Preparation of Cu–Cu2O–CuO by solid combustion ignited by dielectric barrier discharge and its activity towards p-nitrophenol reduction

Abstract

Cu–Cu₂O–CuO samples were prepared by solid combustion ignited by dielectric barrier discharge (DBD) plasma at room temperature and atmospheric pressure. The solid is proportionally composed of copper nitrate and citric acid (φ = 0.5–2.0, which is a ratio of citric acid to copper nitrate). The ignition of solid primarily depends on the highly active species produced by DBD plasma rather than the generated heat. The water content in the precursor is a key factor in initiating combustion because water can produce more active oxidizing species in plasma discharge. XPS results show that all samples are composed of three different valence coppers: Cu²⁺, Cu⁺, and Cu⁰. XRD confirms that the main crystalline phase of the samples is changed from Cu₂O (φ = 0.5) to Cu (φ = 0.75–1.0), and then to the mixed phase of Cu₂O and CuO (φ = 1.5, 2.0). The samples take on spheres or flakes, respectively, which form H₃-type mesoporous. These samples showed high activities in the catalytic reduction of p-nitrophenol using sodium borohydride as a reducing agent. In addition, the sample prepared by inducing combustion in muffle furnace (chemical method) shows completely different physical and crystal structures compared with the DBD-prepared sample. The differences in nature are due to the low temperature properties of DBD plasma and inducing solid combustion by its unique active species. For the φ = 1.5 sample, the catalytic activity for p-nitrophenol reduction over the DBD sample was 6–7 times higher than that over the chemical method sample.