RESUMO
A Pr-doped p-Cu2O thin film was prepared on indium tin oxide conductive glass by electrochemical deposition; the effect of Pr doping on the structure, morphology, and physicochemical properties of p-Cu2O was investigated. The results show that with the increase in Pr doping amount, the particle size of p-Cu2O increases, the absorption boundary redshifts, and the band-gap width decreases. Pr doping increases the flat band potential and carrier concentration of p-Cu2O; when the doping amount is 1.2 mM, the carrier concentration reaches 1.14 × 1024 cm-3. Compared with pure p-Cu2O, the charge transfer resistance of Pr-doped p-Cu2O decreases and the photocurrent and open circuit voltage increase, indicating that the carrier transfer rate is accelerated, and the separation efficiency of photogenerated electrons and holes is effectively improved. The result of a norfloxacin photocatalytic degradation experiment showed that the degradation rate of norfloxacin increased from 52.3% to 76.2% and Pr doping effectively improved the photocatalytic performance of p-Cu2O. The main reasons for enhancing the photocatalytic performance are that the band gap of Pr-doped p-Cu2O decreases, the Fermi level of Cu2O is closer to the valence band position, the hole concentration near the valence band, and the oxidation capacity increases, and more h+ oxidize norfloxacin molecules. In addition, the Pr in Pr-Cu2O acts as a conductor to guide electrons on the guide band to the crystal surface, which increases the contact between photogenerated electrons and dissolved oxygen, which is conducive to the formation of the active species ·O2- and can effectively reduce the recombination of photogenerated carriers. In the process of photocatalytic degradation of norfloxacin, the main active species are ·O2-, ·OH, and h+, which play auxiliary roles. TOC tests show that the norfloxacin molecules can be effectively degraded into small molecule organic matter, CO2, and H2O in the presence of Pr-doped p-Cu2O.
RESUMO
A two-step electrochemical deposition technique was applied to fabricate p-Cu2O/n-ZnO heterojunction thin films. The influence of the deposition potential upon photoelectric performance of the prepared samples was examined utilizing XRD, XPS, SEM, UV-Vis, and electrochemical tests. The results show that the deposition potential has a substantial influence on the properties of the prepared samples. When the deposition potential is -0.45 V, the peak intensity of the (111) crystal plane of the prepared heterojunction is the highest, the band gap increased, and the morphology changes obviously compared to those of Cu2O. The transient photocurrent value is three times that of pure Cu2O, and the charge transfer resistance significantly reduced. The p-Cu2O/n-ZnO heterojunction has a high carrier concentration. Photocatalytic degradation experiments show that degradation rate of norfloxacin increases by 14.4%-76.6%. The enhanced photocatalytic performance of Cu2O is mainly due to the formation of a high-quality heterojunction and the change in the energy band structure, which promotes the transfer rate of the carrier and the separation of photogenic electron hole pairs, thus effectively improving the catalytic efficiency of photocatalysts. Active species detection experiments reveal that positive hole and superoxide anion radical play leading roles in norfloxacin molecule decomposition. In addition, a possible mechanism for the photocatalytic performance of p-Cu2O enhanced by n-ZnO is proposed according to the analysis of the bandgap of p-Cu2O and n-ZnO, along with the built-in electric field formed in the p-n heterojunction. This study provides an effective and alternative method for removing norfloxacin residues in wastewater.