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A continuous electrocoagulation reactor, with curved electrodes, polarity switch, and cylindrical geometry, was used for emulsified crude oil in water separation. Apparatus novelty consists of an inlet arranged to promote a circular flow regime. The effects of flow rate (2 and 6 mL.s

Os sensores são um dos pilares da tecnologia contemporânea. Suas aplicações são inúmeras para diferentes campos. Assim, torna-se indispensável o desenvolvimento de sensores e métodos de comunicação entre dispositivos, bem como equipamentos de controle. Este trabalho propôs um sistema para detecção em fase gasosa de gás liquefeito de petróleo (GLP) em mistura com ar, utilizando um aparato experimental formado por elemento sensor de gás, controlador de temperatura e uma placa Arduino equipada com um transmissor de dados sem fio Zigbee. O trabalho envolveu a área de química e computação para atingir desde o desenvolvimento do elemento sensor a base de SnO2 até a instrumentação, apresentando assim a preparação da suspensão coloidal, deposição e tratamento térmico do filme, a montagem do sistema de mistura de gases e sistema de aquecimento do elemento sensor, os acoplamentos do microcontrolador para transmissão de dados através de dispositivos Zigbee, a elaboração e construção do circuito eletrônico, bem como a caracterização do filme de óxido e as medidas de sensor em atmosfera de mistura gasosa envolvendo ar e GLP. Um microcomputador, utilizando um programa escrito em linguagem Python, armazenou os dados, condicionados por um microcontrolador, recebidos por meio de rede sem fio Zigbee. Além dos resultados técnicos para o sensor desenvolvido com sensibilidade dentro dos limites de inflamabilidade da mistura ar e GLP, o trabalho permite concluir que o envolvimento de áreas relacionadas permite o desenvolvimento de trabalhos amplos envolvendo desde a elaboração até a instrumentação de sensor.

Made available in DSpace on 2021-06-25T10:16:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 We studied the catalytic and antimicrobial properties of hierarchical architecture of WO3.Ag synthesized at 100, 150, and 200 °C by a very simple and reliable hydrothermal technique. The investigation carried out by XRD showed the amorphous nature of sample grown at 100 °C, while those at 150 and 200 °C crystalline nature of 3D WO3.Ag was confirmed. From FESEM and HRTEM results, it was evident that the silver nanoparticles grew in a 3D WO3.Ag host matrix. The average diameter of Ag nanoparticles by HRTEM was around 5–15 nm. Photocatalytic activities of as-prepared samples were evaluated by the degradation of rhodamine B (RhB). Samples prepared at 150 and 200 °C showed higher activity in comparison to sample prepared at 100 °C. This can be mainly attributed to the suppression of traps states and electron/hole pairs recombination as highlighted by the photoluminescence results. The as-synthetized samples showed promising antimicrobial features against various bacterial strains. The 100 °C WO3.Ag nanospheres exhibited the highest antibacterial activity, with very low minimum inibitory concentration (MIC) values (4.0–8.0 μg/ml) when compared with 150 and 200 °C samples. [Figure not available: see fulltext.] Department of Chemistry Universidade Estadual Paulista—Unesp, P.O. Box 473 Pharmaceutical Science Post-Graduation Program Universidade Federal do Rio Grande do Sul Faculty of Pharmacy Department of Analysis Universidade Federal do Rio Grande do Sul Department of Chemistry Universidade Federal do Espírito Santo—UFES Faculdade de Ciências e Tecnologia—FCT Departament of physics Universidade Estadual Paulista, Rua Roberto Simonsen, 305 Physics Institute of São Carlos (IFSC) University of São Paulo Department of Physics NanO LaB Universidade Federal de São Carlos, Via Washington Luiz, Km 235, P.O. Box 676 Grupo de Nanoestruturas Semicondutoras—Department of Physics Universidade Federal de São Carlos, Via Washington Luiz, Km 235, P.O. Box 676 LIEC—CDMF—Department of Chemistry Universidade Federal de São Carlos, Via Washington Luiz, Km 235, P.O. Box 676 Department of Chemistry Universidade Estadual Paulista—Unesp, P.O. Box 473 Faculdade de Ciências e Tecnologia—FCT Departament of physics Universidade Estadual Paulista, Rua Roberto Simonsen, 305

