One-pot green synthesis of silver/iron oxide composite nanoparticles for 4-nitrophenol reduction

A convenient and efficient precursor transformation route to well-dispersed, stable, and highly accessible supported Au nanocatalysts with excellent catalytic hydrogenation performances

A new, convenient, and efficient precursor transformation route for the synthesis of supported Au nanocatalysts was reported. In this strategy, [Au(en)₂]³⁺-riched titanate nanospheres (en: ethylenediamine) with hierarchical flower-like architecture were pre-synthesized via “ammonia etching-ion exchange” processes and then used as the precursors of the objective catalysts. Direct pyrolysis of these precursors, varying in amount of [Au(en)₂]³⁺, led to the formation of Au nanoparticles (AuNPs) with different contents uniformly supported on highly crystalline titania nanoflowers (fTiO₂). The fTiO₂-supported AuNPs nanocomposites possessed highly open porous structures with large surface areas (142.3–149.3 m² g⁻¹), which could allow guest molecules to diffuse in and out easily. More interestingly, the formed AuNPs with small size (∼3.8 nm) were well-dispersed and partially embedded into the nanosheets of fTiO₂, which was beneficial for achieving high activity while avoiding their detachment from the support during application. Accordingly, the AuNPs/TiO₂ catalysts exhibited superior catalytic properties for 4-nitrophenol hydrogenation with significantly higher catalytic efficiencies than many previously reported heterogeneous catalysts. Moreover, the catalytic activity could remain almost unchanged after being recycled several times, demonstrating their high stability. These findings open up a new possibility for rational design and synthesis of supported catalysts for diverse catalytic applications.

Synthesis of well-dispersed, stable, and highly accessible supported Au nanocatalysts was achieved via a new and efficient precursor transformation route.

Bactericidal and catalytic performance of green nanocomposite based-on chitosan/carbon black fiber supported monometallic and bimetallic nanoparticles

Nanoparticles were synthesized on the surface of green nanocomposite based on carbon black dispersed in chitosan (CB-CS) fibres. The nanoparticles were monometallic Co, Ag and Cu and bimetallic Co + Cu and Co + Ag. The CB-CS fibres were prepared and introduced into separate metal salt solutions containing Co²⁺, Ag⁺ and Cu²⁺ and mixed Co²⁺+Cu²⁺ and Co²⁺+Ag⁺ ions. The metal ions immobilized on the surface of CB-CS were reduced using sodium borohydride (NaBH₄) as reducing agent to synthesize the corresponding zero-valent metal nanoparticles-loaded CB-CS fibres. All the nanoparticles-loaded CB-CS samples were characterized using field emission-scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction techniques. When tested as catalysts, the nanoparticles-loaded CB-CS showed excellent catalytic ability for the reduction of toxic and environmentally unwanted pollutants of para-nitrophenol, congo red and methyl orange dyes. Afterwards, the antimicrobial activities of virgin and metal-loaded CB-CS fibres were tested and the metal-loaded CB-CS fibres were found to be effective against Escherichia coli. In addition, the catalyst can be recovered easily by simply removing the fibres from the reaction mixture and can be recycled several times while maintaining high catalytic efficiency.

Catalytic reduction of 4-nitrophenol with gold nanoparticles synthesized by caffeic acid

In this study, various concentrations of caffeic acid (CA) were used to synthesize gold nanoparticles (CA-AuNPs) in order to evaluate their catalytic activity in the 4-nitrophenol reduction reaction. To facilitate catalytic activity, caffeic acid was removed by centrifugation after synthesizing CA-AuNPs. The catalytic activity of CA-AuNPs was compared with that of centrifuged CA-AuNPs (cf-CA-AuNPs). Notably, cf-CA-AuNPs exhibited up to 6.41-fold higher catalytic activity compared with CA-AuNPs. The catalytic activity was dependent on the caffeic acid concentration, and the lowest concentration (0.08 mM) produced CA-AuNPs with the highest catalytic activity. The catalytic activities of both CA-AuNPs and cf-CA-AuNPs decreased with increasing caffeic acid concentration. Furthermore, a conversion yield of 4-nitrophenol to 4-aminophenol in the reaction mixture was determined to be 99.8% using reverse-phase high-performance liquid chromatography. The product, 4-aminophenol, was purified from the reaction mixture, and its structure was confirmed by ¹H-NMR. It can be concluded that the removal of the reducing agent, caffeic acid in the present study, significantly enhanced the catalytic activity of CA-AuNPs in the 4-nitrophenol reduction reaction.

