Facile strategy for the synthesis of silver nanoparticles on magnetic Fe3O4@C core-shell nanocomposites and their application in catalytic reduction

The integration of noble metal nanoparticles (NPs) on magnetic hollow structures is of particular importance for high catalytic activity, while the magnetic property is useful for the recovery of the composites. Herein, we prepared Ag NP decorated Fe₃O₄@C hollow magnetic microtubes by a facile and controllable approach. To this end, tannic acid-ferric ion (TA-Fe) first polymerized in situ on the MoO₃@FeOOH microrods and served as a reducing/stabilizing agent to integrate Ag NPs with high coverage. Moreover, no extra reductant was required owing to the reducibility of TA for the formation of FeOOH@TA-Fe/Ag microtubes. After thermal treatment under an N₂ atmosphere, hollow Fe₃O₄@C-Ag microtubes are obtained with a high surface area and excellent magnetism. Remarkable catalytic activity was achieved towards the reduction of 4-nitrophenol (4-NP) owing to the high coverage of Ag NPs on the tube-like structure, while the composite was easily collected with an external magnet. The integration of Ag NPs and the magnetic hollow structure provides a great platform for designing hybrid catalysts with high efficiency and recoverability.

Preparation of Reduced-Graphene-Oxide-Supported CoPt and Ag Nanoparticles for the Catalytic Reduction of 4-Nitrophenol

Composite nanostructure materials are widely used in catalysis. They exhibit several characteristics, such as the unique structural advantage and the synergism among their components, which significantly enhances their catalytic performance. In this work, CoPt nanoparticles and reduced-graphene-oxide-based nanocomposite catalysts (rGO/CoPt, rGO/CoPt/Ag) were prepared by using a facile co-reduction strategy. The crystalline structure, morphology, composition, and optical characteristics of the CoPt nanoparticles, rGO/CoPt nanocomposite, and rGO/CoPt/Ag nanocomposite catalysts were investigated by a set of techniques. The ID/IG value of the rGO/CoPt/Ag nanocomposite is 1.158, higher than that of rGO/CoPt (1.042). The kinetic apparent rate constant, k, of the rGO/CoPt/Ag nanocomposite against 4-nitrophenol (4-NP) reduction is 5.306 min−1, which is higher than that of CoPt (0.495 min−1) and rGO/CoPt (1.283 min−1). The normalized rate constant, knor, of the rGO/CoPt/Ag nanocomposite is 56.76 min−1mg−1, which is higher than some other catalytic materials. The rGO/CoPt/Ag nanocomposite shows a significantly enhanced catalytic performance when compared to CoPt nanoparticles and the rGO/CoPt nanocomposite, which may confirm that the novel rGO/CoPt/Ag nanocomposite is a promising catalyst for the application of catalytic fields.

Preparation of Magnetically Recoverable MPCTP-Ag Composite Nanoparticles and Their Application as High-Performance Catalysts

In the present research, magnetically recyclable polyphosphazene (PCTP)/Ag (MPCTP-Ag) nanoparticles are prepared by a green path, in which PCTP was used to modify Fe₃O₄ nanoparticles and provide nucleation sites for the reduction of Ag nanoparticles. The prepared MPCTP-Ag nanoparticles were characterized by TEM, SEM, EDS, BET, XRD, vibrating sample magnometry, XPS, and TGA analysis. The catalytic performances of the MPCTP-Ag nanoparticles for the degradation of 4-nitrophenol (4-NP), methylene blue (MB), methyl orange (MO), and their mixtures in the presence of NaBH₄ were studied. The main factors affecting the catalytic performance, including temperature, reactant concentration, and catalyst dosage, were investigated. The results showed that the MPCTP-Ag nanoparticles exhibited excellent catalytic activity for the degradation of all three targeted organic contaminants (4-NP, MB, and MO). Moreover, the product retains its catalytic activity after being reused five times by magnetic separation. The results showed that MPCTP-Ag composite nanoparticles were efficient recyclable magnetic nanocatalysts with promising application in environment protection.

