Preparation and formation mechanism of wood-block-like calcite particles

Pure calcite crystal with different morphologies such as wood-block and spherical aggregates were prepared by a precipitation reaction in the presence of citric acid. The as-prepared products were characterized with scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that citric acid obviously influenced the formation of precipitates and the morphology of final products. The formation mechanism of wood-block-like particles was proposed according to theoretical deduction and the proposed growth mode.     

Adsorption of benzoic acid from organic solvents on calcite and dolomite: Influence of water

A study has been carried out of the adsorption of benzoic acid from cyclohexane solution onto the hydrophilic surface of calcite.

We determined initially the chemical and mineral composition of the solid, its specific surface area and its granulometry. This was followed by the determination of the enthalpies of immersion of calcite in different solvents. These thermodynamic properties gave information on the energetics of calcite—solvent interactions. In this way, we could construct a scale of affinities of the different organic molecules and water for the calcite surface. It was noted that the enthalpies were higher in unsaturated than in saturated organic solvents, and higher in water than in the organic solvents.

The adsorption isotherms and the differential molar enthalpies of displacement were determined in the presence and the absence of water. The role played by water in the adsorption of polar organic molecules from the oil phase has not been clearly explained previously. In this paper, we indicate how the presence of water can modify the adsorption of aromatic compounds on the surface of calcite. As regards the adsorption isotherms, the presence of water essentially increases the amount of adsorption. The results of the calorimetric studies were found to be surprising; we observed that the differential molar enthalpies of displacement were endothermic.

Similar experiments were carried out with dolomite and n-heptane solution and the results compared with those obtained with calcite and cyclohexane, leading to the formulation of a general model concerning the adsorption of small polar organic molecules from organic solvents onto the surfaces of the carbonates.     

Size-dependent defluoridation properties of synthetic hydroxyapatite

Batch adsorption experiments were conducted to investigate the removal of fluoride from aqueous solution by the addition of synthetic hydroxyapatites (HAps) with different particle sizes. Results showed that size-dependent defluoridation properties of HAps. Better performances were obtained with smaller particle sized HAps, which presented higher adsorption efficiency. Bulk HAp, the HAp sample with the largest particle size, presented the lowest percentage of fluoride removal. The isotherm studies showed that the Freundlich model was the best choice to describe the adsorption behaviors of nanosized HAps. However, the adsorption pattern of the bulk sample followed both Langmuir and Freundlich isotherms. All parameters that might influence the defluoridation process were assessed, which included the effect of adsorbent dose, initial fluoride concentration, contact time and the effect of temperature. The removal efficiency of fluoride increased with increasing adsorbent dose. Decrease of the initial fluoride concentration resulted in the increase of fluoride removal efficiency. The percentage of fluoride removal increased as the ambient pH decreased. Thermodynamic parameters suggested that the adsorption of fluoride onto HAp samples was physisorption and endothermic in nature. Moreover, adsorption kinetic study revealed that the adsorption process followed pseudo-second-order kinetics. This work indicated that synthetic hydroxyapatites, especially the smaller particle sized HAps, were efficient defluoridation materials.     

The defluoridation of drinking water using multi-walled carbon nanotubes

In this study, the potential sorption capacity of multi-walled carbon nanotubes (MWCNTs) was investigated as a means of removing fluoride from the drinking water of a number of regions in Iran and from experimental solutions. The test was conducted in both batch and continuous operation modes. Batch mode experiments were used to study the effect of parameters such as pH, contact time, ionic strength, adsorbent dose, adsorbent capacity, and the presence of foreign anions on the efficiency of fluoride removal. The results showed that the highest level of sorption occurs at pH 5 (about 94% at 18 min). The ionic strength of the solutions and the presence of co-anions such as chloride, nitrate, sulfate, hydrogen carbonate, perchlorate had a negligible effect on the sorption of F⁻ onto MWCNTs. Sorption capacity measurements revealed that MWCNTs have a saturation capacity of 3.5 mg of F⁻ per gram. Sorption data were best fitted with the Fruendlich sorption isotherm equation, which indicates that F⁻ tends to be adsorbed on MWCNTs in a multilayered manner. Experiments using Kohbanan city drinking water, which contains the highest level of F⁻ among the drinking water samples studied, showed that MWCNTs can remove over 85% of fluoride content.     

Flow injection determinations of citric acid: a review

A review of the flow injection (FI) analytical methods used to determine citric acid (CA) is presented. These flow determinations are described and compared according to the detection technique used. In addition to the advantages involving the use of the continuous flow systems, the analytical figures of merit and interferences are also discussed.     

Acetic acid assisted cobalt methanesulfonate catalysed chemoselective diacetylation of aldehydes

Cobalt methanesulfonate in combination with acetic acid catalysed the chemoselective diacetylation of aldehyde with acetic anhydride at room temperature under solvent free conditions. After reaction, cobalt methanesulfonate can be easily recovered and reused many times. The reaction was mild and efficient with good to high yields.     

