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Materials for thermal management of buildings offer an attractive approach to reduce energy demands and carbon emissions in the infrastructure sector, but many of the state-of-the-art insulators are still expensive, flammable, or difficult to recycle. Here, a 3D printing process is developed and studied to create hierarchical porous ceramics for thermal insulation and passive cooling using recyclable and widely available clay as raw material. Inks comprising particle-stabilized foams are employed as a template for the generation of the hierarchical porosity. Using foams with optimized rheological properties, the printing parameters and sintering conditions required for the manufacturing of hierarchical porous ceramics via Direct Ink Writing are established. The sintering temperature is found to strongly affect the size distribution of micropores, thus controlling the mechanical, thermal, and evaporative cooling properties of sintered printed structures. By combining suspension- and foam-based inks in a multimaterial printing approach, inexpensive and recyclable clay-based bricks are manufactured with structural, thermal insulating, and passive cooling capabilities., Advanced Materials Technologies, 8 (4), ISSN:2365-709X

Porous ceramics are demanded in a wide range of high-temperature, biological and energy-related applications, but may show conflicting properties or suffer from poor mechanical properties. Introducing pores at different length scales has been shown to be a promising design strategy to combine antagonistic performance parameters and reach high porosity without severely compromising strength. Here, a cost-effective and simple process to create strong, highly porous ceramics via direct ink writing of suspensions of hollow microspheres into cellular architectures with pores at three hierarchical levels is reported. X-ray diffraction, rheological measurements, scanning electron microscopy, and mechanical tests are conducted to thoroughly study the processing steps and morphology of the printed hierarchical porous ceramics. The presence of pores at multiple length scales increases significantly the mechanical strength of the porous structure, providing a useful platform for the manufacturing of lightweight ceramics from inexpensive and widely available feedstock materials., Advanced Materials Technologies, ISSN:2365-709X

The use of biodegradable and nontoxic cellulose as a renewable alternative to plastic in electronics is a promising way to decrease the environmental pollution. Unfortunately, cellulose lacks one o...

Porous carbon ablators offer cost-effective thermal protection for aerospace vehicles during re-entry into planetary atmospheres. However, the exploration of more distant planets requires the development of ablators that are able to withstand stronger thermal radiation conditions. Here, we report the development of bio-inspired porous carbon insulators with pore sizes that are deliberately tuned to enhance heat-shielding performance by increasing scattering of high-temperature thermal radiation. Pore size intervals that promote scattering are first estimated using an established model for the radiative contribution to the thermal conductivity of porous insulators. On the basis of this theoretical analysis, we identify a polymer additive that enables the formation of pores in the desired size range through the polymerization-induced phase separation of a mixture of phenolic resin and ethylene glycol. Optical and electron microscopy, porosimetry and mechanical tests are used to characterize the structure and properties of porous insulators prepared with different resin formulations. Insulators with pore sizes in the optimal scattering range reduce laser-induced damage of the porous structures by up to 42%, thus offering a promising and simple route for the fabrication of carbon ablators for enhanced thermal protection at high temperatures., Carbon, 195, ISSN:0008-6223

The interest of nanoparticle-based aerogels-3-dimensional (3D) nanoparticle assemblies of macroscopic sizes-in photocatalysis is mainly their versatility for tailoring properties. However, little is known about the true viability of the aerogels as photocatalysts in part because of their 3D structure that is unusual for this application. Here, we investigate the mass and light transport effectiveness in the whole aerogel network and evaluate their photoactivity. We used anatase-based aerogels as model samples and designed a continuous-flow reactor to perform such analyses. It was found that the photons with suitable energy to initiate the reaction can propagate through the entire monolith because of their diffusive transport, making the 3D network fully active. The mass transport in the aerogels was also effective but is influenced by the reactor design. The aerogels showed promising activity, e.g., Pd-anatase aerogels with a volume of only 0.5 +/- 0.04 cm(3) generated 92 mu mol h(-1) of H-2 with an apparent quantum efficiency of 13% at 375 nm., Journal of Materials Chemistry A, 9 (39), ISSN:2050-7488, ISSN:2050-7496

Mesocrystals are superstructures of crystallographically aligned nanoparticles and are a rapidly emerging class of crystalline materials displaying sophisticated morphologies and properties, beyond those originating from size and shape of nanoparticles alone. This study reports the first synthesis of Cu3N mesocrystals employing structure-directing agents with a subtle tuning of the reaction parameters. Detailed structural characterizations carried out with a combination of transmission electron microscopy techniques (HRTEM, HAADF-STEM-EXDS) reveal that Cu3N mesocrystals form by non-classical crystallization, and variations in their sizes and morphologies are traced back to distinct attachment scenarios of corresponding mesocrystal subunits. In the presence of oleylamine, the mesocrystal subunits in the early reaction stages prealign in a crystallographic fashion and afterwards grow into the final mesocrystals, while in the presence of hexadecylamine the subunits come into contact through misaligned attachment, and subsequently, to some degree, realign in crystallographic register. Upon prolonged heating both types of mesocrystals undergo chemical conversion processes resulting in structural and morphological changes. A two-step mechanism of chemical conversion is proposed, involving Cu3N decomposition and anion exchange driven by the nanoscale Kirkendall effect, resulting first in multicomponent/heterostructured Cu3N–Cu2O mesocrystals, which subsequently convert into Cu2O nanocages. It is anticipated that combining nanostructured Cu3N and Cu2O in a mesocrystalline and hollow morphology will provide a platform to expand their application potential.

