In this study, graphene oxide (GO), graphene oxide quantum dots (GOQD) and graphene quantum dots (GQD) were synthesized by Hummers, hydrothermal and the calcination in argon methods, respectively. Then the structure of the samples was characterized by X-ray diffraction, Fourier-transform infrared and Raman spectroscopies and their particle size distribution were investigated by dynamic light scattering. Afterward, the electrical and photoelectric properties of the samples were studied by electrical conductivity meter and diffuse reflectance and photoluminescence spectroscopies. Finally, the photoelectrochemical sensors were designed to detect dopamine (DA) based on GO, GOQD and GQD modified glassy carbon electrodes (GCE). The results showed that the sample of GO has graphene plates with widest particle size distribution (about 1.3 to 5.7 µm) and the highest electrical conductivity (287.9 µS/cm). On the other, the sample of GQD has narrowest particle size distribution (about 5.3 to 12.8 nm) and the lowest electrical conductivity (165.1 µS/cm). The samples of GOQD and GQD have light absorption throughout the range of visible wavelength and therefore have photoelectric behavior better than GO. As a result, in DA detection sensors, the photoresponse of the GCEs modified with GOQD and GQD is 4 times higher than that of GO modified GCE. تفاصيل المقالة

In this study, nitrogen and cerium co-doped titanium dioxide nanoparticles were prepared by the sol-gel method and were calcined in air at550 °C for 2 hours. Then, the surface glassy carbon electrode was modified and coated with synthesized nanoparticles. The crystalline structure of the nanoparticles was characterized by X-ray diffraction (XRD). The topography, surface roughness and particle size distribution of the coatings were investigated by atomic force microscopy (AFM). Photoelectric properties such as the changes of the absorption edges and band gap values of the nanoparticles were studied by diffuse reflectance spectra (DRS). The hydrophilic property of the coatings was also measured by a contact angle device. In all of the analyses, the effect of nitrogen doping amount on the characteristics of N, Ce co-doped titania samples was investigated. According to the results, the band gap of the co-doped titania samples relative to that of pure titania has been decreased (from  3.21 eV to  2.78 eV) and their surface hydrophilicity has been improved (from 1.01 (deg.min-1) to 1.60 (deg.min-1)). Among the samples the co-doped titania contains the ratio of Ce/Ti: 1% and N/Ti: 0.25%, has the highest amount of anatase phase ( 93.1%), the lowest agglomeration at the surface, the smallest band gap energy ( 2.78 eV) and the highest photo-induced super-hydrophilicity (hydrophilizing rate: 1.60 (deg.min-1)). تفاصيل المقالة