关键词: 氮掺杂二氧化钛, 聚丙烯熔喷非织造材料, 光催化, 亚甲基蓝, 自由基, 印染废水, 废水处理

Abstract:

Objective Titanium dioxide (TiO₂) has non-toxicity, low cost, and high photocatalytic activity. However, the photocatalytic ability of TiO₂ itself cannot reach the application level, and the powdered TiO₂ is difficult to recycle and reuse.Thus, it is difficult for TiO₂ to be practically applied in industrial fields. Polypropylene (PP) melt-blown nonwoven material with good chemical stability, low price, and simple manufacturing process has been widely used in air filtration, medical protection, and other fields. However, its single function limits its application. This research aims to improve photocatalytic ability and to tackle the recycling of TiO₂ by doping N with TiO₂ and then loading N-TiO₂ nanoparticles on the surface of PP melt-blown nonwovens.

Method N-TiO₂ photocatalyst was first prepared by sol-gel method, and the optimal doping amount of N was determined by studying the surface morphology, microstructure, chemical structure, and photocatalytic performance of N-TiO₂. The N-TiO₂ photocatalyst with the best performance was loaded on the surface of PP melt-blown nonwovens by ultrasonic impregnation method. The surface morphology, chemical composition and structure, and photocatalytic properties of N-TiO₂/PP composite melt-blown nonwovens with different N-TiO₂ loading concentrations were studied. The photocatalytic mechanism of N-TiO₂/PP composite melt-blown materials for organic dyestuff was verified and analyzed by free radical capture experiments.

Results The particle size of N-TiO₂ reached about 10 nm. N-TiO₂ with N doping amount of 1% was found to have the best photocatalytic performance for MB. After loading the optimal N-TiO₂ on the surface of PP melt-blown nonwovens, N-TiO₂ were found uniformly wrapped on the surface of PP fibers. The agglomeration of N-TiO₂ on the surface of PP fibers occurs when the loading amount of N-TiO₂ exceeds 30 mg. Compared with PP melt-blown materials, the water contact angle of N-TiO₂/PP composite melt-blown materials was significantly reduced, and the thermal stability was also improved. When the N-TiO₂ loading amount is 30 mg, the photocatalytic degradation rate of N-TiO₂/PP composite melt-blown material for MB reached 98% under the conditions of 30 min dark adsorption and 90 min photocatalysis. After trapping superoxide radicals (· {\mathrm{O}}_2^{-}) and hydroxyl radicals (·OH), the photocatalytic MB degradation efficiency of N-TiO₂ with 1% N doping were decreased by 22% and 23%, respectively. After being first used for the MB photocatalytic degradation, the crystalline structure and morphology of N-TiO₂/PP composite melt-blown nonwovens remained the same. After the fourth MB photocatalytic degradation, the photocatalytic degradation efficiency of the composite melt-blown material for MB was about 58%.

Conclusion Low N doping amount can effectively improve the photocatalytic performance of TiO₂. N-TiO₂/PP composite melt-blown material has proved to effectively degrade methylene blue dye. The composite melt-blown material has good stability and is recyclable. The research provides reference for expanding the application of PP melt-blown materials in the water treatment industry.

Key words: nitrogen doped titanium dioxide, polypropylene melt-blown nonwoven, photocatalytic, methylene blue, radical, dyeing and printing wastewater, wastewater treatment