Fabrication of Au/graphene-wrapped ZnO-nanoparticle-assembled hollow spheres with effective photoinduced charge transfer for photocatalysis

Charge Separation between Pt Co-catalysts and Plasmonic Au in Pt-Au/C3N4 Photocatalysts

Chemical processes induced by surface plasmon resonance have received great attention due to the wide spectral absorption and tunable optical property. Co-catalysts have been introduced into plasmonic-metal/semiconductor photocatalysts to inhibit the recombination of plasmon-induced carriers. However, it is unclear how the locations of co-catalysts (on the surface of plasmonic metal or the semiconductor) affect the plasmonic photocatalystic reactions. Herein, we report that Pt co-catalysts can be selectively deposited on Au nanoparticles (NPs) of Au/C₃N₄ photocatalysts through an atomic layer deposition method. Compared with the Pt co-catalysts exclusively on C₃N₄, Pt solely on Au NPs has a 4.5-fold increase in activity for plasmonic hydrogen evolution. The reduced photoluminescence intensity and prolonged photoluminescence lifetime reveal that Pt solely on Au NPs provides higher charge separation efficiency. The enhanced photocatalytic activity of Pt co-catalysts solely on Au NPs is attributable to the more efficient and direct utilization of the plasmon resonance-induced electrons and separation of electrons and holes.

A Study on Doping and Compound of Zinc Oxide Photocatalysts

As an excellent semiconductor photocatalyst, zinc oxide is widely used in the field of photocatalysis and is regarded as one of the most reliable materials to solve environmental problems. However, because its band gap energy limits the absorption of visible light and reduces the efficiency of catalytic degradation, it needs to be doped with other substances or compounded with other substances and precious metal. This paper summarizes the research on this aspect at home and abroad in recent years, introduces the doping of transition metal ions by zinc oxide, the compounding of zinc oxide with precious metals or other semiconductors, and the prospect of further improving the catalytic efficiency of zno photocatalyst is also put forward.

Oxygen-vacancy-mediated photocatalytic degradation of tetracycline under weak visible-light irradiation over hierarchical Bi2MoO6@Bi2O3 core–shell fibers

Novel oxygen-vacancy-rich hierarchical Bi2MoO6@Bi2O3 core–shell fibers were prepared by the in-situ growth of Bi2MoO6 nanosheets on Bi2O3 nanofibers via an electrospinning–calcination–solvothermal method. The in-situ growth contributed to the formation of...

Brief Review of Photocatalysis and Photoresponse Properties of ZnO–Graphene Nanocomposites

As a typical wide bandgap semiconductor, ZnO has received a great deal of attention from researchers because of its strong physicochemical characteristics. During the past few years, great progress has been made in the optoelectronic applications of ZnO, particularly in the photocatalysis and photodetection fields. To enable further improvements in the material’s optoelectronic performance, construction of a variety of ZnO-based composite structures will be essential. In this paper, we review recent progress in the growth of different ZnO–graphene nanocomposite structures. The related band structures and photocatalysis and photoresponse properties of these nanocomposites are discussed. Additionally, specific examples of the materials are included to provide an insight into the common general physical properties and carrier transport characteristics involved in these unique nanocomposite structures. Finally, further directions for the development of ZnO–graphene nanocomposite materials are forecasted.

Photocatalytic Properties of Graphene/Gold and Graphene Oxide/Gold Nanocomposites Synthesized by Pulsed Laser Induced Photolysis

Graphene (Gr)/gold (Au) and graphene-oxide (GO)/Au nanocomposites (NCPs) were synthesized by performing pulsed-laser-induced photolysis (PLIP) on hydrogen peroxide and chloroauric acid (HAuCl₄) that coexisted with Gr or GO in an aqueous solution. A 3-month-long aqueous solution stability was observed in the NCPs synthesized without using surfactants and additional processing. The synthesized NCPs were characterized using absorption spectroscopy, transmission electron microscopy, Raman spectroscopy, energy dispersive spectroscopy, and X-ray diffraction to prove the existence of hybrid Gr/Au or GO/Au NCPs. The synthesized NCPs were further evaluated using the photocatalytic reaction of methylene blue (MB), a synthetic dye, under UV radiation, visible light (central wavelength of 470 nm), and full spectrum of solar light. Both Gr/Au and GO/Au NCPs exhibited photocatalytic degradation of MB under solar light illumination with removal efficiencies of 92.1% and 94.5%, respectively.

