Effect of solution molarity on the optical and photocatalytic properties of sprayed ZnO film

In this paper, we study the effect of solution molarity on the optical and photocatalytic properties of ZnO thin films fabricated by chemical spray pyrolysis. The films were grown on glass substrates for 30 s with a molarity variation of 0.1–0.5 M. From structural, morphological, and compositional analysis, the ZnO films were successfully grown on the substrate for all samples. In the sample with a molarity of 0.1 M, rods with a length of 2–50 μ m and a diameter of ∼1 μ m are formed at the 0.1 M sample. The length of rods decreased to 1–25 μ m, and the diameter decreased to ∼200 nm by increasing solution molarity up to 0.5 M. Furthermore, we found that the solution molarity can narrow the optical bandgap, which is probably caused by the increase of oxygen vacancies concentration. This bandgap narrowing is strongly affected photocatalytic performance, as shown by the optimum photodegradation rate and efficiency. This simple synthesis technique is essential to improve the functionality of ZnO as photocatalytic material. •ZnO films were grown by spray pyrolysis for 30 s with a molarity of 0.1–0.5 M.•The 0.1 M sample, rods with a diameter of ∼1 μ m are formed at the 0.1 M sample.•The diameter decreased to ∼200 nm by increasing the solution molarity to 0.5 M.•Narrowing the optical bandgap is found due to the increase in molarity.•Bandgap narrowing affects the increase of photodegradation rate and efficiency.