Effective removal of quinoline in wastewater using Gd-TiO2 photocatalyst

The coal chemical industry produces significant wastewater containing refractory organic pollutants, with quinoline being a particularly persistent contaminant in secondary biochemical effluents. To overcome the limitations of standard TiO 2 photocatalysts—specifically, their restricted light absorption range and rapid charge recombination—this work created Gd-doped TiO 2 (Gd-TiO 2 ) catalysts using a hydrothermal approach. Comprehensive characterization showed that the optimal 1.5 % Gd-TiO 2 presents three primary advantages: (1) a 55 % increase in specific surface area (174 m 2  g −1 ), (2) enhanced visible-light absorption through bandgap reduction (3.06 eV), and (3) improved charge separation. These modifications enabled the 1.5 % Gd-TiO 2 catalyst to achieve 84 % quinoline degradation within 3 h (mineralization rate: 53.2 %), maintaining 80.3 % efficiency after four cycles, demonstrating exceptional stability. Mechanistic studies revealed a hydroxyl radical-dominated degradation pathway involving sequential benzene-ring opening and pyridine-ring cleavage. This study presents a high-efficiency photocatalyst for industrial wastewater remediation and provides essential insights into rare-earth-modified TiO 2 systems.