Janki Shah

In the present work, we investigate the effect of nanoparticle crystallite size and shape on the thermal, rheological and optical properties of low-cost copper oxide nanofluid. Nanofluids are prepared by suspending 0.3% volume of nanoparticles in the 70:30 ethylene glycol:distilled water mixture using ultrasonic vibration, and followed by the microwave irradiation. Our results indicate that the zeta potential values of the nanofluids decrease as nanoparticle anisotropy or aspect ratio increases, zeta potential values decreases. Moreover, the increase in the thermal conductivity of the nanofluids is maximum for the nanofluids prepared using nanorods having the highest aspect ratio of 5.84. The rheology data of the CuO nanofluids with different shapes of nanoparticles at a particle volume fraction of 0.3% indicates that the nanofluids predominantly show Newtonian behaviour, exemplified by the shear rate independent viscosity. Moreover, the rheological behaviour is observed to depend on crystallite size and the nanoparticles shape as marked by an increase in the viscosity which follows the order, spherical < cubelike < rectangular < nanobar < nanorods. The comparison of the optical transmittance spectra for the base fluid and CuO suspended nanofluids suggests that the latter have higher adsorption capacity than the base fluid in the range 940 and 1165 nm. The CuO nanofluids with different shapes can be potentially utilised as direct solar absorber and heat transfer fluid and also as a coolant owing to their excellent stability, high thermal conductivity and low viscosity.

We present a study on the adsorption process of p-group atoms on the α-Al2O3 corundum phase (0 0 0 1) surface by the density functional theory. The band gap is tuneable from an insulator to wide bandgap semiconducting nature by adsorption of p-group atoms (B, C, N, O, F) owing physisorption and chemisorption process on the alumina (0 0 0 1) surface. Adsorption energies are also calculated for all complex systems for centre top, Al-top and O-top sites. The hybridization of adsorbed p-group atoms, tune the electronic properties along to the n-type and p-type nature, which light up the new way to develop possible nanodevice. We also carried out electronic band structure, projected density of state (PDOS), electron localised function (ELF) and optical properties to understand the behaviour of adsorbed adatoms on the substrate. The result concludes that extra adatoms with α-Al2O3 shows the excellent adsorption in an ultraviolet region and work as UV mirrors.

Unique properties of nanofluids as an absorber fluid, due to the smaller size of nanoparticles, which cover a larger surface area, make a bulkive evolution in heat transfer. Thermophysical properties of nanofluids are increased due to the potential of the nanoparticles surface area increased which is suspended in the conventional fluid. The initial parameter of thermophysical properties which is thermal conductivity (k) enhanced by some parameters like Brownian motion, interface resistance, morphology of suspended nanoparticles and aggregating in nanofluids are reviewed. In the present review paper, we have also mentioned the synthesis of nanofluids by various techniques; methods of stabilization, stability measurement techniques, and thermal conductivity and heat transfer properties, theoretical models of thermal conductivity and their applications are summarized.

In the recent work, we study on the structural and electronic properties of the graphene like Pd monolayer with the adsorption of oxygen adatoms by using first-principles calculations. The electronic band structure and projected density of states investigate that Pd-surface with oxygen molecule adsorption gives metallic behaviour. We found that the behaviour changed at M-point in the electronic band structure as adding oxygen atoms. The oxygen adsorption was dissociative until the Pd surface immersed with oxygen atoms. The electron charge density increases as the number of oxygen atoms on Pd-surface increases. The noticeable observation is that by adding 7th oxygen atom, they started to ripple from fixed Pd-surface without making a bond due to oxygen coverage increases. The results show that Pd monolayer has different applications as a oxygen catalyst and it can be utilized as the pellet, surface, and film materials to safeguard sustenance from oxidation.

In the present work, we focused on the thermal conductivity and viscosity of the synthesis as well as characterize metal oxide α-Al2O3 nanoparticles suspended in distilled water:ethylene glycol (60:40) ratio based stable colloidal nanofluid. The band gap of the α-Al2O3 with and without surfactant is 4.42 and 4.59 eV, respectively. The results show that nanoparticle with polyvinyl alcohol surfactant has smaller crystalline size (~23 nm) than without surfactant (~36 nm). The synthesized nanofluids have good stability after 15 days of synthesis which is characterized by zeta potential analyzer. Thermal conductivity and viscosity are measured for 0.1 and 0.5 wt% concentration of alumina for with and without surfactant. The concentration of particles and added surfactant are responsible for stable fluid, thermal conductivity enhancement, and viscosity of nanofluid with respect to temperature. Therefore, the novel combinations of characterized properties of α-Al2O3 nanofluid has proved to be the best thermally stable heat transfer fluid compared to conventional cooling fluids.

