Influence of Cl− ions on anodic polarization behaviour of API X80 steel in high potential/current density conditions in Na2SO4 solution

Pipeline steel has considerable risk of corrosion in the high voltage direct current interference cases. Thus, under high potential/current density conditions, the anodic polarization behaviour of X80 steel in Na₂SO₄ solution and the influence of Cl⁻ ions were investigated using reversed potentiodynamic polarization, the current interrupt method, galvanostatic polarization, scanning electron microscopy, and X-ray photoelectron spectroscopy. In the Na₂SO₄ solution free of Cl⁻ ions, steel was passivated above 0.120 A cm⁻² and the potential increased from −0.32 V to 1.43 V. The passive film was composed of Fe₃O₄, γ-Fe₂O₃, and FeOOH. The addition of Cl⁻ ions observably influenced the passivation by attacking the passivate film. Low concentration of Cl⁻ ions (<5 mg L⁻¹ NaCl) could set higher demands of current density to achieve passivation and increase the requirement of potential to maintain passivation. A high concentration of Cl⁻ ions (>5 mg L⁻¹ NaCl) completely prevented passivation, showing strong corrosiveness. Thus, the X80 steel was corroded even under high-current-density conditions. The corrosion products were mainly composed of Fe₃O₄, α-Fe₂O₃, and FeOOH.

X80 steel gets passivated in high potential/current density conditions in Na₂SO₄ solution. Low concentration of Cl⁻ ions weakens the passivation. High concentration of Cl⁻ ions totally prevents the passivation.     

Control of Fe3+ coordination by excess Cl− in alcohol solutions

We spectroscopically investigated coordination state of Fe³⁺ in methanol (MeOH) and ethanol (EtOH) solutions against Cl⁻ concentration ([Cl⁻]). In both the system, we observed characteristic absorption bands due to the FeCl₄ complex at high-[Cl⁻] region. In the MeOH system, the proportion (r) of [FeCl₄]⁻ exhibits a stationary value of 0.2–0.3 in the intermediate region of 10 mM < [Cl⁻] < 50 mM, which is interpretted in terms of [FeCl_nL_6−n]³⁻ⁿ (n = 1 and 2). In the EtOH system, r steeply increases from 0.1 at [Cl⁻] = 1.5 mM to 0.7 at [Cl⁻] = 3.5 mM, indicating direct transformation from [FeL₆]³⁺ to [FeCl₄]⁻. We further found that the coordination change significantly decreases the redox potential of Fe²⁺/Fe³⁺.

Fe³⁺ coordination in alcohol solution can be controlled by the Cl⁻ concentration ([Cl⁻]). The coordination state changes from FeL₆ (L: solvent molecule) to FeCl₄ type via FeCl_nL_6−n with increases in [Cl⁻].     

Anti-corrosion porous RuO2/NbC anodes for the electrochemical oxidation of phenol

Efficient anode materials with porous structures have drawn increasing attention due to their high specific surface area, which can compensate for the slow reaction rate of electrochemical oxidation. However, the use of these materials is often limited due to their poor corrosion resistance. Herein, we report a facile scale-up method, by carbothermal reduction, for the preparation of porous niobium carbide to be used as an anode for the electrochemical oxidation of phenol in water. No niobium ions were detected when the anodes were under aggressive attack by sulfuric acid and under electrochemical corrosion tests with a current density less than 20.98 mA cm⁻². The porous niobium carbide was further modified by applying a ruthenium oxide coating to improve its catalytic activity. The removal rates of phenol and chemical oxygen demand by the RuO₂/NbC anode reached 1.87 × 10⁻² mg min⁻¹ cm⁻² and 6.33 × 10⁻² mg min⁻¹ cm⁻², respectively. The average current efficiency was 85.2%. Thus, an anti-corrosion, highly catalytically active and energy-efficient porous RuO₂/NbC anode for the degradation of aqueous phenol in wastewater was successfully prepared.

Efficient anode materials with porous structures have drawn increasing attention due to their high specific surface area, which can compensate for the slow reaction rate of electrochemical oxidation.     

Correlation between electrochemical properties and stress corrosion cracking of super 13Cr under an HTHP CO2 environment

The susceptibility of super 13Cr steel to stress corrosion cracking (SCC) was assessed through slow strain rate testing in simulated formation water saturated with CO₂ under a high-temperature and high-pressure (HTHP) environment. The evolution, morphology, and chemistry of fracture and corrosion products on the steel surface were evaluated using in situ electrochemical methods and surface analysis. Results indicate that the occurrence of pitting corrosion increases SCC susceptibility. At 150 °C, the degradation of a surface film induces pitting corrosion because of an increase in anodic processes. The presence of Cl⁻ causes film porosity, and CO₂ reduces the Cr(OH)₃/FeCO₃ ratio in the inner film, which further promotes Cl⁻-induced porosity.