Anticorrosion Coated Stainless Steel as Durable Support for C-N-TiO2 Photo Catalyst Layer

The development of durable photocatalytic supports resistant in harsh environment has become challenging in advanced oxidation processes (AOPs) focusing on water and wastewater remediation. In this study, stainless steel (SS), SS/Ti (N,O) and SS/Cr-N/Cr (N,O) anticorrosion layers on SS meshes were dip-coated with sol gel synthesised C-N-TiO₂ photo catalysts pyrolysed at 350 °C for 105 min, using a heating rate of 50 °C/min under N₂ gas. The supported C-N-TiO₂ films were characterised by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Raman spectroscopy. The results showed that C-N-TiO₂ was successfully deposited on anticorrosion coated SS supports and had different morphologies. The amorphous C and TiO₂ were predominant in C-N-TiO₂ over anatase and rutile phases on the surface of SS and anticorrosion supports. The C-N-TiO₂ coated films showed enhanced photocatalytic activity for the decolouration of O.II dye under both solar and UV radiations. The fabricated C-N-TiO₂ films showed significant antibacterial activities in the dark as well as in visible light. Herein, we demonstrate that SS/Ti(N,O) and SS/Cr-N/Cr(N,O) anticorrosion coatings are adequate photocatalytic and corrosion resistant supports. The C-N-TiO₂ photo catalytic coatings can be used for water and wastewater decontamination of pollutants and microbes.

ZnO encapsulants: Design and new view

ZnO encapsulants with capsular configurations (e.g. a large inner cavity, sizeable pore, low density and high specific surface area) have attracted considerable attention as effective and promising candidates in various fields owing to the merits of ZnO (e.g. UV protection, photoelectric catalysis, gas sensitivity, antibacterial effect). However, the research on ZnO encapsulants has not yet reached the eruptive stage. This probably due to their high morphological flexibility and relatively low structural strength that is not easy to control during the preparation process. In this review, the principles of cavity-generating and pore-forming are firstly discussed in depth after going through the synthesis of hollow ZnO in the past ten years. Moreover, the regulation of cavity diameter and pore size of different synthetic strategies is investigated. Then, the research progress of ZnO encapsulants is debated in detail from the loading and release of functional materials and the corresponding characterization. Finally, some potential designs and new views on the future research and development of ZnO encapsulants are concluded.

One-Pot Sonochemical Synthesis of ZnO Nanoparticles for Photocatalytic Applications, Modelling and Optimization

This present study proposed a successful one pot synthesis of zinc oxide nanoparticles (ZnO NPs) and their optimisation for photocatalytic applications. Zinc chloride (ZnCl2) and sodium hydroxide (NaOH) were selected as chemical reagents for the proposed study. The design of this experiment was based on the reagents' amounts and the ultrasonic irradiations' time. The results regarding scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy confirmed the presence of ZnO NPs with pure hexagonal wurtzite crystalline structure in all synthesised samples. Photocatalytic activity of the developed samples was evaluated against methylene blue dye solution. The rapid removal of methylene blue dye indicated the higher photocatalytic activity of the developed samples than untreated samples. Moreover, central composite design was utilised for statistical analysis regarding the obtained results. A mathematical model for the optimisation of input conditions was designed to predict the results at any given point. The role of crystallisation on the photocatalytic performance of developed samples was discussed in detail in this novel study.

Hollow Nanostructures for Photocatalysis: Advantages and Challenges

Photocatalysis for solar-driven reactions promises a bright future in addressing energy and environmental challenges. The performance of photocatalysis is highly dependent on the design of photocatalysts, which can be rationally tailored to achieve efficient light harvesting, promoted charge separation and transport, and accelerated surface reactions. Due to its unique feature, semiconductors with hollow structure offer many advantages in photocatalyst design including improved light scattering and harvesting, reduced distance for charge migration and directed charge separation, and abundant surface reactive sites of the shells. Herein, the relationship between hollow nanostructures and their photocatalytic performance are discussed. The advantages of hollow nanostructures are summarized as: 1) enhancement in the light harvesting through light scattering and slow photon effects; 2) suppression of charge recombination by reducing charge transfer distance and directing separation of charge carriers; and 3) acceleration of the surface reactions by increasing accessible surface areas for separating the redox reactions spatially. Toward the end of the review, some insights into the key challenges and perspectives of hollow structured photocatalysts are also discussed, with a good hope to shed light on further promoting the rapid progress of this dynamic research field.

