Facile ultrasonic synthesis of silver-based bimetal nanoparticles for efficient catalytic reduction of 4-nitrophenol

Electron transfer enhanced catalytic activity of nitrogen doped reduced graphene oxide supported CuCo2O4 towards the fast reduction of 4-nitrophenol in water

There has been a growing interest in the design and development of graphene based composite materials with superior performances for environmental catalytic applications. But in most of the studies the synthesis conditions require elevated temperatures and expensive working setups (high temperature furnaces, autoclaves, inert atmosphere conditions etc.). In this reported work, the nitrogen doped reduced graphene oxide supported CuCo2O4 (NG/CuCo2O4) composites were prepared through a simple one pot synthesis method under mild conditions (∼95 °C and air atmosphere) and successfully employed as catalysts for the reduction of toxic 4-nitrophenol (4NP). The characterization results revealed the successful formation of NG/CuCo2O4 composites with a possible charge transfer interaction between nitrogen doped reduced graphene oxide support of CuCo2O4. The NG/CuCo2O4 hybrids exhibited robust catalytic activity in 4NP reduction with an activity factor of 261.5 min-1 g-1. A 4NP conversion percentage which is as high as 99.5% was achieved within 11 min using the NG/CuCo2O4 catalyst. The detailed kinetic analysis confirmed the Langmuir-Hinshelwood model for the NG/CuCo2O4 catalysed 4NP reduction. The nitrogen doped reduced graphene oxide support modified the electronic levels of CuCo2O4 nanoparticles through electron transfer interactions and enhanced the catalytic activity of CuCo2O4 in NG/CuCo2O4 through improved adsorption of reactant ions and effective generation of active hydrogen species. The good reusability and stability along with profound activity of NG/CuCo2O4 catalyst makes it a promising material for wide scale catalytic applications.

SiO2@AuAg/PDA hybrid nanospheres with photo-thermally enhanced synergistic antibacterial and catalytic activity

Wastewater discharged from industrial, agricultural and livestock production contains a large number of harmful bacteria and organic pollutants, which usually cause serious harm to human health. Therefore, it is urgent to find a "one-stone-two-birds" strategy with good antimicrobial and pollutant degradation activity for treating waste water. In this paper, SiO2@AuAg/Polydopamine (SiO2@AuAg/PDA) core/shell nanospheres, which possessed synergistic "Ag+-release-photothermal" antibacterial and catalytic behaviors, have been successfully prepared via a simple in situ redox polymerization method. The SiO2@AuAg/PDA nanospheres showed good catalytic activity in reducing 4-nitrophenol to 4-aminophenol (0.576 min-1 mg-1). Since the AuAg nanoclusters contain both gold and silver elements, they provided a high photothermal conversion efficiency (48.1%). Under NIR irradiation (808 nm, 2.5 W-2), the catalytic kinetics were improved by 2.2 times. Besides the intrinsic Ag+-release, the photothermal behavior originating from the AuAg bimetallic nanoclusters and the PDA component of SiO2@AuAg/PDA also critically improved the antibacterial performance. Both E. coli and S. aureus could be basically killed by SiO2@AuAg/PDA nanospheres at a concentration of 90 μg mL-1 under NIR irradiation. This "Ag+-release-photothermal" coupled sterilization offers a straightforward and effective approach to antimicrobial therapy, and further exhibits high potential in nanomedicine for combating bacterial contamination in environmental treatment and biological fields.

Rapid Plasma Electrolytic Oxidation Synthesis of Intermetallic PtBi/MgO/Mg Monolithic Catalyst for Efficient Removal of Organic Pollutants

The intermetallic PtBi/MgO/Mg monolithic catalyst was first prepared using non-equilibrium plasma electrolytic oxidation (PEO) technology. Spherical aberration-corrected transmission electron microscope (ACTEM) observation confirms the successful synthesis of the PtBi intermetallic structure. The efficiency of PtBi/Mg/MgO catalysts in catalyzing the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of NaBH4 was demonstrated. The activity factor for the catalyst is 31.8 s-1 g-1, which is much higher than reported values. In addition, the resultant catalyst also exhibits excellent catalytic activity in the organic pollutant reaction of p-nitrobenzoic acid (p-NBA) and methyl orange (MO). Moreover, benefiting from ordered atomic structures and the half-embedded PtBi nanoparticles (NPs), the catalyst demonstrates excellent stability and reproducibility in the degradation of 4-NP. This study provides an example of a simple method for the preparation of intermetallic structures as catalysts for organic pollutant degradation.

