Inner-pore reduction nucleation of palladium nanoparticles in highly conductive wurster-type covalent organic frameworks for efficient oxygen reduction electrocatalysis

Covalent organic frameworks(COFs)have emerged as a class of promising supports for electrocatalysis because of their advantages including good crystallinity,highly ordered pores,and structural diversity.However,their poor conductivity represents the main obstruction to their practical application.Here,we reported a novel synthesis strategy for synergistically endowing a triphenylamine-based COFs with improved electrical conductivity and excellent catalytic activity for oxygen reduction,via the in-situ redox deposition and confined growth of palladium nanoparticles inside the porous structure of COFs using reductive triphenylamine frameworks as reducing agent;meanwhile,the triphenylamine unit was oxidized to radical cation structure and affords radical cation COFs with conductivity as high as3.2*10^(-1) S m^(-1).Such a uniform confine palladium nanoparticle on highly conductive COFs makes it an efficient electrocatalyst for four-electron oxygen reduction reaction(4e-ORR),showing excellent activities and fast kinetics with a remarkable half-wave potential(E_(1/2))of 0.865 V and an ultralow Tafel slope of 39.7 mV dec^(-1) in alkaline media even in the absence of extra commercial conductive fillers.The generality of this strategy was proved by preparing the different metal and metal alloy nanoparticles supported on COFs(Au@COF,Pt@COF,AuPd@COF,AgPd@COF,and PtPd@COF)using reductive triphenylamine frameworks as reducing agent.This work not only provides a facile strategy for the fabrication of highly conductive COF supported ORR electrocatalysts,but also sheds new light on the practical application of Zn-air battery.

Carboxylative Suzuki coupling reactions of benzyl chlorides with allyl pinacolborate catalyzed by palladium nanoparticles

Palladium-catalyzed carboxylative Suzuki coupling reactions of benzyl chlorides with allyl pinacol-borate were successfully conducted in the absence of any extra ligand to produce β,γ-unsaturated esters in satisfactory to good yields. The carboxylative Suzuki coupling reaction proceeded smooth-ly under mild conditions in the presence of palladium nanoparticles generated in situ through the formation of a π-benzylpalladium chloride intermediate.

Catalytic dehydrogenation of formic acid over palladium nanoparticles immobilized on fibrous mesoporous silica KCC-1

Uniform Pd nanoparticles immobilized on N-(3-trimethoxysilylpropyl)diethylenetriamine (PDETA)-functionalized fibrous silica KCC-1 (Pd/KCC-1-PDETA) were prepared with a mean Pd particle size of 2.8 nm. After characterization using powder X-ray diffraction, X-ray photoelectron spectroscopy, and N2 adsorption-desorption isotherms, Pd/KCC-1-PDETA was used as catalyst for additive-free dehydrogenation of formic acid to produce H2. Pd nanoparticle catalysts supported on two other mesoporous silica materials (MSF and KIT-6) were also synthesized to examine how the support affects the reaction. Among the three catalysts, Pd/KCC-1-PDETA exhibited significant catalytic activity (a turnover frequency of 332 h?1 at 323 K and 100% selectivity towards hydrogen), owing to the unique fibrous morphology of KCC-1 and the presence of amine groups that reduced the Pd particle size and improved the access of reactant to the catalytically active Pd sites. The influence of Pd loading (2–10 wt.%), reaction temperature, and reaction time was also examined for the dehydrogenation reaction. Pd/KCC-1-PDETA was recovered easily after the reaction and showed good reusability up to five times without any significant loss in catalytic performance.

A ligand-free Heck reaction catalyzed by the in situ-generated palladium nanoparticles in PEG-400

A ligand-free Heck reaction catalyzed by in situ-generated palladium nanoparticles in PEG-400 has been developed.This catalytic system is a simple and active protocol for the Heck reaction of aryl halides under mild conditions.Comparative experiments demonstrated that the Heck reaction catalyzed by the palladium nanoparticles in situ-generated under the Heck reaction conditions was carried out much quicker than that by the in ex situ-generated ones.

