Basic Aqueous Solution Research Articles

Nanofillers dissolution as a crucial challenge for the performance stability of thin-film nanocomposite desalination membranes

With the aim to improve the intrinsic separation performance, integration of nanofillers toward polyamide thin-film nanocomposite (TFN) membranes is a very active research area. Mesoporous silica nanoparticles (MSN), among other types of nanomaterials, are often used for that purpose. However, one of the distinguishing features of MSN is their dissolution in basic aqueous solutions. To date, no investigation in the literature has considered to study the influence of MSN nanofillers dissolution on the separation performance of the respective TFN polyamide membranes. This paper investigates how hydrophobic functionalization of MSN can improve the stability of MSN in aqueous solutions and enhance the stability of the respective TFN membranes over a prolonged filtration time at different pH values. The results showed that TFN membranes containing the octadecyltrichlorosilane-functionalized MSN had only ≈ 6% decline in salt rejection compared to ≈ 35% decline for the membrane containing unfunctionalized nanofillers accompanied by increasing water permeability after 240 h filtration time (120 h at pH 5, then 120 h at pH 9). Furthermore, the durability of the barrier layer after a prolonged use for desalination was also investigated via filtration of solutions of dextran with different molecular weight and assessing the dextran rejection for the native and used membranes. From the results of all parallel analyses of nanofiller and TFN membrane structure it is concluded that OTS functionalization of MSN cannot only enhance the TFN membrane separation performance, but also reduce the dissolution tendency of MSN. This was attributed to the formation of a protective organic layer leading to significantly enhanced long-time stability of the respective TFN membranes.

Prebiotic Sugar Formation Under Nonaqueous Conditions and Mechanochemical Acceleration.

Monosaccharides represent one of the major building blocks of life. One of the plausible prebiotic synthesis routes is the formose network, which generates sugars from C1 and C2 carbon sources in basic aqueous solution. We report on the feasibility of the formation of monosaccharides under physical forces simulated in a ball mill starting from formaldehyde, glycolaldehyde, DL-glyceraldehyde as prebiotically available substrates using catalytically active, basic minerals. We investigated the influence of the mechanic energy input on our model system using calcium hydroxide in an oscillatory ball mill. We show that the synthesis of monosaccharides is kinetically accelerated under mechanochemical conditions. The resulting sugar mixture contains monosaccharides with straight and branched carbon chains as well as decomposition products. In comparison to the sugar formation in water, the monosaccharides formed under mechanochemical conditions are more stable and selectively synthesized. Our results imply the possibility of a prebiotic monosaccharide origin in geochemical environments scant or devoid of water promoted by mechanochemical forces such as meteorite impacts or lithospheric activity.

Mechanistic Studies on the Reaction of [FeIII(edta)(H2O)]– with Piloty′s Acid as Source for HNO

In earlier work performed in our laboratories, the reaction of [FeII(edta)(H2O)]2– with ·NO(g) was studied as a trap for ·NO(g) and found to be very efficient with a formation constant of ca. 106 M–1 at 25 °C. The formed nitrosyl complex was shown to have substantial FeIII‐NO–, i.e. nitroxyl, character in line with detailed computational studies performed before. In recent years, we developed an interest in the chemistry of HNO/NO– (nitroxyl) and decided to use [FeIII(edta)(H2O)]– as starting material to see whether the reaction of this complex would lead directly to the formation of the nitroxyl complex by using a source for HNO. In the present study, Piloty's acid (benzenesulfonylhydroxamic acid) was used as source for HNO, since it cleanly hydrolysis in basic aqueous solution to release HNO. The results of our studies clearly indicate that the same reaction product as found for the reaction of [FeII(edta)(H2O)]2– with ·NO(g), was formed in the reaction of [FeIII(edta)(H2O)]– with Piloty's acid. A detailed spectroscopic and mechanistic study of the latter reaction is reported.

