HCl Aqueous Solution Research Articles

The Role of Fluorine-Substituted Positions on the Phase Transition in Organic-Inorganic Hybrid Perovskite Compounds.

Although research on organic-inorganic hybrid perovskites (OIHPs) has grown exponentially in the past two decades, the high phase transition temperature of OIHP materials is still one of the insurmountable difficulties. Herein, a series of A2BX4 type OIHP materials [(2,n-DFBA)2PbCl4] (n = 3, for 1; n = 4, for 2; n = 5, for 3; n = 6, for 4) have been prepared by reactions of double-substituted difluorobenzylamine (difluorobenzylamine = DFBA) with lead chloride in concentrated HCl aqueous solution. It was found the OIHP compounds 1-3 proceed a switchable phase transition with phase transition temperatures (Tc) at 449 K (1), 462 K (2) and 500 K (3), higher than that of the parent compound [(BA)2PbCl4] (BA = benzylammonium) at 438 K, but compound 4 exhibits no phase transition. A crystal structure analysis elucidated that the organic template ligands DFBA lead in the inorganic part in compounds 1-3 to a two-dimensional (2D) perovskite structure, while that in compound 4 leads to a one-dimensional (1D) chain structure. The different double-substituted positions of fluorine atoms on benzylamine have important influences on the phase transition in compounds 1-4.

Effects of alkali and alkaline earth metals of inherent minerals on Fe-catalyzed coal pyrolysis

In this work, the effects of alkali and alkaline earth metals (AAEM (K, Na, Ca and Mg)) on Fe (5 wt%) loaded-coal pyrolysis were conducted using the fixed-bed reactor at 700 °C with 0.1 MPa N2. The coal was pretreated by HCl and HF aqueous solutions (De-2 coal). These effects were investigated with AAEM additive into Fe loaded De-2 coal. The results indicate that K, Na, Ca and Mg (0.1 wt%-1.5 wt%) enhanced the catalytic effect of Fe catalyst, leading to the high H2 selectivity (59.34 ml/g →85.94 ml/g), as well as the low yield toward CO2 (157.50 ml/g →148.62 ml/g), and the catalytic activity follows the order of Na ≈ K > Ca > Mg. Characterization results reveal that the inherent AAEM promote the reduction of Fe species and the dispersion of Fe particles. The reason for that was AAEM combined with oxygen-containing functional group generated C–O-AAEM and COO-AAEM, and released active oxygen sites to activate carbon sites, leading to Fe catalyst bound with active oxygen sites formed iron oxide and Fe-(O)–C on char surface. This study was helpful to understand the promotion mechanism of AAEM on Fe catalyzed coal pyrolysis.

Novel Immobilized Ligand on Polymer Matrix as Adsorbent for Water Purification

Abstract A novel polymer material that is capable of adsorption of Pb2+ and Cu2+ in aqueous solutions has been synthesized. 3-Aminopropyltriethoxysilane was reacted with tetraethylethoxysilane in methanol and aqueous solution of HCl to yield 3-aminopropypolysiloxane (APP). Reacting the APP with ethylchloroacetate in triethylamine yielded a functionalized 3-aminopropypolysiloxane (FAPP). The FAPP was reacted with urea to yield urea immobilized polysiloxane. FTIR spectra of the APP showed major absorption bands (cm−1) at: 1032.5-1042.7 (Si-O-Si), while the Urea-immobilized polysiloxanes (APPU) showed major absorption bands (cm−1) at: 3200 − 3400 υ(NH), 2929 − 2957 υ(C-H), 1505-1643 (C=O, C=C, C=N), and 1032.5-1042.7 (Si-O-Si). SEM-EDX analysis of APP and APPU showed mean pore volumes (nm3) of 113.49 ± 7.91 and 44.89 ± 7.44 respectively, and elemental composition (%) as follows: APP, O (36.68), Si (39.91); FAPP, O (29.43), Si (41.64), Cl (9.06); APPU, O (32.15), Si (28.42), N (25.42). APP maximum percentage adsorption of Pb2+ and Cu2+ in simulated water were 79.44 and 74.81 respectively, while APPU maximum percentage adsorption of Pb2+ and Cu2+ were in the range of 78.36 − 85.44 and 79.63 − 82.87 respectively. The maximum percentage adsorption of Pb2+ and Cu2+ which indicate the sorption capacities of the adsorbents occurred within the pH range of 8-10, contact time between 70-90 min, metal ion concentration of 20-25 ppm, dosage of adsorbent of 0.01 − 0.03 g for Pb2+ adsorption, and 0.04 − 0.05 g for Cu(II), and at a temperature of 90°C. The statistical analyses showed significant difference in the means of the effects of pH, time and concentration as F > Fcrit, except in the case of contact time for Cu2+. Temkin isotherm gave values of R2 in the range of 0.9210 − 0.9735 and best fitted the adsorption process. The urea immobilized polysiloxane (APPU) exhibited very high potential for adsorption of Pb2+ and Cu2+ in industrial effluent up to 100 %.

