Towards a new avenue for rapid synthesis of electrocatalytic electrodes via laser-induced hydrothermal reaction for water splitting

Electrochemical production of hydrogen from water requires the development ofelectrocatalysts that are active,stable,and low-cost for water splitting.To address these challenges,researchers are increasingly exploring binder-free electrocatalytic integratedelectrodes (IEs) as an alternative to conventional powder-based electrode preparation methods,for the former is highly desirable to improve the catalytic activity and long-term stability for large-scale applications of electrocatalysts.Herein,we demonstrate a laser-inducedhydrothermal reaction (LIHR) technique to grow NiMoO4nanosheets on nickel foam,which is then calcined under H2/Ar mixed gases to prepare the IE IE-NiMo-LR.This electrode exhibits superior hydrogen evolution reaction performance,requiring overpotentials of 59,116 and143 mV to achieve current densities of 100,500 and 1000 mA·cm-2.During the 350 h chronopotentiometry test at current densities of 100 and 500 m A·cm-2,the overpotentialremains essentially unchanged.In addition,NiFe-layered double hydroxide grown on Ni foam is also fabricated with the same LIHR method and coupled with IE-NiMo-IR to achieve water splitting.This combination exhibits excellent durability under industrial current density.The energy consumption and production efficiency of the LIHR method are systematicallycompared with the conventional hydrothermal method.The LIHR method significantly improves the production rate by over 19 times,while consuming only 27.78%of the total energy required by conventional hydrothermal methods to achieve the same production.

Reaction behaviour of Al_2O_3 and SiO_2 in high alumina coal fly ash during alkali hydrothermal process

The reaction behaviours of A1203 and SiO2 in high alumina coal fly ash under various alkali hydrothermal conditions were studied. The means of XRD, XRF, FTIR and SEM were used to measure the mineral phase and morphology of the solid samples obtained by different alkali hydrothermal treatments as well as the leaching ratio of SiO2 to A1203 in alkali solution. The results showed that with the increase of the hydrothermal treating temperature from 75 to 160 ~C, phillipsite-Na, zeolite A, zeolite P, and hydroxysodalite were produced sequentially while the mullite and corundum phase still remained. Zeolite P was massively formed at low-alkali concentration and the hydroxysodalite was predominantly obtained at high-alkali concentration. By the dissolution of aluminosilicate glass and the formation of zeolites together, the leaching efficiency of SiO2 can reach 42.13% with the mass ratio of A1203/SIO2 up to 2.19：1.

LiFePO_4 doped with magnesium prepared by hydrothermal reaction in glucose solution

Lithium iron phosphate （LiFePO4） doped with magnesium was hydrothermally synthesized from commercial LiOH, FeSO4, H3PO4 and MgSO4 with glucose as carbon precursor in aqueous solution. The samples were characterized by X-ray powder diffraction, scanning electron microscopy and constant charge-discharge cycling. The results show that the synthesized powders have been in situ coated with carbon precursor produced from caramel reaction of glucose. At ambient temperature （28±2℃）, the electrochemical performances of LiFePO4 prepared exhibit the high discharge capacity of 135 mAh g^-1 at 5C and good capacity retention of 98% over 90 cycles. The excellent electrochemical performances should be correlated with the intimate contact between carbon and LiFePO4 primary and secondary particles, resulting from the in situ formation of carbon precursor/carbon, leading to the increase in conductivity of LiFePO4.

Kinetics of Hydrothermal Reactions of Minerals in Near-critical and Supercritical Water

This work presents new experimental results on the kinetics of mineral dissolution in near-critical and supercritical water in a temperature range (T) from 25 to 400°C and a constant pressure of 23 MPa. Kinetic experiments were carried out by using a flow reactor (packed bed reactor) of an open system. The dissolution rates of albite and magnetite were measured under these experimental conditions. Na, Al and Si release rates for albite dissolution in water were measured as a function of the temperature and flow velocity in the reaction system. The maximum release rates of Na, Al and Si of albite dissolution in the hydrothermal flow systems under different flow velocities were always obtained at 300°C, that is to say, the maximum albite dissolution rates in the flow systems, regardless of different flow rates, were repeatedly measured at 300°C. Results indicate a wide fluctuation in albite dissolution rates occurring close to the critical point of water. The dissolution rates increased when the temperatures increased from 25 to 300°C and decreased when the temperatures increase from 300 to 400°C. At some flow velocities, the dissolution rates rose as the temperature surpassed 374°C. Albite dissolution was incongruent in water at most temperatures. It was only at 300°C that albite dissolution was congruent. The albite dissolution from 25 to 300°C (at 23 MPa) will change from incongruent to congruent, whereas from subcritical 300 to 400°C (at 23 MPa), the dissolution will change from congruent to incongruent. The release ratio of Al/Si (or Na/Si) is positive at T<300°C, and it is negative at T>300°C. The dissolution rates of magnetite in water increased with increasing T until T at the critical point of water or around it. The authors believe that this is caused by the wide fluctuations in water properties under the conditions from the near-critical to supercritical state.

