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Human exposure to atmospheric particulate matter (PM) is of great interest owing to its carbonaceous nature with potential health impact.

Silver nanoparticles/nanocomposites are gaining popularity for their unique features and wide-range of applications including bactericidal behaviour, sensing, and photocatalysis. In this report, a novel, single-step, sustainable, and low-cost fabrication of silver carbon quantum dots (Ag/CQDs) nanocomposites by using coal-derived carbon quantum dots (CQDs)as a reductant as well as stabilizer having great potential for simple and quick synthesis of silver nanocomposites has been documented for the first time in this paper. The HRTEM image of the Ag/CQDs nanocomposite depicts the crystalline nature with two distinct d-spacings of 0.22and 0.24 nm attributed to the in-plane (100) and (110) of the graphitic core or aromatic carbon and d-spacings of 0.24and 0.27 nm were also observed which is attributed to the (111) and (122) lattice planes of Ag.The size distribution histogram derived from the TEM image indicates the particles to be within 2-12 nm in diameter, complying with the Gaussian distribution. SAED patterns of the Ag/CQDs nanocomposite showed concentric diffraction rings with (111), (200), (220), and (311) lattice planes of fcc-structured silver metal, which indicates the composition of silver nanoparticles. From the XPS deconvoluted Ag3d spectrum of thenanocomposites represents the binding energies of Ag 3d5/2 and Ag 3d3/2 at 367 and 373 eV which indicates the silver to be present as metallic zerovalent [Ag (0)] oxidation state in the nanocomposite. Moreover, UV-vis spectra show a major absorption peak at 422.47 nm that contributes to surface plasmon resonance of the Ag/CQDs nanocomposite.The nanocomposite shows a zeta potential of -9.91 mV, signifying theirhigh stability. The effect of base and concentrations of the CQDs in the synthesis of Ag/CQDs nanocomposites has also been studied. The oxygen possessing functional groups present on CQDs surfacewere observed to play a significant role in reduction of Ag/CQDs nanocomposites. In addition, the nanocomposite has promising bactericidal behaviour for both gram positive and negative bacterial strains for application as an antibacterial material. The Ag/CQDs nanocomposite shows a maximum inhibition against bacterial strain Rhodococcus soli with an inhibition zone diameter of 17 mm as compared to the other strains.

This short communication reports the synthesis of carbon quantum dots (CQDs) from US anthracite and bituminous coals by oxidation in presence of ultrasonic stimulation. The CQDs formed were examined by using chemical analysis, UV–Visible spectroscopy (UV–Vis), Fluorescence spectroscopy (FL), High resolution transmission microscopy (HRTEM), and X-ray Photoelectron spectroscopy (XPS), revealing the formation of the varied sizes of CQDs ranging from about 2–12 nm. The present method could serve as a simple and a large-scale synthesis of CQDs from abundant and economical coal resources for high-end application.

Carbon dots/carbon nanodots/carbon quantum dots (C-Dots/CDs/CQDs) are nascent carbon-based materials in the nano family with several interesting features and characteristics. Generally, they can be defined as tiny surface-functional carbonic nano-particles with a high level and modifiable fluorescence property. These nano-structures have currently gained much prominence in the field of sensors, energy storage, light-emitting diodes, bioimaging, composite products, catalysis, and drug delivery, etc. because of their exceptional chemical, electrical, thermal, and mechanical characteristics. C-Dots can be synthesized basically by two processes i.e., the top-down process mainly including the arc-discharge method, laser ablation, chemical oxidation; and the bottom-up process that comprises of the hydrothermal method, microwave pyrolysis, electrochemical treatment, etc. Due to the incredible properties of these carbon nano-structures, it has become an interesting chapter in the field of nano-research. Moreover, the recent studies focus on the doping/co-doping of C-Dots, synthesis of nanocomposites, and nano-hybrids along with their evolving feasible applications. In this chapter, the key information on C-Dots along with their luminescence mechanism is summarized prior to the progress of C-Dots in preparation techniques, their amazing physical and electronic features, and applications in sensing, catalysis, bio-imaging and optronics. This chapter provides a review on the synthesis of C-Dots from various natural sources including coal and graphite. It also includes some of the important aspects of doping and co-doping C-Dots and formation of nano-composites along with preparation techniques, and their various applications. This chapter provides an overview and outlines the challenges faced while synthesizing C-Dots with different color emissions.