Fluorescence pH-dependent sensing of Zn(II) by a tripodal ligand. A comparative X-ray and DFT study

A new complex was obtained starting from a pyridyl/phenolic/benzothiazole functionalized ligand (BPAP) with zinc acetate. The structural and photoluminescence properties of the complex were investigated by X-ray diffraction and confirmed by DFT calculations. By comparing the results with previous studies, we found that the mode of binding of the sensor was influenced by the pH of the medium, changing the zinc coordination sphere. In a basic aqueous solution, the metal coordinates two neutral nitrogen atoms and two negative sites, the phenate oxygen and the deprotonate amide nitrogen and a water molecule. In this condition, the ligand was found to behave as a more sensitive naked eye fluorescence chemosensor towards Zn2+, showing blue photoluminescence with a lower detection limit of 375 nM.

The Effect of Gamma Irradiation on the Ion Exchange Properties of Caesium-Selective Ammonium Phosphomolybdate-Polyacrylonitrile (AMP-PAN) Composites under Spent Fuel Recycling Conditions

The caesium radioisotopes 134Cs, 135Cs, and 137Cs are highly problematic medium-lived species produced during nuclear fission, due to their high radioactivity and environmental mobility. While many ion exchange materials can readily isolate Cs+ ions from neutral or basic aqueous solutions, only ammonium phosphomolybdate (AMP) functions effectively in acidic conditions, removing caesium even down to trace levels. Composites of AMP in a porous polymeric support such as polyacrylonitrile (PAN) can be used to selectively remove Cs+ ions from acidic aqueous decontamination liquors as well as other liquid wastes, and are promising for the isolation of Cs+ isotopes in spent fuel reprocessing. While both AMP and PAN have demonstrable acid stability, and PAN has known resistance to gamma radiation, AMP-PAN composites have received only a limited analysis of their physiochemical and ion exchange performance following irradiation. In this publication, we explore the effect of high levels of gamma irradiation on the ion exchange properties of AMP and AMP-PAN as a Cs+-selective adsorbent under spent fuel dissolver liquor concentrations and acidity. We demonstrate no significant reduction in performance with respect to uptake kinetics or capacity upon irradiation, abiding by the same absorption mechanism observed in the established literature.

A versatile cyclic dipeptide hydrogelator: Self-assembly and rheology in various physiological conditions

Peptide-based supramolecular hydrogels as functional soft materials hold great promising for biomedical applications. However, much effort has been devoted to the finding and development of linear peptide hydrogelators and related hydrogel materials. Usually, linear peptide hydrogels are subject to the environmental variations and suffer from rapid enzymatic degradation in physiological conditions, limiting their more broad range of applications. Herein, we discover that a cyclic dipeptide (Cyclo-(Leu-Phe), CLF) can serve as a versatile hydrogelator for formation of supramolecular hydrogels at various physiological and harsh environments including the presence of salts, proteins and enzymes as well as acidic and basic aqueous solutions. Importantly, the CLF hydrogels show robust stability and excellent rheological properties at the various conditions, which are attributable to the rigid molecular structure of cyclic dipeptides and their strong 3-dimentional intermolecular hydrogen bonding networks. Hence, cyclic dipeptides provide a new alternative for development of peptide-based hydrogel materials with properties and functions more adapted for the complex and harsh environments.

A Potential Amphiprotic Sponge with a Controlled Release Characteristic of Protons on Demand for Oil/Water Separation and Acid/Base Neutralization