Effect of inorganic anions on the morphology and structure of magnesium calcite

Calcium carbonate was precipitated from calcium hydroxide and carbonic acid solutions at 25 degrees C, with and without addition of different magnesium (MgSO(4), Mg(NO(3))(2) and MgCl(2)) and sodium salts (Na(2)SO(4), NaNO(3) and NaCl) of identical anions, in order to study the mode of incorporation of magnesium and inorganic anions and their effect on the morphology of calcite crystals over a range of initial reactant concentrations and limited c(i)(Mg(2+))/c(i)(Ca(2+)) molar ratios. The morphology, crystal size distribution, composition, structure, and specific surface area of the precipitated crystals, as well as the mode of cation and anion incorporation into the calcite crystal lattice, were studied by a combination of optical and scanning electron microscopy (SEM), electronic counting, a multiple BET method, thermogravimetry, FT-IR spectroscopy, X-ray diffraction (XRD), and electron paramagnetic resonance (EPR) spectroscopy. In the systems of high initial relative supersaturation, precipitation of an amorphous precursor phase preceded the formation of calcite, whereas in those of lower supersaturation calcite was the first and only polymorphic modification of calcium carbonate that appeared in the system. The magnesium content in calcite increased with the magnesium concentration in solution and was correlated with the type of magnesium salt used. Mg incorporation caused the formation of crystals elongated along the calcite c axis and, in some cases, the appearance of new [011] faces. Polycrystalline aggregates were formed when the c(i)(Mg(2+))/c(i)(Ca(2+)) molar ratios in solution were increased. Addition of sulfate ions, alone, caused formation of spherical calcite polycrystalline aggregates.     

Gas chromatographic determination of isocitric and malic acid in the presence of a large excess of citric acid

Derivatization yields of different esters (methyl, ethyl, n-propyl, isopropyl, n-butyl and isobutyl) of citric, malic and isocitric acids with various acylating agents, such as acetic anhydride, propionic anhydride, trifluoroacetic anhydride and heptafluorobutyric anhydride, were investigated. The formation of acylated malic and isocitric acid esters is rapid and quantitative whereas the acylation of citric acid esters was slow and partial in most instances. It was found that selective analytical conditions can be achieved with the O-heptafluorobutyryl n-butyl esters. The analytical applicability of the separation and determination of the malic, isocitric and citric acid contents of model solutions and of pressed lemon juice is discussed. Concentrations of 1.2 × 10^?3 ?9.0 × 10^?3g per 100 g of isocitric acid and 4.2 × 10^?3 ?3.5 × 10^?2 g per 100 g of malic acid in the presence of 9.3 × 10^?1 g per 100 g of citric acid were measured with relative standard deviations of 7.5 and 4.2%, respectively.     

Sequential injection redox or acid-base titration for determination of ascorbic acid or acetic acid

Two sequential injection titration systems with spectrophotometric detection have been developed. The first system for determination of ascorbic acid was based on redox reaction between ascorbic acid and permanganate in an acidic medium and lead to a decrease in color intensity of permanganate, monitored at 525 nm. A linear dependence of peak area obtained with ascorbic acid concentration up to 1200 mg l⁻¹ was achieved. The relative standard deviation for 11 replicate determinations of 400 mg l⁻¹ ascorbic acid was 2.9%. The second system, for acetic acid determination, was based on acid–base titration of acetic acid with sodium hydroxide using phenolphthalein as an indicator. The decrease in color intensity of the indicator was proportional to the acid content. A linear calibration graph in the range of 2–8% w v⁻¹ of acetic acid with a relative standard deviation of 4.8% (5.0% w v⁻¹ acetic acid, n=11) was obtained. Sample throughputs of 60 h⁻¹ were achieved for both systems. The systems were successfully applied for the assays of ascorbic acid in vitamin C tablets and acetic acid content in vinegars, respectively.     

Enantioseparation of DL-isocitric acid by a chiral ligand exchange CE with Ni(II)-D-quinic acid system

The ratio of citric acid to D ‐isocitric acid can be used to distinguish authentic and adulterated fruit juices. To separate DL ‐isocitric acid enantiomers, we used ligand exchange CE. D ‐Quinic acid was used as a chiral selector ligand and Mn(II), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) ions were used as the central ions of the chiral selector in the BGE. DL ‐Isocitric acid was found to be enantioseparated with the above metal ions except for Mn(II) ion. The optimum running conditions for the analysis of D ‐ and L ‐isocitric acids along with citric acid, an isomer of isocitric acid, were found to be a BGE (pH 5.0) containing 30% ACN, 20 mM acetic acid, 20 mM NiSO₄, and 80 mM D ‐quinic acid. Under these conditions, DL ‐isocitric and citric acids in fruit juices were analyzed successfully.     

