Template free synthesis of ZnO/Ag2O nanocomposites as a highly efficient visible active photocatalyst for detoxification of methyl orange

Biological Renewable Cellulose-Templated Zn1-XCuXO/Ag2O Nanocomposite Photocatalysts for the Degradation of Methylene Blue

Herein, Cellulose-templated Zn1-XCuXO/Ag2O nanocomposites were prepared using biological renewable cellulose extracted from water hyacinth (Eichhornia crassipes). Cellulose-templated Cu-doped ZnO catalysts with different amounts of Cu as the dopants (1, 2, 3, and 4%) were prepared and denoted CZ-1, CZ-2, CZ-3, and CZ-4, respectively, for simplicity. The prepared catalysts were tested for the degradation of methylene blue (MB), and 2% Cu-doped ZnO (CZ-2) showed the best catalytic performance (82%), while the pure ZnO, CZ-1, CZ-3, and CZ-4 catalysts exhibited MB dye degradation efficiencies of 54, 63, 65, and 60%, respectively. The best catalyst (CZ-2) was chosen to further improve the degradation efficiency. Different amounts of AgNO3 (10, 15, 30, and 45 mg) were used for the deposition of Ag2O on the surface of CZ-2 and denoted CZA-10, CZA-15, CZA-30, and CZA-45, respectively. Among the composite catalysts, CZA-15 showed remarkable degradation efficiency and degraded 94% of MB, while the CZA-10, CZA-30, and CZA-45 catalysts showed 90, 81, and 79% degradation efficiencies, respectively, under visible light within 100 min of irradiation. The enhanced catalytic performance could be due to the smaller particle size, the higher electron and hole separation and charge transfer efficiencies, and the lower agglomeration in the composite catalyst system. The results also demonstrated that the Cu-doped ZnO prepared with cellulose as a template, followed by the optimum amount of Ag2O deposition, could have promising applications in the degradation of organic pollutants.

Ag2O@UiO-66 new thin film as p-n heterojunction: permanent photoreduction of hexavalent Cr

The new nanosphere Ag2O@UiO-66 thin-film was synthesized on a stainless steel mesh surface via an electrophoretic deposition method, and is used as an effective and low-cost photocatalyst using visible light. The synthesized nanocomposite was used to perform photo-reduction of Cr(vi) ions under white light irradiation. The best removal rate (72% after 15 minutes) was obtained by the film with 0.034 grams of deposited composite having relative percentages of Ag2O : UiO-66 of 70 : 30. The interesting obtained results confirm that the p-n heterojunction of the composite is the main cause of the desired charge separation and the photoreduction speed increase. In the following, the resulting compounds were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmittance electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy diffraction X-ray spectroscopy (EDAX) and the Brunauer, Emmett, and Teller (BET) method. Scavenging studies performed in the presence of familiar scavengers confirmed that superoxide radicals (˙O2-) and dissolved oxygen gas have a significant role in the photocatalytic reduction process.

Bioinspired palladium-doped manganese oxide nanocorns: a remarkable antimicrobial agent targeting phyto/animal pathogens

Microbial pathogens are known for causing great environmental stress, owing to which emerging challenges like lack of eco-friendly remediation measures, development of drug-resistant and mutational microbial strains, etc., warrants novel and green routes as a stepping stone to serve such concerns sustainably. In the present study, palladium (Pd) doped manganese (II, III) oxide (Mn3O4) nanoparticles (NPs) were synthesized using an aqueous Syzygium aromaticum bud (ASAB) extract. Preliminary phytochemical analysis of ASAB extract indicates the presence of polyphenolics such as phenols, alkaloids, and flavonoids that can act as potential capping agents in NPs synthesis, which was later confirmed in FTIR analysis of pure and Pd-doped Mn3O4 NPs. XRD, Raman, and XPS analyses confirmed the Pd doping in Mn3O4 NPs. FESEM and HRTEM study reveals the mixed morphologies dominated by nanocorns appearance. Zeta potential investigation reveals high stability of the synthesized NPs in colloidal solutions. The developed Pd-doped Mn3O4 NPs were tested against two fungal phytopathogens, i.e., Sclerotinia sclerotiorum and Colletotrichum gloeosporioides, known for causing great economic losses in yield and quality of different plant species. The antifungal activity of synthesized Pd-doped Mn3O4 NPs displayed a dose-dependent response with a maximum of ~92%, and ~72% inhibition was recorded against S. sclerotiorum and C. gloeosporioides, respectively, at 1000 ppm concentration. However, C. gloeosporioides demonstrated higher sensitivity to Pd-doped Mn3O4 NPs upto 500 ppm) treatment than S. sclerotiorum. The prepared NPs also showed significant antibacterial activity against Enterococcus faecalis. The Pd-doped Mn3O4 NPs were effective even at low treatment doses, i.e., 50-100 ppm, with the highest Zone of inhibition obtained at 1000 ppm concentration. Our findings provide a novel, eco-benign, and cost-effective approach for formulating a nanomaterial composition offering multifaceted utilities as an effective antimicrobial agent.

