pH Region Research Articles

The influence of temperature on the charging of polytetrafluoroethylene surfaces in electrolyte solutions

The surface properties of Polytetrafluoroethylene (PTFE) depend on the pH and the ionic strength of the electrolyte solution. The point of zero charge (pHpzc) and the isoelectric point (pHiep) of PTFE were found to be 2.9 and 3.2 at 25 °C, respectively. The electrophoretic mobility at pH > pHiep indicates that the PTFE particles are negatively charged in the neutral pH region. In absence of surface functional groups, this observation can be explained by the distribution of OH− and H+ ions between the PTFE interface and the remaining solution. A thermodynamic model of ion distribution and the temperature dependency of the electroneutrality points which enables evaluation of the thermodynamic parameters is proposed. The enthalpies of interfacial reactions were indirectly determined by measuring the temperature dependency of the electroneutrality points by potentiometric mass titration and streaming current measurements. It was found that the exchange of the H+ and OH− ions between the interfacial region and bulk of the solution is an endothermic reaction. The specific enthalpy of dilution of PTFE dispersions was found to be pH dependent, with the lowest value at pH ≈ 3, i.e. in the zero surface charge region.

Assessment of the adsorption kinetics, equilibrium, and thermodynamic for Pb(II) removal using a low-cost hybrid biowaste adsorbent, eggshell/coffee ground/sericite.

A hybrid adsorbent (CES), coffee grounds, eggshell powder and sericite as a binder, was prepared to remove Pb(II) from aqueous solution. The Fourier-transform infrared spectroscopy analysis showed that the CES contained a large amount of OH groups and had a favorable structure for adsorbing heavy metals. The value of pHpzc of CES was estimated at 7.08. In the neutral pH region, the surface of CES is negatively charged and favorable for adsorption of Pb(II). The maximum Langmuir adsorption amount was 155.67mg/g, and the adsorption process of Pb(II) using CES fitted pseudo-second-order kinetic model and Langmuir isotherm model. Moreover, the analysis of adsorption energy, free energy, enthalpy, and entropy found that the adsorption of Pb(II) onto CES was physical and a spontaneous exothermic reaction. CES is a hybrid adsorbent using general municipal waste and has great advantages in terms of environmental conservation and sustainable environmental circulation. This allows it to compete with other adsorbents. PRACTITIONER POINTS: A hybrid adsorbent, coffee grounds, eggshell, and sericite (CES), was used to remove Pb(II) Adsorption of Pb(II) using CES in an aqueous solution was physical rather than chemical CES contained a large amount of OH groups and had a favorable structure for adsorbing heavy metals The reactivity and strength of the adsorption of Pb(II) onto CES was very good CES has great advantages in terms of environmental conservation and sustainable environmental circulation.

Temperature-responsive biodegradable injectable polymer systems with conveniently controllable properties

Biodegradable injectable polymers (IPs) that exhibit temperature-responsive sol–gel transitions have recently drawn much attention as promising biomedical materials, such as in drug delivery systems, cell implantation, and tissue engineering. Typical examples of temperature-responsive IPs are block copolymers of poly(ethylene glycol) (PEG) and aliphatic polyesters. The use of biodegradable IP systems in clinical applications has faced several issues. In this review, after a brief introduction of IP systems, our recent progress on controllable IP systems using simple mixing strategies is introduced. Control of the gelation pH region of a dual-stimuli (both temperature and pH)-responsive IP system was achieved by changing the mixing ratio of cationic and anionic polymers. Temperature-triggered covalent (irreversible) gelation systems were developed by mixing IPs with reactive termini and appropriate cross-linker molecules. The duration of the gel state (decomposition period) of IP hydrogels was easily controlled by changing the mixing ratio of the components. The developed biodegradable IP systems with controllable properties are promising for future applications in clinical stages. Biodegradable injectable polymer systems exhibiting temperature-triggered formation of chemically cross-linked hydrogel were developed by “mixing strategy”. The mixture of triblock copolymer of poly(e-caprolactone-co-glycolic acid) and poly(ethylene glycol) (PCGA-b-PEG-b-PCGA, tri-PCG) solution containing hexafunctional polythiol (DPMP) and tri-PCG with terminal acryloyl groups (tri-PCG-Acryl) solution showed temperature-responsible sol–gel transition, and the gelation was irreversible. Duration time of the gel state under physiological condition and physical property of the hydrogel could be controlled by a simple method, just changing the mixing ratio of tri-PCG-Acryl to tri-PCG.

