J. Cent. South Univ. (2015) 22: 1066−1070 DOI: 10.1007/s11771-016-0356-9 Increased photo-catalytic removal of sulfur using titania/MWCNT composite Molood Barmala, Abdolsamad Zarringhalam Moghadam, Mohammad Reza Omidkhah Chemical Engineering Department, Tarbiat Modares University, Jalal Ale Ahmad Highway, P. O. Box: 14155-143, Tehran, Iran © Central South University Press and Springer-Verlag Berlin Heidelberg 2015 Abstract: Titania coating of multi wall carbon nano tube (MWCNT) was carried out by sol-gel method in order to improve its photo catalytic properties. The effect of MWCNT/TiO 2 mass to volume ratio on adsorption ability, reaction rate and photo-catalytic removal efficiency of dibenzothiophene (DBT) from n-hexane solution was investigated using a 9 W UV lamp. The results show that the addition of nanotubes improves the photo-catalytic properties of TiO 2 by two factors; however, the DBT removal rate versus MWCNT content is found to follow a bimodal pattern. Two factors are observed to affect the removal rate of DBT and produce two optimum values for MWCNT content. First, large quantities of MWCNTs prevent light absorption by the solution and decrease removal efficiency. By contrast, a low dosage of MWCNT causes recombination of the electron holes, which also decreases the DBT removal rate. The optimum MWCNT contents in the composite are found to be 0.25 g and 0.75 g MWCNT per 80 mL of sol. Key words: photo oxidation; desulfurization; sol-gel; titania; multi wall carbon nano tube (MWCNT) 1 Introduction Sulfur removal from liquid fuels has been increased in importance in recent years. In addition to environmental concerns, it is also a factor in combustion systems. Although hydrodesulfurization is the usual method for removing sulfur, it requires high energy, high temperatures, high pressure and high consumption of hydrogen in the presence of a metal catalyst. Yet the elimination of dibenzothiophene (DBT) compounds using this process is difficult [1−4]. Alternative processes such as alkylation, extraction, sedimentation, oxidation and adsorption have been investigated to decrease energy consumption during sulfur removal [1]. Among these, adsorption and oxidation processes are favoured because they can be used at ambient temperatures and pressure [1, 5−6]. Oxidation converts thiophene into easily separable compounds like sulfone and sulfoxide [1, 3, 5]. DBT is a compound that cannot be removed by photolysis [1, 6]. TAO et al [1] showed that there is sulfide compounds in Kerosene whose photo oxidation removal rates are up to a hundred times greater than those of Dibenzo thiophene, and even with the use of low-pressure lamps, they can be completely removed within the first an half hour of photo oxidation. DBT is more highly resistant and there is no noticeable change in concentration after 5 h [1]. When a catalyst is employed (photo-catalytic oxidation), the removal rate of sulfur compounds increases or oxidation occurs in less time. Also oxidants could be added to increase the hydroxyl radical concentration [2]. Among semiconductors, titania (TiO 2 ) shows good potential as a photo-catalyst for the removal of dyes and organic materials to produce hydrogen by water splitting. It is highly stable, resistant to corrosion, relatively non-toxic and chemically inert [7−10]. Despite these good properties, its low photo-catalytic efficiency resulting from the quick recombination of electron holes hinders its commercial use [3, 7, 10−11]. Photo-catalytic reaction rate can be controlled by light absorption, the transmission of electron holes to the photo-catalytic surface, the recombination of electron holes, the electron-hole reaction and mass transfer rate of the reactant on the surface of the photo-catalyst. Efficient photo-catalysts must have high photon conversion efficiency and a large specific surface area [9]. Photo-catalytic efficiency can be improved by decreasing the possibility of recombination of electron holes, preventing agglomeration of particles, increasing adsorption of the catalyst and decreasing the band gap [3, 7]. One way of achieving these is using TiO 2 combined with a suitable substrate [7−8, 12]. Carbon nanotubes (CNTs) have chemical stability, high specific surface areas and high electrical conductivity and they are materials considered applicable as substrates for catalysts [3, 7, 11, 13−14]. CNTs show Received date: 2014−09−17; Accepted date: 2015−01−25 Corresponding author: Abdolsamad Zarringhalam Moghadam; Tel: +98−2182883337; E-mail: zarrin@modares.ac.ir