Strong Acidic Conditions Research Articles

Short Review on the Synthesis of Thiophene, Pyrazole, and Thiazole Derivatives

The review summarizes the synthesis of different thiophene, pyrazole, and thiazole derivatives by refluxing 9a in ethanol with a catalytic amount of TEA or leaving it in DMF containing potassium carbonate at room temperature overnight to afford the corresponding thiophene derivative 10a. In addition, cyclization of Schiff bases with thioglycollic acid in the presence of a catalytic amount of ZnCl2 yielded novel thiophene derivatives. Condensation of 2‐substituted‐4‐methylythio semi‐carbazides 92 with carbonyl compounds under strong acidic conditions afforded 2‐thiazolines. Also, carboxylic acid reacted with 2‐thioethylamine in the presence of triphenylphosphine and triethylamine to afford 2‐thiazolines 98.

Electrochemical Conversion of Fe3O4 Magnetic Nanoparticles to Electroactive Prussian Blue Analogues for Self-Sacrificial Label Biosensing of Avian Influenza Virus H5N1.

A serious impetus always exists to exploit new methods to enrich the prospect of nanomaterials. Here, we report electrochemical conversion (ECC) of magnetic nanoparticles (MNPs) to electroactive Prussian blue (PB) analogues accompanied by three interfacial effects and its exploitation for novel label self-sacrificial biosensing of avian influenza virus H5N1. The ECC method involves a high-potential step to create strong acidic condition by splitting H2O to release Fe3+ from the MNPs, and then a low-potential step leading to the reduction of coexisting K3Fe(CN)6 and Fe3+ to K4Fe(CN)6 and Fe2+, respectively, which react to form PB analogues. Unlike conventional solid/liquid electrochemical interfaces that need a supply of reactants by transportation from bulk solution and require additional template to generate porosity, the proposed method introduces MNPs on the electrode surface and makes them natural nanotemplates and nanoconfined sources of reactants. Therefore, the method presents interesting surface templating, generation-confinement, and refreshing effects/modes, which benefit the produced PB with higher porosity and electrochemical activity, and 3 orders of magnitude lower requirement for reactant concentration compared with conventional methods. Based on the ECC methods, a sandwich immunosensor is designed for rapid detection of avian influenza virus H5N1 using MNPs as self-sacrificial labels to produce PB for signal amplification. Taking full advantages of the high abundance of Fe in MNPs and three surface effects, the ECC method endows the biosensing technology with high sensitivity and a limit of detection down to 0.0022 hemagglutination units, which is better than those of most reported analogues. The ECC method may lead to a new direction for application of nanomaterials and new electrochemistry modes.

Effect of pH conditions on the depolymerization of Wucaiwan coal by mixed acids/ultrasound method and the product structures and performance

The cleavage of the aliphatic chain or ether bond connecting the polycyclic aromatic hydrocarbons in coal can be achieved by not only hydrogenation reduction but also oxidative acid treatment. In this paper, coal samples from Wucaiwan in Xinjiang were pretreated with HNO3 followed by mixed acids/ultrasound treatment. The depolymerized coal samples obtained under different pH conditions were then separated by fractional washing. The structures and properties of the resulting coal samples were studied by elemental analysis, FT-IR, XRD, TG–DTA, TEM, UV–Vis, and PL. The results showed that when pH = 0.012, the obtained coal samples were fragments stripped off from the raw coal samples by ultrasound in strong acid conditions, aliphatic hydrocarbons linked with oxygen-containing groups such as nitro group, a small amount of small aromatic molecules and mineral salts; when pH = 1.99–4.09, the obtained coal samples were polycyclic aromatic hydrocarbons linked with oxygen-containing groups such as nitro group,possessing the annulus wall of multilayer graphene fragment structures built up by sp2 carbons, and they are typical fluorescent substances of carbon nanoparticle structure. The former has no solubility in organic solvents, while the latter can be well dissolved in polar solvents such as acetone. All the depolymerized coal samples obtained under different pH conditions exhibited good absorption and ability of fluorescence emission.Graphical

Stable and ordered amide frameworks synthesised under reversible conditions which facilitate error checking

