Keywords : graphene oxide

Chemical Reactivity and Electronical Properties of Graphene and Reduced Graphene Oxide on Different Substrates

E. Celasco

Advanced Materials Letters, 2019, Volume 10, Issue 8, Pages 545-549
DOI: 10.5185/amlett.2019.2204

The chemical reactivity and the electronical properties variation of graphene (G) supported on Ni(111) and of the reduced Graphene Oxide (rGO) will be described thanks to the framework of University of Genoa and Polytechnic of Turin. We will present the main results obtained on the reactivity, towards CO, of pristine graphene grown on Ni(111). Single layer graphene films are grown by ethene dehydrogenation on Nickel, under different experimental conditions, and the system is studied in-situ by X-ray Photoemission and High-Resolution Electron Energy Loss Spectroscopies before and after CO exposure at 87 K and at room temperature. The main results were: the best CO reactivity in the top-fcc configuration of graphene on Ni(111), at low temperature. the higher reactivity occurs in the case of minimum percentage of contaminant or Ni2C still present during the grown process. a reactivity toward CO at room temperature on graphene with punctual controlled defects by sputtering, with possible applications e.g., gas sensing. More applicative aspect is the modification of GO in rGO, by UV based process. During the reduction, electrical properties is improved, opening possible application in the ink-jet printing mechanism as conductive printing system, coating or in the functionalization of G. Copyright © VBRI Press.

Functionalized graphene oxide as an electrochemical sensing platform for detection of Bisphenol A

Upama Baruah;Devasish Chowdhury

Advanced Materials Letters, 2018, Volume 9, Issue 7, Pages 516-525
DOI: 10.5185/amlett.2018.2067

The present work demonstrates the electrochemical detection of the endocrine disruptor Bisphenol A in solution by three different types of functionalized graphene samples viz. graphene oxide (GO), ester functionalized graphene oxide (GO-ES) and amine functionalized graphene oxide (GO-en) modified glassy carbon electrode (GCE) using a very simple drop casting method without the use of any toxic organic compounds or polymeric binders via cyclic voltammetry. The system developed showed detection of BPA via formation of a π-stacked layered functionalized graphene oxide-BPA (π-s-GO-BPA) nanocomposite accompanied by a reduction in the oxidation peak current value associated with a significant shift in the peak potential value. The electrochemical sensing materials developed showed good sensitivity compared to already reported systems and furthermore high selectivity in presence of other structurally similar kinds of molecules in solution without the use of any toxic organic chemicals thereby demonstrating the practical applicability of the material and the technique developed. The practical viability of the material developed is also demonstrated via testing with a real low quality plastic sample that contains Bisphenol A. A plausible mechanism to justify the detection process is also being discussed. 

Synthesis of rGO via UV-assisted photocatalytic reduction of graphene oxide

Rui Liu; Wein-Duo Yang; Qiao Ying Jie; Ying Jin Song; Yan-Ru Li

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 436-438
DOI: 10.5185/amlett.2018.1884

We perform a novel strategy for the synthesis of reduced graphene oxide (rGO) with an 18 W UV-assisted photocatalytic reduction method. The surface morphology and internal structure of the obtained rGO were identified by Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). The rGO electrode materials have 2-6 layers graphene layers with a thickness of 1.1 nm to 2.2 nm after the photocatalytic reduction for 10 h. The rGO shows a superb capacitance of 250.41 Fg -1 with obvious triangles in the electrochemical charge-discharge analysis, which indicates good reversibility between the graphene oxide and reduced graphene oxide. This research may provide new insights that contribute to resolving the capacity issues of lithium batteries. 

