Pd/δ-MnO2 nanoflower arrays cordierite monolithic catalyst toward toluene and o-xylene combustion.

Exploring high-efficiency and stable monolithic structured catalysts is vital for catalytic combustion of volatile organic compounds. Herein, we prepared a series of Pd/δ-MnO2 nanoflower arrays monolithic integrated catalysts (0.01-0.07 wt% theoretical Pd loading) via the hydrothermal growth of δ-MnO2 nanoflowers onto the honeycomb cordierite, which subsequently served as the carrier for loading the Pd nanoparticles (NPs) through the electroless plating route. Moreover, we characterized the resulting monolithic integrated catalysts in detail and evaluated their catalytic activities for toluene combustion, in comparison to the controlled samples including only Pd NPs loading and the δ-MnO2 nanoflower arrays. Amongst all the monolithic samples, the Pd/δ-MnO2 nanoflower arrays monolithic catalyst with 0.05 wt% theoretical Pd loading delivered the best catalytic performance, reaching 90% toluene conversion at 221°C at a gas hourly space velocity (GHSV) of 10,000 h-1. Moreover, this sample displayed superior catalytic activity for o-xylene combustion under a GHSV of 10,000 h-1. The monolithic sample with optimal catalytic activity also displayed excellent catalytic stability after 30 h constant reaction at 210 and 221°C.

Fabrication of Co3O4 NPs-graphene oxide nanocomposites as an efficient catalyst towards oxygen reduction and its catalytic applications.

Co3O4 nanoparticles-graphene oxide (Co3O4 NPs-GO) nanocomposites with good solubility were successfully synthesized and well characterized. As a nanocatalyst with oxidase-mimicking activity, the nanocomposites can catalyze the oxidation of 3',5,5'-tetramethylbenzidine (TMB) with high efficiency. The catalyzing reaction was rapid and no extra H2O2 was needed compared with other similar TMB oxidation reactions. The catalyzing reaction mechanism of the system was investigated in detail. And it was demonstrated that the oxygen involved in the reaction came from the oxygen absorbed on the nanocomposites which oxidized TMB. Based on this reaction, a colorimetric system for vitamin C detection in vegetable and fruits was established. Under the optimum conditions, the detection can be achieved within 10 min and a linear relationship in concentration range of 2.5 × 10-6 to 1.8 × 10-5 M and 3.4 × 10-5 to 1.7 × 10-4 M was obtained with a detection limit of 7.0 × 10-7 M. The colorimetric system exhibited good selectivity, sensitivity and satisfactory recoveries ranged from 93.1% to 101.1%.

Investigation on the Transformation of Absorbed Oxygen at ZnO {101Ì 0} Surface Based on a Novel Thermal Pulse Method and Density Functional Theory Simulation.

Absorbed oxygen plays a key role in gas sensing process of ZnO nanomaterials. In this work, the transformation of absorbed oxygen on ZnO (101̅0) and its effects on gas sensing properties to ethanol are studied by a novel thermal pulse method and density functional theory (DFT) simulation. Thermal pulse results reveal that the absorbed O2 molecule dissociates into two individual oxygen adatoms by extracting electrons from ZnO surface layers when temperature is above 443 K. The temperature at which absorbed O2 molecule begins to dissociate is the lowest working temperature for gas sensing. DFT simulation demonstrates the dissociation process of O2 at ZnO (101̅0) surface, and the activation energy (Ea) of dissociation is calculated to be 351.71 kJ/mol, which suggests that the absorbed O2 molecule is not likely to dissociate at room temperature. The reactions between ethanol and absorbed O2 molecule, as well as reactions between ethanol and O adatom, are also simulated. The results indicate that ethanol cannot react with absorbed O2 molecule, while it can be oxidized by O adatom to acetaldehyde and then to acetic acid spontaneously. Mulliken charge analysis suggests electrons extracted by O adatom return to ZnO after the oxidation of ethanol.

Avaliação do volume de oxigênio absorvido por sachê absorvedor de oxigênio em diferentes temperaturas e umidades relativas / Evaluation of the amount of oxygen absorbed by oxygen absorbers at different temperatures and relative humidities

O uso de absorvedores de oxigênio em embalagens de produtos alimentícios acondicionados tem apresentado uma demanda crescente. Assim, o conhecimento da eficiência desses absorvedores em diferentes condições de umidade relativa e temperaturas definidas, são de fundamental importância. Portanto, foram determinadas equações para predizer o volume absorvido de oxigênio para as temperaturas de 10±2 ºC e 25±2 ºC, dependendo da umidade relativa na faixa de 75 por cento a 85 por cento e da taxa de permeabilidade a oxigênio da embalagem. Para a temperatura de 25±2ºC a equação é: V = -32,770+10,440*UR-104,385*ln(TPO2), com um R² = 0,9151. Para a temperatura de 10±2ºC a equação é: V=107,321+6,221*UR-105,166 ln(TPO2) com um R² = 0,8729. Dessa forma, o tempo de atividade do sachê pode ser determinado pela equação T = (V-Vi) / (TPO2*A). Utilizando essas equações e, considerando uma embalagem de área 0,05m² por face, com uma permeabilidade de 8,63 cm3.m-2.dia-1, uma umidade relativa de 80 por cento e o volume de oxigênio inicial dentro da embalagem de 2,5 mL, após o envase, o tempo de atividade do sachê quando armazenado a 10±2ºC foi de 435 dias e a 25±2ºC de 666 dias.

Oxygen absorbers have been presenting a growing demand for application in food packaging. Thus, it is important to know the efficiency of those absorbers in different relative humidity and temperatures. Therefore, equations were developed to predict the volume of absorbed oxygen at 10±2 ºC and 25±2 ºC, according as the relative humidity ranging from 75 percent to 85 percent and the oxygen transmission rate through the package. At 25±2ºC the equation was V = -32,770+10,440*RH-104,385*ln(O2 TR), with R² = 0,9151. At 10±2ºC, V=107,321+6,221*RH-105,166 ln(O2 TR) with R² = 0,8729. As a consequence, activity time for the oxygen absorbers can be calculated with the following equation: T = (V-Vi) / (ln(O2 TR*A). Using these equations and considering a packaging area of 0,05m² for each face, oxygen transmission rate of 8,63 cm³.m-².dia-1, relative humidity of 80 percent and an initial oxygen volume inside the package of 2,5 mL, absorber activity times when stored at 10±2ºC and 25±2ºC were 435 and 666 days, respectively.