Pd catalyst is most widely used in the selective reaction of 1,3-butadiene hydrogenation. To improve the butenes selectivity, a series of biogenic Pd/γ-Al2O3 catalysts were prepared by adding different halide ions. The catalyst obtained by adding 0.1 mM KBr exhibited the best catalytic performance, and the selectivity was remarkably enhanced from 57.6% to 80.1% with 100% conversion at 35 °C when compared with the catalyst without halide ions. In addition, it presented desired stability within 24 h. To investigate the influence of halide ions on the catalytic performance, prepared Pd catalysts were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, and ultraviolet–visible diffuse reflectance spectroscopy. The results revealed that particle size, Pd0/Pd2+, and hydrogen spillover caused by halide ions are closely related with catalytic performance.

Reactive kinetics coupled with population balance model (PBM) and computational fluid dynamics (CFD) was implemented to simulate silver nanoparticles (AgNPs) formation in a microtubular reactor. The quadrature method of moments, multiphase model theory, and kinetic theory of granular flow were employed to solve the model, and the particle size distributions (PSD) were calculated. The simulation results were validated by synthesizing AgNPs experimentally in an actual microtubular reactor for comparison with the PSD. The results confirmed the effectiveness of the model and its applicability in predicting AgNPs formation and its PSD evolution in the microtubular system. Finally, benefiting from its superiority, in that the influence of reactive kinetics and fluid dynamics on particle evolution could be considered separately, the model was employed to verify predictions and inferred conclusions in our previous works, which were difficult to verify through experiment.

•Biogenic Fe NPs were synthesized via an eco-friendly process.•The NPs exhibited good dispersion without further modification.•The removal capacity as high as 983.2 mg Cr(VI)/g Fe was achieved.•A removal mechanism including three steps were proposed.Iron based nanoparticles were synthesized through an eco-friendly one-step reaction of FeCl3 and Syzygium jambos (L.) Alston leaf extract in water. The morphology and structure of the SJA-Fe nanoparticles were characterized by UV–vis, TEM and XRD. The obtained biogenic SJA-Fe nanoparticles demonstrated very high efficiency in removing chromium Cr(VI), a toxic pollutant in surface and ground water. The removal capacity as high as 983.2 mg Cr(VI)/g Fe was achieved. It was found that increased temperature and lowered pH were favored in the Cr(VI) removal. In addition, most of the typical coexisting substances such as humic acid showed insignificant effects on Cr(VI) removal. A pseudo second-order model was developed to simulate the kinetics of this process. Furthermore, a reaction mechanism was proposed.

Low temperature 1,3-butadiene hydrogenation over biosynthesized Pd/γ-Al2O3 catalysts annealed under different atmospheres (H2 and air) was compared in a fixed bed reactor, and the catalysts were prepared using a facile sol-immobilization method. The structural properties of the Pd/γ-Al2O3 catalysts in relation to their activities in 1,3-butadiene hydrogenation were investigated by X-ray photoelectron spectroscopy, X-ray diffraction, hydrogen temperature-programmed reduction, thermogravimetry, transmission electron microscopy, CO chemisorption measurement techniques and Fourier transform infrared spectroscopy. The results of characterization revealed that the calcination atmosphere (H2 and air) exhibited a remarkable impact on the chemical state of Pd species and catalytic activity, and the coexistence of the metallic state and oxidation state of Pd was a key factor for higher catalytic activity and butene selectivity, while the catalyst with the existence of the metallic state only (H2–Pd/γ-Al2O3) showed lower butene selectivity, and the catalyst with the oxidation state alone (air–Pd/γ-Al2O3) hardly showed any activity in 1,3-butadiene hydrogenation. Therefore, the chemical state of Pd played an important role in the 1,3-butadiene hydrogenation reaction.

