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

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.