The Preparation And Properties Of Geopolymer-based Photocatalytic Membrane

Circulating fluidized bed fly ash is the fly ash collected from flue gas when circulating fluidized bed boiler burns low-grade coal fuel,and its emissions gradually increase with the promotion and use of circulating fluidized bed boiler.The existing resource utilization has some disadvantages,such as low added value or complicated disposal process.It is one of the effective ways to realize the efficient resource utilization of geopolymer by using circulating fluidized bed fly ash as raw material,using its potential volcanic ash activity,and further researching the high value-added application of geopolymer.As a new type of chemically activated inorganic cementitious material,geopolymer has a unique three-dimensional network structure,endowing it with high strength,corrosion resistance,high temperature resistance and other properties,and rich internal pore structure,so that it can be used as an inorganic membrane material in water treatment and other fields to achieve high-value utilization..In this paper,using circulating fluidized bed fly ash as raw materials,two kinds of geopolymer membrane materials were prepared by using alkali activator and acid activator respectively,and they were used in wastewater treatment of cationic dyes and anionic dyes.The main research results were as follows:（1）The compressive strength of alkali-activated geopolymer decreases with the increase of water-cement ratio,and the maximum compressive strength was 42.75 MPa when the water-cement ratio was 0.3.The compressive strength of acid-activated geopolymer first increased and then decreased with the increase of acid concentration,and the maximum compressive strength was 38.08 MPa when the concentration of phosphoric acid was 6 mol/L.The strength of the corresponding proportions of geopolymers after heat treatment was 39.75 MPa and 34.25 MPa,respectively,which could meet the strength requirements of self-supporting inorganic membrane.Experimental analysis shows that the geopolymer membranes has an amorphous gel phase and mesoporous structure.（2）The alkali-activated geopolymer membrane had stable retention rates（≥99%）for the four cationic dyes before heat treatment,and stable retention rates（≥99%）for the two cationic dyes methylene blue and methyl violet after heat treatment.The acid-activated geopolymer membrane had stable retention rates（≥99%）against anionic dyes titan yellow,eosin Y and methyl blue before heat treatment,stable retention rates（≥99%）for cationic dyes methylene blue,basic orange and methyl violet after heat treatment,and stable retention rates（≥99%）for anionic dyes titan yellow.（3）Alkali-activated geopolymer photocatalytic membrane（CdO/Al GM）and acid-activated geopolymer photocatalytic membranes（Ag₃PO₄/AcGM）were prepared by interception method,respectively.Within 180 min,the degradation rates of CdO/Al GM and Ag₃PO₄/AcGM static photocatalytic degraded methylene blue solution were 68.7%and 73.4%,respectively.Under negative pressure of 0.08MPa,when CdO/Al GM and Ag₃PO₄/AcGM photocatalytic-membrane separation co-degradation of methylene blue solution,CdO/Al GM achieved complete degradation of dye after 140 min,Ag₃PO₄/AcGM achieved complete degradation of dye after 40 min.