Unbuffered Aqueous Solution Research Articles

Probing Local pH Change during Electrode Oxidation of TEMPO Derivative: Implication of Redox-Induced Acidity Alternation by Imidazolium-Linker Functional Groups.

The chemical degradation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-based aqueous energy storage and catalytic systems is pH sensitive. Herein, we voltammetrically monitor the local pH (pHlocal) at a Pt ultramicroelectrode (UME) upon electro-oxidation of imidazolium-linker functionalized TEMPO and show that its decrease is associated with the greater acidity of the cationic (oxidized) rather than radical (reduced) form of TEMPO. The protons that drive the decrease in pH arise from hydrolysis of the conjugated imidazolium-linker functional group of 4-[2-(N-methylimidazolium)acetoxy]-2,2,6,6-tetramethylpiperidine-1-oxyl chloride (MIMAcO-T), which was studied in comparison with 4-hydroxyl-TEMPO (4-OH-T). Voltammetric hysteresis is observed during the electrode oxidation of 4-OH-T and MIMAcO-T at a Pt UME in an unbuffered aqueous solution. The hysteresis arises from the pH-dependent formation and dissolution of Pt oxides, which interact with pHlocal in the vicinity of the UME. We find that electrogenerated MIMAcO-T+ significantly influences pHlocal, whereas 4-OH-T+ does not. Finite element analysis reveals that the thermodynamic and kinetic acid-base properties of MIMAcO-T+ are much more favorable than those of its reduced counterpart. Imidazolium-linker functionalized TEMPO molecules comprising different linking groups were also investigated. Reduced TEMPO molecules with carbonyl linkers behave as weak acids, whereas those with alkyl ether linkers do not. However, oxidized TEMPO+ molecules with alkyl ether linkers exhibit more facile acid-base kinetics than those with carbonyl ones. Density functional theory calculations confirm that OH- adduct formation on the imidazolium-linker functional group of TEMPO is responsible for the difference in the acid-base properties of the reduced and oxidized forms.

Selection and Evaluation of Model Pollutants for Performance Assessment of Advanced Treatment of Industrial Park Wastewater by Ozonation

Ozonation has gradually become a routine process for advanced wastewater treatment. During the technology innovation on the advanced treatment of wastewater by ozonation, researchers have to assess the performance of abundant new technologies, new reactors, and new materials. However, they are usually puzzled by the rational selection of model pollutants to assess the capability of such new technologies to eliminate the chemical oxygen demand (COD) and total organic carbon (TOC) of practical wastewater. It is unclear how well the various model pollutants reported in the literature could represent the COD/TOC removal of actual wastewater. The rational selection and evaluation of model pollutants for advanced treatment of industrial wastewater is of great significance in establishing the technological standard system for advanced treatment of wastewater via ozonation. Herein, the aqueous solutions (including unbuffered solutions and bicarbonate-buffered solutions) of 19 model pollutants and four practical secondary effluents from industrial parks were investigated through ozonation under identical conditions. The similarity in COD/TOC removal of the above wastewater/solutions were evaluated using mainly clustering analysis. The results showed that the dissimilarity among the model pollutants was greater than that among the actual wastewaters, thus enabling the rational selection of several model pollutants to assess the performance of advanced treatment of wastewater using ozonation by different technologies. The errors of predicting the COD removal of secondary sedimentation tank effluent by ozonation in 60 min using the unbuffered aqueous solutions of ketoprofen (KTP), dichlorophenoxyacetic acid (2,4-D), and sulfamethazine (SMT) were less than 9%, and those using the bicarbonate-buffered solutions of phenacetin (PNT), SMT, and sucralose were less than 5%. The evolution of pH by using the bicarbonate-buffered solutions was more similar to that in practical wastewater than by using unbuffered aqueous solutions. In the similarity evaluation of COD/TOC removal between the bicarbonate-buffered solutions and the practical wastewaters, the results were almost the same whether considering different input ozone concentration conditions. Therefore, the protocol proposed in this study based on similarity evaluation to assess the performance treating actual wastewater could be extended to different ozone concentration conditions with certain universality.

