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A novel Eu(tta)3([4,4′-(t-bu)2-2,2′-bpy)] complex (tta-thenoyltrifluoroacetone), a ratiometric luminescent-based optical sensor for the quantitative determination of aluminum ion, is synthesized and characterized using XRD and 1H NMR. The XRD data reveal the slightly distorted octahedral structure. The complex displays a bright red emission at 613 nm in methanol which is characteristic of europium (III) complexes. Upon the addition of Al3+ ions, the red emission disappears, and a new blue emission at 398 nm emerges, manifesting the ratiometric nature of the complex. The turn-off of the red emission and turn-on of the blue emission are attributed to Eu-Al trans-metalation, as supported by Raman data that show the emergence of Al-O vibrations at 418, 495, and 608 cm−1 concomitant with the disappearance of Eu-O and Eu-N bond vibrations. Most aluminum sensors are known to suffer from interferences from other metals including Cu2+, Co2+, and Cd2+. However, the sensor reported here is tested for 11 common cations and shows no interference on sensitivity. To the best of our knowledge, this is the first known Eu-based luminescence sensor that successfully exhibited the ability to detect aluminum ions in ppb levels in aqueous environments. The calculated Al3+ binding constant is 2.496 × 103 ± 172. The complex shows a linear relationship in the range of 0–47.6 ppb (1.76 × 10−6 M) Al3+ and the limit of detection (LOD) is 4.79 ppb (1.77 × 10−7 M) in MeOH. ICP-OES is used for validation of the sensor complex in water and then it was used for quantitative detection of Al3+ ions in water as a real-life application. The complex can accurately detect Al3+ ions in the range of 4.97–24.9 ppb (1.84 × 10−7 M–9.2 × 10−7 M) with an LOD of 8.11 ppb (2.99 × 10−7 M). Considering that the aluminum ion serves no recognized function within the human body, its accumulation can lead to severe neurological disorders, including Parkinson's and Alzheimer's diseases. With the LOD value significantly lower than the WHO-recommended maximum permissible level of 200 ppb for aluminum in drinking water, even without high-power laser-aided signal enhancement, the sensor shows promise for detecting trace amounts of aluminum contamination in water. Therefore, it can significantly aid in the monitoring of even the smallest aluminum ion contamination in drinking water, industrial effluents, and natural water bodies. [ABSTRACT FROM AUTHOR]

This research presents a novel and environmentally friendly approach for the synthesis of multifunctional nanobiocomposites for the efficient removal of toxic heavy metal and dye, as well as the disinfection of wastewater microorganisms. The nanobiocomposites (KAC-CS-AgNPs) were prepared by incorporating photochemically generated silver nanoparticles (AgNPs) within a chitosan (CS)-modified, high-surface-area activated carbon derived from kenaf (KAC), using a unique self-activation method. The even distribution of AgNPs was visible in the scanning electron microscopy images and a Fourier transform infra red study demonstrated major absorption peaks. The experimental results revealed that KA-CS-AgNPs exhibited exceptional adsorption efficiency for copper (Cu2+), lead (Pb2+), and Congo Red dye (CR), and showed potent antibacterial activity against Staphylococcus aureus and Escherichia coli. The maximum adsorption capacity (mg g−1) of KAC-CS-AgNPs was 71.5 for Cu2+, 72.3 for Pb2+, and 75.9 for CR, and the adsorption phenomena followed on the Freundlich and Langmuir isotherm models and the second-order kinetic model (R2 > 0.99). KAC-CS-AgNPs also exhibited excellent reusability of up to four consecutive cycles with minor losses in adsorption ability. The thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic in nature. The bacterial inactivation tests demonstrated that KAC-CS-AgNPs had a strong bactericidal effect on both E. coli and S. aureus, with MIC calculated for E. coli and S. aureus as 32 µg mL−1 and 44 µg mL−1, respectively. The synthesized bioinspired nanocomposite KAC-CS-AgNPs could be an innovative solution for effective and sustainable wastewater treatment and has great potential for commercial applications. [ABSTRACT FROM AUTHOR]

