Photochemical stability and reactivity of graphene oxide (original) (raw)
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Effect of Dissolved Oxygen Content on Photocatalytic Performance of Graphene Oxide
arXiv: Materials Science, 2018
Graphene, a two-dimensional (2D) promising emergent photocatalyst consisting of earth-abundant elements. This study evaluated the potential of graphene oxide (GO) towards photocatalytic degradation of a novel organic dye, Methylene Blue (MB). In this work, photocatalytic activity of graphene oxide (GO), graphene oxide (GO) along with hydrogen peroxide (H2O2) were tested by photodegrading Methylene Blue (MB) in aqueous solution. The resulted GO nanoparticles were characterized by X-ray powder diffraction, Scanning Electron Microscopy, Energy Dispersive Spectroscopy and Fourier Transform Infrared Ray Spectroscopy. The XRD data confirms the sharp peak centered at 2Theta=10.44 degree corresponding to (002) reflection of GO. Based on our results, it was found that the resulted GO nanoparticles along with H2O2 achieved ~92% photodecolorization of MB compared to ~63% for H2O2 under natural sunlight irradiation at pH~7 in 60 min. The influences of oxygen and hydrogen peroxide (H2O2) on the ...
Carbon, 2012
The use of UV light to trigger different processes involving graphene oxide sheets suspended in aqueous medium at room temperature has been investigated. These processes include (1) deoxygenation of the sheets in the absence of photocatalysts, reducing agents and stabilizers, (2) selective nucleation and growth of metal nanoparticles on the sheets to yield graphene-based hybrids and (3) decomposition of the dye molecule rhodamine B in the presence of only graphene oxide. Photoinduced heating of the suspended graphene oxide sheets by intense UV irradiation ($1 W cm À2 delivered at the surface of the dispersion) was interpreted to generate at high temperature and reactive environment strictly localized at the sheets and their immediate aqueous medium, which in turn brings about the mentioned processes. In addition to providing a simple route toward reduction of graphene oxide dispersions, the present results suggest that intense UV light can be used to promote reactions at ambient conditions with this material that would otherwise require high temperatures, chemical reactants and/or catalysts.
Hummers’ and Brodie’s graphene oxides as photocatalysts for phenol degradation
Journal of Colloid and Interface Science, 2020
h i g h l i g h t s Hummers' (GO-H) and Brodie's (GO-B) GO materials were tested in photocatalysis. GO-B promoted high phenol degradation under near UV/Vis and visible irradiation. GO-H and GO-B had different surface chemistries, d-distance and photoluminescence. Holes and hydroxyl radicals were the main reactive species in play. GO-B is active under visible illumination and stable in reusing cycles.
Photochlorination-induced transformation of graphene oxide: Mechanism and environmental fate
Water research, 2017
With the increasing production and wide utilization of graphene oxide (GO), the nanomaterials are expected to be released into the environment, and end up in surface waters, and/or wastewater treatment plants. This study explored the changes in the physicochemical properties of GO resulting from photochlorination- simulating the reactions that occur during water and wastewater treatment. Photochlorination resulted in significant changes in the surface oxygen-functionalities of the nanomaterials, and fragmenting of the graphenic carbon sheets was observed. We found that photochlorination can enhance the decomposition of GO through the formation of reduced GO. The changes in surface oxygen-functionalities of GO were attributed to the oxidation by chlorine of the nanomaterials' quinone groups, and further oxidation by and/or radicals. The surface charge of GO, measured by its zeta potential, increased in magnitude with chlorination but decreased in magnitude with photochlorination,...
