Shell thickness dependent photocatalytic activity of EDTA-assisted Ag/ZnO core-shell nanoparticles under sunlight irradiation

Functionalized Ag/ZnO core-shell (CS) nanoparticles (NPs) with ethylenediaminetetraacetic acid (EDTA) having same core size but with different shell thickness are successfully prepared through a simple and low cost wet chemical process. Different physiochemical characterizations including transmission electron microscopy, x-ray diffraction, Brunauer-Emment-Teller surface area analysis, zeta potential analysis, thermal gravimetric-differential analysis, UV-visible absorption spectroscopy, Photoluminescence Spectroscopy and Fourier-transform infrared Spectroscopy have been involved to characterize the samples. The thickness of ZnO shell of Ag/ZnO CS NPs is found to be increasing with increasing molar ratio of EDTA/Zn2+. The LSPR wavelength of Ag core is shifting to longer visible wavelength with increasing the shell thickness of Ag/ZnO CS NPs because of the increase in the dielectric constant of the sourrounding environment. The increasing shell thickness of Ag/ZnO CS NPs makes a strong effect on the decrease in the fluorescence intensity of UV emission of ZnO. This quenching of PL intensity has been further verified by transient fluorescence (FL) spectra. The Nyquist plots also provide evidence of higher electron-transfer rate of the Ag/ZnO CS NPs of having higher shell thickness. The photocurrent measurement confirms electron-charging of Ag core in Ag/ZnO CS NPs. Variation of concentration of EDTA as anionic surfactant causes variation of surface charge of Ag/ZnO CS NPs. With increasing the shell thickness, photodegradation efficiency of Ag/ZnO CS NPs towards methylene blue (MB) degradation enhances under sunlight irradiation. This enhancement in photocatalytic efficiency with increasing the shell thickness is achieved due to the higher surface area, higher charge transfer efficiency, extended light absorption towards visible region and more negative zeta potential of Ag/ZnO CS NPs.