Transformation of oil palm biomass to optical carbon quantum dots by carbonisation-activation and low temperature hydrothermal processes

Large amounts of biomass produced by the palm oil industry are either burnt in open air or disposed in waste ponds and contribute to global climate. Therefore, these biomasses should be utilised to obtain functional materials, such as carbon-based nanomaterials, including carbon quantum dots (CQDs), which are facile, cheap and environmentally friendly. This study has successfully converted the biomass from oil palm empty fruit bunch-derived activated carbon to CQDs through low-cost processes, involving carbonisation-activation and low-temperature hydrothermal carbonisation. The obtained CQDs have spherical shapes with diameter range of 5-7 nm and exhibit excellent water stability and solubility properties due to the presence of hydroxyl and carboxyl groups. CQDs are amorphous carbon structures due to high-temperature treatment during carbonisation activation and exhibit the Raman D and G bands, conforming to the formation of low-dimensional carbon nanostructure. The optical properties of CQDs show that Ultraviolet-visible (UV-vis) are in strong blue absorption and exhibit high excitation-emission dependence for photoluminescence. MTT assay has revealed that these CQDs have low toxicity and favourable biocompatibility. Therefore, CQDs prepared from oil palm biomass possess excellent optical properties, water stability and solubility and may have a wide range of applications, such as in bioimaging, antioxidation and pH sensors.