Adsorption of Methylene Blue from Aqueous Solutions by Polyvinyl Alcohol/Graphene Oxide Composites.

As a new member of the carbon family, graphene oxide (GO) has shown excellent adsorption ability to micro-pollutants in aqueous solutions. However, its tiny size makes it difficult to be removed from aqueous solutions using the conventional separation methods, which limits its practical application in the environmental protection. In this study, polyvinyl alcohol (PVA) was used as carrier immobilizing GO, and novel PVA/GO composites were prepared. The morphology and physicochemical properties of the composites were characterized by SEM, FTIR and TGA analysis. The adsorption properties of methylene blue (MB) onto the composites were studied through investigating the experimental parameters such as solution pH, adsorbent dosage, contact time and temperature. The isotherm data were analyzed using the Langmuir, Freundlich and Dubinin-Radushkevich models. The calculated maximum adsorption capacity reached 476.2 mg/g at 50% GO content. The pseudo-first-order kinetic, pseudo-second-order kinetic and intra-particle diffusion models were used to explore the adsorption kinetics. The results showed that the dynamic data were fitted to the pseudo-second-order kinetic model.

Theoretical study on the structures and optical absorption of Si172 nanoclusters.

The structures and optical properties of silicon nanoclusters (Si NCs) have attracted continuous interest in the last few decades. However, it is a great challenge to determine the structures of Si NCs for accurate property calculation due to the complication and competition of various structural motifs. In this work, a Si172 NC with a size of about 1.8 nm was investigated using a genetic algorithm combined with tight-binding and DFT calculations. We found that a diamond crystalline core with 50 atoms (1.2 nm) was formed in the Si172 NC. It can be expected that at a size of about 172 atoms, a diamond crystalline structure can nucleate from the center of the Si NCs. The optical properties of the pure and hydrogenated Si172 NC structures also have been studied using the TDDFT method. Compared with the pure Si172 NC, the absorption peaks of the hydrogenated Si172 NC are obviously blue-shifted.

Biosorption Behavior of Ciprofloxacin onto Enteromorpha prolifera: Isotherm and Kinetic Studies.

The studies aimed at the feasibility of using Enteromorpha prolifera for the removal of ciprofloxacin from aqueous solutions. Batch experiments were carried out for the biosorption of ciprofloxacin onto Enteromorpha prolifera. The factors affecting the biosorption process such as the initial concentration, dosage, pH and the contact time were studied. Enteromorpha prolifera exhibited a maximum biosorption capacity of 21.7 mg/g. The pseudo-second-order kinetic model described the ciprofloxacin biosorption process with a good fitting. The optimum pH of ciprofloxacin adsorbed by Enteromorpha prolifera was 10. Biosorption equilibrium studies demonstrated that the biosorption followed Freundlich isotherm model, which implied a heterogeneous biosorption phenomenon.

Highly effective removal of basic fuchsin from aqueous solutions by anionic polyacrylamide/graphene oxide aerogels.

Novel anionic polyacrylamide/graphene oxide aerogels were prepared by a freeze drying method and used to remove basic fuchsin from aqueous solutions. These aerogels were sponge-like solid with lightweight, fluffy and porous structure. The batch adsorption experiments were carried out to study the effect of various parameters, such as the solution pH, adsorbent dose, contact time and temperature on adsorption properties of basic fuchsin onto anionic polyacrylamide/graphene oxide aerogels. The kinetics of adsorption corresponded to the pseudo-second-order kinetic model. The Langmuir adsorption isotherm was suitable to describe the equilibrium adsorption process. The maximum adsorption capacity was up to 1034.3 mg/g, which indicated that anionic polyacrylamide/graphene oxide aerogels were promising adsorbents for removing dyes pollutants from aqueous solution.

Single electrode biosensor for simultaneous determination of interferon gamma and lysozyme.

