Strong Acid Base Research Articles

Interaction of Small Gases with the Unsaturated Metal Centers of the HKUST-1 Metal Organic Framework

The interactions of CO, CO2, OCS, SO2, NO, NO2, N2O, NH3, PH3, and other small molecules with the undercoordinated metal centers of the HKUST-1 metal organic framework are studied by means of density functional theory. These molecules are potentially harmful for humans and the environment and are widely studied because of their spectroscopic properties. In this work, the energetic and vibrational characteristics of the adsorbed species are calculated. Adsorption energies on the Cu2+ sites of the paddlewheel have been calculated, and the order is: NH3 > H2O > PH3 > H2S > SO2 > CO ∼ OCS ∼ CO2 ∼ NyOx > N2 > O2. The results show that the interactions can be classified into three categories: (1) weak physisorption, (2) polarization and electrostatics, and (3) strong acid–base. Moreover, interesting vibrational properties are calculated especially for carbonyl sulfide and dinitrogen monoxide, which can be bound via two different configurations on the metal atoms. The vibrational modes are shifting in different ...

Corolla of Roselle (Hibiscus sabdariffa L.) as acid-base indicator

Acid-base titration requires indicators to show color change at each pH interval. Synthetic indicators applied recently have some negatives, such as chemical pollution, availability and expensive production cost. Effort to obtain natural product-based-indicator from corolla of Roselle ( Hibiscus sabdariffa L.) has been conducted. Firstly, anthocyanin contained in the Roselle’s corolla was identified. Then, the indicator was obtained by extracting the corolla consecutively with n-hexane, ethyl acetate and methanol-HCl 0.5%. Then the filtrate was evaporated at 65 o C. The obtained indicator was applied in weak base-strong acid and weak acid-strong base titrations. The comparison indicators used in this research were methyl orange and phenolphthalein. The results showed that the Roselle’s corolla indicator gave red color in acidic solution, while green in basic solution. Additionally, its performance is similar to that of methyl orange.

Boerhavia Erecta Linn. Stem Bark Extract A Natural Acid-Base Indicator

Synthetic indicators have been tried as indicators in acid-base titrations but due to environmental pollution, availability and cost, natural compounds are best alternate. Natural pigments in plants are highly colored substances and may show sharp color changes with variation in pH .An attempt has been made to extract natural indicator by maceration from stem bark of Boerhavia erecta Linn. The equivalence points obtained by the BEI strong acid-strong base, strong acid-weak base, weak acid-strong base and weak acid weak base titrations were coincident with the equivalence points obtained by synthetic indicators. Thus natural indicator was found to be eco-friendly, economical, simple and accurate for all acid-base titrations. Phytochemical analysis and spectral studies confirmed presence of anthocyanins and flavonoids in BEI responsible for accurate and sharp colour change at equivalence point. The present study reports the use of this natural indicator in different acid base titrations.

Generalized and high temperature synthesis of a series of crystalline mesoporous metal oxides based nanocomposites with enhanced catalytic activities for benzene combustion

We report here a generalized synthesis of various crystalline mesoporous metal oxides including CeO2, Cr2O3, Fe2O3, SnO2, Ce0.5Zr0.5O2, TiO2, Al2O3 and ZrO2 from the self-assembly of a basic poly 4-vinylpyridine (P4VP) template with various metal precursors based on their strong acid–base interaction under high temperature (180 °C) hydrothermal conditions. Using the typically crystalline mesoporous metal oxide of CeO2, after removing the template by calcination at 550 °C and loading with various transition metal oxides such as MnOx, various transition metal oxide functionalized crystalline mesoporous CeO2 (MnOx/P4VP–CeO2) were obtained. X-ray diffraction (XRD) patterns show that the resulting mesoporous metal oxides exhibit a high degree of crystallinity, and the transition metal oxides active sites have been successfully loaded into these samples. N2 sorption–desorption isotherms, SEM images show that the resulting crystalline mesoporous metal oxides, such as CeO2, have a large BET surface area (94 m2 g−1) and abundant mesopores, which exhibit monolithic morphology with crystal sizes ranging from 5 to 15 μm, giving a uniform pore size centered at 5 nm. XPS spectra show that the active sites such as MnOx exhibit the phases of MnO2 and Mn2O3 in P4VP–CeO2. H2-TPR curves show that MnOx/P4VP–CeO2 exhibits decreased reductive temperatures of both active sites of the MnOx and P4VP–CeO2 supporter when compared with the samples reported previously. More importantly, MnOx/P4VP–CeO2 exhibits much better catalytic activities and good recyclability for catalyzing the oxidation of benzene than that of MnOx loaded commercially crystalline CeO2, which will be very important for their wide applications for VOCs removal in industry.