Surface-stabilization of LMR-NCM by Washing with Aqueous Buffers to Reduce Gassing and Improve Cycle-Life

Li- and Mn-rich battery active materials like Li1.14(Ni0.26Co0.14Mn0.60)0.86O2 (LMR-NCM) are promising cathode active materials (CAMs) for next-generation Li-Ion batteries, as they combine a higher energy density than state-of-the-art materials at lower materials cost. However, they suffer from high gassing, particularly during formation, and from voltage and capacity fading over their cycle life. While electrolyte additives are known to alleviate these issues, it will be shown that a surface modification of LMR-NCM CAMs can also reduce their gassing during formation and improve their long-term stability. Here, we present a detailed analysis of a water-based post-treatment for LMR-NCMs, which not only lowers their initial gassing by more than 90%, but also avoids the issue of transition metal dissolution observed with conventionally used washing procedures at low ph. We thus utilized a buffered solution to increase the pH into the stability window of LMR-NCM materials (near/above pH 7), while also providing a controlled Li+/H+-exchange that is not possible with unbuffered aqueous solutions like pure H2O, H2O/alcohol mixtures, or acids. TGA-MS experiment showed that heating of Li+/H+-exchanged LMR-NCM leads to the formation of a protective (near-)surface spinel layer, and full-cell cycling displayed a drastic improvement of the capacity retention.

Proton-Coupled Electron Transfer of Coenzyme Q in Unbuffered Solution by Pore Confined In Situ Liquid ToF-SIMS

Proton-coupled electron transfer (PCET) process of coenzyme Q in buffered solutions, which is a well-defined overall 2 e−, 2 H+ process, has been systematically studied, while that in unbuffered aqueous solutions is still too complicated to be fully understood, primarily due to the uncontrolled local proton concentration at the electrode-electrolyte interface. Herein, time-of-flight secondary ion mass spectrometry (ToF-SIMS) coupled with a microfluidic electrochemical reactor, namely pore confined in situ liquid ToF-SIMS analysis, was adopted to monitor the PCET process of coenzyme Q0 (CoQ0) at the electrode-electrolyte interface in unbuffered aqueous solution. Evolutions of CoQ0 and related intermediates during the electrochemical reaction were measured in real-time, which provided direct molecular evidences for the PCET process. The direct observation of CoQ0H2 and hydrated CoQ0 dianion implied that the reduction of CoQ0 in unbuffered electrolyte was not a simple overall 2 e−, 2 H+ procedure. Moreover, the identification of the CoQ0H2 dimer and the quinone-hydroquinone complex demonstrated the further transformation of CoQ0 and CoQ0H2 by hydrogen bonding interaction or π-interaction. These results provided a full picture of the mechanism for the PCET process of CoQ0 in unbuffered aqueous solution, which could contribute to the comprehensive understanding of the electrochemical reactions of coenzyme Q.

Intramolecular hydrogen bonds induced high solubility for efficient and stable anthraquinone based neutral aqueous organic redox flow batteries

Solubility of redox active materials (RAMs) is key to realize high volume capacity and energy density in aqueous organic redox flow batteries (AORFBs). In anthraquinone (AQ)-based RAMs, hydrophilic groups substituted at β-sites (2,3,6,7) are expected to improve water-miscibility much better than α-sites (1,4,5,8). In this work, we find an anomalous case: 3-((9,10-dioxo-9.10-dihydroanthracen-2-yl)amino)-N,N,N-trimethylpropan-1-aminium chloride (2-DPAQCl) functioned with the hydrophilic groups surprisingly exhibits poor solubility with less than 0.05 M, however its isomer 3-((9,10-dioxo-9,10-dihydroanthracen-1-yl)amino)-N,N,N-trimethylpropan-1-aminium chloride (1-DPAQCl) shows high solubility at 1.44 M in water. The results from 1H nuclear magnetic resonance (NMR) and infrared (IR) spectra suggest that intermolecular hydrogen bonds (HBs) are formed between N–H donors and Cl− acceptors in 2-DPAQCl, which is different from the case for 1-DPAQCl that N–H donors interact with neighboring CO acceptors as intramolecular HBs. Benefited from the intramolecular HBs, water is prone to break the interaction between solute molecules than that in 2-DPAQCl, leading to better water-solubility. Electrochemical investigations indicate that the peak-to-peak separations ΔEpp of 1-DPAQCl is very narrow in unbuffered aqueous solution as well as in buffered aqueous solution at pH 7.0, implying its highly electrochemical reversibility and facile reaction kinetics, which further indicates 1-DPAQCl is suitable to serve as a negative RAM for neutral AORFBs.

Rapid, Biomimetic Degradation of a Nerve Agent Simulant by Incorporating Imidazole Bases into a Metal-Organic Framework.

