Development of Nylon 6 nanofibers modified with Cyanex-272 for cobalt recovery.

With a worldwide ever increasing demand for metals, particularly for the manufacture of electronics and batteries, there is not only a concurrent need to recover these materials from their subsequent waste streams but also a need to make advancements to do this via development of more efficient and eco-friendly processes for metal recovery; solid-phase extraction can be considered a promising alternative to conventional processes. This work studied the production of novel nanofibers modified with Cyanex 272 and their application in the recovery of cobalt present in aqueous solution The nanofibers produced by forcespinning were characterized by SEM, FT-IR and TGA and the extraction of cobalt was evaluated by variation of the pH, solid:liquid (S:L) ratio, extraction time and Cyanex 272 content in the nanofibers. The best extraction efficiency was 99.96%, achieved under the following conditions: pH 8; (S:L) ratio of 1:200; 25% of Cyanex 272; Extraction time of 60 min. The maximum extraction capacity obtained was 15.46 mg Co/g of nanofiber and 70.15 mg Co/g of extractor. In successive reuse cycles, the results demonstrated that the extraction efficiency was maintained at over 85%. The findings showed that Nylon 6/Cyanex 272 nanofibers are a new robust and promising material for the recovery of heavy metals from aqueous solution, confirming that nanofibers have an efficiency similar to conventional liquid-liquid extraction, without the disadvantage of volatile organic compounds emissions generated by the use of organic diluents.

Investigating the effect of N-doping on carbon quantum dots structure, optical properties and metal ion screening.

Carbon quantum dots (CQDs) derived from biomass, a suggested green approach for nanomaterial synthesis, often possess poor optical properties and have low photoluminescence quantum yield (PLQY). This study employed an environmentally friendly, cost-effective, continuous hydrothermal flow synthesis (CHFS) process to synthesise efficient nitrogen-doped carbon quantum dots (N-CQDs) from biomass precursors (glucose in the presence of ammonia). The concentrations of ammonia, as nitrogen dopant precursor, were varied to optimise the optical properties of CQDs. Optimised N-CQDs showed significant enhancement in fluorescence emission properties with a PLQY of 9.6% compared to pure glucose derived-CQDs (g-CQDs) without nitrogen doping which have PLQY of less than 1%. With stability over a pH range of pH 2 to pH 11, the N-CQDs showed excellent sensitivity as a nano-sensor for the highly toxic highly-pollutant chromium (VI), where efficient photoluminescence (PL) quenching was observed. The optimised nitrogen-doping process demonstrated effective and efficient tuning of the overall electronic structure of the N-CQDs resulting in enhanced optical properties and performance as a nano-sensor.

Surface Functionalized MXenes for Wastewater Treatment-A Comprehensive Review.

Over 80% of wastewater worldwide is released into the environment without proper treatment. Whilst environmental pollution continues to intensify due to the increase in the number of polluting industries, conventional techniques employed to clean the environment are poorly effective and are expensive. MXenes are a new class of 2D materials that have received a lot of attention for an extensive range of applications due to their tuneable interlayer spacing and tailorable surface chemistry. Several MXene-based nanomaterials with remarkable properties have been proposed, synthesized, and used in environmental remediation applications. In this work, a comprehensive review of the state-of-the-art research progress on the promising potential of surface functionalized MXenes as photocatalysts, adsorbents, and membranes for wastewater treatment is presented. The sources, composition, and effects of wastewater on human health and the environment are displayed. Furthermore, the synthesis, surface functionalization, and characterization techniques of merit used in the study of MXenes are discussed, detailing the effects of a range of factors (e.g., PH, temperature, precursor, etc.) on the synthesis, surface functionalization, and performance of the resulting MXenes. Finally, the limits of MXenes and MXene-based materials as well as their potential future research directions, especially for wastewater treatment applications are highlighted.

Continuous flow vortex fluidic-mediated exfoliation and fragmentation of two-dimensional MXene.

MXene (Ti2CT x ) is exfoliated in a vortex fluidic device (VFD), as a thin film microfluidic platform, under continuous flow conditions, down to ca 3 nm thin multi-layered two-dimensional (2D) material, as determined using AFM. The optimized process, under an inert atmosphere of nitrogen to avoid oxidation of the material, was established by systematically exploring the operating parameters of the VFD, along with the concentration of the dispersed starting material and the choice of solvent, which was a 1 : 1 mixture of isopropyl alcohol and water. There is also some fragmentation of the 2D material into nanoparticles ca 68 nm in diameter.

Selective Calixarene-Directed Synthesis of MXene Plates, Crumpled Sheets, Spheres, and Scrolls.