Impacts of greenwaste biochar on ammonia volatilisation from bauxite processing residue sand

The objective of this study was to test the suitability of greenwaste biochar to aid nitrogen (N) retention in rehabilitated bauxite-processing residue sand (BRS). Bauxite residue sand was collected from the Alcoa of Australia Pinjarra refinery. The pH of BRS was adjusted to values of 5, 7, 8 and 9 and subsequently amended with different rates (1, 5, 10 and 20 %, w/w) of greenwaste biochar. The loss of N via NH3 volatilization following addition of di-ammonium phosphate (DAP) was determined using an acid trapping method. At low pH (5), increasing pH rather than adsorption capacity, resulting from biochar addition, caused greater losses of N through volatilization from BRS. In BRS with medium pH (7, 8), increasing adsorption capacity, induced by biochar addition, played the more dominant role in enhancing adsorption of NH 4 + -N /NH3-N and lowering NH3 volatilization. In the BRS with high pH (9), the majority of NH 4 + -N /NH3-N pools was lost via NH3 volatilization due to the strong acid-base reaction at this pH. It is concluded that the interaction of changes in pH and adsorption capacity induced by greenwaste biochar addition affects the availability and dynamics of NH 4 + -N/ NH3-N in BRS amended with DAP.

Origins of the deactivation process in the conversion of methylbutynol on zinc oxide monitored by operando DRIFTS

The catalytic behavior of zinc oxide samples was studied thanks to a model methylbutynol (MBOH) conversion reaction. The formation of acetone and acetylene is indicative of the basic properties of the zinc oxide surface. This basic catalyst, whose conversion level depends on the nature of the pre-treatment, was found to deactivate versus time on stream. Poisoning the basic sites by CO2 pre-adsorption only affects the active sites working at the beginning of the reaction, those still working at steady state being not impacted. This is consistent with the modification of the strength and population of the active sites during the catalytic reaction. Indeed, from operando DRIFTS experiments, at the beginning of the reaction, the strong acid base pairs generated upon inert treatment at 773K promote the self aldol condensation of acetone, leading to oligomers. This reaction also produces water, which dissociates on the surface, filling up oxygen vacancies. This contributes to the lowering of the strength of the active sites, resulting in the quenching of polymerization of acetone at a certain stage, at the benefit of the increase of the amount of diacetone alcohol. Consistently, pre-adsorption of water was shown to lead to a decrease of the conversion level, resulting in a conversion profile similar to that obtained after 10min of reaction in the absence of pre-adsorbed water. The poisoning mechanism proposed is based on the evolution of the IR bands versus time and is in line with the evolution of the deactivation profile versus time. It is concluded that both the control of the conversion level and the dependence of the reaction toward deactivation are associated to the formation of oxygen vacancies during the pre-treatment step but also on their stability in the conditions on the implemented catalytic reaction.

An Alternative to Synthetic Acid Base Indicator-Tagetes Erecta Linn

The present work highlights the use of the methanolic extract of the flowers of Tagetes erecta as an acid-base indicator in acid-base titrations. This natural indicator is easy to extract as well as easily available. Indicators used in titration show well marked changes of colour in certain intervals of pH. Most of these indicators are organic dyes and are of synthetic origin. Today synthetic indicators are the choice of acid-base titrations. But due to environmental pollution, availability and cost, the search for natural compounds as an acid-base indicator was started. Herbal indicators are evaluated by using strong acid-strong base, strong acid-weak base, weak acid-strong base and weak acid weak base. In all these titrations the methanolic extract of the flowers of Tagetes erecta was found to be very useful, economical, simple and accurate for acid base titration.

