Revealing antimicrobial and contrasting photocatalytic behavior of metal chalcogenide deposited P25-TiO2 nanoparticles

Accepted Manuscript Title: Antimicrobial and Photocatalytic Behavior of Metal Chalcogenide Deposited P25-TiO2 Nanoparticles Authors: Madiha Nazir, Mansoor Irfan Aziz, Ijaz Ali, Muhammad Abdul Basit PII: DOI: Article Number:

S1569-4410(18)30173-1 https://doi.org/10.1016/j.photonics.2019.100721 100721

Reference:

PNFA 100721

To appear in:

Photonics and Nanostructures – Fundamentals and Applications

Received date: Revised date: Accepted date:

24 May 2018 23 March 2019 5 June 2019

Please cite this article as: Nazir M, Aziz MI, Ali I, Basit MA, Antimicrobial and Photocatalytic Behavior of Metal Chalcogenide Deposited P25-TiO2 Nanoparticles, Photonics and Nanostructures - Fundamentals and Applications (2019), https://doi.org/10.1016/j.photonics.2019.100721 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.

Antimicrobial and Photocatalytic Behavior of Metal Chalcogenide Deposited P25-TiO2 Nanoparticles

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Madiha Nazir1, Mansoor Irfan Aziz1, Ijaz Ali2, and Muhammad Abdul Basit1*

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Department of Materials Science and Engineering, Institute of Space Technology, Islamabad 44000,

Pakistan 2

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Department of Materials Science and Chemical Engineering, Hanyang University, Ansan 15588, Korea

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*Corresponding author: [email protected]; [email protected]

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Graphical Abstract

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Highlights  PbS and CdS quantum-dots deposited on TiO2 using p-SILAR method.

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 PbS and CdS nanocomposites (TPbS and TCdS, respectively) degraded a cid orange-56.  TPbS had a higher dye degradation rate under visible light. 

TCdS had higher antimicrobial effect against Bacillus subtilis.

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Abstract

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In this study, quantum dot (QD)-sensitized P25-TiO2 based nanocomposites were developed using the

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pseudo-successive ionic layer adsorption and reaction (p-SILAR) technique and then applied in the

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photocatalytic degradation of an azo-type dye under visible and ultraviolet (UV) irradiation. The presence of PbS and CdS QDs on the P25-TiO2 nanoparticles facilitated visible light absorbance by P25-TiO2 and

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increased the photocatalytic activity under visible irradiation, whereas the efficacy of P25-TiO2 as a

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photocatalyst was reduced under UV light. We confirmed the successful deposition of PbS and CdS QDs

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on TiO2 under analogous QD sensitization conditions with p-SILAR, and showed that the PbS QDsensitized TiO2 nanocomposite (TPbS) harvested more visible light than the CdS QD-sensitized TiO2

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nanocomposite (TCdS), thereby resulting in greater dye degradation under visible light. In particular, TPbS degraded ~57% of the dye acid orange-56 and TCdS degraded ~16%. The nanocomposites

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exhibited antimicrobial activity against Bacillus subtilis where the most effective antimicrobial agent with the highest activity was TCdS.

Keywords: Antimicrobial activity, Bacillus subtilis, Photocatalysis, Quantum dot, SILAR, TiO2

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1. INTRODUCTION Engineering products such as furniture, textiles, papers, and automotive parts are common in our daily lives. Adding bright colors to these products can make them more attractive. In the textile industry, fabrics are soaked in dyes that change their chemical properties, so they are permanently colored and

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unaffected by repeated washing cycles [1]. However, the frequent usage of dyes is problematic in terms of their safe disposal and about 15% of all dyes used in industry are released into rivers or the sea without being treated. Most of these dyes are azo-dyes [2] from the class of nitrogen-based dyes, which are

commonly used for producing bright red, yellow, and orange colors. Azo-dyes are highly carcinogenic [3] and are considered threats to humans, plants, animals, and aquatic life. Recently, nanoscience has

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facilitated the development of nanomaterials for medical applications, such as antimicrobial agents in

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drug delivery systems or to enhance the performance of medical equipment, but they can also be used for

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degrading dyes via photocatalysis to address the problem of dye waste. Antimicrobial agents can prevent

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the growth of microorganisms [4] and they have various industrial applications, such as in synthetic

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textiles, packaging products, medicine, therapeutics, water treatment, and food processing [5].

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In order to eliminate the toxicity associated with organic dyes, semiconductor photocatalytic materials have been investigated to exploit solar energy and facilitate the degradation of toxic dyes via visible

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and/or ultraviolet (UV) light. The conventionally used photocatalysts, such as TiO2 [6, 7], ZnS [8], ZnO [9], and SnO2 [10], are active under UV light due to their wide band gap. These materials harvest light

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from the UV region, which covers only a narrow portion of the solar radiation spectrum. Thus, various strategies have been proposed for extending the absorption of light to more wavelengths by altering the