Graphene oxide as a photocatalytic material
Applied Physics Letters, 2011
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Engineering a Water-Dispersible, Conducting, Photoreduced Graphene Oxide
A critical limitation that has hampered widespread application of the electrically conducting reduced graphene oxide (r-GO) is its poor aqueous dispersibility. Here we outline a strategy to obtain water-dispersible conducting r-GO sheets, free of any stabilizing agents, by exploiting the fact that the kinetics of the photoreduction of the insulating GO is heterogeneous. We show that by controlling UV exposure times and pH, we can obtain r-GO sheets with the conducting sp 2-graphitic domains restored but with the more acidic carboxylic groups, responsible for aqueous dispersibility, intact. The resultant photoreduced r-GO sheets are both conducting and water-dispersible. ■ INTRODUCTION Graphene sheets, one-atom thick, two-dimensional layers of carbon atoms, have gained enormous importance over the past few years due to their unique attributes: high electronic and thermal conductivities and exceptional mechanical strength. 1,2 These properties have led to the development of graphene-based field-effect transistors, 3 ultrasensitive sensors, 4 and electromechanical resonators. 5 Current procedures, such as mechanical exfoliation 6 or chemical vapor deposition, 7 are not ideal for the large-scale manufacture of processable graphene sheets and are unlikely to meet current requirements. 8 The chemical reduction of suspensions of graphene oxide (GO) has emerged as a viable route for large-scale production of graphene sheets. 8,9 Over the years various procedures have been developed for the reduction of GO that include the widely used chemical reduction reaction using either hydrazine or sodium borohydride, plasma or thermally induced reduction, and photochemical methods. 8,10−12 Irrespective of the method of reduction, the resultant reduced GO (r-GO) contains residual oxygen functionalities, holes, and defects, and consequently conductivities are considerably lower than that of graphene obtained by mechanical exfoliation. 12 The conductivity, unlike in graphene where electrons and holes undergo ballistic transport, is by an activated mechanism. 13 Nevertheless, r-GO is a versatile material with conductivities appreciably higher than that of GO and which can tailored over several orders of magnitude by controlling the degree of oxidation. Developing effective techniques to reduce graphene oxide as well as deciphering the underlying reduction mechanism are important both from a fundamental and an applied perspective considering the number of potential applications. The light-induced reduction of GO, by exposure to UV radiation, is especially attractive, for apart from being rapid and facile the avoidance of hazardous chemicals makes it a " green " procedure. 14−20 Recent studies have shed light on the mechanism of the photochemical transformation of GO to r-GO. In GO the sp 2-bonded carbon network of graphite is strongly disrupted, and a significant fraction of this carbon network is bonded to hydroxyl groups (C−OH) or participates in epoxide (C−O−C) groups with minor components such as carboxylic or carbonyl groups populating the edges of the GO sheets. 21,22 In aqueous dispersions the photoreduction of GO on exposure to UV radiation has been shown, by pump−probe femtosecond spectroscopy, to be an indirect process, wherein the transformation to r-GO is initiated after the capture of solvated electrons, produced by the UV photoionization of water. 23,24 It is the chemical potential of the photogenerated solvated electrons that drives the reduction of GO, and not simple heating effects. Earlier studies, too, had indicated that the UV light induced transformation of GO to r-GO in aqueous media is not a thermal event, but the mechanism suggested involved band gap excitation and subsequent photocatalytic reductionthe semiconductor domains of GO catalyzing its own photoreduction. The photoreduction of GO using a semiconductor photocatalyst such as TiO 2 is well documented. 25 It has also been established from laser-induced photolysis of single GO sheets that the photoreduction is both spatially and temporally heterogeneous. 26 Reduction arises from the photoinduced migration and subsequent dissociation of hydroxyl groups located on the basal plane. The last step may also be accompanied by dissociation of carbonyl and
Current Applied Physics, 2011
Novel grapheneeTiO 2 (GReTiO 2 ) composite photocatalysts were synthesized by hydrothermal method. During the hydrothermal process, both the reduction of graphene oxide and loading of TiO 2 nanoparticles on graphene were achieved. The structure, surface morphology, chemical composition and optical properties of composites were studied using XRD, TEM, XPS, DRS and PL spectroscopy. The absorption edge of TiO 2 shifted to visible-light region with increasing amount of graphene in the composite samples. The photocatalytic degradation of methyl orange (MO) was carried out using grapheneeTiO 2 composite catalysts in order to study the photocatalytic efficiency. The results showed that GReTiO 2 composites can efficiently photodegrade MO, showing an enhanced photocatalytic activity over pure TiO 2 under visible-light irradiation. The enhanced photocatalytic activity of the composite catalysts might be attributed to great adsorptivity of dyes, extended light absorption range and efficient charge separation due to giant p-conjugation system and two-dimensional planar structure of graphene.
2011
Novel grapheneeTiO 2 (GReTiO 2 ) composite photocatalysts were synthesized by hydrothermal method. During the hydrothermal process, both the reduction of graphene oxide and loading of TiO 2 nanoparticles on graphene were achieved. The structure, surface morphology, chemical composition and optical properties of composites were studied using XRD, TEM, XPS, DRS and PL spectroscopy. The absorption edge of TiO 2 shifted to visible-light region with increasing amount of graphene in the composite samples. The photocatalytic degradation of methyl orange (MO) was carried out using grapheneeTiO 2 composite catalysts in order to study the photocatalytic efficiency. The results showed that GReTiO 2 composites can efficiently photodegrade MO, showing an enhanced photocatalytic activity over pure TiO 2 under visible-light irradiation. The enhanced photocatalytic activity of the composite catalysts might be attributed to great adsorptivity of dyes, extended light absorption range and efficient charge separation due to giant p-conjugation system and two-dimensional planar structure of graphene.