Photocatalytic Activity and Selectivity of ZnO Materials in the Decomposition of Organic Compounds

Abstract

ZnO and Li‐doped ZnO photocatalysts were prepared by using a solvothermal method, aided by a supercritical drying technique. The structure and morphology of the photocatalysts were investigated by using SEM, X‐ray diffraction (XRD), UV/Vis and Raman spectroscopy. The photocatalytic activity and selectivity were investigated in the aqueous‐phase photodegradation of methylene blue and phenol as model reactions. Herein, it is reported for the first time that Li doping can lead to significant deactivation of the photocatalytic activity (i.e., decreased oxidization capability) of ZnO materials. The distribution of intermediate products (i.e., selectivity) was also significantly modified in the decomposition of phenol catalyzed by Li‐doped ZnO compared to that catalyzed by ZnO. Photoluminescence (PL) and soft X‐ray absorption spectroscopy (XAS) studies suggested that dopant‐induced surface‐defect states acted as electron–hole combination centers and changed the adsorbate/surface binding, thus causing the deactivation of photocatalytic activity and altering the photocatalytic selectivity in Li‐doped ZnO materials.

Exciton Emission and Light‐Induced Charge Separation in Colloidal ZnO Nanocrystals

“…In composite materials systems the hybrid functionality emerges from the distinct properties of the inorganic/organic interface. This study underlines the sensitive dependence of non‐radiative transitions on changes at the nanoparticle interface, which naturally occur during formation of organic‐inorganic hybrids and further materials processing ,. While radiative exciton annihilation or energy transfer (Figure ) is the key process in light emission, charge separation is the essential mechanism in solar cells and photocatalysis .…”

“…This study underlines the sensitive dependence of non‐radiative transitions on changes at the nanoparticle interface, which naturally occur during formation of organic‐inorganic hybrids and further materials processing ,. While radiative exciton annihilation or energy transfer (Figure ) is the key process in light emission, charge separation is the essential mechanism in solar cells and photocatalysis . The experiments performed in this study accounted for the comparability of colloid concentration and UV excitation parameters during the intrinsically different PL and EPR spectroscopic measurements.…”

“…On the one hand, this underlines that the experiments using different emission profiles of excitation light are not comparable with each other, since the overall process starting with exciton formation and ending with the surface chemistry of photogenerated holes and electrons is complex. Most likely, it involves more than one photoinduced reaction step, and different paramagnetic and diamagnetic intermediates and products . On the other hand, the enhanced signal‐to‐noise ratio of the obtained EPR spectra (Figures 5 and 6) has enabled us to isolate the different paramagnetic species present (Table ) and to learn that the relative abundance of the two trapped electron centers e st depends on the composition of the interface, i. e. on the nature of the ions adsorbed (Figure ).…”

Fabrication of Zinc Oxide Composite Microfibers for Near‐Infrared‐Light‐Mediated Photocatalysis

“…[17,18] Kubelka-Munk plots derived from the Kubelka-Munk function [F(R)hn] 2 versus the photon energy (hn)w ereu sed to evaluate the band-gap energy of the ZnO and ZnO/UCNPs microfibers by the extrapolation of the linear portion of the graph. [19] The estimated band-gap energies for the ZnO and ZnO/UCNPs microfibersa re 3.20 and 3.21 eV,w hich are lower than values re- ported previously for bulk ZnO (3.35 eV) ande ven single-crystalline ZnO (3.27 eV).…”

Photocatalytic activity of zinc oxide (ZnO) synthesized through different methods

“…The reduction of COD value correlated to the degradation of the pollutant. Under UV irradiation, photocatalytic reactions with semiconductor materials involve the generations and separation electron-hole pairs [44] and consequently degraded the pollutant.…”