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band gap [11]. The photocatalytic materials employed for dye degradation include Zn-TiO2/RH/Fe3O4 [12], TiO2/activated carbon [13], BiVO4 [14], and ZnO-graphene [15]. Moreover, nanocomposites have been developed to improve the optoelectronic properties of photocatalysts, such as Ta3N5/W18O49 [16], zirconium phosphate/AgCl [17], graphene-gold [18], CdS-graphene, and CdS-carbon nanotubes [19]. Balkus et al. studied the photocatalytic activity of PbS quantum dot (QD)/TiO2 nanotube composites 3

against many organic dyes, and they showed that the deposition of PbS on TiO2 nanotubes improved the dye degradation effect [20], and similar materials were also studied for energy applications [21, 22]. These nanocomposites have attracted attention for dye degradation applications as well as for uses in QDsensitized solar cells and hydrogen evolution [23] due to the emergence of simple wet-chemical

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techniques for developing size-tuned and band-aligned nanocomposites. The antimicrobial properties of TiO2 were also improved when Pt was deposited on TiO2 and subjected to UV irradiation, and many other studies have investigated this property [24]. Furthermore, the presence of metal chalcogenides such as PbS can have strong quantization effects due to the small masses of electrons and holes [25]. An

improved antimicrobial agent was developed by exploiting the properties of a PbS nanopowder and PbS-

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CdO nanocomposite, which performed better than the PbS nanopowder [4]. Selma et al. compared the

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chemical bath deposition and successive ionic layer adsorption and reaction (SILAR) processes for

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depositing a CdS layer on a TiO2 film [26]. In addition, Balkus et al. deposited PbS on TiO2 nanorods

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with high temperature annealing [20]. Similarly, the TiO2/CdS composite reported by Kaur et al. was treated in an autoclave at 110°C for 17 h and then heat treated at 450°C [28]. Li et al. utilized a synthesis

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process that consumed more time (18 h + 24 h + 20 min + 120 min + 24 h) and with a greater number of

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steps [27]. In the present study, we employed the pseudo-SILAR (p-SILAR) method, which is a simple method for depositing QDs and post-heat treatment is not required [28-31]. Moreover, our synthetic

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method involved a low number of steps and only 45 min was required for the deposition of CdS or PbS on TiO2. Thus, we employed a novel method for depositing PbS and CdS QDs on P25-TiO2 [28], and we

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determined the photocatalytic behavior and antimicrobial effects of the product obtained under UV and

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visible light.

We synthesized PbS QD-sensitized TiO2 (TPbS) and CdS QD-sensitized TiO2 (TCdS) nanocomposites for the photocatalytic degradation of the azo-dye called acid orange-56, and we also assessed their antimicrobial activities. Scanning electron microscopy (SEM) was conducted to confirm the successful deposition of PbS and CdS QDs on TiO2, and we also determined the enhanced visible light absorbance 4

by TiO2 based on UV-visible (UV-Vis) spectroscopic measurements. Furthermore, we compared the difference in the photocatalytic activity of TiO2 under visible and UV light, and considered the dye degradation mechanisms with TPbS and TCdS. Under similar conditions in terms of visible light exposure and time, TPbS degraded ~31% and ~55% more acid orange-56 compared with TCdS and TiO2,

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respectively. In addition, TPbS and TCdS decreased the dye degradation rate compared with TiO2 under exposure to UV light from ~26.32% to ~5.35% and ~3.46% respectively. TCdS performed better as an antimicrobial agent than TPbS, and also better than the positive controls comprising streptomycin and ampicillin.

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2. EXPERIMENTAL

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2.1. Deposition of QDs

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p-SILAR was utilized to deposit QDs on P25-TiO2, as described previously [28, 29]. Briefly, Pb(NO3)2

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and Cd(NO3)2 were dissolved in methanol to obtain separate cationic solutions of 0.02 M Pb and 0.05 M Cd. Next, Na2S.5H2O was dissolved in a solution of water and methanol (1:1) to prepare an anionic

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solution. In order to deposit the PbS QDs, an appropriate amount of P25-TiO2 was placed in a 50 mL

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centrifuge tube and 20 mL of the Pb2+ precursor was added (Figure 1). The mixture was centrifuged for 4 min at 6000 rpm after stirring for 1 min. The excess liquid was removed by decanting and then washed

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with 20 mL of methanol after centrifugation for 4 min at 6000 rpm. The sample was centrifuged again with 0.02 M S2– and the same procedure was repeated. After washing, the first cycle of p-SILAR was

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completed and three cycles were then conducted to ensure the optimal deposition of PbS on TiO2.The same method was employed for the deposition of CdS at a concentration of 0.05 M. Two more cycles of

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p-SILAR were conducted to passivate PbS and CdS with ZnS. The cationic solution was obtained from 0.02 M Zn(CH3COO)2 and the anionic solution was obtained from Na2S.5H2O in methanol to deposit ZnS. The powder was then prepared by drying in an oven at 60C for 48 h. All of the chemicals used in the experiments were purchased from Sigma-Aldrich. 5

2.2. Characterization High-resolution transmission electron microscopy and SEM (TESCAN MIRA3) were employed to characterize the morphology of the P-25TiO2 and the QD-sensitized TiO2 nanocomposites. The deposition

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and distribution of the QDs on TiO2 were estimated using energy dispersive spectroscopy (EDS, Oxford). The compositions were confirmed by X-ray florescence spectroscopy (XRF). UV-Vis spectrometry

(Shimadzu 2550 UV-Vis spectrophotometer) was used to determine the light harvesting capacities of the QD-sensitized P25-TiO2 nanocomposites. Moreover, atomic force microscopy (FlexAFM, Nanosurf

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Switzerland) was conducted to observe the antimicrobial effects of the nanocomposites on bacteria.

