Transition-Metal Ion-Doped Flower-Like Titania Nanospheres as Nonlight-Driven Catalysts for Organic Dye Degradation with Enhanced Performances

Titania has recently been identified as a new and effective nonlight-driven catalyst for degradation of organic pollutant with the use of H 2 O 2 as an oxidant; however, either relatively low surface area or lack of diversity in chemical composition largely limits its catalytic performance. In this work, a series of transition-metal ion (Mn 2+ , Co 2+ , Ni 2+ , and Cu 2+ )-doped titania nanomaterials with regular flower-like morphology, good crystallinity (anatase), and large specific surface areas (71.4-124.4 m 2 g -1 ) were facilely synthesized and utilized as catalysts for methylene blue (MB) degradation in the presence of H 2 O 2 without light irradiation. It was revealed that the doping of transition-metal ions (especially Mn 2+ ) into titania could significantly improve the catalytic efficiency. At 30 °C, 10 mL of MB with a concentration of 50 mg L -1 could be completely degraded within 60-100 min for these doped samples, whereas the removal rate was only 35.1% within 100 min with the use of pure flower-like titania. Temperature-dependent kinetic studies indicated that the presence of transition-metal ion dopants could markedly lower the activation energy and thus resulted in enhanced catalytic performances. Test of reusability exhibited that these doped catalysts could well keep their original catalytic activities after reuse for several cycles, indicating their excellent catalytic durability.