Efficient photocatalytic disinfection of Escherichia coli by N-doped TiO2 coated on coal fly ash cenospheres

Accepted Manuscript Title: Efficient photocatalytic disinfection of Escherichia coli by N-doped TiO2 coated on coal fly ash cenospheres Authors: Yichang Yan, Xiaoqin Zhou, Juanru Lan, Zifu Li, Tianlong Zheng, Wenbin Cao, Nan Zhu, Wenxiu Liu PII: DOI: Reference:

S1010-6030(18)30710-X https://doi.org/10.1016/j.jphotochem.2018.08.045 JPC 11459

To appear in:

Journal of Photochemistry and Photobiology A: Chemistry

Received date: Revised date: Accepted date:

23-5-2018 23-8-2018 29-8-2018

Please cite this article as: Yan Y, Zhou X, Lan J, Li Z, Zheng T, Cao W, Zhu N, Liu W, Efficient photocatalytic disinfection of Escherichia coli by N-doped TiO2 coated on coal fly ash cenospheres, Journal of Photochemistry and amp; Photobiology, A: Chemistry (2018), https://doi.org/10.1016/j.jphotochem.2018.08.045 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Efficient photocatalytic disinfection of Escherichia coli by N-doped TiO2 coated on coal fly ash cenospheres

Yichang Yan1, Xiaoqin Zhou1, Juanru Lan1, Zifu Li1*, Tianlong Zheng1,2, Wenbin Cao3，Nan

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Zhu3, Wenxiu Liu3

1School

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of Energy and Environmental Engineering, Beijing Key Laboratory of Resource-oriented Treatment of Industrial Pollutants, University of Science and Technology Beijing, Beijing 100083, PR China. 2State

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Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuangqing Road, Haidian District, Beijing, China, 100085. 3School

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of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083.

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These two authors contributed equally to this work. author. Tel: +86-010-62334378. Email address: [email protected] (Prof. Zifu Li)

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Graphical abstract

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*Corresponding

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The disinfection efficiency of E. coli under three different light sources, namely, ultraviolet A (UVA), visible light (VL), and light emitting diodes

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with a wavelength of 420 nm (LED-420), were investigated. The TiON-CFACs were effective under UVA, LED-420, and VL irradiation, with disinfection efficiencies of 5.78 log (45 min UVA), 5.84 log (180 min LED-420) and 5.97 log (300 min VL), respectively.

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Coal fly ash cenospheres (CFACs), a kind of industrial solid waste, were applied as the

Ultraviolet A, visible light, and LED with a wave length of 420 nm were used as the light

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support material of N-doped TiO2 (TiON);

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Highlights:

CFACs reduced the reunion effect and improved the operation recycle ability.

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sources to achieve photocatalytic disinfection;

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Abstract: In this study, N-doped TiO2 (TiON) coated coal fly ash cenospheres (CFACs) was synthesized for photocatalytic disinfection against Escherichia coli (E. coli). Based on the

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physi-chemical evaluation of the TiON coated CFACs (TiON-CFACs), the disinfection efficiencies of E. coli under three different light sources, namely, ultraviolet A (UVA), visible light (VL), and the light emitting diodes with a wavelength of 420 nm (LED-420), were investigated. Then, a three-factor, four-level orthogonal experiment was designed to evaluate the influences of dosage, pH, and light intensity on its disinfection efficiency. The TiON-CFACs were effective

under UVA, LED-420, and VL irradiation, with disinfection efficiencies of 5.78 log (45 min UVA), 5.84 log (180 min LED-420) and 5.97 log (300 min VL), respectively. The optimal disinfection efficiency was achieved at an initial pH of 6 under LED-420 irradiation at 40 mW/cm2 with a dosage of 4 g/L TiON-CFACs. The mechanism of disinfection was further investigated using a

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range of free radical scavengers. Findings indicated that H2O2 appeared to play an indispensable role in E. coli disinfection. Moreover, the TiON-CFACs showed a stable disinfection efficiency of

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5 log, even when the substance was recycled for four times, indicating the reliability and stability of the material. The results showed that the TiON-CFACs are promising in water treatment for

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photocatalytic disinfection of E. coli.

1. Introduction

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Keywords: Coal fly ash cenospheres; N-doped TiO2; Photocatalytic disinfection; Mechanism

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Photocatalytic disinfection is becoming a promising process for water and wastewater disinfection

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because it is cost-effective and environmentally safe. Compared with conventional disinfection technologies, photocatalytic disinfection is an outstanding method because it disinfects a broad spectrum of microorganisms, including viruses, bacteria, spores, and protozoa. Moreover, it does

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not form disinfection byproducts nor use extensive chemicals during disinfection[1]. Additionally, the photocatalyst has long-term photocatalytic ability. Several compounds have been investigated as potential photocatalytic materials in water purification, including metal oxides (TiO2, ZnO, ZrO2, V2O5, Fe2O3, SnO2) and metal sulphides (CdS and ZnS)[2-4]. Among them, titanium

dioxide (TiO2) is the most suitable photocatalyst for water purification and one of the most extensively studied materials for photocatalysis due to its high photoactivity, nontoxicity, chemical inertness, low cost, and abundance[5-7]. Therefore, TiO2-based photocatalytic disinfection technology has been extensively studied in the past decades[8-11]. Research on TiO2-based

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photocatalysts in the field of microbial inactivation mainly focuses on (1) disinfection factors, including TiO2 dosage, light intensity, bacterial species and contamination load, and the role of

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reactive oxygen species[12-15]; (2) modification of TiO2 materials for more sufficient use of solar

energy[16-19]; and (3) developing coated TiO2 materials instead of powdery ones[20-22]. Pure

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TiO2 photocatalysts require ultraviolet (UV) irradiation, which only accounts for less than 5% of

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the solar spectrum[23,24], thus, many efforts have been made to broaden the adsorption spectrum

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toward the visible light (VL) region. The effective methods include chemical modifications and

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morphological modifications[16,25]. To narrow the bandgap of TiO2 phases, Asahi [26] used the

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nonmetallic element N to substitute for the lattice oxygen of TiO2 to achieve visible activity and improve its utilization of solar energy. Many studies have validated that N-doping produces

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effective photocatalytic effects to destroy pathogenic microorganisms under VL[27-29]. Light

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emitting diodes (LEDs) are compact, shock-resistant, and energy efficient, with a lifetime greater than 100,000 h[30]. In addition, they are free of toxic or polluting substances[31] and are used as an alternative to mercury vapor lamps. However, studies on water disinfection by LED-irradiated

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photocatalysis have been few.

