P-N Junction Oxide Nanoparticle as a Novel Photocatalyst for Solar Applications

Due to the spectral limitation of popular photocatalysts (PC) TiO2 and ZnO, there is quest for modification of the existing PC to enhance their photocatalytic performance. It has been demonstrated that the coupled nanostructured semiconductors in the form of nanocomposites (NC) enhance the performance by the mutual charge transfer of carriers between each semiconductor components with compatible chemical and electrical properties. ZnO (Bg: 3.37 eV) n-type semiconductor, is most important PC because of its high photosensitivity and stability. CuO (Bg: 1.85 eV), a p-type semiconductor, can be used in conjunction with ZnO to further improve its photocatalytic activity (PCA). Herein, a p-n junction oxide photocatalyst was synthesized by using a simple ball milling technique. The structural, optical and surface properties of the p-n junction photocatalyst CuO/ZnO were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV-Vis spectroscopy, Zetasizer Nano ZS (Malvern). The PCA of the photocatalyst was evaluated by photocatalytic oxidation of Methylene Blue (MB). Our study demonstrates a novel p-n junction oxide photocatalyst CuO (wt. 10%)/ZnO having superior PCA for the degradation of model dye under the illumination of UV-Vis light. The MB solution was degraded by 100% within 15 min by the use of CuO (wt. 10%)/ZnO photocatalyst. The enhanced PCA is anticipated from many micro p-n junction formed between ZnO-CuO upon ball milling, which helps in efficient electron/hole pair charge separation upon excitation

Preparation and photocatalytic activity study of p-CuO/n-ZnO composites

In this paper, efficacy of p-n junction p-CuO/n-ZnO composite is assessed as a potential photocatalyst by monitoring degradation of methylene blue (MB) in the presence of UV light. The p-n junction photocatalyst, p-CuO/n-ZnO, was prepared by ball milling of ZnO and CuO in water. The structural properties of p-CuO/n-ZnO composite were characterized by x-ray diffractometer and surface charge properties via zeta potential measurement. The degradation of MB in the presence of composite powder was monitored via UV-vis spectrometer. Various studies affecting the degradation rate of MB were conducted as a function of weight fraction of CuO in the composite and ball milling time. The highest degradation rate of MB was achieved in CuO (10 Wt.%)/ZnO for which high negative zeta potential was recorded. The MB degradation efficiency was found to decrease with the samples ball milled for time longer than 12 hours due to increased agglomeration of particles. The mechanisms that influence the photocatalytic activity of p-CuO/n-ZnO are discussed based on the p-n junction principle. © 2012 Materials Research Society

Eco-Friendly Cellulose Nanofiber Extraction from Sugarcane Bagasse and Film Fabrication

The development of cost-effective cellulose fibers by utilizing agricultural residues have been attracted by the scientific community in the past few years; however, a facile production route along with minimal processing steps and a significant reduction in harsh chemical use is still lacking. Here, we report a straightforward ultrasound-assisted method to extract cellulose nanofiber (CNF) from fibrous waste sugarcane bagasse. X-ray diffraction-based crystallinity calculation showed 25% increase in the crystallinity of the extracted CNF (61.1%) as compared to raw sugarcane bagasse (35.1%), which is coherent with Raman studies. Field emission scanning electron microscopy (FE-SEM) images revealed thread-like CNF structures. Furthermore, we prepared thin films of the CNF using hot press and solution casting method and compared their mechanical properties. Our experiments demonstrated that hot press is a more effective way to produce high strength CNF films; Young’s modulus of the thin films prepared from the hot press was ten times higher than the solution casting method. Our results suggest that a combination of ultrasound-based extraction and hot press-based film preparation is an efficient route of producing high strength CNF films

Author Correction: High permeability sub-nanometre sieve composite MoS2 membranes

An amendment to this paper has been published and can be accessed via a link at the top of the paper

High permeability sub-nanometre sieve composite MoS2 membranes

Two-dimensional membranes have gained enormous interest due to their potential to deliver precision filtration of species with performance that can challenge current desalination membrane platforms. Molybdenum disulfide (MoS2) laminar membranes have recently demonstrated superior stability in aqueous environment to their extensively-studied analogs graphene-based membranes; however, challenges such as low ion rejection for high salinity water, low water flux, and low stability over time delay their potential adoption as a viable technology. Here, we report composite laminate multilayer MoS2 membranes with stacked heterodimensional one- to two-layer-thick porous nanosheets and nanodisks. These membranes have a multimodal porous network structure with tunable surface charge, pore size, and interlayer spacing. In forward osmosis, our membranes reject more than 99% of salts at high salinities and, in reverse osmosis, small-molecule organic dyes and salts are efficiently filtered. Finally, our membranes stably operate for over a month, implying their potential for use in commercial water purification applications

Polystyrene activated linear tube carbon nanofiber for durable and high-performance supercapacitors

With increasing demand for sustainable energy, it is essential to develop low cost, high performance, and environment-friendly materials for energy storage application. Metal oxides and sulfides are mostly being used as electrode materials for energy storage devices. However, their wide applications are precluded due to their higher cost, low stability, and adverse effect on the environment. Therefore, development of environment-friendly supercapacitors with low cost, high performance, and stable performance is a big challenge. Here, we report surface engineered carbon nanofibers for durable and high-performance supercapacitor. Surface engineered carbon nanofibers showed the highest specific capacitance of 277 F/g (at 1 mV/s), along with superior flexibility and cyclic stability. Moreover, they showed high energy and power density of 30.5 Wh/kg and 8.3 kW/kg, respectively. The cyclic stability showed almost 100% retention in charge storage capacity up to 5000 cycles. Electrochemical properties of a fabricated symmetrical supercapacitor device using these carbon nanofibers showed improved charge storage capacity at elevated temperatures. The charge storage capacity improved by over 150% by increasing temperature from 10 to 60 °C. Our results suggest that surface engineered carbon nanofibers could be a potential candidate for higher performance and durable supercapacitors

Peptide-Decorated Tunable-Fluorescence Graphene Quantum Dots

We report here the synthesis of graphene quantum dots with tunable size, surface chemistry, and fluorescence properties. In the size regime 15–35 nm, these quantum dots maintain strong visible light fluorescence (mean quantum yield of 0.64) and a high two-photon absorption (TPA) cross section (6500 Göppert–Mayer units). Furthermore, through noncovalent tailoring of the chemistry of these quantum dots, we obtain water-stable quantum dots. For example, quantum dots with lysine groups bind strongly to DNA in solution and inhibit polymerase-based DNA strand synthesis. Finally, by virtue of their mesoscopic size, the quantum dots exhibit good cell permeability into living epithelial cells, but they do not enter the cell nucleus