Optical and electrical properties of graphene oxide and reduced graphene oxide films deposited onto glass and Ecoflex® substrates towards organic solar cells

Agnieszka Iwan; Felipe Caballero-Briones; Krzysztof A. Bogdanowicz; José D. O. Barceinas-Sánchez; Wojciech Przybyl; Adam Januszko; Javier A. Baron-Miranda; Ana P. Espinosa-Ramirez; Jesus Guerrero-Contreras

Advanced Materials Letters, 2018, Volume 9, Issue 1, Pages 58-65
DOI: 10.5185/amlett.2018.1870

Graphene oxide (GO) was synthesized using modified Hummers method. GO films were deposited by doctor blade onto glass slides and Ecoflex® membranes using GO suspensions, or dip-coated onto molecular functionalized glass substrates. Doctor bladed films were studied by optical transmittance, linear sweep voltammetry and by thermal imaging under applied potential. Dip coated films were reduced with different chemical agents to produce transparent, conductive, reduced graphene oxide (rGO) films that were characterized by optical transmittance, current sensing atomic force microscopy and X-ray photoelectron spectroscopy. Doctor bladed GO films were mechanically stable, with resistances ranging 10 6 to 10 11 ohm depending on the film thickness, which in turn depended on the GO precursor solution concentration. Thermal imaging did not provided evidence of visible voltage-activated conduction. The best reduction treatment to obtain transparent and conductive rGO films comprised a primary reduction with NaBH4 followed by an air annealing at 120 ºC. Conductive atomic force microscopy indicated that rGO film conductivity is governed by the superposition of individual sheet and X-ray photoelectron spectroscopy suggested that the C/O ratio is not determinant for conduction. The better-reduced films had transmittances ca. 85% with sheet resistances around 10 3 ohm/sq, making them feasible as transparent electrodes. Finally, a short discussion about location of GO/rGO in organic solar cells is presented.

Lanthanum doped–TiO2 decorated on graphene oxide nanocomposite: A photocatalyst for enhanced degradation of acid blue 40 under simulated solar light 

Samuel O.B. Oppong; William W. Anku; Sudheesh K. Shukla; Poomani P. Govender

Advanced Materials Letters, 2017, Volume 8, Issue 3, Pages 295-302
DOI: 10.5185/amlett.2017.6826

La-TiO2-GO nanocomposites were successfully synthesised via sol-gel method. Structures, morphologies and photocatalytic activities of the as-synthesized nanocomposites were determined using X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy (RS) and scanning electron microscopy (SEM). UV-Vis diffuse reflectance spectroscopy was used to estimate band gap energies. The photocatalytic activities of the as-synthesized nanocomposites were evaluated for the degradation of Acid Blue 40 in aqueous solutions under simulated solar light. The photocatalytic results show that the as-synthesized La-doped TiO2-GO (0.3% La) nanocomposite shows good photocatalytic activity and can be considered as a promising photocatalyst for the degradation of organic pollutants in water. The good photocatalytic efficiency is ascribed to the cooperative effect of improved visible light absorbance and separation of charge carriers due to the combined effect of La and the GO in the composite. Analysis from Total organic carbon (TOC) shows a high degree of complete mineralisation of Acid Blue 40 (TOC removal of 75%) which decreases the formation of possible degradation by-products. Due to the stability of La-TiO2-GO (0.3% La) nanocomposite, it was reused for five times reaching 84.0% maximum degradation efficiency during the five cycles.

Temperature dependence green reduction of graphene oxide by urea

Pankaj Chamoli; Malay K. Das; Kamal K. Kar

Advanced Materials Letters, 2017, Volume 8, Issue 3, Pages 217-222
DOI: 10.5185/amlett.2017.6559

In the present study, temperature dependence reduction of graphene oxide into graphene nanosheets has been demonstrated using green reducing agent, urea. As synthesized graphene nanosheets have been characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy(UV-Vis), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and X-ray photon spectroscopy (XPS). Raman analysis confirms that the maximum reduction of graphene oxide is observed at 140 o C, and reached to high Raman D to G band intensity ratio of ~ 1.41. FTIR analysis supports the Raman signature of maximum reduction of oxygen functional groups from graphene oxide at 140 o C. XPS analysis validates the Raman and FTIR signature of maximum removal of oxygen species from graphene oxide at 140 o C, and confirms the attainment of the C/O ratio of ~ 5.66. Result indicates that the urea offers excellent reductive ability at high temperature to produce graphene nanosheets.

