Controlling reduction degree of graphene oxide-based electrode for improving the sensing performance toward heavy metal ions

Effect of Electrolytic Medium on the Electrochemical Reduction of Graphene Oxide on Si(111) as Probed by XPS

“…As has been said above, it is commonly accepted that on GO nanosheets the carboxyl (–COOH) and carbonyl (C=O) groups are mainly located on sp 2 hybridized carbon atoms placed at the edges of GO nanosheets, while the phenolic hydroxyl (–OH) and epoxy (C–O–C) groups are primarily located on sp 3 hybridized carbon atoms placed on the basal plane [ 14 , 62 ]. Moreover, in relation to their chemical reactivity, the OFGs located on the basal planes and on the edges and basal plane defects are characterized as weak and strong OFGs, respectively [ 14 , 62 , 63 ]. For instance, the functional groups on the edges, such as carboxylic acids, are much more stable and less likely to react first.…”

“…These values are not as large as the value of −0.5 characteristic of a diffusionally controlled process, whereas they are closer to the value of zero, characteristic of an ideal surface-confined redox couple, as expected for OFGs decorating the 2D graphene oxide network [ 66 , 67 ]. It should be noted that the reaction path of the electrochemical reduction to obtain erGO is not exactly known and few studies have focused so far on the elucidation of the electrochemical reduction mechanism [ 10 , 41 , 63 ]. Reasonably, the electrochemical reduction of GO is expected to take place in several steps, due to the varied chemical structure of graphene oxide nanosheets [ 15 , 40 , 48 ].…”

“…It can be appreciated that in both aqueous and non-aqueous media, three of the four resulting peaks ( i to iii ) exhibited a very important contribution to the voltammetric wave. Such features probably represent a very specific stage of the electrochemical reduction process, which is not a straightforward matter to assign [ 10 , 18 , 19 , 41 , 63 ]. Based on the relative stability of each of the OFGs, one can expect that a possible reduction sequence would be as follows: epoxy, carbonyl, hydroxyl then carboxyl.…”

Effect of Graphene Additives on the Structure and Optical Parameters of Pure Sodium Borate Glass

“…However, BO3 is still the dominant structure which consequently means existence of a large number of the non-bridging oxygens. While the increase in BO4 concentration may explain the appeared peak at 1730 cm -1 for all graphene-doped samples due to the vibration of C=O, terminal oxygens [29]. Such peak has low intensity as well as a small creative area, which means that a small amount of graphene has been oxidized by the oxygen atoms that are linked to the boron cations.…”

Effect of Graphene additives on the structure and the optical parameters of the pure sodium borate glass

“…It's clear that at constant photon energy, the absorbance increased while the transmittance decreased when the content of graphene was increased. since all samples have been adjusted to have the same thickness, the increase of absorbance value can be assigned to more than one factor, such as the density value increase, the abundance of the nonbridging oxygens, as well as the formation of C=O bonds where the electronic n-π * transitions can take place [29]. To determine the values of the direct and indirect optical transitions energy gaps Tauc's relation (r1) has been used, where the absorption coefficient α has been calculated using relation ( 2) by the values of absorbance A of the sample and its thickness t [30][31][32][33][34].…”