The degradation of a surface film induces pitting corrosion, which further increases SCC susceptibility.     

Ion-triggered calcium hydroxide microcapsules for enhanced corrosion resistance of steel bars

Herein, we synthesized Ca(OH)₂ microcapsules with ion-responsive shells composed of cross-linked poly-ionic liquids (CPILs). By exchanging PF₆⁻ with Cl⁻ in water, the hydrophobic poly-ionic liquids (PILs) on the shell are converted to hydrophilic channels. The encapsulated Ca(OH)₂ can permeate through the hydrophilic channels and release OH⁻. Meanwhile, the Cl⁻ content can be reduced. The release rate of Ca(OH)₂ is influenced by the content of monomers and concentration of Cl⁻ ions in water. SO₄²⁻ can also trigger the release of Ca(OH)₂ from the microcapsule. With these microcapsules, Q235 steel exhibited promising corrosion resistance in simulated seawater. These results indicate that encapsulation of corrosion inhibitors is highly desirable for enhanced corrosion resistance of steel bars and the proposed approach can be used to encapsulate various corrosion inhibitors and functional materials for a wide range of applications.

By exchanging PF₆⁻ of the CPILs with Cl⁻, Ca(OH)₂ can penetrate out of the microcapsule through the formed hydrophilic channels.     

Structure-modulated CaFe-LDHs with superior simultaneous removal of deleterious anions and corrosion protection of steel rebar

The three anionic species; chloride (Cl⁻), sulfate (SO₄²⁻), and carbonate (CO₃²⁻), are typical chemical factors that environmentally accelerate failure of concrete structures with steel rebar through long-term exposure. Efficient removal of these deleterious anions at the early stage of penetration is crucial to enhance the lifespan and durability of concrete structures. Here, we synthesize CaFe-layered double hydroxide (CaFe-LDHs) by a simple one-step co-precipitation technique and structural modulation by calcination process. It is applied for the removal of Cl⁻, SO₄²⁻, and CO₃²⁻ anions as well as corrosion inhibition on steel rebar in aqueous solutions. The synthesized CaFe-LDHs with phase transfer show notable improvement of removal capacity (Q_max) toward Cl⁻ and SO₄²⁻ over 3.4 times and over 5.69 times, respectably, then those of previous literatures. Furthermore, the steel rebar exposed to an aqueous solution containing the three anionic sources shows a fast corrosion rate (1876.56 × 10⁻³ mm per year), which can be remarkably inhibited showing 98.83% of corrosion inhibition efficiency when it is surrounded by those CaFe-LDHs. The novel adsorption mechanisms of these CaFe-LDHs-induced crystals and corresponding corrosion protection properties are elucidated drawing on synergy of memory effects and chemical reactions.

The three anionic species; chloride (Cl⁻), sulfate (SO₄²⁻), and carbonate (CO₃²⁻), are typical chemical factors that environmentally accelerate failure of concrete structures with steel rebar through long-term exposure.     

Kinetic and mechanistic investigations of the degradation of propranolol in heat activated persulfate process

This study investigated the heat activated persulfate (heat/PS) process in the degradation of propranolol from water. Various factors (e.g., temperature, persulfate dose, initial pH and natural water constituent) on PRO degradation kinetics have been investigated. The results showed that the PRO degradation followed a pseudo-first-order kinetics pattern. As temperature rises, the pseudo-first-order rate constant (k_obs) was improved significantly, and the k_obs determined at 40–70 °C satisfied the Arrhenius equation, yielding an activation energy of 99.0 kJ mol⁻¹. The radical scavenging experiments and the EPR tests revealed that both SO₄˙⁻ and ·OH participated in degrading PRO, with SO₄˙⁻ playing a dominant role. Higher PS concentration and neutral pH favored PRO degradation. The impact of Cl⁻ and HCO₃⁻ were concentration-dependent. A lower concentration of Cl⁻ and HCO₃⁻ could accelerate PRO degradation, while the presence of HA showed inhibitory effects. Seven degradation products were recognized through LC/MS/MS analysis. Cleavage of ether bond, hydroxylation, and ring-opening of naphthol moiety are involved in the PRO''s degradation pathway. Finally, the formation of disinfection byproducts (DBPs) before and after pre-treated by heat/PS was also evaluated. Compared with direct chlorination of PRO, the heat/PS pre-oxidation greatly impacted the DBPs formation. The higher PRO removal efficiency in natural water indicated the heat/PS process might be capable of treating PRO-containing water samples, however, its impacts on the downstream effect on DBPs formation should be also considered.

The degradation kinetics and mechanism of propranolol by heat activated persulfate oxidation were investigated.     

