The preparation of nanostructured carbon materials from chosen biomass through hydrothermal carbonization and pyrolysis processes by optimizing the reaction conditions is one of the bases for applying the product in certain of the development activities. The finished product more or less reflects the raw material and the way of preparation. Among the many products, carbon quantum dots (CQDs) have gained importance due to their bolstered characteristics and facile preparation. CQDs are zero‐dimensional (0D) nanomaterials which attracted attention in the recent past due to their excellent water solubility, unique optical properties, good electrical conductivity, eco‐friendliness, and biocompatibility. Small‐sized CQDs offer high surface area per unit volume, strong tunable fluorescence, photo‐luminescent emissions, and semiconducting properties. In this paper, identification of ideal raw materials, process parameters being followed in the preparation of CQDs through hydrothermal carbonization and pyrolysis techniques, and the properties of the resultant CQDs commensurate with the nature of process are reviewed.

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Carbonaceous materials with large interlayer spacing and disordered structure are considered suitable as electrodes in sodium-ion batteries so as to overcome the problem encountered in conventional electrodes. In this study, carbon quantum dots (CQDs) decorated with SnO2 and NaVO3 are used as electrodes in the fabrication of flexible Na-ion batteries. CQDs are prepared from dead leaves of the Samanea saman tree through alkaline-peroxide treatment and hydrothermal carbonization. As-prepared CQDs exhibit a quantum yield of 21.03% at an excitation wavelength of 360 nm. Various separators such as indium-doped tin oxide/polyoxyethylene tridecyl ether (ITO/PTE), rice paper (RP), silicone with three big holes (SIL BH), silicone with many small holes (SIL SH) and cellulose paper (CP) have been tried in flexible Na-ion batteries. SIL SH achieved higher specific capacitance (881 F g–1) than other separators due to the function of many small holes on the surface of the silicone. The SIL SH separator delivered higher discharge capacities of 141 and 114 mC g–1 at 1.5 and 2.5 V than SIL BH. The RP separator delivered specific discharge capacities of 1087 and 347 mC g–1 in the 1st and 50th cycles, respectively, at 1 V. The RP separator delivered a high initial specific discharge capacity of 698 mC g–1 at 2 V and maintained a good discharge capacity of 222 mC g–1 in the 50th cycle. As compared to RP, SIL SH delivered high specific discharge capacity of 4246 in 1st cycle at 2 V but maintained a capacity of 71 mC g–1 in the 50th cycle. This study reveals the scope of developing flexible Na-ion batteries with high capacity and cyclability using carbonaceous materials derived from the leaves of the S. saman tree. Carbon quantum dots (CQDs)-decorated with SnO2 and NaVO3 are used as electrodes in the fabrication of flexible Na-ion batteries. CQDs exhibit a quantum yield of 21% at the excitation wavelength of 360 nm. The electrochemical performances of fabricated batteries are investigated by cyclic voltammetry.

This research work undertook a comparative study of the promoting effects of graphene in TiO2 photoanodes. The aim of this work was to investigate the effects of the types and concentration of reduced graphene oxides (rGO) on structure properties and the photovoltaic performance of TiO2 based electrodes. Graphene oxide (GO) was prepared by using modified Hammer’s method. Next, GO was reduced by using two different approaches, which were the chemical reduction with vitamin C and thermal reduction. The latter approach was also carried out in situ during the fabrication and heat treatment processes of the dye-sensitized solar cells (DSSCs). From the results, it was found that the photovoltaic performance of the DSSCs containing the GO/TiO2 electrode, in which the GO phase experienced an in situ thermal reduction, was superior to those containing rGO/TiO2. It was also found that the power conversion efficiency of the DSSCs changed with the concentration of graphene in a nonlinear fashion. The optimum concentrations of graphene, corresponding to the highest PCE values of the GO/TiO2 based DSSC (3.69%) and that of the rGO/TiO2 based cell (2.90%), were 0.01 wt% and 0.03 wt%, respectively.