Metal Oxide Nanocomposites. Группа авторов

the water to be incised, which was caused by UV light. This was conducted by Honda and Fujishima in 1972. It has been issued that the charge clipping and photocatalytic performance can be improved by combination of semiconductor with a wide band gap like SnO₂ with TiO₂ [76, 77]. There is an effective of promoting the photocatalytic performance of visible light, namely TiO₂ matrix is inserted with the combination of metal ions. The principle of this approach is through blocked charge carrier recombination [78]. The insertion of the metal ion promotes the shape of Ti³⁺ ions, thus improving the photocatalytic performance. Transforming the TiO₂ through incorporation of two or more than two dopants is issued, which makes great combination influence. On the contrary, the undoped TiO₂ or the TiO₂ with one ion incorporated is less effective [79, 80]. Surface spots, oxygen vacancies and polar planes contribute the difference in photocatalytic performance of ZnO. With solvothermal technique, Xu et al. synthesized carious forms of ZnO and adopted them as photocatalyst to degrade the phenol [81].

      These researchers proposed that nanoflowers and NPs indicated boosted photodegradation outcomes in comparison to nanoflowers, nanorods, nanotubes, as well as hour-glass-like ZnO spheres. To photodegrade phenol, Liu et al. used TiO₂ nanostructures with various forms such as microspheres, NPs and nanorods though hydrothermal approach [82]. With nanorods to be photocatalyst, this group of researchers gained marvelous photodegradation outcomes. ZnO has come into the researchers’ focus since 1935, but its excellent features are discovered through modern methods and improved equipment [83]. Liang et al. [84] found that the generated graphene–TiO₂ nanocrystal combination featured advanced photocatalytic performance in contrast to other TiO₂ materials like P25, bare TiO₂ and mixture of P25 and GO handled by hydrothermal procedure, in the splitting process of rhodamine B with UV irradiation, boosting a three-fold photocatalytic influence on P25. Metal oxide appearances indicate that it is good at decomposing organic molecules with great oxidizing ability for and superhydrophilicity [85, 86] and such traits could be adopted to generate wettability patterns, which have been adopted in many areas like in printed-circuit boards and offset printing, and can be used for fluid microchips in the future [87, 88].

1.5 Metal Oxide Nanomaterials for Sensor Applications

Research into imidazole chemistry has been quite comprehensive, single-site functionalizations and substitution as well as various annulation strategies has been well documented [89]. Recently, the interest in this heterocyclic system has been widened as it is a precursor to a class of compounds, called room temperature ionic liquids. Microwave-assisted synthesis of the substituted imidazoles on a solid support under solvent-free conditions in a three-component reaction [90] and efficient synthesis of imidazoles from aldehydes, 1,2-diketones and ammonium acetate in acetic acid have been reported [91]. Noble metal Au, Ag, or Pt coated ZnO is important for photoelectron transfer (PET) in the bulk and interface of ZnO semiconductors. Under illumination of UV light, the exciton absorption bands of ZnO are strongly bleached due to the accumulation of conduction band electrons. Thus, the efficiency of both the photocatalysis and photoelectric energy conversion can be greatly enhanced by depositing noble metals on the surface of ZnO [92–94]. The principle terms involved in a photoactive semiconductor are conduction band (CB), valence bands (VB), band gap, trap sites and Fermi level. The bands are the allowed energy states that an electron can occupy in a material. The highest energy band occupied by an electron is called the valence band while the next available lowest empty energy level, next to valence band is called the conduction band. The metal oxide samples were deoxygenated by bubbling with pure nitrogen gas. An ethanolic solution of the imidazole derivative of required concentration was mixed with nanoparticles dispersed in ethanol at different loading and the absorbance and emission spectra were recorded. The nanocrystals were dispersed under sonication in ethanol using ethylene glycol followed by dilution with ethanol. Surface modification of Fe₂O₃ has been performed as follows [95]. 2 g of Fe₂O₃ nanoparticles has been kept in a vacuum chamber at 110 °C for 75 min and then dispersed in acetone by stirring for 1 h at ambient temperature and finally has been sonicated for 20 min. Then, 1 g APTS (50 wt%) has been gradually added to the dispersed solution and stirred for further 24 h at ambient temperature.