Fluorinated Reduced Graphene Oxide-Encapsulated ZnO Hollow Sphere Composite as an Efficient Photocatalyst with Increased Charge-Carrier Mobility

Zinc oxide (ZnO) hollow spheres were prepared by the hydrothermal method and encapsulated with fluorinated reduced graphene oxide (FRGO) using a tetra- n-butylammonium bromide (TBAB) linker to give an FRGO/ZnO composite. X-ray diffraction and microscopic studies revealed their hexagonal-wurtzite structure, spherical morphology, and size of the crystallite to be 26.7 nm. Diffuse reflectance UV-visible spectroscopy showed an optical band gap and semiconductive nature of the composite. Atomic force microscopy images show the surface topography of FRGO-encapsulated ZnO hollow spheres. The photoluminescence spectra depicted the electron-hole pair recombination order to be ZnO > RGO/ZnO > FRGO/ZnO. The electrochemical impedance spectroscopy (EIS) demonstrates the increased charge-carrier mobility of the FRGO/ZnO composite; the R_ct values of ZnO, RGO/ZnO, and FRGO/ZnO were found to be 6.18 × 10³, 4.07 × 10³, and 3.45 × 10³ Ω, respectively. All the three materials were employed as photocatalysts in the degradation of methylene blue under UV-365 nm radiation and the results exposed the higher photocatalytic activity of reduced fluorinated graphene oxide/ZnO than RGO/ZnO and bare ZnO hollow spheres. The increased photocatalytic activity of the composite is due to the enhanced vectorial transport of charge carriers at the interface of the FRGO/ZnO composite and suppression of charge-carrier recombination. The presence of fluorine in the RGO sheet introduces additional defects and leverages heterogeneous electron transport. In turn, mobility of light-generated charge carriers is increased and results in suppression of their recombination, which facilitates the photocatalytic process.

Design, preparation and evaluation of a high performance sensor for formaldehyde based on a novel hybride nonocomposite ZnWO3/rGO

The ultrasound wave assisted synthesis of a novel ZnWO₃/rGO hybrid nono composition (ZnWO₃/rGO HNC) as a high performance sensor for formaldehyde (FA) has been reported. Different techniques of analysis such as XRD, FE-SEM, TGA, XPS, HRTEM and BET were applied for morphological and spectroscopic characterization of the ZnWO₃/rGO HNC. The sensing evaluation of the constructed sensor showed high selectivity, sensitivity and a linear correlation between achieved responses and concentration of target gas (1-10 ppm) with R² = 0.993 at temperature of 95 °C. The determination of FA was validated and performed using gas chromatography-mass spectrometry combined by solid phase micro-extraction after derivatization with O-(2,3,4,5,6-pentafluoro-benzyl)-hydroxylamine hydrochloride. Validation was carried out in terms of limit of detection linearity, precision, and recovery. The mechanistic evaluation of sensing behavior of the ZnWO₃/rGO HNC was interpreted based on large specific surface area (SSA) to volume, mesoporous structure and the heterojunction between rGO and ZnWO₃ at the interface between the rGO and ZnWO₃.

TiO2/graphene/CuSbS2 mixed-dimensional array with high-performance photoelectrochemical properties

The growing demands for reproducible and clean sources of power has prompted the exploitation of novel materials for solar-energy conversion; in any case, the improvement of their conversion efficiency remains a big challenge.

Synthesis of graphenized Au/ZnO plasmonic nanocomposites for simultaneous sunlight mediated photo-catalysis and anti-microbial activity