Titanium dioxide (TiO2) is a semiconductor that can be applied in different technological areas. In this work, we investigated the modifications of the electrical properties of thin films composed of TiO2 nanoparticles produced with different morphologies. The solvothermal route used for the synthesis allowed the production of nanoparticles with functionalized surfaces due to oleate groups. It was possible to modulate nanocrystals shape and size due to the detachment crystal growth mechanism, by changing the reaction time. Nanorods were obtained using 4 h of synthesis, and an increase in the reaction time to 64 h led to a bipyramidal morphology. The functionalization by the organic ligand allowed the preparation of stable colloidal solutions, which were used to prepare thin films by the dip-coating method. The films presented a homogeneous surface, an average thickness around 100 nm, and no agglomerations were observed. The electrical resistance measurements indicated a typical behavior of semiconductors, and they were dependent on the nanoparticle morphology. An exploratory test indicated that the thin films prepared using nanorod particles presented a higher electrical response compared with isotropic particles, when exposed in a liquefied petroleum gas vapor atmosphere. Therefore, the morphology of the nanoparticles is a key factor for the further application of these thin films in gas sensing. Employing an easy methodology which required simple apparatus, and by using reaction time modulation only, it was possible to prepare homogeneous thin films with a tunable electrical response.

Design of metal oxide nanoparticles is a key study for obtaining high-functional materials with tunable properties. For that purpose, great progress on chemical methods for controlling the growth of nanoparticles during the synthesis has been made. However, an important challenge faced by this field of study is to completely understand the crystallization process and the chemical pathways during the syntheses that use growth-controlling agents. In this study, the synthesis of ZrO2 was conducted by a solvothermal methodology using three different organic solvents (oleic acid, benzyl alcohol and octyl alcohol) and adjusting the Zr precursor concentration, aiming to control the ZrO2 nanocrystal growth and obtain single-phase nanocrystalline particles. X-ray diffraction and Raman spectroscopy experiments indicated the formation of pure monoclinic, cubic and tetragonal ZrO2 nanocrystals for the syntheses using oleic acid, benzyl alcohol and octyl alcohol as solvents with precursor concentrations of 0.25, 0.50 and 0.50 mol L−1, respectively. Transmission electron microscopy was used to analyze the nanocrystal structure and to assess the crystal size distribution. Infrared and solid-state 13C nuclear magnetic resonance spectroscopy confirmed the presence of the organic ligands chemically bonded to the surface of the nanocrystals. Thermogravimetric analysis indicated an increasing ratio of ligand molecules/surface area as the acidity of the solvent increased. With the observations from this study, the solvent pKa value, the chemical structure and the type of coordination of the capping agents are ascribed as responsible for promoting different growth pathways, allowing pure crystalline phase zirconium oxide nanocrystals to be obtained.

Biomedical applications with emphasis on the design of smart materials, specifically magnetic nanoparticles (MNPs) are considered to have technological benefits because they can be manipulated using magnetic fields. Magnetic NPs have been widely used in hyperthermia, target drug delivery system, imaging, and extraction of biomolecules, postulating them also as an important tool in cancer treatment. Morphological structures of magnetic materials have drawn tremendous attention from diverse scientific fields due to their unique surface chemistry, nontoxicity, biocompatibility, and particularly their inducible magnetic moment. This review features recent research accomplishments made in the biomedical field using magnetic nanoparticles. The first part gives a comprehensive overview of magnetic nanoparticles in the treatment of chronic diseases and drug targeting. The second part includes the role of magnetic nanoparticles in electrochemical, optical-based immunoassays. The review also outlines the current challenges and future research perspectives for fostering advanced and high-performance magnetic nanoparticles in technological applications.

Made available in DSpace on 2021-06-25T10:23:08Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-04-01 ZrO2 nanoparticles (ZrO2 NPs) and Ag@ZrO2 nanocomposite (Ag@ZrO2 NCs) were prepared from zirconium (IV) butoxide in the absence of base or acid mineraliser by the advanced oxidation processes (AOP) and subsequent hydrothermal treatment. Samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), Raman, Photoluminescence (PL), Fourier transform infrared (FTIR), and diffuse reflectance spectroscopy (DRS). XRD and Raman analyses confirmed ZrO2 NPs and Ag@ZrO2 NCs tetragonal crystalline phase synthesized at 200 °C for 1 h. HRTEM images of ZrO2 NPs and Ag@ZrO2 NCs after treatment at 200 °C indicated small nanoparticles with characteristic size of 5–8 nm (ZrO2) and 40–50 nm (Ag NPs). It was found that Ag@ZrO2 NCs showed outstanding photocatalytic activity in photodegradation Rhodamine B dye compared with pure ZrO2 NPs. Antibacterial activity tests of ZrO2 NPs and Ag@ZrO2 NCs were carried out using E. coli and S. aureus as model strains of Gram-negative and Gram-positive bacteria, respectively. Ag@ZrO2 NCs were capable of efficiently growth inhibition of bacteria cultures in more than 75% E. Coli compared to ZrO2 NPs that exhibited