Numerical simulation of hydrothermal mineralization associated with simplified chemical reactions in Kaerqueka polymetallic deposit, Qinghai, China

The Kaerqueka polymetallic deposit, Qinghai, China, is one of the typical skarn-type polymetallic ore deposits in the Qimantage metallogenic belt. The dynamic mechanism on the formation of the Kaerqueka polymetallic deposit is always an interesting topic of research. We used the finite difference method to model the mineralizing process of the chalcopyrite in this region with considering the field geological features, mineralogy and geochemistry. In particular, the modern mineralization theory was used to quantitatively estimate the related chemical reactions associated with the chalcopyrite formation in the Kaerqueka polymetallic deposit. The numerical results indicate that the hydrothermal fluid flow is a key controlling factor of mineralization in this area and the temperature gradient is the driving force of pore-fluid flow. The metallogenic temperature of chalcopyrite in the Kaerqueka polymetallic deposit is between 250 and 350 ℃. The corresponding computational results have been verified by the field observations. It has been further demonstrated that the simulation results of coupled models in the field of emerging computational geosciences can enhance our understanding of the ore-forming processes in this area.

Highly electroactive N–Fe hydrothermal carbons and carbon nanotubes for the oxygen reduction reaction

Glucose-derived carbons were prepared by hydrothermal carbonization of glucose followed by carbonization or activation to obtain carbon materials with different microporosities. These microporous carbons and carbon nanotubes(CNTs) were functionalized with melamine and/or iron(Ⅱ) phthalocyanine(FePc)following three different methodologies:(i) Functionalization with melamine via thermal treatment,(ii)incorporation of the lowest amount of FePc reported in the literature via incipient wetness impregnation followed by thermal treatment and(iii) functionalization with melamine followed by Fe Pc incorporation.The chemical and textural characterization of the prepared materials and their electrochemical assessment allowed to understand the role of microporosity in the incorporation of FePc and its effect on the oxygen reduction reaction(ORR). It was observed that FePc was preferentially incorporated inside the porous structure, especially in samples with more developed microporosity. However, functionalization with melamine modified the textural properties and the surface chemistry, favoring the incorporation of FePc on the surface. Regarding the electrochemical performance, the presence of FePc greatly enhanced the electroactivity of the microporous catalysts. An onset potential of 0.88 V and a four-electron pathway were obtained for glucose-derived carbons, whereas the limiting current densities and kinetic current densities rose by 126% and 222%, respectively, in comparison to the base sample. Notwithstanding, the highest electrochemical activity was observed for the sample prepared with CNTs, due to the synergy between the active metal centers and their highly graphitic carbon structure. The electrochemical parameters of CNTFeP csurpass the commercial Pt/C. The half-wave potential is 40 mV higher, the limiting current density increases by 17%, and a negligible production of by-products(< 1%) was observed.

Improved two-step hydrothermal process for acetic acid production from carbohydrate biomass

An improved two-step process for converting carbohydrate biomass to acetic acid under hydrothermal conditions is proposed. The first step consists of the production of lactic acid from carbohydrate biomass, and the second step consists of conversion of the lactic acid obtained in the first step to acetic acid using CuO as an oxidant. The results indicated that CuO as an oxidant in the second step can significantly improve the production of high-purity acetic acid from lactic acid, and the maximum yield of acetic acid was 61%, with a purity of 90%. The yield of acetic acid obtained using the improved two-step hydrothermal process from carbohydrate biomass, such as glucose, cellulose and starch, was greater than that obtained using traditional two-step process with H_2O_2 or O_2. In addition, a proposed pathway for the production of acetic acid from lactic acid in the second step with CuO was also discussed. The present study provides a useful two-step process for the production of acetic acid from carbohydrate biomass.

