Visible Light-Induced Marine Bacterial Inactivation in Seawater by an In Situ Photo-Fenton System without Additional Oxidants: Implications for Ballast Water Sterilization

Abstract

Harmful non-indigenous microorganism invasion caused by ballast water discharge poses severe threats to marine environments. In this study, a conceptual in situ photo-Fenton system without additional oxidants was first established for ballast water sterilization. Pyromellitic acid diimine (PDI)-modified g-C3N4 was utilized as a photocatalyst to produce H2O2, which was in situ activated by Fe­(II) to produce •OH for deep oxidation. Marine bacterium Vibrio alginolyticus (7 log) in ballast seawater was totally inactivated within 35 min of visible light irradiation. Simultaneous bacterial inactivation and H2O2 production was monitored to confirm the in situ coupling mechanism, and •OH instead of H2O2 was determined to be the dominant reactive species. The influence of seawater parameters, such as salinity, pH, and dissolved oxygen, on the inactivation efficiency was revealed. In addition, the bacterial inactivation mechanisms in terms of cell membrane rupture, intracellular enzyme activity, and total protein change were clarified. The organic matter release profile during bacterial lysis was probed by fluorescence excitation–emission matrix technology, which revealed minimal acute toxicity and impacts on the marine environment. This work not only advances an external oxidant-free system for on-board ballast water sterilization using sustainable solar energy but also creates an avenue for exploring bacterial inactivation mechanisms in seawater.

Mechanistic Insight into the Heterogeneous Electro-Fenton/Sulfite Process for Ultraefficient Degradation of Pollutants over a Wide pH Range

“…Hydrogen peroxide (H 2 O 2 ), as a green and highly efficient oxidant used in advanced oxidation processes (AOPs), is commonly produced by an anthraquinone method, an electrochemical method, and photocatalysis. − Electro-Fenton (EF) is a new type of AOP, which can generate H 2 O 2 in situ on the surface of the cathode through a two-electron oxygen reduction reaction (ORR) (eq ), avoiding the risk of reagents in transportation, storage, or treatment. , The basic principle of this process is that Fe 2+ added to the solution reacts with the continuously produced H 2 O 2 to form a strong oxidant of hydroxyl radical ( • OH) (eq ); thus, it is efficient and environmentally friendly. However, traditional homogeneous EF has disadvantages such as a narrow pH application range (2.8–3.5), a slow rate of reduction of iron ions, and difficult recovery of the catalyst, which greatly limit its wide application …”

Extended Conjugation Tuning Carbon Nitride for Non‐sacrificial H2O2Photosynthesis and Hypoxic Tumor Therapy**

“…To further estimate the conduction band (CB) and valence band (VB) position of C 5 N 2 , we recorded and compared XPS VB scans of C 5 N 2 and g‐C 3 N 4 (Figure S7) and the flat band potential ( E fb ) of g‐C 3 N 4 (Figure S8) [25] . Interestingly, a significant downshift of the CB and VB position of C 5 N 2 with respect to conventional g‐C 3 N 4 and other metal‐free polymers was observed (Figure 2d and Figure S9) [2a,c,d, 10, 11, 12b, 13, 14, 23] . The CB position of C 5 N 2 was even significantly lower than 0 V vs. NHE, which was in favor of driving highly selective O 2 reduction in thermodynamics instead of competitive HER; meanwhile the lower CB would enhance WOR kinetics.…”

“…c) Experimental and Pawley‐refined PXRD patterns of C 5 N 2 . d) CB/VB position of C 5 N 2 and other reported metal‐free photocatalysts [2a,c,d, 10, 11, 12b, 13, 14, 23] . e,f) Simulated HOMO–LUMO electronic structure distribution of g‐C 3 N 4 (e) and C 5 N 2 (f) by DFT calculations.…”

Reaction Pathways toward Sustainable Photosynthesis of Hydrogen Peroxide by Polymer Photocatalysts

“…Two electrons and two protons are consumed simultaneously to generate H 2 O 2 . This reaction pathway has now been found in various photocatalysts. − g -C 3 N 4 is the first polymer photocatalyst to exhibit high selectivity (90%) toward photocatalytic H 2 O 2 production via the direct two-electron ORR pathway (Figure a) . Based on Raman and electron spin resonance (ESR) spectroscopic characterizations, it was shown that the high H 2 O 2 selectivity was attributed to the formation of 1,4-endoperoxide species on the heptazine structure (Figure b).…”