Growth Of Nanomaterials Research Articles

Selective synthesis of carbon nanotubes by catalytic decomposition of methane using Co-Cu/cellulose derived carbon catalysts: A comprehensive kinetic study

Determination of the optimal operating conditions for large-scale production of carbonaceous nanomaterials (CNTs), mainly carbon nanotubes (CNTs) but also graphene-related materials (GRMs), remains as a major industrial and scientific challenge. For this purpose, our group is conducting an extensive study to evaluate the effect of the reaction conditions and catalyst compositions on the productivity and selectivity to different carbonaceous nanomaterials. In the case of Co-based catalysts, we have found that the promotion with Cu or Mn has a dramatic effect on the type of carbon nanomaterials synthesized. Thus, the presence of Cu promotes the growth of CNTs, while Mn favors the formation of two-dimensional GRMs. In this context, we present here a comprehensive study of the CNTs growth via catalytic decomposition of methane using a Co-Cu/cellulose derived carbon catalyst. The influence of the reaction temperature (650–950 °C) and feed composition (7.1%–42.9% of CH4 and H2) on the yield and CNTs quality was evaluated. A transition in the characteristics of the carbonaceous nanomaterial growth was observed at about 800 °C. Below this temperature, the reaction was selective towards the formation of CNTs, while above 800 °C, the obtained nanomaterial exhibited a graphite-like morphology. In addition, the catalyst deactivation was quite low in the CNTs growth regime, attaining high productivity under 11 h of operation. The model used to study the kinetics of carbon formation allowed understanding the most influential variables in the growth process, revealing the existence of a transition temperature at which there is a change in the preferential path for the formation of CNTs or GRMs. After exploring a large set of reaction conditions, the best operating parameters for growing CNTs with high productivity (0.29 gC/gcat∙h) and quality (ID/IG = 1.10, I2D/IG = 0.13) were found at 750 °C under 28.6% CH4:14.3% H2:57.1% N2.

On the Distance Directional Growth of Ga<sub>x</sub>O<sub>y</sub> Nanomaterials Concerning the Surface Au Droplets and Au/Ga/O Clusters Outward Diffusion on the Separated Au Islands/Strips on Gaas Substrate Using Thermal Vapor-Liquid-Solid Method

This paper outlines some experimental results and discusses the new growth method for growing the different GaxOy nanomaterials formed during the outward diffusion of the surface nanoclusters (SNCs) including the Au droplets and/or surface Au/Ga/O nanoclusters from the Au separated islands/strips being on GaAs substrate during the thermal Vapor -Liquid -Solid method with two steps temperature mode. Depending on the technological conditions, during the outward diffusion of the SNCs from the Au catalyst island/strip, the different sizes, morphologies and features of nanomaterials will be formed along the surface diffusion direction with the decreasing sizes. This growth method to be so called the distance directional growth method, it has not reported in the Literature. The nanomaterial growth process here could be explained by the solid - solid phase with the self-growth mechanism from the moving-diffusing SNCs with the features formed already before based on their chemical- physical interactions between the Au catalyst island/strip and GaAs substrate. In the suitable technological conditions the surface nanoscale Kirkendall effect with Kirkendall voids also completely formed... Based on the results of Field Emission Scanning electron Microscope (FESEM), the Energy-Dispersive X-ray diffraction (EDX) measurements, the formation mechanism and effect of the SNCs outward diffusion on the growth of different GaxOy nanomaterials have discussed more in detailed.. The diffusivities of the SNCs depending on technological conditions in the different samples have estimated by the random walk theory, their values are in the range of 8.35x10-10 to 10-11 m2/sec. The distance directional growth method could be applied for the growing and controlling the nanomaterials configurations outside the Au catalyst island/strip on GaAs substrate with the different sizes for nano devices application.

Controllable Growth of Copper on TiO2 Nanoparticles by Photodeposition Based on Coupled Effects of Solution Viscosity and Photoreduction Rate for Catalysis-Related Applications

The wet chemical growth of nanomaterials is widely reported as an alternative to high vacuum growth. There have been numerous studies that investigate the morphology change of formed nanomaterials ...

