The effects of hematite nanoparticles concentration (0-1600 mg/L) and initial pH (4.0-10.0) on hydrogen production were investigated in batch assays using sucrose-fed anaerobic mixed bacteria at 35 degrees C. The optimum hematite nanoparticles concentration with an initial pH 8.48 was 200 mg/L, with the maximum hydrogen yield of 3.21 mol H(2)/mol sucrose which was 32.64% higher than the blank test. At 200 mg/L hematite nanoparticles concentration, further initial pH optimization experiments indicated that at pH 6.0 the maximum hydrogen yield reached to 3.57 mol H(2)/mol sucrose and hydrogen content was 66.1%. The slow release of hematite nanoparticles had been recorded by transmission electron microscopy (TEM). In addition, TEM analysis indicated that the hematite nanoparticles can affect the shape of bacteria, namely, its length increased from ca. 2.0-3.6 mu m to ca. 2.6-5.6 mu m, and width became narrower. (C) 2011 Elsevier Ltd. All rights reserved.