Metal-organic frameworks (MOFs) are excellent catalytic materials for the hydrolytic degradation of nerve agents and their simulants. However, most of the MOF-based hydrolysis catalysts to date are reliant on liquid water media buffered by a volatile liquid base. To overcome this practical limitation, we developed a simple and feasible strategy to synthesize MOF composites that structurally mimic phosphotriesterase's active site as well as its ligated histidine residues. By incorporating imidazole and its derivative into the pores of MOF-808, the obtained MOF composites achieved rapid degradation of a nerve agent simulant (dimethyl-4-nitrophenyl phosphate, DMNP) in pure water as well as in a humid environment without liquid base. Remarkably, one of the composites Im@MOF-808 displayed the highest catalytic activity for DMNP hydrolysis in unbuffered aqueous solutions among all reported MOF-based catalysts. Furthermore, solid-phase catalysis showed that Im@MOF-808 can also rapidly hydrolyze DMNP under high-humidity conditions without bulk water or external bases. This work provides a viable solution toward the implementation of MOF materials into protective equipment for practical nerve agent detoxification.

Mixed-Metal Cerium/Zirconium MOFs with Improved Nerve Agent Detoxification Properties.

A series of Ce/Zr mixed-metal-organic frameworks with different topology/connectivity, namely, Ce/Zr-UiO-66 (U01, U02, and U03) (fcu (12-c)), Ce/Zr-DUT-67-PZDC (D01 and D02) (reo (8-c)), and Ce/Zr-MOF-808 (M01, M02, and M03) (spn (6-c)) were evaluated toward the detoxification of toxic nerve agent model diisopropylfluorophosphate (DIFP) at room temperature in unbuffered aqueous solution. Noteworthily, the catalytic rate for P-F bond cleavage increased with increasing Ce/Zr molar ratio. A further increase in catalytic activity can be achieved by Mg(OMe)2 doping of the mixed-metal MOFs as exemplified with M01@Mg(OMe)2 and M02@Mg(OMe)2 systems. The results show that Mg(OMe)2 incorporation into the mesoporous cavities of M01 and M02 give rise to P-F hydrolytic degradation half-lives of nearly 5 and 2 min with 100% degradation of DIFP after 55 and 65 min for M01@Mg(OMe)2 1:2 and M02@Mg(OMe)2 1:4, respectively.

Functions of MnOx in NaCl Aqueous Solution for Artificial Photosynthesis.

SummaryPhotoelectrochemical water splitting has been intensively investigated as artificial photosynthesis technology to convert solar energy into chemical energy. The use of seawater and salted water has advantages for minimum environmental burden; however, the oxidation of Cl− ion to hypochlorous acid (HClO), which has toxicity and heavy corrosiveness, should occur at the anode, along with the oxygen evolution. Here, O2 and HClO production in aqueous solution containing Cl− on photoanodes modified with various metal oxides was investigated. The modification of MnOx resulted in the promotion of the O2 evolution reaction (OER) specifically without HClO production over a wide range of conditions. The results will contribute not only to the practical application of artificial photosynthesis using salted water but also to the elucidation of substantial function of manganese as the element for OER center in natural photosynthesis.

Magnesium Exchanged Zirconium Metal-Organic Frameworks with Improved Detoxification Properties of Nerve Agents.

UiO-66, MOF-808 and NU-1000 metal-organic frameworks exhibit a differentiated reactivity toward [Mg(OMe)2(MeOH)2]4 related to their pore accessibility. Microporous UiO-66 remains unchanged while mesoporous MOF-808 and hierarchical micro/mesoporous NU-1000 materials yield doped systems containing exposed MgZr5O2(OH)6 clusters in the mesoporous cavities. This modification is responsible for a remarkable enhancement of the catalytic activity toward the hydrolytic degradation of P-F and P-S bonds of toxic nerve agents, at room temperature, in unbuffered aqueous solutions.

Surface-Modified Metal Sulfides As Stable H2 Evolving Photocatalyst in Z-Scheme Water Splitting System with [Fe(CN)6]3–/4– Redox Mediator Under Visible Light Irradiation