Powder catalysts have a large specific surface area, however, the practical application of photocatalysis for water treatment is usually hindered by difficulties in post-reaction catalyst

separation. Thus, many efforts have been devoted to the development of highly active supported photocatalysts[32]. Recent studies have reported the application of activated carbon, graphite, glass, mica, attapulgite minerals, and steel webnet to increase catalyst efficiency and immobility[33-37]. However, the costs of substrate materials should be considered when using

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them for practical applications. Coal fly ash cenospheres (CFACs), which are aluminosilicate-rich industrial byproducts generated in coal-firing powder plants, have become the largest industrial

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solid waste in China and have initiated environmental issues owing to their considerable

amount[38]. Recycling CFACs could be one of the effective ways to minimize its environmental

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impact. They mainly consist of spherical porous solid and hollow particles (0.5–300 µm in size)

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with high specific surface areas[39]. Their main chemical compositions are SiO2, Al2O3, MgO,

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K2O, and Fe2O3. Because of their nontoxicity, low cost, extensive chemical/physical stability, and

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low density, CFACs have been used as substrates in catalysis[40-42]. For instance, Wang et al.

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prepared polypyrrole-sensitized hollow TiO2/fly ash beads composites which showed improved

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photocatalytic efficiency under VL[43].

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As previously mentioned, CFACs were employed as supports of N-doped TiO2 (TiON), and the N-doped TiO2 coated on CFACs (TiON-CFACs) was used for photocatalytic disinfection of Escherichia coli (E. coli) in this study. The photo-response behavior of photocatalytic disinfection

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efficiency was examined under three different light sources, including ultraviolet A (UVA), VL, and LEDs with a wavelength of 420 nm (LED-420) and orthogonal and stability experiments were performed to test the technical feasibility of TiON-CFAC for further applications. The results could fill in the gap of the applications of photocatalytic disinfection.

2. Material and methods 2.1 Preparation of TiON-CFACs.

The TiON was synthesized by precipitation-peptization method following with hydrothermal

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crystallization, as reported in the previous study[44]. In detail, certain amount of aqueous TiOSO4 solution (1 mol/L) and ammonium solution (5 mol/L) was simultaneously dripped into deionized

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(DI) water while the pH value of the reaction system was maintained at 7. Then, the white

precipitates were filtered and wash until no SO42- could be detected. Afterwards, the collected

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precipitates were resuspended in DI water and ultrasonicated for 30 min. Then the solution was

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heated to 40℃ and peptized with H2O2 solution (30%) by titrimetric method under constant

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stirring. The obtained orange transparent peroxo titanic acid sol was mixed with melamine

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solution to form an intermediated suspension with nominal nitrogen doping concentration of 3%.

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Finally, the suspension was hydrothermally treated at 110℃ for 6 h in an autoclave and the TiON hydrosol was obtained. The yellowish TiON hydrosol was then uniformly loaded on the surface of

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CFACs purchased from Qikang Water Treatment Material Co. (Henan, China) by sol-gel method.

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Typically，CFACs were sieved and those that passed through a 140-mesh screen and retained on a 170-mesh screen (particle size 30-90 μm) were chosen for the experiments. Sieved particles were placed in DI water and sonicated at 40 kHz for 30 min to clean the CFACs surfaces to improve the

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adhesion between TiON and CFACs. Next, the substrates were washed with absolute ethanol for 30 min. Afterward, 20 g CFACs was added into 50 mL saturated Ca(OH)2 solution (25°C) under stirring for 2 h in a constant oil bath at 80°C. The resultant mixed solution was filtered by 300-mesh nylon screen, washed with DI water thrice, and dried at 50°C. Treated CFACs were then

added into the prepared TiON sol with continuous stirring in a constant water bath at 50°C. Next, the mixture was filtered by a 300-mesh nylon screen, washed with DI water, and dried in an oven at 50°C. To enhance the loading amount, the obtained particles were again placed into the sol followed by the same subsequent processes thrice. After the loading, the powders were calcinated

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at 350°C for 2 h and cooled to room temperature, resulting in the TiON-CFAC photocatalysts.

2.2 Characterization

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The catalysts were characterized by several techniques. The surface morphology was recorded using a scanning electron microscope (SEM). The crystal structure of the synthesized materials

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was characterized by X-ray diffraction (XRD) on a Bruker D8 Advance X-ray diffractometer (Cu

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Kα, λ=1.5418Å) over the range of 20° ≤ 2θ ≤ 80° at a scan rate of 5°·min-1. X-ray photoelectron

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spectroscopy (XPS) with Al Kα X-ray (hα=1486.6 eV) radiation operated at 150 W (Thermo

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ESCALAB 250Xi, USA) was used to investigate the surface properties. UV-vis reflectance

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spectra (UV-vis DRS) of photocatalysts were recorded in the range from 200 nm to 800 nm using a PerkinElmer spectrometer Lambda 750. The specific surface area of the samples was measured

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system.

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by the dynamic Brunauer-Emmett-Teller (BET) method using a Micromeritics ASAP 2020

2.3 Water samples

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E. coli (ATCC 15597) was selected as the target microorganism. To revive frozen cells, 20 µL of E. coli strain was added into 50 mL sterilized Luria–Bertani (LB) broth and the mixture was incubated at 37°C for 12 h at 130 rpm under continuous shaking. The nutrient-rich E. coli suspension was subsequently centrifuged at 4000 rpm for 10 min at 4°C to isolate the cells from the broth. The bacterial pellet was washed with phosphate buffered saline twice to minimize the

non-cell-associated constituents in the solution and then re-suspended in 30 mL sterilized DI water to achieve an E. coli concentration of approximately 109 colony-forming unit per milliliter (CFU/mL). Before performing the irradiation experiments, the E. coli solution was diluted with sterilized DI water to achieve the target initial concentration for experimental purposes.

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2.4 Photocatalytic disinfection experiment set up

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The experiment was performed in scenarios, namely, photocatalytic disinfection with different

irradiation lights, orthogonal experiment, and stability experiments. All experiments were conducted in laboratory-scale photo-reactors at room temperature (25°C), and the solutions were

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constantly stirred at the same speed with a magnetic stirrer throughout the experiment.

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(1) Photocatalytic disinfection with different irradiation lights

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Two photocatalytic reactors (CEL-LAB500, CeAulight Co., Ltd., and PCX50A Discover, Perfect

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Light, Co., Ltd.) were employed in this research (Fig. S1). The CEL-LAB500 reactor is equipped with a 500 W high-pressure mercury lamp (CEL-WLAM500, CeAulight Co., Ltd.) and a 500 W

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xenon ozone-free lamp (CEL-WLAX500, CeAulight Co., Ltd.). The PCX50A Discover reactor is

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equipped with multiple arrays of LEDs with different wavelengths at 535, 450, 420, and 385 nm for VL and UV, respectively[45,46].

