Hollow AgI:Ag nanoframes as solar photocatalysts for hydrogen generation from water reduction

Fabricating a 3D floating porous PDMS - Ag/AgBr decorated g-C3N4 nanocomposite sponge as a re-usable visible light photocatalyst

In this study, polymeric graphitic carbon nitride (g-C3N4) semiconductors was synthesized via a thermal condensation method. Subsequently, Ag/AgBr nanoparticles with varying ratios were decorated onto the g-C3N4 surface using the water/oil emulsion method. The resulting nanocomposites were characterized using XRD for phase identification and structural analysis, HR-TEM and SEM&EDAX for morphological structure, particle size, and elemental composition analysis, and XPS for investigating the chemical state and electronic structure. The impact of Ag/AgBr content on the optical properties of g-C3N4 were also studied such as (optical bandgap (Eg), refractive index (n), extinction coefficient (k), optical conductivity (σopt) and dielectric function (ε*)), Electrochemical impedance spectroscopy (EIS), PL spectroscopy and Chrono-amperometric investigations were conducted to assess the charge transfer capabilities and long-term durability of the prepared nanocomposites. The results revealed a reduction in Ag/AgBr particle size with an increase in g-C3N4 content, accompanied by a decrease in the optical bandgap from 2.444 eV to 2.393 eV. Furthermore, the nanocomposites exhibited enhanced degradation efficiencies of RhB dye, with the highest tested content of Ag/AgBr achieving 100% degradation after 120 min of irradiation. However, the challenge of catalyst separation after the degradation process remained. To address this issue, we developed a novel approach by impregnating Ag/AgBr@g-C3N4 photocatalyst onto a floating porous sponge using a simple sugar-template technique, offering potential as a reusable photocatalyst material. Furthermore, the 3D PDMS - Ag/AgBr@g-C3N4 photocatalyst was evaluated and found to maintain nearly the same photocatalytic efficiency for up to 5 consecutive cycles.

Assessment of antimicrobial and anthelmintic activity of silver nanoparticles bio-synthesized from Viscum orientale leaf extract

BACKGROUND

Viscum orientale is a largely used parasitic plant with traditional medicinal properties. They are considered to possess the medicinal properties of host tree which they grow on. It's a least explored plant with ethanopharmacological importance. As a result, the current work aimed to investigate the biological effects of Viscum orientale extract and silver nanoparticles (AgNPs) generated from it.

METHODS

AgNPs synthesized using Viscum orientale plant extract and analysed on time dependent series and was characterized using Ultra Violet UV-visible spectra, Fourier Transform Infrared Spectroscopy FTIR, X-ray diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDX), Scanning Electron Microscopy (SEM). Further using disc method anti-microbial assay was performed following antioxidation screening using 1,1-diphenyl-2-picryl-hydrazyl (DPPH), reducing power and nitric oxide content and heamgglutination with human blood.

RESULTS

On green synthesis using silver, the phyto contituents of plant Viscum orientale effectively reduced silver ions at 3-4 h of continuous stirring to form AgNPs. UV-vis spectra showed a typical peak of AgNPs at 480 nm. The FTIR analysis confirmed the covering of silver layers to bio-compounds of the extract. SEM analysis represented AgNPs as spherical morphologies ranging from 119-222 nm. AgNPs exhibited impressive zone of inhibition against Escherichia coli (8.1 ± 0.3 mm), Staphylococcus aureus (10.3 ± 0.3 mm), Bacillus subtilis (7.3 ± 0.3 mm), Bacillus cereus (8.2 ± 0.3 mm), Salmonella typhi (7.1 ± 0.2 mm). AgNps exhibited efficiency against DPPH at EC₅₀ value of 57.60 µg/ml. and reducing power at EC₅₀ of 53.42 µg/ml and nitric oxide scavenging of EC₅₀ of 56.01 µg/ml concentration. Further, anthelmintic activity results showed synthesized nanoparticles significant reduction in the paralysis time to 5.4 ± 0.3 min and death time to 6.5 ± 0.6 min in contrast to the individual factors. On hemagglutination using AgNPs, above 80 µg/ml of concentration showed very significant effect on comparison with water extract.

