Optical and photocatalytic properties of ZnO and ZnS structures formed as controlled calcination products of L-cysteine assisted aqueous precipitation

ZnO and ZnS structures were obtained by the calcination of the aqueous precipitation products of Zn(NO3)(2), NaOH and L-cysteine (Cys). Initial Cys:Zn molar ratios were changed as 0.1:1, 0.5:1, 1:1 and 1.5:1. All the precursors were transformed into ZnO upon calcination at 700 degrees C. ZnS structures were obtained by calcining the precursors prepared at the Cys:Zn ratios of 1 and 1.5 at 350 degrees C. In addition to changing chemical composition of the precipitation products, calcination temperature and initial Cys:Zn ratio also affected morphology, surface area, photoluminescence and photocatalytic properties of the final products. Free exciton energy values of the ZnO samples were observed to be between 3.29 eV and 3.35 eV. PL spectra of the ZnO samples indicated blue and green emission centers. Zinc interstitials (Zni), revealed by the blue emissions in the PL spectra were also confirmed by Auger Zn L3M4.5M4.5 spectra. The samples calcined at 350 degrees C removed rhodamine B mainly by adsorption. All the samples calcined at 700 degrees C successfully degraded the dye under UV light. Among the samples calcined at 700 degrees C, ZnO sample prepared at Cys:Zn = 0.5, which has the highest surface area and unique photoluminescence spectrum exhibited the fastest photodegradation rate.