Ultrasonic and vitamin C mediated synthesis of plasmonic Ag-, Cu-, and Ag/Cu-TiO2 for photocatalytic degradation of Rhodamine B

Industrial activities are an essential driver of the global-economy growth. However, those activities release large amount of wastewater which can seriously contaminate water supplies in the environment. Titanium dioxide (TiO2) nanoparticles have been extensively utilized in photocatalytic water remediation due to their non-toxic, chemical stability, and optical properties. However, the limitation of TiO2’s absorption band (only in the UV spectrums) has initiated many researchers to modify the TiO2 photocatalyst with various elements to extend its light absorption into the visible range. Herein, TiO2 has been successfully modified with Ag, Cu, and Ag/Cu using double green approaches including vitamin C (ascorbic acid) as a reducing agent and utilizing ultrasonication during the reaction to minimize the energy consumption. The XRD pattern exhibited that all modified TiO2 was in the anatase phase with crystallite sizes from 10.75 nm to 16.45 nm. Due to the plasmonic properties of Ag and Cu nanoparticles, the band-gap energies of modified TiO2 reduced from 3.08 eV to 2.79 eV. In addition, FE-SEM and TEM images showed porous morphologies with irregular shapes. HR-TEM and SAED analysis of the Ag/Cu-TiO2 sample was also in line with the XRD result i.e., anatase phase. The presence of Ag and Cu nanoparticles was successfully detected using EDX and XPS investigations. Furthermore, the photocatalytic activities of the samples were examined for Rhodamine B (RhB) degradation under both UV and visible irradiation. The results showed that modification of TiO2 with Ag/Cu was most favorable for RhB degradation under UV light with the degradation percentage and rate of 96.29 % and k = 0,0415 min-1, respectively. However, under visible light, Cu-TiO2 revealed more efficient RhB degradation (97.93 %; k = 0.0787 min-1) compared with Ag/Cu-TiO2 (95.00 %; k = 0.0542 min-1). Interestingly, all samples showed more favorable for RhB degradation under visible light than UV light. It might be due to their synergic effect of plasmonic and electron acceptor properties of Ag and Cu nanoparticles. From this point of view, the determination of mono- (Ag or Cu) or bimetallic (Ag/Cu) modifications of TiO2 and the utilization of suitable light spectra (UV or visible light) have played a critical role in efficient RhB degradation.