CONCLUSION

Synthesized AgNPs using Viscum orientale water extract displayed versatile biological activity than individual extract. This study has forecasted a new path to explore more on this AgNPs for further research.

Nano Ag/AgBr/g-C3N4 catalyzed the production of hydrogen and reduction of d-glucose to sorbitol under visible light irradiation

In this study, the polymeric graphitic carbon nitride (g-C3N4) was modified by anchoring Ag/AgBr to improve its charge separation efficiency.

Silver-based semiconductor Z-scheme photocatalytic systems for environmental purification

Silver-based semiconductor photocatalysts are promising materials for solving environmental and energy issues due to their strong optical absorption, excellent quantum efficiency and photoelectrochemical properties. However, the uncontrollable photocorrosion and high use cost of single silver-based semiconductor photocatalysts limit its practical application. The construction of Z-scheme photocatalytic systems that mimic natural photosynthesis can not only enhance the photocatalytic activity of silver-based semiconductor photocatalysts, but also improve their stability and reduce the use costs. This critical review concisely highlights the basic principles of Z-scheme photocatalytic systems, and discusses the construction of silver-based semiconductor Z-scheme photocatalytic systems and the roles of metallic Ag in there and summarizes the synthesis methods of silver-based semiconductor Z-scheme photocatalytic systems. Then, a series of the solar-driven applications are elaborated, including organic pollutants degradation, hydrogen production, and carbon dioxide reduction. Meanwhile, the mechanism and difficult level of these photocatalytic reactions are also described. Besides, metal organic frameworks (MOFs) as a novel type of photocatalysts have attracted growing attention. The novel combination of silver-based semiconductors with typical photoactive MOFs is highlighted based on the Z-scheme photocatalytic systems. Eventually, the future challenges and prospects in the development of silver-based semiconductor Z-scheme photocatalytic systems are presented.

Plasmonic ternary hybrid photocatalyst based on polymeric g-C3N4 towards visible light hydrogen generation

Surface plasmon resonance (SPR) effect of noble metal nanoparticles (NPs) for photocatalysis has a significant enhancement. In this system, a plasmonic ternary hybrid photocatalyst of Ag/AgBr/g-C₃N₄ was synthetized and used in water splitting to generation H₂ under visible light irradiation. 18%Ag/AgBr/g-C₃N₄ showed the highest photoactivity, with the efficiency of hydrogen generation as high as 27-fold to that of pristine g-C₃N₄. Compared to simple mixture of Ag/AgBr and g-C₃N₄, hetero-composite Ag/AgBr/g-C₃N₄ showed a higher photoactivity, even though they contained same content of Ag/AgBr. We find that significant factors for enhancing properties were the synergistic effect between Ag/AgBr and g-C₃N₄, and the light absorption enhancing by SPR effect of Ag NPs. Ag/AgBr NPs firmly anchored on the surface of g-C₃N₄ and their high dispersion were also responsible for the improved activity and long-term recycling ability. The structure of Ag/AgBr/g-C₃N₄ hybrid materials and their enhancement to photocatalytic activity were discussed. Meanwhile, the possible reaction mechanism of this system was proposed.

Oxidative nucleation and growth of Janus-type MnOx-Ag and MnOx-AgI nanoparticles

Janus nanoparticles (NPs) containing two chemically distinct materials in one system are of great significance for catalysis in terms of harnessing catalytic synergies that do not exist in either component. We herein present a novel synthetic method of two Janus-type MnOx-Ag and MnOx-AgI NPs. The synthesis of Janus-type MnOx-AgI NPs is based on the oxidative nucleation and growth of Ag domains on MnO first and the subsequent iodization of Ag. A mild and non-disruptive iodization strategy is developed to yield Janus MnOx-AgI NPs, in which converting Ag to AgI domains with iodomethane (CH3I) is achieved through partial iodization. Simultaneously, Mn2+ species in the primary MnO octahedra are oxidized during the growth of Ag NPs, leading to the formation of amorphous p-type MnOx domains. Therefore, the as-resultant Janus-type MnOx-AgI NPs combining two semiconductors into an integrated nanostructure can be used as an efficient photocatalyst for visible-light-driven water oxidation. Janus MnOx-AgI NPs show an expected photocatalytic activity even in the absence of Ru(bpy)3Cl2 as an electron mediator. This intriguing synthesis may offer a new opportunity to develop asymmetric nanostructures of two semiconductors that will potentially be efficient photocatalysts for solar-driven water splitting.