Core/shell hybrid fiber with aminated PAN and Fe2O3 as a high-capacity adsorbent for phosphate ions.

APANF@Fe2O3, a phosphate adsorbent, was synthesized in two steps: the immobilization of an amine group onto polyacrylonitrile fiber (PANF) and the adsorption of an iron ion on aminated PANF (APANF). The amination degree of the PANF was adjusted considering its mechanical properties. The Fe2O3 on the surface of the APANF played a role as a phosphate-grasping layer via a ligand-exchange reaction. The APANF@Fe2O3 showed a considerable PO43- adsorption amount of ca. 6 mmol/g at a low pH region (ca. 2-7) and 3 mmol/g at a high pH region (ca. 8-12). The adsorption data were interpreted with various kinetic and isotherm models. The Langmuir model was more suitable than the Freundlich and Redlich-Peterson models to fit the experimental data of the phosphate adsorption on the APANF@Fe2O3 and the pseudo-second-order model was better matched than the pseudo-first-order and Elovich's models. The results of this study demonstrate that the surface of the fibrous adsorbent was homogenous and the phosphate adsorption behavior of the APANF@Fe2O3 followed a simultaneous chemisorption process into the Fe2O3 layer.

Poly(diallyldimethylammonium-MoS4) based amorphous molybdenum sulphide composite for selectively mercury uptake from wastewater across a large pH region

Amorphous molybdenum sulphide materials are attracting more attention in heterogeneous catalysis, gas adsorption and water remediation fields. Herein, a new type of amorphous molybdenum sulphide composite (poly(diallyldimethylammonium-MoS4), shorten as PDADMA-MoS4) was synthesized via a facile precipitation reaction. Metal adsorption tests of prepared PDADMA-MoS4 composite shows that Hg2+ and Pb2+ concentrations in solution can decrease from 10 ppm to <0.5 ppb level much lower than the drinking water requirement (<2 ppb) in 10 min. The metal adsorption isotherms suggest that maximum metal-uptake capacities are 1460.0 mg/g for Hg (pH = 5) and 433.7 mg/g for Hg (pH = 1), indicating that this sorbent works over a wide pH range (1.0–7.0) to effectively remove Hg from aqueous solution. More importantly, at very low pH = 1, this sorbent material exhibits extraordinarily high selectivity of Hg over Pb and Cu (separation factors βHg/Cu=4.5×104 and βHg/Pb=3.6×104). The excellent Hg capacity and selectivity at low pH region (pH < 2) has shed light on the new generation of adsorbent materials for acidic wastewater treatment.

Enhanced solar light photoreduction of innovative TiO2 nanospherical shell by reduced graphene oxide for removal silver ions from aqueous media

TiO2 nanospherical shell incorporated reduced graphene oxide (RGO) as photoreduction adsorbent catalyst was successfully synthesized via a one-step ecofriendly hydrothermal colloidal suspension solution technique to remove the risk of Ag+ from potable water samples under solar light irradiation. The fabricated photoreduction adsorbent catalyst exhibited an excellent, efficient result by reducing the silver ions to nanoparticles, which can facilely adsorb on its surface under optimum conditions. Several factors were investigated in details, such as solution pH, kinetic isotherm models, competing foreign ions, reduced graphene oxide ratio (rGO) and elution/reuses. The prepared photoreduction adsorbent catalyst effectively utilized in the acidic pH region of 6.5. The results shown that remarkable photoreduction of Ag+ onto TiO2 nanospherical shell surface enhanced by the rGO which has a superior photogenerated carrier recombination as well as high specific surface area obtaining a maximum adsorption capacity of 34.8 mg/g. Moreover, the data confirmed that the foreign competing ions have no affected on the photoreduction adsorption capacity in aqueous media. The used of photoreduction adsorbent catalyst was eluted with 0.5 M thiourea/0.1 M HNO3 to its original form without significant loss in its performance although several cycles after extraction/elution processes were conducted. This photoreduction ecofriendly adsorbent nanocomposite has a potential application in large scale heavy metal ion wastewater treatment process.

