<p>The traditional wastewater treatment processes are usually inefficient and therefore require more sustainable remediation approaches. Copper-modified nano TiO₂ (Cu/TiO₂) nanoparticles have been produced through an impregnation-assisted sol-gel process and tested as a promising visible-light-driven photocatalyst to degrade dye. Structural characterization confirmed anatase TiO₂ with homogeneously dispersed Cu and reduced crystallite size. XPS analysis showed that there were mixed states of Cu⁺/Cu²⁺ oxidation and the concentration of surface hydroxyl groups and oxygen vacancies was greater which are favorable in photocatalysis. The optical measures revealed that there was a strong red-shift in the light absorption and band gap reduction between 3.20&#xa0;eV (TiO₂) and 2.85&#xa0;eV (Cu/TiO₂) which allowed the exploration of the usefulness of visible light. Photoluminescence measurements showed suppressed electron–hole recombination after Cu incorporation. Cu/TiO₂ photocatalyst has shown better photocatalytic performance in the treatment of methylene blue, achieving approximately 96% degradation of methylene blue in 60&#xa0;min and has a reaction rate constant three times higher than the pristine TiO₂. Experiments using reactive species trapping revealed that the active species was principally the hydroxyl radicals. Minimal copper leaching, great reusability and good mineralization efficiency also confirmed the stability of the catalyst. This increased performance is explained by the increased charge separation, enhanced light absorption and effective redox cycling at the Cu-TiO₂ interface. These findings indicate that Cu/TiO₂ has good potential as a cheap and sustainable photocatalyst that can be used in the treatment of wastewater.</p>