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2.3. Photocatalytic activity

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The photocatalytic activities of TPbS and TCdS were evaluated based on the degradation of the azo-dye

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called acid orange-56 [32]. First, 50 mL of the dye solution was mixed with 0.1g of TPbS or TCdS and the pH was maintained at 7. Each suspension was kept in dark conditions for 10 min, before exposure to

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visible light irradiation to determine the performance of each catalyst. To assess the reaction process, a 4

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mL aliquot was removed from each suspension at intervals of 15 min until 180 min. A UV-Vis

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spectrometer was used to measure the absorbance to calculate the dye degradation rate.

2.4. Antimicrobial activity

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The antimicrobial activities of P25-TiO2, TPbS, and TCdS were determined using the well diffusion method, as described previously (Clinical and Laboratory Standards Institute, 2007). This method was

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used to determine the antimicrobial activities of the test products. First, 28 g of nutrient agar (Oxoid, UK) was suspended in distilled water and mixed well to ensure a homogeneous distribution. The medium was sterilized in an autoclave at 121C for 15 min. Next, 100 μL/100 mL of bacterial inoculum (Bacillus subtilis) was added to the medium, which was then transferred to sterilized Petri dishes. After 6

solidification, wells with a diameter of 6 mm were made in the solidified agar gel and 50–70 µL of each test sample was poured into the well. Streptomycin and ampicillin powder were also tested as positive controls. Sterile conditions were maintained for all procedures. The plates were incubated at 37C for 24 h. Inhibition of bacterial growth was indicated by a clear zone around each well, which was measured

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with a zone reader.

3. RESULTS AND DISCUSSION

p-SILAR is employed for developing nanocomposites, especially solar paints [28]. In the present study, the p-SILAR process was used to deposit appropriate amounts of PbS QDs [21] and CdS QDs on P25-

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TiO2 to obtain TPbS and TCdS nanocomposites for photocatalytic applications [28]. Figure 1 shows the

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scheme followed for producing TPbS and TCdS with the p-SILAR method. The four steps in this scheme

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comprised one cycle of p-SILAR. Three and five cycles were used to deposit PbS and CdS by p-SILAR

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on P25-TiO2, respectively, to achieve the optimal deposition rate, as reported previously [21, 28].

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SEM was conducted to examine the morphology of the TPbS and TCdS nanocomposites. Figure 2 shows

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that there were no significant changes in the morphology of the P25-TiO2 nanopowder after the deposition of PbS/CdS QDs, as found in previous studies [28, 33], which was attributed to the very small

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size of the QDs. The presence of PbS and CdS QDs on the P25-TiO2 in TPbS and TCdS was confirmed by EDS (Figure S1), which determined 12.48wt% Pb and 0.78wt% S in TPbS, and 7.29wt% Cd and

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1.73wt% S in TCdS. The amounts of Pb and S in TPbS were higher than those of Cd and S in TCdS because of the 10 times lower solubility product constant for PbS (10–28) compared with CdS (10–27). The

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higher deposition of PbS QDs on TPbS was also confirmed by XRF (Figure 3), which indicated the higher atomic concentration ratios of Pb (~0.17) and S (~0.07) than Cd (~0.13) and S (0.05) in TCdS [34, 35]. We also observed no agglomeration of the PbS or CdS QDs in TPbS and TCdS according to the elemental area mapping results shown in Figure 4a and Figure 4b, respectively. We performed transmission electron microscopy to further determine the qualitative characteristics of the TPbS and 7

TCdS products (Figure 5), which confirmed the ~0.27 nm (200) crystallographic planes of PbS in TPbS and the ~0.336 nm (220) crystallographic planes of CdS in TCdS. Figure 5a shows a transmission electron microscopy image of the P25-TiO2 nanoparticles. Figures 5b and 5c show higher magnification

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images of the same nanopowder after the deposition of PbS and CdS QDs, respectively. TPbS and TCdS were developed for applications in photocatalysis, which involves the activation of a

semiconductor by the generation of electron–hole pairs in the presence of sunlight or artificial light to

provide sufficient energy for the excitation of electrons in the valence band to the conduction band and

leaving the holes behind [11]. These electrons react with the surrounding oxygen and convert it into O2–

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ions. The O2– ions react with the neighboring water to produce OH– radicals [29]. The OH– radicals attack toxic dyes to degrade them, as shown in Figure 6, and the holes may also react with toxic dyes via

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oxidation. Thus, the efficiency of a photocatalyst depends on the recombination of electron–hole pairs and

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the reactions with electrons on the surfaces of the nanocomposite. In general, reduction occurs due to the

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photogenerated electrons and oxidation is attributable to the photogenerated holes [11]. The two essential

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conditions for the efficient operation of nanocomposites are that the deposited semiconductor must have

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an absorbance threshold in the visible region and the conduction band edge potential of the semiconductor must be higher than that of P25-TiO2 to ensure smooth electron transfer. Wu et al. showed that the direct

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formation of CdS on TiO2 nanoparticles at a low temperature resulted in the more rapid degradation of methylene blue in the visible region, as also found in the present study [36]. Similar materials such as PbS

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QDs/TiO2 nanotube composites [20], CdS/TiO2 nanocomposites [37], TiO2 nanotubes incorporated with CdS [27], one-dimensional CdS/TiO2 nanofiber composites [38], and CdS, PbS, and CuxS nanoparticles

