Desenvolvimento de sensores para detecção de ácido gálico e galato de propila explorando sistemas fotoeletroquímicos autoalimentados

Abstract

The present work is based on the development of two sensors for the determination of gallic acid (AG) and propyl gallate (GP) antioxidants exploiting self-powered photoelectrochemical systems. The first photoelectrochemical system exploits titanium dioxide sensitized with CdSe/ZnS (FTO/TiO2/CdSe/ZnS) as a photoanode and a photocathode based on copper oxides (FTO/CuO/Cu2O) for the determination of gallic acid (AG) in green tea samples. The second photoelectrochemical system exploits a copper sulfide modified TiO2 as photocathode (FTO/TiO2/CuS) and a photoanode based on the combined use of CdS and CdSe (FTO/CdS/CdSe) for the determination of propyl gallate (GP) in dehydrated broth samples. The photoelectrochemical systems were based on a self-powered photoelectrochemical cell contructed by using two plastic cuvettes and a polyester cloth as separating membrane. The two-compartment cell was used to maintain separated photoelectrodes. In the cathodic compartment was performed the water and oxygen reduction while in the anodic compartment, the AG or GP were oxidized by heversting the photogenerated holes to produce power. The morphological characterization of the FTO/TiO2/CuS and FTO/CdS/CdSe photoelectrodes was carried out by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy while the, FTO/TiO2/CdSe/ZnS photoelectode was characterized by scanning electrochemical microscopy (SECM). Electrochemical impedance spectroscopy measurements (EIS) were performed to evaluate the electrical characteristics of the photoelectrodes (FTO/CuO/Cu2O and FTO/TiO2/CuS) in terms of flatband potential, carrier density and semiconductor nature. Under optimized conditions, self - powered photoelectrochemical systems presented linear respons e range of 1 μmol L- 1 to 200 μmol L- 1 and recovery values between 96% and 103% for GA and a linear response range from 10 μmol L- 1 to 400 μmol L- 1 and a recovery 95.35% for GP. The standard addition method was applied to determine the analytes in both types of samples. The photoelectrochemical systems presented good selectivity against the interfering species commonly found in these samples.