Nanomaterials

In this investigation, the electrospraying of CNTs on an electrospun PVDF-Co-HFP membrane was carried out to fabricate robust membranes for the membrane distillation (MD) process. A CNT-modified PVDF-Co-HFP membrane was heat pressed and characterized for water contact angle, liquid entry pressure (LEP), pore size distribution, tensile strength, and surface morphology. A higher water contact angle, higher liquid entry pressure (LEP), and higher tensile strength were observed in the electrosprayed CNT-coated PVDF-Co-HFP membrane than in the pristine membrane. The MD process test was conducted at varying feed temperatures using a 3.5 wt. % simulated seawater feed solution. The CNT-modified membrane showed an enhancement in the temperature polarization coefficient (TPC) and water permeation flux up to 16% and 24.6%, respectively. Field-effect scanning electron microscopy (FESEM) images of the PVDF-Co-HFP and CNT-modified membranes were observed before and after the MD process. Energy dispersive spectroscopy (EDS) confirmed the presence of inorganic salt ions deposited on the membrane surface after the DCMD process. Permeate water quality and rejection of inorganic salt ions were quantitatively analyzed using ion chromatography (IC) and inductively coupled plasma-mass spectrometry (ICP-MS). The water permeation flux during the 24-h continuous DCMD operation remained constant with a >99.8% inorganic salt rejection.

Thermoelectricity is a promising technology that directly converts heat energy into electricity and finds its use in enormous applications. This technology can be used for waste heat recovery from automobile exhausts and industrial sectors and convert the heat from solar energy, especially in hot and humid areas such as Qatar. The large-scale, cost-effective commercialization of thermoelectric generators requires the processing and fabrication of nanostructured materials with quick, easy, and inexpensive techniques. Moreover, the methods should be replicable and reproducible, along with stability in terms of electrical, thermal, and mechanical properties of the TE material. This report summarizes and compares the up-to-date technologies available for batch production of the earth-abundant and ecofriendly materials along with some notorious works in this domain. We have also evaluated and assessed the pros and cons of each technique and its effect on the properties of the materials. The simplicity, time, and cost of each synthesis technique have also been discussed and compared with the conventional methods.

A numerical investigation of three-dimensional hybrid nanomaterial micropolar fluid flow across an exponentially stretched sheet is performed. Recognized similarity transformations are adopted to convert governing equations from PDEs into the set ODEs. The dimensionless system is settled by the operating numerical approach bvp4c. The impacts of the nanoparticle volume fraction, dimensionless viscosity ratio, stretching ratio parameter, and dimensionless constant on fluid velocity, micropolar angular velocity, fluid temperature, and skin friction coefficient in both x-direction and y-direction are inspected. Graphical outcomes are shown to predict the features of the concerned parameters into the current problem. These results are vital in the future in the branches of technology and industry. The micropolar function  Rη increases for higher values of the micropolar parameter and nanoparticle concentration. Micropolar function Rη declines for higher values of the micropolar parameter and nanoparticle concentration. Temperature function is enhanced for higher values of solid nanoparticle concentration. Temperature function declines for higher values of the micropolar parameter. The range of the physical parameters are presented as: 0.005<ϕ2<0.09, Pr=6.2, 0<K<2, 0<a<2.0, ϕ1=0.1, and 0<c<1.5.

The low-power, high-performance graphene/ZnO Schottky photodiodes were demonstrated through the direct sputter-growth of ZnO onto the thermally-cleaned graphene/SiO2/Si substrate at room temperature. Prior to the growth of ZnO, a thermal treatment of the graphene surface was performed at 280 °C for 10 min in a vacuum to desorb chemical residues that may serve as trap sites at the interface between graphene and ZnO. The device clearly showed a rectifying behavior with the Schottky barrier of ≈0.61 eV and an ideality factor of 1.16. Under UV illumination, the device exhibited the excellent photoresponse characteristics in both forward and reverse bias regions. When illuminating UV light with the optical power density of 0.62 mW/cm2, the device revealed a high on/off current ratio of >103 even at a low bias voltage of 0.1 V. For the transient characteristics upon switching of UV light pulses, the device represented a fast and stable photoresponse (i.e., rise time: 0.16 s, decay time: 0.19 s). From the temperature-dependent current–voltage characteristics, such an outstanding photoresponse characteristic was found to arise from the enhanced Schottky barrier homogeneity via the thermal treatment of the graphene surface. The results suggest that the ZnO/graphene Schottky diode holds promise for the application in high-performance low-power UV photodetectors.

Nanoparticles are coated in-flight with a plasma-enhanced chemical vapor deposition (PECVD) process at ambient or elevated temperatures (up to 300 °C). Two silicon precursors, tetraethyl orthosilicate (TEOS) and hexamethyldisiloxane (HMDSO), are used to produce inorganic silica or silica-organic shells on Pt, Au and TiO2 particles. The morphology of the coated particles is examined with transmission electron microscopy (TEM) and the chemical composition is studied with Fourier-transform infrared spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). It is found that both the precursor and certain core materials have an influence on the coating composition, while other parameters, such as the precursor concentration, aerosol residence time and temperature, influence the morphology, but hardly the chemical composition. The coated particles are used to demonstrate simple applications, such as the modification of the surface wettability of powders and the improvement or hampering of the photocatalytic activity of titania particles.