Carbon quantum dots (CQDs) have several novel opto-chemical characteristics and potential uses in biomedicine, imaging, catalysis, and sensing. However, there are cost and technical limitations with scaling up the synthesis of CQDs for fulfilling its current demand. We propose a simplistic, innovative, sustainable, and economically scalable method for the formation of fluorescent nitrogen and sulphur co-doped CQDs (NS-CQDs) by utilizing bulk, low-grade subbituminous coal as feedstock. The co-doped NS-CQDs were identified using a suite of microscopic and spectroscopic approaches. We suggest that heteroatoms (i.e., N and S) are effectively self-doped on CQDs surfaces/edges of the carbon nanostructure either by functionalization or by getting incorporated on the edges during the oxidative process. The coal-derived CQDs show blue and cyan fluorescence with quantum yields of 9.35 and 16.96%, respectively. The cytotoxicity, genotoxicity, and reactive oxygen species (ROS) of the coal-derived CQDs were evaluated using a rodent hepatocyte cell line, which revealed that these CQDs are biocompatible, non-cytotoxic, and non-genotoxic. Moreover, these coal-derived CQDs also have proved to be good carriers of nutrients and microbes for plant growth promotion, effectively behaving as a nanofertilizer. Their phytotoxicity and impact on plant metabolites and antioxidant properties of the carbon quantum dot products have also been examined in our study.

The present environmentally-friendly coal processing technology discussed herewith focuses on the combined effect of ultrasonic and microwave energy in the extent of mineral matter (ash yield) removal from high-sulfur, low-quality coals for their clean utilization. The novelty of this study is that the technique is very efficient instead of using drastic chemicals with less treatment time, less amount of reagent in comparison to the conventional method, and has the potential to adopt in large-scale commercial production of cleaner coals. The quality of the cleaner coal products was examined by using chemical analysis and advanced analytical techniques (electron beam analysis). The combined irradiation process of ultrasonic and microwave energy is observed to be the most effective for the beneficiation of high-sulfur coal than the single process. The result showed a maximum of 51.28% and 66.34% ash (mineral matter) removal from the coal samples by microwave followed by an ultrasonic process. The X-ray photoelectron spectroscopy (XPS) analysis revealed that both inorganic and organic sulfur is present in these Cenozoic low-rank, high-sulfur Indian coals. The high resolution-transmission electron microscopy (HR-TEM) image analysis of the treated coal samples showed nearly agglomerated collections of nanomaterials; carbon spheres/flacks with an irregular shape; and the elements such as oxygen, iron, silicon, sulfur, and aluminum in the beneficiated coal samples. The major mineral phases, including quartz, kaolinite, and gypsum, are found to be removed during the beneficiation process. The thermal analysis (TGA-DTG) also showed the suitability of the beneficiated coals for the power plant application.

This communication reports the thermo-kinetic behaviours of three different types of biomass samples and their blends with a sub-bituminous high-sulphur coal. Physicochemical properties were evaluated by various fuel characterization methodologies as well as instrumental methods such as thermal (TG/DTG) analysis, Fourier transforms infrared (FTIR) spectrophotometry, scanning electron microscopic (SEM) technique. Thermo-kinetic parameters of various samples were also evaluated by using Coats and Redfern method. Results indicate that the pyrolytic thermal decomposition behaviours of woody biomass samples are quite different from plant leaf-based biomass sample due to the differences in the chemical compositions. Similarly, thermo-kinetic behaviours of coal-biomass blends are significantly different from the pure coal and pure biomass samples. The lowering of reaction order and activation energy of coal decomposition with increasing biomass contents in the blend can be related with the increasing biomass-based volatile matter content in the blends as well as the catalytic effect of biomass-based alkali and alkaline metal enriched biochar. On the other hand, catalytic effect of coal on the pyrolytic biomass decomposition is only observed at higher biomass replacement level. Analyses of the results obtained from calorific value and apparent activation energy reveal the presence of synergistic effects during the combustion of coal-biomass blend in calorimeter as well as the thermal decomposition of blend under nitrogen atmosphere.

