Ag Nanocatalyst Research Articles

Understanding How Anion Exchange Membranes and Cationic Polymer/Catalyst Interactions Behave with Time in Alkaline Electrolysis

We are leveraging our existing success with anion exchange membranes (AEM) to develop new highly stable and highly conductive membranes and ionomers for AEM electrolysis. Our novel and scalable tri-block co-polymers ABA or BAB, where the A block can be functionalized with an advanced chemically stable cation and the B block is an unsaturated polymer that when hydrogenated results in high anion conduction membranes with exceptional mechanical strength and durability analogous to polyethylene (PE). We have also developed a novel immobilization technology for processable catalyst inks. Synergistically the A and B block lengths and chemistries are tuned to achieve all the properties desirable for an anion exchange membrane for electrolyzer applications. Random polymers of the same A and B chemistries can also be formulated for additional fidelity in chemically compatible ionomers for the membrane electrode assemblies (MEA). These systems are unique in that they achieve very high dissociation of anions beyond OH-, giving CO3 2- σ<100 mS cm-1 ca. 60°C and enhanced chemical stability as the water is separated from the high MW polyethylene backbone that additionally gives the materials unprecedented strength. This will allow us to fabricate thinner membranes for long durability pressure differentiated operation. Because of the unusual and exceptional CO3 2- conductivity that we have designed into our membrane, we are able to optimize these for a carbonate electrolyte electrolyzer. While we lose a 100 mV in activity compared to operation in OH-, the advantages including high current densities enabled by our novel membrane outweigh that disadvantage. Chemical stability of the membrane is not a concern, and the system is less complicated as we do not need to use expensive components to protect against caustic corrosion or protect the hydroxide electrolyte from carbon dioxide present in air to avoid its inevitable conversion to CO3 2-.Not all proposed AEM polymer chemistries are scalable, many involve too many synthetic steps, suffer from low overall yields, and are highly exothermic reactions (thus only safely executed on a small scale), or do not produce sufficiently high molecular weight for film formation. The polymer systems proposed here have already been demonstrated on the 1 kg scale. This novel AEM intellectual property, jointly invented by Mines and UMass, has been licensed to Spark Ionix who are commercializing an early version of this polymer technology. The next generation of tailored polymers proposed are increasingly robust, scalable, efficient and more amenable to high volume manufacture to produce inexpensive hydrocarbon polymer membranes for use in electrolyzers. The block lengths, overall molecular weight and chemistries are completely tunable to fabricate AEMs with all desired properties or compatible ionomer chemistries that allow high levels of catalyst utilization, through both ionic conductivity and chemical transport. We have been investigating this polymer system in 1M K2CO3 at 50°C with great success and have shown good performance and durability in 5cm2cells. We are developing the system for >60°C and 25 cm2 cells. We have begun to understand the science behind ionomer catalyst interactions and initially used a commercial Ag nano-catalyst as a model system. Few ave studied the effect of ionomer chemistry and catalyst or catalyst type and loadings on performance. We have shown durability of > 600 h at 0.5 A cm-2 and continue to see improvements. It should be noted that the voltage is dropping in theses tests, at end of test at –ve 60 µV h-1 is achieved, while this may be interpreted as evidence of membrane thinning when the cell was dissembled the membrane thickness was ca. the same as at the beginning of test (80 µm), indicating slow, but long term conditioning, the cell did not reach the point at which a +ve degradation rate was observed. Further investigation of cell conditioning indicated that these cells currently take 40-50 hs under load to reach steady state operation (this break in time will be understood and significantly shortened) giving 400MV improvement at 1 A cm-2. With a MnO2 catalyst the voltage at 0.5 A cm-2drops to 1.5 V indicating that the target of 2 A cm-2 at 1.8 V will be easily achieved with further investigation.

