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

Synergistic effect of Cu loading on Fe sites of fly ash for enhanced catalytic reduction of nitrophenol

A novel Cu catalyst was developed using water-washed coal fly ash (WFA) as a support material for catalytic reduction of p-nitrophenol (p-NP) in the presence of NaBH₄. Cu/WFA showed ~ × 10⁵ times higher estimated rate constant k_obs-p-NP/C_Cu (L min^-1 g_Cu^-1) compared with Cu/SiO₂, Cu/Al₂O₃, and other Cu catalysts previously reported. Surprisingly, we obtained a significant lower price value (Price'/K) (0.027-0.068 USD/L min^-1) for Cu/WFA in comparison with other Cu catalysts and precious metallic catalysts (Pd, Au, Ag, and Pt). Various surface analyses and additional experiments using Fe/SiO₂, Cu/Fe₂O₃/SiO₂, and Cu/HCl-treated WFA demonstrated that Cu(0) nanoparticles were well loaded on the surface of WFA, where Fe elements were abundant, resulting in a dramatic enhancement of the Cu/WFA catalytic activity. Particularly, X-ray photoelectron spectroscopy revealed the abundance of Cu(0)/Fe(III) and Cu(0)/Fe(II) in the WFA surface. This indicates that Cu(0) was the main driving force for the activation of H_ad molecule, and that the reduction of Fe(III) to Fe(II) by NaBH₄ can accelerate the reduction of Cu(II) to Cu(0). Recycling and phytotoxicity tests showed that Cu/WFA can be applied as a reusable catalyst with low environmental impact, revealing the remarkable potential of non-precious metal/WFA catalyst in the field of environmental remediation.

AgNPs encapsulated by an amine-functionalized polymer nanocatalyst for CO2fixation as a carboxylic acid and the oxidation of cyclohexane under ambient conditions

A novel catalyst comprising Ag NPs grafted to a porous polystyrene material was synthesized for the production of valuable propiolic acid derivativesviaCO₂(1 atm) incorporation, and the oxidation of cyclohexane under ambient reaction conditions.

Preparation of CdS-TiO2-Based Palladium Heterogeneous Nanocatalyst by Solvothermal Route and Its Catalytic Activity for Reduction of Nitroaromatic Compounds

In this study, bare CdS nanoparticles (NPs) were prepared by solvothermal method using CdCl₂(3-methylbenzaldehyde thiosemicarbazone)₂ as a single-source molecular precursor in the presence of ethylene glycol. Further, these CdS NPs were used for the preparation of binary (CdS-TiO₂) and ternary (CdS-TiO₂/Pd) heterogeneous nanocatalysts. Characterization of the as-prepared nanocatalysts has been carried out using different techniques such as powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy, and photoluminescence studies. The peak observed at 2θ = 39.5° in XRD confirms the successful doping of noble metal (Pd) on the surface of CdS-TiO₂ nanocatalyst, which is well supported by Raman analysis. From FESEM and TEM analyses, mixed morphology has been observed and elemental composition was confirmed by energy-dispersive X-ray spectroscopy elemental mapping. Furthermore, the as-prepared bare CdS NPs, binary CdS-TiO₂, and ternary CdS-TiO₂/Pd heterogeneous nanocatalysts were used for the reductive transformation of various nitroaromatic compounds to their corresponding aromatic amines at room temperature. It has been observed that among all of the catalysts, ternary CdS-TiO₂/Pd heterogeneous nanocatalyst has excellent catalytic property to reduce all nitroaromatic compounds in very short time span.

