Addition Of Mineral Acids Research Articles

Improved extraction of anthocyanins with antibacterial activity from fresh roselle (Hibiscus sabdariffa L.) calyces

Roselle (Hibiscus sabdariffa L.) flower is a commonly consumed vegetable in Bangladesh and have culinary value to preparation of soup, jelly, and baking. Since previous studies suggested the presence of anthocyanins in roselle calyces, this study was designed to enrich anthocyanins from the calyces of this flower. This study explored that addition of mineral acid during the extraction process further enriched the anthocyanins content of the fresh roselle calyces extract. Also, methanol acidified with 1% (v/v) HCl was found as the best solvent to extract anthocyanins from the calyces resulting 7.621±0.001 mg crude anthocyanins per gram of fresh sample. Anthocyanin extraction decreased if 1% (v/v) HCl was replaced with 10% (w/v) tartaric acid or 10% (v/v) acetic acid. The extracted anthocyanins showed minimal antibacterial activity. A further study will explore the possibility of use these anthocyanins for industrial purposes. Dhaka Univ. J. Biol. Sci. 33(2): 139-147, 2024 (July)

STUDY OF THE PROCESS OF OXIDATIVE DESULFURIZATION OF DIESEL FUEL IN THE PRESENCE OF CO-CATALYSTS

Continuous growth in consumption of oil in the world, as well as ever-increasing quality requirements stimulate the search for new scientific and technological solutions to directionally affect the characteristics of petroleum products, including their chemical composition. The advantages of oxidative desulfurization before hydrotreating are the absence of the need to use hydrogen, as well as small capital and energy costs, since the method does not require high temperatures and pressures. The purpose of this work was to study the oxidation process of diesel fuel and to search for the optimal mode of oxidative desulfurization of diesel fuel in the presence of transition metals salts with the addition of mineral acids. The object of the study is a straight-run diesel fraction of the Pavlodar Petrochemical Plant with boiling temperatures of 180-350°C. The oxidation process was carried out with hydrogen peroxide in the presence of salts of the transition metals molybdenum, vanadium and tungsten. The article defined the basic physico-chemical characteristics of straight-run and desulfurized diesel fractions. The optimal catalyst (Na2MoO4) was selected at a molar ratio of metal to sulfur of 1:100 for the oxidation process of straight-run diesel fractions. As a result of oxidative desulfurization of diesel fuel in the presence of sodium molybdenum perox complexes, the total sulfur content decreased by 42.9%, and with the addition of sulfuric acid by 56.5%. An increase in the cetane index from 56.3 to 58.6 was revealed in the presence of sodium molybdate with the addition of sulfuric acid.

A novel and simple strategy for the direct synthesis bimetallic mesoporous materials Zr–La-SBA-15

A series of Zr and La incorporated SBA-15 mesoporous materials (ZLS) were synthesized through a direct hydrothermal route without addition of mineral acids and characterized by FT-IR, XRD, TEM and N2 adsorption–desorption isotherm techniques. The results indicated that the heteroatoms were successfully incorporated into the framework of SBA-15 after modification. The modified materials still preserved a desirable ordered two-dimensional P6mm hexagonal structure and possessed high specific surface area, large pore volume and narrow pore size distribution.

A modified biphasic system for the dehydration of d-xylose into furfural using SO42−/TiO2-ZrO2/La3+ as a solid catalyst

One of the most promising strategies for furfural production is to extract continually the target product from the aqueous solution utilizing organic solvents. With the aim to develop an ecologically viable catalytic pathway for furfural production without the addition of mineral acids, we presented a modified biphasic system using a solid acid (SO42−/TiO2-ZrO2/La3+) as catalyst for producing furfural from xylose. Different kinds of aprotic organic solvents (DMSO, DMF and DMI) in water phase and 2-butanol in organic phase (MIBK) were investigated as reaction media. Furfural yield and xylose conversion efficiency were dependent on the amounts of aprotic organic solvents and 2-butanol, the solid/liquid ratio, and the volume ratio of the organic phase and the aqueous phase as well as the reaction temperature and time. As a result, DMI showed the best performance on improving furfural yield during the furfural production. 3563.3μmol of furfural/g of xylose with 97.9% xylose conversion efficiency was obtained after 12h at 180°C when the volume ratios of water to DMI and MIBK to 2-butanol were 8:2 and 7:3, respectively.

