Laser-Ablated ZnO Nanoparticles and Their Photocatalytic Activity toward Organic Pollutants

Abstract

This work aimed to prepare nanostructures of ZnO with various lasers, testing them as photocatalysts, and comparing their morphology and activity in the degradation of organic pollutants in aqueous media. ZnO nanospheres (ns-ZnO) and ZnO nanorods (ms-ZnO) were prepared via the laser ablation of a Zn metal plate in water using nanosecond- and millisecond-pulsed lasers, respectively. The obtained materials were characterized using a set of optical, structural, and surface-science techniques, such as UV-vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Under visible-light irradiation, both nanostructures were found to be catalytically active toward the oxidation of methylene blue, which was used as a model compound. The ZnO nanorods fabricated with the millisecond laser showed better photocatalytic performance than their spherically shaped counterparts obtained by means of the nanosecond laser, which could be assigned to a larger number of defects on the ms-ZnO surface.

Hybrid TiO2-ZnO Nanomaterials Prepared Using Laser Ablation in Liquid

“…The surface composition of the prepared hybrid materials was eValuated by carrying out XPS measurements and analyzing Zn 2p, Ti 2p, and O 1s peaks presented below in Figures 7-10. The spin-orbit splitting observed between Zn 2p 3/2 and Zn 2p 1/2 levels in all Zn 2p XPS spectra was the same (23.0 eV), being in agreement with the literature [42,44,51]. Therefore, for convenience, only Zn 2p 3/2 peaks are exhibited in Figure 7.…”

“…The beam was focused on the target surface by a lens with the focal length of 9.0 cm, with a spot diameter of~150 µm. The experimental conditions and sample descriptions are given in Table 1, while more details on the setup used can be found elsewhere [42][43][44]. For simplicity, in Table 1, the samples are divided into two groups: (i) the lower-energy series, which includes samples of TiO 2 -1, ZnO-1, ZnO/TiO 2 -1, and TiO 2 /ZnO-1 and was prepared with a pulse energy of 2.0 J/pulse; and (ii) the higher-energy series, which includes samples of TiO 2 -2, ZnO-2, ZnO/TiO 2 -2, and TiO 2 /ZnO-2, all being prepared with a pulse energy of 5.0 J/pulse.…”

“…Figure 11 presents the UV-vis absorption spectra of all the samples measured as freshly prepared colloids, with the nanomaterials prepared at lower and higher pulse energy being presented in panels (a) and (b), respectively. The characteristic peak of ZnO NPs is observed at 360 and 355 nm for ZnO-1 and ZnO-2, respectively (black spectra) [44]. Both show a blue shift with respect to the bulk ZnO (380 nm) [52], which resulted from a decrease in particle size.…”

“…Interestingly, ZnO nanorods with different aspect ratios depending on pulse width and pulse energy of millisecond-long pulses were obtained by ablating a Zn metal plate in water [42]. Predictably, spherical and rod-shaped ZnO NPs prepared by ns-and ms-pulsed lasers demonstrated different properties when tested as gas sensors and photocatalysts with different morphology and surface defects [43][44][45].…”

Room-Temperature Synthesis of ZnS Nanoparticles Using Zinc Xanthates as Molecular Precursors

“…The photocatalytic experiments were performed using 100 mL of aqueous methylene blue (MB) solution (with concentration 8 × 10 −6 mol/L) and 10 mg of each catalyst according to previously described methodology [39]. Prior to irradiation with visible light, the mixture was stirred in the dark for 30 min to achieve adsorption-desorption equilibrium for each sample tested.…”