A new europium-based complex, K[Eu(hfa)4] with hfa = hexafluoroacetylacetonate is synthesized and its structure confirmed via X-ray crystallography. The structure unravels an anionic octa-coordinate complex, K[Eu(hfa)4], as opposed to the neutral hexacoordinate complex Eu(hfa)3 routinely/ubiquitously presumed to be the case in the literature. The complex displayed pH-dependent, "on–off" emission changes in solution and exhibited a pKa of 6.13 ± 0.06 in ethylene glycol. In solution, the sensor complex exhibited drastic variation in emission intensity corresponding to changes in the concentration of CO2 gas purged. Based on multiple purge cycles of N2 and CO2, the emission intensity changes can be correlated to the concentration of CO2 in the solution. The sensor's ability to quantify the CO2 presence is based on emission variations of the 5D0 → 7F2 line in the Eu(III) complex at 618 nm. The sensor exhibits a linear response to CO2 concentrations in the range of 0–25% (0–8.50 mM or 0–189.95 mmHg). Based on calibration data, the limit of detection (LOD) is determined to be 0.57% (0.19 mM or 4.33 mmHg) in solution. The I100/I0 ratio is determined to be 80.29 ± 3.79. The percent change in intensity from purging N2 to 100% CO2 is 7911.16%. Over the course of seven cycles of purging different concentrations of CO2, there is essentially no deviation in the emission intensity of the sensor in solution, indicating stability and reversibility. In addition to the analytical characterization of the sensor, the mechanism of CO2 sensing is investigated using cyclic voltammetry, IR, and Raman spectroscopy. These data indicate the reduction of europium(III) to europium(II) in an alkaline medium and suggest changes in the hfa ligand chemistry (association/dissociation and protonation) due to CO2 purging. The potential use of the sensor complex for real-life applications is herein evaluated via a well-known fermentation reaction. The CO2 generated during yeast's anaerobic respiration in sucrose media is quantified using the sensor complex and a calibrated, commercial CO2 probe; both exhibit similar CO2 concentration values, validating the calibration curve and the viability of the complex as a bona fide sensor. Based on the data collected, a highly stable, brightly red-emissive Eu(III) complex with the ability to differentiate concentrations of CO2 in solution is hereby developed and characterized with benefits for various CO2 sensing applications. [ABSTRACT FROM AUTHOR]

The cadmium-contaminated water body is a worldwide concern for the environment and toxic to human beings and the removal of cadmium ions from drinking and groundwater sustainably and cost-effectively is important. A novel nano-biocomposite was obtained by impregnating silver nanoparticles (AgNPs) within kenaf-based activated carbon (KAC) in the presence of chitosan matrix (CS) by a simple, facile photoirradiation method. The nano-biocomposite (CS-KAC-Ag) was characterized by an environmental scanning electron microscope equipped with energy dispersive X-ray spectroscopy (ESEM-EDX), Fourier-transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) method. A Box–Behnken design of response surface methodology (RSM) was used to optimize the adsorption of Cd2+. It was found that 95.1% of Cd2+ (10 mg L−1) was eliminated at pH 9, contact time of 120 min, and adsorbent dosage of 20 mg, respectively. The adsorption of Cd2+ by CS-KAC-Ag is also in agreement with the pseudo-second-order kinetic model with an R2 (coefficient of determination) factor greater than 99%. The lab data were also corroborated by tests conducted using water samples collected from mining sites in Mexico. Along with Cd2+, the CS-KAC-Ag exhibited superior removal efficiency towards Cr6+ (91.7%) > Ni2+ (84.4%) > Co2+ (80.5%) at pH 6.5 and 0.2 g L−1 dose of the nano-adsorbent. Moreover, the adsorbent was regenerated, and the adsorption capacity remained unaltered after five successive cycles. The results showed that synthesized CS-KAC-Ag was a biocompatible and versatile porous filtering material for the decontamination of different toxic metal ions. [ABSTRACT FROM AUTHOR]

