Mild Hydrothermal Conditions Research Articles

Same Not the Same: Thermally Driven Transformation of Nickel Phosphinate-Bipyridine One-Dimensional Chains into Three-Dimensional Coordination Polymers

Three one-dimensional nickel coordination polymers (CPs) based on P,P′-diphenylethylenediphosphinic acid and three different bis-pyridine coligands, namely, 4,4′-bipyridine (bipy), 1,2-bis(4-pyridyl)ethane (bpy-ane), and 1,2-bis(4-pyridyl)ethylene (bpy-ene), were prepared in mild hydrothermal conditions from water solutions containing the dissolved reagents. The CPs have the formula [Ni(H2O)4(bipy)·pc2p]n (1), [Ni(H2O)4(bpy-ane)·pc2p]n (2), and [Ni(H2O)4(bpy-ene)·pc2p]n (3), and their structural features were investigated by single crystal X-ray diffraction, UV–vis, Fourier transform infrared spectroscopies, and magnetic measurements. They are constituted of infinite Ni(H2O)4(bis-pyridine) one-dimensional rows connected, through hydrogen bonds, with the phosphinic acids placed among adjacent rows. Although the formulas and the structural topologies of the three compounds are almost identical, they behave in different manners upon heating. Compound 1 yields an amorphous phase when water molecules are therm...

A rapid and efficient hydrothermal conversion of coconut husk into formic acid and acetic acid

Abstract Coconut husk is an abundant cellulose/lignin-rich biomass waste in tropic and subtropical zone. Although the resource utilization of coconut husk has aroused considerable concerns, highly-efficient and selective conversion of coconut husk into chemicals is difficult due to its stable coexistence structure of cellulose and lignin components. Herein, a facile and high selectively conversion of coconut husk into value-added organic acids of formic and acetic under mild hydrothermal conditions was proposed for the first time. It was found that a simple acidic pretreatment is efficient for obtaining high yield of formic and acetic acids. The highest yield of total acids can reach up to 50.2%, which is the reported highest yield of formic acid and acetic acid from ligno-cellulosic biomass. This work exemplifies the possibility of complex coconut husk waste valorization to value-added chemicals, which is not only solve the problems of coconut husk waste pollution, but also provide an alternative route for fuel production from renewable resources.

TEOA-induced in situ formation of wurtzite and zinc-blende CdS heterostructures as a highly active and long-lasting photocatalyst for converting CO2 into solar fuel

Herein, the wurtzite and zinc-blende CdS heterostructures were designed and in situ synthesized by tuning triethanolamine (TEOA) usage amount under a mild hydrothermal condition.

Expanding pentafluorouranates: hydrothermal synthesis and characterization of β-NaUF5 and β-NaUF5·H2O.

Two new sodium uranium(iv) pentafluorides were synthesized from uranium dioxide, HF, and NaF using mild hydrothermal conditions. β-NaUF5·H2O has greater lattice energy than previously-known α-NaUF5·H2O and possesses lower symmetry with the latter compound being orthorhombic, whereas β-NaUF5·H2O is monoclinic. Trigonal β-NaUF5 also possesses different connectivity between the [UFn] building units than the α-phase, with higher symmetry and greater lattice energy than orthorhombic α-NaUF5. The single crystal absorption spectra of these compounds are also reported and compared.

Copper ferrite supported gold nanoparticles as efficient and recyclable catalyst for liquid-phase ethanol oxidation