Bimetallic Nanoparticles Anchored on Core-Shell Support as an Easily Recoverable and Reusable Catalytic System for Efficient Nitroarene Reduction

We report an easily recoverable and reusable versatile magnetic catalyst (Fe3O4@CS_AgNi, where CS = chitosan) for organic reduction reactions. The catalytic system is prepared by dispersing AgNi bimetallic nanoparticles on the magnetite core-shell (Fe3O4@CS). The as-synthesized catalyst has been characterized by spectroscopic techniques, such as IR, UV-vis, and X-ray photoelectron spectroscopy (XPS), and analytical tools, such as thermogravimetric analysis, powder X-ray diffraction, Brunauer-Emmett-Teller adsorption, FEG-scanning electron microscopy, high-resolution transmission electron microscopy (HR-TEM), inductively coupled plasma-atomic emission spectroscopy, and magnetic measurements. HR-TEM studies indicate the core-shell structure of Fe3O4@CS and confirm the presence of AgNi nanoparticles on the surface of Fe3O4@CS spheres. IR spectral and XPS studies lend evidence for the occurrence of a strong chemical interaction between the amino groups of CS and AgNi nanoparticles. The nano-catalyst Fe3O4@CS_AgNi rapidly reduces p-nitrophenol to p-aminophenol using NaBH4 as the reductant within a few minutes under ambient conditions (as monitored by UV-visible spectroscopy). The utility of this catalytic system has also been extended to the reduction of other nitroarenes. A strong interaction between Fe3O4@CS and AgNi nanoparticles impedes the leaching of AgNi nanoparticles from the core-shell support, leading to excellent reusability of the catalyst.

Recyclable Au/SiO2-Shell/Fe3O4-Core Catalyst for the Reduction of Nitro Aromatic Compounds in Aqueous Solution

Highly stable gold nanoparticles immobilized on the surface of amine-functionalized nanocomposite microspheres possessing a magnetite (Fe₃O₄) nanoparticle core and a silica (SiO₂) shell (Au/SiO₂-shell/Fe₃O₄-core) were prepared. These gold nanocomposite catalysts were tested for 4-nitrophenol (4-NP) and 2-nitroaniline (2-NA) reduction in aqueous solution in the temperature range 293-323 K and in the presence of aqueous NaBH₄ reducing agent. The magnetically recyclable gold catalyst showed high stability (∼3 months), efficient recyclability (up to 10 cycles), and high activity (∼100% conversion within 225 s, ∼700 ppm 4-NP or 2-NA). The pseudo-first-order apparent reaction rate constants (k) of 4-NP and 2-NA reduction were 7.5 × 10^-3 and 4.1 × 10^-3 s^-1, respectively, and with an apparent catalytic activity of 4.48 × 10^-8 kmol/(m³ s).

Encapsulation of AgNPs within Zwitterionic Hydrogels for Highly Efficient and Antifouling Catalysis in Biological Environments

Silver nanoparticles (AgNPs) have been widely used as catalysts in a variety of chemical reactions owing to their unique surface and electronic properties, but their practical applications have been hindered by severe aggregation. The immobilization of AgNPs is crucial to preventing their aggregation or precipitation as well as to improving their reusability. Herein, we developed a facile route for the reductant-free in situ synthesis of AgNPs in zwitterionic hydrogels. Via this method, the embedded AgNPs had a uniform distribution, high activity, and antibiofouling capability. The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using polycarboxybetaine-AgNPs (PCB-AgNPs) could achieve >95% conversion efficiency within 5 min. Meanwhile, the normalized rate constant k_nor (10.617 s^-1mmol^-1) was higher than that of most of the reported immobilized nanocatalysts. More importantly, in a biofouling environment, PCB-AgNPs could still exhibit >97% initial catalytic activity while AgNPs in the PSB or PHEMA hydrogel lost ∼60% activity. This strategy holds great potential for the immobilization of nanoparticle catalysts, especially for applications in biological environments.

