Thinnest two-dimensional nanomaterial-graphene for solar energy

Study on the modulation mechanism of the optoelectronic properties based on common electrode metal atom adsorption on graphene/MoTe2

CONTEXT

The two-dimensional graphene/MoTe2 heterostructure holds extensive potential applications in optoelectronic devices, sensors, and catalysts. To expand its optical applications, this study systematically investigates the adsorption stability of metal atoms (Au, Pt, Pd, and Fe) on the graphene/MoTe2 and their influence on its optoelectronic properties employing first-principles methods. The findings indicate that after the adsorption of Au and Pd, the structure retains its direct bandgap properties, while the adsorption of Pt and Fe exhibits indirect bandgap characteristics. The work functions for all adsorbed structures are lower compared to the pristine graphene/MoTe2. The total density of states is primarily derived from the C-2p, Mo-4d, Te-5p orbitals, as well as the d and s orbitals of the adsorbed atoms. The pristine graphene/MoTe2 exhibits significant absorption in the ultraviolet range. Once graphene/MoTe2 is adsorbed by metal atoms, it can significantly enhance the optical absorption across the spectrum from infrared to ultraviolet light. These findings provide important theoretical guidance for regulating the application of graphene/MoTe2 in optoelectronics and related fields.

METHODS

All analyses are grounded in density functional theory first principles and computed using CASTEP. Graphene/MoTe2 consists of 4 × 4 × 1 single-layer, graphene single layer, and 3 × 3 × 1 single-layer MoTe2. To prevent interactions between neighboring unit cells, a 20 Å vacuum space in the z-direction is employed. The electronic exchange-correlation interactions are treated using the Perdew-Burke-Ernzerhof functional within the framework of the generalized gradient approximation. Van der Waals (vdW) interactions are incorporated using the vdW correction function proposed by Grimme, which effectively describes vdW interactions. During the simulation, the cutoff energy for plane wave expansion is set to 420 eV, and the k-point grid is set to 4 × 4 × 1. The atomic displacement convergence standard is 0.002 Å, the internal stress convergence standard is 0.1GPa, and the interaction force convergence standard between atoms is 0.05 eV/Å. The convergence threshold for the iteration precision is set to ensure that the total energy for each atom is not less than 2 × 10-5 eV/atom.

First-principle study on the photoelectric properties of monolayer h-BN under different strain types

CONTEXT

Two-dimensional materials are a new and promising research field in materials science. This is mainly attributed to their unique photoelectric and chemical properties. In addition to possessing unique optoelectronic and chemical properties, two-dimensional materials also have important application prospects in the field of field-effect devices. Based on density functional theory, the effects of uniaxial strain and equibiaxial strain on the mechanical properties, electronic structure, and optical properties of monolayer h-BN were studied using first principles. The results indicate that compressive strain has a significant impact on the stability of monolayer h-BN. The band gap width of monolayer h-BN decreases with increasing strain, and the optical properties of monolayer h-BN exhibit a relative trend under tensile and compressive strains. The influence of biaxial strain on the mechanical properties, electronic structure, and optical properties of monolayer h-BN is greater than that of uniaxial strain.

METHODS

All the calculations were done by the VASP software based on density functional theory. The interaction between atomic nuclei and electrons is described by the projected added wave pseudopotential (PAW), using the generalized gradient approximation (GGA) to exchange the Perdew-Burke-Ernzerhof (PBE) of the functional. To avoid interlayer interactions, a 15-Å vacuum layer was set up. The Brillouin zone selects the Monkhorst-Pack method to generate 9 × 9 × 1 of k-point grid, the cut off energy is set to 500 eV, the energy convergence standard of the system is 1 × 10-5 eV, and the interaction force between atoms is 0.01 eV/Å.

3D graphene: synthesis, properties, and solar cell applications

Three-dimensional (3D) graphene is one of the most important nanomaterials. This feature article highlights the advancements, with an emphasis on contributions from our group, in the synthesis of 3D graphene-based materials and their utilization in solar cells. Chemistries of graphene oxides, hydrocarbons, and alkali metals are discussed for the synthesis of 3D graphene materials. Their performances in dye-sensitized solar cells and perovskite solar cells (as counter electrodes, photoelectrodes, and electron extracting layers) were correlatively analyzed with their properties/structures (accessible surface area, electrical conductivity, defects, and functional groups). The challenges and prospects for their applications in photovoltaic solar cells are outlined.

