Papers by Keyword: Hydrothermal Synthesis

Abstract: The nature of the precursor material used in the synthesis of carbon dots can easily affect their properties. Biomass-derived carbon sources are encouraged because they are ecologically sustainable and provide numerous benefits compared to alternative carbon sources. This work presents the synthesis of carbon dots derived from Moringa oleifera leaves using a hydrothermal synthesis technique. The optical, morphological and structural properties of the obtained carbon dots were characterized using UV-vis absorption spectrophotometer, photoluminscence (PL), transition electron microscopy (TEM) and X-ray diffraction (XRD) spectroscopy, respectively. The TEM revealed nearly spherical-shaped dot particles with an average size of 11.24 nm in diameter. The optical properties showed that the obtained carbon dots have green fluorescence, and the fluorescence spectra were found to red-shift as the excitation wavelength increased.

Abstract: In this study, ZnO-TiO₂ nanocomposites with varying molar ratios were synthesized using a hydrothermal method and characterized for H₂S gas sensing applications. Thick films of the nanocomposites were fabricated using a screen-printing technique, and their gas sensing performance was evaluated at different operating temperatures. The diffraction peaks of ZnO and TiO₂ are hexagonal (rutile), and tetragonal (anatase) phase, respectively. The crystallite sizes were determined to be 37.34 nm for 1M ZnO : 1M TiO₂ composition, and 45.17 nm, 44.03 nm, 41.22 nm, 36.14 nm, and 36.65 nm for the (1M : 9M, 3M : 7M, 7M : 3M, 9M : 1M, and 0.1M CuCl₂-doped in 1M ZnO : 1M TiO₂) compositions, respectively. SEM and EDAX analyses revealed formation of heterogeneous structure with well-distributed nanospheres and nanorods. The I-V characteristics of ZnO-TiO₂ thick films show a proportional but slightly non-linear response to voltage, indicating a mix of ohmic and non-ohmic conduction. The average thickness of the thick film of 1M ZnO : 1M TiO₂ sample is 29 (µM). The gas sensing performance was evaluated at different operating temperatures and among the compositions studied, the 7M ZnO : 3M TiO₂ thick film exhibited superior sensitivity, selectivity, and response to 286 ppm H₂S gas at 40°C. These findings demonstrate the potential of ZnO-TiO₂ nanocomposites as highly selective and low-temperature H₂S sensor for industrial and environmental monitoring applications.

Abstract: Mössbauer spectroscopy (MS), was used to characterize the synthesized materials prepared from the elemental powders by hydrothermal method which are binary iron-based nanoparticles (NPs) Fe₁₅Co₈₅ and Fe₁₀Co₉₀ alloys. The transmission ⁵⁷Fe Mössbauer spectra were measured at room temperature RT (T~300K), using ⁵⁷Co γ-ray source with an Activity ~ 1.85 GBq (50 mCi). The analysis of Mössbauer spectra curves was by using WinNormos with two subspectra with the “Site” option and then with the “Dist” option in order to learn more about hyperfine interactions and parameters such as isomer shifts IS, quadruple splitting QS and hyperfine magnetic field B_hf. MS results observe only one Zeeman sextet with a relative area of ~77.125% with parameter B_hf = 32.727 T and line width Γ=0.693 mm/s for Fe₁₀Co₉₀, and a relative area of ~84.719% with parameter B_hf = 34.354 T and line width Γ=1.043 mm/s for Fe₁₅Co₈₅ and one broad singlet which confirms the body-centered cubic structure BCC. The main contribution to the spectra comes from the magnetic sextet which is assigned to ferromagnetic FeCo phase which is the dominant one while the singlet is assigned to paramagnetic phase. As a result of the analysis of the distributions hyperfine magnetic field the average values of the hyperfine parameters of the Mössbauer spectra were obtained <B_hf>Fe₁₀Co₉₀ = 28.3363 T and <B_hf>Fe₁₅Co₈₅ = 31.4657 T. Therefore, it is observed that the increasing of the cobalt concentration decreases the hyperfine field. The results observe indicates Co concentration dependence, where for Co-rich alloys (Fe₁₀Co₉₀) the FCC (face-centered cubic structure) contributing to the decrease in B_hf due to the absence of BCC. the obtained NPs most likely to be in disordered structure A2.

