Green preparation of graphene oxide nanosheets as adsorbent.

As a basic building block of graphene-based materials, graphene oxide (GO) plays an important role in scientific research and industrial applications. At present, numerous methods have been employed to synthesize GO, there are still some issues that need to be solved, thus it is of importance to develop a green, safe and low-cost GO preparation method. Herein, a green, safe and fast method was designed to prepare GO, namely, graphite powder was firstly oxidized in a dilute sulfuric acid solution (H2SO4, 6 mol/L) with hydrogen peroxide (H2O2, 30 wt%) as oxidant, and then exfoliated to GO by ultrasonic treatment in water. In this process, H2O2 was the only oxidant, and no other oxidants were used, thus the explosive nature of GO preparation reaction in the conventional methods could be completely eliminated. This method has other advantages such as green, fast, low-cost and no Mn-based residues. The experimental results confirm that obtained GO with oxygen-containing groups has better adsorption property compared to the graphite powder. As adsorbent, GO can remove methylene blue (50 mg/L) and Cd2+ (56.2 mg/L) from water with removal capacity of 23.8 mg/g and 24.7 mg/g, respectively. It provides a green, fast and low-cost method to prepare GO for some applications such as adsorbent.

Facile preparation of Ti3C2Tx sheets by selectively etching in a H2SO4/H2O2 mixture.

MXenes and MXene-based composite materials have potential applications in a wide range of areas due to their unique physical and chemical characteristics. At present, it is still a major challenge to develop a simple, safe, and efficient route to prepare MXenes without using fluorinated etchants. Herein, we design a facile method to prepare Ti3C2Tx MXene sheets by selectively etching Ti3AlC2 powders in an aqueous diluted H2SO4 solution with H2O2 as an oxidant. In a system of H2SO4 and H2O2, an aqueous H2SO4 solution with a concentration of 6 mol/L is a strongly acidic medium with no volatility, and 30% H2O2 acts as a strong green oxidizer without harmful by-products. The experimental process is safe and convenient to conduct in a beaker under a water bath of 40°C. The etching process can be completed in 1 h under the air atmosphere conditions. The experimental results confirmed that the etched Ti3AlC2 powders can be successfully separated into Ti3C2Tx nanosheets under ultrasound treatment without using any intercalation agent. The relevant etching mechanism is may be attributed to the synergy effect of H2SO4 and H2O2, which triggers sequential selective etching of Al layers from the Ti3AlC2 phase. It may provide a new green way to prepare MXene-based materials without using toxic HF or HF-containing etchants.

3D Graphene Oxide Hydrogel Derived from Waste Toner as Adsorbent.

Waste toner powders are considered as hazardous materials to human and living things, and should be properly recycled by many effective ways due to their fine particle sizes and complex components. In this paper, waste toner powders were used as raw materials to successfully synthesize three dimensions (3D) graphene oxide (GO) hydrogel by means of a one-pot chemical transformation based on the improved Hummers' method. The obtained 3D GO hydrogel has porous structure and abundant oxygen-containing functional groups because of the inherent 3D solid structure of waste toner powder and the strong oxidation process of the improved Hummers' method. Interestingly, the as-prepared 3D GO hydrogel with excellent adsorptive property could quickly remove Pb(II) ions (100 mg/L, removal efficiency of 96% and removal capacity of 144 mg/g) and methylene blue (50 mg/L, removal efficiency of 97% and removal capacity of 48 mg/g) from water, respectively. The preparation process of 3D GO hydrogel was simple and easy to operate, and the output can be moderately mass produced, thus it would provide a new and effective disposal way for the recycling and reusing of waste toner.

Facile preparation of porous biomass charcoal from peanut shell as adsorbent.

Activated carbons derived from biomass have been proved to be one of the most promising adsorbents due to their abundance, low cost, reproducibility and environmental friendliness. In this study, a simple, facile and effective pyrolysis method was demonstrated to prepare hierarchical porous biomass charcoal by using peanut shells as precursor without chemical activation in an electric muffle furnace. The obtained products hold porous structure and abundant oxygen-containing functional groups, which were mainly due to in-built template of the structure of peanut shell and the preparation process without nitrogen protection, respectively. Interestingly, the obtained biomass charcoal sample with excellent adsorptive property quickly removed Pb2+ (100 mg/L) and methylene blue (50 mg/L) from water with removal efficiency of 96.5% and 97.1%, and removal capacity of 48 mg/g and 24 mg/g, respectively. The synthetic process was simple and economical, and it could be used as a beneficial reference in the recycling of biomass waste.