Most of metal sulfide semiconductors, such as CdS, possess appropriate band levels for water reduction and oxidation as well as a narrow band gap allowing visible light absorption because the valence bands of them are mainly formed by S 3p orbital. However, the most of sulfides have no capability of O2 evolution from water due to the occurrence of self-oxidative deactivation by photogenerated holes. Even for the sacrificial H2 evolution, they require particular electron donor such as S2– and SO3 2– to generate H2 stably. In the present study, we introduce a new and versatile way that can stabilize metal sulfides, not only CdS but also others such as ZnIn2S4 and CdIn2S4, as H2-evolving photocatalyst in Z-scheme water splitting with [Fe(CN)6]3–/4– redox. K2Cd[Fe(CN)6], which is one of metal hexacyanoferrates (MHCF), was formed on the CdS surface via photocorrosion and suppressed further photocorrosion. Additionally, influence of other MHCFs (M = In, Zn, Cu, Ag) on photocatalytic H2 evolution over ZnIn2S4 was investigated. Pt/CdS was found to generate considerable amount of H2 from water in the presence of [Fe(CN)6]4– under visible light, while the H2 evolution was soon terminated at ca. 28 mmol in the unbuffered aqueous solution. However, the production of nearly the twice amount (ca. 53.6 mmol) of oxidant, i.e., [Fe(CN)6]3–, was confirmed in the solution after the reaction. This result indicated that photocatalytic H2 evolution over Pt/CdS proceeded under visible light, accompanied by the oxidation of [Fe(CN)6]4– to [Fe(CN)6]3–. The cease of H2 evolution was due to increased pH value (6.7 → 10.7). Then, it was found that the use of borate buffer (BB) was effective to suppress such decrease in H2 evolution rate. Photocatalytic H2 evolutions over other metal sulfides (ZnIn2S4 and CdIn2S4) were also examined in the presence of [Fe(CN)6]4–. Pt/ZnIn2S4 showed appreciable H2 evolution rate (4.8 mmol/h). On the other hand, Pt/CdIn2S4 showed quite low activity (0.8 mmol/h). ATR-FTIR analysis revealed that MHCF, such as K2Cd[Fe(CN)6]1 and K2Zn[Fe(CN)6]2 were formed on Pt/CdS and Pt/ZnIn2S4, respectively, after each reaction, both of which showed appreciable H2 evolution. These hexa-cyanometallates would be generated from the reaction of [Fe(CN)6]4– and Cd2+ or Zn2+ ion derived from photocorrosion during photo-catalytic reaction. Rubin et al. have reported that such MHCF formed on CdS electrode efficiently scavenged photogenerated holes, leading to increased rate of oxidation of [Fe(CN)6]4– and also suppression of photocorrosion of CdS. To improve the activity for H2 evolution, the hexa-cyanoferrate K2[CdFe(CN)6] prepared in advance, was loaded onto ZnIn2S4 and CdIn2S4 particles. The loading indeed improved the H2 evolution rate in both cases (ZnIn2S4: 4.8 → 15 mmol/h, CdIn2S4: 0.8 → 6 mmol/h). Finally, we demonstrated that combination of metal sulfides as H2-evolving photocatalyst and O2 evolution system (TaON photoanode3) could split water stably into H2 and O2 under visible light irradiation. We investigated influence of other MHCFs (M = In, Zn, Cu, Ag) on photocatalytic H2 evolution from water over ZnIn2S4 in the presence of [Fe(CN)6]4­–­­ as an electron donor. The modification with ZnHCF or InHCF was found to improve the activity as well as that of CdHCF, as shown in Fig. 1. In contrast, the modification with AgHCF or CuHCF showed no photocatalytic H2 evolutoin. We found that their activities strongly depend the redox properties of MHCFs. As for ZnHCF, InHCF, and CdHCF, which show higher activity, stable redox currents derived from Fe3+/Fe2+ in MHCFs were observed around 0.72 ~ 0.99 VSHE. These MHCFs effectively scavenged photogenerated holes and thus improved H2 evolution. On the other hand, AgHCF showed irreversible behavior. The intensity of peaks corresponding to both the oxidation and reduction drastically decreased after the 2nd cycle, indicating some irreversible reactions occurred. Such irreversible species were formed on the surface, resulting in suppression of the oxidation reaction. As for CuHCF, a reversible redox wave for Fe3+/Fe2+ was observed at 0.94V, whereas an irreversible peak, which probably corresponds to the reduction of Cu2+ included in CuHCF, also appeared at –0.2 VSHE. Photoexcited electrons in ZnIn2S4 were consumed for reduction of Cu2+, instead of H2 evolution. References Rubin, H. D.; Arent, D. J.; Humphrey, B. D.; Bocarsly, A. B. Electrochem. Soc. 1987, 134, 93.Reguera, E.; Gomez, A.; Balmaseda, J.; Contreras, G..; Escamilla, A. Struct. Chem., 2001, 12. 59.Higashi, M.; Domen, K.; Abe, R. J. Am. Chem. Soc. 2012, 134, 6968 Figure 1

Molecular aspects on the amino acid-mediated sol–gel process of tetramethoxysilane in water

