Role of Gd3+ and Ho3+ doping on the structure, physical properties and applications of ZnO

ZnO, Zn 0.97 Gd 0.03 O and Zn 0.97 Ho 0.03 O were prepared via a citrate auto-combustion method. X-ray diffraction (XRD) demonstrated that the investigated nanoparticles were prepared in a hexagonal structure, with crystallite sizes averaging between 12 and 60 nm. The morphology of the samples is illustrated by the field emission scanning electron microscope (FESEM) images. The paramagnetic behavior of the investigated nanoparticles is demonstrated by VSM. The value of the optical band gap (E g ) of Zn 0.97 Gd 0.03 O was higher than the E g of ZnO due to the Moss–Burstein effect. Heavy metal Cd 2+ ions from water are effectively adsorbed by rare earth-doped ZnO. At pH = 8, Zn 0.97 Ho 0.03 O exhibits a maximum removal efficiency of 91%. The Freundlich isotherm model fits the experimental results well.