Facile fabrication of functionalized graphene sheets (FGS)/ZnO nanocomposites with photocatalytic property

Functionalized graphene sheets (FGS)/ZnO nanocomposites were fabricated via thermal treatment method, using graphene oxide as a precursor of graphene, Zn(NH(3))(4)CO(3) as a precursor of zinc oxide, and poly(vinyl pyrrolidone) as an intermediate to combine zinc with carbon materials. Thermogravimetric analysis, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to characterize crystal structure and morphology of FGS/ZnO nanocomposites. It was shown that the well-dispersed ZnO nanoparticles were deposited on FGS homogeneously. The composites exhibited photocatalytic activity to decompose rhodamine 6G efficiently under low-power ultraviolet (UV) light. This facile and low-cost method makes the composite a perfect candidate in applications of catalysis and other areas.     

Transparent and flexible ultraviolet photodetectors based on colloidal ZnO quantum dot/graphene nanocomposites formed on poly(ethylene terephthalate) substrates

Transparent colloidal ZnO quantum-dot (QD)/graphene nanocomposites were formed on poly(ethylene terephthalate) (PET) substrates. Ultraviolet (UV)–visible absorption spectra showed a shoulder peak around 350 nm corresponding to the absorption of ZnO QDs. Optical transmittance of the ZnO QD/graphene/PET multilayer was approximately 80%. High-resolution transmission electron microscopy images showed that the ZnO QDs were distributed along the circumferences of the surfaces on the graphene layers. Current–voltage and current–time measurements on the UV photodetector after bending at 300 K exhibited the ON/OFF switching states and stability resulting from the light-induced conductivity of the flexible graphene layer.     

Effect of ZnO nanoparticles doped graphene on static and dynamic mechanical properties of natural rubber composites

In this work, effect of ZnO nanoparticles doped graphene (Nano-ZnO–GE) on static and dynamic mechanical properties of natural rubber composites were studied. Nano-ZnO–GE was synthesized by sol–gel method and thermal treatment. With the incorporation of nano-ZnO–GE into the matrix, the mechanical properties of NR nanocomposite significantly improved over that of NR composite containing with 5 phr of conventional-ZnO. The results demonstrated that the presence of nano-ZnO on the surface of graphene sheets not only conduces to suppressing aggregation of graphene sheets but also acts as a more efficient cure-activator in vulcanization process, with the formation of excellent crosslinked network at low nano-ZnO–GE content. This work also showed that NR/Nano-ZnO–GE nanocomposites exhibited higher wet grip property and lower rolling resistance compared with NR/Conventional-ZnO composite, which makes nano-ZnO–GE very competitive for the green tire application as a substitute of conventional-ZnO, enlarging versatile practical application to prepare high-performance rubber nanocomposites.     

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.     

Basic zinc carbonate as a precursor in the solvothermal synthesis of nano-zinc oxide

ZnO nanoparticles were synthesized solvothermally in various diols (ethylene glycol, di(ethylene glycol), tetra(ethylene glycol), 1,2-propanediol, 1,4-butanediol), using basic zinc carbonate (2ZnCO₃·3Zn(OH)₂) as a precursor for the first time. Since ZnCO₃ was sparingly soluble in diols the transformation reaction proceeded at a low reaction rate. Ethylene glycol was found as the most suitable medium among five diols studied yielding the smallest ZnO particles (~ 55 nm) and short reaction time, t_r (2 h). Diols with shorter chain length produced smaller ZnO particles. p-Toluene sulfonic acid (p-TSA) acted as a catalyst and reduced t_r from 8 h to 2 h in concentration of 0.02 M. Optimum reaction conditions for the synthesis in ethylene glycol were 185 °C and 2 h. At higher p-TSA concentrations (0.04–0.08 M) the size of ZnO particles was reduced from 500–800 nm to 50–100 nm and crystallite size to 25–30 nm. Benzene sulfonic acid (BSA) and inorganic bases (LiOH, NaOH, and KOH) also showed catalytic activities. Raman and photoluminescence spectroscopies revealed high concentration of defects on ZnO surface causing the emission of visible light and giving this type of ZnO higher potential in various (opto)-electronic application in comparison to Zn(II) acetate based ZnO.     

