Photo-induced toxicity of tungsten oxide photochromic nanoparticles
Graphical Abstract
Introduction
The modern technological paradigm requires research and development into new materials with specific physical and chemical properties. Recently, much attention has been paid to the development of various types of stimuli-responsive materials, which are able to change their characteristics in response to external factors. For instance, in the context of energy-saving, smart photo- or electrochromic materials have been developed which are able to control the throughput of visible light and solar radiation into buildings by having different transmittance levels depending on changing needs [1]. One of the most promising materials for photochromic films or coatings is nanocrystalline tungsten oxide, an n-type wide-bandgap semiconductor with a chemical type of chromism [2], [3]. The electro-, photo- and chemochromic properties of tungsten oxide (WO3) are widely used in electronic displays, optical modulators, windows with adjustable light transmission, rear-view mirrors in cars, etc. [4], [5], [6], [7]. Under light irradiation, exposure to chemical reagents or the application of an electric field, stoichiometric WO3 (faintly yellowish) undergoes a number of serial transformations, reversibly forming brightly coloured products [8]:
In addition to the above-mentioned applications, tungsten oxide is one of the most thoroughly studied photocatalysts [9], [10], [11], [12], [13], [14], [15] for organic dye degradation. WO3 nanoparticles of different morphologies, obtained by the hydrothermal-microwave method, have been shown to possess photocatalytic properties with respect to the discolouration of rhodamine B, indigo carmine and tetracycline hydrochloride under UV–vis irradiation [11]. WO3 nanoparticles obtained by surfactant-assisted sonication have provided a high rate of rhodamine B and indigo carmine degradation under xenon lamp irradiation [12]. Multi-phase WO3 samples possess improved photocatalytic activity, (as demonstrated by the bleaching of rhodamine B), that can be attributed to a decrease in the electron-hole recombination rate, owing to the formation of interphase junctions [13]. The efficient degradation of methylene blue dye by tungsten oxide nanoplates, synthesised using a hydrothermal or microwave-hydrothermal method, has been shown under UV light irradiation [14]. The photocatalytic activity of WO3 nanoparticles (obtained by annealing (NH4)xWO3 − y at 500 °C in air) and nanorods (prepared using a hydrothermal method using Na2WO4, HCl, (COOH)2 and NaHSO4 precursors at 200 °C) has been confirmed by the decomposition of methyl orange in an aqueous solution under UV light irradiation [15].
The common mechanism for organic dye degradation by photoactive semiconductor (photocatalyst) is represented in the left part of Fig. 1, A:
When a photocatalyst absorbs light that has an energy that exceeds the semiconductor's bandgap, an electron of the valence band is promoted to the conduction band, thus creating an electron (e−)/hole (h+) pair. Due to the semiconductor's photoexcitation (WO3 → WO3⁎) and the generation of electron/hole pairs, oxidation-reduction reactions take place at the surface: electrons reduce and holes oxidise the molecules of the surrounding substrate (Sub). Upon contact between the dye and the photoexcited nanoparticle, direct redox decomposition of the dye molecule occurs (Sub = Dye). More often, the first stage of photocatalysis is the redox transformation of water and/or oxygen (Sub = H2O, O2), forming the reactive oxygen species (ROS), which then destroy other substances, (the indirect redox decomposition of the dye molecule). Obviously, the photocatalytic activity of the material can affect not only the decomposition of organic dyes, but also the biological components of living cells.
The mechanism of tungsten oxide photo-induced chromism (autophotoreduction) is represented in the right part of Fig. 1, A. The excited electrons cause the reduction of tungsten (6 +) to (5 +) ions, leading to the formation of coloured, non-stoichiometric, hydrated tungsten oxide (HxWO3, 0 < x < 1); the holes oxidise substrate (for example, water [16]), forming ROS, such as hydroxyl radicals. Upon contact with living cells, these ROS can cause oxidative stress, resulting in cell death. Another specific tungsten oxide feature is that it possesses photoactivity at a wide range of wavelengths. The most widely explored TiO2-photocatalysts are effective under UV light only, while WO3-based ones can change their bandgap upon irradiation, and thus tungsten trioxide could be an effective visible light photocatalyst, wherein the absorbed efficiency of sunlight can be enhanced enormously.
The autophotoreduction of tungsten oxide is accompanied by formation of free charge carriers, so photochromic colouration of tungsten oxide occurs due to the local surface plasmon resonance (LSPR) arising from appreciable free carrier concentrations [17], [18]. It is well known that the interaction of plasmonic particles and light (HxWO3 → HxWO3⁎ photoexcitation) leads not only to redox processes on their surface (left part of Fig. 1, B), but also to the partial conversion of electromagnetic energy into heat (right part of Fig. 1, B). The volumetric generation of heat within the plasmonic nanoparticle Q(r, t) is affected by the intensity of light, the particle's internal electromagnetic field distribution, and the thermal and electrical conductivity of the particle's material [18]:where Ẽ(r, t) and Ẽ∗(r, t) are the generated electric field and its complex conjugate within the nanoparticles; σ – electrical conductivity at optical frequencies; λi – incident light wavelength; μ – relative magnetic permeability of the nanoparticle, and n and k – the real and imaginary parts of the refraction index of the nanoparticle, respectively. Plasmonic nanoparticles of non-stoichiometric tungsten oxide have been used for photothermal cancer treatment upon IR irradiation [18], [19], [20], [21], [22], [23]. Thus, volumetric heating of WO3 nanoparticles upon irradiation can bring an additional contribution to cytotoxicity, and thus should be taken into account.
