High Temperature Hydrothermal Method Research Articles

The effect of hydrothermal pretreatment on the catalytic performance of Zn/HZSM-5 catalysts for ethylene aromatization reaction

To address the issue of coking and deactivation of Zn/HZSM-5 catalysts used for lightolefins aromatization, a high-temperature hydrothermalmethod was employed for catalyst pretreatment. The catalysts were characterized using XRD, N2 physical adsorption-desorption, NH3-TPD, Py-FTIR, XPS, and TG techniques. The effect of high-temperaturehydrothermal pretreatment on the catalytic performance and stability of the catalyst was investigated using ethylene aromatization as a probe reaction. The results showed that the Zn/HZSM-5 catalyst exhibited excellent catalytic performance after48 h of high-temperature hydrothermal pretreatment. Although the conversion of ethylene slightly decreased, the catalyst lifetime was significantly extended, increasing from 72to 216 h, while the aromatics selectivity remained above 60%. It was suggested that the hydrothermal treatment enhanced the interaction between ZnO species and Brønsted acid sites, promoting the generation of ZnOH+ species. This not only suppressed the hydrogen transfer reaction but also significantly enhanced the dehydrogenation performance of the catalyst, improving the selectivity towards hydrogen. Additionally, the catalyst exhibited increased carbon capacity and reduced carbon deposition rate after hydrothermal treatment, demonstrating excellent anti-coking properties.

Preparation of SnOx/N-GQDs composites with oxygen-rich vacancies for enhanced photoelectric properties

SnOx with oxygen-rich vacancies and SnOx/N-GQDs (Nitrogen-doped graphene quantum dots) composites were prepared by high temperature annealing and hydrothermal method, respectively. The annealing process introduced a large number of oxygen vacancies and produced defect energy levels in the band gap. The existence of the defect level effectively reduced the band gap of SnOx, enlarged the optical absorption range, and improved the light utilization. The introduction of N-GQDs also improved the carrier density and electron transport rate, and extended the carrier lifetime (τ = 7.44 ms). I-T (Transient photocurrent response) analysis results showed that when the mass ratio of Sn/SnO2 was 1:4 and N-GQDs doping content was 1 wt%, the transient photocurrent response of SnOx/N-GQDs could reach 5.51 × 10−4 A/cm2, which was 25 times higher than that of pure SnO2, and the photocurrent response value maintained 80.1 % within 500 s. EIS (Electrochemical impedance) and M-S (Mott-Schottky) analyses indicated that the appropriate amount of oxygen vacancies and N-GQDs were beneficial to reducing the charge transport resistance, inhibiting the electron-hole pair recombination, and increasing the carrier density of SnOx. The results show that SnOx/N-GQDs composites present the improved photoelectric properties with the addition of oxygen vacancies and N-GQDs, which provides a new idea for promoting the properties of semiconductors.

Soaking the Rare-Earth Carbonates for a Change: An Alternative Approach to Explore Carbonate Nonlinear Optical Crystals.

Alkali-metal rare-earth carbonates (ARECs) find great potential in nonlinear optical applications. As the most common method, the hydrothermal reaction is widely used in synthesizing ARECs. The black-box nature of the hydrothermal reaction makes it difficult for understanding the formation processes and therefore may slow down the pace of structural discovery. Here, by simply soaking the rare-earth carbonates in Na2CO3 solutions, we successfully obtain a series of noncentrosymmetric Na3RE(CO3)3·6H2O (RE = Tb 1, Sm 2, Eu 3, Gd 4, Dy 5, Ho 6, and Er 7) compounds without using the high-temperature hydrothermal method. The transformation process, investigated by powder X-ray diffraction and scanning electron microscopy, is governed by the concentration of the soaking solutions. Na3Tb(CO3)3·6H2O, as an example, is studied structurally, and its physical properties are characterized. It exhibits a second harmonic generation effect of 0.5 × KDP and a short UV cutoff edge of 222 nm (5.8 eV). Our study provides insights for exploring new AREC structures, which may further advance the development of carbonate nonlinear optical crystals.