Aqueous synthesis of highly monodisperse sub-100 nm AgCl nanospheres/cubes and their plasmonic nanomesh replicas as visible-light photocatalysts and single SERS probes

Despite the distinctive electrochemical and photocatalytic properties of nanostructured silver chloride (AgCl), the shape- and size-dependence of their properties have not been thoroughly investigated to date. The most substantial reason responsible for this incomplete study and the subsequent limited applications is the failure in controlling the structure of AgCl nanomaterials, mainly owing to the challenging synthetic conditions including organic phase and high reaction temperature. In this work, we reported a rapid one-pot room-temperature aqueous synthesis of highly monodisperse sub-100 nm AgCl nanomaterials with various shapes and sizes by controlling the precursor (Ag⁺ and AuCl₄ ^-) ratios. The remaining unreacted metal precursors (Ag⁺ and AuCl₄ ^-) used to produce AgClNC were subsequently reduced by ascorbic acid on the surface of the synthesized AgCl nanomaterials to form Ag/Au bimetallic nanomesh structures (AgClNC#AuAgCMs and SMs). After the removal of the AgCl nanotemplates, only nanomesh structures (AuAgCMs and SMs) were obtained. Importantly, we successfully decreased the size of the AgCl nanomaterials which were replicated into bimetallic spherical and cubic nanomesh structures that were small enough (∼100 nm) to show intense surface-plasmon-absorption bands. Based on these unique chemical and physical properties, we could take advantage of the plasmonic photocatalysis properties of the complex comprising semiconducting AgCl/metallic nanomesh replica for the complete removal of the environmentally harmful Cr⁶⁺ in the presence of sacrificial agents such as formic acid. Finally, the novel bimetallic nanomesh structures proved themselves to exhibit intense surface-enhanced Raman scattering properties in a single-particle enhancing the electromagnetic field.

Ternary Silver Halide Nanocrystals

Nanocrystalline silver halides (AgX) such as AgCl, AgBr, and AgI, a class of semiconductor materials with characteristics of both direct and indirect band gaps, represent the most crucial components in traditional photographic processing. The nanocrystal surfaces provide sensitivity specks that can turn into metallic silver, forming an invisible latent image, upon exposure to light. The photographic processing implies that the AgX nanoparticles possess unique properties. First, pristine AgX nanoparticles absorb light only at low efficiency to convert surface AgX into tiny clusters of silver atoms. Second, AgX nanoparticles represent an excellent class of materials to capture electrons efficiently. Third, small metallic silver clusters can catalyze the reduction of AgX nanoparticles to Ag nanoparticles in the presence of mild reducing reagents, known as self-catalytic reduction. These properties indicate that AgX nanoparticles can be partially converted to metallic silver with high precision, leading to the formation of hybrid AgX/Ag nanoparticles. The nanosized metallic Ag usually exhibit intense absorption bands in the visible spectral region due to their strong surface plasmon resonances, which make the AgX/Ag nanoparticles a class of promising visible-light-driven photocatalysts for environmental remediation and CO₂ reduction. Despite the less attention paid to their ability of capturing electrons, AgX nanoparticles might be a class of ideal electron shuttle materials to bridge light absorbers and catalysts on which electrons can drive chemical transformations. In this Account, we focus on ternary silver halide alloy (TSHA) nanoparticles, containing two types of halide ions, which increase the composition complexity of the silver halide nanoparticles. Interdiffusion of halide ions between two types of AgX at elevated temperatures has been developed for fabricating ternary silver halide alloy crystals, such as silver chlorobromide optical fibers for infrared communications. This solid state process is not feasible for synthesizing TSHA nanoparticles since it is hard to form two different types of AgX nanoparticles in direct contact. In contrast, coprecipitation of silver ions with different halide ions via colloidal chemistry represents the most promising strategy to synthesize TSHA nanoparticles. Forming uniform and phase-pure ternary silver halide nanocrystals requires that the rate ratio for precipitating both halide ions remains constant throughout the synthesis. However, the significant difference in solubility among different AgX usually leads to a nonuniform compositional distribution in the resulting nanoparticles because the halide ions corresponding to the less soluble AgX precipitate faster at the early reaction stage. This Account summarizes the methods recently developed for the successful synthesis of phase-pure TSHA nanoparticles with uniform sizes and morphologies, which involve precise control over the balanced diffusion of different halide ions to react with silver ions. Typical methods include the use of microemulsion capsules and high-viscosity solvents to lower and even the diffusion coefficients of various halide ions, thus maintaining the precipitation rates of both AgX in single nanoparticles at a constant ratio. The availability of high-quality TSHA nanoparticles provides promising opportunities to explore their new properties and applications.

