An optical sensor based on H-acid/layered double hydroxide composite film for the selective detection of mercury ion

Controlled preparation of multiple mesoporous CoAl-LDHs nanosheets for the high performance of NO x detection at room temperature

By fine tuning the metal mole ratio, CoAl-LDHs (CA) with a 2D nanosheet structure were successfully prepared via a one-step hydrothermal method using urea as both precipitator and pore-forming agent. The morphology of CA samples shows uniform and thin porous hexagonal nanosheets. In particular, CA2-1, prepared with the 2 : 1 molar ratio for Co and Al, respectively, has the highest surface area (54 m2 g-1); its average transverse size of platelets is 2.54 μm with a thickness of around 19.30 nm and inter-plate spacing of about 0.2 μm. The sample exhibits a high sensing performance (response value of 17.09) towards 100 ppm NO x , fast response time (4.27 s) and a low limit of detection (down to 0.01 ppm) at room temperature. Furthermore, CA2-1 shows long -term stability (60 days) and a better selectivity towards NO x at room temperature. The excellent performance of the fabricated sensor is attributed to the special hexagonal structure of the 2D thin nanosheets with abundant mesopores, where the active sites provide fast adsorption and transportation channels, promote oxygen chemisorption, and eventually decrease the diffusion energy barrier for NO x molecules. Furthermore, hydrogen bonds between water molecules and OH- could serve as a bridge, thus providing a channel for rapid electron transfer. This easy synthetic approach and good gas sensing performance allow CoAl-LDHs to be great potential materials in the field of NO x gas sensing.

Interaction of Carbohydrate Coated Cerium-Oxide Nanoparticles with Wheat and Pea: Stress Induction Potential and Effect on Development

: Reports about the influence of cerium-oxide nanoparticles (nCeO₂) on plants are contradictory due to their positive and negative effects on plants. Surface modification may affect the interaction of nCeO₂ with the environment, and hence its availability to plants. In this study, the uncoated and glucose-, levan-, and pullulan-coated nCeO₂ were synthesized and characterized. The aim was to determine whether nontoxic carbohydrates alter the effect of nCeO₂ on the seed germination, plant growth, and metabolism of wheat and pea. We applied 200 mgL^-1 of nCeO₂ on plants during germination (Ger treatment) or three week-growth (Gro treatment) in hydroponics. The plant response to nCeO₂ was studied by measuring changes in Ce concentration, total antioxidative activity (TAA), total phenolic content (TPC), and phenolic profile. Our results generally revealed higher Ce concentration in plants after the treatment with coated nanoparticles compared to uncoated ones. Considering all obtained results, Ger treatment had a stronger impact on the later stages of plant development than Gro treatment. The Ger treatment had a stronger impact on TPC and plant elongation, whereas Gro treatment affected more TAA and phenolic profile. Among nanoparticles, levan-coated nCeO₂ had the strongest and positive impact on tested plants. Wheat showed higher sensitivity to all treatments.

A novel polyvinyl chloride-membrane optical sensor for the determination of Cu(2+) ion based on synthesized (N'(1)E,N'(2)E)-N'(1),N'(2)-bis(pyridine-2-ylmethylene)oxalohydrazide: experimental design and optimization

A copper (Cu(2+)) ion-selective bulk optode was constructed by using (N'(1)E,N'(2)E)-N'(1),N'(2)-bis(pyridine-2-ylmethylene)oxalohydrazide as ionophore and NaTPB in DBP matrices. Central composite design under response surface methodology was applied for the optimization of variables including pH, amount of ligand, amount of additive and response time which significantly affect the response of proposed sensor. At optimum specified conditions, the high stability, reproducibility and relatively long lifetime of the optical sensor suggest its ability for accurate and precise monitoring of Cu(2+) ion content in various real samples over a concentration range of 1.6×10(-6) to 3.17×10(-5)molL(-1) with a limit of detection of 8.1×10(-7)molL(-1) during response time 6.9min. The proposed optical sensor was successfully applied for the determination of Cu(2+) ion in tap water and different samples.

