Modified Sepiolite Nanoclays in Advanced Composites for Engineering Applications.

Clay-polymer nanocomposites (CPNs) containing a small weight fraction of nanoclay are known to display enhanced mechanical and thermal properties compared to neat polymers. However, the preparation and application of such nanocomposites remain challenging owing to the difficulties in dispersing nanoclays in polymer matrices. This study focuses on two surfactant-modified organophilic sepiolite clays to demonstrate the simplicity of the modification process, as well as on the use of a benzoxazine monomer (i.e., a CPN matrix precursor) itself as the modifier. Our in-house modified bespoke sepiolites achieve much better dispersion in a benzoxazine matrix, compared to the pristine clay, revealing their potential for applications as nanoenhancers for advanced composites.

Impact of Cations and Framework on Trapdoor Behavior: A Study of Dynamic and In Situ Gas Analysis.

Due to their distinct and tailorable internal cavity structures, zeolites serve as promising materials for efficient and specific gas separations such as the separation of /CO2 from N2. A subset of zeolite materials exhibits trapdoor behavior which can be exploited for particularly challenging separations, such as the separation of hydrogen, deuterium, and tritium for the nuclear industry. This study systematically delves into the influence of the chabazite (CHA) and merlinoite (MER) zeolite frameworks combined with different door-keeping cations (K+, Rb+, and Cs+) on the trapdoor separation behavior under a variety of thermal and gas conditions. Both CHA and MER frameworks were synthesized from the same parent Y-zeolite and studied using in situ X-ray diffraction as a function of increasing temperatures under 1 bar H2 exposures. This resulted in distinct thermal responses, with merlinoite zeolites exhibiting expansion and chabazite zeolites showing contraction of the crystal structure. Simultaneous thermal analysis (STA) and gas sorption techniques further demonstrated how the size of trapdoor cations restricts access to the internal porosities of the zeolite frameworks. These findings highlight that both the zeolite frameworks and the associated trapdoor cations dictate the thermal response and gas sorption behavior. Frameworks determine the crystalline geometry, the maximum porosities, and displacement of the cation in gas sorption, while associated cations directly affect the blockage of the functional sites and the thermal behavior of the frameworks. This work contributes new insights into the efficient design of zeolites for gas separation applications and highlights the significant role of the trapdoor mechanism.

Removal of antiretroviral drugs from wastewater using activated macadamia nutshells: Adsorption kinetics, adsorption isotherms, and thermodynamic studies.

Antiretroviral drugs (ARVDs) have been extensively employed in health care to improve the quality of life and lifecycle longevity. However, overuse and improper disposal of ARVDs have been recognized as an emerging concern whereby wastewater treatment major recipients. Therefore, in this work, the activated macadamia nutshells (MCNs) were explored as low-cost adsorbents for the removal of ARVDs in wastewater samples. Fourier transform infrared spectroscopy (FTIR), Scanning Electron microscopy (SEM), Brunauer-Emmet-Teller (BET), and Powder X-ray diffraction (PXRD). The highest removal efficiency (R.E) was above 86% for the selected analytes nevirapine, abacavir, and efavirenz. The maximum adsorption capacity of the functionalized MCN adsorbent was 10.79, 27.44, and 38.17 mg/g for nevirapine, abacavir, and efavirenz for HCl-modified adsorbent. In contrast, NaOH modified had adsorption capacities of 13.67, 14.25, and 20.79 mg/g. The FTIR showed distinct functional groups OH and CO, which facilitate the removal of selected ARVDs. From studying kinetics parameters, the pseudo-second-order (R2 = 0.990-0.996) was more dominant than the pseudo-first-order (R2 = 0.872-0.994). The experimental data was most fitted in the Freundlich model with (R2 close to 1). The thermodynamic parameters indicated that the adsorption process was spontaneous and exothermic. The study indicated that MCNs are an eco-friendly, low-cost, and effective adsorbent for the removal of nevirapine, abacavir, and efavirenz. PRACTITIONER POINTS: Modification macadamia nutshell with HCl and NaOH improved physio-chemical properties that yielded high removal efficiency compared with raw macadamia nutshells. Modification of macadamia by HCl showed high removal efficiency, which could be attributed to high interaction such as H-bonding that improves adsorption. The macadamia nutshell as an adsorbent showed so much robustness with regeneration studies yielding to about 69.64% of selected compounds.