The technology of electrochemical flexible nanosensors is growing rapidly due to the innumerable advantages that these devices offer, such as quick detection of pathogens or biomarkers, high sensitivity of detection, and accessibility of the tools. With the advances in data sciences, it is possible to connect these sensors with the Internet of Things (IoT) and make use of artificial intelligence systems as a diagnostic tool. Also, these sensors avoid the costs of large equipment and complex laboratories for detection. These systems have evolved effective methods for diagnosing diseases, detecting pathogens, and improving treatment efficacy, consequently improving patient quality of life. This chapter gives a brief overview of flexible electrochemical smart nanosensors, including definitions, smart materials, and advances in this field regarding preventive and personalized medical devices.

Made available in DSpace on 2020-12-12T01:15:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 Hierarchical architecture self-assembled three-dimensional WO3 and WO3·Ag with high uniformity have been successfully obtained using peroxopolytungstic acid as precursor and silver in a morphological engineering approach under moderate hydrothermal conditions. The as-grown samples were characterized by XRD, FEG-SEM, HRTEM, TGA, Raman, FTIR, UV-Vis, and XPS. In addition, the photocatalytic performance of the hierarchical architecture self-assembled three-dimensional WO3 and WO3·Ag has also been investigated through degradation of Rhodamine B (RhB) dye under 467 nm LED light irradiation. Results show that the hierarchical architecture self-assembled three-dimensional shapes evolve (depending on the silver amount) from 3D irregular-platelet-like building blocks to 3D hexagonal building blocks then to three-dimensional hexagonal-football-like and finally to 3D multi-branched spiky ball-like microcrystals. Also, high-magnification FEG-SEM and HRTEM images showed that the Ag nanoparticles with diameter about 5-15 nm were anchored on the surface of the 3D hierarchical architecture. UV-Vis measurements demonstrated that the 3D hierarchical structures gradually absorbed more light when the Ag content was increased. Moreover, the band-gap energy to WO3·0.20Ag was from Eg = 2.48 eV. It was found that 3D multi-branched spiky ball-like WO3·0.20Ag (corresponding to 1.2748 g of the AgNO3) microcrystals show outstanding photocatalytic activity in the photodegradation of RhB dye compared with other 3D hierarchical architectures. Department of Chemistry Universidade Estadual Paulista-Unesp, P. O. Box 473 Department of Chemistry Universidade Federal Do Espírito Santo-UFES Departament of Physics Faculdade de Ciências e Tecnologia-FCT Universidade Estadual Paulista, Rua Roberto Simonsen, 305 Physics Institute of São Carlos (IFSC) University of São NanO LaB-Department of Physics Universidade Federal de São Carlos, Via Washington Luiz km 235, P. O. Box 676 LIEC-CDMF-Department of Chemistry Universidade Federal de São Carlos, Via Washington Luiz, km 235, P. O. Box 676 Department of Chemistry Universidade Estadual Paulista-Unesp, P. O. Box 473 Departament of Physics Faculdade de Ciências e Tecnologia-FCT Universidade Estadual Paulista, Rua Roberto Simonsen, 305

The influence of the distance between electrodes, electrical current, and flow rate of emulsified crude oil in water effluent through an electrocoagulation reactor was studied. Power switch at an interval of 30 s was used to reduce electrode passivation. The output variables were power consumption, pH, and oil removal from effluent. There was no significant change in the output variables with the working time of the reactor. The final pH was between 7.5 and 9.5 depending on the input variables. It increases with higher electrical current and tends to decrease with increased flow rate. Increasing electrical current tends to increase while increasing either distance between electrodes or the flow rate tends to reduce oil removal. Using a 2.88 L reactor, it is possible to treat 7.12 L of effluent in one hour, removing 78% of the crude oil, keeping final pH at 8.3, and this system will have an energy consumption of 21.6 kWh.

