Intensifying heterogeneous TiO2 photocatalysis for bromate reduction using the NETmix photoreactor.

Affiliation

Laboratory of Separation and Reaction Engineering - Laboratory of Catalysis and Materials (LSRE-LCM), Departamento de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal. Electronic address: [Email]

Abstract

This work focuses on the intensification of BrO3- (200 μg L-1) reduction by TiO2-assisted heterogeneous photocatalysis, using the NETmix mili-photoreactor illuminated by UVA light-emitting diodes (UVA-LEDs). The mili-photoreactor was assembled in two configurations: i) catalyst deposition on the channels and chambers of a back stainless steel slab (SSS) and ii) catalyst deposition on the front borosilicate glass slab (BGS), allowing the study of front-side (FSI) and back-side (BSI) illumination mechanisms, respectively. The BrO3- reduction rate in aqueous solution was assessed as a function of: i) pH; ii) dissolved oxygen (DO); iii) addition of formic acid (CH2O2) as a sacrificial agent (SA); iv) photocatalyst film thickness; v) illumination mechanism; vi) irradiation intensity; vii) temperature; and viii) water matrix. Higher BrO3- reduction rates were observed using the FSI mechanism and lower pH values. Nitrogen injection (to eliminate DO) did not significantly improve the reaction rate and the addition of CH2O2 had a negative effect at pH 6.5. Neither temperature nor irradiance increase showed a considerable improvement on the reduction rate. Moreover, TiO2 film remains stable for at least 13 consecutive reactions without significant catalyst leaching. The chemically pre-treated fresh water (FW) matrix negatively affected the reaction rate when compared with the synthetic water (SW), under the best operational conditions (SSS: pH = 5.5, 287 mg of TiO2, 25 °C, SA absence, [DO] = 232-263 μM). This was associated with the presence of both inorganic and organic matter at much higher concentrations than BrO3-. Notwithstanding, heterogeneous TiO2 photocatalysis, using the NETmix mili-photoreactor, was successfully applied to fresh water, achieving [BrO3-] < 10 μg L-1 (guideline value) after 2-hour reaction.

Keywords

Bromate,Heterogeneous TiO(2) photocatalysis,Microscale illumination,NETmix mili-photoreactor,Process intensification,

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