In this study, nanotubes/nanorods-like structures of Zn0.97La0.03O compound were synthesized at different pH values (pH = 8, 9, 10, 11, and 12), and the photocatalytic response for Methylene Blue (MB) dye and Ciprofloxacin (CIP) drug were investigated. It was verified that the pH variation directly impacts the ZnO crystal structure, morphology, optical and photocatalytic properties. The basic and alkaline pH values cause a decrease in the crystallite size and these differences may have contributed to the band gap energy values variations. Oxygen vacancy defects (VO, VO+, and VO++) were abundant in the La-doped ZnO samples, which also demonstrated to be formed from mesopores, as seen in N2 adsorption/desorption results. The photocatalytic response of the materials was verified in MB and CIP solutions under UV irradiation conditions. The sample synthesized at pH 9 (ZL9) demonstrated greater capacity to remove MB (91.45 %) and CIP (87.6 %) in typical pseudo-first-order kinetics. Using different inhibitors, it was observed that the •OH radicals were the species involved in the photocatalysis of pollutants for the ZL9 sample. In addition, this material demonstrated a satisfactory ability to remove pollutants even after three consecutive uses. This study demonstrates that pH is an important parameter to consider in the synthesis process of ZnO nanostructures, directly influencing the structural, optical, and morphological properties and the degradation of highly dangerous dyes and drugs. 

Nanotubes/nanorods-like structures of La-doped ZnO for degradation of Methylene Blue and Ciprofloxacin

Zinc oxide is a wonder of nature because it has infinite properties. The boom of this semiconductor arises due to its versatility in optoelectronic applications and for being a hopeful material for environmental remediation. Changes in the synthesis parameters and one or more cations inclusion in the structure are alternatives used to make ZnO the most impressive semiconductor material. In this study, we synthesize and characterize the Zn1-x-yPrxAlyO system, [x, y] = (0.00, 0.00); (0.03, 0.01); (0.03, 0.03) for use in the photocatalytic discoloration of methyl orange. Variations in structural parameters are linked to the Zn2+ cations with Pr3+ and Al3+ cations replacement, as well as atomic disorder in the structure. According to Raman spectra, the E2(high) characteristic of oxygen vibration in the ZnO crystal structure undergoes a small shift toward higher wavenumbers, suggesting the oxygen defects presence. The PL spectra were fitted using a Gaussian function, and the results confirmed high zinc vacancy (VZn) and neutral oxygen vacancy (VO) concentrations in the Zn1-x-yPrxAlyO compound. In addition, the Pr3+ and Al3+ ions insertion into ZnO causes variations in the band gap and Urbach energy. The Field Emission Scanning Electron Microscopy (FE-SEM) micrographs confirmed that the samples have irregular particle clusters. The photocatalytic tests demonstrated that the dopant contributed to increased methyl orange dye (MO) discoloration, reaching values between 53.7 and 90.0% of pollutant removal. The scavenger tests suggested that the reactive species responsible for the photodegradation/discoloration mechanism of the MO dye in solution are in the next order: •O2− > •OH > e− > h+. Finally, the samples maintained structural integrity after three consecutive reuse cycles while removing 22.7% of the MO dye. This study demonstrates the viability of inserting Pr3+ and Al3+ cations into the ZnO crystal structure to improve semiconductor efficiency for environmental applications. 

Influence of Al cations insertion on the structural, morphological, optical properties, and methyl orange photocatalytic remotion of Pr-doped ZnO system

We present a study on the green synthesis of undoped and Er-doped ZnO compounds using Mangifera indica gum (MI). A set of tests were conducted to assess the structure of the material. The tests included X-ray diffraction, Raman, and Fourier-transform infrared spectroscopy. Optical properties were studied using diffuse reflectance and photoluminescence. Morphological and textural investigations were done using SEM images and N2 adsorption/desorption. Furthermore, photocatalytic tests were performed with methylene blue (MB), yellow eosin (EY), and the pharmaceutical drug ibuprofen (IBU) under UV irradiation. The study demonstrated that replacing the stabilizing agent with Mangifera indica gum is an effective method for obtaining ZnO nanoparticles. Additionally, the energy gap of the nanoparticles exhibits a slight reduction in value. Photoluminescence studies showed the presence of zinc vacancies and other defects in both samples. In the photocatalytic test, the sample containing Er3+ exhibited a degradation of 99.7% for methylene blue, 81.2% for yellow eosin, and 52.3% for ibuprofen over 120 min. In the presence of methyl alcohol, the degradation of MB and EY dyes is 16.7% and 55.7%, respectively. This suggests that hydroxyl radicals are responsible for the direct degradation of both dyes. In addition, after the second reuse, the degradation rate for MB was 94.08%, and for EY, it was 82.35%. For the third reuse, the degradation rate for MB was 97.15%, and for EY, it was 17%. These results indicate the significant potential of the new semiconductor in environmental remediation applications from an ecological synthesis.

