Photocatalytic Degradation Of Quinolone Antibiotics By 3D Pt/g-C₃N₄/Agar Composites

Quinolone antibiotics are widely used in livestock breeding,medical and other industries.These substances can enter the environment through various ways and accumulate in the environment.After a long time,microorganisms in the environment will develop resistance to them,interfere with the natural ecosystem of bacteria and do harm to the ecological environment.Photocatalysis technology is an efficient treatment technology.Graphite carbon nitride（g-C₃N₄）is a semiconductor catalyst widely used in photocatalytic technology.However,it has high photogenerated electron-hole recombination rate and low utilization rate of visible light,so its photocatalytic performance needs to be improved by noble metal deposition.Noble metal platinum（Pt）nanoparticles effectively capture the photogenerated electrons that transition to the conduction band in the photocatalyst,realize more efficient separation between electron and hole,improve the catalytic performance of the photocatalyst,and effectively treat quinolone antibiotic pollutants.The photocatalyst was characterized by SEM,TEM,XRD,FT-IR,EDS,UV-Vis/DRS,PL and so on.Three quinolone antibiotics ciprofloxacin（CIP）,norfloxacin（NOF）and levofloxacin（LEV）were used as the target degradationp roducts to carry out photocatalytic experiments.The photocatalytic performance of the photocatalyst was evaluated,the degradation mechanism and possible degradation pathway were studied.The main research contents and conclusions were as follows:（1）The characterization results and degradation activity of antibiotics of g-C₃N₄prepared by different precursors were compared,the results showed that g-C₃N₄（U-CN）prepared by urea had higher adsorption capacity and photocatalytic capacity.The specific surface area was as high as 75.712 m~2/g,and the degradation rate was 70.19%after 180 min illumination of 10 mg/L CIP simulated wastewater（100 m L）.It is determined that the subsequent experiments were conducted using g-C₃N₄ prepared from urea.（2）A series of highly dispersed platinum deposited carbon nitrides（Pt（x%）/CN）were prepared by in-situ photoreduction method.Compared with U-CN,Pt（x%）/CN has smaller pore size,larger specific surface area,stronger absorption of visible light,and better photocatalytic performance.In addition,for Pt（x%）/CN photocatalyst,the effects of platinum loading of photocatalyst,initial concentration of antibiotic solution and p H of solution on antibiotic degradation were investigated.The results showed that when the initial concentration of antibiotics was 10 mg/L and p H was 7,the best composite catalyst was Pt（3%）/CN.At this time,the degradation rates of CIP,NOF and LEV antibiotic solutions were 92.43%,94.71%,and 90.18%,respectively,after photocatalytic degradation for 3 h.Through the degradation experiment of 10 mg/L CIP solution,the reusability of Pt（3%）/CN was explored（cycle five times）.It was found that the degradation rate decreased from 92.43%to 87.92%,which proved that the material had stability and reusability.（3）Through the free radical capture experiment,the full wavelength scanning of UV-Vis absorption spectrum and the monitoring of removal rate for TOC,it was found that the main active groups in the system are hole（h⁺）and·O₂^-in the degradation of antibiotics by Pt/g-C₃N₄.The TOC removal rates of CIP,NOF and LEV reaction solutions are 49.81%,45.86%and 27.98%,respectively,after 3 hours of degradation,indicating that the three antibiotics can produce small molecular substances after photocatalytic degradation in this system.Combined with LC-MS technology,the reaction intermediates were determined,their possible degradation mechanism and degradation pathway were analyzed.The results showed that the degradation was mainly realized by the substitution of fluorine atoms and the oxidation of piperazine ring.（4）In order to find an effective carrier,platinum supported carbon nitride（Pt/g-C₃N₄）and agar were further used to prepare three-dimensional（3D）platinum supported carbon nitride/agar composite,which has excellent properties and overcomes the problem that the powder catalyst is not easy to recover.According to the different dosage of agar powder and Pt（3%）/CN,three-dimensional platinum supported carbon nitride agar composite photocatalysts（3D Pt（3%）/CN-AG）with different composite ratios were prepared by heating cooling polymerization.The samples were characterized by XRD,SEM,UV-Vis/DRS and so on.The characterization results showed that the 3D Pt（3%）/CN-AG composite had enhanced visible light absorption compared with pure Pt（3%）/CN.At the same time,the degradation efficiency of the material to CIP,NOF and LEV antibiotics under visible light was investigated.The results showed that the photocatalytic performance of the synthesized3D x%-Pt（3%）/CN-AG composite gradually improved with the increase of Pt（3%）/CN content.In the reaction system with 3D 80%-Pt（3%）/CN-AG,the degradation rates of 10mg/L CIP,NOF and LEV reached 96.76%,95.67%and 95.17%,respectively,after 180 min.However,the structure of the catalyst is loose and unstable.Considering the stability and visible light catalytic performance of the material,3D 60%-Pt（3%）/CN-AG is considered to be the best photocatalyst.（5）The cyclic stability experiment showed that the degradation rate of 10 mg/L CIP solution of 3D 60%-Pt（3%）/CN-AG composite is only reduced by 6.61%after being recycled for 5 times.The main active groups in the reaction system are·OH and h⁺,Under photocatalytic conditions,the antibiotics are degraded to form small molecules,and the degradation mechanism of antibiotics in this system was explored.In addition,3D Pt（3%）/CN-AG photocatalyst not only has good photocatalytic degradation performance,but also solves the problem of difficult recovery of powder photocatalyst.Figure[47]table[7]reference[122]...