Photocatalytic study of composites based on titanium dioxide (TiO2) and graphitic carbon nitride (g-C3N4) under artificialand natural light

Abstract

Photocatalytic treatment has attracted the scientific community due to the production of reactive oxygen species (ROS). In recent years, ROS has shown the potential to eliminate several pollutant types. The search to develop semiconductor materials with efficient use of light and utilization of cleaner energy sources has been increasingly common in publications. In this context, the first study aimed to systematize innovations in composite synthesis constituted by the titanium dioxide (TiO2) and graphitic carbon nitride (g-C3N4). Some terms were used to search the publications in Compendex bibliographic database between 2015 and 2021. Papers were included and excluded according to specific criteria. Subsequently, the remaining papers were organized from TiO2 morphology and the number of publications. This systematic review allowed the identification of morphological variability in composites and the predominance of TiO2 nanoparticles. In addition, new synthetic methods, such as atomic layer deposition, vapor deposition, and charge-induced aggregation, were developed. The second part of this work developed a photocatalytic study from composite synthesis based on titanium dioxide (P25) and graphic carbon nitride (CN). For this purpose, two reactors were designed to observe materials responses (CN, CN25, CN75, and P25) to the artificial and natural light sources provided by a halogen lamp and sun exposure, respectively. Solutions containing methylene blue (MB) with an initial concentration of 10 mg/L were treated by photocatalysis. The application of Central Composite Design (CCD) aided in understanding parameters influence (pH, MB initial concentration, and P25 dosage) on the dye removal. The findings showed that P25 improved the photocatalytic response of the CN. However, pristine P25 achieved the highest removals in both light sources. P25 reached the average removal of 99.4% at 1 h under sunlight. The critical points determined by CCD for pH, P25, and MB were 6.6, 1.2 g/L, and 1 mg/L, respectively. The First-order kinetic model adjusted to the photocatalytic process generated the k value of 0.07 min-1. This modeling showed that the removal rate doubled after 30 minutes of testing. Experimental results indicated a high potential for the utilization of heterogeneous photocatalysis activated by sunlight.