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Enhanced Photocatalytic Degradation of Organic Pollutants and Inactivation of Listeria Monocytogenes by Visible Light Active Rh-Sb co-doped TiO Nanorods 2

Love Kumar Dhandole, Su-Gyeong Kim, Young-Seok Seo, Mahadeo A. Mahadik, HeeSuk Chung, Su Yong Lee, Sun Hee Choi, Min Cho, Jungho Ryu, and Jum Suk Jang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04764 • Publication Date (Web): 29 Jan 2018 Downloaded from http://pubs.acs.org on January 29, 2018

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ACS Sustainable Chemistry & Engineering

Enhanced Photocatalytic Degradation of Organic Pollutants and Inactivation of Listeria Monocytogenes by Visible Light Active Rh-Sb codoped TiO2 Nanorods Love Kumar Dhandole†a, Su-Gyeong Kim†a, Young-Seok Seoa, Mahadeo A. Mahadika, Hee Suk Chungb, Su Yong Leec, Sun Hee Choic, Min Choa, Jungho Ryu*d and Jum Suk Jang*a a

Division of Biotechnology, Advanced Institute of Environment and Bioscience, College of

Environmental and Bioresource Sciences, Chonbuk National University, Iksan, 54596, Korea. b

Analytical Research Division, Korea Basic Science Institute, Jeonju, Jeollabuk-do, 54907, South Korea. c

Pohang Accelerator Laboratory (PAL), Pohang University of Science and Technology (POSTECH), Pohang 790-784, Republic of Korea

d

†

Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Republic of Korea

Equal contribution

*Corresponding authors. Tel.: +82 63 850 0846; fax: +82 63 850 0834. E-mail address: [email protected] (J.S. Jang), [email protected] (J. Ryu)

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KEYWORDS Co-doping, Molten salt, CuxO loading, visible light, photocatalytic degradation

ABSTRACT

In this work, we prepared visible-light active, rhodium and antimony co-doped rutile TiO2 nanorod (Rh-Sb:TiO2 NR) for the degradation of organic pollutants and inactivation of microbial pathogens. Rh-Sb:TiO2 NR sample showed a shift in the absorption band in the visible light region (650 nm). Initially, photocatalytic activity of the Rh-Sb:TiO2 NR was hindered due to its poor surface properties. To improve the surface quality of the less active Rh-Sb:TiO2 NR photocatalyst, the effect of the acid treatment and CuxO impregnation on the Rh-Sb:TiO2 NR were evaluated (CuxO/A-Rh-Sb:TiO2 NR). The photocatalytic activity of CuxO/A-Rh-Sb:TiO2 NR photocatalyst was remarkably higher than that of the as-prepared sample. The improved photocatalytic activity of less active Rh-Sb:TiO2 NR is due to the synergistic effect of acid treatment and finely dispersed CuxO nanoparticles which improve the charge transfer near the interface of A-Rh-Sb:TiO2 NR photocatalyst toward CuxO nanoparticles. Deconvolution of Cu result indicated that CuxO have mixed phase of 2+ and 1+ oxidation state which facile the charge transfer at the conduction band of photocatalyst. The optimization of CuxO loading was achieved by measuring the photocatalytic degradation efficiencies at controlled Cu concentrations on the A-Rh-Sb:TiO2 NRs. Furthermore, the optimized CuxO sample was used for photocatalytic degradation of bisphenol A (BPA) and inactivation of L. monocytogenes pathogen. This work provides an efficient visible light photocatalyst for a broad range of environmental applications, such as pathogenic bacterial inactivation and decomposition of organic pollutants.


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INTRODUCTION It’s a great concern over the practice of discharging the industrial effluents of liquid waste and sewage into the freshwater streams.1-3 Wastewater that contains different kinds of organic pollutants such as dye wastes, organic synthetic compounds and microbial pathogens could be a risk to the ecosystem and also over the human health.4,5 Dye wastewater and dissolved organic synthetic compounds have presented serious problems worldwide, because of its huge volume of production, chemical stability, and constituent contaminants, which include acids, bases, dissolved solids, and toxic compounds.6,7 Microbial pathogens such as Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium and Listeria monocytogenes are high-risky and fatal bacterium that can cause disease in plants and animals, including humans.8 Recently, photocatalysis has emerged as an alternative technology that has major advantages to limit the concern of organic pollutants and inactivation of microbial pathogens.9 Several studies have reported TiO2 based photocatalytic disinfection and degradation strategies for microbial pathogens and organic pollutants, respectively.3,10 However, TiO2 has photocatalytic limitations due to its wide band gap of 3.2 eV that results in activity only under ultra-violate light.11 Therefore, recent research is focusing on the design of efficient TiO2-based visible-light photocatalysts to improve energy use, environmental impact, and economics of its use. Transition metal ion doping is very easy and feasible, whereby the dopants produce donor or acceptor states within the band gap of TiO2.12 However, doping with transition metal ions leads to introducing new states inside the bandgap of TiO2.13-16 Recently, it has been found that dopant strategies suppress the redox reaction ability of titania under UV light irradiation. Therefore, new mechanism of two-photon band-gap excitation is introduced for developing a visible light active TiO2 based photocatalyst.17 Kuncewicz et al. have