Dynamics of Ion Pairing in Dilute Aqueous HCl Solutions by Spectroscopic Measurements of Hydroxyl Radical Conversion into Dichloride Radical Anions.

The rate of formation of dichloride anions (Cl2•–) in dilute aqueous solutions of HCl (2–100 mmol·kg–1) was measured by the technique of pulse radiolysis over the temperature range of 288–373 K. The obtained Arrhenius dependence shows a concentration averaged activation energy of 7.3 ± 1.8 kJ·mol–1, being half of that expected from the mechanism assuming the •OHCl– intermediate and supporting the ionic equilibrium-based mechanism, i.e., the formation of Cl2•– in the reaction of •OH with a hydronium–chloride (Cl–·H3O+) contact ion pair. Assuming diffusion-controlled encounter of the hydronium and chloride ions and including the effect of the ionic atmosphere, we showed that the reciprocal of τ, the lifetime of (Cl–·H3O+), follows an Arrhenius dependence with an activation energy of 23 ± 4 kJ·mol–1, independent of the acid concentration. This result indicates that the contact pair is stabilized by hydrogen bonding interaction of the solvent molecules. We also found that at a fixed temperature, τ is noticeably increased in less-concentrated solutions (mHCl < 0.01 m). Since this concentration effect is particularly pronounced at near ambient temperatures, the increasing pair lifetime may result from the solvent cage effect enhanced by the presence of large supramolecular structures (patches) formed by continuously connected four-bonded water molecules.

Nanotubular OMS-2 Supported Single-Atom Platinum Catalysts Highly Active for Benzene Oxidation

The cryptomelane-type octahedral molecular sieve (OMS-2) exhibits excellent catalytic activity for the oxidation of volatile organic compounds (VOCs) due to its unique structure, and single-atom catalysts (SACs) have recently attracted much attention in heterogeneous catalysis. Herein, we adopted the hydrothermal redox reaction of KMnO4 and HCl aqueous solution at 120 °C for 12 h to first synthesize the nanotubular OMS-2 support and used the vitamin C and NaBH4 reduction methods to prepare the OMS-2-supported single-atom Pt and PtNP catalysts for benzene oxidation, respectively. It was found that the OMS-2-supported single-atom Pt catalyst with a Pt loading of 0.0383 wt % (0.0383Pt1/OMS-2) exhibited the best catalytic performance for benzene oxidation (a 90% benzene conversion was achieved at 189 °C and 20 000 mL g–1 h–1 (space velocity)), which was associated with its high surface oxygen vacancy density, good low-temperature reducibility, and strong benzene adsorption ability. It was also shown that benzene could be dissociated more readily over the supported single-atom Pt1 catalyst than over the supported PtNP catalyst, and the phenolates or benzoquinone as well as methyl groups, lipid, and vinyl species were the main intermediates in the oxidation of benzene over 0.0383Pt1/OMS-2. The results of this study are useful in developing the high-performance single-atom catalysts that can be applied for the oxidative removal of VOCs.