Palladium Nanoparticles Loaded on Carbon Modified TiO_2 Nanobelts for Enhanced Methanol Electrooxidation

Carbon modified TiO_2 nanobelts(TiO_2-C) were synthesized using a hydrothermal growth method,as a support material for palladium(Pd) nanoparticles(Pd/TiO_2-C) to improve the electrocatalytic performance for methanol electrooxidation by comparison to Pd nanoparticles on bare TiO_2 nanobelts(Pd/TiO_2)and activated carbon(Pd/AC). Cyclic voltammetry characterization was conducted with respect to saturated calomel electrode(SCE) in an alkaline methanol solution, and the results indicate that the specific activity of Pd/TiO_2-C is 2.2 times that of Pd/AC and 1.5 times that of Pd/TiO_2. Chronoamperometry results revealed that the TiO_2-C support was comparable in stability to activated carbon, but possesses an enhanced current density for methanol oxidation at a potential of -0.2 V vs. SCE. The current study demonstrates the potential of Pd nanoparticle loaded on hierarchical TiO_2-C nanobelts for electrocatalytic applications such as fuel cells and batteries.

Bio-synthesized palladium nanoparticles using alginate for catalytic degradation of azo-dyes

Palladium nanoparticles(PdNPs)were synthesized in a green way using sodium alginate functioning as both reductant and stabilizer.The formation of as-synthesized Pd NPs was supervised by Ultraviolet–visible(UV–Vis)spectroscopy and confirmed by the surface plasmon resonance(SPR)band.The effect of several synthesis factors such as precursor ratio,solution p H,reaction time,and temperature were investigated by the factorial design of experiments in order to optimize the experimental conditions.The optimal synthesis parameters were achieved by heating 1.0 ml of 1.0%sodium alginate(SA),3.0 ml of 10-2 mol·L-1 H2PdCl4 at 80°C for a period of 30 min in a neutral reaction medium(pH=6).High-resolution transmission electron microscope(HRTEM),energy dispersive X-ray(EDX)spectroscopy,selected area electron diffraction(SAED)pattern,X-ray powder diffraction(XRD),and dynamic light scattering(DLS)were used to confirm the uniform spherical shapes and high crystallinity of Pd NPs with average particle size of(2.12±1.42)nm.The SEM images show the distribution of Pd NPs presented among the SA.FTIR spectra indicate that SA is a good capping agent to stabilize Pd NPs for a long time.The catalytic degradation of model azo-dyes such as mono-azo(Cibacron Yellow FN–2R)and di-azo(Cibacron Deep Red S–B)were confirmed the catalytic activity of Pd NPs.The Pd NPs can accelerate the degradation rate by more than 80 and 10 times respectively as confirmed by kinetics constant(k)values.

Palladium nanoparticles/wool keratin-assisted carbon composite-modified flexible and disposable electrochemical solid-state pH sensor

Several p H-dependent processes and reactions take place in the human body;hence,the p H of body fluids is the best indicator of disturbed health conditions.However,accurate and real-time diagnosis of the p H of body fluids is complicated because of limited commercially available p H sensors.Hence,we aimed to prepare a flexible,transparent,disposable,userfriendly,and economic strip-based solid-state p H sensor using palladium nanoparticles(Pd NPs)/N-doped carbon(NC)composite material.The Pd NPs/NC composite material was synthesized using wool keratin(WK)as a precursor.The insitu prepared Pd NPs played a key role in the controlled switching of protein structure to the N-doped carbon skeleton withπ–πarrangement at the mesoscale level,which mimics the A–B type polymeric structure,and hence,is highly susceptible to H+ions.The optimized carbonization condition in the presence of Pd NPs showed that the material obtained using a modified Ag/Ag Cl reference electrode had the highest p H sensitivity with excellent stability and durability.The optimized p H sensor showed high specificity and selectivity with a sensitivity of 55 m V/p H unit and a relative standard deviation of 0.79%.This study is the first to synthesize Pd NPs using WK as a stabilizing and reducing agent.The applicability of the sensor was investigated for biological samples,namely,saliva and gastric juices.The proposed protocol and material have implications in solid-state chemistry,where biological material will be the best choice for the synthesis of materials with anticipated performance.