Synthesis of Low-cost LiFePO_4 from Li_2CO_3 by a Novel Hydrothermal Method and Investigation on the Reaction Mechanism

Phspho-olivine Li Fe PO4 was synthesized from the relatively insoluble lithium source Li2CO3, proper iron and phosphorus sources（n（Li）：n（Fe）：n（P）=1：1：1） by a novel hydrothermal method. Afterwards, the optimal sample was mixed with glucose and two-step calcinated（500 ℃ and 750 ℃） under high-purity N2 to obtain the Li Fe PO4/C composite. The resultant samples were characterized by X-ray diffraction（XRD）, atomic absorption spectrometry（AAS）, scanning electron microscops（SEM）, transmission electron microscopy（TEM）, energy dispersive spectrometry（EDS）, elementary analysis（EA） and electrochemical tests. The results show that the optimal reaction condition is to set the reactant concentration at 0.5 mol·L^-1, the reaction temperature at 180 ℃ for 16 h duration. During the reaction course, an intermediate product NH4 Fe PO4·H2O was first synthesized, and then it reacted with Li＋ to form Li Fe PO4. The optimized Li Fe PO4 sample with an average particle size（300 to 500 nm） and regular morphology exhibits a relatively high discharge capacity of 84.95 m Ah· g^-1 at the first charge-discharge cycle（0.1C, 1C=170 m A·g^-1）. Moreover, the prepared Li Fe PO4/C composite shows a high discharge capacity of 154.3 m Ah·g^-1 at 0.1C and 128.2 m Ah·g^-1 even at 5C. Besides it has good reversibility and stability in CV test.

Characteristics of Eu²⁺, Dy³⁺-Doped SrAl₂O₄Synthesized by Hydrothermal Reaction and Its Photocatalytic Properties

Eu2+, Dy3+-doped SrAl2O4 was prepared by a hydrothermal reaction through the process of calcination at lower temperature. The physicochemical properties of the SrAl2O4: Eu2+, Dy3+ phosphor were characterized and compared to those of the SrAl2O4: Eu2+, Dy3+ prepared by sol-gel method. The photocatalytic properties of the SrAl2O4: Eu2+, Dy3+ were evaluated in photocatalytic water decomposition for hydrogen production. The SrAl2O4: Eu2+, Dy3+ prepared by hydrothermal reaction exhibited excellent phosphor properties which were similar with that prepared by sol-gel method. Its photocatalytic activity for hydrogen evolution was higher than that of TiO2 photocatalyst.

Simulating Some Complex Phenomena in Hydrothermal Ore-Forming Processes by Reaction-Diffusion CNN

Complexity phenomena like dynamic and static patterns, order from disorder, chaos and catastrophe were simulated by the application of 2-D reaction-diffusion CNN of two state variables and two diffusion coefficients transformed from Zhabotinksii model. They revealed somehow the mechanism of hydrothermal ore-forming processes, and answered several questions about the onset of ore forming.

Nepheline Syenite Decomposition Using NaOH by Hydrothermal Reaction

Nepheline syenite is an important potassium-rich rock resource. Nepheline syenite powder was decomposed successfully by hydrothermal reaction using NaOH additive. Hydroxycancrinite (Na8(Al6Si6O24)(OH)2·2H2O ) solid and (K,Na)2SiO3 solution was obtained as a result of the hydrothermal reaction.

Carbon encapsulated magnetic nanoparticles produced by hydrothermal reaction

Carbon encapsulated magnetic nanoparticles （CEMNs） were synthesized by heating an aqueous glucose solution containing Fe-Au （Au coated Fe nanoparticles） nanoparticles at 160-180 ℃ for 2 h. This novel hydrothermal approach is not only simple but also provides the surface of CEMNs with functional groups like--OH. The formation of carbon encapsulated magnetic nanoparticles was not favored when using pure Fe nanoparticles as cores because of the oxidation of Fe nanoparticles by 1-120 during the reaction and, therefore, the surfaces of the naked Fe nanoparticles had to be coated by Au shell in advance. TEM, XRD, XPS and VSM measurments characterized that they were uniform carbon spheres containing some embedded Fe-Au nanoparticles, with a saturation of 14.6 emu/g and the size of the typical product is -350 nm.