Abstract: Nanocarbon synthesis from diverse sources has garnered significant attention, with a particular focus on materials derived from biomass. Carbon dots (CDs), due to their water solubility, low toxicity, and biocompatibility, have emerged as promising candidates for a wide range of applications. In recent years, CDs have found utility in several applications such as bioimaging, drug delivery, and biosensors. In this study, we present an eco-friendly, straightforward, and cost-effective technique for the synthesis of carbon dots through a hydrothermal reaction, utilizing peeled date palm midribs as the source material. High-resolution transmission electron microscopy, X-ray diffraction, UV-visible absorption spectroscopy, photoluminescence analysis, Fourier-transform infrared spectroscopy, and zeta potential measurements services to investigate the synthesized carbon dots' morphology, crystal and structure, and optical properties. The results show that the carbon dots had a size distribution ranging from 2.5 to 6 nm, and a crystallographic interplanar distance of 0.23 nm corresponding to the graphitic structure. When excited at a wavelength of 340 nm, the synthesized dots exhibited a prominent bluish emission at 420 nm, highlighting their potential for use in optical and biological applications. This work underscores the feasibility of harnessing sustainable biomass sources, such as date palm midribs, for the green synthesis of carbon dots with desirable properties, opening up new avenues for their utilization in cutting-edge technologies.

Abstract: Increasing amounts of agricultural and industrial wastes have prompted researchers to re‑use the wastes as prospective cement replacement materials. Sugarcane bagasse is an agricultural waste that is widely available as a by-product of sugar and ethanol industries. As sugarcane bagasse possesses a high pozzolanic reactivity owing to its high silica content, the potential of extracting silica from sugarcane bagasse ash (SCBA) for cement replacement has to be explored. In the present study, analytical and compressive strength tests were performed on concrete samples to determine the effect of replacing cement with silica extracted from SCBA. Influences of treatment and burning temperature for conversion of sugarcane bagasse to SCBA on the analytical and compressive strength test results were also investigated. Raw and treated bagasse were burned in a muffle furnace for one hour at 600, 700 and 800°C to produce untreated and treated SCBA, respectively. Hydrothermal synthesis was performed on the SCBA for extraction of silica gel. Three types of concrete samples were prepared, which are the control sample that does not contain any cement replacement material and samples that contain 5% silica from untreated and treated SCBA. Compressive strength tests were performed on the samples after seven days of curing. Findings indicate that treatment of the bagasse was essential to produce SCBA of adequate silica content that can improve the compressive strength of the concrete. The increase in compressive strength is at its highest at the burning temperature of 700°C, where a change of +8.05% was achieved.

Abstract: Advances in radar technology today are experiencing rapid development based on the latest findings that complement each other. BaFe₁₂O₁₉ is a type M hexagonal ferrite material as the best candidate for absorber material applications. Manganese dioxide (MnO₂) is a transition metal that has a high dielectric loss and has the opportunity to increase the absorption of electromagnetic waves. The BaFe₁₂O₁₉@MnO₂ core-shell composite produces the combined characteristics of BaFe₁₂O₁₉ and MnO₂, which can improve performance as radar-absorbing material. The BaFe₁₂O₁₉@MnO₂ core-shell composite is synthesized in two stages: molten salt synthesis in manufacturing BaFe₁₂O₁₉ as a core and hydrothermal synthesis to grow MnO₂ nanoflowers as a shell. The research objective was to produce BaFe₁₂O₁₉@MnO₂ core-shell composite for radar absorbing applications in the x-band with absorption of ~99%. In molten salt synthesis, using two calcination operations at 1000 °C for two hours to create BaFe₁₂O₁₉ as a template, then combining BaFe₁₂O₁₉ template with Fe₂O₃ and BaCl₂.2H₂O for eight hours at 1100 °C prepared for MnO₂ pathways on the BaFe₁₂O₁₉ surface. Hydrothermal synthesis occurs by dissolving BaFe₁₂O₁₉ and KMnO₄ in deionized water with a mass ratio of BaFe₁₂O₁₉ to KMnO₄ is 1:1, followed by hydrothermal synthesis at a holding time of 12 hours with a temperature of 150 °C; 170 °C; 190 °C. Characterization of vector network analysis on a variation of sample thickness (1; 1.5; 2; 2.5; 3) mm were analyzed in the x-band frequency on 8-12 GHz. BaFe₁₂O₁₉@MnO₂ core-shell composite was hydrothermally produced at 170 °C with a particle size of 197.1 nm, a thickness of 2.5 mm, and a reflection loss of -20.31 dB at 8.7 GHz. The absorber material from the combined synthesis of molten salt and hydrothermal synthesis to make BaFe₁₂O₁₉@MnO₂ core-shell composite successfully produced microwave absorption up to 99.06%.

