Highly Selective Ratiometric Sensors for Pb2+ Based on Luminescent Zn(II)-Coordination Polymers with Thiophenedicarboxylate. Crystal Structures and Spectroscopic Studies.

The development of luminescent coordination polymers for the selective sensing of Pb2+ in water constitutes an active area of research that impacts analytical, environmental, and inorganic chemistry. Herein, two novel water-stable 2D Zn-coordination polymers {[Zn2(H2O)2(tdc)2(bpy)]·(H2O)}n 1 and [Zn(tdc)(tmb)]n 2 (tdc = thiophenedicarboxylate; bpy = 4,4'-bipyridine and tmb = 4,4'-trimethylenebipyridine) were synthesized, structurally determined by single crystal X-ray diffraction, and studied in-depth as luminescent sensors for a series of cations (Ca2+, Mg2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+ Cd2+, Hg2+ and Pb2+) in 20% aqueous ethanol. These Zn-polymers possess photostability in 20% aqueous ethanol with a strong emission at 410 upon excitation at 330 nm and quantum yields of around Φ = 0.09. Under these conditions, Pb+2 can be efficiently sensed with polymer 2 through a fluorescent ratiometric response with selectivity over common interfering metal ions such as Cu2+, Cd2+ and Hg2+ in the micromolar concentration range (detection limit = 1.78 ± 10 µM). Such selectivity/affinity of Pb2+ over Hg2+ for luminescent chemosensors is still rare. On the basis of spectroscopic tools (1H NMR, far ATR-IR, PXRD), the X-ray crystal structure of 2, and Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopic analysis, the ratiometric fluorescent response is proposed via an efficient metal-ion exchange driven through interactions between thiophenedicarboxylate rings and Pb2+ ions. The use of flexible luminescent Zn-coordination polymers as sensors for selective and direct detection of Pb2+ in aqueous media has been unexplored until now.

Antimicrobial Activity of Biogenic Silver Nanoparticles from Syzygium aromaticum against the Five Most Common Microorganisms in the Oral Cavity.

Syzygium aromaticum (clove) has been used as a dental analgesic, an anesthetic, and a bioreducing and capping agent in the formation of metallic nanoparticles. The main objective of this study was to evaluate the antimicrobial effect in oral microorganisms of biogenic silver nanoparticles (AgNPs) formed with aqueous extract of clove through an ecofriendly method "green synthesis". The obtained AgNPs were characterized by UV-Vis (ultraviolet-visible spectroscopy), SEM-EDS (scanning electron microscopy-energy dispersive X-ray spectroscopy), TEM (transmission electron microscopy), and ζ potential, while its antimicrobial effect was corroborated against oral Gram-positive and Gram-negative microorganisms, as well as yeast that is commonly present in the oral cavity. The AgNPs showed absorption at 400-500 nm in the UV-Vis spectrum, had an average size of 4-16 nm as observed by the high-resolution transmission electron microscopy (HR-TEM), and were of a crystalline nature and quasi-spherical form. The antimicrobial susceptibility test showed inhibition zones of 2-4 mm in diameter. Our results suggest that AgNPs synthesized with clove can be used as effective growth inhibitors in several oral microorganisms.

Efficient chemosensors for toxic pollutants based on photoluminescent Zn(ii) and Cd(ii) metal-organic networks.

Optical sensors with high sensitivity and selectivity, as important analytical tools for chemical and environmental research, can be realized by straightforward synthesis of luminescent one-, two- and three-dimensional Zn(ii) and Cd(ii) crystalline coordination arrays (CPs and MOFs). In these materials with emission centers typically based on charge transfer and intraligand emissions, the quantitative detection of specific analytes, as pesticides or anions, is probed by monitoring real-time changes in their photoluminescence and color emission properties. Pesticides/herbicides have extensive uses in agriculture and household applications. Also, a large amount of metal salts of cyanide is widely used in several industrial processes such as mining and plastic manufacturing. Acute or chronic exposure to these compounds can produce high levels of toxicity in humans, animals and plants. Due to environmental concerns associated with the accumulation of these noxious species in food products and water supplies, there is an urgent and growing need to develop direct, fast, accurate and low-cost sensing methodologies. In this critical frontier, we discuss the effective strategies, chemical stability, luminescence properties, sensitivity and selectivity of recently developed hybrid Zn(ii)/Cd(ii)-organic materials with analytical applications in the direct sensing of pesticides, herbicides and cyanide ions in the aqueous phase and organic solvents.

Low-cost sugarcane bagasse and peanut shell magnetic-composites applied in the removal of carbofuran and iprodione pesticides.

In the present study, two agro-industrial wastes, sugarcane bagasse, and peanut shell were employed as support of magnetite nanoparticles for the synthesis of magnetic bio-composites: magnetic sugarcane bagasse (MBO) and magnetic peanut shell (MPSo). The presence of magnetite was verified by Raman spectroscopy. Magnetic nanoparticles shape and size distribution were studied by TEM, while composites morphologies were observed by SEM. Structural characteristics of the pesticides and their possible chemical adsorption on composites were analyzed by FTIR. The removal was carried out by a batch adsorption process, and UV-VIS technique was used for pesticide concentration estimation. Elovich model described better all systems pointing out to a chemical adsorption process occurring. Experimental data isotherms of carbofuran and iprodione can be best explained by more than one mathematical model, but Sip was the ordinary equation in all systems. Maximum adsorption capacities of 175 and 89.3 mg/g for carbofuran, and 119 and 2.76 mg/g for iprodione, were obtained for MBo and MPSo, respectively.

