Kaijun Xiao

Synthesis of Ultrafine Pt Nanoparticles Stabilized by Pristine Graphene Nanosheets for Electro-oxidation of Methanol

In this study, the pristine graphene nanosheets (GNS) derived from chemical vapor deposition process were employed as catalyst support. In spite of the extremely hydrophobic GNS surface, ultrafine Pt nanoparticles (NPs) were successfully assembled on the GNS through a surfactant-free solution process. The evolution of Pt NPs in the GNS support was studied using transmission electron microscopy. It was found that the high-energy surface sites in the GNS, such as edges and defects, played a critical role on anchoring and stabilizing Pt nuclei, leading to the formation of Pt NPs on the GNS support. The concentration of the Pt precursor, i.e., H2PtCl6 solution had significant effects on the morphology of Pt/GNS hybrids. The resulting Pt/GNS hybrids were examined as catalysts for methanol electro-oxidation. It was indicated that the electrochemical active surface area and catalytic activity of the Pt/GNS hybrids were highly dependent on Pt loadings. The superior activity of the catalysts with low Pt loadings was attributed to the presence of Pt subnanoclusters as well as the strong chemical interaction of Pt NPs with the GNS support.

Modified QuEChERS combined with ultra high performance liquid chromatography tandem mass spectrometry to determine seven biogenic amines in Chinese traditional condiment soy sauce

A rapid and sensitive UHPLC-MS/MS method followed by modified QuEChERS was developed for the simultaneous determination of seven biogenic amines in soy sauce. Samples were firstly diluted by water and pH values of which were adjusted using ammonia water. Modified QuEChERS method was adopted for the purification and 1, 7-heptyldiamine was used as the internal standard. Analysis of seven biogenic amines was within 4min. Under the optimized conditions, linear relations were favorable over the selected concentration ranges of 3.0-600μg/L with correlationcoefficients greater than 0.999. The average accuracy was between 84% and 115%. Intra- and inter- assay precisions for six replicates ranged from 2.2% to 8.8% or below 12%, respectively. The method limits of detection and the method limits of quantitation were 4-8μg/kg and 15-30μg/kg, respectively. The method was successfully applied to determine the concentrations of seven biogenic amines in soy sauces.

Synthesis of Pt, PtRh, and PtRhNi Alloys Supported by Pristine Graphene Nanosheets for Ethanol Electrooxidation

Ultrafine Pt, PtRh, and PtRhNi particles were assembled on pristine graphene nanosheets (GNSs), and the resulting hybrids were examined as electrocatalysts for ethanol oxidation. The structures of the catalysts were characterized by using transmission electron microscopy and X‐ray diffraction. The bulk composition of the catalysts was determined by using energy‐dispersive X‐ray spectroscopy, and the surface composition of the nanoparticles was analyzed by using X‐ray photoelectron spectroscopy. The activity of the catalysts for ethanol electrooxidation was studied by using cyclic voltammetry, linear sweeping voltammetry, and chronoamperometry. The activity of the catalysts followed the order of Pt/GNS

In Situ Assembly of Ultrathin PtRh Nanowires to Graphene Nanosheets as Highly Efficient Electrocatalysts for the Oxidation of Ethanol

One-dimensional (1D) anisotropic platinum-based nanowires are promising electrocatalysts in polymer electrolyte membrane fuel cells owing to the inherent structural merits. Herein, we report an in situ growth of ultrathin PtRh nanowires (diameters of 2-3 nm) on graphene nanosheets via the oriented attachment pathway. Mechanistic studies reveal that graphene nanosheets play a critical role in the nucleation and growth of PtRh nanowires. The resulting hybrid of PtRh nanowire decorated graphene nanosheets shows outstanding activity and durability toward ethanol electro-oxidation. It exhibits a specific current density of 2.8 mA cm-2 and a mass-normalized current density of 1 A mg-1 metal, which are 5.4 and 3.1 times those of the state-of-the-art Pt/C catalyst, respectively. After 2000 cyclic tests, it maintains 86% of the initial electrochemically active surface area, which is larger than that of 63% obtained from the Pt/C catalyst. The superior performance is attributed to the combination of the advantageous 1D morphological motif with the synergistic effects of PtRh alloys and graphene nanosheet support.

