An in situ microwave-assisted synthesis approach has been developed to prepare N-TiO2/g-C3N4 composites using H2TiO3 as the reactant and NH3·H2O as the N-doping source. In this way, the N-TiO2/g-C3N4 composite catalysts have a porous structure and large surface areas, which increase the contact area of pollutants. Degradation of rhodamine B (Rh B) and methylene blue (MB) were carried out to evaluate the photocatalytic activity of samples under visible light irradiation. N-TiO2/g-C3N4 composite with 40 wt % N-TiO2 exhibits the highest photocatalytic activity and the optimal temperature is 400 °C. The increased photocatalytic activity of N-TiO2/g-C3N4 composites can be attributed to the formation of the heterojunction between N-TiO2 and g-C3N4, which suppresses the recombination of photoinduced electron–hole pairs. The tests of radical scavengers confirmed that •O2 – was the main reactive species during the photocatalytic process.

Seeking a simple and moderate route to generate reactive oxygen species (ROS) for antibiosis is of great interest and challenge. This work demonstrates that molecule transition and electron rearrangement processes can directly occur only through chemisorption interaction between the adsorbed O and high-energy {111} facet-exposed MgO with abundant surface oxygen vacancies (SOVs), hence producing singlet oxygen and superoxide anion radicals without light irradiation. These ROS were confirmed by electron paramagnetic resonance, in situ Raman, and scavenger experiments. Furthermore, heat plays a crucial role for the electron transfer process to accelerate the formation of ·O, which is verified by temperature kinetic experiments of nitro blue tetrazolium reduction in the dark. Therefore, the presence of oxygen vacancy can be considered as an intensification of the activation process. The designed MgO is acquired in one step via constructing a reduction atmosphere during the combustion reaction process, which has an ability similar to that of noble metal Pd to activate molecular oxygen and can be used as an effective bacteriocide in the dark.

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