Growth of Cu2O nanoparticle on reduced graphene sheets with high photocatalytic activity for degradation of Rhodamine B

Cu₂O–reduced graphene oxide (RGO) nanocomposite was synthesized by a simple one-pot solvothermal method. The morphology and properties of Cu₂O/RGO nanocomposites were characterized by scanning electron microscope, Raman spectroscopy, X-ray diffraction, photoluminescence spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activities of the as-prepared nanocomposites were investigated by photodegrading Rhodamine B under visible light. Results show that Cu₂O/RGO nanocomposites exhibited a remarkably enhanced photocatalytic efficiency compared with pure Cu₂O nanoparticles and commercial P25. Moreover, we found that the content of graphene oxide introduced into composite material was a crucial factor for its improved photocatalytic performance.     

Cu2O-Au nanocomposites with novel structures and remarkable chemisorption capacity and photocatalytic activity

The decomposition of CuH nanoparticles in aqueous solution has been successfully developed as a novel method for the preparation of Cu₂O nanoparticles. In particular, we found that the decomposition of CuH nanoparticles in aqueous solution could be catalyzed by Au colloids, forming Cu₂O-Au nanocomposites. The composition and structure of the resulting Cu₂O-Au nanocomposites have been characterized in detail by inductively coupled plasma atomic emission spectroscopy, powder X-ray diffraction, N₂ adsorption-desorption isotherms, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. Their visible-light-driven photocatalytic activity toward various dye molecules has also been investigated. Depending on the Au:Cu ratio, Cu₂O-Au nanocomposites exhibit different novel nanostructures including a beautiful flower-like nanostructure that consists of polycrystalline Cu₂O, amorphous Cu₂O and Au colloids. We propose that the rapidly-generated bubbles of H₂ during the course of the catalytic decomposition reaction drive the simultaneously-formed Cu₂O to form amorphous curved thin foils and might also act as a template to assemble curved thin foils of amorphous Cu₂O, polycrystalline Cu₂O and Au colloids into uniform nanostructures. A Cu₂O-Au nanocomposite with a Cu:Au ratio of 40 exhibits remarkable chemisorption capacity and visible-light-driven photocatalytic activity towards methyl orange and acid orange 7 and is a promising chemisorption-photocatalysis integrated catalyst. The catalytic decomposition of the metal hydride might open up a new approach for the fabrication of other metal/metal oxide nanocomposites with novel nanostructures and properties.      

Synthesis of Cu2O/T-ZnOW nanocompound and characterization of its photocatalytic activity and stability property under UV irradiation

Cu₂O/tetrapod-like ZnO whisker (T-ZnO_W) nanocompound was synthesized by a simple hydrothermal chemical method. The chemical composition, morphology, band gap and photocatalytic property of the Cu₂O/T-ZnO_W nanocompound were studied in detail. It was observed that the Cu₂O particles deposited on T-ZnO_W surface had a cubic structure and the crystallinity of T-ZnO_W did not change with the increase of Cu₂O crystals. The morphology and content of Cu₂O in the Cu₂O/T-ZnO_W nanocompound played an important role on the photocatalytic activity. In addition, the coexistence of Cu₂O and T-ZnO_W nanoparticles was propitious to the high photocatalytic activity owing to their hetero-junction effect. The Cu₂O/T-ZnO_W nanocompound prepared by 7.2% Cu/Zn MR exhibited the best photocatalytic activity on the degradation of MO solution under UV light irradiation. At the first 100 min of irradiation, the photodegradation efficiency of MO solution reached up to 99.16%, which still retained its high photocatalytic activity about 89.10% even at the end of the fourth cycle. Little change was found in their phase compositions after the photocatalytic reaction process, except partial oxidation of particles’ surface. The mechanism for UV light driven photocatalytic activity enhancement over Cu₂O/T-ZnO_W nanocompound was discussed.     

