Narrow Results

Exploring the morphogical and structural properties along with gas sensing applications both pure and Ti-doped SnO₂ ultra-thin films, were meticulously crafted on micromachined silicon substrate heater devices using a combination of classical soft chemical processes and hydrothermal techniques (SCPHTP). The fabrication process involved a two-step approach: initially, a 20nm layer of tin oxide was hydrothermally deposited onto the substrates, followed by annealing in wet air at 600^∘C for 5h using a standardized temperature variation protocol. Subsequently, secondary layers with thicknesses of 20, 40 and 60nm were sequentially deposited onto the tin dioxide devices and oxidized in wet air at 550^∘C and 600^∘C for 20h each, using the same temperature modulation scheme. Throughout this process, the hydrothermal deposition temperature remained constant at 180^∘C for both the initial and secondary layers of tin dioxide deposition. Additionally, Ti layers with thicknesses of 4 and 8nm were deposited onto the 20nm + 40nm system, subjected to annealing at 550^∘C for 20h, followed by 1-min annealing in dry O₂ at 700^∘C and 800^∘C, respectively, using a Rapid Thermal Annealing (RTA) system. Characterization of the crystalline and surface structures of the devices revealed a transformation of the soft chemical tin dioxide solution into the cassiterite structure of SnO₂, resulting in uniform large surface areas for the sensor devices. Moreover, Ti metal layers of 4 and 8nm thicknesses were fully converted into TiO₂ on the surface of the devices. Subsequent testing showcased higher current values in sandwich systems of 20nm + 60nm and 20nm + 40nm compared to the 20nm + 20nm configuration. Sensitivity and stability assessments for various volatile organic compounds (VOCs) and CO gases at a constant DC temperature of 400^∘C indicated excellent performance, with sensitivity to CO gas being contingent on relative humidity (RH). Notably, RTA-annealed and Ti-8 nm-doped sensor devices exhibited superior sensitivity and reproducibility, particularly when treated at 800^∘C in dry O₂ for 1min. This heightened performance can be attributed to the occupation of chloride ions in the oxygen sites of the as-synthesized SnO₂, resulting in enhanced sensing capabilities for VOC gases.

A well-aligned single-crystalline barium titanate (BaTiO₃) nanostructured layer was prepared by the growth and conversion of vertically aligned TiO₂ nanorods. This was achieved through a two-step hydrothermal method on fluorine-doped tin oxide (FTO)-coated glass substrates via the dissolution-nucleation-recrystallization mechanism. The morphology, crystal structure and optical properties were investigated using field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), Raman spectroscopy, photoluminescence (PL) and Z-scan techniques. The X-ray and selected area diffraction patterns (SAED) confirmed the formation of the aligned single-crystalline tetragonal BaTiO₃ layer. The room temperature Raman spectrum showed the tetragonal TiO₂-related vibrational modes in BaTiO₃. The PL spectra indicated the coalescence of band edge emissions of BaTiO₃ and TiO₂ in the blue and visible regions of the investigated spectra. The Z-scan experiments performed using the CW Nd:YAG laser revealed a positive nonlinear refractive index on the order of 10${}^{-7}$ cm²W${}^{-1}$, indicating the self-focusing type of cation in the BaTiO₃ sample. The nonlinear absorption coefficient of the BaTiO₃ nanostructures in the order of 10${}^{-7}$ cm W${}^{-1}$ was also calculated. As expected, the BaTiO₃ nanostructure synthesized in this study is a good candidate for use in nonlinear optics.

Rocks and melt inclusions (MI) from 11 volcanic centers of the Kermadec-Tofua arc, in the South West Pacific, were petrographically studied prior to chemical analysis under the ion beam. The abundance of MI with daughter minerals are volcano-specific with the most abundant found in "U", Putoto, and Hinepuia volcanoes where >50% of MI contain daughter minerals. The B, Li, Cl and S contents in MI generally increase with the silica content of the rock. Fe, Ni, Mn, Cu and Zn are common in MI of all rock types but Mo, Hg and Cu have the highest concentrations in dacite-rhyodacites. The highest concentrations of B, Ti, V, Fe, Co and Mo occur in plagioclase MI; S, Ni, Ge and Hg in pyroxene MI; Cl and Li in quartz MI; and Cu, Zn and M in hornblende MI. Different ore-forming components in volcanic rocks can be correlated with rock composition, Cl/S and B/S of the melts, the presence and abundance of mineral sinks for various elements and the occurrence of hydrothermally altered rock at depth and on the seafloor.

