Hydrothermal Reaction Temperature Research Articles

Enhancement of hydrothermal carbonization of chitin by combined pretreatment of mechanical activation and FeCl3

In this work, a combined mechanical activation and FeCl3 (MA + FeCl3) method was applied to pretreat chitin to enhance the degree of hydrothermal carbonization. MA + FeCl3 pretreatment significantly disrupt the crystalline region of chitin and Fe3+ entered into the molecular chain, resulting in the destruction of the stable structure of chitin. The chemical and structural properties of hydrochars were characterized by EA, SEM, FTIR, XRD, XPS, 13C solid state NMR, and N2 adsorption-desorption analyses. The results showed that the H/C and O/C atomic ratios of HC-MAFCT/230 (the hydrochar derived from MA + FeCl3 pretreated chitin with hydrothermal reaction temperature of 230 °C) were 0.96 and 0.34, respectively. Van Krevelen diagram indicated that the hydrothermal carbonization of chitin underwent a series of reactions such as dehydration, decarboxylation, and aromatization. HC-MAFCT/230 had abundant oxygen- and nitrogen-containing functional groups. HC-MAFCT/230 exhibited a porous structure, with the specific surface area of 128 m2 g−1, which was a promising carbon material.

Catalytic hydrothermal carbonization of microalgae biomass for low-carbon emission power generation: the environmental impacts of hydrochar co-firing

This work aims to improve the synthesis of renewable hydrochar (HC) co-fired with coal to reduce grenhouse gas (GHG) emission. Acetic acid catalyzed hydrothermal carbonization (cHTC) of Chlorella vulgaris microalgae biomass was investigated based on a 33−1 fractional statistical design of the experiment to examine the effects of hydrothermal reaction temperature (T = 180–220 °C), biomass-to-suspension- (BSR = 5–25 wt.%), and catalyst-to-suspension (CSR = 0–10 wt.%) ratios on process performance indicators. Analysis of variance was used to assess the experimental data. The results show that the application of homogeneous catalyst improves the fuel ratio and energy recovery efficiency up to 0.38 and 36.3%. Ex-ante cradle-to-gate life cycle assessment was performed to evaluate the impacts of co-firing ratio (CFR) and hydrochar quality on multi-perspective mid-, and endpoint environmental indicators. The highest decarbonization potential (−1.54 kg CO2,eq kWh−1) is achieved using catalytic hydrochar biofuel produced at 195 °C, 25 wt.% BSR, and 8 wt.% CSR levels. The application of catalytic and autocatalytic hydrochar blends improves the overall environmental impacts and greenhouse gas footprint of solid fuel firing facilitating the transition toward low-carbon emission power generation.

Study on the Preparation of Zn‐Al‐LDHs by Different Reaction Methods with Ion Exchange Resin

AbstractZn‐Al layered double hydroxides (Zn‐Al‐LDHs) were successfully prepared with ion exchange resin and mixed hydroxide by pneumatic stirring, constant temperature oscillation, magnetic stirring and hydrothermal reaction methods. The products were characterized by SEM, EDS, XRD, FT‐IR and TG‐DSC. The advantages and disadvantages of various preparation methods were compared systematically. On the basis of the unique internal structure of ion exchange resin, the resin could effectively control the rate of product generation, and ensure the formation of LDHs slowly and evenly in the whole solution, so that the product morphology was more uniform and dispersed, and the product could be used directly without washing. SEM and XRD results show that the single constant temperature oscillation method and magnetic stirring method could obtain the products with better micromorphology than the pneumatic stirring method, presenting a clear hexagonal sheet structure. At the same time, the two methods can obtain nanoscale Zn‐Al‐LDHs with better crystal structure and higher purity. FT‐IR and TG‐DSC characterization further confirmed the composition of the product and the carbonate intercalation structure of the hydrotalcite.