A sensitive photoluminescent chemosensor for cyanide in water based on a zinc coordination polymer bearing ditert-butyl-bipyridine.

Sensitive and direct sensing of cyanide in buffered aqueous solutions at pH = 7.0 by three new blue photoluminescent zinc-1,4-cyclohexanedicarboxylato coordination polymers bearing di-alkyl-2,2'-bipyridines has been achieved. Specifically, a Zn-polymer with the general formula: {[Zn2(H2O)2(e,a-cis-1,4-chdc)2(4,4'-dtbb)2]·7H2O}n, (1,4-chdc = 1,4-cyclohexanedicarboxylato and 4,4'-dtbb = 4,4'-ditert-butyl-2,2'-bipyridine) has been synthesized in high yield and studied as a luminescent chemosensor for halides, pseudohalides and a series of oxyanions in neutral water. CN- ions can be quantitatively detected by this polymer based on complete quenching (λem = 434 nm) in the sub-micromolar concentration range with a pronounced selectivity over common anions such as acetate, bromide and iodide. The quenching response (KSV = 9.7(±0.2) × 104 M-1) by the addition of CN- was also observed in the presence of typical interfering anions with a very low detection limit of 0.9 µmol L-1 in buffered water at pH = 7.0. On the basis of the crystal structure and solid state CPMAS 13C-NMR correlation and 1H NMR, IR-ATR, MS-ESI(+) and SEM-EDS experiments, the optical change is attributed to the efficient release of its corresponding ditert-butyl-bipyridine, with the simultaneous formation of a zinc cyanide complex. The CPMAS 13C-NMR spectrum of the coordination polymer is consistent with the symmetry of the crystal structure. The use of flexible coordination polymers as fluorescent sensors for fast and selective detection of cyanide ions in pure aqueous solutions has been unexplored until now.

Influence of the chain length of surfactant in the modification of zeolites and clays. Removal of atrazine from water solutions.

Removal potentials of a surfactant modified zeolite (SMZ) and clay (SMC) for atrazine adsorption were evaluated. Materials were modified with hexadecyl trimethyl ammonium bromide (HDTMA-Br) and benzyl octadecyl dimethyl ammonium (BODA) chloride considering the critical micellar concentration (CMC) of each one (0.94 and 0.041 meq/L, respectively). The influence of the surfactant was analyzed in detail, particularly the formation of surfactant layers (complete or partial) connected with the length of the surfactant tail (16 and 18 methyl groups or number of carbons in the chain). Raw materials were characterized by XRD and Fourier transform infrared spectroscopy (FTIR), SMZ and SMC were analyzed by FTIR. Results obtained from kinetic adsorption experiments shown that equilibrium time is less for materials modified with HDTMA (8 h) than materials with BODA (10 and 12 h). Materials modified with the largest chain surfactant (BODA) showed more resistance to atrazine masse transference. The chemisorption was presented in the adsorption mechanisms of atrazine and adsorbent materials. Based on the results of adsorption isotherms Langmuir isotherms showed the better correlation coefficients value. The qmax is greater for materials modified with BODA (0.9232 and 4.2448 mg/g) than for materials modified with HDTMA (0.6731 and 3.9121 mg/g). Therefore, SMZ and SMC modified with the largest chain surfactant has more affinity for the pesticide. The removal process at high concentration of atrazine depends of the partition process but at lower concentration, it occurs not only by this process but also by absorption process.

Cadmium-1,4-cyclohexanedicarboxylato coordination polymers bearing different di-alkyl-2,2'-bipyridines: syntheses, crystal structures and photoluminescence studies.