Tuning Pd-to-Ag Ratio to Enhance the Synergistic Activity of Fly Ash-Supported PdxAgy Bimetallic Nanoparticles

Fly ash (FA)-supported bimetallic nanoparticles (PdxAgy/FA) with varying Pd:Ag ratios were prepared by coprecipitation of Pd and Ag involving in situ reduction of Pd(II) and Ag(I) salts in aqueous medium. All the supported nanoparticles were thoroughly characterized with the aid of powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), electron microscopy (field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM)), and elemental analyses, which include inductively coupled plasma-optical emission spectroscopy (ICP-OES) and energy-dispersive X-ray spectroscopy (EDS). A gradual broadening and shifting of PXRD peaks, ascribable to Ag, to higher angles with an increase in the Pd:Ag ratio affirms the alloying of interface between Pd and Ag nanoparticles. The coexistence of Pd and Ag was further confirmed by EDS elemental mapping as well as by the presence of bimetallic lattices on the FA surface, as evident from the high-resolution TEM analysis. The dependency of crystallite size and average size of bimetallic nanoparticles on Ag loading (mol %) was elucidated with the help of a combination of PXRD and TEM studies. Based on XPS analysis, the charge transfer phenomenon between contacting Pd-Ag sites could be evident from the shifting of 3d core electron binding energy for both Pd and Ag compared with monometallic Pd and Ag nanoparticles. Following a pseudo-first-order reaction kinetics, all the nanocatalysts were able to efficiently reduce 4-nitrophenol into 4-aminophenol in aqueous NaBH4. The superior catalytic performance of the bimetallic nanocatalysts (PdxAgy/FA) over their monometallic (Pd100/FA and Ag100/FA) analogues has been demonstrated. Moreover, the tunable synergistic effect of the bimetallic systems has been explored in detail by varying the Pd:Ag mol ratio in a systematic manner which in turn allowed us to achieve an optimum reaction rate (k = 1.050 min-1) for the nitrophenol reduction using a Pd25Ag75/FA system. Most importantly, all the bimetallic nanocatalysts explored here exhibited excellent normalized rate constants (K ≈ 6000-15,000 min-1 mmol-1) compared with other supported bimetallic Pd-Ag nanocatalysts reported in the literature.

Efficient nitrophenol reduction with Noria-GO nanocomposite decorated with Pd-Cu nanoparticles

We report a facile approach to synthesize Pd-Cu nanoparticles immobilized on a Noria-GO nanocomposite for efficient nitrophenol reduction. The unique architecture of the Noria and the hydrophilic nature of GO contribute to the improved performance and structure of the resulting nanocomposite. The simple sol-immobilization approach employed NaBH4 as a reductant and polyvinyl alcohol as a capping agent to evenly decorate small Pd-Cu nanoparticles with a diameter of 1.4 nm on the Noria-GO surface. The prepared Pd-Cu@Noria-GO nanocomposite was utilized as a nanocatalyst in converting of nitrophenol to aminophenol using NaBH4 solution. Our Pd-Cu@Noria-GO nanocomposite exhibited superior catalytic efficacy with large conversion percentages, Kapp, and KAF values of 95%, 0.225 min-1, and 225 min-1g-1, respectively. X-ray photoemission spectroscopy confirmed the oxidation state of the prepared nanoparticles, and TEM findings demonstrated the homogenous decoration of Pd-Cu NPs on the Noria-GO surface. Additionally, the durability of the Pd-Cu@Noria-GO nanocomposite shown its potential as a robust and promising material for remediating organic contaminants. Our results indicate that Pd-Cu@Noria-GO nanocomposite can be an effective and sustainable approach for mitigating the hazards associated with nitrophenols.

