Inactivation Mechanism Of Karenia Mikimotoi Under Visible Light Photocatalysis

Harmful algal blooms(HABs)caused by red tide microalgae frequently erupt in coastal waters around the world.In recent years,red tides have become one of the major marine environmental disasters along the coast of my country.They have not only caused serious damage to marine ecosystems,but also caused marine fisheries.The economy has brought huge economic losses,and it has also seriously threatened the production,life and social and economic development of local residents.Photocatalytic technology can utilize sustainable sunlight resources and has great potential to inhibit the growth of algae in situ.However,there is still a lack of research on the inactivation mechanism of photocatalysis on red tide microalgae in seawater environment.The photocatalyst TiO₂ has the characteristics of large specific surface area,regular morphology and high catalytic activity.The photocatalyst g-C₃N₄has a unique layered structure and excellent chemical stability.Studies have shown that g-C₃N₄ and nano The composite of TiO₂ can improve the photocatalytic activity,and further loading the composite powder catalyst can avoid the problems of secondary pollution and difficult recovery.Therefore,this article takes the typical red tide microalgae in the coastal areas of my country--Karenia mikimotoi as an example,for the first time to carry out the research on the visible light photocatalytic activity and mechanism of the supported composite photocatalyst g-C₃N₄/TiO₂ on K.mikimotoi by visible light.The toxic effects of organic matter released by K.mikimotoi on marine ecosystems during the photocatalytic inactivation process were carried out.The main research results obtained are as follows:(1)The composite photocatalyst g-C₃N₄/TiO₂ was prepared,and its powder successfully loaded on substrate to construct a recyclable photocatalytic system,which overcomes the secondary pollution caused by the difficulty of recycling powder materials to the marine environment,and uses XRD,FESEM,UV-vis and other characterization techniques have analyzed the apparent morphology,structural characteristics and element composition of g-C₃N₄,TiO₂ and g-C₃N₄/TiO₂.The photocatalytic properties of the composite catalysts 20,50,70 and 90 wt%g-C₃N₄/TiO₂ with different mass ratios were explored through photocatalytic algae killing experiments,and their deactivation efficiency on algae was measured in combination with the chlorophyll in vivo fluorescence method.It was found that the50 wt%g-C₃N₄/TiO₂ supported composite catalyst has an inactivation rate of 64%within 60 min,and its inactivation efficiency is the best,showing the highest photocatalytic activity,which is used for the entire research.(2)The inactivation mechanism of K.mikimotoi under visible light photocatalysis has been studied in detail.Through free radical annihilation experiments,combined with quantitative detection of free radicals,it is proved that h⁺and ¹O₂ are the main factors in the process of photocatalytic inactivation of algae.The algae cells are stained with SYTO 9 to observe the morpholgy changes,combined with intracellular ROSs,SOD,CAT and MDA activity,as well as the Fv/Fm and ETRmax and other physiological characteristic parameters clarify the physiological changes of K.mikimotoi during the process of photocatalytic inactivation.This research found that the photocatalyst produces active species h⁺and ¹O₂ attack the algae cells under visible light,resulting in damage to the algae cell membrane oxidation,cellular oxidative stress defense system and photosynthesis system collapses,the cell gradually swell to rupture,and the cell content overflows,resulting the inactivation and death of algal cells.(3)The release characteristics of cell organic matter and its toxicity to marine ecosystems during the process of photocatalytic deactivation of K.mikimotoi were investigated.The total organic carbon analyzer,three-dimensional fluorescence spectrometer,ion detector and acute toxicity test were used to analyze the toxicity of cell contents and algal toxin overflow caused by cell membrane rupture,and it is concluded that the contents of algal cell overflow during the photocatalysis process are nutrient proteins of aquatic organisms.The substance tyrosine is non-toxic and harmless to the marine environment and aquatic organisms,and the acute toxicity test results show that the toxicity of the algae cell suspension is significantly reduced after photocatalysis,indicating that the photocatalysis can not only inactivate the algae cells but also achieve the detoxification of algal and have no negative effects on the marine ecosystem.Based on the above research results,this article uses photocatalytic technology to successfully and efficiently inactivate a typical red tide microalgae--K.mikimotoi under visible light,and analyzes its inactivation mechanism,biological stress response and inactivation in detail.The toxic effects of post-cell organic matter release on marine aquatic ecosystems was also studied.The research results not only provides a new method with potential for in-situ treatment of K.mikimotoi using sunlight in marine environments,but also proposed an inactivation and destruction mechanism of photocatalytic treatment of red tide microalgae and the toxic effect on the marine environment are also proposed.It provides a theoretical basis and new research ideas for photocatalytic technology in the field of red tide control,and is of great significance for promoting the application of photocatalytic technology to the treatment of harmful red tide microalgae.