Cu doped ZnO nanoparticle sheets

Cu doped ZnO nanoparticle sheets were synthesized via a proposed solution route with mixed Zn(NO₃)₂ and Cu(NO₃)₂ precursors at a low temperature of 95 °C. Scanning electron microscopy, transmission electron microscopy, and X-ray energy dispersive spectrometry results demonstrate that the nanostructues synthesized by solutions with higher Cu(NO₃)₂ concentration are nanoparticle sheets comprised of uniform Cu doped ZnO nanoparticles with diameters around 20 nm. Room-temperature photoluminescence spectra of the nanoparticle sheets show tunable near band emissions centered at 390–405 nm and strong yellow emissions at 585–600 nm. Absorbance spectra show gradual redshift in the UV range with the increase of Cu concentrations in the ZnO nanomaterials. The study provides a simple and efficient route to prepare Cu doped ZnO nanomaterials at low temperature. The as-synthesized products with both violet and yellow emissions are promising for white light-emitting diode applications.     

Hydrothermal synthesis of graphene-ZnS quantum dot nanocomposites

ZnS nanodots highly dispersed on the surfaces of graphene sheets were successfully synthesized via an easy hydrothermal method by using Na₂S as reducing agent as well as sulfide source. The reduction of graphite oxide (GO) to graphene was accompanied by the deposition of ZnS particles on the surface of graphene sheets. The results of X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) demonstrate the efficient reduction of GO to graphene sheets. The morphology characterization of the sample shows a wrinkled paper-like structure of the graphene sheets decorated with ZnS nanoparticles. Moreover, photoluminescence (PL) measurement shows a smooth spectrum, indicating fewer defects in the composite.     

One‐Step Formation of a Single Atomic‐Layer Transistor by the Selective Fluorination of a Graphene Film

In this study, the scalable and one‐step fabrication of single atomic‐layer transistors is demonstrated by the selective fluorination of graphene using a low‐damage CF₄ plasma treatment, where the generated F‐radicals preferentially fluorinated the graphene at low temperature (<200 °C) while defect formation was suppressed by screening out the effect of ion damage. The chemical structure of the C–F bonds is well correlated with their optical and electrical properties in fluorinated graphene, as determined by X‐ray photoelectron spectroscopy, Raman spectroscopy, and optical and electrical characterizations. The electrical conductivity of the resultant fluorinated graphene (F‐graphene) was demonstrated to be in the range between 1.6 kΩ/sq and 1 MΩ/sq by adjusting the stoichiometric ratio of C/F in the range between 27.4 and 5.6, respectively. Moreover, a unique heterojunction structure of semi‐metal/semiconductor/insulator can be directly formed in a single layer of graphene using a one‐step fluorination process by introducing a Au thin‐film as a buffer layer. With this heterojunction structure, it would be possible to fabricate transistors in a single graphene film via a one‐step fluorination process, in which pristine graphene, partial F‐graphene, and highly F‐graphene serve as the source/drain contacts, the channel, and the channel isolation in a transistor, respectively. The demonstrated graphene transistor exhibits an on‐off ratio above 10, which is 3‐fold higher than that of devices made from pristine graphene. This efficient transistor fabrication method produces electrical heterojunctions of graphene over a large area and with selective patterning, providing the potential for the integration of electronics down to the single atomic‐layer scale.     

Synthesis of zinc oxide/silica composite nanoparticles by flame spray pyrolysis

Zinc oxide (ZnO)/silica (SiO₂) composite nanoparticles were made by flame spray pyrolysis. The effects of the Zn/Si ratio on particle properties were examined and compared with those of the pure ZnO and SiO₂ particles made at the same conditions. Polyhedral aggregates of nano-sized primary particles were obtained in all experiments. The mixed-oxide primary particle size was smaller than that of pure oxides. The primary particles consisted of ZnO nano-crystals and amorphous SiO₂, as seen by high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD) analysis using the fundamental parameter approach. The XRD size of ZnO was controlled from 1.2 to 11.3 nm by the initial precursor composition and it was consistent with HR-TEM. The composite particles exhibited an excellent thermal stability and little crystalline growth of ZnO (e.g., from 1.9 to 2.2 nm) was observed even after calcination at 600°C.     