Phosphoric acid doped sulfonated poly(tetra phenyl isoquinoline ether sulfone) copolymers for high temperature proton exchange membrane potential application

Phosphoric acid-doped sulfonated poly(tetra phenyl isoquinoline ether sulfone)s (PA-SPTPIESs) were successfully synthesized for high temperature proton exchange membrane. Poly(tetra phenyl ether ketone sulfone)s (PTPEKS) were prepared from 1,2-bis(4-fluorobenzoyl)-3,4,5,6-tetraphenyl benzene (BFBTPB) and bis(4-fluorohenyl) sulfone with bis(4-hydroxyphenyl) sulfone. The synthesis of the poly(tetra phenyl isoquinoline ether sulfone)s (PTPIESs), was carried out via an intramolecular ring-closure reaction of dibenzoylbenzene of PTPEKS with benzylamine. The sulfonated poly(tetra phenyl isoquinoline ether sulfone)s (SPTPIESs) were obtained by following sulfonation with concentrated sulfuric acid and doped by phosphoric acid. Different contents of sulfonated unit on PTPIESs (8, 12, 16 mol% of BFBTPB) and PA-SPTPIESs were studied by FT-IR, 1H NMR spectroscopy, and thermogravimetric analysis (TGA). Strong acid–base interaction effect between poly benzisoquinoline (PBI) and sulfonic acid groups formed ionic crosslinking network between polymer chains. The ion exchange capacity (IEC) and proton conductivity of PA-SPTPIESs were evaluated with degree of sulfonation and doping of phosphoric acid.

Proton exchange in acid–base complexes induced by reaction coordinates with heavy atom motions

We extend previous work on nitric acid–ammonia and nitric acid–alkylamine complexes to illustrate that proton exchange reaction coordinates involve the rocking motion of the base moiety in many double hydrogen-bonded gas phase strong acid–strong base complexes. The complexes studied involve the biologically and atmospherically relevant glycine, formic, acetic, propionic, and sulfuric acids with ammonia/alkylamine bases. In these complexes, the magnitude of the imaginary frequencies associated with the proton exchange transition states are <400cm−1. This contrasts with widely studied proton exchange reactions between symmetric carboxylic acid dimers or asymmetric DNA base pair and their analogs where the reaction coordinate is localized in proton motions and the magnitude of the imaginary frequencies for the transition states are >1100cm−1. Calculations on complexes of these acids with water are performed for comparison. Variations of normal vibration modes along the reaction coordinate in the complexes are described.

Microgel/SiO2 hybrid colloids prepared using a water soluble silica precursor

In the present work we demonstrate that functional polymer microgels may act as smart self-catalyzing system inducing controlled formation of silica nanoparticles inside the polymer network and formation of hybrid colloids. We synthesized a water soluble silica precursor PEG-PEOS via post-modification of hyperbranched poly(ethoxysiloxane) (PEOS) with poly(ethylene glycol) monomethyl ether. We used poly(N-vinylcaprolactam)-based microgel functionalized with imidazole and β-diketone groups as a matrix for biomimetic deposition of silica. Composite microgel particles containing silica nanoparticles (up to 20 wt.-%) have been prepared by simultaneous PEG-PEOS conversion and silica deposition in the microgels. TEM studies indicate the infiltration of silica nanoparticles (∼10 nm) inside the corona region of the microgels due to the strong acid–base interaction between the acidic silica and basic imidazole groups. The resulting composite particles were found to be colloidally stable and no aggregation was observed even after months of storage. The incorporation of silica nanoparticles increased the rigidity of the microgel particles and reduced their thermal sensitivity.