Thermochromic Cs2NaInCl6: Sb3+/Ln3+ (Ln = Er, Dy, Tb, Ho) phosphors for multifunctional applications

The intrinsic challenge to thermally responsive photoluminescent materials is pertaining to the limited thermal stability and reproducibility. Most prevailing photoluminescent agents suffer from constraints imposed by their frail chemical structure, rendering them fail to work at elevated temperatures for a long time. This inherent limitation curtails their utility within domains in anti-counterfeiting and encoded information storage. Herein, a series of double perovskite Cs2NaInCl6: Sb3+/Ln3+ (Ln = Er, Dy, Tb, Ho) phosphors were synthesized using the high-temperature hydrothermal method. Upon ultraviolet light illumination, the blue emission band of self-trapped excitons (STEs) and intrinsic emissions of Ln3+ are observed. In light of the variations in thermal quenching levels of the two emission centers and the effect of temperature on the lifetime of Ln3+, multi-mode thermometers with superior sensitivity are established. Moreover, they also can be used in anti-counterfeiting and encoding information storage, relying on the significant temperature-dependent color variation, excellent thermal stability and repeatability. The unique thermochromic properties and satisfactory stability of Cs2NaInCl6: Sb3+/Ln3+ (Ln = Er, Dy, Tb, Ho) phosphors bring forward a new concept of developing multi-mode thermometers and reliable information encryption systems with the application of thermochromic materials.

In situ construction of epoxy crosslinked Si-Al zeolite-like catalytic structure in wood to achieve high flame retardancy

As green renewable resources, wood and its composites are widely used in the construction field, which puts forward higher requirements for their flame-retardant performance. In this study, a high-temperature hydrothermal crystallization method for in situ constructing an epoxy crosslinked Si–Al zeolite-like structural wood composite (WZLC) was reported. Under the action of amine guiding agents and epoxy resin, the zeolite-like catalytic structure constructed in poplar wood comprised negative electrocatalytic sites, which can efficiently catalyze the formation of the carbon layer and endow WZLC with excellent flame retardant, smoke-suppression, and self-extinguishing properties. Compared with the untreated wood (WN), the thermal stability of the treated wood (WZLC) was greatly improved, and the amount of volatile organic compounds released during the decomposition process was significantly reduced. The heat release rate, total heat release, smoke production rate, and total smoke production of WZLC1 decreased by 50.23%, 44.14%, 45.21%, and 28.46%, respectively. Particularly, CO and CO2 yields of WZLC significantly decreased by 92.26% and 92.02%, respectively, indicating that the Si–Al zeolite-like catalytic structure displayed excellent catalytic flame retardant properties, which can effectively decrease the thermal decomposition rate and combustion risk of the WZLC. This method uses less flame retardants to achieve a good flame retardant and smoke suppression effect, thereby reducing the risk of environmental pollution caused by too many flame retardants.

The electromagnetic wave absorption composite of flower-like structure NiCo2O4 and Fe3O4 derived from low-temperature preparation method

The NiCo2O4@Fe3O4 composites with excellent electromagnetic wave absorption performance was prepared by the low-temperature (50 °C) co-precipitation method, avoiding the traditional high-temperature hydrothermal synthesis method. The specific surface area of the composite material was increased due to the combination of NiCo2O4 with 3D hierarchical flower-like structure and Fe3O4 with spherical structure, which is conducive to the full reflection and scattering of electromagnetic waves. The combination of typical magnetic material and excellent dielectric material could adjust the impedance matching value of the material and thus the absorption loss performance of electromagnetic wave was improved. The ε value of the dielectric material was larger than those of magnetic materials and the maximum reflection loss value appeared at the high frequency (the thickness is small), while the μ value of magnetic materials was larger than those of dielectric materials and the maximum reflection loss value generally appeared at low frequency (the thickness is large).The results showed that the maximum RL value reached −53.35 dB at about 13 GHz with the thickness of 2.0 mm and the effective absorption bandwidth was 4.4 GHz when the weight ratio (NiCo2O4:Fe3O4) of composite samples was 6:1. The excellent EMW absorption property was mainly due to the combination of NiCo2O4 and Fe3O4, which could achieve impedance matching to loss EMW by dielectric loss and magnetic loss.

