Solvothermal Synthesis of ZnO Nanoparticles for Photocatalytic Degradation of Methyl Orange and p-Nitrophenol

Abstract

The photocatalytic degradation of organic pollutants is an effective method of controlling environmental pollution. ZnO nanoparticles (ZnO NPs) were prepared by the solvothermal method and characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–visible diffuse reflectance spectroscopy (UV–Vis DRS). The results showed that the ZnO NPs had a uniform size of 25–40 nm, hexagonal wurtzite structure, and a band gap of 2.99 eV. The photocatalytic degradation of methyl orange (MO) and p-nitrophenol (PNP) was used as a model reaction to evaluate the photocatalytic activity of ZnO NPs. The photocatalytic degradation rates (pseudo-first-order kinetics) of MO and PNP were 92% (0.0128 min−1) and 56.2% (0.0042 min−1), respectively, with a 25 W ultraviolet lamp, MO/PNP concentration = 20 mg/L, ZnO NPs dose = 1.5 g/L, and time = 180 min. The photocatalytic mechanism of ZnO NPs and degradation pathways of MO and PNP were also proposed. The results provide valuable information and guidance for the treatment of wastewater via photocatalytic methods.

Antibacterial Activity of Solvothermal Obtained ZnO Nanoparticles with Different Morphology and Photocatalytic Activity against a Dye Mixture: Methylene Blue, Rhodamine B and Methyl Orange

“…The theoretical value for the band-gap energy is 3.37 eV and is higher than the calculated band-gap energy values for all three samples. Nevertheless, they are in concordance with other literature reports [ 41 , 42 ]. The existence of crystalline defects on the nanoparticle surface, as determined by the XRD data, creates inside the band-gap additional electronic levels, which in turn leads to smaller energy values [ 43 ].…”

Black ZnO nanoparticles synthesized by a green chemistry process

“…Through the estimation of the valence band maximum (VBM) and the energy band gap (E g ) from XPS and UV-vis spectroscopy; it was possible to build a schematic band edge representation of the two ZnO compounds, figure 9. It is observed that vacancies in the black ZnO structure causes a modification of the band edges moving into a region within a more oxidative character, proposing to black ZnO as a reasonable promotor of OH radicals [14,18]; and thus, opening their exploration as a feasible photocatalyst in the UV visible region; in good concordance with preceding reports where vacancies in the structure of the compounds promotes their catalytic performance [74][75][76][77][78][79].…”

“…Zinc oxide nanoparticles (NPs) have been synthesized through soft chemical and physical pathways; chemical routes include techniques such as precipitation, sol-gel, hydrothermal, solvothermal and microemulsion [7][8][9][10][11][12][13][14][15] while physical methods comprise ball milling, laser ablation, continuous arc discharge under controlled atmosphere [16][17][18]. Irrespective of which of these two methods is used, ZnO NPs exhibit a reasonable performance as photocatalyst [14,18,19] or as antibacterial activity material [12,13,[20][21][22].…”

“…ZnO NPs have been successfully attained within the green chemistry approach with potential applications for industrial wastewater treatment [31,32,[35][36][37][38] biological control of plant diseases and plant growth promoter [29,39], anti-cancer drug or as antiangiogenic agent [27,28,33]; and also demonstrating a good biocompatibility, antibacterial, antimicrobial, antifungal activity [12,13,29,30]. The photocatalytic performance of ZnO NPs for degradation of malachite green (MG), methylene blue (MB), rhodamine B dyes and dibenzothiophene contaminant (DBT) has been positively tested [14,18,31,32,35].…”

Influence of the Alcohols on the ZnO Synthesis and Its Properties: The Photocatalytic and Antimicrobial Activities

“…we can determine the direct band-gap energy values by graphical extrapolation to [F(R)•hν] 2 = 0 (Figure 7b). The determined band-gap energy values are smaller than the theoretical value of 3.37 eV, but still close to it [21,34,98]. The multiple surface defects of the nanoparticles, as indicated by the XRD study, induce additional electronic levels inside the band-gap, leading to decreased energy values.…”