Preparation Of N-TiO₂@PP Composite Melt-blown Nonwovens And Study Of Photocatalytic Properties

With the development of global industrialization,the environmental pollution has become increasingly severe.The textile industry is an important traditional industry in China,however,the dye wastewater generated by the textile industry poses a serious threat to global sustainable usage of water resource.Organic dyes are the main component of dye wastewater,so the preparation of low-cost and efficient organic dye degradation materials has become a research focus.Titanium dioxide（TiO₂）has become one of the most widely used photocatalysts in the field of environmental treatment due to the ideal photocatalytic activity,stability,non-toxicity,and low cost.However,TiO₂ has a large bandgap,and is not high for the utilization efficiency of the sunlight.The electron-hole pairs of TiO₂ are easy to recombine and lead to a decrease in its photocatalytic activity,which limits its application in the treatment of difficult-to-degrade pollutants.Nitrogen-doped TiO₂（N-TiO₂）can effectively enhance the photocatalytic activity of TiO₂ under visible light condition.In addition,TiO₂ has strong intermolecular forces and is easy to aggregate.Thus,it is difficult for TiO₂to disperse and exert its performance.Additionally,after being used in water treatment,TiO₂ cannot be effectively collected.Therefore,selecting a continuous carrier compounding with TiO₂is an effective method to solve this problem.Polypropylene（PP）melt-blown non-woven materials have simple processing technology,a large specific surface area,excellent mechanical properties,and high chemical stability.Therefore,PP melt-blown non-woven material can be selected as carriers,and N-TiO₂ can be loaded on the surface of PP melt-blown materials to prepare N-TiO₂@PP composite melt-blown materials for degrading organic dyes in wastewater.TiO₂ nanoparticles were first prepared by the sol-gel method and then mixed with urea in different mass ratios.The mixture was calcined by high-temperature calcination to prepare N-TiO₂ nanoparticles with different N doping contents,and were wet-milled.Through testing and characterization,the results showed that compared with TiO₂,the average particle size of the wet-milled N-TiO₂ nanoparticles was about 10 nm,the degree of aggregation increased.The proportion of anatase crystal phase to rutile crystal phase of N-TiO₂was higher than those of TiO₂.N atom were added to the TiO₂ crystal structure in the form of interstitial doping,which effectively improves the visible light absorption capacity of N-TiO₂.When the N doping content was 1%,the prepared N-TiO₂nanoparticles showed the best photocatalytic degradation efficiency for methylene blue（MB）of 98%under dark adsorption for 30 min and light irradiation for 90 min,and had the best pseudo-first-order reaction rate.Then,PP melt-blown non-woven materials were used as carriers,and N-TiO₂ with the best photocatalytic performance was used as a photocatalyst and loaded on the surface of PP melt-blown non-woven materials using ultrasonic impregnation to prepare N-TiO₂@PP composite melt-blown materials with different N-TiO₂ loading contents.Through testing and characterization,the results showed that after being loaded on the surface of PP melt-blown non-woven materials,N-TiO₂ could be wrapped on the surface of PP fibers.When the loading content of N-TiO₂ exceeded 30 mg,N-TiO₂ particles started to aggregate on the surface of PP fibers.Compared with pure PP melt-blown non-woven materials,the thermal stability of the composite melt-blown non-woven materials was improved and the water contact angle significantly decreased.The N-TiO₂@PP composite melt-blown material with a loading content of 30 mg exhibited the optimal photocatalytic degradation performance.Under the conditions of 30 min dark adsorption and 90 min light irradiation conditions,the degradation efficiency of N-TiO₂@PP composite melt-blown material for MB reached 98%.Through free radical trapping experiments,it was determined that N-TiO₂ generated superoxide radicals（·O₂^-）and hydroxyl radicals（·OH）under light excitation condition,and these two radicals worked together to achieve MB degradation.The stability experiments showed that the structure of N-TiO₂@PP composite melt-blown nonwoven materials remained intact after the first photocatalytic degradation for MB.After the fourth photocatalytic degradation,the photocatalytic degradation efficiency for MB was approximately 58%.To further improve the dispersion of N-TiO₂ on the surface of PP melt-blown materials and the organic dye degradation performance of the N-TiO₂@PP composite melt-blown materials,biomass carbon（BC）was prepared by alkali activation and high temperature carbonization of bagasse.Then N-TiO₂/BC composite material were prepared by the ultrasonic mixing.N-TiO₂/BC composite material was loaded on the surface of PP melt-blown nonwoven materials to obtain N-TiO₂/BC@PP composite melt-blown nonwoven material were prepared by the ultrasound-assisted impregnation.The results from testing and characterization showed that BC had a micrometer-level porous laminar structure and the certain degree of graphitization.The dispersion of N-TiO₂ in N-TiO₂/BC composite materials was significantly improved,and the N-TiO₂/BC composite materials could be uniformly loaded on the surface of PP melt-blown nonwoven materials.BC had good UV-visible light absorption ability.After BC was added,the visible light absorption ability of N-TiO₂ was further enhanced.Compared to N-TiO₂@PP composite melt-blown nonwoven materials,N-TiO₂/BC@PP composite melt-blown materials also showed a significant enhancement of light absorption ability.Under the 30 min dark adsorption condition,the addition of BC increased the adsorption efficiency of N-TiO₂/BC composite materials for MB.Under the 90 min light irradiation condition,the degradation efficiency of N-TiO₂/BC composite materials for MB was also increased.When N-TiO₂/BC was loaded on the surface of PP melt-blown nonwoven material,N-TiO₂/BC@PP composite melt-blown nonwoven materials showed the high photocatalytic degradation efficiency of MB.