Preparation of a uniform thin-film Pd-Au electrocatalyst via electroreduction of a palladium hexacyanoferrate(II)-Au electrodeposit for alkaline oxidation of methanol

A uniform thin-film Pd-Au electrocatalyst on multiwalled carbon nanotubes/glassy carbon electrode was prepared via the electroreduction of a palladium hexacyanoferrate(II)-Au electrodeposit, which shows high catalysis performance for alkaline methanol oxidation. • Electrodeposition of palladium hexacyanoferrate(II) (PdHCF)-Au composite. • Electroreduction of the PdHCF-Au deposit. • Uniform Pd-Au thin film on multiwalled carbon nanotubes/glassy carbon electrode. • Alkaline electrocatalytic oxidation of methanol. • Electrogeneration of Prussian blue from K 3 [Fe(CN) 6 ] without added ionic iron. A multiwalled carbon nanotubes (MWCNTs) and then Pd-Au thin film modified glassy carbon electrode (GCE) was prepared for alkaline electrocatalytic oxidation of methanol, by means of the cathodic deposition of a composite of palladium hexacyanoferrate(II) and gold (PdHCF-Au) on a MWCNTs-modified GCE in 10 mM PdCl 2 + 10 mM K 3 [Fe(CN) 6 ] + 1.2 mM HAuCl 4 + 0.5 M KCl + 0.5 M HCl aqueous solution, and then the cathodic reduction of the PdHCF-Au deposit in an alkaline aqueous solution to yield a uniform thin-film Pd-Au electrocatalyst. The materials and electrodes were characterized by cyclic voltammetry (CV), scanning electron microscopy and X-ray energy dispersive spectrometry. Under the optimal conditions, the electrocatalytic methanol-oxidation peak current (CV, −0.8 V ~ 0.5 V, 50 mV/s) on Pd-Au (PdHCF-Au) /MWCNTs/GCE was 15.4 mA cm Pd −2 in 0.5 M aqueous KOH containing 1 M methanol, which is higher than those of the examined control electrodes and many reported Pd-based electrocatalysts. The use of electron-insulating PdHCF as a Pd precursor first suggested here can notably improve the Pd utilization and the electrocatalysis performance. The possible mechanism for the electrogeneration of Prussian blue from K 3 [Fe(CN) 6 ] in the absence of added ionic iron is also discussed.

Toward a mechanistic understanding of the magnetic field effect on N-80 carbon steel corrosion in aqueous HCl solution

PurposeThis study aims to describe the effect of magnetic field (MF) on the corrosion rate of N-80 carbon steel [N-80 carbon steel (CS)] in concentrated (12.5 Wt.%, 3.8 M) hydrochloric acid (HCl) using gravimetric weight loss (WL) measurements and potentiodynamic polarization (PDP) in various conditions at ambient temperature.Design/methodology/approachThe effects of MF intensity, magnetization time and elapsed time on corrosion rate (CR) reduction (η) were studied.FindingsThe experimental results show that pre-magnetization of HCl sharply decreases the corrosion rate of N-80 carbon steel (CS) in acid. The maximumηwas found to be 94%. The surface of CS was analyzed with scanning electron microscope in normal and magnetized acid.Originality/valueTo the best of the authors’ knowledge, no studies have delved into the effects of magnetization on the corrosion rate of CS in concentrated HCl solutions. All of the previous research studies deal with an external MF that is applied on the reaction cell, but the magnetization of fluid before coming in contact with CS is investigated for the first time. In the present work, the influence of MF on the corrosion rate of CS in HCl is illustrated using gravimetric WL and PDP methods. The effects of MF intensity as well as period of magnetization and elapsed time were verified in more than 35 tests.

Nepheline Syenite as an Alternative Source for Aluminum Production

The increasing demand for aluminum in conjunction with the limited available bauxite deposits in Europe results in the dire need for the evaluation of alternative raw materials for the whole value chain of alumina production. The present paper focuses on the possible use of nepheline syenite, originated as a mine byproduct, in alumina production through leaching with an azeotropic HCl solution. Previous work on nepheline syenite dissolution focused more on the extraction of potassium and sodium values. In this work, emphasis is given at the characteristics and leachability of aluminum content phases by applying a high temperature HCl leaching in untreated material. From this point of view, leaching experiments were conducted on nepheline syenite, at a temperature range of 90 °C to 150 °C and with aqueous azeotropic HCl solution. Leaching, in the aforementioned conditions, is a process, characterized by medium aluminum dissolution. The results show that the aluminum-bearing phases that withstand the dissolution process are mainly the ones of sodium and potassium feldspars.

