A reactivity index study to monitor the role of solvation on the interaction of the chromophores with amino-functional silanol surface for colorimetric sensors.

Amino-functional silanol surface are mostly used for the immobilization of inorganic ions, molecules, organic or biochemical molecules onto the mesopore surface. In analytical chemistry, the metal ion uptake was visualized through colorimetric sensors using chromophore molecules. One needs to know the structure-property correlation between the chromophore and silylating agent while choosing chromophore, which is very important to design the sensors. We have used two chromophores representative of hydrophobic and hydrophilic type. We used density functional calculation on all the interacting molecules in both the unsolvated phase and solvated medium within the domain of hard soft acid base principle (HSAB) to look at the localized activity of the interacting atoms of these reacting molecules to formulate a priori rule to choose of the best chromophore. We have as well postulated the mechanism of interaction between chromophore and the silylating agent. The results were compared with experiment and it is observed that solvation plays a detrimental role in the binding of chromophore with silylating agent. The results also show that, the range of reactivity index can be used as a suitable property to scale activity of chromophore molecules suitable for the sensing process. It is observed that the hydrophobic chromophore binds stronger with both the metal and the silylating agent; whereas for the hydrophilic one, it binds only with the silylating agent when solvated and in all cases the metal ion binding is weaker compared to that of the hydrophobic one.

Naked eye detection of cadmium using inorganic-organic hybrid mesoporous material.

A novel and low-cost optical sensor for the naked eye detection of Cd2+ in aqueous media based on mesoporous silica containing 4-(2-pyridylazo)resorcinol (PAR) as a probe molecule anchored by N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TMAC) was prepared. The effects of various factors such as pH, solvent volume, temperature, reaction time, amount of the material, and the presence of various ions were studied in order to optimize operating conditions. The detection was based on the color change of PAR from orange-yellow to purple as a result of complexation with Cd2+. The intensity of the Cd-PAR complex varies linearly with the Cd2+ concentration, from zero to 1.78x10(-7) mol dm(-3). The detection and quantification limits for the method when determining Cd2+ were 1.75x10(-8) and 5.77x10(-8) mol dm(-3), respectively, with a correlation coefficient of 0.99. Good chemical stability of the material was observed for a period of five months. The developed sensor was applied to the analysis of various industrial effluents and tap water samples.

Naked-eye detection of fluoride using Zr(IV)-EDTA complex and pyrocatechol violet.

A method for the visual detection of fluoride is presented using an aqueous solution of Pyrocatechol Violet (PV), which changes its color from yellow to blue by the formation of a ternary complex with Zr(H2O)2EDTA; also, the blue color of PV-Zr-EDTA readily shifts to orange red upon the addition of a moderate concentration of fluoride. The mechanism has been interpreted by a ligand-exchange reaction of PV coordinated to Zr(IV) with fluoride. The effect of various factors, such as the pH, ratio of Zr(H2O)2EDTA and PV, and diverse ions were studied to optimize the conditions for the reaction of PV-Zr-EDTA with fluoride. The present naked-eye detection system provides a simple, quick, and sensitive method for the determination of fluoride in the concentration range 1.5 x 10(-5) to 1.5 x 10(-4) mol dm(-3). The detection limit of the method was observed to be 4.5234 x 10(-4) mol dm(-3) with a correlation coefficient of 0.9955. The developed chemosensor was applied to the detection of fluoride in industrial effluents.

Optical sensor for the visual detection of mercury using mesoporous silica anchoring porphyrin moiety.

A low cost, solid optical sensor for the rapid detection of low concentrations of Hg2+ in aqueous media was prepared by the monolayer functionalization of mesoporous silica with 5,10,15,20-tetraphenylporphinetetrasulfonic acid (TPPS), anchored by N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TMAC). The detection is based on the color change of TPPS from orange to green as a result of the formation of a charge-transfer complex with Hg2+. The intensity of the charge-transfer band varies linearly with Hg2+ in the concentration range from zero to 2.5 x 10(-7) mol dm(-3). The lower detection limit observed for Hg2+ concentration is 1.75 x 10(-8) mol dm(-3). The material exhibits good chemical and mechanical stability, and did not show any degradation of TPPS for a period of eight months. The sensor was applied for the analysis of various environmental samples. The effects of pH, sample volume, reaction time, amount of material, and the presence of foreign ions on the detection method are discussed.

Adsorption and removal of As(V) and As(III) using Zr-loaded lysine diacetic acid chelating resin.

An adsorption process for the removal of As(V) and As(III) was evaluated under various conditions using zirconium(IV) loaded chelating resin (Zr-LDA) with lysine-Nalpha,Nalpha diacetic acid functional groups. Arsenate ions strongly adsorbed in the pH range from 2 to 5, while arsenite was adsorbed between pH 7 and 10.5. The sorption mechanism is an additional complexation between arsenate or arsenite and Zr complex of LDA. Adsorption isotherm data could be well interpreted by Langmuir equation for As(V) at pH 4 and As(III) at pH 9 with a binding constant 227.93 and 270.47 dm3 mol(-1) and capacity constant 0.656 and 1.1843 mmol g(-1), respectively. Regeneration of the resin was carried out for As(V) using 1 M NaOH. Six adsorption/desorption cycles were performed without significant decrease in the uptake performance. Column adsorption studies showed that the adsorption of As(V) is more favorable compared to As(III), due to the faster kinetics of As(V) compared to As(III). Influence of the coexisting ions on the adsorption of As(V) and As(III) was studied. The applicability of the method for practical water samples was studied.

Adsorption characteristics of as(III) and as(V) with titanium dioxide loaded Amberlite XAD-7 resin.

The adsorption characteristics of As(V) and As(III) on titanium dioxide loaded Amberlite XAD-7 resin have been studied. The resin was prepared by impregnation of Ti(OC2H5)4 followed by hydrolysis with ammonium hydroxide. Batch adsorption experiments were carried out as a function of the pH, shaking time and the concentration of As(V) and As(III) ions. The resin showed a strong adsorption for As(V) from pH 1 to 5 and for As(III) from pH 5 to 10. The adsorption isotherm data for As(V) at pH 4 fitted well to a Langmuir equation with a binding constant of 59 dm3 mol(-1) and a capacity constant of 0.063 mmol g(-1). The data for As(III) at pH 7 also fitted well to a Langmuir equation with a binding constant of 5.4 dm3 mol(-1) and a capacity constant of 0.13 mmol g(-1). The effect of diverse ions on the adsorption of arsenic was also studied. Column adsorption experiments showed that the adsorption of As(III) is more favorable compared to As(V), due to both the faster adsorption and larger capacity for As(III) than As(V).