Radiosensitization of Nasopharyngeal Carcinoma by Graphene Oxide Nanosheets to Reduce Bcl-2 Level

There are many treatments for nasopharyngeal carcinoma (NPC), but none of them are very effective. Radiotherapy is used extensively in NPC treatment, but radioresistance is a major problem. Graphene oxide (GO) has been previously studied in cancer treatment, and this study is aimed to explore its role in radiosensitization of NPC. Therefore, graphene oxide nanosheets were prepared, and the relationship between GO and radioresistance was explored. The GO nanosheets were synthesized by a modified Hummers' method. The morphologies of the GO nanosheets were characterized by field-emission environmental scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The morphological changes and radiosensitivity of C666-1 and HK-1 cells with or without the GO nanosheets were observed by an inverted fluorescence microscopy and laser scanning confocal microscopy (LSCM). Colony formation assay and Western Blot were applied for analysis of NPC radiosensitivity. The as-synthesized GO nanosheets have lateral dimensions (sizes ∼1 μm) and exhibit a thin wrinkled two-dimensional lamellar structure with slight folds and crimped edges (thickness values ∼1 nm). C666-1 cells with the GO was significantly changed the morphology of cells postirradiation. The full field of view visualized by a microscope showed the shadow of dead cells or cell debris. The synthesized graphene oxide nanosheets inhibited cell proliferation, promoted cell apoptosis, and inhibited the expression of Bcl-2 in C666-1 and HK-1 cells but increased the level of Bax. The GO nanosheets could affect the cell apoptosis and reduce the pro-survival protein Bcl-2 related to the intrinsic mitochondrial pathway. The GO nanosheets could enhance radiosensitivity, which might be a radioactive material in NPC cells.

Simulation of a New CZTS Solar Cell Model with ZnO/CdS Core-Shell Nanowires for High Efficiency

The numerical modeling of Cu2ZnSnS4 solar cells with ZnO/CdS core-shell nanowires of optimal dimensions with and without graphene is described in detail in this study. The COMSOL Simulation was used to determine the optimal values of core diameter and shell thickness by comparing their optical performance and to evaluate the optical and electrical properties of the different models. The deposition of a nanolayer of graphene on the layer of MoS2 made it possible to obtain a maximum absorption of 97.8% against 96.5% without the deposition of graphene.The difference between generation rates and between recombination rates of electron–hole pairs of models with and without graphene is explored.The electrical parameters obtained, such as the filling factor (FF), the short-circuit current density (Jsc), the open-circuit voltage (Voc), and the efficiency (EFF) are, respectively, 81.7%, 6.2 mA/cm2, 0.63 V, and 16.6% in the presence of graphene against 79.2%, 6.1 mA/cm2, 0.6 V, and 15.07% in the absence of graphene. The suggested results will be useful for future research work in the field of CZTS-based solar cells with ZnO/CdS core-shell nanowires with broadband light absorption rates.

Pd-Pd/PdO as active sites on intercalated graphene oxide modified by diaminobenzene: fabrication, catalysis properties, synergistic effects, and catalytic mechanism

Pd-Pd/PdO nanoclusters well dispersed on intercalated graphene oxide (GO) (denoted as GO@PPD-Pd) were prepared and characterized. GO@PPD-Pd exhibited high catalytic activity (a TOF value of 60 705 h-1) during the Suzuki coupling reaction, and it could be reused at least 6 times. The real active centre was Pd(200)-Pd(200)/PdO(110, 102). A change in the Pd facets on the surface of PdO was a key factor leading to deactivation, and the aggregation and loss of active centres was also another important reason. The catalytic mechanism involved heterogeneous catalysis, showing that the catalytic processes occurred at the interface, including substrate adsorption, intermediate formation, and product desorption. The real active centres showed enhanced negative charge due to the transfer of electrons from the carrier and ligands, which could effectively promote the oxidative addition reaction, and Pd(200) and the heteroconjugated Pd/PdO interface generated in situ also participated in the coupling process, synergistically boosting activity. Developed GO@PPD-Pd was a viable heterogeneous catalyst that may have practical applications owing to its easy synthesis and stability, and this synergistic approach can be utilized to develop other transition-metal catalysts.