Resource-recycling and energy-saving innovation for iron removal in hydrometallurgy: Crystal transformation of ferric hydroxide precipitates by hydrothermal treatment

In hydrometallurgy industry, the accumulation of iron removal residues containing heavy metal elements and toxic elements poses great threats to ecological systems. We propose a novel method to prevent the production of hazardous iron removal residues: firstly, neutralization precipitation is used to purify iron ions in solution; after sedimentation of the obtained suspension, only dense underflow is subjected to hydrothermal reaction, in which ferric hydroxide transforms into hematite crystal. Results showed that ferric hydroxide precipitated into a thin sedimentation layer at temperature greater than 60 °C. For hydrothermal treatment of the sedimentation layer, a high hydrothermal reaction temperature was conducive to complete transformation of ferric hydroxide into hematite. The precipitated ferric hydroxide firstly changed from the crystallite of goethite or lepidocrocite to amorphous particles, and then gradually formed spherical α-Fe2O3 monocrystalline with diameter of around 50 nm, as indicated by TEM and XRD results. At 200 °C, hematite precipitates with iron content of about 65% can be obtained. For iron-containing zinc/nickel/cobalt sulfate solution, controlling hydrothermal reaction temperature and acidity of the underflow solution can effectively avoid the generation of zinc/nickel/cobalt hydroxides or subsulfates in the hematite precipitates, thereby significantly reducing the loss of those valuable metals.

Optimizing the Hydrothermal Carbonization of Sewage Sludge—Response Surface Methodology and the Effect of Volatile Solids

This study focuses on identifying the optimum conditions of sewage sludge hydrothermal carbonization by Box–Behnken Design and on the effects of volatile solids on heating value and on process water load. To get insight into the solid and process water characteristics, we applied the Box–Behnken Design on the hydrothermal reaction temperature (190, 220, 250 °C), reaction time (0.5, 2.25, 4 h) and pH (3.9, 5, 6.1). The response surface of the liquid phase revealed decreasing dissolved organic carbon (DOC) concentrations with increasing temperature from 9446 mg/L (190 °C) to 7402 mg/L (250 °C) at 4 h reaction time. For the same hydrothermal conditions, NH4-N concentration increased from 754 to 1230 mg/L. Reaction temperature was identified as the most important process parameter, whereas reaction time and pH had only minor effects. Moreover, linear coefficients of the models were more decisive than the interrelation and quadratic coefficients. Volatile solids (VS) of the feedstock were found to significantly influence both the load of the process water and the change in heating value of the hydrochars. Process water load increased steadily with higher VS. The heating value only increased with more than around 65–80% VS in feedstock.

Controllable crystallization of pure vaterite using CO2-storage material and different Ca2+ sources

The controllable synthesis of pure vaterite with the good properties and broad application prospects is considered as an important, yet a challenging task because the product properties are greatly affected by reaction conditions. In the present work, the controllable synthesis of pure vaterite crystals was explored with four different Ca2+ sources including CaCl2, Ca(NO3)2, CaBr2 and Ca(Ac)2 using an CO2-storage material (CO2SM) prepared by an indirect CO2 utilization approach as the CO32− source. The effects of five major reaction conditions including reaction medium, hydrothermal reaction temperature, hydrothermal reaction time, Ca2+ concentration and sources, and pH and conductivity on the crystallization of CaCO3 were systemically investigated. It is found that the amounts of CO2SM required for the formation of pure vaterite phase are in the order of CaBr2 (20 g/L CO2SM) > Ca(NO3)2 (16 g/L CO2SM) > Ca(Ac)2 (8 g/L CO2SM) due to the effects of ethylenediamine (EDA), diethylene glycol (DEG) and their anions. Especially, vaterite was not found in CaCl2 system. The effects of Ca2+ sources on the crystal phase composition of CaCO3 are revealed for the controllable synthesis of CaCO3 crystals. Our work not only provides a controllable synthesis method of pure vaterite, but also an indirect CO2 utilization strategy.