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explained the titania particle-based rhodium redox mechanism in which the rhodium species (Rh3+-Rh4+) act as an external redox couple. In this proposed mechanism, the conduction band electron can be used in the reduction steps after UV band-gap excitation and oxidation is induced through localized species Rh4+ and not by valance band positive holes.17-19 Generally, when di or tri-valent (Cr3+ or Ni2+) ions substituted the Ti4+ sites in the crystal lattice of TiO2, the charge compensation by co-doping of the high-valent ions as Sb5+, Ta5+ and Nb5+ improves their photocatalytic activity under visible light irradiance.19-22 Co-doping can enhance the visible light performance of the TiO2 photocatalyst by reducing its existing band gap but it cannot improve the charge separation efficiency as a result of the high recombination factor and the poor photocatalytic performance.23,24 These concerns have encouraged the search for a visible light photocatalyst material with high charge separation efficiency. There are several studies has shown the approach to reduce the charge recombination rate. Jang et al. fabricated a p-n junction composite by using p-type metal oxides to reduce the electron-hole recombination rate in n-type BiVO4.25 Hou et al. studied the effect of Cu2O nanoparticles over TiO2 nanotube arrays, the improved photoelectrocatalytic activity attributes to reduction in the recombination of electron−hole by sending the electrons to the conduction band of TiO2 nanotubes and enhanced the decomposition of 4-chlorophenol by oxidization.26 The surface charge recombination is a big concern in heterojunction composite materials.27 A high effectively approach of n-types CulnS2 modified TiO2 nanotubes heterojunction enhance the visible-light activity of TiO2 NTs electrode where n–n heterojunction structure could favor the surface-interface charge separation and transfer followed by dramatic suppression of the electron–hole recombination.28


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In the present work, we report for the first time facile synthesis of one-dimensional crystalline rhodium and antimony co-doped rutile TiO2 nanorod (Rh-Sb:TiO2 NR) via molten salt flux method. To improve the surface characteristics Rh-Sb co-doped TiO2 NR photocatalysts were acid treated and copper oxide loaded by wet impregnation. Synergistic effect of acid treatment and copper oxide impregnation over Rh-Sb co-doped TiO2 NR was observed in higher photocatalytic degradation of Orange (II) dye. The optimum amount of copper oxide loading to achieve the maximum degradation was also determined. The systematic structural characterizations of the photocatalyst are carried out using STEM, XRD, UV-DRS and XPS measurements. Furthermore, the CuxO/ A-Rh-Sb:TiO2 NR sample was successfully used for photocatalytic degradation of Orange (II) dye, bisphenol A and to inactivate the L. monocytogenes pathogens under visible light (cut-off filter λ ≥ 420 nm) irradiation. The photocatalytic degradation mechanism of the enhanced photoactivity of 2 wt % copper loaded Rh-Sb co-doped TiO2 NR was also proposed. EXPERIMENTAL SECTION Chemicals and reagents All chemical reagents Na2HPO4 (Kanto chemicals, 99 %), NaCl (JUNSEI, 99.5 %), Cu(NO3)2.3H2O (JUNSEI, 99 %), RhCl3.3H2O (Kojima, 99%), Sb2O3 (Acros, 99 %), Orange (II) sodium salt dye (Aldrich, USA) were used without further purification. HCl (Assay 35 %, JUNSEI Japan) acid was diluted with deionized (DI) water (CBNU, pH 7) at a 25 % volume ratio. Preparation of the Rh-Sb co-doped TiO2 nanorod catalysts In this work, we synthesized rhodium-antimony co-doped rutile TiO2 nanorods using a molten salt flux method.29 In a typical synthesis procedure P25-Degussa, NaCl and Na2HPO4 at a ratio


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of 1:4:1 (by weight percentage) were ground together with a quantified amount of rhodium (1 at %) or/and antimony (2 at %) metal precursors. The grinding followed up to one hour to prepare a homogeneous mixture of metal precursors with salts and TiO2 nanoparticles. Then, the mixture was transferred into an alumina crucible boat. The mixture was calcined at 825 ˚C for 8 h inside a box furnace. At ambient temperature, the calcined sample was collected from a box furnace. Then the mixture was washed with an excessive amount of boiled DI water and filtered to remove all soluble salts. After the filtration process, the filtrate was dried overnight at 80 ˚C inside an oven. For further experiments, the dried sample was collected by mild grinding and was named as-prepared Rh-Sb:TiO2 NR sample. For the acid treatment, 300 mg of as-prepared Rh-Sb:TiO2-NR powder were mixed into 300 mL of 1.0 M HCl solution. This mixture solution was stirred to up to 9 h duration at ambient temperature. After, the resulting mixture was filtered using a vacuum filtration system with an excess amount of deionized water. The washed powder was collected on a filter paper (

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