Pulse electrodeposition of Ag,Cu nanoparticles on TiO2 nanoring/nanotube arrays for enhanced photoelectrochemical water splitting

In this paper, plasmonic Ag and Cu nanoparticles were co-deposited on TiO₂ nanoring/nanotube arrays (TiO₂ R/T) by using two-step pulse electrodeposition method for investigating the optical and photoelectrochemical properties, in comparison to monometallic Ag, Cu decoration. By optimizing the electrodeposition cycle times and electrolyte concentration, bimetallic Ag–Cu/TiO₂ R/T-0.5 with moderate densities and sizes of Ag and Cu nanoparticles was fabricated and shows great photocatalytic potential, in which, Ag mainly facilitates the generation of hot electrons by absorbing visible light and Cu plays an important role in accelerating the separation and transportation of hot electrons. The hydrogen production rate was tested as 425 μL h^?1 cm^?2, which is about 1.34-fold enhanced H₂ production over TiO₂ R/T. Furthermore, molecular dynamics simulations were made for analyzing the interface electrostatic properties between plasmonic nanoparticles of Ag or Cu and the semiconductor TiO₂. It is calculated that bimetallic Ag–Cu/TiO₂/H₂O system has larger interfacial Helmholtz potential than monometallic Ag/TiO₂/H₂O, Cu/TiO₂/H₂O and pure TiO₂/H₂O systems, accelerating the four-electron reaction occurring at the semiconductor/electrolyte interface. This research put forward a feasible and simple pulse electrodeposition method to fabricate bimetallic photoanodes for enhanced hydrogen evolution and an important analysis method of semiconductor/ metal/electrolyte interface characteristics.     

Enhanced photocatalytic activity of flowerlike Cu2O/Cu prepared using solvent-thermal route

Cu₂O/Cu nanocomposites (NCs) with flowerlike nano-architecture were prepared using template-free stepwise solvent-thermal synthesis route with Cu(NO₃)₂·3H₂O as a precursor. With the precursor concentration increasing gradually from 0.01 to 0.1 M, the morphology of the NCs evolves from nano-flower to microsphere. The content of Cu in the NCs can be easily controlled by adjusting the concentration of precursor and synthesis time. Using photocatalytic degradation of monoazo dye Procion Red MX-5B (PR) and phenol as the probe molecules under visible-light illumination, we have investigated the influence of Cu on the photocatalytic activity of Cu₂O. When the content of Cu lies in the range of 27–71 wt%, the samples exhibit higher photocatalytic performance, indicating that these flowerlike Cu₂O/Cu NCs are promising candidates for pollutant processing.     

Microwave Synthesis of Cu/Cu<Subscript>2</Subscript>O/SnO<Subscript>2</Subscript> Composite with Improved Photocatalytic Ability Using SnCl<Subscript>4</Subscript> as a Protector

Cu/Cu₂O/SnO₂ composites were successfully prepared with a facile microwave synthesis method. The structure of Cu/Cu₂O/SnO₂ composite was studied by morphology characterizations, such as X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy, which showed that the size of the Cu/Cu₂O/SnO₂ particles is 20–50 nm. The synthesis mechanism revealed that SnCl₄ obstructed between Cu(OH) and ethylene glycol, preventing Cu(OH) being reduced into Cu at high temperature. The photocatalytic property of Cu/Cu₂O/SnO₂ composite was investigated by degrading the mixed dyestuff under the irradiation of visible light at room temperature. Benefiting from the effect of electron transfer, the photocatalytic performance of the microwave-prepared Cu/Cu₂O/SnO₂ composite was much better than that of pure Cu₂O. The possible photocatalytic mechanism of the Cu/Cu₂O/SnO₂ composite catalysts was proposed and elaborated in this study. This synthesis of Cu/Cu₂O/SnO₂ composite may provide a method for other Cu₂O/semiconductor composites microwave preparation.     

Controlled reduction of Cu to Cu with an N,O-type chelate under hydrothermal conditions to produce Cu2O nanoparticles

N,O-type organic chelates reduced coordinated Cu²⁺ ions under hydrothermal reaction conditions to produce Cu₂O/CuO nanoparticles. Chelates in which the N and O atoms are closely spaced produced smaller amounts of CuO nanoparticles, indicating their higher ability to reduce Cu²⁺ ions to Cu⁺ ions. [Cu(Gly)₂]² with the shortest ligand chain length produced only Cu₂O nanoparticles and, therefore, can be used as a single molecule precursor for the synthesis of Cu₂O nanoparticles.     