Hydrothermal Synthesis and Thermal Decomposition Mechanism of Alkaline Earth Benzoates

Alkaline earth benzoates were synthesized using hydrothermal reaction. The complexes were characterized by elemental analysis, IR, X ray powder diffraction. All of them are monoclinic and have layered structure. The mechanism of thermal decomposition of alkaline earth benzoates was studied by using TG, DTA, IR and gas chromatography mass spectrometry. The thermal decomposition of alkaline earth benzoates in nitrogen proceeded in one or two stages: they decomposed to form MCO 3 (M=Ca,Sr,Ba) or MgO and organic compounds, respectively. The organic compounds obtained from decomposition reaction are mainly benzophenone, triphenylmethane and so on.

High quality Sb-doped SnO2 electrodes with high oxygen evolution potential prepared by in situ hydrothermal synthesis method

High quality Sb-doped SnO2 electrode, with high oxygen evolution potential of 3.0 V, was successfully synthesized on the Ti substrates by in situ hydrothermal synthesis method.

Microwave Hydrothermal Synthesis PZT of Nanometer Crystal

It was focused on the applications and developments of microwave hydrothermal synthesis piezoelectric ceramic powder. The microwave hydrothermal vessel was designed and manufactured. The microwave hydrothermal synthesis system was established and the PZT piezoelectric ceramic powder was synthesized. XRD and TEM have been used to characterize the products in detail. The diameter of the PZT powder particle is from 40 to 60 nm.

A New Cadmium(Ш) Polymer Based on 3,5-Pyrazoledicarboxylic Acid:Hydrothermal Synthesis and Crystal Structure

The reaction of CdCl3.2.5H2O with 3,5-pyrazoledicaiboxylic acid under hydrother-mal conditions produce a novel three-dimensional（3-D） coordination polymer [Cd2（C5H2O4N2）2.2H2O]n.The title compound crystallizes in the monoclinic system,space group P21/c with a = 6.422（4）,b = 12.334（7）,c = 8.936（6） ,β = 104.793（7）°,V = 684.4（7） 3,Z = 4,Dc = 2.761 g/cm3,μ = 3.181 mm-1,F（000） = 544,R = 0.0248 and wR = 0.0624.In the crystal structure of the title compround,molecules are linked through N-H...O hydrogen bonds,forming chains running along the a axis.Every Cd（Ш） coordinates with four molecules of ligand and one water molecule,forming a pentagomal-bipyramidal geometry.

Two-step pyrolysis of ZIF-8 functionalized with ammonium ferric citrate for efficient oxygen reduction reaction

Zeolitic imidazolate frameworks（ZIFs） are widely employed in catalyst synthesis as parental materials for electrochemical energy storage and conversion. Herein, we have demonstrated a facile synthesis of highly efficient catalyst for oxygen reduction reaction in both alkaline and acidic medium, which is derived from ZIF-8 functionalized with ammonium ferric citrate via two-step pyrolysis in Ar and NHatmosphere.The results reveal that the catalytic activity improvement after NH3 pyrolysis benefits from mesoporedominated morphology and high utilization of Fe-containing active sites. The optimum catalyst shows excellent performance in zinc-air battery and polymer electrolyte membrane fuel cell tests.

Double Convective Hydrothermal System beneath Massive Sulfide Orebody in Gacun Deposit,Southwestern China

