Sustainable stabilization of oil in water emulsions by cellulose nanocrystals synthesized from deep eutectic solvents

There is an urgent global need to develop novel types of environmentally safe dispersing chemicals from renewable resources in order to reduce the environmental impact of oil spills. For this goal, cellulose, the most abundant natural polymeric source, is a promising green, nontoxic alternative that could replace the current synthetic surfactants. In this study, cellulose nanocrystals (CNC) synthesized using a deep eutectic solvent (DES) and two commercially available cellulose nanocrystals were used as marine diesel oil–water Pickering emulsion stabilizers. In particular, oil in water (o/w) emulsion formation and stability of emulsified oil during storing were addressed using a laser diffraction particle size analyzer, image analysis, and oil emulsion volume examination. The particle size of the o/w reference without CNCs after dispersing was over 50 µm and coalescence occurred only a few minutes after the emulsifying mixing procedure. All three investigated CNCs were effective stabilizers for the o/w system (oil droplets size under 10 µm) by preventing the oil droplet coalescence over time (6 weeks) and resulting in a stable creaming layer. The CNCs prepared using green DES systems boasted performance comparable to that of commercial CNCs, and they showed effectiveness at 0.1% dispersant dosage.     

Dual fluorescent labelling of cellulose nanocrystals for pH sensing

Cellulose nanocrystals were converted into ratiometric pH-sensing nanoparticles by dual fluorescent labelling employing a facile one-pot procedure. A simple and versatile three-step procedure was also demonstrated extending the number of fluorophores available for grafting. In this method an amine group was introduced via esterification followed by a thiol-ene click reaction.     

Room temperature synthesis of upconversion fluorescent nanocrystals

Synthesis of nanocrystals that exhibit strong upconversion (UC) luminescence upon infrared excitation has been challenging due to the stringent control needed over experimental variables. Herein, we report a method to synthesize nanocrystals demonstrating high UC at room temperature in aqueous solution on graphene.     

荧光CdS纳米晶的合成与表征

采用有机金属液相法,在较低温度下制备了高质量的荧光CdS纳米晶.TEM、UV-Vis、PL及XRD等研究表明,表面活性剂的浓度、反应时间及反应物配比等对所制备的CdS纳米晶的形貌与尺寸、光谱性能及结晶性能等具有显著的影响.控制合适的反应条件,可以获得单分散、光谱性能优异且结晶性好的CdS纳米晶.     

Monodisperse silica nanoparticles encapsulating upconversion fluorescent and superparamagnetic nanocrystals

A new type of multifunctional silica-coated nanocomposites, detectable by their upconversion fluorescence and addressable by a magnetic field, was synthesized.     

Silica nanocapsules of fluorescent conjugated polymers and superparamagnetic nanocrystals for dual-mode cellular imaging

We describe here a facile and benign synthetic strategy to integrate the fluorescent behavior of conjugated polymers and superparamagnetic properties of iron oxide nanocrystals into silica nanocapsules, forming a new type of bifunctional magnetic fluorescent silica nanocapsule (BMFSN). The resultant BMFSNs are uniform, colloidally stable in aqueous medium, and exhibit the desired dual functionality of fluorescence and superparamagnetism in a single entity. Four conjugated polymers with different emissions were used to demonstrate the versatility of employing this class of fluorescent materials for the preparation of BMFSNs. The applicability of BMFSNs in cellular imaging was studied by incubating them with human liver cancer cells, the result of which demonstrated that the cells could be visualized by dual-mode fluorescence and magnetic resonance imaging. Furthermore, the superparamagnetic behavior of the BMFSNs was exploited for in vitro magnetic-guided delivery of the nanocapsules into the cancer cells, thereby highlighting their potential for targeting biomedical applications.     

Use of fluorous chemistry in the solubilization and phase transfer of nanocrystals, nanorods, and nanotubes

Fluorous chemistry, involving the use of a fluorous label for the functionalization of a substrate and a fluorous solvent for extraction of the functionalized substrate, is shown to be effective in solubilizing gold and CdSe nanoparticles in a fluorous medium, through phase transfer from an aqueous or a hydrocarbon medium. While these nanoparticles were functionalized with a fluorous thiol, single-walled carbon nanotubes and ZnO nanorods could be solubilized in a fluorous medium by reacting them with a fluorous amine. Fluorous chemistry enables the solubilization of the nanostructures in the most nonpolar liquid medium possible.     

