A highly sensitive and selective colorimetric chemosensor for Hg2+ ions was prepared by the use of the well-known isatin chromophore, hydrazine hydrate, and 4-hydroxybenzaldehyde. In EtOH solution, the synthesized adsorbent showed a visual color change from melon yellow to dark orange with a remarkably large red shift (75 nm) in the presence of Hg2+. This color change is due to the formation of a 1:1 metal-ligand complex. In complex, nitrogen atom of hydrazone group and oxygen atom of lactam group were coordinated to Hg2+, while the hydroxyl group on the phenyl ring plays an important role in color change. The detection limit of the synthesized colorimetric chemosensor for mercury ions was 1.8±0.2 μM. The H1 was synthesized as a colorimetric chemosensor based on isatin hydrazone and 4-hydroxy benzaldehyde for monitoring mercury ions. The H1 probe showed a high sensitivity to Hg2+ ions, that interact from its nitrogen and oxygen atoms against mercury cations, with a detection limit of 1.8±0.2 μM. In future research, we intend to modify the structure of isatin hydrazone so that it acts as a logic gate to detect two or more agents, showing different color changes.

The key to simple and rapid detection of a large volume of samples lies in the hands of solution-based nanomaterial sensors. Quantification of mercury in the river and coastal water is analytically challenging due to the potential interference of the matrix. In this endeavor, lysine-capped gold nanoparticles (Lys-AuNPs) based colorimetric sensors are demonstrated here towards efficient detection of trace amounts of mercury ions (Hg2+) in coastal and estuarine water. The colorimetric behavior of Lys-AuNPs is related to surface plasmon resonance (SPR)During analysis, interestingly a decrease in the intensity of the original SPR peak at 530 nm was observed, with the concomitant appearance of a new peak at a longer wavelength due to agglomerated Lys- AuNPs. Developed sensors exhibit excellent performance in different environmental samples with high selectivity towards Hg2+ ions in the presence of other metal ions. For the analysis of coastal water samples, a low value of regression coefficient was observed due to the potential interference of salt in the sample. To overcome this, matrix-matching experiments were carried out. Developed Lys- AuNPs show good selectivity towards Hg2+ in matrixed matched diluted coastal water samples. With a sensitivity of 0.02 ppm, the sensor can be utilized to screen large numbers of coastal water samples for their Hg2+ content to satisfy coastal regulation norms. As a whole, this method is simple, sensitive, selective, cost-effective and can be used to screen large numbers of samples across the coastal area for monitoring Hg2+ concentration.

Mercury (Hg) is one of the water pollutants and its removal from the aqueous environment is important. The major goal of this study was to remove the Hg (II) from aqueous solution by synthesizing a modified nanochitosan with carbon disulfide functional groups. Nanochitosan was synthesized using citric acid as an environmentally friendly crosslinking agent, and then it was modified with a carbon disulfide functional group. The characteristics of synthesized nanocomposite were studied by using proton nuclear magnetic resonance (1HNMR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Batch adsorption experiments of Hg (II) in metal ion solution were conducted under different conditions such as pH, temperature, contact time, initial concentration of metal ion and adsorbent dosage. The adsorption process was conducted to investigate the compatibility of data with isotherms models (Freundlich and Langmuir), kinetics (pseudo-first-and second-order rate equations) and adsorption thermodynamics in a batch system. Reusability of adsorbent using 0. 5 mol/L HCl and also effect of ion interferences were investigated for selectivity of adsorbent. Obtained results from this study confirmed the successful synthesis and functionalizing process of the nano-adsorbent. The optimal values were reported as pH=7, adsorbent dosage of 0. 2 g/L, initial concentration of 30 mg/g Hg (II) and contact time of 120 min. Sorption of mercury agreed well with the Langmuir isotherm model, confirming a monolayer adsorption. The maximum equilibrium adsorption capacity for mercury ions was 303. 03 mg/g. The results of kinetic studies showed that the sorption process followed the second order model. The results of thermodynamics showed that the adsorption process was exothermic and spontaneous. Possibility of recovery of adsorbent was investigated up to five cycles and desorption percentage of mercury ions was more than 95%. Also, the results of ion interferences effect in mixed solution showed that the percentage of mercury removal with the functionalization of nanochitosan by carbon disulfide increased up to 88% and the synthesized adsorbent has a high selectivity for mercury ions. Based on the high adsorption efficiency obtained for mercury ions in the mixed solution, the synthesized adsorbent can be at promising approach in treatment of real wastewaters with low concentrations of mercury ions and other interfering ions in order to obtain an admissible effluent standard. The results showed that the synthesized nanoadsorbent is an efficient low cost adsorbent for mercury removal from wastewater due to its high adsorption capacity, as well as its reusability and selectivity for mercury.

Mercury, one of the common pollutants in water, is known to affect human health adversely upon exposure. It is released in water not only by various natural processes but also by human activities. Methods developed so far for the detection of mercuric ions in water have limitations like sensitivity range, complex setup, skillful operation etc. Silver nanoparticles, due to unique properties, have been explored by researchers to develop better detection systems.  Stable silver nanoparticles can be easily synthesized by methods of green chemistry, its reaction with mercuric ion can be easily observed by changes in color and UV-Vis spectra. The absorbance data from UV-Vis spectra can also be used in quantifying mercury concentration. In this paper, stable silver nanoparticles synthesized using silver nitrate as precursor, sodium lignosulphonate (LS) as reducing and stabilizing agent under microwave radiation are explored for detection of mercuric ions in water. Formation of AgNP was confirmed by UV-Vis band at 403.5nm. The intensity of this band showed a proportional decrease with increasing Hg+2 concentration. Hg+2 ions were detected by a distinct color change at higher concentration of Hg+2 also.  The limit of detection (LOD) calculated from the observed absorbance data to be 0.7 ppm.