Improvement of photocatalytic activity of tantalum nitride by ammonothermal treatment at high pressure

Tantalum nitride (Ta3N5) was treated under ammonothermal conditions with the ammonia pressure of 10 to 100 MPa at 823 K for 24 h to enhance the photocatalytic activity for hydrogen evolution from aqueous methanol solution under visible light irradiation. The rates of hydrogen evolution for all treated Ta3N5 were faster than those for untreated Ta3N5. Treated Ta3N5 showed higher enhanced activity for hydrogen evolution when treated with high-pressure ammonia at more than 50 MPa. The photocatalytic activity for hydrogen evolution of treated Ta3N5, related to the amount of defects, is due to reduced tantalum species. The enhancement in the activity is brought about by a decrease in surface defects, which contributes to improved electron transfer from the surface of Ta3N5 to the loaded Pt co-catalyst.