Nahar Singh

Effect of soil temperature on methane emission from paddy fields

Abstract Methane emission measurements using the closed chamber method from Indian paddy fields, specially prepared to study the effect of soil temperature, indicate a definite increase in methane emissions with soil temperature up to 34.5 ± 0.5°C and a decrease in the rate of emission above this temperature.

Methane budget from paddy fields in India

Abstract Results of national methane campaign launched in 1991 to assess methane budget from Indian paddy fields are reported. The campaign involved a number of scientific institutions and universities with National Physical Laboratory at Delhi operating as a nodal agency and covered most of the major rice growing regions of India. Methane emission rates ranged between −0.64 and 84.1 mg −2 h −1 . The methane budget from Indian paddies has been estimated to be around 4.0 TgY −1 with a range between 2.7 to 5.4 TgY −1 .

Synthesis of optically active silica-coated NdF3 core-shell nanoparticles

Silica surface-modified NdF(3) core-shell nanoparticles were prepared by sol-gel route. The prepared core-shell nanoparticles were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), UV-vis absorption and photoluminescence (PL) spectroscopy studies. Phase identification of the NdF(3) and silica-coated NdF(3) core-shell nanoparticles which was carried-out by XRD, confirms the formation of a well-crystallized hexagonal phase structure. Due to the silica-surface modification, the nanoparticles were not found to be well-separated (agglomerated) in ethanol solvent as scanned by TEM. The results of the FTIR studies conducted on these core-shell reveal the binding of silica with the NdF(3) nanoparticles. The largest intensity and shape variation were observed in all transitions as compared to non-silica modified NdF(3) nanoparticle spectra, and were attributed to the environment around the Nd(III) ion due to coordination of silica molecule(s). A significant enhancement in the emission intensity was measured in silica surface modified NdF(3) core-shell nanoparticles due to the successful silica coating on the surface of nanoparticles. The results of these studies suggest that these nanoparticles may find potential applications in the areas of bioimaging, protein-labeling, optical biosensors and drug delivery, etc.

Electrospun chitosan–polyvinyl alcohol composite nanofibers loaded with cerium for efficient removal of arsenic from contaminated water

Contamination of water due to arsenic has been extensively reported all over the world. It has led to massive epidemics of arsenic poisoning. An urgent need is being felt to develop efficient techniques for the removal of arsenic from contaminated water. In this context, cerium (Ce) loaded chitosan (CHT)–polyvinyl alcohol (PVA) composite (Ce-CHT/PVA) nanofibers were developed by electrospinning technique and have been employed for removing As(III). The Ce-CHT/PVA composite nanofibers efficiently adsorb As(III) and purify water below the prescribed limit of WHO/EPA. As(III) adsorption over the surface of Ce-CHT/PVA has been confirmed by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDAX), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The quantitative estimation of As(III) has been carried out by flameless atomic adsorption spectrophotometer-hydride generator (AAS-HG) system. The As(III) adsorption efficiency of Ce-CHT/PVA composite nanofibers has been established as a function of pH, time, temperature and adsorbent dose. The adsorption data were best fitted to Langmuir isotherm, and the maximum adsorption capacity (qm) was found to be 18.0 mg g−1. The interference studies of several ionic species individually as well multi-element for As removal have also reported. The measurement of the uncertainty of As(III) determination was calculated after determining the contributing factors. The data are reported with a confidence level of 95% (K = 2). The Ce-CHT/PVA composite nanofibers are non toxic and can be directly used for water purification or after being embedded in the form of membrane or candles.

Comparative study of leaching of silver nanoparticles from fabric and effective effluent treatment

Nano silver (Ag(n)) is employed as an active antimicrobial agent, but the environmental impact of Ag(n) released from commercial products is unknown. The quantity of nanomaterial released from consumer products during use should be determined to assess the environmental risks of advancement of nanotechnology. This work investigated the amount of silver released from three different types of fabric into water during washing. Three different types of fabric were loaded with chemically synthesized Ag nanoparticles and washed repeatedly under simulated washing conditions. Variable leaching rates among fabric types suggest that the manufacturing process may control the release of silver reaching the waste water treatment plants. In an attempt to recover the Ag(n) for reutilization and to save it from polluting water, the effluents from the wash were efficiently treated with bacterial strains. This treatment was based on biosorption and was very efficient for the elimination of silver nanoparticles in the wash water. The process ensured the recovery of the Ag(n) leached into the effluent for reutilization, thus preventing environmental repercussions.

Immobilization of enzyme on long period grating fibers for sensitive glucose detection.

