 content in passive film increased but the Fe3O4 content changed little. The results show that after connecting to Pd the corrosion resistance of the passive film on 316 L stainless steel increases obviously, which may be attributed to the more compact passive film because of higher Cr, Cr(OH)3 and Fe3O4 contents and less point defects in the film. Originality/value The effects and mechanism of Pd on passivation of SS was studied.

Effect of temperature on process and kinetic parameters of the hydrogen evolution reaction of X80 under CP

Purpose This paper aims to study the effect of temperature on the process and kinetic parameters of the hydrogen evolution reaction of X80 under cathodic protection (CP) in 3.5% NaCl solution. Design/methodology/approach Potentiodynamic polarization combined with the hydrogen permeation test is used to analyze the hydrogen evolution reaction (HER) process and the rate-determining step for which is diagnosed through the electrochemical impedance spectrum method. Then, the influence of temperature on kinetic parameters of HER can be known from the results obtained by using the Iver-Pickering-Zamenzadeh model for data analysis. Findings The results show that the HER proceeds through Volmer–Tafel route with the Volmer reaction acting as the rate-controlling step; Increasing temperature gives a higher activity of the HER on X80, it also accelerates the hydrogen desorption and diffusion of hydrogen into the metal. Originality/value There exist few studies on the topic of how temperature affects the HER process. It is imperative to conduct a relevant study to give some instruction in cathodic protection system design and this paper fulfills this need.

The Influence of Dopant Concentration on Optical-Electrical Features of Quantum Dot-Sensitized Solar Cell

In this study, TiO2/CdS/CdxCu1−xSe, TiO2/CdS/CdxMn1−xSe, and TiO2/CdS/CdxAg2−2xSe thin films were synthesized by chemical bath deposition for the fabrication of photoanode in quantum-dot-sensitized solar cells. As a result, the structural properties of the thin films have been studied by X-ray diffraction, which confirmed the zinc Blende structure in the samples. The optical films were researched by their experimental absorption spectra with different doping concentrations. Those results were combined with the Tauc correlation to estimate the absorption density, the band gap energy, valence band and conduction band positions, steepness parameter, and electron–phonon interaction. Furthermore, the electrical features, electrochemical impedance spectrum and photocurrent density curves were carried out. The result was used to explain the enhancing performance efficiency.

An Experimental Study on the Fretting Corrosion Behaviours of Three Material Pairs at Modular Interfaces for Hip Joint Implants

The fretting corrosion behaviours of Al2O3 ceramic/Ti6Al4V alloy, 316 L stainless/Ti6Al4V alloy, and CoCrMo alloy/Ti6Al4V alloy pairs were studied in an in-house developed fretting-corrosion tester. The fretting behaviours were characterized by the Ft-D-N and Ft/Fn curves. The morphology of the worn surface was analyzed by energy dispersive X-ray spectrometry (EDX), a scanning electron microscope (SEM), and a white light interferometer (WLI). The fretting regimes were found to vary from slip regime (SR) to mixed fretting regime (MFR), with an increase in loads for the Al2O3/Ti6Al4V and 316 L/Ti6Al4V pairs, while for the CoCrMo/Ti6Al4V pair the fretting always remained in SR. The damage mechanism of the Al2O3/Ti6Al4V pair was mainly abrasive wear and corrosive wear, while for the 316 L/Ti6Al4V pair and CoCrMo/Ti6Al4V pair, the wear mechanism was mainly adhesive wear and corrosive wear with slight abrasive wear. The electrochemical impedance spectrum results show that the material transfer layer formed on the surface of the material can protect the material from corrosion for the 316 L/Ti6Al4V and CoCrMo/Ti6Al4V pairs.

Using real-time UV–visible spectrophotometer to assess an Al–Zn–Mg–Cu alloy's dissolution in acidic solution

Applicability and limitations of using online non-destructive ultraviolet–visible (UV–vis) spectrophotometer to monitor the dissolution of an Al–Zn–Mg–Cu alloy in HCl-containing solution were studied. Inductively coupled plasma atomic emission spectrometry results indicate that the spectrum absorbance at 252 nm is mainly attributed to Cu-containing complexes. Surprisingly, an hours-long ‘induction' period was observed from UV–vis results. This is not a real indicator of induction for Al dissolution as revealed by electrochemical impedance spectrum, actually it reflects the alloy's galvanic corrosion nature that Cu species are released after Al, Zn and Mg species.

Fe-Doped UiO-66 Combined with ZnIn2S4 for Adsorption and Degradation of RhB Under Visible Light

Novel ZnIn2S4/FeUiO-66 (ZFeU) photocatalyst with different proportion of FeUiO-66 has been successfully prepared by a facile one-pot solvothermal reaction. The as-synthesized nanocomposites have been thoroughly characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform-infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), Brunauer–Emmett–Teller (BET) characterization, photoluminescence (PL) analysis and electrochemical impedance spectrum (EIS). The photocatalytic performance of ZFeU nanocomposites for the photodegradation of RhB under visible light irradiation was better than that of ZnIn2S4 and FeUiO-66 alone. The experiment results showed the 20% ZFeU nanocomposites had the best photocatalytic properties. At the same time, a probable mechanism was discussed and it was believed that introduction of FeUiO-66 on ZnIn2S4 would minimize the recombination of photogenerated electron-hole pairs, leading to the enhancement of the photocatalytic activity.