Influence Of Hydrothermal Synthesis Conditions Research Articles

Hydrothermal Synthesis of Carbon Quantum Dots: An Updated Review

Carbon Quantum Dots (CQDs) have exceptionally solid and tuneable fluorescence properties which empower their application in vast fields. The hydrothermal approach is regarded as direct and efficient, through polymerization and carbonization reactions, and has been widely applied to prepare various materials due to the high reactivity of the reactants, easy control of the solution, little harm to the environment and low energy consumption under hydrothermal condition. The attracting feature of this route is that neither any strong acid nor post-synthetic surface passivation is necessary. As of now, a lot of important progress in the hydrothermal synthesis of carbon quantum dots such as materials use as precursors and influence of hydrothermal synthesis parameters. Hydrothermal synthesis is one of the most commonly used methods for preparation of nanomaterials. It is basically a solution reaction-based approach. In this review, the main focus is to review the hydrothermal route for carbon quantum dots using different source of materials and their fundamental characterizations, followed by the influence of hydrothermal synthesis conditions to carbon quantum dots.

Influence of hydrothermal synthesis conditions and carbonation on physical properties of xonotlite-based lightweight material

This paper investigates the effect of the hydrothermal synthesis conditions on the formation of xonotlite and the change of xonotlite-based lightweight material’s (Xo_AAC) physical properties under carbonation. Experiments included: quantitative X-ray diffraction, scanning electron microscopy, thermogravimetric differential thermal analysis, drying shrinkage, carbonation shrinkage, compressive strength, mercury intrusion porosimetry, thermomechanical analysis, solid-state nuclear magnetic resonance, water vapor absorption isothermal, and nanoindentation test. The pure crystalline xonotlite was formed at 230 °C for the autoclaving time of more than 18 h and at short heating time (2 h). The drying shrinkage and dimensional change rate of Xo_AAC were smaller than that of autoclaved aerated concrete (AAC). The compressive strength of Xo_AAC was slightly increased after carbonation. The carbonation of Xo_AAC occurred more quickly than AAC containing silicone oil. However, the amount of carbonation shrinkage was almost the same for both Xo_AAC and AAC in a later period.

Influence of hydrothermal synthesis conditions on lattice defects in cerium oxide

Cerium oxide makes one of the most promising materials for chemical transformations in environmental and energy applications. Herein, the influence of hydrothermal conditions on the physico-chemical characteristics of cerium oxide prepared from salt solution via ammonia precipitation is analyzed. The systems are well characterized using SEM, TEM, XRD analysis, photoluminescence spectra, Raman spectra, TPR study. and XPS analysis. Normal aqueous conditions lead to particles of size ~8 ​nm, with truncated octahedral geometry, closer to spheroid shape (RT-Ce) bound by {111} and {100} planes. Elevated temperature facilitated preferential exposed {100} plane bounded cubic ceria structures of size ~15 ​nm (HT-Ce), which are stabilized by more number of anion vacancies. Low temperature synthesis yielded smaller sized particles with less crystallinity and higher surface area, when compared to hydrothermal route. Lattice defects, represented in terms of Ce3+ ions and associated lattice oxygen vacancies are seen in higher amounts in ceria synthesised via hydrothermal path, as supported by various characterization results. CeO2 achieved via hydrothermal path exhibited higher catalytic oxidation activity, which is examined using a model oxidation reaction, vis., CO oxidation. The enhanced activity of HT-Ce is explained through the defect structure induced facile redox shift in the system.

Influence of hydrothermal synthesis conditions on the morphology and sorption properties of porous aluminosilicates with kaolinite and halloysite structures

The influence of hydrothermal synthesis conditions on the crystallization of aluminosilicates of the kaolin group – kaolinite and halloysite with various morphologies – was studied. Unique studies using focused ion beam-scanning microscopy (FIB-SEM) to determine the morphology and microstructure of the samples were carried out. The samples were studied by X-ray diffraction, low-temperature nitrogen adsorption, thermal analysis coupled with mass spectrometry, and IR absorption spectroscopy. The sorption ability of the samples with respect to the cationic dye methylene blue was also studied. The synthesis conditions were determined, which made it possible to obtain aluminosilicates with a certain morphology that included the thin nanolayers of particles, spherical particles, nanotubes, nanosponges or plates, as well as the conditions for their transformation. It was shown that in the range of 200 to 220 °C, primarily aluminosilicates with halloysite structure (Al2Si2O5(OH)4.nH2O) crystallized. Depending on the synthesis conditions, halloysite particles had spherical, tubular, or nanospongy morphologies. An increase in temperature to 350 °C favoured the crystallization of kaolinite Al2Si2O5(OH)4 with a predominant platy morphology of particles. For the first time, kaolinite group aluminosilicates with a nanosponged morphology, were obtained and were characterized by a high specific surface area (300–350 m2/g) and a high sorption capacity with respect to methylene blue (more than 100 mg/g after two hours of treatment). It is shown that the porous-textural characteristics and sorption properties of aluminosilicates of the kaolinite group are largely determined by the synthesis conditions and the morphology of the particles.