Zinc Ferrite Nanoparticles: Unusual Growth Mechanism for Size‐Dependent Properties

AbstractHerein, non‐stoichiometric zinc ferrite nanoparticles, Zn0.86Fe2.14O4+δ,with grain sizes of being smaller than 11 nm were successfully prepared by varying the hydrothermal reaction duration and temperature. The influence of reaction temperature and time on the grain size of zinc ferrite nanoparticles was investigated. Non‐stoichiometric zinc ferrite nanoparticles underwent distinct processes at different reaction temperatures: at 200 °C, the growth mechanism follows an Ostwald ripening model with activation energy 124.7 kJ/mol, while at 120 °C, the particle growth is governed by aggregation and coalescence, Ostwald ripening mechanism with the activation energy 27.5 kJ/mol and digestive ripening process.The abnormal growth behavior of zinc ferrite nanoparticles is completely different from previous reports on the oxides. Detailed analysis of XPS, XRD, FT‐IR and Mössbauer spectra revealed that the presence of rich iron oxides on the surface of nanoparticles is responsible to the non‐stoichiometry. Moreover, unit cell volume and magnetic property of non‐stoichiometric zinc ferrite exhibited two extremum as the increase of grain size, which was closely related to the grain size‐dependent structure changing. The unusual growth behavior and the size dependent structure and property changes of non‐stoichiometric zinc ferrite nanoparticles reported in this work may be beneficial to guide the future development of magnetic materials.

Flexible Ethanol Sensor Based on ZnO-Based Nanomaterials Prepared by Hydrothermal Method

Metal oxide semiconductor ethanol sensor is widely used in alcohol driving detection, biomedical and industrial fields. As a typical n-type semiconductor, ZnO has a certain response to ethanol at a certain temperature, but there is still a large room for improvement in gas sensing characteristics such as sensitivity, response and recovery time, selectivity and so on. In this paper, the orthogonal experiment is used to design the experiment. Taking the hydrothermal reaction time, hydrothermal reaction temperature and the molar ratio of zinc oxide to thiourea as the three important variables in the orthogonal experiment, nine groups of representative ZnO-ZnS powder samples with different process combinations are prepared by hydrothermal method. The structure and morphology of the nine samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Energy Dispersive Spectrometer (EDS). The optimal preparation scheme of ZnO-ZnS is selected, and the sensor based on polyimide is integrated. The gas sensing characteristics of ZnO-ZnS and pure ZnO sensors are tested by static gas distribution method. The results show that ZnO-ZnS nano materials have good sensitivity to ethanol, and the sensitivity to 100 ppm ethanol gas is 67.35 at 300 °C, and the response and recovery time is about 15 seconds. The prepared flexible sensor also shows good selectivity and stability, which provides a reference for the preparation of high-performance flexible ethanol sensor in the future test.

A facile two-step synthesis of an efficient narrow-band red-emitting K2NbF7:Mn4+ phosphor for warm white LEDs and its thermal quenching behavior

Mn4+-doped fluoride phosphors exhibit narrow red line emission under blue light excitation. Such phosphors can improve the color rendering index (CRI) and reduce the color temperature of white LEDs. In this study, a series of K2NbF7:Mn4+ red phosphors were successfully synthesized by a facile two-step synthesis. The structure, composition, morphology and spectral properties were studied by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and photoluminescence spectroscopy. The obtained K2NbF7:Mn4+ can emit multiple sharp emission peaks in the range of 600–650 nm under excitation of ~371 nm or ~471 nm. In particular, this phosphor has a strong zero phonon line (ZPL) emission at 620 nm and an internal quantum efficiency (IQE) ~82%. The effects of Mn4+ doping amount, hydrothermal reaction temperature and HF concentration on spectral properties were discussed and the optimal synthesis conditions were obtained. The thermal quenching behavior of K2NbF7:Mn4+ red phosphor was studied and the activated energy was determined to be 0.66 eV. The fabricated white light-emitting diode (w-LED) with a low correlated color temperature (CCT) at 3426 K and a high luminous efficiency of 134.4 lm/W was obtained by using the K2NbF7:Mn4+, which indicates that K2NbF7:Mn4+ could be a potential red component for warm w-LEDs.

Pr-doped NiCoP nanowire arrays for efficient hydrogen evolution in both acidic and alkaline media

Enhancing the hydrogen evolution reaction (HER) performance of electrocatalysts is essential for developing clean energy, in which doping is one of the most effective ways. In this work, praseodymium-doped NiCoP nanowire arrays grown on nickel foam (Pr-NiCoP NWAs/NF) as electrocatalysts were synthesized through hydrothermal reaction and low temperature phosphating. The subsequent tests revealed that the introduction of Pr can modulate the morphology, density of the active sites and electrical conductivity of the NiCoP NWAs/NF. Thereby, the Pr-NiCoP NWAs/NF realized the fast reaction kinetics and exceptional HER performance. When the additive molar amount of Pr is 10%, Pr-NiCoP NWAs/NF electrode exhibited the highest electrocatalytic activity. Its overpotential corresponding to current density of 10 mA•cm−2 were 91 and 88 mV in 0.5 mol•L−1 H2SO4 and 1 mol•L−1 KOH, the Tafel slope of which were 45.5 and 69.2 mV•dec−1, respectively. Further, this work provides a promising strategy to explore highly efficient HER electrocatalysts.

