Introduction

New method of synthesis for the preparation of fluorescent “carbon quantum dots” using residual/waste biomass arising from the agricultural and agro-industrial sectors (e.g., sugar beet pulp, tomato peels and seeds, grape marc, olive pomace) as a carbon source using γ-Al2O3 spheres as catalyst at moderate temperatures (250-300 °C) nitrogen as carrier gas.

Technical features

The method consists of heating a batch of γ-Al2O3 spheres in the presence of a residual biomasses arising from the agricultural and agro-industrial sectors (e.g., sugar beet pulp, tomato peels and seeds, grape marc, olive pomace)  at moderate temperatures (250-300 °C) and relatively long residence times (30 min) by using nitrogen as carrier gas.  No additional surface passivation step is required. The alumina spheres, which during the thermal treatment undergo coking and fouling processes accompanied by the formation of self-passivated carbon quantum dots (CQDs), are subsequently separated from the residual torrefied biomass by mechanical sieving. The recovery of CQDs deposited on the γ-Al2O3 surface is achieved by exploiting the unique feature of such carbon nanomaterials to be soluble in water and several organic media.

Compared to wet-chemistry-based approaches, like hydro/solvothermal methods, the γ-alumina-assisted dry synthesis avoids the use of  solvents, eliminates safety risks associated with high-temperature and  high-pressure reaction conditions,. No further surface passivation of the carbon core is required. Lower production costs.

Possible Applications

• Medical diagnostic;
• Biosensors;
• Photocatalysis;
• Materials for optoelectronic devices (solar cells and LEDs);
• Drug delivery system;
• Energy storage applications.

Advantages

• Single-step synthetic route (surface passivation in situ);
• No need for sophisticated and/or expensive instrumentations;
• Use of cheap raw materials (residual biomass);
• No use of harsh solvents;
• No safety risks associated with high-temperature and high-pressure reaction conditions.