Unified concept of solubilization in water by hydrotropes and cosolvents

In the present work hydrophobic dyes, i.e. disperse red 13 (DR-13; (2-[4-(2-chloro-4-nitrophenylazo)-N-ethylphenylamino]ethanol) and Jaune au gras W1201 (1H-indene-1,3(2H)-dione,2-(2-quinolinyl)), are solubilized in water with the help of different additives: acetone and 1-propanol as typical cosolvents, sodium xylene sulfonate (SXS) as a representative of a classical hydrotrope, sodium dodecyl sulfate (SDS) as a typical surfactant, and finally some "solvosurfactants" [ propylene glycol monoalkyl ether derivatives (CiPOj: i = 1, j = 1 and 3; i = 3, j = 1 and 2; i = 4 and tertio-butyl, j = 1) and 1-propoxy-2-ethanol (C3EO1)]. These solvosurfactants are short amphiphiles that do not form well-defined structures in water such as micelles. For all additives an exponential increase in the solubilizations of the two studied hydrophobic dyes was observed when their concentrations in water were increased. Except for the SDS solution, no difference in the overall shapes of the solubilization curves (dye solubility against additive concentration) was found. All the studied molecules were classified according to their hydrotropic efficiencies, i.e., their abilities to solubilize a hydrophobic, sparingly soluble compound in water. The volume of the hydrophobic parts of the studied additives, roughly evaluated by simple calculations, was found to influence strongly the hydrotropic efficiency; i.e. the larger the hydrophobic part of the additive, the better the hydrotropic efficiency. By contrast, the hydrophilic part carrying a charge or not is of minor importance. Taking the hydrophobic part of the molecules as the key parameter, the water solubilization efficiency of cosolvents, hydrotropes, and solvosurfactants can be described in a coherent way.     

Flow injection analysis of volatile phenols in environmental water samples using CdTe/ZnSe nanocrystals as a fluorescent probe

On the basis of flow injection analysis technology, a simple, accurate, and sensitive method has been developed for the determination of volatile phenols in environmental water samples by using CdTe/ZnSe nanocrystals as a fluorescent probe. The influences of coexisting metal ions and volatile phenol substitutes were also investigated. The method developed for analysis of volatile phenols displayed very good linearity in the range from 1.0 × 10⁻⁸ to 4.0 × 10⁻⁷ g L⁻¹, with a correlation coefficient greater than 0.995 and a detection limit down to 2.7 × 10⁻⁹ g L⁻¹ (signal-to-noise ratio 3). The proposed method was successfully applied to determine the content of volatile phenols in environmental water samples, and the quantitative recoveries were 93.4–106.1%. A possible reaction mechanism for the quenching of fluorescence is discussed using UV–vis absorption spectra, fluorescence spectra, and time-resolved luminescence spectra of volatile phenols obtained by titrating a CdTe/ZnSe nanocrystal aqueous solution and zeta potential data.     

Sodium 2-mercaptoethanesulfonate in reversible adduct formation and water solubilization

Sodium 2-mercaptoethanesulfonate (MESNA, coenzyme M) forms 1:1 covalent adducts with highly pi-electron deficient heterocycles. The addition is caused by the thiol function, and the adducts become water soluble as sulfonates. 1H NMR spectroscopy has been used to obtain information about electronic and steric effects on the equilibria between 2-pyrimidinones and their 1:1 MESNA adducts. The adducts are potential prodrugs for biologically interesting 2-pyrimidinones.     

Highly selective fluorescent chemosensors for cadmium in water

The design, synthesis and photophysical evaluation of two new chemosensors 1 and 2 is described for the selective detection of Cd(II) in water at pH 7.4. Both are based on the use of aromatic iminodiacetate receptors that connected to an anthracene fluorophore by covalent methyl spacers. These are highly water-soluble sensors where the fluorescence is ‘switched off’ between pH 3-11, due to photoinduced electron transfer (PET) quenching of the anthracene excited state by the receptor. Upon protonation of the receptor, the emission was however, ‘switched on’. From these changes pK_as of 1.8 and 2.5 were determined for 1 and 2 respectively. Both showed good selectivity for Cd(II) over competitive ions such as group II and Zn(II), Cu(II), Co(II). For 1, having a single receptor, only a weak monomer anthracene emission was observed for the free sensor at pH 7.4 (HEPES buffer, 135 mM NaCl). Upon Zn(II) titration, a broad red shifted emission occurred, centred at 468 nm. In the presence of Cd(II), a similar red shifted emission was also observed, however, this time centred at 506 nm. In contrast to these results, the fluorescence of 2 in the presence of Zn(II) gave rise to typical monomeric anthracene emission, due to suppression of PET, that is, the anthracene emission was ‘switched on’. Nevertheless, in the presence of Cd(II) a broad emission centred at 500 nm was observed, similar to that seen for 1. These ion induced long wavelength emission bands were assigned to the formation of charge-transfer complexes (exciplexes) between the anthracene moieties and the ion-receptor complexes. Importantly, for both 1 and 2, a selective detection of Cd(II) was possible, even in the presence of Zn(II).     