Preparation of Red Iron by Magnetization Roasting-Hydrothermal Method Using Ultra-Low-Grade Limonite

Iron is one of the most important strategic materials in national production, and the demand for iron ore is huge in the world. High quality iron ore reserves have been almost exhausted, and it is necessary to develop a technology that utilizes low-grade iron ore. Limonite is a representative low-grade iron ore due to its complex mineral and elemental composition. In this paper, the union process was employed to separate the iron elements in low-grade limonite. Firstly, a rough iron concentrate was obtained under 1.0 T of magnetic field intensity and −0.074 mm > 94.84% of grinding fineness; then, the rough iron concentrate was magnetization roasted under a temperature of 700 °C, 60 min of retention time, 3 wt% of biochar consumption, and 0.15 T of magnetic field intensity. The grade of iron concentrate was 59.57% and the recovery of iron was 90.72%. Finally, the red iron pigment was produced via a high temperature hydrothermal method in order to increase the additional value of this ultra-low-grade limonite. The optimal parameters were 10.0 g/L of solution acidity, a 200 °C reaction temperature, 5 h of reaction time, and a 6:1 solid-to-liquid ratio. The reaction mechanism was also discussed.

Hydrothermal synthesis of lanthanide ruthenate single crystals

A series of lanthanide ruthenates were synthesized as large single crystals using a high temperature hydrothermal method (600–650 °C, 200 MPa). In all cases, the lanthanide sesquioxides (Ln2O3) and RuO2 were used as starting materials in various ratios. A range of products containing ruthenium in a variety of oxidation states were isolated, including LnRuO3, Ln2Ru2O7, Ln2RuO5(OH), and Ln5Ru2O12, depending on the size of the rare earth and the relative ratio of starting materials. In most cases, the products were formed in good yield as high-quality single crystals. This approach provides a route to single crystals of the perovskite and pyrochlore structure types to enable advanced physical properties measurements. The study also introduces the Ln2RuO5(OH) structure type for Ru5+, and significantly expands the phase space for Ln5Ru2O12 to the later lanthanides, also as well-formed single crystals. Careful analyses of diffraction data suggest that the materials contain minimal site disorder or nonstoichiometry.

Synergistic effect of double solvent and accelerator on efficient synthesis of nickel phyllosilicate for CO2 methanation

In order to facilitate the synthesis of nickel phyllosilicate through the hydrothermal method, different process parameters including high or low hydrothermal temperature, single or double solvent, and with or without accelerator were investigated in this work. The Ni/DA-150-6 catalyst prepared in the presence of double solvent and the accelerator exhibited high Ni content, small Ni crystal size, and large H2 and CO2 chemisorption capacity, leading to the highest catalytic activity for CO2 methanation. Meanwhile, Ni/S-200-12 synthesized by the high-temperature (200 °C) hydrothermal method or Ni/D-150-12 prepared at 150 °C in the presence of double solvent displayed low catalytic activity owing to the low Ni content. In short, the synergistic effect of double solvent and accelerator is the most significant strategy for the efficient synthesis of Ni-phyllosilicate.