The aqueous sol–gel process of (TMOS) in conjunction with several natural amino acids (AAs) is employed for synthesis of amino acid/silica hybrid materials. These hybrid materials contain the amino acid physically bonded within the matrix. The sol–gel process occurs readily in unbuffered aqueous amino acid solution. The pH value during the processing is only determined by the dissolved amino acid. It ranges between pH 3–11 as function of the isoelectrical point (IEP) of the AAs. Systematic study of the influence of molecular structure of the AAs L-alanine, e-aminocaproic acid, L-arginine, L-asparagine, L-aspartic acid, L-glutamic acid, L-glutamine, glycine, L-histidine, L-hydroxyproline, L-leucine, L-lysine, L-methionine, L-phenylalanine, L-proline, L-serine, L-threonine, L-tryptophan, and L-valine on the gelation time and dissolution behavior of TMOS in water is discussed. The IEP of the AA determines both dissolution and gelation of TMOS in water. Glycine was used as a model compound to investigate how concentration affects dissolution and gelation time of TMOS as well as porosity of resulting silica. As a result, the hydrolysis rate of TMOS in water and therewith dissolution is decelerated and gelation process is accelerated by increasing glycine concentration. Glycine-mediated sol–gel processes of TMOS were additionally examined by 1H NMR spectroscopy, dynamic light scattering, and ATR-FTIR spectroscopy as a function of reaction time to support the visual observed results. Furthermore, various glycine derivatives such as N-acetylglycine, N-benzoylglycine, glycine ethylester, glycine ethylester·HCl, N-methylglycine, N,N-dimethylglycine, N,N-dimethylglycine methylester, and N-phenylglycine are used for studying the influence of amino acid structure functionalities on dissolution and gelation time of TMOS.

Deconvoluting Surface-Bound Quinone Proton Coupled Electron Transfer in Unbuffered Solutions: Toward a Universal Voltammetric pH Electrode.

While quinone proton coupled electron transfer (PCET) under buffered conditions is well understood, the situation is more complicated in unbuffered aqueous solutions. With a view to producing a quinone-based voltammetric pH electrode that can function universally in both buffered and unbuffered solutions by following a two-electron (2e-)/two-proton (2H+) Nernstian pathway over a wide pH range, the voltammetric response of strongly electronically coupled surface-bound quinones, directly integrated into a boron-doped diamond (BDD) electrode, is investigated. A laser ablation process enables integration of quinones into the BDD electrode surface with a high p Ka1 (first protonation state) and with controllable, very low surface coverages (as low as 2 orders of magnitude below monolayer coverage). Under buffered conditions, one wave results for all pH values, and the 2e-/2H+ pathway is followed across the entire pH range. The measured ET rate constant values, from Laviron analysis, are also high, indicative of fast ET pathways. Under unbuffered conditions, one wave is again observed for all pH values; however, deviations from the buffered 2e-/2H+ behavior are seen in the neutral region (pH 6-8). While 2e-/2H+ transfer is maintained at all times, we attribute the observed deviation to local pH changes caused by the consumption and generation of protons at the electrode surface during the redox electrochemistry of the quinone. The associated proton fluxes generated at such sparse surface coverages are thought to be sufficiently high enough to prevent ET from occurring exclusively via a proton-independent route. By reducing surface coverage (down to ∼4 × 10-12 mol cm-2; the limit of our laser ablation process) local pH changes can be reduced but are not eradicated completely. By moving to a pulsed voltammetric technique, where for each potential step protons consumed at the electrode are immediately replaced, it is possible, provided the surface coverage is low enough, to obtain a Nernstian 2e-/2H+ response across a wide pH range in unbuffered solution.

New cathodic peak of quinone caused by the ultrafast diffusion of protons in unbuffered aqueous solution

The electrochemical behavior of hydroquinone in unbuffered aqueous solution was investigated using cyclic voltammetry. Subsequent cathodic scan showed a new cathodic peak at the negative potential and another similar cathodic peak for catechol. The peak current increased with the increasing pH of the bulk solution and concentration of hydroquinone. We observed that only the new cathodic peak increased, whereas the other peaks remained constant with the addition of quinone to the test solution. This new cathodic peak was caused by the ultrafast diffusion of proton from the electrode surface to the bulk solution. The results can help us understand the unique characteristics of hydroquinone in unbuffered solution.

Radical oxidation of methyl vinyl ketone and methacrolein in aqueous droplets: Characterization of organosulfates and atmospheric implications

In-cloud processing of volatile organic compounds is one of the significant routes leading to secondary organic aerosol (SOA) in the lower troposphere. In this study, we demonstrate that two atmospherically relevant α,β-unsaturated carbonyls, i.e., but-3-en-2-on (methyl vinyl ketone, MVK) and 2-methylopropenal (methacrolein, MACR), undergo sulfate radical-induced transformations in dilute aqueous systems under photochemical conditions to form organosulfates previously identified in ambient aerosols and SOA generated in smog chambers. The photooxidation was performed under sun irradiation in unbuffered aqueous solutions containing carbonyl precursors at a concentration of 0.2 mmol and peroxydisulfate as a source of sulfate radicals (SO4–) at a concentration of 0.95 mmol. UV–vis analysis of solutions showed the fast decay of unsaturated carbonyl precursors in the presence of sulfate radicals. The observation confirms the capacity of sulfate radicals to transform the organic compounds into SOA components in atmospheric waters. Detailed interpretation of high-resolution negative ion electrospray ionization tandem mass spectra allowed to assign molecular structures to multiple aqueous organosulfate products, including an abundant isoprene-derived organosulfate C4H8SO7 detected at m/z 199. The results highlight the solar aqueous-phase reactions as a potentially significant route for biogenic SOA production in clouds at locations where isoprene oxidation occurs. A recent modelling study suggests that such processes could likely contribute to 20–30 Tg year−1 production of SOA, referred to as aqSOA, which is a non-negligible addition to the still underestimated budget of atmospheric aerosol.