G-C3N4 Sensitized by an Indoline Dye for Photocatalytic H2 Evolution

Protonated g-C3N4 (pCN) formed by treating bulk g-C3N4 with an aqueous HCl solution was modified with D149 dye, i.e., 5-[[4[4-(2,2-diphenylethenyl) phenyl]-1,2,3,3a,4,8b-hexahydrocyclopent[b]indol-7-yl] methylene]-2-(3-ethyl-4-oxo-2-thioxo-5-thiazolidinylidene)-4-oxo-thiazolidin-2-ylidenerhodanine, for photocatalytic water splitting (using Pt as a co-catalyst). The D149/pCN-Pt composite showed a much higher rate (2138.2 µmol·h−1·g−1) of H2 production than pCN-Pt (657.0 µmol·h−1·g−1). Through relevant characterization, the significantly high activity of D149/pCN-Pt was linked to improved absorption of visible light, accelerated electron transfer, and more efficient separation of charge carriers. The presence of both D149 and Pt was found to be important for these factors. A mechanism was proposed.

Comparative study of oxazolidine and imidazolidine compounds as inhibitors of SAE 1020 steel corrosion in aqueous HCl solution

In many industries, safe organic inhibitors that are soluble in corrosive media, environmentally friendly, and effective need to be developed for protection against corrosion during descaling and steel pickling in dilute acids. In this work we describe, for the first time, the effects of 2-(nitromethylene) oxazolidine (OXA) and 2-(nitromethylene) imidazolidine (IMD) as inhibitors of the corrosion of SAE 1020 steel in 0.1 mol L−1 HCl aqueous solution. Electrochemical analyses showed that the IMD inhibitor was most effective, acting as a mixed type inhibitor. SEM analysis confirmed the electrochemical results, clearly showing the excellent corrosion inhibition effect of IMD. The corrosion inhibition was related to the protective film deposited on the surface, forming a layer that reduced the corrosion reactions. DFT calculations showed that donor and acceptor interactions between the heterocyclic nitrogen lone pair electrons and the vacant d orbitals of the metal surface atoms could explain the better corrosion inhibition values obtained for IMD. Finally, in addition to its efficiency, in silico toxicity predictions indicated that IMD could be considered environmentally friendly.

Adding olivine micro particles to Portland cement based wellbore cement slurry as a sacrificial material: A quest for the solution in mitigating corrosion of wellbore cement

Invasion of Portland cement-based wellbore cement sheath and plugs by acidic subsurface geofluids (pH 2–5) causes compositional change due to leaching of Calcium Hydroxide (CH), Calcium Silicate Hydrate (CSH) and precipitation of Si(Al)-anhydrous gel translating to strength loss and physical failure and olivine is a promising additive for mitigation. This study aims to characterize the pH variation of olivine microparticles (30–90 μm) in simulated subsurface fluids, and reaction in high pH Portland cement, w/c ratio 0.404 cured for 3weeks, all at 90 °C and 95% RH. Results show olivine reacts with HCl aqueous solution between pH 1.0 to 1.92 and no significant reactivity in other fluids. SEM/EDS and Raman spectroscopy all indicate unreacted olivine particles embedded in hydrated cement. Therefore, olivine could serve as a micro-sacrificial material within hydrated Portland cement exposed to low pH fluids to form carbonates, mitigating potential CSH and CH leaching, enhancing wellbore cement resistance to leakage.

Cyanoacetamide derivatives as corrosion inhibitors; Synthesis, Characterization, DFT and Monte Carlo simulation

