Graphene Zinc Oxide Research Articles

UV-assisted synthesis of reduced graphene oxide zinc sulfide composite with enhanced photocatalytic activity

Abstract We report the ultra violet (UV) light assisted photocatalytic reduction of Graphene Oxide (GO) in aqueous suspension by accepting the photo induced electrons from Zinc Sulfide (ZnS) and simultaneous synthesis of RGO-ZnS composite. The XRD and FTIR studies authenticate the reduction of GO and synthesis of RGO-ZnS composite. The reduction is also confirmed by Raman spectroscopy. The RGO-ZnS composite shows an enhancement of photo catalytic activity in compared to ZnS towards degradation of Rhodamine B under UV light irradiation. Enhanced photocatalytic degradation is attributed to the synergistic effect between favorable matching of the conduction band of ZnS to the work function of conductive RGO. The recycled use of RGO-ZnS composite does not noticeably decrease its photodegradation efficiency. The composite synthesized via photocatalytic reduction process not only provide us to control the reduction of GO but also opens up new avenues to synthesis photo sensitive RGO based composite materials for optoelectronic devising.

Graphene-ZnO nanocomposite for highly efficient photocatalytic degradation of methyl orange dye under solar light irradiation

A facile synthesis of graphene oxide-zinc oxide nanocomposite (GO-ZnO) was performed by using wet chemical method of graphene oxide and zinc acetate precursors. The nanocomposite was characterized and intercalated with Raman spectroscopy, FE-SEM, TEM, SAED and EDAX. The crystalline nature was studied from P-XRD, and surface area of the sample was analyzed by BET. The chemical composition was explained in the light of XPS phenomenon. The photo electron-excitation (PL) studies were conducted for understanding the photocatalytic mechanism, and photocatalytic degradation of methyl orange was studied by using UV-VIS spectrophotometer. We investigated the photocatalytic activity involving GO-ZnO nanocomposite besides checking the re-stability of the composite. Significant high-performance photocatalytic activity of GO-ZnO nanocomposite was exhibited on methyl orange degradation under solar light.

Microwave assisted facile hydrothermal synthesis and characterization of zinc oxide flower grown on graphene oxide sheets for enhanced photodegradation of dyes

Microwave assisted hydrothermal process of synthesis of ZnO–GO nanocomposite by using ZnCl2 and NaOH as precursors is being reported first time. In this investigation, a novel route to study on synthesis, interaction, kinetics and mechanism of hybrid zinc oxide–graphene oxide (ZnO–GO) nanocomposite using microwave assisted facile hydrothermal method has been reported. The results shows that the ZnO–GO nanocomposite exhibits an enhancement and acts as stable photo-response degradation performance of Brilliant Yellow under the UV light radiation better than pure GO and ZnO nanoparticles. The microwave exposure played a vital role in the synthesis process, it facilitates with well define crystalline structure, porosity and fine morphology of ZnO/GO nanocomposite. Different molar concentrations of ZnO precursors doped to GO sheets were been synthesized, characterized and their photodegradation performances were investigated. The optical studies by UV–vis and Photo Luminescence shows an increase in band gap of nanocomposite, which added an advantage in photodegradation performance. The in situ flower like ZnO nano particles are were densely decorated and anchored on the surfaces of graphene oxide sheets which aids in the enhancement of the surface area, adsorption, mass transfer of dyes and evolution of oxygen species. The nanocomposite having high surface area and micro/mesoporous in nature. This structure and morphology supports significantly in increasing photo catalytic performance legitimate to the efficient photosensitized electron injection and repressed electron recombination due to electron transfer process with GO as electron collector and transporter dependent on the proportion of GO in ZnO/GO composite.

