Broad-spectrum light-responsive deep eutectic solvents for ambient microalgae disintegration with intact fractions

Rationally integrating microalgae valorization is pivotal to sustainable and cost-competitive biorefineries. However, a trade-off exists between effective disintegration of recalcitrant microalgae and retention of biomolecular integrity.

This study aims to develop a mild, light-responsive pretreatment platform that reconciles structure integrity-efficiency trade-off without relying on energy-intensive external reinforcement.

An "(in)organic hybridizing dual-amplification" maneuver is delivered to construct a ternary deep eutectic solvent (DES) system composed of Fe³⁺, α-hydroxycarboxylic acid, and water. The system's performance is evaluated under ambient light irradiation for a short duration (2 h). Mechanistic insights are obtained through theoretical calculations and spectroscopy, while the economic viability was assessed via life cycle cost analysis.

Under ambient light, this light-responsive DES system fractionates microalgae into lipids (extraction efficiency of 91.6%, based on saponifiable lipids), conserving functional fatty acids, carbohydrates amenable to digestibility, and high-recovery protein (80.4%, comprising 16.2% soluble and 64.2% natively conformation-preserved fraction). Furthermore, both the extracted microalgal lipids and microbial lipids synthesized from carbohydrates can be converted into ASTM D6751-compliant biodiesel, with the DES retaining efficiency and stability after six recycles. Life cycle cost analysis verifies the economic competitiveness of the developed protocol. Mechanism studies revealed that α-hydroxycarboxylic acid, featuring dual H-bond donor/acceptor characters, cooperates with Fe³⁺ and water to form a supramolecular network that competitively reconfigures the cell wall hydrogen-bonding architecture and lowers constituents' binding energy. Meanwhile, Fe³⁺ forms photo-active complexes with α-hydroxycarboxylic acid as electron shuttles, coupling broad-spectrum ligand-to-metal charge transfer with oxidant-free photo-Fenton process, propelling controllable Fe-redox cycling and sustained radical generation for efficient and facile microalgae disintegration cooperatively.

The dual-amplification strategy successfully overcomes the kinetic constraints of traditional photo-Fenton processes and the recalcitrance of cell walls. By enabling efficient, ambient-light-driven disintegration while preserving component integrity, this work provides a scalable and sustainable technological strategy for biomass biorefining.