Harvesting solar energy and efficiently converting it into a chemical energy carrier like hydrogen (H-2) is an important topic in photocatalysis. Here, we present a fast and simple approach for the one-pot synthesis of crystalline semiconductor nanoparticles modified with co-catalysts that can be used as nanobuilding blocks for nanoparticle-based aerogels with excellent visible-light photocatalytic activity. The microwave-assisted nonaqueous sol-gel method allows titanium dioxide (TiO2) nanoparticles to be synthesized and modified with palladium (Pd) ions and Pd metal nanoparticles in a single step. Their assembly into aerogel monoliths preserves the modified properties of the TiO2 nanobuilding blocks, resulting in morphological properties that are advantageous for the photocatalytic H-2 production from methanol (CH3OH) oxidation. By controlling the amount of Pd doping and Pd nanoparticle loading, the nanoparticle-based aerogels showed significantly improved photoexcited charge generation and separation efficiency under visible light. In addition, we present a novel reactor design specifically developed for 3D aerogel monoliths that allows control of light intensity, gas flow, reactant concentration, and temperature, enabling the study of all key experimental parameters to optimize photocatalytic H-2 production. The visible light absorbed by the aerogels was found to be the driving force behind the efficient photocatalytic activity. Our Pd modified TiO2 nanoparticle-based aerogels achieved H-2 production rate of 117.5 mmol g(-1) h(-1) with good stability for 3 days under visible light thanks to the prevention of carbon monoxide (CO) poisoning. The simultaneous optimization of the material composition and the matching photoreactor form the decisive basis for getting the most out of monolithic 3D photocatalysts., Journal of Materials Chemistry A, 10 (35), ISSN:2050-7488, ISSN:2050-7496

The cost benefit and inherent safety conferred by the energy-dense metallic zinc anode and mildly acidic aqueous electrolytes are critical to aqueous zinc batteries’ (AZBs) large-scale energy-storage ambition. Aggressive research efforts in the past five years have resulted in the discovery of several high-energy positive (cathode) host materials, but understanding of the Zn anode rechargeability and any influence of the electrolyte, which are critical for AZBs’ practical development, remains limited. As we unravel here, under realistic test conditions, when parameters are set keeping practical applications in mind, Zn anode cycling appears vulnerable to dendritic failure in all common AZB electrolytes. While 3 M ZnSO4 delivers the best overall performance for the Zn anode cycling, viability of the oxidatively stable “water in salt” electrolyte appears gravely restricted. Defying the general understanding of metal electrodeposition, a high current density is found to dramatically prolong the Zn cycling li...

Monolithic aerogels composed of crystalline nanoparticles enable photocatalysis in three dimensions, but they suffer from low mechanical stability and it is difficult to produce them with complex geometries. Here, an approach to control the geometry of the photocatalysts to optimize their photocatalytic performance by introducing carefully designed 3D printed polymeric scaffolds into the aerogel monoliths is reported. This allows to systematically study and improve fundamental parameters in gas phase photocatalysis, such as the gas flow through and the ultraviolet light penetration into the aerogel and to customize its geometric shape to a continuous gas flow reactor. Using photocatalytic methanol reforming as a model reaction, it is shown that the optimization of these parameters leads to an increase of the hydrogen production rate by a factor of three from 400 to 1200 µmol g−1 h−1. The rigid scaffolds also enhance the mechanical stability of the aerogels, lowering the number of rejects during synthesis and facilitating handling during operation. The combination of nanoparticle-based aerogels with 3D printed polymeric scaffolds opens up new opportunities to tailor the geometry of the photocatalysts for the photocatalytic reaction and for the reactor to maximize overall performance without necessarily changing the material composition. ISSN:1613-6810 ISSN:1613-6829

The development of visible light-active photocatalysts is essential for increasing the conversion efficiency of solar energy into hydrogen (H2). Here, we present a facile method for nitrogen doping of monolithic titanium dioxide (TiO2) nanoparticle-based aerogels to activate them for visible light. Plasma-enhanced chemical vapor deposition at low temperature enables efficient incorporation of nitrogen into preformed TiO2 aerogels without compromising their advantageous intrinsic characteristics such as large surface area, extensive porosity, and nanoscale properties of the semiconducting building blocks. By balancing the dopant concentration and the defects, the nitridation improves optical absorption and charge separation efficiency. The nitrogen-doped TiO2 nanoparticle-based aerogels loaded with palladium (Pd) nanoparticles show a significant enhancement in visible light-driven photocatalytic H2 production (3.1 mmol h–1 g–1) with excellent stability over 5 days. With this method, we introduce a powerful tool to tune the properties of nanoparticle-based aerogels after synthesis for a specific application, as exemplified by visible light-driven H2 production. ISSN:1944-8244 ISSN:1944-8252

The development of visible light-active photocatalysts is essential for increasing the conversion efficiency of solar energy into hydrogen (H