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To investigate the activity of the prepared catalysts under different light spectra, experiments were performed with three light sources: 1) UVA by applying cut-off filters to block radiations with wavelengths higher than 370 nm of the high-pressure mercury lamp (light intensity 40.1 mW/cm2), 2) VL by xenon ozone-free lamp with 400 nm cut-off filter (light intensity 40.3 mW/cm2), and 3) LED light at 420 nm (LED-420, 39.8 mW/cm2). 300 mg TiON-CFAC was added into 50 mL E.

coli suspension (6 g/L) and then the solution was transferred to the quartz container of the photocatalytic reactor. The photocatalytic experiments were carried out for 300 min, and samples were collected at certain intervals. The number of E. coli in the system was analyzed subsequently.

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Before the experiments, the system was left in the dark under continuous stirring to establish an adsorption–desorption equilibrium. E. coli suspensions without photocatalysts were irradiated

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under different light sources as light controls. Reaction solutions containing bacteria and photocatalysts wrapped in tin foil were set as dark controls. (2) Orthogonal experiment

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A three-factor and four-level orthogonal experiment was designed to investigate the effects of

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catalyst dosage, pH, and light intensity on disinfection efficiencies. All disinfection experiments

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were conducted under LED-420 illumination for 60 min with an initial E. coli concentration of 106 CFU/mL. As shown in Table 1, parameters were selected by reported articles and previous

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experiments[47]. Normally, the TiO2 dosage is between 2 and 12 g/L and the amount of dosage

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depends on the particle size, specific surface area, and light transmission performance of the catalysts. In previous experiments, the photocatalytic disinfection experiments of 6 g/L CFACs

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loaded with TiON achieved the best results. Therefore, the orthogonal experiment was based on this loading, and catalyst dosages of 2, 4, and 8 g/L were selected. The pH was also chosen as the

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factor that affects the disinfection process. E. coli, as a representative of the large neutrophilic bacterial group, can survive in the pH from 4.3 to 9.5, and the optimal pH for E. coli growth is between 6.0 and 8.0. Hence, 5.0, 6.0, 7.0, and 8.5 were selected as the pH values. The pH was adjusted at the beginning of the experiments by adding NaOH (0.1 M) or HCl (0.1 M). The max light intensity for LED-420 was 46 mW/cm2, and the factor levels of light intensity were set as 30,

35, 40, and 45 mW/cm2.

Table 1 Levels and factors affecting the photocatalytic disinfection effect. Factors A: Dosage (g/L)

C: Light intensity (mW/cm2)

B: pH

2.0

5.0

30

2 3 4

4.0 6.0 8.0

6.0 7.0 8.5

35 40 45

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1

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Level

(3) Disinfection mechanism experiments

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The photocatalytic disinfection mechanism of TiO2 involves the degradation of cell and

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cytoplasmic membranes by photo-generated holes (h+) and reactive oxygen species (e.g. hydroxyl

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radicals (·OH) and hydrogen peroxide (H2O2))[48]. Thus, t-butanol (0.1 M), catalase (100 units/mL) and ammonium oxalate (0.1 M) were utilized to quench the reaction with hydroxyl

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radicals (·OH), hydrogen peroxide (H2O2), and photo-generated holes (h+), respectively. These

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three scavengers were individually added into the solution to investigate the roles they played during the TiON-CFACs photocatalytic inactivation process. The concentrations of the three

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selected scavengers were determined empirically to ensure maximum scavenging effects without biological toxicity to the bacterial cells (Fig. S5). The photocatalytic disinfection process was

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performed as described above. Experiment parameters were selected based on orthogonal experiment result.

(4) Photocatalytic stability experiments Durability of TiON-CFACs for photocatalytic inactivation was investigated under identical

reaction conditions from the orthogonal experiment (4 g/L of photocatalysts under 420 nm LED lamp at 40 mW/cm2 with an initial E. coli concentration of 106 CFU/mL), and four cycles of disinfection were conducted. During each cycle, E. coli concentration was sampled and tested at 0, 15, 30, 60, 90, and 120 min. To recollect sufficient materials from the previous cycle, several sets

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of parallel experiments were set up. After each cycle, the material was filtered, washed with

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sterilized DI water, and dried at 80°C.

2.5 Microbial analysis

The E. coli concentration was detected using the spread plate method. According to the expected

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number of colonies, serial 10-fold dilutions were performed in saline solution (0.9% NaCl), and

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100 µL samples were spread on LB agar. The limit of detection for diluted samples was 10

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CFU/mL. The plates were incubated at 37°C for 24 h before enumeration. Inactivation values were expressed as log10 (C0/C), where C0 and C are the concentrations of E. coli that survived in

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the sample before and after disinfection, respectively. The time-dependent survival data of bacteria

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were fitted into the Chick–Watson model for a batch process: ln (C/C0) = −kt,

(1)

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where C0 and C represent the cell concentrations of E. coli before and after irradiation, respectively, and k is the pseudo-first-order kinetics constant[49]. All solutions and glass

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apparatuses used for culture preparation were autoclaved at 121°C for 20 min to ensure sterility. Each treatment including control groups was conducted in triplicate and results are presented as mean ± SD.

3. Results and discussion

3.1 Characterization

Micrographs of CFACs before and after TiON loading are presented in Fig. 1. As shown in Fig. 1(a, b), the CFACs are spheres with small pores distributed on the surface which may improve their adsorption properties. A typical SEM photo of the TiON-CFACs is shown in Fig. 1(c), which

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exhibits a relatively uniform TiON coating on the surface of CFACs with some ridges in partial

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regions. The nonuniformity could be attributed the drying process during the synthesis[50].

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Fig. 1. SEM images of fly ash cenospheres (a, b) before and (c) after TiON loading.

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A certain area was selected on a typical TiON-CFAC (Fig. 2(a)) to evaluate the elemental composition of the material. EDS (Fig. 2(b)) showed that the elemental composition of

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TiON-CFACs and the detected Ti element indicated that the N-doped TiO2 was loaded on the

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content.

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CFACs. However, the N element was not observed in the EDS spectrum because of its low

Fig. 2. SEM-EDS images of TiON-CFAC photocatalysts. Note: The samples were sprayed with gold for conductivity.

Fig. 3 shows the XRD patterns of CFACs and TiON samples. CFACs are predominantly amorphous glass with a small component of aluminosilicate crystal structure[50], and the major crystal phases of CFACs are mullite, sillimanite and quartz. As shown in Fig. 3(b), characteristic peaks for the TiO2 anatase phase are detected, which confirms anatase is the main crystalline

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phase for TiON.

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Fig. 3. XRD patterns of (a) CFAC and (b) TiON.

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The surface chemical states of the TiON were characterized by XPS and the results are shown in Fig.4. According to the XPS survey spectra (Fig. 4(a)), the main elements on the surface of TiON

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are Ti, O, N and C. The appearance of C element can be attributed to the carbon contamination.

