Ginkgo biloba leaf polysaccharide stabilized palladium nanoparticles with enhanced peroxidase-like property for the colorimetric detection of glucose

Sensitive glucose detection based on nanoparticles is good for the prevention of illness in our bodies. However, many nanoparticles lack stability and biocompatibility, which restrict their sensitivity to glucose detection. Herein, stable and biocompatible Ginkgo biloba leaf polysaccharide (GBLP) stabilized palladium nanoparticles (Pd_n-GBLP NPs) were prepared through a green method where GBLP was used as a reducing and stabilizing agent. The results of Pd_n-GBLP NPs characterized by UV-visible spectroscopy (UV-Vis), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS) confirmed the successful preparation of Pd_n-GBLP NPs. TEM results indicated that the sizes of Pd NPs inside of Pd_n-GBLP NPs (n = 41, 68, 91 and 137) were 7.61, 9.62, 11.10 and 13.13 nm, respectively. XPS confirmed the successful reduction of PdCl₄²⁻ into Pd (0). Dynamic light scattering (DLS) results demonstrated the long-term stability of Pd_n-GBLP NPs in different buffer solutions. Furthermore, Pd₉₁-GBLP NPs were highly biocompatible after incubation (500 μg mL⁻¹) with HeLa cells for 24 h. More importantly, Pd₉₁-GBLP NPs had peroxidase-like properties and followed a ping-pong mechanism. The catalytic oxidation of substrate 3,3′,5,5′-tetramethylbenzidine (TMB) into blue oxidized TMB (oxTMB) by Pd₉₁-GBLP NPs was used to detect the glucose concentration. This colorimetric method had high selectivity, wide linear range from 2.5 to 700 μM and a low detection limit of 1 μM. This method also showed good accuracy for the detection of glucose concentrations in blood. The established method has great potential in biomedical detection in the future.

Ginkgo biloba leaf polysaccharide stabilized palladium nanoparticles had high stability, good biocompatibility and low detection limit for glucose.     

Peptide-directed Pd-decorated Au and PdAu nanocatalysts for degradation of nitrite in water

In this work, a palladium binding peptide, Pd4, has been used for the synthesis of catalytically active palladium-decorated gold (Pd-on-Au) nanoparticles (NPs) and palladium–gold (Pd_xAu_100−x) alloy NPs exhibiting high nitrite degradation efficiency. Pd-on-Au NPs with 20% to 300% surface coverage (sc%) of Au showed catalytic activity commensurate with sc%. Additionally, the catalytic activity of Pd_xAu_100−x alloy NPs varied based on palladium composition (x = 6–59). The maximum nitrite removal efficiency of Pd-on-Au and Pd_xAu_100−x alloy NPs was obtained at sc 100% and x = 59, respectively. The synthesized peptide-directed Pd-on-Au catalysts showed an increase in nitrite reduction three and a half times better than monometallic Pd and two and a half times better than Pd_xAu_100−x NPs under comparable conditions. Furthermore, peptide-directed NPs showed high activity after five reuse cycles. Pd-on-Au NPs with more available activated palladium atoms showed high selectivity (98%) toward nitrogen gas production over ammonia.

In this work, a palladium binding peptide, Pd4, has been used for the synthesis of catalytically active palladium-decorated gold (Pd-on-Au) nanoparticles (NPs) and palladium–gold (Pd_xAu_100−x) alloy NPs exhibiting high nitrite degradation efficiency.     

Palladium/graphene oxide nanocomposites with carbon nanotubes and/or magnetite for the reduction of nitrophenolic compounds

