Deposition of anatase on the surface of activated carbon

As part of a program looking into utilization of activated carbon prepared from waste material, titanium dioxide was deposited on the surface of active carbon (AC). This will be used in future work as potential photo-catalyst for treatment of chlorinated phenols in aqueous medium. Three different techniques were used: chemical vapour deposition (CVD), direct air-hydrolysis (DAH) and high-temperature impregnation (HTI) techniques. The total TiO2 deposited and amount crystallized into anatase TiO2 by each technique is estimated. The pre-sonication was found useful in introducing part of the hydrolysis step within the small pores. The effect of each deposition procedure on surface area, porosity and thermal stability of the sample was studied by nitrogen adsorption, mercury intrusion, methylene blue (MB) adsorption and thermal gravimetric analysis. Surface texture of the potential catalysts was studied by electron microscopic techniques. Results showed that different procedures gave different yields of total and anatase TiO2. On the other hand, there was significant reduction, which may be due to TiO2 deposition, in porosity and surface area. The reduction in MB adsorption was proportional to anatase TiO2 but not to the total TiO2 deposited. Chemical vapour deposition gave more anatase TiO2 than the direct air-hydrolysis technique, which is thought to form the deposit within the micro-meso pores, and caused more porosity-surface area reduction. It is thought that TiO2 particles inside the pores have more opportunity to crystallize into the anatase form. The deposited layer of TiO2 apparently catalyzed slight weight loss at low temperatures but generally gave more thermal stability for the support. Non-activated carbon (C) was used and its thermal stability, porosity and surface area were not affected by TiO2 deposition. The deposition, in non-activated carbon, is thought to occur on external surface, which may be due to absence of large micropores.