High-performance catalytic reduction of 4-nitrophenol to 4-aminophenol using M-BDC (M = Ag, Co, Cr, Mn, and Zr) metal-organic frameworks

The catalytic activity of pure metal nanoparticles is always limited by aggregation during the reaction. Therefore, promising candidates such as metal-organic frameworks possess benefits due to their 3D porous structures, high stability, and high specific surface area. In this study, effective and reusable catalysts based on M-BDC metal-organic frameworks were synthesized utilizing five different coordinating metal ions (M = Ag, Co, Cr, Mn, and Zr) as metal nodes and 1-4-benzene dicarboxylic acid (BDC) as an organic linker and used in catalytic reduction of 4-Nitrophenol (4-NP) to 4-Aminophenol (4-AP) for the first time. The as-prepared catalysts were characterized using SEM, EDX, XRD, and FTIR techniques. Based on catalytic performance, Co-BDC showed the best catalytic efficiency compared to the other M-BDC MOF catalysts with a conversion yield of about 99.25 in 2 min. All of the catalysts could catalyze the complete reduction of 4-NP to 4-AP at different reaction times (2-10); however, Mn-BDC could not finish the catalytic reduction reaction even after 20 min. The two more efficient catalysts including Co-BDC and Cr-BDC demonstrated high stability and reusability (more than 85% catalytic efficiency) even after 5 cycles.

Remediation of wastewater containing 4-nitrophenol using ionic liquid stabilized nanoparticles: Synthesis, characterizations and applications

In the present study, an ionic liquid (IL) based on 1-butyl-3- (trimethoxysilylpropyl) -imidazolium tetrafluoroborate (IL) was prepared using metathesis and anion exchange reactions and used to stabilize silver (AgNPs) nanoparticles. The IL-stabilized silver nanoparticles AgNPs@[BMSI]BF₄ were produced in an aqueous solution with NaBH₄ as a reducing agent. TGA, FTIR, XRD, BET, FSEM, TEM/HRTEM, XPS, and UV-Vis spectra were used to analyze AgNPs@[BMSI]BF₄ and were used for the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of NaBH₄. AgNPs@[BMSI]BF₄ showed excellent catalytic properties for the reduction of 4-NP to 4-AP and showed 100% conversion of 4-NP to 4-AP within 6 min and the rate constant (k) was found to be 8.33 × 10^-3 s^-1. The reusability results indicated that 97.8% of 4-NP was converted to 4-AP with highly stable rate constants over six consecutive cycles. The activity factor (AF) and the turn-over frequency (TOF) at room temperature were 3.33 s^-1 gm^-1 and 0.166 s^-1, respectively. This study extends a new approach to the production of stable catalysts for the growing needs in wastewater treatment.

Cu-Doped 1D Hydroxyapatite as a Highly Active Catalyst for the Removal of 4-Nitrophenol and Dyes from Water

Metallic copper nanoparticle (Cu NP)-doped 1D hydroxyapatite was synthesized using a simple chemical reduction method. To describe the structure and composition of the Cu/HAP nanocomposites, physicochemical techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, inductively coupled plasma, N₂ adsorption-desorption, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy were used. The TEM scan of the Cu/HAP nanocomposite revealed a rod-like shape with 308 nm length and 117 nm width on average. The catalytic activity of Cu/HAP nanocomposites for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of NaBH₄ has been thoroughly investigated. The 0.7% Cu/HAP nanocomposite was shown to have superior catalytic activity than the other nanocomposites, converting 4-NP to 4-AP in ∼1 min with good recyclability. Moreover, this nanocomposite showed excellent catalytic performance in the organic dye reduction such as Congo red and acriflavine hydrochloride dyes. The high dispersion of Cu NPs on HAP support, the high specific surface area, and the small Cu particles contributed to its remarkable catalytic performance.

A study on the high efficiency reduction of p-nitrophenol (4-NP) by a Fe(OH)3/Fe2O3@Au composite catalyst

Precious metal nanometric catalysts are widely used in the removal of harmful substances. In the process of synthesis and catalytic reaction, it is particularly important to study green and simple synthesis methods and high catalytic efficiency. In this paper, a green one-step method was used to synthesize the Fe(OH)₃/Fe₂O₃@Au composite catalyst, in which Au was single atom-dispersed. The removal of 4-nitrophenol (4-NP), a typical dangerous chemical widely existing in factory waste gas, waste water and automobile exhaust gas, was catalysed by Fe(OH)₃/Fe₂O₃@Au. The catalytic performance of Fe(OH)₃/Fe₂O₃@Au with different synthesis conditions (different amounts of MES, NaBH₄, FeSO₄, Au and Pt) on the 4-NP reduction reaction were systematically studied. Finally, the stability and recyclability of Fe(OH)₃/Fe₂O₃@Au composite nanocatalyst were investigated thoroughly.