Selective colorimetric sensing of nickel (II) ions using 2-hydroxy-5-nitrobenzaldehyde-4-hydroxybenzoylhydrazone ligand: Spectroscopic and DFT insights

Fluorescent and chromogenic organic probes to detect group 10 metal ions: design strategies and sensing applications

Group 10 metals including Ni, Pd and Pt have been extensively applied in various essential aspects of human social life, material science, industrial manufactures, medicines and biology. The ionic forms of these metals are involved in several biologically important processes due to their strong binding capability towards different biomolecules. However, the mishandling or overuse of such metals has been linked to serious contamination of our ecological system, more specifically in soil and water bodies with acute consequences. Therefore, the detection of group 10 metal ions in biological as well as environmental samples is of huge significance from the human health point of view. Related to this, considerable efforts are underway to develop adequately efficient and facile methods to achieve their selective detection. Optical sensing of metal ions has gained increasing attention of researchers, particularly in the environmental and biological settings. Innovatively designed optical probes (fluorescent or colorimetric) are usually comprised of three basic components: an explicitly tailored receptor unit, a signalling unit and a clearly defined reporter unit. This review deals with the recent progress in the design and fabrication of fluorescent or colorimetric organic sensors for the detection of group 10 metal ions (Ni(II), Pd(II) and Pt(II)), with attention to the general aspects for design of such sensors.

Rice husk derived Aminated Silica for the efficient adsorption of different gases

In this present work, we successfully prepared aminated silica (ASiO2) from rice husk ash (RHA) and functionalized with 3-aminopropyltriethoxysilane (APTES). Physical and chemical properties of the synthesized material were investigated by various techniques SEM-EDX, XPS, FTIR, TGA. The surface area of RHA was 223 m2/g, while for ASiO2 was 101 m2/g. Molecular level DFT calculations revealed that the functionalization of ASiO2 resulted in a significant decrease in the HOMO-LUMO energy gap, a reduction in hardness, and a consequent increase in charge transfer characteristics. The adsorption behavior at low pressure (1 atm.) of aminated silica on different gases CO2, CH4, H2, and N2 at temperatures 77, 273, 298 K was studied. The adsorption of hydrogen was reported for the first time on aminated silica with an excellent adsorption capacity of 1.2 mmol/g. The ASiO2 exhibited excellent performance in terms of gas separation in binary mixtures of CO2/CH4, CO2/N2 and CO2/H2 at 273, and 298 K, respectively. The catalyst further exhibits high stability during three cycles with less than 10% variation in the separation capacity.

Sensitive and selective colorimetric nitrite ion assay using silver nanoparticles easily synthesized and stabilized by AHNDMS and functionalized with PABA

Nitrite ions (NO₂ ^-), as one of the important inorganic anions, exhibit considerable effects towards the environment and human health. Moreover, over intake of this anion may cause dangerous diseases. Herein, we successfully fabricated silver nanoparticles (AgNPs) using 4-amino-5-hydroxynaphthalene-2, 7-disulphonic acid monosodium salt (AHNDMS) and functionalized them with p-aminobenzoic acid (PABA), and used the functionalised AgNPs as a sensitive and selective colorimetric sensor for nitrite ions. The structure of the as-prepared pure AgNPs was experimentally characterized by different characterizations methods, namely, UV-vis, FT-IR, CV, DPVs, SEM, TEM, and XRD. Additionally, the nitrite ion sensitively and selectively changes the brownish yellow color of the dispersed AgNPs to pinkish red, indicating aggregation of AgNPs, with a detection limit of 0.016 ppm (0.348 μM) and 0.0069 ppm (0.149 μM) by the naked-eye and by UV-vis spectroscopy, respectively. The color change suggested that the aggregation of AgNPs was induced by nitrite-selective diazo-coupling. UV-vis spectra show the disappearance of the absorbance at 474 nm and appearance of a new peak at 532 nm, presumably due to the conversion of AgNPs to silver ions. Moreover, the studies of interference in the proposed sensor confirm its selectivity in the presence of anions as well as cations. Furthermore, linearity was observed between the absorption and the concentration of nitrite ions. More importantly, the proposed sensor was practicably applied for the determination of nitrite in different water samples, such as distilled water, river water, and tap water.

A selective detection approach for copper(ii) ions using a hydrazone-based colorimetric sensor: spectroscopic and DFT study

The development of an efficient and miniaturized analytical approach to determine trace levels of toxic ions in aqueous fluids presents a current research challenge. Hydrazone-based chemosensors are considered potential candidates due to their high sensitivity and selectivity towards heavy metal ions. Computational techniques can be properly implemented to elucidate possible modes of ligand-metal interaction and provide an in-depth understanding of the chemistry involved. The present study reports the use of 3-hydroxy-5-nitrobenzaldehyde-4-hydroxybenzoylhydrazone (3-HNHBH) ligand for highly sensitive, quick and re-usable colorimetric sensing of copper(ii) ions in aqueous media. DFT calculations suggest that the complexation of 3-HNHBH with copper(ii) ions adopts a seesaw coordination geometry and results in the largest HOMO-LUMO gap and most effective coulombic interaction compared to Zn and Ni counterparts. It demonstrated a high selectivity towards copper ions with a detection limit of 0.34 μg L-1. The ligand was readily regenerated using a 0.5 M HCl solution, indicating its feasibility to be used as a re-usable sensor for the convenient detection of copper ions in aqueous media. The influence of metal interference, pH and solvents on the selectivity and regeneration of the ligand was also investigated.