Cu-Ag bimetallic nano-catalyst anchored on polyvinyl alcohol sponge for catalytic reduction of 4-nitrophenol

With increasing interest and demand for treating organic wastewater, fabricating a heterogeneous catalyst combining low-cost, excellent catalytic efficiency, and good recyclability is necessary but remains challenging. In this work, we developed a kind of low-cost Cu-Ag bimetallic nano-catalyst anchored on polyvinyl alcohol sponge (Cu-Ag/PVA) via step impregnation and reduction method, which demonstrated excellent catalytic efficiency and good recyclability for the reduction of the organic pollutant 4-nitrophenol (4-NP). The compositional and microstructural results confirmed that Cu-Ag bimetallic nanoparticles with an average size of tens of nanometers were uniformly anchored on the porous PVA sponge. The catalytic results showed that the prepared Cu-Ag/PVA exhibited an appealing catalytic performance and recyclability compared with monometallic Cu or Ag nano-catalyst, which is ascribed to the reason that bimetallic Cu-Ag has lower binding energy and is easier to transfer electrons in the catalytic reduction of 4-NP compared to monometallic catalyst. The optimal kinetic catalytic rate constants for Cu-Ag/PVA is 0.54 min−1, and the conversion of 4-NP maintained above 98% after twelve consecutive catalytic cycles. Therefore, this inexpensive, efficient, and recyclable Cu-Ag/PVA catalyst has potential application in organic wastewater treatment.

Preparation of Nano Ag Loaded Wood Filter Material and Its Catalytic Degradation of Dyes

Using porous light wood as raw material, Ag/wood composite filter material was prepared by loading metal Ag nano catalyst in wood matrix by in-situ reduction of silver ammonia solution. The catalytic degradation of organic pollutants in dye wastewater was realized by using the characteristics of high fluid transmission efficiency of wood and catalytic activity of silver nanoparticles. The morphology and structure of the material were characterized by scanning electron microscope, transmission electron microscope and X-ray diffraction, and the catalytic degradation of organic dye methylene blue by nano Ag loaded wood filter material was investigated. The results show that the prepared Ag/wood composite filter material retains the pore structure of wood, Ag nanoparticles are successfully loaded on the inner wall of the catheter and evenly distributed, and the particle size range is 5 nm-20 nm; The silver nanoparticles on the inner wall of the wood duct have good catalytic activity, and the wood filter material can effectively catalyze the degradation of methylene blue in water. Its degradation efficiency and water flux are closely related to the thickness of the filter material; The catalytic degradation efficiency of methylene blue by 6 mm thick filter material driven by gravity is 94.03%, and the water flux is up to 2600 L/(M2•h), which realizes the optimization of dye degradation efficiency and water flux. Nano Ag loaded wood filter material has the advantages of simple preparation process, low cost and large-scale. It has a good application prospect in the field of dye wastewater treatment.

(Invited) Electrocatalyst Development for Efficient CO2 Electrolysis

This talk will discuss recent efforts at the National Energy Technology Laboratory (NETL) to develop efficient electrocatalysts that convert CO2 and water into C1 products, such as carbon monoxide (CO) and formic acid (HCOOH). The first example combines advanced surface science techniques, computational modeling, and electrochemical evaluation to track the size-dependent CO2 reduction vs. HER selectivity of silver nanocatalysts with sub-nanometer resolution. Understanding size-dependent catalytic properties is important to maximize the utilization of costly, state-of-the-art catalyst materials. Experimental efforts synthesized and evaluated Ag nanocatalysts with controlled diameters between 2-6 nm, and we identified ~4 nm Ag particles as the optimum balance of activity, selectivity, and catalyst utilization. Computational modeling techniques, including DFT, transition state theory, and microkinetic modeling identified key catalytically active surface sites that were responsible for HER vs. CO2 reduction, determined the respective active sites’ population as a function of particle size, and then predicted HER vs. CO2 reduction rates and selectivity for Ag nanocatalyst with diameters between 1-10 nm. Our computational results predicted ~4 nm particle provided the highest combination of product selectivity, catalyst utilization, and catalytic activity based on a total metal basis, which was in near perfect agreement with experiential results. These experimental and computational results should guide future catalyst design efforts by placing a lower bound on the size of practical Ag catalysts. A second example will highlight efforts to develop 3D structured and chemically-doped SnO2 catalysts for the conversion of CO2 into formate and formic acid. We coupled novel synthetic techniques with advanced synchrotron characterization, computational modeling, and evaluation MEA-style electrolyzer devices. In the case of 3D structured SnO2 catalysts we found CO2 conversion activity was substantially improved by increasing the electrocatalytically active surface area, while doping SnO2 catalysts with heteroatoms created new active sites that lowered the CO2 conversion overpotential and boosted performance.

