Construction of biomass derived carbon quantum dots modified TiO2 photocatalysts with superior photocatalytic activity for methylene blue degradation

Titanium dioxide (TiO 2 ) photocatalyst has been extensively studied due to its high photocatalytic activity under UV radiation, chemical stability, and low cost. However, its photocatalytic efficiency is limited by the low harvest of visible light due to larger energy band gap (Eg =3.2 eV) and the rapid recombination of photo-generated carriers. Herein, N-doped carbon quantum dots (NCQDs) were utilized to decorate TiO 2 via a facile hydrothermal-calcination synthesis approach, wherein NCQDs were prepared using spent coffee grounds as biomass carbon source and urea as nitrogen source. The NCQDs increase the absorption of visible light, and facilitate electron transfer and separation of photo-generated electron-hole pairs. A very low NCQDs content of 3 wt.% (3- NCQDs/TiO 2 ) resulted in 2.25 times faster photodegradation rate for methylene blue (MB) than pristine TiO 2 . 3-NCQDs/TiO 2 exhibited efficient and stable photocatalytic degradation over MB with photodegradation rate of 93.1% within 60 min and more than 86% after 4 cycles. Besides, it shows enhanced degradation performance in alkaline conditions. This work provides a new attempt to boost the photocatalytic activities of the photocatalysts by biomass-derived NCQDs for water remediation. • Spent coffee grounds derived carbon quantum dots (NCQDs) were utilized to decorate TiO 2 . • The NCQDs increase the absorption of visible light, and facilitate transfer and separation of photo-generated carriers. • NCQDs/TiO 2 exhibit outstanding photocatalytic activities over methylene blue. • NCQDs/TiO 2 shows enhanced degradation performance in alkaline conditions.