Synergistic antibacterial effects of curcumin modified silver nanoparticles through ROS-mediated pathways

Due to their remarkable antibacterial properties, silver nanoparticles (Ag NPs) and curcumin (CCM) have been widely used in the antimicrobial field. In our study, we have fabricated the uniform and stable silver/curcumin composite nanoparticles by a facile ultrasound treatment process and the synergistic antibacterial activity were evaluated. The curcumin not only played a role of reducing agent but also acted as a capping agent. The antibacterial effects of silver/curcumin (cAgNPs) were studied by measuring the growth curve and surface plate assay based on the E. coli and B. subtilis, which showed concentration dependent bacteriostatic and bactericidal effects of cAgNPs. The presence of CCM enhance the binding of Ag to bacterial membrane and Ag⁺ release in comparison to that without CCM, so that creating a temporary and local high Ag⁺ concentration near the surface of the bacterium, meanwhile, generation of more reactive oxygen species, lead to membrane damage, bacterial lipases and induce leakage of intracellular contents followed by bacterial death that lead to growth inhibition of the bacteria. The antibacterial effects were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the effect which were further found to decrease by introducing antioxidant N-acetyl-l-cysteine (NAC) act as a reactive oxygen species (ROS) scavenging agent. These initial data suggest that cAgNPs have a highly antibacterial efficient and might have potential to be developed as an effective antimicrobial nanomaterial.

Ordered mesoporous silica cubic particles decorated with silver nanoparticles: a highly active and recyclable heterogeneous catalyst for the reduction of 4-nitrophenol

An Ag–OMS-C nanocomposite with a high surface area was proposed, and its potential application for catalytic activity was highlighted.

One-step green synthesis of composition-tunable Pt-Cu alloy nanowire networks with high catalytic activity for 4-nitrophenol reduction

Controlling the structure, morphology, and composition of noble metals is of great significance to improve the catalytic activity and stability of catalysts. Herein, we have successfully synthesized self-interconnecting Pt-Cu alloy nanowire networks (NWNs) with controllable compositions via the co-reduction of the metal precursors potassium chloroplatinate (K2PtCl6) and CuCl2 with sodium borohydride (NaBH4). Owing to the hydrogen bubbles formed by NaBH4 hydrolysis and oxidation as a dynamic template, the facile strategy was carried out without any organic solvent, capping agent, polymer, or special experimental device, ensuring that the surfaces of NWNs were definitely "clean". The performance of the as-prepared Pt-Cu alloy NWNs for the reduction of 4-NP was dramatically improved compared with that of pure Pt NWNs and the commercial Pt/C catalyst. Particularly, the PtCu NWNs with a Pt/Cu atomic ratio of 1 : 1 exhibited excellent catalytic activity and reusability for the reduction of toxic 4-NP. The reaction rate constant and activity factor of the PtCu NWNs reached 1.339 × 10-2 s-1 and 66.95 s-1 g-1, respectively, which were dramatically better than those of pure Pt NWNs (11.5-fold) and commercial Pt/C (13-fold). The superior catalytic activity and reusability can mainly be attributed to the clean surface, the synergistic effect of Cu and Pt atoms and the self-interconnecting nanowire network structure.

Engineering of responsive polymer based nano-reactors for facile mass transport and enhanced catalytic degradation of 4-nitrophenol

Silver nanoparticles with average diameter of 10±3nm were synthesized within the sieves of poly(N-isopropylacrylamide-2-hydroxyethylmethacrylate-acrylic acid) (p(NIPAAm-HEMA-AAc)) polymer microgels. Free radial emulsion polymerization was employed for synthesis of p(NIPAAm-HEMA-AAc) polymer microgels. Silver nanoparticles were introduced within the microgels sphere by in situ reduction method. Microgels and hybrid microgels were characterized by Fourier transform infrared spectroscopy, ultra violet-visible spectroscopy, transmission electron microscopy and dynamic light scattering measurements. Catalytic activity of Ag-p(NIPAAm-HEMA-AAc) hybrid microgels was studied using catalytic reduction of 4-nitrophenol (4-NP) as a model reaction in aqueous media. The influence of sodium borohydride (NaBH₄) concentration, catalyst dose and 4-NP concentration on catalytic reduction of 4-NP was investigated. A linear relationship was found between catalyst dose and apparent rate constant (k_app). The mechanism of catalysis by hybrid microgels was explored for further development in this area. The deep analysis of catalytic process reveals that the unique combination of NIPAAm, HEMA and AAc does not only stabilize silver nanoparticles in polymer network but it also enhances the mass transport of hydrophilic substrate like 4-NP from outside to inside the polymer network.