AbstractUltralight sponges with the ability to release protons on demand, namely, superhydrophobic melamine formaldehyde sponges (SHpho‐MFSs), which are characterized as being safe‐to‐handle, convenient‐to‐use, easy‐to‐store, easy‐to‐carry, and easy‐to‐collect, are switched from superhydrophilic MFSs (SHphi‐MFSs) by a one‐step ultrasound treatment at a low pH. The wettability of the SHphi‐MFS is completely switched from the outside to the inside of the MFS. After wettability switching is achieved, the SHpho‐MFS that is prewetted with water and oil is able to selectively separate both water and oil, respectively. A compressed SHpho‐MFS also exhibits excellent separation performance of a water‐in‐oil emulsion. Furthermore, since the SHpho‐MFS can linearly release protons in an aqueous solution, during the oil/water separation (water‐removing), an aqueous solution of a strong base is neutralized or changed into a certain solution with a tailored pH by a simple filtration step using an appropriately sized SHpho‐MFS. The SHpho‐MFS can maintain a slow reaction rate and reduce the sudden release of heat during neutralization. Controlled release of the SHpho‐MFS capable of the ordered production of protons on demand is also achieved because the release “on and off” behavior of protons is repeatedly observed for every cycle.

Reactivity of uranium in geopolymers, confinement matrices proposed to encapsulate MgZr waste

The U reactivity has been examined in three geopolymer (GP) formulations: GP, GP containing 1.25 M of NaF (GP-NaF) and GP containing 1.25 M of NaF and a double concentration of NaOH (GP-NaF-NaOH). In a previous study, two mechanisms representative of uranium oxidation in basic aqueous solutions have been proposed, depending on the ratio of the fluoride and hydroxide ions concentrations (RF/OH). For RF/OH < 1, U is protected by the oxides layer UO2+x (mechanism A), while for RF/OH > 1, U is continuously corroded (mechanism B). We have exploited the results on the GP pH evolution to understand the uranium behavior in geopolymers. With NaF at the saturated concentration in the geopolymers, if pH > 13.8, RF/OH is lower than 1, while for pH < 13.8, this ratio is higher than 1. Moreover, the pH would be stabilized at 13.4 for GP and GP-NaF and 14.1 for GP-NaF-NaOH. The ratio RF/OH can thus reach values higher than 1 in GP-NaF but not in GP-NaF-NaOH. Consequently, mechanism A can be applied for the U behavior in GP and GP-NaF-NaOH and mechanism B can occur in GP-NaF because of the pH decrease. The open circuit potential measurements confirm that in GP and GP-NaF-NaOH, U is protected by the oxides layer UO2+x while in GP-NaF, corrosion is observed after 10 days. In GP and GP-NaF-NaOH, the presence of the redox couple UO2+x/UO2 has been put in evidence by electrochemical impedance spectroscopy. This technique confirms a different behavior of uranium in GP-NaF. In the presence of fluoride ions, cracks in the GP have been observed and a great quantity of uranium oxide has been produced.

Effect of Naphthenate Formation on the Anti-Adhesive Behavior of Clathrate Hydrates at a Water–Oil Interface

This work investigates the effect of naphthenic acid and naphthenate on the adhesion behavior of a clathrate hydrate probe at a water–oil interface. The addition of 0.5 wt % myristic acid in the cyclopentane (CP)/n-decane mixture reduces the adhesion force acting on the probe by 51.8% from the lowered interfacial tension between the hydrate probe and aqueous phase. With the basic aqueous solution, the precipitate layer of calcium naphthenate is formed at the water–oil interface. When the concentration of myristic acid rises above 0.1 wt %, the precipitate layer formed at the interface blocks the contact between the hydrate probe and aqueous phase completely. The anti-adhesive force pushing on the hydrate probe is induced toward the positive vertical direction. In this case, the precipitated calcium naphthenate acts like an anti-agglomerant (AA) that inhibits the agglomeration of hydrate particles. Our present findings imply that the crude oil of high acidity may alleviate the agglomeration of hydrate particles in the oil pipeline by inducing naphthenate formation.

