Porous Ga2 O3 Nanotubes Derived from Urease-Mediated Interfacially-Grown NH4 Ga(OH)2 CO3 for High-Efficient Hydrogen Evolution.

Abstract

The authors proposed a novel template-free strategy, urease-mediated interfacial growth of NH4 Ga(OH)2 CO3 nanotubes at 20-50°C, to fabricate the porous Ga2 O3 nanotubes. The subtlety of the proposed strategy is all the products from urea enzymolysis are utilized in formation of NH4 Ga(OH)2 CO3 precipitates, and the key for interfacial growth of NH4 Ga(OH)2 CO3 nanotubes is the dynamic match between the rate of CO2 bubble fusion and NH4 Ga(OH)2 CO3 precipitation. The proposed strategy works well for the doped porous Ga2 O3 nanotubes. As a proof-of-concept, the porous β-Ga2 O3 and β-Ga2 O3 :Cr0.001 nanotubes are used as photocatalysts or co-catalysts with Pt, for H2 evolution from water splitting. The H2 evolution rate of porous β-Ga2 O3 nanotubes reach 39.3 mmol g-1 h-1 with solar-to-hydrogen (STH) conversion efficiency of 2.11% (Hg lamp) or 498 µmol g-1 h-1 with STH of 0.03% (Xe lamp) respectively, both about 3 times of β-Ga2 O3 nanoparticles synthesized at pH 9.0 without urease. The Cr-doping enhances the in-the-dark H2 evolution rate pre-lighted by Hg lamp, and Pt co-catalysis further elevates the H2 evolution rate, for instance, the H2 evolution rate of Pt-loaded β-Ga2 O3 :Cr0.001 nanotubes reaches 54.7 mmol g-1 h-1 with STH of 2.94% under continuous lighting of Hg lamp and 1062 µmol g-1 h-1 in-the-dark.