Bare, gold and silver nanoparticle decorated, monodisperse-porous titania microbeads for photocatalytic dye degradation in a newly constructed microfluidic, photocatalytic packed-bed reactor

doi:10.1016/j.jphotochem.2016.08.015

Journal of Photochemistry and Photobiology A: Chemistry

Volume 332, 1 January 2017, Pages 60-65

https://doi.org/10.1016/j.jphotochem.2016.08.015 Get rights and content

Highlights

•
Bare, gold and silver nanoparticle decorated, monodisperse-porous titania microbeads.
•
Their size and porous properties are suitable for packed bed reactors.
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‘Microfluidic, Photocatalytic Packed Bed Reactor’ for continuous photocatalysis.

Abstract

Monodisperse porous titania microbeads were synthesized by a sol-gel templating protocol. Gold nanoparticles (AuNPs) synthesized by Turkevich and Martin methods 16 and 5 nm in size, respectively and silver nanoparticles (AgNPs) 12 nm in size were decorated onto the primary amine attached titania microbeads. Both size and porous properties of bare or AuNP/AgNP decorated monodisperse-porous titania microbeads were suitable for using them as a photocatalyst in a “Microfluidic, Photocatalytic Packed Bed Reactor (MPPBR)” with reasonable pressure drops in the microflow rate range. Then, a MPPBR system for “continuous photocatalytic dye degradation” was first constructed by slurry packing of bare or AuNP/AgNP decorated titania microbeads into a fused silica capillary 320 μm in diameter. The photocatalytic activities of bare and AuNP/AgNP decorated titania microbeads were determined in MPPBR using a textile dye, Remazol Black 5 (RB5). The complete removal of RB5 was achieved in continuous mode and an appreciable enhancement in the photoremoval rate of RB5 was observed with the MPPBR containing Martin AuNP decorated titania microbeads. The system constructed can be evaluated as a promising tool for both pre-column and post-column applications involving the removal of coloured contaminants in the assays conducted in micro-liquid chromatography systems.

Graphical abstract

Introduction

Wastewaters generated by textile industries contain large amounts of toxic aromatic compounds, especially azo dyes. Various combinations of conventional methods like biological, physical and chemical processes have been used to deal with textile wastewaters [1], [2]. Due to the limitations of these processes, investigations have been focused on the treatment of wastewater using heterogeneous photocatalysis (UV/TiO₂) [1], [3]. This process, in which semiconductor metal oxides are used, is based on the formation of hydroxyl radicals and reaction of these hydroxyl radicals with organic contaminants. Due to high activity, low cost and non-toxicity, TiO₂ is one of the most suitable semiconductors that have been used for photocatalysis [4], [5], [6], [7]. Among the other noble metal nanoparticles, gold nanoparticles (AuNPs) have received great attention due to their effectiveness in the enhancement of the photocatalytic activity of TiO₂. Referring to literature, there has been an increasing research on using AuNPs for the modification of TiO₂ and the results showed that the band gap energy of TiO₂ was decreased by AuNPs which resulted in a better photocatalytic activity [8], [9], [10], [11], [12], [13]. By considering this, we planned to apply Au nanoparticle decoration onto the monodisperse-porous titania microbeads synthesized in our recent studies for obtaining a high performance new photocatalyst.

Most of reported studies on using heterogeneous photocatalysis were carried out in batch reactors [14], [15], [16], [17], [18], [19], [20], [21]. However, several studies were reported in which the decolorization of azo dyes was performed in continuous processes. Merzouk et al. [22] used continuous electro-coagulation for decolorization of a synthetic textile wastewater by aluminum electrodes. In another study, Li and Jia [23] designed a packed-bed bioreactor for continuous decolorization of synthetic dyes using rice hull Schizophyllum sp. F17. Rahimi et al. designed a continuous Y-shaped microreactor in which the Fenton degradation of an azo dye was taken place [24]. Sun et al. proposed a microporous tube-in-tube microchannnel reactor for the decolorization of azo dye Acid Red 14 [25].

In most of the photocatalytic processes, titania nanoparticles were used in batch reactors since both their size and porous properties are not suitable to work in continuous reactors by forming packed beds within the tubular systems. In this work, we synthesized bare and AuNP/AgNP decorated forms of monosized-porous titania microbeads with size and porous properties extremely suitable for the construction of packed-beds in a tubular reactor with reasonable column-permeabilities. Then, a “Microfluidic, Photocatalytic Packed Bed Reactor”, MPPBR system was first constructed by slurry-packing of bare and AuNP/AgNP decorated, monodisperse-porous titania microbeads into fused silica capillary tubing. By using the microfluidic system, the complete removal of a textile dye, Remazol Black 5 (RB5) was achieved under UV-irradiation in continuous mode with different flow mobile phase rates and dye feed concentrations.

Section snippets

Materials

All the chemicals used for the preparation of sodium sulfonate attached-poly(3-chloro-2-hydroxypropyl methacrylate-co-ethylene glycol dimethacrylate) (−SO₃Na attached-poly(HPMA-Cl-co-EDMA)) microbeads were purchased from Sigma Chemical Co., St. Louis, MO, USA, as reported in earlier studies [26]. Titanium chloride (TiCl₄) as precursor, ammonium hydroxide solution (NH₄OH, 26%w/w) and hexadecyltrimethylammonium bromide (CTAB) were also purchased from Sigma. For the derivatization of

Results and discussion

The TEM photographs of Turkevich AuNPs, Martin AuNPs and AgNPs are given in Fig. S1 in Supplementary material. As seen in Fig. S1, Turkevich AuNPs, Martin AuNPs and AgNPs were synthesized with narrow size distribution and 16, 5 and 12 nm in size, respectively. Bare titania microbeads, Turkevich AuNP decorated titania, Martin AuNP decorated titania and AgNP decorated titania microbeads were synthesized. The gold and silver contents of decorated microbeads were measured by EDAX and the spectras

Conclusion

The size and porous properties of bare or AuNP/AgNP decorated titania microbeads are very suitable for being used as a photocatalyst in the microfluidic reactors. The microfluidic columns with suitable column-permeability values were obtained by slurry-packing of bare or AuNP/AgNP decorated titania microbeads into the fused silica capillary tubings. Hence, “microfluidic, photocatalytic packed bed reactor, MPPBR” was first constructed as a new tool for continuous photocatalytic dye degradation

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Citation Excerpt :
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Invited feature articleBare, gold and silver nanoparticle decorated, monodisperse-porous titania microbeads for photocatalytic dye degradation in a newly constructed microfluidic, photocatalytic packed-bed reactor

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Results and discussion

Conclusion

J. Hazard. Mater.

C. R. Acad. Sci. II C

Chemosphere

Appl. Catal. B

J. Mol. Catal. A

Catal. Commun.

J. Photochem. Photobiol. A

J. Hazard. Mater.

J. Photochem. Photobiol. A

J. Mol. Catal. A—Chem.

J. Photochem. Photobiol. A

Appl. Catal. B—Environ.

J. Photochem. Photobiol. A

Chem. Eng. J.

Chem. Eng. J.

Invited feature article
Bare, gold and silver nanoparticle decorated, monodisperse-porous titania microbeads for photocatalytic dye degradation in a newly constructed microfluidic, photocatalytic packed-bed reactor