Fe_(3)O_(4)-carbon spheres core–shell supported palladium nanoparticles:A robust and recyclable catalyst for suzuki coupling reaction

Suzuki-Miyaura(S-M)is regarded the most powerful way for synthesis biaryls,triaryls,or incorporating of substituted aryl moieties in organic preparation by the cross-coupling of aryl boronic acid with aryl halides using the Pd catalyst.This work reports the combining of the hydrothermal and microwaveassisted protocol to convert the glucose to magnetic carbon spheres(Fe_(3)O_(4)-CSPs)decorated with Pd nanoparticles(NPs)as the catalyst for Suzuki-Miyaura cross-coupling reactions.The physicochemical properties in the produced composite were examined using FESEM,HRTEM,nitrogen isotherms,Raman spectroscopy,FTIR,XPS,and XRD.The as-fabricated composite Pd/Fe_(3)O_(4)-CSPs is mostly spherical with a core–shell structure and possesses a great surface area of 253.2 m^(2).g^(-1).Its catalytic performance demonstrates that the composite has excellent stability and high tolerance Suzuki-Miyaura crosscoupling reactions in 30 min at 80℃.Both activated and deactivated aryl halides provided excellent yield.The as-fabricated catalyst was recycled for up to four catalytic cycles without a substantial decline in performance.Moreover,this research offers a facile roadmap for synthesizing Pd/Fe_(3)O_(4)-CSPs composites and promoting the practical implementation of Pd/Fe_(3)O_(4)-CSPs catalysts for organic transformation processes.

Palladium-Carbon Composite Nanoparticle Films with Enhanced Electrocatalytic Activity for Hydrogen Peroxide Sensors

A nanocomposite electrocatalyst was prepared with the method of cluster beam deposition of palladium nanoparticle thin lms on carbon nanoparticle supporting layers and used as sensitive nonenzyme hydrogen peroxide sensors. An enhancement on the electrocatalytic activity of the palladium nanoparticles toward H2O2 reduction was observed, which was related to the coverage of the carbon nanoparticles. With one monolayer of carbon nanoparticles, the H2O2 detection sensitivity reached the maximum, which was more than twice of that of the pure Pd nanoparticles.

Preparation,Characterization and Catalytic Activity of Palladium Nanoparticles Embedded in the Mesoporous Silica Matrices

Novel in-situ reduction approach was applied for the synthesis of palladium nanoparticles in the pores of mesoporous silica materials with grafted siliconhydride groups. Matrices possessing different structural properties (MCM-41, SBA-15 and Silochrom) were used. Samples were studied by nitrogen adsorption-desorption method, low-angle X-ray diffraction, transmission electron microscopy (TEM) and FT-IR/PAS spectroscopy. The temperature-programmed oxidation (TPO) and reduction (TPR) methods were applied to examine reducibility of palladium species. Palladium containing catalysts were tested in methane oxidation reaction. It was demonstrated that relatively large pores in SBA-15 type silica facilitated formation of well-dispersed palladium nanoparticles confined in the pores channels. In the case of MCM-41 support, metallic palladium nanoparticles were formed on the external surface. The obtained materials showed high catalytic activity. Lower activity of the samples containing small crystallites located in the pore volume at high temperatures was related to worse accessibility of active sites to the reation mixture.

