Synthesis of ZnO mesoporous powders and their application in dye photodegradation

Hanna Maltanava,Sergey Poznyak,Evgeni Ovodok,Maria Ivanovskaya,Frederico Maia,Alexander Kudlash,Nico Scharnagl,João Tedim

doi:10.1016/j.matpr.2018.06.043

Abstract

Mesoporous ZnO materials have been synthesized through chemical deposition of different precursors from aqueous or water-ethanol solutions followed by their thermal decomposition at 400°C in air. The microstructure and morphology of the precursors and obtained ZnO powders were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and nitrogen adsorption-desorption (BET) methods. The structure of the precursor and physico-chemical properties of final zinc oxide powders were shown to be considerably influenced by the presence of Cl– ions and ethanol in solution. In water-ethanol solutions, Zn5(OH)8Cl2∙H2O or Zn5(OH)8(NO3)2∙(H2O)2 precursors are formed, while ZnO particles are directly deposited from aqueous solution. The photocatalytic activity of the synthesized ZnO materials was evaluated by the decolorization of Rhodamine B (RhB) upon UV irradiation. The ZnO powders have demonstrated high photocatalytic efficiency, enabling decomposition of 81.4-97.4 % RhB within 3 hours. The increased photocatalytic efficiency of ZnO prepared by annealing of Zn5(OH)8Cl2∙H2O precursor or deposited directly from aqueous chloride-containing solutions can be originated from the presence of Cl-containing compounds remaining after thermal treatment of simonkolleite as well as from introduction of Cl-dopant in ZnO.

Highlights

Among metal oxide semiconductors, zinc oxide is extensively studied material with large-scale potential applications owing to its high thermo-mechanical stability, good piezoelectric, optoelectronic, catalytic and ferromagnetic properties [1, 2]
The synthesis of mesoporous ZnO powders based on the chemical precipitation of different precursors, such as Zn5(OH)8Cl2∙H2O or Zn5(OH)8(NO3)2∙(H2O)2, and their further thermal decomposition has been described
The specific surface area of the resulting ZnO powders was larger for the samples obtained from simonkolleite precursor

Summary

Introduction

Zinc oxide is extensively studied material with large-scale potential applications owing to its high thermo-mechanical stability, good piezoelectric, optoelectronic, catalytic and ferromagnetic properties [1, 2]. The properties of synthesized ZnO materials correlate with shape, size, defect structure and crystallinity of their particles [5−9]. ZnO with different structure and morphology was synthesized and applied to eliminate harmful dyes by photocatalytic reaction under UV illumination. ZnO is usually prepared with a porous structure, providing a large surface area and a high crystallinity for enhancing the system performance [16−18]. Wolski et al have recently shown the correlation between photocatalytic activity and morphology, structure and surface peculiarities of ZnO photocatalysts [6]. The precipitation approach has been utilized to fabricate various structures of ZnO [2, 9, 21−23] Different factors, such as reaction temperature, time, concentration of reagents, pH, capping molecules, were reported to affect the microstructure of the ZnO particles prepared by precipitation process [2, 24−26]. We estimated photocatalytic activity of the prepared ZnO powders towards photodegradation of Rhodamine B under UV irradiation

Experimental

Result and discussions

Findings

Conclusion