AbstarctCovalent organic frameworks (COFs) are network polymers with long-range positional order whose properties can be tuned using the isoreticular chemistry approach. Making COFs from strong bonds is challenging because irreversible rapid formation of the network produces amorphous materials with locked-in disorder. Reversibility in bond formation is essential to generate ordered networks, as it allows the error-checking that permits the network to crystallise, and so candidate network-forming chemistries such as amide that are irreversible under conventional low temperature bond-forming conditions have been underexplored. Here we show that we can prepare two- and three-dimensional covalent amide frameworks (CAFs) by devitrification of amorphous polyamide network polymers using high-temperature and high-pressure reaction conditions. In this way we have accessed reversible amide bond formation that allows crystalline order to develop. This strategy permits the direct synthesis of practically irreversible ordered amide networks that are stable thermally and under both strong acidic and basic hydrolytic conditions.

A coordinated sequence of distinct flagellar waveforms enables a sharp flagellar turn mediated by squid sperm pH-taxis

Animal spermatozoa navigate by sensing ambient chemicals to reach the site of fertilization. Generally, such chemicals derive from the female reproductive organs or cells. Exceptionally, squid spermatozoa mutually release and perceive carbon dioxide to form clusters after ejaculation. We previously identified the pH-taxis by which each spermatozoon can execute a sharp turn, but how flagellar dynamics enable this movement remains unknown. Here, we show that initiation of the turn motion requires a swim down a steep proton gradient (a theoretical estimation of ≥0.025 pH/s), crossing a threshold pH value of ~5.5. Time-resolved kinematic analysis revealed that the turn sequence results from the rhythmic exercise of two flagellar motions: a stereotypical flagellar ‘bent-cane’ shape followed by asymmetric wave propagation, which enables a sharp turn in the realm of low Reynolds numbers. This turning episode is terminated by an ‘overshoot’ trajectory that differs from either straight-line motility or turning. As with bidirectional pH-taxes in some bacteria, squid spermatozoa also showed repulsion from strong acid conditions with similar flagellar kinematics as in positive pH-taxis. These findings indicate that squid spermatozoa might have a unique reorientation mechanism, which could be dissimilar to that of classical egg-guided sperm chemotaxis in other marine invertebrates.

One-Step Synthesis of Acidophilic Highly-Photoluminescent Carbon Dots Modified by Ionic Liquid from Polyethylene Glycol.

Acidophilic highly-photoluminescent ionic liquid (IL)-modified carbon dots (CDs) were fabricated directly from polyethylene glycol-2000 (PEG2000N) by a simple one-step hydrothermal method in a system containing an IL (1-butyl-3-methylimidazolium bromide [C4mim]Br) and hydrochloric acid (HCl). In this process, PEG2000N works as the carbon source, [C4mim]Br as the modifier, and HCl as the accelerator. CDs with low photoluminescence (PL) intensity and quantum yields (QYs) were generated in the system without H+, but CDs with high PL intensity and QYs could be prepared after H+ was introduced. Moreover, with the increase of H+ concentration, the QYs of the prepared CDs increase subsequently, and the highest QY reaches up to 43%. The formation mechanism was explored, and the results showed that H+ changes the surface groups of the CDs generated without H+ into those that exist on the CDs generated with H+, which further improves the PL performance of the CDs. Different from most CDs reported in the literature, the as-prepared CDs can still exhibit high PL intensity even under strong acidic condition.

Influence of pH on the UV photolysis of N-nitrosamines in water: Kinetics and products