This article provides a second manifestation of a new tradition by which the editors of Comments on Inorganic Chemistry wish to lead by example, whereby we start publishing original research content that, nonetheless, preserves the Journal's identity as a niche for "critical discussion of the current literature" of inorganic chemistry. (For the first manifestation, see: Otten, B. M.; Melancon, K. M.; Omary, M. A. "All That Glitters is Not Gold: A Computational Study of Covalent vs Metallophilic Bonding in Bimetallic Complexes of d10 Metal Centers—A Tribute to Al Cotton on the 10th Anniversary of His Passing," Comments Inorg. Chem. 2018, 38, 1-35.) Thus, herein we show that a trinuclear copper (I) complex {[3,5-(CF3)2Pz]Cu}3 (henceforth referred to as the "Cu trimer") can act as a "metal-organic coating" for corrosion protection of aluminum, whereas its silver analogue, {[3,5-(CF3)2Pz]Ag}3 (i.e., the "Ag trimer"), could not. The manuscript was initially submitted to journals that usually publish on "organic coatings" but was rejected on the premise that a metal complex cannot be considered "organic" unless it is incorporated into a polymer. This issue is commented upon herein in the broader context of whether to consider metal complexes "organic," "inorganic," "organometallic," or "metal-organic" materials with manifestations of the use of each classification in the literature. We have found that, upon coating the Cu trimer onto an aluminum (AA 3003) surface, potentiodynamic polarization results in 3.5% NaCl show an increase in corrosion potential (Ecorr) by ~ 0.6 V concomitant with a three-order-of-magnitude decrease in corrosion current density (icorr) from 0.025 µA/cm2 for uncoated aluminum to ~ 9.6 × 10-5 µA/cm2 for the Cu trimer-coated surface. With a double coating, the Cu trimer formed a completely insulating surface with no current flow, even at very high potential magnitude and range. Open circuit potential was used to study the stability of the Cu trimer films on the Al surface in the electrolyte solution. Scanning electron microscopy and Fourier-transform infrared spectroscopy techniques were used to characterize the structure of both the Cu trimer powder and Cu trimer film on the aluminum surface before and after the corrosion tests. The hydrophobicity of the Cu trimer coating was determined by using water drop contact angle measurements, which demonstrated an increase from 65° to 137° for the uncoated and coated aluminum, respectively. The thermal stability of the Cu trimer was analyzed using thermogravimetric analysis, giving rise to weight loss resistance up to ~190 °C. The results clearly demonstrate that the Cu trimer layers exhibit superior stability and potential for corrosion protection of aluminum surfaces in corrosive environments. The Ag trimer analogue, meanwhile, failed the "tape test" that the Cu trimer passed to assess the mechanical stability of such "metal-organic" coatings. Density functional theory (DFT) simulations provide insights on this difference upon modeling the interaction of each cyclotrimer molecule (and other analogous ones) with an Al atom on the one hand and contrasting the resulting binding energies with the corresponding dissociation energies of the metallophically-bound crystalline solid form of each trimer. Thus, it was found that Ag trimer models are bound to the Al atom at least as strongly as Cu trimer models are; yet, that bonding is not sufficiently high so as to overcome the argentophilic attraction, whereas it can overcome the cuprophilic attraction. Other explanations are also given to account for trimer interactions with aluminum oxide as well as partial oxidation of only the Cu trimer, which strengthens the interaction with the Al atom. [ABSTRACT FROM AUTHOR]

