Preparation by High-gravity Technology of a Cu/N-TiO2 Nanophotocatalyst for Photodegradation of Phenol Wastewater

TiO2 is a promising photocatalyst, but its practical use is restricted by its low catalytic efficiency caused by the large particle size and uneven size distribution, which arise from the limited contact area of the liquid-liquid interface during synthesis. Impinging stream-rotating packed bed (IS-RPB) reactors, which are used for process intensification, overcome the mixing limitation of traditional stirred-tank reactors and provide a micromixing environment at the molecular scale for the two liquid phases, which can reduce the particle size and distribution range. Cu/N-TiO2 nanoparticles were prepared in an IS-RPB reactor by the one-step precipitation method using urea as the nitrogen source, titanyl sulfate as the titanium source, copper chloride as the copper source, and ammonium hydroxide as the precipitant. The particle size of the photocatalyst was about 11.40 nm with a narrow size distribution measured by scanning electron microscopy and transmission electron microscopy. X-ray photoelectron spectroscopy showed that N replaced some O and was uniformly dispersed in the TiO2 lattice as interstitial and substitutional N. Cu replaced some Ti and was present as Cu2+. The synergistic effects of these two elements formed a new impurity energy level and reduced the band gap energy of the TiO2 nanoparticles. The specific surface area of the Cu/N-TiO2 nanoparticles was 152.97 m(2)/g. The effects of the main factors on the degradation rate were studied, and the removal efficiency reached 100% under the optimal operating conditions after 2 h ultraviolet irradiation. The electron paramagnetic resonance measurements showed that the superoxide radical played a main role in the degradation process, whereas the photogenerated holes and hydroxyl radicals had weak effects.