Facile Synthesis of ZnO Nanorods/GO Composite and Its Optical Performance.

The ZnO nanorods/GO composite was fabricated by facilely covering monolayer or few-layer graphene oxide (GO) film on the uniformly distributed ZnO nanorods, which was synthesized on Si substrate using a solution method. The as-synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), as well as X-ray diffraction (XRD). The photoluminescence (PL) measurement indicates that the ZnO nanorods have a strong ultraviolet (UV) emission centered at ~391 nm attributed to the recombination of free excitons and a defect-related visible emission centered at ~530 nm. After the nanorods were covered with GO film, the PL intensity of the composite is quenched compared to that of the bare one at the same excitation condition. The fluorescence quenching mechanism suggests that there is an interfacial charge-transfer process between the excited ZnO and the GO film, and the composite fabricated in this experiment be possible to improve the photocatalysis performance.

Hyaluronate-Functionalized Graphene for Label-Free Electrochemical Cytosensing.

Electrochemical sensors for early tumor cell detection are currently an important area of research, as this special region directly improves the efficiency of cancer treatment. Functional graphene is a promising alternative for selective recognition and capture of target cancer cells. In our work, an effective cytosensor of hyaluronate-functionalized graphene (HG) was prepared through chemical reduction of graphene oxide. The as-prepared HG nanostructures were characterized with Fourier transform infrared spectroscopy and transmission electron microscopy coupled with cyclic voltammograms and electrochemical impedance spectroscopy, respectively. The self-assembly of HG with ethylene diamine, followed by sodium hyaluronate, enabled the fabrication of a label-free electrochemical impedance spectroscopy cytosensor with high stability and biocompatibility. Finally, the proposed cytosensor exhibited satisfying electrochemical behavior and cell-capture capacity for human colorectal cancer cells HCT-116, and also displayed a wide linear range, from 5.0 × 10² cells∙mL-1 to 5.0 × 106 cells∙mL-1, and a low detection limit of 100 cells∙mL-1 (S/N = 3) for quantification. This work paves the way for graphene applications in electrochemical cytosensing and other bioassays.

Study on the interaction between cannabinol and DNA using acridine orange as a fluorescence probe.

The interaction between cannabinol (CBN) and herring-sperm deoxyribonucleic acid was investigated by using acridine orange as a fluorescence probe in this work. UV-Vis spectroscopy, fluorescence spectroscopy, and DNA melting techniques were used. The fluorescence of DNA acridine orange was quenched by CBN. The results indicated that CBN can bind to DNA. The binding constant for the CBN and herring-sperm deoxyribonucleic acid was obtained at 3 temperatures, respectively. Results of molecular docking corroborated the experimental results obtained from spectroscopic investigations. The influence of ionic strength on the fluorescence properties was also investigated. The thermodynamic results indicated that hydrophobic interaction played a major role in the binding between CBN and DNA.

Plasmon-enhanced Electrically Light-emitting from ZnO Nanorod Arrays/p-GaN Heterostructure Devices.

Effective and bright light-emitting-diodes (LEDs) have attracted broad interests in fundamental research and industrial application, especially on short wavelength LEDs. In this paper, a well aligned ZnO nanorod arrays grown on the p-GaN substrate to form a heterostructured light-emitting diode and Al nanoparticles (NPs) were decorated to improve the electroluminescence performance. More than 30-folds enhancement of the electroluminescence intensity was obtained compared with the device without Al NPs decoration. The investigation on the stable and transient photoluminescence spectraof the ZnO nanorod arrays before and after Al NPs decoration demonstrated that the metal surface plasmon resonance coupling with excitons of ZnO leads to the enhancement of the internal quantum efficiency (IQE). Our results provide aneffective approach to design novel optoelectronic devices such as light-emitting diodes and plasmonic nanolasers.

Green emission and Ag(+) sensing of hydroxy double salt supported gold nanoclusters.

