Synthesis of Cobalt-Based Nanoparticles as Catalysts for Methanol Synthesis from CO2 Hydrogenation.

The increasing emission of carbon dioxide into the atmosphere has urged the scientific community to investigate alternatives to alleviate such emissions, being that they are the principal contributor to the greenhouse gas effect. One major alternative is carbon capture and utilization (CCU) toward the production of value-added chemicals using diverse technologies. This work aims at the study of the catalytic potential of different cobalt-derived nanoparticles for methanol synthesis from carbon dioxide hydrogenation. Thanks to its abundance and cost efficacy, cobalt can serve as an economical catalyst compared to noble metal-based catalysts. In this work, we present a systematic comparison among different cobalt and cobalt oxide nanocomposites in terms of their efficiency as catalysts for carbon dioxide hydrogenation to methanol as well as how different supports, zeolites, MnO2, and CeO2, can enhance their catalytic capacity. The oxygen vacancies in the cerium oxide act as carbon dioxide adsorption and activation sites, which facilitates a higher methanol production yield.

Addressing the gaseous and odour emissions gap in decentralised biowaste community composting.

Composting has demonstrated to be an effective and sustainable technology to valorise organic waste in the framework of circular economy, especially for biowaste. Composting can be performed in various technological options, from full-scale plants to community or even individual composters. However, there is scarce scientific information about the potential impact of community composting referred to gaseous emissions. This work examines the emissions of methane and nitrous oxide as main GHG, ammonia, VOC and odours from different active community composting sites placed in Spain, treating kitchen, leftovers and household biowaste. Expectedly, the gaseous emissions have an evident relation with the composting progress, represented mainly by its decrease as temperature or biological activity decreases. GHG and odour emission rates ranged from 5.3 to 815.2 mg CO2eq d-1 kg-1VS and from 69.8 to 1088.5 ou d-1 kg-1VS, respectively, generally being lower than those find in open-air full-scale composting. VOC characterization from the community composting gaseous emissions showed a higher VOC families' distribution in the emissions from initial composting phases, even though terpenes such as limonene, α-pinene and ß-pinene were the most abundant VOC along the composting process occurring in the different sites studied. The results presented in this study can be the basis to evaluate systematically and scientifically the numerous current projects for a worldwide community composting implementation in decentralised biowaste management schemes.

Recent Advances in the Catalytic Conversion of Methane to Methanol: From the Challenges of Traditional Catalysts to the Use of Nanomaterials and Metal-Organic Frameworks.

Methane and carbon dioxide are the main contributors to global warming, with the methane effect being 25 times more powerful than carbon dioxide. Although the sources of methane are diverse, it is a very volatile and explosive gas. One way to store the energy content of methane is through its conversion to methanol. Methanol is a liquid under ambient conditions, easy to transport, and, apart from its use as an energy source, it is a chemical platform that can serve as a starting material for the production of various higher-value products. Accordingly, the transformation of methane to methanol has been extensively studied in the literature, using traditional catalysts as different types of zeolites. However, in the last few years, a new generation of catalysts has emerged to carry out this transformation with higher conversion and selectivity, and more importantly, under mild temperature and pressure conditions. These new catalysts typically involve the use of a highly porous supporting material such as zeolite, or more recently, metal-organic frameworks (MOFs) and graphene, and metallic nanoparticles or a combination of different types of nanoparticles that are the core of the catalytic process. In this review, recent advances in the porous supports for nanoparticles used for methane oxidation to methanol under mild conditions are discussed.

Combining nanoscale zero-valent iron and anaerobic dechlorinating bacteria to degrade chlorinated methanes and 1,2-dichloroethane.

Nanoscale zero-valent iron (nZVI) has the potential to degrade a diversity of chlorinated compounds, and it is widely used for remediation of contaminated groundwaters. However, some frequently detected contaminants such as dichloromethane (DCM) and 1,2-dichloroethane (1,2-DCA) have shown nearly no reactivity with nZVI. Here, we tested the feasibility of combining anaerobic dechlorinating bacteria, Dehalobacterium and Dehalogenimonas, and nZVI as a treatment train to detoxify chlorinated methanes (i.e., chloroform-CF- and DCM), and 1,2-DCA. First, we showed that CF (500 µM) was fully degraded by 1 g/L nZVI to DCM as a major by-product, which was susceptible to fermentation by Dehalobacterium to innocuous products. Our results indicate that soluble compounds released by nZVI might cause an inhibitory impact on Dehalobacterium activity, avoiding DCM depletion. The DCM dechlorination activity was recovered when transferred to a fresh medium without nZVI. The increase in H2 production and pH was discarded as potential inhibitors. Similarly, a Dehalogenimonas-containing culture was unable to dichloroeliminate 1,2-DCA when exposed to 1 g/L nZVI, but dechlorinating activity was also recovered when transferred to nZVI-free media. The recovery of the dechlorinating activity of Dehalobacterium and Dehalogenimonas suggests that combination of nZVI and bioremediation techniques can be feasible under field conditions where dilution processes can alleviate the impact of the potential inhibitory soluble compounds.