Graphene oxide (GO) was synthesised via the oxidation of graphite and was characterised using ATR FTIR, PXRD, SEM, TEM and TGA. These techniques confirmed the presence of characteristic oxygen-containing functional groups and the resulting increase in interlayer spacing in the nanostructure. GO is used as the support to form nanocomposites composed of combinations of the following: iron oxide nanoparticles (Fe₃O₄), carbon nanotubes (CNT) and palladium nanoparticles (Pd). The four final nanocomposites formed are: Pd/GO, Pd/Fe₃O₄/GO, Pd/CNT/GO, and Pd/CNT/Fe₃O₄/GO. Key intermediates were analysed using ATR FTIR for the confirmation of the modification. Additionally, all composites and their precursors underwent electron microscopic analysis to visually assess composite morphologies and the size distribution of deposited nanoparticles. The Fe₃O₄ and Pd nanoparticles were indistinguishable from each other in their spherical shape and particle diameters, which were no bigger than 32 nm. From the TGA, incorporation of Fe₃O₄, CNT and finally Pd into the nanocomposites increased total thermal stability in terms of mass percentage lost over the temperature programme. GO showed significant decomposition, with all nanocomposites remaining relatively stable up to 120 °C. ICP OES results showed total Pd content by mass percentage for each final composite, varied from 7.9% to 9.1% mass Pd/collective mass. XPS confirmed the expected elemental compositions of composites according to their structures and the Pd⁰ : Pd^II ratios are obtained. The nanocomposites were tested for the catalytic reduction of nitrophenols. Pd/CNT/Fe₃O₄/GO gave the highest TOF′ for the reduction of 4-NP and 2-NP. For the reduction of 3-NP, Pd/GO showed the highest TOF′. Nitrophenol''s pK_a and catalyst TOF′ correlated in a direct proportional relationship for Pd/GO and Pd/Fe₃O₄/GO. It was found that Pd⁰ surpassed Pd^II in catalytic activity. Reduction of Pd^II to Pd⁰ took place during the first catalytic cycle.

Comparison of the catalytic activity for the reduction of nitrophenol over palladium-supported graphene oxide nanocomposites modified with iron oxide nanoparticles and/or carbon nanotubes.     

Enhanced catalytic activity over palladium supported on ZrO2@C with NaOH-assisted reduction for decomposition of formic acid

A ZrO₂@C support based on t-ZrO₂ embedded in amorphous carbon was obtained via the pyrolysis of a UiO-66 precursor. Highly dispersed Pd nanoparticles (NPs) were subsequently deposited onto this support, using NaOH-assisted reduction, to obtain a formic acid (FA) decomposition catalyst. This material showed a turnover frequency (TOF) for the heterogeneously-catalyzed decomposition of FA of 8588 h⁻¹ at 60 °C, with 100% H₂ selectivity. This performance is ascribed to the uniform dispersion of smaller palladium nanoparticles and a synergistic effect between the metal NPs and support. Even at 30 °C, the complete decomposition of FA was achievable in FA/SF (SF, sodium formate) solution, with a TOF as high as 1857 h⁻¹.

Pd/ZrO₂@C was prepared employing UiO-66-derived ZrO₂@C as the support and showed high catalytic activity for formic acid decomposition.     

Tunable formaldehyde sensing properties of palladium cluster decorated graphene

The ability to tune the adsorption strength of the targeted gas on sensing materials is crucial for sensing applications. By employing first-principles calculations the adsorption and sensing properties of HCHO on small Pd_n (n = 1–6) cluster decorated graphene have been systematically investigated. The adsorption energy is found to depend on the size of the Pd_n cluster and can be tuned in a wide range from −0.68 eV on Pd(111) to −1.98 eV on the Pd₃/graphene system. We also find that the Pd_n/graphene (n = 5 and 6) systems have an appropriate adsorption energy for HCHO gas sensing. The current–voltage curves are calculated by the non-equilibrium Green''s function method for the two-probe nano-sensor devices along both the armchair and zigzag directions. The devices constructed with Pd_n/graphene (n = 5 and 6), having the highest absolute response over 20% at small voltages, should be applicable for HCHO detection. This work provides a theoretical basis for exploring potential applications of metal cluster decorated graphene for gas sensing.

The adsorption strength of formaldehyde gas molecule and sensing response property on palladium cluster decorated graphene can be tuned by controlling the cluster size.     

Ionic-exchange immobilization of ultra-low loading palladium on a rGO electro-catalyst for high activity formic acid oxidation

A formic acid oxidation electro-catalyst with ultra-low palladium (Pd) loading was prepared via an ionic exchange method by utilizing the acidic functional groups on graphene oxide (GO). After simultaneous reduction of exchanged Pd²⁺ and residual functional groups on the GO surface, an ionic exchange reduced Pd catalyst supported on reduced GO (IE-Pd/rGO) was obtained. Three times improved formic acid oxidation mass activity compared with that of the conventional synthesized Pd/C catalyst was exhibited for the IE-Pd/rGO catalyst. More importantly, formic acid oxidation stability on the IE-Pd/rGO catalyst was remarkably improved due to synergistic effect of the strong immobilization of Pd nanoparticles and the effect of in situ doped N on the rGO support.

