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Abstract: Carbon nanoparticles (CNP) have gained significant attention representing unique carbon-based nanomaterials that find applications in various fields of science and technology. Carbon nanotubes (CNTs) and carbon dots (CDs) have now been widely employed as an electrode in super capacitors, as fluorescent nanomaterials for imaging and for fuel cell applications. In the present work, we describe a simple, low cost and chemical free method of synthesizing stable CNPs aligned in the form of a chain popularly known as carbon necklace with CNTs and CDs. Carbon nanoparticles are synthesized by controlled combustion of camphor in a single step flame process. The CNPs synthesized are characterized using X-ray Powder diffraction (XRD), Raman Spectroscopy, Energy Dispersive X ray diffraction (EDX), Fourier Transform Infrared Spectroscopy (FTIR), UV-Visible absorption and Photoluminescent (PL) Spectroscopy. The morphology and size of the CNPs are examined using Field Emission Scanning Electron Microscope (FESEM) which shows ‘necklace’ structure. The CNPs are collected at two different heights and the particles formed are found in the range 30 to 60 nm. The UV- Visible and PL Spectra of the CNPs obtained show the presence CDs. The Raman Spectroscopic and XRD analysis indicate the presence of CNTs in the sample.
Keywords: Carbon nanoparticles, Combustion, Carbon nanotubes, Carbon dots, Carbon necklaces
Published in RUNG: 30.06.2022; Views: 1149; Downloads: 0
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Abstract: Carbon nanoparticles are of considerable interest today because of their unique physical and biological properties. There are several methods of preparation of Carbon Nanoparticles (CNP) with high efficacy and low toxicity. In this paper we describe a simple low cost synthesis of carbon nanoparticle. We present a simple method for the synthesis of carbon nanoparticles from the controlled combustion of coconut oil and ghee. The antibacterial property of CNP enables its use in kajals. The FESEM image of the sample prepared exhibit carbon nanoparticles of size less than 50nm
Keywords: Kajal, carbon nanoparticles, soot
Published in RUNG: 30.06.2022; Views: 1004; Downloads: 0
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Abstract: The work reported in this paper is the first attempt to delineate the molecular or particle dynamics from the thermal lens signal of carbon allotropic nanofluids (CANs), employing time series and fractal analyses. The nanofluids of multi-walled carbon nanotubes and graphene are prepared in base fluid, coconut oil, at low volume fraction and are subjected to thermal lens study. We have studied the thermal diffusivity and refractive index variations of the medium by analyzing the thermal lens (TL) signal. By segmenting the TL signal, the complex dynamics involved during its evolution is investigated through the phase portrait, fractal dimension, Hurst exponent, and sample entropy using time series and fractal analyses. The study also explains how the increase of the photothermal energy turns a system into stochastic and anti-persistent. The sample entropy (S) and refractive index analyses of the TL signal by segmenting into five regions reveal the evolution of S with the increase of enthalpy. The lowering of S in CAN along with its thermal diffusivity (50%–57% below) as a result of heat-trapping suggests the technique of downscaling sample entropy of the base fluid using carbon allotropes and thereby opening a novel method of improving the efficiency of thermal systems.
Keywords: carbon allotropic nanofluids, time series, entropy, MWCNT, thermal lens signal
Published in RUNG: 30.06.2022; Views: 1219; Downloads: 0
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Abstract: The dynamics and distribution of carbon dioxide (CO2) in karst systems are crucial for understanding fundamental karst processes, namely precipitation and dissolution, which drive karst development both at the surface and underground. The study of CO2 transport provides valuable insights into the role of karst systems in the global carbon cycle and the impact on present climate, but also into the growth of speleothems, which are one of the most reliable terrestrial archives for palaeoclimate reconstruction. Due to the complexity of karst systems, long-term monitoring and high-resolution analyses of cave air and water geochemistry are essential to better understand the controlling factors that affect these processes and their outcomes. In the framework of this dissertation, cave climate and water hydrochemistry monitoring was established in a side-passages of the renowned Postojna Cave in Slovenia during 2017–2021. In the Pisani Passage, high CO2 concentrations, large temporal variations and a heterogeneous distribution of CO2, as well as extreme dissolution features, have already been detected in previous studies. The aim of the present study was to investigate these observations in depth and to find the reasons for their occurrence. This led to creating of a conceptual model for CO2 transport in karst systems that would be valid not only in this case but in karst areas worldwide. The first focus of the study is dedicated to understanding the spatio-temporal dynamics of the partial pressure of CO2 (pCO2) in the Pisani Passage, which is mainly transported by advection (i.e., cave ventilation). Continuous measurements of airflow velocity, air temperature and pCO2 showed (1) that airflow through the karst massif is driven by both the action of the chimney effect and external winds, and (2) that the relationship between the direction of airflow, the configuration of airflow pathways and the connection to the outside explains the observed variations in pCO2. Due to the particular configuration of the airflow pathways, the terminal chamber of Pisani Passage accumulates high levels of CO2 (>10,000 ppm) and forms high vertical gradients of up to 1000 ppm/m. The pCO2 is low and uniform during updraft when outside air flows into the cave chamber through open, unobstructed passages (i.e., high-flow, low-pCO2 pathways). When the airflow reverses direction to downdraft, the chamber is fed by low-flow, high-pCO2 pathways that enter the cave passage through a CO2-rich fracture network embedded in a vadose zone. The spatial distribution of inlets and outlets results in minimal mixing between the low and high pCO2 pathways, leading to high and persistent pCO2 gradients. In addition to the chimney effect driving the seasonal ventilation of the cave, the specific signs of a secondary wind-driven effect were also found; which is the second focus of this study. Wind flow over irregular topography leads to near-surface air pressure variations, and thus, pressure differences between cave entrances at different locations. Pressure differences depend on wind speed and direction and their relationship to surface topography and the location of cave entrances. Winds can act in the same or opposite direction as the chimney effect, either enhancing, diminishing or even reversing the direction of density-driven airflows. In the case of Postojna Cave, north and northeast winds enhance the downdraft and limit updraft, while the opposite is true for south winds, which enhance the updraft and limit downdraft. To investigate the importance of wind-driven flow, a computational fluid dynamics model was used to calculate the wind pressure field over Postojna Cave and the pressure differences between selected points for different configurations of wind speed and direction. These values were compared with those obtained from airflow measurements in the cave and from simple theoretical considerations. Despite the simplicity of the approach and the complexity of the ca
Keywords: cave climate, cave ventilation, carbon dioxide, dripwater geochemistry, speleothem corrosion, Postojna Cave, Slovenia
Published in RUNG: 22.06.2022; Views: 1741; Downloads: 67
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Keywords: black carbon, Arctic, gas flaring, wildfire
Published in RUNG: 09.05.2022; Views: 1543; Downloads: 0
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