Zheng Ting-Ting, Sun Zhong-Xi, Yang Xiao-Fang, Holmgren Allan
School of Chemistry and Chemical Engineering, University of Jinan, 250022, Jinan, China.
Chem Cent J. 2012 Apr 3;6(1):26. doi: 10.1186/1752-153X-6-26.
Due to the extensive use of phosphates in industry, agriculture and households, the phosphate - γ-alumina interactions are important for understanding its detrimental contribution to eutrophication in lakes and rivers. In situ Fourier transform infrared (FTIR) spectroscopy can provide more detailed information on the adsorbate-adsorbent interaction and the formation of hydrogen bonds.
In situ ATR-FTIR spectroscopy was used to identify phosphate complexes adsorbed within the three-dimensional network of mesoporous γ-alumina at pH 4.1 and 9.0. The integrated intensity between 850 cm-1 and 1250 cm-1 was used as a relative measure of the amount of adsorbed phosphate. The integrated intensity proved to be about 3 times higher at pH 4.1 as compared with the corresponding intensity at pH 9.0. The adsorption of phosphate at the two pH conditions could be well described by the Langmuir adsorption isotherm at low concentrations and the empirical Freundlich adsorption isotherm for the whole concentration range, viz. 5 - 2000 μM.
From the band shape of infrared spectra at pH 4.1 and pH 9.0, it was proposed that the symmetry of the inner-sphere surface complex formed between phosphate and γ-alumina was C1 at the lower pH value, whilst the higher value (9.0) implied a surface complex with C2v or C1 symmetry. The difference in adsorbed amount of phosphate at the two pH values was ascribed to the reduced fraction of ≡ AlOH2+ surface sites and the increased fraction of ≡ AlO- sites upon increasing pH from 4 to 9.
由于磷酸盐在工业、农业和家庭中的广泛使用，磷酸盐与γ-氧化铝的相互作用对于理解其对湖泊和河流富营养化的有害影响至关重要。原位傅里叶变换红外（FTIR）光谱可以提供有关吸附质-吸附剂相互作用和氢键形成的更详细信息。
采用原位衰减全反射傅里叶变换红外光谱（ATR-FTIR）来识别在pH值为4.1和9.0时吸附在介孔γ-氧化铝三维网络内的磷酸盐络合物。850 cm-1至1250 cm-1之间的积分强度用作吸附磷酸盐量的相对度量。结果表明，与pH值为9.0时的相应强度相比，pH值为4.1时的积分强度高出约3倍。在低浓度下，两种pH条件下磷酸盐的吸附可以用朗缪尔吸附等温线很好地描述，而在整个浓度范围（即5 - 2000 μM）内则可以用经验弗伦德利希吸附等温线描述。
根据pH值为4.1和9.0时红外光谱的谱带形状，提出在较低pH值下，磷酸盐与γ-氧化铝之间形成的内球表面络合物的对称性为C1，而较高pH值（9.0）意味着表面络合物具有C2v或C1对称性。两个pH值下磷酸盐吸附量的差异归因于pH值从4增加到9时≡AlOH2+表面位点分数的降低和≡AlO-位点分数的增加。