Sonochemical green reduction to prepare Ag nanoparticles decorated graphene sheets for catalytic performance and antibacterial application

The emerging popularity and wide acceptance of green chemistry and environmentally benign/ecofriendly approaches have comprehensively considered for catalyst synthesis methods. Natural resource derived carbogenic quantum dots has been used in assistance with ultrasonic shock wave to graphene oxide (GO) aqueous dispersion in order to prepare reduced graphene oxide decorated with silver nanoparticles following the 'top-down' method. The total reduction process is done without using any toxic external reducing agents and any surfactants or stabilizers, thus it can be accepted as green method. Sonochemical destratification of the GO layers provides green attributes due to scalable, non-hazardous and relatively fast reduction to enhance surface area of the GO. Arresting the silver nanoparticles onto basal planes of graphene oxide can act as an efficient solid state support catalyst for fast reduction of toxic nitro aryls. Besides this work also reports bactericidal feature exhibited by the catalyst. Thus a dual functioning nanomaterial has been successfully developed which can be a suitable alternative for reductive forthcoming specialty/multifunctional membrane and other high-end medicinal or industrial applications.

Special Magnetic Catalyst with Lignin-Reduced Au-Pd Nanoalloy

This study describes a new strategy to fabricate a special magnetic catalyst via facile coating Au-Pd nanoalloy catalysts onto a commercial magnetic stirring bar, without the incorporation of iron element. First, the abundant natural "waste" lignin was utilized as the reducing and stabilizing agent to prepare Au-Pd nanoalloys in a green manner. The Au-Pd nanoalloys were assumed to have a core-shell structure with an Au-rich core and a Pd-rich shell. The Au-Pd nanoalloys could be well dispersed in aqueous medium due to the stabilizing effect of lignin and be conveniently coated onto the surface of a commercial stirring bar. The Au_1.0Pd_1.0 nanoalloy catalyst exhibited excellent catalytic activities in the reduction of 4-nitrophenol to 4-amnophenol by NaBH₄, with a rate constant (k) of 0.239 min^-1, which was higher than that of Au_0.5Pd_1.0 and Au_2.0Pd_1.0 nanoalloys and 4 times higher than that of a single-component Au or Pd nanoparticles. Besides, the catalytic ability of Au-Pd nanoalloy catalyst could be maintained even after seven cycles of catalysis. The catalytic rate constant was found to be positively correlated to the stirring speed of the bar. The scanning electron microscopy analysis revealed ravines and pores on the surface of lignin-nanoalloys composites, implying the possible mechanism of the catalytic activities. This study not only proved the feasibility of lignin for green synthesis of Au-Pd nanoalloys but also proposed a facile and innovated strategy for the future production of solid/liquid catalytic platforms where the developed method could be used to coat any surface interfacing the reagents.

Biosynthesis of the CuO nanoparticles using Euphorbia Chamaesyce leaf extract and investigation of their catalytic activity for the reduction of 4‐nitrophenol

Through this study an eco‐friendly, simple, efficient, cheap and biocompatible approach to the biosynthesis and stabilisation of CuO nanoparticles (NPs) using the Euphorbia Chamaesyce leaf extract is presented. The CuO NPs were monitored and characterised by field emission scanning electron microscopy, energy dispersive X‐ray spectroscopy, Fourier transformed infrared spectroscopy, transmission electron microscope and UV‐visible spectroscopy. The biosynthesised CuO NPs showed good catalytic activity for the reduction of 4‐nitrophenol (4‐NP) in water during 180 s and reused 4 times without considerable loss of activity.