The Gacun Kuroko-type deposit, Southwestern China, is hosted in rhyolitic rocks associated with the underlying mafic rocks occurred in the - 1000 m deep fault - bounded basin within the intra -arc rifting zone which formed on the Triassic Yidun island - arc. Two vertically separated alteration systems are recognized: one is conformable or semiconformable alteration zone developed in - 150 m thick mafic unit 1-1.5 km below the massive sulfide ore body; the other is discordant alteration pipe directly surrounded around stockwork ore within rhyolitic unit. The lower conformable alteration zone extending for several kilometers along strike is characterized by silicification and epidotization which result in the development of quartz vein and quartz-epidote vein systems in mafic lava flows and replacement of primary minerals and groundmass in spilitized mafic volcanics and dikes by quartz, epidote - group minerals and sodic plagioclase. Sulfides often occur in the vein system and altered mafic volcanics. Quartz solubility relation indicates that silicification is a consequence of interaction of Si- saturated fluids with mafic rocks in a higher temperature system (T>340℃), intensifying by intrusion of mafic dike or high-level acidic magma chamber. The alteration pipe of diameter about 2 km shows a similar mineralogical zoning to Kuroko deposits of Japan. The sequence is quartz + hyalophane; sericite + chlorite + quartz and zeolite-like zones from core to margins of the pipe. The chlorite core only occurs in the root part of the alteration pipe and downwards transfers into epidote - chlorite and epidote - quartz vein swarm extending 500 m downwards. The felsic rocks away from the orebody and alteration pipe took place district-scale alteration, which has typical low-temperature mineral association: illite + albite + quartz + calcite. Whole -rock and quartz δ18O values indicate that district - scale alteration is a result of interaction of seawater with rocks at lower temperature (T<200℃)under water-dominated condition. However, the altered rocks from the pipe show remarkably δ18O enrichment, and bulk -rock δ18O values decreased gradually toward stockwork orebody from 15.1‰-l5. 75‰ in zeolite-like zone and 12. 05‰-14. 2‰ in sericite - quartz zone to 11.3 ‰ - 14. 4‰ in quartz - hyalophane zone. The filled temperatures of fluid inclusions in quartz and sphalerite lie in the ranges of 280 -320 ℃ for quartz - hyalophane zone and 250 ℃ to 297 ℃ for sericite-quartz zone. The estimated δ18O values of hydrothermal fluids are 7. 98‰ and3.2‰, respectively, based on quartz δ18O data in the deposit. The lower conformable alteration is considered to be approximately coeval with the alteration pipe, based on the SiO2 concentration in the fluids, which restrict the main fluid - rock reaction zone to be located in mafic horizon by quartz barometer, and metal element flux calculation and sulfide - epidote vein system developed both in alteration systems. High - salinity fluid inclusions in gangue quartz (>8% eq. NaCl) from stockwork ore and in quartz phenocryst (>40% eq. NaCl) in footwall rhyolite strongly suggest the existence of hot-saline brine to react with mafic complex and leach metal components, which probably originates mainly from magmatic fluid derived from high-level acidic magma chamber. The brine layer located in mafic unit possibly heats and drives the overlying single -pass convective seawater reacting with felsic rocks. The 'density window' may be expected to occur on the interface between seawater and brine layer, when the brine becomes to be gravitationally instability by the turbulent entrainment of seawater during magmatic and/or tectonic activities. The sulfide mineralization and alteration pipe is inter preted as an effect of the 'density window' through which the mixed fluids of brine with seawater adiabatically discharges upwards.

Hydrothermal Synthesis, Crystal Structure and Photoluminescence of [Sm(PCA)_3(H_2O)_2]_n·6nH_2O

A new one-dimensional （1-D） compound [Sm（PCA）3（H2O）2]n·6nH2O （1, HPCA=pyrazinecarboxylic acid） has been synthesized via hydrothermal reaction and structurally characterized by single-crystal X-ray diffraction. Compound 1 crystallizes in the Pbca space group of orthorhombic system with a=19.465（3）, b=12.034（4）, c=19.842（4） , V=4648（2）3, C15H25N6O14Sm, Mr=663.76, Dc=1.897 g/cm3, S=1.023, μ（MoKα）=2.610 mm-1, F（000）=2648, R=0.0239 and wR=0.0616. Compound 1 is characteristic of an infinite 1-D chain-like structure with the samarium atoms locating at an environment of a monocapped square antiprism. The [Sm（PCA）3（H2O）2]n chains and the lattice water molecules interconnect together through π-π interactions and hydrogen bonding interactions to yield a 3-D supramolecular framework. Photoluminescent investigation reveals that the title compound displays an emission in the greenish blue region.

Temperature-dependent Hydrothermal Synthesis of Two Distinct Three-dimensional Copper Complexes

Two distinct copper coordination polymers, namely [Cu^Ⅱ2（2,5-pydc）2（bpp）2]·H2O（1） and Cu2^ⅠCu^Ⅱ（2,5-pydc）2（bpp）2（2）（2,5-pydc = pyridine-2,5-dicarboxylic acid, bpp = 1,3-bi（4-pyridyl）propane）, have been successfully synthesized through hydrothermal conditions under different temperatures. Single-crystal X-ray structural analysis revealed that both complexes 1 and 2 are 3D frameworks. Complex 1 is an 8-connected 2-fold interpenetrating network based on [Cu（2,5-pydc）]4 molecular building block（MBB）, and also can be simplified as a 4-connected net if the Cu（Ⅱ） ion is regarded as an independent node, whereas 2 shows a（4,4）-connected non-interpenetrated framework which contains mixed valence Cu（Ⅰ/Ⅱ） centers. The results demonstrate that temperature plays a significant role in the final structures of the complexes.