Structural and electrosurface properties of iron-containing nanoporous glasses in KNO3 solutions

The paper is devoted to study and comparison of the structural (volume porosity W, structural resistance coefficient β, tortuosity coefficient K, average pore radius r, specific surface area S0) and electrosurface (efficiency coefficient α, counter-ion transport number n+, electrokinetic potential ζ) properties of micro - and macroporous sodium borosilicate glasses containing (Fe 4–6) and not containing (8 V-NT) magnetite phase in 10−4 – 10−1 M KNO3 solutions. It has been found that the incorporation of an iron (III) oxide into basic sodium-borosilicate glass results in changes in the structure of the pore space of both microporous and macroporous glasses. Moreover, it is shown that the presence of magnetite in the structure of porous glasses does not have a noticeable effect on the values of the efficiency coefficients and potassium counter-ion transport number in the neutral pH region. It has also been established that the absolute values of the electrokinetic potential for microporous membranes of both compositions in the neutral pH region are close to each other. For macroporous membranes obtained under the same conditions, the absolute values of the electrokinetic potential for the iron-containing membrane are higher than these for basic membrane 8 V-NT.

Novel ligand functionalized composite material for efficient copper(II) capturing from wastewater sample

Copper (Cu(II)) is a very toxic heavy metal that even at low concentration can affect living organisms. Therefore, designing effective materials with high selectivity and cost-efficiency is essential for the control capturing of toxic Cu(II) ions. This study was developed a ligand based composite material for simultaneous Cu(II) detection and removal from wastewater samples. The composite material was fabricated based on the ligand anchoring onto the mesoporous silica by direct coating approach. The application of Cu(II) detection and adsorption was measured at neutral pH region with exhibition of significant color visualization. The experiment conditions were optimized based on contact time, solution acidity, initial Cu(II) concentration and pH value and diverse metal salt concentrations. The results were revealed that the composite material was not affected with the existing foreign ions and the signal intensity was observed only toward the Cu(II) ion. The composite material was able to detected the low level Cu(II) ion as the detection limit was 0.25 μg/L and the adsorption of highest removal capacity was 171.33 mg/g. In addition, the diverse ions were not reduced the Cu(II) ion adsorption significantly, and the composite material has approximately no adsorption capacity for other ions at this pH. The elution of Cu(II) ions from the saturated composite material was desorbed successfully with 0.20 M HCl. The regenerated adsorbent that remained maintained the high selectivity to Cu(II) ions and exhibited almost the same sorption capacity as that of the original adsorbent. However, the sorption efficiency slightly decreased after ten cycles. Therefore, the proposed material offered a cost-effective material and may be considered a viable alternative for effectively toxic Cu(II) ion capturing from water samples without the need for sophisticated instrument.

Low-molecular-mass nitrophenol-based compounds suitable for the effective tracking of pH gradient in isoelectric focusing

Low-molecular-mass isoelectric point (pI) markers are a reasonable alternative to commonly used peptide and protein pI markers in the field of isoelectric focusing. We present a comparative study dealing with characterization of 44 nitrophenol-based compounds synthesized by the Mannich reaction which pI values cover a pH range from 3.2 to 10.4. The values of pIs of all the presented nitrophenol-based compounds were precisely determined by capillary isoelectric focusing technique (cIEF) when a standard deviation of measurement reached a value of a few hundredths of a pH unit (n ≥ 3). Differences have been found between in silico analysis of acid-base properties of the investigated compounds and the experimental cIEF data especially at the basic pH region. The data from the acidic pH range showed better correlation between these methods. Only three compounds were excluded from the group of pI markers because they contained impurities originating from the synthesis or long-term storage. Based on the presented results we identified 41 nitrophenol-based pI markers (NPIMs) which can fulfill requirements of the most applications in a field of isoelectric focusing analyses.

