Lignin-derived carbon quantum dot–sensitized TiO$_2$ for enhanced visible-light photocatalytic simultaneous degradation of pharmaceuticals

Ullah, Azmat (author), Šuligoj, Andraž (author), Žener, Boštjan (author), Ribić, Vesna (author), Genorio, Boštjan (author), Ciber, Luka (author), Lavrenčič Štangar, Urška (author), Papan Djaniš, Jelena (author)

Titanium dioxide (TiO$_2$) photocatalysis is a promising advanced oxidation method for water treatment, but its reliance on UV irradiation limits practical solar-driven applications. This study addresses this limitation by synthesizing lignin-based carbon quantum dots (L–CQDs) from kraft lignin and combining them with anatase TiO$_2$ to create a visible-light-active hybrid photocatalyst. L–CQDs/TiO$_2$ composites with 1–4 wt.% L–CQD loadings were prepared, thoroughly characterized, and evaluated for photocatalytic performance under simulated visible light (400–700 nm). The optimized 3 wt.% L–CQDs/TiO$_2$ hybrid achieved simultaneous degradation of sulfamethoxazole (SMX) and ibuprofen (IBU) with removal efficiencies of 98.6% and 79.7%, respectively, after 90 min – representing 118-fold and 5-fold increases in pseudo-first-order rate constants compared to bare TiO2. Radical scavenging experiments revealed a dual degradation mechanism: SMX was degraded mainly by superoxide radicals in the bulk solution, while IBU was degraded at the photocatalyst surface via photogenerated holes, with hydroxyl radicals playing a negligible role. Density functional theory calculations of frontier molecular orbital energies supported this mechanistic distinction. Matrix effects in tap water selectively suppressed IBU degradation due to competing hole consumption by CO$_3$$^{2-}$ and Cl$^-$, while SMX degradation remained unaffected. These findings demonstrate that L–CQDs act as a sustainable photosensitizer, shifting TiO$_2$ activity into the visible range through a charge-transfer mechanism rather than direct band gap modification, enabling efficient multi-pollutant removal under solar-relevant irradiation.

• Language: English
• Keywords: lignin carbon quantum dots, titanium dioxide, photocatalysis, water pollution, sulfamethoxazole, ibuprofen
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: 13 str.
• Numbering: Vol. 28, art. 101465
• PID: 20.500.12556/RUL-188113
• UDC: 546.82-31:544.526.5
• ISSN on article: 2666-8211
• DOI: 10.1016/j.ceja.2026.101465
• COBISS.SI-ID: 291107331
• Publication date in RUL: 18.09.2026

Record is a part of a journal

• Title: Chemical engineering journal advances
• Publisher: Elsevier B.V.
• ISSN: 2666-8211
• COBISS.SI-ID: 56312067

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: ogljikove kvantne pike iz lignina, titanov dioksid, fotokataliza, onesnaževanje vode, sulfametoksazol, ibuprofen