First-principles study of coadsorption of Cu2+ and Cl− ions on the Cu (110) surface

Motivated by the importance of Cl⁻ in the industrial electrolytic Cu plating process, we study the coadsorption of Cl⁻ and Cu²⁺ on the Cu (110) surface using first-principles density functional theory (DFT) calculations. We treat the solvent implicitly by solving the linearized Poisson–Boltzmann equation and evaluate the electrochemical potential and energetics of ions with the computational hydrogen electrode approach. We find that Cl⁻ alone is hardly adsorbed at sufficiently negative electrochemical potentials μ_Cl but stable phases with half and full Cl⁻ coverage was observed as μ_Cl is made more positive. For Cl⁻ and Cu²⁺ coadsorption, we identified five stable phases for electrode biases between −2V < U_SHE < 2V, with two being Cl⁻ adsorption phases, two being Cl⁻ + Cu²⁺ coadsorption phases and one being a pure Cu²⁺ adsorption phase. In general, the free energy of adsorption for the most stable phases at larger |U_SHE| are dominated by the energy required to move electrons between the system and the Fermi level of the electrode, while that at smaller |U_SHE| are largely dictated by the binding strength between Cl⁻ and Cu²⁺ adsorbates on the Cu (110) substrate. In addition, by studying the free energy of adsorption of Cu²⁺ onto pristine and Cl⁻ covered Cu (110), we conclude that the introduction of Cl⁻ ion does not improve the energetics of Cu²⁺ adsorption onto Cu (110).

Free energy of adsorption for the most stable phases predicted by DFT calculations as a function of electrode potential.     

Enhanced detection of toxicity in wastewater using a 2D smooth anode based microbial fuel cell toxicity sensor

As the biological recognition element of microbial fuel cell (MFC) toxicity “shock” sensors, the electrode biofilm is perceived to be the crucial issue that determines the sensing performance. A carbon felt and indium tin oxide (ITO) film anode were utilized to examine the effects of anodic biofilm microstructure on MFC toxicity sensor performance, with Pb²⁺ as the target toxicant. The carbon felt anode based MFC (CF-MFC) established a linear relationship of Pb²⁺ concentration (C_Pb²⁺) vs. voltage inhibition ratio (IR_2h) at a C_Pb²⁺ range of 0.1 mg L⁻¹ to 1.2 mg L⁻¹. The highest IR_2h was only 38% for CF-MFC. An ITO anode based MFC (ITO-MFC) also revealed a linear relationship between C_Pb²⁺ and IR_2h at C_Pb²⁺ of 0.1 mg L⁻¹ to 1.5 mg L⁻¹ but better sensing sensitivity compared with the CF-MFC. The IR_2h of ITO-MFC gradually approached 100% as C_Pb²⁺ further increased. The enhanced sensing sensitivity for the ITO anode possibly originated from the thin biofilm that resulted in the efficient exposure of exoelectrogens to Pb²⁺. The employment of 2D conductive metal oxide with a smooth surface as the anode was able to increase the MFC sensing reliability in real wastewater.

The thin biofilm on the anode surface is more conducive to the diffusion of toxins thus has better sensing performance.     

Deuterium equilibrium isotope effects in a supramolecular receptor for the hydrochalcogenide and halide anions

We highlight a convenient synthesis to selectively deuterate an aryl C–H hydrogen bond donor in an arylethynyl bisurea supramolecular anion receptor and use the Perrin method of competitive titrations to study the deuterium equilibrium isotope effects (DEIE) of anion binding for HS⁻, Cl⁻, and Br⁻. This work highlights the utility and also challenges in using this method to determine EIE with highly reactive and/or weakly binding anions.

We highlight a convenient synthesis to selectively deuterate an aryl C–H hydrogen bond donor in a supramolecular anion receptor and use competitive titrations to study the deuterium equilibrium isotope effects (DEIE) in binding HS⁻, Cl⁻, and Br⁻.