Derivatives of Naphthoquinone As Potential Electroactive Species for Redox FLOW Batteries

The generation of energy from renewable sources (solar and wind) is limited by the weather conditions that turn them into intermittent sources. In addition to this, and due to the large amount of energy produced while minimum demand, energy storage technologies are urgently needed. Redox flow batteries (RFBs) are a very attractive technology for large-scale energy storage [1]. Currently RFB systems are mostly based on redox reactions of electroactive metal ions, which are limited by their abundance, low solubility, high cost and toxicity. However, organic species have generated great interest [2]. Quinones are the main organic redox active species that have a key role in the electron transport processes of biological systems depending on molecular aromaticity and their electronic structures [3]; for example, the synthesis of ATP and photosynthesis [4]. However, the synthesis of redox species based on quinone analogs for RFB is associated with the unnecessary factor of human and monetary capital. Therefore, the current computer tools allow great opportunities to screen for valuable quinone species for RFB, as well to optimize resources. In this work, a chemical system derived from quinones was proposed as possible electroactive species as redox electrolyte for energy storage applications (Figure 1). Computer calculations of the chemical system were carried out to determine the difference in eV between HOMO-LUMO (Egap) in order to predict their electron transfer ability, as well, the relationship towards their redox properties for RFB applications. First, the molecules shown in Figure 1 were modeled in the program molden to obtain the z matrices. Then, theoretical calculations were performed by Gaussian v.0.9 using the functional hybrid B3LYP with the base 6-311 + G (d, p) in order to obtain the difference of eV between the HOMO-LUMO of the molecules. Subsequently, the proposed molecules were synthesized by Michael addition of 1,4 (DNQ1-6) using substituted anilines. Here, the synthesis reactions were carried out at 70°C for 12 h. On the other hand, the triazole in the DNQ8 was synthesized by means of a catalyzed 1,3-dipolar addition cycle of Huisgen. Electrochemical Studies were carried out by cyclic and linear voltammetry to evaluate the redox reactions, reversibility and the diffusion coefficients in order to confirm the theoretical calculations of the proposed system. The theoretical calculations results showed that all materials have a lower Egap compared to their predecessor NQ (Egap=3.984eV), Figure 1. Therefore, it is possible to say that the DNQ1-8 compounds are suitable as redox electrolyte for flow batteries since at lower Egap higher electrical conductivity, according to the theory of frontier molecular orbitals [5]. Particularly, the DNQ3 and DNQ6 presented the lowest Egap, thus, these compounds could be a very attractive option for a fast electron transfer at the electrode/electrolyte interface in a RFB. All the molecules proposed in Figure 1 were synthesized as describe above. The yields were from 63% to 81%. The molecules synthesized with chlorinated reagents exhibit the highest yield and it was attributed to the presence of a better leaving group. UV-vis studies were performed to support the correspondence of the Egap by theoretical calculations. For instance, a batochromic shift of the interactions η → π * was observed at 480 nm approximately for the DNQ1 as compared to this for the DNQ3 at 540 nm approximately. These preliminary results agreed with the theoretical calculations, higher Egap for the DNQ1 as compared to lower Egap for the DNQ3. Overall, the proposed system seems to be suitable for energy storage applications in RFBs, however, electrochemical studies are being carried out and will be presented at the conference in order to confirm these results. References Skyllas-Kazacos, M., Chakrabarti, M. H., Hajimolana, S. A., Mjalli, F. S. & Saleem, M. “Progress in flow battery research and development”, J. Electrochem. No. 158, p. R55-R79 (2011).Song, Z. & Zhou, H. “Towards sustainable and versatile energy storage devices: an overview of organic electrode materials”, Energy Environ. No. 6, p. 2280–2301 (2013).Ding, Y., Li, Y. & Yu, G. “Exploring bio-inspired quinone-based organic redox flow batteries: a combined experimental and computational study”, Chem No.1, p. 790–801 (2016).Quan, M., Sanchez, D., Wasylkiw, M. F. & Smith, D. K. “Voltammetry of quinones in unbuffered aqueous solution”, J Am Chem Soc. No. 129, p. 12847–12856 (2007).Tsuji, Y. & Hoffmann, R. “Frontier orbital control of molecular conductance and its switching”, Chem. Int. Ed. Engl. No. 53, p. 4093–4097 (2014). Figure 1