Flexible cefalexin-immobilized graphene oxide film for antibacterial and drug delivery

Xun Xu; Fangwang Ming; Jinqing Hong; Zhoucheng Wang

Advanced Materials Letters, 2017, Volume 8, Issue 3, Pages 309-314
DOI: 10.5185/amlett.2017.7103

The flexible and freestanding graphene oxide (GO) film was fabricated for drug delivery and antibacterial. The film was synthesized by covalently attaching cefalexin onto graphene oxide sheets and then made by filtration of the colloidal suspension. SEM and optical images show that the Cefalexin-grafted graphene oxide (GO-CE) film possesses the unique 2D layer-by-layer structure and it could form channels for drug release when immersed in water. The drug loading and release tests certify that the GO-CE film is a promising drug delivery membrane with high load capacity (0.621 mg mg -1 ) and long-acting release properties (72 h), and can effectively inhibit the growth of E. coli and S. aureus bacteria while showing minimal cytotoxicity for a long time. The cellular culture results of the HeLa Cells indicate that the GO-CE film exhibits excellent biocompatibility. Based on these advantages, the GO-CE film is expected to be used in the environmental and medical applications.

The freeze-thaw technique for exfoliation of graphite: A novel approach for bulk production of scroll-free graphene oxide sheets

Vishal S. Makadia; Lalit M. Manocha; Satish Manocha; Hasmukh L. Gajera

Advanced Materials Letters, 2017, Volume 8, Issue 3, Pages 262-264
DOI: 10.5185/amlett.2017.6407

A freeze-thaw technique is put forth as a novel approach to exfoliating graphene oxide sheets (GO-sheets) in aqueous media.  This method does not use shear force or high-temperature treatment at any stage. Avoiding these factors prevents scrolling and promotes defect-free synthesis of the graphitic planes.  The research shows how the freeze-thaw technique successfully exfoliates graphitic planes without producing scrolls or defective graphene oxide planes. Further, when compared to conventional exfoliation methods, it was found that the freeze-thaw technique increased the surface area significantly. 

Neodymium Doped ZrO2-graphene Oxide Nanocomposites: A Promising Photocatalyst For Photodegradation Of Eosin Y Dye

M. Mzoughi; William. W. Anku; Samuel O. B. Oppong; Sudheesh K. Shukla; Eric S. Agorku; Penny P. Govender

Advanced Materials Letters, 2016, Volume 7, Issue 12, Pages 946-950
DOI: 10.5185/amlett.2016.6497

Purification of industrial wastewater from dyes receiving increasing attentions. The aim of the present manuscript was to fabricate graphene based nanocomposites using a homogeneous and facile approach. Co-precipitation method was used to synthesize zirconium oxide (ZrO2) and neodymium doped ZrO2-graphene oxide (Nd-ZrO2-GO) nanocomposites with varying weight percent concentrations of neodymium to investigate the increasing photocatalytic activity. The Nd-ZrO2-GO catalysts were characterized using X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (SEM), and ultra violet-visible (UV-vis)-spectroscopy to evaluate their optical, morphological and structural properties respectively. The photocatalytic degradation potential of the nanocatalyst was assessed by the degradation of Eosin Y dye in aqueous solution under simulated solar light irradiation. The Nd-ZrO2-GO was observed to have higher photocatalytic degradation potential than the bare ZrO2. The most efficient photocatalyst for the degradation of Eosin Y dye was 0.3 % Nd-ZrO2-GO with about 80 % efficiency within 180 min and a Ka value of 4.19 x 10 -3 . Nd-ZrO2-GO catalyst would be considered as efficient photocatalyst to degrade the industrial dyes (Eosin Y) avoiding the dreary filtration steps.