Preparation and characterization of Cu2O-TiO2: Efficient photocatalytic degradation of methylene blue

A series of copper-deposited titania were prepared by photoreduction method under irradiation with a 125-W high-pressure mercury lamp. From XPS and AES results, the deposited-copper formed Ti-O-Cu bond on the surface of TiO₂, and the Cu species on the surface of copper-deposited TiO₂ can be identified as Cu(I). The photocatalytic degradation activity of methylene blue for the Cu₂O-TiO₂ series increased with increasing Cu₂O-deposited content, and then decreased. The highest photocatalytic degradation activity of methylene blue was obtained for 0.16% Cu₂O-TiO₂. When copper-deposited content reached to 0.32%, the photocatalytic activity was lower than that of pure TiO₂. It is shown that Cu₂O on the surface of TiO₂ can trap electrons from the TiO₂ conduction band, and the electrons trapped on the Cu₂O-TiO₂ site are subsequently transferred to the surrounding adsorbed O₂, thereby avoiding electron-hole recombination, and enhancing the photocatalytic activity. Excess copper loading may screen the photocatalyst from the UV source, so the photocatalytic activity diminishes with increasing Cu₂O.     

Controllable synthesis and enhanced photocatalytic properties of Cu2O/Cu31S16 composites

The controlled synthesis of Cu₂O/Cu₃₁S₁₆ microcomposites with hierarchical structures had been prepared via a convenient sonochemical route. Ultrasonic irradiation of a mixture of Cu₂O and (NH₂)₂CS in an aqueous medium yielded Cu₂O/Cu₃₁S₁₆ composites. The content of Cu₃₁S₁₆ in the Cu₂O/Cu₃₁S₁₆ can be easily controlled by adjusting the synthesis time. The Cu₃₁S₁₆ layer not only protected and stabilized Cu₂O particles, but also prohibited the recombination of photogenerated electrons–holes pair between Cu₃₁S₁₆ and Cu₂O. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) spectra, ultraviolet–visible (UV–Vis) spectroscopy and photoluminescence (PL) spectroscopy were used to characterize the products. Photocatalytic performance of the Cu₂O/Cu₃₁S₁₆ hierarchical structures was evaluated by measuring the decomposition rate of methyl orange solution under natural light. To the best of our knowledge, this is the first report on the preparation and photocatalytic activity of Cu₂O/Cu₃₁S₁₆ microcomposite. Additionally, the Cu₂O/Cu₃₁S₁₆ core/shell structures were more stable than single Cu₂O particles during photocatalytic process since the photocatalytic activity of the second reused architecture sample was much higher than that of pure Cu₂O. The Cu₂O/Cu₃₁S₁₆ microcomposites may be a good promising candidate for wastewater treatment.     

Rapid preparation and photocatalytic properties of octahedral Cu2O@Cu powders

To improve the photocatalytic properties of Cu₂O, octahedral Cu₂O@Cu powders were prepared by a convenient and rapid two-step liquid phase reduction method. Glucose (C₆H₁₂O₆) and thiourea dioxide (CH₄N₂O₂S, TD for short) were used as pre-reductant and secondary-reductant separately. The microstructure and composition of the products obtained after the reduction processes were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). With the increasing of TD content, the secondary reduced products changed from solid octahedral Cu₂O to octahedral Cu₂O@Cu composites and finally hollow octahedral Cu₂O/Cu composites. The corresponding calculated mass of Cu increased from 6.2 wt% to 80.2 wt%. The photocatalytic behavior of the reduced particles were analyzed by monitoring the degradation of methyl orange solution (MO for short) and electrochemical tests. Photocatalytic performance tests showed that octahedral Cu₂O@Cu powders had an excellent photocatalytic activity. The MO degradation rate was improved from 1.4% for photocatalysts without CuNPs to 92.9% after introducing 13.4 wt% CuNPs under visible light irradiation for 60 min. This simple and rapid synthesis process allowed for the fabrication of octahedral Cu₂O@Cu material with photocatalytic performance superior to pure octahedral Cu₂O and hollow octahedral Cu₂O/Cu materials.     