Molecular recognition and host–guest binding in both biological and synthetic systems are often driven by a mixture of competitive and additive primarily non-covalent interactions. Understanding the role of each of these forces in a host–guest system can reveal insights into the driving forces behind binding and help inform on the molecular design of future hosts.^1–3 Equilibrium isotope effects (EIE), also referred to as binding isotope effects (BIE) in structural molecular biology,⁴ measure the effect of isotopic substitution on supramolecular interactions through changes in the vibrational energy of the substituted bond. These studies can be used to elucidate the complex non-covalent forces involved in host conformational changes and host–guest binding.^5–8Examples from structural molecular biology have demonstrated that EIEs can reveal mechanistic information in enzyme–ligand binding events.^4,9 Isotopic substitution in synthetic supramolecular systems has been used both for labelling purposes and for studying individual non-covalent interactions. For example, Bergman, Raymond, and coworkers used deuterium equilibrium isotope effects (DEIE) to study benzylphosphonium cation guest binding in a self-assembled supramolecular complex in aqueous solution.¹⁰ From these DEIE studies, the authors found that attractive cation⋯π interactions in the interior of the host were important for promoting guest binding, and that C–H⋯π and π⋯π interactions were relatively small contributors. In another example, Shimizu and coworkers studied the DEIE on the strength of C–H⋯π interactions in their molecular balances.¹¹ Both computational and experimental results showed that the strength of C–H⋯π and C–D⋯π interactions were about equal, settling the debate on which interaction is stronger and easing concerns about using deuteration for spectroscopic and labelling applications.Previously, we used DEIE to study Cl⁻ binding with the arylethynyl bisurea anion receptor 1^H/D (Fig. 1) in DMSO-d₆.¹² We found an experimental DEIE of 1.019 ± 0.010, which matched the computationally-predicted DEIE of 1.020. Further computational analysis determined that the DEIE was due to a distorted N–H⋯Cl⁻ hydrogen bond geometry, which resulted in changes in the C–H/D bond vibrational energy in the host–guest complex. In addition, Paneth and coworkers performed a computational study with 1^H and other hydrogen bonding supramolecular Cl⁻ receptors to determine the EIE of ^35/37Cl⁻ binding in these hosts.¹³ Because isotope effects, both equilibrium and kinetic, originate solely from changes in the vibrational energy of the isotopically labelled bond, the EIE arising from this study came from changes in the vibrational energies of the bonds in the supramolecular hosts when participating in hydrogen bonding with Cl⁻ isotopes. Indeed, a linear relationship was observed between the hydrogen bond donor (D) D–H bond lengths in the host–guest complex and the computed ^35/37Cl EIE.Open in a separate windowFig. 1Arylethynyl bisurea receptors 1^H and 1^D used in our previous DEIE study of Cl⁻ binding. Related receptors 2^H and 2^D are used in this study to avoid reaction of the nitro group with HS⁻.Previous EIE studies with receptor 1^H/D have focused on Cl⁻ binding; however, to the best of our knowledge, no work has yet investigated the EIE of hydrosulfide (HS⁻) binding in this or other systems. HS⁻ is a highly reactive anion that plays crucial roles in biology. At physiological pH, HS⁻ is favored in solution by a 3 : 1 ratio over its conjugate acid, hydrogen sulfide (H₂S). H₂S has been identified as the third physiological gasotransmitter alongside CO and NO and plays essential roles in physiological systems.¹⁵ Despite its high nucleophilicity and redox activity, HS⁻ has been observed to be bound through non-covalent interactions in the protein crystal structure of a bacterial ion channel¹⁶ and in the turn-over state of vanadium-containing nitrogenase.¹⁷ The supramolecular chemistry of HS⁻ is under-studied in synthetic supramolecular receptors, likely due to the inherent high reactivity of HS⁻. Indeed, we are aware of only three families of receptors that have been shown to reversibly bind HS⁻.^18–21Recently, we used a series of arylethynyl bisurea anion receptors to investigate and demonstrate a linear free energy relationship between the polarity of a non-traditional C–H hydrogen bond donor and the solution binding energy of HS⁻, HSe⁻, Cl⁻ and Br⁻.¹⁴ A major and unexpected finding of this study was that HS⁻ demonstrated a significant increase in sensitivity towards the polarity of the C–H hydrogen donor over HSe⁻, Cl⁻ and Br⁻. Although increasing the polarity of the C–H hydrogen bond donor did not lead to changes in selectivity between Cl⁻, Br⁻, and HSe⁻, we observed a 9-fold increase in selectivity for HS⁻ over Cl⁻, suggesting a fresh approach to selective HS⁻ recognition using non-covalent interactions. In this current study, we label the C–H hydrogen bond donor in an arylethynyl bisurea receptor with a deuterium atom (2^H/D, Fig. 1) to further investigate this apparent preference of polar C–H H-bond donors for HS⁻ over Cl⁻ and Br⁻ through DEIE.Receptor 2^H is a previously reported anion receptor for HS⁻, Cl⁻, and Br⁻ and was prepared by established methods.¹⁴ Deuterium labelling of the isotopologue 2^D was achieved by selective monodeuteration of intermediates through methods similar to those reported in the literature (Scheme 1).²² The diazonium salt 3 was synthesized in a 71% yield from 2,6-diiodo-4-trifluoromethylaniline.²³ Dediazonation in DMF-d₇ is catalyzed by FeSO₄ and allows for selective synthesis of monodeuterated intermediate 4. The deuteration step proceeds through a radical pathway that uses DMF-d₇ as the deuterium source. This deuteration reaction provides efficient deuterium incorporation even with up to 50% by volume H₂O in the reaction solution due to the differential bond strengths in DMF and H₂O.²² Sonogashira cross-coupling reaction of 4 and 4-t-butyl-2-ethynylaniline²⁴ afforded 5 in 45% yield. Subsequent addition with 4-methoxyphenyl isocyanate gave 2^D in 34% yield. Compound 2^D and intermediates were characterized through ¹H, ²H, ¹³C{¹H}, and ¹⁹F NMR spectroscopy and high-resolution mass spectrometry (see ESI^†).Open in a separate windowScheme 1Synthetic route for the selective deuteration of anion receptor 2^D.Previous work on the DEIE of Cl⁻ binding with 1^H/D in DMSO revealed an experimental isotope effect of 1.019 ± 0.010. Therefore, we expected similar small DEIEs for HS⁻, Cl⁻, and Br⁻ binding with 2^H/D. Typical methods to determine binding constants (K_a) in supramolecular systems use non-linear regression fitting of titration data. Results from this method can be affected by small errors in the known initial host and guest concentration, quality of the titration isotherm, and subsequent data fitting, which when taken together often results in 2–15% errors in K_a. To increase the precision in K^H_a/K^D_a data for this study, we used the Perrin method of competitive titrations,²⁵ which has been shown previously to reduce errors in EIE values significantly with errors as small as 0.0004.²⁶ In this method, a linearized plot of the chemical shifts of 2^H (δ_H) and 2^D (δ_D) in fast exchange with an anionic guest is fit by linear regression to eqn (1):(δ⁰_H − δ_H)(δ_D − δ^f_D) = DEIE(δ⁰_D − δ_D)(δ_H − δ^f_H)1The slope of the linear regression is equal to the DEIE of the system. Because the linear regression only relies on chemical shift values and is independent of host and guest concentration, the precision of the method is limited to the precision of the NMR instrument and quality of data fitting.In addition, ¹³C NMR spectroscopy is sensitive to isotopic labelling and can show changes in chemical shifts between isotopomers. We were able to differentiate between the ¹³C NMR signals for C^ab, C¹ and C² for free and bound 2^H and 2^D (Fig. 2a) in 10% DMSO-d₆/CD₃CN, which were similar to those reported for 1^H/D in DMSO-d₆.¹² Competitive ¹³C NMR spectroscopy titrations were performed in anaerobic and anhydrous 10% DMSO-d₆/CD₃CN at 25 °C with mixtures of 2^H and 2^D in combined concentrations between 5.71 and 13.46 mM. Aliquots of the tetrabutylammonium (TBA) salts of HS⁻, Cl⁻, and Br⁻ were added until the system had reached saturation (Titration method A in ESI^†). In an effort to decrease reactivity of HS⁻ with 2^H/D and DMSO over long periods of time and decrease oxygen and water contaminations, some titrations with HS⁻ were performed by splitting the host solution of 2^H/D between four J-young NMR tubes. For each point in the competitive titration, TBASH was added to a new solution of 2^H/D inside an N₂-filled glovebox shortly before obtaining a ¹³C NMR spectra (Titration method B in ESI^†). The C^ab, C¹ and C^{2 13}C NMR signals were tracked for 2^H and 2^D in each titration for each anion. A representative competitive titration and linearized plots for Cl⁻ binding is shown in Fig. 2.Open in a separate windowFig. 2(a) Representation of the host–guest equilibrium between 2^H/D and Cl⁻. (b) Differences in the chemical shifts between the 2^H and 2^D isotopologues are observed in the ¹³C NMR signals for the C^ab, C¹, and C² carbons. ¹³C NMR signals for the C^ab, C¹, and C² carbons in 2^H and 2^D are tracked throughout a titration. (c–e) Linearized plots from fitting the chemical shifts of the C^ab, C¹, and C² throughout a titration to eqn (1).The DEIE data calculated from tracking the chemical shifts of the C^ab, C¹ and C^{2 13}C NMR signals from Cl⁻ and Br⁻ binding are summarized in eqn (1) through linear regression is included in parentheses

