Influence of the bed geometry on the kinetics of the extraction of clove bud oil with supercritical CO2

There is a need for scientific research that evaluates the influence of important process variables on the scale up of supercritical technology. For supercritical fluid extraction (SFE), one of these variables is the extractor's bed geometry, which can be defined by the ratio of the bed height (H_B) to the bed diameter (D_B). A systematic study is needed to select suitable criteria that can be used to obtain similar extraction curves among beds with different geometries. In this study, maintaining a constant ratio of solvent mass to feed mass for two beds with 1-L volumes but different geometries (E-1: H_B/D_B = 7.1; E-2: H_B/D_B = 2.7) was confirmed as a successful scale up criterion. For constant values of the temperature, pressure and bed porosity, there is experimental evidence that the mass transfer rate is equal in the two beds when the solvent flow rate is high. When 0.6 kg of clove buds was packed in the beds, the extraction rates were 2.10 ± 0.08 and 2.3 ± 0.1 g extract/min for beds E-1 and E-2, respectively. However, when the solvent flow rate was lower, the extraction rates were 0.93 ± 0.06 and 1.12 ± 0.02 g extract/min for beds E-1 and E-2, respectively. This difference in behavior between the extraction beds is associated with the axial dispersion of the fluid, which is more pronounced when the H_B/D_B ratio is increased. Thin particles tend to compact in the beds with high H_B/D_B ratios, which shorten the solvent passage. Non-isothermal profiles and differences in chemical composition of the extracts were also observed: 17% more α-humulene and 9% more eugenol were extracted in E-1 and E-2, respectively.     

Three unique MOFs constructed by 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene and dicarboxylates: From rhombic tetrameric zinc(II) 2D layer to 2D + 2D → 3D polycatenated frameworks

Three metal–organic networks, namely, [Zn₂(Hnip)(4-bpdb)(nip)₂(μ₃-OH)] (1), {[Zn(tbip)(4-bpdb)_1.5]·CH₃OH}_n (2), and {[Ni(1,3-bdc)(4-bpdb)]·2H₂O}_n (3) (4-bpdb = 1.4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene, H₂nip = 5-nitroisophthalic acid, H₂tbip = 5-tert-butylisophthalic acid, and 1,3-H₂bdc = 1,3-benzenedicarboxylic acid) are synthesized under hydrothermal conditions. The structure of 1 is built around uncommon rhombic {Zn₄} clusters with double T_d and double O_h Zn(II) geometries, which extend into a 2D network by the rigid deprotonated H₂nip and 4-bpdb bridges. Meanwhile, 2 presents a novel 2D → 3D parallel polycatenated framework assembled from 2D bilayers with cuboids as the fundamental building units. Compound 3 features an interesting 2D → 3D inclined polycatenated network based on 4⁴-sql subunits. Moreover, the thermal stabilities, photoluminescence, and magnetic properties of the compounds are also discussed.     

Synthesis,luminescence, and structural characterization of Zn and Cd coordination polymers of flexible bis(imidazolyl) derivatives

Coordination polymers [Zn(imc)(L¹)] · H₂O, (1, imc = iminodiacetate, L¹ = bis(N-imidazolyl)methane) [Zn(hba)₂(L²)]₂ · EtOH · 3H₂O, (2, hba = p-hydroxybenzoate, L² = bis(N-benzimidazolyl)methane), [Cd(mal)(H₂O)(L³)](3, L³ = 1,4-bis(N-imidazolyl)butane, mal = maleate) have been prepared and structurally characterized. Complex 1 consists of hexa-coordinated central Zn ions and exhibits 2D network structure. The Zn atoms in 2 have tetrahedral coordination geometry, and are linked by bis(imidazolyl) ligands into 1D chain structure. The cadmium ions in 3 are hepta-coordinated with pentagonal bipyramidal geometry. Complex 3 displays 2D grid structure. The TGA showed that the coordination polymers are stable up to 200 °C. All the three complexes are emissive at room temperature in their solid state.     