Investigation of the Dynamic Behaviour of H2 and D2 in a Kinetic Quantum Sieving System.

Porous organic cages (POCs) are nanoporous materials composed of discrete molecular units that have uniformly distributed functional pores. The intrinsic porosity of these structures can be tuned accurately at the nanoscale by altering the size of the porous molecules, particularly to an optimal size of 3.6 Å, to harness the kinetic quantum sieving effect. Previous research on POCs for isotope separation has predominantly centered on differences in the quantities of adsorbed isotopes. However, nuclear quantum effects also contribute significantly to the dynamics of the sorption process, offering additional opportunities for separating H2 and D2 at practical operational temperatures. In this study, our investigations into H2 and D2 sorption on POC samples revealed a higher uptake of D2 compared to that of H2 under identical conditions. We employed quasi-elastic neutron scattering to study the diffusion processes of D2 and H2 in the POCs across various temperature and pressure ranges. Additionally, neutron Compton scattering was utilized to measure the values of the nuclear zero-point energy of individual isotopic species in D2 and H2. The results indicate that the diffusion coefficient of D2 is approximately one-sixth that of H2 in the POC due to the nuclear quantum effect. Furthermore, the results reveal that at 77 K, D2 has longer residence times compared to H2 when moving from pore to pore. Consequently, using the kinetic difference of H2 and D2 in a porous POC system enables hydrogen isotope separation using a temperature or pressure swing system at around liquid nitrogen temperatures.

Properties and Curing Kinetics of a Processable Binary Benzoxazine Blend.

A benzoxazine system is presented combining liquid cardanol-based benzoxazine (CA-a) and an effective initiator (3,3'-thiodipropionic acid, TDA) to bisphenol A-based benzoxazine (BA-a). The resultant mixture of monomeric precursors shows excellent fluidity and a relatively low peak polymerization temperature of around 200 °C. Moreover, the cured polybenzoxazine displays a high thermal decomposition temperature (Td,5% > 330 °C), a moderately high glass transition temperature (∼148 °C), and robust mechanical strength (storage modulus ∼ 2.8 GPa) comparable to those of the polybenzoxazine homopolymer obtained by curing BA-a. A comprehensive investigation into the microstructure and curing kinetics has also been conducted on the system, offering an extensive background for future studies.

A Photo-degradable Crosslinker for the Development of Light-responsive Protocell Membranes.

The achievement of light-responsive behaviours is an important target for protocell engineering to allow control of fundamental protocellular processes such as communication via diffusible chemical signals, shape changes or even motility at the flick of a switch. As a step towards this ambitious goal, here we describe the synthesis of a novel poly(ethylene glycol)-based crosslinker, reactive towards nucleophiles, that effectively degrades with UV light (405 nm). We demonstrate its utility for the fabrication of the first protocell membranes capable of light-induced disassembly, for the photo-generation of patterns of protocells, and for the modulation of protocell membrane permeability. Overall, our results not only open up new avenues towards the engineering of spatially organised, communicating networks of protocells, and of micro-compartmentalised systems for information storage and release, but also have important implications for other research fields such as drug delivery and soft materials chemistry.

Automated analysis of soft material microindentation.

An understanding of the mechanical properties of soft hydrogel materials over multiple length scales is important for their application in many fields. Typical measurement methods provide either bulk mechanical properties (compression, tensile, rheology) or probing of nano or microscale properties and heterogeneity (nanoindentation, AFM). In this work we demonstrate the complementarity of instrumented microindentation to these techniques, as it provides representative Young's moduli for soft materials with minimal influence of the experimental parameters chosen, and allows mechanical property mapping across macroscopic areas. To enable automated analysis of the large quantities of data required for these measurements, we develop a new fitting algorithm to process indentation data. This method allows for the determination of Young's moduli from imperfect data by automatic selection of a region of the indentation curve which does not display inelastic deformation or substrate effects. We demonstrate the applicability of our approach with a range of hydrogels, including materials with patterns and gradients in stiffness, and expect the techniques described here to be useful developments for the mechanical analysis of a wide range of soft and biological systems.