Progress in modifications of 3D graphene-based adsorbents for environmental applications

3D graphene-based materials are promising adsorbents for environmental applications. Furthermore, increasing attention has been paid to the improvement of 3D graphene adsorbents for removing pollutants. In this article, the progress in the modification of 3D graphene materials and their performance for removing pollutants were reviewed. The modification strategies, which were classified as (1) the activation with CO₂ (steam and other oxidants) and (2) the surface functionalization with polymers (metals, and metal oxides), were evaluated. The performances of modified 3D graphene materials were assessed for the removal of waste gases (such as CO₂), refractory organics, and heavy metals. The challenges and future research directions were discussed for the environmental applications of 3D graphene materials.

High-Responsivity Photodetector Based on a Suspended Monolayer Graphene/RbAg4I5 Composite Nanostructure

Graphene has excellent electrical, optical, thermal, and mechanical properties that make it an ideal optoelectronic material. However, it still has some problems, such as a very low light absorption rate, which means it cannot meet the application requirements of high-performance optoelectronic devices. Here, we produce a high-responsivity photodetector based on a monolayer graphene/RbAg₄I₅ composite nanostructure. With the aid of poly(methyl methacrylate), we suspend the monolayer graphene on a hollow carving groove with a width of 100 μm. A RbAg₄I₅ film evaporated on the back of the graphene causes the composite nanostructure to generate a large photocurrent under periodic illumination. Experimental results show that the dissociation and recombination of ion-electron bound states (IEBSs) are responsible for the excellent photoresponse. The device has very high (>1 A W^-1) responsivity in wide-band illumination wavelength from 375 nm to 808 nm, especially at 375 nm, where it shows a responsivity of up to ∼5000 A W^-1. We designed the dimensions of the carving groove to allow the light spot to cover the entire groove, and we cut the graphene sheet to match the length of the carving groove. With the structural optimizations, the energy of light can be used more efficiently to dissociate the IEBSs, which greatly improves the photoresponse of optoelectronic devices based on the proposed monolayer graphene/RbAg₄I₅ composite nanostructure.

Bacterial Cellulose-Graphene Based Nanocomposites

Bacterial cellulose (BC) and graphene are materials that have attracted the attention of researchers due to their outstanding properties. BC is a nanostructured 3D network of pure and highly crystalline cellulose nanofibres that can act as a host matrix for the incorporation of other nano-sized materials. Graphene features high mechanical properties, thermal and electric conductivity and specific surface area. In this paper we review the most recent studies regarding the development of novel BC-graphene nanocomposites that take advantage of the exceptional properties of BC and graphene. The most important applications of these novel BC-graphene nanocomposites include the development of novel electric conductive materials and energy storage devices, the preparation of aerogels and membranes with very high specific area as sorbent materials for the removal of oil and metal ions from water and a variety of biomedical applications, such as tissue engineering and drug delivery. The main properties of these BC-graphene nanocomposites associated with these applications, such as electric conductivity, biocompatibility and specific surface area, are systematically presented together with the processing routes used to fabricate such nanocomposites.

Few biomedical applications of carbon nanotubes

Nanotubes of carbon are allotropic form of carbon material that rolled to form a cylindrical structure that may be singlewalled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) depending upon the number of carbon layers. These carbon nanotubes have exhibited characteristics properties such as  electrical, optical, thermal and mechanical. Carbon nanotubes can be employed for immobilization matrix for biomolecules such as an enzyme, nucleic acid, etc. Enzymes can be immobilized onto carbon nanotubes via absorption or covalent bonding. Various enzymatic based biosensors are also developed for the detection of various analytes. Present chapter mainly emphasizes characteristics of carbon nanotubes, their preparation methods, purification and exploitation of CNTs as an immobilization matrix for theranostic applications.

A novel Ag-BiOBr-rGO photocatalyst for enhanced ketoprofen degradation: Kinetics and mechanisms

Ag-BiOBr-reduced graphene oxide (rGO) was synthesized for the first time and used to promote photocatalytic activity under visible-light irradiation. The Ag-BiOBr-rGO showed an excellent photocatalytic activity to degrade ketoprofen compared with other photocatalysts. The composites were comprehensively characterized to explore the mechanisms of the enhancement. Electron Paramagnetic Resonance and scavenger experiments demonstrated that the superoxide radical was the active species. Ketoprofen was completely removed in 120 min. The high photocatalytic activity and stability of the catalyst indicated that the Ag-BiOBr-rGO may have broad application prospects for eliminating pharmaceuticals from wastewater. Four reaction intermediates of ketoprofen were detected by LC-MS/MS and degradation routes were proposed.