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The high-resolution N 1s spectrum is shown in Fig. 4(b) and the peak located at 399.9 eV is attributed to the anionic N- in the O-Ti-N linkages, which is consistent with the present characteristics of other literatures[51-53]. However, there is no peak apparent at 397 eV which is

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where nitrogen in the substitutional position in the lattice would appear[53]. This result reinforces the argument that interstitial nitrogen doping is responsible for the improved photocatalysis of TiON[54]. Fig. 4(c) shows a Ti 2p XPS spectra of TiON and 3 deconvoluted peaks at 464.2, 460.2 and 458.3 eV are assigned to the Ti 2p1/2, Ti 2p1/2 and Ti 2p3/2 of TiO2, respectively. The existence

of Ti3+ was caused by the reduction of Ti4+ from the deficiency of oxygen due to N doping[55]. The high-resolution O 1s spectrum is shown in Fig. 4(d), and two deconvolution peaks are displayed at 529.6 and 531.1 eV, respectively. The peak at 529.6 eV is attributed to the O bonded to Ti in the form of Ti-O linkages[56], and the peak with a binding energy of 531.1 eV is ascribed

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to the presence of O-H groups[57]. The Ti/O ratio on the surface of the sample is calculated to be

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2.4 suggesting interstitial doping rather than substitutional.

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Fig. 4. (a) XPS survey spectrum of TiON. The corresponding high-resolution XPS spectra of (b) N 1s, (c) Ti 2p and (d) O 1s.

The light absorption property of TiO2 and TiON are studied by UV-vis DRS, and the results are presented in Fig. 5(a), which reveals that N doping in TiO2 nanoparticles shifts the absorption

edge toward the visible light region. The energy band gaps of the two samples could be calculated according to previous equation that had been widely adopted for crystalline semiconductors:

αhv = A (hv-Eg) n/2

(2)

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Where α, v, A, Eg and n are the absorption coefficient, incident light frequency, Planck constant, band gap energy and an integer, respectively. The n value represents the type of optical transition

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of a semiconductor (n = 1 for direct transition and n = 4 for indirect transition). According to literatures, the n values were decided to be 4 for all the samples. Thus, the Eg of TiO2 and TiON were about 2.77 and 3.14 eV (Fig. 5(b)), respectively. The band gap of TiON decreased compared

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with the undoped TiO2 which contributes to the shift of the optical absorption edges. This could be

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nitrogen atoms into the TiO2 lattice[58].

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ascribed to the electronic transition from the N 2p level, which is formed by incorporation of

Fig. 5. (a) UV-vis absorption spectra of TiO2 and TiON; (b) Plot of (αhv)1/2 versus energy (hv) for the Eg of TiO2 and TiON.

The BET specific surface areas of as-prepared samples are listed in Table. S1. For comparison, the

specific areas of Degussa P25 was also measured and results demonstrated that TiON has a much larger specific surface area than P25. After treated with Ca(OH)2 solution, the specific surface area of CFACs increased from 0.31 m2/g to 1.02 m2/g which is beneficial for the photocatalytic reaction. However, the specific surface area of TiON-CFACs decreased dramatically after the

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loading of TiON sol.

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3.2 Photocatalytic disinfection efficiencies of TiON-CFACs under different light sources

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Fig. 6. Photocatalytic inactivation efficiencies of TiON-CFACs (a) and CFACs (b) against E.

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coli under different light sources.

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Before this experiment, light control experiments (Fig. S2) showed a slight decrease (0.60 log) of E. coli concentration under UVA irradiation of 90 min, and no E. coli was inactivated under LED-420 and VL irradiation. Dark control experiments (Fig. S3) demonstrated that the E. coli

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concentration decreased in the first 60 min and remained almost unchanged afterwards. The decrease of E. coli concentration was attributed to the specific surface area and absorption property of the photocatalysts. Meanwhile, the absorption ability of TiON-CFACs was weaker than that of CFACs because of TiON loading. The dark control experiments also indicated the

innocuous effects of TiON-CFACs against E. coli. Thus, 60 min was selected for adsorption before irradiation. Photocatalytic disinfection efficiencies of TiON-CFACs under three different light sources are presented in Fig. 6(a). Samples irradiated by VL exhibited the weakest photocatalytic bacterial inactivation activities and took 300 min to reduce the E. coli concentration

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to the detection limit. Moreover, 180 min was needed to reach a similar disinfection effect under the illumination of LED-420. However, under UVA illumination, the E. coli concentration was

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reduced to the detection limit within 60 min, and the disinfection efficiency was 5.78 log at the sampling time of 40 min. Meanwhile, the disinfection efficiencies of CFACs alone under the same

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conditions were carried out to deduct out their photo activities, which the results were shown in

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Fig. 6(b). It can be revealed that there is no or few disinfection effect of the CFACs alone under

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the illumination of LED-420 and VL. In comparison, the E. coli concentration decreased under

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UVA, which should be attributed to the inactivation effect of UVA in respected of the results of

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light control (Fig. S2). Thus, the disinfection effect was ascribed to the TiON on the surface of CFACs. Wavelength and light intensity are the two main factors that influence the photocatalytic

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chemical process, and the photocatalytic properties under different light sources depend on

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specific adsorption spectra and electronic structures. In this experiment, the light intensities of UVA, VL and LED-420 were almost the same, therefore, light with a short wavelength possesses high energy, which helps increase free radicals. Thus, the disinfection effect under UVA was

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higher than those of VL and LED-420 treatments. Light intensity remained at the same level, but the germicidal efficiency under LED illumination was higher than that by VL. This result could be attributed to the domains of the light spectrum. By N-doping, the TiON indeed shows absorption in the VL region. However, the thresholds of TiON was around 450 nm and wavelength larger

than 450 nm in the VL could hardly be utilized. Hence, the photocatalyst performed better under LED-420. In general, the TiON-CFACs were reactive not only under the irradiation of UVA, but also under those of VL and LED-420. Nevertheless, the disinfection efficiencies with the irradiation of LED-420 and VL were not as satisfactory as the results achieved by applying UVA,

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and the material is suggested to be used under solar irradiation in collaboration with UVA or LED-420 to save energy. Besides, the pseudo-first-order kinetics constant of the disinfection

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efficiency under light sources regressed, and the fitting results are presented in Fig. S4 and Table 2. The kinetics rate constants were calculated as 0.133, 0.032, and 0.022 min-1 for samples under

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and LED-420 illuminations at the same light intensities.

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UVA, LED-420, and VL, respectively. Thus, UVA treatment efficiency was better compared to VL

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Table 2

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Fitting results of the mathematical model to the inactivation curve of E. coli under different

Light sources UVA

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VL

Kinetics equation

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ln (C/C0) = −0.133t + 6.726 (t ≤ 45 min)

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ln (C/C0) = −0.032t + 7.162 (t ≤ 150 min)

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ln (C/C0) = −0.022t + 7.359 (t ≤ 240 min)

0.981

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LED-420

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light sources.