A formic acid oxidation electro-catalyst with ultra-low palladium (Pd) loading was prepared via an ionic exchange method by utilizing the acidic functional groups on graphene oxide (GO).     

Room-temperature coalescence of Pd nanoparticles with sacrificial templates and sintering agents,and their catalytic activities in the Suzuki coupling reaction

Porous metal structures are very useful for heterogeneous catalysts in organic syntheses. This study reports a novel method to fabricate porous Pd structures by room-temperature (RT) coalescence of Pd nanoparticles (Pd NPs). First, oleylamine-capped Pd NPs were synthesized, and then Pd NP pastes were fabricated by mixing with tri-n-octylphosphine oxide as a sacrificial template. Finally, the Pd NP paste was dipped into methanol containing a sintering agent. When KOH was used as the sintering agent, porous Pd structures could be successfully obtained at RT. The catalytic activities of porous Pd structures were investigated in the Suzuki coupling reaction and they increased with the increase of the KOH concentration in the sintering process. These results indicate that pre-activation of porous Pd structures by KOH increased the catalytic activities.

Porous Pd structures with high catalytic performance were prepared by dipping a tri-n-octylphosphine oxide (TOPO) paste of Pd nanoparticles (Pd NPs) on a glass substrate into a KOH methanol solution at room-temperature.      

Synthesis and characterization of a supported Pd complex on volcanic pumice laminates textured by cellulose for facilitating Suzuki–Miyaura cross-coupling reactions

Herein, a novel high-performance heterogeneous catalytic system made of volcanic pumice magnetic particles (VPMP), cellulose (CLS) natural polymeric texture, and palladium nanoparticles (Pd NPs) is presented. The introduced VPMP@CLS-Pd composite has been designed based on the principles of green chemistry, and suitably applied in the Suzuki–Miyaura cross-coupling reactions, as an efficient heterogeneous catalytic system. Concisely, the inherent magnetic property of VPMP (30 emu g⁻¹) provides a great possibility for separation of the catalyst particles from the reaction mixture with great ease. In addition, high heterogeneity and high structural stability are obtained by this composition resulting in remarkable recyclability (ten times successive use). As the main catalytic sites, palladium nanoparticles (Pd NPs) are finely distributed onto the VPMP@CLS structure. To catalyze the Suzuki–Miyaura cross-coupling reactions producing biphenyl pharmaceutical derivatives, the present Pd NPs were reduced from chemical state Pd²⁺ to Pd⁰. In this regard, a plausible mechanism is submitted in the context as well. As the main result of the performed analytical methods (including FT-IR, EDX, VSM, TGA, FESEM, TEM, BTE, and XPS), it is shown that the spherical-shaped nanoscale Pd particles have been well distributed onto the surfaces of the porous laminate-shaped VPMP. However, the novel designed VPMP@CLS-Pd catalyst is used for facilitating the synthetic reactions of biphenyls, and high reaction yields (∼98%) are obtained in a short reaction time (10 min) by using a small amount of catalytic system (0.01 g), under mild conditions (room temperature).

An efficient natural-based catalyst constructed of volcanic pumice, cellulose polymeric chains, and palladium nanoparticles is presented for Suzuki–Miyaura coupling reaction.     

Interactions of sub-five-nanometer diameter colloidal palladium nanoparticles in solution investigated via liquid cell transmission electron microscopy

Inter-particle interactions play important roles in controlling the structures, dispersion state and chemo-physical properties of colloidal nanoparticles (NPs) in liquid media. In this work, we prepared palladium (Pd) NPs with an average diameter of ∼4.6 nm in situ inside the liquid cell, and investigated their coupled diffusion and aggregation behaviors through liquid cell transmission electron microscopy (LCTEM). Via analyzing the interaction energies and forces, we derived the effective working range for repulsive double layer interaction experimentally, a value larger than two times the Debye length, suggesting a different interaction behavior of sub-5 nm NPs from that of colloidal NPs in larger sizes. Our results provide insights for the interactions between colloidal ultrafine nanoparticles in solution and will also shed light on the precisely controlled assembly of colloidal nanocrystals for practical applications.

