(21a) Anatase Nanoparticles from Low Pressure Flame Synthesis for Enhanced Photocatalytic Activity

Ashley M. Pennington¹, Stephen D. Tse², Fuat E. Celik^1*

¹Department of Chemical and Biochemical Engineering, Rutgers University, Piscataway, NJ 08854

²Department of Mechanical and Aerospace Engineering, Rutgers University, Piscataway, NJ 08854

*fuat.celik@rutgers.edu (corresponding author)

High surface area, carbon doped anatase phase TiO₂ with mesoporosity is synthesized with low pressure flame synthesis employing a burner-stabilized premixed stagnation flat flame. Control of the flame temperature, residence time, and fuel composition permitted precise control of the nucleation and growth of primary particles. Under these conditions, nanoparticle growth was limited to 7 nm, resulting in a 22-fold increase in surface area (187 m² g^-1) compared to commercial anatase samples. Smaller particle size has a number of benefits for photocatalysis. A larger surface area to volume ratio and reduced particle diameter increases the probability of electrons/holes reaching the surface and catalyzing surface reactions, as opposed to recombining in the bulk. As-prepared samples contained 1.2 wt% carbon trapped in the structure during crystallization and quenching. Upon heating in air at 200 °C, the white powder turned brown as carbon migrated and oligomerized on the surface, the sample color reverted to white at 400 °C and 500 °C as the carbon burned off. BET and porosimetry revealed that this heat treatment caused an increase in particles size (8.5 nm) and a decrease in surface area (149 m² g^-1), while simultaneously increasing the pore volume and shifting the pore size distribution to larger pores. The heat-treated samples showed enhanced photocatalytic activity for water reduction with methanol as sacrificial agent, showing three times the hydrogen productivity compared the untreated material, and four times as much as P25 (an anatase-rutile mixture).