Made available in DSpace on 2019-10-06T16:31:41Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-05-15 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) ZrO2@SiO2 core-shell nanostructures were synthesized by a facile two-step hydrothermal plus Stöber chemical route. The structure, morphology and properties of the nanoparticles were characterized using X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy, zeta-potential measurements, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). XRD confirmed the presence of tetragonal ZrO2 crystalline and amorphous SiO2 phases. FTIR analysis confirmed the existence of Zr-O-Si bonds at the surface of the core-shell nanostructures. According to the UV–Vis spectroscopy measurements, the energy band gap value of the uncoated ZrO2 nanoparticles was estimated to be 5.13 eV and the excitation energy (energy band discontinuity) of the ZrO2@SiO2 core-shell nanostructures was found to be 2.31 eV. Transmission electronic microscopy results showed 5–8 nm ZrO2 nanoparticles highly crystalline and fully covered by amorphous and uniform SiO2 layer 10–15 nm wide, which is an evidence of the core-shell structure. Photocatalytic performance of ZrO2@SiO2 core-shell nanostructures was carried out using rhodamine B dye in aqueous solution at room temperature under UV light irradiation. ZrO2@SiO2 core-shell nanostructures showed better photocatalytic activities in comparison to the as prepared ZrO2 and SiO2 samples. The enhanced photocatalytic performance for ZrO2@SiO2 core-shell nanostructures may be the result of the Zr-O-Si interfacial layer narrowing the energy gap needed to electron-hole pairs creation, thus enhancing photoinduced charges generation and reducing charges recombination. LDMFN – Department of Chemistry Universidade Estadual Paulista - Unesp, P.O. Box 473, Bauru LIEC – CDMF – Department of Chemistry Universidade Federal de São Carlos, Via Washington Luiz, Km 235, P.O. Box 676, São Carlos Department of Natural Science Universidade Federal do Espírito Santo - UFES, São Mateus NanO LaB – Department of Physics Universidade Federal de São Carlos, Via Washington Luiz, Km 235, P.O. Box 676, São Carlos LDMFN – Department of Chemistry Universidade Estadual Paulista - Unesp, P.O. Box 473, Bauru CNPq: 470147/2012-1

The solvothermal method is a way to obtain magnetite nanoparticles with uniformity in shape and size, good dispersibility and functionalized surface. These properties are desirable in many applications in materials science and medical area. Although methods for obtaining nanoparticles with these properties are reported, the most their use several reagents to act as solvent, surfactant and reducing agent, which makes the synthesis process more difficult and expensive. In this paper, we introduced a simple method for the preparation of magnetite nanoparticles using only iron (III) acetylacetonate as metal precursor and oleic acid for all the other functions. This is possible due the constant liberation of the acetylacetone formed in the reaction, which favors the formation of the oleate, the responsible for the conditions required to obtain magnetite nanoparticles smaller than 20 nm. By this method, nanoparticles were obtained with an average size of 17 nm in a narrow size distribution, uniformity of morphology, high crystallinity and functionalized surface. The organic capping layer allows the preparation of stable colloidal solutions in organic solvents and facilitates the posterior use of nanoparticles in films, ferrofluids and nanocomposite preparation.

One of the primary challenges in obtaining heterostructures is control of the morphology and surface features of the components that are suitable for a specific application. In this sense, the use of preformed nanoparticles as building blocks is interesting. However, to create heterojunctions between preformed nanoparticles, a further calcination step is usually needed that can result in changes in nanoparticle morphology and surface chemistry. Therefore, the main goal of this study was to explore collision-induced heteroaggregation and oriented attachment under hydrothermal conditions to obtain heterostructures from preformed nanoparticles without further thermal treatment or addition of capping agents. We use anatase TiO2 and rutile SnO2 nanoparticles as a model system. A kinetic model based on a diffusion-controlled reaction is adapted to describe the process. For tracking charge migration across the interface and, consequently, heterojunction formation, we employ an indirect method based on the detection of hydroxyl radicals formed over a semiconductor during UV radiation. The rate of hydroxyl radical formation is directly proportional to the photogenerated charge lifetime, which, in turn, depends on the number of heterojunctions formed. The insights presented here suggest the possibility of obtaining the benefits of heterostructures by using nanoparticles with controlled morphology and surface characteristics.