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3.3 Disinfection efficiency of orthogonal experiments

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Fig. 7. Main effect of (a) catalyst dosage, (b) pH, and (c) light intensity on photocatalytic

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inactivation of E. coli.

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Figure 7 shows the main effects of catalyst dosage, pH, and light intensity of photocatalytic inactivation of E. coli. In Fig. 7(a), the photocatalytic disinfection efficiency initially increased

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and then decreased as the catalyst dosage increased, and the optimal dosage was 4 g/L in the experiments. The saturating photoactivity with increasing catalyst dosage can be explained as the

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competition between surface area and light scattering loss. The active center number on catalyst particle surfaces and the penetration ability of the incident light in the reactor was important to the photocatalytic activity[59]. On the one hand, as the catalyst dosage continuously increased, active centers for the absorption of photons increased, and more electrons and holes were generated[60]. On the other hand, the catalyst dosage would impede light penetration into the bacterial

suspension. As light scattering increased, the efficiency of the photocatalytic inactivation of E. coli was reduced[61,62].

Similar results (Fig. 7(b)) were obtained for the influence of pH on the photocatalytic disinfection,

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and the optimal pH was 6. The alkaline condition (pH = 8.5) was not conducive to photocatalytic inactivation. The cell surface charge of E. coli was negative in the aqueous solution, whereas the

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TiON particle had a point of zero charge pH of about 6.4, and the point of zero charge for CFACs

was approximately pH 3. Thus, the electrostatic repulsion between the catalyst and E. coli at high

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pH would increase due to the same negative charge, which would hinder the adsorption of the

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material to the cells. However, Alrousan et al.[63] reported that adjusting the initial pH within the

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range of 5.5-8.5 did not markedly affect the photocatalytic disinfection efficiency. Similar results

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were observed by Rincón et al.[12] and Watts et al.[64] when the initial pH of the solutions were

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between 4–9 and 6–8. The discrepancy between the results in this and other studies may be associated with the application of CFACs, which have a relatively low zero charge and strengthen

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the electrostatic repulsion between the photocatalyst and bacteria. The modification of pH affected

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the surface electron hole migration. At low pH, the surface of TiON was protonated, which highly favored photoelectron migration. At high pH, it benefited the migration of photo-generated holes. Moreover, the acidic condition promoted the migration of TiON photo-generated electrons to the

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surface to favor the formation of H2O2, which helped with the inactivation process. Furthermore, pH affected the catalyst dispersion. When the pH approached the point of zero charge for the material, the dispersion of the catalyst was poor, and agglomeration occurred and negatively influenced the photocatalytic reaction, thereby clarifying that the photocatalytic effect decreased

in significance when the pH dropped from 6 to 5.

As presented in Fig. 7(c), increased rapid inactivation occurred at high light intensity, but no significant increase was observed when the light intensity exceeded 40 mW/cm2. The associated

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change of suspension temperature was negligible; thus, the increase in inactivation rate was likely due to the accelerated kinetics, which is customarily expected in photochemical reactions when

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the irradiance is increased. With higher light intensity, number of photons and thus number of

photo-generated electron-holes increase resulting in an enhancement of the photocatalytic activity.

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Rincón and Pulgarin[65] showed that the E. coli inactivation rate was augmented by an increase in

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light intensity from 400 W/m2 to 1000 W/m2. Moreover, the photocatalytic response rate is linear

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with the square root of light intensity or light intensity under different conditions[66]. According

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to the results of orthogonal tests, the optimum experimental conditions were the TiON-CFACs

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dosage of 4 g/L with the initial pH 6 under the irradiation of LED-420 at 40 mW/cm2. 3.4 Disinfection mechanism of TiON-CFACs

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Compared with no scavenger addition (3.2 log) the disinfection effect significantly declined (2.49

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log) when catalase was applied to capture H2O2 (Fig. 8). However, slight inhibition of the photocatalytic inactivation was observed when the hydroxyl radical scavenger (0.33 log) and the photo-generated holes scavenger (0.42 log) were added into the solution. Results indicated that

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H2O2 was of great importance in the photocatalytic inactivation process. This conclusion was inconsistent with most previous studies. Indeed, various authors have suggested that the hydroxyl radical is the primary species responsible for microorganism inactivation, rather than hydrogen peroxide [60,61,67]. However, the results observed here support results reported by Yan et al.,

who suggested that ·OH mainly originated from H2O2, via either reduction or photolysis (via electron spin resonance) [68]. Based on this finding and the bactericidal mechanism of action[20], it can be conjectured that the photocatalytic inactivation is a reciprocal effort of the ·OH and H2O2 molecules, in which ·OH acts as the primary bactericidal oxygen radical, and H2O2 acts to both

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supply ·OH and contribute to photocatalytic inactivation.

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These results also correlate with previously published work by Gumy et al., who investigated

thirteen different commercial TiO2 powders with various specific surface areas and different

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isoelectric points (IEP). The IEP was found to correlate with the photocatalytic activity of the

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commercial samples for most of TiO2 samples used in that study except TiO2 Degussa P-25.

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Furthermore, the lower the IEP of the TiO2, the lower the bacterial inactivation activity. Therefore,

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the surface charge of a TiO2 sample was found to significantly affect the inactivation kinetics of E.

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coli. When the IEP dropped below pH 5, the E. coli inactivation process was observed to be less efficient[69]. By applying CFACs as a support, the IEP of the catalyst would decline, enhancing

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the electronic repulsion effect between the photo-catalyst and E. coli. As a result of that, the

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adsorption of catalyst onto E. coli may be less favorable. Although the hydroxyl radicals have drastic oxidization capacities, they are short-lived and will probably not diffuse further than 1 µm from the surface of titanium dioxide which limits their disinfection effects for E. coli[70].

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Meanwhile, H2O2 can kill the E. coli at a distance. The photo-generated holes can directly oxidize the E. coli absorbed onto the surface of TiO2. Furthermore, the photo-generated holes can react with water molecules and form hydroxyl radicals and H2O2. However, the mechanism of these reactions is complex and additional studies are required to allow their application in water

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disinfection[71] .

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Fig. 8. Effects of different scavengers on disinfection effects of TiON-CFACs under visible

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light. Note: t-butanol—— hydroxyl radical scavenger; catalase—— H2O2 scavenger;

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ammonium oxalate—— photo-generated holes scavenger

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3.5 Stability of TiON-CFACs

As shown in Fig. 9, no significant reduction in disinfection efficiency was observed after four

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cycles of reapplication and the disinfection efficiency was maintained at around 5 log (E. coli concentration of 33 CFU/mL), thereby indicating that the photocatalysts still possessed excellent

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photocatalytic disinfection ability. Thus, TiON-CFACs showed good stability and exhibited remarkable recycling potential. Moreover, results also suggested that the TiON particles were firmly combined with the surface of CFACs. The gradually decreasing disinfection efficiency could be ascribed to two reasons. The first one is that a few nano-TiON particles loaded on the surface may fall from the CFACs during stirring, washing, and filtering. The second is that during

photocatalysis, the photo-activated electrons and holes may recombine, which would lead to the decreased disinfection efficiency. Hence, more attention should be paid on the parameters for the

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practical applications for water disinfection.