A new solvent extraction method with gas chromatography–Mass spectrometry for bisphenol a determination in canned foods

A new reliable simple solvent extraction method for the endocrine disruptor bisphenol A (BPA) in canned food was developed employing an aqueous basic extraction solution of 0.25 M K2CO3/0.10 M NaOH after spiking with BPA-d16 as internal standard. The BPA was next extracted into diethyl ether after solution acidification to pH = 4 and filtration. Homogenous acetylation at dry basic conditions (acetic anhydride as derivatization agent and solvent with sodium acetate as catalyst) after diethyl ether evaporation was carried out for 30 min at 110 °C. Detection of the acetylated BPA was carried out by gas chromatography–electrospray ionization/mass spectrometry (GC–EI/MS) in the selected ion monitoring (SIM) mode with pulsed split-less mode. The method was applicable in terms of eliminating the use of solvents like acetonitrile for the extraction step, where relatively long evaporation times may have been needed to evaporate acetonitrile. Also, removing lipids and precipitating most of the proteins at acidic conditions (pH = 4) prior to diethyl ether extraction can replace the often used heptane or hexane or solid sorbents. The method was tested linear with limit of linearity (LOL = 750 μg/L) and with coefficient of determination (R2= 0.998), repeatable with relative standard deviation (RSDr &lt; 7%) with instrument detection limit (IDL) of 0.01 μg/L and limit of quantitation (LOQ) of 0.034 μg/L. The method detection limit (MDL) ranged from 0.3 μg/kg to 3.2 μg/kg based on 1 g sample (wet weight). Recovery ranged from 85% to 94% with the relative standard deviations of 2%–13%. BPA concentrations in tested canned foods from outlet stores ranged from &lt;MDL to 57.4 ± (2.6) μg/kg which were below the specific limit for BPA migration in food proposed by the European Union (EU) and within the food safety and quality criteria. The extraction and derivatization steps for BPA were unique and have not been reported in literature.

Chemically Resistant, Electric Conductive, and Superhydrophobic Coatings

AbstractIn this study, the fabrication of superhydrophobic and conductive coatings applying a facile coating method is reported. The droplet‐assisted growth and shaping (DAGS) method is used to synthesize silicone nanofilament–based superhydrophobic coatings. Dip coating of superhydrophobic substrates in carbon nanofiber suspensions is performed to prepare superhydrophobic/conductive coatings. The prepared coatings combine electric conductivity, optical transparency, and superhydrophobicity with low sliding angles. The coatings show stability to water immersion and exposure to extreme humid conditions. Also, they exhibit good chemical resistance after several days of immersion in acidic and basic aqueous solutions. A key factor of such coatings is the mechanical durability which is improved by the addition of Parafilm‐M.

Stabilization of a Cyclometalated Ruthenium Sensitizer on Nanocrystalline TiO2 by an Electrodeposited Covalent Layer.

A cyclometalated ruthenium sensitizer 3 containing a triphenylamine unit was synthesized and immobilized on a nanocrystalline TiO2 surface. By using oxidative electrochemical deposition, a covalent layer of a related cyclometalated ruthenium complex 2 was coupled to the top of dye 3. Electrochemical studies suggested that complex 2 was immobilized on the TiO2/3 film surface by a tetraphenylbenzidine linker to form a dimer-like structure. The immobilization of 3 and 2 was further supported by absorption spectral analysis. The resulting electrodeposited TiO2/(3+2) film displays significantly enhanced sensitizer stabilization toward basic aqueous NaOH solution with respect to the original TiO2/3 film. The dye-sensitized solar cells with the TiO2/(3+2) photoanode display a power conversion efficiency of 4.4%, which is slightly inferior to that with the TiO2/3 film (5.1%) under the same measurement conditions.

Core-Shell Structured Cobalt Sulfide/Cobalt Aluminum Hydroxide Nanosheet Arrays for Pseudocapacitor Application.

