Finally we would like to stress that the anomalies of

2. Experimental
2.1. Materials
All chemicals were analytical grade, purchased from the commercial market, and used without further purification before utilization. The ferric salt (Fe(NO3)3·9H2O) and aluminum salt (Al(NO3)3·9H2O) solutions were filtered through a 0.22 μm millipore filter to remove any particulate contaminants before utilization. AB 74, MB and PR were of guaranteed reagent grade and they AS-604850 were used without further purification.
2.2. Synthesis
A series of Al-substituted hematite were prepared by co-precipitation method, followed by calcination at 600 °C. 100 mL of 2.0 mol/L Fe3+ solution were mixed with 0, 3, 8, and 14 mL of 2.0 mol/L Al3+ solution, respectively. Then 6.0 mol/L NaOH solution were added to the mixed solution dropwise until pH 9. The above process was carried out under vigorous stirring at room temperature. The gels were collected, thoroughly washed with deionized water and dried at about 50 °C. The xerogels were ground and sintered at 600 °C for 3 h.