New trends in nanoclay-modified sensors

Nanoclays are widespread materials characterized by a layered structure in the nano-scale range. They have multiple applications in diverse scientific and industrial areas, mainly due to their swelling capacity, cation exchange capacity, and plasticity. Due to the cation exchange capacity, nanoclays can serve as host matrices for the stabilization of several molecules and, thus, they can be used as sensors by incorporating electroactive ions, biomolecules as enzymes, or fluorescence probes. In this review, the most recent applications as bioanalyte sensors are addressed, focusing on two main detection systems: electrochemical and optical methods. Particularly, the application of electrochemical sensors with clay-modified electrodes (CLME) for pesticide detection is described. Moreover, recent advances of both electrochemical and optical sensors based on nanoclays for diverse bioanalytes? detection such as glucose, H2O2, organic acids, proteins, or bacteria are also discussed. As it can be seen from this review, nanoclays can become a key factor in sensors? development, creating an emerging technology for the detection of bioanalytes, with application in both environmental and biomedical fields

Adsorptive capture of ionic and non-ionic pollutants using a versatile hybrid amphiphilic-nanomica

A versatile, functional nanomaterial for the removal of ionic and non-ionic pollutants is presented in this work. For that purpose, the high charge mica Na-4-Mica was exchanged with the cationic surfactant (C16H33NH(CH3)2)+. The intercalation of the tertiary amine in the swellable nano-clay provides the optimal hydrophilic/hydrophobic nature in the bidimensional galleries of the nanomaterial responsible for the dual functionality. The organo-mica, made by functionalization with C16H33NH3+, was also synthesized for comparison purposes. Both samples were characterized by X-ray diffraction techniques and transmission electron microscopy. Then, the samples were exposed to a saturated atmosphere of cyclohexylamine for two days, and the adsorption capacity was evaluated by thermogravimetric measurements. Eu3+ cations served as a proof of concept for the adsorption of ionic pollutants in an aqueous solution. Optical measurements were used to identify the adsorption mechanism of Eu3+ cations, since Eu3+ emissions, including the relative intensity of different f–f transitions and the luminescence lifetime, can be used as an ideal spectroscopic probe to characterize the local environment. Finally, the stability of the amphiphilic hybrid nanomaterial after the adsorption was also tested.We would like to thank IDIVAL for financial support, project number INNVAL19/1

Tunable interlayer hydrophobicity in a nanostructured high charge organo-mica

A tunable hydrophobicity, from a fully hydrophobic medium to an amphiphilic quasi-solution, has been obtained in the interlayer space of a synthetic high charged mica by ion exchange reaction with amine cations. The structural and intercalation properties of the hybrids after the exchange with the n-alkylammonium cations: [RNH3]+, [RNH(CH3)2]+ and [RN(CH3]3+ with C16 alkyl chain length have been determined by termogravimetric/differential scanning calorimetry analysis (TGA-DSC) and mass spectrometry (MS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Transmission electron microscopy (TEM) has been used as a complementary technique to provide new insights into the morphology of the exchanged products. Coverage and cation distribution have been correlated with layer charge and steric effects. Thus, a full organo-clay is obtained when the primary amine cations are adsorbed between the layers. However, a homogenous single phase of mixed organic/inorganic cations is formed in the same interlayer with the tertiary amine cations. Mixed ion clays combining both exchangeable inorganic and adsorbent organic ions in their interlayer space can be potential materials to be used as adsorbents for water decontamination, independently of the hydrophilic/hydrophobic nature of the pollutants. For the quaternary amine cations steric effects preclude the coexistence of both organic and inorganic species in the same interlayer of the clay so phase segregation together with a heterogeneous phase of organic and inorganic galleries in the same particle can be observed.Funding from the Ministerio de Economía y Competitividad, under project MAT2015-63929-R is also acknowledged. Fernando Aguado received funding from the Ministerio de Economía y Competitividad, project MAT2015-69508-P

Eu3+ luminescence in high charge mica: an in situ probe for the encapsulation of radioactive waste in geological repositories

Isolation of high-level radioactive waste (HLW) in deep geological repositories (DGR) through a multibarrier concept is the most accepted approach to ensure long-term safety. Clay minerals are one of the most promising materials to be used as engineered barriers. In particular, high charge micas, as components of the engineered barrier, show superselectivity for some radioactive isotopes and a large adsorption capacity, which is almost twice that of the other low charge aluminosilicates. In addition, high charge micas are optimum candidates for decontamination of nuclear waste through two different mechanisms; namely an ion exchange reaction and a nonreversible mechanism involving the formation of new stable crystalline phases under hydrothermal conditions. In this work, we report a new in situ optical sensor based on the incorporation of Eu3+ in these high charge micas for tracking the long-term physical-chemical behavior of HLW contaminants in DRG under mild hydrothermal conditions. The incorporation of Eu3+ into the interlayer space of the mica originates a well resolved green and red luminescence, from both the 5D1 and 5D0 excited states, respectively. The formation of new crystalline phases under hydrothermal conditions involves important changes in the Eu3+ emission spectra and lifetime. The most interesting features of Eu3+ luminescence to be used as an optical sensor are (1) the presence or absence of the Eu3+ green emission from the 5D1 excited state, (2) the energy shift of the 5D0 → 7F0 transition, (3) the crystal-field splitting of the 7F1 Eu3+ level, and (4) the observed luminescence lifetimes, which are directly related to the interaction mechanisms between the lanthanide ions and the silicate network.Funding from projects MAT2015-63929-R, MAT2015-69508-P, PI16/00496, and NVAL16/17-IDIVAL is gratefully acknowledged