Investigation of a Simple and Cheap Source of a Natural Indicator for Acid-Base Titration: Effects of System Conditions on Natural Indicators

This study investigated a natural indicator for acid-base titration which is extracted from guinea corn leaves popularly called “waakye leaves” in Ghana. Four types of acid-base titration were studied: strong acid versus (v/s) strong base, strong acid versus weak base, weak acid versus strong base, and weak acid versus weak base. The indicator color change, pH range and the average titre values were determined for each type of acid-base titration. These values were comparable to those obtained from three standard indicators: methyl orange, methyl red and phenolphthalein. Total flavonoids (TF) and condensed tannin (CT) from the crude leaves extract were determined which might be the major reasons for the activity of the extract as an indicator for simple acid-base titration. The authors suggest that the natural indicator is cheap, available, simple to extract, user and environmentally friendly and could be an excellent replacement for standard indicators.

The Effects of Temperature and pH on Secondary Structure and Antioxidant Activity of Crocodylus siamensis Hemoglobin

Crocodylus siamensis hemoglobin (cHb) was purified by gel filtration chromatography and visualized by SDS-PAGE. Effects of temperature and pH on secondary structure and conformation changes of cHb were studied using circular dichroism spectropolarimeter and fourier transform infrared spectrophotometer. The secondary structure of intact cHb was mainly α-helices. cHb was not heat stable when heated at 65°C and cooled down to original temperature, indicating the irreversible unfolding process. The stability of cHb at different pH ranging from 2.5 to 10.5 was determined. The maximum value of the α-helix content was found at pH 3.5 and tended to decrease at strong acid and strong base. The antioxidant activities of heat treated cHb and cHb in solution with pH range 2.5 to 10.5 were tested by DPPH radical scavenging assay. cHb at pH 4.5, having highest β-turn structure, showed highest radical scavenging activity. In contrast to pH, heat had no effect on antioxidant activity of cHb.

New insights into ion regulation of cephalopod molluscs: a role of epidermal ionocytes in acid-base regulation during embryogenesis

The constraints of an active life in a pelagic habitat led to numerous convergent morphological and physiological adaptations that enable cephalopod molluscs and teleost fishes to compete for similar resources. Here, we show for the first time that such convergent developments are also found in the ontogenetic progression of ion regulatory tissues; as in teleost fish, epidermal ionocytes scattered on skin and yolk sac of cephalopod embryos appear to be responsible for ionic and acid-base regulation before gill epithelia become functional. Ion and acid-base regulation is crucial in cephalopod embryos, as they are surrounded by a hypercapnic egg fluid with a Pco(2) between 0.2 and 0.4 kPa. Epidermal ionocytes were characterized via immunohistochemistry, in situ hybridization, and vital dye-staining techniques. We found one group of cells that is recognized by concavalin A and MitoTracker, which also expresses Na(+)/H(+) exchangers (NHE3) and Na(+)-K(+)-ATPase. Similar to findings obtained in teleosts, these NHE3-rich cells take up sodium in exchange for protons, illustrating the energetic superiority of NHE-based proton excretion in marine systems. In vivo electrophysiological techniques demonstrated that acid equivalents are secreted by the yolk and skin integument. Intriguingly, epidermal ionocytes of cephalopod embryos are ciliated as demonstrated by scanning electron microscopy, suggesting a dual function of epithelial cells in water convection and ion regulation. These findings add significant knowledge to our mechanistic understanding of hypercapnia tolerance in marine organisms, as it demonstrates that marine taxa, which were identified as powerful acid-base regulators during hypercapnic challenges, already exhibit strong acid-base regulatory abilities during embryogenesis.

Control of pH process using double-control scheme

Control of pH is mostly needed in continuous process industries and is difficult and challenging due to its time-varying and nonlinear nature of the chemical or biological process. Conventional controllers do not incorporate nonlinear dynamics of the entire pH range (both acid and alkali) and do not show good performance. Dynamics based on specific process nonlinearity of two different ranges is used to design double-control scheme in a feedback structure to enhance the performance of pH process. The mathematical model of pH for a weak acid-strong base is used to design IMC based PID double-controller scheme which provides outstanding set-point tracking and disturbances rejection simultaneously to control pH processes.