In this paper, sub-5 nm diameter palladium nanoparticles were prepared in situ inside the liquid cell, and the interactions between them were investigated via liquid cell transmission electron microscopy.     

Fabrication of Pd3@Beta for catalytic combustion of VOCs by efficient Pd3 cluster and seed-directed hydrothermal syntheses

Subnanometric Pd clusters confined within zeolite crystals was fabricated using zeolitic seeds with premade [Pd₃Cl(PPh₂)₂(PPh₃)₃]⁺ clusters under hydrothermal conditions. Characterization of the Pd₃@Beta catalysts indicate that the Pd clusters confined in the channels of Beta zeolite exhibit better dispersion and stronger interaction with the zeolite support, leading to stabilized Pd species after heat treatment by high temperature. In the model reaction of toluene combustion, the Pd₃@Beta outperforms both zeolite-supported Pd nanoparticles prepared by conventional impregnation of Pd₃/Beta and Pd/Beta. Temperatures for achieving toluene conversion of 5%, 50% and 98% of Pd₃@Beta are 136, 169 and 187 °C at SV = 60 000 mL g⁻¹ h⁻¹, respectively. Pd₃@Beta could also maintain the catalytic reaction for more than 100 h at 230 °C without losing its activity, an important issue for practical applications. The metal-containing zeolitic seed directed synthesis of metal clusters inside zeolites endows the catalysts with excellent catalytic activity and high metal stability, thus providing potential avenues for the development of metal-encapsulated catalysts for VOCs removal.

Encapsulated Pd₃@Beta was fabricated through a novel Pd₃ cluster and seed-directed method, generating an excellent performance in VOCs catalytic combustion.     

Fabrication of CS/GA/RGO/Pd composite hydrogels for highly efficient catalytic reduction of organic pollutants

In this study, natural polymer material chitosan (CS) and graphene oxide (GO) with large specific surface area were used to prepare a new CS/RGO-based composite hydrogel by using glutaraldehyde (GA) as cross-linking agent. In addition, a CS/GA/RGO/Pd composite hydrogel was prepared by loading palladium nanoparticles (Pd NPs). The morphologies and microstructures of the prepared hydrogels were characterized by SEM, TEM, XRD, TG, and BET. The catalytic performance of the CS/GA/RGO/Pd composite hydrogel was analyzed, and the experimental results showed that the CS/GA/RGO/Pd composite hydrogel had good catalytic performance for degradation of p-nitrophenol (4-NP) and o-nitroaniline (2-NA). Therefore, this study has potential application prospect in wastewater treatment and provides new information for composite hydrogel design.

New functional CS/GA/RGO/Pd composite hydrogels are prepared via a self-assembly process, demonstrating potential applications in catalysis as well as composite materials.     

Bimetallic gold and palladium nanoparticles supported on copper oxide nanorods for enhanced H2O2 catalytic reduction and sensing

The emergence of nanoscience and nanotechnology has revitalised research interest in using copper and its derived nanostructures to find exciting and novel applications. In this work, mono- and bimetallic gold and palladium nanoparticles supported on copper oxide nanorods (CuONRs) were prepared and their catalytic performance towards the reduction of H₂O₂ to form reactive oxygen radical species (ROS) was evaluated. The characterisation using microscopy and spectroscopic techniques confirms the successful synthesis of CuONRs, CuONRs@Au₆NPs, CuONRs@Pd₆NPs and CuONRs@Au₃Pd₃NPs. The efficient generation of ROS was confirmed using UV-vis spectroscopy and 1,3-diphenylisobenzofuran (DPBF) as a radical scavenger. The CuONRs possess excellent catalytic reduction activity for H₂O₂ by generating ROS. However, CuONRs also have lattice oxygens which do not participate in the catalytic reduction step. The lattice oxygens however allowed for the adsorption of gold and palladium nanoparticles (Au₆NPs, Pd₆NPs and Au₃Pd₃NPs) and thus enhanced catalytic reduction of H₂O₂ to produce ROS. The produced ROS was subsequently involved in the catalytic oxidation of a chromogenic substrate (TMB), resulting in blue coloured diimine (TMBDI) complex which was monitored using UV-vis and could also be observed using the naked eye. The catalyst dependence on pH, temperature, and H₂O₂ concentration towards efficient ROS generation was investigated. The gold and palladium-supported CuONRs nanocatalysts were evaluated for their potential applications in the fabrication of colorimetric biosensors to detect glucose oxidation by glucose oxidase (GOx). Glucose was used as a model analyte. The enzymatic reaction between GOx and β-d-glucose produces H₂O₂ as a by-product, which is then catalytically converted to ROS by the nanoparticles.