Copper-containing spinel-supported gold nanoparticle catalysts are optimized toward high activity and stability in liquid-phase aerobic oxidation of aqueous bioethanol to acetic acid under mild hydrothermal conditions (3 MPa O2, 140 °C). In this work, we investigate the structure-performance relationships of supported gold catalysts by changing the composition and calcination temperature of spinel supports to gain insight into the gold-support interaction. The support effect specially acts on the rate-controlling ethanol activation step, with ferrite-spinel outperforming aluminate and chromite-spinels, and the activity increasing with the copper content in the spinels. Moreover, support calcination at 700 °C results in the optimal Au/CuFe2O4 catalyst, which can be magnetically separated and reused at least five times. The improved reusability is likely attributed to the alloying between AuNPs and Cu0 on the partially reduced CuFe2O4. The presence of negatively charged Auδ− and redox active Fe2+ species in the spent Au/CuFe2O4 catalyst points to a specific Auδ−-Fe2+ synergy for the enhanced activation of O2 and ethanol. With the help of negatively charged AuNPs, heterogeneous Fenton-like reaction is suggested to provide hydroxyl radicals for the CH bond activation of ethanol.

Highly luminescent Ln-MOFs based on 1,3-adamantanediacetic acid as bifunctional sensor

A series of lanthanide metal-organic-frameworks (Ln-MOFs) are synthesized under mild hydrothermal condition by introducing the ligand of 1,3-adamantanediacetic acid (H2ADA). They are three dimentional (3D) structures and have the formula of [Ln(ADA)1.5(phen)]n (Ln3+=Eu3+1a, Gd3+1b, Tb3+1c, La3+1d, Ce3+1e, Pr3+1f, Nd3+1g, Y3+1h; phen=1,10-phenanthroline). These Ln-MOFs are fully characterized by single-crystal X-ray diffraction, PXRD, TGA, EA and FT-IR. Luminescence properties, including luminescence spectra, luminescence decay lifetimes and luminescence quantum yields (QYs) are analyzed in detail. Eu3+ complex of 1a shows highly luminescence QYs of 58.61%, which due to that the triplet state of phen competes well with the excited emission state of Eu3+. Further investigation reveals that 1a is a bifunctional sensor, which can be used as a turn-off luminescence sensor for detecting Ni2+ and turn-on luminescence sensor for probing Val at the same time. Interestingly, the limit of detect (LOD) for sensing Ni2+ is an ultrahigh sensitive value of 1.0×10−9M (5.9×10−5mg/L), which is lower than the Chinese environmental quality standard (0.5mg/L of total Ni2+ content, GB25467-2010), and it is the most sensitive chemosensor for detecting Ni2+, to the best of our knowledge. Investigation also reveals there is a good linear relationship between luminescence intensity and the concentration of Ni2+ in 0.2–0.6μM. The sensing mechanism for detecting Ni2+ and Val are also discussed.

M(1,2-dap)3][B10O13(OH)6] (M = Co, Ni): Two New Borates Containing [B10O13(OH)6]2− Cluster Units

Two novel isomorphic decaborates, [M(1,2-dap)3][B10O13(OH)6] (M = Co (1) and Ni (2); dap = 1,2-diaminopropane), with transition metal complexes [M(1,2-dap)3] as templates have been synthesized successfully under mild hydrothermal conditions and characterized by powder X-ray diffraction, thermogravimetric analysis, IR spectrum, single crystal X-ray diffraction and UV–Vis spectroscopy. The noodle-like orange/purple crystals crystallize in triclinic space group P-1. Their structure contain the isolated [B10O13(OH)6]2− clusters and further link together to produce a 3-D supramolecular framework with large channels by H-bonding interactions. The UV–Vis–NIR diffuse reflectance spectrum showed a wide-band-gap of 1 and 2. Notice that compounds 1 and 2 are not only the first isolated decaborate cluster and fill the gap left by the absence of isolated structures in the borate family but also could be considered as the structural building units to construct extended oxoboron cluster frameworks.