Preparation of Fe3O4-Ag Nanocomposites with Silver Petals for SERS Application

The formation of silver nanopetal-Fe3O4 poly-nanocrystals assemblies and the use of the resulting hetero-nanostructures as active substrates for Surface Enhanced Raman Spectroscopy (SERS) application are here reported. In practice, about 180 nm sized polyol-made Fe3O4 spheres, constituted by 10 nm sized crystals, were functionalized by (3-aminopropyl)triethoxysilane (APTES) to become positively charged, which can then electrostatically interact with negatively charged silver seeds. Silver petals were formed by seed-mediated growth in presence of Ag+ cations and self-assembly, using L-ascorbic acid (L-AA) and polyvinyl pyrrolidone (PVP) as mid-reducing and stabilizing agents, respectively. The resulting plasmonic structure provides a rough surface with plenty of hot spots able to locally enhance significantly any applied electrical field. Additionally, they exhibited a high enough saturation magnetization with Ms = 9.7 emu g-1 to be reversibly collected by an external magnetic field, which shortened the detection time. The plasmonic property makes the engineered Fe3O4-Ag architectures particularly valuable for magnetically assisted ultra-sensitive SERS sensing. This was unambiguously established through the successful detection, in water, of traces, (down to 10-10 M) of Rhodamine 6G (R6G), at room temperature.

Aptasensor based on a flower-shaped silver magnetic nanocomposite enables the sensitive and label-free detection of troponin I (cTnI) by SERS

Acute myocardial infarction (AMI) is nowadays the leading death cause worldwide. For that reason, the early diagnosis of AMI is of central importance to reduce the risk of death. In this sense, aptamer-based sensors for surface-enhanced Raman spectroscopy (SERS aptasensors) emerged as an interesting alternative for future high-performance diagnostic tools. SERS aptasensors combine the fast, precise, and sensitive nature of SERS measurements with the selectivity of aptamers for specific biological targets. Herein, we report an efficient SERS aptasensor for the detection of cardiac troponin I (cTnI), a gold-standard biomarker for AMI. Our SERS platform comprises a magnetite core with an intermediate silica shell, and a flower-shaped silver layer (Fe₃O₄@SiO₂@Ag) to confer excellent plasmonic properties and ease of collection by magnetism. The branched silver structure combined with magnetic aggregation offers a high near-field amplification to superior SERS performance. Additionally, a tailored DNA aptamer with high specificity for cTnI was anchored to the silver surface to produce the aptasensor with increased sensing capability towards cTnI. With our SERS aptasensor, a cTnI concentration as low as 10 ng ml^-1 (10^-11 mol l^-1) could be detected. This value is ten times lower than the upper threshold of the typical concentration range of cTnI of AMI patients. Hence, our SERS aptasensor holds great promise to be explored in AMI diagnosis.

Highly efficient and recyclable catalyst: porous Fe3O4-Au magnetic nanocomposites with tailored synthesis

In this work, we reported the tailored design of highly efficient Fe₃O₄-Au magnetic nanocomposite (MNP) catalysts. Fe₃O₄ nanocrystals with three different morphologies have been developed with engineered amounts of urea, and the plausible mechanism has been proposed. Then by controlling the amount of Au seeds, Fe₃O₄-Au MNPs with different morphologies and tunable Au deposition have been realized. Characterizations including x-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectra, and elemental mapping are implemented to unveil the structural and physical characteristics of the successfully developed Fe₃O₄-Au MNPs with different morphologies. The catalytic ability of Fe₃O₄-Au MNPs with different morphologies have been compared by applying them to degrading RhB and 4-NP, meanwhile the correlation between the amount of Au seeds and the turnover frequency as well as the catalytic ability of Fe₃O₄-Au MNPs is investigated systematically. We found that the flower-like Fe₃O₄-Au MNPs with 20 ml Au seeds added achieved the best degradation efficiency of 96.7%, and their catalytic ability were almost unchanged after recycling. Out study sheds the light into the tailored design of highly efficient and recyclable catalysts for RhB and 4-NP.