Removal of antibiotics from water and waste milk by ozonation: kinetics, byproducts, and antimicrobial activity

The use of antibiotics in the dairy farming for curing and growth promotion results in the production of massive quantities of non-recyclable wastewater by the conventional purification techniques. Additionally, waste milk is produced during the drug withholding periods, which is not suitable for human or animal consumption and cause huge economic loss as well as present serious environmental waste. This study was designed to investigate the decomposition of various antibiotic compounds in un-buffered aqueous solutions and milk samples by ozonation process. Commonly administered broad-spectrum antibiotics such as amoxicillin, doxycycline, ciprofloxacin, and sulphadiazine were selected as model examples in the current investigation. Gradual exposure of these antibiotics to increasing ozone gas concentration induced increasing removal percentages of the antibiotics in spiked water and milk samples. The removal reached 95% across all the tested treated antibiotics with ozone dose as low as 75 mg L−1. It was noted that the removal of antibiotics in milk samples is more efficient with faster rate constants. This was attributed to the self-buffering characteristic of milk that maintains the neutral pH, keeping the amine groups un-protonated and more reactive towards the electrophilic attack by the molecular ozone. 1H NMR as well as HPLC experiments support the near complete removal of antibiotics and indicated the break down to simpler and more soluble fragments of acidic nature. Bacterial growth experiments, conducted with E. coli, and milk ageing experiments provided clear evidences that the resulting decomposition byproducts lack both toxicity effect and antimicrobial activity. This study provides a viable route to remove hazardous materials, which contribute to a growing issue of antibiotic resistance of pathogenic bacteria.

Adsorption Kinetics and Thermodynamics of Hydroquinone onto a Polycrystalline Gold Electrode

The adsorption kinetics and thermodynamics of hydroquinone (QH2) onto a polycrystalline gold electrode surface in an unbuffered aqueous solution as a function of concentration have been investigated using cyclic voltammetry. The adsorption kinetics appeared to be kinetic control rather than diffusion control. The adsorption thermodynamics was represented by the Langmuir isotherm as the interaction parameter of the Frumkin isotherm was found to be 0.01, indicating small interaction between the adsorbate molecules. The saturation surface coverage was found to be 1.8 × 10−10 mol cm−2, which suggested that QH2 adsorbs on a polycrystalline gold electrode in horizontal orientation at the close packing state. The free energy of the adsorption was calculated to be –23 kJ mol−1, indicating moderate adsorption force.

Chemical Warfare Agents Detoxification Properties of Zirconium Metal-Organic Frameworks by Synergistic Incorporation of Nucleophilic and Basic Sites.

The development of protective self-detoxifying materials is an important societal challenge to counteract risk of attacks employing highly toxic chemical warfare agents (CWAs). In this work, we have developed bifunctional zirconium metal-organic frameworks (MOFs) incorporating variable amounts of nucleophilic amino residues by means of formation of the mixed ligand [Zr6O4(OH)4(bdc)6(1-x)(bdc-NH2)6x] (UiO-66-xNH2) and [Zr6O4(OH)4(bpdc)6(1-x)(bpdc-(NH2)2)6x] (UiO-67-x(NH2)2) systems where bdc = benzene-1,4-dicarboxylate; bdc-NH2= benzene-2-amino-1,4-dicarboxylate; bpdc = 4,4'-biphenyldicarboxylate; bpdc-(NH2)2 = 2,2'-diamino-4,4'-biphenyldicarboxylate and x = 0, 0.25, 0.5, 0.75, 1. In a second step, the UiO-66-xNH2 and UiO-67-x(NH2)2 systems have been postsynthetically modified by introduction of highly basic lithium tert-butoxide (LiOtBu) on the oxohydroxometallic clusters of the mixed ligand MOFs to yield UiO-66-xNH2@LiOtBu and UiO-67-x(NH2)2@LiOtBu materials. The results show that the combination of pre and postsynthetic modifications on these MOF series gives rise to fine-tuning of the catalytic activity toward the hydrolytic degradation of both simulants and real CWAs in unbuffered aqueous solutions. Indeed, UiO-66-0.25NH2@LiOtBu is able to hydrolyze both CWAs simulants (diisopropylfluorophosphate (DIFP), 2-chloroethylethylsulfide (CEES), and real CWAs (soman (GD), sulfur mustard (HD)) quickly in aqueous solution. These results are related to a suitable combination of robustness, nucleophilicity, basicity, and accessibility to the porous framework.