Pretreatment by recyclable Fe3O4@Mg/Al-CO3-LDH magnetic nano-adsorbent to dephosphorize for the determination of trace F− and Cl− in phosphorus-rich solutions

The magnetic nano-adsorbent Fe₃O₄@Mg/Al-CO₃-LDH (Mg/Al-type layered double hydroxide) with a CO₃²⁻ interlayer anion has been synthesized successfully on Fe₃O₄ nanoparticles via a urea hydrothermal method. It is confirmed that the nano-adsorbent can adsorb PO₄³⁻ rapidly and efficiently in multi-ion solutions; meanwhile, it did not adsorb any F⁻ and Cl⁻, even with a high amount of the nano-adsorbent or a longer adsorption time. This behaviour is beneficial for applications to remove PO₄³⁻ in phosphorus-rich solutions, and especially can be utilized to determine trace F⁻ and Cl⁻ anions in phosphorus-rich solutions by physical and chemical analysis methods including ion chromatography without serious interference from PO₄³⁻ for trace determinations. Herein, the hydrothermally synthesized Fe₃O₄@Mg/Al-CO₃-LDH was characterized via SEM, TEM, SAED, XRD, FTIR, magnetic hysteresis loop analysis and adsorption–desorption isotherm analysis. The structure and stability, adsorption mechanism, magnetic saturation value, specific surface area, total pore volume, phosphate adsorption capacity and recyclability are discussed. Using the optimized pretreatment conditions, Fe₃O₄@Mg/Al-CO₃-LDH was utilized successfully to adsorb PO₄³⁻ in real samples and determine trace F⁻ and Cl⁻ accurately by ion chromatography; this would be very beneficial for continuous analysis and on-line tests by physical and chemical analysis methods without interference from PO₄³⁻ in phosphorus-rich samples, leaving F⁻ and Cl⁻ even if in a trace content.