Simultaneous detection of multiple biomarkers holds great promise for acute leukemia evaluation. Here, a novel biosensor is developed for simultaneous electrochemical detection of interferon gamma (IFN-γ) and lysozyme (Lys) based on aptamer recognition by coupling "signal-on" and "signal-off" modes. On one Au electrode, two kinds of signaling probes labeled by the thiolated ferrocene (Fc)- and methy blue (MB)- were designed to hybridize with IFN-γ and Lys aptamers respectively to form partial complementary DNA duplexes. In the presence of IFN-γ and Lys, the target-aptamer interaction led to the release of aptamer from duplex DNA structure. The single-stranded signaling probes thus suffered from the conformation changes, which resulted in the decreased (or increased) oxidation peak current of Fc (or MB) according to the "signal-off (or signal-on)" mode. Electrodes were characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under the optimized conditions, the signal changes were quantified using square wave voltammetry (SWV). This proposed biosensor for IFN-γ and Lys possessed linear detection range from 0.01 to 10 nM and 0.1 to 100 nM, with the detection limits of 1.14×10(-3) nM and 0.0164 nM, respectively. Moreover, this biosensor was readily regenerated and proved successful toward the practical analysis. The proposed strategy could provide more integrated and reliable information for acute leukemia evaluation.

Removal of nitric oxide by the highly reactive anatase TiO2 (001) surface: a density functional theory study.

In this paper, density functional theory (DFT) calculation was employed to study the adsorption of nitric oxide (NO) on the highly reactive anatase TiO2 (001) surface. For comparison, the adsorption of NO on the (101) surface was also considered. Different from the physical adsorption on the (101) surface, NO molecules are found to chemisorb on the TiO2 (001) surface. The twofold coordinate oxygen atoms (O2c) on the anatase (001) surface are the active sites. Where NO is oxidized into a nitrite species (NO2(-)) trapping efficiently on the surface, with one of the surface Ti5c-O2c bonds adjacent to the adsorption site broken. Our results, therefore, supply a theoretical guidance to remove NO pollutants using highly reactive anatase TiO2 (001) facets.

An ionic liquid-modified graphene based molecular imprinting electrochemical sensor for sensitive detection of bovine hemoglobin.

A novel kind of molecular imprinted polymers based on ionic liquid-functionalized graphene (MIPs/IL/GR) was prepared by electro-polymerization, which was applied as a molecular recognition element to modify glassy carbon electrode (GCE) to construct an electrochemical sensor (MIPs/IL/GR/GCE) for sensitive detection of bovine hemoglobin (BHb). The fabrication conditions that affect the performance of the imprinted sensor, such as pyrrole concentration, scan cycles and scan rates, have been discussed. Under the optimized conditions, the prepared molecular imprinting electrochemical sensor showed a fast rebinding dynamics, which was successfully applied to BHb detection with a wide linear range from 1.0 × 10(-10) to 1.0 × 10(-3)g/L (R=0.998) and a detection limit of 3.09 × 10(-11)g/L. Moreover, the fabricated sensor possessed a good selectivity and stability, providing a promising tool for immunoassays and clinical applications.

Mechanical and dye adsorption properties of graphene oxide/chitosan composite fibers prepared by wet spinning.

Graphene oxide/chitosan composite fibers were prepared by a wet spinning method, and their mechanical properties were investigated. Experimental results showed that the introduction of graphene oxide at 4 wt% loading can improve the tensile strengths of chitosan fibers. Batch adsorption experiments were carried out to study the effect of various parameters, such as the initial pH value, adsorbent dosage, contact time and temperature on adsorption of fuchsin acid dye. The Langmuir model was used to fit the experimental data of adsorption isotherm, and kinetic studies showed that the adsorption data followed the pseudo-second order model. Thermodynamic studies indicated that the adsorption of fuchsin acid dye on graphene oxide/chitosan fibers was a spontaneous and exothermic process. Our results indicate that the graphene oxide/chitosan fibers have excellent mechanical properties and can serve as a promising adsorbent for the removal of dyes from aqueous solutions.

Continuous-wave and passive Q-switching laser performance of Yb:YSGG crystal.

We report, for the first time, on the passive Q-switching laser performance of Yb:YSGG disordered garnet crystal. An average output power of 2.6 W at 1025.8 nm was produced at a pulse repetition rate of 11 kHz with a slope efficiency of 47%; the resulting pulse energy, duration, and peak power were respectively 236 µJ, 3.6 ns and 65.6 kW. The laser performance in continuous-wave mode under 935-nm diode pumping was also investigated, with output coupling changed over a wide range from 0.5% to 60%.

