Facile Synthesis of Mesoporous Ag2O-ZnO Heterojunctions for Efficient Promotion of Visible Light Photodegradation of Tetracycline

Assignment of the antibacterial potential of Ag2O/ZnO nanocomposite against MDR bacteria Proteus mirabilis and Salmonella typhi isolated from bone marrow transplant patients

The rate of infectious diseases started to be one of the major mortality agents in the healthcare sector. Exposed to increased bacterial infection by antibiotic-resistant bacteria became one of the complications that occurred for bone marrow transplant patients. Nanotechnology may provide clinicians and patients with the key to overcoming multidrug-resistant bacteria. Therefore, this study was conducted to clarify the prevalence of MDR bacteria in bone marrow transplant recipients and the use of Ag2O/ZnO nanocomposites to treat participants of diarrhea brought on by MDR bacteria following bone marrow transplantation (BMT). Present results show that pathogenic bacteria were present in 100 of 195 stool samples from individuals who had diarrhea. Phenotypic, biochemical, and molecular analysis clarify that Proteus mirabilis and Salmonella typhi were detected in 21 and 25 samples, respectively. Successful synthesis of Ag2O/ZnO nanocomposites with a particle enables to inhibition of both pathogens. The maximum inhibitory impact was seen on Salmonella typhi. At low doses (10-5 g/l), it prevented the growth by 53.4%, while at higher concentrations (10-1 g/l), Salmonella typhi was inhibited by 95.5%. Regarding Proteus mirabilis, at (10-5 g/l) Ag2O/ZnO, it was inhabited by 78.7%, but at higher concentrations (10-1 g/l), it was inhibited the growth by 94.6%. Ag2O/ZnO nanocomposite was therefore found to be the most effective therapy for MDR-isolated bacteria and offered promise for the treatment of MDR bacterial infections that cause diarrhea.

Solvothermal-based synthesis of barium stannate nanosheets coupled with copper manganate nanoparticles for efficient photooxidation of tetracycline under visible light

Photocatalytic oxidation of antibiotic waste over semiconducting heterojunction photocatalysts is considered eco-friendly because it is simple and operates under light irradiation. In this work, we apply a solvothermal-based process for obtaining high surface area barium stannate (BaSnO₃) nanosheets followed by adding 3.0-12.0 wt% of spinel copper manganate (CuMn₂O₄) nanoparticles to form n-n CuMn₂O₄/BaSnO₃ heterojunction photocatalyst after calcination process. The CuMn₂O₄-supported BaSnO₃ nanosheets exhibit mesostructure surfaces with a high surface area range of 133-150 m²g^-1. Moreover, introducing CuMn₂O₄ to BaSnO₃ shows a significant broadening in visible light absorption range due to bandgap reduction down to 2.78 eV in 9.0% CuMn₂O₄/BaSnO₃ compared to 3.0 eV for pure BaSnO₃. The produced CuMn₂O₄/BaSnO₃ is used for photooxidation of tetracycline (TC) in water as emerging antibiotic waste under visible light. The photooxidation of TC exhibits the first-order reaction model. The specific dose of 9.0 wt% CuMn₂O₄/BaSnO₃ at 2.4 gL^-1 displays the highest-performed and recyclable photocatalyst for total oxidation of TC after 90 min. This sustainable photoactivity is attributed to the improved light harvesting and charges migration upon coupling between CuMn₂O₄ and BaSnO₃.

Ag2O-adorned ZnO nanostructures: cooperative and sustainable nanomaterial system for effective reduction and mineralization of hazardous water pollutants

Organic water pollutants like nitroaromatics and synthetic dyes are causing serious threats to water. Ever-growing urban and industrial activities along with population explosion are rapidly contributing severe level of water contamination. Semiconducting nanomaterial-based photocatalysis has been proven to be an effective process for degradation of organic water pollutants. In the current study, visible light active Ag₂O-adorned ZnO nanostructures were fabricated by a simple two-step hydrothermal method and the prepared nanostructures were utilized for the photocatalytic mineralization of rhodamine B (RhB) dye with visible light radiation. The catalytic potential of as-synthesized nanostructures was also investigated for the reduction of nitroaromatics (4-NP and 4-NA) and RhB dye in the presence of NaBH₄. The Ag₂O-adorned ZnO nanostructures prepared with 5% of silver nitrate denoted as ZnO/Ag₂O (5%) demonstrated stupendous photomineralization activity against RhB dye as almost 100% degradation of RhB dye was achieved within 100 min of reaction time at pH = 6. The kinetic study revealed that the degradation reaction followed the pseudo-first-order kinetics and the kinetic rate constant (k) of photodecolorization reaction for optimal catalyst was calculated to be 61.4 × 10^-3 min^-1. The nanostructures revealed excellent recyclability and photostability as 95% activity of the catalyst was preserved even after the fifth cyclic run. The catalytic reduction of the 4-NP, 4-NA, and RhB dye was completed in 21, 12, and 40 min, respectively, in the presence of ZnO/Ag₂O (5%) and NaBH₄ solution. The kinetic rate constant values for the reduction reactions were determined to be 229.6 × 10^-3, 454.2 × 10^-3, and 105.5 × 10^-3 min^-1 for 4-NP, 4-NA, and RhB dye, respectively. Thus, the obtained results suggest that the components of the prepared nanosystem help in mutually strengthening the catalytic and photocatalytic abilities of each other, indicating the development of a cooperative and sustainable nanomaterial system in the current study.

