Here, we report ultraspeed preparation of highly emissive nitrogen‐doped carbon dots (NCDs) using threonine and guanidine hydrochloride by the microwave irradiation method. Experimental conditions such as microwave power, irradiation time, and reactant ratio were varied to achieve high‐quality NCDs. NCDs were thoroughly characterized using transmission electron microscopy, X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV–visible spectroscopy, and fluorescence spectroscopy. NCDs presented high aqueous solubility, bright emission with a quantum yield of 30%, and excitation‐dependent emission. Investigation of optical properties unveiled their admirable characters of tolerance to photobleaching, high salinity, pH, and long shelf life. Evaluation of their metal ion detection ability unveiled their selective fluorescence quenching response to Mn (VII), and further explorations revealed the application of NCDs as a label‐free probe for Mn (VII) detection. The probe presented a good linear response (R2 = 0.992) in the concentration range of 5–35 μM with a detection limit of 0.66 μM. Mechanistic studies disclosed that the inner filter effect was responsible for fluorescence quenching. The probe presented no significant interference and was successfully applied for the quantification of Mn (VII) in spiked real‐water samples.
A simple technique for the interpretation of gravimagnetic anomalies by a numerical differentiation is presented. The ratio of horizontal gradient to the observed field was used for the location of the origin and depth to the causative body_ This technique was tested by using fundamental expressions due to sphere, horizontal cylinder and vertical fault models and field data over a spherical body. It has been found that the depth to the centre of the body can be determined accurately by this technique.
Microwave-assisted synthesis of silver nanoparticles (AgNPs) was investigated using passion fruit peel (PF) extract as a stabilizer and reductant. In synthesis process, the effect of several synthetic factors such as pH, silver nitrate concentration and microwave irradiation time were studied. The obtained AgNPs were well characterized by several analytical techniques including UV-vis, FTIR, XRD, TEM and zeta-potential. The presence of strong surface plasmon resonance (SPR) peak around 400-410 nm indicated the formation of AgNPs. FTIR analysis revealed the biomolecules present in the PF extract was responsible for the reduction of silver ions and stabilization of formed AgNPs. The TEM images presented that the formed AgNPs were dispersed, nearly spherical shape and with average diameter of 12±3 nm. The powder XRD patterns of AgNPs revealed the face-centered cubic (FCC) structure. The catalytic activity of AgNPs was evaluated by NaBH4 mediated reduction of Methylene Blue (MB) and Rhodamine B (RhB) and the kinetic analysis revealed pseudo-first-order nature of these reactions.
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