Reaction pathways for the highly selective and durable electrochemical CO2 to CO conversion on ZnO supported Ag nanoparticles in KCl electrolyte

Electrochemical CO2reduction (ECR) is a promising approach for recycling atmospheric CO2into value-added fuels. However, due to the sluggish ECR, highly effective ctalysts are needed. ZnO supported Ag nanocatalyst (NC) ((ZnO)3@Ag) is developed for CO2 to CO conversion where the faradaic efficiency (FE) was ∼95% in 0.5 M KCl at −1.1 V, and that progressively decreased in 0.1 M KCl (89.7%) and 0.1 M KHCO3 (84.6%). Besides, (ZnO)3@Ag NC exhibited unprecedented stability in 0.5 M KCl with only 6.3% decay after 8 h while 14% and 14.3% decay were observed in 0.1 M KCl and 0.1 M KHCO3, respectively. The cross-referencing results of materials analyses and in-situ X-ray absorption spectroscopy suggest that the high CO selectivity of (ZnO)3@Ag NC in KCl originates from the synergistic collaboration between ZnO and Ag, where, ZnO supplies electrons to Ag for adsorption/structural rearrangement of CO2 molecule and subsequent desorption of CO. On the other hand, the presence of CO32− ions in KHCO3 hinder the mass transportation (i.e. the adsorption) of CO2, resulting in the decrease in selectivity and stability. Hereby, this study will spark motivation for designing the highly selective and stable ECR catalysts and uncover the mechanistic aspects of ECR.

Synthesis of Ag nanoparticles by Celery leaves extract supported on magnetic biochar substrate, as a catalyst for the reduction reactions

Green synthesis of a noble metal such as Ag nanoparticles is an enormously developed research area. In this study, a biochar/Fe3O4–Ag magnetic nanocatalyst was produced via a green path by using Celery stalk as a carbon-based substrate and Celery leaf extract as reducing and stabilizing agents to construct Ag nanoparticles. The synthesized nanocatalyst was determined using various techniques, such as UV–Vis spectroscopy, FT-IR spectroscopy, XRD (X-ray diffraction), SEM/EDX spectroscopy (scanning electron microscopy/energy-dispersive X-ray), TEM (transmission electron microscopy), and VSM (vibrating sample magnetometer). To survey the catalytic action of the biochar/Fe3O4–Ag nanocatalyst, it was used in the reduction reaction of disparate nitroaromatics, aldehydes, and ketones. This catalyst has demonstrated good characteristics in terms of the amount, reusability, recoverability, activity, and structural integrity of the catalyst during the reaction. In addition, biochar/Fe3O4–Ag could be detached magnetically and recycled multiple times without significantly reducing its catalytic performance.

Structural, chemical, optical and photocatalytic properties of Zr co-doped anatase-rutile mixed phase TiO2: Ag nanoparticles

Zr co-doped TiO2:Ag nanoparticles were synthesized by the co-precipitation method and the influence of Zr co-dopant with varying content on the structural, optical and photocatalytic properties of TiO2:Ag photocatalysts was investigated. X-ray diffraction and Raman spectroscopy confirmed the anatase-rutile mixed phase of TiO2 and Zr content eased the anatase-rutile phase transformation. X-ray diffraction peak shift with Zr content indicated the substitutional doping of Zr4+ ions into TiO2 lattice. The optical properties of the nanoparticles were investigated with diffuse reflectance spectroscopy, photoluminescence and Fourier transform infrared spectroscopy. Zr dopants induced the Burstein-Moss effect, resulting in the broader bandgap and photoluminescence shift. X-ray photoelectron spectroscopy was utilized to reveal the surface chemical environment of the Zr co-doped TiO2:Ag nanoparticles and found the presence of Zr4+ ions on the photocatalyst surface, which act as electron traps. The dependence of operational parameters such as photocatalytic load, dye concentration and pH on Zr co-doped TiO2:Ag nanocatalyst was also monitored. The photocatalysts demonstrate improved photocatalytic activity toward methylene blue degradation with maximum efficiency achieved by the photocatalyst having the highest Zr content. 20 mg and 10.35 μM were found to be the optimum values for photocatalytic load and initial methylene blue concentration, respectively. Further, at alkaline pH, complete decolorization of the reaction mixture was observed in only 60 min with 92.6% efficiency by highest co-doped photocatalyst. The effect of Zr content on degradation rate with different parameters was also explored with a possible mechanism to understand the effect of dopants on photocatalytic activity of the photocatalysts.

