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.

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.

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.

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.

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.

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.

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.

Hydrothermal Synthesis, Crystal Structure and Luminescent Property of a Cd(Ⅱ) Compound with(4,6)-Connected Topology

A new Cd（Ⅱ） coordination polymer, namely {Cd_2（L）（biimpy）（H_2O）}_n（1, H4 L = 3-（3？,5？-dicarboxylphenoxy）phthalic acid, biimpy = 2,6-bis（1-imdazoly）pyridine）, has been successfully synthesized via the hydrothermal reactions of Cd（Ⅱ） ions, H_4L and biimpy. The crystal structure is of triclinic, space group P1 with a = 7.7874（5）, b = 9.9716（5）, c = 18.5278（6） ？, α = 91.327（4）, β = 96.689（4）, γ = 111.896（5）o, V = 1322.39（12） ？~3, C_（27）H_（17）Cd_2N_5O_（10）, M_r = 796.26, Z = 2,D_c = 2.000 g/cm^3, F（000） = 780, μ = 1.679 mm^（-1）, R = 0.0345 and wR = 0.0767 for 3890 observed reflections（I 〉 2s（I））. Single-crystal X-ray structural analysis reveals that compound 1 features a three-dimensional（3D） framework based on two different dinuclear [Cd_2（COO）_2] building subunits, and topological analysis shows that it can be simplified into a binodal（4,6）-connected topological network with the point symbol of {3.4~2.5~2.6}{3~2.4~2.5~2.6~4.7~4.8}. Moreover, the thermal stability and luminescent property of compound 1 were also studied.

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.

Synthesis of Coordination Polymers Using Different Maleic Acid Ligands under Hydrothermal Conditions

A novel coordination polymer, [ Ni （mal） （1,10＇-phen） （ H2O） ] n （ 1 ） （ mal = malate, 1,10＇-phen = 1,10- phenanthroline） was synthesized using malic acid which was generated from maleic acid via hydrothermal reaction. Complex 1, which displays a two-dimensional supramolecular network, was formed by the addition reaction of Ni and maleic acid with water molecules. To our knowledge, several coordination polymers have been directly synthesized from malic acid, but these types of complexes have seldom been synthesized from maleic acid via hydrothermal reactions. When Ni（ Ⅱ ） ion was changed to Zn（ Ⅱ） ion under the same condition, two-dimensional covalent complex 2 [ Zn2 （fma） 2 （1,10＇-phen） 2 ] n （fma = fumatic acid） was formed. Furthermore, complex 2 exhibits intense photolumi- nescent property at room temperature.

Hydrothermal Assembly and Structural Characterization of a Novel 3D Coordination Polymer: [Cd_2Zn(BTC)_2(H_2O)_4]_n·2nH_2O

A hydrothermal reaction of 1,3,5-benzene-tricarboxylic acid (H3BTC) with cad- mium acetate, zinc acetate and pyridine led to the formation of pink crystals of [Cd2Zn(BTC)2- (H2O)4]n?2nH2O 1. Single-crystal X-ray diffraction analysis has revealed that 1 (Cd2ZnC18H18O18) crystallizes in the monoclinic system, space group C2/c with a = 19.4328(7), b = 7.1420(3), c = 18.0426(5) ?, β = 118.035(1)o, V = 2210.3(1) ?3, Mr = 812.49, Dc = 2.442 g/cm3, Z = 4, μ(MoKα) = 3.081 mm-1 and F(000) =1584. A total of 10735 reflections were collected, of which 2544 were unique. The structure was refined to R = 0.0200 and wR = 0.0603 for 2388 observed reflections with I>2σ(I). The crystal structure consists of cadmium(II)/zinc(II) carboxylates of BTC as well as coordination and discrete water molecules. Extension of the coordination geometry around three metal centers (Cd(1), Cd(2) and Zn(1)), two BTC3- ligands and four coordinated water molecules generates a three-dimensional coordination polymer.

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, Crystal Structure and Fluorescence Property of a Novel Coordination Polymer [Eu_2(C_6H_8O_4)_3(H_2O)_2]_n·n(4,4′-bpy)

A novel coordination polymer [Eu2(C6H8O4)3(H2O)2]n?n(4,4?-bpy) (Mr = 928.51) was synthesized by the hydrothermal reaction of EuCl3?6H2O, adipic acid and 4,4?-bpy, and determined by elemental analysis, IR spectroscopy, thermal gravimetric analysis, single-crystal diffraction and fluorescence property. X-ray analysis reveals that a three-dimensional network has been formed between Eu3+ by carboxyl of adipic acid. The crystal is of orthorhombic, space group Pbcn with a = 21.870(7), b = 7.652(2), c = 19.624(6) ?, V = 3284.1(17) ?3, Z = 4, Dc = 1.878 g/cm3, μ = 3.854 mm-1, F(000) = 1824, R = 0.0345 and wR = 0.0565. The coordination polymer exhibits intensive red light under UV excitation at room temperature, which is attributed to the 5D0→7F2 transition of Eu(Ⅲ) ions.

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.

Heterogeneous Cu_2O-mediated ethylene glycol production from dimethyl oxalate

An efficient process for the conversion of dimethyl oxalateinto ethylene glycol with high selectivity and high yield over CuO was investigated. In situ formed Cu as a true catalytically active species showed a good catalytic performance for DMO conversion to produce EG in 95% yield.