Corrosion behavior of X65-type carbon steel exposed to 1M HCl aqueous solution was studied in the absence and presence of various concentrations of new synthesized 3-(4-chlorophenyl)-2-cyano-N-(4-hydroxyphenyl) acrylamide, abbreviated as (P2), and 6-amino-4-(4-chlorophenyl)-1-(4-hydroxyphenyl)-2-oxo-1,2-dihydropyridine-3,5-dicarbonitrile, abbreviated as (P3), at 25oC. Potentiodynamic polarization data indicated that the synthesized Cyanoacetamide derivatives suppress both anodic and cathodic reactions via adsorption on the carbon steel surface and blocking the active sites. The adsorption of the inhibitor molecules forms a protective film which decreases the surface heterogeneity. Electrochemical impedance spectroscopy (EIS) measurements reveal that as the inhibitor concentration is increased, both the inhibition efficiency (η%) and the charge transfer resistance (Rt) are increased while the electrochemical double layer capacity (Cdl) is decreased. The experimental impedance data were analyzed according to a proposed equivalent circuit model for the electrode/electrolyte interface. Chemical descriptors are calculated through the density functional theory (DFT), also adsorption of inhibitors on the metal surface investigated through Monte Carlo simulation. The mechanism of corrosion inhibition was discussed given the obtained results of surface analysis and the molecular structure of the additive obtained from quantum chemical calculations. Keywords: Corrosion inhibition; Polarization; Electrochemical impedance spectroscopy (EIS); Surface analysis; Quantum chemical calculations

Two-Dimensional Covalent Organic Frameworks with Cobalt(II)-Phthalocyanine Sites for Efficient Electrocatalytic Carbon Dioxide Reduction.

The rapid development in synthesis methodology and applications for covalent organic frameworks (COFs) has been witnessed in recent years. However, the synthesis of highly stable functional COFs still remains a great challenge. Herein two-dimensional polyimide-linked phthalocyanine COFs (denoted as CoPc-PI-COF-1 and CoPc-PI-COF-2) have been devised and prepared through the solvothermal reaction of the tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalocyaninato cobalt(II) with 1,4-phenylenediamine and 4,4'-biphenyldiamine, respectively. The resultant CoPc-PI-COFs with a four-connected sql net exhibit AA stacking configurations according to powder X-ray diffraction studies, showing permanent porosity, thermal stability above 300 °C, and excellent resistance to a 12 M HCl aqueous solution for 20 days. Current-voltage curves reveal the conductivity of CoPc-PI-COF-1 and CoPc-PI-COF-2 with the value of 3.7 × 10-3 and 1.6 × 10-3 S m-1, respectively. Due to the same Co(II) electroactive sites together with similar permanent porosity and CO2 adsorption capacity for CoPc-PI-COFs, the cathodes made up of COFs and carbon black display a similar CO2-to-CO Faradaic efficiency of 87-97% at applied potentials between -0.60 and -0.90 V (vs RHE) in 0.5 M KHCO3 solution. However, in comparison with the CoPc-PI-COF-2&carbon black electrode, the CoPc-PI-COF-1 counterpart provides a larger current density (jCO) of -21.2 mA cm-2 at -0.90 V associated with its higher conductivity. This cathode also has a high turnover number and turnover frequency, amounting to 277 000 and 2.2 s-1 at -0.70 V during 40 h of measurement. The present result clearly discloses the great potential of 2D porous crystalline solids in electrocatalysis.

Nonselective etching of As and P based III‒V solar cell heterostructures with aqueous solutions of HIO3 and HCl

Etching characteristics of lattice-matched GaInP/GaAs/GaInNAsSb heterostructures by aqueous solutions of iodic acid (HIO3) and hydrochloric acid (HCl) is reported. The study aims at optimization of mesa fabrication process involved in the development of III‒V multijunction solar cells. The effects of temperature, agitation, etchant composition, and illumination on the etching selectivity are investigated. Varying the etchant composition and agitation rate at room temperature results in various mesa sidewall morphologies, ranging from rough surfaces and significant undercut to smoother sidewall profiles with only minor undercut. Especially, the undercut emerging in the GaInNAsSb junction, as well as in the AlInP layers, was observed for several etching conditions. Increasing the etching temperature also caused an unwanted increase in the selectivity, whereas reducing the temperature below the room temperature enhanced remarkably the formation of smooth morphology. Illumination during the etching resulted in a severe undercut in the GaAs junction, due to an increased selectivity caused by photoetching. This points out the need of controlled illumination condition to avoid unwanted reactions in wet etching of such multijunction structures. The etching process resulting in the best morphology was used for electrical isolation of triple-junction GaInP/GaAs/GaInNAsSb solar cells. The good photovoltaic performance exhibited by these devices proves the suitability of the nonselective etch process in developing multijunction solar cells.

