From peels and coffee grounds to tunable carbon nanodots: waste-derived biocarbon meets ultrafast laser ablation

Abstract

Water-soluble, photoluminescent carbon nanodots (CNDs) were produced in minutes by picosecond-laser ablation of biocarbons obtained from orange peel, avocado peel, and spent coffee grounds. Mild pyrolysis at 350 °C first transformed the wastes into ash-free biocarbon with distinct degrees of aromatic ordering. Subsequent irradiation with 1064 nm, 150 ps laser pulses in water generated stable brown colloids whose optical and structural characteristics could be traced back to the precursor composition. Avocado-derived dots were the most abundant and smallest (2.2 ± 0.3 nm), displaying amorphous structure and bright blue-green emission centred at 430 nm under 330 nm excitation. In contrast, orange- and coffee-derived dots were larger (5–40 nm), partially graphitic, and markedly less emissive. Thermogravimetric and Raman analyses linked the superior yield and fluorescence of the avocado system to its …