Synthesized recyclable Fe₃O₄@Mg/Al-CO₃-LDH magnetic nano-adsorbent is utilized to dephosphorize phosphorous-rich solutions but leave F⁻ and Cl⁻ to be detected chromatographically.     

Rapid and selective electrochemical transformation of ammonia to N2 by substoichiometric TiO2-based electrochemical system

In this study, we have developed a continuous-flow electrochemical system towards the rapid and selective conversion of ammonia to N₂, based on a tubular substoichiometric titanium dioxide (Ti₄O₇) anode and a Pd–Cu co-modified Ni foam (Pd–Cu/NF) cathode, both of which are indispensable. Under the action of a suitable anode potential, the Ti₄O₇ anode enables the conversion of Cl⁻ to chloride radicals (Cl˙), which could selectively react with ammonia to produce N₂. The anodic byproducts, e.g. NO₃⁻, were further reduced to N₂ at the Pd–Cu/NF cathode. EPR and scavenger experiments confirmed the dominant role of Cl˙ in ammonia conversion. Complete transformation of 30 mg L⁻¹ ammonia could be obtained over 40 min of continuous operation under optimal conditions. The proposed electrochemical system also exhibits enhanced oxidation kinetics compared to conventional batch systems. This study provides new insights into the rational design of a high-performance electrochemical system to address the challenging issue of ammonia pollution.

A continuous-flow electrochemical system for rapid and selective conversion of ammonia to N₂ was proposed. The system consists of a tubular substoichiometric titanium dioxide (Ti₄O₇) anode and a Pd–Cu co-modified Ni foam (Pd–Cu/NF) cathode.     

Zinc vacancy modulated quaternary metallic oxynitride GeZn1.7ON1.8: as a high-performance anode for lithium-ion storage

The development of alternative anode materials to achieve high lithium-ion storage performance is crucial for the next-generation lithium-ion batteries (LIBs). In this study, a new anode material, Zn-defected GeZn_1.7ON_1.8 (GeZn_1.7−xON_1.8), was rationally designed and successfully synthesized by a simple ammoniation and acid etching method. The introduced zinc vacancy can increase the capacity by more than 100%, originating from the additional space for the lithium-ion insertion. This GeZn_1.7−xON_1.8 particle anode delivers a high capacity (868 mA h g⁻¹ at 0.1 A g⁻¹ after 200 cycles) and ultralong cyclic stability (2000 cycles at 1.0 A g⁻¹ with a maintained capacity of 458.6 mA h g⁻¹). Electrochemical kinetic analysis corroborates the enhanced pseudocapacitive contribution and lithium-ion reaction kinetics in the GeZn_1.7−xON_1.8 particle anode. Furthermore, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses at different electrochemical reaction states confirm the reversible intercalation lithium-ion storage mechanism of this GeZn_1.7−xON_1.8 particle anode. This study offers a new vision toward designing high-performance quaternary metallic oxynitride-based materials for large-scale energy storage applications.

Zn-defected GeZn_1.7ON_1.8 (GeZn_1.7−xON_1.8) was successfully synthesized by a simple ammoniation and acid etching method. This well-designed Zn cation-deficient GeZn_1.7−xON_1.8 anode shows enhanced lithium-ion storage performance.     

Extraction of polyoxotantalate by Mg–Fe layered double hydroxides: elucidation of sorption mechanisms

The extraction of Ta(v) as polyoxometallate species (H_xTa₆O₁₉^(8−x)−) using Mg–Fe based Layered Double Hydroxide (LDH) was evaluated using pristine material or after different pre-treatments. Thus, the uptake increased from 100 ± 5 mg g⁻¹ to 604 ± 30 mg g⁻¹, for respectively the carbonated LDH and after calcination at 400 °C. The uptake with calcined solid after its reconstruction with Cl⁻ or NO₃⁻ anions has also been studied. However, the expected exchange mechanism was not found by X-ray Diffraction analysis. On the contrary, an adsorption mechanism of Ta(v) on LDH was consistent with measurements of zeta potential, characterized by very negative values for a wide pH range. Moreover, another mechanism was identified as the main contributor to the uptake by calcinated LDH, even after its reconstruction with Cl⁻ or NO₃⁻: the precipitation of Ta(v) with magnesium cations released from MgO formed by calcination of the LDH. This latter reaction has been confirmed by the comparison of the uptake of Ta(v) in dedicated experiments with solids characterized by a higher magnesium solubility (MgO and MgCl₂). The obtained precipitate has been analyzed by X-ray diffraction (XRD) and would correspond to a magnesium (polyoxo)tantalate phase not yet referenced in the powder diffraction databases.

