CHARACTERIZATION-PERFORMANCE OF ZnO AND ZnO/ZnFe2O4 CATALYST USING ARTIFICIAL AND SOLAR LIGHT FOR MERCURY (II) REDUCTION

Ana L S Coelho,Ambrósio F De Almeida Neto,Onélia A A Dos Santos,Luiz M De M Jorge,Giane G Lenzi,Flávio F Ivashita

doi:10.1590/0104-6632.20190362s20180280

Abstract

This study describes the application of ZnO commercial oxide and ZnO/ZnFe2O4 mixed oxides to reduce the mercury ion (Hg2+) in the aqueous phase. The catalysts synthesized were characterized by thermogravimetric analysis, adsorption and desorption of N2, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, photoacoustic spectroscopy and Mössbauer spectroscopy. The heterogeneous photocatalysis process was studied in synthetic effluent treatment containing mercury chloride (HgCl2) in a batch and solar reactor. The results indicated that commercial ZnO catalyst totally reduced the Hg (II), in all conditions and reaction systems studied. On the other hand, for the mixed oxides (ZnO/ZnFe2O4), there was a decrease in the reduction efficiency in the batch reactor, indicating no ability to reduce Hg(II) in the presence of sunlight.

Highlights

Nowadays, one of the main environmental problems is the increasing contamination of water bodies by an excess of heavy metals, such as mercury (Hg), which is an environmental hazard, and a serious public health problem (Zhou et al, 2017; Mudasir et al, 2016; Botta et al.2002).Once present in water bodies, Hg is mainly in the form of HgCl2
Characterization of catalysts The Thermogravimetric Analysis (TGA) / Differential Scanning Calorimetry (DSC) profiles obtained for the mixed oxides containing 5 and 15% wt
The mass loss observed from room temperature up to 400 °C is attributed to the H2O adsorbed on the catalyst surface

Summary

Introduction

One of the main environmental problems is the increasing contamination of water bodies by an excess of heavy metals, such as mercury (Hg), which is an environmental hazard, and a serious public health problem (Zhou et al, 2017; Mudasir et al, 2016; Botta et al.2002).Once present in water bodies, Hg is mainly in the form of HgCl2. Particles containing Hg2+ can be methylated by the action of specific bacteria, such as Desulfovibrio desulfuricans ND132 and Geobacter sulfurreducens PCA, resulting in monomethylmercury (MMHg, CH3Hg+) and dimethylmercury (DMHg, CH3HgCH3), which are considered the most toxic forms of Hg (Pieve et al, 2014). In this context, heterogeneous photocatalysis is a promising environmental decontamination method, since it allows the removal of recalcitrant substances, and their complete mineralization, avoiding the deposition of these compounds in the receiving aquatic bodies (Lenzi et al, 2011). ZnO absorbs more of the solar spectrum than other semiconductors, and it is considered an ideal material to be used in the presence of solar energy (Kumar et al, 2015; Mohamed et al, 2014; Lee et al, 2016)

Objectives

Results

Conclusion