Mesocrystals are superstructures of crystallographically aligned nanoparticles and are a rapidly emerging class of crystalline materials displaying sophisticated morphologies and properties, beyond those originating from size and shape of nanoparticles alone. This study reports the first synthesis of Cu

Transparent electronic devices are opening up unprecedented possibilities in display technology and virtual reality. For some of these applications, it would be advantageous if optical transparency could be combined with stretchability. Of course, all portable electronic devices need an energy source, which is ideally integrated in the form of a battery and must therefore fulfill the same physical properties. However, it is quite challenging to develop a battery in which all the components (electrodes, current collectors, separator/electrolyte, and packaging) are transparent and stretchable. Here we present the development of a transparent and stretchable full zinc ion battery comprising two electrodes deposited on a polydimethylsiloxane (PDMS) substrate and a polyacrylamide (PAM) hydrogel electrolyte. The resulting stretchable battery shows a high transmittance of 72.6% and 64.7% at 550 nm without and with 50% strain, respectively. The battery provides a capacity of 176.5 mA h g–1 after 120 cycles under varying strain conditions up to 50%. The battery’s multifunctionality, linking energy storage with stretchability and transparency, makes it attractive for powering future transparent and stretchable electronics. ISSN:2574-0962

Thermal insulators are crucial to reduce the high energy demands and greenhouse emissions in the construction sector. However, the fabrication of insulating materials that are cost-effective, fire ...

Benzyl alcohol is a versatile reaction medium for the synthesis of different types of nanoparticles. Its ability to act as an oxygen source gave access to metal oxide nanoparticles, while its reducing properties can be harnessed for the preparation of metals. Here we report the synthesis of Pd and PdCu nanoparticles in benzyl alcohol supplemented by a detailed mechanistic study for both systems. To elucidate the chemical formation mechanism of the Pd nanoparticles, we performed in situ attenuated total reflection ultraviolet–visible (ATR-UV–vis) and Fourier transform infrared spectroscopy (ATR-FTIR), providing information on the organic as well as on the inorganic side of the reaction. Potential gaseous products were analyzed by in situ gas chromatography (GC) and mass spectrometry (MS). We observed the formation of benzaldehyde, toluene, and dibenzyl ether as the three main organic products. The formation of the PdCu alloy nanoparticles was studied by ex situ powder X-ray diffraction (PXRD). A time-resolved study of the synthesis at 100 °C indicated that initially three types of particles formed, composed of an alloy with high Pd content, an alloy with high content of copper, and palladium particles, and only later in the reaction course they transformed into an alloy with a Pd-to-Cu ratio close to 1. ISSN:0928-0707 ISSN:1573-4846

Hollow and dense SnS sub-microspheres constructed from self-assembled nanosheets wrapped in a nitrogen-doped carbon shell were prepared by a low-cost, facile solvothermal process followed by annealing. The lithium-ion storage capacities of the hollow and dense spheres were tested and compared as anodes in lithium-ion battery half cells. The hollow microspheres showed low internal charge transfer resistance, good buffering of volume changes during lithiation and delithiation and good rate and cycling performance. After 1000 cycles, the hollow SnS composite still delivered a capacity of 420 mA h g−1 at 1.0 A g−1, which is 2.5 times higher than that of the dense spheres. The capacity retention from the second cycle on was 84% and 75%, respectively. The superior lithium storage performance of the hollow particles arise from their pronounced porosity, hierarchical architecture from the self-assembled nanosheets and well-controlled uniform carbon shells., CrystEngComm, 22 (9), ISSN:1466-8033

Motivated by the hierarchical micro and nanoscale features in terms of porosity of diatomite, the production of ceramic-graded porous foams with tailored porosity, obtained by using it as raw material, has been proposed. The main challenge during the foam-production process has been the preservation of diatomite nanometric porosity and the addition of other levels of hierarchical porosity. The coupled use of two techniques of direct foaming (chemical and mechanical), combined with the use of 3D printing inverse replica method, assured the achievement of porosity of, respectively, microscopic and macroscopic dimensions. Optical and scanning electron microscopies have been performed for an in-depth characterization of the final microstructure. XRD analysis has been carried out to check the influence of sacrificial templates on the matrix mineralogical composition. The porosity of the diatomite-based foams has been investigated by means of nitrogen-adsorption analysis and mercury-intrusion porosimetry. The experimental tests confirmed the presence of different porous architectures ranging over several orders of magnitudes, giving rise to complex systems, characterized by hierarchical levels of porosity. The presence of porosity of graded dimensions affects the final mechanical performances of the macroporous diatomite-based foams, while their mineralogical composition does not result to be affected by the addition of templates., Scientific Reports, 10 (1), ISSN:2045-2322

Hybrid aerogels composed of functional low-dimensional nanomaterials (LDNs) and reduced graphene oxide (rGO) hold great promise in fields ranging from catalysis to energy storage and conversion. However, the challenge of developing a general strategy for the hierarchical assembly of LDNs on rGO aerogels remains unsolved. Here, we propose a surface energy-driven strategy for ex situ hierarchical assembly of LDNs on preformed rGO aerogels. This strategy is versatile and generally applicable to a broad variety of LDNs regardless of their composition, shapes, and dimensionalities. Experimental and simulation results reveal that the organically modified, energetically stable LDNs thermodynamically tend to uniformly and densely reside on the rGO aerogels, thereby reducing the surface energy of the aerogels and the free energy of the solution system. Four kinds of LDNs are successfully decorated on rGO aerogels, including 0D Mn3O4 nanocubes and Ag nanospheres, and 1D TiO2 nanochains and SnO2 nanowires. As a possible application harnessing the unique structural features of these materials, the Mn3O4@rGO hybrid aerogels were tested as anodes in lithium ion battery half cells, delivering a high reversible lithium storage capacity (1.35 mA h cm−2 at 3.5 mA cm−2) at high mass loading density (up to 7 mg cm−2).