Influence of hydrothermal synthesis conditions on the composition of the pyrochlore phase in the Bi2O3-Fe2O3-WO3 system

Influence of hydrothermal synthesis conditions on the composition of the pyrochlore phase in the Bi2O3-Fe2O3-WO3 system

Influence of Hydrothermal Synthesis Conditions on the Formation of Calcium Silicate Hydrates: from Amorphous to Crystalline Phases

Hydrothermal treatment has been widely applied in the synthesis of well crystalline calcium silicate hydrate (CSH), such as tobermorite and xonotlite. However, both morphology and crystallinity of CSH are greatly affected by the conditions of hydrothermal treatment including siliceous materials, temperature increase rate and isothermal periods. In this study, the influence of hydrothermal conditions on the growth of nano-crystalline CSH was investigated based on XRD analysis. Results showed that siliceous materials with amorphous nature (i e, nano silica powder) are beneficial to synthesize pure amorphous CSH, while the use of more crystallized siliceous materials (i e, diatomite and quartz powder) leads to producing crystalline CSH. Results also indicate that the formation of tobermorite and xonotlite is greatly affected by the temperature rise rate during hydrothermal treatment.

Research on Hydrothermal Decoration of TiO2 Nanotube Films with Nanoplatelet MoS2 Species

In this study, novel electrodes were prepared via decoration of nanotubed TiO2 (TiNT) films with crystalline two-dimensional (2D) MoS2 species by a one-step hydrothermal synthesis approach. Obtained products were characterized in detail by scanning electron microscopy, Raman spectroscopy, U-I measurements and X-ray diffraction techniques. The influence of hydrothermal synthesis conditions on the composition and morphology of the products formed in the solution and within the TiNT film are also discussed. For the first time, acceptable decoration of TiNT films, by tethering 2D layered MoS2 leaflets onto the TiO2 nanotubes, and on the film surface was obtained in the low concentration solutions, while the performance of these heterostructures in relation to electrochemical hydrogen evolution reaction (HER) was tested. Stable catalytic activity of the obtained 2D MoS2-in-TiNT films was demonstrated under intense HER conditions within the potential window [−0.2 to −0.4 V] vs. RHE with a notably low Tafel slope of 33 mV/decade.

Influence of hydrothermal synthesis conditions on size, morphology and colloidal properties of Hematite nanoparticles

The synthesis, morphological characterization, and colloidal properties of Hematite nanoparticles (hemNP) with different sizes and shapes were presented. To prepare hemNP we used hydrothermal synthesis with different combinations of reaction conditions. Various characterization techniques involving XRD, TEM, AFM and DLS were employed to describe the dependence of the hemNP size, charge and morphology on different synthesis conditions. Spheroidal Hematite nanoparticles from 20 to 60 nm were obtained by varying the rate of addition of iron precursor solutions and the aging time (Δt) at ca. 100∘C. The transformation from Ferrihydrite to Hematite (α-Fe2O3) started with a burst nucleation of nanosized crystallites, followed by a first-order kinetic growth of primary grains up to a final threshold size of ca 30 nm. Colloidal behavior was also checked at pH 4 and 7, finding interparticle aggregation at circumneutral pH only for hemNP obtained for Δt<2 h. Electrophoretic ζ potential measurements yield positive values at pH 4 and negative at pH 7. The shifts in (IEP) at lower values depended on the adsorption of appreciable counterions on the particle surface and reduced at pH 7 the charge–charge repulsion, whereas the attractive forces became predominant. The results confirmed that the particle size of the Hematite nanoparticle critically affected their colloidal behavior with significant consequences for sorption and aggregation processes. Particularly for low particle sizes of the order of 10–20 nm, the surface charge and surface reactivity also could differ in important ways compared to 40–60 nm size particles.