Cleaning the arsenic(V) contaminated water for safe-guarding the public health using novel composite material

With increasing arsenic contamination scenes reported around the globe, the highly promising materials are important to remove the arsenic from industrial and specified contaminated for safe-guarding the public health. In this study, we have prepared ligand anchoring inorganic-organic frameworks based well-ordered, high surface area composite materials for selective arsenic(V) (As(V)) removal from contaminated water. Adsorption studies were evaluated in batch mode with the function of pH, time, initial As(V) concentration, counter-ions and reuses by suitable eluent. Before starting the As(V) adsorption, the composite materials were protonated using 2.0 M HCl. The materials exhibited high adsorption efficiency in low pH area, however; the neutral pH region (7.0) was selected to avoid the divalent anions effect as the monovalent arsenate species were dominated. In the neutral pH region, the basicity of divalent HAsO42− was much greater than the divalent SO42− and the divalent HAsO42− was easily made the strong hydrogen bonding with the protonated composite materials surface. Then the effects of monovalent and divalent anions were not affected in the selective As(V) adsorption by the composite materials. In addition, the other cations did not affect the As(V) adsorption as the data clarified. The composite material was highly matched to the Langmuir model with the monolayer coverage. In addition, the determined maximum adsorption capacity was 142.25 mg/g. The As(V) was eluted from the composite materials with 2.0 M HCl, and the regenerated to the original pattern. The regenerated materials were exhibited the same functionality and used successively in several adsorption-elution-reuses cycles. Therefore, the newly fabricated composite material is an interesting, efficient and economical sustainable composite material and could be used selective As(V) removal from real contaminated water.

Promising Additives for the Stability of Vanadium Flow Battery Catholytes

The redox flow battery (RFB) has seen an explosion in research activity in recent years due to its attractiveness for large scale energy storage applications (e.g. grid level storage).1-5 RFBs offer many advantages over conventional batteries including their relatively high reliability and long cycle life, as well as the ability to scale their energy and power output independently. The vanadium flow battery (VFB) (also known as the vanadium redox flow battery or all-vanadium flow battery) is currently the most promising of these technologies, with a number of large scale applications and demonstration projects already underway.6 The primary advantage of VFBs is that cross-contamination due to transport through the separating membrane is effectively eliminated because the anolyte and catholyte differ only in the oxidation state of the vanadium. One of the primary disadvantages of VFBs (and RFBs in general) is their relatively low energy density which is limited by the solubility of the different vanadium (reduced/oxidized) species in the electrolyte. In the anolyte, the solubility of V2+ and V3+ generally increases with temperature and decreases with increasing concentration of H2SO4 and this is also true for the solubility of the VIV species, vanadyl (typically in the form of VO2+) ions, in the catholyte.7 However, the solubility characteristics of the VV species, pervanadyl (typically in the form of VO2 +) ions, are considerably more complex. For example, the solubility of vanadium(V) oxide, V2O5, in this region of pH is ~0.1 mol dm-3 or less. Thus, at the concentrations typically encountered in VFB catholytes (>1.5 mol dm-3), VV is expected to be thermodynamically unstable in solution. However, precipitation is usually found to be very slow and, in practice, supersaturated solutions of VV in sulfuric acid can persist for very long periods of time. The stability of these metastable solutions (VFB catholytes) decreases, as expected, as the concentration of VV increases.8, 9 Stability improves with increasing concentration of sulfate and in the presence of certain additives such as H3PO4.9, 10 We have previously reported quantitative studies of the kinetics of VV precipitation from VFB catholytes and demonstrated that the induction time for this process (i.e. the time until precipitation is observed) has an Arrhenius-type dependence on temperature.4 Comprehensive experiments on the variation of the rate of this process with vanadium concentration, sulfate concentration and temperature have allowed us to develop a model which can predict the induction time (and hence, the stability) of VFB catholytes over a wide range of compositions and temperatures.9 We have also published the first quantitative analysis of the effect of H3PO4 and other phosphate based additives on the induction time of VFB catholytes.10 In this talk, we will extend this research to other additives and show the resulting very promising effects on the stability of VFB catholytes. REFERENCES M. Skyllas-Kazacos, M. H. Chakrabarti, S. A. Hajimolana, F. S. Mjalli and M. Saleem, J. Electrochem. Soc., 158, R55 (2011).A. Weber, M. Mench, J. Meyers, P. Ross, J. Gostick and Q. Liu, J. Appl. Electrochem., 41, 1137 (2011).M. A. Miller, A. Bourke, N. Quill, B. J. S. Wainright, R. P. Lynch, D. N. Buckley and R. F. Savinell, J. Electrochem. Soc., 163, A2095 (2016).D. Oboroceanu, N. Quill, C. Lenihan, D. N. Eidhin, S. P. Albu, R. P. Lynch and D. N. Buckley, J. Electrochem. Soc., 163, A2919 (2016).C. Petchsingh, N. Quill, J. T. Joyce, D. N. Eidhin, D. Oboroceanu, C. Lenihan, X. Gao, R. P. Lynch and D. N. Buckley, J. Electrochem. Soc., 163, A5068 (2016).Á. Cunha, J. Martins, N. Rodrigues and F. P. Brito, Int. J. Energy Res., 39, 889 (2015).J. Zhang, L. Li, Z. Nie, B. Chen, M. Vijayakumar, S. Kim, W. Wang, B. Schwenzer, J. Liu and Z. Yang, J. Appl. Electrochem., 41, 1215 (2011).M. Kazacos, M. Cheng and M. Skyllas-Kazacos, J. Appl. Electrochem., 20, 463 (1990).D. Oboroceanu, N. Quill, C. Lenihan, D. N. Eidhin, S. P. Albu, R. P. Lynch and D. N. Buckley, J. Electrochem. Soc., 164, A2101 (2017).D. N. Buckley, D. Oboroceanu, N. Quill, C. Lenihan, D. Ní Eidhin and R. P. Lynch, MRS Advances, 3, 3201 (2018).