AbstractThe biosynthesized gold/activated carbon catalysts for glucose oxidation were prepared with Cacumen platycladi leaves extract, and activated carbon (AC) was modified with hydrochloric acid and nitric acid to modify its surface chemistry and used as supports. The catalysts with acid-treated AC exhibited improving activity for the selective oxidation of glucose, when compared to that with untreated one. In order to investigate the influence of the acid treatment for the catalysts performance, the surface chemical properties of AC were characterized by Brunauer- Emmett-Teller surface area characterization, Boehm titration, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, respectively. The dispersion of AuNPs on AC was observed by transmission electron microscopy and X-ray diffraction. The results indicated that the catalysts with acid treated supports showed improved dispersion than that of untreated one, which may be the result that the supports significantly increase the surface functional groups and remove the ash after acid treatment.

Nanoparticles of Au–Pd with core–shell structure were synthesized through the coreduction of HAuCl4 and Na2PdCl4 in aqueous media by using cetyltrimethylammonium chloride as a reducing agent. The morphology and structure of the core–shell NPs were confirmed by transmission electron microscopy, X-ray diffraction, and UV–vis spectroscopy. We further demonstrate that the core–shell structure is formed as a synergistic result of low interfacial energy and small lattice mismatch between Au and Pd, different redox potentials of PdCl42–/Pd and AuCl4–/Au, and low reduction rates of HAuCl4 and Na2PdCl4. The catalyst of Au–Pd core–shell nanoparticles supported on Ni2P–graphite nanoplatelets (Au@Pd/Ni2P-GNPs) exhibits a noticeably higher activity than Pd and Pt catalysts in electrochemical ethanol oxidation. Moreover, we show that the activity and stability of Au–Pd core–shell for ethanol oxidation can be significantly enhanced using Ni2P nanoparticles as a cocatalyst. The prepared Au@Pd/Ni2P-GNPs catalyst exhibits a current density of 1.348 A mg–1metal, which is 2.1 times as high as that of Au@Pd/GNPs without Ni2P nanoparticles deposited.

∼40 nm flower-shaped Au–Pd bimetallic nanoparticles were prepared in a facile and eco-friendly way based on the simultaneous bioreduction of HAuCl4 and Na2PdCl4 with ascorbic acid and Cacumen Platycladi leaf extract at room temperature. Characterization techniques, such as transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction, were employed to confirm that the as-synthesized nanoparticles were alloys. The obtained flower-shaped Au–Pd alloy nanoparticles exhibited an excellent surface enhanced Raman spectroscopic activity with rhodamine 6G and efficient catalytic ability for the oxidation of benzyl alcohol to benzaldehyde.

Herein, we reported the green synthesis of Ag–Pd alloy nanoparticles (NPs) using the aqueous extract of the Cacumen platycladi leaves as well as their application as catalyst for hydrogenation of 1,3-butadiene. The biosynthetic NPs were characterized to confirm the nature of alloy by UV–vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). The possible functional groups responsible for the reduction and protection of NPs were identified through Fourier transform infrared spectroscopy (FTIR). The results revealed that biomolecules like saccharides, polyphenols, or carbonyl compounds were related to the reduction process, and the (NH)C═O groups were responsible for the stabilization of the NPs. Furthermore, the as-formed Ag–Pd bimetallic-supported catalysts especially Ag1Pd3/γ-Al2O3 was found to possess excellent catalytic performance toward hydrogenation of 1,3-butadiene. A butene yield of 84.9% was obtained, which was remarkably enhanced when compared with monometallic counterparts. Moreover, the activity of it maintained stability within 12 h of durable experiments.Keywords: Ag−Pd Nanoparticles; Alloy; Biosynthesis; Cacumen platycladi

Biosynthesized Ag/α-Al2O3 catalysts toward ethylene epoxidation were prepared with Cinnamomum camphoratrees (CC) extract using AgNO3, silver–ammonia complex ([Ag (NH3)2]+) and silver–ethylenediamine complex ([Ag(en)2]+) as the silver precursors. The catalyst from [Ag(en)2]+ demonstrated better activity compared to the catalysts from the other two precursors, 1.41% EO concentration with EO selectivity of 79.1% and 12.0% ethylene conversion were achieved at 250 °C. To investigate the influence of silver precursors on the catalytic performance, three catalysts were characterized by XRD, UV-Vis, XPS, SEM and O2-TPD techniques. The results indicated that [Ag(en)2]+ precursors could be reduced more effectively by CC extract, and Ag particles were successfully immobilized onto the α-Al2O3 support under mild conditions. Moreover, a silver defects surface on the Ag/α-Al2O3 catalyst from [Ag(en)2]+ precursors had the best oxygen activation ability, playing an important role in the generation of electrophilic oxygen species which were responsible for the epoxidation reaction of CC to EO.