Direct imaging of the structural transition and interconversion of macroporous bicontinuous diamond-surface structure

Abstract The porous solids with bicontinuous structures have received significant attention due to their complex structure with unique physical functionalities. They are often obtained through structural transformation from lamellae or cylindrical precursors. However, the experimental verification of this relationship is challenging due to the short life-living of the structural intermediates and the soft nature of the assembled amphiphilic systems. Herein, we report the observation of the structural change of macroporous bicontinuous diamond-surface structure in the self-assembly of block copolymeric system with inorganic precursors in a mixture solvent of tetrahydrofuran (THF) and HCl aqueous solution. By controlling the addition amount of HCl/H2O, both the electrostatic interactions of the organic/inorganic precursor and the hydrolyzation and condensation rate of tetraethyl orthosilicate (TEOS) can be controlled. A structural transformation from bicontinuous diamond-surface to several intermediates between lamellar and bicontinuous structures has been observed with increasing the concentration of HCl. Our results show that the transition centers play an important role in the formation of the bicontinuous structure from the lamellae. Furthermore, we have proved the formation of interlamellar attachments (ILAs) and stalks as the intermediate phase. This study may bring new insights into the formation and the structural relationship of the bicontinuous porous solids and the corresponding relevant biological structures.

A New Approach to the Dissolution Tests Management to Obtain Kinetic and Thermodynamic Data: Release of a Model Drug from Glyceryl Behenate Matrix Tablets

AbstractThis study is focused on the use of glyceryl behenate as a lipophilic excipient of matrix tablets providing controlled drug release. The aim of this study is to evaluate activation energy (EA) and changes of the thermodynamic parameters (ΔH, ΔS, ΔG) of a dissolution process. These values, which have not yet been published, can lead to better understanding of a drug release mechanism and can extend the use options of glyceryl behenate in the pharmaceutical industry. Values of ΔH, ΔS, ΔG and EA, providing an overall thermodynamic view on the studied matrix tablets, are evaluated based on the temperature‐dependences of the release rate constant of a model drug (temperature range 25 ‐ 45 °C). The studied lipophilic matrix tablets contain 10% to 50% of glyceryl behenate. Dissolution testing is carried out in an aqueous solution of HCl with addition of NaCl (pH1.2). Positive values of ΔH in the range of 3.83 to 56.13 kJ mol‐1 and positive values of ΔG indicate that the dissolution of the studied glyceryl behenate matrix tablets is an endothermic process which does not proceed spontaneously (in a temperature range of 25 ‐ 45 °C). The negative slope of the linear curves of enthalpy‐entropy compensation confirms the entropy‐driven dissolution.Practical Applications: A better understanding of the dissolution process is an important aspect, e.g., in the field of drug formulation strategy. In this study, it is confirmed that the influence of temperature on the model drug release rate is negligible for tablets containing more than 40% of glyceryl behenate. It is an important result for drug design due to the reduction of risk of a possible dose dumping effect induced by temperature and the prevention of in vivo therapeutic failure.

Sample Preparation for Determining Heavy-Metal Contents in Fatty Oils

Two methods were compared to select the optimum sample-preparation option for determining the heavy-metal contents in fatty oils. The first (GOST 26929–94) employed extraction of the metal ions from an oil sample by refluxing aqueous HCl solution. The second (European Pharmacopoeia, 8th Ed.) employed complex oxidative thermal destruction of an oil sample followed by processing in a mixture of conc. HNO3 and HCl with completion of the process by adding conc. H2SO4 . The mineralization was carried out at high pressure in sealed Teflon containers with microwave heating. Extraction of metals from the weighed portions of fatty oils by HCl solution provided accurate and satisfactorily reproducible results. This method was shown not to require special apparatus and was expedient for determining metal impurities in fatty oils. Sample preparation using oxidative thermal destruction required the use of expensive equipment and was unsafe.