An acid-free route for the facile synthesis of iron-functionalized mesoporous silicas: Transformation between hollow nanospheres and cage-like mesostructures

Iron-substituted silicas with hollow nanospherical morphology and cage-like mesostructure have been synthesized using triblock copolymer F127 as surfactant and tetramethoxysilane (TMOS) as silica source with no necessary addition of mineral acids. Iron-functionalized hollow nanospheres were obtained using Fe(acac)3 as iron source. When Fe(NO3)3 was employed as iron source, iron-containing cage-like FDU-12 mesostructure and hollow nanospheres were formed with Fe/Si molar ratio lower than 0.008 and higher than 0.015, respectively. The formation of hollow spheres at high Fe/Si ratio can be regarded as gradually dissociation of nanocages from Fe-FDU-12. The structure of the iron centers was determined by spectroscopic methods (UV–vis and UV–Raman measurements) and by elemental analyses. The facile structural evolution between cage-like and nanospherical structures may be helpful for further understanding the formation mechanism of mesoporous silicas.

Enhanced Trapping Efficiency in Acid-Treated Silica Nanostructures

The color of the photoluminescence (PL) of silica nanostructures changes remarkably from blue to bluish green, with the addition of mineral acids. This remarkable observation is rationalized in light of an excited-state protonation of some of the trap states, as well as electrostatic assistance provided by the H3O+ ions adsorbed at the surface. A combination of these two leads to more efficient trapping. The enhanced trapping is manifested in the time-resolved PL parameters and spectra. A fast decay of PL is observed in the higher-energy region of the spectrum, while a rise, with an almost equal time constant, is observed at the lower-energy end. Time-resolved area-normalized emission spectra are dominated by a structured spectrum in the high-energy region at shorter times and a broad, red shifted spectrum at longer times.

Short channeled Zr-Ce-SBA-15 supported palladium catalysts for toluene catalytic oxidation

Short channeled Zr-Ce-SBA-15 (ZCS) mesoporous materials were synthesized through hydrothermal routes without addition of mineral acids. 0.5 wt.% palladium was loaded on ZCS and SBA-15 via an ethanol reduction approach. Pd/ZCS possesses unique hexagonal platelet morphologies with short channels running parallel to the thickness in the range of 400–500 nm, while Pd/SBA-15 has a fibrous macrostructure with channels at the micrometer scale. Palladium species present in supports as well dispersed PdO nanocrystals with diameter of ca. 5–6 nm. Comparing with Pd/SBA-15, Pd/ZCS shows enhanced catalytic activity for toluene oxidation, which is ascribed to short channeled supports facilitating the molecular diffusion. ► Short channeled Zr-Ce-SBA-15(ZCS) was synthesized without addition of mineral acids. ► ZCS possesses unique hexagonal platelet morphologies. ► Pd/ZCS catalysts were prepared by ethanol reduction approach. ► Palladium species well dispersed in supports as PdO nanocrystals of ca. 5–6 nm. ► Pd/ZCS catalysts show enhanced catalytic activity for toluene oxidation.