Hydrophobic Electrode Design for CO2 Electroreduction in a Microchannel Reactor.

Microchannel reactor is a novel electrochemical device to intensify CO2 mass transfer with large interfacial areas. However, if the catalyst inserted in the microchannel is wetted, CO2 is required to diffuse across the liquid film to get access to reaction sites. In this paper, a hydrophobic polytetrafluoroethylene (PTFE)-doped Ag nanocatalyst on a Zn rod was synthesized through a facile galvanic replacement of 2Ag++Zn → 2Ag + Zn2+. The catalyst layer, which was PTFE incorporated into the Ag matrix, was detected to distribute uniformly on the Zn substrate with a thickness of 77 μm. Consequently, the PTFE-doped electrode demonstrated enhanced activity with an optimal 96.19% CO faradaic efficiency (FECO) in the microchannel reactor. Typically, the catalyst could maintain over 90% FECO even at the current density of 24 mA cm-2, which was nearly 30% higher than that of a similar catalyst without PTFE. In addition, influences of the concentration of PTFE and deposition time were also investigated, determining that 1 vol % of PTFE and 30 min of coating yielded best electrocatalytic efficiency. To achieve a further breakthrough of CO2 mass transfer limitations, reactions were applied under relatively high pressures (3-15 bar) in a single-compartment high-pressure cell. The maximum CO partial current density (jCO) can reach 106.76 mA cm-2 at 9 bar.

Single-Molecule Nanocatalysis Reveals the Kinetics of the Synergistic Effect Based on Single-AuAg Bimetal Nanocatalysts.

Decades of extensive research efforts by scientists in the field of catalysis and nanomaterials have led to a large number of excellent bimetallic nanocatalysts. However, in many cases, the mechanism of the synergistic effect in bimetal catalyst-catalyzed reactions has been systematically neglected due to technical limitations. Herein, we use single-molecule fluorescence microscopy (SMFM) to reveal the mechanism of the synergy of the Au and Ag bimetal catalyst. Compared with that of the Ag nanocatalyst, the incorporation of Au changes the reaction pathway of Amplex Red and H2O2 from a noncompetitive to a competitive reaction mechanism, showing much higher catalytic efficiency. Additionally, the incorporation also inhibits the spontaneous surface reconstruction and facilitates the reaction-induced surface restructuring of the nanocatalyst, resulting in the enhancement of stability and reactivity. These findings provide useful insights into tailoring the reactivity of metal catalysts. This work also confirms the power of SMFM in revealing the origin of the catalytic activity of composite catalysts.

In situ deposition of silver nanoparticles on polydopamine‐coated manganese ferrite nanoparticles: Synthesis, characterization, and application to the degradation of organic dye pollutants as an efficient magnetically recyclable nanocatalyst

The present paper reports a facile in situ synthesis strategy for the production of MnFe2O4@PDA‐Ag magnetically recyclable core–shell nanospheres by the deposition of silver nanoparticles (AgNPs) to the surface of MnFe2O4@PDA nanocomposites through the reduction of silver ions by the outer polydopamine (PDA) layer. The deposition of AgNPs over MnFe2O4@PDA was validated by scanning electron microscopy–energy‐dispersive X‐ray spectroscopy (SEM‐EDX), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X‐ray diffraction (XRD), and vibrating sample magnetometer (VSM) analysis. The catalytic reduction performance of the obtained MnFe2O4@PDA‐Ag nanospheres were tested over model organic dye pollutants (i.e., methylene blue [MB] and 4‐nitrophenol [4‐NP]) by sodium borohydride. Notably, the as‐prepared MnFe2O4@PDA‐Ag nanocatalyst exhibited significantly enhanced catalytic activity for the reduction of MB (296.52 s−1 g−1) and 4‐NP (92.02 s−1 g−1) compared with the other types of similar Ag‐ and PDA‐based catalytic systems in the recent literature. Moreover, the MnFe2O4@PDA‐Ag nanocatalyst showed excellent recyclability, ease of magnetic separation, and rapid and higher recovery ability with insignificant loss in their catalytic efficiencies even after several cyclic uses. The PDA coating on the surface of MnFe2O4 NPs allocates the surface functionalization for the building of novel catalyst systems. This work presents a simple and practicable for the synthesis of MnFe2O4@PDA‐Ag nanospheres that could have a great potential for the treatment of organic pollutants in wastewater and variety of applications in catalysis.