Design of Cu–Ce co-doped TiO<Subscript>2</Subscript> for improved photocatalysis

The fast recombination of photo-generated conduction band electrons (e _cb ^? ) and valance band holes (h _vb ⁺ ) of TiO₂ results in an unsatisfactory photocatalytic performance for organic degradation. To increase the efficiency of charge separation, TiO₂ was modified by Cu–Ce co-doping considering the better redox properties of copper–ceria oxide with respect to the single oxide, i.e., an easier electron capturing ability. An optimal Cu–Ce co-doped TiO₂ with the initial molar ratio of Cu/Ce at 3:1 was prepared by a hydrothermal method with the aim to greatly promote the charge separation, and characterized by XRD, BET, DRS, PL, HR-TEM, and XPS techniques. Upon ultraviolet light irradiation, it exhibits significantly enhanced photocatalytic activity, about 5.8 times that of Ti–HF. The presence of Cu²⁺ and Ce³⁺/Ce⁴⁺ benefits electrons captured by molecular oxygen, while an increased hydroxyl groups upon Cu–Ce co-doping consume more holes, resulting in prolonged lifetime of photo-generated carriers. Moreover, it is proved that electron transfers preferably from conduction band (CB) of TiO₂ to CB of CuO and then to nearby CeO₂.     

Construction of hierarchical TiO<Subscript>2</Subscript> nanorod array/graphene/ZnO nanocomposites for high-performance photocatalysis

The photocatalytic performance of heterostructure photocatalysts is limited in practical use due to the charge accumulation at the interface and its low efficiency in utilizing solar energy during photocatalytic process. In this work, a ternary hierarchical TiO₂ nanorod arrays/graphene/ZnO nanocomposite is prepared by using graphene sheets as bridge between TiO₂ nanorod arrays (NRAs) and ZnO nanoparticles (NPs) via a facile combination of spin-coating and chemical vapor deposition techniques. The experimental study reveals that the graphene sheets provide a barrier-free access to transport photo-excited electrons from rutile TiO₂ NRAs and ZnO NPs. In addition, there generates an interface scattering effect of visible light as the graphene sheets provide appreciable nucleation sites for ZnO NPs. This synergistic effect in the ternary nanocomposite gives rise to a largely enhanced photocurrent density and visible light-driven photocatalytic activity, which is 2.6 times higher than that of regular TiO₂ NRAs/ZnO NPs heterostructure. It is expected that this hierarchical nanocomposite will be a promising candidate for applications in environmental remediation and energy fields.     

Visible light degradation of Orange II using xCuyOz/TiO2 heterojunctions

Cu₂O/TiO₂, Cu/Cu₂O/TiO₂ and Cu/Cu₂O/CuO/TiO₂ heterojunctions were prepared and studied for their potential application as photocatalysts able to induce high performance under visible light. Orange II was used as a representative dye molecule. The effect of the amount and composition of the photosensitizers toward the activation of TiO₂ was studied. In each case, the global mechanism of Inter Particle Electrons Injection (IPEI) was discussed. The highest photocatalytic activity was observed for the system Cu/Cu₂O/CuO (MB2 catalyst) under visible light (t_1/2 = 24 min, k = 159.7 × 10⁻³ min⁻¹) and for the heterojunction cascade Cu/Cu₂O/CuO/TiO₂ (MB2 (50%)/TiO₂) under UV–vis light (t_1/2 = 4 min, k = 1342 × 10⁻³ min⁻¹). In the last case, the high performance was attributed firstly to the electromotive forces developed under this configuration in which CuO energy bands mediate the electrons transfer from Cu₂O to TiO₂. The formation of monobloc sensitizers also accounts for the decrease of the probability of the charges lost. It was demonstrated that “Cu₂O/CuO” governs the capability of the heterojunction cascade and Cu does not play a significant role regardless of the heterojunction cascade efficiency. The electrical energy consumption per order of magnitude for photocatalytic degradation of Orange II was investigated for some representative catalytic systems. Visible/MB2 and UV/vis MB2 (50%)/TiO₂ exhibited respectively 0.340 and 0.05 kWh m⁻³ demonstrating the high efficiency of the systems.     