Macroscopic, flexible, high-performance graphene ribbons.

Tailoring the structure and properties of graphene fibers is an important step toward practical applications. Here, we report macroscopic, long graphene ribbons formed by combining electrostatic interaction and shear stress during the wet-spinning process. The graphene ribbons are flexible and can be woven into complex structures, and the ribbon morphology can be tailored by controlling the orientation of wrinkles to obtain elasticity within a modest strain. We demonstrate several potential applications of pure or Pt-graphene hybrid ribbons as elastic strain sensors, counter electrodes for dye-sensitized fiber solar cells with cell efficiencies reaching 4.69% under standard illumination and 6.41% with a back reflector, and woven fabric supercapacitor electrodes. Our method can directly fabricate meter-long graphene ribbons with controlled structure and high performance as both energy conversion and energy storage materials.

Fabrication and characterization of a zirconia/multi-walled carbon nanotube mesoporous composite.

A zirconia/multi-walled carbon nanotube (ZrO2/MWCNT) mesoporous composite was fabricated via a simple method using a hydrothermal process with the aid of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Transmission electron microscopy (TEM), N2 adsorption-desorption, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were used to characterize the as-made samples. The cubic ZrO2 nanocrystallites were observed to overlay the surface of MWCNTs, which resulted in the formation of a novel mesoporous-nanotube composite. On the basis of a TEM analysis of the products from controlled experiment, the role of the acid-treated MWCNTs and CTAB was proposed to explain the formation of the mesoporous-nanotube structure. The as-made composite possessed novel properties, such as a high surface area (312 m(2)·g(-1)) and a bimodal mesoporous structure (3.18 nm and 12.4 nm). It was concluded that this composite has important application value due to its one-dimensional hollow structure, excellent electric conductivity and large surface area.

Graphene as an efficient sorbent for the SPE of organochlorine pesticides in water samples coupled with GC-MS.

The determination of organochlorine pesticides in water samples, which are harmful to humans, is very important for environmental risk assessment. Based on the excellent adsorption properties of graphene, an SPE coupled with GC-MS method for the monitoring of organochlorines (four hexachlorcyclohexanes and four dichlorodiphenyltrichloroethanes) was developed. Owing to the hydrophobic interaction and π-π stacking interaction between the analytes and graphene, the analytes quantitatively adsorbed onto the graphene-based SPE cartridge were eluted by ethyl acetate for analysis. Several parameters influencing the analytical performance, such as the kind of elution, sample volume, reusability of the cartridge, have been investigated in detail. Under the optimal conditions, detection of limits of 1.95-9.38 ng/L, recoveries of 83.9-107.3% at two spiked concentration levels (0.1 and 10 ng/mL) and RSDs in the range of 2.9-7.4% for real water samples were obtained for all the analytes. This work reveals the great potential of graphene in sample preparation procedures.

Synthesis of strongly green-photoluminescent graphene quantum dots for drug carrier.

A novel approach has been developed for the preparation of strongly green-photoluminescent graphene quantum dots (GQDs-PEG) which have been surface-passivated by polyethylene glycol. The photoluminescence (PL) quantum yield of the GQDs-PEG with 400 nm excitation was about 18.8%, which was higher than other GQDs reported in the literature. More importantly, the surface-passivated PEG on GQDs can not only enhance PL intensity but also load drug by hydrogen bonding. Moreover, the high specific surface area of GQDs-PEG endowed them high loading capability (2.5 mg/mg) to carry drug. The results demonstrated that the GQDs-PEG were suitable for drug carrier and cell imaging.

Passive Q-switching laser performance of Yb:Gd3Ga5O12 garnet crystal.

We report on the passive Q-switching laser performance of the Yb:Gd3Ga5O12 garnet crystal. With a Cr4+:YAG crystal used as saturable absorber for passive Q-switching, an average output power of 5.31 W was produced at a pulse repetition rate of 62.5 kHz, the optical-to-optical and slope efficiencies being, respectively, 45% and 61%. Laser pulses of 140 µJ in energy and 5.8 ns in duration were also obtained at 22.2 kHz, with a corresponding peak power amounting to 24.1 kW.

