Study On The Structure And Properties Of Iron And Aluminum Oxides Doped With Boron

Goethite(G), Al hydroxide, Goethite adsorbed boron (ad-B-Goethite or ad-B-G), Goethite occluded boron(oc-B-Goethite or oc-B-G) and Aluminium hydroxide occluded boron(oc-B-Al hydroxide) were synthesized. ad-B-G was prepared by adsorption of the original goethite to B in borax solution, oc-B-G and oc-B-Al hydroxide were prepared in the presence of boric acid solution by hydrolyzation. Composition, morphology, structure and properties of goethite and Al hydroxide doped with boron were discussed; Al³⁺ adsorption on goethite and goethite doped with boron, Mn²⁺ adsorption on Al hydroxide and oc-B-Al hydroxide, and adsorption and degradation of aniline on goethite and goethite doped with boron were studied. The main results for the study were:1) The IR bands of Fe-OH-Fe, Fe-OH in-plane bending, and the IR bands of free OH of ad-B-goethite and oc-B-goethite were weaker than those of the original goethite. The IR bands of bending modes of trigonal and tetrahedral B were found in oc-B-goethite and ad-B-goethite. The results suggested that boron in boron-doped goethites replaced some free OH groups of the original goethite.2) Analysis of XRD patterns indicated ad-B-goethite remained the characteristic ofα-FeOOH, while oc-B-goethite did not. XPS region spectrum of O_1S, Fe_3S, Fe_3p and Fe_2P of ad-B-goethite, oc-B-goethite were different with goethite for boron doping. Judging by TEM graphs, the particle of oc-B-goethite was smaller than that of goethite. The specific surface area of goethite, ad-B-goethite and oc-B-goethite was in the order of oc-B-goethite>goethite>ad-B-goethite. All those support the hypothesis that ad-B-goethite remainedα-FeOOH, however, oc-B-goethite may be a different mineral.3) The isotherms of Al³⁺ adsorbed by goethite and goethite doped with boron at 15℃and 25℃were in good agreement with Langmuir equation, Al³⁺ adsorptive reactions were endothermic and the enthalpy of Al³⁺ sorption on goethite, ad-B-goethite and oc-B-goethite were 27.56 kJ/mol, 23.18 kJ/mol and 49.93 kJ/mol, respectively. Al³⁺ adsorption amount of the original goethite and boron-doped goethites all increased with pH, boron-doped goethites always adsorbed more Al³⁺ than the original goethite at the same pH solution. Therefore, boron-doped goethites should be helpful in reducing the toxicity of Al³⁺ in acidic soil.4) The isotherms of aniline on goethite and goethite doped with boron at 25℃were in good agreement with Langmuir equation, aniline adsorption amount of the original goethite, ad-B-goethite and boron-doped goethites was in the order of oc-B-goethite> goethite> ad-B-goethite. Aniline degradation was fast under higher temperature and higher aniline concentration, it was very fit for H-L equation in visible light/iron oxides and it had highest degradation effect about pH=5. The catalysis on aniline degradation was in the order of oc-B-goethite> ad-B- goethite> goethite. Aniline degradation prefer visible light /H₂O₂/ iron oxides to visible light/ iron oxides. Aniline degradation was fit for H-L equation in UV/iron oxides excellently. The catalysis on aniline degradation was in the order of oc-B-goethite> goethite> ad-B-goethite. Nitrobenzene, azobenzene, 4-nitro-6-formaldehydel-hexanoic acid and aminophenol were main intermediates of degradation of aniline.5) Analysis of XRD patterns indicated that oc-B-Al hydroxide was more poorly crystalline boehmite than the Al hydroxide. TEM observation showed that the Al hydroxide and oc-B-Al hydroxide had different morphology. Analysis of TEM and XRD all demonstrated that the presence of boron significantly decreased the size of Al hydroxide particles. The specific surface area of oc-B-Al hydroxide using BET method was larger than that of Al hydroxide. The IR band of Al-OH at 1074 cm^-1 of oc-B-Al hydroxide was weaker than that of Al hydroxide. The results suggested that boron in boron-doped Al hydroxide replaced some free OH groups of the Al hydroxide. The qualification of the peak intensities by XPS revealed that the surface atomic ratio of Al : O : B of oc-B-Al hydroxide was 29.56 : 66.9 : 3.45. Curve-fitted B(ls) XPS spectrum of oc-B-Al hydroxide demonstrated that the boron atom was probably incorporated with Al hydroxide to some extent. Oc-B-Al hydroxide always adsorbed more Mn²⁺ and stabilized the sample solution pH to a higher value than Al hydroxide, therefore, oc-B-Al hydroxide should be helpful in reducing the toxicity of Mn²⁺ in acidic soil and slow soil acidification.