An Eco-friendly Conductive Fly Ash Geopolymer Composite: Synthesis And Photocatalytic Degradation Of Dye

Fly ash(FA)is the fine ash collected by the dust collector during the combustion of coal and is the main solid waste discharged from the thermal power plant.With the increase demand for electricity in national economic development at present,a large amount of fly ash has emerged at the right moment.Therefore,the high value-added resource utilization of fly ash enables not only to solve the environment pollution problem caused by the accumulation of large amounts of fly ash,but also to have of great significance for the construction of resource-conserving and environment-friendly society.This paper,the conductive carbon black/fly ash geopolymer(CCB/FAG)were prepared by use of FA as raw material,conductive carbon black(CCB)as the conductive medium and Na2SiO3·9H2O and KOH as the chemical alkaline activators.Subsequently,NiO loaded on the conductive fly ash-based geopolymers(NiO/CFAG)composites were synthesized by loading nano NiO semiconductor on the support of CFAG by wet impregnation method.NiO/CFAG composites were characterized by XRD,FESEM,FT-IR,TGA/DSC,XPS and other analysis methods;Finally,photocatalytic properties of NiO/CFAG composites were evaluated though the degradation of basic royal blue dye by response surface methodology(RSM).The results of XRD,FESEM and FT-IR showed that the mullite and amorphous aluminosilicate vitreous in fly ash reacted with the activator KOH and Na2SiO3·9H2O to produce a large amount of fly ash-based geopolymer.A possible reaction mechanism was proposed that amorphous aluminosilicate was dissolved in alkaline medium to form active tetrahedral monomers of [SiO4]4-and [AlO4]5-.Then,the new network structure of amorphous Si-O-Si(Al)was formed by polycondensation reaction between monomers.The electrically conductive property of FAG was improved significantly by incorporation of CCB.When the content of CCB was up to 4.5wt%,the CCB/FAG composite showed the best(0.64 S/m)electrical conductivity and possessed the compressive strength of 18 MPa in curing time of 3d.XRD characterization results showed that the CCB did not participate in the hydration reaction,it formed conductive network in the geopolymer matrix and played a significant role in the electron transmission.A series of NiO/CFAG composite catalysts with different contents of Ni O were synthesized by wet impregnation of Ni(NO3)2·6H2O on the carrier of NH4+-CCB/FAG.XRD and XPS results showed that the NiO dispersed on the surface of carrier in amorphous state when the NiO was less than 9wt%.There was Ni O crystal phase in NiO/CFAG composite catalyst when the content of NiO was 9wt% corresponding to nickelous binding energy of 2p3/2 and 2p1/2 at 853.2 eV and 871.2eV,repectively.The properties of photocatalytic degradation of basic royal blue dye by CCB/FAG were evaluated.The results showed that the photocatalytic degradation efficiency was improved by incorporation of CCB.The electrical conductivity was direct proportion to the degradation rate of dye.When the content of CCB was 4.5wt%,the degradation of dye approached to 82.79% at 120 min,indicating that the conductive carbon black played an important role in electron transmission and impelled the separation of photoelectrons from vacancies.The influences of dosage of the NiO/CFAG catalyst,dye concentration and the loading of NiO on the degradation rate were evaluated by response surface methodology.The results indicated that three factors affecting degradation rate showed as below: the loading of NiO > dye concentration > the dosage of catalyst,Under the optimal experimential condition,that is,the dosage of the catalyst was 0.07 g,the dye concentration was 20 mg/L,and the loading of NiO was 5wt%,the degradation rate reached 100%.The experimental result was extremely close to the predicted value,indicating that the regression model was reliable.