Tat-functionalized Ag-Fe3O4 nano-composites as tissue-penetrating vehicles for tumor magnetic targeting and drug delivery

In this paper, we prepared a dual functional system based on dextrin-coated silver nanoparticles which were further attached with iron oxide nanoparticles and cell penetrating peptide (Tat), producing Tat-modified Ag-Fe₃O₄ nanocomposites (Tat-FeAgNPs). To load drugs, an –SH containing linker, 3-mercaptopropanohydrazide, was designed and synthesized. It enabled the silver carriers to load and release doxorubicin (Dox) in a pH-sensitive pattern. The delivery efficiency of this system was assessed in vitro using MCF-7 cells, and in vivo using null BalB/c mice bearing MCF-7 xenograft tumors. Our results demonstrated that both Tat and externally applied magnetic field could promote cellular uptake and consequently the cytotoxicity of doxorubicin-loaded nanoparticles, with the IC₅₀ of Tat-FeAgNP-Dox to be 0.63 µmol/L. The in vivo delivery efficiency of Tat-FeAgNP carrying Cy5 to the mouse tumor was analyzed using the in vivo optical imaging tests, in which Tat-FeAgNP-Cy5 yielded the most efficient accumulation in the tumor (6.7±2.4% ID of Tat-FeAgNPs). Anti-tumor assessment also demonstrated that Tat-FeAgNP-Dox displayed the most significant tumor-inhibiting effects and reduced the specific growth rate of tumor by 29.6% (P = 0.009), which could be attributed to its superior performance in tumor drug delivery in comparison with the control nanovehicles.

Ligand-Free Nano-Au Catalysts on Nitrogen-Doped Graphene Filter for Continuous Flow Catalysis

In this study, the authors rationally designed a high-performance catalytic filter for continuous flow catalysis. The catalytic filter consisted of ligand-free nanoscale gold (nano-Au) catalysts and nitrogen-doped graphene (N-rGO). The Au catalyst was fabricated in situ onto a pre-formed N-rGO support by the NaBH₄ reduction of the Au precursor, and the size of the nano-Au was fine-tuned. A hydrothermal pretreatment of graphene oxide enriched nitrogen-containing species on the surface of two-dimensional graphene supports and enhanced the affinity of Au precursors onto the support via electrocatalytic attraction. The nano-Au catalysts acted as high-performance catalysts, and the N-rGO acted as ideal filter materials to anchor the catalysts. The catalytic activity of the as-designed catalytic filter was evaluated using 4-nitrophenol (4-NP) hydrogenation as a model catalytic reaction. The catalytic filters demonstrated superior catalytic activity and excellent stability, where a complete 4-nitrophenol conversion was readily achieved via a single pass through the catalytic filter. The as-fabricated catalytic filter outperformed the conventional batch reactors due to evidently improved mass transport. Some key operational parameters impacting the catalytic performance were identified and optimized. A similar catalytic performance was also observed for three 4-nitrophenol spiked real water samples (e.g., surface water, tap water, and industrial dyeing wastewater). The excellent catalytic activity of the nano-Au catalysts combined with the two-dimensional and mechanically stable graphene allowed for the rational design of various continuous flow catalytic membranes for potential industrial applications.