In this paper, a complex of Zn-containing hydroxy double salt (Zn-HDS) supported gold nanoclusters (AuNCs) has been synthesized. The formation of the complex (denoted as the AuNCs/Zn-HDS complex) has been analyzed by Transmission Electron Microscopy (TEM), IR spectroscopy and X-ray Photoelectron Spectroscopy (XPS). It is noteworthy that the AuNCs/Zn-HDS complex emits green fluorescence and the quantum yield is 7.6%. Based on the fluorescence quenching effect, the AuNCs/Zn-HDS complex has been employed for the sensitive detection of Ag(+) and the limit of detection is 2.32 nM. The mechanisms of fluorescence generation and quenching are discussed in detail.

Facile synthesis of highly conductive sulfur-doped reduced graphene oxide sheets.

A facile hydrothermal strategy to synthesize sulfur-doped reduced graphene oxide (S-RGO) sheets with good conductivity is proposed by using only graphene oxide (GO) sheets and sodium sulphide (Na2S) as precursors through a hydrothermal reaction process at 200 °C in one pot. The introduced Na2S can act as not only a sulfur dopant, but also as a highly efficient reducing agent in the formation of S-RGO sheets, which dramatically improves the electrical conductivities of the resulting S-RGO sheets compared with previous reports. The current reaches about 50.0 mA at an applied bias of 2.0 V for the optimized sample with 2.22 at% sulfur doping. This current value is much higher than that of RGO sheets (∼1.2 mA) annealed at 200 °C, and very close to that of single-layer graphene sheets (∼68.0 mA) prepared using chemical vapor deposition under the same test conditions. The resulting highly conductive S-RGO sheets offer many promising technological applications such as efficient metal-free electrocatalysts in oxygen reduction reactions in fuel cells and as supercapacitor electrode materials for high-performance Li-ion batteries.

Ultrasonication-Assisted Controllable Self-Assembly of Graphene Oxide.

A facile, and cost-efficient ultrasonication-assisted exfoliation strategy is proposed to fabricate GO sheets with various sizes. Just by controlling the original GO sizes as basic building blocks in deionized water, various aligned architectures, such as films, microfibers, submicron rods, and nanorods, are self-assembled at the water/air interface. The formation mechanisms are analyzed on the basis of the morphology evolutions of various aligned architectures. It is very interesting to note that various functional structures are generally aligned in a certain direction, which is probably attributed to the intrinsic lamellar orientation and the corresponding polarity of the GO sheets. This work provides a beneficial reference for controlling the assembling behaviors of GO in a broad range of applications.

Self-assembled free-standing graphene oxide fibers.

It is a great challenge to directly assemble two-dimensional (2D) graphene oxide (GO) sheets into 1D fibers without any polymer or surfactant for their promising multifunctional applications. Herein, a facile self-assembly strategy is proposed to fabricate neat GO fibers from cost-efficient, aqueous GO suspension at a liquid/air interface based on the repulsive electrostatic forces, attractive van der Waals forces, and π-π stacking. During the self-assembly process and ultrasonic cleaning, the morphology variated from the source graphite powder through GO sheets to GO fibers and finally to neat GO fiber films. It is interesting to note that the electrical property of the GO fiber films was improved dramatically after subsequent low-temperature thermal annealing. The morphological evolution process and formation mechanism were analyzed on the basis of optical microscopy, scanning electron microscopy, and transmission electron microscopy observation, and the electrical characteristics was also discussion.

Lasing behavior modulation for ZnO whispering-gallery microcavities.

Four configurations of whispering-gallery-mode (WGM) microcavities were designed and fabricated to modulate the optically pumped lasing characteristics by polymer modification on hexagonal ZnO microrod surfaces. On the basis of the total internal reflection (TIR) at the boundary of microcavities, the lasing characteristics were improved by raising the relative refractive index. Considering the different reflective conditions at various side surfaces, the typical lasing mode equation for whispering-gallery microcavity was modified to adapt for general situation even with unsymmetrical structure, and then employed to discuss the observed lasing behaviors, in the polyvinylcarbazole (PVK) modified ZnO microrods, such as mode position, mode numbers and quality factor. The optical field distributions for TE modes of the four configurations were also simulated by 2-dimensional finite difference time-domain (FDTD) method. The simulation agreed well with the experimental results to support the resonance mechanism.