The direct synthesis of nanostructured electrode materials on three-dimensional substrates is important for their practical application in electrochemical cells without requiring the use of organic additives or binders. In this study, we present a simple two-step process to synthesize a stable core-shell structured cobalt sulfide/cobalt aluminum hydroxide nanosheet (LDH-S) for pseudocapacitor electrode application. The cobalt aluminum layered double hydroxide (CoAl-LDH) nanoplates were synthesized in basic aqueous solution with a kinetically-controlled thickness. Owing to the facile diffusion of electrolytes through the nanoplates, thin CoAl-LDH nanoplates have higher specific capacitance values than thick nanoplates. The as-grown CoAl-LDH nanoplates were transformed into core-shell structured LDH-S nanosheets by a surface modification process in Na2 S aqueous solution. The chemically robust cobalt sulfide (CoS) shell increased the electrochemical stability compared to the sulfide-free CoAl-LDH electrodes. The LDH-S electrodes exhibited high electrochemical performance in terms of specific capacitance and rate capability with a galvanostatic discharge of 1503 F g-1 at a current density of 2 A g-1 and a specific capacitance of 91 % at 50 A g-1 .

A heterometallic metal-organic framework based on multi-nuclear clusters exhibiting high stability and selective gas adsorption.

The design and synthesis of porous heterometallic metal-organic frameworks (MOFs) with high thermal and chemical stability is a challenging task at present. In this work, by the heterometallic cooperative crystallization (HCC) approach, an original heterometallic MOF based on a tetra-carboxylic ligand has been solvothermally synthesized [In6O3Tb3O(CBDA)3]·18DMF·3H2O (In/Tb-CBDA) [CBDA = 5,5'-(carbonylbis(azanediyl))-diisophthalic acid, DMF = N,N-dimethylformamide]. The framework of In/Tb-CBDA is cooperatively assembled from the rarely reported tetra-nuclear In4O2(COO)4 and tri-nuclear Tb3O(COO)6 clusters, and an organic ligand. Topological analysis indicates that In/Tb-CBDA exhibits a new (4,4,6)-connected topology with the Schläfli symbol (4·63·82)6(43·69·83)2(62·84)3. Noteworthy, forming multi-nuclear metal clusters prompts the framework to maintain high stability under the conditions of heating to 150 °C, exposure to air, and soaking in acidic and basic aqueous solutions for 12 h. After desolvation, In/Tb-CBDA shows permanent porosity proved by N2 adsorption isotherms. In addition, theoretical ideal adsorption solution theory (IAST) calculation indicates that In/Tb-CBDA displayed high selective adsorption of CO2/CH4, C2H6/CH4 and C3H8/CH4 at room temperature. This work shows a striking example of a porous heterometallic MOF material with high thermal and chemical stability, which exhibits high-efficiency selective gas adsorption behaviour.

Highly-Soluble Cyanine J-aggregates Entrapped by Liposomes for In Vivo Optical Imaging around 930 nm.

Near infrared (NIR) dyes are useful for in vivo optical imaging. Liposomes have been used extensively for delivery of diverse cargos, including hydrophilic cargos which are passively loaded in the aqueous core. However, most currently available NIR dyes are only slightly soluble in water, making passive entrapment in liposomes challenging for achieving high optical contrast.Methods: We modified a commercially-available NIR dye (IR-820) via one-step Suzuki coupling with dicarboxyphenylboronic acid, generating a disulfonated heptamethine; dicarboxyphenyl cyanine (DCP-Cy). DCP-Cy was loaded in liposomes and used for optical imaging.Results: Owing to increased charge in mildly basic aqueous solution, DCP-Cy had substantially higher water solubility than indocyanine green (by an order of magnitude), resulting in higher NIR absorption. Unexpectedly, DCP-Cy tended to form J-aggregates with pronounced spectral red-shifting to 934 nm (from 789 nm in monomeric form). J-aggregate formation was dependent on salt and DCP-Cy concentration. Dissolved at 20 mg/mL, DCP-Cy J-aggregates could be entrapped in liposomes. Full width at half maximum absorption of the liposome-entrapped dye was just 25 nm. The entrapped DCP-Cy was readily detectable by fluorescence and photoacoustic NIR imaging. Upon intravenous administration to mice, liposomal DCP-Cy circulated substantially longer than the free dye. Accumulation was largely in the spleen, which was visualized with fluorescence and photoacoustic imaging.Conclusions: DCP-Cy is simple to synthesize and exhibits high aqueous solubility and red-shifted absorption from J-aggregate formation. Liposomal dye entrapment is possible, which facilitates in vivo photoacoustic and fluorescence imaging around 930 nm.