Preparation of Magnetic CuFe2O4@Ag@ZIF-8 Nanocomposites with Highly Catalytic Activity Based on Cellulose Nanocrystals

A facile approach was successfully developed for synthesis of cellulose nanocrystals (CNC)-supported magnetic CuFe2O4@Ag@ZIF-8 nanospheres which consist of a paramagnetic CuFe2O4@Ag core and porous ZIF-8 shell. The CuFe2O4 nanoparticles (NPs) were first prepared in the presence of CNC and dispersant. Ag NPs were then deposited on the CuFe2O4/CNC composites via an in situ reduction directed by dopamine polymerization (PDA). The CuFe2O4/CNC@Ag@ZIF-8 nanocomposite was characterized by TEM, FTIR, XRD, N2 adsorption-desorption isotherms, VSM, and XPS. Catalytic studies showed that the CuFe2O4/CNC@Ag@ZIF-8 catalyst had much higher catalytic activity than CuFe2O4@Ag catalyst with the rate constant of 0.64 min-1. Because of the integration of ZIF-8 with CuFe2O4/CNC@Ag that combines the advantaged of each component, the nanocomposites were demonstrated to have an enhanced catalytic activity in heterogeneous catalysis. Therefore, these results demonstrate a new method for the fabrication of CNC-supported magnetic core-shell catalysts, which display great potential for application in biocatalysis and environmental chemistry.

Enhanced Catalytic Reduction of 4-Nitrophenol Driven by Fe₃O₄-Au Magnetic Nanocomposite Interface Engineering: From Facile Preparation to Recyclable Application

In this work, we report the enhanced catalytic reduction of 4-nitrophenol driven by Fe₃O₄-Au magnetic nanocomposite interface engineering. A facile solvothermal method is employed for Fe₃O₄ hollow microspheres and Fe₃O₄-Au magnetic nanocomposite synthesis via a seed deposition process. Complementary structural, chemical composition and valence state studies validate that the as-obtained samples are formed in a pure magnetite phase. A series of characterizations including conventional scanning/transmission electron microscopy (SEM/TEM), Mössbauer spectroscopy, magnetic testing and elemental mapping is conducted to unveil the structural and physical characteristics of the developed Fe₃O₄-Au magnetic nanocomposites. By adjusting the quantity of Au seeds coating on the polyethyleneimine-dithiocarbamates (PEI-DTC)-modified surfaces of Fe₃O₄ hollow microspheres, the correlation between the amount of Au seeds and the catalytic ability of Fe₃O₄-Au magnetic nanocomposites for 4-nitrophenol (4-NP) is investigated systematically. Importantly, bearing remarkable recyclable features, our developed Fe₃O₄-Au magnetic nanocomposites can be readily separated with a magnet. Such Fe₃O₄-Au magnetic nanocomposites shine the light on highly efficient catalysts for 4-NP reduction at the mass production level.

Highly Efficient, Low-Cost, and Magnetically Recoverable FePt⁻Ag Nanocatalysts: Towards Green Reduction of Organic Dyes

Nowadays, synthetic organic dyes and pigments discharged from numerous industries are causing unprecedentedly severe water environmental pollution, and conventional water treatment processes are hindered due to the corresponding sophisticated aromatic structures, hydrophilic nature, and high stability against light, temperature, etc. Herein, we report an efficient fabrication strategy to develop a new type of highly efficient, low-cost, and magnetically recoverable nanocatalyst, i.e., FePt⁻Ag nanocomposites, for the reduction of methyl orange (MO) and rhodamine B (RhB), by a facile seed deposition process. X-ray diffraction results elaborate that the as-synthesized FePt⁻Ag nanocomposites are pure disordered face-centered cubic phase. Transmission electron microscopy studies demonstrate that the amount of Ag seeds deposited onto the surfaces of FePt nanocrystals increases when increasing the additive amount of silver colloids. The linear correlation of the MO and RhB concentration versus reaction time catalyzed by FePt⁻Ag nanocatalysts is in line with pseudo-first-order kinetics. The reduction rate constants of MO and RhB increase with the increase of the amount of Ag seeds. FePt⁻Ag nanocomposites show good separation ability and reusability, and could be repeatedly applied for nearly complete reduction of MO and RhB for at least six successive cycles. Such cost-effective and recyclable nanocatalysts provide a new material family for use in environmental protection applications.