Achieving electromagnetic wave absorption capabilities by fabrication of flower-like structure NiCo2O4 derived from low-temperature co-precipitation

In this work, The NiCo2O4 with 3D hierarchical multilayer flower-like structure was prepared by the low-temperature (55 °C) co-precipitation method combined with the calcination process, avoiding the traditional high-temperature hydrothermal synthesis method. The prepared flower-like NiCo2O4 with a large specific surface area was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and automatic surface area and porosity analyzer (BET) and vector network analyzer (VNA). A novel evaluation approach was proposed to evaluate the electromagnetic wave (EMW) absorbing properties of various samples (different calcination temperatures), which was to defined the ΔS as the area enclosed by the curve when the reflection loss (RL) value was less than −10. In order to take the material thickness into account, and then the effective reflection loss (RLE) value was defined ΔS/d to measure the electromagnetic wave (EMW) loss capability of the different samples. The results showed that NiCo2O4 exhibited excellent EMW absorption effect when the calcination temperature was 400 °C, and the maximum RL value reached −43.17 dB at 14.32 GHz with the thickness of 1.5 mm and the effective absorption bandwidth (fe) was 4.48 GHz (12.08 GHz–16.56 GHz). The excellent EMW absorption property was mainly due to NiCo2O4 with particular porous flower-like structure, which could achieve impedance matching to loss EMW by dielectric loss and magnetic loss.

Solar-Driven Generation of Hydrogen Peroxide on Phenol-Resorcinol-Formaldehyde Resin Photocatalysts.

Photocatalytic generation of H2O2 from water and O2 under sunlight is a promising artificial photosynthesis reaction to generate renewable fuel. We previously found that resorcinol-formaldehyde resin powders prepared with a high-temperature hydrothermal method become semiconductors comprising π-conjugated/π-stacked benzenoid-quinoid donor-acceptor resorcinol units and are active for photocatalytic H2O2 generation. Here, we have prepared phenol-resorcinol-formaldehyde resins with small amounts of phenol (∼5 mol % relative to resorcinol), which show enhanced photocatalytic activity. Incorporating phenol bearing a single -OH group in the resin matrices relaxes the restriction on the arrangement of the aromatic rings originating from the H-bonding interactions between the resorcinol -OH groups. This creates stronger donor-acceptor π-stacking and increases the electron conductivity of the resins. We have demonstrated that simulated sunlight illumination of the resins in water under an atmospheric pressure of O2 stably generated H2O2 with more than 0.9% solar-to-chemical conversion efficiency.

Bandgap-engineered ferroelectric single-crystalline NBT-BT based nanocomposites with excellent visible light-ultrasound catalytic performance

Bandgap engineered ferroelectrics exhibit encouraging multi-energy catalytic performance by coupling the piezoelectricity and photoexcitation, which shows immense potential for environmental remediation and fuel production. However, it is challenging to prepare nano single-crystalline ferroelectric piezo-photoelectric with strong visible light absorption ability. Here, Ni mediated NBT-BT(NBT-BNT) single-crystalline nanocubes around 100 nm with considerable visible light absorption were synthesized by a high-temperature hydrothermal method. The mechanism of Ni2+ on the formation of NBT-BT nanocubes was proposed. The catalytic efficiency of NBT-BNT nanocubes is enhanced by decorating carbon quantum dots (CQDs). The RhB can be degraded within 8 min and the hydrogen production rate reaches up to ∼350 μmol g-1h-1 under visible light-ultrasonic condition. Moreover, under the simulated sunlight-ultrasound condition, RhB can be degraded within merely 3 min and a high H2 production rate of ∼747 μmol g-1h-1 is achieved. This work presents a paradigm for preparing ferroelectric single-crystalline nanocatalysts for multi-energy catalytic application.

Synthesis of heterostructured dual metal sulfides by a high-temperature mixing hydrothermal method as an ultra-high rate anode for Li-ion batteries

A novel approach is reported to fabricate flower-like Cu2S/MoS2/rGO by using a high-temperature mixing hydrothermal method. The synthesized Cu2S/MoS2/rGO composite shows excellent rate capability and long cycling durability.