Facile synthesis of ZnO nanostructures and enhancement of their sinterability via short-time cryo-milling

Zinc oxide (ZnO), a wide band-gap semiconductor, has received a great interest due to its potential applications in various fields both as nanostructures and as sintered compacts. In this study, we report on the synthesis of the ZnO nanostructures and facilitation of their sintering for the production of fine-grained dense compacts. The facile synthesis of gram scale ZnO nanostructures was achieved by thermal decomposition of zinc acetate dihydrate (Zn(Ac)₂·2H₂O) or Zn(Ac)₂·2H₂O/graphite mixtures at 300 °C for 12 h. Thermal decomposition of Zn(Ac)₂ resulted in the formation of mostly ZnO nanoparticles with wurtzite structure along with ZnO nanorods, while the addition of graphite significantly promoted the growth of ZnO nanowires. Microstructural and phase properties of the obtained ZnO nanostructures were determined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) techniques, all of which revealed the successful synthesis of high quality ZnO nanostructures. In addition to synthesis and characterization of the ZnO nanostructures, we report on the enhancement of their sinterability by a subsequent cryogenic milling for a short duration of 5 min. As a result of the applied cryo-milling, fabrication of highly dense (96.2%) sintered compacts with fine grain sizes (572 nm) could be achieved after pressureless sintering at 1000 °C for 2 h.     

In situ UV–vis and EXAFS studies of ZnO quantum-sized nanocrystals and Zn-HDS formations from sol–gel route

We have pointed out that, zinc-based particles obtained from zinc acetate sol–gel route is a mixture of quantum-sized ZnO nanoparticles, zinc acetate, and zinc hydroxide double salt (Zn-HDS). Aiming the knowledge of the mechanisms involved in the formation of ZnO and Zn-HDS phases, the thermohydrolysis of ethanolic zinc acetate solutions induced by lithium hydroxide ([LiOH]/[Zn²⁺] = 0.1) or water ([H₂O]/[Zn²⁺] = 0.05) addition was investigated at different isothermal temperatures (40, 50, 60 and 70 °C) by in situ measurements of turbidity, UV–vis absorption spectra and extended X-ray absorption fine structures (EXAFS). Only the growth of ZnO nanoparticles was observed in sol prepared with LiOH, while a two-step process was observed in that prepared with water addition, leading the fast growth of Zn-HDS and the formation of ZnO nanoparticles at advanced stage. A mechanism of dissolution/reprecipitation governed by the water/ethanol proportion is proposed to account for relative amount of ZnO.     

A molecular layer “fabric” with orthogonally woven coordination polymer chains

Crystals of [Cu(ox)(dpa)(H₂O)]_n (1, ox = oxalate, dpa = 4,4′-dipyridylamine) were prepared by hydrothermal reaction of potassium copper oxalate and dpa. Single-crystal X-ray diffraction showed the formation of orthogonally oriented sets of 1D [Cu(ox)(dpa)(H₂O)]_n chains that interlock in a 1D + 1D ➔ 2D manner to form woven “warp-and-woof” supramolecular layers. Thermogravimetric analysis indicated that the structure of 1 remained stable to about 175 °C.     

Diversity of carboxylate coordination in two novel zinc(II) cinnamate complexes

Two novel mixed-ligand zinc(II) complex compounds [Zn(cinn)₂(mpcm)]_n (1) and [Zn(p-HO-cinn)₂(nia)(H₂O)₂] · H₂O (2) (cinn = cinnamato, mpcm = methyl-3-pyridylcarbamate, nia = nicotinamide) were prepared and characterized by elemental analysis, infrared spectroscopy, single crystal X-ray diffraction and thermal analysis. Diverse modes of carboxylate coordination were found in the complexes. In 1 the cinnamate ligands coordinate as monodentate and bridging (syn–anti), respectively. The syn–anti carboxylate bridges connect the molecules of 1 to infinite polymeric helical chains. The structure of 2 is monomeric. One of the carboxylate oxygens of p-hydroxycinnamate is semi-coordinated (Zn–O = 2.549(2) Å).     

