Abstract
Surface enhanced Raman spectroscopy (SERS) is considered a versatile and multifunctional technique with the ability to detect molecules of different species at very low molar concentration. In this work, hierarchical ZnO microspheres (ZnO MSs) and Ag/ZnO MSs were fabricated and decorated by hydrothermal and photodeposition methods, respectively. For Ag deposition, precursor molar concentration (1.9 and 9.8 mM) and UV irradiation time (5, 15, and 30 min) were evaluated by SEM, TEM, X-ray diffraction and Raman spectroscopy. X-ray diffraction showed a peak at 37.9° corresponding to the (111) plane of Ag, whose intensity increases as precursor concentration and UV irradiation time increases. SEM images confirmed the formation of ZnO MSs (from 2.5 to 4.5 µm) building by radially aligned two-dimensional ZnO nanosheets with thicknesses below 30 nm. The Raman spectra of Ag/ZnO MSs exhibited a vibration mode at 486 cm−1 which can be directly associated to Ag deposition on ZnO MSs surface. The performance of SERS substrate was evaluated using rhodamine 6G. The SERS substrate grown at 9.8 mM during 30 min showed the best SERS activity and the ability to detect methylene blue at 10−9 M.
Highlights
The first step involves the synthesis of the hierarchical zinc oxide microspheres (ZnO MSs), where Zn (CH3 COO)2 ·2H2 O and NaOH were used as precursors, which were mixed and taken to an autoclave at 100 ◦ C for 5.5 h, cooled down to room temperature and the product was dried
It is easy to observe that absorption intensity is increased when the Ag amount is as AgNO3 concentration or the photodeposition time increase, similar to the behavior reported by other authors [13,14,15]
Was uated according to their growth conditions
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Many SERS substrates have been proposed to enhance the Raman signals with metal nanoparticles (NPs) fixed over surface of cellulose fibers [1], metals [2], polymers [3], or metal-oxide nanostructures [4,5,6], with an extensive variety of shapes and sizes to take advantage of the higher surface-volume ratio They are usually made in a two-step process, harmonizing chemical and physical methods to successfully synthesize a high-surface template first, and decorate it with metal NPs. Some combinations observed are hydrothermal in the first step and use chemical reduction in the second step [4], such as hydrothermal and in situ solution crystal growth [5], hydrothermal/magnetron sputtering [6], and solvothermal/Sn (II) ion activation [7]. The performance of the SERS substrate was probed with R6G and methylene blue (MB) detection
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