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.

Surface functionalized silver-doped ZnO nanocatalyst: a sustainable cooperative catalytic, photocatalytic and antibacterial platform for waste treatment

The different dyes used and discharged in industrial settings and microbial pathogenic issues have raised serious concerns about the content of bodies of water and the impact that dyes and microbes have on the environment and human health. Efficient treatment of contaminated water is thus a major challenge that is of great interest to researchers around the world. In the present work, we have fabricated functionalized silver-doped ZnO nanoparticles (Ag-doped ZnO NPs) via a hydrothermal method for wastewater treatment. X-ray photoelectron spectroscopy analysis confirmed the doping of Ag with ZnO NPs, and X-ray diffractometry analysis showed a decreasing trend in the crystallite size of the synthesized ZnO NPs with increased Ag concentration. Field emission scanning electron microscopy study of pure ZnO NPs and Ag-doped ZnO NPs revealed nanocrystal aggregates with mixed morphologies, such as hexagonal and rod-shaped structures. Distribution of Ag on the ZnO lattice is confirmed by high-resolution transmission electron microscopy analysis. ZnO NPs with 4 wt% Ag doping showed a maximum degradation of ∼95% in 1.5 h of malachite green dye (80 mg L-1) under visible light and ∼85% in 4 h under dark conditions. Up to five successive treatment cycles using the 4 wt% Ag-doped ZnO NP nanocatalyst confirmed its reusability, as it was still capable of degrading ∼86% and 82% of the dye under visible light and dark conditions, respectively. This limits the risk of nanotoxicity and aids the cost-effectiveness of the overall treatment process. The synthesized NPs showed antibacterial activity in a dose-dependent manner. The zone of inhibition of the Ag-doped ZnO NPs was higher than that of the pure ZnO NPs for all doping content. The studied Ag-doped ZnO NPs thus offer a significant eco-friendly route for the effective treatment of water contaminated with synthetic dyes and fecal bacterial load.

Anti-diabetic efficacy and selective inhibition of methyl glyoxal, intervention with biogenic Zinc oxide nanoparticle

Non-enzymatic glycation of biomolecules results in advanced glycation end products (AGEs), which are responsible for secondary complications in diabetes. Inhibiting methyl glyoxal (MGO) induced advanced glycation end product (AGE) formation is the only way to alleviate diabetic complications. This study aimed to look into the abilities of herbal extract Kigelia africana and K. africana synthesized zinc oxide nanoparticles (ZnONPs) to inhibit the emergence of MG-derived AGEs. The study intended to determine antioxidant and AGE inhibition of the plant extract and ZnONPs. ZnONPs were tested for the efficiency of anti-diabetic activity in streptozotocin-induced diabetic Wister rats. We discovered that the MGO-trapping effects on the prevention of AGE production were mediated by the downregulation of the amplification of MGO-trapping impacts on the hypoglycemic and antihyperlipidemic mechanisms of ZnONPs. According to histological findings, the treatment with ZnONPs also successfully lowers inflammation in the hepatic and renal tissues. Overall, future mechanistic research could establish ZnONPs potential anti-diabetic properties.

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.

A zero-dimensional/two-dimensional Ag-Ag2S-CdS plasmonic nanohybrid for rapid photodegradation of organic pollutant by solar light