Regenerable urchin-like Fe3O4@PDA-Ag hollow microspheres as catalyst and adsorbent for enhanced removal of organic dyes

In this work, novel urchin-like Fe₃O₄@polydopamine (PDA)-Ag hollow microspheres have been prepared via a facile synthesis method by in situ reduction and growth of Ag nanoparticles on mussel-inspired PDA layers coated on Fe₃O₄ hollow cores. The catalytic reduction efficiency and adsorption performance of the as-prepared urchin-like Fe₃O₄@polydopamine (PDA)-Ag hollow microspheres for model organic dyes (i.e., methylene blue and rhodamine B) under varying pH condition have been systematically investigated, which are demonstrated to be significantly enhanced as compared to that of spherical (relatively smooth) solid Fe₃O₄@PDA-Ag microspheres. The as-prepared urchin-like Fe₃O₄@PDA-Ag hollow microspheres show high reusability, easy separability, and fast regeneration ability, with no obvious drop in the catalytic and adsorption efficiency after cyclic reuse. The versatile PDA coatings on the urchin-like microspheres allow further surface functionalization for development of multifunctional catalyst and adsorbent materials. This work provides a very useful and facile methodology for synthesizing and tuning the urchin-like morphology of Fe₃O₄@PDA-Ag microspheres, with great potential applications in catalysis and wastewater treatment.

Exploring drying pattern of a sessile droplet of genomic DNA in the presence of hematite nanoparticles

For the first time, drying pattern of a sessile droplet of genomic DNA, in the presence of hematite nanoparticles was sighted by polarizing optical microscopy (POM) in this research article. POM results indicated that only at an appreciably high concentration of hematite nanoparticles dried pattern of deoxyribonucleic acid from calf thymus (CT-DNA) was altered. Iron hybridized cetylpyridinium chloride was utilized for the preparation of iron oxide nanoparticles through hydrothermal method. Fourier transforms infrared spectroscopy (FTIR) and powder x-ray diffraction (PXRD) studies confirmed the formation of highly crystalline hematite i.e. α-Fe₂O₃ nanoparticles. Morphology of the synthesized nanoparticle was visualized by transmission electron microscope (TEM) and field emission scanning electron microscope (FESEM), which revealed that nanoparticles were rhombohedral in shape with a size of 45 ± 10 nm. Based upon all the findings, hydrothermal growth mechanism was also proposed having bilayer protection of surfactant around the nanoparticles. UV-Vis spectroscopy and fluorescence spectroscopy were explored to study the affinity of thus prepared nanoparticles towards calf thymus deoxyribonucleic acid (CT-DNA). The low value of binding constant calculated from the spectroscopy data confirmed the weak interaction between nanoparticles and the CT-DNA.

Albizia chevalier based Ag nanoparticles: Anti-proliferation, bactericidal and pollutants degradation performance

The eco-friendly biosynthesis of silver nanoparticles (AgNps) from bark extract of Albizia chevalier are reported here for their anti-proliferative, antibacterial and pollutant degradation potentials. The synthesized AgNps were characterized by FTIR spectroscopy, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X-rays spectrometry (EDS) and X-ray diffraction studies. The TEM and FESEM images show a monodispersed spherical shaped particles of approximately 30 nm. Crystalline peaks were obtained for the synthesized AgNps in XRD spectrum. The AgNps were investigated for in vitro anticancer and antibacterial activities and its potential to degrade 4-nitrophenol (4-NP) and congo red dye (CR). The MTT results shows a significant dose-dependent antiproliferation effect of the AgNps on the cell lines HepG2, MDA-MB-231 and MFC7. The effect was found more pronounced in MDA-MB-231 as compared to MFC-7 cell lines. The antibacterial results indicated 99 and 95% killing of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) respectively, after 24 h of incubation with the AgNps. The AgNps were found to speed up the reductive degradation of 4-NP and CR dye, which give an alternative route for the removal of toxic organic pollutants from the wastewater. The synthesized AgNps were not only used as a bactericidal and anticancer agent, but also effectively used for the reductive degradation of carcinogenic compounds which are listed as the priority pollutants. Therefore, AgNps have the potential for the treatment of various cancers, bacterial infections and for industrial detoxification of wastewater.