Effect of substituent groups on the structures of two semi-flexible bis(imidazole) directed Zn(II)-5-sulfoisophthalate coordination polymers: Syntheses, structures and photoluminescent properties

Two new metal organic architectures, formulated as {(pbetixH2)0.5[Zn(µ-sip)(µ-pbetix)0.5]}n (1) and {[Zn2(µ-sip)2(pbisopix)(pbisopixH)2]·4H2O}n (2), were synthesized based on the rarely employed 1,4-bis((2-ethylimidazol-1-yl)methyl)benzene (pbetix) and 1,4-bis((2-isopropylimidazol-1-yl)methyl)benzene (pbisopix) ligands, along with the 5-sulfoisophthalate (sip) ligand. Complexes 1 and 2 were synthesized in basic medium and under mild hydrothermal conditions. Both complexes were characterized by elemental analysis, FT-IR spectroscopy and single crystal X-ray diffraction studies. Crystallographic studies of complexes 1 and 2 reveal that the Zn(II) ions are µ-bridged by trianionic sip3− ligands in the bis(monodentate) coordination mode to generate 1D polymer chains. In the complexes, adjacent chains are linked by the bis(imidazole) ligands to form a 2D structure. Complex 1 is the first example containing a protonated bis(imidazole) ligand, namely the pbetixH2 cation, while complex 2 is the first example with a monoprotonated bis(imidazole) ligand, namely pbisopixH. Topological analyses of the 2D coordination polymers reveal that complex 1 is a 3-fold polycatenated 4-connected uninodal net with the point symbol of {44.62}, whereas complex 2 is a 3-connected uninodal net with the point symbol of 63. The thermal behavior, photoluminescent properties and topological analysis of the complexes are also discussed herein.

MIn(HAsO4)2 (M = K, Rb, Cs): three new hydrogen-arsenates adopting two different structure types.

Potassium indium bis-[hydrogen arsenate(V)], KIn(HAsO4)2, rubidium indium bis-[hydrogen arsenate(V)], RbIn(HAsO4)2, and caesium indium bis-[hydrogen arsenate(V)], CsIn(HAsO4)2, were grown under mild hydro-thermal conditions (T = 493 K, 7-8 d). KIn(HAsO4)2 adopts the KSc(HAsO4)2 structure type (space group C2/c), while RbIn(HAsO4)2 and CsIn(HAsO4)2 crystallize in the space group R-3c and are the first arsenate representatives of the RbFe(HPO4)2 structure type. All three compounds have tetra-hedral-octa-hedral framework topologies. The M+ cations, located in voids of the respective framework, are slightly disordered in RbIn(HAsO4)2. In KIn(HAsO4)2, there is a second K-atom position with a very low occupancy, which may suggest that the K atom can easily move in the channels extending along [101].

Hydrothermal Syntheses and Crystal Structure of a New Organic Hybrid Holmium–Germanate Oxo-Cluster

A new organic hybrid holmium–germanate oxo-cluster [Ho8(phen)2Ge12(μ 3-O)24(CH2CH2COO)12(H2O)16]·2H2O (1, phen = 1,10-phenanthroline) was prepared under mild hydrothermal conditions and structurally characterized by elemental analysis, UV/Vis, IR spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. Compounds 1 contains cage clusters [Ho8(phen)2Ge12(μ 3-O)24(CH2CH2COO)12(H2O)16] and free H2O molecules. The cage cluster is constructed by the combination of two [Ho(phen)(H2O)2] units, two [Ge6O12(CH2CH2COO)6] rings and one circular [Ho6O36] fragment via sharing O atoms. 1 is the rare example of organic hybrid holmium–germanate oxo-cluster decorated by phen ligands.

Valorization of wheat straw: Rapid reduction of CuO into Cu and production of organic acids under mild hydrothermal conditions

Abstract Resource utilization of biomass waste has attracted considerable attention as an important method to reduce greenhouse gas emissions and also to alleviate the current dependence on fossil fuels. Herein, wheat straw, an abundant agriculture waste, was employed as a green reducing agent for direct reduction of CuO into metallic Cu under mild hydrothermal temperatures. Meanwhile, wheat straw was converted to value-added organic acid such as lactic acid and acetic acid. More than 90% yield of Cu with 40–80 mmol/L lactic acid was obtained at 220–250 °C for 1–3 h. This study provides a promising low-carbon and energy-saving approach for Cu smelting and an alternative route for the chemical production from renewable resources.