Evidencing Fast, Massive, and Reversible H+ Insertion in Nanostructured TiO2 Electrodes at Neutral pH. Where Do Protons Come From?

Ongoing developments of sustainable energy technologies based on high-surface-area semiconductive metal oxide electrodes operating under mild and safe aqueous conditions require deep understanding of proton and electron transfer/transport throughout their porous structure. To address this issue, we investigated the electrochemical reductive protonation of high surface area nanostructured amorphous TiO2 electrodes (produced by glancing angle deposition) in both buffered and unbuffered aqueous solutions. Quantitative analysis of the two charge storage mechanisms was achieved, allowing proper deconvolution of the electrical double-layer capacitive charge storage from the reversible faradaic one resulting from the proton-coupled reduction of bulk TiO2. We evidence that this latter process occurs reversibly and extensively (up to an intercalation ratio of 20%) not only under strongly acidic pH conditions but also, more interestingly, under neutral pH with the intercalated proton arising from the buffer rather ...

Surface-Modified Metal Sulfides As Stable H2 Evolving Photocatalyst in Z-Scheme Water Splitting System with [Fe(CN)6]3–/4– Redox Mediator Under Visible Light Irradiation

Photocatalytic water splitting using semiconductor materials has attracted considerable attention due to the potential for the clean production of H2 from water by utilizing solar energy. Since nearly half of the solar energy incident on the Earth’s surface lies in the visible region, an efficient harvest of wide range of visible light is essential for realizing practically high efficiency in the photocatalytic H2 production under natural sunlight. Most of metal sulfide semiconductors, such as CdS, possess appropriate band levels for water reduction and oxidation as well as a narrow band gap allowing visible light absorption because the valence bands of them are mainly formed by S 3p orbital. However, the most of sulfides have no capability of O2 evolution from water due to the occurrence of self-oxidative deactivation by photogenerated holes. Even for the sacrificial H2 evolution, they require particular electron donor such as S2– and SO3 2– to generate H2 stably. In the present study, we introduce a new and versatile way that can stabilize metal sulfides, not only CdS but also others such as ZnIn2S4 and CdIn2S4, as H2-evolving photocatalyst in Z-scheme water splitting with [Fe(CN)6]3–/4– redox. Pt/CdS was found to generate considerable amount of H2 from water in the presence of [Fe(CN)6]4– under visible light, while the H2 evolution was soon terminated at ca. 28 µmol in the unbuffered aqueous solution (Fig. 1). However, the production of nearly the twice amount (ca. 53.6 µmol) of oxidant, i.e., [Fe(CN)6]3–, was confirmed in the solution after the reaction. This result indicated that photocatalytic H2 evolution over Pt/CdS proceeded under visible light irradiation, accompanied by the oxidation of [Fe(CN)6]4– to [Fe(CN)6]3–. The cease of H2 evolution was due to increased pH value (6.7 → 10.7). Then, it was found that the use of borate buffer (BB) was effective to suppress such decrease in H2evolution rate. Photocatalytic H2 evolutions over other metal sulfides (ZnIn2S4 and CdIn2S4) were also examined in the presence of [Fe(CN)6]4–. Pt/ZnIn2S4 showed appreciable H2 evolution rate (4.8 µmol/h). On the other hand, Pt/CdIn2S4 showed quite low activity (0.8 µmol/h). ATR-FTIR analysis revealed that hexacyano complexes, such as M x [CdFe(CN)6]1) and M x [ZnFe(CN)6]2) were formed on Pt/CdS and Pt/ZnIn2S4, respectively, after each reaction, both of which showed appreciable H2 evolution. These hexacyano complexes would be generated from the reaction of [Fe(CN)6]3–/4– and Cd2+ or Zn2+ ion derived from photocorrosion during photocatalytic reaction. Rubin et al. have reported that such hexacyano complex formed on CdS electrode efficiently scavenged photogenerated holes, leading to increased rate of oxidation of [Fe(CN)6]4– and also suppression of photocorrosion of CdS. To improve the activity for H2 evolution, the hexacyano complex K2[CdFe(CN)6] prepared in advance, was loaded onto ZnIn2S4 and CdIn2S4 particles. The loading indeed improved the H2 evolution rate in both cases (ZnIn2S4: 4.8 →15 µmol/h, CdIn2S4: 0.8 → 6 µmol/h). Finally, we demonstrated that combination of metal sulfides as H2-evolving photocatalyst and O2 evolution system (TaON photoanode3)) could split water stably into H2 and O2 under visible light irradiation (Fig. 2).