Carbon nanotube-reinforced magnesium matrix (CNTs/Mg) composite has great application potential in the transportation industry, but the trade-off between strength and ductility inhibits its widespread application. In order to balance the strength and plasticity of the composite, in this work, on the basis of the AZ61 matrix composite homogeneously reinforced by Ni-coated CNTs (hard phase), 30 vol.% large-size AZ61 particles are introduced as an isolated soft phase to fabricate hierarchical CNTs/AZ61 composites. The compression tests show the fracture strain and compressive strength of this composite increases by 54% and 8%, respectively, compared with homogeneous CNTs/AZ61 composite. During deformation, the hard phase is mainly responsible for bearing the load and bringing high strength, due to the precipitation of the Mg17Al12 phase, uniformly dispersed CNT and strong interfacial bonding of the CNTs/Mg interface through nickel plating and interfacial chemical reaction. Furthermore, the toughening of the soft phase results in high ductility. With the increase in CNT content, the compressive strength of composites is nearly unchanged but the fracture strain gradually decreases due to the stress concentration of CNT and its agglomeration.

Carbon nanotubes (CNTs) reinforced magnesium matrix composites have great application potential in the transportation industry, but the low absolute strength is the main obstacle to its application. In this paper, copper-coated CNTs and AZ61 powder were used as raw materials to prepare CNTs/refined-AZ61 composites with good interfacial bonding, uniformly dispersed CNTs and fine grains by the process of ball milling refinement of AZ61 powder, ball milling dispersion and hot-pressing sintering. When the volume fraction of CNTs is less than or equal to 1 vol.%, CNTs can be uniformly dispersed and the yield strength and compressive strength of composites increase with higher CNT content. When the volume fraction of CNTs is 1 vol.%, the compressive strength and yield strength of composites reach 439 MPa and 361 MPa, respectively, which are 14% and 9% higher than those of matrix composites with nearly the same value of fracture strain. When the volume fraction of CNTs is greater than 1 vol.%, with the increase in CNT content, CNT clustering becomes more and more serious, resulting in a decrease in the strength and fracture strain of composites.

Dispersion of carbon nanotubes and carbon nanofibers is a crucial processing step in the production of polymer-based nanocomposites and poses a great challenge due to the tendency of these nanofillers to agglomerate. Besides the well-established three-roll mill, the ultrasonic dispersion process is one of the most often used methods. It is fast, easy to implement, and obtains considerably good results. Nevertheless, damage to the nanofibers due to cavitation may lead to shortening and changes in the surface of the nanofillers. The proper application of the sonicator to limit damage and at the same time enable high dispersion quality needs dedicated knowledge of the damage mechanisms and characterization methods for monitoring nano-particles during and after sonication. This study gives an overview of these methods and indicates parameters to be considered in this respect. Sonication energy rather than sonication time is a key factor to control shortening. It seems likely that lower powers that are induced by a broader tip or plate sonicators at a longer running time would allow for proper dispersions, while minimizing damage.

In this paper, CNT/Mg composites with high compressive properties were prepared by using Ni-plated CNT and pure magnesium powder as raw materials through the grinding of magnesium powder, ball-milling mixing and hot-pressing sintering. The effect of grinding time for finer magnesium powder on the microstructure and properties of the final composites was studied mainly by SEM, XRD, HRTEM and compression tests. The results show that with the prolongation of milling time, the magnesium particle size decreases gradually and the CNT dispersion becomes more uniform. Moreover, the nickel layer on the surface of CNT reacts with highly active broken magnesium powder in the sintering process to generate MgNi2 intermediate alloy, which significantly improves interface bonding. The strength and fracture strain of composites are significantly increased by the combined action of the uniform distribution of CNTs and strong interface bonding from the MgNi2 phase. The compressive strength, yield strength and fracture strain of the composites, prepared with a 60 h grinding of magnesium powder, reached 268%, 272% and 279% of those in composites without the grinding of magnesium powder.

The dispersion of carbon nanotubes (CNTs) is the bottleneck in CNT-reinforced metal matrix composites. In this work, CNT/Mg composites were prepared by grinding Mg powder and then dispersing CNTs via ball milling and hot pressing. The uniform distribution of Ni-coated CNTs in the matrix was achieved by optimizing the content of CNTs. Scanning electron microscope, high-resolution transmission electron microscopy and X-ray diffraction, optical microscopy, and compression tests were employed. With the CNT content being less than 1%, the CNTs can be evenly distributed in CNT/Mg composites, resulting in a sharp increase in strength. However, with the higher CNT content, the CNTs gradually cluster, leading decreased fracture strain and strength. Furthermore, the coated Ni in the CNTs reacts with the magnesium matrix and completely transforms into Mg2Ni, significantly enhancing the interface bonding. This strong interface bonding and the diffusely distributed Mg2Ni in the matrix significantly strengthen the CNT/Mg composite.