In this study, titanium dioxide (TiO 2 ) nanoparticles were synthesized via a sol-gel method and immobilized onto humic acid (HA) extracted from leonardite to enhance their photocatalytic efficiency under both UV and visible light. The nanomaterial containing 0.03 g of HA (per 0.1 g TiO 2 ) exhibited the highest performance, achieving a degradation efficiency of 99.36% for Methyl Orange (MO) under UV irradiation within 25 min and 98.43% under visible light within 180 min. The apparent reaction rate constant (k) of the optimized TiO 2 /HA nanomaterial reached 1.3252 min −1 under UV irradiation and 0.0957 min −1 under visible light. These values are approximately 39.3 and 15.4 times higher, respectively, than those of pure TiO 2 , indicating a substantial enhancement in catalytic activity.
Mazuchi et al. (Tue,) studied this question.