Preparation of Zinc Oxide-Graphene Composite Modified Electrodes for Detection of Trace Pb(II)

ZnO nanotubes were prepared via electrospinning Zn(Ac)2-polyacrylonitrile-polyvinyl pyrrolidone precursor, followed by thermal decomposition of the above polymers from the precursor fibers. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) characterization confirmed that the as-prepared ZnO nanofibers presented the hollow nanotube form, which was composed of ZnO nanoparticles with the size of about 40 nm in wurtzite crystal structure. By mixing with reduced grapheme oxide (RGO), the obtained ZnO-RGO composite modified glassy carbon electrode (ZnO-RGO/GCE) was successfully constructed by drop-coating, and used for the determination of Pb2+ in water. The sensitive response of the ZnO-RGO/GC electrode to Pb2+ in solution was demonstrated by square wave stripping voltammetry, with the response potential at −0.4 V. Under the optimized conditions, a good linear relationship between peak current and Pb2+ concentration was obtained in the range of 2.4 × 10−9–4.8 × 10−7 M (R = 0.9970) by 10 min preconcentration at −1.0 V in 0.1 M HAc-NaAc buffer solution (pH 4.6). The detection limit was 4.8 × 10−10 M (S/N ≥ 3). The ZnO-RGO/GC electrode had good stability. The practical analytical application of the ZnO-RGO modified electrode was assessed by the measurement of the actual water sample and the result was consistent with that obtained by ICP-MS.

Synthesis of uniformly distributed single- and double-sided zinc oxide (ZnO) nanocombs

Uniformly distributed single- and double-sided zinc oxide (ZnO) nanocomb structures have been prepared by a vapor–liquid–solid technique from a mixture of ZnO nanoparticles and graphene nanoplatelets. The ZnO seed nanoparticles were synthesized via a simple precipitation method. The structure of the ZnO nanocombs could easily be controlled by tuning the carrier-gas flow rate during growth. Higher flow rate resulted in the formation of uniformly-distributed single-sided comb structures with nanonail-shaped teeth, as a result of the self-catalysis effect of the catalytically active Zn-terminated polar (0001) surface. Lower gas flow rate was favorable for production of double-sided comb structures with the two sets of teeth at an angle of ~110° to each other along the comb ribbon, which was attributed to the formation of a bicrystal nanocomb ribbon. The formation of such a double-sided structure with nanonail-shaped teeth has not previously been reported.

Kinetic Study on Mutagenic Chemical Degradation through Three Pot Synthesiszed Graphene@ZnO Nanocomposite.

The study was taken up with the objective to synthesize graphene-zinc oxide nano particles (NPs) nanocomposite (Gr@ZnO-Nc) via In-situ synthesis method. The structural, optical, thermal, electrical and photocatalytic properties of the synthesized Gr@ZnO-Nc were studied. The characterization data confirmed that the ZnO NPs were successfully incorporated into the graphene sheets. Further, TGA/DTA results exhibited an enhanced thermal stability of the Gr@ZnO-Nc compared with the graphene. The Gr@ZnO-Nc, graphene sheets were uniformly wrapped by ZnO NPs, which can protect graphene and delay their oxidation in air. The synthesized Gr@ZnO-Nc was used for the efficient photodegradation of a carcinogenic methyl orange (MO) dye. The results exhibited promising photodegradation of the MO dye under UV light irradiation through the production of reactive oxygen species (ROS). The promising effect of Gr@ZnO-Nc on the photodegradation properties was conferred by the large surface area which increased adsorption capacity, and the strong electron transfer ability. Thus, it is encouraging to conclude that the synthesized Gr@ZnO-Nc has environmental significance with its utility in remediation in the hazardous MO dye.