Preparation of monodisperse ZnO/SiO2 composite particles using spray drying with an anionic surfactant template and their photoluminescence characteristics

The photoluminescence (PL) characteristics of ZnO/SiO₂ composite particles were investigated. ZnO/SiO₂ composite particles were synthesized utilizing the consecutive sol–gel spray drying method by incorporating sodium lauryl sulfate (SLS) as a particle morphology control agent. The effect of SLS concentration and ZnO ratio on precursors was studied further on the composite particle morphology and PL performance. Elevating the SLS concentration exhibited a reduction in the particle diameter and an increase in particle uniformity. The particle diameter without SLS was 6.18 µm and reduced to 2.6 µm with the addition of SLS at 3 critical micelle concentrations (CMC). The decrease in ZnO concentration also reduced the particle diameter of the ZnO/SiO₂ composite to 1.74 µm at a ZnO concentration of 25% mol. In addition, the increase in the excitation wavelength from 230 nm to 320 nm indicates a shift in the peak emission intensity at higher wavelengths from 467 nm to 645 nm. The excitation wavelength-dependent photoluminescence phenomenon was exhibited by incorporating silica into the ZnO precursor pre- and post-drying to deliver composite particles. The addition of silica to the composite particles can augment the PL emission intensity without causing a shift in the PL emission peaks when excited at the same wavelength. The 25% mol ZnO composite particles with the addition of SLS 3 CMC had the highest PL emission intensity. The amount of silica nanoparticles sufficient to trap the ZnO nanoparticles in the droplet is an important factor besides the size and uniformity of the particles, which causes the high intensity of PL emission.     

Depositing ZnO nanoparticles onto graphene in a polyol system

In this work, graphene-ZnO nanocomposites were prepared through a one-step solvothermal approach, using ethylene glycol as the solvent and reducing agent. ZnO particles can attach on the surfaces and edges of graphene oxide sheets. The in situ formed ZnO nanoparticles were randomly decorated on the surfaces of graphene oxide sheets, which were simultaneously reduced directly capable of forming the graphene sheets by the ethylene glycol. In addition, photoluminescence spectra of graphene-ZnO nanocomposites display the fluorescence quenching property.     

Preparation and characterization of TiO2/ZnO composite coating on carbon steel surface and its anticorrosive behavior in seawater

The TiO₂/ZnO composite coatings with various atomic ratios of Ti to Zn were prepared on carbon steel surface via sol–gel process followed by thermal treatment at different temperature. The as-prepared coatings were characterized through X-ray diffraction method, scanning electron microscopy, energy dispersive X-ray spectroscopy, and their anticorrosive behaviors in sterilized seawater were electrochemically assessed. The obtained coatings were quite thin even for the 8-layer samples. The thermal treatment at 500 °C led to severe oxidation of the steel substrate. The incorporation of ZnO avoided crack formation and refined the particles of the composite coatings. The electrochemical measurements of both the potentiodynamic polarization curves and electrochemical impedance spectroscopy revealed a substantial protection of the coatings for the substrate. In particular, the 8-layer TiO₂/ZnO composite coatings with atomic molar ratios of Ti to Zn of 1/1 and 1/3 after thermal treatment at 500 °C showed better anticorrosive performances than others.     

A novel route to ZnO nanorods with small diameters of 20 nm

The ZnO nanorods with small diameters of 20 nm were prepared successfully by an easy “in situ consumed template” route. In the synthesis, Zn(Ac)₂ were used as Zn source and dodecanethiol (DT) was used as coordinated agents in ethanol solvent. The samples were characterized detailed by XRD, TEM and IR techniques. The results indicated that the ZnO rods were uniform in diameters with good crystallinity. Time-dependent experiments indicated that the ZnO rods are grown within the Zn–DT complex (a complex composed of Zn and DT) that was formed at the beginning of the reaction. With prolonging the reaction time, the Zn–DT “template” was gradually in situ consumed and transformed into ZnO, and finally, the ZnO nanorods with diameters of 20 nm were obtained. The method here provides the new route for ZnO nanorods with small diameters.     

