Synthesis, characterisation and thermo-physical properties of highly stable graphene oxide-based aqueous nanofluids for potential low-temperature direct absorption solar applications

Abstract

Two types of highly stable 0.1% graphene oxide-based aqueous nanofluids were synthesised and investigated. The first nanofluid (GO) was prepared under the influence of ultrasonic irradiation without surfactant. The second nanofluid was treated with tetra ethyl ammonium hydroxide to reduce the graphene oxide to form reduced graphene oxide (RGO) during ultrasonic irradiation. The GO and RGO powders were characterised by various techniques such as field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman. Also UV–visible absorption spectroscopy was carried out and band gap energies were determined. Optical band gap energies for indirect transitions ranged from 3.4 to 4.4 eV and for direct transitions they ranged between 2.2 and 3.7 eV. Thermal conductivity measurements of the GO-based aqueous nanofluid revealed an enhancement of 9.5% at 40 °C compared to pure water, while the RGO-based aqueous nanofluid at 40 °C had a value 9.23% lower than pure water. Furthermore, the photothermal response of the RGO-based aqueous nanofluid had a temperature increase of 13.5 °C, (enhancement of 60.2%) compared to pure water, the GO-based aqueous nanofluid only displayed a temperature rise of 10.9 °C, (enhancement of 46.6%) after 20 min exposure to a solar irradiance of 1000 W m−2. Both nanofluid types displayed good long-term stability, with the GO-based aqueous nanofluid having a zeta potential of 30.3 mV and the RGO-based aqueous nanofluid having a value of 47.6 mV after 6 months. The good dispersion stability and photothermal performance makes both nanofluid types very promising working fluids for low-temperature direct absorption solar collectors.

Iron oxide/hydroxide–nitrogen doped graphene-like visible-light active photocatalytic layers for antibiotics removal from wastewater

“…The linear fit was applied for the slope below and above the absorption edge of the composite Fe oxide/Fe hydroxide and Fe oxide/Fe hydroxide/N-rGO layers, the intersection of the two fitting lines giving the band gap energy 66 . For the pure GO6 layer a band gap range was determined, in accordance with reported data for rGO 67 . Similarly, the band gap range was estimated for the rGO containing composite samples.…”

Synthesis and Characterization of Some Graphene Oxide Powders Used as Additives in Hydraulic Mortars

“…Moreover, in the GO spectrum, several peaks of higher intensity could be observed at 1718 cm −1 corresponding to the stretching vibrations of carbonyl groups [22], and at 1619 cm −1 assigned to the C=O stretching vibrations from carbonyl or carboxyl groups [23], but also to the physically adsorbed water molecules on or between the graphene sheets [24]. The peak at 1361 cm −1 corresponds to the stretching vibration of C=O group, while the one observed at 1222 cm −1 can be assigned to the stretching vibration of the C-O bond; the last was found in the GO-ATPES spectrum at 1220 cm −1 [25].…”

The Thermophysical and Physicochemical Properties of the Aqueous Dispersion of Graphene Oxide Dual-Beam Thermal Lens Spectrometry

“…An analysis of the existing data has shown that, in many cases, the presence of carbon nanomaterials in large quantities (mg/mL level) increases the thermal conductivity of the dispersion [28,[84][85][86]. As previously shown [27,78,[87][88][89][90], an increase in the GO concentration leads to an increase in k of the dispersion, which is the main reason for the increase in thermal diffusivity.…”