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Commercially available high quality 9B pencil graphite was used for sensing of trace concentrations of nitrogen dioxide (NO2) and ammonia (NH3) at sub-ppm levels in air at ambient temperature and pressure. The pencil graphite was characterized using scanning electron microscopy (SEM), Raman spectroscopy and powder X-ray diffraction (XRD) techniques. In comparison to other sensing materials pencil graphite is very well recognized owing to its cheaper price, simplicity of fabrication, abundant over-the-counter obtainability and easy modification. The principal of operation of the chemiresistive gas sensor is based on the variation in the electrical resistance due to the selective interaction between the pencil graphite network and the specific gaseous analyte in a two-pole format. The degree of change in electrical resistance of the pencil graphite network depends on the concentration of the gaseous analyte to which it is exposed. On the basis of this fact qualitative as well as quantitative detection of the gaseous analytes can be achieved. The sensing limits of 100 parts-per-billion (ppb) and 500 ppb with sensor response times of ∼30 s and ∼50 s for NO2 and NH3, respectively is recorded using our gas detector, and are found significantly efficient in comparison to the NO2 and NH3 detectors available commercially in market. [ABSTRACT FROM AUTHOR]

CdSexS1-x quantum dots (QDs) have been grown in borosilicate glass matrix using two step annealing technique and are characterized by AFM, XRD, UV-Vis absorption, HRTEM and Raman spectroscopy measurements. AFM studies show that nearly spherical clusters of about 5-10 nanocrystals were grown. From XRD measurements, it is found that the nanocrystals are grown in hexagonal phase. From HRTEM measurements, it is observed that the size of QDs increases from 5.1 to 9.5 nm with increasing annealing duration from 3 to 10 hrs. Blue shift in absorption spectrum indicates that quantum confinement increases with decreasing annealing durations. Raman spectrum of CdSexS1-x QDs shows two mode type of behavior i.e., CdSe like longitudinal optical phonon mode (LO1) and CdS like longitudinal optical phonon mode (LO2). It has been observed that with increasing the size of QDs from 5.1 to 9.5 nm, LO1 shifts from 205 to 210 cm-1 while LO2 shifts from 278 to 291 cm-1. The shift in the LO1 and LO2 Raman peaks towards high frequencies has been interpreted due to increase in the lattice compressive strain with the increase in QDs size. The effect of phonon negative dispersion on the shift of LO1 and LO2 is found to be comparatively insignificant. It is also found that the ratio of intensity of overtones to the fundamental mode increases from 0.34 to 0.48 with decreasing QD size. This indicates that the electron-phonon coupling increases with the decrease in size of QD due to increasing overlap of electron and hole wave function in small size QDs. It is further observed that the frequency of the surface optical phonon mode remains unchanged as the size of QD changes but the intensity decreases with the increase in the size of QDs finally merging in LO mode Raman spectrum. [ABSTRACT FROM AUTHOR]

• A hand-held portable, point of care (POC) device for detection of Chromium in liquid medium. • The method involves the detection of hexavalent chromium in water as well as biological samples using citrate-capped silver nanoparticle (C-AgNPs) leading to reduction of Cr(VI) to Cr (III). • The device was tested and results were calibrated with flame AAS. • The limit of detection (LOD) and limit of quantitation (LOQ) is 26 ppb and 79 ppb, respectively. The present work describes a novel handheld pocket-friendly device for on the spot detection of chromium. The device gives not only qualitative but also the quantitative determination of chromium in environmental wastewater samples. The qualitative detection can be made visually by the naked eye while for the quantitative detection a colorimetric device has been fabricated in-house. The system comprises a source, sample holder, detector, and a microcontroller-processing unit with a display unit. The method involves the detection of hexavalent chromium Cr (VI) in aqueous systems by using citrate-capped silver nanoparticle (C-AgNPs) leading to a reduction of Cr (VI) to Cr (III). The citrate capped silver nanoparticles were synthesized and characterized using a blend of characterization techniques like ultra-violet visible (UV-Vis) spectrophotometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques. The device performance remained unaffected even in the presence of various interfering cations present in the wastewater. The device was tested, and results were calibrated with standard atomic absorption spectroscopy (AAS), it showed linearity from 0.01-0.7 ppm for wastewater samples tested with spiking different known concentrations of chromium. The limit of detection (LOD) of the method is 26 ppb and the limit of quantitation (LOQ) of 79 ppb. The development of a low-cost, simple colorimeter employing the same sensor principle underlines the on-site applicability of this method. [ABSTRACT FROM AUTHOR]

Commercially available high quality 9B pencil graphite was used for sensing of trace concentrations of nitrogen dioxide (NO2) and ammonia (NH3) at sub-ppm levels in air at ambient temperature and pressure. The pencil graphite was characterized using scanning electron microscopy (SEM), Raman spectroscopy and powder X-ray diffraction (XRD) techniques. In comparison to other sensing materials pencil graphite is very well recognized owing to its cheaper price, simplicity of fabrication, abundant over-the-counter obtainability and easy modification. The principal of operation of the chemiresistive gas sensor is based on the variation in the electrical resistance due to the selective interaction between the pencil graphite network and the specific gaseous analyte in a two-pole format. The degree of change in electrical resistance of the pencil graphite network depends on the concentration of the gaseous analyte to which it is exposed. On the basis of this fact qualitative as well as quantitative detection of the gaseous analytes can be achieved. The sensing limits of 100 parts-per-billion (ppb) and 500 ppb with sensor response times of ∼30 s and ∼50 s for NO2 and NH3, respectively is recorded using our gas detector, and are found significantly efficient in comparison to the NO2 and NH3 detectors available commercially in market. [ABSTRACT FROM AUTHOR]