Interchangeable Biomass Fuels for Paper-Based Microfluidic Fuel Cells: Finding Their Power Density Limits.

Paper batteries are self-pumping emerging tools for powering portable analytical systems. These disposable energy converters must be low-cost and must achieve enough energy to power electronic devices. The challenge is reaching high energy while keeping the low cost. Here, for the first time, we report a paper-based microfluidic fuel cell (PµFC) equipped with Pt/C on a carbon paper (CP) anode and a metal-free CP cathode fed by biomass-derived fuels to deliver high power. The cells were engineered in a mixed-media configuration, where methanol, ethanol, ethylene glycol, or glycerol is electro-oxidized in an alkaline medium, while Na2S2O8 is reduced in an acidic medium. This strategy allows for optimizing each half-cell reaction independently. The colaminar channel of the cellulose paper was chemically investigated by mapping the composition, which reveals a majority of elements from the catholyte and anolyte on each respective side and a mixture of both at the interface, assuring the existing colaminar system. Moreover, the colaminar flow was studied by investigating the flow rate by considering recorded videos for the first time. All PµFCs show 150-200 s to build a stable colaminar flow, which matches the time to reach a stable open circuit voltage. The flow rate is similar for different concentrations of methanol and ethanol, but it decreases with the increase in ethylene glycol and glycerol concentrations, suggesting a longer residence time for the reactants. The cells perform differently for the different concentrations, and their limiting power densities are composed of a balance among anode poisoning, residence time, and viscosity of the liquids. The sustainable PµFCs can be interchangeably fed by the four biomass-derived fuels to deliver ∼2.2-3.9 mW cm-2. This allows choosing the proper fuel due to their availability. The unprecedented PµFC fed by ethylene glycol delivered 6.76 mW cm-2, which is the benchmark output power for a paper battery fed by alcohol.

Host-Guest Chemistry in Boron Nitride Nanotubes: Interactions with Polyoxometalates and Mechanism of Encapsulation.

Boron nitride nanotubes (BNNTs) are an emerging class of molecular container offering new functionalities and possibilities for studying molecules at the nanoscale. Herein, BNNTs are demonstrated as highly effective nanocontainers for polyoxometalate (POM) molecules. The encapsulation of POMs within BNNTs occurs spontaneously at room temperature from an aqueous solution, leading to the self-assembly of a POM@BNNT host-guest system. Analysis of the interactions between the host-nanotube and guest-molecule indicate that Lewis acid-base interactions between W═O groups of the POM (base) and B-atoms of the BNNT lattice (acid) likely play a major role in driving POM encapsulation, with photoactivated electron transfer from BNNTs to POMs in solution also contributing to the process. The transparent nature of the BNNT nanocontainer allows extensive investigation of the guest-molecules by photoluminescence, Raman, UV-vis absorption, and EPR spectroscopies. These studies revealed considerable energy and electron transfer processes between BNNTs and POMs, likely mediated via defect energy states of the BNNTs and resulting in the quenching of BNNT photoluminescence at room temperature, the emergence of new photoluminescence emissions at cryogenic temperatures (<100 K), a photochromic response, and paramagnetic signals from guest-POMs. These phenomena offer a fresh perspective on host-guest interactions at the nanoscale and open pathways for harvesting the functional properties of these hybrid systems.

Blurring the boundary between homogenous and heterogeneous catalysis using palladium nanoclusters with dynamic surfaces.

Using a magnetron sputtering approach that allows size-controlled formation of nanoclusters, we have created palladium nanoclusters that combine the features of both heterogeneous and homogeneous catalysts. Here we report the atomic structures and electronic environments of a series of metal nanoclusters in ionic liquids at different stages of formation, leading to the discovery of Pd nanoclusters with a core of ca. 2 nm surrounded by a diffuse dynamic shell of atoms in [C4C1Im][NTf2]. Comparison of the catalytic activity of Pd nanoclusters in alkene cyclopropanation reveals that the atomically dynamic surface is critically important, increasing the activity by a factor of ca. 2 when compared to compact nanoclusters of similar size. Catalyst poisoning tests using mercury and dibenzo[a,e]cyclooctene show that dynamic Pd nanoclusters maintain their catalytic activity, which demonstrate their combined features of homogeneous and heterogeneous catalysts within the same material. Additionally, kinetic studies of cyclopropanation of alkenes mediated by the dynamic Pd nanoclusters reveal an observed catalyst order of 1, underpinning the pseudo-homogeneous character of the dynamic Pd nanoclusters.