Herein, the two synthesis strategies are employed for rational design of 0D/2DAg-Ag₂S-CdS heterojunctions towards photocatalytic degradation of methyl orange (MO) under simulated solar light. As the first strategy, a ternary Ag-Ag₂S-CdS nanosheet (NS) heterojunction was fabricated via combined cation exchange and photo-reduction (CEPR) method (Ag-Ag₂S-CdS/CEPR). The second strategy employed coprecipitation (CP) method (Ag-Ag₂S-CdS/CP). Strikingly, SEM, TEM and HR-TEM images are manifested the first strategy is beneficial for retaining the original thickness (20.2 nm) of CdS NSs with a dominant formation of metallic Ag, whereas the second strategy increases the thickness (33.4 nm) of CdS NSs with a dominant formation of Ag₂S. The Ag-Ag₂S-CdS/CEPR exhibited 1.8-fold and 3.5-fold enhancement in photocatalytic activities as compared to those of Ag-Ag₂S-CdS/CP and bare CdS NSs, respectively. This enhanced photocatalytic activity could be ascribed to fact that the first strategy produces a high-quality interface with intimate contact between the Ag-Ag₂S-CdS heterojunctions, resulting in enhanced separation of photo-excited charge carriers, extended light absorption, and enriched active-sites. Furthermore, the degradation efficiency of Ag-Ag₂S-CdS/CEPR was significantly reduced to ∼5% in the presence of BQ (•O₂^- scavenger), indicating that •O₂^- is the major active species that can decompose MO dye under simulated solar light.

Biogenic Synthesis of Cu-Doped ZnO Photocatalyst for the Removal of Organic Dye

The Cu-doped ZnO photocatalysts were prepared with a green and coprecipitation approach by using water hyacinth (Eichhornia crassipes) aquatic plant extract. In the preparation process, different amount of copper precursors such as 1, 2, 3, 4, and 5% of molar ratio were added to zinc nitrate precursors and abbreviated as Cu-ZnO (1%), Cu-ZnO (2%), Cu-ZnO (3%), Cu-ZnO (4%), and Cu-ZnO (5%), respectively. The characterization of the obtained samples was carried out, and the removal of the methylene blue (MB) dye was examined. Out of all catalysts, Cu-ZnO (3%) had the best photocatalytic performance and 89% of the MB dye was degraded. However, the degradation performances of blank (without catalysts), ZnO, Cu-ZnO (1%), Cu-ZnO (2%), Cu-ZnO (4%), and Cu-ZnO (5%) catalysts were 6, 54, 69, 83, 80, and 73%, respectively. Therefore, the use of water hyacinth plant extract with the optimum amount of Cu added to ZnO during the preparation of the catalyst could have a promising application in the degradation of organic pollutants.

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.

ZrO2-Ag2O nanocomposites encrusted porous polymer monoliths as high-performance visible light photocatalysts for the fast degradation of pharmaceutical pollutants

This work reports a unique ZrO₂-Ag₂O heterojunction nanocomposite uniformly dispersed on a macro-/meso-porous polymer monolithic template to serve as simple and effective visible light-driven heterogeneous plasmonic photocatalysts for water decontamination. The monolithic photocatalysts' structural properties and surface morphology are characterized using various surface and structural characterization techniques. The photocatalytic performance of the proposed photocatalysts is evaluated by optimizing multiple operational parameters. The photocatalytic properties of the fabricated monolithic nanocomposite are monitored through time-dependent photocatalytic disintegration of norfloxacin drug, a widely employed antimicrobial, with considerable aquatic persistence. The analytical results conclude that a (60:40) ZrO₂-Ag₂O nanocomposite embedded polymer monolith exhibits superior photocatalytic activity for the complete mineralization of norfloxacin molecules under optimized conditions of solution pH (3.0), photocatalyst quantity (100 mg), pollutant concentration (15 mg/L), photosensitizers (2.0 mM KBrO₃), visible light intensity (300 W/cm² tungsten lamp) and irradiation time (≤ 1 h). The proposed new-age inorganic-organic hybrid visible light photo-catalysts with superior structural and surface properties exhibit brilliant performance and fast responsiveness for water decontamination applications, in addition to their excellent chemical stability, high durability, multi-reusability, and cost-effectiveness.

Enhanced Photocatalytic Activity of Hierarchical Bi2WO6 Microballs by Modification with Noble Metals

Visible-responsive photocatalysts for environmental purification and fuel generation are, currently, highly sought after. Among the possible candidates, Bi2WO6 (BWO) has been considered due to its efficient light harvesting, stability, and promising activities. Here, hierarchical BWO microballs have been prepared using a hydrothermal method, and additionally modified with deposits of noble metals (gold, silver, copper, palladium and platinum) by the photodeposition method. The structure, morphology, photoabsorption properties, and surface composition of bare and metal-modified BWO samples were investigated by XRD, SEM, DRS and XPS analyses. The photocatalytic activity was evaluated by the oxidative degradation of model dye (methyl orange (MO)) under UV/vis, and hydrogen generation under vis and/or UV irradiation. It was found that hierarchical morphology is detrimental for high photocatalytic activity in both tested systems, resulting in the improved degradation of MO (ca. 65% during 90 min of UV/vis irradiation), and hydrogen evolution (0.1 and 0.4 μmol h−1 under vis and UV/vis irradiation, respectively). Moreover, the type of noble metal and its properties influence the overall photocatalytic performance. It was found that, under UV/vis irradiation, only platinum accelerates hydrogen evolution, whereas under vis irradiation the activity follows the order: BWO < BWO/Cu < BWO/Ag < BWO/Pt < BWO/Pd < BWO/Au. It was concluded that zero-valent metal is recommended for high vis response, probably due to plasmonic photocatalysis, efficient light harvesting ability, and co-catalytic role.