Development of highly active, chemically stable and recyclable magnetic nanophotocatalyst based on plasmonic silver nanoparticles and photosensitive trans‐3‐(trans‐4‐imidazolyl) acrylic acid molecules

This study relates to the preparation of a novel nanophotocatalyst comprising of plasmonic silver nanoparticle, photosensitive trans‐3‐(trans‐4‐imidazolyl) acrylic acid (T3TTIA) and superparamagnetic iron oxide nanoparticles (SPION). This heterogeneous nano‐photocatalyst has been synthesized via hydrothermal route where T3TTIA works as a capping agent and linker for SPION and plasmonic Ag NPs, respectively. Structural, morphological, thermal, magnetic, optical, and catalytic properties have been analyzed in detailed. The spinel cubic type structure of nanocrystals of SPION and silver has been confirmed by XRD analysis. XPS analysis has confirmed the presence of Ag0, Fe3O4, and integral functional group. The strong chemical interaction of localized surface plasmonic Ag nanoparticles and SPION with photosensitive T3TIAA molecule has been revealed by both the IR and XPS analysis. The shape of the final products has been observed as spherical with average particle size of 12 ±0.8 nm (with low degree of agglomeration) as analyzed by scanning electron microscope (SEM) and high resolution transmission electron microscope (HR‐TEM). The superparamagnetic nature and high thermal stability of the products have been revealed by vibrating sample magnetometry (VSM) and thermogravimetric (TG) analysis, respectively. UV‐visible spectrophotometry analysis has confirmed the maximum absorbance peak at ~420 nm, indicates as the characteristic peak of surface plasmon resonance (SPR) for silver nanoparticles with a band gap value of 1.43 eV. Furthermore, Brunauer−Emmett−Teller (BET) analysis has demonstrated mesoporous characteristic of the product which follows type IV isotherms with the average surface area and pore size as 250.492 m2/g and 6.1442 nm, respectively. The potential catalytic applications of the as‐prepared nanocatalysts have been explored for the decolorization of methyl orange (MO), methylene blue (MB), and photo‐reduction of 4‐nitrophenol (4‐NP) under both Visible and UV light irradiations. The catalytic activity of the as‐prepared nanocatalyst has been compared with the recent reported magnetic nano‐catalysts. The SPION@T3TIAA‐Ag nanocatalyst has shown excellent catalytic behavior toward the treatment of the selected industrial dyes and organic pollutant with recovery and reusability capacity up to seven cycles without losing significant catalytic efficiency.

Study of growth of silver nano catalyst for carbon nano tube growth

Abstract Silver (Ag) nanocatalyst has been deposited on SiO2 glass substrate by the thermal evaporation method. The layer thickness was about 2.42 mm. The Ag nanocatalyst was then annealed at a temperature of 400 °C with the variation of annealing time for 1, 2, 3, and 4 h. Several spectroscopy methods were carried out to characterize the samples. From the scanning electron microscope (SEM) images showed that the diameter size of the nanoparticles were mostly 0.252 μ m, 0.236 μ m, 0.193 μ m, and 0.108 μ m, respectively. Energy Dispersive X-ray (EDX) spectroscopy revealed that composition of Ag for each sample are 0.26%, 0.14%, 0.48% and 0.04% respectively. Based on the SEM, the smallest diameter of particles was obtained after annealing for 4 h, and EDX results, the most Ag composition was obtained after annealing for 3 h. The results from Fourier transform infrared (FTIR) spectroscopy do not indicate the presence of Si O Ag bonds at SiO2/Ag, where based on literature, their peaks are at 827 cm−1 and 1749 cm−1.

Radio-Frequency Thermal Plasma Treated Activated Carbon Impregnated with Mn and Ag for Volatile Organic Compounds Adsorption.

In this study, we have prepared a composite adsorbent with highly dispersed Mn and Ag nanocatalyst on the surface of activated carbon (AC) by applying the Radio-Frequency (RF) thermal plasma technique for the efficient removal of VOCs. The ACs before and after metal impregnation with RF plasma treatment were characterized by SEM, TEM, EDS, and nitrogen adsorption analysis. Adsorption behaviors of toluene, acetaldehyde, and formaldehyde on ACs before and after modification were also investigated in fixed-bed systems. The experimental adsorption results for VOCs on parent ACs and metal impregnated ACs (Mn-AC and Mn/Ag-AC) were well explained by modified continuous sigmoidal (MCS) model.