Colorimetric and orange light-emitting fluorescent probe for pyrophosphate in water

A dual-mode probe based on a benzothiazolium hemicyanine chromophore was designed and synthesized for the detection of pyrophosphate (PPi) in water. The use of a fluorescent probe for colorimetric and long-wavelength fluorescence detection of PPi could be suitable for both rapid in-field and bioimaging experiments.     

Determination of antimony in waste water by micelle solubilization spectrophotometry

A simple, sensitive and selective micelle solubilization spectro-photometric method is described for the determination of micro amounts of antimony(III) in waste water with 2-(3,5-dibromo-2-pyri-dylazo)-5-diethylaminophenol (3,5-dibromo-PADAP) as colour reagent and emulsifier OP as solubilizing and sensitizing agent. In 0.15M HCl, antimony forms a blue-green ternary complex with the above-mentioned reagents. The complex exhibits maximum absorption at 630nm, and the value of the apparent molar absorption coefficient is found to be 5.2 × 10⁴1 mol^–1 cm^–1. The complex is stable up to 7 days at room temperature. The system obeys Beer's Law in the range 0–25 g Sb(III) per 10 ml. Most metal ions do not interfere with the determination of antimony.     

CdTe-CdSe nanocrystals capped with dimethylaminoethanethiol as ultrasensitive fluorescent probes for chromium(VI)

We report on the synthesis of water-soluble luminescent colloidal CdTe nanocrystals capped with various stabilizers (mercaptopropanol, thioglycolic acid, mercaptosuccinic acid, mercaptopropionic acid, L-cysteine, reduced L-glutathione, mercaptoethanol and dimethylaminoethanethiol), and their use as fluorescent probes for chromium(VI) ions. The results show that Cr(VI) ions can be ultrasensitively detected with CdTe NCs capped with dimethylaminoethanethiol (DMAET), with high selectivity over Cr(III) and other ions. Synchronous fluorescence spectroscopy was applied to quantify trace levels of Cr(VI) ions with this probe in the 3.0 nM to 0.2 μM concentration range, with a detection limit as low as 0.57 nM. The interaction between the nanocrystals and Cr(VI) ions was investigated in a study on the zeta potentials, UV-Vis absorption spectroscopy and time-resolved luminescence spectroscopy. Electron transfer process occurred and the decay times of the probe remain constant (about 14 ns). This simple and ultrasensitive analytical method was successfully applied to the direct determination of Cr(VI) in spiked samples of environmental waters.

Molecular recognition and stabilization of iminium ions in water

Iminium ions are known to exist only transiently in aqueous solution due to their high reactivity toward hydrolysis. In this communication, we report on the generation and stabilization of iminium ions in aqueous solution via molecular encapsulation using a K12Ga4L6 host. Our studies revealed that tetrahedral host 1 can encapsulate a variety of iminium cations in a molecular recognition process that is selective based on the charge, hydrophobicity, size, and shape of the guest.     

Forming biocompatible and nonaggregated nanocrystals in water using amphiphilic polymers

High-quality nanocrystals formed in organic solvents can be completely solubilized in water using amphiphilic copolymers containing poly(ethylene glycol) or PEG. These copolymers are generated using a maleic anhydride coupling scheme that permits the coupling of a wide variety of PEG polymers, both unfunctionalized and functionalized, to hydrophobic tails. Thermogravimetric analysis, size exclusion chromatography, cryogenic transmission electron microscopy, and infrared spectroscopy all indicate that the copolymers effectively coat the nanocrystals surfaces. The composite nanocrystal-polymer assemblies can be targeted to recognize cancer cells with Her2 receptor and are biocompatible if their surface coatings contain PEG. In the particular case of semiconductor nanocrystals (e.g., quantum dots), the materials in water have the same optical spectra as well as quantum yield as those formed initially in organic solutions.     

Synthesis of organic monolayer-stabilized copper nanocrystals in supercritical water

When water is heated and pressurized above the critical point, it becomes a suitable solvent to employ organic capping ligands to control and stabilize the synthesis of nanocrystals. Without alkanethiol ligands, Cu(NO(3))(2) hydrolyzes to form polydisperse copper(II) oxide particles with diameters from 10 to 35 nm. However, in the presence of 1-hexanethiol, X-ray photoelectron spectroscopy, selected area electron diffraction, and transmission electron microscopy reveal the formation of copper nanocrystals approximately 7 nm in diameter. The use of a different precursor, Cu(CH(3)COO)(2), leads to particles with significantly different morphologies. A mechanism is proposed for sterically stabilized nanocrystal growth in supercritical water that describes competing pathways of hydrolysis to large oxidized copper particles versus ligand exchange and arrested growth by thiols to produce small monodisperse Cu nanoparticles.