Functionality of Silk Cocoon (Bombyx mori L.) Sericin Extracts Obtained through High-Temperature Hydrothermal Method

Sericin, a textile waste, can be used for antioxidant and skin-whitening purposes. The hydrothermal method of extracting sericin is more eco-friendly than are chemical and enzymatic methods. In this study, silk cocoons were cut into pieces and then subjected to hydrothermal extraction at three temperatures (160, 200, and 220 °C) to obtain sericin extracts (Sericin160, Sericin200, and Sericin220, respectively). Antioxidant activity and tyrosinase inhibition were measured to determine the extracts’ effectiveness. Sericin220 was the strongest antioxidant, with total phenol content, total flavonoid content, and ferric reducing power of 62.19 ± 0.04 mg gallic acid equivalents/g dry weight, 0.07 ± 0.01 mg quercetin equivalent/g dry weight, and 181.49 ± 0.024 mg vitamin C equivalent/g dry weight, respectively. The half-maximal inhibitory concentrations for DPPH and ABTS free-radical scavenging ability were 6.41 ± 0.05 and 0.79 ± 0.37 mg/mL, respectively. Sericin220 also exhibited the highest tyrosinase inhibition activity (70.82 ± 4.1 mg vitamin C equivalent/g), indicating its whitening potential.

A Review on Luminescent Rare Earth Complexes

At present, rare earth elements are widely used in various industries. In this paper, luminescent rare earth complexes are taken as a starting point to explore the luminescence principles of several important rare earth elements. The commonly used synthesis methods of luminescent rare earth complexes in recent year are also summarized, mainly including co-precipitation method, high temperature solid phase method, sol-gel method and hydrothermal synthesis method. And prospects for the future research on luminescent rare earth complexes are made.

Efficient degradation of tetracycline by RGO@black titanium dioxide nanofluid via enhanced catalysis and photothermal conversion

The applications of photocatalytic pollutant degradation have remained limited due to the low efficiency of solar energy utilization. In this study, a photothermal catalyst consisting of reduced graphene oxide @ black TiO2 (RGO@BT) nanofluid with effective full-spectrum (from ultraviolet to infrared light) absorption was synthesized by a typical two-step method of high temperature calcination and hydrothermal method. Moreover, the photothermal catalytic performance of the RGO@BT nanofluid on tetracycline was verified. Compared with individual processes (i.e, photocatalysis and thermocatalysis), the photothermal catalytic process significantly enhanced tetracycline degradation under simulated global standard spectrum sunlight (AM 1.5G, 1000 W m−2). The maximum photothermal conversion efficiency reached 91.8%, which resulted in 94.7% tetracycline degradation (40 mg L−1) after 120 min of treatment with 200 mg L−1 RGO@BT nanofluid. Holes, OH, and O2− were found to be the main active species during the photothermal catalytic process. Moreover, heat was spontaneously converted from light energy without the use of any external energy source. The elevated system temperature facilitated the tetracycline degradation based on the Arrhenius behavior. These findings provide insights into the improvement of photocatalytic efficiency in organic contaminant degradation via solar energy-efficient photothermal conversion materials.

Highly defective, doping-free graphene framework: A rapid one-step formation avenue

Defective carbon material, especially for graphene, has attractive in the energy conversion and storage field due to its fascinating surface structural and electronic properties. The defective graphene has been synthesized either by high temperature calcination of inorganic salt or from the pristine graphene (or graphene oxide) by violent chemical reaction, both of which are destructiveness and harsh tedious preparation process. The existing mild preparation methods can effectively preserve the planar structure of graphene, but at the expense of defect density. Here, we demonstrate a simple and direct one-step high-temperature hydrothermal method to synthesize doping-free, multi-defect graphene (DMG) framework. During the thermal vapor process under high-temperature and high-pressure, graphene layers are etched and exfoliated layer by layer within a short time. Accompanied by rapidly increasing of edge structures, the resulting DMG presents a superior defect density to those graphene materials reported previously, leading to a robust electrocatalytic activity in oxygen reduction reaction as well as achieving a significantly high capacitance in supercapacitor. This work presents a facile effective synthetic route for realizing high defective graphene materials and also confirms the important role of defective graphene in electrochemical domain without any other dopants.

