Carboxylated graphene oxide nanosheets as efficient electrodes for high-performance supercapacitors.

In the presence of dry ice, a series of graphitic materials with carboxylated edges (ECGs) were synthesized by ball milling graphite for varied times (24, 36, and 46 h). The influence of carboxylation on the physiochemical characteristics and electrochemical performance as effective electrodes for supercapacitors were assessed and compared with pure graphite. Several characterization techniques were employed to investigate into the morphology, texture, microstructure, and modification of the materials. Due to its interconnected micro-mesoporous carbon network, which is vital for fast charge-discharge at high current densities, storing static charges, facilitating electrolyte transport and diffusion, and having excellent rate performance, the ECG-46 electrode among the investigated samples achieved the highest specific capacitance of 223 F g-1 at 0.25 A g-1 current density and an outstanding cycle stability, with capacitance retention of 90.8% for up to 10,000 cycles. Furthermore, the symmetric supercapacitor device based on the ECG-46 showed a high energy density of 19.20 W h kg-1 at 450.00 W kg-1 power density. With these unique features, ball milling of graphitic material in dry ice represents a promising approach to realize porous graphitic material with oxygen functionalities as active electrodes.

Three-dimensional hierarchical frameworks based on molybdenum disulfide-graphene oxide-supported magnetic nanoparticles for enrichment fluoroquinolone antibiotics in water.

Recently, water pollution caused by antibiotics is rapidly increasing. Thus, developing efficient, fast and sensitive detection methods for environmental antibiotics monitoring are still remaining elusive. Herein, a method for antibiotics analysis including lecofloxacin, pazcofloxacin and gatifloxacin in water by high performance liquid chromatography (HPLC) using molybdenum disulfide-graphene oxide-supported magnetic nanoparticles (Fe3O4/GO/MoS2) as the adsorbent of magnetic solid-phase extraction was developed. The as-prepared magnetic Fe3O4/GO/MoS2 nanocomposite exhibited good enrichment capability toward fluoroquinolone antibiotics and the analytes were absorbed within a short time ca. 2 min. The main drive forces of Fe3O4/GO/MoS2 nanocomposite and antibiotics were most likely attributed to hydrogen bonding and electrostatic attraction. A sensitive and effective MSPE-HPLC method was developed with low detection limits (LODs) ranging from 0.25 to 0.50 ng mL-1. The recoveries obtained from the analysis of water sample were between 85.6% and 106.1% with relative standard deviations (RSDs, n = 5) lower than 9.5%. The developed method has a good potential for the analysis of organic contaminants in water with low cost and high sensitivity. Therefore, this finding is a promising strategy for designing high efficiency and fast antibiotics detection system.

A simple yet sensitive colorimetric nitrite ions assay based on diazotization with p­Aminobenzoic and coupling with phloroglucinol in acidic medium.

Immoderate intake of nitrite (NO2-) is deleterious human health and may result in causing dangerous diseases. In this study, nitrite detection system was successfully fabricated based on a unique diazo-coupling reaction of p­Aminobenzoic acid (PABA) and phloroglucinol (1, 3, 5­trihydroxybenzene). Upon the presence of NO2- in an acid medium, p­Aminobenzoic acid could not only form diazonium ion easily but also couple with p­Aminobenzoic acid, and results forming yellow water-soluble azo dye that shows maximum absorption at 434 nm. Under the further accurate determination condition, such as acid concentration, amount of reagents and time required, the naked-eye detection of NO2- showed excellent selectivity in compared with some anions. Especially, diazotization and coupling reaction proposed here is very fast and control of pH and temperature are unnecessary. Moreover, the color is stable for several days and Beer's law is obeyed over a wide range. Reliable detection can be made in the range of 0.05 to 1 p.p.m. of nitrite ion. Detection limit was calculated to be 0.024 p.p.m. (0.52 µâ€¯M) by UV-visible spectroscopy and 0.05 p.p.m. (1.09 µâ€¯M) by naked-eye. By using an electrochemical method, IR, SEM, and 1HNMR, the sensing mechanism can be easily verified. More importantly the proposed method was successfully applied for the determination of nitrite in a real water sample.

Sensitive and selective colorimetric nitrite ion assay using silver nanoparticles easily synthesized and stabilized by AHNDMS and functionalized with PABA.

Nitrite ions (NO2 -), as one of the important inorganic anions, exhibit considerable effects towards the environment and human health. Moreover, over intake of this anion may cause dangerous diseases. Herein, we successfully fabricated silver nanoparticles (AgNPs) using 4-amino-5-hydroxynaphthalene-2, 7-disulphonic acid monosodium salt (AHNDMS) and functionalized them with p-aminobenzoic acid (PABA), and used the functionalised AgNPs as a sensitive and selective colorimetric sensor for nitrite ions. The structure of the as-prepared pure AgNPs was experimentally characterized by different characterizations methods, namely, UV-vis, FT-IR, CV, DPVs, SEM, TEM, and XRD. Additionally, the nitrite ion sensitively and selectively changes the brownish yellow color of the dispersed AgNPs to pinkish red, indicating aggregation of AgNPs, with a detection limit of 0.016 ppm (0.348 µM) and 0.0069 ppm (0.149 µM) by the naked-eye and by UV-vis spectroscopy, respectively. The color change suggested that the aggregation of AgNPs was induced by nitrite-selective diazo-coupling. UV-vis spectra show the disappearance of the absorbance at 474 nm and appearance of a new peak at 532 nm, presumably due to the conversion of AgNPs to silver ions. Moreover, the studies of interference in the proposed sensor confirm its selectivity in the presence of anions as well as cations. Furthermore, linearity was observed between the absorption and the concentration of nitrite ions. More importantly, the proposed sensor was practicably applied for the determination of nitrite in different water samples, such as distilled water, river water, and tap water.