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on nanocrystalline TiO2 films [39] were synthesized in previous studies, where their photocatalytic activities were evaluated in the visible region, but none of these studies compared their effects in the UV and visible regions. Figure 6 shows the photocatalytic behavior of TPbS and TCdS compared with P25TiO2 under UV and visible irradiation. When exposed to visible irradiation, the deposited QDs were responsible for the production of more electrons. The electrons generated by the QDs were injected into 8

the conduction band of P25-TiO2 (Figure 6a) and then scavenged by molecular oxygen to yield O2– in the oxygen equilibrated atmosphere. Figure 6b shows the generation of electrons when the QD-sensitized TiO2 nanocomposite was exposed to UV irradiation. In addition, Figure 7 indicates that when TPbS or TCdS was exposed to UV light, the absorbance was reduced in the range from 300–400 nm. P25-TiO2

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was more effective at photocatalysis under UV irradiation than visible light irradiation due to the wide

band gap of 3.2 eV [40]. However, only 8% of the radiation that passes through the Earth’s atmosphere falls within the UV region whereas 50% is visible radiation (~400–700 nm) [41].

TPbS and TCdS exhibited superior photocatalytic activities under visible light irradiation due to the

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deposition of PbS and CdS QDs, respectively. As shown in Figure 7, UV-Vis spectroscopy detected the highest absorbance of P25-TiO2 in the UV region, which is a narrow range (~200–400 nm) for

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absorbance, and the insets show the colors of the TiO2, TPbS, and TCdS powders, i.e., white, dark gray,

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and yellow, respectively. When photons of higher energy interacted with the CdS or PbS QDs, the surplus

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energy led to thermal relaxation of the excited electrons so they could reach the conduction band edge

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[42]. Hence, the thermal relaxation caused energy loss from the lattice and lattice distortion occurred due

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to the strong phonon mode coupling [22, 43], which ultimately reduced the performance of the QDsensitized P25-TiO2 nanocomposites in the UV region because of their thermal losses (Eqs 1, 2, and 3).

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The decreased absorbance by TPbS and TCdS was possibly due to the non-parachromatic absorption caused by the low band gaps of the QDs and the high band gap of P25-TiO2. The absorbance of light

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reduced the light harvesting capacity of the photocatalysts while also leading to undesirable thermal losses [44].

(1)

𝐶𝑑𝑆 + ℎ𝑣 → 𝐶𝑑𝑆 (𝑒 − + ℎ°) (λ < 550𝑛𝑚) + 𝑇ℎ𝑒𝑟𝑚𝑎𝑙 𝑙𝑜𝑠𝑠

(2)

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𝑃25 − 𝑇𝑖𝑂2 + ℎ𝑣 → 𝑃25 − 𝑇𝑖𝑂2 (𝑒 − + ℎ°) (λ < 496𝑛𝑚) + 𝑇ℎ𝑒𝑟𝑚𝑎𝑙 𝑙𝑜𝑠𝑠

𝑃𝑏𝑆 + ℎ𝑣 → 𝑃𝑏𝑆 (𝑒 − + ℎ°) (λ < 1200𝑛𝑚) + 𝑇ℎ𝑒𝑟𝑚𝑎𝑙 𝑙𝑜𝑠𝑠 9

(3)

Similarly, ZnS has an absorption band in the range from ~250 nm to 280 nm [45] and it might also lead to reduced absorbance. In the UV region, TPbS exhibited higher absorbance than TCdS because of the greater exposure of P25-TiO2. Moreover, PbS is slightly larger than CdS (Figure 5) but the higher concentration of PbS reduced the effect of size. TPbS exhibited the highest absorbance in the visible light

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region (400–700nm), whereas P25-TiO2 had no detectable absorbance. At the start of the visible region, the QD-sensitized TiO2 operated efficiently but the absorbance of TCdS decreased to its minimum value at 550 nm. However, TPbS exhibited absorbance at more than 700 nm. These results can be explained by the band gap values of ~3.20 eV for P25-TiO2, ~2.5 eV for CdS, and ~1 eV for PbS QDs [22, 29]. The

absorbance area was greater for TPbS (above ~700 nm) because the PbS QDs could absorb light in the

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visible region as well as the infrared region (40% infrared irradiation in the solar spectrum) [46, 47].

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Thus, it was expected that TPbS would obtain better photocatalytic performance compared with TCdS

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and P25-TiO2. The dye degradation results were in agreement with the UV visible spectroscopy findings

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(Table 1). Most previous studies of the photocatalytic activity of TiO2/CdS or TiO2/PbS employed methyl orange, rose Bengal, methylene blue, indigo carmine, methylene green, or rhodamine B, whereas we

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investigated the degradation of acid orange-56 dye, which is an important organic dye for the fiber, silk,

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and wool dyeing industries, as well as being used for leather shading and paper coatings [20, 48]. The concentration of acid orange-56 (C32H22N6Na2O8S2) under UV irradiation was decreased to 36.84 ppm,

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47.33 ppm, and 48.27 ppm with P25-TiO2, TPbS, and TCdS (Table 1a and Figure 8a), respectively. Thus, P25-TiO2 performed better than the QD-sensitized P25-TiO2 nanocomposite, and TPbS decreased