酸和CTAB对聚糠醇膜形貌的影响

本文采用静态界面聚合法,首次成功地制备出不同形貌的聚糠醇(PFA)膜,用SEM、TEM及TG-DTA等对其形貌、结构进行了表征。结果表明:通过改变催化剂酸的种类及表面活性剂(CTAB)用量可得到不同形貌的聚糠醇膜。该法具有合成条件温和、易于控制、能一步合成大量不同形貌的聚糠醇膜等众多优点。     

Phosphomolybdic acid supported on silica gel and promoted with alkali metal ions as catalysts for the esterification of acetic acid by ethanol

Different ratios of phosphomolybdic acid PMA supported on silica gel (1–30 wt%) and promoted with alkali metal hydroxide have been prepared by an impregnation method and calcinated at 350 °C for 4 h. The catalysts were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray diffraction, FT-IR spectroscopy and N₂ adsorption measurements. The surface acidity and basicity of the catalysts were determined by adsorption of pyridine and the dehydration–dehydrogenation of 2-propanol. The gas-phase esterification of acetic acid by ethanol was carried out in a conventional flow bed reactor. The results clearly revealed that among the PMA loading, the use of 10 wt% catalyst showed maximum yield of ethyl acetate. This catalyst also improved on addition of Na or K-hydroxide. These results were correlated with the structure and the acid–base properties of the prepared catalysts.     

Covalent attachment of proteins to calcite surface for the single molecule experiments

Two protocols of covalent attachment of proteins onto the calcite surface, viz. one using the metallochelat and second using the aminohexil, are elaborated. Single molecule force spectroscopy method has been used to test their efficiency and practical applicability. Experiments were performed measuring the specific interaction force between bovine serum albumin (BSA) fixed onto the freshly cleaved calcite single crystal surface (procedure under the study here) and its polyclonal antibody (Ab-BSA) immobilized onto an AFM tip using standard and well studied procedure. We found the conditions, when up to 3–3.5% of tip-sample approaches lead to the formation of a single specific bond.     

A quinoline-based tripodal fluororeceptor for citric acid

The quinoline-based tripodal fluororeceptor 1 has been designed and synthesized for the detection of citric acid in less polar solvents. Receptor 1 shows monomer emission quenching followed by excimer emission upon hydrogen bond-mediated complexation of citric acid. In comparison, receptor 2, in presence of the same acid, gives rise to a decrease in the monomer emission of the naphthyl moiety without showing any peak for the excimer. Receptor 1 is found to bind citric acid more strongly than receptor 2 in CHCl₃.     

近红外光谱法快速检测烟草中部分香气物的应用研究

应用傅立叶变换近红外漫反射光谱仪,从500个样品中按高、中、低含量挑选出具代表性的150～172个烟草样品建立了近红外光谱与烟草中的苹果酸、柠檬酸和石油醚提取物成分含量间的数学模型,用建立的模型对36个样品进行预测,结果表明,各成分近红外预测值与实测值之间的平均偏差:苹果酸为0.090,柠檬酸为0.040,石油醚提取物为0.124;且近红外预测值与化学法不存在显著性差异,近红外光谱分析技术可初步用于烟草部分香气成分的快速定量分析.     

柠檬酸试剂中痕量无机阴阳离子的离子色谱法测定

选用柱容量较高、亲水性较强的阴离子分析柱IonPac AS18,以30mmol／L KOH为淋洗液,等度淋洗分析了高浓度柠檬酸中的痕量无机阴离子。选用柱容量较高的阳离子分析柱IonPac CS12A,以H2SO4作淋洗液分析了柠檬酸试剂中的痕量阳离子。在所选色谱条件下,无需样品前处理,直接进样,电导检测,高浓度柠檬酸不影响痕量阴离子或阳离子的测定。方法具有良好的线性(r=0．9941～1．000),样品中所测离子峰面积的相对标准偏差(RSD)均在9．0％以下(n=7),回收率在82．7％～110％之间,检出限低于3．7μg/L。     

阻抑动力学荧光法测定柠檬酸

基于在高氯酸介质中柠檬酸能抑制铁(Ⅲ)催化H2O2氧化吡咯红Y的反应，建立了一种测定柠檬酸的动力学荧光分析法。方法的线性范围为0．12-2．4μg/mL，检出限为0．05μg/mL。将方法用于汽水中柠檬酸的测定，回收率为97％-106％。     

Visualizing the toughening origins of gel-grown calcite single-crystal composites

The mechanical properties of gel-grown calcite single-crystal composites can be modified by incorporation of guest materials including agarose gel fiber, MWCNTs and GO. The in-situ observation of the crystal deformation suggests that the guest incorporation toughens the single-crystal host by the shielding effect of nanofiber on crack-bridging at nanoscale.     

离子色谱法测定威力酸中的有机酸

采用离子排斥分离,电导检测模式,对威力酸中的4种有机酸成份进行分离测定。将威力酸样品通过萃取、洗涤、过滤之后进样,可以测定其柠檬酸、乳酸、苹果酸、富马酸4种有机酸,在一定的色谱条件下,4种阴离子都具有很好的线性和较低的检出限。威力酸中的柠檬酸,乳酸,苹果酸,富马酸的检出限分别是0.10、0.14、0.30和0.12μg/L,线性相关系数r2在0.9997~0.9999范围内,样品中待测离子峰面积的RSD在4.3%以下(n=10),回收率在94%~105%之间。采用抑制电导的离子色谱法是分析威力酸中的有机酸成份的高效与准确的方法。