Current Trends in MXene-Based Nanomaterials for Energy Storage and Conversion System: A Mini Review

MXene is deemed to be one of the best attentive materials in an extensive range of applications due to its stupendous optical, electronic, thermal, and mechanical properties. Several MXene-based nanomaterials with extraordinary characteristics have been proposed, prepared, and practiced as a catalyst due to its two-dimensional (2D) structure, large specific surface area, facile decoration, and high adsorption capacity. This review summarizes the synthesis and characterization studies, and the appropriate applications in the catalysis field, exclusively in the energy storage systems. Ultimately, we also discussed the encounters and prospects for the future growth of MXene-based nanomaterials as an efficient candidate in developing efficient energy storage systems. This review delivers crucial knowledge within the scientific community intending to design efficient energy storage systems.

Low-temperature growth of Three dimensional ReS2/ReO2 metal-semiconductor heterojunctions on Graphene/polyimide film for enhanced hydrogen evolution reaction

Flexible inorganic electronics (FIE) have shown unique advantages in energy conversion, aerospace and wearable devices due to excellent electronic properties and thermostability of inorganic materials. The industrialization of high-performance flexible inorganic electronics (FIE) devices requires universal approaches to fabricate inorganic crystal on polymer substrates at acceptable temperature. Herein, we firstly developed the vortex flow chemical vapor deposition (VFCVD) for low temperature synthesis of high-quality vertical ReO2 arrays at 450 °C on flexible graphene-polyimide (G-PI) conductive film. The Euler equations suggest that the vapor pressure of ReO2 is almost 100-times higher than that of free space with VFCVD at identical conditions. The derived ReS2/ReO2 metal-semiconductor heterojunction arrays are performed outstanding hydrogen evolution reaction (HER) activity with high long-term stability as an energy conversion device. This work opens up an opportunity for low temperature growth of inorganic nanomaterials on polymer substrates by VFCVD for the industrialization of high-performance flexible energy devices.

The non-stationary case of the Maxwell-Garnett theory: growth of nanomaterials (2D gold flakes) in solution.

The solution-based growth mechanism is a common process for nanomaterials. The Maxwell-Garnett theory (for light–matter interactions) describes the solution growth in an effective medium, homogenized by a mean electromagnetic field, which applies when materials are in a stationary phase. However, the charge transitions (inter- and intra-transitions) during the growth of nanomaterials lead to a non-stationary phase and are associated with time-dependent permittivity constant transitions (for nanomaterials). Therefore, time-independence in the standard Maxwell-Garnett theory is lost, resulting in time dependence, εi(t). This becomes important when the optical spectrum of a solution needs to be deconvoluted at different reaction times since each peak represents a specific charge/energy transfer with a specific permittivity constant. Based on this, we developed a time-resolved deconvolution approach, f(t) ∝ εi(t), which led us to identify the transitions (inter- and intra-transitions) with their dominated growth regimes. Two gold ion peaks were precisely measured (322 nm and 367 nm) for the inter-transition, and three different polyaniline oxidation states (PAOS) for the intra-transition, including A (372 nm), B (680 nm), and C (530 nm). In the initial reaction time regime (0–90 min), the permittivity constant of gold was found to be highly dependent on time, i.e. fE ∝ εi(t), since charge transfer takes place from the PAOS to gold ions (i.e. inter-transition leads to a reduction reaction). In the second time regime (90–180 min), the permittivity constant of gold changes as the material deforms from 3D to 2D (fS ∝ ε3D–2D), i.e. intra-transition (combined with thermal reduction). Our approach provides a new framework for the time-dependent modelling of (an)isotropic solutions of other nanomaterials and their syntheses.

Recovery of waste gold for the synthesis of gold nanoparticles supported on radially aligned nanorutile: the growth of carbon nanomaterials.

