Mn 3 O 4 Nanozyme Coating Accelerates Nitrate Reduction and Decreases N 2 O Emission during Photoelectrotrophic Denitrification by Thiobacillus denitrificans -CdS

Biosemiconductors are highly efficient systems for converting solar energy into chemical energy. However, the inevitable presence of reactive oxygen species (ROS) seriously deteriorates the biosemiconductor performance. This work successfully constructed a Mn 3 O 4 nanozyme-coated biosemiconductor, Thiobacillus denitrificans -cadmium sulfide ( T. denitrificans -CdS@Mn 3 O 4 ), via a simple, fast, and economic method. After Mn 3 O 4 coating, the ROS were greatly eliminated; the concentrations of hydroxyl radicals, superoxide radicals, and hydrogen peroxide were reduced by 90%, 77.6%, and 26%, respectively, during photoelectrotrophic denitrification (PEDeN). T. denitrificans -CdS@Mn 3 O 4 showed a 28% higher rate of nitrate reduction and 78% lower emission of nitrous oxide (at 68 h) than that of T. denitrificans -CdS. Moreover, the Mn 3 O 4 coating effectively maintained the microbial viability and photochemical activity of CdS in the biosemiconductor. Importantly, no lag period was observed during PEDeN, suggesting that the Mn 3 O 4 coating does not affect the metabolism of T. denitrificans -CdS. Immediate decomposition and physical separation are the two possible ways to protect a biosemiconductor from ROS damage by Mn 3 O 4 . This study provides a simple method for protecting biosemiconductors from the toxicity of inevitably generated ROS and will help develop more stable and efficient biosemiconductors in the future.