Catalysts prepared through biosynthesis have aroused wide concern recently, but the detailed role of biomolecules and the identification of the main components have not been figured out yet. In this study, biogenic Pd/MgO catalysts were prepared through sol-immobilization (SI) and absorption-reduction (AR) methods, respectively, using Artocarpus heterophyllus Lam leaves extracts as reductant and stabilizer. The catalyst prepared by SI method showed obviously higher benzaldehyde selectivity than that by AR method under the same conditions. The difference can be attributed to the different oxidation behaviors of phenolic hydroxyls between the two synthetic procedures. In the SI procedure, the phenolic hydroxyls were oxidized to semiquinone, while in the AR procedure, the phenolic hydroxyls were oxidized to hydroxyquinone, resulting in less carboxyls binding onto the surface of the Pd nanoparticles (NPs), thus inhibiting the formation of the byproducts. Moreover, gallic acid, chlorgenic acid, and rutin were identified as the most active ingredients in the Artocarpus heterophyllus Lam leaves extracts. Similar catalytic performances were achieved when the model solution containing the three components was used instead of the original plant extracts. The biogenic Pd/MgO-SI catalyst also showed superior stability toward the oxidation of benzyl alcohol.

A series of Au/TiO2 catalysts for CO oxidation with same Au loading but different Au nanoparticles (NPs) sizes were prepared by varying the calcination temperatures and biomass concentration via a biosynthetic approach. The resulting catalysts were characterized by DRUV–vis, TEM, and TG techniques. The experimental results showed that the activity of the gold catalysts for CO oxidation was very sensitive to the particle size. Among the tested catalysts, the one with mean size of 3.8 nm was the most active. As determined by TEM, the contact boundary between the Au NPs and the TiO2 support was related to the size of the Au NPs. For the most active catalyst, hemispherical Au NPs (3.8 ± 0.6 nm) had the best contact boundary with the TiO2 support, yielding the longest perimeter interface, suggesting that the contact boundary was the most critical factor for the CO oxidation. The in-situ FTIR study of CO adsorption on the catalysts showed that CO was not adsorbed on the Au surface. This might be due to the modification of the Au/TiO2 catalysts by the residual biomass. The intensity of the peak at 2185 cm–1 for the Au/TiO2 catalysts with the longest perimeter interface was highest, demonstrating that the Au–TiO2 contact boundary played an important role in the adsorption of CO.

Flat Ag nanoflowers were directly synthesized from the bioreduction of AgNO3 using Flos Magnoliae Officinalis extract without any additional stabilizer or protective agent at room temperature. Effects of concentrations of the Flos Magnoliae Officinalis extract on the Ag nanostructures were investigated. The main components containing flavone, polyphenol, protein, and reducing sugar in the plant extract were thoroughly determined before and after the reaction, and the dialysis experiments were also conducted. The results of components analysis and dialysis showed that gallic acid representing polyphenols played an important role in the biosynthesis of silver nanoplates. Trisodium citrate combined gallic acid solution, instead of Flos Magnoliae Officinalis extract, was employed and successfully simulated the biosynthesis process of the flat Ag nanoflowers.

Size- and shape-based separation is an effective complementary process to prepare well-defined materials for fundamental studies and applications. However, the separation of nanoparticles polydisperse in both shape and size remains a great challenge. A mixture of gold nanospheres and nanoplates with a wide standard deviation (SD) (21% for the former and 30% for the latter) were synthesized in the same batch using sun-dried Cacumen Platycladi leaf extract. Size-separation of Au nanoparticles was achieved via density gradient centrifugation and the subsequent shape separation was achieved via agarose gel electrophoresis. Transmission electron microscopy (TEM) revealed that, monodispersed nanospheres (SD: 4–5%) and nanoplates (SD: 6–7%) were obtained separately after the two-step separation below.Graphical abstractHighlights► Green synthesis of gold nanoparticles by the extract of Cacumen Platycladi leaf. ► Size separation of nanoparticles was achieved by density-gradients centrifugation. ► Shape separation of nanoparticles was achieved by agrose gel electrophoresis. ► Monodisperse nanoparticles with uniform morphology were obtained via separation.

