Photocatalytic decomposition of glycerol solution on TiO₂ nanotube arrays (TNTA) doped with C and N to produce hydrogen

Carbon and Nitrogen-doped TNTA were synthesized by in-situ anodic oxidation of Ti using glycerol containing NH₄F followed by annealing with 20% H₂/Argon at 500 oC. Variation water content in the electrolyte solution (25 and 37.5 v%) and time of anodic oxidation (1, 2, 4 and 6 h) that influence the morphology of TNTA and H₂ produced was examined. At water content 37.5 v% in the electrolyte solution, FESEM results indicated that the disorder with not vertically oriented of the tube were observed. For water content 25 v%, TNTA with average inner diameters of 81 to 105 nm, wall thicknesses from 15 to 27 nm and lengths from 882 to 1705 nm were synthesized for 1-6 h anodization. Morphology of TNTA such as well developed, vertically oriented, ordered and long could influence photon absorption and, therefore, influence the accumulative H₂ production. The result indicated that the average inner diameter of the tubes increase as anodic oxidation time increased up to 6 h, on the other hand, the tube length reached the maximum at 4 h anodic oxidation. TNTA that anodized for 2 h, water content in the electrolyte solution 25 v% with average tube length 1570 nm showed the highest accumulative H₂ production (47 mmol/m²photocatalyst).