Fluorescent Carbon Dots: Aggregation-Induced Emission Enhancement, Application as Probe for CN- and Cr2O7-2, Sensing Strips and Bio-imaging Agent.

Fluorescent carbon dots (Trp-CDs) were prepared using tryptophan as precursor and were characterized on the basis of elemental analysis, powder-XRD, IR, Raman spectroscopy, 13C-NMR, UV-Vis, fluorescence and TEM. Trp-CDs exhibit poor fluorescence in 100% water but showed strong Aggregation Induced Emission (AIE) in ethanol and higher alcohols. The anion sensing study of Trp-CD revealed that it selectively detects CN- and Cr2O7-2 and from fluorescence quenching titration study, quenching constant, LOD and range of detection were evaluated. The emission life-time of Trp-CD before and after addition of CN- and Cr2O7-2 were measured, the decay curve before addition of anion was best fitted with a bi-exponential function with life-time of τ1 2.79 ns (10.74%) and τ2 18.93 ns (89.26%). The mechanistic study revealed that for CN-, the fluorescence quenching is due to its interaction with protons attached to surface functional groups and for Cr2O7-2, it is due to inner filter effect (IFE). Sensing strips were prepared by coating Trp-CDs onto various solid surfaces including agarose films and were used for detection of CN- and Cr2O7-. Trp-CD was found to be nontoxic and biocompatible and used as staining agent for Artemia and Bacteria (Bacillus Subtilis, Pseudomonas) and detection of CN- and Cr2O7-.

Green route for synthesis of multifunctional fluorescent carbon dots from Tulsi leaves and its application as Cr(VI) sensors, bio-imaging and patterning agents.

We report a one pot green strategy for the synthesis of carbon dots using tulsi leaves and their potential application in sensing of Cr(VI) selectively. The detection mechanism is based on the phenomenon called inner filter effect (IFE) and a good linear static quenching was observed in the range of 1.6 µM to 50 µM with a detection limit of 4.5 ppb. The reversible switching in fluorescence has been tested and a good recovery in fluorescence was observed up to three consecutive cycles upon addition of ascorbic acid as reducing agent. Also the low toxicity, high fluorescence and photostabilty of the CDs make them excellent imaging and patterning agent. The acid and alkali resistant property of these CDs makes it suitable for real sample analysis. The fluorescent CDs were applied for successful detection of Cr(VI) in water with spike-recoveries ranging from 93 to 99%.

Solvent-free production of nano-FeS anchored graphene from Ulva fasciata: A scalable synthesis of super-adsorbent for lead, chromium and dyes.

Here we demonstrate, a simple and solvent-free synthetic route for the production of FeS/Fe(0) functionalized graphene nanocomposite (G-Fe) via a one-step pyrolysis of seaweed biomass (Ulva fasciata). It is proposed that the natural abundance of both inorganic and organic sulfur in the seaweed induces the reduction of exfoliated graphitic sheets at elevated temperatures. FeCl3 was employed both as the iron precursor as well as the templating agent. Iron doping played a dual-faceted role of exfoliating as well as activating agent, producing composite with high adsorption capacity for Pb2+ (645 ±â€¯10 mg/g), CR (970 mg/g), CV(909 mg/g), MO (664 mg/g), MB (402 mg/g) dyes and good recyclability (8 cycles). Pb2+ adsorption was irreversible even at low pH values and the spent composite (G-Fe-Pb) was utilized for efficient Cr(IV) removal (Ì´100 mg/g). The adsorption data followed the pseudo second order kinetics while the equilibrium data fitted perfectly into the Langmuir adsorption equation. Further, a thin layer of composite was deposited on a filter paper by vacuum filtration which was tested under continuous filtration mode for RB5 dye removal. Preliminary results highlight the potential of this composite to be used in pretreatment steps in hybrid membrane processes for filtration of complex wastewater feeds.

New Route for Synthesis of Fluorescent SnO2 Nanoparticles for Selective Sensing of Fe(III) in Aqueous Media.

A simple new route for synthesis of fluorescent SnO2 and its application as an efficient sensing material for Fe3+ in aqueous media is reported. The fluorescent SnO2 nanoparticles were obtained by oxidation of SnCl2, which when used as reducing agent for the reduction of organic nitro compounds to corresponding amino compounds in ethanol. The SnO2 nanoparticles have been characterized on the basis of powder-XRD, IR, UV-Vis, TEM, FESEM and EDX analysis and found that this material is highly fluorescent in aqueous media. Detail study revealed that this material functions as a selective probe for Fe3+ out of a large number of metal ions used. The oxygen vacancies (defects) generated on the surface of the SnO2 during synthesis, are the source of emission due to recombination of electrons with the photo-excited hole in the valance bond. The quenching of emission intensity in presence of Fe3+ is due to the nonradiative recombination of electrons and holes at the surface. This material is used for estimation of Fe3+ in real samples such as drinking water, tap water and soil.

Sunlight Induced Preparation of Functionalized Gold Nanoparticles as Recyclable Colorimetric Dual Sensor for Aluminum and Fluoride in Water.

A sunlight induced simple green route has been developed for the synthesis of polyacrylate functionalized gold nanoparticles (PAA-AuNPs), in which poly(acrylic acid) functions as a reducing as well as stabilizing agent. This material has been characterized on the basis of spectroscopic and microscopic studies; it exhibited selective colorimetric detection of Al3+ in aqueous media, and the Al3+ induced aggregated PAA-AuNPs exhibited detection of F- with sharp color change and high selectivity and sensitivity out of a large number of metal ions and anions tested. The mechanistic study revealed that, for Al3+, the color change is due to a shift of the SPR band because of the Al3+ induced aggregation of PAA-AuNPs, whereas for F-, the reverse color change (blue to red) with return of the SPR band to its original position is due to dispersion of aggregated PAA-AuNPs, as F- removes Al3+ from the aggregated species by complex formation. Only concentration-dependent fluoride ion can prevent Al3+ from aggregating PAA-AuNPs. The method is successfully used for the detection of F- in water collected from various sources by the spiking method, in toothpastes of different brands by the direct method. The solid Al3+-PAA-AuNPs were isolated, adsorbed on ZIF@8 (zeolitic imidazolate framework) and on a cotton strip, and applied as solid sensing material for detection of F- in aqueous media.

Silver nanoparticle based highly selective and sensitive solvatochromatic sensor for colorimetric detection of 1,4-dioxane in aqueous media.

A citrate stabilised silver nanoparticle (Ci-AgNP) based solvatochromic sensor, which functions as a highly selective and sensitive colorimetric probe for 1,4-dioxane in aqueous media is reported. The surfaces of the AgNPs generate reactive oxygen species, which promote the degradation of 1,4-dioxane assembled in the vicinity of the nanoparticle surfaces through charge transfer interactions. During this process, Ag(0) is oxidised to Ag(+) and the yellow colour of the solution turns to colourless. The sensor was used for the estimation of 1,4-dioxane in ground water and also 1,4-dioxane vapour diffused in aqueous media.