Intensifying heterogeneous TiO2 photocatalysis for bromate reduction using the NETmix photoreactor

Sara G S Santos; Larissa O Paulista; Tânia F C V Silva; Madalena M Dias; José Carlos B Lopes; Rui A R Boaventura; Vítor J P Vilar

doi:10.1016/j.scitotenv.2019.02.045

Intensifying heterogeneous TiO₂ photocatalysis for bromate reduction using the NETmix photoreactor

Sci Total Environ. 2019 May 10:664:805-816. doi: 10.1016/j.scitotenv.2019.02.045. Epub 2019 Feb 5.

Authors

Sara G S Santos¹, Larissa O Paulista¹, Tânia F C V Silva², Madalena M Dias¹, José Carlos B Lopes¹, Rui A R Boaventura¹, Vítor J P Vilar³

Affiliations

¹ 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.
² 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: tania.silva@fe.up.pt.
³ 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: vilar@fe.up.pt.

PMID: 30763860
DOI: 10.1016/j.scitotenv.2019.02.045

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.