We report a phosphorescent chemosensor based on a trinuclear Au(I) pyrazolate complex or [Au(3-CH3,5-COOH)Pz]3 (aka Au3Pz3) stabilized in aqueous chitosan (CS) polymer media. Au3Pz3 is synthesized in situ within aqueous CS media at pH ~ 6.5 and room temperature (RT). Au3Pz3 exhibits strong red emission (λmax ~ 690 nm) in such solutions. On addition of silver salt to Au3Pz3/CS aqueous media, a bright-green emissive adduct (Au3Pz3/Ag+) with a peak maximum within 475-515 nm is developed. The silver adduct exhibits a 4-fold increase in quantum yield (0.19 ± 0.02) compared to Au3Pz3 alone (0.05 ± 0.01), along with a corresponding increase in phosphorescence lifetime. With almost zero interference from 15 other metal ions tested, Au3Pz3 exhibits extreme selectivity for Ag+ with nM/ppb detection limits (6.4-72 ppb, depending on %CS and on the sensitivity basis being a signal-to-noise ratio (S/N) = 3 or a baseline-corrected signal change = 10%). Au3Pz3 exhibits sensitivity to higher concentrations (>1 mM) of other metal ions (Tl+/Pb2+/Gd3+). The sensing methodology is simple, fast, convenient, and can even be detected by the naked eye. On addition of ethylenediaminetetraacetic acid (EDTA), the red Au3Pz3 emission can be restored. Au3Pz3 and its silver adduct retain their characteristic photophysical properties in thin film forms. Remarkable photostability with <7% photobleaching after 4 h of UV irradiation is attained for Au3Pz3 solutions or thin films. [ABSTRACT FROM AUTHOR]

Neutral Red (NR), a eurhodin dye, is often used for staining living cells, but we demonstrated for the first time that NR can also serve as a CO2 sensor, because of NR's unique optical properties, which change with dissolved carbon dioxide (dCO2) concentrations. In the present study, optical sensitivity of NR was quantified as a function of changes in absorption and emission spectra to dCO2 in a pH 7.3 buffer medium at eight dCO2 concentrations. NR exhibited a response time of two minutes for equilibration in pure N2 to 100% CO2 with an ~200% percent change (%∆) in emission intensity and >400%∆ in absorbance, with full reversibility. Important to its application to biological systems, NR exhibited zero sensitivity to dissolved oxygen, which has routinely caused interference for CO2 measurements. NR exhibited pH sensitive emission and excitation energies with dual excitation wavelengths at 455 nm and 540 nm, and a single emission at 640 nm. The CO2 sensing properties of NR were benchmarked by a comparison to pyranine (8-hydroxypyrene-1, 3,6-trisulfonic acid trisodium salt) (HPTS). Future studies will evaluate the feasibility of NR as an intracellular in vivo pCO2 sensor in aquatic organisms critically impacted by increasing global CO2 levels. [ABSTRACT FROM AUTHOR]

This work demonstrates the dynamic potential for tailoring the surface plasmon resonance (SPR), size, and shapes of gold nanoparticles (AuNPs) starting from an Au(I) precursor, chloro(dimethyl sulfide)gold (I) (Au(Me2S)Cl), in lieu of the conventional Au(III) precursor hydrogen tetrachloroaurate (III) hydrate (HAuCl4). Our approach presents a one-step method that permits regulation of an Au(I) precursor to form either visible-absorbing gold nanospheres or near-infrared-window (NIRW)-absorbing anisotropic AuNPs. A collection of shapes is obtained for the NIR-absorbing AuNPs herein, giving rise to spontaneously formed nanomosaic (NIR-absorbing anisotropic gold nanomosaic, NIRAuNM) without a dominant geometry for the tesserae elements that comprise the mosaic. Nonetheless, NIRAuNM exhibited high stability; one test sample remains stable with the same SPR absorption profile 7 years post-synthesis thus far. These NIRAuNM are generated within thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) microgels, without the addition of any growth-assisting surfactants or reducing agents. Our directed-selection methodology is based on the photochemical reduction of a light-, heat-, and water-sensitive Au(I) precursor via a disproportionation mechanism. The NIRAuNM stabilized within the thermoresponsive microgels demonstrates a light-activated size decrease of the microgels. On irradiation with a NIR lamp source, the percent decrease in the size of the microgels loaded with NIRAuNM is at least five times greater compared to the control microgels. The concept of photothermal shrinkage of hybrid microgels is further demonstrated by the release of a model luminescent dye, as a drug release model. The absorbance and emission of the model dye released from the hybrid microgels are over an order of magnitude higher compared to the absorbance and emission of the dye released from the unloaded-control microgels. [ABSTRACT FROM AUTHOR]