Precious and expensive metals are lost each year through the discarding of old jewellery pieces and mine tailings. In this work, small amounts of gold were recovered by digestion with aqua regia from waste tailings. The recovered gold in the form of HAuCl4 was then used to deposit Au0 onto radially aligned nanorutile (RANR) to form a supported catalyst material. The support material, RANR, was synthesized using the hydrothermal technique whereas the deposition of gold was achieved using the deposition–precipitation with urea method at various loadings. Electron microscopy was used to show that the structure of the support is a sphere formed by multiple nanorods aligned in a radial structure. The Au nanoparticles were observed at the tips of the nanorods. It was confirmed by XRD that the support was indeed a rutile phase of TiO2 and that the Au nanoparticles had a face-centred cubic structure. The various catalysts were then used to synthesize carbon nanomaterials (CNMs) using the chemical vapour deposition technique. A parametric study varying the reaction temperature, duration and carbon source gas flow rate was conducted to study the effects these conditions have on the structural properties of the resulting CNMs. Here, it was found that mainly carbon nanofibers were formed and that the different reaction conditions influenced their graphicity, width, structure and thermal properties.

Rapid assessment of nanomaterial homogeneity reveals crosswise structural gradients in zinc-oxide nanowire arrays.

In an effort to scale-up nanomaterial growth over large surface areas, we aim to effectively study the structural non-homogeneities within the arrays of zinc oxide nanowires (ZnO-NWs). The assessment of the lateral gradient of the nanowires' characteristics is presented including their height and surface density. To this end, spectroscopic ellipsometry and the rather recently reported technique of spectral domain attenuated reflectometry are used as two fast, simple and non-invasive characterization methods with further capabilities of scanning over the sample surface. Simple models are proposed by considering ZnO-NWs as the equivalent of thin stratified layers based on the effective medium approach. The methodology not only reveals the presence of gradients, but also enables quantitative analysis for all the samples grown using the hydrothermal method with different growth times ranging from 0.5 h up to 4 h. The gradients are confirmed using scanning electron microscopy (SEM) observations taken as a reference. The results also suggest that the sample orientation during the growth influences the NW growth besides the other parameters already known to affect the growth mechanisms.

Effect of hydrothermal synthesis on physical property modulation and biological activity of ZnO nanorods

Influence of hydrothermal synthesis route on various defect states of ZnO nanomaterial and this specific synthesis route induced physical property modulation and the biological activity of ZnO nanomaterial has been considered here for the first time ever. X-ray diffraction (XRD) and Field emission scanning electron microscopy (FESEM) reveal the presence of single phase wurtzite structure of ZnO nanomaterial with hexagonal rod like morphology. Photoluminescence (PL) study confirms the presence of structural defects in form of oxygen vacancy defects, zinc vacancy defects, zinc interstitial defects etc in the ZnO nanomaterial. The detail analysis of magnetic response at different temperatures reveals the presence of vacancy mediated room temperature ferromagnetism (RTFM) in rod like ZnO nanomaterial. Dielectric response as a function of frequency has also been measured for ZnO nanorods. The result of this dielectric study shows that the nanomaterial of ZnO exhibits superior dielectric constant due to the grain boundary defect. Hydrothermal synthesis route influences the structure of ZnO nanomaterial mostly towards rod like in nature and the grain boundary defect of rod like structure creates large space charge polarization. In addition to the significant modulation of all these physical properties based on the hydrothermal synthesis route, various biological activities such as antibacterial and antifungal activities of these rod like ZnO nanomaterial has also been observed on the Gram negative clinical isolates like, Escherichia coli, Klebsiella pneumoniae, and plant pathogen Alternaria alternate. Hydrothermal synthesis route creates such an impact on the growth of ZnO nanomaterial that the material evolves with significant modulations of physical properties and biological activities.

Synthesis of Boron Nanosheets in Copper Medium

Boron has a tendency to form bulk structures due to its unique electron-deficient property, so it’s hard for boron to form sheets in large quantities. Here, we report a novel method for the preparation of boron nanosheets in large quantities by copper medium. The method mainly includes mechanical exfoliation, recombination and extraction. A large number of boron nanosheets with a height of below 6 nm have been prepared in this work. X-ray photoelectron spectroscopy and Raman spectroscopy results confirmed that the nanosheets possess the characteristics of α-rhombohedra boron and β-rhombohedra boron with a high content of boron. Hexagonal and rhombic sheets have been observed and two different growth processes are revealed successfully, which are also the basic structures of boron nanosheets. An interesting phenomenon also have been discovered that high density nanotwins exist in β-Rhombohedra boron sheets and it might stimulate more interest in growth of nanomaterials.