Direct Synthesis of Zr‐Containing Hybrid Periodic Mesoporous Organosilicas with Tunable Zirconium Content

AbstractHighly ordered Zr‐containing periodic mesoporous organosilicas (ZrPMO) with different Zr/Si ratios were successfully synthesized, for the first time, by employing a ZrOCl2/NaCl combination as the promoting agent and by simply adjusting the molar ratio of the zirconium species to the organosilica precursor; no addition of mineral acids was necessary. The effect of preparation parameters on the structural and textural properties were carefully investigated by using different ratios of NaCl/Si and Zr/Si. It was found that both salts are essential for this system and highly ordered ZrPMOs can be prepared within fairly wide Si/Zr ratios (5–100) while keeping the NaCl/Si ratio constant. To prove the effectiveness of this synthetic pathway with a higher Zr incorporation, ZrPMO materials were also synthesized under strongly acidic conditions for the purpose of comparison. The synthesized ZrPMO materials were thoroughly characterized by ICP‐AES, SAXS, N2 sorption, TEM, SEM, 13C CP/29Si MAS NMR spectroscopy, XPS, and TGA. Elemental analyses show that the amount of Zr incorporated into ZrPMO, which was synthesized under mild conditions, is greater than that obtained in a strongly acidic environment, and the Zr content, with a Si/Zr ratio up to 12, is close to that in the initial gel composition. A plausible assembly mechanism based on the synergistic effect of both “nonhydrolyzable” (NaCl) and “hydrolyzable” (ZrOCl2) inorganic salts was discussed in detail, where the “salting out” effect and self‐generated acidity from both inorganic salts, respectively, are believed to be key factors for the formation of ordered SBA‐15‐type ZrPMO materials under the synthetic conditions.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Synthesis and characterization of periodic mesoporous organosilicas from bridged organosilanes in the presence of mixed salts

A simple but effective synthetic pathway to periodic mesoporous organosilicas (PMOs) has been put forward in this article. The novelty of the present preparative route lies in that, for specific examples, highly ordered ethane- and benzenesilica PMOs can be facilely prepared in the presence of an inorganic salt pair within a wide compositional range, where no addition of mineral acids was necessary. Most of interest is that crystal-like pore walls were observed for the large-pore benzenesilica PMO promoted by this novel system, which has rarely been reported for copolymer-assembled organosilicas, even though the degree of molecular order is not as perfect as those benzenesilicas prepared under basic conditions utilizing cationic surfactants as template. Characterization results based on a series of techniques indicated that both inorganic salts are important for the assembly of ordered mesostructures under the present system, and a plausible formation mechanism deduced from the “salt-assisted” concept as previously reported for mesoporous nonsiliceous materials was discussed.

Strong photoresponse of nanostructured tungsten trioxide films prepared via a sol–gel route

A simple route for synthesizing nanostructured tungsten trioxide (WO3) films on conducting glass substrates has been developed. Films with different morphologies were synthesized by the addition of mineral acids (such as HCl) to an aqueous peroxopolytungstic acid precursor solution. The films were characterized by SEM, SAXS, in-situ X-ray diffraction, cyclic voltammetry, optical absorption and photoelectrochemical measurements. The best of these films generated anodic photocurrents as high as 4.0 mA cm−2 for oxidization of methanol and 2.3 mA cm−2 for water splitting, under Xe lamp illumination at 86 mW cm−2. The improvement of photocurrent can be attributed to enhanced light harvesting and charge transport arising due to the nanostructure.

Preparation of poly(vinyl alcohol) membranes grafted with N-vinyl imidazole/acrylic acid binary monomers

Poly(vinyl alcohol) films were grafted with two monomers using gamma radiation, acrylic acid and N-vinyl imidazole. The influence of different parameters on the grafting yield was investigated as: type of solvent and solvent composition, comonomer concentration and composition, addition of mineral acids, and irradiation dose. Water uptake in respect to the grafting yield was also evaluated.The ability of the grafted films to adsorb copper ions was elaborated and discussed for different grafting yields and pH values of the solution.