Fiber optic Lossy Mode Resonance based sensor for aggressive liquids

A fiber-optic sensor for chemically aggressive environments, such as concentrated solutions of acids and alkalis, has been manufactured. The sensor is based on a single-mode optical fiber with a chemically etched cladding, coated with a thin film of tin dioxide (SnO2) by metalorganic chemical vapor deposition (MOCVD). In the transmission spectra of a SnO2 coated taper lossy mode resonances (LMRs) were observed, the maximum of which shifted to the long-wavelength part of the spectrum, with an increase in the thickness of the deposited film. At a deposition temperature of 345 °C, it was possible to detect the separation of the transverse electric (TE) and transverse magnetic (TM) LMRs for resonances up to the third order. From the change in the position of the 1-st TE LMR, the refractive index and the molar concentration of acids and alkalis in such aggressive liquids as aqueous solutions of HCl, HNO3, H2SO4, NaOH were determined, which, according to our information, is demonstrated for the first time. The high chemical durability of the coating was confirmed by its insusceptibility to aqua regia (AR). The sensitivity of the sensor to changes in the surrounding medium refractive index (SMRI) and the molar concentration of acids was more than 5260 nm/RIU and 32 nm/M, respectively.

Control of aragonite formation and its crystal shape in CaCl2-Na2CO3-H2O reaction system

Calcium carbonate (CaCO3) was synthesized in the CaCl2-Na2CO3-H2O reaction system at the reaction temperature of 40, 50, 60, and 70℃. The initial pH was changed to 2.4–11.0 at 50–70 ℃. The initial pH was adjusted by changing the pH of CaCl2 aqueous solution using HCl and NH3 aqueous solution. The CaCO3 precipitates obtained were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), and specific surface area measurement. In the case of no adding the pH adjustment solution, the product was a mixture of calcite and vaterite at 40 ℃. The formation of aragonite was observed at ≥50 ℃, and single-phase aragonite was obtained at ≥60 ℃, according to XRD measurements. Thus, Aragonite could be synthesized by changing the reaction temperature. At 70 ℃, the synthesis of CaCO3 was performed by changing the initial pH of 2.4–11.0. The formation of single-phase aragonite was detected in the initial pH range of 2.4–10.4. However, a small amount of calcite was contained in aragonite at the initial pH ≥ 10.8. The crystal shape of obtained aragonite was needle-like, and its particle size became finer as the initial pH increased. At an initial pH 2.4, the length and width of the crystals were 2–7 μm and 0.5–1.0 μm, respectively. The finest particles were samples synthesized at the initial pH 11.0, its length and width were 1–2 μm and 0.1–0.2 μm, respectively. The specific surface area of the products was 4.12–14.88 m2 g−1 at the initial pH of 2.4–11.0. The particle size of aragonite could be controlled by changing the initial pH at 70 ℃.

Dual solid electrolytes for aluminium-air batteries based on polyvinyl alcohol acidic membranes and neutral hydrogels

Water-based electrolytes are generally preferable to organic electrolytes due to their low cost and higher safety standard. However, their widespread use is generally limited by recharging issues. In the case of Al-air cells, water on the anode prevents aluminium deposition during recharging by producing hydrogen at more positive standard potentials. This promotes parasitic reactions that consume the anode and shorten the cell shelf life. On the cathode side, depending on the pH, water allows efficient oxygen reduction or oxygen evolution reactions. To produce electrolytes with different water contents on the two electrodes, we prepared solid electrolytes using polyvinyl alcohol (PVA) and aqueous HCl solutions with ionic conductivity ranging from 0.7 to 2.2 × 10−3 S cm−1 and electrochemical windows wider than 2.2 V. The new materials resembled a thin plastic membrane (0.6–0.9 mm thick) and were able to oxidise the Al-air cell anode. We also explored the possibility of using a dual electrolyte to allow the presence of water mainly on the cathode side. Specifically, cells assembled with two electrolytes in contact, with an acidic PVA membrane as anolyte and saline hydrogel as catholyte without separator, showed discharge capacity more than one order of magnitude greater than cells with single acidic PVA electrolytes. Electrochemical impedance spectroscopy (EIS) characterisation verified that the improved cell discharge capacity was attributed to the soft aqueous catholyte on the cathode-electrolyte interface and to the membrane conductivity stabilisation during cell use through the saline gel water. Cyclic voltammetry (CV) characterisation suggested the possibility of recharging the dual electrolyte cells thanks to the substantial absence of water on the anode side.