Structure of graphene and its disorders: a review

Monolayer graphene exhibits extraordinary properties owing to the unique, regular arrangement of atoms in it. However, graphene is usually modified for specific applications, which introduces disorder. This article presents details of graphene structure, including sp² hybridization, critical parameters of the unit cell, formation of σ and π bonds, electronic band structure, edge orientations, and the number and stacking order of graphene layers. We also discuss topics related to the creation and configuration of disorders in graphene, such as corrugations, topological defects, vacancies, adatoms and sp³-defects. The effects of these disorders on the electrical, thermal, chemical and mechanical properties of graphene are analyzed subsequently. Finally, we review previous work on the modulation of structural defects in graphene for specific applications.     

Synthesis, characterization and magnetic properties of nanocrystalline Ni-Zn-Co ferrites

Nanocrystalline magnetic particles of Ni_0.7−xZn_0.3Co_xFe₂O₄ with x lying between 0.0 and 0.3 were synthesized by combustion method using metal nitrates, sucrose and polyvinyl alcohol (PVA). The synthesized powders where characterized by X-ray diffraction and Transmission electron microscopy (TEM). The average crystallite size determined from XRD data using Scherrer formula lie in the range of 20-30 nm. TEM micrographs show a well defined nano-crystallite state with an average particle size of around ~ 10 nm. The electron diffraction patterns confirm the spinel crystal structure of the ferrite. Magnetic properties measured at room temperature by vibrating sample magnetometer (VSM) reveal an increase in saturation magnetization with increase in cobalt concentration. Non-linear increase in saturation magnetization is related to surface effects and method of preparation.     

Crossing the blood–brain barrier with graphene nanostructures

Therapeutic approaches for the delivery of drugs to the central nervous system are hampered by the presence of the blood–brain barrier (BBB); overcoming this barrier is the clinical goal for the treatment of neurological disorders, including Alzheimer’s disease and Parkinson’s disease. The BBB is a cellular barrier of a highly impermeable nature that is predominantly formed by a tightly bound continuous layer of endothelial cells; it acts as a gatekeeper to restrict the free diffusion of bloodborne pathogens into the central nervous system. Targeted drug delivery systems have been explored over the past decade for crossing the BBB. Very recently, graphene nanostructures have shown great potential for crossing the BBB due to their exceptional features such as high electron mobility, ease of synthesis and functionalization, as well as control over size, shape, and the drug release profile. Graphene is evolving as a system not only to detect diseased lesions but also, in parallel, to treat neurological disorders while demonstrating minimal side effects. Given the rapid developments of innovative graphene-based delivery platforms, the present review sheds light on the status and prospects of graphene for crossing the BBB by improving, preserving, or rescuing brain energetics, with a specific focus on how graphene alters neuronal cell function.     

Preparation of α-Fe_2O_3 Nanodisks by Blocking the Growth of (001) Plane

Based on the difference of hydroxy group configuration on different planes of α-Fe2O3 nanoparticles, using the special adsorption and coordination of phosphate on the (001) plane of α-Fe2O3, well-crystallized and well dispersed α-Fe2O3 nanodisks with diameter of 150–200 nm and thickness of 40–80 nm were synthesized via a hydrothermal method. The magnetic properties of synthesized nanodisks were investigated. It was found that the nanodisks possessed a saturation magnetization (Ms) of 0.38 emu/g, a remanent ...     

Preparations of porous AlN particles from an aluminum–magnesium alloy melt solution

Porous AlN particles were prepared from an aluminum–magnesium melt solution. These samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and N₂-adsorption isotherms. The results show that there are many pore formations in every AlN particle, and the wall thickness of the pores is about 10 nm, the diameter of the pores is hundreds of nanometers and the Brunauer–Emmett–Teller (BET) surface area of the samples is 65.183 m²/g.     

Preparation of B-doped titania hollow sphere and its photocatalytic activity under visible light

In this study, B-doped titania hollow spheres were prepared using hydrothermally prepared carbon spheres as template. The photocatalytic activity of as-prepared hollow titania spheres was determined by degradation of Reactive Brilliant Red dye X-3B (C.I. reactive red 2) under visible light irradiation, and was compared to commercial P25 titania. It was revealed that the photocatalytic activity of the hollow titania spheres enhanced a lot. The apparent rate constant of the hollow titania spheres was almost 22 times as that of P25 titania. A photocurrent-time spectrum was also applied to investigate the efficiency of electron transfer in the process of photocatalysis reactions by different samples.     

Synthesis of Ni nanoparticles by reduction of NiCl2 ionic clusters in the confined space of AOT reversed micelles

Stable Nickel nanoparticles have been synthesized by a novel synthetic route based on the reduction of NiCl₂ ionic clusters in the confined space of reversed micelles. The reaction was carried out by adding anhydrous NaBH₄/ethanol solution to a solution of NiCl₂ ionic clusters nanoencapsulated in bis(2-ethylhexyl)sulfosuccinate (AOT) reversed micelles in the presence of n-dodecylmercaptane as capping agent. As highlighted by FT-IR, an extraction with water eliminates surfactant and side products leaving lipophilic Nickel nanoparticles to be dispersed in the organic solvent. UV-Vis investigation ascertained the formation of stable metal Nickel nanoparticles exhibiting novel optical properties.     

Synthesis and luminescence properties of YVO4:Eu nanocrystals grown in nanoporous glass

We report on a feasible method to synthesize luminescence nanocrystals in porous glass in this paper. Well dispersed YVO₄:Eu nanocrystals were proved being grown in nanoporous glass by XRD, micro-Raman spectra and HRTEM equipped with EDS. The YVO₄:Eu³⁺ nanocrystal grown in porous glass herein shows very different luminescence properties compared with single Eu-doped sample. By this method, intense red emission from high silica glass due to energy transfers VO₄³⁻ → Eu³⁺ was obtained. The results show that the reduction from Eu³⁺ to Eu²⁺ in porous glass impregnated with Eu³⁺ ions was avoided effectively.     