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the dye concentration more than TCdS in the UV region. The changes in the dye concentrations were the opposite when the same experiment was performed with visible irradiation, as shown in Table 1a and

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Figure 8b, where the dye concentration decreased to 21.33 ppm, 42.13 ppm, and 48.95 ppm with TPbS, TCdS, and P25-TiO2, respectively. Thus, the dye degradation rates with P25-TiO2, TPbS, and TCdS were 26.3%, 5.3%, and 3.4%, respectively, under UV irradiation, but 2.1%, 57.3%, and 15.7 under visible light irradiation (Table 1b and Figure 8c). The photocatalytic activity of TPbS was greater due to the higher 10

concentration of PbS on P25-TiO2 (Figure 4) and the broader absorption range (Figure 7), which allowed more visible light to be harvested to generate photoelectron-hole pairs and degrade the dye. The calibration curve for the absorbance is shown in Figure S2. We assessed the possibility of using P25-TiO2, TPbS, and TCdS as antimicrobial agents with the well

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diffusion method, where the two positive controls comprised streptomycin (Figure S3a) and ampicillin

(Figure S3b). The antimicrobial activities of P25-TiO2 and the QD-sensitized P25-TiO2 nanocomposites were confirmed by the clear zones of inhibition, as shown in Figures S3a and S3b. The zones of

inhibition were due to the generation of reactive oxygen species, such as hydroxyl ions, hydrogen

peroxide, and the superoxide radical, as well as the penetration of the samples into the bacterial cell

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membrane [49]. The generation of reactive oxygen species may damage the bacterial cell wall (B. subtilis

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in this study), which can lead to membrane lipid oxidation [4]. The antimicrobial activities were assessed

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by measuring the diameter from the edge of the well to the end of the clear zone in millimeters (mm).

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Samples were tested three times and the average was calculated. The antibacterial effect of TCdS (the most active nanocomposite) was also assessed based on SEM and atomic force microscopy images of B.

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subtilis obtained under untreated and treated conditions. The cell surface was smooth on the untreated B.

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subtilis cells (Figure 9b, d) but ruptured in the treated bacteria (Figure 9c, 9e). This change in the appearance of the outer cell surface in bacteria was also described in a previous study [50] and it

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confirmed the antibacterial effect of TCdS. Figure 9c shows that the antimicrobial activity increased significantly after sensitizing TiO2 with QDs. With the positive control comprising streptomycin, TiO2

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produced a zone of inhibition measuring 14 mm, whereas the diameters were 16 mm and 18 mm with TPbS and TCdS, respectively. The same trend was observed when ampicillin was used, which is in

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agreement with a previous report [51]. TCdS had a greater antimicrobial effect than TPbS because it is well known that the Cd atom is lethal, where it damages the functions of proteins by binding to sulfhydryl groups [52, 53]. Thus, the cell density was reduced due to the toxic effect of Cd, and even pathogenic microorganisms can be exterminated because of the extended lag phase with protein denaturation, 11

membrane damage, and thiol binding removing protective functions. The smaller grain size might also have contributed to the antimicrobial activity of the CdS-sensitized TiO2 nanocomposite due to the greater

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surface area to volume ratio giving a higher contact area with the microorganism [54].

4. CONCLUSION

In this study, the novel and cost-effective p-SILAR method was successfully employed to fabricate PbS and CdS QD-sensitized nanocomposites using P25-TiO2, i.e., TPbS and TCdS. The low photocatalytic activity of P25-TiO2 under visible light irradiation was significantly improved by 57% and 15% with

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TPbS and TCdS, respectively, and the photocatalytic behavior of P25-TiO2 was attributed to its high

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absorbance. TPbS and TCdS obtained lower photocatalytic degradation rates with acid orange-56 under

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UV light compared with visible light. Moreover, despite its lower visible light absorbance tendency,

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TCdS exhibited the best antimicrobial activity against B. subtilis, which may have been due to the smaller

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particle size.

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REFERENCES 1.

Hasan, K.F., et al., Coloration Process & Parameters for Knit Fabric Dyeing along with Different forms of Dyeing Faults & Correlated Remedies in Textile Dyeing Industries. Zollinger, H., Color chemistry: syntheses, properties, and applications of organic dyes and pigments. 2003: John Wiley & Sons.

3.

Hunger, K., et al., Azo Dyes in Ullmann’s Encyclopedia of Industrial Chemistry. 2005, WileyVCH Weinheim, Germany.

4.

Suganya, M. and A. Balu, PbS nanopowder–synthesis, characterization and antimicrobial

U

activity. Materials Science-Poland, 2017. 35(2): p. 322–328.

Gajjar, P., et al., Antimicrobial activities of commercial nanoparticles against an environmental

N

5.

SC RI PT

2.

soil microbe, Pseudomonas putida KT2440. Journal of Biological Engineering, 2009. 3(1): p. 9. Lachheb, H., et al., Photocatalytic degradation of various types of dyes (Alizarin S, Crocein

A

6.

M

Orange G, Methyl Red, Congo Red, Methylene Blue) in water by UV-irradiated titania. Applied

Škorić, M.L., et al., Chitosan-based microparticles for immobilization of TiO2 nanoparticles and

TE

7.

D

Catalysis B: Environmental, 2002. 39(1): p. 75–90.

their application for photodegradation of textile dyes. European Polymer Journal, 2016. 82: p.

