Fluorescent Nanomaterials from Biomass: Synthesis and Applications

Abstract

Energy crisis, environmental deterioration and dwindling fossil resources are the rising global concerns. As a result, utilising biomass waste as a green and renewable resource into valueadded materials is highly appealing for the sustainable world. Among various materials explored, carbon and its derivatives attract much more attention due to their intriguing properties and broad range of applications. This work focused on the conversion of biomass into activated carbon (AC) and its further development into fluorescent carbon nanomaterials for the energy and sensing applications. ‘Spent tea’ was selected as a food waste feedstock. A systematic study was carried out to produce char by pyrolysis and activate it using chemical activation. Consequently, a series of ACs with varying levels of porosity and surface areas (10 to >2000 m2 g -1 ) were produced. These ACs were employed as an alternate electrode material to study the effect of porosity on the charge transfer in vanadium redox flow battery. A thorough investigation on the further transformation of char into fluorescent nanomaterials lead to the production of graphene quantum dots (GQDs). An upgraded approach was adopted for the purification of these GQDs. The results showed that GQDs possessed 3-5 layered graphene structure with a size range of 2-20 nm and band gap varying from 2.67 to 2.95 eV. Under the premise of acquiring high yield, the activation and synthesis steps were combined into a single-step microwave treatment and GQDs were synthesised with a high yield of ~84%. Finally, the intensified and green synthesis of GQDs was accomplished under the direct hydrothermal carbonisation of biomass waste. The as-prepared GQDs were applied to design a selective and sensitive sensor for Fe3+ ions with a detection limit of as low as 2.5 x 10–6 M. The present work highlights the significance of preparing high-value nanomaterials from little value biomass waste.