Synthesis of Zr-Incorporated SBA-15 Mesoporous Materials in a Self-generated Acidic Environment

An environmentally friendly process of synthesizing Zr-incorporated mesoporous SBA-15 silica materials with the Zr content up to 0.1 Zr/Si atomic ratio and of well-ordered pore structure, high surface area, and narrow pore-size distribution was developed, where no addition of mineral acids was necessary. The main strategy of this method was to utilize the acidity self-generated in the aqueous solutions of the zirconium precursors as the catalyst for TEOS hydrolysis. In addition, the zirconium precursors also contributed to salt effect in increasing the ordering of the mesostructure. SBA-15 materials of highly ordered pores were obtained without the addition of mineral acids when the Zr/Si ratios were around 0.05. For those with the Zr/Si ratios smaller or greater than this value, the introduction of some salts, such as NaCl, in the synthesis gel was found essential in order to obtain mesostructure of high ordering and narrow pore size distribution. The amount of Zr incorporated in SBA-15 synthesized under...

Optical properties of the oligomer of resorcinol and benzaldehyde

Condensation of resorcinol with benzaldehyde in the presence of an acid gives an oligomeric product having a quinonic end group. The presence of the quinonic end group acts as a chromophore, and provides distinct visible absorptions at 450 and 475 nm. The oligomer interacts with different amines in a non-stoichiometric manner to give new absorptions at 525 nm. On addition of mineral acid, a new state can be generated having absorbance at 455 nm. This absorption can also be obtained from the interaction of an ammonium salt with the oligomer. The absorptions at 455 nm due to interaction with ammonium cation can be pushed back and forth to 525 nm by adding amine and acid, respectively showing the property of chemically driven reversible optical switching.

The effect of soil acidification on atmospheric methane uptake by a Maine forest soil(1).

Soil from the zone of maximal methanotrophic activity (approximately 5-8 cm depth) in a mixed coniferous-hardwood forest consumed atmospheric methane over a wide pH range (3.5-7.5) with a broad optimum between 4.8 and 6.0. Methane uptake at native soil pH values (4.4-4.8) was only slightly less rapid than rates at optimal pH values. Addition of mineral acids to intact soil cores in pulsed applications decreased atmospheric methane consumption. The extent of inhibition varied with the type, concentration and volume of acid added: nitric acid was more inhibitory than sulfuric acid at an equivalent soil pH, and methane uptake decreased with increasing volumes and concentrations of added acid. Although ammonium chloride at 1 µmol g fresh weight (gfw) soil(-1) inhibited methane uptake, the extent of inhibition did not vary significantly with decreasing soil pH below values of 4.4.

Acid-Aided Selectivity in Bromination of 1-Aminoanthraquinones

Abstract : Selectivity in the bromination of 1-aminoanthraquinones was studied. The addition of mineral acids was surprisingly found to enhance selectivity for the four isomer and consequently givean enhanced yield.

Inhibitory effect of ruthenium(III) on the oxidation of dimethyl sulphoxide byN-bromosuccinimide andN-bromophthalimide. A novel observation

RuIII exerts an inhibitory effect on the oxidation of DMSO byN-bromosuccinimide and byN-bromophthalimide in the presence of Hg(OAc)2 in aqueous AcOH at 15°C. The reaction order is unity with respect to the oxidant and substrate, but less than one at low substrate concentrations; fractional for higher concentrations. The effect of the ionic strength of the medium is negligible, while that of dielectric constant is positive. Added acrylonitrile is not polymerised. Addition of mineral acid increases the reaction rate. A probable mechanism is proposed, rationalising the inhibitory effect of RuIII.

Determination of Antimony in River Water by Hydride-Generation Atomic Absorption Spectrometry

Trace antimony in river water was determined by hydride-generation atomic absorption spectrometry. The water was concentrated after the addition of mineral acids. Siliceous residues deposited during the concentration were solubilized with hydrofluoric acid and expelled by evaporation in the presence of sulfuric acid. After chelating resin separation, the effluent was acidified with sulfuric acid to ionize the hydrolyzed antimony. The accuracy checked with a biological standard reference material was satisfactory when the insoluble residues in the material were treated with hydrofluoric acid after acid digestion. Antimony contents in the water ranged between 0.1 and 0.9ng ml-1.