8.

EP

57–70.

Dong, F., et al., Size-controllable hydrothermal synthesis of ZnS nanospheres and the application

CC

in photocatalytic degradation of organic dyes. Materials Letters, 2013. 97: p. 59–63. 9.

Jiang, J., et al., Porous Ce-doped ZnO hollow sphere with enhanced photodegradation activity for

A

artificial waste water. Journal of Alloys and Compounds, 2017. 699: p. 907–913.

10.

Bharati, B., et al., Enhanced photocatalytic degradation of dyes under sunlight using biocompatible TiO2 nanoparticles. Materials Research Express, 2017.

11.

Egerton, T.A., UV-absorption—the primary process in photocatalysis and some practical consequences. Molecules, 2014. 19(11): p. 18192–18214. 13

12.

Ge, Y., et al., Preparation of Zn-TiO2/RH/Fe3O4 composite material and its photocatalytic degradation for the dyes in wastewater. Desalination and Water Treatment, 2016. 57(21): p. 9837–9844.

13.

Andriantsiferana, C., E.F. Mohamed, and H. Delmas, Photocatalytic degradation of an azo-dye

SC RI PT

on TiO2/activated carbon composite material. Environmental Technology, 2014. 35(3): p. 355– 363. 14.

Pingmuang, K., et al., Composite Photocatalysts containing BiVO4 for degradation of cationic dyes. Scientific Reports, 2017. 7(1): p. 8929.

15.

Fan, H., et al., ZnO–graphene composite for photocatalytic degradation of methylene blue dye.

Jones, D.R., et al., Active removal of waste dye pollutants using Ta3N5/W18O49 nanocomposite

Pica, M., et al., Nanosized zirconium phosphate/AgCl composite materials: a new synergy for

M

17.

A

fibres. Scientific Reports, 2017. 7(1): p. 4090.

N

16.

U

Catalysis Communications, 2012. 29: p. 29–34.

efficient photocatalytic degradation of organic dye pollutants. Journal of Materials Chemistry A,

Xiong, Z., et al., Photocatalytic degradation of dyes over graphene–gold nanocomposites under

TE

18.

D

2015. 3(10): p. 5525–5534.

visible light irradiation. Chemical Communications, 2010. 46(33): p. 6099–6101. Ye, A., et al., CdS–graphene and CdS–CNT nanocomposites as visible-light photocatalysts for

EP

19.

hydrogen evolution and organic dye degradation. Catalysis Science & Technology, 2012. 2(5): p.

CC

969–978.

A

20.

21.

Ratanatawanate, C., Y. Tao, and K.J. Balkus Jr, Photocatalytic activity of PbS quantum dot/TiO2 nanotube composites. The Journal of Physical Chemistry C, 2009. 113(24): p. 10755–10760. Basit, M.A., et al., Strategic PbS quantum dot-based multilayered photoanodes for high efficiency quantum dot-sensitized solar cells. Electrochimica Acta, 2016. 211: p. 644–651.

14

22.

Abbas, M.A., et al., Enhanced performance of PbS-sensitized solar cells via controlled successive ionic-layer adsorption and reaction. Physical Chemistry Chemical Physics, 2015. 17(15): p. 9752–9760.

23.

Štengl, V. and D. Králová, TiO2/ZnS/CdS nanocomposite for hydrogen evolution and orange II

24.

SC RI PT

dye degradation. International Journal of Photoenergy, 2011. 2011.

Pigeot-Rémy, S., et al., Photocatalysis and disinfection of water: identification of potential bacterial targets. Applied Catalysis B: Environmental, 2011. 104(3–4): p. 390–398.

25.

Mohamed, H., et al., Spectral characteristics and morphology of nanostructured Pb–S–O thin films synthesized via two different methods. Materials Science in Semiconductor Processing,

Al-Jawad, S.M., Comparative study between CBD and SILAR methods for deposited TiO2, CdS,

N

26.

U

2014. 27: p. 725–732.

A

and TiO2/CdS core-shell structure. Materials Science in Semiconductor Processing, 2017. 67: p.

27.

M

75–83.

Li, C., et al., TiO2 nanotubes incorporated with CdS for photocatalytic hydrogen production from

28.

TE

35(13): p. 7073–7079.

D

splitting water under visible light irradiation. International Journal of Hydrogen Energy, 2010.

Genovese, M.P., I.V. Lightcap, and P.V. Kamat, Sun-believable solar paint. A transformative

29.

EP

one-step approach for designing nanocrystalline solar cells. ACS Nano, 2011. 6(1): p. 865–872. Abbas, M.A., et al., Revival of solar paint concept: air-processable solar paints for the

CC

fabrication of quantum dot-sensitized solar cells. The Journal of Physical Chemistry C, 2017. 121(33): p. 17658–17670.

A

30.

Mughal, F., et al., Multiple energy applications of quantum-dot sensitized TiO2/PbS/CdS and TiO2/CdS/PbS hierarchical nanocomposites synthesized via p-SILAR technique. Chemical Physics Letters, 2019.

15

31.

Aziz, M.I., et al., Evolution of photovoltaic and photocatalytic activity in anatase-TiO2 under visible light via simplistic deposition of CdS and PbS quantum-dots. Materials Chemistry and Physics, 2019.

32.

Ashiq, M.N., et al., Visible-light active tin selenide nanostructures: synthesis, characterization

33.

