No abstract

Graphene oxide (GO) and reduced graphene oxide (rGO) have congregated much interest as promising active materials for a variety of applications such as electrodes for supercapacitors. Yet, partially given the absence of comparative studies in synthesis methodologies, a lack of understanding persists on how to best tailor these materials. In this work, the effect of using different graphene oxidation-reduction strategies in the structure and chemistry of rGOs is systematically discussed. Two of the most popular oxidation routes in the literature were used to obtain GO. Subsequently, two sets of rGO powders were synthesised employing three different reduction routes, totalling six separate products. It is shown that the extension of the structural rearrangement in rGOs is not just dependent on the reduction step but also on the approach followed for the initial graphite oxidation.

The impact of post-synthesis processing in reduced graphene oxide materials for supercapacitor electrodes has been analyzed. A comparative study of vacuum, freeze and critical point drying was carried out for hydrothermally reduced graphene oxide demonstrating that the optimization of the specific surface area and preservation of the porous network are critical to maximize its supercapacitance performance. As described below, using a supercritical fluid as the drying medium, unprecedented values of the specific surface area (364 m g) and supercapacitance (441 F g) for this class of materials have been achieved.

Mn 2+ -doped II-VI semiconductor quantum dots reveal remarkably intense photoluminescence with a short lifetime associated with the 4 T 1 ( 4 G) f 6 A 1 ( 6 S) transition, which is spin-forbidden and is allowed because of crystal field effects. We explored the photophysical properties of high-quality, narrow-size-distribution Mn 2+doped ZnSe (ZnSe:Mn 2+ ) quantum dots. ZnSe:Mn 2+ quantum dots with varying amounts of dopant were studied at temperatures down to 10 K. Substitutional incorporation of Mn 2+ in ZnSe quantum dots was confirmed by electron paramagnetic resonance measurements as well. Photoluminescence emission (PL) and photoluminescence excitation (PLE) spectroscopies at low temperature were employed to examine the sp-d interactions. PL measurements of ZnSe:Mn 2+ quantum dots show Mn 2+ -related orange luminescence. PLE measurements were carried out at a fixed emission wavelength related to Mn 2+ orange luminescence. Five excited states corresponding to Mn 2+ d-d transitions were observed. The crystal field strength (10Dq) increases with increasing Mn 2+ concentration, increasing size, and decreasing temperature. In contrast to earlier conjectures about transition-metal-doped quantum dots, Mn 2+ -related photoluminescence feature could be observed in ZnSe:Mn 2+ quantum dots even when the excitation energy was lower than the forbidden gap but was equal to the energy of the d-d transitions. The behavior of ZnSe:Mn 2+ quantum dots was also compared with that of their bulk counterpart.

Synthesis of CNT-HKUST-1 composite thin films.  Investigation of morphological, crystalline, and Raman-scattering characteristics of composite thin films.  Coating of HKUST-1 and CNT-HKUST-1 thin films on QCM.  Optimization of CNT-HKUST-1 composite ratio for enhanced humidity detection.