Surface roughness regulation of reduced-graphene oxide/iodine - Based electrodes and their application in polymer solar cells

The current work presents an iodine-mediated fine-tuning method for the electrical and electrochemical properties of reduced-graphene oxide (r-GO)/iodine - based electrodes for application in ITO-free polymer solar cells (PSCs). A multi-technique investigation was applied to correlate the morphological features of GO thin films (GO TFs) with iodine adsorption during the reduction process by HI vapor, electrochemical band gap, Fermi potential, charge carrier mobility and charge density of iodine/r-GO based electrodes. The electrical and electrochemical characteristics of iodine/r-GO electrodes changed considerably by alteration of their surface roughness and iodine content. Iodine/r-GO TFs with the lowest surface roughness and the highest iodine content exhibited the highest charge carrier density and Fermi potential. Electrochemical impedance spectroscopy (EIS) and quantum Hall effect (QHE) results confirmed the p-type conductivity of r-GOs/iodine-based electrodes. PSCs were fabricated using r-GO/iodine electrodes as the photo-anode to follow the influences of iodine content and surface roughness on the photovoltaic performance of the cells. PSCs prepared based on r-GO/iodine electrodes possessing the lowest surface roughness and the highest iodine content provided the lowest charge transfer resistance (R_ct) and remarkably higher (∼48%) PCE.

Optical Properties of Graphene/MoS₂ Heterostructure: First Principles Calculations

The electronic structure and the optical properties of Graphene/MoS₂ heterostructure (GM) are studied based on density functional theory. Compared with single-layer graphene, the bandgap will be opened; however, the bandgap will be reduced significantly when compared with single-layer MoS₂. Redshifts of the absorption coefficient, refractive index, and the reflectance appear in the GM system; however, blueshift is found for the energy loss spectrum. Electronic structure and optical properties of single-layer graphene and MoS₂ are changed after they are combined to form the heterostructure, which broadens the extensive developments of two-dimensional materials.

Research Progress in Application of 2D Materials in Liquid-Phase Lubrication System

Two-dimensional (2D) materials are ultra-thin crystals with layered structures that have a monolayer and multiple layers of atomic thickness. Due to excellent performance, 2D materials represented by graphene have caused great interest from researchers in various fields, such as nano-electronics, sensors, solar cells, composite materials, and so on. In recent years, when graphite was used for liquid phase lubrication, there have been many disadvantages limiting its lubrication properties, such as stable dispersion, fluidity and so on. Therefore, 2D materials have been used as high-performance liquid-phase lubricant additives, which become a perfect entry point for high-performance nano-lubricants and lubrication applications. This review describes the application of 2D materials as additives in the field of liquid-phase lubrication (such as lubricating oil and water lubrication) in terms of experimental content, lubrication performance, and lubrication mechanism. Finally, the challenges and prospects of 2D materials in the lubrication field were also proposed.

Cu2ZnSnS4/MoS2-Reduced Graphene Oxide Heterostructure: Nanoscale Interfacial Contact and Enhanced Photocatalytic Hydrogen Generation

Hydrogen generation from water using noble metal-free photocatalysts presents a promising platform for renewable and sustainable energy. Copper-based chalcogenides of earth-abundant elements, especially Cu₂ZnSnS₄ (CZTS), have recently arisen as a low-cost and environment-friendly material for photovoltaics and photocatalysis. Herein, we report a new heterostructure consisting of CZTS nanoparticles anchored onto a MoS₂-reduced graphene oxide (rGO) hybrid. Using a facile two-step method, CZTS nanoparticles were in situ grown on the surface of MoS₂-rGO hybrid, which generated high density of nanoscale interfacial contact between CZTS and MoS₂-rGO hybrid. The photoexcited electrons of CZTS can be readily transported to MoS₂ through rGO backbone, reducing the electron-hole pair recombination. In photocatalytic hydrogen generation under visible light irradiation, the presence of MoS₂-rGO hybrids enhanced the hydrogen production rate of CZTS by 320%, which can be attributed to the synergetic effect of increased charge separation by rGO and more catalytically active sites from MoS₂. Furthermore, this CZTS/MoS₂-rGO heterostructure showed much higher photocatalytic activity than both Au and Pt nanoparticle-decorated CZTS (Au/CZTS and Pt/CZTS) photocatalysts, indicating the MoS₂-rGO hybrid is a better co-catalyst for photocatalytic hydrogen generation than the precious metal. The CZTS/MoS₂-rGO system also demonstrated stable photocatalytic activity for a continuous 20 h reaction.