SC RI PT

and photocatalytic activity. New Journal of Chemistry, 2017.

Andrade, G.R., et al., One-step preparation of CdS nanocrystals supported on thiolated silica-gel matrix and evaluation of photocatalytic performance. Journal of Hazardous Materials, 2012. 203: p. 151–157.

34.

Kotz, J.C., P.M. Treichel, and J. Townsend, Chemistry and chemical reactivity. 2012: Cengage

Masterton, W.L. and E.J. Slowinski, Chemical principles with qualitative analysis. 1978: WB

N

35.

U

Learning.

Wu, L., C.Y. Jimmy, and X. Fu, Characterization and photocatalytic mechanism of nanosized

M

36.

A

Saunders Company.

CdS coupled TiO2 nanocrystals under visible light irradiation. Journal of Molecular Catalysis A:

Kaur, A., et al., Facile synthesis of CdS/TiO2 nanocomposite and their catalytic activity for

TE

37.

D

Chemical, 2006. 244(1–2): p. 25–32.

ofloxacin degradation under visible illumination. Journal of Photochemistry and Photobiology A:

38.

EP

Chemistry, 2018. 360: p. 34–43. Qin, N., et al., One-dimensional CdS/TiO2 nanofiber composites as efficient visible-light-driven

CC

photocatalysts for selective organic transformation: synthesis, characterization, and performance. Langmuir, 2015. 31(3): p. 1203–1209.

A

39.

Zhukovskiy, M.A., et al., Photocatalytic growth of CdS, PbS, and CuxS nanoparticles on the nanocrystalline TiO2 films. Journal of Photochemistry and Photobiology A: Chemistry, 2009. 203(2–3): p. 137–144.

16

40.

Zhu, H., et al., Photocatalytic decolorization and degradation of Congo Red on innovative crosslinked chitosan/nano-CdS composite catalyst under visible light irradiation. Journal of Hazardous Materials, 2009. 169(1–3): p. 933–940.

41.

Moan, J., Visible light and UV radiation. Radiation at Home, Outdoors and in the Workplace.

42.

SC RI PT

Oslo: Scandinavian Publisher, 2001: p. 69–85.

Tong, X., et al., Pinning mass-selected Ag n clusters on the TiO2 (110)− 1× 1 surface via

deposition at high kinetic energy. The Journal of chemical physics, 2005. 123(20): p. 204701. 43.

Quintero, J. and Y. Xu, Heterogeneous Photocatalysis: From Fundamentals to Green Applications. 2015, Springer Google Scholar.

King, R., et al., 40% efficient metamorphic GaInP∕ GaInAs∕ Ge multijunction solar cells. Applied

U

44.

Rajabi, H.R. and M. Farsi, Effect of transition metal ion doping on the photocatalytic activity of

A

45.

N

Physics Letters, 2007. 90(18): p. 183516.

M

ZnS quantum dots: Synthesis, characterization, and application for dye decolorization. Journal of Molecular Catalysis A: Chemical, 2015. 399: p. 53–61. Poinern, G.E.J., A laboratory course in nanoscience and nanotechnology. 2014: CRC Press.

47.

H Sargent, E., Infrared quantum dots. Advanced Materials, 2005. 17(5): p. 515–522.

48.

Ullah, K., et al., Synthesis and characterization of novel PbS–graphene/TiO2 composite with

TE

D

46.

EP

enhanced photocatalytic activity. Journal of Industrial and Engineering Chemistry, 2014. 20(3): p. 1035–1042.

Wang, Y., Nonlinear optical properties of nanometer-sized semiconductor clusters. Accounts of

CC

49.

Chemical Research, 1991. 24(5): p. 133–139.

A

50.

Gholap, H., et al., CdTe–TiO2 nanocomposite: an impeder of bacterial growth and biofilm. Nanotechnology, 2013. 24(19): p. 195101.

17

51.

Suganya, M., et al., Thermal behavior, magnetic and antimicrobial properties of PbS–CdO nanocomposite synthesized by a simple soft chemical route. Journal of Materials Science: Materials in Electronics, 2017. 28(16): p. 12348–12355.

52.

Cunningham, D. and L. Lundie, Preparation of cadmium by clostridium thermoaceticilm. Appl.

53.

SC RI PT

Environ. Microb., 1993. 5: p. 7–14.

Shivashankarappa, A. and K. Sanjay, Study on biological synthesis of cadmium sulfide

nanoparticles by Bacillus licheniformis and its antimicrobial properties against food borne pathogens. Nanoscience and Nanotechnology Research, 2015. 3(1): p. 6–15. 54.

Vijayalakshmi, K. and D. Sivaraj, Enhanced antibacterial activity of Cr doped ZnO nanorods

A

CC

EP

TE

D

M

A

N

U

synthesized using microwave processing. RSC Advances, 2015. 5(84): p. 68461–68469.

18

FIGURE CAPTIONS

Figure 1. Schematic illustration of the method employed for producing QD-sensitized P25-TiO2

SC RI PT

nanocomposites, showing one cycle of the pseudo-successive ionic layer adsorption and reaction method. Figure 2. Scanning electron microscopy images of P25-TiO2 nanopowder (a) without and (b) with QD sensitization. Inset shows higher magnification (150,000) image of the same powder.

