Synthesis and Enhanced Photocatalytic Activity of a Hierarchical Porous Flowerlike p-n Junction NiO/TiO2 Photocatalyst

Hierarchical flowerlike beta-Ni(OH)(2) superstructures composed of intermeshed nanoflakes are synthesized by hydrothermal treatment with a mixed solution of C2H4(NH2)(2), NaOH, and Ni(NO3)(2). The as-prepared beta-Ni(OH)(2) superstructures could be easily changed into NiO superstructures without great morphology change by calcination at 400 degrees C for 5 h. Furthermore, the TiO2 nanoparticles can be homogeneously deposited on the surface of NiO superstructures by dispersing beta-Ni(OH)(2) powders in Ti-(OC4H9)(4)-C2H5OH mixed solution and then vaporizing to remove the ethanol at 100 degrees C, and finally calcination at 400 degrees C for 5 h. The prepared NiO/TiO2 p-n junction superstructures show much higher photocatalytic activity for photocatalytic degradation of p-chlorophenol aqueous solution than conventional TiO2 powders and NiO superstructures prepared under the same experimental conditions. An obvious enhancement in the photocatalytic activity can be related to several factors, including formation of hierarchical porous structures, dispersion of TiO2 particles on the surface of NiO superstructures, and production of a p-n junction. Further results show that NiO/TiO2 composite superstructures can be more readily separated from the slurry system by filtration or sedimentation after photocatalytic reaction and re-used, compared with conventional powder photocatalysts. After many recycling experiments for the photodegradation of p-chlorophenol, the NiO/TiO2 composite sample does not exhibit any great activity loss, confirming that NiO/TiO2 sample is stable and not photocorroded.