Visible-light-sensitive Na-doped p-type flower-like ZnO photocatalysts synthesized via a continuous flow microreactor

A Na-doped p-type flower-like ZnO photocatalyst (Na:ZnO) that is highly visible-light-sensitive in air at room temperature was synthesized by a continuous flow microreactor, where NaOH was used as both the precipitating and doping agent. The results of various characterization techniques (XPS, ICP, ToF-SIMS, XRD, and HRTEM) indicated that the Na ions have been successfully doped into the ZnO lattice. The Na: ZnO demonstrated a much higher photocatalytic degradation rate of methylene blue under simulated sunlight (lambda(max) = 494 nm) than the rates obtained from commercially available TiO2 photocatalysts (P-25) and pure ZnO. This much enhanced rate is likely a result of increased surface defect sites associated with oxygen when Na replaces Zn in the crystal structure. A possible mechanism of the photocatalytic degradation of methylene blue on the Na: ZnO is suggested.