Study on Control of pH-Modulation Crystallization Utilizing Concept of Dissociation Equilibrium.

Crystallization by pH adjustment, as a type of reaction crystallization, is a solid-liquid separation method widely used in the area of pharmaceutical and pharmaceutical intermediate manufacturing. On the other hand, 3-alkenyl cephem compound is a typical zwitterionic pharmaceutical intermediate that possesses both an amino group and a carboxylic acid group. Such structure affords three main pH regions in solution and results in difficulties using crystallization by pH adjustment for isolation. As a consequence, 3-alkenyl cephem compound is usually crystallized at the point away from the solubility curve, causing unrestricted nucleation and flocculation behavior for the deposited particles which is difficult to filtrate. In this study, the pKa of 3-alkenyl cephem compound was intensively investigated to inhibit the nucleation. An optimal pH level point was also sought to make monodisperse particles. In particular, during crystallization by pH-modulation operation, the key point was identified to be the number of primary particles aggregated in the secondary particles. It was revealed that the increment number of primary particles led to the generation of larger monodisperse particles. This investigation, combined with solid-liquid equilibrium, enabled the acquisition of target species with good operability for filtration process. This present investigation becomes the prosperity in the zwitterion compound production that it has hardships to crystallize and filtrate.

Electrocatalysis of N-doped carbons in the oxygen reduction reaction as a function of pH: N-sites and scaffold effects

Metal-free nitrogenated amorphous carbon electrodes were synthesised via dc plasma magnetron sputtering and post-deposition annealing at different temperatures. The electrocatalytic activity of the electrodes towards the oxygen reduction reaction (ORR) was studied as a function of pH using cyclic voltammetry with a rotating disk electrode. The trends in onset potential were correlated to the carbon nanostructure and chemical composition of the electrodes as determined via Raman spectroscopy and X-ray photoelectron spectroscopy analysis. Results suggest that: 1) the ORR activity in acidic conditions is strongly correlated to the concentration of pyridinic nitrogen sites. 2) At high pH, the presence of graphitic nitrogen sites and a graphitized carbon scaffold are the strongest predictors of high ORR onsets, while pyridinic nitrogen site density does not correlate to ORR activity. An inversion region where pyridine-mediated activity competes with graphitic-N mediated activity is identified in the pH region close to the value of pKa of the pyridinium cation. The onset of the ORR is therefore determined by the activity of different sites as a function of pH and evidence for distinct reduction reaction pathways emerges from these results.

