Driving multicolor lignin-based carbon quantum dots into selective metal-ion recognition and photocatalytic antibiotic decomposition

Abstract

The controllable synthesis of high-performance multicolor light-emitting carbon quantum dots (CQDs) that present photoinduced charge transfer and reservoir is of great concern for advancing their optical physics with versatile functions. In view of the incorporation of conjugated structures into phenylpropanoid building blocks, renewable lignin with abundant functional groups (e.g., hydroxyl, carboxyl, and methoxyl) is well-suited to prepare polycyclic aromatic CQDs. Herein, we propose a universal acidic approach to fabricating multicolor lignin-derived CQDs with heteroatom-doping for double-edged water decontamination involving switchable metal-ions sensing and photocatalytic antibiotic abatement. The N,S co-doped multicolor CQDs with a size distribution of 3.84–5.85 nm facilitate the selective identification abilities of the intricate metal-ion systems of Fe³⁺, Ag⁺, Cu²⁺, and/or Co²⁺ in a broad response range with excellent accuracy and the limit of detection of 0.55–2.77 μM. The tunable factors of quantum size, surface potential, electrostatic attraction, molecular state, and cation–π interactions that endow the unique CQDs with optical–structure–performance relationships provoked by lignin-oxidized cleavage are underlined. Taking advantage of the Fe-modified yellow-emitting CQDs with high yield, an efficient photocatalytic persulfate activation is proposed to mineralize tetracycline (∼80% removal efficiency at an ultrahigh concentration of 50 mg L⁻¹) under visible-light irradiation. Benefitting from the successful armoring of Fe into the sp² graphitic CQD structure with the Fe–OH and Fe–N complexes, the electron transition can be expedited via available light-harvesting behavior, enhanced photoactive sites, and Fe-ion durability. The synergetic photoredox manner of extracting electrons/holes maneuvers the generation of free radicals and singlet-oxygen, wherein the produced ˙O₂⁻ and surface charge migration-dominant photocatalytic reaction. With the perspective of achieving waste-treats-pollutant, this work not only delivers the rationally engineered lignin valorization but also highlights the well-defined CQDs in multifunctional water purification.