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4. Conclusions

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the irradiation of LED-420.

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Fig. 9. Repeated experiments of photocatalytic inactivation of E. coli by TiON-CFACs under

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In this study, TiON-CFACs were successfully prepared and tested for the disinfection of E. coli. The photocatalysts were effective under various of irradiation lights employed in the experiment, including UVA, LED-420, and VL, and 5.84 and 5.97 log reductions of E. coli were observed at

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180 and 300 min under the irradiation of LED-420 and VL, respectively. With the analysis of orthogonal experiment, the TiON-CFAC dosage of 4 g/L, pH of 6, and light intensity of 40 mW/cm2 were proposed as the optimum operation condition under the irradiation of LED-420. The results of scavenger experiments indicated that the H2O2 molecules are critical and made

major contribution in the bacterial photocatalytic inactivation process. Further, the TiON-CFACs were proven to own high stability according to the recycling test, indicating a potential application of these materials during photocatalytic disinfection.

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5. Acknowledgments

The authors would like to acknowledge the financial support provided by the Fundamental

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Research Funds for the Central Universities (Project No. FRF-IC-15-004) and China Postdoctoral Science Foundation (2017M620627). Gratitude is also given for the experimental support from the

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National Environmental and Energy International cooperation base of China.

References: [1] M.A. Shannon, P.W. Bohn, M. Elimelech, J.G. Georgiadis, B.J. Mariñas, A.M. Mayes, Science and technology for water purification in the coming decades, Nature. 452 (2008) 301.

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[2] C. Karunakaran, S. Senthilvelan, S. Karuthapandian, K. Balaraman, Photooxidation of iodide ion on some semiconductor and non-semiconductor surfaces, Catal. Commun. 5 (2004) 283-290.

SC R

[3] J.M. Herrmann, Heterogeneous photocatalysis: fundamentals and applications to the removal of various types of aqueous pollutants, Catal. Today. 53 (1999) 115-129.

U

[4] Z. Zhu, W. Fan, Z. Liu, Y. Yu, H. Dong, P. Huo, Y. Yan, Fabrication of the metal-free

N

biochar-based graphitic carbon nitride for improved 2-Mercaptobenzothiazole degradation activity,

A

Journal of Photochemistry & Photobiology A Chemistry. 358 (2018).

ED

Water Res. 47 (2013) 3931-3946.

M

[5] X. Qu, P.J.J. Alvarez, Q. Li, Applications of nanotechnology in water and wastewater treatment,

[6] S. Malato, P. Fernández-Ibáñez, M.I. Maldonado, J. Blanco, W. Gernjak, Decontamination and

PT

disinfection of water by solar photocatalysis: Recent overview and trends, Catal. Today. 147

CC E

(2009) 1-59.

[7] A.E. Cassano, O.M. Alfano, Reaction engineering of suspended solid heterogeneous

A

photocatalytic reactors, Catal. Today. 58 (2000) 167-197.

[8] M. Pelaez, N.T. Nolan, S.C. Pillai, M.K. Seery, P. Falaras, A.G. Kontos, P.S.M. Dunlop, J.W.J. Hamilton, J.A. Byrne, K. O'Shea, A review on the visible light active titanium dioxide photocatalysts for environmental applications, Appl. Catal. B-Environ. 125 (2012) 331-349. [9] N. Savage, M.S. Diallo, Nanomaterials and Water Purification: Opportunities and Challenges, J.

Nanopart. Res. 7 (2005) 331-342. [10] C. Wei, W.Y. Lin, Z. Zalnal, N.E. Williams, K. Zhu, A.P. Kruzic, R.L. Smith, K. Rajeshwar, Bactericidal activity of TiO2 photocatalyst in aqueous media, Environ. Sci. Technol. 28 (2015) 934-938.

IP T

[11] C. Mccullagh, J.M.C. Robertson, D.W. Bahnemann, P.K.J. Robertson, The application of TiO 2 photocatalysis for disinfection of water contaminated with pathogenic micro-organisms: a review,

SC R

Res. Chem. Intermediat. 33 (2007) 359-375.

[12] A.G. Rincon, C. Pulgarin, Effect of pH, Inorganic Ions, Organic Matter and H 2O2 on E. coli K12

U

Photocatalytic Inactivation by TiO2: Implications in Solar Water Disinfection, Appl. Catal.

N

B-Environ. 51 (2004) 283-302.

A

[13] A.K. Benabbou, Z. Derriche, C. Felix, P. Lejeune, C. Guillard, Photocatalytic inactivation of

M

Escherischia coli: Effect of concentration of TiO2 and microorganism, nature, and intensity of UV

ED

irradiation, Appl. Catal. B-Environ. 76 (2007) 257-263. [14] H. Takashima, Y. Lida, K. Nakamura, Y. Kanno, Microwave sterilization by TiO 2 filter coated

PT

with Ag thin film, IEEE International Conference on Systems, Man and Cybernetics, 2006,

CC E

pp.1413-1418.

[15] M. Cho, Y. Choi, H. Park, K. Kim, G.J. Woo, J. Park, Titanium dioxide/UV photocatalytic

A

disinfection in fresh carrots, J Food Prot. 70 (2007) 97-101.

[16] J. Lv, T. Sheng, L. Su, G. Xu, D. Wang, Z. Zheng, Y. Wu, N, S co-doped-TiO2/fly ash beads composite material and visible light photocatalytic activity, Appl. Surf. Sci. 284 (2013) 229-234. [17] J.A. Rengifo-Herrera, J. Kiwi, C. Pulgarin, N, S co-doped and N-doped Degussa P-25 powders with visible light response prepared by mechanical mixing of thiourea and urea. Reactivity

towards E. coli inactivation and phenol oxidation, J. Photoch. Photobio. A. 205 (2009) 109-115. [18] M. Wong, W. Chu, D. Sun, H. Huang, J. Chen, P. Tsai, N. Lin, M. Yu, S. Hsu, S. Wang, Visible-light-induced bactericidal activity of a nitrogen-doped titanium photocatalyst against human pathogens, Appl. Environ. Microb. 72 (2006) 6111-6116.

IP T

[19] Y. Nosaka, M. Matsushita, J. Nishino, A.Y. Nosaka, Nitrogen-doped titanium dioxide photocatalysts for visible response prepared by using organic compounds, Sci. Technol. Adv. Mat.

SC R

6 (2005) 143-148.

[20] K. Sunada, T. Watanabe, K. Hashimoto, Studies on photokilling of bacteria on TiO 2 thin film, J.

