Facile preparation of small-sized gold nanoparticle decorated silica nanocomposites and their morphological changes in catalytic reactions

Due to the unique physicochemical properties of gold nanoparticles (AuNPs) decorated silica nanostructures (SiO2@AuNPs), they show great potential for applications in catalysis, biosensing, optical devices and medicine. It is essential to explore the catalytic effect of SiO2@AuNPs and the understanding of the essential process of catalytic reactions. We have prepared SiO2@AuNPs by loading small-sized AuNPs on surface-modified silica nanospheres. SiO2@AuNPs was used as a catalyst for the catalytic reduction of 4-nitrophenol (4-NP) in the presence of excess NaBH4, and the results showed that with the increase of the amount of catalyst from 30 to 100μl, the corresponding rate constantKappwas increased from 6.44 × 10-3to 1.45 × 10-2s-1, and its TOF was as high as 1.326 × 103h-1, and the catalytic rate could still be maintained at 87% after five cycles. By analyzing the morphology and size of the SiO2supported AuNPs before and after the catalytic reaction, it can be seen that the atoms on the surface of small-sized AuNPs supported by silica have migrated during the catalytic process, which subsequently affects the catalytic efficiency of the structure. This study proves the good catalytic effect of SiO2@AuNPs structure and lays the foundation for its wider application.

In-situ preparation of sulfonated carbonaceous copper oxide-zirconia nanocomposite as a novel and recyclable solid acid catalyst for reduction of 4-nitrophenol

The missing-linker defects of UiO-66 were exploited to covalently anchor Cu nanoclusters (Cu/UiO-66). The molecular interactions between the metals and oxides as copper-zirconia interfaces in Cu/UiO-66 are essential for heterogeneous catalysis, leading to remarkable synergistic impacts on activity and selectivity. Homogeneously distributed carbonaceous mixed metal oxides (CuO/ZrO₂@C) nanocomposite was prepared via carbonization of the Cu/UiO-66 at 600 °C for 3 h in air. To enhance the acidity properties of the CuO/ZrO₂@C nanocomposite, a small amount of sulfuric acid was added and heated at 150 °C under an N₂ atmosphere (CuO/ZrO₂-SO₃H@C). The synthesised Cu/UiO-66 and CuO/ZrO₂-SO₃H@C catalysts were used as novel catalysts in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The Cu/UiO-66 and CuO/ZrO₂-SO₃H@C catalysts displayed complete conversion of the 4-NP solution during (4 and 2 min) stirring at room temperature, respectively. These two catalysts exhibited a high reduction rate of 8.61 × 10^-3 s^-1, and 18.3 × 10^-3 s^-1, respectively. The X-ray photoelectron spectroscopic (XPS) analysis showed the charge of copper atoms in the Cu/UiO-66 catalyst was Cu⁰/Cu^II and in the CuO/ZrO₂-SO₃H@C catalyst was Cu^I/Cu^II with nearly the same ratio (65/35). The particle size and the elemental composition of the CuO/ZrO₂-SO₃H@C catalyst were analysed by using high resolution transmission electron microscopy (HR-TEM), and energy-dispersive X-ray spectroscopy (EDS), and elemental mapping, respectively. The key point beyond the high catalytic activity and selectivity of the CuO/ZrO₂-SO₃H@C catalyst is both the carbon-metal oxides heterojunction structure that leads to good dispersion of the CuO and ZrO₂ over the carbon sheets, and the high acidity properties that come from the combination between the Brønsted acid sites from sulfuric acid and Lewis acid sites from the UiO-66. The catalysts exhibited good recyclability efficiency without significant loss in activity, indicating their good potential for industrial applications.

Ultrafine and well-dispersed Pd-Ni bimetallic catalyst stabilized by dendrimer-grafted magnetic graphene oxide for selective reduction of toxic nitroarenes under mild conditions

A facile and efficient strategy is introduced for growing a dendrimer structure on the surface of magnetic graphene oxide by using thiol-ene click reaction. The as-synthesized dendrimer-grafted magnetic graphene oxide was used as a suitable support for bimetallic Pd-Ni nanoparticles. The prepared nanocomposite was utilized for the reduction of toxic nitroarenes to aminoarenes by using sodium borohydride in aqueous medium at room temperature. Various nitroarenes with functional groups like nitrile, halogen, carbonyl, hydroxyl, acid, and heterocycles were converted to their corresponding anilines with good to excellent yields. The enhanced performance of the catalyst could be attributed to the synergistic effect between Ni and Pd which causes the reaction to proceed more efficiently. Moreover, the catalyst could be readily isolated from the reaction mixture by utilizing an external magnet and reused till 5th cycles with marginal loss of activity.

Intrinsic Blue Fluorescence of 2.0G PAMAM-DCM Polymer Dots and Its Applications for Fe3+ Sensing

A typical and environment-friendly fluorescent polyamine-amine (PAMAM) features good compatibility and unique surface modification, while it is restricted by a low fluorescence property performance and an unclear fluorescence mechanism. In this work, we prepared blue fluorescent PAMAM polymer dots (PDs) via a simple hydrothermal method based on dichloromethane (DCM) and 2.0G PAMAM. The quantum yield achieved was 32.1%, which was 25 times stronger than that of 2.0G PAMAM due to the lone-pair electron leap of the amine groups, the aggregation of carbonyl groups, as well as the crosslinking induced by DCM inside the PAMAM. In addition, the fluorescent 2.0G PAMAM-DCM PDs show a great Fe3+ sensing property with the detection limit of 56.6 nM, which is much lower than the safety limits (5.36 μM) in drinking water, indicating its great potential for Fe3+ detection in aqueous media.

The advanced synthetic modifications and applications of multifunctional PAMAM dendritic composites

The profound advances in dendrimer chemistry have led to new horizons in polymer science.

Remote controlled optical manipulation of bimetallic nanoparticle catalysts using peptides

Remote optical manipulation of peptide ligands on bimetallic nanoparticle surfaces allows for tunable catalytic reactivity.

Green synthesis of palladium nanoparticles using lentinan for catalytic activity and biological applications

The green synthesis of palladium nanoparticles (Pd NPs) for catalysis and biological applications has been gaining great interest. To replace complex plant extracts, lentinan (LNT) may be a good reducing and stabilizing agent. In this work, a simple and green method using LNT to reduce and stabilize palladium Pd NPs was verified. The resulting LNT stabilized palladium nanoparticles (Pd_n-LNT NPs) were characterized by UV-Vis spectroscopy, DLS, TEM, and XPS. The results indicated that Pd NPs inside of Pd_n-LNT NPs had a small size (2.35–3.32 nm). Pd_n-LNT NPs were stable in solution for 7 days. In addition, Pd_n-LNT NPs had higher catalytic activity towards the reduction of 4-nitrophenol than other catalysts. More importantly, Pd_n-LNT NPs had negligible cytotoxicity towards cells and showed good antioxidant activity. Taken together, the prepared Pd_n-LNT NPs have great potential bio-related applications.

Lentinan stabilized palladium nanoparticles had high catalytic activity, negligible cytotoxicity and good antioxidant activity.