Mechanistic study of the visible-light-driven photocatalytic inactivation of bacteria by graphene oxide–zinc oxide composite

The visible-light-driven (VLD) photocatalytic activity of graphene oxide–zinc oxide (GO–ZnO) composite prepared by a simple hydrothermal method was evaluated toward the inactivation of Escherichia coli K-12. The results showed that GO–ZnO composite had excellent VLD photocatalytic bacterial inactivation activity, comparing with those of ZnO and GO, which was attributed to the strong interaction between ZnO and GO in the composite. Accordingly, an interaction induced VLD photocatalytic inactivation mechanism of the strong interaction of GO with ZnO within the GO–ZnO composite was proposed. GO served as a photosensitizer and facilitated the charge separation and transfer, thus boosted the massive production of reactive oxygen species such as OHbulk, which was identified as the major reactive species from conduction band of ZnO, and resulted in a remarkable enhancement of bacterial inactivation efficiency. Moreover, GO–ZnO composite showed obviously superior photocatalytic bacterial inactivation within 10min under natural solar light irradiation, indicating that GO–ZnO composite has great potential in wastewater treatment and environmental protection.

Electrical and photoresponse properties of graphene oxide:ZnO/Si photodiodes

The nanocomposites of zinc oxide/graphene oxide (ZnO-GO) were synthesized to fabricate the photodiodes. The ZnO-GO/p-Si and ZnO-GO/n-Si diodes were prepared for various GO contents. The electrical characteristics of the ZnO-GO/p-Si and ZnO-GO/n-Si diodes were analyzed under dark and light illuminations. The photocurrent of ZnO-GO/p-Si and ZnO-GO/n-Si diodes increases with increasing GO content. The ZnO-GO/p-Si diode having 0.03 M ratio of GO:ZnO exhibited the highest photoresponsivity with 0.5 A/W under 100 mW/cm2. It is evaluated that ZnO-GO composites can be used in fabrication of high photosensitivity diodes.

ZnO nanoparticles decorated on graphene sheets through liquid arc discharge approach with enhanced photocatalytic performance under visible-light

We present an innovative approach for synthesis of zinc oxide–graphene (ZnO–G) hybrid nanostructures through combination of improved hummer and arc discharge methods in liquid. A detailed study of the considerable visible-light photocatalytic activities of these nanostructures for the degradation of Phenol red (PR) and Methyl orange (MO) as standard organic compounds under the irradiation of 90W halogen light for 2h has been performed. The ZnO–G nanostructures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer Emmett Teller (BET) and ultra violet–visible absorption spectroscopy (UV–vis). The results revealed that the ZnO–G nanostructures extended the light absorption spectrum toward the visible region and remarkably enhanced the photodegradation of standard dyes under visible-light irradiation. It has been confirmed that the ZnO–G nanostructures could be excited by visible-light (E∼2.6eV). The major enhancement in the photocatalytic activity of ZnO–G nanostructures under visible-light irradiation can be attributed to the effect of electron transport among ZnO nanoparticles (NPs) and graphene sheets. A mechanism for photocatalytic degradation of organic pollutants over ZnO–G photocatalyst was proposed based on our observations.

Electrostatically Gated Graphene-Zinc Oxide Nanowire Heterojunction.

This paper presents an electrostatically gated graphene-ZnO nanowire (NW) heterojunction for the purpose of device applications for the first time. A sub-nanometer-thick energy barrier width was formed between a monatomic graphene layer and electrochemically grown ZnO NWs. Because of the narrow energy barrier, electrons can tunnel through the barrier when a voltage is applied across the junction. A near-ohmic current-voltage (I-V) curve was obtained from the graphene-electrochemically grown ZnO NW heterojunction. This near-ohmic contact changed to asymmetric I-V Schottky contact when the samples were exposed to an oxygen environment. It is believed that the adsorbed oxygen atoms or molecules on the ZnO NW surface capture free electrons of the ZnO NWs, thereby creating a depletion region in the ZnO NWs. Consequentially, the electron concentration in the ZnO NWs is dramatically reduced, and the energy barrier width of the graphene-ZnO NW heterojunction increases greatly. This increased energy barrier width reduces the electron tunneling probability, resulting in a typical Schottky contact. By adjusting the back-gate voltage to control the graphene-ZnO NW Schottky energy barrier height, a large modulation on the junction current (on/off ratio of 10(3)) was achieved.