Four coordination polymers have been synthesized using self-assembly solution reactions under ambient conditions, reacting Cd(ii) ions with 1,4-cyclohexanedicarboxylic acid in the presence of different 2,2'-bipyridine co-ligands: {[Cd(H2O)(e,a-cis-1,4-chdc)(2,2'-bpy)]·H2O}n (1); [Cd2(H2O)2(e,a-cis-1,4-chdc)2(4,4'-dmb)2]n (2); {[Cd(e,a-cis-1,4-chdc)(5,5'-dmb)]·H2O·CH3OH}n (3) and {[Cd(e,e-trans-1,4-chdc)(4,4'-dtbb)]·CH3OH}n (4), where 1,4-chdc = 1,4-cyclohexanedicarboxylato, 2,2'-bpy = 2,2'-bipyridine, 4,4'-dmb = 4,4'-dimethyl-2,2'-bipyridine, 5,5'-dmb = 5,5'-dimethyl-2,2'-bipyridine and 4,4'-dtbb = 4,4'-di-tert-butyl-2,2'-bipyridine. Crystallographic studies show that compound 1 has a 1D structure propagating along the crystallographic b-axis; the Cd ion in 1 is six-coordinated with a distorted-octahedral coordination sphere. Compound 2 has two crystallographic different Cd ions and both are six-coordinated with a distorted-octahedral coordination sphere. Compound 3 exhibits a seven-coordinated Cd ion having a distinctive distorted-monocapped trigonal prismatic geometry. In compound 4, the Cd ion is also seven-coordinated in a distorted monocapped octahedral geometry. Compounds 2, 3 and 4 possess rhombic-shaped dinuclear units (Cd2O2) as nodes to generate larger cycles made up of four dinuclear units, a Cd4 motif, bridged by four 1,4-chdc ligands, accomplishing, thus, 2D structures. Remarkably, in compound 4 the 1,4-chdc ligand conformation changes to the equatorial, equatorial trans, unlike the other compounds where the bridging ligand conformation is the more typical equatorial, axial cis. The solid state luminescence properties of 1-4 were investigated; polymers 3 and 4 exhibited a strong blue emission (λem = 410-414 nm) compared to 1 and 2; structure-related photoluminescence is attributed to the degree of hydration of the compounds. Furthermore, Cd-polymer 3 suspended in acetone allows the fluorescence selective sensing of acetonitrile over common organic solvents such as alcohols and DMF, based on turn-on fluorescence intensity with a limit of 53 µmol L-1.

Synthesis of silver nanoparticles using aqueous extracts of Heterotheca inuloides as reducing agent and natural fibers as templates: Agave lechuguilla and silk.

Silver nanoparticles (Ag NPs) were synthesized using a one-pot green methodology with aqueous extract of Heterotheca inuloides as a reducing agent, and the support of natural fibers: Agave lechuguilla and silk. UV-Vis spectroscopy, X-Ray photoelectron spectroscopy XPS and transmission electron microscopy TEM were used to characterize the resulting bionanocomposite fibers. The average size of the Ag NPs was 16nm and they exhibited low polydispersity. XPS studies revealed the presence of only metallic Ag in the nanoparticles embedded in Agave. lechuguilla fibers. Significant antibacterial activities against gram-negative Escherichia coli and gram-positive Staphylococcus aureus were determined. AgO as well as metallic Ag phases were detected when silk threads were used as a substrates hinting at the active role of substrate during the nucleation and growth of Ag NPs. These bionanocomposites have excellent mechanical properties in tension which in addition to the antibacterial properties indicate the potential use of these modified natural fibers in surgical and biomedical applications.

Removal of remazol yellow from aqueous solution using Fe-Cu and Fe-Ni nanoscale oxides and their carbonaceous composites.

Fe-Cu and Fe-Ni nanoscale oxides and their carbonaceous composites (C/Fe-Cu and C/Fe-Ni, 75/25 wt.%; C/Fe-Cu and C/Fe-Ni 95/5 wt.%), made from pyrolysis of sewage sludge, have been evaluated to remove remazol yellow textile dye from aqueous solution. The kinetic and sorption isotherms experimental results were best fitted to the pseudo-second-order kinetic and Langmuir-Freundlich isotherm models, which indicates that the sorption mechanism may be chemisorption onto heterogeneous surfaces. Fe-Ni and Fe-Cu nanoscale oxides adsorption capacities were 157.8 mg/g and 117.6 mg/g, resulting in nearly 83% and 70% of dye removal, respectively, using 100 mg/L of initial dyestuff concentration and 10 mg of each material. The adsorption capacities of Fe-Cu, Fe-Ni oxides and C/FCu 75/25%, C/Fe-Ni 75/25% composites provide better results at pH between 3 and 5. In addition, three sorption-desorption cycles using 30% H2O2 solution and distilled water were performed: sorption efficiencies for all materials decreased after each cycle; nevertheless, Fe-Cu and Fe-Ni nanoscale oxides were the best materials for the removal of remazol yellow dye.

Cr(VI) reduction in wastewater using a bimetallic galvanic reactor.

The electrochemical reduction of Cr(VI)-Cr(III) in wastewater by iron and copper-iron bimetallic plates was evaluated and optimized. Iron has been used as a reducing agent, but in this work a copper-iron galvanic system in the form of bimetallic plates is applied to reducing hexavalent chromium. The optimal pH (2) and ratio of copper to iron surface areas (3.5:1) were determined in batch studies, achieving a 100% reduction in about 25 min. The Cr(VI) reduction kinetics for the bimetallic system fit a first order mechanism with a correlation of 0.9935. Thermodynamic analysis shows that the Cr(VI) reduction is possible at any pH value. However, at pH values above 3.0 for iron and 5.5 for chromium insoluble species appear, indicating that the reaction will be hindered. Continuous column studies indicate that the bimetallic copper-iron galvanic system has a reduction capacity of 9.5890 mg Cr(VI) cm(-2) iron, whereas iron alone only has a capacity of 0.1269 mg Cr(VI) cm(-2). The bimetallic copper-iron galvanic system is much more effective in reducing hexavalent chromium than iron alone. The exhausted plates were analyzed by SEM, EDS, and XRD to determine the mechanism and the surface effects, especially surface fouling.