Authenticity determination of honeys with non-extractable proteins by means of elemental analyzer (EA) and liquid chromatography (LC) coupled to isotope ratio mass spectroscopy (IRMS)

The present work aims to systematically demonstrate the authenticity of honeys with non-extractable proteins for the first time, by means of EA-IRMS and LC-IRMS. Fifty-three pure honeys of various botanical and geographical origins were studied and a criterion on the basis of the stable carbon isotope ratio characterization of total honey and the main sugars was established for pure honeys. Parameters such as δ13C values of total honey and the main sugars were well utilized to identify honeys with non-extractable proteins. Thirty-five honeys from which protein could not be extracted were all identified as adulterated with C-4 sugars or C-3 sugars. The use of isotopic compositions and some systematic differences permit the honeys with non-extractable proteins to be reliably identified. The findings obtained in this work could supplement the AOAC 998.12 C-4 sugar method, with regard to honeys from which protein cannot be extracted.

Preparation of PVDF/Al2O3 hybrid membrane via the sol–gel process and characterization of the hybrid membrane

Abstract In this study we present a new method to prepare organic–inorganic hybrid polyvinylidene fluoride (PVDF)/Al2O3 membranes via in situ polymerization of aluminum isopropoxide (AIP) using the sol–gel process. FTIR analysis showed the existence of Al in hybrid membrane when AIP was added to the casting solution. The effects of AIP on the performances of hybrid membranes were investigated. The results showed that the pure water flux and the bovine serum albumin (BSA) rejection increased firstly and then decreased with increasing AIP content. When AIP content was 12 wt.%, compared with PVDF membrane without the addition of AIP, the pure water flux of hybrid membrane was increased by 83.4% and the BSA rejection was improved from 88.3 to 96.6%. In addition, other performances of the hybrid membrane such as hydrophilicity, mechanical properties, and antipollution were also improved.

Evaluation of cobalt oxide, copper oxide and their solid solutions as heterogeneous catalysts for Fenton-degradation of dye pollutants

A series of CoO, Co0.75Cu0.25O, Co0.5Cu0.5O and CuO nanoparticles were synthesized via the calcination of corresponding oxalates and further examined as catalysts for the heterogeneous Fenton reaction. The structures of the as-prepared oxides were characterized by field emission electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The catalytic activity of the oxides was evaluated by the degradation of Congo red. It was found that, among the four catalysts, Co0.5Cu0.5O showed the best catalytic performance. Subsequently, the effects of operating parameters including the substrate concentration, pH, H2O2 concentration and reaction temperature in the catalytic performance of the Co0.5Cu0.5O were systematically studied. Under optimized conditions of catalyst loading = 200 mg L−1, pollutant concentration = 100 mg L−1, H2O2 concentration = 3 wt%, temperature = 30 °C and pH = 9, the Co0.5Cu0.5O catalyst could completely degrade the Congo red within 60 min. The degradation products were analyzed by a liquid chromatography-mass spectrometer and the degradation pathway was revealed. To investigate the catalytic mechanism, the pH and concentrations of H2O2 and metal ions were monitored during the Fenton process. Mechanistic studies revealed that hydroxyl radicals and superoxide radicals derived from the activation of H2O2 molecules by metal centers were mainly responsible for the degradation of Congo red, and that copper ions played a critical role in the superior catalytic performance of the Co0.5Cu0.5O catalyst. The Co0.5Cu0.5O catalyst showed negligible metal leaching and outstanding recyclability, which are highly favorable for the practical application in the Fenton process.