Preparation and electrical erosion resistance of TiB2/Cu nanocomposites

A procedure is described for producing nanocomposite TiB₂/Cu powders containing up to 57 vol % TiB₂. Using shock compression of composite powders, we have prepared electrode materials offering enhanced electrical erosion resistance at high arc discharge currents. The effect of titanium diboride nanoparticles embedded in the copper matrix on the erosion behavior of the nanocomposites is examined. The nanoparticles are shown to suppress the copper droplet entrainment during the service of the electrode. TiB₂/Cu nanocomposite electrodes containing more than 10 vol % TiB₂ retain their shape and dimensions in the course of electrical erosion tests and offer enhanced service life.     

Synthesis and enhanced photocatalytic activity of regularly shaped Cu2O nanowire polyhedra

A series of unique nanowire superstructures, Cu2O nanowire polyhedra, have been synthesized through a cost-effective hydrothermal route. Three types of nanowire polyhedra, namely octahedra, concave octahedra, and hexapods, were formed in high morphological yields (90%) by reducing cupric acetate with o-anisidine or o-phenetidine in the presence of carboxylic acids. The architectures of these Cu₂O nanowire polyhedra were examined by electron microscopy, which revealed ordered, highly aligned Cu₂O nanowires within the polyhedral outlines. The growth of the Cu₂O nanowire polyhedra is controlled by the orientation and growth rates of the nanowire branches which are adjusted by addition of carboxylic acids. Compared to the Cu₂O samples reported in the recent literature, the Cu₂O nanowire octahedra exhibit notably enhanced photocatalytic activities for dye degradation in the presence of H₂O₂ under visible light, probably due to the high-density charge carriers photoexcited from the branched nanowires with their special structures. Additionally, the discussion in the recent literature of the photocatalytic activity of Cu₂O in the absence of H₂O₂ for direct photodegradation of dyes seems questionable.     

Enhanced photocatalytic performance of Cu2O nano-photocatalyst powder modified by ball milling and ZnO

In this paper, a ball milled Cu₂O-ZnO nano-photocatalyst with good photocatalytic performance in visible light range was prepared. Effect of ZnO presence and ball milling of Cu₂O on the structure, microstructure, optical properties and photocatalytic performance were studied. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), high resolution transmission electron microscopy (HRTEM), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) analysis and UV–Vis spectrophotometer were used as characterization techniques. FESEM results indicated that ball milling of Cu₂O changed the morphology of Cu₂O-ZnO composite. The uniform formation of ZnO particles with average size of 30 nm over the Cu₂O surface was observed. The formation of p-n heterostructure with good contact between Cu₂O and ZnO nanoparticles was found by HRTEM image. Ball milling of Cu₂O promotes visible light absorption and reduction band gap to 1.9 eV in Cu₂O-ZnO photocatalyst. Intensity of PL spectra for the ball milled Cu₂O-ZnO photocatalyst was obviously lower. Ball milled Cu₂O-ZnO photocatalyst shows the highest photocatalytic activity and degradation efficiency of 98% was obtained for 2 mg/L methylene blue (MB) solution after 240 min. The kinetics of the photodegradation was followed the Langmuir-Hinshelwood (L-H) model and degradation rates were decreased by increase of MB concentration. In the case of ball milled Cu₂O and presence of ZnO, the MB degradation kinetics was two times faster.     

Highly dispersible and uniform size Cu2ZnSnS4 nanoparticles for photocatalytic application

Highly dispersible, uniform size (～7 nm) single-phase Cu₂ZnSnS₄ nanoparticles have been synthesized by hydrothermal method using non-toxic surfactant (oleic acid). High resolution transmission electron microscopy image indicates good crystallinity of the Cu₂ZnSnS₄ nanoparticles with the growth along (1 1 2) plane. X-ray photoelectron spectroscopy analyses suggested that the formation of with Cu, Zn, and Sn in +1, +2 and +4 oxidation states. The optical absorption spectrum of Cu₂ZnSnS₄ nanoparticles exhibits an absorption in the visible region and its optical band gap was found to be ～1.72 eV, which could be much more appropriate for photocatalytic application under visible light irradiation. These Cu₂ZnSnS₄ nanoparticles have been shown high photocatalytic degradation activity of methylene blue (MB) dye in the presence of visible light irradiation. The rate constant (k) value of Cu₂ZnSnS₄ nanoparticles is found to be 0.0144 min^?1. We have discussed the mechanism of dye degradation process that drives the photocatalytic degradation process. The reusability of the Cu₂ZnSnS₄ nanoparticles for the dye degradation is also demonstrated.     

