S,N co-doped graphene quantum dots-induced ascorbic acid fluorescent sensor: Design, characterization and performance.

In this work, new detection route for ascorbic acid was designed. First, highly luminescent sulfur and nitrogen doped graphene quantum dots (S,N-GQDs) were prepared via simple hydrothermal method using citric acid and thiourea as the C, N and S sources respectively. The prepared S,N-GQDs are characterized by XRD, HRTEM, FTIR, EDS and PL. Investigations showed that prepared S,N-GQDs have a good photostability and excitation-dependent emission fluorescence. Prepared S,N-GQDs showed maximum excitation wavelength and emission wavelength at 400 and 462 nm, respectively. In the following, prepared S,N-GQDs were applied as a photoluminescence probe for detection of ascorbic acid (AA). The designed sensor was based on "off-on" detection mode. The developed sensor had a linear response to AA over a concentration range of 10-500 µM with a detection limit of 1.2 µM. The regression equation is Y = 0.0014 X + 1.2036, where Y and X denote the fluorescence peak intensity and AA concentration, respectively.

A simple sonochemical approach for synthesis of selenium nanostructures and investigation of its light harvesting application.

Selenium (Se) nanostructures were synthesized by a sonochemical method using SeCl4 as a new precursor for Se nanostructures. Moreover, hydrazine, potassium borohydride, and thioglycolic acid were used as reducing reagents in aqueous solution. Ultrasonic power, irradiation time, reducing agent, solvent, HCl, NaOH, and the surfactant were changed in order to investigate the effect of preparation parameters on the morphology and particle size of selenium. The obtained Se with different morphologies and sizes was characterized by XRD, SEM, TEM, EDS, and DRS. The selenium nanostructures exhibited enhanced photocatalytic activity in the degradation of methylene blue (MB) under visible light irradiation. Furthermore, to examine the solar cell application of as-synthesized selenium nanostructure, FTO/TiO2/Se/Pt-FTO and FTO/Se/CdS/Pt-FTO structures were created by deposited selenium film on top of the TiO2 layer and FTO glass prepared by Doctor's blade method, respectively.