Preparation And Photocatalytic Properties Of Nano-titanium Dioxide/Fly Ash Microspheres Composites

Fly ash is one of the large effluent solid waste produced by coal-fired thermal power plants and various large-scale boilers.Its open-air dumping takes up a lot of land resources and causes serious environmental pollution.In the formation of fly ash,due to the role of surface tension,fly ash particles are mostly hollow beads.Since the fly ash cenospheres?FACs?are hollow and large in size,the beads are porous,making it easy to be dispersed in solution,and inexpensive,so it can be used as an ideal carrier.TiO₂ is an n-type semiconductor photocatalytic material,its chemical properties are stable,insoluble,non-toxic,low cost,has a strong oxidative and reducible,it is widely used in photocatalytic treatment of organic or inorganic wastewater.At present,there are two main problems in the photocatalytic process of TiO₂: one is low photocatalytic and quantum efficiency,and the other is difficult to be separated and recovered due to the smaller particle size.Therefore,TiO₂ need to be modified and load,in order to improve its photocatalytic performance and recovery rate.In this paper,TiO₂/FACs were prepared by TiO₂ loaded with fly ash ?N-TiO₂/FACs were prepared by different methods using N element doping modified TiO₂ and g-C₃N₄/N-TiO₂/FACs were prepared by in-situ hydrolysis method.Study on the ability of composite materials to degrade methyl orange in visible light.This paper mainly includes the following three aspects:?1?Preparation of TiO₂/FACs Photocatalytic composites by Sol-Gel Method.The effects of the activation method of FACs,the type and amount of surfactants coated on FACs and the ratio of TiO₂ to FACs on the photocatalytic degradation of methyl orange were studied.It was found that the use of NaOH solution activated fly ash with the largest specific surface area?87.19 m2/g?;the mass ratio of TiO₂ to FACs was 1:1.5,the amount of surfactant SDBS was 20%when the catalyst TiO₂/FACs-1.5 had the highest degradation rate,and the degradation rate reached 52% at 180 min.?2?N-TiO₂/FACs composite photocatalytic material were prepared by sol-gel method,homogeneous precipitation method,in-situ hydrolysis method,hydrothermal method and ultrasonic hydrolysis method.The effects of preparation methods on the structural properties and photocatalytic activity of the composite photocatalytic materials were investigated.And the recycling performance of N-TiO₂/FACs was studied under the optimum preparation method.It was found that the N-TiO₂ particle size was the smallest and uniform in the FACs surface under in situ hydrolysis.The combine between N-TiO₂ andFACs is mainly physical adsorption.The prepared N-TiO₂/FACs-i composite photocatalytic material had the largest specific surface area and the minimum band gap?2.44 eV?;It was the best catalyzed by photocatalytic degradation of methyl orange.and the degradation rate reached 61% at 180 min.belongs to the first order reaction kinetic model.At the same time,cyclic experiments show that the catalyst has a strong stability,and the rate of degradation is basically the same after 6 times.?3?The photocatalytic composites of g-C₃N₄/N-TiO₂/FACs?CTF?were prepared by in-situ hydrolysis method.The effects of calcination temperature,calcination time and the ratio between g-C₃N₄ and N-TiO₂ on the photocatalytic activity of the catalyst were investigated,and the catalysts under the optimum conditions were characterized and photocatalytic experiments were carried out.It was found that 1:1-CTF-550?-3h had the maximum specific surface area?97.83 m2/g?and smallest band gap energy?2.75 e V?;The degradation rate of methyl orange reached 72% after 180 min of light,which was 1.3 times that of N-TiO₂/FACs and 3.5 times that of g-C₃N₄.Moreover,the composite photocatalytic materials are easy to disperse in the solution,easy to separate,recycle and reuse.Under the experimental conditions,the degradation rate is maintained above 63.2% after 7 times.