Abstract: Photocatalysts that can utilize sunlight energy have attracted attention. In this study, g-C₃N₄ and mesoporous SiO₂@TiO₂ particles were mixed by hydrothermal synthesis. g-C₃N₄ was made by a simple method of directly heating melamine. Mesoporous SiO₂@TiO₂ was prepared using the stover method. These two types of particles were then mixed by hydrothermal synthesis. Hydrothermal synthesis reduced the size of the g-C₃N₄ particles, and they bound more closely with the TiO₂ particles. The degradation of methylene blue dye by visible light was performed to evaluate the organic degradation of the mixed particles. In addition, the mixed particles were formed into a thin film by the spin-coating method. The film's methylene blue degradation performance and the film's power generation performance in a battery were evaluated. The film showed high convenience in the practical application of photocatalytic degradation of organic pollutants because it can be easily separated from the treated liquid after organic matter degradation.

Abstract: In this work, the influence of KOH and complex KOH and granite cutting waste additives on the formation of calcium silicate hydrates under hydrothermal conditions at a temperature of 200 °C was examined. For the synthesis, the pure mixture of calcium oxide and quartz, as well as the mixtures with different additives (KOH and complex KOH and granite cutting waste), were performed. The molar ratio of CaO/SiO₂ in the primary mixtures was equal to 1:1.5. The hydrothermal synthesis of calcium silicate hydrates has been carried out in unstirred suspensions in an autoclave under saturated steam pressure at 200 °C, when the duration of the synthesis was equal to 16, 48, and 72 h. It was determined that the used additives significantly change the formation sequence and stability of calcium silicate hydrates. The additive of KOH promotes the reactivity of quartz, while the additive of granite cutting waste promotes the formation of lower basicity calcium silicate hydrates. Synthesized products were characterized by powder X-ray diffraction analysis, simultaneous thermal analysis, and Fourier-transform infrared spectroscopy.

Abstract: A well-controlled multistage hydrothermal technique was developed to synthesise hierarchical zinc oxide (ZnO) nanomaterials with a high surface-to-volume ratio. Hierarchical ZnO nanomaterials, hierarchical nanowires (HNWs) and hierarchical nanodiscs (HNDs), assembled from initial mono-morphological nanomaterials, ZnO nanowires, and ZnO nanodiscs respectively were prepared by sequential nucleation and growth following a hydrothermal course. The hierarchical nanomaterials composed of one-dimensional nanowire building blocks were obtained by introducing zinc nitrate as a source of zinc ions during the second growth phase. In comparison to their initial monomorphological counterparts, the prepared HNWs and HNDs showed superior photocatalytic performances. The improvement in the photocatalytic performance was ascribed to the reduction in dimensionality, the ultrahigh surface-to-volume ratio, the expanded proportion of the exposed polar area, and the creation of nanojunctions between the secondary nanowires and initial ZnO nanowires or nanodiscs. This work paves the way for the low-cost, large-scale, and low-temperature production of ZnO nanomaterials with superior photocatalytic properties.

Abstract: Photodynamic therapy (PDT) is a promising modern method for treatment of oncological, bacterial, fungal and viral diseases. However, its application is limited to diseases with superficial localization since the body tissues are not transparent for visible light. To address this problem and extend PDT application to abdominal diseases, an enhanced method of X-ray photodynamic therapy (XRPDT) is suggested, involving X-ray radiation easily penetrating the body tissues. The implementation of this approach requires the development of a pharmacological drug including a photosensitizer stimulated by visible light to yield active oxygen and a nanosized phosphor converting X-ray radiation into visible light with the wavelength required for the photosensitizer activation. This study is aimed at obtaining X-ray stimulated phosphors with nanosized particles suitable for XRPDT application. For this purpose, Y₂O₃:Eu phosphors were synthesized via hydrothermal processing of the corresponding mixed acetate followed by annealing. To prevent from the undesirable agglomeration of the particles in the course of hydrothermal synthesis and subsequent annealing, different techniques were used, including rapid thermal annealing (RTA), microwave annealing and addition of finely dispersed pyrogenic silica (aerosil) to the phosphor. The microwave annealing was carried out using a special installation including a resonance chamber for maintaining a standing wave of microwave radiation. The performed research allowed the determination of hydrothermal processing optimal duration affording the synthesis of phosphors with the highest luminescence brightness. The application of microwave annealing is found to provide phosphors with a more perfect crystal structure compared with RTA. The developed method of Y₂O₃:Eu phosphor synthesis involving pyrogenic silica addition to the autoclave allowed the preparation of samples with the amorphous structure and significantly reduced the particle size without a considerable decrease in the luminescence brightness. The particle size of the phosphor synthesized with aerosil addition is less than 100 nm that allows its implementation in pharmacological drugs for XRPDT.