Nanocrystalline Ba0.5Sr0.5Co0.8Fe0.2O3-? powders were prepared by a cost-effective solvent-deficient method using metal nitrates and ammonium bicarbonate as precursors. X-ray diffraction (XRD), specific surface determination (BET), thermal analyses (TG-DTA-DSC), dynamic light scattering (DLS) and scanning electron microscopy (SEM) were used to examine the effects of the calcination temperature on the Ba0.5Sr0.5Co0.8Fe0.2O3-? (BSCF) formation. XRD analysis showed that a cubic Ba0.5Sr0.5Co0.8Fe0.2O3-? was obtained after heating for 1 h at 1000?C. BSCF nanocrystals with a diameter of about 25 nm were obtained. On the other hand, the sample mass was stabilized at 915?C as recorded by thermogravimetric analysis (TG), indicating a formation of the complex BSCF oxide already at this temperature. The phase transformations during the synthesis of BSCF oxide are defined and confirmed with the note on the instability of the cubic phase. Using the four-point DC measurements between ?73?C and 127?C, the band gap of 0.84 eV was determined. The solvent-deficient method used in this study to synthesize Ba0.5Sr0.5Co0.8Fe0.2O3-? showed distinct advantages in comparison with other synthesis techniques considering simplicity, rapid synthesis, and quality of the produced nanocrystals.

Luminescent nanoparticles are researched for their potential impact in medical science, but no materials approved for parenteral use have been available so far. To overcome this issue, we demonstrate that Eu3+-doped hafnium dioxide nanocrystals can be used as non-toxic, highly stable probes for cellular optical imaging and as radiosensitive materials for clinical treatment. Furthermore, viability and biocompatibility tests on artificially stressed cell cultures reveal their ability to buffer reactive oxygen species, proposing an anti-cytotoxic feature interesting for biomedical applications.

3D printing via direct ink writing (DIW) is a versatile additive manufacturing approach applicable to a variety of materials ranging from ceramics over composites to hydrogels. Due to the mild processing conditions compared to other additive manufacturing methods, DIW enables the incorporation of sensitive compounds such as proteins or drugs into the printed structure. Although emulsified oil-in-water systems are commonly used vehicles for such compounds in biomedical, pharmaceutical, and cosmetic applications, printing of such emulsions into architectured soft materials has not been fully exploited and would open new possibilities for the controlled delivery of sensitive compounds. Here, we 3D print concentrated emulsions into soft materials, whose multiphase architecture allows for site-specific incorporation of both hydrophobic and hydrophilic compounds into the same structure. As a model ink, concentrated emulsions stabilized by chitosan-modified silica nanoparticles are studied, because they are sufficiently stable against coalescence during the centrifugation step needed to create a bridging network of droplets. The resulting ink is ideal for 3D printing as it displays high yield stress, storage modulus and elastic recovery, through the formation of networks of droplets as well as of gelled silica nanoparticles in the presence of chitosan. To demonstrate possible architectures, we print biocompatible soft materials with tunable hierarchical porosity containing an encapsulated hydrophobic compound positioned in specific locations of the structure. The proposed emulsion-based ink system offers great flexibility in terms of 3D shaping and local compositional control, and can potentially help address current challenges involving the delivery of incompatible compounds in biomedical applications.

We present the nonaqueous sol–gel synthesis of crystalline SrTi1−xCrxO3 (x = 0, 0.3, 2, 5, 10%) nanoparticles and their processing into highly concentrated dispersions in ethanol by surface functionalization with 2-[2-(2-methoxyethoxy) ethoxy] acetic acid (MEEAA). These stable nanoparticle dispersions can then be assembled into 2- and 3-dimensional architectures such as films and aerogels. Homogeneous transparent films with a compact microstructure and a thickness of 140 nm are prepared from the dispersion by dip coating, while efficient destabilization and supercritical drying results in nanostructured bulk aerogels with a high surface area of up to 370 m2 g−1.

Although aerogels prepared by the colloidal assembly of nanoparticles are a rapidly emerging class of highly porous and low-density materials, their ambient dried counterparts, namely xerogels, have hardly been explored. Here we report the use of nanoparticle-based BaTiO3 xerogels as green bodies, which provide a versatile route to ceramic materials under the minimization of organic additives with a significant reduction of the calcination temperature compared to that of conventional powder sintering. The structural changes of the xerogels are investigated during ambient drying by carefully analyzing the microstructure at different drying stages. For this purpose, the shrinkage was arrested by a supercritical drying step under full preservation of the intermediate microstructure, giving unprecedented insight into the structural changes during ambient drying of a nanoparticle-based gel. In a first step, the large macropores shrink because of capillary forces, followed by the collapse of residual mesopores ...