A new strategy to construct cellulose-chitosan films supporting Ag/Ag2O/ZnO heterostructures for high photocatalytic and antibacterial performance

The industrial wastewater contaminants including dyes and bacteria have caused serious environmental pollutions. Herein, ternary Ag/Ag₂O/ZnO heterostructure decorating cellulose-chitosan films were constructed via in situ synthesis. Cellulose and chitosan dissolved in alkali/urea solvent and regenerated in ethylene glycol to form cellulose/chitosan nanofiber network, which was an ideal supporter for ZnO and Ag nanoparticles and beneficial for recycle usage. The hydroxyl groups of cellulose and chitosan chains exposed and were utilized for the synthesis of Ag particles, as well as ZnO nanoparticles by biomineralization. The Ag/Ag₂O/ZnO decorating cellulose/chitosan (AZ@CC) films exhibited excellent antibacterial activity against Staphylococcus aureus and Escherichia coli. The width of inhibition zones around AZ@CC films reached 10.0-19.6 mm and 12.4-15.0 mm for S. aureus and E. coli, respectively. Moreover, AZ@CC films exhibited good photocatalytic activity against methyl orange (MO), almost 97% degradation of methyl orange (MO) within 50 min was achieved with the assistance of AZ@CC film. Importantly, the nanocomposite films exhibited excellent tensile strength and thermal stability. This facile and eco-friendly approach provided a new route to utilize cellulose and chitosan advantages for constructing multifunctional materials.

Microwave-assisted assembly of Ag2O-ZnO composite nanocones for electrochemical detection of 4-Nitrophenol and assessment of their photocatalytic activity towards degradation of 4-Nitrophenol and Methylene blue dye

4-Nitrophenol (4-NP) is an extensively utilized industrial chemical and one of major toxic water pollutant. Therefore, there is an urgent need to monitor the levels of 4-NP from environmental samples as well as its eradication are extremely important. Keeping this as a motivation, this research for the first-time reports microwave-assisted cost-effective synthesis of silver oxide (Ag₂O)-zinc oxide (ZnO) composite nanocones (CNCs, 80-100 nm) for simultaneous electrochemical detection and photodegradation of 4-NP from aqueous solutions. The Ag₂O-ZnO CNCs modified gold electrode was fabricated for electrochemical detection of 4-NP. Such fabricated sensor exhibited a sensitivity of 1.6 µA µM^-1cm^-2, wide linear detection range of 0.4-26 µM & 28-326 µM, and a low limit of detection of 23 nM. The sensor also exhibited good selectivity in real water samples. Also, an outstanding photocatalytic performance of Ag₂O-ZnO CNCs was evaluated towards UV-assisted degradation of 4-NP and organic water pollutant dye, methylene blue. The Ag₂O-ZnO CNCs exhibited excellent electro- and photocatalytic activities due to the formation of p-n nano-heterojunction comprising of p-type Ag₂O and n-type ZnO semiconductor nanoparticles within the composite. Therefore, herein reported smart CNCs can be projected as applied nano-system for cost-effective and rapid simultaneous detection and removal of 4-NP from aqueous solutions. Such nano-system can be useful for industrial application where detection and removal of 4-NP is a key issue to resolve.

In situ growth of 1D/2D CdS-Bi2MoO6 core shell heterostructures for synergistic enhancement of photocatalytic performance under visible light