Reaction of polyoxotantalate ions and MgFe Layered Double Hydroxide leads to magnesium polyoxotantalate precipitate.     

Organic/inorganic double solutions for magnesium–air batteries

In order to limit the anode corrosion and improve the battery activity, magnesium–air batteries with organic/inorganic double solutions (0.5 M Mg(ClO₄)₂–N,N-dimethylformamide (DMF)/0.6 M NaCl–H₂O, 0.5 M Mg(ClO₄)₂–acetonitrile (AN)/0.6 M NaCl–H₂O) were prepared. The discharge performance, discharge morphology, and corrosion performance of magnesium anode were researched. Results obtained show that organic electrolytes separate the anode from the aqueous electrolyte, thus improving the anode utilization rate. Due to the NaCl electrolyte used in the air cathode side, batteries show higher discharge voltages. As an example, a better discharge performance has been observed in Mg(ClO₄)₂–DMF/NaCl–H₂O double electrolytes at 1 mA cm⁻² discharge. This is attributed to there being no obvious absorption of corrosion products on the anode surface. The results of the discharge morphology and electrochemical impedance spectroscopy agree well with the discharge performance. The magnesium anode discharge mechanism is different for different solutions.

In order to limit the anode corrosion and improve the battery activity, magnesium–air batteries with organic/inorganic double solutions (0.5 M Mg(ClO₄)₂–N,N-dimethylformamide (DMF)/0.6 M NaCl–H₂O, 0.5 M Mg(ClO₄)₂–acetonitrile (AN)/0.6 M NaCl–H₂O) were prepared.     

Kinetics and mechanisms of flumequine degradation by sulfate radical based AOP in different water samples containing inorganic anions

Many studies have reported that hydroxyl radical (HO˙) driven advanced oxidation processes (AOPs) could degrade fluoroquinolones (FQs) antibiotics effectively. Compared with HO˙, sulfate radical (SO₄˙⁻) shows a similar oxidation capacity but a longer half-life. SO₄˙⁻ could cause chain reactions and resulted in the generation of halogen radicals and carbonate radicals from the main anions in sea water including Cl⁻, Br⁻ and HCO₃⁻. However, few studies were focused on the degradation of FQs in marine aquaculture water and seawater, as well as the bioaccumulation of transformation products. As a typical member of FQs, flumequine (FLU) was degraded by UV/peroxodisulfate (PDS) AOPs in synthetic fresh water, marine aquaculture water and seawater. The reaction rate constants in the three water samples were 0.0348 min⁻¹, 0.0179 min⁻¹ and 0.0098 min⁻¹, respectively. The reason was attributed to the inhibition of the anions as they could consume SO₄˙⁻ and initiate the quenching reaction of free radicals. When the pH value increased from 5 to 9, the reaction rate decreased from 0.0197 min⁻¹ to 0.0066 min⁻¹. The energy difference between HOMO and LUMO of FLU was calculated to be 8.07 eV indicating that FLU was a stable compound. The atoms on quinolone ring of FLU with high negative charge would be more vulnerable to attack by free radicals through electrophilic reactions. Two possible degradation pathways of FLU were inferred according to the degradation products. Preliminary bioaccumulation analysis of transformation products by the EPI suite software proved that the values of log K_ow and log BCF of the final product P100 were less than those of FLU and the intermediates.

Many studies have reported that hydroxyl radical (HO˙) driven advanced oxidation processes (AOPs) could degrade fluoroquinolones (FQs) antibiotics effectively.     

A PVA/LiCl/PEO interpenetrating composite electrolyte with a three-dimensional dual-network for all-solid-state flexible aluminum–air batteries

Aluminum–air batteries are promising electronic power sources because of their low cost and high energy density. However, traditional aluminum–air batteries are greatly restricted from being used in the field of flexible electronics due to the rigid battery structure, and the irreversible corrosion of the anode by the alkaline electrolyte, which greatly reduces the battery life. To address these issues, a three-dimensional dual-network interpenetrating structure PVA/LiCl/PEO composite gel polymer electrolyte (GPE) is proposed. The gel polymer electrolyte exhibits good flexibility and high ionic conductivity (σ = 6.51 × 10⁻³ S cm⁻¹) at room temperature. Meanwhile, benefiting from the high-performance GPE, an assembled aluminum–air coin cell shows a highest discharge voltage of 0.73 V and a peak power density (P_max) of 3.31 mW cm⁻². The Al specific capacity is as high as 735.2 mA h g⁻¹. A flexible aluminum–air battery assembled using the GPE also performed stably in flat, bent, and folded states. This paper provides a cost-effective and feasible way to fabricate a composite gel polymer electrolyte with high performance for use in flexible aluminum–air batteries, suitable for a variety of energy-related devices.

