Photocatalytic degradation of organic pollutants using green oil palm frond-derived carbon quantum dots/titanium dioxide as multifunctional photocatalysts under visible light radiation

The present work suggested the use of waste oil palm frond as an alternative precursor for nitrogen-doped carbon quantum dots (NCQDs) and proposed a straightforward in-situ hydrothermal method for the preparation of NCQDs/TiO₂ nanocomposites. The elemental composition, morphological, structural and optical characteristics of NCQDs/TiO₂ nanocomposites have been comprehensively investigated. The successful grafting of NCQDs on TiO₂ matrix was confirmed by the formation of TiOC bond and the electronic coupling between the π-states of NCQDs and the conduction band of TiO₂. For the first time, the oil palm frond-derived NCQDs/TiO₂ was adopted in the photodegradation of methylene blue (MB) under visible-light irradiation. As a result, the photocatalytic efficiency of NCQDs/TiO₂ nanocomposites (86.16%) was 2.85 times higher than its counterpart TiO₂ (30.18%). The enhanced performance of nanocomposites was attributed to the pivotal roles of NCQDs serving as electron mediator and visible-light harvester. Besides, the optimal NCQDs loading was determined at 4 ml while the removal efficiency of NCQDs/TiO₂-4 was the highest at a catalyst dosage of 1 g·L^-1 under alkaline condition. This research work is important as it proposed a new insight to the preparation of biomass-based NCQDs/TiO₂ using a facile synthetic method, which offers a green and sustainable water remediation technology.