Photocatalytic Water Splitting for Hydrogen Production with Gd₂MSbO₇ (M = Fe, In, Y) Photocatalysts under Visible Light Irradiation

Abstract

Novel photocatalysts Gd₂FeSbO₇, Gd₂InSbO₇ and Gd₂YSbO₇ were synthesized by the solid state reaction method for the first time. A comparative study about the structural and photocatalytic properties of Gd₂MSbO₇ (M = Fe, In, Y) was reported. The results showed that Gd₂FeSbO₇, Gd₂InSbO₇ and Gd₂YSbO₇ crystallized with the pyrochlore-type structure, cubic crystal system and space group Fd3m. The lattice parameter a for Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ was 10.276026 Å, 10.449546 Å or 10.653651 Å. The band gap of Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ was estimated to be 2.151 eV, 2.897 eV or 2.396 eV. For the photocatalytic water-splitting reaction, H₂ or O₂ evolution was observed from pure water with Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ as catalyst under visible light irradiation (wavelength > 420 nm). Moreover, H₂ or O₂ also spilt by using Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ as catalyst from CH₃OH/H₂O or AgNO₃/H₂O solutions under visible light irradiation (λ > 420 nm). Gd₂FeSbO₇ showed the highest activity compared with Gd₂InSbO₇ or Gd₂YSbO₇. At the same time, Gd₂InSbO₇ showed higher activity compared with Gd₂YSbO₇. The photocatalytic activities were further improved under visible light irradiation with Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ being loaded by Pt, NiO or RuO₂. The effect of Pt was better than that of NiO or RuO₂ for improving the photocatalytic activity of Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇.

Keywords: Gd2MSbO7 (M = Fe; In; Y); photocatalytic property; photocatalytic water splitting; visible light irradiation.

Figure 1

X-ray powder diffraction pattern of Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ prepared by a solid-state reaction method at 1250 °C, 1320 °C or 1320 °C

Figure 2

The diffuse reflection spectrum of Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇.

Figure 3

(a) Photocatalytic H₂ evolution and photocatalytic O₂ evolution from pure water with Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ as catalyst under visible light irradiation (λ > 420 nm, 0.5 g powder sample, 250 mL pure water). Light source: 300 W Xe lamp; (b) Photocatalytic H₂ evolution from aqueous methanol solution with Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ as catalyst under visible light irradiation (λ > 420 nm, 0.5 g 0.1 wt% Pt-loaded powder sample, 50 mL methanol solution, 200 mL pure water). Light source: 300 W Xe lamp.

Figure 4

Photocatalytic O₂ evolution from AgNO₃ solution with Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ as catalyst under visible light irradiation (λ > 420 nm, 0.5 g photocatalyst, 1 mmol AgNO₃, 270 mL pure water). Light source: 300 W Xe lamp.

Figure 5

Photocatalytic H₂ evolution from aqueous methanol solution with Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ as catalyst under light irradiation (390 nm cut-off filter, 0.5 g 0.1 wt% Pt-loaded powder sample, 50 mL CH₃OH, 200 mL pure water). Light source: 300 W Xe lamp.

Figure 6

Photocatalytic H₂ evolution from aqueous methanol solution with Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ as catalyst under light irradiation (No cut-off filter, 0.5 g 0.1 wt% Pt-loaded powder sample, 50 mL CH₃OH, 200 mL pure water). Light source: 300 W Xe lamp.

Figure 7

Effect of Pt, NiO and RuO₂ co-catalysts on the photoactivity of Gd₂FeSbO₇ under visible light irradiation (λ > 420 nm, 0.5 g powder sample, 50 mL methanol solution, 200 mL pure water). Light source: 300 W Xe lamp.