CdS-coated thin plastic films for visible-light photocatalysis

Aaron Mcneill,Andrew Mills

doi:10.1088/2515-7655/abb927

Abstract

The preparation of a visible light-absorbing, very thin (2.5 μm), flexible CdS nanoparticle coated polystyrene (PS) film, CdS-PS, with a 3D-printed backing is described. Scanning electron microscopy confirms that the CdS-PS film comprise a thin layer of CdS nanoparticles (26 ± 4 nm) on just one side of the PS film, with no nanoparticles on the other side. When irradiated with 420 nm or 365 nm radiation, in air-saturated water, the CdS film is photobleached, and dissolved O2 consumed, due to the photoinduced oxidative corrosion of the CdS by O2. In contrast, under the same aerobic conditions, the CdS-PS film is very stable, when a sacrificial electron donor (SED) is present, such as EDTA or ascorbate/ascorbic acid, with the latter appearing the most effective. In the presence of an SED, the CdS-PS film photocatalyses the reduction of the dyes, methyl orange and crystal violet, and the electron-relay, methyl viologen, by different SEDs, using visible and UV light. In the photocatalysed reduction of methyl viologen by EDTA, colloidal Pt reacts with the highly coloured blue methyl viologen radicals generated to produce H2. Visible light irradiation of the CdS-PS/MV2+/EDTA/colloidal Pt system promotes the reduction of water to H2 by the SED, EDTA, mediated by methyl viologen. A colourless, TiO2-PS film, made using P25 TiO2, is used to effect the same photocatalytic reduction reactions as the CdS-PS film, but only when irradiated with UV (365 nm) radiation. In both cases the films are used repeatedly with no evidence of deterioration in activity or film stability. This is the first example of the preparation and testing of a visible light absorbing photocatalytic, i.e. CdS, thin plastic film, the preparation of which is very simple and inexpensive and may prove invaluable for the production of thin, flexible plastic photocatalytic films for solar research.

Highlights

cadmium sulfide (CdS) is a well-known semiconductor photocatalyst, due to its ability to absorb visible light and, in theory at least, to photodissociate water into H2 and O2, given the highly reducing nature of its photogenerated conductance band electrons (ECB(e-) = −0.93 V vs NHE at pH 7 [2]) and the highly oxidising nature of its photogenerated valence band holes (ECB(h+) = 1.47 V vs NHE at pH 7 [2])
CdS-PS film characterisation The CdS-PS film was pale yellow-coloured, as shown by its photograph illustrated in figure S3 and its UV–vis spectrum illustrated in figure 2(a)
The emission spectra of the three different LEDs used in this work, with λmax values of 365, 420 and 595 nm, are illustrated in figure 2(a) and show that while the 365 nm LED’s emission spectrum overlaps with absorption spectra of the CdS- and TiO2-PS films, that of the 420 nm LED only overlaps with the CdS-PS absorption spectrum

Summary

Introduction

CdS is a well-known semiconductor photocatalyst, due to its ability to absorb visible light (bandgap: 2.4 eV [1]) and, in theory at least, to photodissociate water into H2 and O2, given the highly reducing nature of its photogenerated conductance band electrons (ECB(e-) = −0.93 V vs NHE at pH 7 [2]) and the highly oxidising nature of its photogenerated valence band holes (ECB(h+) = 1.47 V vs NHE at pH 7 [2]). This is true in aerobic aqueous solution, as the dissolved O2 is usually a very effective scavenger of photogenerated conductance band electrons, i.e., e - + O2 → O2- (2). The role of the SED is to react rapidly and irreversibly with the photogenerated holes, before they are able to oxidise the CdS itself, i.e., h + + SED → SED + (3). The remaining photogenerated conductance band electrons are able to effect the reduction of an electron acceptor, A, i.e., ne− + A → An−

Methods

Results

Conclusion