Natural nanofiber-based stacked porous nitrogen-doped carbon/NiFe2O4 nanohybrid nanosheets

The traditional hydrolysis/hydrothermal two-step preparation method of carbon/inorganic nanohybrid material usually exhibit the disadvantage of aggregation and precipitation. Therefore, the above method has certain difficulty in the synergistically regulation of the aggregation morphology and microscopic morphology of carbon/inorganic nanohybrid materials. In this paper, cellulose nanofiber and chitin nanofiber are used as the carrier material of inorganic nanomaterials, which can maintain the uniform and stable dispersed state during the hydrolysis of metal ions and hydrothermal treatment. The uniform inorganic nanoparticles uniformly distributed in the randomly stacked nanosheets even if the total content of metal ions increases to 6 mmol. The natural nanofibers/NiFe2O4 nanoparticles composite nanosheets with adjustable stacked pore structure can be prepared from natural nanofibers/NiFe2O4 nanoparticles composite hydrogel via unidirectional freeze-shaping. The carbonization temperature and carbonization time are more effective in synergistically regulation of the stacked porous nitrogen-doped carbon/NiFe2O4 nanohybrid nanosheets. Extending carbonization time or increasing carbonization temperature not only allows the growth of inorganic nanomaterials, but also causes damage to the nanosheets (such as broken pore and the small, wrinkled morphology of the nanohybrid nanosheets). NC/NiFe2O4-1.5/700/3 exhibits the highest gravimetric capacitance (up to 458 F g−1 at a constant current density of 0.5 A g−1).

Quality-by-Design Concepts to Improve Nanotechnology-Based Drug Development.

The purpose of this review is to discuss the challenges associated with the development of nanoparticle-based quality drug products in adhering to the principles of quality by design (QbD) and defining appropriate quality parameters towards successful product development. With the advent of nanotechnology into the pharmaceutical field, the novel field of nanomedicine was born. Due to their unique properties in terms of size, conformation and targeted delivery, nanomedicines are able to overcome many drawbacks of conventional medicine. As nano-sized formulations have made their way into more and more therapies, it has became clear that these very unique properties create hurdles for nanomedicines in successfully traversing the regulatory pathways and there is a need to develop nanomedicines in a more controlled and consistent fashion. The elements of a QbD methodology explained in this review enable the development of nano-based formulations in a way that maximizes the possibility of success. The identification of critical quality attributes (CQA) of the drug product and its intermediates are discussed in detail with a focus on nanomaterial-based formulations. In conclusion, QbD and the identification and specification of CQAs at its core are critical to the design, development and growth of nanomaterials in pharmaceuticals.

Effect of Mo on the catalytic activity of Ni-based self-organizing catalysts for processing of dichloroethane into segmented carbon nanomaterials

A series of micro-disperse Ni-Mo alloys with the sponge-like structure was prepared by a simultaneous precipitation method followed by sintering of the sediment in H2 atmosphere at 800 °C. According to XRD data, the formation of single-phase solid solution Ni1-xMox took place for the samples with Mo content of 0.6–8.3 wt.%. Synthesized samples were studied in a process of the catalytic CVD of C2H4Cl2 at 550–700 °C. In situ kinetic studies of carbon deposition process were carried out in a flow gravimetric setup equipped with McBain balances. An interaction of Ni-Mo alloys with C2H4Cl2 is accompanied by their rapid disintegration with formation of disperse active particles catalyzing the growth of carbon nanomaterials (CNM). The strong boosting effect of Mo on the catalytic performance of Ni was revealed. The maximum yield of CNM product (8.3 wt.% Mo, 600 °C, 120 min) was as high as 45 g/gM. The study on effect of the reaction temperature on the CNM yield allowed one to define an optimal temperature regime. The impact of Mo concentration upon the morphology, structural features and textural properties of the produced carbon fibers was investigated by means of SEM, TEM, Raman spectroscopy and low-temperature nitrogen adsorption. The role of chemisorbed chlorine species in a pulse-to-pulse regime of the segmented carbon filaments formation was discussed.