Magnetite-based nanoparticles and nanocomposites for recovery of overloaded anaerobic digesters.

The effect of magnetite nanoparticles and nanocomposites (magnetite nanoparticles impregnated into graphene oxide) supplement on the recovery of overloaded laboratory batch anaerobic reactors was assessed using two types of starting inoculum: anaerobic granular sludge (GS) and flocculent sludge (FS). Both nanomaterials recovered methane production at a dose of 0.27 g/L within 40 days in GS. Four doses of magnetite nanoparticles from 0.075 to 1 g/L recovered the process in FS systems between 30 and 50 days relaying on the dose. The presence of nanomaterials helped to reverse the effect of volatile fatty acids inhibition and enabled microbial communities to recover but also favoured the development of certain microorganisms over others. In GS reactors, the methanogenic population changed from being mostly acetoclastic (Methanothrix soehngenii) to being dominated by hydrogenotrophic species (Methanobacterium beijingense). Nanomaterial amendment may serve as a preventative measure or provide an effective remedial solution for system recovery following overloading.

Conversion of Carbon Dioxide into Methanol Using Cu-Zn Nanostructured Materials as Catalysts.

Nowadays, there is a growing awareness of the great environmental impact caused by the enormous amounts of carbon dioxide emitted. Several alternatives exist to solve this problem, and one of them is the hydrogenation of carbon dioxide into methanol by using nanomaterials as catalysts. The aim of this alternative is to produce a value-added chemical, such as methanol, which is a cheaply available feedstock. The development of improved materials for this conversion reaction and a deeper study of the existing ones are important for obtaining higher efficiencies in terms of yield, conversion, and methanol selectivity, in addition to allowing milder reaction conditions in terms of pressure and temperature. In this work, the performance of copper, zinc, and zinc oxide nanoparticles in supported and unsupported bimetallic systems is evaluated in order to establish a comparison among the different materials according to their efficiency. For that, a packed bed reactor operating with a continuous gas flow is used. The obtained results indicate that the use of bimetallic systems combined with porous supports, such as zeolite and activated carbon, is beneficial, thus improving the performance of unsupported materials by four times.

Sustained effect of zero-valent iron nanoparticles under semi-continuous anaerobic digestion of sewage sludge: Evolution of nanoparticles and microbial community dynamics.

The effects of adding zero-valent iron nanoparticles (nZVI) on the physicochemical, biological and biochemical responses of a semi-continuous anaerobic digestion of sewage sludge have been assessed. Two sets of consecutive experiments of 103 and 116 days, respectively, were carried out in triplicate. nZVI were magnetically retained in the reactors, and the effect of punctual doses (from 0.27 to 4.33 g L-1) over time was studied. Among the different parameters monitored, only methane content in the biogas was significantly higher when nZVI was added. However, this effect was progressively lost after the addition, and in 5-7 days, the methane content returned to initial values. The increase in the oxidation state of nanoparticles seems to be related to the loss of effect over time. Higher dose (4.33 g L-1) sustained positive effects for a longer time along with higher methane content, but this fact seems to be related to microbiome acclimation. Changes in microbial community structure could also play a role in the mechanisms involved in methane enhancement. In this sense, the microbial consortium analysis reported a shift in the balance among acetogenic eubacterial communities, and a marked increase in the relative abundance of members assigned to Methanothrix genus, recognized as acetoclastic species showing high affinity for acetate, which explain the rise in methane content in the biogas. This research demonstrates that biogas methane enrichment in semicontinuous anaerobic digesters can be achieved by using nZVI nanoparticles, thus increasing energy production or reducing costs of a later biogas upgrading process.

The use of magnetic iron oxide based nanoparticles to improve microalgae harvesting in real wastewater.

A novel approach for harvesting Scenedesmus sp. microalgae from real wastewater by using adsorbents of magnetite-based nanoparticles (Fe3O4 NPs) was tested in this study for the first time for this microalgae. Using these NPs, the harvesting efficiency was even higher than 95%. The optimal conditions (0.14 gNPs/L, a short magnetic separation time of only 8 min and 27 min of contact time) were found using the response surface methodology. The best fitting of the adsorption equilibrium results was achieved by the Langmuir isotherm model, and the maximum adsorption capacity for Scenedesmus sp. reached 3.49 g dry cell weight (DCW)/g Fe3O4 NPs. Zeta potential measurements and the Dubinin-Radushkevich isotherm model analysis pointed out that the main adsorption mechanism between Scenedesmus sp. cells and Fe3O4 NPs was electrostatic interaction. Finally, Fe3O4 NPs were six times successfully reused by combining an alkaline treatment with an ultrasonication process, which implies microalgae lysis. The results herein obtained highlight the potential for magnetic separation of microalgae from wastewater, which is capable of reaching a high harvesting efficiency in a very short time.

Biosafety assessment of conducting nanostructured materials by using co-cultures of neurons and astrocytes.

