Preparation Of Amorphous Iron Doped Hydroxyapatite And Its Photocatalytic Performance For Degradation Of Dye Pollutants In Water

Synthetic dye is one of the most persistent pollutants in environment for their stable chemical structures and high resistance to microbial degradation. Semiconductor photocatalytic technique is one of ideal methods for the treatment of dye pollutants by the characters of utilizing solar energy directly and making organic pollutant mineralize completely. A ideal semiconductor photocatalyst would have enough surface active sites and can utilize visible light. However, most current studies are focused on crystallized semiconductor photocatalysts, and the calcination necessary for their preparation slows down their industrial application for the decrease of surface area and surface active sites. Meanwhile, amorphous materials are getting more attentions for the advantages of simple preparation, unnecessary calcination and remarkable surface area. Therefore, the study on treating dye pollutants with cheap and harmless amorphous materials would be valuable in both scientific researches and industrial applications.In this paper, a large surface area amorphous semiconductor photocatalyst Fe（Ⅲ）–HAP₅₀ was prepared from cheap Fe（Ⅲ） ions and hydroxyapatite via simple ion-exchange method. The amorphous Fe（Ⅲ）–HAP₅₀ with the largest surface area（204m2/g）, uniform pore size distribution and stable photocatalytic activity was obtained at room temperature, 50mmol/L Fe（Ⅲ） ions and 15 minutes fast stirring. The as prepared Fe（Ⅲ）–HAP₅₀ was suggested a high degree of Fe（Ⅲ）-substituted HAP by the microstructure of nanocrystalline embedded in the amorphous environment. The pore size distribution calculated by the nonlocalized density functional theory suggested that the high surface area of Fe（Ⅲ）–HAP₅₀ is related to the special structure of it.The photocatalytic performance of Fe（Ⅲ）–HAP₅₀ was evaluated under visible light and significant results were obtained for the degradation of methylene blue（MB）, rhodamine B（Rh B） and acid blue（AB62）. The photocatalytic performance of Fe（Ⅲ）–HAP₅₀ was higher than that of amorphous Fe PO4·2H2O. Meanwhile, the performance of Fe（Ⅲ）–HAP₅₀ under H2O2 was evaluated by the treatment of methylene blue simulating dye wastewater with high concentration of inorganic salts and high p H, as presented in real dye wastewater. A competitive adsorption among Na+,Ca2+,Mg2+and MB molecular was suggested, and the effects of Cl-,SO42-and NO3- on the degradation of MB were neglected. The disadvantages of HCO3-and CO32- can be decreased in the real p H range of dye wastewater. Meanwhile, the degradations of MB,（Rh B） and（AB62） was evaluated with Fe（Ⅲ）–HAP₅₀ and H2O2 under real outdoor solar light. The performance of Fe（Ⅲ）–HAP₅₀ under solar light was demonstrated better than that under visible light.A photocatalytic mechanism of Fe（Ⅲ）–HAP₅₀ was also investigated with methylene blue as a probe molecular. The Fe O（OH）–like cluster on the surface of Fe（Ⅲ）–HAP₅₀ was suggested to be the surface active site by the fact that these independent Fe O（OH）–like cluster did not act in photocatalytic process and the activity of Fe（Ⅲ）–HAP₅₀ decreased dramatically after calcination. The photocatalytic activity of Fe（Ⅲ）–HAP₅₀ was suggested to be the synthetic effect of both bulk semiconductor and these surface Fe O（OH）–like clusters. Meanwhile, the photosensitization effect of MB was ruled out by a test with monochromatic visible light centred at 600 nm. In order to investigate the effect of surface Fe O（OH）–like cluster, a hydroxyl protector n-butanol was used to cover these active sites and the degradation of MB and H2O2 were monitored at the same time. The existence of peroxide complex was proved by the spectra characterization of Fe（Ⅲ）–HAP₅₀ during MB degradation.Finally, a pathway of MB on the Fe O– sites involving a electronic reorganization and a sulfoxide intermediate product was suggested by a combination of UV-vis scan and GC-MS techniques. Meanwhile, a discussion about the decomposition of surface Fe（Ⅲ）–peroxo complexe was conducted and a photocatalytic mechanism of Fe（Ⅲ）–HAP₅₀ was proposed.