Preparation of Au nanoparticle-decorated ZnO/NiO heterostructure via nonsolvent method for high-performance photocatalysis

In this paper, we present a novel physical (or nonsolvent) route to fabricate a kind of Au/ZnO/NiO heterostructure photocatalytic composite. That is, a Zn layer upon Ni foam substrate is prepared by pulse electrodeposition, then the ZnO nanoneedle/NiO heterostructural composite is obtained via thermal oxidation, and at last, the composite is modified with the dispersively deposited Au nanoparticles (Au NPs) by ion sputtering. The surface plasmon resonance effect of the Au NPs significantly enhances the light absorption. Meanwhile, the Au NPs form a Schottky barrier with ZnO nanoneedles and further inhibit the recombination of photogenerated electron–hole pairs. In addition, due to the nonsolvent conditions, the introduction of impurities is avoided, and thus it shows strong photocatalytic stability. The experimental results reveal that, the optimized Au/ZnO/NiO composite exhibits up to two times photocatalytic performance on RB degradation and higher stability than that of regular ZnO/NiO composite. The present experimental strategy can also be used for other noble metals, and it is expected to have important application prospects in the fields of environmental purification, solar cells, hydrogen generation, etc.     

ZnO Film UV Photodetector with Enhanced Performance: Heterojunction with CdMoO4 Microplates and the Hot Electron Injection Effect of Au Nanoparticles

A novel CdMoO₄–ZnO composite film is prepared by spin‐coating CdMoO₄ microplates on ZnO film and is constructed as a heterojunction photodetector (PD). With an optimized loading amount of CdMoO₄ microplates, this composite film PD achieves a ≈18‐fold higher responsivity than pure ZnO film PD at 5 V bias under 350 nm (0.15 mW cm⁻²) UV light illumination, and its decay time shortens to half of the original value. Furthermore, Au nanoparticles are then deposited to modify the CdMoO₄–ZnO composite film, and the as‐constructed photodetector with an optimized deposition time of Au nanoparticles yields an approximately two‐fold higher photocurrent under the same condition, and the decay time reduces by half. The introduced CdMoO₄ microplates form type‐II heterojunctions with ZnO film and improve the photoelectric performance. The hot electrons from Au nanoparticles are injected into the CdMoO₄–ZnO composite film, leading to the increased photocurrent. When the light is off, the Schottky barriers formed between Au nanoparticles and CdMoO₄–ZnO composite film block the carrier transportation and accelerate the decay process of current. The study on Au‐nanoparticle‐modified CdMoO₄–ZnO composite film provides a facile method to construct ZnO film based PD with novel structure and high photoelectric performance.     

Synthesis of visible-light-responsive Fe(III)-doped TiO2 films using graphene oxide-based composite sheets as sacrificial building blocks

Graphene oxide sheets have been utilized as both carriers and sacrificial building blocks to prepare freestanding Fe(III)-doped TiO₂ composite films. First, graphene oxide sheets are decorated by TiO₂ particles, and the as-obtained products are further modified by Fe(III) precursors, forming relatively uniform composite sheets. Assembling of these composite sheets enables different substances (Ti and Fe) to be distributed uniformly in the as-formed bulk films, which results in the formation of homogeneous freestanding Fe(III)-doped TiO₂ composite films under calcinations. Furthermore, the contents of Fe(III) in TiO₂ films can be controlled easily by adjusting deposition amount of Fe(III) precursors in graphene oxide-TiO₂ composite sheets. UV–vis diffuse reflectance results and photocurrent tests indicate that addition of Fe can enhance visible light responses of TiO₂ films. At certain doping amount of Fe(III), the as-prepared TiO₂ films display the strongest photocurrent signals under visible light irradiation.     

