Enhancement of photocatalytic H2 evolution of eosin Y-sensitized reduced graphene oxide through a simple photoreaction

Abstract

A graphene oxide (GO) solution was irradiated by a Xenon lamp to form reduced graphene oxide (RGO). After irradiation, the epoxy, the carbonyl and the hydroxy groups are gradually removed from GO, resulting in an increase of sp(2) π-conjugated domains and defect carbons with holes for the formed RGO. The RGO conductivity increases due to the restoration of sp(2) π-conjugated domains. The photocatalytic activity of EY-RGO/Pt for hydrogen evolution was investigated with eosin Y (EY) as a sensitizer of the RGO and Pt as a co-catalyst. When the irradiation time is increased from 0 to 24 h the activity rises, and then reaches a plateau. Under optimum conditions (pH 10.0, 5.0 × 10(-4) mol L(-1) EY, 10 μg mL(-1) RGO), the maximal apparent quantum yield (AQY) of EY-RGO24/Pt for hydrogen evolution rises up to 12.9% under visible light irradiation (λ ≥ 420 nm), and 23.4% under monochromatic light irradiation at 520 nm. Fluorescence spectra and transient absorption decay spectra of the EY-sensitized RGO confirm that the electron transfer ability of RGO increases with increasing irradiation time. The adsorption quantity of EY on the surface of RGO enhances, too. The two factors ultimately result in an enhancement of the photocatalytic hydrogen evolution over EY-RGO/Pt with increasing irradiation time. A possible mechanism is discussed.

Keywords: H2 evolution; eosin Y sensitization; graphene oxide; photocatalysis; photoreduction; sp2 conjugated domains.

Figure 1

UV–vis spectra of (a) GO, (b) RGO4, (c) RGO12, (d) RGO24, and (e) RGO36 solution (20 μg mL⁻¹). The inset is an image of GO and RGO24.

Figure 2

(A) ATR-IR spectra of GO-p, RGO4-p and RGO24-p, (B) XPS spectra of C1s for GO-p, RGO4-p and RGO24-p, and (C) Nyquist diagrams of GO, RGO4 and RGO24.

Figure 3

Chemical structure of EY.

Figure 4

Fluorescence spectra of EY-RGOx in TMA solution. The inset shows the fluorescence spectrum of EY in TMA solution. Conditions: 30 μg mL⁻¹ GO or RGOx; 1.0 × 10⁻⁵ mol L⁻¹ EY; 7.7 × 10⁻² mol L⁻¹ TMA.

Figure 5

Transient absorption decay of ³EY^* followed at 580 nm for (A) EY, (B) EY−GO, (C) EY−RGO4, and (D) EY−RGO24 under pulse irradiation of 532 nm. Conditions: 30 μg mL⁻¹ GO or RGOx; 2.0 × 10⁻⁵ mol L⁻¹ EY.

Figure 6

Photocatalytic H₂ evolution of EY sensitized GO and RGOx. Conditions: 30 μg mL⁻¹ GO or RGOx; 1.45 × 10⁻⁴ mol L⁻¹ EY; 4.6 × 10⁻⁶ mol L⁻¹ H₂PtCl₆; 7.7 × 10⁻² mol L⁻¹ TMA, pH 11.9; irradiation 2 h.

Figure 7

(A) The effect of the pH value on the photocatalytic activity of EY-RGO24/Pt. Conditions: 30 μg mL⁻¹ RGO24; 1.45 × 10⁻⁴ mol L⁻¹ EY; 4.6 × 10⁻⁶ mol L⁻¹ H₂PtCl₆; 7.7 × 10⁻² mol L⁻¹ TMA; irradiation 2 h. (B) The effect of the EY concentration on the photocatalytic H₂ evolution over EY-RGO24/Pt. Conditions: 30 μg mL⁻¹ RGO24; 4.6 × 10⁻⁶ mol L⁻¹ H₂PtCl₆; 7.7 × 10⁻² mol L⁻¹ TMA, pH 10.0; irradiation 2 h. (C) The effect of the RGO24 concentration on the photocatalytic H₂ evolution over EY-RGO24/Pt. Conditions: 5.0 × 10⁻⁴ mol L⁻¹ EY; 4.6 × 10⁻⁶ mol L⁻¹ H₂PtCl₆; 7.7 × 10⁻² mol L⁻¹ TMA, pH 10.0; irradiation 2 h.

Figure 8

AQY of the EY-RGO24/Pt photocatalyst plotted as a function of the wavelength of the incident light. Conditions: 10 μg mL⁻¹ RGO24; 5.0 × 10⁻⁴ mol L⁻¹ EY; 4.6 × 10⁻⁶ mol L⁻¹ H₂PtCl₆; 7.7 × 10⁻² mol L⁻¹ TMA, pH 10.0; irradiation 2 h. The inset is the UV–vis absorption spectrum of EY in TMA solution.

Scheme 1

Schematic diagram of the reduction of GO by irradiation.

Figure 9

TEM images of GO (A), RGO24 (B), RGO24 with deposited Pt (C), and HRTEM image of deposited Pt (D). The inset of Figure 9D is the EDS spectrum.

Scheme 2

Proposed mechanism for the photocatalytic hydrogen evolution of a EY-RGOx/Pt system under visible light irradiation.