Anchoring of silver nanoparticles on graphitic carbon nitride sheets for the synergistic catalytic reduction of 4-nitrophenol

In this paper, a facile process was developed for anchoring of silver nanoparticles on graphitic carbon nitride sheets (Ag/g-C₃N₄) with high catalytic activity for reduction of 4-nitrophenol. The morphology and structure of the as-prepared Ag/g-C₃N₄ composite were investigated by FESEM, TEM, XRD and XPS. The reaction mechanism and the reduction kinetics of 4-nitrophenol under different light irradiation were systematically studied. The results showed that the obtained Ag/g-C₃N₄ composite exhibited a much higher electro/photo catalytic activity and stability for reduction of 4-nitrophenol. Significantly, due to the synergistic effect and interaction between highly dispersed Ag nanoparticles (Ag NPs, ∼7.2 nm) and lamellar g-C₃N₄, not only transfer of interfacial charge, but also the separation of photoinduced electrons occurred when the reaction was proceeded under light. In addition, the composite exhibited high stability and reusability during the cycling experiments. The results showed that the Ag/g-C₃N₄ composite is an effective and stable electro/photo catalyst for reduction of 4-nitrophenol.

Reversible control of solubility using functionalized nanoparticles

The paper provides a novel method for the reversible control of solubility by use of functionalized nanoparticles. The nanoparticles are functionalized with functional groups that can act as a co-solvent or anti-solvent and thus can induce either dissolution or crystallization.

Catalytic hydrogenation performance of an in situ assembled Au@g-C3N4–PANI nanoblend: synergistic inter-constituent interactions boost the catalysis

A novel gold–graphitic carbon nitride–polyaniline (Au@g-C₃N₄–PANI) nanoblend was synthesized via in situ oxidative polymerization of aniline using auric acid as an oxidant in the presence of g-C₃N₄.

Morphology tuning of assembled Au–Cu nicotinate rings by ligand coordination and their use as efficient catalysts

In this work, cyclic annular Au–Cu nicotinates were synthesized through a facile one-pot method.

Fabrication of Sesame Sticks-like Silver Nanoparticles/Polystyrene Hybridnanotubes and Their Catalytic Effects

A novel and efficient catalyst is one of the goals in the material field, and the involvement of nanoscience and technology has brought new vigor to the development of catalyst. This research aimed to develop a simple two-step route to fabricate Fe3O4@PS/PDA-Ag hybridnanotubes with size-controllable and highly dispersed silver nanoparticles (NPs). First, Fe3O4@PS nanotubes of a sound mechanical property were prepared using polystyrene (PS)/toluene solution containing highly dispersed oleic acid modified Fe3O4 particles in a commercial AAO template. Next, the facile technique was used to form in situ silver NPs on the surface of magnetic PS (Fe3O4@PS) nanotubes through dopamine coating. The catalytic effects of the prepared Fe3O4@PS/PDA-Ag hybridnanotubes with highly dispersed AgNPs were characterized using a range of analytical methods, including transmission electron microscopy, thermogravimetric analysis, UV-Visible spectroscopy, and X-ray diffraction. It was found that such prepared Fe3O4@PS/PDA-Ag hybridnanotubes had a large specific surface area. They possessed excellent activities in catalyzing the reduction of 4-nitrophenol (4-NP) by NaBH4 in the aqueous phase. Furthermore, they were readily separated from fluid and retrieved by an external magnet. Their catalyst activity and recyclability demonstrated that this approach we proposed had the potential to become a new idea and route for catalytic platform.

Catalytic reduction of 4-nitrophenol over Ni-Pd nanodimers supported on nitrogen-doped reduced graphene oxide

Catalytic reduction of toxic 4-nitrophenol to 4-aminophenol over magnetically recoverable nanocatalysts has attracted much attention. Herein, we report a Ni-Pd/NrGO catalyst through the growth of Ni-Pd nanodimers (NDs) on nitrogen-doped reduced graphene oxide (NrGO). The Ni-Pd NDs show a heterogeneous nanostructure with Ni and Pd subparts contacting with each other, remarkably different from the frequently-observed core/shell nanoparticles (NPs) or nanoalloy. The formation of Ni-Pd NDs follows an initial deposition of Pd NPs on the graphene and in-situ catalytic generation of Ni subparts over the newly-generated Pd NPs. The resulting Ni-Pd/NrGO exhibits a superior catalytic activity towards the reduction of 4-nitrophenol at room temperature with a high rate constant (3400s^-1g^-1) and a low activated energy (29.1kJmol^-1) as compared to unsupported Ni-Pd NDs and supported monometallic catalysts. The conversion rate of 4-NP is calculated to be 99.5% and the percent yield (%) of 4-AP is as high as 99.1%. A synergistic catalysis mechanism is rationally proposed, which is ascribed to the electronic modification of Ni-Pd metals due to the strong metal/support interaction (SMSI) effect as well as the electron transfer between Ni and Pd. The hybrid catalyst shows soft ferromagnetic properties and can be magnetically separated and recycled without obvious loss of activity.