Immobilization of photocatalytic materials for (waste)water treatment using 3D printing technology - advances and challenges

Photocatalysis has been considered a promising technology for the elimination of a wide range of pollutants in water. Various types of photocatalysts (i.e., homojunction, heterojunction, dual Z-scheme photocatalyst) have been developed in recent years to address the drawbacks of conventional photocatalysts, such as the large energy band gap and rapid recombination rate of photogenerated electrons and holes. However, there are still challenges in the design of photocatalytic reactors that limit their wider application for real (waste)water treatment, such as difficulties in their recovery and reuse from treated (waste)waters. 3D printing technologies have been introduced very recently for the immobilization of materials in novel photocatalytic reactor designs. The present review aims to summarize and discuss the advances and challenges in the application of various 3D printing technologies (i.e., stereolithography, inkjet printing, and direct ink writing) for the fabrication of stable photocatalytic materials for (waste)water treatment purposes. Furthermore, the limitations in the implementation of these technologies to design future generations of photocatalytic reactors have been critically discussed, and recommendations for future studies have been presented.

Enhanced Visible-Light-Driven Photocatalysis of Ag/Ag2O/ZnO Nanocomposite Heterostructures

Visible-light-driven photocatalysis is one promising and efficient approach for decontaminating pollutants. Herein, we report the combination of localized surface plasmon resonance (LSPR) and p-n heterojunction structure Ag-Ag₂O-ZnO nanocomposite synthesized by a hydrothermal process for the suppression of photogenerated electron-hole pair recombination rates, the extension of the absorption edge to the visible region, and the enhancement of photocatalytic efficiency. The prepared nanocomposites were investigated by standard analytical techniques and the results revealed that the synthesized powders were comprised of Ag, Ag₂O, and ZnO phases. Photocatalytic activity of the photocatalyst tested for methylene blue, methyl orange, and rhodamine B showed the highest photocatalytic degradation efficiency: 97.3%, 91.1%, and 94.8% within 60 min under visible-light irradiation. The average lifetime of the photogenerated charge carriers was increased twofold in the Ag-Ag₂O-ZnO photocatalyst (~10 ns) compared to the pure ZnO (~5.2 ns). The enhanced photocatalytic activity resulted from a decrease of the charge carrier recombination rate as inferred from the steady-state and time-resolved photoluminescence investigations, and the increased photoabsorption ability. The Ag-Ag₂O-ZnO photocatalyst was stable over five repeated cyclic photodegradation tests without showing any significant changes in performance. Additionally, the structure indicated a potential for application in environmental remediation. The present study showcases the robust design of highly efficient and reusable visible-light-active photocatalysts via the combination of p-n heterojunction and LSPR phenomena.

Two-Step Visible Light Photocatalytic Dye Degradation Phenomena in Ag2O-Impregnated ZnO Nanorods via Growth of Metallic Ag and Formation of ZnO/Ag0/Ag2O Heterojunction Structures

Visible light photocatalytic activity follows the single-slope pseudo-first-order reaction kinetics in pristine ZnO nanorods, while for pure Ag₂O, a two-slope paradigm is pursued with a higher slope at a later period. For the Ag₂O-impregnated ZnO heterostructured nanorod photocatalyst, the two-step photocatalysis phenomena proceed with dye degradation rate constants emerging higher than those of individual ZnO and Ag₂O, at both time zones. Improved performance of ZnO/Ag₂O heterostructures arises initially from the reduced e^-/h⁺ recombination rate by the synergistic effect between ZnO and Ag₂O. At a later phase, metallic Ag is produced, which traps the valence electrons of Ag₂O nanoparticles and advances the e^-/h⁺ separation across the ZnO/Ag⁰/Ag₂O heterojunction structures, rendering them promptly accessible for dye degradation. At an increased Ag₂O loading, the photodegradation rate constants boost up in both time zones, and the corresponding crossover time (t_C) between the two phases steadily diminishes, leading toward a unique photocatalytic phenomenon that prevails with a superior rate constant. The optimized ZAO₂₅ heterostructure photocatalyst demonstrates ∼96.24% photodegradation of methylene blue (MB) dye within 30 min of visible light exposure, and its degradation rate constant is ∼0.24848 min^-1, which is ∼26.75 times superior than that of pristine ZnO samples. The metal-induced biphasic photocatalysis phenomena have never been reported earlier.