In this communication, we present a streamlined, reproducible synthetic method for the production of size-tunable poly(methyl methacrylate) (PMMA) nanoparticles (PMMANPs) and amine-functionalized block-copolymer PMMANPs (H2N-PMMANPs) by varying subcritical concentrations (i.e., below the concentration required to form micelles at 1 atm and 20 °C) of sodium dodecyl sulfate (SDS). We plotted the Z-average size data against SDS concentration, which revealed a second-order exponential decay function, expressed as A 1 e − x t 1 + A 2 e − x t 2 + y 0 . The surfactant concentration (wt./wt.%) has been selected as independent variable x. This function is valid at least for the size range of 20 nm to 97 nm (PMMANPs) and 20 nm to 133 nm (H2N-PMMANPs). [ABSTRACT FROM AUTHOR]

A simple photochemical method for making conjoined bi-metallic gold-silver (Au/Ag) nanotwins, a new breed of nanoparticles (NPs), is developed. To the best of our knowledge, the photochemical method resulted in distinct, conjoined, bimetallic nanotwins that are different from any well-established alloyed or core-shell nanostructures in the literature. The conjoined Au-Ag NPs possessed surface plasmon resonance (SPR) properties of both metals. The bimetallic nanostructures possessing distinctive optical properties of both metals were obtained using Au NPs as seeds in the first step, followed by the addition of a silver precursor as feed in the second step during a photochemical irradiation process. In the first step, small, isotropic or large, anisotropic Au NPs are generated by photoinduced reduction within a biocompatible chitosan (CS) polymer. In the second step, a silver precursor (AgNO3) is added as the feed to the AuNPs seed, followed by irradiation of the solution in the ice-bath. The entire photochemical irradiation process resulting in the formation of bimetallic Au-AgNPs did not involve any other reducing agents or stabilizing agents other than the CS polymer stabilizer. The small, conjoined Au-Ag bi-metallic NPs exhibited SPR with peak maxima centering at ~400 nm and ~550 nm, whereas the large conjoined nanoparticles exhibited SPR with peak maxima centering at ~400 nm, 550 nm, and 680 nm, characteristic of both gold and silver surface plasmons in solution. The tunability in the SPR and size of the bimetallic NPs were obtained by varying the reaction time and other reaction parameters, resulting in average sizes between 30 and 100 nm. The SPR, size, distribution, and elemental composition of the bi-metallic NPs were characterized using UV-Vis absorption, electron microscopy, and energy dispersive X-ray spectroscopy (EDS) studies. [ABSTRACT FROM AUTHOR]

Chitosan (CS) is a natural polymer derived from chitin that has found its usage both in research and commercial applications due to its unique solubility and chemical and biological attributes. The biocompatibility and biodegradability of CS have helped researchers identify its utility in the delivery of therapeutic agents, tissue engineering, wound healing, and more. Industrial applications include cosmetic and personal care products, wastewater treatment, and corrosion protection, to name a few. Many researchers have published numerous reviews outlining the physical and chemical properties of CS, as well as its use for many of the above-mentioned applications. Recently, the cationic polyelectrolyte nature of CS was found to be advantageous for stabilizing fascinating photonic materials including plasmonic nanoparticles (e.g., gold and silver), semiconductor nanoparticles (e.g., zinc oxide, cadmium sulfide), fluorescent organic dyes (e.g., fluorescein isothiocyanate (FITC)), luminescent transitional and lanthanide complexes (e.g., Au(I) and Ru(II), and Eu(III)). These photonic systems have been extensively investigated for their usage in antimicrobial, wound healing, diagnostics, sensing, and imaging applications. Highlighted in this review are the different works involving some of the above-mentioned molecular-nano systems that are prepared or stabilized using the CS polymer. The advantages and the role of the CS for synthesizing and stabilizing the above-mentioned optically active materials have been illustrated. [ABSTRACT FROM AUTHOR]