Hybridization of carbon-dots with ZnO nanoparticles of different sizes (original) (raw)
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Effects of carbon dots on ZnO nanoparticle-based dye-sensitized solar cells
Electrochimica Acta, 2019
ZnO nanoparticles have been assessed the effects of added carbon dots (Cdots) on the performance of photovoltaic devices: ZnO(100) and ZnO(20) with particle sizes of 94 and 20 nm, respectively, were hybridized with Cdots and characterized by currentevoltage measurements under the illumination condition. The photovoltaic conversion of dye-sensitized solar cells (DSSCs) was effective for ZnO(20) superior to Zn (100) and for the incorporation of 10 wt% Cdots in the hybrid nanostructures. Moreover, when the mole ratio (ethylenediamine:citric acid) between raw materials of Cdots was 2:1, the conversion efficiency was highest (5.9%), and this value was 7 times higher than that of ZnO(20) DSSC without Cdots. Electrochemical impedance spectroscopy also showed that the charge transfer resistance property was lowest for Cdots(2:1)-hybridized ZnO(20) DSSC. It can be thus concluded that the performance of ZnO-based DSSCs is improved by the size-minimization of ZnO and the addition of adequate amount of Cdots. The effect of carbon dots was discussed based on electron transfer between ZnO and Cdots under the illumination.
Due to their applications in cosmetology, medicine, antibacterial and other fields, zinc oxide nanoparticles (ZnO-NPs) are among the nanoscale materials experiencing exponential growth. In contrast, pure ZnO-NPs have been reported to have a very large energy bandgap, a large exaction binding energy, electron-hole recombination, no visible light absorption, and poor photocatalytic activities, which limit their potential uses. ZnO-NPs can be further extended through the incorporation of trace amounts of carbon materials to engulf these problems. We investigate the photocatalytic degradation of methylene blue (MB) dye with pure ZnO-NPs infused with a limited amount of carbon dot (C-dot) materials. Consequently, adding 10% C-dot to ZnO-NPs reduced their energy bandgap from 3.1 to 2.8 eV and significantly increased their photocatalytic activity. MB was almost completely degraded (98.4%) after 60 min when 50 mg of C-dot-incorporated ZnO-NPs were added. By comparison, the nanocomposite's photocatalytic activity exceeded that of pure ZnO-NPs by more than 50%. A surface charge and stability improvement are responsible for the extraordinary photocatalytic improvement. As far as we know, this is the best-ever photocatalytic improvement achieved by incorporating a trace amount of C-dot material into pure ZnO-NPs.
Catalysts
Different nanostructured semiconducting ZnO photoanodes were prepared by Hydrothermal (HT), Co-precipitation (CoP) and Chemical Bath Deposition (CBD) methods for their use in the Dye Sensitized Solar Cells (DSSCs) in the present study. Additionally, different ZnO nanocomposites were synthesized by mixing the Carbon Nanotubes (CNTs), Graphene Oxide (GO) and their combination with the ZnO nanostructures. Scanning electron microscopy (SEM) revealed various morphologies of ZnO nanostructures and nanocomposites such as nanoflowers, nanorods, rhombohedral, cubic, and cauliflower-like nanorods, and nanorods with hexagonal symmetry. Energy Dispersive X-ray (EDX) spectra confirmed the purity of the synthesized samples. X-ray Diffraction (XRD) demonstrated the hexagonal wurtzite phase of ZnO and a minor presence of CNTs and graphene. The UV-Visible, transmittance and diffuse reflectance spectra demonstrated that the ZnO synthesized through the CBD method exhibits the highest transmittance as ...
Optical Materials, 2020
In this study, we report a facile and green chemistry technique to produce ZnO nanorods decorated with carbon nanodots (C-dots) to yield good photocatalytic for degradation of methyl blue. C-dots dispersed solution was obtained via simple carbonization of cassava peels at low temperature followed by ageing process for 6 days in absolute ethanol. The ZnO/C-dots heterostructure has been prepared by spin-coating C-dots dispersed solution onto ZnO nanorods surface. The impact of doping metal such as Co and Mn and the attachment of C-dots nanoparticles onto the surface of ZnO nanorods on their morphology, optical properties and photocatalytic activity were examined. The experimental results reveal that C-dots have successfully been attached onto the surface ZnO nanorods through strong physical interaction between C-dots and ZnO without modifying the morphology, surface area and crystallinity of ZnO nanorods. However, the energy bandgap of ZnO slightly decreases. This condition turns into increasing the charge separation efficiency of its electron-hole pairs which significantly enhances the visible light photocatalytic activity of the sample. The photodegradation rate of methyl blue was found to depend on the number of layers of C-dots. The Co doped ZnO nanorods coated with 4 layers C-dots particles was found to effectively degrade methyl blue solution compared to pristine ZnO nanorods. It is believed that high photocatalytic activity of metal doped ZnO/C-dots nanocomposite under UV light irradiation originates from their outstanding unique properties and the stimulated separation of photogenerated electron-hole pairs based on C-dots.
Journal of Materials Science: Materials in Electronics, 2018
Synthesis of carbon nanoparticles (CNPs) and their composite with ZnO has proposed for the first time by combustion of camphor and chemical precipitation method. TEM image shows the surface of ZnO covered by tiny CNPs and acts as structure directing agent that transforms ZnO nanorods to uniform spherical ZnO. CNPs play a vital role to improve the photocatalytic activity and photostability of ZnO up to five runs due to impeding the photo-corrosion of ZnO. Enhance in the photocatalytic activity of ZnO-carbon nanocomposite could be attributed to the excellent dye adsorption capacity, direct photooxidation of dye and suppression of photoinduced electron-hole recombination. The presence of CNPs in nanocomposite served as the main role in accepting the photogenerated electrons due to electronic interaction between ZnO and CNPs. The cytotoxicity studies of meristematic root tip cells of Allium cepa reveals that photocatalytically degraded products were less toxic.
