Development of zinc oxide functionalized fly ash based geopolymer for photodecomposition of methylthioninium chloride dye

Abstract

Zinc oxide functionalized fly ash geopolymer paste was prepared through in situ method by using mixed solution of sodium hydroxide(NaOH) and sodium silicate(Na2SiO3) of modulus Ms : 1.1 and its mechanical properties including compressive strength as well as photo catalytic removal of methylthioninium chloride dye in the waste water were investigated. Fly ash geopolymer , control samples (G1) having a base strength of 35.2 MPa at room temperature, gained strength to 55.6MPa in Zinc oxide incorporated matrix (G2). Raw fly ash, zinc oxide catalyst and geopolymer matrices were characterized by XRD, FTIR..Geopolymeric amorphous phases identified from the halo in the 2theta value at 22-28 along with crystalline phases of mullite and quartz. The zinc oxide phases embedded in the amorphous bonding gel are stabilized by changing the sodium ions in G2 to maintain the charge balance and by integrating with non-bridging oxygen.The fingerprint IR band of geopolymer, Si-O-(Si or Al) stretching frequency appeared at 1027 cm−1 in G1 and further lowered to 990 cm-1 in.G2 evidenced the change in bond length of Si-O-(Si or Al) of fly ash (1057 cm-1) due to the incorporation of Al in the network. Photo catalytic function of the zinc oxide doped geopolymer verified by UV-DRS spectra. The performance of the photocatalytic system on the methylthioninium chloride, a model dye, employing G2/UV light was observed to be better than G1/UV. The complete decolourization was observed after 100 min in pure ZnO whereas with G2 only50% of dye degradation and in G1 it is 34% in 100 min. In the case of fly ash raw materials, adsorption of the dye on the surface was notified for the same duration. Thus zinc oxide incorporation improved the adsorption cum photo degradation of dye in the fly ash geopolymer.