Although the molecular modeling of self-assembling processes stands as a challenging research issue, there have been a number of breakthroughs in recent years. This report describes the use of large-scale molecular dynamics simulations with coarse grained models to study the spontaneous self-assembling of capped nanoparticles in chloroform suspension. A model system comprising 125 nanoparticles in chloroform evolved spontaneously from a regular array of independent nanoparticles to a single thread-like, ramified superstructure spanning the whole simulation box. The aggregation process proceeded by means of two complementary mechanisms, the first characterized by reactive collisions between monomers and oligomers, which were permanently trapped into the growing superstructure, and the second a slow structural reorganization of the nanoparticle packing. Altogether, these aggregation processes were over after ca. 0.6 μs and the system remained structurally and energetically stable until 1 μs. The thread-like structure closely resembles the TEM images of capped ZrO2, but a better comparison with experimental results was obtained by the deposition of the suspension over a graphene solid substrate, followed by the complete solvent evaporation. The agreement between the main structural features from this simulation and those from the TEM experiment was excellent and validated the model system. In order to shed further light on the origins of the stable aggregation of the nanoparticles, the Gibbs energy of aggregation was computed, along with its enthalpy and entropy contributions, both in chloroform and in a vacuum. The thermodynamic parameters arising from the modeling are consistent with larger nanoparticles in chloroform due to the solvent-swelled organic layer and the overall effect of the solvent was the partial destabilization of the aggregated state as compared to the vacuum system. The modeling strategy has been proved effective and reliable to describe the self-assembling of capped nanoparticles, but we must acknowledge the fact that larger model systems and longer timescales will be necessary in future investigations in order to assess structural and dynamical information approaching the behavior of macroscopic systems.

Electronic properties of self-assembled high crystalline quality fluorine-doped tin oxide (FTO) nanobelts were studied. We report the experimental transport data of a thin film made using a dispersion of these single-crystal nanobelts. We have shown that the theory of weak localization in a weak disorder regime provides a reasonable description of the observed electrons’ transport characteristics of fluorine doped tin oxide nanobelts thin films. Also, our results suggest that the macroscopic extrinsic disorder, related to the random distribution of nanobelts, does not give a noticeable contribution to the whole transport mechanism.

Strontium titanate (SrTiO3) is an n-type semiconductor with high chemical and photochemical stability. This wide band gap oxide has a band gap energy of about 3.2 eV as well as a favorable energy for photocatalysis. In this study, we demonstrate an alternative and superior method to produce Nb-doped and undoped SrTiO3 photoanode thin films based on a colloidal deposition process which possess good activity under standard solar illumination conditions. Methanol was used as “hole scavenger,” and the results showed that the semiconductor–liquid junction (SCLJ) charge accumulation is not an important mechanism to control the photocurrent density and overpotential. In addition, experimental results suggest that the dominance of photocurrent density is controlled by the potential at the surface space charge layer for the Nb-doped SrTiO3 and by recombination at the depletion layer for the undoped oxide.

In this paper, a combined theoretical and experimental study on the electronic structure and photoluminescence (PL) properties of beta zinc molybdate ( -ZnMoO4) microcrystals synthesized by the hydrothermal method has been employed. These crystals were structurally characterized by means of X-ray diffraction (XRD), Rietveld refinement, Fourier transform Raman (FT-Raman) and Fourier transform infrared (FT-IR) spectroscopies. Their optical properties were investigated by ultraviolet-visible (UV-vis) absorption spectroscopy and PL measurements. First-principles quantum mechanical calculations based on the density functional theory at the B3LYP calculation level have been carried out. XRD patterns, Rietveld refinement, FT-Raman and FT-IR spectra showed that these crystals have a wolframite-type monoclinic structure. The Raman and IR frequencies experimental results are in reasonable agreement with theoretically calculated results. UV-vis absorption measurements shows an optical band gap value of 3.17 eV, while the calculated band structure has a value of 3.22 eV. The density of states indicate that the main orbitals involved in the electronic structure of -ZnMoO4 crystals are (O2p-valence band and Mo 4d-conduction band). Finally, PL properties of -ZnMoO4 crystals are explained by distortions effects in octahedral [ZnO6] and [MoO6] clusters and inhomogeneous electronic distribution into the lattice with the electron density map.

The comprehension of the physical-chemistry processes related to the nanocrystals growth mechanism is fundamental in controlling the shape and assembly of inorganic nanoparticles. In this paper, we describe TiO2 nanocrystal synthesis by a colloidal process where the final shape and size of the nanocrystal is influenced by a phenomenon similar to the Rayleigh-instability of freestanding TiO2 nanorods in solution. In this process, a larger structure (the nanorod) is divided into smaller units (nanocrystals), by a kind of detachment process. A detailed high-resolution transmission electron microscopy (HRTEM) characterization facilitates the identification of a morphological feature, which characterizes a surface diffusion process. Through a classical thermodynamic analysis, energetic and geometrics parameters, which lead to fragmentations of TiO2 nanorods, were established.