SOLUBLE ALUMINUM IN ACIDIFIED ORGANIC HORIZONS OF FOREST SOILS

Concentrations of labile and total Al in soil extracts were measured as a function of equilibrium solution pH in six forest soil organic horizons acidified with HNO3 (0–20 cmol H+∙kg−1) under controlled conditions of ionic strength (0.05 M NaNO3), temperature (23 °C), and solution:soil ratio (25:1). Decreases of 0.1–0.2 in solution pH in the range of pH 2.4–4.5 resulted in increases and decreases in concentrations of labile and total Al. Organic acids and soluble C were the dominant Al-complexing ligands in solution, and acidification of each horizon decreased their concentration. Silicon and F concentrations in the equilibrium solutions were lower than that of C, but levels were similar to those of nonlabile Al. Nonlabile complexes were the dominant forms of soluble Al in horizons above pH 4, and labile Al comprised an increasing percentage of total Al as pH decreased, especially below pH 3. The results showed pH alone to be a poor predictor of log nonlabile (r2 = 0.06) or total Al (r2 = 0.33) concentration in these soils, but a good predictor of log labile forms (r2 = 0.77). Solution pH, however, was positively correlated with the log of the ratios of C-to-total Al (r2 = 0.78), C-to-nonlabile Al (r2 = 0.68), and C-to-labile Al (r2 = 0.88). The results should aid in predicting the changes in speciation and solubility of Al due to inputs of acid precipitation to forest soil organic horizons with variable pH and content of dissolved organic C. The observed variability in response of Al to acidification of organic horizons of forest soils indicated that it is not possible to generalize whether nonlabile and labile forms of Al will increase, decrease, or not change upon addition of mineral acid. Besides pH, concentrations of different Al-complexing ligands should be measured in equilibirum soil extracts. Key words: Acid precipitation, fluoride, silica, fulvic acid

New, high sensitive organic reagents for cobalt

Heterocyclic azo dyestuffs, 5-(2-pyridylazo)-2, 4-diaminotoluene(PADAT) and its analogs have been prepared, and their possible use as spectrophotometric reagents has been investigated. Cobalt(II) and PADAT in a slightly acid, neutral or alkaline medium form a yellowish brown complex. This complex, on addition of mineral acid, changes into a species of a deep violet color. The reagent itself and the violet complex are very stable even in strongly acid solutions, and the system follows Beer's law; the optimal range for measurements in a 1-cm cell is 0.0010.4 ppm cobalt in 27 N hydrochloric acid. The yellowish complex which is formed at pH 411 can be extracted with 3-methyl-butanol or n-butyl phosphate. The reagent blank is also negligiable at an absorption peak of the violet complex. Common anions and cations do not interfere. The molar absorption coefficient of 5-[ (3-benzyloxy-2-pyridyl) azo]-2, 4-diaminotoluene (3-Benzyloxy-PADAT), PADAT, 5-[(5-chloro-2-pyridyl) azo]-2, 4-diaminotoluene (5-Cl-PADAT), 5-[ (5-bromo-2-pyridyl) azo]-2, 4-diaminotoluene (5-Br-PADAT) and 5-[(3, 5-dichloro-2-pyridyl)azo]-2, 4-diaminotoluene (3, 5-diCl-PADAT) are 1.10×105, 1.16×105, 1.26×105, 1.30×105 and 1.38×105 cm2mol-1 at 591, 561, 573, 574 and 590 nm, respectively.

A thin-layer chromatographic method for the rapid separation of porphyrin dimethyl esters

The addition of iron salts to thin-layer plates of Silica Gel G was found to facilitate the separation of porphyrin dimethyl esters so greatly that rapid separation in one dimension and in one solvent system could be carried out. A somewhat similar result, although not so marked, was also observed with iron-impregnated paper. It was shown that pH adjustment of the medium by addition of mineral acid alone, to the value resulting from iron-salt hydrolysis in the medium, will not duplicate the effect. Addition of Cu, Mn or Mg to Silica Gel G was ineffective.