In the reported work, we have approached the interaction of the amino acids onto the antimonene (Sb) monolayer by using density functional theory (DFT). Here, we have considered glycine (Gly), glutamic (Glu), histidine (HIE/His) and phenylalanine (Phe) biomolecules for interaction. The structural, electronic and optical properties have been investigated to understand the behavior. The adsorption of the biomolecules on Sb monolayer show the physisorption process. The adsorption energy of the phenylalanine (Phe) biomolecules is the most favorable. The optical absorption peaks of systems come in the near visible region. The studies conclude that Sb monolayer is useful for the bio-integrated electronics based devices.

The present study deals with the synthesis and characterization of aluminum oxide (Al2O3) nanopowders, it is very useful material as dielectric, ceramic and catalyst. The high-quality nanopowders were obtained by adding surfactants urea and sodium acetate. Further, all characterizations are done for with (urea and sodium acetate) and without surfactant. X-ray diffraction was used to characterize phase formation and the crystallite size of powder while, FTIR gives information about the particle composition and surface intermediates. X-ray diffraction spectra revealed the synthesized nanoparticles phase transformation were γ-Al2O3 to α-Al2O3 phase. Furthermore, the addition of urea and sodium acetate significantly reduced the crystalline size of α-Al2O3 nanoparticles from 43.94 nm to 35.12 nm respectively.

In the developing era, metal oxide nanomaterials are intensively pursued due to their prominence applications in different applied and technological fields. The transition metal oxide, copper oxide is a dominant candidate for magnetic storage devices, sensor, and solar energy transfer as a heat absorber, super capacitors and mainly as a good catalyst in chemical reactions. Here, CuO nanostructures with different shapes (nanoparticle, cubelike, rectangular, nanobar and nanorod) are synthesized by precipitation method from CuCl2 precursors. The CuO all structures are characterized by X-ray diffraction for the structural study. CuO different shapes morphological phenomena are carried out from SEM and TEM. The thermal properties are calculated by recording thermo-curves, viz. thermogravimetric (TG), differential thermogravimetric (DTG). Thermogravimetric analysis revealed CuO all structures show weight loss at 340 K to 380 K and 1000 K to 1250 K region because of water evaporation and combustion of organic compounds respectively. Activation energy, Arrhenius factor, activation enthalpy, activation entropy and Gibbs free energy for the decomposition of CuO were determined using the Coats-Redfern (CR) method for all shaped structures.

In recent work, CuO nanofluid is prepared with and without PVA (poly(vinyl alcohol)) coated surfactant nanoparticles suspension in distilled water: ethylene glycol (DW:EG) (60:40) ratio for 0.1 wt% and 0.5 wt% concentration of fluid by two-step technique. Our work describes a simple and cost effective chemical precipitation method to synthesis CuO nanoparticles with the addition of synthetic polymer (PVA) allows the modification of physical properties of copper oxide (CuO) nanoparticles. The scanning electron microscopy (SEM) shows the morphological difference in nanocrystallite size and shape between without surfactant coated nanoparticles and with PVA coated particles. XRD pattern of CuO particles reveal that high crystal quality with the monoclinic crystal structure where PVA coated particles have crystallite size 15 nm and without coating it is 31 nm. UV-Vis (ultraviolet absorption spectroscopy) spectra confirmed that the CuO absorption peak at 292 nm and 445 nm for CuO+ PVA. Fourier transform infrared spectra (FTIR) spectroscopy studies show the interaction between PVA and CuO nanoparticles. Experimental results concluded that for CuO + PVA nanofluid, particle size is smaller and showing more stable fluid from zeta potential values. Thermal conductivity results are carried from sound velocity of fluid by Bridgman’s equation. As the particle concentration increases in fluid, thermal enhancement is noted. It was found that the viscosity of nanofluid is lower with a larger size particle at the same temperature and for the same concentration. Therefore, our result shows that CuO nanofluids have good potential for effective heat transfer application.

The objective of this research is to examine how ultrasonication time affects agglomeration, stability, thermal conductivity, and viscosity of CuO nanofluid. Using different reaction conditions, distinct shaped CuO nanoparticles are synthesised and dispersed in an EG: DW (70:30) ratio with 0.3 vol%. Microscopic and TEM images are used to analyze colloidal solutions with varying sizes and shapes of nanoparticles. After 30 days of preparation, the zeta potential is measured to ensure that the suspension is stable. The Bridgman equation is used to compute thermal conductivity using sound velocity values. Viscosity of colloidal suspension is measured by viscometer. All of the studies are performed at 30° ± 2 °C room temperature for ultrasonication times ranging from 30–120 min. At an optimal sonication time of 80 min, there is less agglomeration and more stable particle dispersion. In comparison to other morphological suspensions, CuO spherical shape suspended nanofluid has the lowest viscosity and maximum thermal conductivity, as well as the most stable fluid. At the optimal sonication period, measured results demonstrate thermal increase and decreased viscosity, which could have implications for heat transfer applications.