Ag(0) nanocatalyst stabilized with networks of p(SPA-co-AMPS) for the hydrogen generation process from ethylenediamine bisborane hydrolysis

In this study, the hydrogen generation from the catalytic hydrolysis of the ethylenediamine bisborane (EDAB) was performed. For this purpose, the p(sulfopropyl acrylate potassium salt-co-2-acrylamido-2-methylpropansulfonic acid sodium salt)@Ag(0) (p(SPA-co-AMPS)@Ag) catalyst was prepared. Later the p(SPA-co-AMPS)@Ag containing Ag(0) particles with nanodimensions was used as catalyst in EDAB hydrolysis. Our study is the first in the literature from this aspect, and investigated in detail the effect of catalyst amount, reactive concentration, temperature and dry or swollen nature of the catalyst on the EDAB hydrolysis. At the end of the reaction series, the hydrolysis reaction of EDAB with p(SPA-co-AMPS)@Ag catalyst was determined to have activation energy (Ea) of 43.24 kJmol-1. Additionally, the turn over frequency (TOF) was 0.560 mol H2(mol Ag(0).min)−1 at 30 °C. The p(SPA-co-AMPS)@Ag catalyst had perfect reusability with 95% of initial activity after the 5th use for the hydrogen generation from EDAB.

Green synthesis of silver nanoparticles using Eucalyptus comadulensis leaves extract and its immobilization on magnetic nanocomposite (GO‐Fe3O4/PAA/Ag) as a recoverable catalyst for degradation of organic dyes in water

The magnetically recyclable graphene oxide‐Fe3O4/polyallylamine (PAA)/Ag nanocatalyst was prepared via a green route using Eucalyptus comadulensis leaves extract as both reducing and stabilizing agent. The catalytic activity of this nanocatalyst was investigated for the reduction reaction of methylene blue and methyl orange in the presence of NaBH4 in aqueous medium at room temperature. The prepared nanocatalyst was characterized by different methods such as Fourier transformed infrared spectroscopy, X‐ray diffraction, scanning electron microscopy–energy dispersive X–ray spectroscopy, thermogravimetric analysis, vibrating sample magnetometer, transmission electron microscopy, and UV–visible spectroscopy. The results show that graphene oxide/PAA/Ag nanocatalyst has good activity and recyclability, and can be reused several times without major loss of activity in the reduction process. The apparent rate constants of the methyl orange (MO) and methylene blue (MB) were calculated to be 0.077 s−1 (3 mg of catalyst) and 0.15 s−1 (2 mg of catalyst), respectively.

Fly ash supported Pd–Ag bimetallic nanoparticles exhibiting a synergistic catalytic effect for the reduction of nitrophenol

Coal fly ash (FA) supported Pd-Ag bimetallic nanoparticles (FA-Pd-Ag) were prepared by reducing Pd(II) and Ag(I) salts together onto the dispersed solid support in aqueous medium. Electron microscope analysis (FE-SEM, HRTEM) in combination with elemental mapping (EDS) suggests that the nanoparticles are well dispersed on fly ash with an average diameter of 6-8 nm. The powder XRD analysis indicates that alloying of the interface occurs between Pd and Ag nanoparticles in FA-Pd-Ag, while XPS reveals that charge transfer takes place between the Pd and Ag moieties that come into contact with each other. The FA-Pd-Ag in aqueous NaBH4 solution exhibits an efficient catalytic reduction of 4-nitrophenol into 4-aminophenol and follows pseudo-first-order reaction kinetics (kPd-Ag = 0.7176 min-1). The higher rate constant for FA-Pd-Ag compared to that for their monometallic analogues (FA-Pd (kPd = 0.5449 min-1)) and (FA-Ag (kAg = 0.5572 min-1)) as well as their physical mixture ((FA-Pd + FA-Ag) (kPd+Ag = 0.4075 min-1)) suggests the synergistic catalytic effect of the bimetallic system. Moreover, the present bimetallic nanocatalyst exhibits the highest normalized rate constant (KPd-Ag ≈ 51 100 min-1 mmol-1) compared to the reported bimetallic Pd-Ag nanocatalysts.

