Cyclic Photocatalytic Degradation Of Methylene Blue By Nano-TiO₂ In The Membrane Reactor

Titanium dioxide is one kind of the semiconductors which is widely used in industry water treatment. Recently some research was focused on the preparation of nano-TiO₂ and TiO₂ nanocomposites. The photocatalytic performance of nano-TiO₂ and their influencing factors have been studied. However relatively few research has been carried on the recycling of nano-TiO₂ in the process of waste water treatment. Though the fixation of nano-TiO₂ resolves the problem to a certain extent, it reduces the photocatalytic degradation velocity of nano-TiO₂ at the same time. In this paper, photocatalytic degradation of methylene blue by nano-TiO₂ was conducted in conventional way and in a hollow fibriform membrane reactor, the photocatalytic performance of nano-TiO₂ was investigated systematically.In the conventional photocatalytic experiment, the effects of nano-TiO₂ dosage, MB initial concentration, MB initial pH value and assistant catalyst Fenton on the efficiency of photocatalytic degradation of MB were studied. Results show that the initial photocatalytic degradation velocity and the photocatalytic degradation efficiency of nano-TiO₂ closely relate to its high adsorption ability to MB which belongs to Langmuir type. The photocatalytic degradation efficiency of nano-TiO₂ increased with increasing of nano-TiO₂ dosage, decreasing of MB initial concentration and increasing of MB initial pH value. The initial photocatalytic degradation velocity decreased with increasing of the dispersion of UV light by TiO₂, MB initial concentration and pH value. The optimum condition for highest initial photocatalytic degradation velocity is that MB initial concentration is 50mg/L,TiO₂ dosage is 4.0 g/L and MB initial pH value is 8.5. The photocatalytic degradation efficiency of nano-TiO₂ was much enhanced when assistant catalysts were added and in the order of TiO₂ >Fenton > H₂O₂+ TiO₂> TiO₂.The influences of several factors (nano-TiO₂ dosage, MB addition velocity, initial pH value and the addition of assistant catalyst Fenton) on the photocatalytic degradation of MB by nano-TiO₂ in hollow fibriform membrane reactor were investigated systematically. Results show that the photocatalytic degradationefficiency in hollow fibriform membrane reactor is higher than that of conventional experiment. When the dosages of nano-TiO₂ are 0.5, 1.0, 2.0, 4.0g/L the photocatalytic degradation efficiency increased 5.52%, 8.74%, 7.9%, 0.84% respectively. The photocatalytic degradation efficiency increased with increasing of nano-TiO₂ dosage and decreasing of MB addition velocity. An inflexion is observed on the curve of the photocatalytic degradation efficiency of MB in the cyclic membrane reactor versus degradation time. The shortest inflexion is 180min and the highest degradation efficiency is 88% when the dosage of nano-TiO₂ is 2.0g/L and the MB addition velocity is 15mL/h. Assistant catalyst and basic environment can increase the reaction velocity. The filtering ability of the hollow fibriform membrane for nano-TiO₂ was checked by analysing the amount of nano-TiO₂ on their surface and in the effluent. Results show up to 99.8% of the nano-TiO₂ can be intercepted by the hollow fibriform membrane within the experimental time.