하수처리수 재이용을 위한 막분리 공정시 응집조건에 따른 투과효율 변화에 관한 연구

The objectives of this research are to investigate the proper coagulation conditions which are a type and doses of coagulants, mixing conditions (velocity gradients and mixing times), pH and so on through Jar-test, to evaluate the flux variations, permeate, backwashing according to characteristics of pretreatment of the wastewater by means of MF membranes for river maintenance water reuse. The effluent water from B-city K-sewage treatment plant are used for this research. Turbidity and suspended solids(SS) are 14.2 NTU and 10.4 mg/L respectively. This condition causes fouling for membrane process. The flux decline could be reduced when coagulation pretreatment was carried out. Optimal coagulations PAC which are commonly used in the sewage treatment plant was observed in this research. The results indicate that an optimal coagulation dose and pH are 80 ppm and pH of 7 respectively, but coagulation efficiency was lower at strong acid or strong base. Results showed that continuous and steady operations in membrane separation process by means of the effective removal of organic matter and turbidity with coagulation pretreatment of sewage secondary effluent were achieved.

Fischer–Tropsch synthesis: Effect of promoter type on alumina-supported Mo carbide catalysts

Molybdenum carbide catalysts promoted with K, Na, Co, and Ce have been synthesized by temperature-programmed carburization using a mixture of H 2/C 3H 8 and evaluated for the Fischer–Tropsch synthesis. Both α- and β-Mo carbide catalysts were produced during carburization via the formation of oxycarbide intermediate phase. The two-stage Mo carbide synthesis appeared to be characterized by a compensation effect and isokinetic relationship for both promoted and undoped catalysts suggesting that the solid state transformation mechanism was similar across the promoters. The catalysts possessed relatively high BET area (177–210 m 2 g cat −1) with finely dispersed Mo carbide particles (ca. 10 nm) on the alumina support. The presence of weak and strong acid–base sites was also confirmed by NH 3 and CO 2-TPD runs. CO hydrogenation rate increased with H 2 composition reaching optimal activity at y H 2 between 0.67 and 0.75. FT activity improved with promoter addition in the order; K–MoC 1− x /Al 2O 3 > Na–MoC 1− x /Al 2O 3 > Ce–MoC 1− x /Al 2O 3 > Co–MoC 1− x /Al 2O 3 > MoC 1− x /Al 2O 3 while chain growth probability varied with feed composition and was enhanced by all promoters. The reaction rate data were adequately described by an Eley–Rideal model.

Guest release and solution behavior of a hydrogen-bonding physical micelle during chemoresponsive shell disruption

The guest release and solution behavior during shell disruption of a polymeric nanocapsule are described. Hyperbranched polyethylenimine (PEI, M n = 10 000) is chemically functionalized with multiple DAD hydrogen-bonding motifs (D and A: hydrogen-bonding donor and acceptor), leading to PEI 232–(DAD) x ( 3) ( x = 93 ( 3a), x = 46 ( 3b), x = 23 ( 3c), x = 12 ( 3d)). Meanwhile, polyethylene oxide ( M n = 2 200) is end-capped with thymine moieties (PEO–ADA) ( 4). Mixing of the hydrogen-bonding complementary 3 and 4 (DAD/ADA = 1) leads to a physical micelle ( 3· 4) in apolar media, and the resulting micelle can completely and irreversibly transfer the ionic and water-soluble Congo red (CR) into chloroform phase by encapsulation. Experiment proves that the micelle can exist as a pseudo-unimolecular micelle ( p-UIM, meaning one PEI in one micelle) or as aggregate, depending on the shell density. As a result, 3b· 4 generally exists as a p-UIM while 3d· 4 can exist as p-UIM only in a very narrow range of concentrations. The critical aggregation concentration (CAC) is also dependent on the core structure of the micelle, thus when the residual amines in the core of 3b are transformed into amide, the resulting 5b· 4 shows a very low CAC. Small chemicals bearing DAD hydrogen-bonding motif can compete to bind with the PEO–ADA shell and destruct the p-UIM, leading to aggregation and precipitation of the p-UIM along with the CRs. Experiment proves that the CR has strong acid–base interaction with the PEI core of the p-UIM, but when the basicity of the PEI core is reduced by amidation, partial CRs can be released into the water phase.

