Work

Ultrasonication-assisted carbonization of Gracilaria fisheri: effects on physicochemical, and structural properties, and bioactivities

Year: 2026

Type: article

Abstract: Conventional hydrothermal carbonization of biomass generally renders carbon dots (CD) with low yield and quality, mainly due to incomplete hydrolysis. This study evaluated how ultrasonication pretreatment and sequential pre/post-treatment influenced hydrothermal carbonization of Gracilaria fisheri and the properties of resulting CD. Probe ultrasonication (Sonics VC750, 20 kHz, 13 mm probe) was applied to 50 mL suspensions at 20, 50, and 80% amplitude for 5 or 15 min cumulative ultrasonication-on time, using 5 s on/5 s off pulses and ice-bath cooling. Hydrothermal carbonization was performed at 200 °C for 8 h. Recovered-solid yield and physicochemical parameters were used to select optimal conditions. Pre CD 80%/5min showing the highest yield and zeta potential among Pre CD was selected for subsequent post-treatment. Pre/Post CD further increased the recovered-solids yield to 90.47% ( Pre/Post CD 80%/5min ). FTIR spectra confirmed the retention of oxygen-rich functional groups, while TEM images showed smaller, more dispersed particles following sequential treatment. Pre/Post CD 80%/5min exhibited stronger UV-C attenuation and excitation-dependent photoluminescence, whereas Pre CD 80%/5min showed greater photostability under 254 nm irradiation. Pre/Post CD 80%/5min exhibited the highest antioxidant activity, including ABTS radical-scavenging activity of 68.03 mmol Trolox equivalent/mg and metal-chelating ability of 0.13 mmol ethylenediaminetetraacetic acid equivalent/mg. All tested CDs exhibited minimum inhibitory concentrations of 3.50 mg/mL against S. aureus , Listeria monocytogenes , Vibrio parahaemolyticus , and P. aeruginosa . These findings demonstrate that the sonication sequence influenced the recovered-solids yield and bioactivities. The different antioxidant and antibacterial activities as affected by ultrasonication warrant further investigation of ultrasonication-induced changes and functionalities. The produced CD requires the validation in food application and safety assessment.

Source: Ultrasonics Sonochemistry

DOI: 10.1016/j.ultsonch.2026.108106

Authors: Arunachalasivamani Ponnusamy, S.R. Radhika Rajasree, Shivraj Nile, Rasool Abdul Nazeer, George Ninan, Soottawat Benjakul