TiO2 hollow sphere multimer photocatalyst (SPMP) was synthesized by a one-step hydrothermal method using titanium plate (TP) as the titanium source and NH4F as the structure regulator. The structural properties of prepared photocatalysts were characterized using X-ray diffraction, UV-vis absorption spectra, N-2 adsorption-desorption, scanning electron microscopy and transmission electron microscopy. The results indicated that the additional amount of NH4F and hydrothermal time played significant roles in the formation of the TiO2 SPMP. TiO2 SPMP could be obtained only when 0.80 g NH4F as well as TP were added to 40 mL of deionized water and then hydrothermally treated for 22 h at 120 degrees C. The photocatalytic activity of multimer photocatalysts fabricated under various conditions was evaluated and optimized to decompose gaseous styrene. The results revealed that all prepared photocatalysts (hollow or solid sphere multimers) showed better photocatalytic activity than Degussa P25 in the decomposition of gaseous styrene. TiO2 SPMP displayed the highest photocatalytic activity due to the synergistic effects of its large surface area, good anatase crystallinity, and unique hollow multimer structure as well as its relatively wide band energy. A preliminary two-major-step formation mechanism for hollow sphere multimers was proposed: The multimers were formed on the TP, followed by a hollowing process for multimers in the solution. (C) 2013 Elsevier B.V. All rights reserved.