Stability of the photocatalyst, maximum solar energy harvesting and effective photogenerated charge carrier separation are yet demanding key features of the photocatalysis for pollutant abetment and photo-electrochemical applications. Herein, we report the in situ solvothermal synthesis of CdS-Bi₂MoO₆ core-shell heterostructures (CdS-Bi₂MoO₆ CSHs) for the photocatalytic elimination of methyl orange (MO) under visible light. The as-synthesized CdS-Bi₂MoO₆ CSHs exhibited highest photocatalytic performance of 98.5%, which is approximately 10 and 4 folds higher than pristine Bi₂MoO₆ nanosheets (NSs) and CdS nanorods (NRs), respectively. This significantly enhanced photocatalytic performance is attributed to the core-shell heterostructure that improves the visible-light harvesting ability, facilitates efficient separation and transfer of the photogenerated charge carriers, as well as synergistic band alignment of both CdS NRs and Bi₂MoO₆ NSs. The CdS-Bi₂MoO₆ CSHs also showed efficient photocatalytic performance toward methylene blue (MB) as colored dye and tetracycline hydrochloride (TCH) as a colorless emerging contaminant. Additionally, the outcomes of transient photocurrent, electrochemical impedance, and photoluminescence study further corroborate that the construction of core-shell heterostructures with tight contact, leading to effective charge carrier separation. The hole (h⁺) and superoxide radical anion (^•O₂^-) were determined to be the predominant active species accountable for the MO dye degradation. Furthermore, the CdS-Bi₂MoO₆ CSHs exhibited a satisfactory recycling efficiency over five cycles (reduced by approximately 6%), owing to the protective Bi₂MoO₆ NSs shell over the CdS NRs core, demonstrating their applicability in wastewater purification and photo-electrochemical applications.

Utilization of Ag2O-Al2O3-ZrO2 decorated onto rGO as adsorbent for the removal of Congo red from aqueous solution

The water resources contamination in an alarming concern for sustainable environment. This has led to development of new technologies and materials for waste water detoxification. In the present study, we have fabricated novel trimetallic based mixed oxides decorated reduced graphene oxide (rGO) composite using facile microwave method and utilized it as an adsorbent for the removal of congo red dye from aqueous solution. The final composite showed highly agglomerated metal oxides present on the rGO surface. The high surface area and activity of the synthesized adsorbent resulted in its high adsorption capacity of 333.32 mg/g for congo red. The Langmuir model better explained the isotherm data indicating the monolayer adsorption of congo red molecules onto Ag₂O-Al₂O₃-ZrO₂/rGO surface. The grander adsorption ability of Ag₂O-Al₂O₃-ZrO₂/rGO towards organic dye indicate its probable utilization in the removal of other dyes also from wastewater.

Controlled Growth of Silver Oxide Nanoparticles on the Surface of Citrate Anion Intercalated Layered Double Hydroxide

Silver oxide nanoparticles with controlled particle size were successfully obtained utilizing citrate-intercalated layered double hydroxide (LDH) as a substrate and Ag+ as a precursor. The lattice of LDH was partially dissolved during the reaction by Ag+. The released hydroxyl and citrate acted as a reactant in crystal growth and a size controlling capping agent, respectively. X-ray diffraction, X-ray photoelectron spectroscopy, and microscopic measurements clearly showed the development of nano-sized silver oxide particles on the LDH surface. The particle size, homogeneity and purity of silver oxide were influenced by the stoichiometric ratio of Ag/Al. At the lowest silver ratio, the particle size was the smallest, while the chemical purity was the highest. X-ray photoelectron spectroscopy and UV-vis spectroscopy results suggested that the high Ag/Al ratio tended to produce silver oxide with a complex silver environment. The small particle size and homogeneous distribution of silver oxide showed advantages in antibacterial efficacy compared with bulk silver oxide. LDH with an appropriate ratio could be utilized as a substrate to grow silver oxide nanoparticles with controlled size with effective antibacterial performance.

Design of Mn and Zr incorporated Ag2O nanoparticles and their enhanced photocatalytic activity driven by visible light irradiation for degradation of rose bengal dye

Mn, Zr co-doped Ag₂O nanoparticles were blended through a wet chemical strategy, and the physicochemical properties of doped and co-doped silver oxide nanoparticles were characterized.

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

Fabrication of 3D mesoporous Ag₂O-ZnO heterojunctions at varying Ag₂O contents has been achieved through poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Pluronic F-108) as the structure-directing agent for the first time. The mesoporous Ag₂O-ZnO nanocomposites exhibited a mesoporous structure, which revealed a large pore volume and high surface area. The photocatalytic efficiency over mesoporous Ag₂O-ZnO nanocomposites for tetracycline (TC) compared with that over commercial P-25 and pristine ZnO NPs through the visible light exposure was studied. Mesoporous 1.5% Ag₂O-ZnO nanocomposites indicated the highest degradation efficiency of 100% of TC during 120 min of the visible light exposure compared with 5% and 10% for pristine ZnO NPs and commercial P-25, respectively. The TC degradation rate took place much rapidly over 1.5% Ag₂O-ZnO nanocomposites (0.798 μmol L^-1 min^-1) as compared to either commercial P-25 (0.097 μmol L^-1 min^-1) or ZnO NPs (0.035 μmol L^-1 min^-1). The mesoporous 1.5% Ag₂O-ZnO nanocomposite revealed the highest degradation rate among all synthesized samples, and it was 23 and 8 orders of magnitudes greater than those of pristine ZnO NPs and P-25, respectively. The photoluminescence and transient photocurrent intensity behaviors have been discussed to explore photocatalysis mechanisms. It is anticipated that the present work will contribute some suggestions for understanding other heterojunctions with outstanding behaviors.

