Nanopowders of Yttria-Stabilized Zirconia Doped with Rare Earth Elements as Adsorbents of Humic Acids.

Małgorzata Suchanek,Władysław W Kubiak,Ewa Niewiara,K Wilkosz

doi:10.3390/ma12233915

Abstract

The aim of the investigations was to use, for the first time, zirconia nanopowders stabilized with yttria (YSZ) and rare element oxides (YSZ-Nd, YSZ-Gd) for removal of humic acids (HA) from aqueous solutions. Nanopowders were synthesized by means of hydrothermal crystallization and characterized using scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) methods and analysis of zeta potential. The adsorption processes analysis was carried out in a series of experiments depending on: initial concentration of humic acids, contact time, pH and mass of the used adsorbent. It was found, that the YSZ-Nd exhibits strong and much higher effectiveness of HA adsorption than YSZ and YSZ-Gd. The HA adsorption rate reached 96.8% for YSZ-Nd dosage of 100 mg, pH 4, and 15 min reaction time and for HA initial concentration equal to 25 mg/L. According to the Langmuir model simulation, the maximum adsorption capacity of HA on YSZ-Nd at pH 4 was calculated to be 2.95 mg/g. Changes in the FT-IR spectra of YSZ-Nd confirmed humic acids’ adsorption on the tested nanopowders, by the presence of additional bands representing carboxylic, alcohol, carbonyl and amino groups in humic acid structure. These functional groups could represent humic acids binding on the YSZ, YSZ-Nd or YSZ-Gd surfaces.

Highlights

Humic substances constitute a group of natural organic matter present in soil, water reservoirs, sediments and natural water bodies
When humic acids concentrations were below 25 mg/L, the HA adsorption efficiency was contact time 15 min, pH value of 4 and humic acids concentrations of 5, 10, 15, 20, 25, 30, 50 and 70 over 95% on the yttria-stabilized zirconia (YSZ)-Nd adsorption process, while HA initial concentrations were above 25 mg/L, mg/L
The YSZ, YSZ-Nd and YSZ-Gd nanopowders were synthesized by crystallization under hydrothermal conditions and for the first time were applied for humic acids removal from

Summary

Introduction

Humic substances constitute a group of natural organic matter present in soil, water reservoirs, sediments and natural water bodies. They are formed by decomposition of plants and animal remains. The chemical composition of humic acids are different according to geographical origin, age, climate and biological conditions. Therefor characterization of those substances are difficult [3]. Humic acids (HA) have a complex structure, they are hydrophobic, heterogeneous and mostly aromatic They contain mainly acidic functional groups such as carboxylic and phenolic, which induce negative charge in natural waters.

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