Mechanosynthesis of MFe 2

Adsorption of Pb(II) from aqueous solution using MFe2O4 nanoferrites (M = Co, Ni, and Zn) was studied. Nanoferrite samples were prepared via the mechanochemical method and were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), micro-Raman, and vibrating sample magnetometry (VSM). XRD analysis confirms the formation of pure single phases of cubic ferrites with average crystallite sizes of 23.8, 19.4, and 19.2 nm for CoFe2O4, NiFe2O4, and ZnFe2O4, respectively. Only NiFe2O4 and ZnFe2O4 samples show superparamagnetic behavior at room temperature, whereas CoFe2O4 is ferromagnetic. Kinetics and isotherm adsorption studies for adsorption of Pb(II) were carried out. A pseudo-second-order kinetic describes the sorption behavior. The experimental data of the isotherms were well fitted to the Langmuir isotherm model. The maximum adsorption capacity of Pb(II) on the nanoferrites was found to be 20.58, 17.76, and 9.34 mg·g−1 for M = Co, Ni, and Zn, respectively

Adsorción de gases en mordenita modificada con metales de transición

Las zeolitas poseen extraordinarias propiedades, por las cuales han encontrado importantes aplicaciones en catálisis heterogénea, procesos de separación y secado, suavizado de agua, saneamiento ambiental, etc. El intercambio iónico es probablemente, el método más utilizado para modificar zeolitas y comúnmente se lleva a cabo en solución acuosa, aunque también se puede utilizar el método de estado sólido. Este último, entre múltiples ventajas, facilita la difusión del catión a través de los canales de la zeolita. Las zeolitas intercambiadas con cobre, además del interés que despiertan como materiales ideales para el estudio de la interacción del Hidrógeno con la materia, han recibido una gran atención por su actividad catalítica en la conversión de óxidos de Nitrógeno, en especial las Mordenitas. Este comportamiento se le atribuye a la formación del dímero Cu(III) μ-oxo durante su activación a altas temperatura. Con el objetivo de estudiar la adsorción de H2 y CO2 en Cu-Mordenita; así como la influencia del método de intercambio iónico en la formación de diferentes especies de Cobre; se prepararon varias muestras de Mordenita intercambiadas con Cu2+, utilizando ambos métodos de intercambio iónico, en solución y en estado sólido. Estos materiales se caracterizaron mediante las técnicas de UV-vis, XPS y Reducción a Temperatura Programada (TPR) para obtener información sobre el estado del Cobre en los mismos. Los resultados permiten identificar tres diferentes estados del Cobre en las muestras: clústeres de CuO en la superficie, cationes Cu2+ hidratados, en dos diferentes sitios, y el dímero Cu(III) (μ-oxo) en el poro menos accesible de las muestras calcinadas. La formación de esta última especie se favorece particularmente por la reacción de intercambio iónico en estado sólido y se detecta por la presencia de una intensa banda de transferencia de carga a los 400 nm en el espectro UV-vis. Esta es la diferencia más significativa entre las reacciones de intercambio en estado sólido y en solución. La presencia de la especie Cu(III) (μ-oxo) también fue detectada en el espectro de XPS y en los perfiles de TPR. De acuerdo con las isotermas de adsorción de H2 y CO2, el proceso de intercambio iónico modifica el volumen de accesibilidad de los poros, aunque el material conserva su estructura porosa. Abstract Zeolites, related to their extraordinary properties have found industrial applications in heterogeneous catalysis, separation and drying processes, water softening, environmental remediation, etc. The ionic exchange process is probably the most widely used route to modify the zeolites properties and it is commonly carried out from aqueous solution of the ion to be introduced as charge-balancing species. The ionic exchange is also possible in the solid state. The latter, among others advantages, facilitates cation diffusion through the zeolites channels. Copper exchange zeolites also aroused interest as ideal material for the study of the interaction of hydrogen with matter, have received large attention for their catalytic activity in nitrogen oxides conversion, especially Mordenites. Such behavior of this zeolite is ascribed to the formation of Cu(III) μ-oxo dimmers during its activation process under heating. With the aim of studying the adsorption of H2 and CO2 in Cu-Mordenite, as well as the influence of the ion exchange method in the formation of different copper species, various Cu-exchanged mordenite samples were prepared using both solid state and aqueous solution ionic reactions. The obtained materials were then characterized from UV-vis, XPS, and TPR data in order to obtain information on the state of copper in the exchanged samples. Three types of copper were identified, surface clusters of CuO in two different sites, and as Cu(III) μ-oxo dimmer, within the porous framework for the calcined samples. The formation of this last specie is particularly favored for the solid state ionic reaction, and it is detected as an intense charge transfer band at 400 nm in the recorded UV-vis spectra. This is the main distinctive difference between the exchange reactions in the solid state and in solution. The appearance of Cu(III) μ-oxo dimmer was also detected in the XPS spectra and TPR profiles. According to the recorded H2 and CO2 adsorption isotherms, the ionic exchange process modifies the accessible pore volume but the material preserves its porous features