Synthesis of Pd nanoparticles supported on CeO_2 nanotubes for CO oxidation at low temperatures

Developing efficient supported Pd catalysts and understanding their catalytic mechanism in CO oxidation are challenging research topics in recent years.This paper describes the synthesis of Pd nanoparticles supported on CeO2 nanotubes via an alcohol reduction method.The effect of the support morphology on the catalytic reaction was explored.Subsequently,the performance of the prepared catalysts was investigated toward CO oxidation reaction and characterized by Nitrogen sorption,X-ray diffraction,X-ray photoelectron spectroscopy,transmission electron microscopy,and CO-temperature-programmed desorption techniques.The results indicated that the catalyst of Pd on CeO2 nanotubes exhibits excellent activity in CO oxidation at low temperatures,due to its large surface area,the high dispersion of Pd species,the mesoporous and tubular structure of the CeO2-nanotube support,the abundant Ce3＋,formation of Pd–O–Ce bonding,and enhanced metal–support interaction on the catalyst surface.

Composition-controlled synthesis of platinum and palladium nanoalloys as highly active electrocatalysts for methanol oxidation

Platinum and palladium(PtPd)alloy nanoparticles(NPs)are excellent catalysts for direct methanol fuel cells.In this study,we developed PtPd alloy NPs through the co‐reduction of K2PtCl4and Na2PdCl4in a polyol synthesis environment.During the reaction,the feed molar ratio of the two precursors was carried over to the final products,which have a narrow size distribution with a mean size of approximately4nm.The catalytic activity for methanol oxidation reactions possible depends closely on the composition of as‐prepared PtPd alloy NPs,and the NPs with a Pt atomic percentage of approximately75%result in higher activity and stability with a mass specific activity that is7times greater than that of commercial Pt/C catalysts.The results indicate that through composition control,PtPd alloy NPs can improve the effectiveness of catalytic performance.

Catalytic activity of recyclable resorcinarene-protected antibacterial Pd nanoparticles in C-C coupling reactions

Novel tetra-methoxy resorcinarene tetra-hydrazide（TMRTH） has been synthesized and used as a reducing agent and a capping agent for the synthesis of water-dispersible stable palladium nanoparticles（PdNPs）.The TMRTH-PdNPs were characterized by UV-Vis spectroscopy,transmission electron microscopy,energy-dispersive X-ray spectroscopy,and powder X-ray diffraction.The synthesized nanoparticles are polydispersible with a size of 5 ± 2 nm and were found to be recyclable over five cycles maintaining a catalytic activity in the Suzuki-Miyuara cross-coupling reaction.The nanocatalyst was superior in catalytic performance to conventional palladium catalysts with respect to reaction time,catalyst loading and recyclability.TMRTH-PdNPs show promise for their use in biological applications as they exhibit good antibacterial activity against gram-positive bacteria.

Synthesis of Catalytic Systems Based on Nanocomposites Containing Palladium and Hydroxycarbonates of Rare-Earth Elements

The purpose of this work is to synthesize the catalytic systems containing palladium nanoparticles and using hydroxycarbonates of yttrium and cerium as supports,and to test the catalytic activity of the obtained catalysts in the Suzuki cross-couping reaction.Nanocomposites Pd/Y(OH)CO 3 and Pd/Ce(OH)CO 3 were synthesized according to two methods:the first one-simultaneous production of nanoscale substrate and immobilization of palladium nanoparticles on its surface(nanocomposites 1),the second one-the prior synthesis of polyvinylpyrrolidone stabilized palladium nanoparticles followed by their immobilization on the nano sized substrate surface(nanocomposites 2).The reaction between phenylboronic acid and iodobenzene is chosen as a model one.The dependence of the catalytic activity of catalysts on the method of their synthesis was established.It was established that nanocomposites 2 exhibit higher catalytic activity in the selected reaction compared to the nanocomposites 1.The TOF values for the nanocomposites 1 are 6663～14617 h 1 when using the substrate Ce(OH)CO 3 and 13774～27084 h 1 when using the substrate Y(OH)CO 3,while the nanocomposites 2 reveal TOF = 87287 h 1 for the substrate Ce(OH)CO 3 and TOF = 97746 h 1 for the substrate Y(OH)CO 3 under other equal conditions.In addition,nanocomposites 2 "work" at room temperature giving a high yield of the desired product.It is noted that the support nanoparticles Y(OH)CO 3 and Ce(OH)CO 3 also exhibit catalytic activity.The yield of the final product of the reaction using them as catalysts is 55%(TOF = 11 and 8 h 1,respectively).Thus,the use of yttrium and cerium hydroxycarbonates as supports allows to decrease the palladium content in the nanocomposites to 0.01%～1% and,consequently,reduce the cost of the catalyst while maintaining its high catalytic activity.