Bio Framework-Derived Facile MoO3-NiO-PdO-Pd Nanomaterial for Detoxification of Organic Pollutants

INTRODUCTION

The catalytic behavior of metal oxide nanomaterials for removal of organic pollutants under dark ambient conditions, without any additional stimulant, is of great interest among the scientific community.

METHODS

In this account, a nanomaterial of ternary metal oxides (MoO3-NiO-PdO-Pd) was synthesized via greener approach and was explored for degradation of methyl orange in water environment in dark ambient conditions in comparison with light conditions. The biochemical species of Abies pindrow were treated with aqueous solution of precursor's salt following sol gel synthesis strategy. We further attuned morphology and chemistry of MoO3-NiO-PdO-Pd by incorporating bioactive compounds of A. pindrow.

RESULT AND DISCUSSION

The bio-fabricated MoO3-NiO-PdO-Pd revealed outstanding catalytic behavior with 92% degradation of methyl orange within 15 min in the dark at ambient temperature and pressure. Whereas, in the presence of visible light irritation, the catalyst degraded 97% of methyl orange in 15 min. According to the reaction kinetics of degradation, the catalysts illustrated good stability in light (R2=0.93) as well as in dark conditions (R2=0.98). Furthermore, the outstanding reusability and recyclability of the synthesized nanomaterial was observed for four runs of the experiment under dark and light conditions.

CONCLUSION

Therefore, A. pindrow-synthesized MoO3-NiO-PdO-Pd nanocatalyst demonstrated significant potential for detoxification of organic pollutants for water remediation.

Photocatalytic Degradation of Methyl Orange by Magnetically Retrievable Supported Ionic Liquid Phase Photocatalyst

A magnetically retrievable ferrocene appended supported ionic liquid phase (SILP) photocatalyst containing a molybdate anion has been synthesized and characterized by Fourier transform infrared, X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction, energy dispersive spectroscopy, and vibrating sample magnetometer analysis. The optical properties of the photocatalyst were probed by photoluminescence and UV-vis diffuse reflectance spectroscopy. The discharge of undesirable dye effluents from textile industrial plants in the environment is the major concern of environmental pollution and toxicity. In this context, we employed the as-prepared SILP photocatalyst for degradation of methyl orange (MO) under UV light (365 nm) irradiation, and subsequently, recycling studies were performed. The histological alteration in gills of the fish is employed as a tool for monitoring toxins in the environment. In view of this, the histo-toxicological assessment on freshwater fish Tilapia mossambica gills asserted the damage of secondary gill lamellae due to MO. Conversely, structural modifications in the gill architecture were not observed by virtue of photodegraded products confirming that the degraded product is nontoxic in nature. Additionally, the normal behavior of fishes on exposure to photodegraded products reveals that research findings are beneficial for the aquatic ecosystem.

Direct hydrothermal synthesis of amine-functionalized cubic hematite (C-Fe2O3) and sonochemical deposition of nanosized Au for its application as a visible-light photocatalyst

Cubic-shaped hematite (C-Fe2O3) functionalized with amine groups was directly prepared via one-pot hydrothermal reaction of Fe3+ with 1,12-diaminododecane (DA-12) in aqueous solution (50% ethanol). Herein, DA-12 (as a Lewis acid) promoted the aggregation of α-FeOOH nanorods with Lewis base sites, leading to the rapid recrystallization and conversion into uniform C-Fe2O3. C-Fe2O3 was subsequently deposited with nanosized Au via sonochemical reduction of 1.0 wt% HAuCl4 (0.1-0.8 mL), hereafter referred to as Au-deposited C-Fe2O3 (C-Fe2O3@Au). X-ray diffraction patterns of C-Fe2O3@Au confirmed the hexagonal crystalline phases of hematite and crystalline Au (111) and showed a weak broad band attributed to the amorphous carbon of DA-12. C-Fe2O3@Au was tested as a visible-light photocatalyst towards the degradation of methylene blue (MB) dye. C-Fe2O3@Au (0.1-0.4 mL of 1.0 wt% HAuCl4) exhibited 6-8 times higher photocatalytic activity than the Au-free counterpart (C-Fe2O3). The enhanced photocatalysis was mainly attributed to the improved separation efficiency of photo-excited charge carriers, i.e., the facilitated transport of electrons from the conduction band to the lower lying Fermi level of Au. However, the photocatalytic activity of C-Fe2O3@Au (0.8 mL of 1.0 wt% HAuCl4) was decreased probably due to the reduction of active sites for MB adsorption by the high coverage of the Au layer. The combined hydrothermal and sonochemical methods provided the direct synthetic route to cubic-shaped hematite decorated with nanosized Au and surface amine functionality as a promising visible-light photocatalyst.