Core–shell structured nanocomposites Ag@CeO2 as catalysts for hydrogenation of 4-nitrophenol and 2-nitroaniline

A combination of the redox reaction and reverse micelle technique was used for synthesis of core–shell Ag@CeO₂ nanocomposites, which shows superior catalytic activity and durability for the hydrogenation of 4-NP and 2-NA with NaBH₄, respectively.

Room temperature complete reduction of nitroarenes over a novel Cu/SiO2@NiFe2O4 nano-catalyst in an aqueous medium – a kinetic and mechanistic study

The current investigation reports the preparation of a novel system, Cu/SiO₂@NiFe₂O₄, as characterised by XRD, XPS, IR, SEM-EDS, TEM, ICP-AES and VSM data.

Facile fabrication of a Cu@g-C3N4 nanocatalyst and its application for the aerobic oxidations of alkylaromatics and the reduction of 4-nitrophenol

In this study, the Cu@g-C₃N₄ exhibited excellent catalytic performance for the oxidation of ethylbenzene with 98.8% conversion and 94.0% selectivity, and the active parameter k as 1.134 s⁻¹ mM⁻¹ for the reduction of 4-nitrophenol.

Size dependence of silver nanoparticles in carboxylic acid functionalized mesoporous silica SBA-15 for catalytic reduction of 4-nitrophenol

Silver nanoparticles with a size around 3 nm are formed within the mesopores of –COOH functionalized mesoporous silica SBA-15, and they are highly active in the catalytic reduction of 4-nitrophenol.

Supported polymer magnets with high catalytic performance in the green reduction of nitroaromatic compounds

We exhibit the synthesis of magnetic core–shell nanocomposites as solid phase catalysts in the reduction of nitroaromatics.

In situ synthesized Au–Ag nanocages on graphene oxide nanosheets: a highly active and recyclable catalyst for the reduction of 4-nitrophenol

Graphene oxide-supported hollow Au–Ag alloy nanocages were synthesized here, which exhibited short induction time, high catalytic activity and good stability against agglomeration for the reduction of 4-nitrophenol to 4-aminophenol.

Tuned depositing Ag clusters on ZrO2 nanocrystals from silver mirror reaction of silver–dodecylamine complexes

A series of Ag/ZrO₂ nanocomposites have been synthesized from silver mirror reaction in toluene and show excellent catalytic performance for reduction of 4-NP.

Defect-meditated efficient catalytic activity toward p-nitrophenol reduction: A case study of nitrogen doped calcium niobate system

This work reported on the synthesis of a series of nitrogen doped Ca2Nb2O7 with tunable nitrogen content that were found to be efficient and green noble-metal-free catalysts toward catalytic reduction of p-nitrophenol. XPS and ESR results indicated that the introduction of nitrogen in Ca2Nb2O7 gave rise to a large number of defective nitrogen and oxygen species. Defective nitrogen and oxygen species were found to play synergetic roles in the reduction of p-nitrophenol. The underlying mechanism is completely different from those reported for metallic nanoparticles. Moreover, the more negative conduction band edge potential enabled nitrogen doped Ca2Nb2O7 to show photo-synergistic effects that could accelerate the reduction rate toward p-nitrophenol under UV light irradiation. This work may provide a strategy for tuning the catalytic performance by modulating the chemical composition, electronic structure as well as surface defect chemistry.

In situ synthesis of gold nanoparticles on LBL coated nanofibers by tannic acid for catalytic application

Electrospinning nanofibrous mats are extensively studied as efficient two-dimensional nanomaterials and applied in the fields of filtration, catalysis, and biosensors due to their flexibility and porosity.