Electrochemically assisted production of biogenic palladium nanoparticles for the catalytic removal of micropollutants in wastewater treatment plants effluent

Biogenic palladium nanoparticles(bio-Pd NPs)are used for the reductive transformation and/or dehalogenation of persistent micropollutants.In this work,H2(electron donor)was produced in situ by an electrochemical cell,permitting steered production of differently sized bio-Pd NPs.The catalytic activity was first assessed by the degradation of methyl orange.The NPs showing the highest catalytic activity were selected for the removal of micropollutants from secondary treated municipal wastewater.The synthesis at different H2 flow rates(0.310 L/hr or 0.646 L/hr)influenced the bio-Pd NPs size.The NPs produced over 6 hr at a lowH2 flow rate had a larger size(D50=39.0 nm)than those produced in 3 hr at a high H2 flow rate(D50=23.2 nm).Removal of 92.1%and 44.3%of methyl orange was obtained after 30 min for the NPs with sizes of 39.0 nm and 23.2 nm,respectively.Bio-Pd NPs of 39.0 nm were used to treat micropollutants present in secondary treated municipal wastewater at concentrations ranging fromμg/L to ng/L.Effective removal of 8 compounds was observed:ibuprofen(69.5%)<sulfamethoxazole(80.6%)<naproxen(81.4%)<furosemide(89.7%)<citalopram(91.7%)<diclofenac(91.9%)<atorvastatin(>94.3%)<lorazepam(97.2%).Re-moval of fluorinated antibiotics occurred at>90%efficiency.Overall,these data indicate that the size,and thus the catalytic activity of the NPs can be steered and that the removal of challengingmicropollutants at environmentally relevant concentrations can be achieved through the use of bio-Pd NPs.

Amine-functionalized hierarchically porous carbon supported Pd nanocatalysts for highly efficient H2 generation from formic acid with fast-diffusion channels

Formic acid(FA)has come to be considered a potential candidate for hydrogen storage,and the development of efficient catalysts for H2releasing is crucial for realizing the sustainable process from FA.Herein,we have developed the ultrafine Pd nanoparticle(NPs)with amine-functionalized carbon as a support,which was found to show an excellent catalytic activity in H_(2)generation from FA dehydrogenation.The synergetic mechanism between amine-group and Pd active site was demonstrated to facilitate H2generation byβ-hydride elimination.Moreover,the texture of support for Pd NPs also plays an important role in determining the reactivity of FA,since the diffusion of gaseous products makes the kinetics of diffusion as a challenge in this high performance Pd catalysts.As a result,the as-prepared Pd/NH_(2)-TPC catalyst with the small sized Pd nanoparticles and the hierarchically porous structures shows a turnover of frequency(TOF)value of 4312 h^(-1)for the additive-free FA dehydrogenation at room temperature,which is comparable to the most promising heterogeneous catalysts.Our results demonstrated that the intrinsic catalytic activities of active site as well as the porous structure of support are both important factors in determining catalytic performances in H2generation from FA dehydrogenation,which is also helpful to develop high-activity catalysts for other advanced gas-liquid-solid reactions systems.

