Photoreactivity of ZnO nanoparticles in visible light: Effect of surface states on electron transfer reaction

Abstract

Wide band gap metal oxide semiconductors such as zinc oxide ͑ZnO͒ show visible band photolysis that has been employed, among others, to degrade harmful organic contaminants into harmless mineral acids. Metal oxides show enhanced photocatalytic activity with the increase in electronic defects in the crystallites. By introducing defects into the crystal lattice of ZnO nanoparticles, we observe a redshift in the optical absorption shifting from the ultraviolet region to the visible region ͑400-700 nm͒, which is due to the creation of intermediate defect states that inhibit the electron hole recombination process. The defects were introduced by fast nucleation and growth of the nanoparticles by rapid heating using microwave irradiation and subsequent quenching during the precipitation reaction. To elucidate the nature of the photodegradation process, picosecond resolved time correlated single photon count ͑TCSPC͒ spectroscopy was carried out to record the electronic transitions resulting from the de-excitation of the electrons to their stable states. Photodegradation and TCSPC studies showed that defect engineered ZnO nanoparticles obtained through fast crystallization during growth lead to a faster initial degradation rate of methylene blue as compared to the conventionally synthesized nanoparticles.

Effect of solvents on ZnO nanostructures synthesized by solvothermal method assisted by microwave radiation: a photocatalytic study

“…MB is a heteroaromatic, cationic dye, containing an absorption band associated to the monomeric MB at 665 nm with a shoulder attributed to the 0-1 vibronic transitions of monomers at 605 nm [59]. It is an electroactive substance with the ability to accept electrons, and further degradate into leucomethylene blue, which is a colourless substance [60].…”

Role of Resonance Energy Transfer in Light Harvesting of Zinc Oxide-Based Dye-Sensitized Solar Cells

“…It has to be noted that ZnO can absorb high-energy photons (>3.37 eV) and offers photoluminescence (PL) in the visible region (2.25 eV). 24 Careful use of the defect mediated ZnO PL for the excitation of the surface adsorbed SD, in order to enhance the overall efficiency of the ZnO-based DSSC, is the motive of the present study. In this article we have explored the FRET dynamics from a ZnO semiconductor nanoparticle to a surface adsorbed N719 dye used as sensitizer.…”

Photoselective excited state dynamics in ZnO–Au nanocomposites and their implications in photocatalysis and dye-sensitized solar cells

“…Thus we compared the role of a Au layer in promoting photogenerated charges in ZnO-Au and ZnO colloids by carrying out photo-reduction of a test contaminant [MB, purchased from Carlo Erba]; MB is known to be an excellent probe for the study of interfacial electron transfer in colloidal semiconductor systems. 34 In general, the higher the charge migration from the surface of the ZnO semiconductor, the faster will be the degradation of the surface-attached MB. We have used a fiber-optic based system for the measurement of light-induced chemical processes with spectroscopic precision.…”