Graphene-based Recyclable Photo-Absorbers for High-Efficiency Seawater Desalination

Today's scientific advances in water desalination dramatically increase our ability to transform seawater into fresh water. As an important source of renewable energy, solar power holds great potential to drive the desalination of seawater. Previously, solar assisted evaporation systems usually relied on highly concentrated sunlight or were not suitable to treat seawater or wastewater, severely limiting the large scale application of solar evaporation technology. Thus, a new strategy is urgently required in order to overcome these problems. In this study, we developed a solar thermal evaporation system based on reduced graphene oxide (rGO) decorated with magnetic nanoparticles (MNPs). Because this material can absorb over 95% of sunlight, we achieved high evaporation efficiency up to 70% under only 1 kW m(-2) irradiation. Moreover, it could be separated from seawater under the action of magnetic force by decorated with MNPs. Thus, this system provides an advantage of recyclability, which can significantly reduce the material consumptions. Additionally, by using photoabsorbing bulk or layer materials, the deposition of solutes offen occurs in pores of materials during seawater desalination, leading to the decrease of efficiency. However, this problem can be easily solved by using MNPs, which suggests this system can be used in not only pure water system but also high-salinity wastewater system. This study shows good prospects of graphene-based materials for seawater desalination and high-salinity wastewater treatment.

The Assembling of Poly (3-Octyl-Thiophene) on CVD Grown Single Layer Graphene

The interface between organic semiconductor and graphene electrode, especially the structure of the first few molecular layers at the interface, is crucial for the device properties such as the charge transport in organic field effect transistors. In this work, we have used scanning tunneling microscopy to investigate the poly (3-octyl-thiophene) (P3OT)-graphene interface. Our results reveal the dynamic assembling of P3OT on single layer graphene. As on other substrates the epitaxial effect plays a role in determining the orientation of the P3OT assembling, however, the inter-thiophene distance along the backbone is consistent with that optimized in vaccum, no compression was observed. Adsorption of P3OT on ripples is weaker due to local curvature, which has been verified both by scanning tunneling microscopy and density functional theory simulation. Scanning tunneling microscopy also reveals that P3OT tends to form hairpin folds when meets a ripple.

In Situ Formation of ZnO in Graphene: A Facile Way To Produce a Smooth and Highly Conductive Electron Transport Layer for Polymer Solar Cells

A novel electron transport layer (ETL) based on zinc oxide@graphene:ethyl cellulose (ZnO@G:EC) nanocomposite is prepared by in situ formation of zinc oxide (ZnO) nanocrystals in a graphene matrix to improve the performance of polymer solar cells. Liquid ultrasound exfoliation by ethyl cellulose as stabilizer not only allows for uniform dispersion of graphene solution but also maintains an original structure of graphene gaining a high conductivity. The ZnO@G:EC ETL displays a quite smooth morphology and develops the energy-level alignment for the electron extraction and transportation. Subsequently, the device based on poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C61 butyric acid methyl ester (PC61BM) with the ZnO@G:EC as ETL obtains a power conversion efficiency (PCE) of 3.9%, exhibiting a ∼20% improvement compared to the familiar device with bare ZnO nanocrystals as ETL. Replacing the active layer with polythieno[3,4-b]thiophene/benzodithiophene (PTB7): (6,6)-phenyl-C71 butyric acid methyl ester (PC71BM), the PCE can be dramatically improved to 8.4%. This facile and fascinating method to produce a smooth and highly conductive electron transport layer provides an anticipated approach to obtain high performance polymer solar cells.

