Study On Structural Regulation And Photocatalytic Behavior Of Ti-bearing Blast Furnace Slag

The treatment of toxic and refractory organic pollutants in industrial wastewater is an urgent problem in the field of environmental treatment.Photocatalytic degradation with titanium containing functional materials is a promising water treatment technology.Titanium-bearing blast furnace slag（TBFS）generally contains high Ti O₂（5-25 wt.%）,which is a good resource to prepare titanium containing photocatalyst.In this paper,the structure and performance regulation mechanism of new-typed materials prepared from TBFS,and the technical path of photocatalytic degradation towards organic pollutants were systematically studied,which has theoretical and practical significance for the full resource utilization of TBFS and efficient treatment of organic wastewater.TiO₂/zeolite photocatalysts were prepared by different commercial aluminosilicate zeolites（X-type,Y-type and ZSM-5-type）as carriers.Methyl orange solution（MO）was chosen as model organic pollutant to characterize photocatalytic performance under ultraviolet light.The effects of zeolite types,loading methods and preparation conditions on the performance of Ti O₂/zeolite photocatalyst were thoroughly investigated.ZSM-5 zeolite is regarded suitable for photocatalyst support and can be used as the target product of comprehensive utilization of TBFS.Titanium containing zeolite and hydrotalcite-like materials with excellent adsorption and photocatalytic properties were developed from TBFS,which provided a new idea for the full resource utilization of TBFS and efficient treatment of organic wastewater.High purity Ti-ZSM-5 zeolite was achieved from TBFS by"acid leaching-seed assisted hydrothermal synthesis"method.The effects of silicon aluminum ratio,water silicon ratio,crystallization temperature and time on the crystallization of ZSM-5 zeolite were investigated;the structural change law of Ti-ZSM-5 zeolite in the synthesis process and structural regulation mechanism were expounded thoroughly.Under the conditions of silicon aluminum ratio of 27,water silicon ratio of 50,sodium silicon ratio of 0.12,crystallization temperature of 170°C and crystallization time of 48h,a single spindle Ti-ZSM-5 zeolite can be obtained,of which the ratio of Si:Al:Ti is 1:0.0463:0.0324.Titanium species is in the form of skeleton titanium and anatase Ti O₂.Furthermore,the synthesized Ti-ZSM-5 zeolite showed photocatalytic performance,and the photodegradation efficiency of MO reached 45%after illumination for 90 min.Zeolite based photocatalysts,Ti O₂/ZSM-5 and g-C₃N₄-Ti O₂/ZSM-5（TCNZ）,were prepared by"solid phase diffusion（SSD）&calcination"method,which realized the effective regulation of energy band structure and enhanced photocatalytic performance.Through SSD and calcination at 450°C,specific surface area,the light capture efficiency and charge separation/transmission efficiency of Ti O₂/ZSM-5 can be significantly improved,resulting in its optimum photocatalytic performance,which is66.7%higher than that of uncalcined ones.As researched,the action mechanism of"SSD&calcination"on photocatalyst is to increase MO adsorption sites and photocatalytic action sites on zeolite surface in TCNZ,promote the direct interaction between Ti O₂ and g-C₃N₄,shift the valence band of TCNZ towards positive position,narrow the energy band gap of TCNZ,reduce the recombination rate of photogenerated electron-hole pairs,and improve the oxidation capacity of photogenerated holes.Above mentioned enhanced the response of TCNZ to visible light.Hydrotalcite-like materials（LDHs and LDOs）were successfully fabriated from the acid leaching solution of Ti-ZSM-5 zeolite by"coprecipitation&roasting"method,which realized the full resource utilization of TBFS.The results showed that the LDH-100 sample exhibited the best layered structure and optimal adsorption performance.After coprecipitation at 100°C,the yields of Ca,Mg,Al and Ti in the leaching solution reached 72.33%,99.24%,95.60%and 99.84%,respectively.The amount ratio of each element component in LDH-100 sample was:Ca:Mg:Ti:Al=1:0.533:0.464:1.013;the adsorption capacity of MO was about 5.2 mg/g;the adsorption process of MO by the LDHs accorded with the quasi second-order kinetic model.After calcination,LDHs with low adsorption capacity can be transformed into LDOs materials with excellent adsorption performance and photocatalytic activity.When the calcination temperature was lower than 550°C,the synthesized LDOs was mainly amorphous layered metal mixed oxide.While LDH-100 sample would be transformed into composites containing perovskite phase after calcined at 650°C.Moreover,LDO-550 had the best photocatalytic performance and LDO-450 showed the best adsorption capacity of MO,approximately 4.4 times higher than that before calcination.The kinetic analysis showed that the adsorption process of LDOs conformed to the quasi first-order reaction kinetic model,and the reaction rate constant was 0.0297 min^-1.