Edible solid particles constitute an attractive alternative to surfactants as stabilizers of food-grade emulsions for products requiring a long-term shelf life. Here, we report on a new approach to stabilize edible emulsions using silica nanoparticles modified by noncovalently bound chitosan oligomers. Electrostatic modification with chitosan increases the hydrophobicity of the silica nanoparticles and favors their adsorption at the oil-water interface. The interfacial adsorption of the chitosan-modified silica particles enables the preparation of oil-in-water emulsions with small droplet sizes of a few micrometers through high-pressure homogenization. This approach enables the stabilization of food-grade emulsions for more than 3 months. The emulsion structure and stability can be effectively tuned by controlling the extent of chitosan adsorption on the silica particles. Bulk and interfacial rheology are used to highlight the two stabilization mechanisms involved. Low chitosan concentration (1 wt % with respect to silica) leads to the formation of a viscoelastic film of particles adsorbed at the oil-water interface, enabling Pickering stabilization of the emulsion. By contrast, a network of agglomerated particles formed around the droplets is the predominant stabilization mechanism of the emulsions at higher chitosan content (5 wt % with respect to silica). These two pathways against droplet coalescence and coarsening open up different possibilities to engineer the long-term stabilization of emulsions for food applications.

Compared to the progress made in high-rate anodes, the exploration of cathode materials with comparable performance remains a challenge in the fabrication of high power Li-ion storage devices. Here a cathode material with fast Li-ion storage is reported, which is composed of Ni0.25V2O5·nH2O nanobelts with a layered structure and reduced graphene oxide. Operando X-ray diffraction and ex situ X-ray photoelectron spectroscopy results reveal an electrochemical process with high structural reversibility during charging/discharging. Kinetics analysis based on cyclic voltammetry measurements demonstrates fast Li-ion storage in the cathode material. These positive properties lead to high rate capability and cycling stability of the composite. Even at a high mass loading of 11.3 mg cm−2, the material still offers high-performance Li-ion storage, indicating its great promise for practical applications. Furthermore, we report for the first time the combination of such a high-rate cathode with a surface redox pseudocapacitive anode made of N-doped reduced graphene oxide foam for a fast-charging Li-ion storage full-cell device with a long lifespan. The high performance of the full cell suggests that the concept of using materials with fast Li-ion storage in both the positive and negative electrodes represents a promising strategy to develop high-power and high-energy Li-ion storage devices., Journal of Materials Chemistry A, 7 (39), ISSN:2050-7488, ISSN:2050-7496

Layer-structured metal vanadates have been regarded as promising candidates for high-rate Na-ion storage. However, without a detailed understanding of the relationship between the interlayer metal ions and the cycling performance, it remains a difficult task to systematically explore layered metal vanadates as high performance electrode materials. Herein, a series of metal vanadates with different interlayer cations such as Co2+ and Zn2+ are prepared and applied as Na-ion battery anodes. First principles simulations and ex situ X-ray diffraction measurements demonstrate that the Na-ion storage performance of the layered metal vanadates is closely related to the structural stress induced by Na+ insertion, and the ion diffusion barrier, as well as the structural reversibility. In addition, a double-interlayer-cation metal vanadate, i.e., Co0.16Zn0.09V2O5·nH2O, is reported for the first time as a high-rate Na-ion battery anode. This compound successfully combines the favorable features of Co0.25V2O5·nH2O and Zn0.25V2O5·nH2O, resulting in the best cycling performance. CV analysis and operando X-ray diffraction measurements reveal a large pseudocapacitive contribution and small volume change of Co0.16Zn0.09V2O5·nH2O during cycling. Our study presents a versatile concept for the optimization of metal vanadates for Na-ion storage, which may open a promising direction for developing high-rate energy storage materials., Journal of Materials Chemistry A, 7 (27), ISSN:2050-7488, ISSN:2050-7496

Agglomeration of copper nanowires (aspect ratios on the order of 1000) in polyethylene, commonly a major problem, could be prevented by modification of the nanowires with a surface layer of oleylamine. Nanocomposite films were prepared by mixing nanowire dispersions in organic solvents with polyethylene solutions followed by casting, drying, and sometimes hot pressing. Orientation of the copper nanowires by solid-state drawing of the composites at elevated temperatures led to preferential alignment of the nanowires in the drawing direction. This arrangement gave rise to a uniform dichroism in the near-infrared (NIR) region, which is uncommon in the case of the hitherto reported dichroic nanocomposites. The NIR dichroism is ascribed to the high aspect ratio of the metal wires. Hence, drawing of isotropic nanocomposites with metal wires may serve for the manufacture of NIR polarization filters., ACS Omega, 4 (6), ISSN:2470-1343

Hierarchical porous materials are widespread in nature and find an increasing number of applications as catalytic supports, biological scaffolds and lightweight structures. Recent advances in additive manufacturing and 3D printing technologies have enabled the digital fabrication of porous materials in the form of lattices, cellular structures and foams across multiple length scales. However, current approaches do not allow for the fast manufacturing of bulk porous materials featuring pore sizes that span broadly from macroscopic dimensions down to the nanoscale. Here, ink formulations are designed and investigated to enable 3D printing of hierarchical materials displaying porosity at the nano-, micro- and macroscales. Pores are generated upon removal of nanodroplets and microscale templates present in the initial ink. Using particles to stabilize the droplet templates is key to obtain Pickering nanoemulsions that can be 3D printed through direct ink writing. The combination of such self-assembled templates with the spatial control offered by the printing process allows for the digital manufacturing of hierarchical materials exhibiting thus far inaccessible multiscale porosity and complex geometries., Scientific Reports, 9, ISSN:2045-2322

Electrodes for metal-ion batteries should combine high specific capacity with fast cycling-rate capability. Although the use of mesoporous particles is an attractive approach to reconciling these c...