Improving Sensitivity of a Chemoresistive Hydrogen Sensor by Combining ZIF-8 and ZIF-67 Nanocrystals

In the present work, nanostructures of zeolitic imidazolate frameworks (ZIF-8 and ZIF-67) were combined to obtain a novel chemoresistive sensor, improving the sensitivity of ZIF-67 and facilitating measurement of ZIF-8 by decreasing the resistivity. The sensor detected concentrations as low as 10 ppm of hydrogen increasing its resistivity about 4.5 times. The response of the sensor was compared with a similar chemoresistive sensor based exclusively on ZIF-67, and the sensitivity was around three times higher in the case of the sensor with ZIFs combination.This research is supported by project DGAPA-PAPIIT IA-103016 from Universidad Nacional Autónoma de México and the project TEC-2013-48147 (AEI/FEDER, EU) from Ministerio de Economía y Competitividad of Spain. A. Sainz-Vidal thanks CONACYT for the postdoctoral fellowship at CCADET-UNAM

ZIF Nanocrystal-Based Surface Acoustic Wave (SAW) Electronic Nose to Detect Diabetes in Human Breath

In the present work, a novel, portable and innovative eNose composed of a surface acoustic wave (SAW) sensor array based on zeolitic imidazolate frameworks, ZIF-8 and ZIF-67 nanocrystals (pure and combined with gold nanoparticles), as sensitive layers has been tested as a non-invasive system to detect different disease markers, such as acetone, ethanol and ammonia, related to the diagnosis and control of diabetes mellitus through exhaled breath. The sensors have been prepared by spin coating, achieving continuous sensitive layers at the surface of the SAW device. Low concentrations (5 ppm, 10 ppm and 25 ppm) of the marker analytes were measured, obtaining high sensitivities, good reproducibility, short time response and fast signal recovery.This work has been supported by Universidad Nacional Autónoma de México via Grants DGAPA-UNAM-PAPIIT TA100118 and DGAPA-UNAM-PAPIIT IT100518, the Fundación General CSIC via Programa ComFuturo, and the Spanish Ministry of Science and Innovation via Grant TEC2016-79898-C6-(AEI/FEDER,EU). This research has used the Spanish ICTS Network MICRONANOFABS (partially funded by MINECO)We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)Peer reviewe

Mechanosynthesis of MFe2O4 (M = Co, Ni, and Zn) Magnetic Nanoparticles for Pb Removal from Aqueous Solution

Adsorption of Pb(II) from aqueous solution using MFe2O4 nanoferrites (M = Co, Ni, and Zn) was studied. Nanoferrite samples were prepared via the mechanochemical method and were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), micro-Raman, and vibrating sample magnetometry (VSM). XRD analysis confirms the formation of pure single phases of cubic ferrites with average crystallite sizes of 23.8, 19.4, and 19.2 nm for CoFe2O4, NiFe2O4, and ZnFe2O4, respectively. Only NiFe2O4 and ZnFe2O4 samples show superparamagnetic behavior at room temperature, whereas CoFe2O4 is ferromagnetic. Kinetics and isotherm adsorption studies for adsorption of Pb(II) were carried out. A pseudo-second-order kinetic describes the sorption behavior. The experimental data of the isotherms were well fitted to the Langmuir isotherm model. The maximum adsorption capacity of Pb(II) on the nanoferrites was found to be 20.58, 17.76, and 9.34 mg·g−1 for M = Co, Ni, and Zn, respectively