An environmentally-friendly method for the synthesis of Au–Ag alloy nanoparticles with controlled composition is proposed. The method involves the simultaneous bioreduction of HAuCl4 and AgNO3 using Cacumen Platycladi leaf extract at 90 °C. The formation of the Au–Ag alloy nanoparticles was monitored by recording the absorbance, using UV-visible light spectroscopy as a function of the reaction time and the formation process. The as-synthesized nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy to verify the nature of the alloy. The Fourier transform infrared spectra show that the CC, N–H, (NH) CO, and –OH groups in the C. Platycladi extract served as a reducing agent, whereas the peptides or proteins prevented the aggregation of alloy nanoparticles. The process can be described as a purely “green technique” because no additional synthetic reagents were used as reductants or stabilizers.

The effects of different biomolecules in Artocarpus heterophyllus Lam leaf extract on the morphology of obtained gold nanoparticles were investigated in this study. The results indicated that reducing sugars, flavones, and polyphenols consisting of about 79.8 % dry weight of the leaf extract were mainly involved in providing the dual function of reduction and the size/shape control during the biosynthesis. The gold nanoparticles present included 64 ± 10 nm nanospheres, 131 ± 18 nm nanoflowers, and 347 ± 136 nm (edge length) nanoplates and they were synthesized using the main content of reducing sugars, flavones, and polyphenols, respectively, after they were desorbed by the AB-8 macroporous adsorption resin column. Particularly, flower-like and triangular/hexagonal gold nanoparticles with a yield more than 80 % were obtained. Possible shape-directed agents for the nucleation and growth were characterized by FTIR, it can be seen that ketones were bound on the surface of the spherical and flower-like GNPs, while both the ketones and carbonyls bound on the Au {111} plane this may have favored the formation of the twin defects, which are very essential for nanoplates’ formation.

Monodisperse 7 nm CoPd nanoparticles (NPs) with controlled compositions were synthesized and studied for their catalyzing methanolysis of ammonia borane (AB). The NPs were prepared by the reduction of cobalt(II) acetylacetonate and palladium(II) bromide in the presence of oleylamine and trioctylphosphine. Deposited on a carbon support without any specific surface treatment, these NPs were active catalysts for methanolysis of AB, and their activities were composition-dependent. Among all CoPd catalysts tested, Co48Pd52 NPs exhibited the highest catalytic activity and stability. Kinetic study showed that the catalytic methanolysis of AB was first-order with respect to catalyst concentration and zero-order with respect to AB concentration. The activation energy for the methanolysis was calculated to be 25.5 kJ mol–1. These CoPd NPs are a promising catalyst for AB methanolysis and for developing a highly efficient hydrogen generation system for power applications.Keywords: ammonia borane; bimetallic nanoparticles; cobalt−palladium alloy; hydrogen generation; methanolysis;

Anisotropic Au nanoplates are particularly important owing to their unusual properties. Herein, we describe a plant-mediated bioreduction method to increase the yield of Au nanoplates and shorten the reaction time through a kinetically manipulated procedure. More specifically, the reduction rate was controlled by modulating experimental factors such as the addition mode and rate of the feed solutions, the temperature, and the pH based on a syringe-pumps apparatus. The dimensions of the obtained Au nanoplates were measured using TEM and AFM. The single-crystalline structure was demonstrated by HRTEM, SAED, and XRD. The results of XPS, FTIR, and TG analyses indicated strong affinity of the biomolecules binding to the Au nanoplate facets. In particular, the nanoplate films exhibited strong surface plasmon absorbance in the near-infrared range of 700–3000 nm, vital for optical applications. Furthermore, we propose a mechanism for this formation following the time-resolved studies.

