A facile strategy for synthesis of Ni@C(N) nanocapsules with enhanced catalytic activity for 4-nitrophenol reduction

One-Pot Facile Synthesis of Noble Metal Nanoparticles Supported on rGO with Enhanced Catalytic Performance for 4-Nitrophenol Reduction

In this study, reduced graphene oxide (rGO)-supported noble metal (gold, silver, and platinum) nanoparticle catalysts were prepared via the one-pot facile co-reduction technique. Various measurement techniques were used to investigate the structures and properties of the catalysts. The relative intensity ratios of I_D/I_G in rGO/Au, rGO/Ag, rGO/Pt, and GO were 1.106, 1.078, 1.047, and 0.863, respectively. The results showed the formation of rGO and that noble metal nanoparticles were decorated on rGO. Furthermore, the catalytic activities of the designed nanocomposites were investigated via 4-nitrophenol. The catalysts were used in 4-nitrophenol reduction. The catalytic performance of the catalysts was evaluated using the apparent rate constant k values. The k value of rGO/Au was 0.618 min^-1, which was higher than those of rGO/Ag (0.55 min^-1) and rGO/Pt (0.038 min^-1). The result proved that the rGO/Au catalyst exhibited a higher catalytic performance than the rGO/Ag catalyst and the rGO/Pt catalyst. The results provide a facile method for the synthesis of rGO-supported nanomaterials in catalysis.

Enhanced activity for reduction of 4-nitrophenol of Ni/single-walled carbon nanotube prepared by super-growth method

In this study, we synthesised the Ni/single-walled carbon nanotube prepared by the super-growth method (SG-SWCNTs). In this approach, the Ni nanoparticles were immobilised by an impregnation method using the SG-SWCNTs with high specific surface areas (1144 m²g^-1). The scanning electron microscopy images confirmed that the SG-SWCNTs exhibit the fibriform morphology corresponding to the carbon nanotubes. In addition, component analysis of the obtained samples clarified that the Ni nanoparticles were immobilised on the surface of the SG-SWCNTs. Next, we evaluated the activity for the reduction of 4-nitoropenol in the presence of the Ni/SG-SWCNTs. Additionally, the Ni/graphene, which was obtained by the same synthetic method, was utilised in this reaction. The rate of reaction activity of the Ni/SG-SWCNTs finished faster than that of the Ni/GPs. From this result, the pseudo-first-order kinetic rate constantkfor the Ni/SG-SWCNTs and the Ni/GPs was calculated respectively at 0.083 and 0.070 min^-1, indicating that the Ni/SG-SWCNTs exhibits higher activity.

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.

Low density magnetic silicate-nickel alloy composite hollow structures: seed induced direct assembly fabrication and catalytic properties

An efficient seed induced direct assembly route is designed for the controlled synthesis of hollow microsphere supported catalysts (HMSCs) with nickel alloy as the active material. The inherent magnetic response of nickel alloy endows HMSCs magnetic separability, and the hollow interior of the support opens a new avenue for self-floating separation. It is found that the introduction of P and Co contributes largely to the improvement of the catalytic performance of the products, which may attributed to synergistic effects and electron transfer. Moreover, the loading amounts of alloy nanoparticles can be easily tailored through properly monitoring the reaction conditions. With the optimized loading of 2.68 wt%, the k_N of HMSC–NiCoP-2.68 wt% reaches 14.0 s⁻¹ g⁻¹ for the catalytic reduction of p-nitrophenol (4-NP), which is higher than commercial 5 wt% Pd/C of 11.6 s⁻¹ g⁻¹ under the same conditions. This work provides additional insights into preparation and property control of an easily separable supported non-noble metal catalyst, which holds potential to be extended to the preparation and property control of other metal nanocatalysts on various supports.

Synthesized HMSC–NiCoP-2.68 wt% catalyst exhibits excellent catalytic reduction activity of 4-NP, which can be separated by self-floating and external magnetic field.

Synergism of transition metal (Co, Ni, Fe, Mn) nanoparticles and "active support" Fe3O4@C for catalytic reduction of 4-nitrophenol

Research reports, up to date, on supports for non-noble metal catalyst focus mainly on tuning their surface functionality and increasing surface area to maximize metal loading for high catalytic reduction of 4-nitrophenol. However, the "passive" role of these supports leads to inefficient hydride formation on the metal surface which limits catalytic activity. Herein, we present Fe₃O₄@porous-conductive carbon (Fe₃O₄@C-A) core-shell structure as an "active" support for non-noble metals (M = Co, Ni, Fe, and Mn) nanoparticles. Fe₃O₄@C-A was prepared by annealing Fe₃O₄@dense-carbon (Fe₃O₄@C) under N₂. The resultant M-Fe₃O₄@C-A catalysts show high catalytic performance at very low metal loading, while non-noble metals supported on a "passive" support (Fe₃O₄@C) shows very low activity even at high metal loading. The significant difference in catalytic activity is ascribed to the synergistic effect amongst Fe₃O₄, conductive carbon and metal nanoparticles which leads to efficient hydride formation. Amongst the prepared catalysts, Ni-Fe₃O₄@C-A and Co-Fe₃O₄@C-A show the best catalytic activity, completing 4-nitrophenol reduction within 50 s and 80 s, respectively, in the presence of NaBH₄. This result is comparable with previously reported noble-metal-based nanocomposites. In addition, Co-Fe₃O₄@C-A shows high recyclability in 5 consecutive catalytic reactions. In the broader context, our finding highlights how an "active support" together with non-noble metals can provide an efficient mechanism for hydride formation, subsequently accelerating the catalytic reduction of 4-nitrophenol.

Core-shell structured Co@CN nanocomposites as highly efficient dual function catalysts for reduction of toxic contaminants and hydrogen evolution reaction

In this study, we have reported nitrogen-doped graphite C coated Co nanocomposite (Co@CN) catalysts synthesized by one-step arc discharge method. The surface compositions, morphologies and the catalytic properties of the Co@CN nanocomposites were studied minutely. The results reveal that the prepared Co@CN nanocomposites have typical core-shell structure and show highly efficient catalytic performance in a reduction of 4-nitrophenol (4-NP), rhodamine and methylene blue. Their rate constant (K_app) is 0.074 s^-1 in a reduction of 4-NP, which is much higher than that of reported transition metal-based catalysts. Moreover, the overpotential of Co@CN is only 96 mV at a current density of 10 mA cm^-2 in alkaline solution, showing high electrocatalytic activities in the hydrogen evolution reaction. The excellent synergistic effect between nitrogen-doped graphite C shell and magnetic Co core enables the Co@CN nanocomposites catalysts to hold abundant active sites and to transmit rapidly electron ability, resulting in Co@CN nanocomposite catalysts having a highly efficient catalytic nature.