Highly enhanced photocatalytic performance of Zn(1−x)MgxO/rGO nanostars under sunlight irradiation synthesized by one-pot refluxing method

The current research presents a simple, coast-effective, and one-pot refluxing method to synthesize Zn_(1?x)Mg_xO nanostructures, which were decorated on graphene oxide (GO) sheets. In the first step, the effect of refluxing time on structure and morphology of the pristine ZnO nanostructures was investigated. X-ray diffraction (XRD) patterns indicated that the pristine ZnO nanostructures were formed after 8?h of the refluxing process. Field emission electron microscope (FESEM) images showed that stars-shape ZnO nanostructures were formed after 10?h of refluxing time. Further refluxing process for 12?h showed that morphology and structure of the ZnO nanostructures were not changed. However, after 14?h additional phases were formed. Therefore, ZnO and Zn_(1?x)Mg_xO nanostars that were decorated on GO sheets were synthesized during 10?h. XRD patterns indicated that GO sheets were changed into reduced graphene oxides (rGO) during the refluxing process. Transmission electron microscope (TEM) images revealed that ZnO nanostars with more branches were decorated on rGO sheets. However, the TEM images showed that the morphology of Zn_xMg_(1?x)O/rGO nanocomposites were changed significantly with the increase of Mg concentration up to 6%. Photocatalytic performance of the products was examined under natural sunlight irradiation. The results showed that the rGO and Mg concentrations had significant roles in the photocatalytic performance of ZnO nanostars. The concentrations of Mg and rGO increased up to 4% were the optimum concentration for enhancing photocatalytic performance of Zn_(1?x)Mg_xO/rGO nanocomposites. In addition, room temperature photoluminescence (PL) spectroscopy and photocurrent measurement results indicated that Mg and rGO with optimum concentration caused decrease of electron-hole recombination rate.     

One-step hydrothermal synthesis,characterization and visible-light catalytic property of Ag-reduced graphene oxide composite

In this paper, a nanocomposite consisting of Ag nanoparticles and reduced graphene oxide sheets was synthesized via a one-step hydrothermal method using glucose as a reducing agent. The as-prepared sample was characterized systematically, and the results indicated that the graphene oxide was reduced and an Ag-reduced graphene oxide hybrid material was formed. It was shown that the as-prepared Ag-reduced graphene oxide was in a layered structure stacked by reduced graphene oxide sheets. The Ag nanoparticles decorated on the reduced graphene oxide sheets. The analysis revealed that there was strong interaction between the Ag nanoparticles and reduced graphene oxide sheets. A photodegradation study was also performed on the Ag-reduced graphene oxide composite. It showed that the composite exhibited a high catalytic activity for the photodegradation of Rhodamine B pollutant under visible-light irradiation, which made Ag-reduced graphene oxide a promising candidate as photocatalyst for Rhodamine B.     

Fabrication of novel ZnO/MnWO4 nanocomposites with p-n heterojunction: Visible-light-induced photocatalysts with substantially improved activity and durability

We report, for the first time, binary ZnO/MnWO₄ nanocomposites with p-n heterojunction fabricated by a simple ultrasonic-calcination route. The phase structure, morphology, and optical along with textural properties were comprehensively characterized. The photocatalytic performance was studied via degradations of rhodamine B, methyl blue and methyl orange (RhB, MB, MO), and fuchsine pollutants under visible-light illumination. The ZnO/MnWO₄ nanocomposites exhibited better photocatalytic performance than their single components and the nanocomposite with 30?wt% MnWO₄ showed the highest activity. Photocatalytic performance of this nanocomposite is 22.5, 17.7, 26.8, and 23.9 times higher than that of the ZnO sample in degradations of RhB, MB, MO, and fuchsine dyes, respectively. The improved photocatalytic performance was ascribed to the formation of p-n heterojunction between ZnO and MnWO₄ with high charge separation efficiency as well as strong visible-light absorption ability. The possible mechanism for the improved photocatalytic performance was proposed. This study revealed that the novel ZnO/MnWO₄p-n heterojunction can act as a promising visible-light-active photocatalyst for environmental applications.     

Flower-like zinc oxide deposited on the film of graphene oxide and its photoluminescence

The graphene oxide films have been fabricated by simply filtering the graphene oxide solution through the micropore filter. Then the flower-like ZnO grows on the graphene layer by immersing the seed-coated graphene oxide films in the dilute growing solution containing NH₃·H₂O and Zn(NO₃)₂·6H₂O. The morphologies of the as-obtained ZnO deposited on the graphene oxide layer are characterized by using scanning electron microscope (SEM), X-ray powder diffraction (XRD) and photoluminescence (PL). The formation mechanism of the flower-like ZnO has also been investigated. The results show that the morphology of the finally-obtained ZnO is tunable by seeds, the concentration of growing solution and the reaction time.