Solvent Sorption-Induced Actuation of Composites Based on a Polymer of Intrinsic Microporosity.

Materials that are capable of actuation in response to a variety of external stimuli are of significant interest for applications in sensors, soft robotics, and biomedical devices. Here, we present a class of actuators using composites based on a polymer of intrinsic microporosity (PIM). By adding an activated carbon (AX21) filler to a PIM, the composite exhibits repeatable actuation upon solvent evaporation and wetting and it is possible to achieve highly controlled three-dimensional actuation. Curled composite actuators are shown to open upon exposure to a solvent and close as a result of solvent evaporation. The degree of curling and actuation is controlled by adjusting the amount of filler and evaporation rate of the solvent casting process, while the actuation speed is controlled by adjusting the type of solvent. The range of forces and actuation speed produced by the composite is demonstrated using acetone, ethanol, and dimethyl sulfoxide as the solvent. The maximum contractile stress produced upon solvent desorption in the pure PIM polymer reached 12 MPa, with an ultimate force over 20 000 times the weight of a sample. This form of the composite actuator is insensitive to humidity and water, which makes it applicable in an aqueous environment, and can survive a wide range of temperatures. These characteristics make it a promising actuator for the diverse range of operating conditions in robotic and medical applications. The mechanism of actuation is discussed, which is based on the asymmetric distribution of the carbon filler particles that leads to a bilayer structure and the individual layers expand and contract differently in response to solvent wetting and evaporation, respectively. Finally, we demonstrate the application of the actuator as a potential drug delivery vehicle, with capacity for encapsulating two kinds of drugs and reduced drug leakage in comparison to existing technologies.

Nanowire Chemical/Biological Sensors: Status and a Roadmap for the Future.

Chemiresistive sensors are becoming increasingly important as they offer an inexpensive option to conventional analytical instrumentation, they can be readily integrated into electronic devices, and they have low power requirements. Nanowires (NWs) are a major theme in chemosensor development. High surface area, interwire junctions, and restricted conduction pathways give intrinsically high sensitivity and new mechanisms to transduce the binding or action of analytes. This Review details the status of NW chemosensors with selected examples from the literature. We begin by proposing a principle for understanding electrical transport and transduction mechanisms in NW sensors. Next, we offer the reader a review of device performance parameters. Then, we consider the different NW types followed by a summary of NW assembly and different device platform architectures. Subsequently, we discuss NW functionalization strategies. Finally, we propose future developments in NW sensing to address selectivity, sensor drift, sensitivity, response analysis, and emerging applications.

Fluorescence sensing of amine vapors using a cationic conjugated polymer combined with various anions.

A series of conjugated cationic polymers, differentiated only by their accompanying counter-anions, was prepared and characterized. The choice of counter-anion (CA) was found to drastically impact the solubility of the polymers and their optical properties in solution and in the solid state. Fluorescent polymer thin films were found to be instantaneously quenched by volatile amines in the gas phase at low ppm concentrations, and a mini-array with CAs as variable elements was found to be able to differentiate amines with good fidelity.

Water-soluble cationic conjugated polymers: response to electron-rich bioanalytes.

We report the concise synthesis of a symmetrical monomer that provides a head-to-head pyridine building block for the preparation of cationic conjugated polymers. The obtained poly(pyridinium-phenylene) polymers display appealing properties such as high electron affinity, charge-transport upon n-doping, and optical response to electron-donating analytes. A simple assay for the optical detection of low micromolar amounts of a variety of analytes in aqueous solution was developed. In particular, caffeine could be measured at a 25 µM detection limit. The reported polymers are also suitable for layer-by-layer film formation.

Conjugated amplifying polymers for optical sensing applications.

Thanks to their unique optical and electrochemical properties, conjugated polymers have attracted considerable attention over the last two decades and resulted in numerous technological innovations. In particular, their implementation in sensing schemes and devices was widely investigated and produced a multitude of sensory systems and transduction mechanisms. Conjugated polymers possess numerous attractive features that make them particularly suitable for a broad variety of sensing tasks. They display sensory signal amplification (compared to their small-molecule counterparts) and their structures can easily be tailored to adjust solubility, absorption/emission wavelengths, energy offsets for excited state electron transfer, and/or for use in solution or in the solid state. This versatility has made conjugated polymers a fluorescence sensory platform of choice in the recent years. In this review, we highlight a variety of conjugated polymer-based sensory mechanisms together with selected examples from the recent literature.