Sunlight mediated photo-degradation and anti-bacterial activity of hetero junctioned plasmonic binary (Au/ZnO, RGO/ZnO) and ternary (RGO/Au/ZnO) nanocomposites (NC) have been reported. Higher photo-charge carrier generation, increased charge separation, improved active sites for catalysis, enhanced LSPR and larger photo-response regions have been achieved. Decoration with Au nanoparticles (ca. 11 ± 3 and 48 ± 5 nm) and RGO of ZnO (3D/1D) microstructures (aspect ratio 15.18) provides ternary NCs an edge over mono/bi component catalysts. The ternary NC have shown improved dye degradation capacity with 100% efficiency (5 μM MB solution) and average adsorption degradation capacity (Q°) of 83.34 mg/g within 30 min of sunlight exposure (900 ± 30 Wm^-2). Elaborated studies by varying reaction parameters like initial dye concentration, contact time, type of NCs and initial loading of NCs reveals pseudo first order degradation kinetics. 100% microbial killing of Gram positive S.aureus strain with 60 μg/ml of NC using sunlight as activator has proven the simultaneous multiple functionality of the NC. Further, facile green one pot hydrothermal synthesis with water as reaction medium, absence of photo-corrosion of NCs, regeneration ability (ca. 90% for 10 μM solution) of NCs, projects a broader potential application of the synthesized NCs and could reduce the continuous requirement of such material, limiting the environmental toxicity.

Sustainable superior function of the synthesized NixCo1-xFe2Oz nanosphere on the destruction of chlorinated biphenyls in the effluent

Ni_xCo_1-xFe₂O_z composite oxide nanosphere was successfully prepared, to degrade 2-monochlorobiphenly (CB-1) in continuous-flow fixed-bed microreactor at GHSV of 20000h^-1. The five cycles of temperature-dependent run experiments between 150 and 350°C showed its superior activity with a CB-1 conversion of more than 95% above 300°C over Ni_0.5Co_0.5Fe₂O_z. Importantly, the sustainable higher reactivity could be observed over prolonged 600min reaction times after the 5th run test. The degradation products detected as biphenyl and monochlorobenzene with yield ratio of 129, account for 0.24% and 0.0011% of initial CB-1 respectively. This indicated the weak occurrence of hydrodechlorination and breakage of CC bridge bond during the degradation of CB-1. The possibly dominant occurrence of oxidative degradation probably follows Mars-van Krevelen mechanism, resulting in the generation of the formic, acetic, propanoic and butyric acids and so on. Due to the high oxygen mobility over Ni_0.5Co_0.5Fe₂O_z nanosphere, the consumed oxygen species could be compensated rapidly by the gas phase oxygen via O₂→O₂^- → 2O^- → 2O^2-. The interaction among different elements in Ni_0.5Co_0.5Fe₂O_z nanosphere confirmed by the derivation of the electron cloud, enhanced the mobility of the reactive oxygen species, which would be beneficial for the oxidation of chlorinated biphenyls.

Chemical Sensing Applications of ZnO Nanomaterials

Recent advancement in nanoscience and nanotechnology has witnessed numerous triumphs of zinc oxide (ZnO) nanomaterials due to their various exotic and multifunctional properties and wide applications. As a remarkable and functional material, ZnO has attracted extensive scientific and technological attention, as it combines different properties such as high specific surface area, biocompatibility, electrochemical activities, chemical and photochemical stability, high-electron communicating features, non-toxicity, ease of syntheses, and so on. Because of its various interesting properties, ZnO nanomaterials have been used for various applications ranging from electronics to optoelectronics, sensing to biomedical and environmental applications. Further, due to the high electrochemical activities and electron communication features, ZnO nanomaterials are considered as excellent candidates for electrochemical sensors. The present review meticulously introduces the current advancements of ZnO nanomaterial-based chemical sensors. Various operational factors such as the effect of size, morphologies, compositions and their respective working mechanisms along with the selectivity, sensitivity, detection limit, stability, etc., are discussed in this article.

Design and application of Au decorated ZnO/TiO2 as a stable photocatalyst for wide spectral coverage