Fabrication of iron oxide nanocolloids using metallosurfactant-based microemulsions: antioxidant activity, cellular, and genotoxicity toward Vitis vinifera

The present work aims at the fabrication of iron oxide nanocolloids using biocompatible microemulsion and their cytotoxic, genotoxic effect on Vitis vinifera plant has been evaluated. The three iron-based metallosurfactant complexes were synthesized. Nanosuspensions (Ns) were prepared using microemulsion technique and for the purpose, the microemulsion was prepared using oleic acid, butanol, tween 80 and as synthesized iron metallosurfactant. In this technique, no additional capping agent and/or reducing agent was added. Tween 80 which is a biocompatible surfactant acted as a reducing agent as well as stabilizing for the iron oxide Ns. Characterization of Ns's was done using TEM, FESEM, EDX, XRD, AFM, and zeta potential. Mixed type of iron oxide nanoparticles i.e. magnetite (Fe₃O₄), and maghemite (Fe₂O₃) with a size range of 1-16 nm was found to be present in the nanosuspensions prepared from all the three precursors. The antioxidant activity of the Fe Ns was also confirmed using DPPH assay, with order of activity FeDDA > FeCTAC > FeHEXA. The cellular toxicity of Ns was evaluated by observing the morphological changes on V. vinifera plant (petiole) using a light microscope. Further, the interactions of iron oxide Ns with V. vinifera's DNA (plant-DNA) was assessed using circular dichroism (CD) and gel electrophoresis. For the case of FeCTAC Ns, a decrease in the intensity of bands was observed indicating fragmentation or adduct formation resulting in DNA damage. In the case of FeDDA, a modest decrease in the intensity of bands was observed. However, for FeHEXA Ns, complete neutralization of bands was confirmed implying maximum damage to the plant DNA. CD, gel electrophoresis and antioxidant activity confirmed that FeHEXA Ns were most toxic and FeDDA Ns were safest among the three as-fabricated nanosuspensions.

Synthesis of cobalt-impregnated carbon composite derived from a renewable resource: Characterization and catalytic performance evaluation

A novel nitrogen-doped biochar embedded with cobalt (Co-NB) was fabricated via pyrolysis of glucose pretreated with melamine (N donor) and Co(II). The Co-NB showed high catalytic capability by converting p-nitrophenol (PNP) into p-aminophenol (PAP) by NaBH₄. The analyses of FE-SEM, TEM, BET, XRD, Raman, and X-ray photoelectron spectroscopy XPS of the Co-NB showed hierarchical porous structure (BET 326.5m²g^-1 and pore volume: 0.2403cm³g^-1) with well-dispersed Co nanoparticles (20-60nm) on the N-doped graphitic biochar surface. The Co-NB showed higher PNP reduction capability compared to the Co-biochar without N-doping, achieving 94.3% removal within 4min at 0.24gL^-1 catalyst dose and initial concentration of 0.35mM PNP. Further conversion experiments under varying environmental conditions (e.g., NaBH₄ concentration (7.5-30mM), biochar dosage (0.12-1.0gL^-1), initial PNP concentration (0.08-0.17mM)) were conducted in batch mode. The reusability of Co-NB was validated by the repetitive conversion experiments (5cycles). The overall results demonstrated biochar potential as catalysts for environmental applications if properly designed.

The reduction of 4-nitrophenol and 2-nitroaniline by the incorporation of Ni@Pd MNPs into modified UiO-66-NH2 metal–organic frameworks (MOFs) with tetrathia-azacyclopentadecane

UiO-66-NH₂/TTACP/Ni@Pd MNPs exhibited excellent catalytic activity for the reduction of 2-nitroaniline and 4-nitrophenol.

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.