Pulsed Laser Deposition Assisted van der Waals Epitaxial Large Area Quasi‐2D ZnO Single‐Crystal Plates on Fluorophlogopite Mica

AbstractThere are still challenges in growth of transferable large area orientated ultrathin high‐melting‐point metal oxide single crystals with conventional methods. Herein, a new pathway to produce high quality single‐crystal ZnO nanoplates with more than 400 µm crystal size is revealed by using the van der Waals epitaxy (vdWE) combined with pulsed laser deposition (PLD) method on fluorophlogopite mica. The quasi‐2D ZnO plates as thin as 5 nm on fluorophlogopite mica without transition layer are achieved, showing an excellent thickness and orientation control while maintaining the excellent crystalline. ZnO nanoplates grown on conducting graphite and insulating hexagonal boron nitride (h‐BN) 2D substrates are also obtained through PLD assisted vdWE. The transfer of 15 nm thick quasi‐2D ZnO plates with 8 mm × 8 mm area onto a SiO2/Si substrate is successfully demonstrated. Based on the ZnO nanoplates, semitransparent self‐powered ultraviolet (UV) photodetectors and light‐emitting diodes centered at 400 nm UV region are demonstrated. This research highlights that the PLD assisted vdWE method is a fascinating way to fabricate high coverage ultrathin 2D ZnO plates with precisely thickness control for optoelectronic applications and may have enormous inspiration for other 2D nanomaterials growth.

Plasmon-Driven Catalysis on Molecules and Nanomaterials

As a new class of photocatalysts, plasmonic noble metal nanoparticles with the unique ability to harvest solar energy across the entire visible spectrum and produce effective energy conversion have been explored as a promising pathway for the energy crisis. The resonant excitation of surface plasmon resonance allows the nanoparticles to collect the energy of photons to form a highly enhanced electromagnetic field, and the energy stored in the plasmonic field can induce hot carriers in the metal. The hot electron-hole pairs ultimately dissipate by coupling to phonon modes of the metal nanoparticles, resulting in a higher lattice temperature. The plasmonic electromagnetic field, hot electrons, and heat can catalyze chemical reactions of reactants near the surface of the plasmonic metal nanoparticles. This Account summarizes recent theoretical and experimental advances on the excitation mechanisms and energy transfer pathways in the plasmonic catalysis on molecules. Especially, current advances on plasmon-driven crystal growth and transformation of nanomaterials are introduced. The efficiency of the chemical reaction can be dramatically increased by the plasmonic electromagnetic field because of its higher density of photons. Similar to traditional photocatalysis, energy overlap between the plasmonic field and the HOMO-LUMO gap of the reactant is needed to realize resonant energy transfer. For hot-carrier-driven catalysis, hot electrons generated by plasmon decay can be transferred to the reactant through the indirect electron transfer or direct electron excitation process. For this mechanism, the energy of hot electrons needs to overlap with the unoccupied orbitals of the reactant, and the particular chemical channel can be selectively enhanced by controlling the energy distribution of hot electrons. In addition, the local thermal effect following plasmon decay offers an opportunity to facilitate chemical reactions at room temperature. Importantly, surface plasmons can not only catalyze chemical reactions of molecules but also induce crystal growth and transformation of nanomaterials. As a new development in plasmonic catalysis, plasmon-driven crystal transformation reveals a more powerful aspect of the catalysis effect, which opens the new field of plasmonic catalysis. We believe that this Account will promote clear understanding of plasmonic catalysis on both molecules and materials and contribute to the design of highly tunable catalytic systems to realize crystal transformations that are essential to achieve efficient solar-to-chemical energy conversion.

Gas Phase Electrodeposition Enabling the Programmable Three-Dimensional Growth of a Multimodal Room Temperature Nanobridge Gas Sensor Array.