Pillar-layered Zn–triazolate–carboxylate frameworks tuned by the bend angles of ditopic ligands

In the utilization of three ditopic ligands with different bend angles as pillars, we reported herein three pillar-layered Zn–triazolate–carboxylate frameworks, namely, [Zn₂(ATRZ)₂(BDC)]_n (1), [Zn₂(ATRZ)₂(TPDC)]_n·2nDMF (2) and [Zn₂(ATRZ)₂(ADDC)]_n (3) (ATRZ = 3-amino-1,2,4-triazole, H₂BDC = 1,4-benzenedicarboxylic acid, H₂TPDC = 2,5-thiophenedicarboxylic acid, and H₂ADDC = 1,3-adamantanedicarboxylic acid). Single crystal structural analyses demonstrate that different geometries of ditopic carboxylate pillars not only result in Zn–ATRZ layers adopting various corrugated configurations, but also give rise to 3,4-connected self-interpenetrated net of 1 and non-interpenetrated nets of 2 and 3. All these compounds exhibit high thermal stability and blue photoluminescence.     

Low temperature sintering of ZnTiO3/TiO2 based dielectric with controlled temperature coefficient

Structure, microstructure and dielectric properties of ZnTiO₃ and rutile TiO₂ mixtures (ZnTiO₃ + xTiO₂ with x = 0, 0.02, 0.05, 0.1, 0.15 and 0.2) sintered using ZnO–B₂O₃ glass phase (5 wt.% added) as sintering aid have been investigated. For all compounds, the sintering temperature achieves 900 °C. The X-ray diffraction patterns indicate for x = 0.1 that the material is composed by three phases identified as ZnTiO₃ hexagonal, TiO₂ rutile and ZnO. The presence of ZnO is explained by the introduction of Ti into Zn site to form the (Zn_1−xTi_x)TiO_3+x solid solution in resulting the departure of ZnO from the ZnTiO₃ structure. The ZnTiO₃ + 0.15TiO₂ composition sintered at 900 °C with glass addition exhibits attractive dielectrics properties (ɛ_r = 23, tan(δ) < 10⁻³ and a temperature coefficient of the dielectric constant near zero (τ_ɛ = 0 ppm/°C)) at 1 MHz. It is also shown that the introduction of TiO₂ allows to tune the temperature coefficient of the permittivity. All these properties lead this system compatible to manufacture silver based electrodes multilayer dielectrics devices.     

Influence of the bed geometry on the kinetics of rosemary compounds extraction with supercritical CO2

Bed geometry plays an important role in supercritical fluid extraction kinetics. Thus, the objective of this study was to compare the overall extraction curves (OEC's) of rosemary compounds obtained in two beds of 1 L each with different geometries (in terms of height to bed (H_B) diameter (D_B) ratios, H_B/D_B). A scale-up study was carried out maintaining the solvent mass to feed mass (S/F) ratio equal for both beds. Other process variables, such as bed porosity, apparent and true densities of the raw material, particle average size, temperature, pressure and time of extraction, were also maintained constant. The kinetic parameters were obtained by fitting the OEC to a spline model. The results revealed differences of mass transfer rates, mass ratios of solute in the fluid phase and yields of extract in the constant extraction rate period. The evaluation of the OEC's and kinetic parameters indicated that the bed with lower H_B/D_B ratio (H_B/D_B = 2.7) was more favorable for obtaining rosemary extract. The kinetics of extraction of oxygenated monoterpenes (i.e., 1,8-cineole and camphor) and phenolic diterpenes (i.e., carnosic acid) were also different for both bed geometries. These behaviors suggest that the bed geometry presents a pronounced influence in the mass transport properties in supercritical media. Thus, in spite of the scale-up criterion be successful for several botanic matrices such as clove buds, sugarcane residue and grape seeds residue, the criterion applied in this study (maintaining a constant S/F ratio for a given time of extraction) was not suitable for this raw material.     

Pure white-light and color-tuning of PMMA-supported hybrid materials doped with (TTA)3-Zn2 +-Eu3 + and (BA)3-Zn2 +-Tb3 + complexes

Based on the doping of red-light-emitting 2 ([Zn(L)(4-vinyl-Py)Eu(TTA)₃]; H₂L = N,N′-bis(salicylidene)cyclohexane-1,2-diamine, 4-vinyl-Py = 4-vinyl-pyridine, HTTA = 2-thenoyltrifluoroacetonate) and cyan-light-emitting 4 ([Zn(L)(4-vinyl-Py)Tb(BA)₃]; HBA = 1-phenyl-1,3-butanedione) in PMMA, hybrid materials of 2@4@PMMA with improved physical properties including color-tunable for white-light (CIE coordinate 0.373, 0.319) were obtained.     

