Investigation of the Photocatalytic Performance, Mechanism, and Degradation Pathways of Rhodamine B with Bi2O3 Microrods under Visible-Light Irradiation.

In the present work, the photodegradation of Rhodamine B with different pH values by using Bi2O3 microrods under visible-light irradiation was studied in terms of the dye degradation efficiency, active species, degradation mechanism, and degradation pathway. X-ray diffractometry, polarized optical microscopy, scanning electron microscopy, fluorescence spectrophotometry, diffuse reflectance spectra, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, UV-visible spectrophotometry, total organic carbon, and liquid chromatography-mass spectroscopy analysis techniques were used to analyze the crystal structure, morphology, surface structures, band gap values, catalytic performance, and mechanistic pathway. The photoluminescence spectra and diffuse reflectance spectrum (the band gap values of the Bi2O3 microrods are 2.79 eV) reveals that the absorption spectrum extended to the visible region, which resulted in a high separation and low recombination rate of electron-hole pairs. The photodegradation results of Bi2O3 clearly indicated that Rhodamine B dye had removal efficiencies of about 97.2%, 90.6%, and 50.2% within 120 min at the pH values of 3.0, 5.0, and 7.0, respectively. In addition, the mineralization of RhB was evaluated by measuring the effect of Bi2O3 on chemical oxygen demand and total organic carbon at the pH value of 3.0. At the same time, quenching experiments were carried out to understand the core reaction species involved in the photodegradation of Rhodamine B solution at different pH values. The results of X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffractometer analysis of pre- and post-Bi2O3 degradation showed that BiOCl was formed on the surface of Bi2O3, and a BiOCl/Bi2O3 heterojunction was formed after acid photocatalytic degradation. Furthermore, the catalytic degradation of active substances and the possible mechanism of the photocatalytic degradation of Rhodamine B over Bi2O3 at different pH values were analyzed based on the results of X-ray diffractometry, radical capture, Fourier-transform infrared spectroscopy, total organic carbon analysis, and X-ray photoelectron spectroscopy. The degradation intermediates of Rhodamine B with the Bi2O3 photocatalyst in visible light were also identified with the assistance of liquid chromatography-mass spectroscopy.

Determination of dopamine based on a temperature-sensitive PMEO2MA and Au@rGO-MWCNT nanocomposite-modified electrode.

First, the nanocomposite Au@rGO-MWCNT was synthesized by a hydrothermal method. Next, a temperature-controlled composite sensing film was prepared by composite modification of poly(2-(2-methoxyethoxy)ethyl methacrylate) (PMEO2MA) and Au@rGO-MWCNT on a glassy carbon electrode (GCE). This sensor was shown to exhibit good temperature sensitivity and reversibility to dopamine. When the testing temperature is lower than the lower critical solution temperature (LCST) of the polymer, the PMEO2MA chain is in a stretched state, which increases the distance between the Au@rGO layers and leads to the inability of MWCNTs in one layer to contact another Au@rGO layer and to low conductivity. Therefore, in this state, dopamine cannot detect an electrochemical signal, and it is termed an "off" state. When the temperature is higher than the LCST of the polymer, the PMEO2MA chain shrinks, allowing the MWCNTs to make contact with another layer of Au@rGO; the electron transfer rate of the modified film increases, and the electrochemical behavior of dopamine turns to an "on" state. Moreover, the sensor has a wide detection range (0.1 to 9.0 µM and 9.0 to 239.0 µM), and the limit of detection of dopamine is as low as 30 nM. This method has been successfully applied to the determination of dopamine in human serum samples. The on-off sensor provides a new avenue for the application of temperature-sensitive polymers.

Room temperature synthesis of 2D CuO nanoleaves in aqueous solution.

A simple room temperature method was reported for the synthesis of CuO nanocrystals in aqueous solution through the sequence of Cu(2+) → Cu(OA)2 → Cu(OH)2 → Cu(OH)(2-)4 → CuO. Sodium oleate (SOA) was used as the surfactant and shape controller. The as-prepared samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible absorption spectroscopy (UV-vis) and differential thermal analysis (DTA). It can be seen that 1D Cu(OH)(2) nanowires were first obtained from Cu(OA)(2) and, at room temperature, converted into 2D CuO nanoleaves (CuO NLs) in a short time under a weakly basic environment. On prolonging the reaction time, the top part of these 2D nanoleaves branched and separated along the long axis to form 1D rod-like nano-CuO because of the assistance of SOA. A possible transformation mechanism of Cu(OH)(2) to CuO nanostructures at room temperature in aqueous solution is discussed. The transformation velocity can be controlled by changing the pH value of the system. The prepared CuO NLs were used to construct an enzyme-free glucose sensor. The detecting results showed that the designed sensor exhibited good amperometric responses towards glucose with good anti-interferent ability.