Comparison of synthesis methods for BiOI/g-C3N4 heterojunction photocatalysts and testing their visible light activity in sugar processing wastewater treatment

The study focused on synthesis of BiOI/g-C3N4 heterojunction photocatalysts by various methods to investigate their physicochemical properties as well as their performances on photocatalytic treatment of sugar processing wastewater. The heterojunction catalysts possessed enhanced catalytic activity compared to the pristine BiOI and g-C3N4. In-situ growth of BiOI on g-C3N4 was determined as the most promising method when the pH of the synthesis medium was adjusted to 10. This method provided a more homogeneous distribution and smaller size for the BiOI clusters that formed a unique flower shape which enhanced the catalytic activity remarkably. This depicts that synthesis conditions are especially important to obtain desired physicochemical properties for a photocatalyst since it has a key role in the crystal structure of BiOI. The optimum nominal weight ratio was determined as 75:25 for BiOI and g-C3N4, respectively by considering the superior morphology and the highest photocatalytic activity for 45.30% and 23.40% total saccharide (TSC) and total organic carbon (TOC) removal, respectively. The photocatalytic mechanism depicted that charge separation in the heterojunction structure was accomplished via the new S-scheme and the oxidation of saccharides and intermediates followed different pathways by reacting with different radicals.