Mn₃O₄ Nanozyme Coating Accelerates Nitrate Reduction and Decreases N₂O Emission during Photoelectrotrophic Denitrification by Thiobacillus denitrificans-CdS

Abstract

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.

Biophotoelectrochemistry for renewable energy and environmental applications

“…The denitrification performance of the T. denitrificans-CdS system was found to be sensitive to the input nitrate and nitrite (NO ), and hydroxyl radicals ($OH) to the inhibition of N 2 O reduction were >15.0%, >5.4% and 1.3% for a reduction of 13.5 mg/L NO 3 --N, respectively (Chen et al, 2020a). To weaken the inhibiting effect of ROS, a Mn 3 O 4 nanozyme-coated BPEC system (T. denitrificans-CdS@Mn 3 O 4 ) was constructed and significantly reduced the concentrations of multiple ROS for stable microbial viability, resulting in a 28% higher NO 3 reduction and 78% lower emission of N 2 O than that of the T. denitrificans-CdS system (Chen et al, 2020b). Recently, a novel concept of dark photocatalyst was introduced, e.g., cyanamide-functionalized heptazine-based polymer (NCN-CN x ) that could store photoelectrons under irradiation and release them in a dark environment.…”

Anthraquinone-2-Sulfonate as a Microbial Photosensitizer and Capacitor Drives Solar-to-N2O Production with a Quantum Efficiency of Almost Unity

“…With 0.75% lactate addition, the photocurrent was increased more than 100 times and accounted for ∼15 μA cm –2 , which indicates that lactate effectively promotes the charge separation of AQS (Figure C). The constant photocurrent of AQS in the lactate solution demonstrates that AQS is more stable than the easy-corrosive semiconductor (e.g., CdS) as a photosensitizer for microorganisms …”

Inflammation-sensing catalase-mimicking nanozymes alleviate acute kidney injury via reversing local oxidative stress

“…Despite the great promise, Mn 3 O 4 -based nanoparticles have not been exploited much for in vivo applications. Previously, the ROS-scavenging property of Mn 3 O 4 nanoparticles was utilized for cytoprotection [ 22 ], for developing bio-semiconductors [ 20 ], and for relieving oxidative stress in plants [ 23 ]. However, the small particle size and the instability or possible agglomeration of these nanoparticles can adversely affect the proper distribution and circulation half-life when used in in vivo conditions.…”