Influence of Hydrothermal Synthesis Conditions and Device Configuration on the Photoresponse of UV Sensors Based on ZnO Nanorods

Zinc oxide nanorods in the form of powder or nanostructured films were synthesized by the hydrothermal method using aqueous solutions. Once the synthesis time was completed, the reaction vessel was naturally cooled or submitted to a quenching process. X-ray diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy techniques were employed to characterize the crystallinity, morphology, and dimensions of the nanorods, as well as their growth direction. Suspensions of powder material were spin-coated over oxidized silicon substrates in order to obtain nanostructured layers. Photo detectors based on in-situ grown and spin-coated films were prepared in order to evaluate the influences of cooling rate and device configuration on the UV sensing characteristics. Spin-coated layers showed an excellent performance (current change by more than four orders of magnitude), better than nanorods grown directly on the substrate during the hydrothermal process. For both configurations, the sensitive layers built from quenched samples exhibited enhanced UV photoresponses when compared to the naturally cooled ones.

Influence of hydrothermal synthesis conditions on BNT-based piezoceramics

The Bi 0.5Na 0.5TiO 3 perovskite (BNT) is a very promising lead-free candidate for piezoelectric applications. Nevertheless a low reproducibility is commonly reported for the solid state synthesized BNT. In this work, the hydrothermal synthesis was investigated to improve the BNT ceramics characteristics reproducibility. The synthesis conditions were studied in order to control more particularly the BNT grain size, crystallinity and stoichiometry. Thanks to the slow hydrolysis of titanium isopropoxide with bismuth nitrate pentahydrate, well crystallized BNT-based powder was synthesized at 265 °C. Nevertheless this powder exhibited secondary amorphous phases. Such secondary phases synthesis was limited and prevented by both lowering the temperature synthesis down to 160 °C and optimizing the washing conditions of the powder. The BNT was finally made free of any amorphous phase by using a hydrochloric solution. The BNT sinterability was improved and BNT-based piezoceramics exhibiting a d 33 as high as 60 pC/N were successfully produced.

The influence of hydrothermal synthesis conditions on gyrolite texture and specific surface area

Influence of hydrothermal synthesis conditions on the gyrolite specific surface area, dominant pore size and their differential distribution by the radius were determined. The synthesis of gyrolite has been carried out in unstirred suspensions within 32, 48, 72, 120, 168 h at 200°C temperature from a stoichiometric composition (the molar ratio of CaO/SiO2 was equal to 0.66 where water/solid ratio of the suspension was equal to 10.0) of the initial CaO and SiO2·nH2O mixture. It was found that the structure of gyrolite and the shape of dominated pores (from pores between parallel plates to cylindrical pores) changes prolonging the duration of hydrothermal synthesis. The stable gyrolite crystal lattice was formed only after 120 h of isothermal curing. Its specific surface area S BET = 38.28 m2/g, the radius of dominant plate pores r p = 30–40 A, the cumulative pore volume ΣV p = 0.08 cm3/g. It was determined that the pores with 4.0–5.0 nm radius were dominated in gyrolite structure after 168 h of synthesis. It was estimated that the ion exchange between gyrolite with less orderly structure in Zn(NO3)2 + NH4OH alkaline solution (\({c_{{{\text{Zn}}^{2+}}}}\)—0.3 g/dm3) proceeds more faster and effectively.

Synthesis and characterization of silver molybdate nanowires, nanorods and multipods

Silver molybdate nanowires, nanorods and multipods like structures have been prepared by an organic free hydrothermal process using ammonium molybdate and silver nitrate solutions. The powder X-ray diffraction (PXRD) patterns reveal that the silver molybdate belongs to anorthic structure. The thickness, 200–500 nm, for silver molybdate nanorods/wires and 2–5 μm for microrods are identified from SEM images. UV-visible spectrum of silver molybdate nanorods/nanowires shows maximum absorbance at 408 nm. Photo-luminescence (PL) spectrum exhibits UV emission at 335 nm, violet emission at 408 nm and a weak green emission at 540 nm. The influence of hydrothermal synthesis conditions on silver molybdate nanowires, nanorods and multipods compositions were established.

Synthesis of ZrO 2 and TiO 2 nanocrystalline powders by hydrothermal process

In present work, nanocrystalline zirconia and titania were synthesized by hydrothermal treatment of zirconyl ZrO(NO 3) 2 and titanyl TiO(NO 3) 2 nitrates aqueous solutions and amorphous gels of the corresponding hydroxides. The hydrothermal synthesis was performed in a wide range of temperatures (150–250 °C), concentration of starting solutions (0.25–0.5 M) and duration of the process (from 10 min to up to 24 h). The hydrothermal treatment at high pressure about 2.0–4.0 GPa was also carried out. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and BET. Particle sizes, morphology and properties of the products were investigated. The influence of hydrothermal synthesis conditions on ZrO 2 and TiO 2 phase compositions were established.