Improvement of solution based conjugate polymer organic light emitting diode by ZnO–graphene quantum dots

In this paper conjugate polymer organic light emitting diode (OLED) device is improved by the insertion of electron transport layer of zinc oxide–graphene quantum dots (QDs). Prior to device fabrication, ZnO–graphene QDs thin film is thoroughly characterized by X-ray diffraction, X-ray photoelectron spectroscopy and field emission scanning electron microscopy. Aluminum is employed as the cathode of the device while ITO is used as the anode. Conjugate polymer layer of Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) and Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] are used as hole injection layer and emissive layer respectively. The device performance is analyzed by the current–voltage method. The hybrid OLED is showing four times higher current densities and improved turn on voltage of 2.5 V while the device without QD has turn on voltage of 3.5 V. Improvement of luminance is achieved by the insertion of QD layer at color coordinates of (0.56, 0.43).

Facile electrochemical assisted synthesis of ZnO/graphene nanosheets with enhanced photocatalytic activity

In the present study, an electrochemical exfoliation technique was used to synthesize a series of zinc oxide/graphene (ZnO/Gr) nanocomposites using different concentrations of zinc nitrate in an electrolyte solution.

The effect of peripheral substituents attached to phthalocyanines on the third order nonlinear optical properties of graphene oxide–zinc(ii)phthalocyanine hybrids

Both kinds of GO–ZnPc hybrid materials exhibit transformation of the NLO response from SA to RSA, and the β value of GO–ZnPc(DG)4 is larger than that of GO–ZnPc(TD)4 because of the stronger electron-donating peripheral substituents.

One-step synthesis of magnetic 1,6-hexanediamine-functionalized reduced graphene oxide–zinc ferrite for fast adsorption of Cr(vi)

A one-step solvothermal method was developed to prepare nearly cubic ZnFe2O4 nanoparticles loaded on 1,6-hexanediamine-functionalized reduced graphene oxide (HDA–RGO–ZnFe2O4) for fast removal of Cr(vi).

Graphene-zinc oxide nanorod nanocomposite as photocatalyst for enhanced degradation of dyes under UV light irradiation

Nanocomposite of zinc oxide nanorods(ZnONR) and reduced graphene(RGO) oxide has been prepared and characterized by XRD, TEM, UV–vis and spectroflurometric techniques. The nanocomposite material is found to be an efficient photocatalyst for degradation methylene blue(MB), methyl orange(MO) and their mixture at room temperature. The electron-hole pair recombination in the prepared material has been decreased as observed from photoluminescence(PL) spectral study. The excitation of both ZnONR and methylene blue occurs during photodegradation and the generated electrons are transferred to the RGO. The oxidation of dyes occurs by path I and path II as a result excitation of MB and ZnONR respectively and these electrons are transfereed to the RGO. The excitation of MB during leads to the photodegradation MO in absence of composite through path I as evidenced by its PL spectra.

A novel three-dimensional interconnected graphene–zinc oxide nanowall via one-step co-electrochemical deposition

One-step co-electrodeposition was applied to prepare graphene–zinc oxide nanowalls (GZNWs) composite, where graphene oxide was electrochemically reduced and zinc oxide was electrodeposited simultaneously. The morphologies and the electrochemical properties of GZNWs were obviously influenced by the electrodeposition time. The contrast experiments illuminate that GZNWs presented superior electrochemical activity.

Graphene oxide-zinc oxide nanocomposite as channel layer for field effect transistors: effect of ZnO loading on field effect transport.

