Photocatalytic and Sonocatalytic Degradation of EDTA and Rhodamine B over Ti0 and Ti@TiO2 Nanoparticles

Sara El Hakim,Tony Chave,Sergey I Nikitenko

doi:10.3390/catal11080928

Abstract

Herein, we report a comparative study of photocatalytic (Xe-lamp) and sonocatalytic (345 kHz power ultrasound) degradation of Ethylenediaminetetraacetic acid (EDTA) and Rhodamine B (RhB) in the presence of Ti0 and Ti@TiO2 core-shell nanoparticles (NPs). Ti@TiO2 NPs have been obtained by sonohydrothermal treatment (20 kHz, 200 °C) of commercially available Ti0 NPs in pure water. The obtained material is composed of quasi-spherical Ti0 particles (30–150 nm) coated by 5–15 nm crystals of anatase. In contrast to pristine TiO2, the Ti@TiO2 NPs exhibit the extend photo response from UV to NIR light region due to the light absorption by nonplasmonic Ti core. EDTA can be oxidized effectively by photocatalysis in the presence of Ti@TiO2 NPs. By contrast, air passivated Ti0 nanoparticles was found to be inactive in the photocatalytic process for both EDTA and RhB. Photocatalytic degradation of EDTA over Ti@TiO2 NPs exhibits strong photothermal effect, which has been attributed to the higher yield of oxidizing radicals produced by light at higher bulk temperature. The efficiency of RhB photocatalytic degradation depends strongly on RhB concentration. At [RhB] ≥ 1 × 10−3 M, its photocatalytic degradation is not feasible due to a strong self-absorption. At lower concentrations, RhB photocatalytic degradation is observed, but at lower efficiency compared to EDTA. We found that the efficient sonochemical degradation of RhB does not require the presence of any catalysts. For both processes, EDTA and RhB, sonochemical and photocatalytic processes are more effective in the presence of Ar/O2 gas mixture compared to pure Ar. The obtained results suggest that the choice of the optimal technology for organic pollutants degradation can be determined by their optical and complexing properties.

Highlights

Within the progressive increase in the level of wastewater contamination, more efforts are directed towards finding promising methods for the removal of organic substances, such as dyes, chlorinated organics, antibiotics, complexing agents and other pollutants from wastewater [1,2]
This study pointed out that the choice of a suitable treatment process, sonochemistry, sonocatalysis or photocatalysis, for the degradation of organic pollutants in wastewater is highly dependent on the nature of chosen pollutant and the catalyst
For strongly complexing but weakly light absorbing species, like Ethylenediaminetetraacetic acid (EDTA), photocatalysis is more efficient than sonocatalysis, and the use of catalyst influences greatly the kinetics of both processes

Summary

Introduction

Within the progressive increase in the level of wastewater contamination, more efforts are directed towards finding promising methods for the removal of organic substances, such as dyes, chlorinated organics, antibiotics, complexing agents and other pollutants from wastewater [1,2]. Rhodamine B (RhB) poses a major threat to human health, aquatic life and environmental safety. It is widely used in industry and its uncontrolled disposal into the environment can cause serious health problems, including major irritation to skin eyes and respiratory tract. EDTA removal throughout conventional aerobic biodegradation is hardly accessed [5] and hydrothermal thermolysis is energy consumable [6]. For such reasons, advanced oxidation processes (AOPs) have attracted a lot of attention, among which ultrasound-based degradation and photocatalysis seem quite promising [7,8]. The energy released from so-called the cavitation process is sufficient to split water vapor molecules, allowing the in situ production of hydroxyl radicals (OH·) [12]

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