Facile assembly of 2D α-zirconium phosphate supported silver nanoparticles: superior and recyclable catalysis

A novel, efficient and durable two-dimensional ZrP@PDA/Ag nanocatalyst for the reduction of 4-nitrophenol.

Selenium-doped graphitic carbon nitride decorated with Ag NPs as a practical and recyclable nanocatalyst for the hydrogenation of nitro compounds in aqueous media

In the present study, in situ selenium-doped graphitic carbon nitride, showed as Se-g-C3N4, was prepared by applying low-cost melamine and 2,4,6-triselenocyanato-1,3,5-triazine as the precursor materials through a simple thermal condensation strategy and used as an ideal catalyst support. Ag NPs were anchored on the Se-g-C3N4 through the co-reduction method with NaBH4 as a reductant to fabricate the Se-g-C3N4/Ag nanocatalyst. Various microscopic and spectroscopic techniques confirmed the construction of Se-g-C3N4/Ag nanocatalyst and the obtained results have been well interpreted in the context. The Se-g-C3N4/Ag indicated excellent catalytic efficiency and exclusive chemoselectivity in the hydrogenation of nitroaromatic compounds using a green reducing agent (NaBH4) in an environmentally friendly aqueous media, and the corresponding anilines were produced as sole products. The supreme catalytic activity and durability of the Se-g-C3N4/Ag can be ascribed to the synergetic interaction between the highly dispersed Ag NPs and the support.

Nano silver imprinted graphene oxide as catalyst in reduction of 4‐nitrophenol

AbstractHerein, a low‐cost and eco‐friendly approach is adopted for the synthesis of L‐cysteine–assisted silver/reduced graphene oxide (L‐cys‐rGO/Ag) nanocomposites using sodium citrate as reducing agent. The morphology of graphene oxide (GO) and L‐cys‐rGO/Ag nanocomposites are studied by scanning electron microscope (SEM). The strong interactions of rGO/Ag with L‐cysteine are established by Fourier transferred infrared (FTIR) study. The average diameter of dispersed Ag NPs is 40 to 70 nm, which is evidenced by transmission electron microscope (TEM). In the preparation of L‐cys‐rGO/Ag nanocomposites, both GO and L‐cysteine are used as supporting and stabilising media to avoid the unexpected agglomeration in the in situ formed Ag NPs and to get high surface area in the nanocomposites. The excellent behaviour of L‐cys‐rGO/Ag nanocomposites acting as a heterogeneous catalyst for the conversion of 4‐nitrophenol to 4‐aminophenol with NaBH4 is achieved that is due to the high adsorption of reactant on the surface rGO and more transfers of electron from rGO to Ag NPs. Beside this, L‐cys‐rGO/Ag nanocatalyst can be reused several times with negligible loss of catalytic efficiency. Further, the as‐synthesised nanocomposites show good antioxidant behaviour.

Silver nanoparticle-decorated on tannic acid-modified magnetite nanoparticles (Fe3O4@TA/Ag) for highly active catalytic reduction of 4-nitrophenol, Rhodamine B and Methylene blue

Tannic acid, as a humic-like substance with phenolic hydroxyl and carbonyl functional groups, can modify the surface of Fe3O4 nanoparticles (NPs). Moreover, it can improve surface properties and capacity of Fe3O4 for adsorption and reduction of silver ions through complexing with them, in aqueous solutions. Therefore, Fe3O4@TA NPs have potential of reducing, stabilizing and immobilizing silver nanoparticles to generate novel magnetic silver nanocatalyst. The nanocatalyst was characterized by several techniques such as Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP), Transmission electron microscopy (TEM), Field Emission Scanning Electron Microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), Energy-dispersive X-ray spectroscopy (EDS), Vibrating Sample Magnetometer (VSM) and Fourier-transform infrared spectroscopy (FTIR). The results of characterization showed that the Fe3O4@TA/Ag nanocatalyst was successfully synthesized. It was observed that the Fe3O4@TA/Ag NP is the useful and recyclable, which can catalyze the reduction of different dyes, including 4-nitrophenol (4-NP), Rhodamine B (RhB), and Methylene blue (MB) in the presence of NaBH4 in the aqueous medium at room temperature. With the help of UV–Vis spectroscopy, catalysis reactions were controlled. According to results, these reactions followed the pseudo-first-order rate equation.