Glucose oxidase (GOD) immobilized long period grating (LPG) fibers have been proposed for the specific and sensitive detection of glucose. The treatment of LPG fibers with aminopropyl triethoxysilane has induced biding sites for the subsequent GOD immobilization. Field emission scanning electron microscopy, confocal laser scanning microscopy, infrared spectroscopy and Raman spectroscopy have provided detailed evidences about the effectiveness of the adopted biofunctionalization methodology. The enzyme activity is conserved during the immobilization step. Fabricated LPG sensor was tested on different glucose solutions to record the transmission spectra on an optical spectrum analyzer. The wavelength shifts in the transmission spectra are linearly correlated with the glucose concentration in the range of 10-300 mg dL(-1). The fabricated sensor gives fast response and is demonstrated to be of practical utility by determining glucose contents in blood samples. Proposed technique can further be extended to develop LPG fiber based novel, sensitive and label free nanosensors for disease diagnosis and clinical analysis.

Adsorptional photocatalytic mineralization of oxytetracycline and ampicillin antibiotics using Bi2O3/BiOCl supported on graphene sand composite and chitosan

In present study, heterojunctioned Bi2O3/BiOCl (BO/BOC) was synthesized via in situ chemical reduction and oxidation of BiOCl nanoplates. BiOCl was reduced to metallic Bi in KHB4 solution followed by oxidation in H2O2 solution to produce BO/BOC. The BO/BOC was supported over graphene sand composite and also on chitosan using wet impregnation method to report BO/BOC/GSC and BO/BOC/CT nanocomposite. The morphology and compositional characteristics of BO/BOC/GSC and BO/BOC/CT were investigated by FESEM, TEM, HRTEM, FTIR, XRD, EDX, RAMAN, BET and UV-visible diffuse reflectance spectral analysis. The photocatalytic activity of BO/BOC/GSC and BO/BOC/CT was performed for mineralization of ampicillin (AMP) and oxytetracycline (OTC) antibiotics under solar light. The adsorption process had significant effect on photodegradation of AMP and OTC. The adsorption of both OTC and AMP onto BO/BOC/GSC and BO/BOC/CT followed pseudo second order kinetics. Simultaneous adsorption and degradation process (A+P) resulted in higher degradation rate of investigated antibiotics. The applicability of power law model indicates the intricacies of mineralization process. During A+P process, OTC and AMP were mineralized to CO2·H2O, NO3(-) and SO4(2-) ions. Both BO/BOC/GSC and BO/BOC/CT exhibited significant recycle efficiency.

Aligned nanogold assisted one step sensing and removal of heavy metal ions

We depict a novel strategy exploiting the chemistry of metal ion adsorption for detection and sequestration of toxic heavy metal from processed water using gold nanoparticles capped with 4-aminothiophenol. The interaction between 4-aminothiophenol capped gold nanoparticles and heavy metal ions was studied as a function of time and concentration using TEM, HRTEM, SEM, EDS, and I-V characterization. Experiments confirmed that pH is one of the crucial controlling parameters. Adsorption capacity was monitored using AAS, UV-vis spectroscopy and I-V measurement. In the absence of any alloy formation between Au and heavy metal ions, the desorption of the heavy metal ions from 4-aminothiophenol capped gold nanoparticles surface by pH modulation serves as a mean of collection of heavy metal ions. Experiments revealed that the concentration of heavy metal ions in processed water after adsorption is below the maximum permissible limit set by the WHO.

Facile synthesis and step by step enhancement of blue photoluminescence from Ag-doped ZnS quantum dots

Our results pertaining to the step by step enhancement of photoluminescence (PL) intensity from ZnS:Ag,Al quantum dots (QDs) are presented. Initially, these QDs were synthesized using a simple co-precipitation technique involving a surfactant, polyvinylpyrrolidone (PVP), in de-ionised water. It was observed that the blue PL originated from ZnS:Ag,Al QDs was considerably weak and not suitable for any practical display application. Upon UV (365 nm) photolysis, the PL intensity augmented to ~170% and attained a saturation value after ~100 min of exposure. This is attributed to the photo-corrosion mechanism exerted by high-flux UV light on ZnS:Ag,Al QDs. Auxiliary enhancement of PL intensity to 250% has been evidenced by subjecting the QDs to high temperatures (200 °C) and pressures (~120 bars) in a sulphur-rich atmosphere, which is due to the improvement in crystallanity of ZnS QDs. The origin of the bright-blue PL has been discussed. The results were supported by X-ray phase analysis, high-resolution electron microscopy and compositional evaluation.

Optical fiber nanoprobe preparation for near-field optical microscopy by chemical etching under surface tension and capillary action

We propose a technique of chemical etching for fabrication of near perfect optical fiber nanoprobe (NNP). It uses photosensitive single mode optical fiber to etch in hydro fluoric (HF) acid solution. The difference in etching rate for cladding and photosensitive core in HF acid solution creates capillary ring along core-cladding boundary under a given condition. The capillary ring is filled with acid solution due to surface tension and capillary action. Finally it creates near perfect symmetric tip at the apex of the fiber as the height of the acid level in capillary ring decreases while width of the ring increases with continuous etching. Typical tip features are short taper length (approximately 4 microm), large cone angle (approximately 38 degrees ), and small probe tip dimension (<100 nm). A finite difference time domain (FDTD) analysis is also presented to compare near field optics of the NNP with conventional nanoprobe (CNP). The probe may be ideal for near field optical imaging and sensor applications.