Synthesis of ZnO Nanoparticles by Chemical Method and its Structural and Optical Characterization
BIBECHANA
In this report, ZnO nanoparticles (NPs) was synthesized by chemical method using Zinc Acetate dehydrate [Zn(CH3COO)2.2H2O)] as precursors and Ethanol and distilled water as solvent. Sodium hydroxide (NaOH) was used to maintain the pH and helps to establish the NPs. The NPs are characterized by XRD, UV-visible spectroscopy and SEM image analysis. The XRD characterization gives the polycrystalline nature of ZnO NPs with the size ~23 nm and ~27 nm calculated by Scherrer’s method and Williamson–Hall method respectively. The crystalline size of these NPs calculated using XRD pattern is validated by SEM image analysis. Using the UV-Visible spectrophotometer and Tauc plot method, the optical band gap of ZnO is found to be 3.35 eV. The uniform size distribution of NPs shown in SEM image and strong UV absorption shown in UV-Visible spectra indicate that thus prepared NPs are highly desirable for photo-catalytic activity and detection applications. BIBECHANA 19 (2022) 90-96
International Journal of Technology, 2015
Zinc oxide (ZnO) nanoparticles have been investigated in depth, due to their potential as a semiconductor material in dye sensitized solar cell applications. In this current research, ZnO nanostructure was synthesized using a simple precipitation technique with the addition of citric acid (C 6 H 8 O 7) as the capping agent. Various ratios of ZnO and citric acid were prepared, i.e. 1:1, 2:1, 4:1 and calcination temperatures of 150 and 400°C were used to investigate the effect of those parameters on the ZnO nanostructure and its crystallinity. The nanostructure characteristics, i.e. nanocrystallite size, crystallinity, and optical properties were determined by using x-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet visible (UV-Vis) spectroscopy, respectively. The investigation results showed that ZnO nanostructure was formed as spherical shapes and rods in the range of 19.8-30.8 nm with the lowest band gap energy (E g) of 3.15 eV obtained under conditions of a 4:1 ratio and calcined at 400°C. Considering nanostructural characteristics, the ZnO nanostructures in this study would be suitable for application as a semiconductor oxide layer in a dye sensitized solar cell.
Synthesis and Characterization of ZnO Nanoparticles
ZnO nanoparticles with particle size less than 50nm are synthesized by simple sol gel method. These nanoparticles can be used as a source layer for the extraction of electrons in heterojunction organic solar cells. Zinc acetate is used as a precursor material in this case. X-Ray powder Diffraction, Ellipsometery and Scanning Electron Microscopy are used to study the crystal structure, optical properties and surface morphology of the synthesized nanoparticles, respectively. The presence of (100), (002) and (101) planes in the XRD graphs strongly indicates that ZnO has wurtzite structure even under as-synthesized conditions. Surface morphology was studied by SEM which indicates that the nanoparticles are of spherical shape with size less than 100 nm. Large area growth of these nanoparticles is also observed with uniform size distribution. A remarkable decrease in the transmission values is observed by increasing the pH from 2 to 9. Refractive index ~ 1.5 is observed at 350nm for all of the samples except the one synthesized with pH 9.
Solar Energy Materials and Solar Cells, 2015
Zinc oxide (ZnO), tin oxide (SnO 2 ) and zinc-tin oxide (ZnO-SnO 2 ) nanostructures were successfully synthesized from vapor phase by heating well mixed various ratios of ZnO and/or SnO 2 powders with carbon in the temperature range of 1000-1200 1C in a loosely closed porcelain crucibles. The prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Various morphologies including tetrapods, nanorods, nanowires, nanobelts and nanoparticles in the size range of 150-350 nm were microscopically observed. The photocatalytic activity of the prepared samples was tested toward the degradation of 2-chlorophenol (2-CP) in water. The photo-intermediate products were determined by high performance liquid chromatography (HPLC). The produced chloride and acetate ions during the degradation process were also monitored by ion chromatography. The results showed that ZnO was the most photoactive prepared nanostructures. The order of the photoactivity is ZnO 4 SnO 2 4 ZnO-SnO 2 . Light-harvesting nanohybrids (LHNs) systems composed of the ZnO, SnO 2 and ZnO-SnO 2 nanostructures associated with the Rose Bengal as an organic dye has been employed to improve the light-harvesting performance of the cell. The open circuit-voltage (V oc ), short circuit current density (J sc ) and conversion efficiency (η) are found to be 715 mV, 17.52 mA/cm 2 and 6.74% for ZnO electrode, respectively. It is observed that the photoelectrochemical outputs for ZnO electrode increased by $ 10% in J sc and 30% in η compared with that obtained for SnO 2 and ZnO-SnO 2 electrodes, respectively. The use of branched tetrapods ZnO nanostructures improved the efficiency of DSSC significantly in presence of a low cost Rose Bengal dye compared with the commonly used N719 one. The results of DSSCs application are compatible with that obtained from photocatalysis. We believe that surface-to-volume aspect ratio, morphology and type of combination have a great effect on the photoelectrochemical properties.