Reported is an electrical transduction platform for real‐time wireless anion sensing using single‐walled carbon nanotubes (SWCNTs) noncovalently functionalized with squaramide‐based anion binding selectors. Systematically studied are anion‐binding properties and efficiency of the electrical transduction of the functionalized SWCNT composites using the squaramide‐based selectors with two similar electron‐withdrawing groups, 3,5‐bis(trifluoromethyl)benzyl (1) and 3,5‐bis(trifluoromethyl)phenyl (2), which induce hydrogen‐bonding interaction with anions and deprotonation of a squaramide N–H proton upon addition of acetate (AcO−), respectively. Charge transduction occurs with AcO− as a result of charge transfer from the deprotonated selector 2, whereas less sensitive transduction is observed with selector 1 via hydrogen‐bonding interaction. These results provide guidelines to efficiently transduce the chemical interaction between selectors and anions to create resistive transduction with functionalized SWCNTs. Electron‐withdrawing groups adjacent to the squaramide as well as proximate cationic pyridyl groups, enhance the anion binding affinity and also lower the selector's pKa. The chemiresistive sensor arrays are readily integrated with a wireless sensing module and demonstrated real‐time sensing of multiple anions with a smartphone readout.
Coatings prepared from titania-thiol-ene compositions were found to be both self-cleaning, as measured by changes in water contact angle, and photocatalytic toward the degradation of an organic dye. Stable titania-thiol-ene dispersions at approximately 2 wt % solids were prepared using a combination of high-shear mixing and sonication in acetone solvent from photocatalytic titania, trisilanol isobutyl polyhedral oligomeric silsesquioxane (POSS) dispersant, and select thiol-ene monomers, i.e., trimethylolpropane tris(3-mercaptopropionate) (TMPMP), pentaerythritol allyl ether (APE), and 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TTT). The dispersed particle compositions were characterized by DLS and TEM. The synthetic methods employed yield a strongly bound particle/POSS complex, supported by IR, 29Si NMR, and TGA. The factors of spray techniques, carrier solvent volatility, and particle size and size distributions, in combination, likely all contribute to the highly textured but uniform surfaces observed via SEM and AFM. Polymer composites possessed thermal transitions (e.g., Tg) consistent with composition. In general, the presence of polymer matrix provided mechanical integrity, without significantly compromising or prohibiting other critical performance characteristics, such as film processing, photocatalytic degradation of adsorbed contaminants, and the hydrophobic-hydrophilic transition. In all cases, coatings containing photocatalytic titania were converted from superhydrophobic to superhydrophilic, as defined by changes in the water contact angle. The superhydrophilic state of samples was considered persistent, since long time durations in complete darkness were required to observe any significant hydrophobic return. In a preliminary demonstration, the photocatalytic activity of prepared coatings was confirmed through the degradation of crystal violet dye. This work demonstrates that a scalable process can be found to prepare titania-thiol-ene coatings having improved coating properties which also exhibit photocatalytic and self-cleaning attributes.
Trace analysis of heavy metals in complex, environmentally relevant matrices remains a significant challenge for electrochemical sensors employing stripping voltammetry-based detection schemes. We present an alternative method capable of selectively preconcentrating Cu 2+ ions at the electrode surface using chelating polymer-wrapped multiwalled carbon nanotubes (MWCNTs). An electrochemical sensor consisting of poly-4vinyl pyridine (P4VP)-wrapped MWCNTs anchored to a poly(ethylene terephthalate) (PET)-modified gold electrode (r = 1.5 mm) was designed, produced, and evaluated. The P4VP is shown to form a strong association with Cu 2+ ions, permitting preconcentration adjacent to the electrode surface for interrogation via cyclic voltammetry. The sensor exhibited a detection limit of 0.5 ppm with a linear range of 1.1−13.8 ppm (16.6−216 μM) and a relative standard deviation (RSD) of 4.9% at the Environmental Protection Agency (EPA) limit of 1.3 ppm. Evaluation in tap water, lake water, ocean water, and deionized water rendered similar results, highlighting the generalizability of the presented preconcentration strategy. The advantages of electrochemical analysis paired with polymeric chelation represent an effective platform for the design and deployment of heavy metal sensors for continuous monitoring of natural waters.
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