Bal Govind Vats

Green, Water-Dispersible Photoluminescent On–Off–On Probe for Selective Detection of Fluoride Ions

Considering the high toxicity and widespread availability of fluoride ions in different environmental matrices, it is imperative to design a probe for its detection. In view of this, a selective fluorescent on-off-on probe based on carbon quantum dots (CQDs) and Eu3+ has been designed. We have synthesized water-soluble carboxylic acid-functionalized CQDs and monitored their interaction with Eu3+. Luminescence quenching in the CQD emission was observed (switch-off) on adding Eu3+ ions. We investigate the reason for this luminescence quenching using time-resolved emission and high-resolution transmission electron microscopy (HRTEM) studies and observed that both electron transfer from CQDs to Eu3+ and aggregation of CQDs are responsible for the luminescence quenching. ζ-Potential and X-ray photoelectron spectroscopy studies confirm Eu3+ binding with the COOH groups on CQD surface. Interestingly, luminescence regains after the addition of fluoride ions to the CQDs/Eu3+ system (switch-on). This has been assigned to the removal of Eu3+ from the CQD surface due to the formation of EuF3 and is confirmed by X-ray diffraction and HRTEM measurements. The sensitivity of the probe was tested by carrying out experiments with other competing ions and was found to be selective for fluoride ions. Experiments with variable concentrations of fluoride ions suggest that the working range of the probe is 1-25 ppm. The probe has been successfully tested for the detection of fluoride ions in a toothpaste sample and the results were compared to those of ion chromatography. To the best of our knowledge, this is the first report based on CQDs and Eu3+ for the detection of fluoride ions, wherein a clear mechanism of the detection has been demonstrated, which, in turn, will help to develop better detection methods. The suggested probe is green, economical, rapid, efficient, and, most importantly, selective and can be used for the detection of fluoride ions in real environmental samples.

The effect of vanadium substitution on photoluminescent properties of KSrLa(PO4)x(VO4)2−x:Eu3+ phosphors, a new variant of phosphovanadates

Eu3+ doped red emitting phosphors of formulae KSrLa1−y(PO4)x(VO4)2−x:yEu3+ (where x = 0, 1 and 2 and y = 0, 0.02, 0.05, 0.10 and 0.015) were synthesized by a high temperature solid state reaction route. The compounds were characterized by a powder XRD method, and a complete structure determination for KSrLa(PO4)(VO4) was carried out using the Rietveld refinement method. The compound crystallized in the rhombohedral system with space group (Rm). The structure of the compound shows that La3+ is occupied at two positions, namely, trigonal antiprism (six coordinated) and truncated hexagonal bipyramidal (10 coordinated) centres, with occupancy of 0.94 and 0.06, respectively. The effect of vanadium substitution on excitation and emission spectra of the compounds was investigated using time resolved photoluminescence spectroscopy (TRPLS). The lifetimes of 5D0 → 7F2 transition were determined for all the compounds, which are in agreement with emission spectroscopic results. Judd–Ofelt analysis of the compounds clearly shows that the more polarized environment around Eu3+ in the case of the vanadate and phosphovanadate in comparison to the phosphate leads to more colour purity of the emission, when excited by UV light.

Electron-Transfer-Mediated Uranium Detection Using Quasi-Type II Core–Shell Quantum Dots: Insight into Mechanistic Pathways

Uranium is one of the most toxic and important elements present in the environment, and because of its high toxicity, ultra-trace-level detection is of utmost importance. Many methods were reported earlier for this purpose, but each has its own limitations such as high cost, sophisticated instrumentation, sample processing, and so forth. Herein we have demonstrated an alternate method that is much simpler and can be used for the ultra-trace-level detection of uranium. We have synthesized 3-mercaptopropionic acid (MPA)-capped CdSe/CdS core-shell quantum dots (CSQDs) and used its photoluminescence properties to detect uranium in solution. Steady-state emission studies suggest the luminescence quenching of CSQDs in the presence of uranium. Redox levels of CSQDs and uranium suggests that the electron-transfer process from photoexcited CSQDs to uranium is a thermodynamically viable process, which has subsequently been confirmed by time-resolved studies. A Stern-Volmer plot of CSQDs with uranium suggests that the detection limit of this method is 74.5 ppb. The method has an advantage over other reported methods for being simple and low cost and requiring a small amout of sample processing. To the best of our knowledge, we are reporting for the first time uranium detection using quasi-type II CSQDs and proposing the mechanistic path through luminescence spectroscopy, which in turn helps us to design an efficient detection method.

Extraction and electrochemical investigations of Pu(IV) employing green solvent system containing new bifunctional ligand and Bmim[NTf2] ionic liquid

Electrochemical investigations and extraction of Pu(IV) was investigated employing a new bifunctional ligand system (N,N-dialkyl carbamoyl methyl) (2-pyridyl-N-Oxide) sulfide C5H4NOSCH2CONR2, (where R = octyl) (NOSCO) dissolved in 1-butyl-3-methylimidazolium bis (trifluoromethanesulphonyl) imide ([Bmim][NTf2]). The extraction efficiency was found to be 84% in single contact. Cyclic voltammetry (CV) of Pu(IV) in aqueous and in ([Bmim][NTf2] + NOSCO) was carried out. Shifts of cathodic and anodic peak potentials of Pu(IV) in cyclic voltammograms were observed towards negative potentials in the extended electrochemical window for ionic liquid medium compared to aqueous medium. The diffusion coefficient and heterogeneous charge transfer coefficient were calculated for both aqueous and ionic liquid media. The redox reaction were found to be quasi reversible for both the media while the CV was broader in case of ionic liquid suggesting slow kinetics.

A novel approach for extraction of plutonium and americium from aqueous complexing media

A new approach for the extraction of plutonium and americium from aqueous media containing complexing ligands has been investigated using a new extractant N,N′-dioctyl-α-hydroxy acetamide. Studies have been carried out on the extraction of Am(III) and Pu(IV) by this extractant from media containing complexing ligands such as PO43−, C2O42− and F− which are difficult to extract due to the non-extractability of the complexed form of these metal ions. Present study has revealed that, addition of non-complexing anions such as ClO4−, I−, SCN− into the medium containing complexing ligand greatly enhanced extraction of Pu(IV) and Am(III), making the extraction of these nuclides possible.