Fully exploiting the electronic and mechanical properties of 2D laminar materials not only requires efficient and effective means of their exfoliation into low dimensional layers, but also necessitates a means of changing their morphology so as to explore any enhancement that this may offer. MXenes are a rapidly emerging new class of such laminar materials with unique properties. However, access to other morphologies of MXenes has not yet been fully realised. To this end we have developed the synthesis of MXenes (Ti2 C) as plates, crumpled sheets, spheres and scrolls, which involves selective intercalation of p-phosphonic calix[n]arenes, with control in morphology arising from the choice of the size of the macrocycle, n=4, 5, 6, or 8. This opens up wider avenues of discovery/design for new morphologies from the wider family of MXenes beyond Ti2 C, along with opportunities to exploit any new physico-chemical properties proffered.

Calixarene Assisted Rapid Synthesis of Silver-Graphene Nanocomposites with Enhanced Antibacterial Activity.

Demonstrated herein is a single rapid approach employed for synthesis of Ag-graphene nanocomposites, with excellent antibacterial properties and low cytotoxicity, by utilizing a continuous hydrothermal flow synthesis (CHFS) process in combination with p-hexasulfonic acid calix[6]arene (SCX6) as an effective particle stabilizer. The nanocomposites showed high activity against E. coli (Gram-negative) and S. aureus (Gram-positive) bacteria. The materials were characterized using a range of techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-vis spectrophotometry, FT-IR, and X-ray powder diffraction (XRD). This rapid, single step synthetic approach not only provides a facile means of enabling and controlling graphene reduction (under alkaline conditions) but also offers an optimal route for homogeneously producing and depositing highly crystalline Ag nanostructures into reduced graphene oxide substrate.

Protein camouflage in cytochrome c-calixarene complexes.

Small molecules that recognize protein surfaces are important tools for modifying protein interaction properties. Since the 1980s, several thousand studies concerning calixarenes and host-guest interactions have been published. Although there is growing interest in protein-calixarene interactions, only limited structural information has been available to date. We now report the crystal structure of a protein-calixarene complex. The water-soluble p-sulfonatocalix[4]arene is shown to bind the lysine-rich cytochrome c at three different sites. Binding curves obtained from NMR titrations reveal an interaction process that involves two or more binding sites. Together, the data indicate a dynamic complex in which the calixarene explores the surface of cytochrome c. In addition to providing valuable information on protein recognition, the data also indicate that the calixarene is a mediator of protein-protein interactions, with potential applications in generating assemblies and promoting crystallization.

Dimeric nanocapsule induces conformational change.

An induced cis-trans-trans (rctt) chair to cone structural rearrangement is forced by the addition of a pentacoordinate zinc(II) complex, overcoming thermodynamic and kinetic factors to produce the first phenyl-substituted zinc dimeric nanocapsule.

Magnetism in metal-organic capsules.

Nickel and cobalt seamed metal-organic capsules have been isolated and studied using structural, magnetic and computational approaches. Antiferromagnetic exchange in the Ni capsule results from coordination environments enforced by the capsule framework.

A family of double-bowl pseudo metallocalix[6]arene discs.

We report the synthesis and magnetic characterisation of a series of planar [M7] (M= Ni(II), Zn(II)) disc complexes [Ni7(OH)6(L1)6](NO3)2 (1), [Ni7(OH)6(L1)6](NO3)2·2MeOH (2), [Ni7(OH)6(L1)6](NO3)2·3MeNO2 (3), [Ni7(OH)6(L2)6](NO3)2·2MeCN (4), [Zn7(OH)6(L1)6](NO3)2·2MeOH·H2O (5) and [Zn7(OH)6(L1)6](NO3)2·3MeNO2 (6) (where HL1 = 2-iminomethyl-6-methoxy-phenol, HL2 = 2-iminomethyl-4-bromo-6-methoxy-phenol). Each member exhibits a double-bowl pseudo metallocalix[6]arene topology whereby the individual [M7] units form molecular host cavities which are able to accommodate various guest molecules (MeCN, MeNO2 and MeOH). Magnetic susceptibility measurements carried out on complexes 1 and 4 indicate weak exchange between the Ni(II) centres.

Rapid formation of metal-organic nano-capsules gives new insight into the self-assembly process.

Metal-organic pyrogallol[4]arene nano-capsules, mixed pyrogallol[4]arene nano-capsules, and mixed metal analogues have been rapidly synthesised by addition of excess copper nitrate to a methanol solution of the corresponding macrocycle(s) (or gallium nano-capsules for the mixed metal system); improved solubility allows for thorough study and elucidation of the assembly process for these discrete metal-organic assemblies.

Ionic dimeric pyrogallol[4]arene capsules.

