Novel Multiphase CO2 Photocatalysis System Using N-TiO2/CNCs and CO2 Nanobubble

Abstract

In this study, a novel CO2 photocatalysis system was developed by modifying TiO2 as a photocatalyst and introducing CO2 nanobubble to the system. TiO2 photocatalyst is modified by adding CNCs as support to increase the surface area and adding nitrogen doping to reduce the band gap and minimize electron–hole recombination. CO2 nanobubbles are introduced to increase the surface area between the CO2 gas and liquid phases to reduce mass transfer limitations. Thus, the amount of CO2 in the liquid phase increases. Nanobubbles have been successfully generated by the hydrodynamic cavitation method, which produces bubbles with two size clusters, namely 200–400 nm, which belong to nanobubbles, and 2–10 um, which belong to microbubbles. The TiO2 has an anatase phase and crystallite size of 20.90 nm for TiO2/CNCs and 19.20 nm for N-TiO2/CNCs. The activity test without nitrogen doping produced a methanol product of 0.77 mmol/g catalyst, which shows that this multiphase CO2 photocatalytic system is feasible for CO2 photocatalytic reactions. The addition of nitrogen doping succeeded in reducing the band gap from 3.20 eV to 3.10 eV and increasing the methanol yield. The photocatalysis activity test with N-doped TiO2/CNCs resulted in a higher methanol yield, which is 1.13 mmol/g catalyst under UV-C irradiation for 6 hours.