KInAs2O7, a new diarsenate with the TlInAs2O7 structure type.

Potassium indium diarsenate(V) was grown under mild hydro-thermal conditions (T = 493 K, 7 d) at a pH value of about 1. It adopts the TlInAs2O7 structure type (P-1, Z = 4) and is closely related to the KAlP2O7 (P21/c) and RbAlAs2O7 (P-1) structure types. The framework topology of KInAs2O7 is built of two symmetrically non-equivalent As2O7 groups which share corners with InO6 octa-hedra. The K atoms are located in channels extending along [010].

Crystal structures, Hirshfeld surface analysis, thermal behavior and dielectric properties of a new organic–inorganic hybrid [C6H10(NH3)2]Cu2Cl8

A novel organic-inorganic hybrid sample [C6H10(NH3)2]Cu2Cl8 has been prepared under mild hydrothermal conditions and characterized by single crystal X-ray diffraction, Hirshfeld surface analysis, FT-IR,NMR and UV–Vis spectroscopies, differential scanning calorimetric and dielectric measurement. It is crystallized in the monoclinic system with P21/c space group. The cohesion and stabilization of the structure are provided by the hydrogen bond interactions, (NH⋯Cl and CH⋯Cl), between [C6H10(NH3)2]2+ cation and [Cu2Cl8]2- anion. The Hirschfeld surface analysis has been performed to explore the behavior of these weak interactions. The presence of different functional groups and the nature of their vibrations were identified by FT-IR and Solid state NMR. The thermal study revealed that this compound undergoes two structural phase transitions around 353 and 376 K. Electrical measurements of our compounds have been investigated using complex impedance spectroscopy (CIS) in the frequency and temperature range 331–399 K and 200 Hz–5 MHz, respectively. The AC conductivity is explained using the correlated barrier hopping model (CBH) conduction mechanism. The nature of DC conductivity variation suggests Arrhenius type of electrical conductivity. A relationship between crystal structure and ionic conductivity was established and discussed. Finally, the real and imaginary parts of the permittivity constant are analyzed with the Cole–Cole formalism and the optical spectra indicate that the compound has a direct band gap (3.14 eV) due to direct transition. The wide band gap is due to low defect concentration in the grown crystal, which is more useful for the laser/optical applications.

Hydrothermal synthesis, structural and thermal characterizations of three open-framework gallium phosphites

Three new gallium phosphites A[Ga(HPO3)2], where A = K (1), NH4 (2), Rb (3), have been synthesized by using mild hydrothermal conditions under autogeneous pressure. Their structures have been determined by single-crystal X-ray diffraction. These compounds crystallize in the hexagonal P63mc space group with a = 5.2567 (2)Å and c = 12.2582 (3)Å for 1, a = 5.2576 (2)Å and c = 12.9113 (4)Å for 2, a = 5.27020 (10)Å and c = 12.7619 (5)Å for 3, with Z = 2 in the three phases. The three compounds are isostructural and exhibit the same framework topology, consisting of a layered structure stacked along the c-axis with the A+ cations located in the interlayer spaces. The [Ga(HPO3)2]- sheets contain GaO6 octahedra interconnected by phosphite units through sharing vertices. Thermal analysis under air atmosphere shows a large range stability for alkali cations containing compounds with decomposition starting around 750K leading to phosphate phases. Under nitrogen, a disproportionation of the phosphite into red phosphorus and phosphates is expected, accompanied by a release of H2.