Aqueous Zn-ion batteries, which are being proposed as large-scale energy storage solutions because of their unparalleled safety and cost advantage, are composed of a positive host (cathode) material, a metallic zinc anode, and a mildly acidic aqueous electrolyte (pH approximate to 3-7). Typically, the charge storage mechanism is believed to be reversible Zn2+ (de)intercalation in the cathode host, with the exception of alpha-MnO2, for which multiple vastly different and contradicting mechanisms have been proposed. However, our present study, combining electrochemical, operando X-ray diffraction, electron microscopy in conjunction with energy-dispersive X-ray spectroscopy, and in situ pH evolution analyses on two oxide hosts-tunneled alpha-MnO2 and layered V3O7 center dot H2O vis-a-vis two nonoxide hosts-layered VS2 and tunneled Zn-3[Fe(CN)(6)](2), suggests that oxides and nonoxides follow two dissimilar charge storage mechanisms. While the oxides behave as dominant proton intercalation materials, the nonoxides undergo exclusive zinc intercalation. Stabilization of H+ on the hydroxyl-terminated oxide surface is revealed to facilitate the proton intercalation by a preliminary molecular dynamics simulation study. Proton intercalation for both oxides leads to the precipitation of layered double hydroxide (LDH)-Zn4SO4(OH)(6)center dot 5H(2)O with a ZnSO4/H2O electrolyte and a triflate anion (CF3SO3-)-based LDH with a Zn(SO3CF3)(2)/H2O electrolyte-on the electrode surface. The LDH precipitation buffers the pH of the electrolytes to a mildly acidic value, sustaining the proton intercalation to deliver large specific capacities for the oxides. Moreover, we also show that the stability of the LDH precipitate is crucial for the rechargeability of the oxide cathodes, revealing a critical link between the charge storage mechanism and the performance of the oxide hosts in aqueous zinc batteries.

Bulk hierarchical porous ceramics with unprecedented strength-to-weight ratio and tunable pore sizes across three different length scales are printed by direct ink writing. Such an extrusion-based process relies on the formulation of inks in the form of particle-stabilized emulsions and foams that are sufficiently stable to resist coalescence during printing.

We present different strategies to improve the electrical conductivity of antimony-doped tin oxide aerogels assembled from preformed nanosized building blocks. By adjusting the annealing atmosphere and temperature conditions, additional UV treatment to remove surface organics prior to annealing and by tuning the antimony content of the nanoparticles, different strategies are employed to influence the properties of the supercritically dried aerogels before and after gelation. In the framework of this study, also the formation of pure SnO2 particle-based aerogels could be achieved. Furthermore, we present an experimental setup for analyzing the electrical conductivity of porous and fragile aerogel monoliths based on a four-point probe. While the annealing atmosphere does not significantly affect the resistivity, UV treatment leads to a resistivity decrease in around 50 %. It is found that the resistivity of the samples can be tuned by altering the antimony content, offering very low-resistivity levels down to 4.5 Ω cm, while the surface areas remained high without significant crystal growth for the doped samples., Journal of Sol-Gel Science and Technology, 80 (3), ISSN:0928-0707, ISSN:1573-4846

We present for the first time the synthesis of transition metal nitride aerogels, specifically Cu3N aerogels by destabilizing colloidal Cu3N nanoparticles into gels using controlled heat treatment. The resulting aerogels consist of interconnected three-dimensional networks with ultrasmall-sized nanoparticle bridges of a surface area of 381 m(2) g(-1) and only 5% relative density.

Nanoparticle-based aerogels are 3-dimensional (3D) assemblies of macroscopic size that maintain the intrinsic properties of the initial nanoparticles. Accordingly, they bear immense potential to become an emerging platform for designing new and efficient photocatalysts. However, to take full advantage of this strategy, understanding of the multiscale processes occurring in such 3D-architectures is essential. Here, we prepared aerogels by co-assembling spherical Au, Pd, and PdAu with TiO2 nanoparticles and investigated their photocatalytic properties for hydrogen generation. During gelation, the anatase nanoparticles undergo oriented attachment, homogeneously entrapping the metal nanoparticles in the growing network. The aerogels offer a high porosity with a mean pore size of ca. 34 nm and a large surface area of about 450 m2 g−1. The porous structure enhances the light-harvesting, reagent transport, and electron migration process, generating 3.5-fold more hydrogen in comparison to the corresponding powders., Applied Catalysis B: Environmental, 267, ISSN:1873-3883, ISSN:0926-3373