In situ synthesis of SnO2/graphene nanocomposite and their application as anode material for lithium ion battery

SnO₂/graphene nanocomposite was prepared via an in situ chemical synthesis method. The nanocomposite was characterized by X-ray diffraction, filed emission scanning electron microscope and transmission electron microscope, which revealed that tiny SnO₂ nanoparticles could be homogeneously distributed on the graphene matrix. The electrochemical performance of the SnO₂/graphene nanocomposite as anode material was measured by galvanostatic charge/discharge cycling. The SnO₂/graphene nanocomposite showed a reversible capacity of 665 mAh/g after 50 cycles and an excellent cycling performance for lithium ion battery, which was ascribed to the three-dimensional architecture of SnO₂/graphene nanocomposite. These results suggest that SnO₂/graphene nanocomposite would be a promising anode material for lithium ion battery.     

Standardization for advanced materials: experience and strategies for the future

Materials technology has been identified by most industrialized nations as a key enabling technology which will provide major economic and competitive advantages to industry. Numerous market forecasts show a strong growth potential in advanced materials applications in diverse industrial sectors. This paper discusses the need for standards and standardized methods for material specification and how this can stimulate the market by providing increased confidence in the design and performance of products. Only a limited number of standards exist for advanced materials, but recently there has been an upsurge of interest worldwide and some countries are very active in developing standards. This is illustrated for some key materials sectors such as advanced ceramics and polymer-matrix composites. Standardization of test and evaluation methods for advanced materials is seen by many countries as a priority area. Methods used for conventional materials can be modified but in some cases new methods have to be developed, both of which approaches require underpinning research. Trade in materials is international in nature and therefore it is very important to harmonize national standards and develop truly international standards which will help remove technical barriers to trade. This requires effort at a national level in order to collaborate in the international fora and negotiate from a position of strength. Both producers and users of materials need to become involved in standards-related activities. In underpinning prestandards research VAMAS, the Versailles Project on Advanced Materials, plays an important role and is developing an internationally recognized technical infrastructure from which standards can be developed. This paper discusses the need and scope for international collaboration in standards-related activities. This paper was presented at the National Workshop on Standardization for Advanced Materials, Strategic Issues, a collaborative effort of Bureau of Indian Standards (BIS), National Materials Policy Project (TIFAC/DST) and Confederation of Engineering Industry (CEI).     

Preparation of LiMn2O4 nanoparticles for Li ion secondary batteries by laser ablation in water

The laser ablation technique in liquids was applied for preparing LiMn₂O₄ nanoparticles for Li ion secondary batteries. A new optical configuration for laser irradiation was also developed to increase irradiation intensity. SEM observation proved that the amount of nanoparticles obtained drastically increased with an increase in laser intensity. On the other hand, the composition change caused by laser ablation was very small. The improvement in the rate capacity of the electrodes composed of the nanoparticles could be explained in terms of particle size reduction.     

X-ray diffraction of permalloy nanoparticles fabricated by laser ablation in water

Permalloy (NiFeMo) nanoparticles were fabricated by laser ablation of bulk material in water with a UV pulsed laser. Transmission electron microscope images showed that approximately spherical particles about 50 nm in diameter were formed in the ablation process. All diffraction peaks corresponding to the bulk material were present in the nanoparticles. In addition to these peaks several new peaks were observed in the nanoparticles, which were attributed to nickel oxide.     

Synthesis and magnetic properties of Mn-doped ZnO nanorods via radio frequency plasma deposition

Well-aligned Mn-doped ZnO nanorods were synthesized by simple radio frequency (RF) plasma deposition in the absence of extra catalysts. The synthesized nanorods having a typical average diameter of about 25 nm, were about 310 nm in length and well-aligned along the normal direction of the substrate. Magnetic measurements indicate that the nanorods are ferromagnetic at room temperature (RT). The presence of considerable shallow donor defects in the nanorods does allow possible defect mediated mechanisms (e.g., bound magnetic polarons) for mediating exchange coupling of the dopant Mn ions resulting in RT ferromagnetism.     

Synthesis and characterization of Fe-Co binary ferrospinel nanospheres via one-step nonaqueous solution pathway

Fe-Co binary ferrospinel (CoFe₂O₄) nanospheres were synthesized by a facile nonaqueous solution route. X-ray diffraction (XRD) and electron diffraction (ED) showed that the obtained nanospheres had the cubic spinel structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the samples consisted of abundant uniform CoFe₂O₄ nanospheres with the particle size in the range of 35-40 nm. The magnetic properties of the sample were measured by using a vibrating sample magnetometer (VSM) at room temperature, which showed that the nanospheres exhibited a typical ferromagnetic behavior.     

Synthesis of Cd1 − xMnxS nanoclusters by surfactant-assisted method: Structural, optical and magnetic properties

Cd_1 − xMn_xS nanoclusters were synthesized by surfactant-assisted chemical method for different Manganese (Mn) concentration (0.40 ≤ x ≥ 0.10) at 60 °C in argon atmosphere. Incorporation of magnetic ions (Mn) results a decrease in band gap of Cd_1 − xMn_xS nanoclusters. The room temperature ferromagnetic behaviour is demonstrated first time in Cd_0.60Mn_0.40S nanoclusters by vibrating sample magneto (VSM) measurements and the origin of magnetization has been discussed.