Preparation of PVDF/Al2O3 hybrid membrane via alkaline modification and chemical coupling process

Abstract Polyvinylidene fluoride (PVDF)/Al2O3 hybrid membrane (PAHM) was prepared via alkaline modification and chemical coupling using PVDF modified by KOH in the solution of methanol as a membrane-forming polymer, using vinyl-trimethoxy-silicane as a coupling agent and aluminum isopropoxide (AIP) as an inorganic precursor, respectively. PAHM, linking PVDF and Al2O3 with chemical bond, was obtained by sol–gel method. FT-IR spectroscopy, surface contact angle testing, differential scanning calorimetry, and atomic force microscope were applied to characterize the PAHM. The effects of the coupling agent on the structure and properties of the hybrid membrane were also investigated. The results showed that the hydrophilicity of the modified PVDF were the best with 5 wt% of KOH solution at 60°C for 30 min. When PAHM is prepared with 1% coupling agent, the average pore size and the pure water flux decreased compared to PAHM without coupling agent, while the rejection rate significantly increased. Along with the...

Stability of carbon and nitrogen isotopic compositions of the protein extracted from milk and their potential as “fingerprints” of geographical origin

The present work aimed to determine whether isotopic compositions can be used as “fingerprints” in identifying the geographical origin of milk. For this purpose, δ13C and δ15N values of the proteins extracted from fifty-six Tetra Pak milk samples originating from four continents, including Australia (with New Zealand), Europe (Germany and France), North America (the United States) and Asia (China), were determined using elemental analyzer-isotope ratio mass spectrometry (EA-IRMS). The effects of storage time and temperature on the δ13C and δ15N values were also studied in order to evaluate the stability of the isotopic composition and hence the ability of the developed EA-IRMS method to identify the geographical origin of milk. The results indicated that there were no significant differences (P > 0.05) for δ13C and δ15N values for the samples stored under different conditions, demonstrating the stability of the isotopic compositions in the proteins extracted from these milk samples. The δ13C values of these extracted proteins ranged from −29.36‰ to −15.02‰. Their mean δ15N values were calculated to be between 4.55‰ and 5.80‰, with the highest, second-highest, third-highest, and lowest values for the samples from Australia (with New Zealand), Europe, America, and Asia, respectively. Significant differences (P < 0.05) were found in the δ13C and δ15N values between these four regions, verifying their potential as “fingerprints” of the geographical origin of milk. The results obtained confirm the suitability and potential of stable isotopic composition (δ13C and δ15N) analysis in determining the geographical origin of milk.

A sulfonated polymer membrane with Ag-based graft: morphology, characterization, antimicrobial activity and interception ability

Ag-based nano-graft is a common approach used to impart broad-spectrum antimicrobial activity to a polymer membrane. The primary problem with this approach is low compatibility between the grafted particles and the polymer main-body, followed by its low anti-adhesion for undesired membrane fouling. To overcome these problems, this study functionalized polyethersulfone (PES) materials by a sulfonation process to form the membrane backbone. FTIR, thermogravimetry (TG) and contact angle (CA) analysis showed that sulfonate treatment improved hydrophilicity and surface activity. Accordingly, the Ag-based nano-grafts were embedded on the membrane by immersing into a Ag+ solution and then reducing. The resulting membrane was characterized by a series of assays. SEM and AFM scans were used to examine the membrane surface for Ag nanoparticles (AgNPs) distribution. XRD and XPS analysis determined the AgNPs state. A concentration assay revealed that the Ag release from the membrane was maintained within the safety range during the filtration process. An antimicrobial ring test showed the antimicrobial activities of the membrane for different microbial strains. BET analysis and the water-absorption test analyzed the porosity properties of the membrane. The filtration performance assay proved that the membrane had remarkable interception ability for various solutes. Consequently, it showed that the prepared SPES-AgNPs membrane will have a promising application as an antimicrobial filtration membrane for water treatment.