Correction for ‘Nanocrystals self-assembled in superlattices directed by the solvent–organic capping interaction’ by Cleocir José Dalmaschio et al., Nanoscale, 2013, 5, 5602–5610.

Intense violet–blue photoluminescence (PL) emission at room temperature was verified in BaZrO3 (BZO) powders with structural order–disorder. Ab-initio calculations, ultraviolet–visible absorption spectroscopy and PL were performed. Theoretical results showed that the local disorder in the network-formed Zr clusters present an important role in the formation of hole–electron pair. The experimental data and theoretical results are in agreement, indicating that the PL emission in BZO powders can be related to the structural order–disorder degree in the lattice.

The nanowires were synthesized by the vapor-liquid-solid (VLS) mechanism on quartz substrates in a tube furnace, using gold seeds as catalysts. The nanowires were examined by XRD, SEM and HRTEM analysis showing InP nanowires with a single-crystalline core covered by an amorphous sheath with diameters ranging from 40 - 100 nm and lengths of tens of micrometers. Single nanowire devices were fabricated by conventional photolithography techniques, using Ti metallic contacts. I-V curves were obtained under dark conditions and under focused illumination. Aiming the illustration of the samples for optoelectronic devices, photoconductivity measurements were conducted, submitting the samples to repeated dark-light cycles under 1 V bias. The presented delay in photo-response can be caused by the presence of carrier trap states originated from the self-organized growth mechanism or from the crystalline/amorphous interface.

This work reports the analysis of the distributionof Gd atoms and the quantification of O vacancies appliedto individual CeO 2 and Gd-doped CeO 2 nanocrystals by elec-tron energy-loss spectroscopy. The concentration of O va-cancies measured on the undoped system (6.3 2.6%)matches the expected value given the typical Ce 3+ contentpreviously reported for CeO 2 nanoparticles. The doped nano-particles have an uneven distribution of dopant atoms andan atypical amount of O vacant sites (37.7 4.1%). The mea-sured decrease of the O content induced by Gd dopingcannot be explained solely by the charge balance includingCe 3+ and Gd ions. Introduction Oxygen vacancies are responsible for many interesting proper-ties of oxide materials, and their controlled manipulation canlead to remarkable technological impact. Many applications, in-cluding solid oxide fuel cells (SOFCs), [1] catalysts, [2] sensors, [3] and optoelectronic devices, [4] depend on the amount of equi-librium O vacancies, their localization, and mobility.

Close-packed arrays of ZrO2 nanocrystals (NCs) have been self-assembled from a colloidal solution in a withdrawal dip coating process. A benzyl alcohol route was used to obtain NCs of narrowly controlled size, and then the capping layer was replaced by oleate using solvothermal treatment. The oleate solubility was explored in chloroform, hexane and toluene to prepare thin films of NCs using a dip coating process. From TEM images, the final structures show that increasing the solvent polarity improved self-assembly to prepare mono- and multi-layer superlattices, during solvent evaporation in a short time. The entangled organic chain in the NC surface offsets the limitations of the faceted NCs, improving the assembly quality, allowing the NC assembly to approach the formation of a hard sphere model, resulting in a FCC close-packed structure. Furthermore, the low interaction of chloroform with the capping layer reduces the shrinkage effect during the solvent evaporation preserving the array in the final self-assembled structure. Molecular dynamics simulations with soft potentials supported the conclusion that hexane interacts with the organic capping ligand, increasing the apparent radius of each NC and stabilizing the colloidal suspension, whereas chloroform is partially removed from the capping layer during the aggregation process, forming an array of nanoparticles.

We merged the microwave synthesis approach with an extension of the nonhydrolytic sol-gel method to induce highly selective crystallization of MoS(2) layers over graphene sheets. This hybrid material showed superior electrocatalytic activity in hydrogen evolution reactions.

This communication is a report of our initial research to obtain iron tungstate (FeWO4) nanocrystals by the microwave-hydrothermal method at 170 °C for 45 min. X-ray diffraction patterns showed that the FeWO4 nanocrystals prepared with polyethylene glycol-200 have a partial preferential orientation in the (011) plane in relation to other nanocrystals prepared with sodium bis(2-ethylhexyl)sulfosuccinate and water. Rietveld refinement data indicates that all nanocrystals are monophasic with wolframite-type monoclinic structures and exhibit different distortions on octahedral [FeO6]/[WO6] clusters. High resolution transmission electron microcopy revealed an oriented attachment mechanism for the growth of aggregated FeWO4 nanocrystals. Finally, we observed that the photoluminescence properties of these nanocrystals are affected by partial preferential orientation in the (011) plane and distortions on [FeO6]/[WO6] clusters.