Carbonaceous materials and their advances as a counter electrode in dye-sensitized solar cells: challenges and prospects

Dye-sensitized solar cells (DSSCs) serve as low-costing alternatives to silicon solar cells because of their low material and fabrication costs. Usually, they utilize Pt as the counter electrode (CE) to catalyze the iodine redox couple and to complete the electric circuit. Given that Pt is a rare and expensive metal, various carbon materials have been intensively investigated because of their low costs, high surface areas, excellent electrochemical stabilities, reasonable electrochemical activities, and high corrosion resistances. In this feature article, we provide an overview of recent studies on the electrochemical properties and photovoltaic performances of carbon-based CEs (e.g., activated carbon, nanosized carbon, carbon black, graphene, graphite, carbon nanotubes, and composite carbon). We focus on scientific challenges associated with each material and highlight recent advances achieved in overcoming these obstacles. Finally, we discuss possible future directions for this field of research aimed at obtaining highly efficient DSSCs.

Edge reconstruction-mediated graphene fracture

Creation of free edges in graphene during mechanical fracture is a process that is important from both fundamental and technological points of view. Here we derive an analytical expression for the energy of a free-standing reconstructed chiral graphene edge, with chiral angle varying from 0° to 30°, and test it by first-principles computations. We then study the thermodynamics and kinetics of fracture and show that during graphene fracture under uniaxial load it is possible to obtain fully reconstructed zigzag edges through sequential reconstructions at the crack tip. The preferable condition for this process is high temperature (T ∼ 1000 K) and low (quasi-static) mechanical load (KI ∼ 5.0 eV Å(-5/2)). Edge configurations of graphene nanoribbons may be tuned according to these guidelines.

Doping of wide-bandgap titanium-dioxide nanotubes: optical, electronic and magnetic properties

Doping semiconductors is an important step for their technological application. While doping bulk semiconductors can be easily achieved, incorporating dopants in semiconductor nanostructures has proven difficult. Here, we report a facile synthesis method for doping titanium-dioxide (TiO₂) nanotubes that was enabled by a new electrochemical cell design. A variety of optical, electronic and magnetic dopants were incorporated into the hollow nanotubes, and from detailed studies it is shown that the doping level can be easily tuned from low to heavily-doped semiconductors. Using desired dopants - electronic (p- or n-doped), optical (ultraviolet bandgap to infrared absorption in co-doped nanotubes), and magnetic (from paramagnetic to ferromagnetic) properties can be tailored, and these technologically important nanotubes can be useful for a variety of applications in photovoltaics, display technologies, photocatalysis, and spintronic applications.

Fluorescence from graphene oxide and the influence of ionic, π-π interactions and heterointerfaces: electron or energy transfer dynamics

2D crystals such as graphene and its oxide counterpart have sought good research attention for their application as well as fundamental interest. Especially graphene oxide (GO) is quite interesting because of its versatility and diverse application potential. However the mechanism of fluorescence from GO is under severe discussion. To explain the emission in general two interpretations were suggested, viz localization of sp(2) clusters and involvement of oxygeneous functional groups. Despite this disagreement, it should be acknowledged that the heterogeneous atomic structure, synthesis dependent and uncontrollable implantation of oxygen functional groups on the basal plane make such explanations more difficult. Nevertheless, a suitable explanation enhances the applicability of the material which also enables the design of novel materials. At this juncture we believe that given the complexity in understanding the emission mechanism it would be very useful to review the literature. In this perspective we juxtapose various results related to fluorescence and influencing factors so that a conclusive interpretation may be unveiled. Apparently, the existing interpretations have largely ignored the factors such as self-rolling, byproduct formation etc. Vis-a-vis previous reviews did not discuss the interfacial charge transfer across heterostructures and the implication on the optical properties of GO or reduced graphene oxide (rGO). Such analysis would be very insightful to determine the energetic location of sub band gap states. Moreover, ionic and π-π type interactions are also considered for their influence on emission properties. Apart from these, quantum dots, covalent modifications and nonlinear optical properties of GO and rGO were discussed for completeness. Finally we made concluding remarks with outlook.

Electrochemically reduced graphene oxide multilayer films as efficient counter electrode for dye-sensitized solar cells

We report on a new counter electrode for dye-sensitized solar cells (DSCs), which is prepared using layer-by-layer assembly of negatively charged graphene oxide and positively charged poly (diallyldimethylammonium chloride) followed by an electrochemical reduction procedure. The DSC devises using the heteroleptic Ru complex C106TBA as sensitizer and this new counter electrode reach power conversion efficiencies of 9.5% and 7.6% in conjunction with low volatility and solvent free ionic liquid electrolytes, respectively. The new counter electrode exhibits good durability (60°C for 1000 h in a solar simulator, 100 mW cm⁻²) during the accelerated tests when used in combination with an ionic liquid electrolyte. This work identifies a new class of electro-catalysts with potential for low cost photovoltaic devices.