A ternary nanostructured photocatalyst consisting of ZnO/TiO₂/Au was designed to achieve an enhanced solar absorption due to the coupling of surface enhanced plasmonic absorption of metal and semiconductor excitons. TiO₂ coated ZnO rods with an aspect ratio of 8-12 were decorated with citrate capped gold nanoparticles for photocatalytic degradation of organic pollutants in simulated waste water under solar irradiation. Simulated waste water was prepared so as to get a mixture exhibiting a wide range of spectral distribution in the UV-visible region by deliberately mixing congo red, methylene blue and malachite green. Photo-oxidation of few phenolic compounds such as phenol, 4-chlorophenol and polycyclic aromatic hydrocarbons viz. anthracene and phenanthrene were also investigated in order to rule out the visible light sensitization of the dye molecules and confirm the photocatalytic efficacy of the ternary composite for a wide range of water pollutants under simulated solar irradiation. The composite exhibited enhanced photocatalytic activity and photoelectrochemical stability upon UV and visible light exposure. This enhanced efficiency was also corroborated with the photocarrier lifetime and chronoamperometric studies. Under simulated solar irradiation, UV light induced well separated charge carriers coupled with the visible light induced local surface plasmon resonance of AuNPs to exert significantly enhanced photocatalytic activity in a broad spectral region. This type of material may evolve as a novel photocatalyst for the efficient removal of organic contaminants in waste water and photoelectrochemical water splitting under the solar spectrum.

Reducing the barrier effect of graphene sheets on a Ag cocatalyst to further improve the photocatalytic performance of TiO2

By avoiding the possible barrier influence of graphene on other cocatalysts, the photocatalytic properties of the composites containing multi-cocatalysts could be further improved.

In situ decoration of plasmonic Au nanoparticles on graphene quantum dots-graphitic carbon nitride hybrid and evaluation of its visible light photocatalytic performance

This work spotlights the development of a plasmonic photocatalyst showing surface plasmon induced enhanced visible light photocatalytic (PC) performance. Plasmonic Au nanoparticles (NPs) are decorated over the hybrid nanosystem of graphitic carbon nitride (GCN) and graphene quantum dots (GQD) by citrate reduction method. Surface plasmon resonance (SPR) induced enhancement of Raman G and 2D band intensity is encountered on excitation of the Plasmonic hybrid at 514.5 nm, which is near to the 532 nm absorption band of Au NPs. Time-resolved photoluminescence and XPS studies show charge transfer interaction between GQD-GCN and Au NPs. Plasmonic hybrid exhibits an enhanced PC activity over the other catalysts in the photodegradation of methylene blue (MB) under visible light illumination. Plasmonic photocatalyst displays more than 6 fold enhancement in the photodecomposition rate of MB over GQD and nearly 2 fold improvement over GCN and GQD-GCN. GQD-GCN absorbs mostly in the near visible region and can be photoexcited by visible light of wavelength ([Formula: see text]) < 460 nm. Plasmon activation in Au NPs decorated GQD-GCN could exploit the entire UV-visible light for photocatalysis. Furthermore, plasmonic Au act as antennas for accumulation and enhancement of localized electromagnetic field at the interface with GQD-GCN, and thereby promotes photogeneration of large numbers of carriers on GQD-GCN. The carriers are separated by charge transfer migration from hybrid to Au NPs. Finally, the carriers on the plasmonic Au nanostructures initiate MB degradation under visible light. Our results have shown that plasmon decoration is a suitable strategy to design a carbon based hybrid photocatalyst for solar energy conversion.

Two-dimensional carbon-based nanocomposites for photocatalytic energy generation and environmental remediation applications

In the pursuit towards the use of sunlight as a sustainable source for energy generation and environmental remediation, photocatalytic water splitting and photocatalytic pollutant degradation have recently gained significant importance. Research in this field is aimed at solving the global energy crisis and environmental issues in an ecologically-friendly way by using two of the most abundant natural resources, namely sunlight and water. Over the past few years, carbon-based nanocomposites, particularly graphene and graphitic carbon nitride, have attracted much attention as interesting materials in this field. Due to their unique chemical and physical properties, carbon-based nanocomposites have made a substantial contribution towards the generation of clean, renewable and viable forms of energy from light-based water splitting and pollutant removal. This review article provides a comprehensive overview of the recent research progress in the field of energy generation and environmental remediation using two-dimensional carbon-based nanocomposites. It begins with a brief introduction to the field, basic principles of photocatalytic water splitting for energy generation and environmental remediation, followed by the properties of carbon-based nanocomposites. Then, the development of various graphene-based nanocomposites for the above-mentioned applications is presented, wherein graphene plays different roles, including electron acceptor/transporter, cocatalyst, photocatalyst and photosensitizer. Subsequently, the development of different graphitic carbon nitride-based nanocomposites as photocatalysts for energy and environmental applications is discussed in detail. This review concludes by highlighting the advantages and challenges involved in the use of two-dimensional carbon-based nanocomposites for photocatalysis. Finally, the future perspectives of research in this field are also briefly mentioned.