U

Photoch. Photobio. A. 156 (2003) 227-233.

N

[21] B. Wang, C. Li, J. Pang, X. Qing, J. Zhai, Q. Li, Novel polypyrrole-sensitized hollow TiO2/fly ash

M

Sci. 258 (2012) 9989-9996.

A

cenospheres: Synthesis, characterization, and photocatalytic ability under visible light, Appl. Surf.

ED

[22] D. Gumy, A.G. Rincon, R. Hajdu, C. Pulgarin, Solar photocatalysis for detoxification and disinfection of water: Different types of suspended and fixed TiO 2 catalysts study, Sol. Energy. 80

PT

(2006) 1376-1381.

CC E

[23] C. Zhang, Y. Li, D. Wang, W. Zhang, Q. Wang, Y. Wang, P. Wang, Ag@helical chiral TiO 2 nanofibers for visible light photocatalytic degradation of 17α-ethinylestradiol, Environ. Sci. Pollut.

A

R. 22 (2015) 10444-10451.

[24] Z. Zhu, W. Fan, Z. Liu, H. Dong, Y. Yan, P. Huo, Construction of an attapulgite intercalated mesoporous g-C3N4 with enhanced photocatalytic activity for antibiotic degradation, Journal of Photochemistry & Photobiology A Chemistry. (2018). [25] G. Li, X. Nie, J. Chen, Q. Jiang, T. An, P.K. Wong, H. Zhang, H. Zhao, H. Yamashita, Enhanced

visible-light-driven photocatalytic inactivation of Escherichia coli using g-C3N4/TiO2 hybrid photocatalyst synthesized using a hydrothermal-calcination approach, Water Res. 86 (2015) 17-24. [26] R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, Y. Taga, Visible-light photocatalysis in

IP T

nitrogen-doped titanium oxides, Science. 293 (2001) 269-271. [27] Y. Chen, K. Liu, Preparation of granulated N-doped TiO2/diatomite composite and its applications

SC R

of visible light degradation and disinfection, Powder Technol. 303 (2016) 176-191.

[28] D. Sethi, A. Pal, R. Sakthivel, S. Pandey, T. Dash, T. Das, R. Kumar, Water disinfection through

U

photoactive modified titania, J. Photoch. Photobio. B. 130 (2014) 310-317.

A

Water Sci. Tech.-W. Sup. 14 (2014) 924.

N

[29] V. Arya, L. Philip, Visible and solar light photocatalytic disinfection of bacteria by N-doped TiO2,

M

[30] M.A. Banas, M.H. Crawford, D.S. Ruby, M.P. Ross, J.S. Nelson, A.A. Allerman, R. Boucher,

applications, (2005).

ED

Final LDRD report: ultraviolet water purification systems for rural environments and mobile

PT

[31] S. Vilhunen, H. Särkkä, M. Sillanpää, Ultraviolet light-emitting diodes in water disinfection,

CC E

Environ. Sci. Pollut. R. 16 (2009) 439-442. [32] J. Marugán, D. Hufschmidt, G. Sagawe, V. Selzer, D. Bahnemann, Optical density and photonic

A

efficiency of silica-supported TiO2 photocatalysts, Water Res. 40 (2006) 833-839.

[33] S. Zhou, J. Lv, L.K. Guo, G.Q. Xu, D.M. Wang, Z.X. Zheng, Y.C. Wu, Preparation and photocatalytic properties of N-doped nano-TiO2/muscovite composites, Appl. Surf. Sci. 258 (2012) 6136-6141. [34] L.I. You, LI, Photocatalytic degradation of rhodamine B on titanium dioxide bonded active carbon

composites, Environ. Chem. (2004). [35] K.I. Shimizu, H. Murayama, A. Nagai, A. Shimada, T. Hatamachi, T. Kodama, Y. Kitayama, Degradation of hydrophobic organic pollutants by titania pillared fluorine mica as a substrate specific photocatalyst, Appl. Catal. B-Environ. 55 (2005) 141-148.

IP T

[36] H.M. Yates, M.G. Nolan, D.W. Sheel, M.E. Pemble, The role of nitrogen doping on the development of visible light-induced photocatalytic activity in thin TiO2 films grown on glass by

SC R

chemical vapor deposition, J. Photoch. Photobio. A. 179 (2006) 213-223.

[37] J. Shang, W. Li, Y. Zhu, Structure and photocatalytic characteristics of TiO 2 film photocatalyst

U

coated on stainless steel webnet, J. Mol. Catal. A-Chem. 202 (2003) 187-195.

A

with a focus in China, Fuel. 120 (2014) 74-85.

N

[38] Z.T. Yao, M.S. Xia, P.K. Sarker, T. Chen, A review of the alumina recovery from coal fly ash,

M

[39] M. Ahmaruzzaman, A review on the utilization of fly ash, Prog. Energ. Combust. 36 (2010)

ED

327-363.

[40] D.C.D. Nath, V. Sahajwalla, Growth mechanism of carbon nanotubes produced by pyrolysis of a

PT

composite film of poly (vinyl alcohol) and fly ash, Appl. Phys. A.-Mater. 104 (2011) 539-544.

CC E

[41] O.M. Dunens, K.J. Mackenzie, A.T. Harris, Synthesis of Multiwalled Carbon Nanotubes on Fly Ash Derived Catalysts, Environ. Sci. Technol. 43 (2009) 7889.

A

[42] S.V.V. And, C.G. Vassileva, Methods for characterization of composition of fly ashes from coal-fired power stations: A critical overview, Energ. Fuel. 19 (2005) 1084-1098.

[43] B. Wang, C. Li, J. Pang, X. Qing, J. Zhai, Q. Li, Novel polypyrrole-sensitized hollow TiO2/fly ash cenospheres: Synthesis, characterization, and photocatalytic ability under visible light, Appl. Surf. Sci. 258 (2012) 9989-9996.

[44] W.X. Liu, P. Jiang, W.N. Shao, J. Zhang, W.B. Cao, A novel approach for the synthesis of visible-light-active nanocrystalline N-doped TiO2 photocatalytic hydrosol, Solid State Sci. 33 (2014) 45-48. [45] A.C. Chevremont, A.M. Farnet, B. Coulomb, J.L. Boudenne, Effect of coupled UV-A and UV-C

IP T

LEDs on both microbiological and chemical pollution of urban wastewaters, Sci. Total Environ. 426 (2012) 304-310.

SC R

[46] A.C. Chevremont, J.L. Boudenne, B. Coulomb, A.M. Farnet, Impact of watering with

UV-LED-treated wastewater on microbial and physico-chemical parameters of soil, Water Res. 47

U

(2013) 1971-1982.

N

[47] N.N. Rao, A. Kornberg, Inorganic Polyphosphate Regulates Responses of Escherichia coli to

M

Berlin Heidelberg, 1999.