Green Synthesis of Er-Doped ZnO Nanoparticles: An Investigation on the Methylene Blue, Eosin, and Ibuprofen Removal by Photodegradation

This work adopted a green synthesis route using cashew tree gum as a mediating agent to obtain Ni-doped ZnO nanoparticles through the sol–gel method. Structural analysis confirmed the formation of the hexagonal wurtzite phase and distortions in the crystal lattice due to the inclusion of Ni cations, which increased the average crystallite size from 61.9 nm to 81.6 nm. These distortions resulted in the growth of point defects in the structure, which influenced the samples’ optical properties, causing slight reductions in the band gaps and significant increases in the Urbach energy. The fitting of the photoluminescence spectra confirmed an increase in the concentration of zinc vacancy defects (VZn) and monovacancies (Vo) as Zn cations were replaced by Ni cations in the ZnO structure. The percentage of VZn defects for the pure compound was 11%, increasing to 40% and 47% for the samples doped with 1% and 3% of Ni cations, respectively. In contrast, the highest percentage of VO defects is recorded for the material with the lowest Ni ions concentration, comprising about 60%. The influence of dopant concentration was also reflected in the photocatalytic performance. Among the samples tested, the Zn0.99Ni0.01O compound presented the best result in MB degradation, reaching an efficiency of 98.4%. Thus, the recovered material underwent reuse tests, revealing an efficiency of 98.2% in dye degradation, confirming the stability of the photocatalyst. Furthermore, the use of different inhibitors indicated that •OH radicals are the main ones involved in removing the pollutant. This work is valuable because it presents an ecological synthesis using cashew gum, a natural polysaccharide that has been little explored in the literature.

Facile Synthesis of Ni-Doped ZnO Nanoparticles Using Cashew Gum: Investigation of the Structural, Optical, and Photocatalytic Properties

In this work, we have investigated the effect of Cr3+ cations addition on the structural, morphological, optical, and photocatalytic properties of Er-doped ZnO structures. The Zn(1-(x-y))ErxCryO compound, where [(x; y) = (0.00; 0.00), (0.02; 0.01), (0.02; 0.02) and (0.02; 0.03)] was synthesized by the co-precipitation method and thermally treated at 100 °C for 6 h. The structural study showed that the dopant cations concentrations, cause variations in lattice constants, and increase the crystallite size and the strain in the ZnO crystal lattice. The structural atomic disorder was confirmed by Raman and photoluminescence spectroscopies, with VO, VO+, and VO++ type oxygen vacancy defects dominating. The samples exhibited different morphologies depending on the dopant concentration (plates-like, irregular hemispherical particles, and octahedrons-like structures). In the photocatalytic test, the methylene blue (MB) dye degradation under UV irradiation increased as a function of Cr3+ cations concentration, achieving a degradation rate of 37.4 ± 1.9% for the sample containing 2% of Er3+ cations and 3% of Cr3+ cations. In addition, the MB dye removal capacity by the Zn(1-(x-y))ErxCryO compound was incremented to above 85% using an optimized H2O2 concentration. Finally, the irradiated solution did not show toxicity against Artemia salina, indicating that the intermediate photoproducts formed are not toxic. 

Effect of Cr cations addition on the structural, morphological, optical, and photocatalytic properties of Er-doped ZnO structures

In this work, a ZnO hemisphere-like structure co-doped with Er and Cr was obtained by the co-precipitation method for photocatalytic applications. The dopant’s effect on the ZnO lattice was investigated using X-ray diffraction, Raman, photoluminescence, UV-Vis and scanning electron microscopy/energy dispersive spectroscopy techniques. The photocatalytic response of the material was analyzed using methylene blue (MB) as the model pollutant under UV irradiation. The wurtzite structure of the Zn0.94Er0.02Cr0.04O compound presented distortions in the lattice due to the difference between the ionic radii of the Cr3+, Er3+ and Zn2+ cations. Oxygen vacancy defects were predominant, and the energy competition of the dopants interfered in the band gap energy of the material. In the photocatalytic test, the MB degradation rate was 42.3%. However, using optimized H2O2 concentration, the dye removal capacity reached 90.1%. Inhibitor tests showed that •OH radicals were the main species involved in MB degradation that occurred without the formation of toxic intermediates, as demonstrated in the ecotoxicity assays in Artemia salina. In short, the co-doping with Er and Cr proved to be an efficient strategy to obtain new materials for environmental remediation.

/pdf/photoresponsive-activity-of-the-zn0-94er0-02cr0-04o-compound-2chafl44.pdf

Photoresponsive Activity of the Zn0.94Er0.02Cr0.04O Compound with Hemisphere-like Structure Obtained by Co-Precipitation

Herein, a study about to eco-friendly synthesis of Zn0.97La0.03O compound using Mangifera Indica gum and its application in the methylene blue and eosin dyes discoloration was conducted. The compound presented lattice and surface defects that enhanced the photocatalytic activity. Defect concentrations were determined by area percentages under Gaussian curves fitted from the Photoluminescence spectrum. The concentrations were V0 = 39.63 %, V0+ = 11.82 %, and VZn = 48.55 %. Furthermore, the compound exhibited a significant surface area measuring 12.2 m2 g−1 and an average particle size of 34 nm. The photocatalytic test showed that the Zn0.97La0.03O compound had a discoloration rate of 100 % for methylene blue and 77.8 % for yellow eosin. The scavenger tests confirmed that holes and hydroxyl radicals were the crucial species in the decolorization mechanisms. Finally, after three cycles, the material effectively removed methylene blue (100 %), but only removed 48.1 % of eosin in the third cycle. 

Eco-friendly synthesis of Zn0.97La0.03O compound with natural polysaccharide and its application in methylene blue and eosin dyes discoloration

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Green Synthesis of Er-Doped ZnO Nanoparticles: An Investigation on the Methylene Blue, Eosin, and Ibuprofen Removal by Photodegradation

Facile Synthesis of Ni-Doped ZnO Nanoparticles Using Cashew Gum: Investigation of the Structural, Optical, and Photocatalytic Properties

Photoresponsive Activity of the Zn0.94Er0.02Cr0.04O Compound with Hemisphere-like Structure Obtained by Co-Precipitation

Eco-friendly synthesis of Zn0.97La0.03O compound with natural polysaccharide and its application in methylene blue and eosin dyes discoloration