Singlet oxygen formation in bio-inspired synthesis of a hollow Ag@AgBr photocatalyst for microbial and chemical decontamination

Singlet oxygen has been identified as a contributor to the degradation of contaminants using biosynthesised hollow Ag@AgBr catalysts.

Controlling the morphology and composition of Ag/AgBr hybrid nanostructures and enhancing their visible light induced photocatalytic properties

Ag/AgBr hybrid nanostructures were prepared by reducing AgBr nanoparticles synthesized by reaction of Ag⁺ with Br⁻. The Ag/AgBr hybrid nanostructures exhibited enhanced photocatalytic activity and recyclability for decomposing methylene blue (MB).

Hollow cobalt phosphonate spherical hybrid as high-efficiency Fenton catalyst

Organic-inorganic hybrid of cobalt phosphonate hollow nanostructured spheres were prepared in a water-ethanol system through a mild hydrothermal process in the absence of any templates using diethylenetriamine penta(methylene phosphonic acid) as bridging molecule. SEM, TEM and N2 sorption characterization confirmed a hollow spherical micromorphology with well-defined porosity. The structure and chemical states of the hybrid materials were investigated by FT-IR, XPS and thermogravimetric analysis, revealing the homogeneous integrity of inorganic and organic units inside the network. As a heterogeneous catalyst, hollow cobalt phosphonate material exhibited considerable catalytic oxidizing decomposition of methylene blue with sulfate radicals as compared to cobalt phosphonate nanoparticles synthesized in single water system, which could be attributed to enhanced mass transfer and high surface area for the hollow material. Some operational parameters, including pH and reaction temperature, were found to influence the oxidation process. The present results suggest that cobalt phosphonate material can perform as an efficient heterogeneous catalyst for the degradation of organic contaminants, providing insights into the rational design and development of alternative catalysts for wastewater treatment.

Hollow manganese phosphonate microspheres with hierarchical porosity for efficient adsorption and separation

Hollow manganese phosphonate microspheres of an inorganic-organic hybrid with hierarchically porous shells were prepared through a template-free hydrothermal method using ethylene diamine tetra(methylene phosphonic acid) as the coupling molecule. The hollow structures with hierarchical porosity were confirmed by SEM, TEM and N2 sorption. FT-IR, XPS and TG-DSC measurements revealed that the organophosphonate linkers were homogeneously incorporated into the hybrid framework. The hierarchical manganese phosphonates could be used as efficient adsorbents for the removal of copper ions, showing fast binding kinetics due to the well-structured porosity. The adsorption process follows pseudo-second order reaction kinetics, as well as Langmuir isotherm, indicating that Cu(2+) was monolayer adsorbed on the hybrid by chemical complexation. Furthermore, the synthesized manganese phosphonates with peculiar porosity exhibited excellent size selectivity for protein adsorption in a complex solution, presenting the promising potential as candidates for biomaterials.