We report a solution-phase approach to the synthesis of crystalline copper nanowires (Cu NWs) with an aspect ratio >1000 via a new catalytic mechanism comprising copper ions. The synthesis involves the reaction between copper(II) chloride and copper(II) acetylacetonate in a mixture of oleylamine and octadecene. Reaction parameters such as the molar ratio of precursors as well as the volume ratio of solvents offer the possibility to tune the morphology of the final product. A simple low-cost spray deposition method was used to fabricate Cu NW films on a glass substrate. Post-treatment under reducing gas (5% H2 + 95% N2) atmosphere resulted in Cu NW films with a low sheet resistance of 24.5 Ω/sq, a transmittance of T = 71% at 550 nm (including the glass substrate), and a high oxidation resistance. Moreover, the conducting Cu NW networks on a glass substrate can easily be transferred onto a polycarbonate substrate using a simple hot-press transfer method without compromising on the electrical performance. Th...

In food-grade emulsions, particles with an appropriate surface modification can be used to replace surfactants and potentially enhance the stability of emulsions. During the life cycle of products based on such emulsions, they can be exposed to a broad range of pH conditions and hence it is crucial to understand how pH changes affect stability of emulsions stabilized by particles. Here, we report on a comprehensive study of the stability, microstructure, and macroscopic behavior of pH-controlled oil-in-water emulsions containing silica nanoparticles modified with chitosan, a food-grade polycation. We found that the modified colloidal particles used as stabilizers behave differently depending on the pH, resulting in unique emulsion structures at multiple length scales. Our findings are rationalized in terms of the different emulsion stabilization mechanisms involved, which are determined by the pH-dependent charges and interactions between the colloidal building blocks of the system. At pH 4, the silica particles are partially hydrophobized through chitosan modification, favoring their adsorption at the oil-water interface and the formation of Pickering emulsions. At pH 5.5, the particles become attractive and the emulsion is stabilized by a network of agglomerated particles formed between the droplets. Finally, chitosan aggregates form at pH 9 and these act as the emulsion stabilizers under alkaline conditions. These insights have important implications for the processing and use of particle-stabilized emulsions. On one hand, changes in pH can lead to undesired macroscopic phase separation or coalescence of oil droplets. On the other hand, the pH effect on emulsion behavior can be harnessed in industrial processing, either to tune their flow response by altering the pH between processing stages or to produce pH-responsive emulsions that enhance the functionality of the emulsified end products.

Emulsions stabilized by mixtures of particles and amphiphilic molecules are relevant for a wide range of applications, but their dynamics and stabilization mechanisms on the colloidal level are poorly understood. Given the challenges to experimentally probe the early dynamics and mechanisms of droplet stabilization, Brownian dynamics simulations are developed here to study the behavior of oil-in-water emulsions stabilized by colloidal particles modified with short amphiphiles. Simulation parameters are based on an experimental system that consists of emulsions obtained with octane as the oil phase and a suspension of alumina colloidal particles modified with short carboxylic acids as the continuous aqueous medium. The numerical results show that attractive forces between the colloidal particles favor the formation of closely packed clusters on the droplet surface or of a percolating network of particles throughout the continuous phase, depending on the amphiphile concentration. Simulations also reveal the importance of a strong adsorption of particles at the liquid interface to prevent their depletion from the droplet surface when another droplet approaches. Strongly adsorbed particles remain immobile on the droplet surface, generating an effective steric barrier against droplet coalescence. These findings provide new insights into the early dynamics and mechanisms of stabilization of emulsions using particles and amphiphilic molecules.

BaTiO3 films are extensively used in many electrical devices, because they offer remarkable dielectric and ferroelectric properties. Here, we demonstrate a powerful, nanoparticle-based deposition route towards BaTiO3 films with systematic thickness control over a wide range up to several microns. The unusual control over the film thickness with the maintenance of crack free nanostructures, phase and ferroelectric properties of the BaTiO3 films allows us to fabricate various future devices of different thicknesses by a single deposition method. For this, films are deposited from stable dispersions of BaTiO3 nanocrystals, synthesized via an efficient microwave-assisted non-aqueous sol–gel approach. Crack-free films of controlled thickness are obtained by a carefully elaborated, alternating process of spin-coating and intermediate drying. According to X-ray diffraction and confocal Raman microscopy, the final, sintered films consist of BaTiO3 nanocrystals of about 20 nm in a hexagonal–tetragonal phase mixture. The nanoparticulate films display outstanding optical characteristics exceeding 90% transparency above 500 nm and a band gap of 3.5 eV. The latter, band gap, is larger than the classic bulk material's band gap of 3.2 eV, indicating a more electrically insulating nature of the films. Piezoresponse force microscopy gives evidence for potent ferroelectric switching. This newly accessible film processing route with wide film thickness tuning allows for desired ferroelectric response with the advantage of a wide film thickness to implicate building blocks for various applications e.g. ferroelectric random access memory devices, microelectromechanical system devices or Bragg reflectors.