In the last five years, several excellent reviews about oriented attachment (OA) have evidenced the advances achieved in this research area, detailing the growth mechanism and the kinetic models. The main focus of this review is to examine the dependence of the OA mechanism on the colloidal state and to demonstrate how the colloidal state modifies the OA mechanism. Basically, we can define two main possible approaches to achieve self-organization or mutual orientation of adjacent nanocrystals. One is the effective collision of particles with mutual orientation controlled by the number of collisions. This type of growth occurs in a well dispersed colloidal suspension and results in a statistical growth process. The second way is through coalescence induced by particle rotation. This mechanism must be dominant in a weakly flocculated colloidal state in which there is significant interaction among particles. This type of process leads to the formation of complex structures.

Four aluminas were used as supports for impregnation with a zirconium oxide with the aim to achieve a coating, without phase separation, between support and modifier. The supports were impregnated with different concentrations of zirconium aqueous resin, obtained through the polymeric precursor method. After impregnation the samples were calcined and then characterized by XRD, which led to identification of crystalline zirconia in different concentrations from each support used. Using a simple geometric model the maximum amount of surface modifier oxide required for the complete coating of a support with a layer of unit cells was estimated. According to this estimate, only the support should be identified below the limit proposed and crystalline zirconium oxide should be identified above this limit when a complete coating is reached. The results obtained from XRD agree with the estimated values and to confirm the coating, the samples were also characterized by EDS/STEM, HRTEM, XPS, and XAS. The results showed that the zirconium oxide on the surface of alumina support reached the coating in the limit of 15 Zr nm −2 , without the formation of the ZrO 2 phase.

Sn3O4 nanobelts were grown by a carbothermal evaporation process of SnO2 powders in association with the well known vapour-solid mechanism (VS). The nanobelts crystal structure was investigated by x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), raman spectroscopy and field emission gun scanning electron microscopy (FEG-SEM). The structural and morphological characterization has confirmed the growth of single crystal nanobelts. The electrical characterization (current-voltage, temperature-dependent resistance curves) of individual Sn3O4 nanobelts was performed at different temperatures and light excitation. The experiments revealed a semiconductor – like character as evidenced by the resistance decreasing at high temperatures. The transport mechanism was identified as the variable range hopping.

InP nanowires were synthesized on quartz substrates via vapour phase deposition using gold seeds and solid source. The properties of the InP nanowires were investigated by x-ray diffraction , scanning electronic microscopy (FEG-SEM) and high resolution transmission electron microscopy demonstrating micrometric lengths and diameter distribution ranging from 40 to 100 nm with crystalline core. Photo-current on-off characteristics were obtained from single nanowire devices, presenting a delay of a few seconds in the current decay when the illumination is turned off. This time is much larger than some usual microseconds decays and may be caused by localized states whose presence was confirmed by thermally stimulated current TSC measurements.

We report on the synthesis and characterization of ZrO2 nanoparticles prepared from zirconium(IV) butoxide in the absence of base or acid mineraliser by an advanced oxidation processes (AOP) and subsequent hydrothermal treatment which involves mixing and dissolution of the precursor for different temperatures. The structure, morphology and properties of the nanoparticles were characterized using XRD, FE-SEM, TEM, HRTEM, Raman spectroscopy, FT-IR spectroscopy, BET measurements and TGA measurements. The structural analysis by XRD and Raman spectroscopy confirms the ZrO2 specimens synthesized at 100 °C for 1 hour are amorphous and those treated at 150 °C and 200 °C for 1 hour were crystalline. Structural analysis by Raman spectroscopy confirms tetragonal ZrO2 specimens obtained at temperatures higher than 100 °C as a majority phase. From FE-SEM images, the AOP/hydrothermal route mainly produced microspheres comprised of primary nanoparticles. HRTEM images of ZrO2 microspheres, after treatment at 100 °C, show the beginning of crystallization, with only a few clear lattice fringes dispersed in the specimens. TEM and HRTEM images of ZrO2, after treatment at 150 °C and 200 °C indicate that the microspheres are the aggregation of small nanoparticles with a size of approximately 5–8 nm, and FFT analysis confirms the high crystallinity of the specimens. TGA analyses show a distinctive behavior for each of the ZrO2 specimens, after treatment at 100 °C, 150 °C and 200 °C. FT-IR analysis of ZrO2 specimens after hydrothermal treatment revealed the presence of groups, such as –OH, –CH2, and –CH at the surface. In addition, FT-IR spectra show a decrease in the amount of functional groups attached to the surface of the nanoparticles when the reaction temperature is increased. This result was also confirmed by TGA analysis. The ZrO2 specimens prepared by the AOP/hydrothermal route exhibited a high surface area of 511–184 m2 g−1.

