Study On The Degradation And Ecological Toxicity Of Tetracycline Antibiotics In Water By Nitrided Carbon Photocatalytic Materials

The environmental problems caused by new environmental pollutants such as antibiotics have received high attention from people.The high productivity and highdose use of tetracycline antibiotics(TCs)by humans leads to a decrease in the antibacterial activity of TCs,their metabolites,and degradation products in water bodies,as well as increased cytotoxicity to animals and plants.They have biological inhibitory and resistant bacterial mutagenic effects.Conventional biological treatment methods are difficult to achieve ideal results.Currently,solar-driven photocatalysis technology is widely used for the removal of antibiotics in aquatic environments due to its sustainable,efficient,and green characteristics.Nitrided carbon-based semiconductors have great potential for application in the field of photocatalysis due to their non-toxic,multi-dimensional structure,and suitable band positions.However,there is still little research on whether photocatalytic materials have toxic effects on aquatic environments and organisms when used.Firstly,this paper studied the growth and toxic effects of Chlorella pyrenoidosa under different concentrations of TC stress.Secondly,a composite photocatalytic material was prepared by modifying carbon nitride(g-C3N4)with coconut shell biochar,and its efficient degradation effect and related mechanism on TC in water were studied.Finally,the ecotoxic effects of the photocatalyst material itself and the treated water on Chlorella pyrenoidosa were explored.The main results are as follows:(1)The toxic effects of different concentrations of TC on Chlorella pyrenoidosa,algal cell density,chlorophyll concentration,superoxide dismutase(SOD)activity,and total protein(TP)content were investigated.The experiment found that Chlorella pyrenoidosa was affected at different TC concentrations,but the changes were more significant after 72 hours of exposure.At high concentrations,as the exposure time increases,the color of the extracted supernatant gradually becomes clear and transparent.The concentration of chlorophyll a is only 0.035 g/L,and almost all algae cells die.The inhibitory rate of high-concentration TC solution(0.5 g/L)on the growth of Chlorella pyrenoidosa reached 81.07%.The TP content and SOD enzyme activity show a similar trend of first decreasing and then increasing with the increase of TC concentration.(2)Biochar/g-C3N4(Br/CN)composite photocatalytic material was synthesized by simply decomposing and synthesizing g-C3N4 surface loaded with Biochar.After that,the structure,activity,and stability of Br/CN photocatalytic materials were characterized using scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),and electron paramagnetic resonance(ESR).The free radical capture experiment and ESR detection results demonstrate that hv+is the main active substance.In addition,the degradation rate of TC in water by Br/CN photocatalytic materials reached 79.06%at room temperature,and after four cycles,the degradation rate remained stable at 76%.(3)Through the toxicity test of Br/CN photocatalysis material itself,it was found that 0.02 g/L of photocatalysis material did not affect the algal cell density,SOD and TP content of Chlorella Chlorella pyrenoidosa.The difference in the optical density(OD)values measured by comparison is only 0.082,with a growth rate 11%higher than that of the unadded sample.Secondly,the physiological indexes of Chlorella pyrenoidosa exposed to the solution before and after Br/CN treatment were measured.It was found that the growth rate of Chlorella pyrenoidosa in the solution after degradation treatment was significantly increased,and the OD value of the algal cell solution was three times higher than that of the untreated solution.The TC toxicity of the treated solution decreased,and the SOD inhibition rate,TP and chlorophyll-a concentrations were similar to those of the culture medium samples without TC addition,with differences of 0.08%,1 g/L,and 0.0004 g/L.Based on the perspective of toxicology,this paper systematically compared the ecotoxicity effects of different concentrations of TC solution on Chlorella pyrenoidosa.A high specific surface area Br/CN composite photocatalytic material was synthesized using the g-C3N4 layered stacking structure,achieving efficient degradation of TC.And take it as the research object,to reveal the toxic effect of photocatalytic materials on Chlorella pyrenoidosa and provide a theoretical basis.A toxicity assessment was conducted on the solution after the degradation of TC by Br/CN photocatalytic materials.The CCK-8 toxicity kit was used to detect the toxicity of the actual degradation system reaction process,providing valuable information for the application of photocatalytic materials in the remediation of antibiotic pollution in water bodies and environmental risk assessment.