The crystal structures, morphological, kinetics and photocatalytic activity studies of Al/Ca co-doped ZnO nanoparticles via the sol–gel process

Abstract

ABSTRACT In this research, the degradation kinetics of methyl orange on Al/Ca co-doped ZnO photocatalysts was investigated. The obtained kinetic parameters were used to analyse the role of Ca co-dopant in the enhancement of the photocatalytic activity of Al-doped ZnO. The kinetic behaviour of samples showed this reaction follows the Langmuir–Hinshelwood kinetics model well. The samples were characterised by XRD, SEM, TEM, and UV–Vis spectroscopy techniques. The XRD analysis indicated that Ca and Al occupied Zn sites and did not change the wurtzite structure of the ZnO nanoparticles. The results of SEM and TEM analysis revealed that increasing Ca co-doping led to rod-like morphology in Al-doped ZnO nanoparticles. The UV–Vis absorption spectra showed that Al/Ca co-doped ZnO nanoparticles exhibited a red-shift of the band-edge compared to the pure ZnO. The Ca co-doping as an intermediate metal inside Al-doped ZnO structure decreased the optical band gap and increased the absorption rate in the visible region. In comparison with Al-doped ZnO nanoparticles, Al/Ca co-doped ZnO nanoparticles showed higher photocatalytic activity. The optimal Al and Ca content to achieve the highest photocatalytic efficiency were 5% Al and 3% Ca doping (Zn0.92 Al0.05 Ca0.03 O).