Oxygen Vacancies in Shape Controlled Cu2O/Reduced Graphene Oxide/In2O3 Hybrid for Promoted Photocatalytic Water Oxidation and Degradation of Environmental Pollutants

A novel shape controlled Cu₂O/reduced graphene oxide/In₂O₃ (Cu₂O/RGO/In₂O₃) hybrid with abundant oxygen vacancies was prepared by a facile, surfactant-free method. The hybrid photocatalyst exhibits an increased photocatalytic activity in water oxidation and degradation of environmental pollutants (methylene blue and Cr⁶⁺ solutions) compared with pure In₂O₃ and Cu₂O materials. The presence of oxygen vacancies in Cu₂O/RGO/In₂O₃ and the formation of heterojunction between In₂O₃ and Cu₂O induce extra diffusive electronic states above the valence band (VB) edge and reduce the band gap of the hybrid consequently. Besides, the increased activity of Cu₂O/RGO/In₂O₃ hybrid is also attributed to the alignment of band edge, a process that is assisted by different Fermi levels between In₂O₃ and Cu₂O, as well as the charge transfer and distribution onto the graphene sheets, which causes the downshift of VB of In₂O₃ and the significant increase in its oxidation potential. Additionally, a built-in electric field is generated on the interface of n-type In₂O₃ and p-type Cu₂O, suppressing the recombination of photoinduced electron-hole pairs and allowing the photogenerated electrons and holes to participate in the reduction and oxidation reactions for oxidizing water molecules and pollutants more efficiently.

Two-Dimensional Au-Nanoprism/Reduced Graphene Oxide/Pt-Nanoframe as Plasmonic Photocatalysts with Multiplasmon Modes Boosting Hot Electron Transfer for Hydrogen Generation

Two-dimensional Au-nanoprism/reduced graphene oxide (rGO)/Pt-nanoframe was synthesized as plasmonic photocatalyt, exhibiting activity of photocatalytic hydrogen generation greater than those of Au-nanorod/rGO/Pt-nanoframe and metallic plasmonic photocatalyst Pt-Au. The single-particle plasmonic photoluminescence study demonstrated that Au-nanorod has only a longitudinal plasmon resonance mode for hot electron transfer to rGO, while Au-nanoprism has in-plane dipole and multipole surface plasmon resonance modes for hot electron transfer, leading to highly efficient charge separation for hydrogen generation.

Solvothermal synthesis of CdIn2S4 photocatalyst for selective photosynthesis of organic aromatic compounds under visible light

Ternary chalcogenide semiconductor, cadmium indium sulfide (CdIn₂S₄), was prepared by a simple solvothermal method using ethylene glycol as a solvent, as well as indium chloride tetrahydrate (InCl₃^.4H₂O), cadmium nitrate tetrahydrate [Cd(NO₃)₂^.4H₂O], and thiacetamide (TAA) as precursors. The resulted sample was subject to a series of characterizations. It is the first time to use CdIn₂S₄ sample as a visible light-driven photocatalyst for simultaneous selective redox transformation of organic aromatic compounds. The results indicate that the as-synthesized CdIn₂S₄ photocatalyst not only has excellent photocatalytic performance compared with pure In₂S₃ and CdS for the selective oxidation of aromatic alcohols in an oxygen environment, but also shows high photocatalytic redox activities under nitrogen atmosphere. A possible mechanism for the photocatalytic redox reaction in the coupled system was proposed. It is hoped that our current work could extend the applications of CdIn₂S₄ photocatalyst and provide new insights for selective transformations of organic compounds.

The physics and chemistry of graphene-on-surfaces

This review describes the major “graphene-on-surface” structures and examines the roles of their properties in governing the overall performance for specific applications.