Linkers and coordinated solvent molecules; the two effective factors on formation of zinc oxide nanoparticles from metal–organic frameworks

The host and the apohost frameworks of Zn₂(ndc)₂(DMF)₂ ∙(H₂O)₄ (1 ∙ DMF ∙ H₂O) and Zn₂(bdc)₂(H₂O)₂ ∙(DMF)₂ (2·H₂O·DMF), (H₂ndc = 2,6-naphthalene dicarboxylic acid, H₂bdc = benzene-1,4-dicarboxylic acid and DMF = N,N-Dimethylformamide), were synthesized, characterized and subsequently used for preparing of ZnO nanoparticles. The morphology of initial precursors has direct influence on agglomeration tendency of resulting ZnO nanoparticles. Linkers and coordinated solvent molecules are the two effective factors on the formation of zinc oxide nanoparticles from these metal–organic frameworks.     

A novel supramolecular adduct formed by CB[6]-based pseudo-rotaxane and hydrated Zn(II) ion

A novel supramolecular adduct of [C6N2(CB[6])]₃ · [Zn(H₂O)₆]Cl₂ · 14H₂O (1) is reported, where C6N2 = N,N′-bis(2-pyridylmethyl)-1,6-diaminohexane, CB[6] = Cucurbit[6]uril. It consists of a CB[6]-based pseudo-rotaxane and a six-hydrated Zn(II) ion, and forms an infinite 2D network and 3D spatial structure by hydrogen bonding interactions.     

Synthesis of zinc oxide nanocrystalline powders for cosmetic applications

The synthesis of zinc oxide (ZnO) nanocrystalline powders for cosmetic applications by a coprecipitation process has been investigated. When the Zn(OH)₂ precipitates are calcined at 373 K for 10 min, the crystalline phases comprise the major phase of Zn(OH)₂ and the minor phase of ZnO. XRD pattern shows that only ZnO is present and no other phase is detected when the Zn(OH)₂ precipitates calcined at 413 K for 10 min. The nanocrystallite size of ZnO increases slightly from 32.3 to 44.3 nm when the calcination temperature increases from 413 to 873 K. The activation energy of ZnO nanocrystallite growth is 2.02 kJ/mol, which reveals that the nanocrystalline ZnO is easily grown at low temperature. The UV transmission of ZnO nanocrystallites in the wavelength range from 290 to 375 nm is about 35%, indicating that the ZnO nanocrystallites have an excellent UV-absorbing capability.     

Desorption of zinc by the kaolin from Suzhou,China

This paper studied the influence of copper concentration, pH, temperature, and the ratio of solid to solution on desorption of Zn in the kaolin from Suzhou, China in a background solution of 0.01 M CaCl₂ by batch extraction experiments. At 0, 5, 50, 100 mg/l Cu concentration, for each 0.5 increase in pH between about 1.80 and 3.04% desorption decreases 3.80, 13.87, 9.97, and 7.65%, respectively. The pH₅₀ (pH at 50% Zn desorption) is found to follow the sequence: Cu (5 mg/l, pH₅₀ = 2.60) < Cu (50 mg/l, pH₅₀ = 2.70) < Cu (100 mg/l, pH₅₀ = 2.95) < Cu (0 mg/l, pH₅₀ = 10.65). The free energy change (ΔG) values, the values of enthalpy change (ΔH), and entropy change (ΔS) have been calculated. There were no large differences in the desorption of Zn from 25 to 50 °C. The concentration of Zn in solution after desorption equilibrium increases and percent desorption decreases when the solid to liquid ratio increases from 0.025 to 0.2. The kaolin possibly cannot be used for the landfill clay liner.     

Deuterium kinetic isotopic study for hydrogenolysis of ethyl butyrate

The hydrogenation of ethyl butyrate, n-butyric acid, and n-butyraldehyde to their corresponding alcohol(s) has been studied over a γ-Al₂O₃-supported cobalt catalyst using a high-pressure fixed-bed reactor in the temperature range of 473–493 K. H₂–D₂–H₂ switching experiments show that ethyl butyrate and n-butyric acid follow an inverse kinetic isotope effect (KIE) (i.e. r^H/r^D = 0.50–0.54), whereas n-butyraldehyde did not display any KIE (i.e. r^H/r^D = 0.98). DRIFTS experiments were performed over the support and catalyst to monitor the surface species formed during the adsorption of ethyl butyrate and n-butyric acid at atmospheric pressure and the desired temperature. Butanoate and butanoyl species are the stable surface intermediates formed during hydrogenation of ethyl butyrate. Hydrogenation of butanoate to a partially hydrogenated intermediate is likely involved in the rate-determining step of ethyl butyrate and butyric acid hydrogenation.     