Sonophotocatalytic degradation of diazinon in aqueous solution using iron-doped TiO2 nanoparticles

Abstract Diazinon is a moderately persistent organophosphorus pesticide used to control a variety of insects in both household and agricultural because of its inhibition ability of acetylcholinesterase in the vast majority of insects .So far, diazinon residues have been found in many agricultural products and affecting a wide range of non-target organisms proving harmful to human and aquatic environments. The aim of this study was to evaluate the sonophotocatalytic degradation of diazinon, in aqueous solution, using iron doped TiO2 nanoparticles .Iron-doped TiO2 nanoparticles were synthesized under mild hydrothermal conditions (T = 110 °C, p = autogenous, t = 12 h). The systematic characterization of nanoparticles was determined using Powder X-ray Diffraction, Fourier transform infrared and Scanning electron microscopy techniques. Moreover, the effects of different parameters such as pH, nanocatalyst dosage, initial diazinon concentration, and Fe doping concentration on the degradation efficiency of diazinon were investigated. The degradation efficiency of diazinon in each sample was measured using a UV–Vis spectrophotometer (λmax = 247 nm) at different time intervals. The results demonstrated that nanoparticles were successfully synthesized and the forms of the nanoparticles synthesized are quite similar to each other and approximately pseudo-spherical. The optimum conditions for sonophotocatalytic degradation of the diazinon obtained were: pH 5.5, nanocatalyst dosage = 0.4 g/l, initial diazinon concentration = 30 mg/l, dopant percentage = 1.5% and contact time = 100 min. Under optimal conditions, the sonophotocatalytic degradation efficiency of diazinon was 85%. In addition, the results showed that the iron-doped TiO2 nanocatalyst, UV irradiation and US irradiation had a positive effect on the sonophotocatalytic degradation of diazinon. The maximum degradation values of diazinon achieved for separate applications, namely, iron-doped TiO2, UV irradiation, and US irradiation was 30, 36, and 19% respectively.

Anatase and rutile in evonik aeroxide P25: Heterojunctioned or individual nanoparticles?

Evonik Aeroxide P25 (formerly Degussa P25) is a flame-made multiphasic TiO2 nanoparticles containing anatase and rutile, as well as a small amount of amorphous TiO2. The past decades have witnessed the wide applications of P25 as a benchmark material for studying photocatalytic mechanism, materials and process. However, controversy remains regarding the microstructure of anatase and rutile: do they interwoven forming heterojunction structure or exist individually? To clarify it, we selected a medium alkaline, LiOH to erode bare P25 under a mild hydrothermal condition. Since rutile presents much higher resistances towards dissolution by LiOH than anatase, it is reasonable to find during hydrothermal reaction that the ratio of anatase to rutile (A/R) gradually decrease if they exist individually. Reversely, the A/R value gradually increases at the beginning of the hydrothermal reaction, implying that rutile shows high activity towards dissolution and phase transformation to lithium titanate. As calculated, around 15% rutile nanoparticles more likely exist on the surface of anatase with the formation of a heterojunction structure, although isolated nanoparticles with sole rutile phase coexist. In addition to XRD analysis, TEM measurement shows that the Moiré fringes frequently present, which further manifests that some anatase particles are covered with rutile clusters or thin overlayers.

Layered Tb‐Doped Yttrium Carboxyphosphonate Nanocrystals as Efficient Filler for PEDOT:PSS Composite Films

AbstractA layered yttrium phosphonate based on N‐(phosphonomethyl)glycine (H3L) and of formula Y(PO3CH2NHCH2COOH)(HPO3CH2NHCH2COOH) was synthesized in mild hydrothermal conditions. Its crystal structure was first determined by single‐crystal X‐ray diffraction. Then, the synthetic parameters were changed in order to reduce the particle size of the compound. The use of microwave (MW) irradiation during the synthesis allowed a) to obtain the compound in form of nanoparticles (NP) in the 50–300 nm range dispersed in water, b) to strongly reduce the reaction time by a factor 150, and c) to successfully introduce into the structure small amounts of a luminescent ion like terbium(III) as an isomorphic substituent of yttrium(III). The obtained NP were used to prepare composite materials by dispersing them in poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The resulting optical, photophysical, morphological and electrical properties of modified and pristine PEDOT:PSS films were investigated and compared, in order to test the potential use of Y(H2L)(HL) NP as luminescent downshifting materials in optoelectronic devices.