For this paper, we synthesised a new type of photochromic tungsten oxide nanoparticles, analysed their photocatalytic activity and carried out a thorough analysis of their effect on prokaryotic and eukaryotic organisms. WO3 nanoparticles possess both dark and light cytotoxicity, which significantly distinguishes them from common photocatalysts, and opens up new possibilities for their practical use.
Section snippets
Tungsten Oxide Nanoparticles
Ultrasmall tungsten oxide nanoparticles were synthesised by means of hydrothermal treatment of tungstic acid in the presence of polyvinylpyrrolidone (PVP K-30, average mol. wt. 40,000) as a template, stabiliser and growth regulator. Tungstic acid was prepared through an ion-exchange method using sodium tungstate (Na2WO4) solution and a strongly acidic cation exchange resin (Amberlite® IR120). Briefly, ion exchange resin (in a hydrogen form) was swollen in water and loaded into a glass column of
Tungsten Oxide Nanoparticles
Highly photochromic, ultra-small, WO3 nanoparticles were synthesised using the protocol proposed, based on the hydrothermal treatment of tungstic acid in the presence of polyvinylpyrrolidone (Fig. 2). Ultra-small WO3 nanoparticles demonstrated a very high rate of photochromic colouration, which takes place especially easily in an aqueous medium. Our preliminary data indicate that the bandgap of thus synthesised tungsten oxide was size-dependent. The optical bandgap calculated using the
Conclusions
A method for tungsten oxide nanoparticles synthesis is proposed. Upon UV irradiation, WO3 nanoparticles possess high photocatalytic activity in an indigo carmine dye photodecomposition reaction. Tungsten oxide nanoparticles showed both light and dark cytotoxic effects against prokaryotic microorganisms and eukaryotic cells. We have identified their different sensitivity to the effects of WO3 nanoparticles, which, apparently, is associated with the morphological features of their cell membrane
Acknowledgment
The procedure for WO3 nanoparticles synthesis was elaborated with support from the Russian Science Foundation (project 16-13-10399).
References (48)
Electrochromics for smart windows: oxide-based thin films and devices
Thin Solid Films
(2014)Opportunities and challenges in science and technology of WO3 for electrochromic and related applications
Sol. Energy Mater. Sol. Cells
(2008)Electrochromic tungsten oxide films: review of progress 1993–1998
Sol. Energy Mater. Sol. Cells
(2000)- et al.
The visible light induced photocatalytic activity of tungsten trioxide powders
Appl. Catal. A Gen.
(2001) - et al.
Characterization and photocatalytic properties of hexagonal and monoclinic WO3 prepared via microwave-assisted hydrothermal synthesis
Ceram. Int.
(2014) - et al.
CTAB-assisted ultrasonic synthesis, characterization and photocatalytic properties of WO3
Mater. Res. Bull.
(2015) - et al.
Fabrication of a monoclinic/hexagonal junction in WO3 and its enhanced photocatalytic degradation of rhodamine B
Chin. J. Catal.
(2016) - et al.
Functionalized biocompatible WO3 nanoparticles for triggered and targeted in vitro and in vivo photothermal therapy
J. Control. Release
(2015) - et al.
Cerium oxide nanoparticles stimulate proliferation of primary mouse embryonic fibroblasts in vitro
J. Mater. Sci. Eng. C
(2016) - et al.
Photocatalytic degradation of dyes in water: case study of indigo and of indigo carmine
J. Catal.
(2001)
Synthesis of WO3 nanoparticles by citric acid-assisted precipitation and evaluation of their photocatalytic properties
Mater. Res. Bull.
Synthesis and characterization of WO3 nanoparticles prepared by the precipitation method: evaluation of photocatalytic activity under vis-irradiation
Solid State Sci.
Antimicrobial activity of nanoparticulate metal oxides against peri-implantitis pathogens
Int. J. Antimicrob. Agents
Direct nanomaterial-DNA contact effects on DNA and mutation induction
Toxicol. Lett.
Visible light photoinactivation of bacteria by tungsten oxide nanostructures formed on a tungsten foil
Appl. Surf. Sci.
Catalytic activity of tungsten phosphate (IV), (V), (VI) at carbon monoxide oxidation
Stud. Surf. Sci. Catal.
Chitosan coated tungsten trioxide nanoparticles as a contrast agent for X-ray computed tomography
Int. J. Biol. Macromol.
Poly-ε-caprolactone tungsten oxide nanoparticles as a contrast agent for X-ray computed tomography
Biomaterials
Photochromic materials based on tungsten oxide
J. Mater. Chem.
Nanostructured tungsten oxide – properties, synthesis, and applications
Adv. Funct. Mater.
Tungsten oxide-based nanomaterials: morphological-control, properties and novel applications, reviews in advanced sciences and
Engineering
The beautiful Colours of tungsten oxides, ITIA
Newsletter
Tungsten oxide in catalysis and photocatalysis: hints from DFT
Top. Catal.
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2021, Journal of Cleaner ProductionCitation Excerpt :It showed that the degradation of LDC in 60 min achieved 95.48% and 97.5% under visible and sunlight, respectively. Other than that, the investigation examined the effect of photocatalytic activity of WO3 nanoparticles on the degradation of Indigo carmine under UV irradiation and diffused daylight filtered through a window glass (Popov et al., 2018). The photocatalytic activity of WO3 nanoparticles performance under UV irradiation similar to that in diffused daylight filter.
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2020, Materials Science and Engineering CCitation Excerpt :wt. 40,000) as a template, stabilizer and growth regulator [20]. Tungstic acid was prepared by an ion-exchange method using sodium tungstate (Na2WO4) solution and strongly acidic cation exchange resin (Amberlite® IR120).