Mechanisms of biochar enhanced Cu2O photocatalysts in the visible-light photodegradation of sulfamethoxazole.

Cu2O nanoparticles are decorated with biochars derived from spent coffee grounds (denoted as Cu2O/SCG) and applied as visible-light-active photocatalysts in the sulfamethoxazole (SMX) degradation. The physicochemical properties of Cu2O/SCG are identified by various spectral analysis, electrochemical and photochemical techniques. As a result, the Cu2O/SCG exhibits the higher removal efficiency of SMX than the pristine Cu2O under visible light irradiation. We can observe that Cu2O could be incorporated onto the SCG biochars with rich oxygen vacancies/adsorbed hydroxyl groups. In addition, the Cu2O/SCG has the lower charge transfer resistance, faster interfacial electron transfer kinetics, decreased recombination of charge carriers and superior absorbance of visible light. The construction of band diagrams for Cu2O/SCG and pristine Cu2O via UV-vis spectra and Mott-Schottky plots suggest that the band energy shifts and higher carrier density of Cu2O/SCG may be responsible for the photocatalytic activity enhancements. From the radical scavenger experiments and electron paramagnetic resonance spectra, the aforementioned energy shifts could decrease the energy requirement of transferring photoinduced electrons to the potential for the formation of active superoxide radicals (·O2-) via one and two-electron reduction routes in the photocatalytic reaction. A proposed degradation pathway shows that ·O2- and h+ are two main active species which can efficiently degrade SMX into reaction intermediates by oxidation, hydroxylation, and ring opening. This research demonstrates the alternative replacement of conventional carbon materials for the preparation of biochar-assisted Cu2O photocatalysts which are applied in the environmental decontamination by using solar energy.

Crystal Facet Dependent Energy Band Structures of Polyhedral Cu2O Nanocrystals and Their Application in Solar Fuel Production.

We demonstrated a facile hydrothermal method to synthesize the (100)-, (110)- and (111)-oriented Cu2O nanocrystals (NCs) by controlling the concentration of the incorporated anions (CO32- and SO32-). The crystal facet dependent activity of the orientation controlled Cu2O NCs in the rhodamine B (RhB) photodegradation and photocatalytic hydrogen (H2) evolution was found to follow the trend: (111) > (110) > (100). The mechanism was investigated by characterizing the optical property, energy band structure, interfacial charge carrier dynamics and reducing ability. The results indicated that the (111)-oriented Cu2O NCs exhibit the higher conduction band (CB) potential as compared with the (110)-oriented and (100)-oriented Cu2O NCs, which resulted in the largest driving force of interfacial electron transfer for (111)-oriented Cu2O NCs to carry out solar fuel generation. The current study offers an easy strategy for crystal facet engineering of semiconductors and provides important physical insights into their electronic properties for the desired solar energy conversions.