Visible light enabled photocapacitive charging and glucose sensing properties of hydrothermally synthesized WO₃/CdS nanocomposites

Nanocrystalline powders of WO₃/CdS nanocomposites were synthesized by a two-step hydrothermal process carried out in the temperature range of 110–170 °C. Morphologies and crystal structures of the above materials were investigated by field emission scanning electron microscopy and x-rays diffraction, respectively. Band gap energies of the nanocomposites and their components were determined by diffuse reflectance spectroscopy. Light emission properties of the nanocomposites were studied by photoluminescence spectroscopy under ultraviolet light excitation. Raman spectroscopy was carried out in order to identify the lattice vibration modes in WO₃/CdS nanocomposite and its components. Photocapacitive performance of doctor blade-coated WO₃/CdS thin films were investigated by using a three electrode photo electrochemical cell containing WO₃/CdS working electrode, platinum counter electrode, saturated calomel type reference electrode and polysulfide electrolyte. WO₃/CdS photocapacitor voltage was significantly enhanced due to addition of glucose solution to the polysulfide electrolyte. Effect of variation of glucose concentration in the electrolyte was successfully monitored by recording the variation in maximum photovoltage produced for a given time of illumination with visible light from a 100-W light emitting diode source. Glucose sensing activities of WO₃/CdS were monitored in milimolar and micromolar concentration ranges. The limit of detection and the sensitivity achieved for the best WO₃/CdS photoelectrode were 9.0 µM and (4.39  \(\pm \hspace{0.17em}\) $\pm$ 0.19) mV µM⁻¹ cm⁻², respectively. The glucose sensing property was observed to be very stable and reliable as indicated by only 1.76% decrease in the sensitivity even after 10 weeks of time.