Simultaneous growth of graphene/mesoporous silica composites using liquid precursor for HPLC separations

Silica intercalated graphene-silica composites (G/SiO2) were prepared by one-step hydrothermal method. In the previously reported one-step method for synthesizing G/SiO2 composites (eg. Bull. Mater. Sci., 37 (2014), 589–595; Applied Surface Science 259 (2012), 566–573), graphene needs to be synthesized first and then used to prepare G/SiO2 composites. In this work, neither the preparation of graphene nor the use of graphite as a carbon source is required for the preparation of G/SiO2 composites. Instead, organic solvent (such as toluene, xylene, mesitylene, n-hexane, n-heptane, and cyclohexane) was directly used as the carbon source, and the growth and recombination of graphene and SiO2 were achieved simultaneously through a one-step hydrothermal method. In a hydrothermal reaction vessel, the mixture consisting of organic solvent, TEOS, H2O, and surfactant was uniformly stirred, and then reacted at 160 °C for 4 h to prepare G/SiO2 composite. The influence of the type of organic solvent, hydrothermal reaction temperature, and calcination temperature on the structure of G/SiO2 composites were studied. The morphology and structure of G/SiO2 composites were characterized by FESEM, TEM, and Raman. The formation mechanism of G/SiO2 composite was proposed. G/SiO2 composite was then grown directly on the SiO2 spheres and used as stationary phase for high performance liquid chromatograph separation. Mixture of hydrocarbons was well separated under reversed phase condition.

Field emission from geometrically modulated tungsten-nickel sulfide / graphitic carbon nanobelts on Si microchannel plates

The low efficiency and instability of electron emission from two-dimensional (2D) materials such as WS2 and NiS hamper application to vacuum microelectronic devices. Although nickel-based alloys have many favorable physicochemical properties suitable for nanoelectronics, electron field emission (FE) from heterostructures comprising tungsten-nickel sulfide alloys and graphite carbon (WNi–S/C) has been seldom studied because it is difficult to fabricate the nanostructures in situ. In this work, field emitters composed of the WNi–S/C nanobelt composite are produced on Si microchannel plates (WNi–S/C@Si) hydrothermally. The structure has a porous and vertically aligned 3D morphology in addition to excellent adhesion strength with the substrate. Geometrical modulation of the WNi–S/C@Si is performed by changing the hydrothermal reaction temperature and an ultralow turn-on electric field of 0.51 V μm−1 for a current density 0.1 mA cm−2, threshold electric field of 0.65 V μm−1 for a current density of 1 mA cm−2, and stability of 97.1% for 8 h are accomplished. The related mechanisms are investigated and discussed. Moreover, finite element simulation shows that not only the shape of the nanostructures but also the high aspect plays a key role in reducing screen effects. These outstanding properties suggest large potential in high-performance FE and vacuum nanodevices.

Preparation and Photocatalytic Activity of TiO2 Film with High Exposure {001} Crystalline Surface

TiO2 films with exposed {001} crystal surface were prepared by hydrothermal method with 10 mm * 20 mm * 0.15 mm titanium sheet as titanium source and substrate and HF as shape control agent. The films were characterized by (XRD), (SEM) and (UV-VIS). The results showed that the TiO2 films with high exposure {001} crystal surface could be obtained by using 0.01 mol/L HF, 11:5 mixture of water and isopropanol as solvent, hydrothermal reaction temperature of 180°C, reaction time of 3H and calcination at 450°C for 2h. In this paper, methylene blue was used as probe and xenon lamp was used as light source to study the photocatalytic activity of TiO2 film.

MOF-Derived Hierarchical CoSe2 with Sheetlike Nanoarchitectures as an Efficient Bifunctional Electrocatalyst.