Comparative study on sample stacking by moving reaction boundary formed with weak acid and weak or strong base in capillary electrophoresis: II. Experiments

To demonstrate the theoretic method on the stacking of zwitterion with moving reaction boundary (MRB) in the accompanying paper, the relevant experiments were performed. The experimental results quantitatively show that (1) MRB velocity, including the comparisons between MRB and zwitterionic velocities, possesses key importance to the design of MRB stacking; (2) a much long front alkaline plug without sample should be injected before the sample injection for a complete stacking of zwitterion if sample buffer is prepared with strong base, conversely no such plug is needed if using a weak base as the sample buffer with proper concentration and pH value; (3) the presence of salt in MRB system holds dramatic effect on the MRB stacking if sample solution is a strong base, but has no effect if a weak alkali is used as sample solution; (4) all of the experiments of this paper, including the previous work, quantitatively manifest the theory and predictions shown in the accompanying paper. In addition, the so-called derivative MRB-induced re-stacking and transient FASI-induced re-stacking were also observed during the experiments, and the relevant mechanisms were briefly demonstrated with the results. The theory and its calculation procedures developed in the accompanying paper can be well used for the predictions to the MRB stacking of zwitterion in CE.

Analysis of the Wettability of Partially Fluorinated Polymers Reveals the Surprisingly Strong Acid-Base Character of Poly(vinylidene Fluoride)

The wettabilities of the partially fluorinated polymers (ethylene-tetrafluoroethylene copolymer (ETFE), ethylene- chlorotrifluoroethylene copolymer (ECTFE), and poly(vinylidene fluoride) (PVDF)) were investigated by contact angle measurements. Zisman plots for ETFE and ECTFE exhibited linear relationships, while the Zisman plot for PVDF show- ed a slight curvature, which was interpreted to indicate strong non-dispersive interactions between the surface and the contacting liquids. The Lifshitz-van der Waals forces of the fluoropolymers were estimated to increase in the order of ETFE < PVDF << ECTFE. An evaluation of the polar or interaction energies showed that PVDF, which possesses the most acidic hydrogens among the examined fluoropolymers, has the strongest acid-base interactions.

Spontaneous gradual accumulation of hexagonally-aligned nano-silica on gold nanoparticles embedded in stabilized zirconia: a pathway from catalytic to NH3-sensing performance

The present study highlights the influence of nano-impurities on the catalytic/sensing performance of nano-structured Au sensing-electrodes (SEs) housed in a quartz reactor and operated at high temperature over a long period of time. The planar sensor, made from a nano-structured Au-SE on a polished-polycrystalline (pp) yttria-stabilized zirconia (YSZ) substrate exhibited initially negligible electromotive force (emf) response to each of the examined gases (CO, CH(4), C(3)H(8), C(3)H(6), NO(x) and NH(3); 400 ppm each) at 700 °C in the presence of 5 vol.% oxygen and 5 vol.% water vapor. Such a poor emf response was attributed to the excellent gas-phase oxidation/reduction ability of Au nanoparticles embedded in the YSZ substrate at high temperature. The response of the planar sensor made up of nano-structured Au-SE was monitored for about 75 days at 700 °C. As a result of this long-term monitoring, we detected the appearance of highly sensitive and selective NH(3) gas-sensing properties after 45-75 days of sensor operation. Detailed observation of the morphology and composition of the as-fabricated nano-structured Au-SE after 75 days operation at 700 °C revealed the gradual accumulation of hexagonally-aligned SiO(2) nano-impurities on the surface of the Au nanoparticles. The NH(3) sensing mechanism of the YSZ-based sensor using the spontaneously-formed composite (nano-Au + nano-SiO(2))-SE is therefore proposed to be based on a strong acid-base interaction between gaseous NH(3) and SiO(2) nano-impurities, followed by spillover of adsorbed NH(3) towards the nano-Au/pp-YSZ interface.