A flower-like ZnO–Ag2O nanocomposite for label and mediator free direct sensing of dinitrotoluene

2,4-Dinitrotoluene (2,4-DNT) is a nitro aromatic compound used as a raw material for trinitrotoluene (TNT) explosive synthesis along with several other industrial applications. Easy, rapid, cost-effective, and selective detection of 2,4-DNT is becoming essential due to its hepato carcinogenic nature and presence in surface as well as ground water as a contaminant. Keeping this in view, this research, for the first-time, reports the synthesis of novel ZnO–Ag₂O composite nanoflowers on a gold (Au) substrate, to fabricate an electrochemical sensor for label-free, direct sensing of 2,4-DNT selectively. The proposed ZnO–Ag₂O/Au sensor exhibits a sensitivity of 5 μA μM⁻¹ cm⁻² with a low limit of detection (LOD) of 13 nM, in a linear dynamic range (LDR) of 0.4 μM to 40 μM. The sensor showed reasonably high re-usability and reproducibility, with reliable results for laboratory and real-world samples.

2,4-Dinitrotoluene (2,4-DNT) is a nitro aromatic compound used as a raw material for trinitrotoluene (TNT) explosive synthesis along with several other industrial applications.

Sputtering control of Ag2O decoration configurations on ZnO nanorods and their surface arrangement effects on photodegradation ability toward methyl orange

In this study, a combinational strategy for synthesizing ZnO nanorod arrays interlaced with Ag₂O particles was proposed. Hydrothermally derived ZnO nanorod templates were sputter coated with Ag₂O particles. The sputtered Ag₂O particles can be decorated on the surfaces of the ZnO nanorod arrays with a randomly dispersive or continuous coverage characteristic by controlling the sputtering duration. Structural analysis revealed the formation of satisfactory crystalline ZnO-Ag₂O composite nanorods through the hydrothermal and sputtering methods. The ZnO-Ag₂O composite nanorods exhibited a significantly enhanced photoactivity compared with that of pristine ZnO nanorods under light irradiation. Moreover, the Ag₂O content and the coverage feature of the ZnO-Ag₂O composite nanorods influence the photodegradation of methyl orange solution by the composite nanorods under light irradiation. The photodegradation efficiency of the ZnO nanorods was substantially enhanced when the Ag₂O particles were decorated on the surfaces in a dispersive manner. This can be attributed to the optimal content of Ag₂O particles and their randomly dispersive characteristic on the surface of the composite nanorods, which resulted in the efficient transfer of photocarriers and markedly suppressed the electron-hole recombination rate.

Electrospun Nanofibers Embedding ZnO/Ag2CO3/Ag2O Heterojunction Photocatalyst with Enhanced Photocatalytic Activity

The immobilization of photocatalyst onto substrate has a great potential for energy-intensive separation to avoid the costly separation process and unwanted release of photocatalyst into the treated water. In this study, electrospun nanofiber composed of polyvinylidene fluoride (PVDF) with the immobilized ZnO, ZnO/Ag2CO3, ZnO/Ag2CO3/Ag2O, and ZnO/Ag2O photocatalysts were prepared via the electrospinning process. The immobilized ZnO and heterojunctioned ZnO in the PVDF electrospun nanofiber were proven via X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The electrospinning allowed high chemical binding of the nanofiber composite with good physical interaction between the photocatalyst and the electrospun nanofiber. AFM images obtained for the nanofibers were found to be rougher than that of the pristine PVDF electrospun nanofiber. Among the photocatalyst embedded, the immobilized ZnO/Ag2CO3/Ag2O had endowed the nanofiber with an excellent photocatalytic activity and recyclability for the degradation of the RR120 under UV light irradiation. Based on the results, effective immobilization of ZnO/Ag2CO3/Ag2O in PVDF nanofiber with 99.62% photodegradation in 300 min compared to PVDF-ZnO, PVDF-ZnO/Ag2CO3, and PVDF-ZnO/Ag2O of 28.14%, 90.49%, and 96.34%, respectively. The effective ZnO/Ag2CO3/Ag2O immobilization into polymers with affinity toward organic dye pollutants could both increase the efficiency and reduce the energy requirements for water treatment via the photocatalytic application.