Carbon quantum dots (CQDs) are among the most feasible allotropes of carbon-based nanomaterials with unique characteristics of photoluminescence, bio-compatibility, and high stability. Herein, a green and eco-friendly approach has been propagated for the fabrication of CQDs from different biomass waste materials including sugarcane bagasse (SCB), garlic peels (GP), and taro peels (TP) by using ultrasonic-assisted wet-chemical-oxidation method. This top-down approach involves oxidation of the carbonized biomass wastes by H2O2. Another purpose of our work is to make a comparative study on the three CQDs produced from the three different biomass wastes. The properties of the fabricated CQDs were evaluated by using High Resolution-Transmission Electron Microscopy (HR-TEM), Fourier Transform-Infrared (FT-IR) spectroscopy, X-ray Diffraction (XRD), and X-ray Photoelectron spectroscopy (XPS), respectively. The CQDs showed the characteristic photo-physical behaviours as evident from the UV-visible and fluorescence (FL) spectroscopic analyses. The CQDs are found to be highly water soluble possessing strong blue-fluorescence under UV light with excellent quantum yield around 4-27%. The comparative study on the different physico-chemical properties of the three wastes biomass-derived CQDs are also discussed in the paper. The FL properties of CQDs derived from taro peels waste shows the best fluorescence quantum yield among the three and keeping in view of this, an on-off-on fluorescence nanoprobe was designed by using taro peels-derived CQDs (i.e. T-CQDs) and Eu3+ ion. The FL emission of T-CQDs was observed to be significantly quenched by Eu3+ leading to the formation of a CQDs-Eu3+ nanoprobe. The CQDs-Eu3+ nanoprobe was promisingly used for sensing of fluoride ions in water.

Carbon quantum dots (CQDs) and graphene nanosheets (GNs) are one of the most attractive fluorescent carbon nano-sized materials with unique features of optical and physico-chemical properties having various applications in chemical sensing, biomedicine, semiconductor devices, photo-catalyzing, and electrocatalysis. The primary purpose of this preliminary work is the feasibility study for synthesis of nano-structured value-added carbon products i.e., CQDs and GNs from cheap and abundant carbon sources, such as coal, petroleum coke, graphite, and coal-based humic acid by hydrothermal techniques. The physico-chemical properties of the raw precursors were evaluated by proximate and ultimate analysis. High resolution-transmission electron microscopy (HR-TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transforms infrared (FT-IR) spectroscopy, X-ray powder diffractometer (XRD), UV–visible (UV–vis), and fluorescence (FL) spectroscopy were used to achieve physico-chemical parameters of carbon nanostructures, to better comprehend the development of carbon quantum dots and graphene nanosheets. HR-TEM analysis indicates that the dimensions of the synthesized CQDs from different carbon sources exist in the range of 3–6.5 nm. The approximate quantum yields (QY) of the synthesized carbon nanomaterials were found to be about 2–22%. The synthesized carbon based nanomaterials (i.e. CQDs and GNs) have been efficiently used in the photo-degradation of harmful 2-nitrophenols (2-NP) with the efficiency of 80.79% for CQDs and 82.53% for GNs, respectively. The present study provides a simple and efficient technique for large-scale fabrication of typical CQDs and GNs from abundantly available low-grade coal and other carbonaceous materials for photo-catalysis application.