Mono- and bimetallic gold and palladium nanoparticles supported on copper oxide nanorods were prepared. Their catalytic performance towards the catalytic reduction of H₂O₂ to produce reactive oxygen radical species was evaluated.     

Insights into the spontaneous formation of hybrid PdOx/PEDOT films: electroless deposition and oxygen reduction activity

Hybrid palladium oxide/poly(3,4-ethylenedioxythiophene) (PdO_x/PEDOT) films were prepared through a spontaneous reaction between aqueous PdCl₄²⁻ ions and a nanostructured film of electropolymerized PEDOT. Spectroscopic and electrochemical characterization indicate the presence of mixed-valence Pd species as-deposited (19 ± 7 at% Pd⁰, 64 ± 3 at% Pd²⁺, and 18 ± 4 at% Pd⁴⁺ by X-ray photoelectron spectroscopy) and the formation of stable, electrochemically reversible Pd⁰/α-PdO_x active species in alkaline electrolyte and furthermore in the presence of oxygen. The elucidation of the Pd speciation as-deposited and in solution provides insight into the mechanism of electroless deposition in neutral aqueous conditions and the electrocatalytically active species during oxygen reduction in alkaline electrolyte. The PdO_x/PEDOT film catalyses 4e⁻ oxygen reduction (n = 3.97) in alkaline electrolyte at low overpotential (0.98 V vs. RHE, onset potential), with mass- and surface area-based specific activities competitive with, or superior to, commercial 20% Pt/C and state-of-the-art Pd- and PEDOT-based nanostructured catalysts. The high activity of the nanostructured hybrid PdO_x/PEDOT film is attributed to effective dispersion of accessible, stable Pd active sites in the PEDOT matrix.

Hybrid PdO_x/PEDOT films efficiently catalyse the direct 4e⁻ oxygen reduction reaction in alkaline electrolyte.     

Bio-engineered palladium nanoparticles: model for risk assessment study of automotive particulate pollution on macrophage cell lines

The surge in vehicular activity in densely populated areas has led to an increased concentration of airborne palladium nanoparticles (PdNPs) in the environment. Recent toxicity data have indicated that PdNPs exhibit adverse effects in in vitro and in vivo models, however, their effect on the immune system is not fully understood. Therefore, in the present study, we aimed to evaluate possible toxic effects of bio-engineered palladium nanoparticles on the murine macrophage cell line (J774). Here we prepared palladium nanoparticles using aqueous leaf extract of Parthenium hysterophorus and characterized them by UV-Vis spectroscopy, XRD, FT-IR spectroscopy, HR-TEM, EDX, SEM and zeta potential. Toxicity parameters such as cell viability, cell membrane integrity, induction of apoptosis and ROS production were assessed on J774 cell lines. Spherical palladium nanoparticles of mean size ∼4 nm, when subjected to time and dose-dependent cytotoxicity assay, showed cell viability was >95% at lower doses (25, 200 μg mL⁻¹) and <50% at higher doses of palladium nanoparticles (400, 500 μg mL⁻¹) after 24 hours of incubation. We also observed cell membrane injury at higher doses by lactate dehydrogenase assay. The induction of apoptosis observed was moderate. H₂DCFDA assay revealed visible cell damage which could be due to modest levels of ROS generation. The detection of Pd in the road-dust samples of New Delhi using inductively coupled plasma-mass spectroscopy (ICP-MS) technique was also investigated.

The surge in vehicular activity in densely populated areas has led to an increased concentration of airborne palladium nanoparticles (PdNPs) in the environment.     