Anatase Ti_1-xCo_xO₂ nanoparticles were prepared by a hydrothermal process at 180 °C. Ferromagnetic hysteresis loops of the as-prepared samples were measured at room temperature. The Ti_1-xCo_xO₂ (x = 0.0376) powder shows coercivity up to 700 Oe, which is the highest value reported for anatase Ti_1-xCo_xO₂. X-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetic measurement results provided evidence that Co was incorporated into TiO₂ lattice. Combined with the fact that the preparation was carried out in an oxidized environment starting from cobalt (II) in the oxidized state, it is suggested that the homogeneous doping of Co into the lattice of anatase should be responsible for the improvement of coercivity in anatase Ti_1-xCo_xO₂ nanoparticles.

Boron nitride nanocrystals have been prepared in a hydrothermal route. The crystalline phases have been identified as cubic boron nitride (cBN) and orthorhombic (oBN) by XRD and FTIR. Further evidences for the formation of cBN have been obtained from microanalysis and composition identification by HRTEM, SAED and EDS.

Nanocrystal MnO₂ was successful synthesized by hydrothermal method under pulsed magnetic field. The effect of pulsed magnetic field on the nucleation and growth of MnO₂ was studied by XRD and SEM analysis. It was found that the morphology of MnO₂ has been changed comparing without magnetic field. However, there were no different phases presented when pulsed magnetic field was applied.

Single crystalline hydroxyapatite nanorods (HAp-NRs) were synthesized using a simple hydrothermal method. The synthesized HApNRs have an aspect ratio of about 8-10. A closer inspection of the nanostructure of a single nanorod revealed a highly regular and defect-free lattice with unique crystallographic plane orientations. X-ray Diffraction (XRD) pattern shows the highly crystalline nature of the product. The Field Emission Scanning Electron Microscopic (FESEM) image shows the uniform size distributed rod like morphology of length 100-150nm and diameter of about 15-20nm. Transmission Electron Microscopic analysis (TEM) and High-Resolution TEM (HRTEM) images provide further insight into the microstructure and morphology of the product. The selected area electron diffraction (SAED) pattern confirms that the nanorods are single crystal in nature. The mechanical strength of hydroxyapatite was studied by reinforcing hydroxyapatite with High Molecular Weight Polyethylene (HMWPE). It clearly shows that the mechanical properties of the nanorods are high when compared to that of bulk HAp. Finally the composites were characterized by means of thermal analysis including thermogravimetry analysis and differential thermal analysis (TGA-DTA) in order to study the thermal stability of the composite and the effect of filler in HMWPE.

In this paper, a newly designed composite of magnetic nano-Co₃O₄ fiber coated on carbon fiber (Cf) is prepared and characterized for the electromagnetic interference (EMI) shielding properties. XRD, SEM and TEM are used to investigate the micromorphology and microstructure evolution during the preparation. By hydrothermal method, the flowerlike clusters of single crystal flake-Co(OH)₂ are first obtained on Cf. The firstly prepared Co(OH)₂ sheets then turn into Co₃O₄ fibers during the next calcination step. The continuous and loose coating of magnetic Co₃O₄ nanofibers is finally obtained on the Cf. The loose coating is in proportion to the weight loss, and the wirelike Co₃O₄ is good for the interface strength for the Cf composite preparation. Based on the above work, the loose magnetic fibers coating on the Cf could be a feasible composite structure for the EMI composite materials integrated with absorbing and reflecting.

In this study, the preparation of ternary photocatalyst using a simple hydrothermal method is shown with high performance. A ternary composite consisting of tungsten sulfide (WS${}_2)$ nanosheets, titanium oxide (TiO${}_2)$ and gold (Au) nanoparticles is used to the extend the visible-light absorption region of TiO₂. The morphological and spectroscopic natures of the prepared sample were analyzed using scanning electron microscopy (SEM), Raman spectroscopy and ultraviolet–visible (UV–vis) photospectroscopy. The photocatalysis measurement for photodegradation of methylene blue dye was performed under the visible light. The photocatalytic studies suggest that in the ternary composite, consisting of three materials with different energy levels, the electrons excited form a cycle to lower the probability for the recombination of electron–hole pairs enhancing the property of photocatalytic activity of TiO₂.

