Iron oxides semiconductor minerals photocatalysis reduce methane fluxes in paddy soils

Dissimilatory iron reduction could reduce ecosystems methane (CH₄) emissions. However, the role of iron oxides especially with photocatalysis in controlling CH₄ emissions is still unclear. In this study, hematite, goethite, and ferrihydrite were added to paddy soil and a 30-day indoor incubation experiment was then carried out. Three distinct treatments of simulating full sunlight illumination with a xenon lamp light source, shielding light at a wavelength of 550 nm, and darkness were designed to comprehensively explore the impact of semiconductor minerals photocatalysis on CH₄ emissions from paddy soil. Our results showed that hematite, goethite, and ferrihydrite have the highest photoelectric conversion efficiencies at wavelengths of 550 nm, 500 nm, and less than 400 nm, respectively. When iron oxide semiconductor minerals receive light wavelengths with high photoelectric conversion efficiencies, they can mediate Geobacter metallirducens to generate highly efficient photocurrent. CH₄ emissions were significantly reduced by adding goethite. In contrast, CH₄ emissions were increased by adding hematite, but when the 550 nm light wavelength was blocked after adding hematite, the CH₄ emissions were effectively inhibited with a reduction rate of 25 %, indicating iron oxide semiconductor minerals photocatalysis is a controlling factor in reducing CH₄ fluxes. In conclusion, this study revealed that hematite and goethite are the main regulatory factors of CH₄ emissions in paddy fields, and CH₄ emissions can be reduced by adding goethite and blocking the 550 nm light wavelength.