The effect of NOM to TiO2: interactions and photocatalytic behavior

• TiO2 binds small MW NOM layers and breaks their aromatic bonds to form stranded alkyl.
• TiO2 activates mechanisms that polymerize the remaining unbound NOM in solution.
• NOM-modified TiO2 has less holes (h+) than purified TiO2.
• Low NOM concentration enhances CBZ photocatalysis creating attraction sites on TiO2.
• High NOM concentration prohibits CBZ photocatalysis competing OH radicals of TiO2.

Natural organic matter (NOM) is ubiquitous in aquatic environment, which plays a predominant role in the sorption of pharmaceuticals onto the TiO2 nanoparticles. It is a matter of concern whether NOM could act as a surface sensitizer of TiO2 or not. In this context, the role of NOM is investigated for the photocatalytic degradation of carbamazepine (CBZ) using TiO2. Four different ratios of NOM:TiO2 were used varying from 400 μg g−1 to 400 mg g−1. The findings reveal that small amounts of NOM could enhance the TiO2 efficiency up to 8%. Electron paramagnetic spectroscopy (EPR), along with size exclusion chromatography with dissolved organic carbon detection (SEC-OCD) and nuclear magnetic resonance spectroscopy (NMR) reveal the occurring mechanism. TiO2 binds small molecular size fractions of NOM and breaks aromatic bonds of adsorbed NOM transforming it to stranded alkyl groups. This modified TiO2 bears a significant amount of electrons (e−) and lesser holes (h+) than the purified TiO2 and when irradiated, produces hydroxyl radicals which degrade CBZ.

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