CaWO₄ crystals were prepared by hydrothermal method assisting with phenol-formaldehyde polymer. The morphology can be controlled by polymer, and X-ray diffraction patterns results present a scheelite-type tetragonal structure, characteristic infrared active modes for O–W–O in the range from 500 cm${}^{-1}$ to 4000 cm${}^{-1}$ by Fourier transform infrared spectroscopic techniques. Raman results indicate that the crystals possess seven Raman active modes in the range from 100 cm${}^{-1}$ to 1000 cm${}^{-1}$. A scanning electron microscopy study reveals that the particles exhibit uniform morphology. Luminescent properties were investigated by photoluminescence measurements, multicolor phosphors were obtained when Ca${}^{2+}$ was substituted partly by lanthanide ions.

In this research, rod-like undoped and Zn doped h-MoO₃ thin films were grown on top of MoO₃ seed layers, using hydrothermal technique without adding any surfactant. Seed layers of MoO₃ were coated on top of glass substrates using spray pyrolysis technique. Structural, morphological and optical properties of thin films were examined. XRD pattern analysis showed that the seed layer has orthorhombic crystal structure. Also, it confirms the formation of hexagonal structure for thin films grown by hydrothermal. FESEM images show the formation of long, well-shaped hexagonal rod-likes. UV-Vis spectroscopy reveals band gap increasing from 3.2 eV to 3.54 eV, by increasing Zn.

In this study, transition metal dichalcogenide (TMD) material WS₂ and Au nanoparticles were combined with TiO₂ to enhance the photocatalytic performance under visible light. The WS₂ nanosheets were synthesized from bulk WS₂ via ultrasonic process, and the Au nanoparticles were prepared through the reduction reaction from HAuCl₄. The composite photocatalysts of WS₂/TiO₂/Au, TiO₂/Au, and WS₂/TiO₂ were synthesized by a one-step hydrothermal process. The light absorption property of the composites was determined by ultraviolet-visible (UV-vis) photospectroscopy. Surface analysis of WS₂ nanosheet, TiO₂ nanoparticles, and Au nanoparticles was performed by scanning electron microscopy (SEM). The chemical structure of composites and thickness of WS₂ nanosheets were analyzed by Raman spectra. The photocatalytic activity was measured by methylene blue degradation reaction under visible light. These results revealed the photocatalytic behavior of WS₂/TiO₂/Au, TiO₂/Au, and WS₂/TiO₂ composites, as well as WS₂ nanosheets. The WS₂/TiO₂/Au composite showed improved photocatalytic behavior among all samples. It is believed that the WS₂ nanosheet and Au nanoparticle extend the light absorption range from UV region to the visible region, as well as the WS₂/TiO₂/Au composite reduces the recombination of electrons. This study shows that the enhanced photocatalytic behavior of WS₂/TiO₂/Au composite can be used as photocatalytic applications in the future.

Thin film technology is significant in technological progress and modern research because it allows for the production of optoelectronic devices with improved characteristics. Because of its superior chromatic efficiency, tungsten oxide (WO₃) is one of the best candidates for energy-saving applications. In this study, undoped and tin (Sn)-doped WO₃ films were grown on top of WO₃ seed layers directly by a facile hydrothermal route at a temperature as low as 110^∘C for 24h. The seed layers were also deposited on top of glass substrates using spray pyrolysis. The results of tin doping on the structural, optical, and morphological characteristics of the WO₃:Sn films were studied. X-ray diffraction patterns show that peak intensities increase significantly by adding Sn and the films’ crystallinity was improved by rising Sn content. In the visible region, the average optical transmittance is around 13% and the optical bandgap changes from 2.61eV to 2.81eV, by increasing the dopant amount. Finally, the room temperature photoluminescence of samples shows intense green light emissions. The results of this research can be beneficial for the fabrication and performance optimization of electrical and optical devices such as gas sensors, electrochromic devices, and photosensors.

The synthesis of novel vanadium dioxide nanorods has been achieved by using V₂O₅ and cetyltrimethyl ammonium bromide (CTAB) in a sol–gel reaction followed by hydrothermal treatment. Morphology and structure of the sample as well as vanadium oxidation state were characterized by XRD, SEM, HRTEM, ESR, XPS and redox titration. The results show that the products are monoclinic (C/2m) B phase VO₂ nanorods and they are 1~2 μm in length. HRTEM micrographs reveal that they indeed form bundles of agglomerated smaller filaments with diameters ranging from 20 to 40 nm besides single nanorod. This filament-like shape in the nanoscale dimension leads to the exposure of a large fraction of the atoms to the surface. Thus, these materials are promising candidates for the development of new functionalized materials. CTAB not only generates a reducing atmosphere, but also plays a key role in the growth of the nanorods. The simplicity of hydrothermal process, as well as cheapness and availability of raw materials are advantages of this method.