Problems relating to the leakage of alkaline liquid electrolyte, the evaporation of water, and flexibility in traditional aluminum–air batteries are solved in this study.     

Eco-friendly synthesis of ionic helical polymers and their chemical properties and reactivity

Reaction of N-(2,4-dinitrophenyl)pyridinium chloride (salt(Cl⁻)) with sodium dicyanamide (Na(CN)₂N) resulted in anion exchange between Cl⁻ and (CN)₂N⁻ to yield a new Zincke salt, salt((CN)₂N⁻). Reactions of salt((CN)₂N⁻) with piperazine, specifically (R)-(−)- or (S)-(+)-2-methylpiperazine under eco-friendly conditions, such as in aqueous solution, in the absence of a catalyst, and at room temperature, resulted in pyridinium ring opening to yield ionic high-molecular-weight polymers with 5-2,4-dienylideneammonium dicyanamide units or chiral 5-(2-methylpiperazinium)-2,4-dienylideneammonium dicyanamide units, namely, polymer(H;(CN)₂N⁻), polymer(R-Me;(CN)₂N⁻), and polymer(S-Me;(CN)₂N⁻). UV-Vis measurements revealed that the π-conjugation system expanded along the polymer chain due to the orbital interaction between the electrons on the two nitrogen atoms of the piperazinium ring. Circular dichroism (CD) measurements revealed a helical conformation of the main chain in polymer(R-Me;(CN)₂N⁻) and polymer(S-Me;(CN)₂N⁻). The reaction of polymer(H;(CN)₂N⁻) with p-phenylenediamine (PDA) caused recyclization of the 2,4-dienylideneammonium unit and resulted in depolymerization to yield N-(4-aminophenyl)pyridinium dicyanamide. Cyclic voltammetry analysis suggested that the polymers obtained in this study undergo electrochemical oxidation and reduction.

Reactions of salt((CN)₂N⁻) with (R)-(−)- or (S)-(+)-2-methylpiperazine under eco-friendly conditions resulted in a yield of ionic helical polymers.     

Preparation of novel two-stage structure MnO micrometer particles as lithium-ion battery anode materials

MnO micrometer particles with a two-stage structure (composed of mass nanoparticles) were produced via a one-step hydrothermal method using histidine and potassium permanganate (KMnO₄) as reagents, with subsequent calcination in a nitrogen (N₂) atmosphere. When the MnO micrometer particles were utilized in lithium-ion batteries (LIBs) as anode materials, the electrode showed a high reversible specific capacity of 747 mA h g⁻¹ at 100 mA g⁻¹ after 100 cycles, meanwhile, the electrode presented excellent rate capability at various current densities from 100 to 2000 mA g⁻¹ (∼203 mA h g⁻¹ at 2000 mA g⁻¹). This study developed a new approach to prepare two-stage structure micrometer MnO particles and the sample can be a promising anode material for lithium-ion batteries.

MnO micrometer particles with a two-stage structure (composed of mass nanoparticles) were produced via a one-step hydrothermal method using histidine and potassium permanganate (KMnO₄) as reagents, with subsequent calcination in a nitrogen (N₂) atmosphere.     

The role of particulate matter in reduced visibility and anionic composition of winter fog: a case study for Amritsar city

Severe fog events during winter months in India are a serious concern due to the higher incidence of road accidents, flight delays and increased occurrence of respiratory diseases. The present paper is an attempt to study the twenty fog samples collected from the rooftop of an academic building of Guru Nanak Dev University, Amritsar, India from November 2017 to January 2018. Fog samples were analysed for various parameters viz. pH, electrical conductivity (EC), chloride (Cl⁻), nitrate (NO₃⁻) and sulphate (SO₄²⁻) levels. The pH, EC, and Cl⁻, NO₃⁻ and SO₄²⁻ levels in the fog samples were estimated as 6.3–7.9, 240–790 μS cm⁻¹, 108–2025 μeq L⁻¹, 105–836 μeq L⁻¹ and 822–5642 μeq L⁻¹, respectively. It was noticed that sulphate was the dominant anion in fog samples. The SO₄²⁻ to NO₃⁻ molar ratio in the fog was estimated as 7.6 which suggests the burning of fossil fuel as the major pollutant from vehicular exhausts. Multiple regression analysis was performed to evaluate the effect of PM_2.5/PM₁₀ ratio and relative humidity (RH) on visibility. A box-cox plot of power transformation produced better model fitting, employing a square root transformation of the visibility which indicated that the PM_2.5/PM₁₀ and RH have an exponential effect on visibility.

Severe fog events during winter months in India are a serious concern due to the higher incidence of road accidents, flight delays and increased occurrence of respiratory diseases.