Fluorine doped SnO2 (FTO) nanobelts were synthesized and their transport properties, such as conduction mechanism, mobility, carrier density and density of states (DOS) were investigated. Variable range hopping was observed as the dominant mechanism in a large range of temperature (40?260?K). Through these data we estimated the localization length and hopping distance at 300?K of FTO nanobelts exhibiting a three-dimensional character for carrier transport. The carrier mobility was calculated to be 48?cm2?V?1?s?1 for samples with carrier density of 2???1018?cm?3. Taking into account the parameters obtained from temperature-dependent resistivity and the above data, the characteristic DOS at Fermi level in our samples was found.

Single crystalline Zn3P2 nanowires were synthesized on Si substrates via vapour phase deposition catalysed by In–Au seeds. Single nanowire devices were fabricated and the metal–Zn3P2 nanowire contacts were studied using a model based on two Schottky barriers as a function of temperature. As far we know, these are the first reported values of Schottky barriers of Ti/Zn3P2 nanowire contacts. The obtained values showed no significant dependence on the temperature, indicating that the defects at the nanowire's surfaces did not affect the device characteristics. We found evidence of an acceptor level at 49 meV, also indicating that the dominant transport mechanism is the thermal activation of carriers as is found in the bulk Zn3P2. It seems that the p-type behaviour is independent of the dimensionality of the Zn3P2 samples and primarily associated with the phosphorous interstitial atoms.

Layered molybdenum disulfi de (MoS 2 ) is deposited by microwave heating on a reduced graphene oxide (RGO). Three concentrations of MoS 2 are loaded on RGO, and the structure and morphology are characterized. The fi rst layers of MoS 2 are detected as being directly bonded with the oxygen of the RGO by covalent chemical bonds (Mo-O-C). Electrochemical characterizations indicate that this electroactive material can be cycled reversibly between 0.25 and 0.8 V in 1 M HClO 4 solution for hybrids with low concentrations of MoS 2 layers (LCMoS 2 /RGO) and between 0.25 and 0.65 V for medium (MCMoS 2 / RGO) and high concentrations (HCMoS 2 /RGO) of MoS 2 layers on graphene. The specifi c capacitance measured values at 10 mV s 1 are 128, 265, and 148 Fg 1 for the MoS 2 /RGO with low, medium, and high concentrations of MoS 2 , respectively, and the calculated energy density is 63 W h kg 1 for the LCMoS 2 /RGO hybrid. This supercapacitor electrode also exhibits superior cyclic stability with 92% of the specifi c capacitance retained after 1000 cycles.

Photoconducting properties of individual single crystalline Sn3O4 nanobelts were investigated by performing transport measurements. The nanobelts were found to exhibit large responsivity under ultraviolet (UV) illumination: the electric current in one single nanobelt greatly increases by about three orders of magnitude. Such photoconductive behavior was ascribed to the photogeneration of electron–hole pairs and to surface effects such as the oxidation and photoreduction of oxygen molecules (trapping). These mechanisms were found to be drastically modulated by the presence of oxygen vacancies which generates additional energy states that provide free electrons for conduction in our samples. In fact, we report the use of the thermally stimulated current spectroscopy as a powerful tool to study the presence of additional energy levels on Sn3O4 nanobelts as an approach to apply this technique in any high-resistivity nanomaterial. The experimental data provided two vacancy-related levels in 0.01 and 0.2 eV. On the basis of the transport measurements, a qualitative model to explain the response of these samples to UV light is proposed.

In this work we report on structural and Raman spectroscopy measurements of pure and Sn-doped In2O3 nanowires. Both samples were found to be cubic and high quality single crystals. Raman analysis was performed to obtain the phonon modes of the nanowires and to confirm the compositional and structural information given by structural characterization. Cubic-like phonon modes were detected in both samples and their distinct phase was evidenced by the presence of tin doping. As a consequence, disorder effects were detected evidenced by the break of the Raman selection rules.