Degradation Of Organic Pollutants Activated By Pms And Self-Degradation Performance Of G-C₃N₄/TiO₂ Composite Photocatalytic Fibers

In recent years,due to the rapid development of science,technology and industry,many complex and highly toxic organic pollutants have been produced around the world,causing serious water pollution problems.Advanced oxidation technologies（AOPs）,which have attracted much attention due to their high adaptability and excellent ability to remove organic pollutants in wastewater,are considered to be one of the most promising wastewater treatment technologies.Among them,the advanced oxidation technology of peroxymonosulfate（PMS-AOP）is a high-efficiency,energy-saving and simple-to-operate treatment technology.It generates a large number of hydroxyl radicals（·OH）through the activation of PMS under the action of a catalyst to decompose organic pollutants..The current methods for activating PMS include transition metal ions and their transition metal catalysts,but there are problems such as overflow of metal ions.Photocatalytic oxidation technology based on semiconductor photocatalysts has been widely used in environmental treatment.Among them,TiO₂ is one of the widely studied inorganic semiconductor photocatalysts.It has the advantages of low cost,non-toxicity,and easy scale.Generates free radicals such as·OH,and has great potential for development in the field of catalytic degradation.However,TiO₂ has the disadvantages of high optical band gap（3.2-3.5 e V）,narrow light absorption range,et al.,and it is easy to agglomerate during use and difficult to recycle,easy to cause secondary pollution.Graphite-like carbon nitride（g-C₃N₄）as an organic semiconductor photocatalyst has a low band gap（2.7 e V）,good chemical stability,unique electronic properties,can absorb visible light wavelengths,and exhibits excellent photocatalytic activity.In addition,powder catalysts have problems such as easy agglomeration and difficulty in recycling.They can be supported on carrier materials to improve dispersibility and recycling rate.The current carrier materials include zeolite,ceramics,glass,et al.After these carrier materials undergo photocatalytic degradation of organic pollutants,secondary pollution is prone to occur,and subsequent treatment problems have also attracted people’s attention.Different from these inorganic carriers,polyester fibers have the advantages of low cost and large-scale processing and production.They have been used for photocatalyst support,and are composed of long carbon chain structures.After being used as catalyst carriers,they can be further processed to prevent waste.The carrier brings secondary pollution.In this paper,PMS-AOP was combined with photocatalytic oxidation technology,and g-C₃N₄/TiO₂ composite photocatalyst was prepared by mixing g-C₃N₄ and TiO₂ by physical ball milling.Using cationically dyeable polyester fiber as a carrier,the composite catalyst was loaded onto the fiber by centrifugal-electrospinning technology to prepare g-C₃N₄/TiO₂@CDP catalytic fiber.Characterized by scanning electron microscope（SEM）,X-ray diffraction（XRD）and fourier transform infrared spectrometry（FTIR）,et al,the results showed that the g-C₃N₄/TiO₂ composite photocatalyst had been successfully prepared and loaded on the fiber.The photoresponse range of g-C₃N₄/TiO₂ catalyst was broadened by ultraviolet-visible diffuse reflectance（UV-vis）test.The catalytic performance of g-C₃N₄/TiO₂ catalyst and g-C₃N₄/TiO₂@CDP catalytic fibers were investigated using carbamazepine（CBZ）as degradation substrate.The results showed that g-C₃N₄/TiO₂ catalyst had excellent photocatalytic activity,and 5%g-C₃N₄/TiO₂（5%g-C3N4 vs TiO2）showed the best catalytic performance,meanwhile,g-C₃N₄/TiO₂@CDP could also effectively activate PMS for photocatalytic degradation of carbamazepine.Fluorescence spectroscopy（PL）test showed that the recombination speed of photogenerated electrons and holes of the g-C₃N₄/TiO₂ catalyst was significantly reduced.The degradation mechanism of g-C₃N₄/TiO₂ was investigated by trapping agent experiment and electron paramagnetic resonance（EPR）technique.·O₂^-,¹O₂,·OH and SO₄·^-radicals were the main active species in the catalytic system,among which·O₂^-and¹O₂ play a major role.In addition,the degradation process of CBZ was analyzed by ultra-performance liquid chromatography-mass spectrometry（UPLC-HDMS）,and some chemical bonds were broken to produce intermediate products which were further mineralized into CO₂,H₂O and small molecular acids.In order to study the self-degradation performance of the carrier used,the g-C₃N₄/TiO₂@CDP fiber was prepared by centrifugation-electrospinning technology,and the self-degradation experiment was carried out under the simulated for a long time.The results showed that g-C₃N₄/TiO₂@CDP fibers had self-degradation properties,and 5%g-C₃N₄/TiO₂ loaded fibers showed the best self-degradation properties.The g-C₃N₄/TiO₂@CDP fibers were characterized by SEM,TEM,XRD et al.The results showed that with the increase of illumination time,dense pores appeared on the surface of the fibers,the fibers were broken,and the catalyst was exposed.The change of the number-average molecular weight of g-C₃N₄/TiO₂@CDP fibers was investigated by ultra-performance polymer chromatography（APC）,and the results showed that the number-average molecular weight of the fibers decreased with the prolongation of illumination time.The degradation process of g-C₃N₄/TiO₂@CDP fibers was analyzed by UPLC-HDMS,and the results showed that the polyester carbon chain was destroyed,and short carbon chain substances were formed.This paper provides a new idea for the removal of organic pollutants in wastewater by using organic fiber carrier and the post-treatment of the carrier.