The exploitation of efficient and stable non-noble-metal bifunctional electrocatalysts is key to the development of hydrogen production technology. Although some progress has been made in the synthesis of transition-metal selenide nanostructures, the preparation of metal-organic framework (MOF)-derived transition-metal selenide electrode materials with more active sites and nanosheet structures remains a significant challenge. Herein, on the basis of the MOFs, the hierarchical CoSe2-160 microcube with sheetlike nanoarchitectures was successfully prepared. In addition, the morphology of cobalt selenides was controlled by adjusting the hydrothermal reaction temperature. Electrochemical experiments show that the CoSe2-160 microcube has a splendid electrocatalytic performance with 10 mA cm-2 at an overpotential of 156 mV and a small Tafel slope of 40 mV dec-1 (in 0.5 M H2SO4) for hydrogen evolution reaction as well as 328 mV and a small Tafel slope of 73 mV dec-1 (in 1 M KOH) for oxygen evolution reaction, respectively. This arises from the nanosheet structures, large surface areas, and abundant active sites. This strategy provides a neoteric synthesis route for the MOF-derived transition-metal selenides with a striking electrocatalytic performance.

Microwave idrothermal synthesis of magnesium-aluminium spinel

Magnesium–aluminium spinel powder was prepared by microwave hydrothermal synthesis method. The phase structure of the samples was analysed using X-ray diffractometer. The microscopic morphology of the samples was analysed by scanning electron microscope. The particle size of the powder was characterised. The effects of different microwave hydrothermal reaction temperatures on the phase structure, micromorphology and particle size distribution of the precursors were studied. Results show that when hydrothermal reaction temperature was controlled at 140 °C-180 °C, pure magnesium–aluminium composite hydroxyl-hydrate precursor can be obtained after 200 min. The median diameter of magnesium–aluminium spinel precursor powder under 150 °C was 5.958 μm, which is the minimum. After calcination, the morphology of the powder underwent a process from flaking and particle stacking to development of complete flake morphology as the microwave hydrothermal reaction temperature increased. The agglomeration phenomenon was very serious when the synthesis temperature was greater than 150 °C.

Photocatalytic water splitting of ternary graphene-like photocatalyst for the photocatalytic hydrogen production

In recent times, there has been an increasing demand for energy which has resulted in an increased consumption of fossil fuels thereby posing a number of challenges to the environment. In the course finding possible solutions to this environmental canker, solar photocatalytic water splitting to produce hydrogen gas has been identified as one of the most promising methods for generating renewable energy. To retard the recombination of photogenerated carriers and improve the efficiency of photocatalysis, the present paper reports a facile method called the hydrothermal method, which was used to prepare ternary graphene-like photocatalyst. A “Design Expert” was used to investigate the influence of the loading weight of Mo and GO as well as the temperature of hydrothermal reaction and their interactions on the evolution of hydrogen (H2) in 4 h. The experimental results showed that the ternary graphene-like photocatalyst has a strong photocatalytic hydrogen production activity compared to that of pure SiC. In particular, the catalyst added 2.5 wt% of GO weight yielded the highest quantum of 21.69 % at 400–700 nm of wavelength. The optimal evolution H2 in 4 h conditions was obtained as follows: The loading weight of Mo was 8.19 wt%, the loading weight of GO was 2.02 wt%, the temperature of the hydrothermal reaction was 200.93°C. Under the optimum conditions, the evolution of H2 in 4 h could reach 4.2030 mL.