Synthesis of a palladium acetylide-based tubular microporous polymer monolith via a self-template approach: a potential precursor of supported palladium nanoparticles for heterogeneous catalysis

A monolithic, palladium acetylide-based conjugated microporous polymer, Pd-CMP, was synthesized from a palladium dichloride and a trialkyne. The polymerization proceeded in two different ways, the dehydrohalogenation reaction between the alkyne and the palladium halide and the homocoupling reaction of the alkyne. Pd-CMP had a rigid hollow tubular structure. The in situ formed crystalline triethylammonium chloride (TEACl) rod played a critical role in the formation of the tubular morphology as a template. Through the attachment of the polymer particles to the surface of the rod and their reactions with soluble alkynes, a core–shell structure with a TEACl core and a polymer shell formed. The TEACl core was removed by washing with methanol to yield a hollow polymer tube. Pd-CMP showed a hierarchical pore structure and reversible compressibility. Supported Pd nanoparticles were prepared by one-step thermolysis of Pd-CMP as a heterogeneous catalyst. The average diameters of NPs in the products thermolyzed at 300 (Pd-CMP₃₀₀) and 500 °C (Pd-CMP₅₀₀) were 2.6 and 4.1 nm, respectively. Pd-CMP₃₀₀ was used in the heterogeneous catalysis of the 4-nitrophenol reduction reaction and Suzuki–Miyaura coupling between iodobenzene and phenylboronic acid. The reaction yields were higher than 95%. The catalyst could be used for a flow reaction and easily recycled without significant activity loss.

A monolithic palladium acetylide-based tubular microporous polymer was synthesized as a promising precursor of a palladium heterogeneous catalyst.     

Au-based bimetallic catalysts: how the synergy between two metals affects their catalytic activity

Supported bimetallic nanoparticles are particularly attractive catalysts due to increased activity and stability compared to their monometallic counterparts. In this work, gold-based catalysts have been studied as catalysts for the selective base-free oxidation of glucose. TiO₂-supported Au–Pd and Au–Cu series prepared by the sol-immobilization and precipitation-reduction methods, respectively, showed a significant synergistic effect, particularly when the theoretical weight ratio of the two metals was close to 1 : 1 (with an actual experimental bulk Au/Pd molar ratio of ca. 0.8 and ca. 0.4 for Au/Cu) in both cases. XPS analysis showed that the presence of Au^δ+, Pd²⁺ and CuOH species played an important role in the base-free glucose oxidation.

Supported bimetallic nanoparticles are particularly attractive catalysts due to increased activity and stability compared to their monometallic counterparts.     

Biosynthesis of Ag–Pd bimetallic alloy nanoparticles through hydrolysis of cellulose triggered by silver sulfate

We report a simple but efficient biological route based on the hydrolysis of cellulose to synthesize Ag–Pd alloy nanoparticles (NPs) under hydrothermal conditions. X-ray powder diffraction, ultraviolet-visible spectroscopy and scanning transmission electron microscopy-energy dispersive X-ray analyses were used to study and demonstrate the alloy nature. The microscopy results showed that well-defined Ag–Pd alloy NPs of about 59.7 nm in size can be biosynthesized at 200 °C for 10 h. Fourier transform infrared spectroscopy indicated that, triggered by silver sulfate, cellulose was hydrolyzed into saccharides or aldehydes, which served as both reductants and stabilizers, and accounted for the formation of the well-defined Ag–Pd NPs. Moreover, the as-synthesized Ag–Pd nanoalloy showed high activity in the catalytic reduction of 4-nitrophenol by NaBH₄.

We report a simple but efficient biological route based on the hydrolysis of cellulose to synthesize Ag–Pd alloy nanoparticles (NPs) under hydrothermal conditions.     

Long chain ionic liquid-assisted synthesis of PS/Pd beads and hierarchical porous Pd–SiO2

