Upcycling wet citrus and apple residues into fluorescent carbon quantum dots for anti-counterfeiting inks

Overview

This technology converts wet citrus and apple side streams from pectin production into fluorescent carbon quantum dots (CQDs) for security printing and anti-counterfeiting applications. The carbohydrate-rich residue is processed by hydrothermal carbonization, with optional nitrogen doping to enhance fluorescence. The resulting CQDs are purified, characterized, and formulated into aqueous printable inks or coatings that provide authentication features visible under UV light.

This approach upgrades a low-value wet biomass stream into a high-value functional nanomaterial while avoiding energy-intensive complete drying. Because hydrothermal processing uses water as the reaction medium, the wet nature of the side stream is advantageous and can potentially reduce drying requirements. The project combines proven chemistry with a realistic pathway to create a higher-value functional material from an existing industrial residue.

Technical specifications

Key features:

• Converts wet citrus and apple side streams from pectin production into fluorescent carbon quantum dots
• Uses hydrothermal carbonization, with optional nitrogen doping to enhance fluorescence
• Formulates CQDs into aqueous security inks or coatings for UV-visible authentication features
• Evaluates feedstock variability, residual acidity and minerals, process yield, colloidal stability, printability, and scale-up potential
• Avoids energy-intensive complete drying by leveraging water as the reaction medium

Validation plan:

• Characterize representative citrus and apple side streams, including moisture, acidity, inorganic content, and major carbohydrate fractions
• Convert feedstocks into native and nitrogen-doped CQDs using aqueous hydrothermal processing
• Optimize reaction conditions to maximize CQD yield, fluorescence, colloidal stability, and reproducibility while establishing tolerance to feedstock variability
• Purify, characterize, and formulate the best-performing CQDs into aqueous security inks or coatings, followed by printing and UV-authentication tests
• Transfer the process to larger batch sizes to evaluate scalability, energy demand, purification requirements, and product consistency
• Combine application performance, mass and energy balances, and preliminary techno-economic analysis to define a practical pathway from industrial side stream to a commercially relevant fluorescent material

Technology readiness level

The research group has already demonstrated the conversion of agricultural biomass into fluorescent CQDs and their successful use in inkjet anti-counterfeiting formulations, providing a validated technical basis for this approach. The current project focuses on adapting this proven chemistry to wet citrus and apple side streams from pectin production, with future validation covering feedstock characterization, process optimization, printing and UV-authentication tests, scale-up evaluation, and techno-economic analysis.