Decoupling manufacturing from application in additive manufactured antimicrobial materials.

3D printable materials based on polymeric ionic liquids (PILs) capable of controlling the synthesis and stabilisation of silver nanoparticles (AgNPs) and their synergistic antimicrobial activity are reported. The interaction of the ionic liquid moieties with the silver precursor enabled the controlled in situ formation and stabilisation of AgNPs via extended UV photoreduction after the printing process, thus demonstrating an effective decoupling of the device manufacturing from the on-demand generation of nanomaterials, which avoids the potential aging of the nanomaterials through oxidation. The printed devices showed a multi-functional and tuneable microbicidal activity against Gram positive (B. subtilis) and Gram negative (E. coli) bacteria and against the mould Aspergillus niger. While the polymeric material alone was found to be bacteriostatic, the AgNPs conferred bactericidal properties to the material. Combining PIL-based materials with functionalities, such as in situ and photoactivated on-demand fabricated antimicrobial AgNPs, provides a synergistic functionality that could be harnessed for a variety of applications, especially when coupled to the freedom of design inherent to additive manufacturing techniques.

Selective suppression of {112} anatase facets by fluorination for enhanced TiO2 particle size and phase stability at elevated temperatures.

Generally, anatase is the most desirable TiO2 polymorphic phase for photovoltaic and photocatalytic applications due to its higher photoconductivity and lower recombination rates compared to the rutile phase. However, in applications where temperatures above 500 °C are required, growing pure anatase phase nanoparticles is still a challenge, as above this temperature TiO2 crystallite sizes are larger than 35 nm which thermodynamically favors the growth of rutile crystallites. In this work, we show strong evidence, for the first time, that achieving a specific fraction (50%) of the {112} facets on the TiO2 surface is the key limiting step for anatase-to-rutile phase transition, rather than the crystallite size. By using a fluorinated ionic liquid (IL) we have obtained pure anatase phase crystallites at temperatures up to 800 °C, even after the crystallites have grown beyond their thermodynamic size limit of ca. 35 nm. While fluorination by the IL did not affect {001} growth, it stabilized the pure anatase TiO2 by suppressing the formation of {112} facets on anatase particles. By suppressing the {112} facets, using specific concentrations of fluorinated ionic liquid in the TiO2 synthesis, we controlled the anatase-to-rutile phase transition over a wide range of temperatures. This information shall help synthetic researchers to determine the appropriate material conditions for specific applications.

Harvesting Energy from an Organic Pollutant Model Using a New 3D-Printed Microfluidic Photo Fuel Cell.

The combination of a fuel cell and photocatalysis in the same device, called a photo fuel cell, is the next generation of energy converters. These systems aim to convert organic pollutants and oxidants into energy using solar energy as the driving force. However, they are mostly designed in conventional stationary batch systems, generating low power besides being barely applicable. In this context, membraneless microfluidics allows the use of flow, porous electrodes, and mixed media, improving reactant utilization and output power accordingly. Here, we report an unprecedented reusable three-dimensional (3D) printed microfluidic photo fuel cell (µpFC) assembled with low-content PtOx/Pt dispersed on a BiVO4 photoanode and a Pt/C dark cathode, both immobilized on carbon paper. We use fused deposition modeling for additive manufacturing a US$ 2.5 µpFC with a polylactic acid filament. The system shows stable colaminar flow and a short time light distance. As a proof-of-concept, we used the pollutant-model rhodamine B as fuel, and O2 in an acidic medium at the cathode side. The mixed-media 3D printed µpFC with porous electrodes produces remarkable 0.48 mW cm-2 and 4.09 mA cm-2 as maximum power and current densities, respectively. The system operates continuously for more than 5 h and converts 73.6% rhodamine by photoelectrochemical processes. The 3D printed µpFC developed here shows promising potential for pollutant mitigation concomitantly to power generation, besides being a potential platform of tests for new (photo)electrocatalysts.

Redox-Active Hybrid Polyoxometalate-Stabilised Gold Nanoparticles.

