Performance of chemically synthesized Mn3O4/rGO nanocomposite for electrochemical supercapacitor: a cost-effective high-performance electrode

The manganese oxide graphene oxide (Mn₃O₄/rGO) composite heterojunction with copper oxide is useful for the production of an electrochemical supercapacitor. The graphene oxide and manganese oxide composite have been synthesized by adopting a method of co-precipitation. The composite of Mn₃O₄/rGO was synthesized with different concentrations of Mn₃O₄ and rGO. The structural, morphological, electrochemical and supercapacitive properties of Mn₃O₄/rGO composite have been examined. The electrochemical and supercapacitive properties have been studied with regard to different substrates. The Mn₃O₄/rGO composite was deposited on different substrates such as steel, copper and brass. The CuO/Mn₃O₄/rGO shows relatively better specific capacitance (856 F g^-1) and better stability (82% retention after 2000 cycles) than other substrates used. The present work describes the development of cost-effective and high-performance CuO/Mn₃O₄/rGO-based nanomaterials for supercapacitors. The CuO/Mn₃O₄/rGO composite can be used as a flexible supercapacitor device.

Functionalizing TiO2 with graphene oxide for enhancing photocatalytic degradation of methylene blue (MB) in contaminated wastewater

Methylene blue is a refractory pollutant commonly present in textile wastewater. This study tests the feasibility of TiO₂/graphene oxide (GO) composite in enhancing photocatalytic degradation of MB in synthetic wastewater with respect to scientific and engineering aspects. To enhance its removal, we vary the composition of the composite based on the TiO₂ weight. Under UV-vis irradiation, the effects of photocatalyst's dose, pH, and reaction time on MB removal by the composites are evaluated under optimum conditions, while any changes in their physico-chemical properties before and after treatment are analyzed by using TEM, SEM, XRD, FTIR and BET. The photodegradation pathways of the target pollutant by the composite and its removal mechanisms are also elaborated. It is found that the same composite with a 1:2 wt ratio of GO/TiO₂ has the largest surface area of 104.51 m²/g. Under optimum reactions (0.2 g/L of dose, pH 10, and 5 mg/L of pollutant's concentration), an almost complete MB removal could be attained within 4 h. This result is higher than that of the TiO₂ alone (30%) under the same conditions. Since the treated effluents could meet the strict discharge standard limit of ≤0.2 μg/L set by China's regulation, subsequent biological treatments are unnecessary for completing biodegradation of remaining oxidation by-products in the wastewater effluents.

Facile One-Step Synthesis and Enhanced Optical Nonlinearity of Graphene-γMnS

Graphene-γMnS were prepared by facile one-step hydrothermal method. Structures and properties of samples were explored by characterization, and nonlinear optical (NLO) enhancement of nanocomposites (NCs) was fully studied. Nanoparticles and NCs were tested at 532 nm by a Z-scan technique. With γMnS attached in G layers, NLO susceptibility of graphene-γMnS was greatly improved under single-pulse laser irradiation compared with G and γMnS. The nonlinearity enhanced was attributed to local field effect and charge transfer between γMnS and graphene layers. And NLO property enhancement was restricted by non-radiative defects in graphene-γMnS. Exploring the mechanism of nonlinearity enhancement was significant for fabrication of NLO devices. However, the optical nonlinearity decreased first and then increased with further increased addition of GO, because the dispersion of γMnS attached on graphene surface might make density of sp² fragment and defects changed. Graphene-γMnS exhibited excellent and tunable NLO performance, illustrating that NCs materials have potential applications in NLO devices.

A Facile Method to Synthesize CdSe-Reduced Graphene Oxide Composite with Good Dispersion and High Nonlinear Optical Properties

CdSe-reduced graphene oxide (CdSe/RGO) composites were synthesized by a hydrothermal method. CdSe/RGO composites with different mass ratios were prepared. The structure and morphology of CdSe/RGO composites were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The synthesis of CdSe/RGO complexes was successfully demonstrated by Fourier infrared (FT-IR) and Raman spectra. CdSe nanoparticles in the CdSe/RGO composite were uniformly dispersed on the graphene surface. The study found that oxygen-containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH) groups in graphene played a decisive role in the dispersion of CdSe. The third-order nonlinear optical properties of CdSe/RGO composites were measured by a single beam Z-scan technique. The experimental results showed that composites exhibited two-photon absorption and self-focusing nonlinear refraction properties. Additionally, the third-order nonlinear susceptibility of the composite material was obviously enhanced, which was mainly due to the good dispersion of CdSe nanoparticles on graphene.

Electrochemical Energy Storage Properties of Ni-Mn-Oxide Electrodes for Advance Asymmetric Supercapacitor Application

In this work, we report a facile one-spot synthesis process and the influence of compositional variation on the electrochemical performance of Ni-Mn-oxides (Ni:Mn = 1:1, 1:2, 1:3, and 1:4) for high-performance advanced energy storage applications. The crystalline structure and the morphology of these synthesized nanocomposites have been demonstrated using X-ray diffraction, field emission scanning electron microscopy, and transmission electron Microscopy. Among these materials, Ni-Mn-oxide with Ni:Mn = 1:3 possesses a large Brunauer?Emmett?Teller specific surface area (127 m² g^?1) with pore size 8.2 nm and exhibits the highest specific capacitance of 1215.5 F g^?1 at a scan rate 2 mV s^?1 with an excellent long-term cycling stability (?87.2% capacitance retention at 10 A g^?1 over 5000 cycles). This work also gives a comparison and explains the influence of different compositional ratios on the electrochemical properties of Ni-Mn-oxides. To demonstrate the possibility of commercial application, an asymmetric supercapacitor device has been constructed by using Ni-Mn-oxide (Ni:Mn = 1:3) as a positive electrode and activated carbon (AC) as a negative electrode. This battery-like device achieves a maximum energy density of 132.3 W h kg^?1 at a power density of 1651 W kg^?1 and excellent coulombic efficiency of 97% over 3000 cycles at 10 A g^?1.

One-pot synthesis of γ-MnS/reduced graphene oxide with enhanced performance for aqueous asymmetric supercapacitors

In this work, γ-MnS/reduced graphene oxide composites (γ-MnS/rGO) were prepared using a facile one-pot hydrothermal method. As an electrode material for supercapacitors, the γ-MnS/rGO-60 composite obtained under dosages of graphene oxide  was 60 mg and exhibited an enhanced specific capacitance of 547.6 F g^-1 at a current density of 1 A g^-1, and outstanding rate capability (65% capacitance retention at 20 A g^-1), with superior cycling stability and electrochemical reversibility. An asymmetric supercapacitor assembled from γ-MnS/rGO-60 composite and rGO (γ-MnS/rGO-60//rGO) showed a voltage window of 0-1.6 V and delivered a high energy density of 23.1 W h kg^-1 at a power density of 798.8 W kg^-1, and 15.9 W h kg^-1 at 4.5 kW kg^-1. Moreover, two such 1.0 × 1.0 cm² devices connected together in series easily light up a group of LED lights, showing its potential practical application as an attractive energy storage device.

Fabrication of 3D structures from graphene-based biocomposites

An overview of recent work on the fabrication of graphene-based biocomposite structures useful for a wide variety of biomedical applications.

An electrochemically deposited graphene@Mn3O4 composite film for supercapacitors

A graphene@Mn₃O₄ composite film with a 3D nanoporous network structure has been successfully fabricated via electrochemical deposition.