Authors: Noniko Civilized Nqakala
Source: University of the Western Cape Electronic Theses and Dissertations Repository (University of the Western Cape) (article, 2018-01-01)
Field: Materials Science — Materials Chemistry

Construction of an enzyme-free electrochemical sensor based on Ag-Fe2O3/POM/RGO novel nanocomposite for hydrogen peroxide detection The motivation to determine H2O2 lies in the fact that this chemical species plays a crucial role in diverse fields of practise such as cosmetic, food, diagnostic, pharmaceutical, clinical and environmental protection industries.Several methods such as chromatography, colorimetry, titrimetry and spectrophotometry have been developed for its detection.However, these methods are known to manifest underlying disadvantages such as high cost, time consuming, instability and complicated immobilization procedures.In this present study an enzyme-less electrochemical sensor based on Ag-Fe2O3/POM/RGO nanocomposite (POM stands for polyoxometalate and RGO stands for reduced graphene oxide) was successfully synthesised via a hydrothermal method and a photochemical reduction method for the detection of hydrogen peroxide (H2O2).Graphene oxide (GO) was chemically reduced by sodium borohydride to RGO.UV-Vis, FTIR, Raman and XRD studies confirmed the reduction process.The disappearance of the vibrational peak at 3126 cm -1 assigned to O-H stretching in the FTIR of RGO and the disappearance of the shoulder located at 291 nm in the Uv-Vis absorption of RGO due to the removal of oxygencontaining functional groups suggested that GO was reduced to RGO.The photochemical reduction of POM at the surface of RGO sheet was followed by hydrothermal synthesis of Ag-Fe2O3 to form the novel Ag-Fe2O3/POM/RGO nanocomposite.The synthesised composites, namely POM/RGO, Ag-Fe2O3 nanoparticles and Ag-Fe2O3/POM/RGO were studied using UV-Vis, FTIR, XRD, SEM, TEM, AFM, EDX and SAXS analysis.The TEM revealed that the Ag-Fe2O3 nanoparticles onto the POM/RGO surface had different shape and size, with the Ag being of a spherical shape with size ranging from (3-5) nm and the Fe2O3 nanoparticles with irregular shapes being (15-16) nm in size.SASX analysis revealed that these nanoparticles on the surface of POM/RGO are very close to each other with the Fe2O3 nanoparticles being more intense than the Ag nanoparticles.XRD analysis showed that the Ag-Fe2O3/POM/RGO nanocomposite had rhombohedral and spherical crystalline structure due to Fe2O3 and Ag nanoparticles respectively, this high crystallinity was further confirmed by the Selected area (electron) diffraction of the novel nanocomposite.The Ag-Fe2O3/POM/RGO nanocomposite was further modified on a glassy carbon electrode (GCE) and was used to investigate its electrochemical properties.The cyclic voltammetry (CV) revealed that the Ag-Fe2O3/POM/RGO nanocomposite has excellent electroreduction behaviour towards H2O2 when compared to the response of GCE due to the presence of POM/RGO which enhanced the rate of transfer of electrons during the electrochemical http://etd.uwc.ac.za/ iii reduction of H2O2.Amperometric method was further used to quantify H2O2 using Ag-Fe2O3/POM/RGO nanocomposite, and the response was linear over the concentration ranging from 0.3 mM to 3.3 mM (R 2 = 0.992).The detection limit and sensitivity were calculated to be 0.0029 mM and 270.96 A.Mm -1 cm -2 , respectively with the response time of about 5 s at a signal to noise ratio (S/N=4).The fabricated sensor was also used for the detection of H2O2 in the presence of potentially active interfering species, and found high selectivity towards H2O2.Further studies of this sensor with real life water samples obtained from the Western Cape Science Services showed that the sensor was able to detect and reduce H2O2 successfully with relative standard deviation (RSD) % values being less than 4.2 %.This sensors good performance is attributed to the synergetic effect of the Ag-Fe2O3 nanoparticles and POM with RGO.RGO is believed to have increase the surface area roughness and therefore acted as an excelled underneath layer.POM served as a matrix for incorporating the nanoparticles.The metal-metal oxide nanoparticles (Ag-Fe2O3) NPs exhibited an irregular size distribution and helped to enhance the electrocatalytic activity and increased the sensitivity of the fabricated sensor. Hydrogen peroxide ; Nanocomposite ; Graphene ; Polyoxometalate ; Colorimetry ; Chemistry ; Electrochemistry ; Electrochemical gas sensor ; Amperometry ; Titration ; Oxide ; Spectrophotometry ; Hydrothermal circulation ; Nanotechnology ; Inorganic chemistry ; Materials science ; Chemical engineering ; Chromatography ; Organic chemistry ; Catalysis ; Electrode Advanced Nanomaterials in Catalysis ; Electrochemical sensors and biosensors ; Advanced biosensing and bioanalysis techniques