Highly selective and sensitive optical sensor for determination of Pb2+ and Hg2+ ions based on the covalent immobilization of dithizone on agarose membrane

A highly sensitive and selective optical membrane for determination of Hg(2+) and Pb(2+) was prepared by covalent immobilization of dithizone on agarose membrane. In addition to its high stability, reproducibility and relatively long lifetime, the proposed optical sensor revealed good selectivity for target ions over a large number of alkali, alkaline earth, transition, and heavy metal ions. The proposed optical membrane displays linear responses from 1.1×10(-8) to 2.0×10(-6) mol L(-1) and 1.2×10(-8) to 2.4×10(-6) mol L(-1) for Hg(2+) and Pb(2+), respectively. The limits of detection (LOD) were 2.0×10(-9) mol L(-1) and 4.0×10(-9) mol L(-1) for Hg(2+) and Pb(2), respectively. The prepared optical membrane was successfully applied to the determination of Hg(2+) and Pb(2+) in industrial wastes, spiked tap water and natural waters without any preconcentration step.

Theoretical assessment of the selective fluorescence quenching of 1-amino-8-naphthol-3,6-disulfonic acid (H-Acid) complexes with Zn(2+), Cd(2+), and Hg(2+): A DFT and TD-DFT study

Density functional theory (DFT) and time-dependent (TD)-DFT calculations at the PBE0/6-31++G** aug-cc-PVDZ (along with corresponding ECP for metal ions) level of theory were carried out to investigate the differences in structure, bonding, and fluorescence behavior of 1-amino-8-naphthol-3,6-disulfonic acid (H-acid) (1) when coordinated to Zn(2+) (2), Cd(2+) (3), and Hg(2+) (4) in a simulated continuous aqueous media (PCM). Ground and excited state calculations were performed on all compounds in order to gain insight on their bonding properties, as well as on their photochemical behavior, since we previously reported that complexation of Hg(2+) quenches the fluorescence properties of ligand (1), while at the same time exhibits a different coordination pattern than the two other remaining complexes. Changes in the excited states' radiative lifetime upon coordination to different metals account for this selective quenching.

Electrophoretic deposition as a new approach to produce optical sensing films adaptable to microdevices

We report the fabrication of optical oxygen sensor films using electrophoretic deposition (EPD) of poly(styrene-co-maleic anhydride) nanoparticles containing the oxygen-sensitive dye platinum(ii) meso-tetra(pentafluorophenyl)porphine. Compared to other deposition methods, the EPD is simple and allows easy control over deposition, which is crucial for the implementation of optical sensing films in microdevices. By optimizing the synthesis of the functional nanoparticles, anodic EPD can be performed. The amount of deposited particles can be tuned by varying either the electrical potential or the deposition time. The sensing phases were characterized using a phase-modulation technique showing a Stern-Volmer constant (kSV1) between 45 and 52 bar(-1) for gas and of 20.72 bar(-1) in the aqueous phase without leaching of the particles from the surface. The small thickness of the layers lead to short response times (<0.4 s). This is the first time that polymeric optical sensing films have been obtained by EPD from dispersions of oxygen sensing nanoparticles.

Facile ultrasensitive monitoring of mercury ions in water by fluorescent ratiometric detection

Prospects for analytical application of 2,5-diphenyloxazole-substituted 3-hydroxychromone for detection of mercury ions are presented. Sensitivity and selectivity for a number of metal ions both in methanol solution and in the plasticized polymer are outlined. Ultrasensitive and highly selective fluorescent ratiometric response of the polymer film containing the title compound for mercury ions in water media is revealed. Reversibility of ratiometric response to mercury ions and influence of plasticizer’s content in the polymer film on the optical feedback are also discussed.

Highly selective and stable florescent sensor for Cd(II) based on poly (azomethine-urethane)

In this study a kind of poly(azomethine-urethane); (E)-4-((2 hydroxyphenylimino) methyl)-2-methoxyphenyl 6-acetamidohexylcarbamate (HDI-co-3-DHB-2-AP) was prepared as in the literature and employed as a new fluorescent probe for detection of Cd(II) concentration. The photoluminescence (PL) measurements were carried out in the presence of several kinds of heavy metals. HDI-co-3-DHB-2-AP gave a linearly and highly stable response against Cd(II) as decreasing a new emission peak at 562 nm. Possible interferences of other ions were found too low. Detection limit of the sensor was found as 8.86 × 10(-4) mol L(-1). Resultantly, HDI-co-3- DHB-2-AP could be effectively used as an optical Cd(II) sensor.