Textile-based solar thermal energy collectors (TSTEC) are one form of novel flexible solar thermal harvesting product, and one that can widely be applied to building roofs and facades [1]. Thin film metal oxides are superior solar light absorbers. Many of the metal oxides are n-type semiconductors. Known p-type oxides include silver (I) oxide. They can be combined into a functional material when deposited on polymeric substrates. The optical band gap for Ag2O ranges from 1.2 eV [2] to 3.4 eV [3] depending on the stoichiometry, structure and physical properties that result from the deposition method.
In this study, silver oxide films were synthesised on a polyvinylchloride textile (PVC), and an investigation was carried out into the structural and optical properties of the treated fabric. The chemical deposition method was used to modify the PVC textile surface. Ag2O can be prepared by combining aqueous solutions of AgNO3 and NaOH:
$$AgNO_3(aq) + NaOH(aq) \rightarrow AgOH(s) + H_2O(l)\tag{1}$$This reaction does not provide appreciable amounts of silver hydroxide due to the favourable energetics for the following reaction:
$$2AgOH(s) \rightarrow Ag_2O(s) + H_2O(l); (K_{SP} = 1.52 \cdot 10^{-8} \text{ (mol/dm}^3)^2 \text{ at } 20^{\circ}\text{C})\tag{2}$$With suitably controlled conditions, this reaction can be used to prepare Ag2O with properties which are suitable for several uses, including as a fine-grained conductive thin films.
Prior to the process of depositing the materials, the mechanically roughened surface was pre-treated with hot alkali solution [4]. Then pre-treated samples were inserted vertically along the reactor wall with a 0.1M AgNO3 solution and were left undisturbed for six hours (Fig. 1). At the end of the exposure time, the samples were taken out, washed with distilled water, and then exposed to freshly prepared 0.35M NaOH solution at room temperature for six hours. Sample immersion in AgNO3 and subsequent immersion in the NaOH solution formed one Ag2O preparation cycle. In summary, six cycles were employed. The obtained samples were cleaned, dried, and then characterized.
An X-ray diffraction (XRD) analysis was carried out to provide a level of understanding in regard to the formation of the silver oxide phase and its crystalline structure of the prepared samples. The XRD analysis revealed that deposited films exist as polycrystalline mixed-phase material, which is composed of Ag2O, AgO, and metallic Ag. Ultraviolet-visible (UV-Vis) diffuse reflectance spectra were recorded to study the optical properties of deposited films. It was found that Ag-O/PVC composites are direct band gap semiconductors; the optical band gap is 0.89±0.02eV.