Facile one-step extraction and oxidative carboxylation of cellulose nanocrystals through hydrothermal reaction by using mixed inorganic acids

A facile and efficient approach to prepare carboxylated cellulose nanocrystals (CCNCs) is presented through a novel one-step hydrothermal procedure by using a mixed acid system of hydrochloric acid and nitric acid (HCl/HNO3). The as-prepared cellulose nanoparticles were characterized by scanning electron microscopy, wide angle X-ray diffraction, conductometric titrations, Fourier transform infrared spectrometry and thermal gravimetric analysis. The results showed that the combination of the mixed acid and hydrothermal reaction can speed up the process of CCNC preparation, and then high quality of the product could be obtained at relatively low acid concentration. It is found that the addition of nitric acid could not only promote the conversion of surface groups on the cellulose nanocrystals (CNCs), but also have significant influences on the yield, particle size and microstructure of CNCs. For the volume ratio of HCl/HNO3 of 7:3, the as-prepared CCNCs exhibited the largest length to diameter ratio and narrowest dimension distributions as well as maximum degree of oxidation of 0.12. In addition, high dispersion stability for the CCNCs could be observed due to the existence of negative carboxyl groups. This approach based on one-step oxidative carboxylation greatly simplified the preparation of CCNCs with high yield and high crystallinity under mild hydrothermal condition.

Two inorganic-organic hybrid polyoxotungstates constructed from tetra-ZrIV-substituted sandwich-type germanotungstates functionalized by tris ligand

Two tris-functionalized Zr4IV-substituted germanetungstates H9KNa2[Zr4(μ3-O)2(tris)2(α-GeW10O37)2]·26H2O (1) and H2K6Na4[Zr4(μ3-O)2(tris)2(α-GeW10O37)2]·20H2O (2) (tris=tris(hydroxymethyl)aminomethane) have been made under mild hydrothermal conditions and characterized by elemental analysis, IR spectra, diffuse reflectance spectra, thermogravimetric analysis, single-crystal X-ray diffraction and powder X-ray diffraction, respectively. 1–2 possess similar sandwich-type polyoxoanion structure built by a tetra-ZrIV cluster and two divacant [α-GeW10O37]10− building blocks. 1 and 2 represent the first [Zr4(μ3-O)2(tris)2]10+-substituted germanotungstates functionalized by tris ligands with O– and N-donors.

Photocatalytic degradation of Aniline from aqueous solutions under sunlight illumination using immobilized Cr:ZnO nanoparticles

The present study aimed at synthesizing chromium doped zinc oxide nanoparticles (Cr:ZnO NPs) under mild hydrothermal conditions (temperature ~100 °C, p = autogenous and time ~12 hr). Chromium oxide and n-butylamine were used as dopant and surface modifier, respectively. The characteristics of the synthesized nanoparticles were determined through conducting specialized experiments including powder XRD, FTIR, SEM, EDX, and UV-VIS spectroscopy. Then, the Cr:ZnO NPs were immobilized on a sandblasted glass through thermal method. The photocatalytic degradation of aniline was conducted in a continuous reactor with a volume of 1.5 liters. Before and after photocatalytic degradation, the immobilized Cr:ZnO NPs were characterized for SEM and EDX to determine the degree of stability of immobilized nanoparticles as well as the influence of the current applied on them. The photodegradation operational parameters investigated were aniline initial concentration (150, 200, and 250 mg/L), pH (5, 7, 6, and 12), and reaction time (2, 4, and 6 hours) under sunlight illumination. The characterization results indicated high purity of the Cr:ZnO NPs and no change in morphology or composition even after the immobilization and photo-oxidation process. Finally, it was found that the optimum conditions for 93% removal of aniline under sunlight illumination was about 6 hours retention time at pH 9.