Amine-based post-combustion CO2 capture is recognized as a promising technique for abating CO2 emissions from anthropogenic sources. A severe drawback of this technique, however, is the formation of carcinogenic N-nitrosamines as a by-product. In this study, the effect of pH was investigated on the UV photodegradation of N-nitrosamines (N-nitrosodiethanolamine (NDELA), N-nitrosodiethylamine (NDEA), and N-nitrosomorpholine (NMOR)) which are closely related to the amine-based CO2 capture technology. A decrease in pseudo-first-order degradation rate constants was observed for NDELA (2.49×10−2–6.48×10−3L/W-min), NDEA (1.56×10−2–5.25×10−4L/W-min), and NMOR (1.68×10−2–7.00×10−4L/W-min) with an increase in pH2−10. The formation of NO2− was more prevalent than that of NO3− at pH4−10, while under strong acidic condition (pH2) NO3− formation was more prevalent. The concentration of secondary amines (diethanolamine, diethylamine, and morpholine) increased from basic (pH10) to weakly acidic conditions (pH4) and then decreased at pH2. Whereas, the concentration of primary amines (monoethanolamine and ethylamine) followed the opposite trend. Furthermore, mechanistic pathways were revealed for N-nitrosamine photodegradation based on the degradation products. A good total nitrogen (TN) balance over the irradiation period confirmed that all the main degradation products were quantified.

Data reconciliation strategy with time registration for the evaporation process in alumina production

In real industrial production, many mass and heat transfer processes are influenced by high temperature, high pressure, and even strong acid or alkali conditions. In addition, some important variables cannot be measured and chemical compositions are analyzed offline with a long time delay, which leads to inaccurate measurements of the process data. In this paper, a layered data reconciliation (LDR) method based on time registration is proposed to improve the measurement accuracy and estimate unmeasured variables. Considering that the material cannot be tagged and tracked in process manufacturing, a temporal and spatial matching strategy for the process data is designed based on a time‐correlation analysis matrix which is determined to describe the correlation of each time sequence in the data matrix. Then, a layered data reconciliation model with time registration is developed by reconciling the mass balance layer and the heat balance layer separately and stepwise, and the model is solved by the state transition algorithm. Meanwhile, regular terms and engineer's knowledge are introduced into the data reconciliation model to solve the problem of insufficient redundancy. The industrial verification results from the actual industrial evaporation process indicate that the accuracy of measured values is improved by using the proposed reconciliation strategy.

Removal of fluoride from zinc sulfate solution by in situ Fe(III) in a cleaner desulfuration process

The desulfuration of fume gas using ZnO slurry is a cleaner process because the SO2 from exhaust is transformed to a valuable ZnSO4 solution, and the ZnSO4 solution can then be reused in industrial processes. However, the existence of fluoride (F) in the cleaner process severely hinders the reuse of the ZnSO4 solution. In this study, an innovative, targeted and simple technique using in situ Fe(III) in the actual ZnSO4 waste liquid for the removal of F was proposed. The results indicated that in situ Fe(III) exhibited a good performance in the removal of F and an increase of Fe concentration is beneficial to the removal of F. The active component in the removal of F was identified as a type of hydroxylation ferric sulfate, schwertmannite, which formed under the strong acidic condition. The removal mechanism of F was recognized as an ionic-exchange with the OH− groups from coordinated FeOH−1/2 and Fe2OH0 and SO42− groups in schwertmannite as well as electrostatic adsorption interactions. Based on above principle, the concentration of F in the actual ZnSO4 solution was successfully reduced to below 50 mg/L, bringing the ZnSO4 solution up to the recycling standard. This research can be used to guide the effective removal of F from the waste liquid with high acidity, salinity and heavy metals, in the practice.

On the synthesis of RuSe oxygen reduction nano-catalysts for direct methanol fuel cells

Oxygen reduction reaction has a crucial role in energy conversion systems such as fuel cells. State-of-the-art Pt-based cathode catalysts suffer from low efficiency which is severely affected by poisoning of methanol fuel crossing the membrane that separates the electrodes and high cost. We have synthesized a non-platinum RuSe 3–15-nm in size catalysts using microwave irradiation technique, which produces nanomaterials at high efficiency and short time spans. Several Ru/Se atomic ratios of RuSe were prepared using both elemental Se powder and H2SeO3 as precursors. The structure and composition of the obtained materials were characterized using XRD, EDX, ICP-OES, and DSC/TGA. Electrochemical study of oxygen reduction reaction (ORR) on these catalysts was conducted using rotating disk electrode (RDE) technique, from which the Tafel slopes and exchanged current densities of ORR were calculated. The use of H2SeO3 as the Se source provides catalysts with controlled composition. All obtained materials show good electrocatalytic activity towards oxygen reduction and maintain high activity in the presence of high methanol contamination. A rigorous kinetic study of ORR on RuSe catalysts show that at Ru to Se ratio is 2 to 1, and the highest kinetic currents are attained. Stability tests at 0.4 V in strong acidic conditions and elevated temperatures, for over 600 hours, exhibit no degradation.