Photo-degradation of Acid-red 3B dye catalyzed by TiO_2 nanotubes

TiO2 nanotube precursor was synthesized by the hydrothermal reaction of TiO2 powders with NaOH solution and the properties of the nanotube materials were tuned using different post-treatments. Transmission electron microscopic （TEM） observation revealed that the nanotube could be obtained by either a direct rinse with acid solution or rinse with distilled water followed by acid solution. The results of X-ray diffraction （XRD） and inductively coupled plasma （ICP） analysis indicated that the nanotube material was composed of H2Ti2O5·H2O. In addition, the photocatalytic activities of the resulting catalysts were found to be strongly dependent on the post-treatment. The results of the photocatalytic reaction showed that the degradation of Acid-red 3B dye fitted pseudo-zero-order kinetics and TiO2 nanotube prepared under direct rinse with acid solution exhibited a higher catalytic efficiency compared to other catalysts.

Organic Carboxylate Ligand Tuned Topological Variations in Three Zn(Ⅱ)Coordination Polymers:Syntheses,Crystal Structures and Photoluminescent Properties

Three new Zn（Ⅱ） coordination polymers, namely [Zn2（suc）2（bib）2]n·nH2 O（1）, [Zn（glu）（bib）]n·4 nH2 O（2）, and [Zn（adp）（bib）]n（3）（bib = 1,4-bis（N-imidazolyl）butane, H2 suc = succinic acid, H2 glu = glutaric acid, H2 adp = adipic acid） have been hydrothermally synthesized and structurally characterized. Compound 1 features a 3D framework with 4-connected hxg-d topological network, compound 2 is comprised of 2D 44-sql-type sheets, and the adjacent 2D sheets are further packed into a 3D supramolecular architecture via intermolecular hydrogenbonding interactions, and compound 3 is a 3D framework with 4-fold interpenetrating dia topology. The structural comparison of these three compounds demonstrates that the topological variations can be well controlled by employing aliphatic dicarboxylate ligands with different spacer lengths. Moreover, the thermal stabilities and photoluminescent properties of them were also studied in detail.

Synthesis and Crystal Structure of [La(BTC)(H_2O)_6]_n

The title compound, [La（BTC）（H2O）6]n1 （H3BTC = benzene-1,3,5-tricarboxylic acid）, has been synthesized by the hydrothermal reaction of La（NO3）3·3H2O with H3BTC and Na2CO3, and its structure was determined by single-crystal X-ray diffraction. The crystal structure is of monoclinic, space group Cc with a = 11.5289（3）, b = 18.0383（7）, c = 7.3507（3） A, β= 119.5680（10）°, V = 1329.59（8）A^3, C9H15LaO12, Mr = 454.12, Z = 4, Dc = 2.269 g/cm^3,μ = 3.280 mm^-1, Flack parameter = 0.07（4）, F（000） = 888, R = 0.0316 and wR = 0.0774 for 1312 observed reflections（I〉 2σ（I））. Complex 1 features a one-dimensional （l-D） parallel ribbon-like structure. There are extensive hydrogen-bonding interactions involving coordinated water molecules and free carboxylate oxygen atoms. In addition, π-π interactions via benzoic multicarboxylate ligands are discussed. These non-covalent interactions lead to the formation of a 3-D framework.

Two New Coordination Polymers Assembled with a Functionalized Ligand:Syntheses and Crystal Structures

Two new transition-metal organic coordination polymers [M（mna）2]（M = Cd（1）,Zn（2）;mna = 2-mercaptonicotinic anion） have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction along with IR and elemental analyses.Compound 1 is generally a one-dimensional linear structure bridged through the sulfur donor of mna ligand,while 2 is a one-dimensional zigzag chain ligated via the oxygen donor of mna ligand.These compounds further result in three-dimensional structures via intermolecular π...π stacking interactions and/or hydrogen bonding interactions.The two compounds were structurally determined by single-crystal X-ray diffraction.Complex 1 crystallizes in monoclinic space group P21/c with a = 3.730（3）,b = 13.973（12）,c = 12.380（11） ,β = 97.953（18）°,V = 639.0（10） 3,Z = 2,CdC12H8O4N2S2,Mr = 420.72,Dc = 2.187 g/cm3,F（000） = 412,Rint = 0.0252,T = 293（2） K,μ = 2.052 mm？1,the final R = 0.0269 and wR = 0.0586 for 1377 observed reflections with I 2σ（I）.Complex 2 belongs to monoclinic space group P21/c with a = 13.376（2）,b = 12.8429（14）,c = 7.4856（10） ,β = 96.190（10）°,V = 1278.5（3） 3,Z = 4,ZnC12H8O4N2S2,Mr = 373.69,Dc = 1.941 g/cm3,F（000） = 752,Rint = 0.0414,T = 293（2） K,μ = 2.264 mm？1,the final R = 0.0418 and wR = 0.0966 for 2396 observed reflections with I 2σ（I）.

A series of rare earth coordination polymer constructed from paddle-wheel building blocks

Three coordination polymers, Ln2（bpdc）3（phen）2（H2O）2 （Ln=Nd（1）, Eu（2）, and Tb （3）; bpdc=2,2＇-bipyridine-3,3＇-dicarboxylate; phen=1,10-phenanthroline）, were obtained by hydrothermal reaction of Ln2O3 with 2,2＇-bipyridine-3,3＇-dicarboxylate acid, and 1,10-phe- nanthroline. They were characterized by single-crystal X-ray diffraction, IR spectra, and photoluminescent spectra. The crystallographic data of 1-3 indicated that they were isostructural. Both complexes contained paddle-wheel building blocks, formed by bpdc and phen ligands. These paddle-wheel secondary building units （SBUs） were further connected to form two-dimensional （2-D） metal organic framework （MOF） networks by 2,2＇-bipyridine-3, and 3＇-dicarboxylate tinkers. A three-dimensional （3-D） supramolecular structure was formed by π-π aromatic interactions between adjacent 2-D infinite networks. Photoluminescent measurements indicated that europium compound 2 and terbium compound 3 were strong, red and green emitters, respectively.