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Organic dyes are used in many industries, e.g., textile, cosmetics and food. Hence, contamination of organic dyes to water sources is a critical issue. To reduce water pollution by organic dyes, we propose a paper-like adsorbent with a practical and economical production procedure. Subsequently, a flexible adsorbent was produced using a one-step approach by vacuum filtration of graphene oxide (GO) and iron oxide nanoparticles (Fe3O4-NPs) containing dispersion through a membrane and quoted as GO/Fe3O4 paper. For comparison, GO paper was also prepared using the same procedure. Both papers were characterized using UV–VIS absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, electron diffraction X-ray analysis, X-ray photoelectron spectroscopy, and powder X-ray diffraction techniques. At the steady-state conditions, GO/Fe3O4 and GO papers were performed as adsorbent for cationic dyes of methylene blue, neutral red, and anionic dyes of methyl orange and fluorescein. In general, the removal efficiency of GO/Fe3O4 paper was higher than that of GO paper for adsorption of all dyes and this adsorbent revealed satisfactory adsorption properties for cationic dyes when compared to anionic dyes.

Simultaneous removal and quantification of heavy metal ions are very important since they threaten human health. In this work, a dual-functional, free-standing and flexible reduced graphene oxide (rGO) based paper-like material including zinc oxide nanoparticles (ZnO-NPs) and ethylenediaminetetraaceticacid (EDTA) was produced using successive vacuum-filtration and hydrothermal reduction processes. First, graphene oxide (GO) layers were coated with ZnO-NPs and then EDTA was immobilized by ultrasonic treatment. Prepared GO/ZnO-NPs-EDTA suspension was vacuum-filtrated on a membrane and peeled to obtain GO/ZnO-NPs-EDTA paper. Hydrothermal reduction resulted in rGO/ZnO-NPs-EDTA paper and this material is first-time performed for two applications: Simultaneous removal of heavy metal ions of Cd2+, Pb2+, Cu2+, and Hg2+ and their further simultaneous electrochemical detection. Structural, chemical, crystallographic, optical, morphological, and electrochemical characterization of this paper-like material was executed using numerous techniques. Maximum adsorption performance of the rGO/ZnO-NPs-EDTA paper was determined as 2963, 8056, 600, and 1753 mg/g, while electrochemical simultaneous determination revealed linear ranges of 18.5-500, 22.4-700, 8.3-200, 3.3- $300~\mu \text{M}$ and detection limit values of 5.6, 6.8, 2.5, $1.0~\mu \text{M}$ for Cd2+, Pb2+, Cu2+, and Hg2+, respectively.

We studied the production and electrochemical performance of NiCo2S4 electrodeposited reduced graphene oxide (rGO) paper for use as a freestanding flexible electrode for the simultaneous determination of folic acid (FA) and ascorbic acid (AA). Production of rGO paper was achieved through vacuum filtration of the aqueous dispersion of graphene oxide, followed by chemical reduction in hydrogen iodide solution. NiCo2S4/rGO paper material was fabricated with a simple approach using electrodeposition of hydrothermal synthesized NiCo2S4 nanoparticles directly on rGO paper. The physicochemical properties of as-prepared flexible NiCo2S4/rGO paper were characterized by means of field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray powder diffraction patterns. This freestanding paper electrode demonstrated high sensitivity, a wide linear range, and a low detection limit towards the simultaneous detection of FA and AA. NiCo2S4/rGO paper sensor, possessing easy preparation, low cost, and high flexibility, was tested in real samples with promising recoveries. This study exhibited that the approach of the electrodeposition of bimetallic sulfides on freestanding graphene paper substrates has great potential to develop high-performance flexible electrochemical sensors.

Graphene (Gr)/methylene blue (MB) composites were successfully prepared and amperometric detection of nicotinamide adenine dinucleotide (NADH) was studied on the Gr/MB composite thin films modified Au(111) electrode. Gr sheets were fabricated by using two-step electrochemical approaches: intercalation of sodium dodecyl sulfate (SDS) into graphite working electrode by electrooxidation and exfoliation of SDS-intercalated graphite electrode by electrochemical reduction to obtain Gr/SDS suspension. In order to prepare Gr/MB composite structure, first SDS was removed from Gr/SDS suspension and then MB was added into Gr suspension. Gr/MB dispersion was ultrasonicated, vacuum-filtered through a membrane, and then re-dispersed into water. Gr/MB nanocomposite was supported on Au(111) substrates by drop-casting of this composite dispersion. Characterization of Gr/MB composites was carried out by using scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), UV–Visible absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), and cyclic voltammetry techniques. Gr-MB/Au(111) electrode, having an excellent electrocatalytic activity, was used for amperometric determination of NADH. The oxidation current density was linearly proportional to NADH concentration in the range between 1.0 to 264 μM. The sensitivity of the sensor was calculated as 0.316 µA µM−1 cm−2 with a detection limit of 0.3 µM at a signal-to-noise ratio of 3.0. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers

Poly(methylene blue)/graphene nanocomposite thin films were prepared by electropolymerization of methylene blue in the presence of graphene which have been synthesized by two different methods of a chemical oxidation process and an electrochemical approach. Synthesized nanocomposite thin films were characterized by using cyclic voltammetry, UV–vis. absorption spectroscopy, powder X-ray diffraction, and scanning tunneling microscopy techniques. Electrocatalytical properties of prepared poly(methylene blue)/graphene nanocomposite films were compared toward electrochemical oxidation of nitrite. Under optimized conditions, electrocatalytical effect of nanocomposite films of chemically prepared graphene through electrochemical oxidation of nitrite was better than that of electrochemically prepared graphene.