CO2 capture at low temperature by nanoporous silica modified with amine groups

MCM-41 and SBA-15 were chosen as nanoporous materials based on silica for its modification with aminegroups. This modification was done by two methods: grafting method and wet impregnation method. The firstmethod grafted-amine groups by chemical reaction between surface silanol groups in the nanoporousmaterials and 3-aminopropyltrimetoxilane (APTMS).In the wet impregnation method, low molecular weightpolyethylenimine (PEI) is incorporated trough this method. These modified materials capture CO2 at lowtemperature. CO2 capture on the sorption sites by amine loading is believed to occur via chemisorptionmechanism by formation of ammonium carbamate. The evaluation and analysis of CO2 adsorption was carriedout by two methods: static mode and dynamic mode. The static mode is a pure CO2 adsorption-desorptionisotherms at 298K. The isotherms of the functionalized materials show a behavior by chemisorption, captureat low pressure, being the desorption branch almost horizontal, while nanoporous silica isotherms is due aphysical adsorption, low CO2 capture at low pressure and dependence with pressure, a complete reversibilityof the desorption process. The dynamic mode is a thermogravimetry study at different N2/CO2 concentrations.Isothermal CO2 captures at 298K were carried out to evaluate the suitability of the samples for cyclicoperation. The mass increase during the capture step was interpreted as CO2 adsorption capacity of thesamples. The results obtained by both methods were compared, and, its differences were analyzed

Exploring the local environment of the engineered nanoclay Mica-4 under hydrothermal conditions using Eu3+ as a luminescent probe

High charge mica Na4Al4Si4Mg6O20F4, Mica-4, is a promising candidate as a filling material to immobilize high-level radioactive waste in deep geological repositories due to its extraordinary adsorption capacity. In contrast to traditional clay materials, the structural composition of this mica, with a high content of aluminum in the tetrahedral sheet, enhances its chemical reactivity, favoring the formation of new crystalline phases under mild hydrothermal conditions, and thus providing a definitive isolation of the radionuclides in the engineered barrier. Moreover, this synthetic clay has some features that allow its use as an optical sensor by doping with luminescent rare earth cations such as Eu3+. In this paper we discuss the local structure of the nanoclay Mica-4 using Eu3+ as a local probe to track the physical and chemical modifications under hydrothermal conditions. For that purpose, a set of hydrothermal experiments has been carried out heating Mica-4 and an aqueous Eu(NO3)3 solution in a stainless steel reactor at different temperatures and times. Optical properties of the as-treated samples were characterized by spectroscopic measurements. The fine peak structure of emission and the relative intensity of different Eu3+ transitions as well as the luminescence lifetime have been correlated with the structure and composition of this nanoclay, and the interaction mechanisms between the lanthanide ions and the clay mineral at different temperatures and times. Special attention has been paid to understanding the role of the aluminum content, which may act as either an aggregating or dispersing agent, in the optical features and reactivity of the system.We would like to thank Instituto de Investigación Marqués de Valdecilla (IDIVAL) (Projects NVAL16/17 and INNVAL19/18) and Ministerio de Ciencia, Innovación y Universidades (Project PGC2018–101464-B-100) for financial support

Bionanocomposites based on chitosan intercalation in designed swelling high-charged micas

Bionanocomposites based on layered inorganic components, as clays, and polymers of biologicalorigin, as chitosan, have a major impact in medical and environmental fields, being economical and environmentally friendly materials. Na-Mn micas (n = 2 and 4) with controlled surface charge, high cation exchange capacity and swelling behaviour, are attractive inorganic composite components that exhibit improved adsorption properties compared to other inorganic solids which makes them potentially useful for bionanocomposites. The goal of this research was to explore the potential use of those synthetic brittle micas to form eco-friendly bionanocomposites with chitosan biopolymer. Hence, chitosan-mica bionanocomposites were prepared by ion-exchange reaction between chitosan solution and synthetic high charge mica. X-ray diffraction, Fourier transform infrared spectroscopy, thermal analysis, MAS-NMR spectroscopy and zeta-potential have been employed for bionanocomposites characterization. The results showed that the adsorption of chitosan is effective, although a chitosan portion remains in the outer surface being hydrogen-bonded to the tetrahedral sheet of the silicate.The authors would like to thank the Junta de Andalucía (Spain) and FEDER (Proyecto de Excelencia de la Junta de Andalucía, project P12-FQM-567), to the Spanish State Program R + D + I oriented societal challenges and FEDER (Project MAT2015-63929-R) for financial support. F.J. Osuna thanks his grant to the training researcher program associated to the excellence project of Junta de Andalucía (P12-FQM-567). Finally, we thanks to the Colloidal Materials Group of the Instituto Ciencia de los Materiales de Sevilla (ICMS) for their help in the Zetapotential measurements

Química (G986). Septiembre 2015

Grado en Ingeniería en Electrónica Industrial y Automátic

Química (G986). Febrero 2014

Grado en Ingeniería en Electrónica Industrial y Automátic