We report the design and preparation of multifunctional hybrid nanomaterials through the stabilization of gold nanoparticles with thiol-functionalised hybrid organic-inorganic polyoxometalates (POMs). The covalent attachment of the hybrid POM forms new nanocomposites that are stable at temperatures and pH values which destroy analogous electrostatically functionalised nanocomposites. Photoelectrochemical analysis revealed the unique photochemical and redox properties of these systems.

Cerium Oxide Nanoparticles Inside Carbon Nanoreactors for Selective Allylic Oxidation of Cyclohexene.

The confinement of cerium oxide (CeO2) nanoparticles within hollow carbon nanostructures has been achieved and harnessed to control the oxidation of cyclohexene. Graphitized carbon nanofibers (GNF) have been used as the nanoscale tubular host and filled by sublimation of the Ce(tmhd)4 complex (where tmhd = tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)) into the internal cavity, followed by a subsequent thermal decomposition to yield the hybrid nanostructure CeO2@GNF, where nanoparticles are preferentially immobilized at the internal graphitic step-edges of the GNF. Control over the size of the CeO2 nanoparticles has been demonstrated within the range of about 4-9 nm by varying the mass ratio of the Ce(tmhd)4 precursor to GNF during the synthesis. CeO2@GNF was effective in promoting the allylic oxidation of cyclohexene in high yield with time-dependent control of product selectivity at a comparatively low loading of CeO2 of 0.13 mol %. Unlike many of the reports to date where ceria catalyzes such organic transformations, we found the encapsulated CeO2 to play the key role of radical initiator due to the presence of Ce3+ included in the structure, with the nanotube acting as both a host, preserving the high performance of the CeO2 nanoparticles anchored at the GNF step-edges over multiple uses, and an electron reservoir, maintaining the balance of Ce3+ and Ce4+ centers. Spatial confinement effects ensure excellent stability and recyclability of CeO2@GNF nanoreactors.

Correction: Highly modulated supported triazolium-based ionic liquids: direct control of the electronic environment on Cu nanoparticles.

[This corrects the article DOI: 10.1039/D0NA00055H.].

Highly modulated supported triazolium-based ionic liquids: direct control of the electronic environment on Cu nanoparticles.

A series of new triazolium-based supported ionic liquids (SILPs), decorated with Cu NPs, were successfully prepared and applied to the N-arylation of aryl halides with anilines. The triazoles moieties were functionalised using copper-catalysed azide-alkyne cycloaddition. SILP surface characterisation showed a strong correlation between the triazolium cation volume and textural properties. STEM images showed well-dispersed Cu NPs on SILPs with a mean diameter varying from 3.6 to 4.6 nm depending on the triazolium cation used. Besides, XPS results suggest that the Cu(0)/Cu(i) ratio can be modulated by the electronic density of triazolium substituents. XPS and computational analysis gave mechanistic insights into the Cu NP stabilisation pathways, where the presence of electron-rich groups attached to a triazolium ring plays a critical role in leading to a cation adsorption pathway (E ads = 72 kcal mol-1). In contrast, less electron-rich groups favour the anion adsorption pathway (E ads = 63 kcal mol-1). The Cu@SILP composite with electron-rich groups showed the highest activity for the C-N Ullmann coupling reaction, which suggests that electron-rich groups might act as an electron-like reservoir to facilitate oxidative addition for N-arylation. This strategy firmly suggests the strong dependence of the nature of triazolium-based SILPs on the Cu NP surface active sites, which may provide a new environment to confine and stabilise MNPs for catalytic applications.

Reverse Semi-Combustion Driven by Titanium Dioxide-Ionic Liquid Hybrid Photocatalyst.

Unprecedented metal-free photocatalytic CO2 conversion to CO (up to 228±48 µmol g-1 h-1) was displayed by TiO2@IL hybrid photocatalysts prepared by simple impregnation of commercially available P25-titanium dioxide with imidazolium-based ionic liquids (ILs). The high activity of TiO2@IL hybrid photocatalysts was mainly associated to (i) TiO2@IL red shift compared to the pure TiO2 absorption, and thus a modification of the TiO2 surface electronic structure; (ii) TiO2 with IL bearing imidazolate anions lowered the CO2 activation energy barrier. The reaction mechanism was postulated to occur via CO2 photoreduction to formate species by the imidazole/imidazole radical redox pair, yielding CO and water.