Carbon-based nanomaterials are gaining more and more interest because of their wide range of applications. Carbon dots (CDs) have shown exclusive interest due to unique and novel physicochemical, optical, electrical, and biological properties. Since their discovery, CDs became a promising material for wide range of research applications from energy to biomedical and tissue engineering applications. At same time several new methods have been developed for the synthesis of CDs. Compared to many of these methods, the sonochemical preparation is a green method with advantages such as facile, mild experimental conditions, green energy sources, and feasibility to formulate CDs and doped CDs with controlled physicochemical properties and lower toxicity. In the last five years, the sonochemically synthesized CDs were extensively studied in a wide range of applications. In this review, we discussed the sonochemical assisted synthesis of CDs, doped CDs and their nanocomposites. In addition to the synthetic route, we will discuss the effect of various experimental parameters on the physicochemical properties of CDs; and their applications in different research areas such as bioimaging, drug delivery, catalysis, antibacterial, polymerization, neural tissue engineering, dye absorption, ointments, electronic devices, lithium ion batteries, and supercapacitors. This review concludes with further research directions to be explored for the applications of sonochemical synthesized CDs.

Carbon quantum dots (CQDs) are one of the most promising types of fluorescent nanomaterials due to their exceptional water solubility, excellent optical properties, biocompatibility, chemical inertness, excellent refractive index, and photostability. Nitrogen-containing CQDs, which include amino acid based CQDs, are especially attractive due to their high quantum yield, thermal stability, and potential biomedical applications. Recent studies have attempted to improve the preparation of amino acid based CQDs. However, the highest quantum yield obtained for these dots was only 44%. Furthermore, the refractive indices of amino acid derived CQDs were not determined. Here, we systematically explored the performance of CQDs prepared from all 20 coded amino acids using modified hydrothermal techniques allowing more passivation layers on the surface of the dots to optimize their performance. Intriguingly, we obtained the highest refractive indices ever reported for any CQDs. The values differed among the amino acids, with the highest refractive indices found for positively charged amino acids including arginine-CQDs (∼2.1), histidine-CQDs (∼2.0), and lysine-CQDs (∼1.8). Furthermore, the arginine-CQDs reported here showed a nearly 2-fold increase in the quantum yield (∼86%) and a longer decay time (∼8.0 ns) compared to previous reports. In addition, we also demonstrated that all amino acid based CQD materials displayed excitation-dependent emission profiles (from UV to visible) and were photostable, water-soluble, noncytotoxic, and excellent for high contrast live cell imaging or bioimaging. These results indicate that amino acid based CQD materials are high-refractive-index materials applicable for optoelectronic devices, bioimaging, biosensing, and studying cellular organelles in vivo. This extraordinary RI may be highly useful for exploring cellular elements with different densities.

This paper describes an approach to the fabrication of flexible electronics i.e., a wearable temperature sensor and infrared (IR) photodetector on flexible polyimide (PI) substrate. Solar exfoliated reduced graphene oxide (SrGO) and graphene flakes are used as the sensing materials for developing the sensors on a PI substrate. PI, apart from being flexible and compatible with microfabrication processes, also helps in reducing the mobility and recombination of the photo-generated electrons of graphene due of its dielectric nature, thus enabling IR detection. Current responsivity and external quantum efficiency of IR photodetector for graphene flake- and SrGO-based devices were found to be 0.4 A W ⁻¹ , 16.53% and 0.8 A W ⁻¹ , 33.06% respectively which are higher than those of commercially available photodetectors. In addition, we demonstrate an ultrasensitive wearable human body temperature sensor in the temperature range of 35 °C to 45 °C, wherein both graphene flake- and SrGO-based devices exhibited a negative temperature coefficient of −41.30 × 10 ⁻⁴ °C ⁻¹ and −74.29 × 10 ⁻⁴ °C ⁻¹ respectively, which are higher than commercially available counterparts. Plausible underlying mechanisms to both IR sensing and temperature sensing have been studied. Furthermore, as a proof of concept, we investigated the effect of IR radiation emitted by a human hand on the device. Interestingly it was found that the device was very sensitive to it, indicating that the sensor can be used for motion detection which has potential applications in security, surveillance etc. The strategy presented here provides a new, simple, cost effective approach for the fabrication of next-generation wearable and bio-implantable devices based on a polyimide substrate that can be easily integrated onto the surface of a leaf, skin, paper, clothes etc owing to its versatile nature.

This work unraveled kinetics, isotherm, and thermodynamic properties of methylene blue (MB) adsorbed on polyaniline (PANI) and polypyrrole (PPY). The two polymers, PANI and PPY, synthesized by a facile C-dot (CD)-initiated polymerization method have been proven as the effective adsorbent materials to remove MB from wastewater. This dye model is also generally employed as a redox indicator in analytical chemistry and exhibits blue in an oxidizing environment, but it is colorless when exposed to a reducing agent. The effects of temperature, adsorbent amount contact time, and dye concentration were consistently examined. The adsorption capacity of the polymers at 28 °C could reach 19.2 mg/g. The adsorption equilibrium of the dye was attained after 90 and 120 min of contact time with PANI and PPY, respectively. The equilibrium details were well described by Freundlich and Langmuir isotherms. Results showed that PANI and PPY prepared using CD-initiated polymerization are better adsorbents compared to the commercial PANI powder for the removal of MB from water.

This paper covers the core-shell nanomaterials, mainly, polymer-core polymer shell, polymer-core metal shell, and polymer-core nonmetal shells. Herein, various synthesis techniques, properties, and applications of these materials have been discussed. The detailed discussion of the properties with experimental parameters has been carried out. The various characterization techniques for the core-shell nanostructure have also been discussed. Their physical and chemical properties have been addressed. The future aspects of such core-shell nanostructures for biomedical and various other applications have been discussed with a special emphasis on their properties.