Methylene blue adsorption on graphene oxide/calcium alginate composites.

Graphene oxide has been used as an adsorbent in wastewater treatment. However, the dispersibility in aqueous solution and the biotoxicity to human cells of graphene oxide limits its practical application in environmental protection. In this research, a novel environmental friendly adsorbent, calcium alginate immobilized graphene oxide composites was prepared. The effects of pH, contact time, temperature and dosage on the adsorption properties of methylene blue onto calcium alginate immobilized graphene oxide composites were investigated. The equilibrium adsorption data were described by the Langmuir and Freundlich isotherms. The maximum adsorption capacity obtained from Langmuir isotherm equation was 181.81 mg/g. The pseudo-first order, pseudo-second order, and intraparticle diffusion equation were used to evaluate the kinetic data. Thermodynamic analysis of equilibriums indicated that the adsorption reaction of methylene blue onto calcium alginate immobilized graphene oxide composites was exothermic and spontaneous in nature.

Graphene-based solid-phase extraction disk for fast separation and preconcentration of trace polycyclic aromatic hydrocarbons from environmental water samples.

Graphene has great potentials for the use in sample preparation due to its ultra high specific surface area, superior chemical stability, and excellent thermal stability. In our work, a novel graphene-based SPE disk was developed for separation and preconcentration of trace polycyclic aromatic hydrocarbons from environmental water samples. Based on the strong π-π stacking interaction between the analytes and graphene, the analytes extracted by graphene were eluted by cyclohexane and then determined by GC-MS. Under the optimized conditions, high flow rate (30 mL/min) and sensitivity (0.84-13 ng/L) were achieved. The proposed method was successfully applied to the analysis of real environmental water samples with recoveries ranging from 72.8 to 106.2%. Furthermore, the property of anticlogging and reusability was also improved. This work reveals great potentials of graphene-based SPE disk in environmental analytical.

Fabrication and characterization of a triple functionalization of graphene oxide with Fe3O4, folic acid and doxorubicin as dual-targeted drug nanocarrier.

A novel triple functionalized drug delivery system was synthesized by encapsulation of superparamagnetic graphene oxide (GO) and doxorubicin (DOX) with folic acid (FA) conjugated chitosan (CHI). The carrier exhibited a high loading efficiency (0.98 mg/mg), a high saturation magnetization (10.5 emu/g) and a prolonged release rate. A real-time monitoring method on the drug release from graphene oxide (GO) was reported using DOX as the model drug. The release mechanism of DOX at different pH was investigated via monitoring the time dependency of the accumulative drug release. Results show that the drug release of DOX was pH sensitive as observed at pH 5.3 and pH 7.4 PBS solutions, the lower pH values lead to weaker hydrogen bonds and degradation of CHI, and thus result in a higher release rate of DOX. Especially, this system could be applied as a dual-targeted drug nanocarrier by combined biological (active) and magnetical (passive) targeting capabilities. Our research suggests that a novel triple functionalized, pH-responsive nanocarrier for anticancer drug has been synthesized.

Adsorption Properties of Doxorubicin Hydrochloride onto Graphene Oxide: Equilibrium, Kinetic and Thermodynamic Studies.

Doxorubicin hydrochloride (DOX) is an effective anticancer agent for leukemia chemotherapy, although its clinical use has been limited because of its side effects such as cardiotoxicity, alopecia, vomiting, and leucopenia. Attention has been focussed on developing new drug carriers with high adsorption capacity and rapid adsorption rate in order to minimize the side effects of DOX. Graphene oxide (GO), a new type of nanomaterial in the carbon family, was prepared by Hummers method and used as adsorbent for DOX from aqueous solution. The physico-chemical properties of GO were characterized by transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), zeta potential, and element analysis. The adsorption properties of DOX on GO were studied as a function of contact time, adsorbent dosage, temperature and pH value. The results showed that GO had a maximum adsorption capacity of 1428.57 mg/g and the adsorption isotherm data fitted the Langmuir model. The kinetics of adsorption fits a pseudo-second-order model. The thermodynamic studies indicate that the adsorption of DOX on GO is spontaneous and endothermic in nature.