Preparation And Catalytic Performance Of Self-shielding Photocatalvtic Fiber Based On Graphitic Carbon Nitride

In recent years,increasing environmental pollution has received great attention,especially in water pollution.The emission of large amounts of organic pollutants poses a potential threat to human health and the ecological environment.Therefore,various methods are applied to water treatment.Among them,semiconductor photocatalysis technology is considered to be one of the most promising wastewater treatment technologies,which can eliminate organic pollutants at low cost and high efficiency.However,most photocatalysts exist in the form of powder,which is easy to agglomerate and difficult to recycle during use,so it is necessary to load them.Compared with inorganic materials,organic materials are considered to be ideal catalyst carriers due to their flexibility and high processability.However,some studies have reported that polymers can be photodegraded in the presence of some photocatalysts.For example,the strong oxidizing hydroxyl radicals(·OH)generated by titanium dioxide(TiO2)can cause damage to organic carriers.In addition,TiO2 can only absorb ultraviolet light in sunlight,resulting in low solar energy utilization,which limits its photocatalytic activity.In recent years,the two-dimensional sheet material graphitic carbon nitride(g-C3N4)has been extensively studied due to its low cost,non-toxicity,stable chemical properties and visible light response.But,the specific surface area of g-C3N4 is small and its quantum efficiency is low,which results in its low photocatalytic activity.Therefore,this work chooses g-C3N4 to coat the surface of organic carriers to avoid the corrosion of organic carriers by TiO2.At the same time,the interaction between TiO2 and g-C3N4 improves the photocatalytic performance of the material.Here,low melting point sheath-core polyester fiber(LMPET)was selected as the carrier,and two-dimensional sheet material g-C3N4 was coated on the surface of the LMPET and then loaded with TiO2 to prepare the g-C3N4-TiO2@LMPET photocatalytic fibers.The scanning electron microscope,X-ray photoelectron spectroscopy,infrared and other characterization methods showed that g-C3N4 was successfully coated on the surface of PET fibers,and TiO2 was uniformly supported on the surface of g-C3N4@LMPET.The results of photoluminescence and transient photocurrent experiments indicated that the combination of g-C3N4 and TiO2 inhibited the recombination of photogenerated electron-hole pairs.The result of UV-visible diffuse reflection test showed that g-C3N4 broadened the absorption range of the composite to visible region.Sulfaquinoxaline(SQX)and thiamethoxam were selected as the target substrates for photocatalytic degradation experiments.The experimental results showed that compared with g-C3N4@LMPET and TiO2@LMPET,g-C3N4-TiO2@LMPET had a significantly enhanced photocatalytic activity.Moreover,g-C3N4-TiO2@LMPET also exhibited good repeatability and stability.The photocatalytic degradation experiments of dihydroxyethyl terephthalate(BHET)by TiO2 and g-C3N4 as well as the UV irradiation experiments of PET catalytic fibers showed that compared with TiO2@LMPET,the g-C3N4 layer on the g-C3N4-TiO2@LMPET can indeed protect PET fiber from the corrosion of ·OH.Furthermore,the results of capture agent experiments and electron paramagnetic resonance(EPR)test showed that there were three kinds of active species ·OH,superoxide radical(·O2-)and hole(h+)in the reaction process,and?OH led to the deep oxidation of SQX and thiamethoxam.In order to further study the self-shielding photocatalytic fiber material based on g-C3N4,cotton fiber was selected as the carrier.However,g-C3N4 cannot be loaded on cotton fibers by padding-thermal bonding.In order to solve this problem,it is necessary to modify g-C3N4.First,g-C3N4 was carboxylated to obtain g-C3N4-COOH,and then an amidation reaction with a silane coupling agent KH-550 was carried out to obtain the photocatalyst with viscosity(g-C3N4-CONH-KH550).After that,the cotton cloth was immersed in its hydrolysate,and g-C3N4-CONH-KH550@cotton was obtained by padding-heat curing method,and then hydrothermal reaction was performed with the TiO2 solution to obtain TiO2/g-C3N4-CONH-KH550@cotton.The photocatalytic fibers were also characterized by scanning electron microscopy,X-ray diffraction,infrared,UV-visible diffuse reflection and other characterization methods.The results of UV light experiments and tensile strength tests showed that the g-C3N4-CONH-KH550 layer can effectively reduce the corrosion of cotton fibers by·OH generated by TiO2.Under solar irradiation,TiO2/g-C3N4-CONH-KH550@cotton exhibited excellent photocatalytic performance and good repeatability for the degradation of SQX and thiamethoxam.In this catalytic system,·O2-and h+were the main active species for the removal of SQX,while ·OH played an important role in the degradation of thiamethoxam.This research provides a new idea for constructing a highly efficient and stable supported photocatalytic material,which is expected to be applied to environmental treatment.