ZnO nanowires (NWs), grown by hydrothermal and vapor phase transport (VPT) methods, were employed as the channel layers to fabricate single nanowire Field Effect Transistors (NWFETs) with a p⁺-silicon as the bottom gate. The FET employing hydrothermal grown ZnO NWs shows n-type depletion mode with a field mobility of 18.27 cm²/V⋅s, an on/off ratio of 10⁶, and a threshold voltage of -48.5 V. In comparison, the device using VPT grown NWs operates in n-type depletion mode with a field effect mobility of 36.94 cm²/V⋅s, a drain current on/off ratio of 10⁵, and a threshold voltage of -14 V. The reason for the difference of threshold voltage and the mobility by two methods was discussed in this paper.

ZnO nanosheets with hexagonal wurtzite structure were successfully synthesized by a microwave assisted hydrothermal process using mild conditions and zinc acetate as a precursor. The obtained powder was characterized by X-ray diffraction, environmental scanning electron microscopy, Fourier transmission infrared and room temperature photoluminescence. The size of as-synthesized ZnO nanosheets depends on the precursor concentration and the average diameter ranged between 50 and 600 nm with a thickness in the range of 8–38 nm. The product shows a strong UV emission at 397 nm and a visible blue emission centered at 466 nm.

To accomplish superior performance in supercapacitors, a fresh class of electrode materials with advantageous structures is essential. Owing to its rich electrochemical activity, vanadium oxides are considered to be an attractive electrode material for energy storing devices. In this work, vanadium pentoxide (V₂O${}_5)$ nanostructures were prepared using surfactant (CTAB)-assisted hydrothermal route. Stacked V₂O₅ sheets enable additional channels for electrolyte ion intercalation. These stacked V₂O₅ nanosheets show highest specific capacitance of 466Fg${}^{-1}$ at 0.5Ag${}^{-1}$. In addition, it exhibits good rate capacity, lower value of charge transfer resistance and good stability when used as an electrode material for supercapacitors. Further, an asymmetric supercapacitor device was assembled utilizing the stacked V₂O₅ sheets and activated carbon as electrodes. The electrochemical features of the device are also discussed.

2-Amino-5-nitropyridinium halides (2A5NPBr)/(2A5NPCl) were synthesized by dissolving 2-amino-5-nitropyridine in hydrobromic/hydrochloric acid. Nanoparticles of 2A5NPBr and 2A5NPCl were attained by hydrothermal method. For comparison and estimation of mechanical properties, single crystals of the samples were grown by slow evaporation process. SEM analysis shows the formation of nanoparticles of 2A5NPBr and 2A5NPCl with average grain size of 50 and 100nm, respectively. UV-Vis analysis reveals that the materials possess low cut-off wavelength and a wide optical transmission window. By Vickers test, the Meyer index (n) was estimated to be 1.33 for 2A5NPBr and 2.49 for 2A5NPCl crystals. The SHG efficiency of 2A5NPBr and 2A5NPCl nanoparticles was calculated to be 1.5 and 4.3 times that of well known NLO material KDP. The role of cations in demonstrating the desired NLO properties were discussed in detail.

Semiconductor quantum dots such as CdSe, PbSe, PbS, CdS, CuInS, CuInSe, etc. have been extensively studied for their size-tunable optical absorption and emission properties, which enable their applications in different optoelectronics applications. Although despite having high photoaborption and photosensing properties these semiconductor quantum dots possess certain limitation due to their high level of toxicity and complex synthesis process. Graphene quantum dots (GQDs) are a zero-dimensional (0D) nontoxic nanomaterial of the carbon family, and have sparked a lot of attention in the domains of optoelectronics and electronics. In this review, a number of GQD synthesis methods such as laser ablation, hydrothermal, solvothermal, thermal pyrolysis, electrochemical, chemical oxidation and cutting have been summarized in detail.

This work presents an important analysis and comparative study between two organic waste rhodamine B (RhB) and methyl orange (MO) dyes as pollutant models degeneration under sunlight. Hematite ($\alpha$-Fe₂O₃) nanorods were synthesized and deposited on glass substrates using an efficient and simple one-step hydrothermal method. The nanorods were characterized by XRD, FESEM, EDX, and UV–Vis equipment. The photodegeneration parameters of $\alpha$-Fe₂O₃ films were calculated by modeling the photodegradation of MO and RhB dyes as pollutants under sunlight irradiation for 150min. Results revealed that the degradation efficiency of $\alpha$-Fe₂O₃ films of MO and RhB dyes was 72.7% and 91.9%, respectively. The optimized photocatalyst degraded RhB more efficiently than the MO solution.