Study On Preparation And Photocatalytic Properties Of Alkali-activated Granulated Blast Furnace Slag-based Conductive Cementitious Composite

Granulated blast furnace slag（GBFS）is a major industrial by-product produced in the blast furnace smelting process of pig iron,and it is also a valuable mineral resource.According to the requirements of developing cyclic economy,the high value-added resourceful utilization of slag has become an important way for the sustainable development of Chinese iron and steel enterprises.In this paper,GBFS was used as a raw material,NaOH as alkaline activator and conductive carbon black（CCB）as conductive medium to prepare the alkali-activated slag-based conductive cementitious composite（ASCCC）.Subsequently,CaWO₄/ASCCC catalysts were synthesized by loading nano CaWO₄ semiconductor on the support of ASCCC by incipient wetness impregnation method.CaWO₄/ASCCC catalysts were characterized by XRD,FESEM,FT-IR,TGA/DSC,XPS,N2 adsorption-desorption and other analysis methods.Finally,the photocatalytic degradation performances of CaWO₄/ASCCC catalysts were evaluated by response surface methodology（RSM）.XRD,FESEM and FT-IR results showed that the GBFS reacted with NaOH to principally form the hydrated calcium silicate（Ca2SiO₄·H2O）,hydrated calcium aluminate（Ca4Al2O7·xH2O）and amorphous alkali-activated slag-based cementitious material（ASCM）.CCB played a role in filling the micropores of ASCCC hydration products and improves the mechanical properties of ASCCC.As the doping content of CCB was 1.5wt%,the compressive strength was 53.3 MPa for the curing period of 3 days,the electrical conductivity was 0.03 S/m.While the doping content of CCB was 4.5wt%,the compressive strength was 29.6 MPa for the curing period of 3 days,and the electrical conductivity was 1.04 S/m.With the development of curing period,the electrical conductivity was very stable which was not changed with the curing time.The mass of CCB nanoparticles which wrapped the surface of slag particles,affected the hydration reaction,and resulted in the compressive strength decrease of material.The CaWO₄/ASCCC catalysts with different contents of CaWO₄ were synthesized by incipient wetness impregnation（NH4）6W7O24·6H2O on the support of NH4+-ASCCC.The XRD and SEM results indicated that the W7O246-ion in the impregnation liquid completely reacted with Ca4Al2O7·xH2O to form CaWO₄ so that the mineral phase of Ca4Al2O7·xH2O was disappeared.The pore size distribution results showed the mesoporous volume percentage of CaWO₄/ASCCC catalyst was slight decrease and the macroporous volume percentage of CaWO₄/ASCCC catalyst was slight increase.The loading of CaWO₄ can have a certain regulation effect on the pore size structure of catalyst.The photocatalytic degradation activities of different CaWO₄/ASCCC catalysts were studied.The results showed that the doping of CCB could greatly improve the photocatalytic degradation efficiency of ASCCC catalyst for direct sky blue 5B dye,and electrical conductivity of CCB/ASCCC cementitious material was direct proportion to the degradation rate of dye.The effects of the amount of catalysts,the loading of active components and the concentration of dye on the degradation rate of the dye were investigated by response surface methodology（RSM）.The main factors affecting the degradation of dye were as follows: the dosage of catalyst > CaWO₄ loading > dye concentration.The optimal experimental condition was 0.6 g of catalyst,5wt% of CaWO₄ loading,40 mg/L of dye concentration which was extremely close to the predicted value and the regression coefficient R2 was up to 0.9952,implying that the regression model has great reliability.The catalyst of 5CaWO₄/ASCCC with the smallest band gap showed the best photocatalytic degradation activity and the direct sky blue 5B dye was completely degraded.