Environment
5.2 Separation of Nano-carbon from Pollutant BC
Not only the air pollution another most challenging global issue for the humankind is to avoid and secure water pollution. As worldwide ~1.8 million child lost their life yearly due to diseases arises from the consumption of contaminated water [68]. Addressing the issues associated with wastewater treatment had a transformative impact, and being of great significance, if BC soot can be utilized to purify water. Currently, there is a significant demand of requirement for the robust of simple and cost-effective technique to disinfect and decontaminate water, especially in developing countries [35].
Many allotropic forms of nano-carbons are currently being used for wastewater management, such as CNTs [69, 70], graphene [71], activated carbons (ACs) [72, 73], and CDs-based nanocomposites [37]. But the wastewater treatment using CDs still needs to be addressed in detail. Till now, only few researches applied CDs in water treatment technology. Sarkar and coworkers report an effective technique for water purification by using low-cost nano-carbons and their composites [37, 70].
5.2 Separation of Nano-carbon from
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G band are more intense in compare to D band hence confirm the presence of sp2 carbon domains, while D band is assigned to surface defects (in terms of sp3 carbons) [44, 75]. The visualization of the surface morphology of Soxhlet purified DPM was done by FESEM (Figure 5.2b), which shows the spherical nature of CDs having the diameter ranges from 60 to 120 nm (histogram shown in inset of the figure) with a lot of amorphous carbon.
In an another report, Dikio and coworkers used the traditional way of pyrolysis to generate DPM soot, instead of collecting waste soot [76]. They pyrolyzed diesel oil (as a carbon source) in a simple laboratory lamp by using a cotton wick, followed by the collection of its soot over the ceramic tile plate. Synthesized CNPs were characterized by using various microscopic and spectroscopic techniques as shown in Figure 5.3. Spherical nature of particles was confirmed by SEM (Figure 5.3a) and TEM (Figure 5.3b and c) micrography. Powder XRD analysis (Figure 5.3d) confirms the graphitic nature of CNPs, showing the presence of two prominent diffraction peak at 2θ = 23.68° and 42.01°. Furthermore, the crystallinity of obtained graphitic was characterized by the Raman spectroscopy for the analysis of characteristic D and G band as illustrated in Figure 5.3e.
Figure 5.3 Characterization of CNPs synthesized by pyrolysis of diesel: (a) FESEM image, (b) low-resolution TEM image, (c) high-resolution TEM image, (d) XRD spectra, and (e) Raman spectra [76].
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In contrast to earlier discussed reports for the separation of CDs and CNPs, Jung et al. reported that combustion condition for the burning of diesel in diesel engine fulfills the requirement for the synthesis of CNTs [33]. DPMs were collected at different experimental condition by using three different diesel engines, as John Deere T04045TF250, Caterpillar 3176 C-12, and Onan-Cummins Quiet diesel engine set. Exhausted DPMs were directly collected over a TEM grid for the direct analysis of its morphological characterization. In entire cases, means for all the three engines they observed rod-like morphology with the contamination of some spherical carbon cluster (these days known as CDs). Finally, they conclude that during burning process of fuel, CNTs were synthesized from both the doped and undoped diesel engine fuels. But in comparisons to doped diesel engine oil CNTs were less in quantity (yield) with undoped diesel fuel. However, releases of CNTs in the environment are assumed to be more pronounced since diesel engine vehicles are too common. In this manner, it is significant to acknowledge the existence of outdoor CNTs in diesel engine exhaust soot even in a small fraction because of their potential hazardous impacts on human health
because depending on the dimensions of nano-particles, they can easily reach the respiratory tract as shown in Figure 5.4 [77].
Figure 5.4 Dependent on particle dimensions, a schematic diagram showing the penetration of inhaled particles in the respiratory tract [77].
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Similarly, for analyzing the indoor BC, Sarkar and coworkers analyzed BC deposited over indoor spider webs and reported the existence of spin frustrated ferromagnetic MWCNTs [5]. These indoor trapped spin frustrated MWCNTs are capable enough of generating ROS [6]. Anthropogenic collected MWCNTs were isolated from indoor spider web via the oxidation method, as shown in Figure 5.5 (a-d) [6] when exposed to aerial oxygen for long term produces ROS. Generation of ROS from atmospheric oxygen was investigated by nitro blue tetrazolium test [78]. Sonkar et al. [5] report the ferromagnetic behavior of indoor collected MWCNTs. They investigated the intrinsic ferromagnetic behavior of indoor MWCNTs at varied temperature (100–600 K) and concluded that ferromagnetic behavior decreases with increase in temperature. Magnetic hysteresis is observed magnetization versus magnetic field at 300 K [5]. Ferromagnetic behavior arises due to combination of diamagnetism arising from the graphitic carbon pools and paramagnetism coming from carbon radicals due to high surfacial defects, knick, and junctions as demonstrated in Figure 5.5 (a-d) [6]. These nano- carbons isolated from indoor deposited BC possess ferromagnetic behavior could used for further applications such as in spintronics.
Figure 5.5 (a) TEM image of insoluble black particulates from spider web showing the presence of MWCNTs with junctions and kinks (inset
corresponding XRD image); (b) high resolution TEM image; (c) shows the defects in channels with blockage (black arrows); (d) broken edges (outer walls) marked with black arrows. [6].
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Using an alternative method, Uchida et al. introduced another fruitful application to recycle diesel exhaust soot, a step toward the clean environment [20]. They collected the DPM, just before to discharged in environment via a special technique designed by Nishimoto [67]. The collected DPMs were used as carbon precursor for the synthesis of SWCNT, by using laser vaporization method. They proposed that diesel soot contains a
portion of C60, C70, and other fullerenes type nanocarbons, which are found to be appropriate for the growth of SWCNT as a carbon precursor when used in laser decomposition method. The diameters of as synthesized SWCNT by waste DPM lie majorly in the range of 1 nm.