Synthesis And Catalytic Activity Study Of Nanoporous Cu-based Oxide Composites

In this thesis, we present a facile two-step strategy to fabricate a novel nanoporous core-shell Cu-based nanocomposite catalyst. The catalyst was synthesized via the combination of dealloying of the as-milled Al66.7Cu33.3(at.%) precursor powders in sodium hydroxide with subsequent surface oxidation in air (or thermal treatment). The microstructure of the as-prepared photocatalyst has been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and specific surface area analyzer.The results show that, as the photocatalyst, the nanocomposite is comprised of Cu (core) and Cu2O (shell) phases. It exhibits an open, bicontinuous interpenetrating ligament (ca.30nm)-channel (ca.15nm) structure, with the BET surface area of19.5m2g-1. During photocatalysis, methyls orange (MO) was used as the model pollutant and photodegradation experiments were monitored by an UV-vis Spectrophotometer. The nanoporous core-shell Cu@Cu2O photocatalyst shows excellent photocatalytic activity towards degradation of MO under sunlight. The MO degradation rate can reach as high as8.04mg min-1gcat-1.In addition, the influence of additive amounts of photocatalyst and initial concentrations of MO on the photodegradation process has been investigated. The photodegradation mechanism of the as-prepared photocatalyst has also been discussed.Adsorption behavior of methyl orange onto nanoporous core-shell Cu@Cu2O nanocomposite is an important precondition of photocatalysis. Hence, it is necessary to perform systematic study on adsorption. To investigate the effects of different conditions on adsorption systems, pH value, temperature, additive amount of nanocomposite and initial methyl orange (MO) concentration have been considered. The adsorption kinetics of MO on the Cu@Cu2O nanocomposite has been discussed based upon the pseudo-first-order model, intraparticle diffusion model and Langmuir adsorption model. Thermodynamic parameters such as change in Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) have also been evaluated. The negative changes in Gibbs free energy (-18.4to-15.1kJ mol-1) and enthalpy (-51.5kJ mol-1) indicate the spontaneous and exothermic nature of the adsorption process of MO. The activation energy (Ea) of12.4kJ mol-1reveals the physisorption nature of MO adsorption onto the nanoporous Cu@Cu20nanocomposite.Thermal treatment has been utilized to further prepare the nanoporous Cu oxide system from the as-dealloyed Cu and Cu2O nanocomposite. The as-prepared Cu-O system exhibits excellent catalytic activity. Although all of the samples can achieve100%conversion below200℃, the catalysts synthesized under different conditions still have apparent difference in catalytic performance. For example, the as-dealloyed catalysts after thermal annealing in air at300℃and subsequent200℃in hydrogen show the most enhanced catalytic activity, with a complete conversion at130℃. The activation energy calculation results reveal the as-synthesized sample owns a comparable activity with the reported CuO catalysts. It should be highly noted that the dealloying and thermal annealing strategy to prepare nanoporous Cu-based oxides is more simple and easy to be operated. Besides, it has a remarkable advantage in the realization of batch production.