Characterization of Gold-Sputtered Zinc Oxide Nanorods-a Potential Hybrid Material

Generation of hybrid nanostructures has been attested as a promising approach to develop high-performance sensing substrates. Herein, hybrid zinc oxide (ZnO) nanorod dopants with different gold (Au) thicknesses were grown on silicon wafer and studied for their impact on physical, optical and electrical characteristics. Structural patterns displayed that ZnO crystal lattice is in preferred c-axis orientation and proved the higher purities. Observations under field emission scanning electron microscopy revealed the coverage of ZnO nanorods by Au-spots having diameters in the average ranges of 5-10 nm, as determined under transmission electron microscopy. Impedance spectroscopic analysis of Au-sputtered ZnO nanorods was carried out in the frequency range of 1 to 100 MHz with applied AC amplitude of 1 V RMS. The obtained results showed significant changes in the electrical properties (conductance and dielectric constant) with nanostructures. A clear demonstration with 30-nm thickness of Au-sputtering was apparent to be ideal for downstream applications, due to the lowest variation in resistance value of grain boundary, which has dynamic and superior characteristics.

Photo-Response of Functionalized Self-Assembled Graphene Oxide on Zinc Oxide Heterostructure to UV Illumination

Convective assembly technique which is a simple and scalable method was used for coating uniform graphene oxide (GO) nanosheets on zinc oxide (ZnO) thin films. Upon UV irradiation, an enhancement in the on-off ratio was observed after functionalizing ZnO films by GO nanosheets. The calculations of on-off ratio, the device responsivity, and the external quantum efficiency were investigated and implied that the GO layer provides a stable pathway for electron transport. Structural investigations of the assembled GO and the heterostructure of GO on ZnO were performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The covered GO layer has a wide continuous area, with wrinkles and folds at the edges. In addition, the phonon lattice vibrations were investigated by Raman analysis. For GO and the heterostructure, a little change in the ratio between the D-band and G-band was found which means that no additional defects were formed within the heterostructure.

Role of RGO support and irradiation source on the photocatalytic activity of CdS-ZnO semiconductor nanostructures

Photocatalytic activity of semiconductor nanostructures is gaining much importance in recent years in both energy and environmental applications. However, several parameters play a crucial role in enhancing or suppressing the photocatalytic activity through, for example, modifying the band gap energy positions, influencing the generation and transport of charge carriers and altering the recombination rate. In this regard, physical parameters such as the support material and the irradiation source can also have significant effect on the activity of the photocatalysts. In this work, we have investigated the role of reduced graphene oxide (RGO) support and the irradiation source on mixed metal chalcogenide semiconductor (CdS-ZnO) nanostructures. The photocatalyst material was synthesized using a facile hydrothermal method and thoroughly characterized using different spectroscopic and microscopic techniques. The photocatalytic activity was evaluated by studying the degradation of a model dye (methyl orange, MO) under visible light (only) irradiation and under natural sunlight. The results reveal that the RGO-supported CdS-ZnO photocatalyst performs considerably better than the unsupported CdS-ZnO nanostructures. In addition, both the catalysts perform significantly better under natural sunlight than under visible light (only) irradiation. In essence, this work paves way for tailoring the photocatalytic activity of semiconductor nanostructures.

Recent advances in 2D materials for photocatalysis

Two-dimensional (2D) materials have attracted increasing attention for photocatalytic applications because of their unique thickness dependent physical and chemical properties. This review gives a brief overview of the recent developments concerning the chemical synthesis and structural design of 2D materials at the nanoscale and their applications in photocatalytic areas. In particular, recent progress on the emerging strategies for tailoring 2D material-based photocatalysts to improve their photo-activity including elemental doping, heterostructure design and functional architecture assembly is discussed.

In situ growth of small Au nanoparticles on ZnO nanorods via ultrasonic irradiation toward super-enhanced catalytic activity

Au/ZnO NRs created via a sonochemical method exhibit superior photocatalytic performance and enhanced CO oxidation activity.

Facile synthesis of MOF 235 and its superior photocatalytic capability under visible light irradiation

MOF 235 was fabricated by a facile microwave-assisted method. It showed excellent visible-light photocatalytic activity in the presence of H₂O₂. It displays a high chemical stability for repeated RhB degradation reactions.

Enhanced photocatalytic activity on polarized ferroelectric KNbO3

In this paper, we demonstrate the enhanced photodegradation of rhodamine B on polarized ferroelectric KNbO₃ (KNO) particles.

Facile fabrication of thermally reduced graphene oxide–platinum nanohybrids and their application in catalytic reduction and dye-sensitized solar cells

We report the fast synthesis of thermally reduced graphene oxide : platinum (TRGO : Pt) nanohybrids by simply spraying a GO:Pt⁴⁺ solution on a hot plate.