Photocatalytic Cementitious Material And Its Air Cleanerresearch

Photocatalysis is one of the promising techniques for large scale air pollution management and indoor air purification.Research on photocatalytic cementitious materials?PCM?could significantly accelerate the practical application of photocatalysis in environmental protection field,considering the advantages of cement based materials,such as wide application range and large consumption.With the cooperation between photocatalyst and substrate,how to maintain the original photocatalytic performance and the stability of cooperation are essential research focuses.In this paper,porous magnesuim oxychloride cement?PMOC?was chosen as cementitious substrate,and Degussa P25-TiO₂as the photocatalyst.Taking account of complexity of cement hydration environment,influences of cooperation microstructure on loading effect had been systematically studied.Meanwhile,based on the enhancement mechanism of adsorbent,cooperation structure between photocatalyst and cementitious substrate had been optimized.In the end,further exploration of practical application methods of photocatalysis had been conducted.The main works and research achievements were as follows:Based on the characteristics of hydration environment of cementitious material,hydration mechanism and crystals development of magnesuim oxychloride cement?MOC?had been analyzed,and then a method of constructing various surface microstructures by controlling hydration reaction process before loading TiO₂ was invented.Phase composition,microstructure,loaded mass of TiO₂,pore distribution and catalytic degradation had been measured to characterize the prepared PCM.Under different substrate microstructures,cooperation mechanism was analyzed.The results showed that controlling hydration process could effectively regulate the substrate surface microstructure,which had a dispersive action on TiO₂ nanoparticles during the loading process.Various cooperation effects between photocatalyst and substrate were obtained by loading TiO₂ on PMOC at different hydration process.With the development of phase 5?main hydration product of PMOC?,its outward crystal whiskers could facilitate the dispersion of TiO₂ on substrate surface by the overlap joint effect.TiO₂ loaded mass,pore structure and specific surface area had also been affected by loading effect.In order to realize the optimization of PCM pore structure and the improvement of catalytic reaction mass transfer,PCM preparation method had been modified based on the absorbent enhancement mechanism.Active carbon was chosen as the absorbent,and its photocatalytic functionalization methods were studied and fixed.After the photocatalytic functionalization,composite catalyst,TiO₂/AC,was prepared,whose microstructure and performances had been characterized.With the cooperation between TiO₂/AC and PMOC,composite structure and collaborative mechanism were studied systematically to determine the optimal cooperation parameters.The AC pretreatmentprocedurescontainedcrushing,acidpickling,negative pressure-ultrasonic dispersing cooperation between AC and TiO₂,thermal treatment.The optimal mass proportion was AC:TiO₂=4:25,with optimal treatment temperature of 350?.According to the photocatalytic degradation texts,excessive TiO₂ could lead to adversely high agglomeration,which may accelerate the recombination of photo-induced electrons and pores.With negative pressure-ultrasonic dispersing cooperation,TiO₂ was thoroughly dispersed on the active carbon surface.However,the surface pores were blocked simultaneously,causing the loss of adsorption capacity.TiO₂/AC with proper thermal treatment had better collaborative effect because of the modification of TiO₂ agglomeration on AC surface.Thermal treatment with lower temperature had restricted adsorption capacity;with higher temperature,adsorption was too strong to collaborate with photocatalytic reaction,considering the collaborative mechanism of adsorption-mass transfer-photocatalytic reaction.TiO₂/AC was introduced into PMOC substrate by one-take formation technology,the experimental optimal density were 0.35g/cm3,and mixing amount 4w.%.Systematic analysis indicated that TiO₂/AC mixing amount,substrate density and stable pore structure were supposed to be coordinated to realize the best adsorption and photocatalytic performances.Increasing the mixing amount of TiO₂/AC did not necessarily mean the enhancement of purification performances;instead,excessive dosage could lead to the adversely high agglomeration and the destruction of substrate pore structure.Three patterns of purification sheets and four air cleaners with different structures were designed.Purification effects of various combinations between purification sheets and air cleaners had been evaluated,as well as the main factors of photocatalysis-applying air cleaner.The optimal combination and feasible technical route to improve purification performance were determined.Analysis based on photocatalytic reaction kinetics revealed that mass transfer of target gas pollutants and reaction adsorption process had significant influences,which could be improved by modifying machine structure and enhancing adsorption capacity of substrate.On the other hand,photocatalytic reactive area could be enlarged by adding more PCM purification sheets on condition that mass transfer and adsorption capacity were guaranteed.In the end,the designed purification sheet and air cleaner were sent to National Building Materials Testing Center to acquire third-part certification.Results of the third-part certification indicated the highly effective purification capacity of designed purification sheet and air cleaner,which shows a competitive potential as compared to similar market products.