Photocatalytic phenol removal in the phenol-urea-formaldehyde solution on cyanamide modified iron (III) oxide

Abstract

Phenolic resin waste contains harmful chemical compounds such as phenol,urea, and formaldehyde that need to be treated before disposal. In this study, a seriesof cyanamide modified Fe2O3 was prepared from FeCl2.4H2O as the iron precursorand cyanamide (CYA) as the carbon and nitrogen source. The cyanamide modifiedFe2O3 was used for photocatalytic removal of phenol in the mixture of phenol-ureaformaldehyde.X-ray diffractometry patterns showed the formation of Fe2O3 peak.The peak intensity decreased with the increased of cyanamide mol ratio. The additionof cyanamide decreased the band gap energy of Fe2O3, showing that carbon andnitrogen-based material might act as a dopant. The presence of carbon species wasconfirmed by diffuse reflectance UV-visible and Fourier transform infraredspectroscopy, as well as thermogravimetric analysis, especially on sample with highmol ratio of cyanamide precursor. Photoluminescence study revealed that addition oflow mol ratio of cyanamide successfully decreased the electron-hole recombination,while the addition of high mol ratio of cyanamide might block the emission sites ofFe2O3. Scanning electron microscope images of the samples also confirmed thatsamples with high mol ratio of cyanamide have a flake-type structure that coated thesurface of Fe2O3. In the photocatalytic removal of phenol both under UV and visiblelight irradiation, all prepared samples gave better photocatalytic activity than thebulk Fe2O3. The best activity was achieved on Fe2O3-CYA(6) catalyst with the molratio cyanamide to iron precursor of 6, in which the percentage of phenol removalwas 75 and 80% under UV and visible light, respectively. The high activity would bedue to the success suppression of electron-hole recombination, decrease of the bandgap energy, and the good interaction between phenol and emission sites of Fe2O3-CYA(6) catalyst, as supported by the fluorescence quenching study. Thephotocatalytic activity for phenol removal decreased in the presence of urea,formaldehyde, and urea-formaldehyde since there were adsorption competition aswell as reaction competitions, such as oxidation of formaldehyde and formation ofphenolic resin.