Growth of ZnO thin Films from Depleted Batteries for Water Remediation

Abstract

ZnO films were obtained by electrodeposition technique from commercial Zn2+ solutions and those obtained from spent alkaline batteries. The type of counterion and pH impact directly on the structural, morphological, and optical properties of the electrodeposited ZnO films. The morphological and crystallographic orientation differences observed by X-ray diffraction (XRD) analysis and high-resolution field emission scanning electron microscopy (HR-FESEM), demonstrates the influence of the type and origin of precursors used in the ZnO synthesis process. Those samples grown from commercial nitrate solutions exhibit nanocolumns revealing a preferential growth in the (002) direction. On the other hand, random growth (hexagonal plates, agglomerations, clusters, etc.) is observed in samples obtained through recycled solutions. All deposited samples achieved a transparency close to 80 % and an optical band gap of around 3.30 eV. The as-deposited films were evaluated toward the photodegradation capacity of methylene blue (MB) for potential technological applications. Results exhibit that samples prepared from recycled ZnCl2 solutions presented more than 80 % degradation per mass of ZnO. This work demonstrates a virtuous circle since ZnO films are deposited by a facile and scalable technique from discarded batteries and used for MB photodegradation. Furthermore, the simplicity of recovery of these substrates after application makes them an attractive and pragmatic option for a range of water treatment applications. Synopsis: Zinc from depleted alkaline batteries is reused to obtain ZnO thin films that remove contaminating dyes from water.