Synthesis,crystal structure,luminescence and thermal behavior of a new energetic zinc(II) compound

An energetic material [Zn₂(btzphda)₂(H₂O)₄(dpp)₂]·2DMF·4H₂O with high decomposition enthalpy of − 748.35 J/g was prepared by the reaction of H₂btzphda, dpp and Zn(NO₃)₂·6H₂O under solvothermal conditions, where btzphda = 1,4-bis(tetrazol-5-yl)benzene-N2,N2′-diacetato, dpp = 1.3-di(4-pyridyl)propane and DMF = N,N′-dimethylformamide. The luminescence properties of H₂btzphda and [Zn₂(btzphda)₂(H₂O)₄(dpp)₂]·2DMF·4H₂O were investigated at room temperature in the solid state (Hitachi F4600 spectrofluorometer). Furthermore, the thermal decomposition behavior of the compound is characterized by differential scanning calorimetry (DSC) and thermogravimetric-differential thermogravimetric (TG-DTG) analyses. The entropy of activation (ΔH), enthalpy of activation (ΔS) and the free energy of activation (ΔG) for the decomposition temperature were ΔH = 250.64 kJ/mol, ΔS = 222.75 J·mol^− 1·K^− 1 and ΔG = 134.10 kJ/mol.     

Highly selective luminescent sensing of xylene isomers by a water stable Zn-organic framework

A new Zn(II) metal-organic framework was synthesized with 5-nitro-1,2,3-benzenetricarboxylic acid and auxiliary triazole ligand via hydrothermal method, namely, {[Zn_2.5(nbta)(trz)₂(H₂O)]·3H₂O}_n (1), where H₃nbta = 5-nitro-1,2,3-benzenetricarboxylic acid and Htrz = 1H-1,2,4-triazole. 1 shows high thermal stability up to 150 °C under air atmosphere and water stability with the pH range from 1 to 12. Luminescent study shows that 1 displays a high-sensitivity sensing function for p-xylene in the three kinds of xylene isomers.     

Hydrothermal synthesis of dumbbell-shaped ZnO microstructures

Dumbbell-shaped ZnO microstructures have been successfully synthesized by a facile hydrothermal method using only Zn(NO₃)₂·6H₂O and NH₃·H₂O as raw materials at 150 °C for 10 h. The results from X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) show that the prepared ZnO samples exhibit dumbbell-shaped morphology and hexagonal wurtzite structure. The length of ZnO dumbbells is about 5–20 μm, the diameters of the two ends and the middle part are about 1–5 μm and 0.5–3 μm, respectively. The dumbbell-shaped ZnO microstructures may be formed by self-assembly of ZnO nanorods with 1–5 μm in length and 100–200 nm in diameter. The photoluminescence (PL) spectrum of dumbbell-shaped ZnO microstructures at room temperature shows three emission peaks at about 362, 384 and 485 nm.     

Coupling of cyclohexene oxide (CHO) and carbon disulfide (CS2) catalyzed by the asymmetric bis-Schiff-base Zn(II) complex

Based on the self-assembly of the asymmetric bis-Schiff-base ligand H₂L (H₂L = 4-((E)-(2-((E)-3,5-dibromo-2-hydroxybenzylideneamino)phenylimino)(phenyl)methyl-1-(4-chlorophenyl)-3-methyl-1H-pyrazol-5-ol) and Zn(OAc)₂·2H₂O, a new [Zn(L)] (1) was obtained and shown to efficiently catalyze the coupling of CHO (cyclohexene oxide) and CS₂ (carbon disulfide) in activation with [PPN]Cl (PPN⁺ = bis(triphenylphosphoranyidene)-ammonium), n-Bu₄NBr or n-Bu₄NI, where both poly[thio]carbonates and cyclic [thio]carbonates were produced, and the strong O/S exchange afforded the limited formation of trithiocarbonate in the cyclic [thio]carbonate byproducts.