Surface potential study of ceria/poly(sodium 4-styrenesulfonate) aqueous solution interface

The interfacial properties of the system cerium(IV) oxide/poly(sodium 4-styrenesulfonate) (NaPSS) aqueous solution were studied in a broad pH region by means of inner surface potential, zeta potential and adsorption measurements. Surface potential data were obtained using a single crystal electrode, while zeta potential and adsorption data were obtained using synthetized CeO2 nanoparticles. In order to examine the adsorption of NaPSS on cerium(IV) oxide in detail, surface and electrokinetic potentials of ceria particles were measured in the absence and in the presence of NaPSS.The results of surface potential measurements showed that negatively charged NaPSS molecules exhibit high adsorption affinity towards the CeO2 surface. Titration with NaPSS in the acidic region, where the ceria surface is originally positively charged, suggested that adsorption of negatively charged NaPSS molecules compensates positive charge at the surface and adsorption proceeds until the reversal of surface charge produces a critical value of the potential affecting the state of adsorbed NaPSS molecules. Adsorption of NaPSS on cerium(IV) oxide in the examined pH range was additionally confirmed by zeta potential and adsorption measurements in sodium chloride aqueous solution. From the measured pH dependence of the electrokinetic potential of CeO2 nanoparticles, isoelectric point was determined to be pHiep ≈ 5.4, while the electrokinetic potential in the presence of NaPSS was found to be negative in the whole investigated pH region. Finally, adsorption measurements were carried out which enabled the determination of the maximum surface concentration of the adsorbed polyelectrolyte as Γmax ≈ 1 μmol m−2.

A spectrophotometric and DFT study of the behavior of 6-bromoquercetin in aqueous solution

Acid–base activity, keto-enol tautomerism and complexing properties of 6-bromoquercetin are investigated in water media under different conditions. The constants of dissociation (pKa) have been determined in pH region at various ionic strengths. The analysis of the protonation process is conducted in strongly acidic solutions of HCl. The complexation was studied with trivalent lanthanides. The formation constants of monocomplex species ML (M(III)=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm, Yb, Lu) have been obtained. DFT calculations were carried out for interpretation and verification of received results.

Acoustic characterisation of pH dependant reversible micellar casein aggregation

Ultrasound and light-based measurements were used to monitor changes in agitated and quiescent solution characteristics such as particle size distribution during casein aggregation and redistribution in a model colloidal system. The precipitation of casein micelles was controlled by adjusting the pH of the solution to alter the stability of the micelles. The studied dispersions were prepared at high pH, taken through the isoelectric point to precipitate and then re-dispersed by further lowering the pH at specific intervals. The isoelectric point was determined by zeta potential measurement at each specific pH interval. The isoelectric point of the casein dispersions was in the region of pH 4.3–4.7. Changes in the particle size of this reversible casein system were successfully measured acoustically. The dissolution rate and solution kinetics were subsequently monitored in a wide pH range using a combination of acoustic and light-based methods.

Facile synthesis and photoluminescence mechanism of green emitting xylose-derived carbon dots for anti-counterfeit printing

The realization of long-wavelength emissions and thoroughly understanding of photoluminescence (PL) mechanism are still huge challenges to be addressed for further development of carbohydrate-derived carbon dots (CDs). Herein, novel CDs with excellent green emission were synthesized from a precursor comprising of xylose and m-phenylenediamine in phosphoric acid solution via a simple microwave-assisted hydrothermal method. The PL efficiency was dependent on the combination of different acids and the precursor as well as the synthesis temperature, while the PL properties were mainly related to the acid base environment of precursor. Optical performance and structural characterization revealed that the oxygen-containing groups and protonated amino groups were mainly responsible for the blue and green emission properties, respectively. Moreover, a multi-center fluorescent mechanism on the different PL performances of xylose-derived CDs was proposed and verified by further investigating the pH-dependent PL behaviors. Based on the switching between green and blue emission in different pH regions, the xylose-derived CDs solution was demonstrated to be a promising fluorescent ink for anti-counterfeit printing. This research open a door for value-added utilization of xylose, as well as providing a facile and green strategy for large-scale preparation of CDs.