Graphene and graphene-like layered transition metal dichalcogenides in energy conversion and storage

Being confronted with the energy crisis and environmental problems, the exploration of clean and renewable energy materials as well as their devices are urgently demanded. Two-dimensional (2D) atomically-thick materials, graphene and grpahene-like layered transition metal dichalcogenides (TMDs), have showed vast potential as novel energy materials due to their unique physicochemical properties. In this Review, we outline the typical application of graphene and grpahene-like TMDs in energy conversion and storage fields, and hope to promote the development of 2D TMDs in this field through the analysis and comparisons with the relatively natural graphene. First, a brief introduction of electronic structures and basic properties of graphene and TMDs are presented. Then, we summarize the exciting progress of these materials made in both energy conversion and storage field including solar cells, electrocatalysis, supercapacitors and lithium ions batteries. Finally, the prospects and further developments in these exciting fields of graphene and graphene-like TMDs materials are also suggested.

Graphene oxide/α-Bi(2)O(3) composites for visible-light photocatalysis, chemical catalysis, and solar energy conversion

The growing challenges of environmental purification by solar photocatalysis, precious-metal-free catalysis, and photocurrent generation in photovoltaic cells receive the utmost global attention. Here we demonstrate a one-pot, green chemical synthesis of a new stable heterostructured, ecofriendly, multifunctional microcomposite that consists of α-Bi2 O3 microneedles intercalated with anchored graphene oxide (GO) microsheets (1.0 wt %) for the above-mentioned applications on a large economical scale. The bare α-Bi2 O3 microneedles display two times better photocatalytic activities than commercial TiO2 (Degussa-P25), whereas the GO-hybridized composite exhibits approximately four to six times enhanced photocatalytic activities than the neat TiO2 photocatalyst in the degradation of colored aromatic organic dyes (crystal violet and rhodamine 6G) under visible-light irradiation (300 W tungsten lamp). The highly efficient activity is associated with the strong surface adsorption ability of GO for aromatic dye molecules, the high carrier acceptability, and the efficient electron-hole pair separation in Bi2 O3 by individual adjoining GO sheets. The introduction of Ag nanoparticles (2.0 wt %) further enhances the photocatalytic performance of the composite over eightfold because of a plasmon-induced electron-transfer process from Ag nanoparticles through the GO sheets into the conduction band of Bi2 O3 . The new composites are also catalytically active and catalyze the reduction of 4-nitrophenol to 4-aminophenol in the presence of borohydride ions. Photoanodes assembled from GO/α-Bi2 O3 and Ag/GO/α-Bi2 O3 composites display an improved photocurrent response (power conversion efficiency ∼20 % higher) over those prepared without GO in dye-sensitized solar cells.

Low temperature reduction of free-standing graphene oxide papers with metal iodides for ultrahigh bulk conductivity

Here we report a green and facile route for highly efficient reduction of free-standing graphene oxide (GO) papers with metal iodide aqueous solutions at low cost. The metal iodides (MgI₂, AlI₃, ZnI₂, FeI₂) were synthesized directly from metal and iodine powder with water as a catalyzer. An extremely high bulk conductivity of 55088 S/m for reduced graphene oxide (rGO) papers were obtained with FeI₂ solution of which pH = 0 at 95°C for 6 hours. The catalytic effect of strong Lewis acid for the promotion of the nucleophilic substitution reaction is responsible for the greatly improved bulk conductivity. Furthermore, it was found that the layer-to-layer distance (d_L) and the crystallinity of the rGO papers are regarded as two main factors affecting the bulk conductivity rather than C/O ratio and defect concentration.

Metal–organic frameworks MIL-88A hexagonal microrods as a new photocatalyst for efficient decolorization of methylene blue dye

Metal–organic framework MIL-88A displays an active MB dye degradation performance.

Solvothermal synthesis of orthorhombic Sb2WO6 hierarchical structures and their visible-light-driven photocatalytic activity

Doughnut-like, concave hierarchical structures of orthorhombic Sb₂WO₆ were firstly prepared and were found to exhibit excellent visible-light-driven photocatalytic performance.