A

Nutritional Stringencies, Environmental Stresses and Survival in the Stationary Phase, Springer

ED

[48] H.A. Foster, I.B. Ditta, S. Varghese, A. Steele, Photocatalytic disinfection using titanium dioxide: spectrum and mechanism of antimicrobial activity, Appl. Microbiol. Biot. 90 (2011) 1847.

PT

[49] A. Sapkota, A.J. Anceno, S. Baruah, O.V. Shipin, J. Dutta, Zinc oxide nanorod mediated visible

CC E

light photoinactivation of model microbes in water, Nanotechnology. 22 (2011) 215703-215709. [50] C. Li, B. Wang, H. Cui, J. Zhai, Q. Li, Preparation and Characterization of Buoyant

A

Nitrogen-doped TiO2 Composites Supported by Fly Ash Cenospheres for Photocatalytic Applications, J. Mater. Sci. Technol. 29 (2013) 835-840.

[51] Z. Jiang, F. Yang, N. Luo, B.T. Chu, D. Sun, H. Shi, T. Xiao, P.P. Edwards, Solvothermal synthesis of N-doped TiO2 nanotubes for visible-light-responsive photocatalysis., Chem. Commun. 47 (2008) 6372-6374.

[52] X. Xing, Z. Du, J. Zhuang, D. Wang, Removal of ciprofloxacin from water by nitrogen doped TiO2 immobilized on glass spheres: Rapid screening of degradation products, J. Photoch. Photobio. A. 359 (2018). [53] Y. Yokosuka, K. Oki, H. Nishikiori, Y. Tatsumi, N. Tanaka, T. Fujii, Photocatalytic degradation

IP T

of trichloroethylene using N-doped TiO2 prepared by a simple sol–gel process, Res. Chem. Intermediat. 35 (2009) 43-53.

SC R

[54] M.J. Powell, C.W. Dunnill, I.P. Parkin, N-doped TiO2 visible light photocatalyst films via a

sol–gel route using TMEDA as the nitrogen source, Journal of Photochemistry & Photobiology A

U

Chemistry. 281 (2014) 27-34.

N

[55] F.N. Sayed, O.D. Jayakumar, R. Sasikala, R.M. Kadam, S.R. Bharadwaj, L. Kienle, U. Schürmann,

A

S. Kaps, R. Adelung, J.P. Mittal, Photochemical Hydrogen Generation Using Nitrogen-Doped

ED

(2012) 12462-12467.

M

TiO2–Pd Nanoparticles: Facile Synthesis and Effect of Ti3+ Incorporation, J. Phys. Chem. C. 116

[56] C.W.H. Dunnill, Z.A. Aiken, J. Pratten, M. Wilson, D.J. Morgan, I.P. Parkin, Enhanced

PT

photocatalytic activity under visible light in N-doped TiO2 thin films produced by APCVD

CC E

preparations using t-butylamine as a nitrogen source and their potential for antibacterial films, Journal of Photochemistry & Photobiology A Chemistry. 207 (2009) 244-253.

A

[57] L. Mi, P. Xu, H. Shen, P.N. Wang, Recovery of visible-light photocatalytic efficiency of N-doped TiO2 nanoparticulate films, Journal of Photochemistry & Photobiology A Chemistry. 193 (2008) 222-227. [58] S. Hu, A. Wang, X. Li, H. Löwe, Hydrothermal synthesis of well-dispersed ultrafine N-doped TiO2 nanoparticles with enhanced photocatalytic activity under visible light, J. Phys. Chem. Solids.

71 (2010) 156-162. [59] S. Ullah, A.H. Dogar, N. Mehmood, S. Hussain, A. Qayyum, Ion-induced secondary electron emission from MgO and Y2O3 thin films, Vacuum. 84 (2009) 509-513. [60] M. Cho, H. Chung, W. Choi, J. Yoon, Linear correlation between inactivation of E. coli and OH

IP T

radical concentration in TiO2 photocatalytic disinfection, Water Res. 38 (2004) 1069-1077. [61] P.C. Maness, S. Smolinski, D.M. Blake, Z. Huang, E.J. Wolfrum, W.A. Jacoby, Bactericidal

SC R

activity of photocatalytic TiO2 reaction: toward an understanding of its killing mechanism, Appl. Environ. Microb. 65 (1999) 4094-4098.

U

[62] M. Bekbölet, Photocatalytic bactericidal activity of TiO 2 in aqueous suspensions of E. coli, Water

N

Sci. Technol. 35 (1997) 95-100.

A

[63] D.M. Alrousan, P.S. Dunlop, T.A. Mcmurray, J.A. Byrne, Photocatalytic inactivation of E. coli in

M

surface water using immobilised nanoparticle TiO2 films, Water Res. 43 (2009) 47-54.

ED

[64] R.J. Watts, S. Kong, M.P. Orr, G.C. Miller, B.E. Henry, S. Kong, M.P. Orr, B.E. Henry, Photocatalytic inactivation of coliform bacteria and viruses in secondary wastewater effluent,

A.G.

Rincón,

C.

Pulgarin,

Photocatalytical

inactivation

of

E.

coli:

Effect

of

CC E

[65]

PT

Water Res. 29 (1995) 95-100.

(continuous-intermittent) light intensity and of (suspended-fixed) TiO2 concentration, Appl. Catal.

A

B-Environ. 44 (2003) 263-284.

[66] M. Kacem, G. Plantard, N. Wery, V. Goetz, Kinetics and efficiency displayed by supported and suspended TiO2 catalysts applied to the disinfection of Escherichia coli, Chinese J. Catal. 35 (2014) 1571-1577. [67] F.M. Salih, Enhancement of solar inactivation of Escherichia coli by titanium dioxide

photocatalytic oxidation, J. Appl. Microbiol. 92 (2002) 920-926. [68] G. Yan, J. Chen, Z. Hua, Roles of H2O2 and OH radical in bactericidal action of immobilized TiO2 thin-film reactor: An ESR study, J. Photoch. Photobio. A. 207 (2009) 153-159. [69] D. Gumy, C. Morais, P. Bowen, C. Pulgarin, S. Giraldo, R. Hajdu, J. Kiwi, Catalytic activity of

Influence of the isoelectric point, Appl. Catal. B-Environ. 63 (2006) 76-84.

IP T

commercial of TiO2 powders for the abatement of the bacteria (E. coli) under solar simulated light:

SC R

[70] W.A. Pryor, Oxy-Radicals and Related Species: Their Formation, Lifetimes, and Reactions, Annu. Rev. Physiol. 48 (1986) 657.

U

[71] T. Vasilache, I. Lazar, M. Stamate, V. Nedeff, G. Lazar, Possible Environmental Risks of

N

Photocatalysis used for Water and Air Depollution-Case of Phosgene Generation, Apcbee

A

CC E

PT

ED

M

A

Procedia. 5 (2013) 181-185.