Fluorescence enhancing arises due to formation of APTS–ZnO complex. The energy transfer competence is related not only to the distance between the acceptor ZnO and donor APTS (r0) but also to critical energy transfer distance (R0). The critical energy transfer distance (R0),

, where, K2 is the spatial orientation factor of the dipole, N is the refractive index of the medium, φ is the fluorescence quantum yield of the donor and J is the overlap integral of the fluorescence emission spectrum of the donor and the absorption spectrum of the acceptor. On the relative positions basis of APTS and interfacial energy levels, the interfacial electron injection would be thermodynamically allowed from the excited singlet of APTS to CB of ZnO. On lighting at excitation wavelength both the APTS and ZnO are excited. Dual emission is anticipated due to LUMO → HOMO and CB → VB electron transfer. The probable is electron jump from the excited APTS to ZnO. Electron in LUMO of the excited APTS is of higher energy compared to that in the CB of ZnO. The inorganic nano size fillers with organic functional groups that attach to their surface by strong chemical bonds can be finally obtained. The interaction increases the surface tension of inorganic nano particles results f-ZnO. Binding interaction studies of NiO with AMB shows the unexpected results. The increased absorption observed with the dispersed NiO is due to the adsorption of AMB on the surface of NiO. Fluorescence enhancement resulted while adding the NiO to AMB. Azomethine nitrogen is involved in the binding process with Ag₃O₄ nanoparticles which was proved by molecular electrostatic potential. Morphological changes of Ag₃O₄ nanoparticles to AMB modified Ag₃O₄ nanoparticles confirm the binding of Ag₃O₄ nanoparticles to AMB. EDX spectrum of AMB modified Ag₃O₄ nanoparticles shows incorporation of AMB to Ag₃O₄ nanoparticles. The interaction between AMB and Ag₃O₄ occurs through static quenching mechanism.

1.6 Metal Oxide Nanocomposites and its Thermal Property Analysis

Metal nanoparticles, due to their special properties and also small dimensions, find important applications in optical, magnetic, thermal, sensoric devices, catalysis, etc. Metals are dominated by the collective oscillation of conduction electrons resulting from the interaction with electromagnetic radiation. In addition to these, many production processes include heat transfer in various forms; it might be the cooling of a machine tool, pasteurization of food, or the temperature adjustment for triggering a chemical process. In most of these applications, heat transfer is realized through some heat transfer devices; such as, heat exchangers, evaporators, condensers, and heat sinks [96–98]. The feasibility of the usage of such suspensions of solid particles with sizes on the order of 2 mm or μm was previously investigated by several researchers and significant drawbacks were observed. These drawbacks are sedimentation of particles, clogging of channels and erosion in channel walls, which prevented the practical application of suspensions of solid particles in base fluids as advanced working fluids in heat transfer applications [99, 100]. Two-step method is the most widely used method for preparing nanofluids. Nanoparticles, nanofibers, nanotubes or other nanomaterials used in this method are first produced as dry powders by chemical or physical methods. Metal, metal oxide and various carbonaceous and nanocomposite based nanofluids are prepared by this method. The surfactants used in this method for stabilization can lower the thermal conductivity [101]. So the nanofluids prepared by this method exhibit lower thermal conductivity compared to the ones prepared by one-step method.

      The formation of silver nanowires was explained by the in situ precipitation of a lamellar silver thiolate, Ag(SC12H), acting as a template for the 1D coalescence of isotropic Ag nanoparticles. Heterogeneous nucleation has also proved to be an efficient method for the control of the particle growth. Using Ruthenium as a seed (Ru is more easily reducible than cobalt or nickel), allows to get nickel–cobalt or cobalt nanowires [102, 103]. The synthesis of metal nanoparticles can be commonly carried out by