New Insights into the Mechanism of Visible Light Photocatalysis

ABSTRACT: In recent years, the area of developing visible-lightactive photocatalysts based on titanium dioxide has been enormously investigated due to its wide range of applications in energy and environment related fields. Various strategies have been designed to efficiently utilize the solar radiation and to enhance the efficiency of photocatalytic processes. Building on the fundamental strategies to improve the visible light activity of TiO2-based photocatalysts, this Perspective aims to give an insight into many contemporary developments in the field of visible-light-active photocatalysis. Various examples of advanced TiO2 composites have been discussed in relation to their visible light induced photoconversion efficiency, dynamics of electron− hole separation, and decomposition of organic and inorganic pollutants, which suggest the critical need for further development of these types of materials for energy conversion and environmental remediation purposes

Polyindole-Derived Nitrogen-Doped Graphene Quantum Dots-Based Electrochemical Sensor for Dopamine Detection

The sensitive monitoring of dopamine levels in the human body is of utmost importance since its abnormal levels can cause a variety of medical and behavioral problems. In this regard, we report the synthesis of nitrogen-doped graphene quantum dots (N-GQDs) from polyindole (PIN) via a facile single-step hydrothermal synthetic strategy that can act as an efficient electrochemical catalyst for the detection of dopamine (DA). The average diameter of N-GQDs was ∼5.2 nm and showed a C/N atomic ratio of ∼2.75%. These N-GQDs exhibit a cyan fluorescence color under irradiation from a 365 nm lamp, while PIN has no characteristic PL. The presence of richly N-doped graphitic lattices in the N-GQDs possibly accounts for the improved catalytic activity of N-GQDs/GCE towards electrocatalytic DA detection. Under optimum conditions, this novel N-GQDs-modified electrode exhibits superior selectivity and sensitivity. Moreover, it could detect as low as 0.15 nM of DA with a linear range of 0.001–1000 µM. In addition, the outstanding sensing attributes of the detector were extended to the real samples as well. Overall, our findings evidence that N-GQDs-based DA electrochemical sensors can be synthesized from PIN precursor and could act as promising EC sensors in medical diagnostic applications

Investigation on swelling behavior of sodium alginate/black titania nanocomposite hydrogels and effect of synthesis conditions on water uptake

Polymeric nanocomposite hydrogels were developed from a hydrophilic natural polymer, sodium alginate (SA) with black nano crystalline titania (black TiO2) by using ionic cross linker CaCl2, in view of the possible enhancement in properties of SA towards water treatment application. The optimum conditions for the preparation of films were done by varying the amount of cross-linking agent, cross-linking time and the amount of black nano crystalline TiO2. The nanocomposite hydrogels were then characterized by X-ray diffraction studies (XRD), fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The surface morphologies of the nanocomposite have been examined by using scanning electron microscopy (SEM). The swelling studies and its kinetics have been investigated under diverse PH conditions. Permeability of the gels were assessed in terms of film characteristics and PH. The results proved that the gels exhibit PH sensitivity. Based on the results, we have proposed a possible mechanism of water transport through the gels. The developed SA/black TiO2 nanocomposite hydrogels have been successfully employed for the efficient degradation organic dyes such as methylene blue and malachite green. The experimental results of dye degradation studies have been compared with theoretical models and it has been observed that the dye degradation follows pseudo second order kinetics for both methylene blue and malachite green. By altering the PH, the nanocomposite hydrogels can be broken and spent TiO2 can be recovered

Control and enhancement of the oxygen storage capacity of ceria films by variation of the deposition gas atmosphere during pulsed DC magnetron sputtering

In this study, nanostructured ceria (CeO2) films are deposited on Si(100) and ITO coated glass substrates by pulsed DC magnetron sputtering using a CeO2 target. The influence on the films of using various gas ambients, such as a high purity Ar and a gas mixture of high purity Ar and O-2, in the sputtering chamber during deposition are studied. The film compositions are studied using XPS and SIMS. These spectra show a phase transition from cubic CeO2 to hexagonal Ce2O3 due to the sputtering process. This is related to the transformation of Ce4+ to Ce3+ and indicates a chemically reduced state of CeO2 due to the formation of oxygen vacancies. TGA and electrochemical cyclic voltammetry (CV) studies show that films deposited in an Ar atmosphere have a higher oxygen storage capacity (OSC) compared to films deposited in the presence of O-2. CV results specifically show a linear variation with scan rate of the anodic peak currents for both films and the double layer capacitance values for films deposited in Ar/O-2 mixed and Ar atmosphere are (1.6 +/- 0.2) x 10(-4) F and (4.3 +/- 0.5) x 10(-4) F, respectively. Also, TGA data shows that Ar sputtered samples have a tendency to greater oxygen losses upon reduction compared to the films sputtered in an Ar/O-2 mixed atmosphere. (C) 2015 Elsevier B.V. All rights reserved