PH-Responsive Pickering Foams Generated by Surfactant-Free Soft Hydrogel Particles.

Pickering foams are foams stabilized by particles and are generally known to have good stability. A special subclass of particle-stabilized foams includes stimuli-responsive Pickering foams that can be formed or deconstructed by applying an external stimuli or changing the environmental conditions; such intelligent particles could find use in many practical applications. Here, we synthesized surfactant-free biocompatible poly[2(diethylamino)ethyl methacrylate] (PDEAEMA) hydrogel particles (HGPs) by emulsion polymerization. The morphology, structure, and surface charge of the HGPs were characterized by TEM, DLS, and the zeta potential, respectively. We have observed that the pH values of the aqueous solution have a strong influence on the formation of the Pickering foams in the presence of PDEAEMA HGPs. Namely, at pH values ≤4.0 no Pickering foams were produced, while at pH values >4.0 stable Pickering foams were formed. Moreover, the height, size and bubble size distribution of Pickering foams are strongly influenced by the pH values of aqueous solution and PDEAEMA HGPs concentration. The formed Pickering foams in basic aqueous solution can all be conveniently deconstructed by changing the pH values to below 4.0. Interestingly, the dried lamellas of the Pickering foams were constituted by either monolayers or multilayers of PDEAEMA HGPs as demonstrated by SEM.

Water-based polyurethane formulations for robust superhydrophobic fabrics

Free radical copolymerization of acrylic acid (AA), 2-hydroxyethyl acrylate (HEA), and monomethacryloxypropyl terminated poly(dimethyl siloxane) (PDMS-MA) yielded graft (g) copolymers P(AA-HEA)-g-PDMS. The molecular weights of the three used PDMS-MA macromers were 0.7, 5.0, and 10.0 kDa, respectively, and the respective weight fractions of AA, HEA, and PDMS-MA in the three synthesized copolymers were 10.0, 20.0, and 70.0 wt%. The copolymers were dispersed in water as micelles due to the water-soluble HEA units and salt formation from the AA groups with added triethylamine. Mixing these aqueous copolymer micellar solutions with a water-soluble blocked tetraisocyanate yielded water-based polyurethane (PU) formulations. Soaking fabric samples in such a water-based formulation and then withdrawing, drying, and heating the samples at 150 or 180 °C produced on the fabric fibers a crosslinked coating that was ∼220 nm thick and surface-enriched with PDMS. A systematic study was performed to investigate factors affecting the hydrophobicity of the coated fabric samples. These factors included varying the concentration of the aqueous P(AA-HEA)-g-PDMS coating solutions, the molar ratio of isocyanate groups to the AA and HEA groups, the coating curing times at 150 °C, and the molecular weight of the PDMS side chains. This study further established that the coatings could be cured in 7 min at 180 °C and fabric samples coated by P(AA-HEA)-g-PDMS10k with PDMS molecular weight at 10.0 kDa were the most hydrophobic. The coatings were stable against real laundry tests, abrasion by sandpaper, and soaking in aqueous acid and base solutions. Thus, robust superhydrophobic fabrics were obtained from using a water-based environmentally friendly formulation and this coating process was convenient, rapid, and practical.

Time-Resolved Spectroscopic and Density Functional Theory Investigation of the Photogeneration of a Bifunctional Quinone Methide in Neutral and Basic Aqueous Solutions.