A selective fluorescent chemosensor for Cd2+ based on 8-hydroxylquinoline-benzothiazole conjugate and imaging application.

A 8-hydroxylquinoline-benzothiazole conjugate (HQ-BT) was facilely synthesized by two steps with >60% total reaction yield. The HQ-BT showed a weak fluorescence that could be strongly enhanced by coordination with various metal ions such as Al3+, Cd2+, Zn2+ in methanol containing 1% water. Interestingly, the selectivity toward Cd2+ was achieved by increasing water fraction to 30% aqueous methanol solution. Thus, the HQ-BT was developed as a new and selective fluorescent chemosensor for Cd2+ in aqueous solution with a broad pH region 4-12. A good linear relationship between the fluorescence intensity and the Cd2+ concentration was found in the range of 0-5 μM with a detection limit of 0.1 μM (S/N = 3). It was also succesfully used for fluorescence imaging of Cd2+ in living cells.

Nanoencapsulation as fluorescence enhancer of vitamin L1 (anthranilic acid). An exhaustive study

This paper describes the guest-host complex formation of anthranilic acid (2-aminobenzoic acid, AA) and different natural and modified cyclodextrins (CDs), using steady state fluorescence. The experimental data point to the formation of 1:1 inclusion complexes with natural (ß and ɣ-CD) and modified (HP-ß, HE-ß and M-ß-CD) CDs. Of the natural CDs, the ß-CD complex showed the highest encapsulation constant (KF) value (14056 ± 1241 M−1). However, modified ß-CDs showed higher binding constants than ß-CDs. Of the modified CDs, M-β-CD showed the highest KF (18622 ± 897 M−1). To gain information on the encapsulation process of M-ß-CD/AA, the thermodynamic parameters of the complexation (ΔH, ΔS and ΔG), were studied. The results showed positive entropy (66 ± 7.9 J mol−1 K−1), negative enthalpy (−5.74 ± 2.96 kJ mol−1) and a change in Gibbs free energy at 25 °C (−24.30 ± 0.27 kJ mol−1). Finally, a computational study carried out using molecular docking simulations showed the high correlation between experimental values and computed scores. The complexation of M-ß-CD/AA depends on several physicochemical factors including temperature and pH. The values of KF exhibited a strong negative relation with temperature and pH. Moreover, the interaction of AA and M-ß-CD was most effective in the pH region where the molecule presents intramolecular hydrogen bonds that neutralize the charge of the protonated species of AA.

Benchmarking the Activity, Stability, and Inherent Electrochemistry of Amorphous Molybdenum Sulfide for Hydrogen Production

AbstractAnodically electrodeposited amorphous molybdenum sulfide (AE‐MoSx) has attracted significant attention as a non‐noble metal electrocatalyst for its high activity toward the hydrogen evolution reaction (HER). The [Mo3S13]2− polymer‐based structure confers a high density of exposed sulfur moieties, widely regarded as the HER active sites. However, their intrinsic complexity conceals full understanding of their exact role in HER catalysis, hampering their full potential for water splitting applications. In this report, a unifying approach is adopted accounting for modifications in the inherent electrochemistry (EC), HER mechanism, and surface species to maximize the AE‐MoSx electroactivity over a broad pH region (0–10). Dramatic enhancements in HER performance by selective electrochemical cycling within reductive (overpotential shift, ηHER ≈ −350 mV) and electro‐oxidative windows (ηHER ≈ −290 mV) are accompanied by highly stable performance in mildly acidic electrolytes. Joint analysis of X‐ray photoelectron spectroscopy, Raman, and EC experiments corroborate the key role of bridging and terminal S ligands as active site generators at low pH, and reveal molybdenum oxysulfides (Mo5+OxSy) to be the most active HER moiety in AE‐MoSx in mildly acidic‐to‐neutral environments. These findings will be extremely beneficial for future tailoring of MoSx materials and their implementation in commercial electrolyzer technologies.