Porous Ga₂O₃ Nanotubes Derived from Urease‐Mediated Interfacially‐Grown NH₄Ga(OH)₂CO₃ for High‐Efficient Hydrogen Evolution

Abstract

by the hollow cavity. [11] Accordingly, many strategies for fabrication of nanotubes, such as arc discharge, [12] chemical vapor deposition (CVD), [13][14][15] ball-milling and annealing, [16] laser ablation, [17] molecular beam epitaxy, [18] sol-gel, [19,20] atomic layer deposition, [21][22][23] hydro/solvothermal, [24,25] electrochemical anode, [26,27] and electrospinning, [28][29][30] have been developed. However, in those strategies, the hightemperature and/or templates are usually acquired to get the hollow structure of nanotubes, and thus high energy-and time-consumption but low productivity are inevitable. Consequently, the green methodologies for massive fabrication of nanotubes are imperative to boost their widespread application.Gallium oxide (Ga 2 O 3 ), [31,32] a nearly direct band gap semiconductor, has found wide applications in optoelectronic devices, [33,34] gas-sensors, [35,36] energy storage, [37,38] photocatalysis, [39,40] photoelectrocatalysis, [41] and solar cells. [42] Numerous morphology of Ga 2 O 3 , including bulk, nanoparticles, nanosheets, nanowires, nanorods, and nanobelts, has been made mainly through GaOOH intermediates. [43] Though nanotubes have many advantages as indicated above, only two researches on Ga 2 O 3 nanotubes were reported, one was fabricated by the Au(Si)-templated CVD for high-temperature nanothermometers, [44] the other was prepared by anodization of Ga metal at −10 °C for generation of hydrogen from water. [45] Herein, we report a novel strategy for massive fabrication of porous Ga 2 O 3 nanotubes, processing from the intermediate of NH 4 Ga(OH) 2 CO 3 nanotubes that are interfacially-grown from the urease-mediated decomposition of urea in aqueous solution of gallium salts at 20-50 °C. The enzymolysis of urea by urease rapidly produces plenty of OH − , NH 3 /NH 4 + , and CO 2 /CO 3 2− , and in the presence of Ga 3+ , the NH 4 Ga(OH) 2 CO 3 nanotubes are interfacially grown. The pH change from urea enzymolysis (i.e. OH − ) has been utilized for regulating the uniform size of TiO 2 nanoparticles [46] and the morphology of Fe 3 O 4 nanomaterials. [47] However, in our case, all the species of OH − , NH 4 + , and CO 3 2− from urea enzymolysis participate in the formation of NH 4 Ga(OH) 2 CO 3 nanotubes. The formation mechanism of NH 4 Ga(OH) 2 CO 3 nanotubes is proposed, and the advantage of Ga 2 O 3 nanotubes over nanoparticles is demonstrated by the enhanced catalytic H 2 evolution from water-splitting. The The authors proposed a novel template-free strategy, urease-mediated interfacial growth of NH 4 Ga(OH) 2 CO 3 nanotubes at 20-50 °C, to fabricate the porous Ga 2 O 3 nanotubes. The subtlety of the proposed strategy is all the products from urea enzymolysis are utilized in formation of NH 4 Ga(OH) 2 CO 3 precipitates, and the key for interfacial growth of NH 4 Ga(OH) 2 CO 3 nanotubes is the dynamic match between the rate of CO 2 bubble fusion and NH 4 Ga(OH) 2 CO 3 precipitation. The proposed strategy works well for the doped porous Ga 2 O 3 nanotubes. As a proof-of...

Self-assembly of Ni2P/γ-Ga2O3 nanosheets for efficient photocatalytic water splitting hydrogen production

“…Gallium oxide (Ga 2 O 3 ) possesses five different crystal types including α-, β-, γ-, δ- and ε-phases, 11,12 and they have been widely used in photocatalytic water splitting, such as in α–β phase junctions, 13 metal doping modification, 14 porous nanotubes, 15 etc. β-Ga 2 O 3 is the only thermodynamically stable phase in all these polymorphs.…”