Rapid High-temperature Synthesis of Nanosized ZSM-22 Zeolite

Nanosized ZSM-22 with high crystallinity was synthesized rapidly by a high-temperature hydrothermal synthesis method. The effects of synthesis conditions such as crystallization temperature, crystallization time, Si/Al ratios and crystallinity of ZSM-22 were investigated, and the relationship between crystallization temperature and crystallization time was calculated by Arrhenius equation. Meanwhile, the rapid high-temperature synthesis method was effective to synthesize ZSM-22 with Si/Al ratio from 35 to 70. The nanosized ZSM-22 exhibited high light olefin selectivity and a long lifetime in the MTO reaction.

Solar-to-hydrogen peroxide energy conversion on resorcinol\u2013formaldehyde resin photocatalysts prepared by acid-catalysed polycondensation

The photocatalytic generation of hydrogen peroxide from water and dioxygen (H2O + 1/2O2 → H2O2, ΔG° = +117 kJ mol–1) under sunlight is a promising strategy for the artificial photosynthesis of a liquid fuel. We had previously found that resorcinol–formaldehyde (RF) resin powders prepared by the base-catalysed high-temperature hydrothermal method act as semiconductor photocatalysts for H2O2 generation. Herein, we report that RF resins prepared by the acid-catalysed high-temperature hydrothermal method (~523 K) using common acids at pH < 4 exhibit enhanced photocatalytic activity. The base- and acid-catalysed methods both produce methylene- and methine-bridged resins consisting of π-conjugated and π-stacked benzenoid–quinoid donor–acceptor resorcinol units. The acidic conditions result in the resins with a lower bandgap (1.7 eV) and higher conductivity because the lower-degree of crosslinking creates a strongly π-stacked architecture. The irradiation of the RF-acid resins with simulated sunlight in water with atmospheric-pressure O2 generates H2O2 at a solar-to-chemical conversion efficiency of 0.7%, which is the highest efficiency ever reported for powder catalysts used in artificial photosynthesis.

Photocatalytic nanocomposite membranes for high-efficiency degradation of tetracycline under visible light: An imitated core-shell Au-TiO2-based design

Herein, Au-TiO2 nanocomposite photocatalysts were initially constructed through a three-step-synthesis strategy including the sodium citrate reduction method, sol-gel method and high-temperature hydrothermal method. After that, Au-TiO2/PVDF photocatalytic nanocomposite membranes with visible light response were synthesized by a phase conversion process, thereinto, the Au-TiO2 nanocomposite and PVDF powder were mixed into casting solutions by physical blending. Various characterization methods, such as SEM, TEM, FTIR, XRD, XPS, WCA and UV-vis DRS, etc., were used to systematically characterize the micromorphology, structural composition, wettability and optical properties of different samples. The UV-vis DRS results showed that the as-prepared nano-Au doping structure effectively enhanced the utilization factor of visible light in the process of photocatalytic degradation. The antifouling results of BSA adsorption experiments showed that 0.3-Au-TiO2/PVDF composite membranes possessed good antifouling performance. By analyzing the regeneration stability experiments, it could be found that the 0.3-Au-TiO2/PVDF composite membranes also exhibited excellent regeneration stability and easy separation and recovery features. The photocatalytic degradation of different membranes under visible light was investigated with tetracycline. The results showed that the photocatalytic degradation rate of 0.3-Au-TiO2/PVDF nanocomposite membranes reached 75% within 120 min. Moreover, the first-order kinetic linear fitting showed that the k value of 0.3-Au-TiO2/PVDF composite membranes was 0.01212 min−1, which was 2.7 times and 2.0 times higher than that of 0.1-Au-TiO2/PVDF and 0.5-Au-TiO2/PVDF composite membranes. That is to say, photocatalytic activity of 0.3-Au-TiO2/PVDF composite membranes were obviously improved.