The effects of ZnO on graphene oxide (GO)-ZnO nanocomposites are investigated to tune the conductivity in GO under field effect regime. Zinc oxides with different concentrations from 5 wt % to 25 wt % are used in a GO matrix to increase the conductivity in the composite. Six sets of field effect transistors with pristine GO and GO-ZnO as the channel layer at varying ZnO concentrations were fabricated. From the transfer characteristics, it is observed that GO exhibited an insulating behavior and the transistors with low ZnO (5 wt %) concentration initially showed p-type conductivity that changes to n-type with increases in ZnO loading. This n-type dominance in conductivity is a consequence of the transfer of electrons from ZnO to the GO matrix. From X-ray photoelectron spectroscopic measurements, it is observed that the progressive reduction in the C-OH oxygen group took place with increases in ZnO loading. Thus, from insulating GO to p- and then n-type, conductivity in GO could be achieved with reduction in the C-OH oxygen group by photocatalytic reduction of GO with varying degrees of ZnO. The restoration of sp(2) electron network in the GO matrix with the anchoring of ZnO nanostructures was observed from Raman spectra. From UV-visible spectra, the band gap in pristine GO was found to be 3.98 eV and reduced to 2.8 eV with increase in ZnO attachment.

Effect of nitrogen doping on wetting and photoactive properties of laser processed zinc oxide-graphene oxide nanocomposite layers

Zinc oxide-graphene oxide nanocomposite layers were submitted to laser irradiation in air or controlled nitrogen atmosphere using a frequency quadrupled Nd:YAG (λ = 266 nm, τFWHM ≅ 3 ns, ν = 10 Hz) laser source. The experiments were performed in air at atmospheric pressure or in nitrogen at a pressure of 2 × 104 Pa. The effect of the irradiation conditions, incident laser fluence value, and number of subsequent laser pulses on the surface morphology of the composite material was systematically investigated. The obtained results reveal that nitrogen incorporation improves significantly the wetting and photoactive properties of the laser processed layers. The kinetics of water contact angle variation when the samples are submitted to laser irradiation in nitrogen are faster than that of the samples irradiated in air, the surfaces becoming super-hydrophilic under UV light irradiation.

Synthesis and nonlinear optical properties of reduced graphene oxide hybrid material covalently functionalized with zinc phthalocyanine

A reduced graphene oxide–zinc phthalocyanine (RGO–ZnPc) hybrid material with good dispersibility has been prepared by covalent functionalization method, based on the initial covalent linkage of ZnPc to GO and subsequent in situ reduction of GO moiety to RGO during mild thermal treatment in DMF solvent. The microscopic structure, morphology and photophysical properties of resultant RGO–ZnPc hybrid are characterized. The nonlinear optical (NLO) properties of the RGO–ZnPc hybrid are also investigated using the Z-scan technique at 532nm with 4ns laser pulses. The results show that the efficient functionalization and reduction of GO make RGO–ZnPc hybrid possess much larger NLO properties and optical limiting performance than those of individual GO, ZnPc and the GO–ZnPc hybrid. It can be ascribed to a combination of different NLO absorption mechanisms for RGO–ZnPc hybrid, including two-photon absorption originating from the sp3 domains, saturable absorption from the sp2 carbon clusters and excited state absorption from numerous localized sp2 configurations in RGO moiety, reverse saturable absorption arising from ZnPc moiety and the contribution of efficient photo-induced electron transfer or energy transfer process between ZnPc and RGO.

A facile route to reduced graphene oxide–zinc oxide nanorod composites with enhanced photocatalytic activity

In this study, highly efficient photocatalysts were synthesized by the successful hybridization of ZnO nanorods (ZnO NRs) with reduced graphene oxide (RGO) by a facile and green hydrothermal process. The photocatalytic experimental results indicated that all the RGO–ZnO NR composite photocatalysts exhibited enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) under UV-light irradiation. It is found that the degree of photocatalytic activity enhancement strongly depends on the mass ratio of RGO in the composites; the highest photocatalytic activity which equals to 6.8 times as that of pristine ZnO NRs can be obtained when the loading amount of RGO is 4.0wt.% of RGO. The enhancement of photocatalytic activity can be attributed to the synergistic effect of the effective inhibition of the recombination of photo-generated electron–hole pairs and the elevated absorption ability for dyes, due to the strong electronic interaction between ZnO NRs and RGO nanosheets. Considering the facile and green method for the reduction of GO, the present investigation can be further employed to fabricate more graphene-based composites for various environmental and energy-related applications.