Fluorescence sensing of caffeine in water with polysulfonated pyrenes.

The commercially available fluorescence dye 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) can be used as a selective molecular probe for the detection of caffeine in aqueous solution.

A simple fluorescence assay for the detection of fluoride in water at neutral pH.

A simple assay for the detection of fluoride in water by fluorescence spectroscopy was developed. The assay is based on commercially available reagents and allows sensing of fluoride in the low millimolar concentration range with high selectivity over other anions.

Fluorescence sensors for lithium ions and small peptides.

Simple but powerful chemosensors were developed by taking advantage of self-assembly processes. First, we will describe a turn-on fluorescent sensor for the pharmacologically important lithium ion. The sensor can be used in purely aqueous solution, and it displays a very high selectivity for lithium over sodium and magnesium ions. It is based on a metallacrown receptor unit, which can be assembled in situ from simple building blocks. Furthermore, we will describe a cross-reactive sensor array for the detection of small peptides. The individual sensors of the array are formed by mixing metal complexes with fluorescent dyes.

Pattern-based sensing with metal-dye complexes: sensor arrays versus dynamic combinatorial libraries.

The dyes Methyl Calcein Blue, Arsenazo I, and Xylenol Orange, and the metal salts CuCl(2) and NiCl(2) were used to generate colorimetric sensors for peptides. Two different approaches were followed: (1) Sensors based on dynamic combinatorial libraries of metal-dye complexes were created by mixing dyes with metal salts in one pot. The optical response of these libraries was analyzed by measuring the spectral changes of the mixtures upon addition of the peptide analytes at six selected wavelengths. (2) Sensor arrays were created from six different metal-dye combinations. The six individual sensors were analyzed at one wavelength, and the resulting data was used as the input for a multivariate analysis. Both types of sensors were evaluated for their ability to differentiate 13 different di- and tripeptides. The sensors based on dynamic combinatorial libraries gave in most cases better results than the sensor array. Furthermore it was found that libraries of intermediate complexity perform best as sensors.

Cross-reactive sensor arrays for the detection of peptides in aqueous solution by fluorescence spectroscopy.

A simple but powerful method for the sensing of peptides in aqueous solution has been developed. The transition-metal complexes [PdCl(2)(en)], [{RhCl(2)Cp*}(2)], and [{RuCl(2)(p-cymene)}(2)] were combined with six different fluorescent dyes to build a cross-reactive sensor array. The fluorescence response of the individual sensor units was based on competitive complexation reactions between the peptide analytes and the fluorescent dyes. The collective response of the sensor array in a time-resolved fashion was used as an input for multivariate analyses. A sensor array comprised of only six metal-dye combinations was able to differentiate ten different dipeptides in buffered aqueous solution at a concentration of 50 muM. Furthermore, the cross-reactive sensor could be used to obtain information about the identity and the quantity of the pharmacologically interesting dipeptides carnosine and homocarnosine in a complex biological matrix, such as deproteinized human blood serum. The sensor array was also able to sense longer peptides, which was demonstrated by differentiating mixtures of the nonapeptide bradykinin and the decapeptide kallidin.

Ruthenium-based metallacrown complexes for the selective detection of lithium ions in water and in serum by fluorescence spectroscopy.

Fluorescent dihydroxypyridine ligands were prepared by attaching pyrene-, dansyl-, and methoxycoumarin-fluorophores via dimethyleneamine linkers. The reaction of these ligands with [(p-cymene)RuCl(2)](2) or [(C(6)H(5)CH(2)NMe(2)H)RuCl(2)](2)Cl(2) resulted in the formation of 12-metallacrown-3 complexes, which possess strong affinity for lithium ions. By a judicious choice of the fluorophore and the arene pi-ligand, a macrocycle was obtained that could be used in aqueous solution to selectively and quantitatively detect lithium ions by fluorescence spectroscopy.