The application of illite supported nanoscale zero valent iron for the treatment of uranium contaminated groundwater

In this study, nanoscale zero valent iron I-NZVI was investigated as a remediation strategy for uranium contaminated groundwater from the former Cimarron Fuel Fabrication Site in Oklahoma, USA. The 1 L batch-treatment system was applied in the study. The result shows that 99.9% of uranium in groundwater was removed by I-NZVI within 2 h. Uranium concentration in the groundwater stayed around 27 μg/L, and there was no sign of uranium release into groundwater after seven days of reaction time. Meanwhile the release of iron was significantly decreased compared to NZVI which can reduce the treatment impact on the water environment. To study the influence of background pH of the treatment system on removal efficiency of uranium, the groundwater was adjusted from pH 2–10 before the addition of I-NZVI. The pH of the groundwater was from 2.1 to 10.7 after treatment. The removal efficiency of uranium achieved a maximum in neutral pH of groundwater. The desorption of uranium on the residual solid phase after treatment was investigated in order to discuss the stability of uranium on residual solids. After 2 h of leaching, 0.07% of the total uranium on residual solid phase was leached out in a HNO3 leaching solution with a pH of 4.03. The concentration of uranium in the acid leachate was under 3.2 μg/L which is below the EPA's maximum contaminant level of 30 μg/L. Otherwise, the concentration of uranium was negligible in distilled water leaching solution (pH = 6.44) and NaOH leaching solution (pH = 8.52). A desorption study shows that an acceptable amount of uranium on the residuals can be released into water system under strong acid conditions in short terms. For long term disposal management of the residual solids, the leachate needs to be monitored and treated before discharge into a hazardous landfill or the water system. For the first time, I-NZVI was applied for the treatment of uranium contaminated groundwater. These results provide proof that I-NZVI has improved performance compared to NZVI and is a promising technology for the restoration of complex uranium contaminated water resources.

The detection of copper ions based on photothermal effect of cysteine modified Au nanorods

The cysteine (CYS)-stimulated aggregation of Au nanorods (NRs) is used as an auxiliary reporting system for the optical detection of copper ions. CYS-Au NRs show end-to-end and side-by-side assembly at strong acidic and basic condition, and corresponding LSPR peaks shift to red or blue. However, Cu2+ can readily induce the end-to-end assembly of CYS-Au NRs based on the coordination between Cu2+ and CYS at weak acidic condition (pH 5). The assembly of Cu2+-CYS-Au make the decrease of LSPR peak at 800nm and appear a new peak at 1050nm, which reduce their photothermal conversion efficiency under 808nm laser irradiation. The different photothermal conversion efficiency has relation with the temperature change of Au NRs solution. So, a new nanosensor for detecting Cu2+ is developed based on the varied photothermal effect. Different from colorimetric detection for Cu2+, the sensor of photothermal effect is more sensitive to low concentration of Cu2+. It shows high sensitivity and selectivity. Here, the detection limit for Cu2+ is 5nM.

Gadolinium Complex for the Catch and Release of Phosphate from Water.

The ability of complexes of hard and labile metal ions with one or more open coordination sites to capture phosphates with high affinity and selectivity directly in water at neutral pH and release them under acidic conditions is evaluated with Gadolinium- 2,2',2''-(((nitrilotris(ethane-2,1-diyl))tris(azanediyl))tris(carbonyl))tris(4-oxo-4H-pyran-3-olate) (Gd-TREN-MAM). This model lanthanide complex has two open coordination sites that, at neutral pH, are filled with water molecules. In water at neutral pH, Gd-TREN-MAM binds phosphate with high affinity (Ka = 1.3 × 104) via the formation of a ternary complex in which one phosphate replaces both inner-sphere water molecules. The formation of this complex is highly pH-dependent; the phosphate is completely released from Gd-TREN-MAM below pH 2. Because the GdIII ion remains complexed by its ligand, even under strong acidic conditions, Gd-TREN-MAM can be used at least 10 times in a pH-based recycling scheme that enables the catch and release of one phosphate per cycle. Gd-TREN-MAM is highly selective for phosphate over other anions of environmental concerns, including HCO3-, HCO2-, CH3CO2-, SO42-, NO3-, NO2-, BrO3-, AsO4-, F-, Cl-, and Br- and, to a lesser extent, ClO3-. The development of such receptors that bind phosphate reversibly in a pH-dependent manner opens the possibility to design catch-and-release systems for the purification of surface waters.