Ionic capsules based on dimeric arrangements of pyrogallol[4]arenes have been structurally authenticated and suggest that there is a degree of flexibility in capsule formation with further potential for multiple guest encapsulation and manipulation in such arrangements.

Synthesis and structural characterisation of lower rim halogenated pyrogallol[4]arenes: bi-layers and hexameric nano-capsules.

Two lower rim halogenated pyrogallol[4]arenes have been synthesised and structurally characterised as either bi-layer or hexameric nano-capsule motifs depending upon chain length and functionalisation.

Chloromethyl chlorosulfate: a new, catalytic method of preparation and reactions with some nucleophiles.

The reaction of liquid (gamma-) SO3 with CH2Cl2 at room temperature leads to SO3 insertion into the C-Cl bonds, giving the useful chloromethylating agent chloromethyl chlorosulfate (CMCS). The process is very slow but becomes rapid on addition of catalytic quantities of trimethyl borate. The product mixture consists almost entirely of CMCS and the product of further sulfation, methylene bis(chlorosulfate)(MBCS), in a ratio of ca. 2 : 1, but typical yields of CMCS, isolated by distillation, are only 30-35%. The catalysed reaction in the homogeneous liquid phase at -45 degrees C has been followed as a function of time and of reactant concentration by 1H nmr spectroscopy. It is observed that, besides CMCS and MBCS, three additional, transient products (designated A, B and C) are formed. Products A, B and C decompose slowly at -45 degrees C but much more rapidly if the reaction mixture is raised to room temperature, giving additional CMCS and MBCS. From an analysis of the SO3 balance, it is inferred that products A, B and C arise from the reaction of one molecule of CH2Cl2 with respectively two, three and four molecules of SO3; they are suggested to be chloromethyl chloropolysulfates. By measuring initial rates of CMCS formation or total CH2Cl2 consumption, it is shown that the reaction is first order in the catalyst and roughly third order in SO3. A mechanistic scheme is proposed in which SO3 forms equilibrating zwitterionic molecular complexes with CH2Cl2. of 1 : 1, 2 : 1 and higher stoichiometries. The boron-containing catalyst can activate these complexes towards nucleophilic attack at carbon by the negatively charged oxygen of another zwitterion. An analogous mechanism can be written for the conversion of CMCS into MBCS by SO3 in the presence of trimethyl borate. CMCS reacts rapidly with anionic nucleophiles, such as halide or acetate ions (X-), in homogeneous solution of their tetrabutylammonium salts in CD3CN, or in a two-phase system (CDCl3/H2O) using alkali-metal salts in conjunction with a phase-transfer catalyst. In both situations the products (ClCH2X) arise by rapid nucleophilic displacement of the chlorosulfate moiety; this then more slowly liberates chloride ion, which converts further CMCS into CH2Cl2. The reactivity of CMCS has been compared with that of MBCS and methyl chlorosulfate (MCS) in competitive experiments; the reactivity order is MCS > MBCS > CMCS >> CH2Cl2. Evidence is also presented suggesting that, in contrast to the halide nucleophiles, reaction of CMCS with sodium phenoxide in tetrahydrofuran solution leads to nucleophilic displacement of the sulfur-bound chloride.

General base catalysis in the urate oxidase reaction: evidence for a novel Thr-Lys catalytic diad.

Urate oxidase catalyzes the oxidation of urate without the involvement of any cofactors. The gene encoding urate oxidase from Bacillus subtilis has been cloned and expressed, and the enzyme was purified and characterized. Formation of the urate dianion is believed to be a key step in the oxidative reaction. Rapid-mixing chemical quench studies provide evidence that the dianion is indeed an intermediate; at 15 degrees C the dianion forms within the mixing time of the rapid-quench instrument, and it disappears with a rate constant of 8 s(-)(1). Steady-state kinetic studies indicate that an ionizable group on the enzyme with a pK of 6.4 must be unprotonated for catalysis, and it is presumed that the role of this group is to abstract a proton from the substrate. Surprisingly, examination of the active site provided by the previously reported crystal structure does not reveal any obvious candidates to act as the general base. However, Thr 69 is hydrogen-bonded to the ligand at the active site, and Lys 9, which does not contact the ligand, is hydrogen-bonded to Thr 69. The T69A mutant enzyme has a V(max) that is 3% of wild type, and the K9M mutant enzyme has a V(max) that is 0.4% of wild type. The ionization at pH 6.4 that is observed with wild-type enzyme is absent in both of these mutants. It is proposed that these residues form a catalytic diad in which K9 deprotonates T69 to allow it to abstract the proton from the N9 position of the substrate to generate the dianion.