Topochemical polymerization of hydrogen-bonded organic framework for supporting ultrafine palladium nanoparticles

Topochemical polymerization of molecular crystals into porous materials is of significance due to their promising applications in the field of adsorption and catalysis,yet rarely reported due to the synthesis difficulty.Herein,a hydrogen-bonded organic framework(HOF-45)has been fabricated by the crystallization of a cage-like building block containing three alkynyl groups.It exhibits almost mesoporous structure demonstrated by single crystal X-ray diffraction study.Light-driven topochemical polymerization of HOF-45 with ethanedithiol covalently links alkynyl groups in HOF-45,generating a hydrogen-bond and covalentbond cross-linked material(HOF-45C).In contrast to HOF-45,cross-linked HOF-45C retains the crystalline nature and displays improved solution resistence according to the powder X-ray diffraction data.In particular,HOF-45C is able to support the growth of ultrafine palladium nanoparticles with the average size of ca.1.9 nm for rapidly promoting the degradation of nitrophenol,methyl orange,and congo red with the help of NaBH_(4)as well as Suzuki-Miyaura coupling reaction.This work inputs a new idea on the HOFs application in preparing covalent-linked porous organic materials.

Photocatalytic aerobic oxidation of toluene and its derivatives to aldehydes on Pd/Bi_2WO_6

The selective oxidation of toluene and its derivatives is extremely important in the chemical industry.The use of photocatalysis in organic synthesis has attracted considerable attention among synthetic chemists because of its ＂green＂ environmental characteristics.In this study,nanoscale Bi_2WO_6with a flower-like morphology was found to be a highly efficient photocatalyst in the catalytic oxidation of toluene and its derivatives using O_2 as the oxidant.The loading of Pd nanoparticles as a cocatalyst onto the flower-like Bi_2WO_6 was found to produce a significant enhancement in the catalytic activity.Mechanistic investigation showed that the superior performance of Pd/Bi_2WO_6 could be attributed to the improvement of both the reductive and oxidative abilities of Bi_2WO_6 by the loading of the cocatalyst.

Palladium Nanoparticles/Graphdiyne Oxide Nanocomposite with Excellent Peroxidase-like Activity and Its Application for Glutathione Detection

In this study, palladium nanoparticles loaded graphdiyne oxide (Pd/GDYO) nanocomposite were fabricated by in-situ reduction of palladium chloride in the dispersion of GDYO, and characte-rized by Raman spectra, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The synthesized Pd/GDYO was first found to have catalytic activities similar to those of the peroxidase enzyme, which can catalyze the oxidation of peroxidase substrate 3,3',5,5'-tetramethylbenzidine(TMB) in the presence of hydrogen peroxide(H2O2). Steady-state kinetic studies showed that the catalytic reaction of Pd/GDYO follows a ping-pong mechanism, and Pd/GDYO has a stronger activity to TMB with a Michaelis constant(Km) value of 5.32×10-4 mmol/L. Based on the shielding effect of glutathione(GSH) on the Pd/GDYO-H2O2-TMB reaction system, a colorimetric detection method for GSH was deve-loped with a wide linear range from 0.1 μmol/L to 40 μmol/L and a limit of detection of 0.1 μmol/L. The method was successfully applied for fast and accurate detection of GSH in injection powder drugs. It was expected that this peroxidase-like Pd/GDYO nano- composite would have wide applications in the fields of biomedicine and environmental chemistry.

A Novel Glucose Biosensor Based on Palladium Nanoparticles and Its Application in Detection of Glucose Level in Urine

A novel glucose biosensor was constructed by electrodeposition of highly dispersed palladium (Pd) nanoparticles on a glassy carbon electrode (GCE). Atomic force microscopy (AFM) was applied to characterize its surface morphology. Electrodeposited Pd nanoparticles exhibited efficiently electrocatalytic oxidation for hydrogen peroxide (H_2O_2) with relatively high sensitivity and stability,which was studied by CV technique and Raman spectroscopy,respectively. The GC/Pd/GOD/Nafion system allowed a low working potential of +0.3 V (vs. SCE). Its signal current was linearly related to the glucose concentration in the range of 1.0×10 -6 —1.2×10 -4 mol·L -1 with a detection limit of 5.0×10 -7 mol·L -1 . The sensor required no special pretreatment to suppress interference from urate and L-ascorbate. It was successfully used in detection of glucose level in human urine with high stability,sensitivity and anti-poisoning ability .