Synthesis and use of bimetals and bimetal oxides in contaminants removal from water: a review

This paper gives an overview of the recent advances of the synthesis methods of bimetals and bimetal oxides and applying them in contaminant removal from water.

In situ synthesis of silver supported nanoporous iron oxide microbox hybrids from metal-organic frameworks and their catalytic application in p-nitrophenol reduction

Ag nanoparticles (NPs) are successfully grown in situ on nanoporous Fe2O3 microboxes (Ag/Fe2O3) simply by annealing Prussian blue (PB) in the presence of silver nitrate for the first time. The catalytic activity of the Ag/Fe2O3 microboxes for the reduction of p-nitrophenol (PNP) with NaBH4 is measured by UV-vis spectroscopy. It is found that the composites exhibit bifunctional properties with high magnetization and excellent catalytic activity toward PNP reduction. The high catalytic activity of the catalyst might be attributed to its high surface area and the synergistic effect on the delivery of electrons between Ag NPs and Fe2O3 microboxes. In addition, efficient reduction is observed and found to depend upon the content of Ag in the Ag/Fe2O3 microboxes. The dosage of the catalyst and the reaction temperature were investigated. Furthermore, the catalysts can be easily recycled by applying an external magnetic field while maintaining the catalytic activity without significant decrease even after running six times. The unique properties provide an ideal platform to study various metal/Fe2O3 catalysts which can be potentially applied in a wide variety of fields of catalysis and green chemistry.

Green synthesis and synergistic catalytic effect ofAg/reduced graphene oxide nanocomposite

A nanocomposite of silver nanoparticles and reduced graphene oxide (Ag/rGO) has been developed as a catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with sodium borohydride, owing to the larger specific surface area and synergistic effect of rGO. A facile and rapid microwave-assisted green route has been used for the uniform deposition of Ag nanoparticles and the reduction of graphene oxide simultaneously with l-arginine as the reducing agent. The resulting Ag/rGO nanocomposite contained about 51 wt% of Ag, and the Ag nanoparticles deposited on the surface of rGO had a mean diameter of 8.6 ± 3.5 nm. Also, the Ag/rGO nanocomposite exhibited excellent catalytic activity and stability toward the reduction of 4-NP to 4-AP with sodium borohydride. The reduction reaction obeyed the pseudo-first-order kinetics. The rate constants increased not only with the increase of temperature and catalyst amount but also with the increase of initial 4-NP concentration, revealing that the support rGO could enhance the catalytic activity via a synergistic effect. A mechanism for the catalytic reduction of 4-NP with NaBH4 by Ag/rGO nanocomposite via both the liquid-phase and solid-phase routes has been suggested.

Nickel-doped cobalt ferrite nanoparticles: efficient catalysts for the reduction of nitroaromatic compounds and photo-oxidative degradation of toxic dyes

This study deals with the exploration of NixCo₁-xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrite nanoparticles as catalysts for reduction of 4-nitrophenol and photo-oxidative degradation of Rhodamine B. The ferrite samples with uniform size distribution were synthesized using the reverse micelle technique. The structural investigation was performed using powder X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray and scanning tunneling microscopy. The spherical particles with ordered cubic spinel structure were found to have the crystallite size of 4-6 nm. Diffused UV-visible reflectance spectroscopy was employed to investigate the optical properties of the synthesized ferrite nanoparticles. The surface area calculated using BET method was found to be highest for Co₀.₄Ni₀.₆Fe₂O₄ (154.02 m(2) g(-1)). Co₀.₄Ni₀.₆Fe₂O₄ showed the best catalytic activity for reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4 as reducing agent, whereas CoFe₂O₄ was found to be catalytically inactive. The reduction reaction followed pseudo-first order kinetics. The effect of varying the concentration of catalyst and NaBH₄ on the reaction rates was also scrutinized. The photo-oxidative degradation of Rhodamine B, enhanced oxidation efficacy was observed with the introduction of Ni(2+) in to the cobalt ferrite lattice due to octahedral site preference of Ni(2+). Almost 99% degradation was achieved in 20 min using NiFe₂O₄ nanoparticles as catalyst.