Photocatalytic Activity of Ga₂O₃ Supported on Al₂O₃ for Water Splitting and CO₂ Reduction

Abstract

We have examined the photocatalytic activity of Ga 2 O 3 supported on Al 2 O 3 (Ga 2 O 3 /Al 2 O 3 catalyst) without a noble metal cocatalyst for water splitting and reduction of CO 2 with water under UV light irradiation by changing the loading amount of Ga 2 O 3 . All prepared Ga 2 O 3 /Al 2 O 3 catalysts show photocatalytic activities for both water splitting and CO 2 reduction, and their activities are significantly improved compared to those of nonsupported Ga 2 O 3 and Al 2 O 3 . The water splitting is dominated for Ga 2 O 3 /Al 2 O 3 with less than 1.0 vol % of Ga 2 O 3 loaded, whereas the CO 2 reduction, for higher Ga 2 O 3 -loaded samples (2.6, 4.2 vol %). Crystalline structure characterizations of Ga 2 O 3 /Al 2 O 3 catalysts indicate that active sites for both reactions are different. The water splitting proceeds on nanometer-sized Ga 2 O 3 rods dispersed on an Al 2 O 3 support consisting of a little distorted α-Ga 2 O 3 phase. On the other hand, the CO 2 reduction proceeds on sub-micrometer-sized Ga 2 O 3 particles consisting of mixed phases of α-Ga 2 O 3 and γ-Ga 2 O 3 or with appearance of boundaries between the α and γ phases, which plays a critical role. Al 2 O 3 used as the support of the Ga 2 O 3 particles does not seem to play an important role in the photocatalytic CO 2 reduction.

Utilization of La₂O₃ as a Support of Ga₂O₃ Photocatalyst to Enhance Activity on CO₂ Reduction with Water

“…It should be noted that Ag was not used as a cocatalyst in the present work. Hence, as noted in our previous papers [24,25], some lattice distortion in Ga2O3 should be introduced during the conversion of the La2O3 support to NaLa(CO3)2 which would provide high activity for CO2 reduction without using the Ag cocatalyst. Table 1: CO production rates for photocatalytic CO2 reduction with water under various conditions.…”

“…The amounts of them were selected to be 6 : 4 for the mass ratio of Ga2O3 and La2O3 (referred as 40 wt% Ga2O3 hereafter). It was the optimum loading amount for Ga2O3/Al2O3 in our previous work [24]. Then, they were dispersed into 200 mL of distilled water.…”

“…For example, Ga2O3 consisting of different two phases shows high photocatalytic activity on the CO2 reduction with water without the Ag cocatalyst [20−22]. We have succeeded to improve the photocatalytic activity of Ga2O3 for water splitting and CO2 reduction without the Ag cocatalyst but employing Al2O3 as a support of Ga2O3 [24,25]. Ga2O3 supported by Al2O3 was consisted of two phases (α and γ) and their particle size was changed depending on the amount of Ga2O3 loaded on the Al2O3 support.…”

“…Thus, the control of the crystal phase and the particle size of Ga2O3 is likely a key factor for the improvement of its photocatalytic activity. In a separate work [26], we have examined various metal oxides as the support of the Ga2O3 photocatalyst. Among all examined oxides, La2O3 supported Ga2O3 (Ga2O3/La2O3) showed the highest photocatalytic activity.…”

Highly Porous and Ultra-Lightweight Aero-Ga2O3: Enhancement of Photocatalytic Activity by Noble Metals

“…Ga 2 O 3 -based pure phases and composites have been examined for energy and environmental applications, including the decomposition of volatile aromatic pollutants in air [ 6 ]; water purification [ 7 , 8 , 9 , 10 , 11 ]; solar water splitting [ 12 , 13 , 14 , 15 ]; photocatalytic carbon dioxide (CO 2 ) reduction with water to produce carbon monoxide (CO), hydrogen (H 2 ), and oxygen (O 2 ) [ 15 , 16 , 17 , 18 , 19 , 20 , 21 ]; photocatalytic reduction of CO 2 to produce methane (CH 4 ) [ 22 ]; as well as solar-driven photoreduction of nitrogen (N 2 ) in a clean route to produce ammonia (NH 3 ) [ 23 ].…”