Parallel three-dimensional (3D) growth of different nanomaterials with submicrometer resolution is a promising approach to overcome some technological and economic limits encountered in planar integrated homogeneous films. The programmable multimaterial gas phase nanoparticle electrodeposition concept enables the fabrication of a 3D multimodal conductometric gas sensor array. The approach requires the deposition of more than one nanomaterial to achieve orthogonal sensing capabilities and multigas sensitivity and selectivity. The demonstrated "electronic nose"-like array contains 1080 self-aligning 3D nanobridge-based electrical connections of platinum, nickel oxide, and gold on a single chip. The nanobridges form through a nearest neighbor Coulombic interaction. Each gas sensitive bridge is a 3D structure composed of a porous but electrically conducting nanoparticle network. It was found that this architecture is unique, because it does not require external heating to operate. A trimodal sensor array will be demonstrated to detect various levels of ammonia (NH3), carbon monoxide (CO), and hydrogen sulfide (H2S). A 3 × 3 transfer matrix will be discussed to correlate the recorded signals with the gas composition.

Incorporation of clusters within inorganic materials through their addition during nucleation steps

Nanomaterials are known to display chemical and physical behaviours that are different from those of their bulk counterparts, but assembly processes in the sub-nanometre region are difficult to control. The early growth of nanomaterials is typically thought to involve two separate steps: nucleation and the growth stage, as described by the LaMer model. Control of the shape and size of the final structure is typically determined during the growth stage by interactions between the nuclei and surrounding monomers. Here, we show that clusters with well-defined structures, such as polyoxometalates, can intervene at the nucleation stage of nickel oxysulfide and nickel-cobalt hydroxide by co-assembling with nuclei to produce uniform binary assemblies. Those can, in turn, incorporate a third, or also a fourth, type of nanocluster to form ternary or quaternary assemblies, respectively. Both binary and ternary assemblies are shown to serve as efficient atomic-site catalysts for room-temperature gasoline desulfurization and stereoselective catalytic reactions.

Growth Dynamics of Gallium Nanodroplets Driven by Thermally Activated Surface Diffusion.

The growth of catalytic liquid-metal nanodroplets on flat substrates is essential for many technological applications. However, the detailed nucleation and growth dynamics of these nanodroplets remain unclear. Here, using in situ transmission electron microscopy (TEM) imaging, we track in real time the growth of individual Ga nanodroplets from a beam of Ga vapor. We show that the nucleation and growth are driven by thermally activated surface diffusion of Ga adatoms, with the diffusion activation energy of ED = 95 ± 10 meV on a SiNx surface. More importantly, our analysis shows that Ga dimers serve as the critical nucleation clusters and that the nanodroplet growth follows a power-law of the form R(t) ∝ e-ED/kBT(t - t0)1/2. These insights into the growth dynamics of metallic nanodroplets are essential for tailoring their size and density for their application in self-catalyzed growth of nanomaterials.

Mineralization-Inspired Synthesis of Magnetic Zeolitic Imidazole Framework Composites.

Metal-organic frameworks (MOFs) capable of mobility and manipulation are attractive materials for potential applications in targeted drug delivery, catalysis, and small-scale machines. One way of rendering MOFs navigable is incorporating magnetically responsive nanostructures, which usually involve at least two preparation steps: the growth of the magnetic nanomaterial and its incorporation during the synthesis of the MOF crystals. Now, by using optimal combinations of salts and ligands, zeolitic imidazolate framework composite structures with ferrimagnetic behavior can be readily obtained via a one-step synthetic procedure, that is, without the incorporation of extrinsic magnetic components. The ferrimagnetism of the composite originates from binary oxides of iron and transition metals such as cobalt. This approach exhibits similarities to the natural mineralization of iron oxide species, as is observed in ores and in biomineralization.

Mineralization‐Inspired Synthesis of Magnetic Zeolitic Imidazole Framework Composites

AbstractMetal–organic frameworks (MOFs) capable of mobility and manipulation are attractive materials for potential applications in targeted drug delivery, catalysis, and small‐scale machines. One way of rendering MOFs navigable is incorporating magnetically responsive nanostructures, which usually involve at least two preparation steps: the growth of the magnetic nanomaterial and its incorporation during the synthesis of the MOF crystals. Now, by using optimal combinations of salts and ligands, zeolitic imidazolate framework composite structures with ferrimagnetic behavior can be readily obtained via a one‐step synthetic procedure, that is, without the incorporation of extrinsic magnetic components. The ferrimagnetism of the composite originates from binary oxides of iron and transition metals such as cobalt. This approach exhibits similarities to the natural mineralization of iron oxide species, as is observed in ores and in biomineralization.