Melamine Formaldehyde Modified Furfurylation to Improve Chinese Fir’s Dimensional Stability and Mechanical Properties

Melamine formaldehyde modified furfurylation (MFMF) was developed in this investigation to overcome the issues encountered by traditional wood furfurylation, the strong acidic reaction condition and the high cost of furfuryl alcohol. In this study, the optimum ratio of melamine, formaldehyde, and furfuryl alcohol constituents and the optimum curing conditions were explored. Then, MFMF was applied to Chinese fir modification and its performance was evaluated by the weight gain rate (WGR), equilibrium moisture content (EMC), dimensional stability (anti-swelling efficiency [ASE]), and parallel-to-grain compressive strength. The results showed that MFMF took place at a pH close to neutral (6.8) and the formulas had good penetration of cell walls. The best stability and improvement to mechanical properties achieved by MFMF were: a WGR of 158.9%; a low EMC of 11.5% under 96% relative humidity conditions; an ASE in high humidity and water-soaked conditions of 58.5% and 64.2%, respectively; and an increase in parallel-to-grain compressive strength by 81.9%, when compared with the control.

Electrochemical properties of Ti3O5 powders prepared by carbothermal reduction

In this work, Ti3O5 powders were successfully synthesized from anatase-TiO2 by carbothermal reduction method. The products synthesized in different carbon black content and reduction temperature were investigated. The results show that Ti3O5 powders with a small amount of Ti4O7 can be obtained with carbon black content of 3.8 wt% at 1300 °C for 3 h in vacuum. The Ti3O5 particles were uniformly and not agglomerated, and the average particle diameter is 3.23 µm. The cyclic voltammetry method was used to investigate the electrochemical properties of Ti3O5. The results show that Ti3O5 powders have good electrochemical activities and electrochemical stability under strong sulfuric acid and alkaline conditions.

Highly Efficient Adsorption of Rh(III) from Chloride Containing Solutions by Triazine Polyamine Polymer

Adsorption of Rh(III) ions from the aqueous phase containing chloride ions was investigated batchwise using 1,3,5-triazine pentaethylenehexamine (TAPEHA) resin, which is highly resistant to strong acidic conditions. The effects of pH, temperature, initial concentration, and contact time on adsorption were examined. Rh(III) adsorption is favorable from the aqueous phase containing 3.0 and 0.1 M HCl. In both acidic cases, Langmuir is best fitting isotherm equation to system. The kinetics of Rh(III) adsorption on TAPEHA polymer was found to obey the pseudo-second-order kinetic equation, at both cases. Langmuir monolayer adsorption capacities were calculated as 327.03 and 113.76 mg/g in 3.0 and 0.1 M HCl, respectively. Experimental maximum adsorption capacities were measured as 198 and 100 mg/g in 3.0 and 0.1 M HCl, respectively. Due to different Rh(III) complexes with chlorine depending on acid concentrations, adsorption of Rh(III) from solutions containing 3.0 and 0.1 M HCl occurred via two different mechanisms; namely, ion exchange and surface complexation. The reuse of TAPEHA was also studied by column procedure, and the adsorption capacity of TAPEHA was not changed by using it five times. Adsorbed Rh(III) ions onto TAPEHA were completely eluted with thiourea 3% (w/v) in 1.0 M HCl. These findings showed that TAPEHA has a high resistance to acidic solutions and a higher Rh(III) uptake capacity than commercial adsorbents. Hence it can be used for rhodium recycling.