Neural electrode implants are made mostly of noble materials. We have synthesized a nanostructured material combining the good electrochemical properties of iridium oxide (IrOx) and carbon-nanotubes (CNT) and the properties of poly(3,4-ethylenedioxythiophene) (PEDOT). IrOx-CNT-PEDOT charge storage capacity was lower than that of IrOx and IrOx-CNT, but higher than that of other PEDOT-containing hybrids and Pt. Cyclic voltammetry, SEM, XPS and micro-Raman spectroscopy suggest that PEDOT encapsulates IrOx and CNT. In our search for a cell culture platform that could optimize modelling the in vivo environment, we determined cell viability, neuron and astrocyte functionality and the response of astrocytes to an inflammatory insult by using primary cultures of neurons, of astrocytes and co-cultures of both. The materials tested (based on IrOx, CNT and PEDOT, as well as Pt as a reference) allowed adhesion and proliferation of astrocytes and full compatibility for neurons grown in co-cultures. Functionality assays show that uptake of glutamate in neuron-astrocyte co-culture was significantly higher than the sum of the uptake in astrocytes and neurons. In co-cultures on IrOx, IrOx-CNT and IrOx-CNT-PEDOT, glutamate was released by a depolarizing stimulus and induced a significant increase in intracellular calcium, supporting the expression of functional NMDA/glutamate receptors. LPS-induced inflammatory response in astrocytes showed a decreased response in NOS2 and COX2 mRNA expression for IrOx-CNT-PEDOT. Results indicate that neuron-astrocyte co-cultures are a reliable model for assessing the biocompatibility and safety of nanostructured materials, evidencing also that hybrid IrOx-CNT-PEDOT nanocomposite materials may offer larger resistance to inflammatory insults.

Controlling Nerve Growth with an Electric Field Induced Indirectly in Transparent Conductive Substrate Materials.

Innovative neurostimulation therapies require improved electrode materials, such as poly(3,4-ethylenedioxythiophene) (PEDOT) polymers or IrOx mixed ionic-electronic conductors and better understanding of how their electrochemistry influences nerve growth. Amphibian neurons growing on transparent films of electronic (metal) conductors and electronic-ionic conductors (polymers and semiconducting oxides) are monitored. Materials are not connected directly to the power supply, but a dipole is created wirelessly within them by electrodes connected to the culture medium in which they are immersed. Without electrical stimulation neurons grow on gold, platinum, PEDOT-polystyrene sulfonate (PEDOT-PSS), IrOx , and mixed oxide (Ir-Ti)Ox , but growth is not related to surface texture or hydrophilicity. Stimulation induces a dipole in all conductive materials, but neurons grow differently on electronic conductors and mixed-valence mixed-ionic conductors. Stimulation slows, but steers neurite extension on gold but not on platinum. The rate and direction of neurite growth on PEDOT-PSS resemble that on glass, but on IrOx and (Ir-Ti)Ox neurites grow faster and in random directions. This suggests electrochemical changes induced in these materials control growth speed and direction selectively. Evidence that the electric dipole induced in conductive material controls nerve growth will impact electrotherapies exploiting wireless stimulation of implanted material arrays, even where transparency is required.

Solid contact ion sensor with conducting polymer layer copolymerized with the ion-selective membrane for determination of calcium in blood serum.

A new solid contact ion selective electrode with intermediate conducting polymer (CP) layer formed by electropolymerization on a gold electrode of a bifunctional monomer, n-phenyl-ethylenediamine-methacrylamide (NPEDMA), which contains a methacrylamide group attached to aniline, is presented. The conducting polymer was studied by means of optical spectroscopy, cyclic voltammetry and potentiometric measurements. Ca2+-ion-selective membrane based on acrylated urethane polymer was shown to co-polymerize with the CP forming highly adhesive boundary that prevents formation of water layers between the CP and membrane, thus enhancing the stability and life-time of the sensor. The designed ion-selective electrode was successfully used for determination of total calcium ion concentration in blood serum samples.

Dual chronoamperometric detection of enzymatic biomarkers using magnetic beads and a low-cost flow cell.

In this work we report on the production of a low cost microfluidic device for the multiplexed electrochemical detection of magneto bioassays. As a proof of concept, the device has been used to detect myeloperoxidase (MPO), a cardiovascular biomarker. With this purpose, two bioassays have been optimized in parallel onto magnetic beads (MBs) for the simultaneous detection of MPO endogenous peroxidase activity and quantification of total MPO. Since the two bioassays produced signals of different magnitude for each concentration of MPO tested, two detection strategies have been compared, which entailed registering steady state currents (Iss) under substrate flow, and measuring the peak currents (Ip) produced in a stopped flow approach. As it will be shown, appropriate tuning of the detection and flow conditions can provide extremely sensitive detection, but also allow simultaneous detection of assays or parameters that would produce signals of different orders of magnitude when measured by a single detection strategy. In order to demonstrate the feasibility of the detection strategy reported, a dual MPO mass and activity assay has been finally applied to the study of 10 real plasma samples, allowing patient classification according to the risk of suffering a cardiovascular event.