Unveiling significant impact of subtle atomic displacement from equilibrium position in crystal lattice on electronic properties and photocatalytic activity of ZnO

Abstract

This work contributes to the unsettling question of the structural parameters' influence on photocatalysts’ performance. Whereas specific surface area, average crystalline domain size, morphology, intrinsic defects and exposed facets are considered the main factors determining photocatalytic activity, we have demonstrated on a model ZnO that even subtle atomic displacement from equilibrium may impact photocatalytic activity dramatically. Synthesis of ZnO with fixed important parameters was realized by thermal decomposition of zinc oxalate precursor differing just in a cooling profile; one sample was left to cool-down naturally (ZnO) while the second one was rapidly quenched in liquid nitrogen medium (ZnO-LNQ). The quenching affected neither morphology nor textural characteristics including average crystalline domain size. The slight difference in Urbach tail associated defects was not evidenced either by visible-band emission in PL spectra or by ESR. However, analysis of E2high and E2low modes of experimental Raman data to Breit-Wigner-Fano (BWF) function and Phonon Confinement Model (PCM) indicates microstructural disorder for the quenched sample assigned to the dislocation of zinc atoms. Results on photocatalytic degradation of commonly used active pharmaceutical ingredients and methylene blue discoloration indicate that even the subtle displacement of zinc atoms from equilibrium position may cause a significant decrease in photocatalytic performance.