Synthesis of hierarchical porous Zeolite-Y for enhanced CO2 capture

Abstract In the present study, a facile and one step approach has been developed for the synthesis of hierarchical porous zeolite-Y using bifunctional cationic polymer, polydiallyldimethyl ammonium chloride (PDDA) as a mesopore directing template. The effects of various synthesis parameters such as hydrothermal reaction temperature, time, amount of PDDA and NaOH were systematically investigated to produce crystalline and hierarchical zeolite-Y crystals (PDYs). All the synthesized zeolite-Y samples were characterized by XRD, FT-IR, SEM, EDAX, TEM, TGA, CO2-TPD and Nitrogen adsorption-desorption measurements. The characterization results showed that the zeolite-Y samples synthesized at optimized ratios of PDDA/Al2O3 and NaOH/Al2O3 exhibited higher crystallinity, higher BET surface area and larger total pore volume in comparison to the sample synthesized in the absence of the template (ZY). Interestingly, the hierarchical porous zeolite-Y samples (PDY-7) displayed substantial enhancement in CO2 adsorption capacity (5.40 mmol/g) at 298 K and 100 kPa as compared to the non-templated one (ZY) (4.5 mmol/g). The effective improvement in CO2 adsorption performance of PDY samples is attributed to the existence of interconnected micro-meso channel network, the higher total pore volume and higher concentration of acid-base sites (due to the lower Si/Al ratio). Owing to the higher CO2 adsorption capacity, the PDY samples also displayed high equilibrium selectivity for CO2 over N2 (∼250) as well as over CH4 (∼110) at 298 K. The enhanced CO2 adsorption capacity combined with the high CO2 adsorption selectivity renders the hierarchical zeolite-Y an excellent contender for the efficient CO2 capture.

Synthesis of amorphous aluminosilicate from impure Indonesian kaolin

AbstractSynthesis of amorphous aluminosilicates from high impurities in Indonesian kaolin were carried out in several ways, directly from kaolin and indirectly from metakaolin (calcined kaolin), both with silica addition and without silica addition. Synthesis was conducted in a gradual temperature hydrothermal reaction and in a constant temperature hydrothermal reaction. Before being synthesized, kaolin impurities were separated according to density and/or particle size by centrifugation. X-Ray Diffraction and FTIR Spectrometry characterization of the synthesized product showed that the results of synthesis of aluminosilicates from metakaolin via hydrothermal with gradual temperature or constant temperature produced aluminosilicates with high quartz impurities, while synthesis with the addition of silica in hydrothermal conditions at 80°C for 12 hours can produce aluminosilicate with a low quartz content. Direct synthesis from kaolin with the addition of silica could produce pure aluminosilicates.

One-step fabrication of TiO2/Ti foil annular photoreactor for photocatalytic degradation of formaldehyde

One-step hydrothermal synthesis approach is applied to prepare oriented TiO2 nanowires on a Ti foil which serves as both the substrate and Ti source. The grown TiO2 nanowires are characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffractometry. The adsorption and photocatalytic performance of the TiO2/Ti foil catalyst in formaldehyde degradation has been explored in detail by a home-made setup, aiming at elucidating the photocatalytic performance of the TiO2/Ti foil catalyst as functions of the experimental preparation parameters, such as NaOH concentration, hydrothermal reaction temperature and time elapse as well as post-annealing temperature. More strikingly, the TiO2/Ti foil catalyst can be directly devised into a self-supporting annular reactor which is at least twice as efficient for the formaldehyde degradation as that based on commercial TiO2 powder catalyst. This study presents a scalable and commercially viable strategy for indoor air purification.

Hydrothermal synthesis of rutile TiO2 nanorods and their decoration with CeO2 nanoparticles as low-photocatalytic active ingredients in UV filtering applications

The use of TiO2 nanoparticles in sunscreen products has raised concern over their oxidative potential and adverse health effects brought about by their propensity to produce free radicals when exposed to UV radiation. In this study, an investigation into industry-scalable methods for synthesizing rutile TiO2 nanorods with controllable morphological characteristics was carried out. The effects of hydrothermal reaction temperature and nitric acid concentration on the crystal phase, composition and morphology were explored to assess the most suitable conditions for reproduction. Optimal reaction conditions for obtaining purely rutile TiO2 nanorods occurred when treating the titania precursor at 150 °C for 24 h with 16 M nitric acid. Here, these rutile nanorods are decorated with CeO2 nanoparticles, as a means of producing a material with high UV attenuation and low photocatalytic activity. The nanocomposite materials are prepared using facile hydrothermal and precipitation methods and showed selective UV absorption whilst also demonstrating a reduction in photocatalytic activity compared to bare rutile TiO2 nanorods of up to 88% and 77% when exposed to UV and solar simulated light. The results suggest CeO2/TiO2 could be safely applied as an ‘active’ inorganic UV absorber in sunscreen products.