Investigating the effect of hydrothermal carbonisation reaction times on the photoluminescence of bio-oil-derived carbon polymer dots†

Carbon dots (CDs) have favourable properties such as broad spectral absorption, strong photoluminescence, low toxicity, and high specific surface area. Here, carbon polymer dots (CPDs), which are CDs with a carbon core and polymeric surface, were synthesised from chitin-derived bio-oil, supporting the transition away from fossil- based feedstocks in carbon nanomaterial synthesis. The influence of hydrothermal carbonisation (HTC) reaction times on the structural, morphological, and optical properties were studied. Structural analysis revealed the formation of nitrogen-doped CPDs with a cross-linked polymeric shell surrounding a crystalline graphitic carbon core, with the size, structure, and surface composition all influenced by HTC reaction time. All CPD samples showed the same excitation dependent emission, with a λ_max of 394 nm. Deconvolution of the photoluminescence showed multiple components with contributions identified from both molecular luminophores and the carbon core. Overall, this work investigates the mechanism of photoluminescence in CPDs, providing insights that could promote application in areas such as bioimaging, sensing, and optoelectronics.