Synthesis of magnetic Cu/CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocomposite as a highly efficient Fenton-like catalyst for methylene blue degradation

A magnetic Cu/CuFe₂O₄ nanocomposite was synthesized by a facile one-pot solvothermal method and characterized as an excellent Fenton-like catalyst for methylene blue (MB) degradation. The content of zero-valent copper (Cu⁰) in Cu/CuFe₂O₄ composite could be simply controlled by changing the dosage of sodium acetate in the synthetic process, and the Fenton-like catalytic performance of Cu/CuFe₂O₄ composite enhanced with increasing the Cu⁰ content. In the presence of H₂O₂ (15 mM), the as-synthesized 3-Cu/CuFe₂O₄ nanocomposite could remove 99% of MB (50 mg/L) after only 4 min at pH 2.50, greatly higher than that of pure CuFe₂O₄ and Cu⁰ under the same condition. The enhancement activity of Cu/CuFe₂O₄ nanocomposite was due to the synergistic effect between Cu⁰ and CuFe₂O₄. The radical capture experiments and coumarin fluorescent probe technique confirmed that MB was degraded mainly by the attack of OH^· radicals in Cu/CuFe₂O₄–H₂O₂ system.     

Thermal evolution of morphological,optical, and photocatalytic properties of Au–Cu2O–CuO nanocomposite thin film

Plasmonic nanocomposite thin films find exciting applications in environmental remediation and photovoltaics. We report on thermal annealing driven development of morphology, structure and photocatalytic performance of Au–Cu₂O–CuO nanocomposite thin film. Nanocomposite thin film coatings of Au–Cu₂O–CuO, prepared by radio frequency (RF) magnetron co-sputtering, were annealed at different temperatures. Thermal annealing driven evolution of morphology of Au–Cu₂O–CuO nanocomposite was studied by field emission scanning electron microscopy (FESEM), which revealed significant growth in size of nanostructures from 10 nm to 69 nm upon annealing. X-ray diffraction (XRD) together with Raman studies confirmed the nanocomposite nature of Au–Cu₂O–CuO film. UV-visible diffuse reflectance spectroscopy (UV-vis-DRS) studies showed band gap variation from 2.44 eV to 1.8 eV upon annealing at 250 °C. Nanocomposite thin film annealed at 250 °C exhibited superior photocatalytic activity for organic pollutants [methylene blue (MB) and methyl orange (MO)] decomposition. The origins of thermal transformation of morphological, optical and photocatalytic behaviour of the Au–Cu₂O–CuO nanocomposite coating are discussed.

     

Green and gentle synthesis of Cu2O nanoparticles using lignin as reducing and capping reagent with antibacterial properties

In this work, Cu₂O nanoparticles of a particular shape were prepared by an eco-friendly, gentle and low-cost synthetic method using lignin as a reducing and capping reagent. Structure and morphology of the Cu₂O nanoparticles were characterised by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction (XRD) and Fourier-transform (FT-IR) spectroscopy. The results established that Cu₂O nanoparticles coated by lignin showed a particular shape. The morphology of Cu₂O nanoparticles presented as some loose accumulation of particles just like broccoli, and the particle size range was between 100 and 200 nm. And, the XRD revealed the structure of crystalline of the Cu₂O nanoparticles. In addition, the sterilisation of Cu₂O nanoparticles on Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) was also investigated. The Cu₂O nanoparticles showed effective bactericidal activity against E. coli and S. aureus. The antibacterial rate could get 100% after 30 min with 4.0 g/L Cu₂O nanoparticles. Furthermore, the Cu₂O nanoparticles were confirmed to have low cytotoxicity.