Solid-State Phosphors from Coal-Derived Carbon Quantum Dots.

With unique optical and chemical properties, carbon quantum dots (CQDs) find tremendous applications in chemistry, biology, and materials science to medicine. To expand the applicability of coal-derived CQDs from the liquid to solid state, we herein report the sustainable synthesis of solid phosphors from coal-derived CQDs using poly(vinyl alcohol) (PVA) and silica (SiO2) as an organic and inorganic matrix. Two coal-derived CQDs were obtained using an eco-friendly ultrasonic-assisted wet oxidation method. The structural and chemical properties of the CQDs were extensively investigated and compared with commercial CQDs. The coal-derived CQDs exhibited blue fluorescence with 8.9 and 14.9% quantum yields. The CQDs were found to be self-co-doped with nitrogen and sulfur heteroatoms through surface and edge functional groups. Solid-state fluorescence of PVA/CQD composite films confirmed that the CQDs retained their excellent blue emission in a dry solid matrix. A facile one-pot sol-gel method was employed to fabricate SiO2/CQD phosphors with the unique fluorescence emission. Due to their special structural features, coal-derived CQDs favored the heterogeneous nucleation and rapid formation of SiO2/CQD phosphors. Further, coal-derived CQDs caused high-intensity white light emission with CIE coordinates of (0.312, 0.339) by endowing a suitable band gap structure in a SiO2/CQD solid phosphor for potential optical applications.

Biocompatible Nanodiamonds Derived from Coal Washery Rejects: Antioxidant, Antiviral, and Phytotoxic Applications.

Coal washery rejects (CWRs) are a major byproduct produced in coal washery industries. We have chemically derived biocompatible nanodiamonds (NDs) from CWRs toward a wide range of biological applications. The average particle sizes of the derived blue-emitting NDs are found to be in the range of 2-3.5 nm. High-resolution transmission electron microscopy of the derived NDs depicts the crystalline structure with a d-spacing of 0.218 nm, which is attributed to the 100 lattice plane of a cubic diamond. The Fourier infrared spectroscopy, zeta potential, and X-ray photoelectron spectroscopy (XPS) data revealed that the NDs are substantially functionalized with oxygen-containing functional groups. Interestingly, the CWR-derived NDs exhibit strong antiviral properties (high inhibition of 99.3% with an IC50 value of 7.664 µg/mL) and moderate antioxidant activity that widen the possibility of biomedical applications. In addition, toxicological effects of NDs on the wheatgrass seed germination and seedling growth showed minimal inhibition (<9%) at the highest tested concentration of 300.0 µg/mL. The study also provides intriguing prospects of CWRs for the creation of novel antiviral therapies.

Synthesis, Characterization, Properties, and Novel Applications of Fluorescent Nanodiamonds.

In the last few years, fluorescent nanodiamonds (FNDs)  have been developed significantly as a new member in the nanocarbon family. The surface of FNDs is embedded with some crystallographic defects containing color centres which surmount the properties of other fluorochromes including up conversion and down conversion nanoparticles, quantum dots, nano tubes, fullerenes, organic dyes, silica etc. Some of the intriguing properties like inevitable photostability, inherent bio-compatibility, outstanding optical and robust mechanical properties, excellent magnetic field, and electric field sensing potentiality make FNDs appealing to some benevolent applications in numerous fields like bio-imaging, delivering drugs, fighting cancer, spin electronics, imaging of magnetic structure at nanoscale and as promising nanometric temperature sensor. The structure of FNDs has certain point defects on the surface among which negatively charged nitrogen vacancy centre (NV-) is the most investigated color centre. The production of NV- fluorescence nanodiamonds is the most challenging task as substitution of carbon atoms is required to create vacancies by causing irradiation from an electron beam which is followed by high temperature annealing. Thus, this review points out the relative advantages of FNDs containing negatively charged nitrogen vacancy centres produced from HPHT method or CVD method with those nanodiamonds produced through detonation process or pulsed laser ablation (PLA) method. The steps involved in the fabrication of FNDs are described along with the major challenges and struggles underwent during the process in this review. This review also summarizes the recent developments made in the functionalization and applications predominantly made in the field of biological science and it is understood that depending on the defect color centres they can exhibit different emitted wavelengths ranging from UV-visible to near infrared with broad or narrow bandwidths. This review also highlights some of the fluorescent NDs that emit stable and strong red or green photoluminescence from the defect centers of NV- which are implanted in the crystal lattice. This critical and extensive review will be useful for the further progress in this futuristic field of FNDs.

Blue-emitting fluorescent carbon quantum dots from waste biomass sources and their application in fluoride ion detection in water.

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.