Mesoporous TiO2 Implanted ZnO QDs for the Photodegradation of Tetracycline: Material Design, Structural Characterization and Photodegradation Mechanism

A sol-gel method was used to prepare a mesoporous TiO2 implanted with a ZnO quantum dot photocatalyst (TZQ) for the photodegradation of tetracycline (TC) under fluorescent light irradiation. Scanning electron microscopy (SEM) shows the presence of cavities on the photocatalyst surface due to the use of starch as a synthetic template, where the nitrogen sorption results indicate that TZQ contains mesopores with reduced size (ca. 4.3 nm) versus the pore size of the parent meso-TiO2 (ca. 7.5 nm). The addition of ZnO quantum dots (QDs) resulted in spherically-shaped binary composite particles in layers onto the surface of TiO2. The coexistence of the ZnO QDs and TiO2 phase was observed using high resolution-transmission electron microscopy (HR-TEM). The photodegradation of TC was carried out in a homemade reactor equipped with two fluorescent lights (24 W each) and within 90 min of irradiation, 94.6% of TC (40 mg L−1) was photodegraded using 250 mg L−1 of TZQ at pH 9. The major reactive oxygen species identified from the scavenging tests were O2●− followed by HO●. The deconvolution of the photoluminescence spectrum of TZQ indicates the presence of a strong quantum confinement effect (QCE) of the ZnO QDs, a defect related to Ti-species and oxygen. The analysis of the intermediates detected by LC-time-of-flight/mass spectrometry (LC/TOF-MS) suggest two photodegradation pathways. The pathways were validated using the Fukui function approach and the Wheland localisation approach. This simple and efficient photocatalytic technology is anticipated to benefit small-scale animal husbandries and aquaculture operators that have limited access to sustainable water treatment technology.

A New Approach for the Green Biosynthesis of Silver Oxide Nanoparticles Ag2O, Characterization and Catalytic Application

In this paper, a facile and green approach for the synthesis of silver oxide nanoparticles Ag2O NPs was performed using the extract of the wild plant Herniaria hirsuta (H. hirsuta). Different spectral methods were used for the characterization of the biosynthesized Ag2O NPs, ultraviolet-visible (UV-Vis) spectroscopy gave a surface plasmon resonance (SPR) peak of Ag2O NPs is 430 nm, estimation of direct and indirect forbidden gap bands are respectively 3.76 eV and 3.68 eV; Fourier transform infrared (FTIR) spectral analysis revealed the groups responsible for the stability and synthesis of Ag2O NPs. The morphology of Ag2O NPs was studied by scanning electron microscopy (SEM) showing a nearly spherical shape of Ag2O NPs, and X-ray diffraction (XRD) study confirmed the crystallinity of Ag2O NPs with a crystallinity size of 15.51 nm. The catalytic activity of Ag2O NPs, as well as the rings number were studied by the degradation of methylene blue dye. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Improving the Performance of ZnS Photocatalyst in Degrading Organic Pollutants by Constructing Composites with Ag2O

ZnS is a promising photocatalyst in water purification, whereas its low photon efficiency and poor visible-light response restrict its application. Constructing composites may help solve these problems. In this work, Ag₂O was introduced to ZnS for the first time based on their energy band characteristics to form a novel ZnS/Ag₂O composite photocatalyst. In the model reaction of degrading methylene blue, the as-designed catalyst exhibited high catalytic activity among a series of ZnS-based composite photocatalysts under similar conditions. The catalytic rate constant was up to 0.138 min⁻¹, which is 27.4- and 15.6-times higher than those of ZnS and Ag₂O. This composite degraded 92.4% methylene blue in 50 min, while the ratios were 31.9% and 68.8% for ZnS and Ag₂O. Catalytic mechanism study based on photoluminescence and radical-scavenging experiments revealed that the enhanced photocatalytic activity was attributed to the composite structure of ZnS/Ag₂O. The structure not only facilitated the separation and transmission of photogenerated carriers but also extended the light response range of the catalyst. The as-designed ZnS/Ag₂O composite is promising in degrading organic pollutants in water.

Fabrication of Mesoporous PtO-ZnO Nanocomposites with Promoted Photocatalytic Performance for Degradation of Tetracycline

Herein, we report a simple incorporation of PtO NPs at diverse percentages (0.2-0.8 wt %) onto a highly crystalline and mesoporous ZnO matrix by the wet-impregnation approach for degradation of tetracycline (TC) upon visible light exposure. These well-dispersed and small-sized PtO NPs provide the mesoporous PtO-ZnO nanocomposites with outstanding photocatalytic performance for complete TC degradation. The optimized 0.6% PtO-ZnO photocatalyst exhibits excellent TC degradation, and its degradation efficiency reached ∼99% within 120 min. The photocatalytic performance of the 0.6% PtO-ZnO nanocomposite is 20 and 10 times higher than that of pristine ZnO and commercial P-25, respectively. The photodegradation rate of TC over the 0.6% PtO-ZnO nanocomposite is 34 and 12.5 times greater than that of pristine ZnO and commercial P-25, respectively. This is because of the large surface area, unique porous structure, synergistic effect, and broad visible light absorption of the PtO-ZnO nanocomposite. Moreover, mesoporous PtO-ZnO nanocomposites showed a high stability and recyclability over five iterations. This work demonstrates the remarkable role of combining PtO and ZnO photocatalysts in providing nanocomposites with significant potential for the preservation of human health through wastewater remediation.