Biosynthesis of Ag nanoparticles (AgNPs) by Cacumen Platycladi extract was investigated. The AgNPs were characterized by ultraviolet–visible absorption spectroscopy (UV–vis), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and X-ray diffraction (XRD). The results showed that increasing the initial AgNO3 concentration at 30 or 60 °C increased the mean size and widened the size distribution of the AgNPs leading to red shift and broadening of the Surface Plasmon Resonance absorption. The conversion of silver ions was determined by atomic absorption spectroscopy (AAS) and to discuss the bioreductive mechanism, the reducing sugar, flavonoid, saccharide, protein contents in the extract, and the antioxidant activity were measured using 3,5-dinitrosalicylic acid colorimetric; Coomassie brilliant blue; phenol-sulfuric acid; rutin-based spectrophotometry method; and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical-scavenging assay methods. The results showed that the reducing sugars and flavonoids were mainly responsible for the bioreduction of the silver ions and their reductive capability promoted at 90 °C, leading to the formation of AgNPs (18.4 ± 4.6 nm) with narrow size distribution. Finally, the antibacterial activity of the AgNPs against E. coli and S. aureus was assessed to determine their potential applications in silver-loaded antibacterial materials. This work provides useful technical parameters for industrialization of the biosynthetic technique and further antibacterial application of the AgNPs. Furthermore, the elucidation of bioreductive mechanism of silver ions by measuring the change of the biomolecular concentrations in plant extract exemplifies understanding the formation mechanism of such biogenic AgNPs.

Monodisperse 8 nm CoPd nanoparticles (NPs) with controlled compositions were synthesized by the reduction of cobalt acetylacetonate and palladium bromide in the presence of oleylamine and trioctylphosphine. These NPs were active catalysts for hydrogen generation from the hydrolysis of ammonia borane (AB), and their activities were composition dependent. Among the 8 nm CoPd catalysts tested for the hydrolysis of AB, the Co35Pd65 NPs exhibited the highest catalytic activity and durability. Their hydrolysis completion time and activation energy were 5.5 min and 27.5 kJ mol–1, respectively, which were comparable to the best Pt-based catalyst reported. The catalytic performance of the CoPd/C could be further enhanced by a preannealing treatment at 300 °C under air for 15 h with the hydrolysis completion time reduced to 3.5 min. This high catalytic performance of Co35Pd65 NP catalyst makes it an exciting alternative in pursuit of practical implementation of AB as a hydrogen storage material for fuel cell applications.Keywords: ammonia borane hydrolysis; bimetallic nanoparticles; cobalt−palladium alloy catalyst; heterogeneous catalysis; hydrogen storage

Rapid development of biosynthesis of metal nanoparticles using plants has attracted extensive interests to further investigate this novel and eco-friendly method. In the biosynthesis process, the plant may act as reducing agent, capping agent or shape directing agent. However, identifying specific roles of various components in the plant is challenging. In this study, we use biosynthesis of silver nanoparticles with Gardenia jasminoides Ellis extract to address this issue. The formation process of silver nanoparticles is investigated and the nanoparticles are characterized with the ultraviolet-visible spectroscopy, Fourier transform infrared spectra and scanning electron microscopy. The results indicate that the Gardenia jasminoides Ellis extract can reduce silver ions to form silver nanoparticles, stabilize the nanoparticles, and affect the growth of silver nanocrystal to form silver nanowires. Only geniposide in the extract exhibits good shape-directing ability for silver nanowires. It is found that bovine albumin is a potential capping agent, whereas rutin, gallic acid and chlorogenic acid possess reducing and capping ability.

∼40 nm flower-shaped Au–Pd bimetallic nanoparticles were prepared in a facile and eco-friendly way based on the simultaneous bioreduction of HAuCl4 and Na2PdCl4 with ascorbic acid and Cacumen Platycladi leaf extract at room temperature. Characterization techniques, such as transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction, were employed to confirm that the as-synthesized nanoparticles were alloys. The obtained flower-shaped Au–Pd alloy nanoparticles exhibited an excellent surface enhanced Raman spectroscopic activity with rhodamine 6G and efficient catalytic ability for the oxidation of benzyl alcohol to benzaldehyde.