LAUSR

Various nitrogen-doped titania particles were prepared and, for visible light sensitizing, the biological pigment hematoporphyrin was grafted onto their surfaces. The nanohybrid products were characterized using X-ray diffraction, Fourier transform infrared and ultraviolet–visible spectroscopies and Brunauer–Emmett–Teller surface area analysis. A high-performance visible light helical flow photoreactor was designed and used for the photocatalytic degradation of methyl orange (MO) over these photocatalyst products. Accordingly, response surface methodology was employed for design of experiments and optimization. The influencing parameters were initial N/Ti molar ratio, dosage of nanohybrids and solution pH. These parameters were statistically significant and a quadratic correlation was developed for degradation efficiency (DE) variations. A maximum DE of 89.2% was attainable, after 60 min treatment, under the optimum conditions of initial N/Ti molar ratio of 4.93 (ca 5), nanohybrid dosage of 0.73 g l−1 and pH of 4.8. The MO degradation kinetics over the catalyst surface followed the modified Langmuir–Hinshelwood model. The important role of hydroxyl radicals was confirmed using mannitol scavenger. Performing the photocatalytic reaction with the developed set-up showed excellent efficiency and energy consumption in comparison with similar processes.