Long-chain ionic liquid, 1-hexadecyl-3-methylimidazolium chloride (C₁₆mimCl), was firstly used as a linking agent to construct polystyrene (PS)/C₁₆mimCl/palladium (Pd) beads. Subsequently, the PS/C₁₆mimCl/Pd beads were used as a macroporous templating agent and C₁₆mimCl was used as a mesoporous templating agent to prepare Pd-loaded hierarchical porous silica. A systematic study was carried out addressing the influence of the amount of C₁₆mimCl and the mass ratios of m(Pd)/m(PS) on the PS/C₁₆mimCl/Pd beads and the Pd-loaded hierarchical porous structures. The samples were characterized by electrophoresis experiments, SEM, TEM, small-angle XRD, and N₂ adsorption–desorption experiments. It was found that the coverage of citrate-coated Pd nanoparticles (Pd NPs) onto the PS beads can be simply tailored by changing the amount of C₁₆mimCl and the mass ratios of m(Pd)/m(PS). The resultant Pd-loaded hierarchical porous silica possessed a 3D ordered macroporous skeleton with a specific surface area of up to 967 m² g⁻¹, ordered mesoporous silica walls (SBA-3 type) and well-dispersed Pd NPs anchored on the inner walls of the spherical macroporous hollow. Importantly, the obtained Pd-loaded hierarchical porous silica exhibited an enhanced catalytic activity for the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H₂O₂.

1-Hexadecyl-3-methylimidazolium chloride (C₁₆mimCl) can be used as “bridges” to prepare PS/C₁₆mimCl/Pd beads, and Pd-loaded hierarchical porous silica was synthesized using dual templates of the PS/C₁₆mimCl/Pd beads and C₁₆mimCl.     

Bimetallic Au–Pd alloy nanoparticles supported on MIL-101(Cr) as highly efficient catalysts for selective hydrogenation of 1,3-butadiene

Gold–palladium (Au–Pd) bimetallic nanoparticle (NP) catalysts supported on MIL-101(Cr) with Au : Pd mole ratios ranging from 1 : 3 to 3 : 1 were prepared through coimpregnation and H₂ reduction. Au–Pd NPs were homogeneously distributed on the MIL-101(Cr) with mean particle sizes of 5.6 nm. EDS and XPS analyses showed that bimetallic Au–Pd alloys were formed in the Au(2)Pd(1)/MIL-101(Cr). The catalytic performance of the catalysts was explored in the selective 1,3-butadiene hydrogenation at 30–80 °C on a continuous fixed bed flow quartz reactor. The bimetallic Au–Pd alloy particles stabilized by MIL-101(Cr) presented improved catalytic performance. The as-synthesized bimetallic Au(2)Pd(1)/MIL-101(Cr) with 2 : 1 Au : Pd mole ratio showed the best balance between the activity and butene selectivity in the selective 1,3-butadiene hydrogenation. The Au–Pd bimetallic-supported catalysts can be reused in at least three runs. The work affords a reference on the utilization of a MOF and alloy nanoparticles to develop high-efficiency catalysts.

Bimetallic Au–Pd alloy particles stabilized by MIL-101(Cr) showed high activity and butene selectivity for 1,3-butadiene hydrogenation reaction.     

Catalysis with magnetically retrievable and recyclable nanoparticles layered with Pd(0) for C–C/C–O coupling in water

Nanoparticles layered with palladium(0) were prepared from nano-sized magnetic Fe₃O₄ by coating it with silica and then reacting sequentially with phenylselenyl chloride under an N₂ atmosphere and palladium(ii) chloride in water. The resulting Fe₃O₄@SiO₂@SePh@Pd(0) NPs are magnetically retrievable and the first example of NPs in which the outermost layer of Pd(0) is mainly held by selenium. The weight percentage of Pd in the NPs was found to be 1.96 by ICP-AES. The NPs were authenticated via TEM, SEM-EDX, XPS, and powder XRD and found to be efficient as catalysts for the C–O and C–C (Suzuki–Miyaura) coupling reactions of ArBr/Cl in water. The oxidation state of Pd in the NPs having size distribution from ∼12 to 18 nm was inferred as zero by XPS. They can be recycled more than seven times. The main features of the proposed protocols are their mild reaction conditions, simplicity, and efficiency as the catalyst can be separated easily from the reaction mixture by an external magnet and reused for a new reaction cycle. The optimum loading (in mol% of Pd) was found to be 0.1–1.0 and 0.01–1.0 for O-arylation and Suzuki–Miyaura coupling, respectively. For ArCl, the required amount of NPs was more as compared to that needed for ArBr. The nature of catalysis is largely heterogeneous.

Fe₃O₄@SiO₂@SePh@Pd(0) (Pd, 1.96%) as the first example of NPs having a Pd(0) layer held by selenium can execute C–C/C–O coupling in 2–6 h (80 °C).