Figure 3. Atomic concentrations of Pb, Cd, and S in P25-TiO2-based PbS and CdS QD-sensitized P25-

U

TiO2 nanocomposites measured by XRF.

N

Figure 4. Elemental area mapping based on scanning electron microscopy images of P25-TiO2

A

nanopowder (a) with PbS QDs and (b) CdS QDs.

M

Figure 5. Transmission electron microscopy image of P25-TiO2 (a) without and (b, c) with PbS and CdS

D

QD sensitization. Inset shows higher magnification (150,000) image of the same powder.

TE

Figure 6. Schematic diagram of dye degradation by QD-sensitized P25-TiO2: (a) more electron–hole pairs are generated by QDs under visible light irradiation; and (b) more electron–hole pairs are generated

EP

by P25-TiO2 under UV irradiation.

CC

Figure 7. UV-Vis spectroscopy results obtained for P25-TiO2 and QD-sensitized nanocomposites. Insets show the colors of P25-TiO2, TPbS, and TCdS.

A

Figure 8. Effects on the dye concentration of P25-TiO2 and QD-sensitized P25-TiO2: (a) under UV irradiation, (b) under visible light irradiation, and (c) dye degradation rates under UV and visible light irradiation.

19

Figure 9. (a) Antimicrobial activities of P25-TiO2 and QD-sensitized P25-TiO2 compared with those of streptomycin and ampicillin. Scanning electron microscopy images of Bacillus subtilis (b) before and (c) after treatment with TCdS. Atomic force microscopy images of Bacillus subtilis (d) without TCdS and (e)

SC RI PT

with TCdS.

TE

D

M

A

N

U

FIGURES

EP

Figure 1. Schematic illustration of the method employed for producing QD-sensitized P25-TiO2

A

CC

nanocomposites, showing one cycle of the pseudo-successive ionic layer adsorption and reaction method.

20

SC RI PT

Figure 2. Scanning electron microscopy images of P25-TiO2 nanopowder (a) without and (b) with QD

EP

TE

D

M

A

N

U

sensitization. Inset shows higher magnification (150,000) image of the same powder.

CC

Figure 3. Atomic concentrations of Pb, Cd, and S in P25-TiO2-based PbS and CdS QD-sensitized P25-

A

TiO2 nanocomposites measured by XRF.

21

SC RI PT

Figure 4. Elemental area mapping based on scanning electron microscopy images of P25-TiO2

CC

EP

TE

D

M

A

N

U

nanopowder (a) with PbS QDs and (b) CdS QDs.

Figure 5. Transmission electron microscopy image of P25-TiO2 (a) without and (b, c) with PbS and CdS

A

QD sensitization. Inset shows higher magnification (150,000) image of the same powder.

22

SC RI PT U

N

Figure 6. Schematic diagram of dye degradation by QD-sensitized P25-TiO2: (a) more electron–hole

M

A

CC

EP

TE

D

by P25-TiO2 under UV irradiation.

A

pairs are generated by QDs under visible light irradiation; and (b) more electron–hole pairs are generated

23

Figure 7. UV-Vis spectroscopy results obtained for P25-TiO2 and QD-sensitized nanocomposites. Insets

M

A

N

U

SC RI PT

show the colors of P25-TiO2, TPbS, and TCdS.

Figure 8. Effects on the dye concentration of P25-TiO2 and QD-sensitized P25-TiO2: (a) under UV

D

irradiation, (b) under visible light irradiation, and (c) dye degradation rates under UV and visible light

A

CC

EP

TE

irradiation.

24

SC RI PT U N A M D TE EP CC A

Figure 9. (a) Antimicrobial activities of P25-TiO2 and QD-sensitized P25-TiO2 compared with those of streptomycin and ampicillin. Scanning electron microscopy images of Bacillus subtilis (b) before and (c) after treatment with TCdS. Atomic force microscopy images of Bacillus subtilis (d) without TCdS and (e) with TCdS. 25

TABLES

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Table 1. Photodegradation of azo-type dye under (a) UV irradiation and (b) visible light irradiation.

Photo-degradation of Azo dye (C32H22N6Na2O8S2)

(a)

-2

(pH= 7, Time= 1.5 hr, Intensity= 460wm , vol= 50 mL, catalyst dose= 0.1gm)

Samples

UV Light (Cf)

Visible Light (Cf)

After 30min

After 60min

After 90min

After 30min

After 60min

After 90min

TiO2

41.30

38.30

36.84

49.70

49.13

48.95

TPbS

49.15

48.05

47.33

U

(Ci= 50 ppm)

33.75

21.33

TCdS

49.45

48.55

48.27

46.45

42.38

42.13

M

A

N

42.85

Photo-degradation of Azo dye (C32H22N6Na2O8S2)

(b)

-2

D

(pH= 7, Time= 1.5 hr, Intensity= 460wm , vol= 50 mL, catalyst dose= 0.1gm)

50

TPbS

50 50

Cf/Ci (%age)

Initial Concentration (Ci) ppm

Final Concentration (Cf) ppm

Cf/Ci (%age)

36.84

26.32

50

48.95

2.10

47.33

5.34

50

21.33

57.34

48.27

3.46

50

42.13

15.74

A

TCdS

CC

TiO2

Visible Light

Final Concentration (Cf) ppm

EP

Initial Concentration (Ci) ppm

TE

UV Light

Samples

26