Binol quinone methides (BQMs) can be generated from 1,1′-(2,2′-dihydroxy-1,1′-binaphthyl-6,6′-diyl)bis(N,N,N-trimethylmethanamiuium) bromide (BQMP-b) in a 1:1 MeCN:H2O mixed solution via a ground state intramolecular proton transfer (GSIPT), as mentioned in our previously reported studies. Here, the photoreaction of BQMP-b in neutral and basic aqueous solution (pH = 7, 10, 12) was investigated to explore the possible mechanisms and the key intermediates produced in the process of the photoreaction and to examine whether they are different from those in a neutral mild-mixed MeCN:H2O solution. The studies were conducted using femtosecond transient absorption (fs-TA), nanosecond transient absorption (ns-TA), and nanosecond time-resolved resonance Raman spectroscopy (ns-TR3) in conjunction with results from density functional theory (DFT) computations. The results showed that BQMP-b was deprotonated initially and produced BQMs species more effectively through an E1bc elimination reaction in a strong basic aqueous condition (pH = 12), which differed from the reaction pathway that took place in the solution with pH = 7 or 10. A related single naphthol ring molecule 1-(6-hydroxynaphthalen-2-yl)-N,N,N-trimethylmethanaminium bromide (QMP-b) that did not contain a second naphthol ring was also investigated. The related reaction mechanisms are elucidated in this work, and it is briefly discussed how the mechanisms vary as a function of aqueous solution pH conditions.

A Stable Zr(IV)-Based Metal-Organic Framework Constructed from C═C Bridged Di-isophthalate Ligand for Sensitive Detection of Cr2O72- in Water.

As the Cr2O72- anion is highly toxic, new sensors have been developing for its effective detection from water, among which metal-organic frameworks (MOFs) show distinct superiority over many other materials. Herein, a new fluorescent Zr(IV)-based MOF, [Zr6O4(OH)8(H2O)4(sbtc)2] (referred to as BUT-28), based on the di-isophthalate ligand with a central CH═CH moiety, trans-stilbene-3,3',5,5'-tetracarboxylate (sbtc4-), has been prepared and structurally determined. The MOF shows excellent stability in neutral, highly acidic, and weakly basic aqueous solutions. Moreover, no essential uptake loss in three cycles of water vapor adsorption-desorption measurements was observed for BUT-28, suggesting the robustness of the porous framework and its great potential for long-term use. Fluorescent measurements were carried out for BUT-28 and an isostructural MOF, Zr-abtc, which is constructed from the di-isophthalate ligand with a central N═N moiety, azobenzene-3,3',5,5'-tetracarboxylate (abtc4-). Interestingly, Zr-abtc shows very weak fluorescent emission. In contrast, BUT-28 exhibits relatively strong fluorescence and serves as a promising sensory material for the detection of trace Cr2O72- (limit of detection: 36 ppb) in aqueous solutions by selective and sensitive fluorescence quenching effect.

Large Swelling Capacities of Crosslinked Poly(N-isopropylacrylamide) Gels in Organic Solvents

ABSTRACTPNIPAM hydrogels are widely studied materials which swell in a great extent in water and water like solvents (e.g. alcohols). The hydrophilic nature of PNIPAM networks is very attractive however it is an important disadvantage at the moment of encapsulating hydrophobic drugs, which minimize their use in other fields. In this work we studied the swelling in different solvent mixtures with water and also in pure nonaqueous solvents, some of them immiscible with water. Accordingly, PNIPAM gels swell strongly in highly polar solvents (e.g. chloroform) but it does not swell in slightly polar solvents (e.g. toluene). The main interaction between the solvent and the polymer chain seems to involve the hydrogen bonding with the amide group, according to the calculated Hansen parameters (δh). It is possible to swell the gel in binary or ternary mixtures containing toluene. In that way, non-polar substances can be loaded inside the gel to change its properties. As a proof of concept, polyaniline (PANI) solubilized in chloroform using camphorsulfonate as solubilizing counterion. The obtained nanocomposites become sensitive to pH changing color and conductivity when exposed to basic or acidic aqueous solutions.