Stable Covalent Organic Frameworks for Exceptional Mercury Removal from Aqueous Solutions.

The pre-designable porous structures found in covalent organic frameworks (COFs) render them attractive as a molecular platform for addressing environmental issues such as removal of toxic heavy metal ions from water. However, a rational structural design of COFs in this aspect has not been explored. Here we report the rational design of stable COFs for Hg(II) removal through elaborate structural design and control over skeleton, pore size, and pore walls. The resulting framework is stable under strong acid and base conditions, possesses high surface area, has large mesopores, and contains dense sulfide functional termini on the pore walls. These structural features work together in removing Hg(II) from water and achieve a benchmark system that combines capacity, efficiency, effectivity, applicability, selectivity, and reusability. These results suggest that COFs offer a powerful platform for tailor-made structural design to cope with various types of pollution.

Reversible Absorption and Emission Responses of Nile Blue and Azure A Derivatives in Extreme Acidic and Basic Conditions.

Oxazinium derivatives have recently played an important role in bioanalysis attributing to the distinguished properties, thus a detailed study of the structure-property relationship is especially significant. Herein, pH-sensitive optical properties of Nile Blue (1a), N-monoalkyl-Nile Blue (1b) and Azure A (1c) have been carried out in extreme acid and base conditions. Dyes 1a and 1c showed colorimetric changes by the protonation of nitrogen atom in strong acidic condition (pH<2.0), and dyes 1a-c exhibited colorimetric changes by equilibrium between amino and imide groups in very strong basic case (pH>7.6). Besides, their fluorescent properties were closed to ON-OFF and OFF-ON emissions at 640-820nm under strong acidic and basic conditions. Moreover, the absorption and emission properties were reversible, and there were no remarkable optical intensity changes of dyes 1a-c under subacidic and neutral solutions (pH=3.0-7.0). The (TD) DFT calculations were used to optimize the most stable structures of their corresponding protonated and deprotonated forms, and their absorption and emission properties were also explained. Their fluorescent properties nearly ON-OFF and OFF-ON in strong acidic and basic conditions at near-infrared region will give the possible application in pH detection for extreme conditions. Graphical abstract ᅟ.

Influence of acidic pH on the formulation of TiO2 nanocrystalline powders with enhanced photoluminescence property.

Titanium dioxide (TiO2) nanoparticles were prepared by the sol-gel method at different pH values (3.2–6.8) with a hydrochloric acid (HCl) solution. Raw samples were calcined at 500 °C for 2 h. The effects of pH on the structural, morphological and optical properties of TiO2 nanoparticles were investigated. At pH 4.4–6.8, only the anatase phase of TiO2 was observed. Under strong acidic condition at pH 3.2 rutile, brookite and anatase co-exist, but rutile is the predominant phase. The strain value increased and the crystallite size decreased as the HCl content increased. The increased crystallite sizes in the range 21–24 nm and enhanced blue emission intensity around 432 nm was obtained for the sample at pH 5.0. Experimental results showed that TiO2 nanoparticles synthesized at pH 5.0 exhibited the best luminescence property with pure anatase phase.

Tuning the Crystal Structure Dimensionality of Cobalt(II)/1,2,4-Triazole Complexes

To control the structure dimensionality of hybrid materials, a common approach consists of selecting ligands with specific bridging modes. Herein, we show that the bridging mode for some azole ligands with Co(II) metal ions can be tuned in situ using different synthesis conditions. For example, the dimensionality of 1,2,4-triazole based materials could be controlled according to their (de)protonation. Under hydrothermal conditions, deprotonation commonly occurs and leads to the tripodal moiety that favors a high dimensional crystal structure. To target low-dimensional 1,2,4-triazole based cobalt materials, deprotonation was prevented by carrying out hydrothermal syntheses under strong acidic conditions. With this strategy, two new compounds with low dimensional crystal structures were obtained: Co(Htrz)Cl2 (1) exhibiting one-dimensional coordination polymers and [Co3(Htrz)6(H2O)6][ZnBr4]3·9H2O (2) containing Co trinuclear complexes (Htrz = 1,2,4-triazole). Magnetic measurements showed weak antiferromagnet...