Removal of a melamine contaminant with Ag-doped ZnO nanocomposite materials

In this approach, Ag-doped ZnO nanosheets (Ag/ZnO NSs) were prepared via a facile wet-chemical method using reducing agents in an alkaline medium at a low temperature.

Biosynthesis of zinc oxide nanoparticles using Albizia lebbeck stem bark, and evaluation of its antimicrobial, antioxidant, and cytotoxic activities on human breast cancer cell lines

Background

Biocompatibility and stability of zinc oxide nanoparticles (ZnO NPs) synthesized using plants is an interesting research area of study in nanotechnology, due to its wide applications in biomedical, industrial, cell imaging, and biosensor fields. The present study reports the novel green synthesis of stable ZnO NPs using various concentrations of zinc nitrate (0.01M, 0.05M, 0.1M) and Albizia lebbeck stem bark extracts as an efficient chelating agent. Antimicrobial, antioxidant, cytotoxic, and antiproliferative activities of the synthesized NPs on human breast cancer cell lines were evaluated using different assays.

Methods

Characterization of the synthesized ZnO NPs were carried out using various spectroscopic and microscopic techniques. Antimicrobial activity evaluation using disc diffusion method, antioxidant activity using hydrogen peroxide (H₂O₂) free radical scavenging assay and cytotoxic activity on MDA-MB 231 and MCF-7 using tryphan blue dye exclusion and MTT assay.

Results

The UV–vis spectroscopy result revealed an absorption peak in the range of 370 nm. The involvements of A. lebbeck bioactive compounds in the stabilization of the ZnO NPs were confirmed by X-ray diffraction and Fourier transform infrared analysis. Zeta sizer studies showed an average size of 66.25 nm with a polydisparity index of 0.262. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses results revealed irregular spherical morphology and the presence of primarily Zn, C, O, Na, P, and K, respectively. The biosynthesized ZnO NPs revealed strong antimicrobial potentials against various gram-negative and gram-positive bacterial pathogens. Antioxidant activities carried out using H₂O₂ free radical scavenging assay revealed higher IC50 values of 48.5, 48.7, and 60.2 µg/mL for 0.1M, 0.05M, and 0.01M ZnO NPs, respectively. Moreover, the biosynthesized ZnO NPs showed significant cytotoxic effects on MDA-MB 231 and MCF-7 breast cancer cell lines (P< 0.001, n≥3) in a concentration-dependent manner.

Conclusion

Overall, various concentrations of ZnO NPs were synthesized through a stable, simple, and eco-friendly green route via the use of A. lebbeck stem bark extract. The biosynthesized ZnO NPs showed strong antimicrobial, antioxidant and cytotoxic activity against strongly and weakly metastatic breast cancer cell lines.

Ag2O and Fe2O3 modified oxides on the photocatalytic treatment of pulp and paper wastewater

The effects of doping of ZnO and Nb₂O₅ solids with Fe₂O₃ (1.4 wt%) and Ag₂O (1.4 wt%) on its surface and catalytic properties were investigated, as well as its photocatalytic performance on the degradation of a pulp and paper wastewater (PPW). The catalysts were characterized by XRD, SEM, photoacoustic spectroscopy (PAS), NH₃-TPD and textural analysis. The results obtained revealed that Fe₂O₃ doping of Nb₂O₅ conducted at 500 °C resulted in an increase of about 116% for S_BET while Ag₂O treatment exerted a decrease of 33% for S_BET of the doped adsorbents. Doping ZnO with Fe₂O₃ or Ag₂O led to an increase of 80% for S_BET. Iron and silver doping also led to a decrease in band gap energy of at least 6%. The addition of 1.4 wt% Ag₂O on ZnO followed by calcination at 500 °C resulted in an increase of 11% in the value of the reaction rate constant (k_ap) for COD reduction under UV radiation. The treatment of Nb₂O₅ with 1.4 wt% Ag₂O increased by a factor of 2.04 the value of k_ap for the reaction taking place under VIS radiation. The catalysts partially reduced the organic load and the real colour of the wastewater, allowing the achievement of the specifications for release into rivers, so photocatalysis could be an alternative for pulp and paper wastewater final polishing.