New chemical pathways are of fundamental interest for materials synthesis. Here, we report a novel surfactant-free, solution-phase, low-temperature route to crystalline, ultrasmall (∼2 nm) Cu3N nanoparticles via a one-step reaction between copper(II) methoxide and benzylamine. We propose a reaction mechanism for Cu3N formation based on the gas chromatography–mass spectrometry (GC–MS) analysis of the organic reaction byproducts. The reaction pathway involves reduction of the Cu(II) to Cu(I) by benzylamine, in situ generation of ammonia, and finally, the reaction between Cu(I) and ammonia to form Cu3N. We tested the Cu3N nanoparticles as an anode material for Li-ion batteries (LIBs). According to cyclic voltammetry, the Cu3N nanoparticles quickly undergo a phase transformation to Cu2O, but then stably deliver a capacity of ∼290 mAh/g at 1 A/g in the following 150 cycles.

Due to their band gap structure, metal tantalates absorb both ultraviolet and visible parts of the solar spectrum, which is beneficial for applications in photocatalysis. However, tantalates are very challenging to synthesize. In comparison to traditional solid-state reactions, which often lead to impurities, wet-chemical approaches starting from molecular precursors offer better homogeneity. In the present study, amorphous InTaO4 nanoparticles were synthesized in a non-aqueous sol-gel method. Subsequent annealing at 800 °C yielded crystalline and phase-pure nanoparticles. In addition, the amorphous nanoparticles could be used as building blocks for the assembly into macroscopic gels by careful centrifugation. After supercritical drying, the three-dimensionally interconnected microstructure was preserved, resulting in highly porous aerogel monoliths with a large surface area of 357 m2 g−1. Upon calcination, crystallization and 46 % shrinkage of the aerogel occurred and a decrease in surface area to 49 m2 g−1 was observed. Uniaxial compression tests revealed the mechanical stability of these nanoparticle-based aerogels. Although the large surface area and the ability to absorb visible light, combined with the unique mechanical properties, are ideal prerequisites to make these aerogels promising for photocatalytic reactions, the degradation of methylene blue only showed limited success. This article is protected by copyright. All rights reserved.

Although aerogels prepared by the colloidal assembly of nanoparticles are a rapidly emerging class of highly porous and low-density materials, their ambient dried counterparts, namely xerogels, have hardly been explored. Here we report the use of nanoparticle-based BaTiO

A major obstacle in the introduction of luminescent nanoparticles (NPs) for medical applications is that quantum dots, the most widely studied luminescent materials, despite being biologically safe after coating with a bioshell, still contain a toxic core mostly consisting of semi-conductor NPs, which are not approved by regulatory agencies. Here we point to a potential solution of this problem by using rare-earth (RE) doped hafnia NPs. Hafnia is approved for medical injections as an effective means for the treatment of radiosensitive and radioresistant tumors and can significantly decrease potential toxicity of RE ions. As a step towards the achievement of this goal we describe the development of a bio-friendly method for the preparation of a stable doped hafnia hydrosol with an isoelectric point (IEP) of 8.2, which shows high fluorescence and biocompatibility in regular coagulant tests and cytotoxic assays.

The high absorption energies of partially wetted particles at fluid interfaces allow the production of macroporous composite materials from particle-stabilized foams. Competition between the different particle types determines how they are distributed in the foam lamella and allow the phase distribution to be controlled; a technique that is useful in the design and engineering of porous composites. Here, we report details on the effects of preferential and competitive adsorption of poly(vinylidene fluoride) (PVDF) and alumina (Al(2)O(3)) particles at the foam interfaces on the consolidated macroporous composite materials. By varying the relative composition and surface energies of the stabilizing particles, macroporous composite materials with a broad range of phase distributions are possible.

Aqueous suspensions containing oppositely charged colloidal particles and amphiphilic molecules can form fluid dispersions, foams, and percolating gel networks, depending on the initial concentration of amphiphiles. While models have been proposed to explain the electrokinetic and flotation behavior of particles in the presence of long amphiphilic molecules, the effect of amphiphiles with less than six carbons in the hydrocarbon tail on the electrokinetic, rheological, and foaming behavior of aqueous suspensions remains unclear. Unlike conventional long amphiphiles (≥10 carbons), short amphiphiles do not exhibit increased adsorption on the particle surface when the number of carbons in the molecule tail is increased. On the basis of classical electrical double layer theory and the formerly proposed hemimicelle concept, we put forward a new predictive model that reconciles the adsorption and electrokinetic behavior of colloidal particles in the presence of long and short amphiphiles. By introducing in the classical Gouy-Chapman theory an energy term associated with hydrophobic interactions between the amphiphile hydrocarbon tails, we show that amphiphilic electrolytes lead to a stronger compression of the diffuse part of the electrical double layer in comparison to hydrophilic electrolytes. Scaling relationships derived from this model provide a quantitative description of the rich phase behavior of the investigated suspensions, correctly accounting for the effect of the alkyl chain length of short and long amphiphiles on the electrokinetics of such colloidal systems. The proposed model contributes to our understanding of the stabilization mechanisms of particle-stabilized foams and emulsions and might provide new insights into the physicochemical processes involved in mineral flotation.

The hydrophilic character of aluminum oxide surfaces may be altered through coating such surfaces with carboxylic acids. The initially hydrophilic nature of the solid substrate changes towards a less hydrophilic character as the bulk concentration and the chain length of the acids increases. The acids employed in this work (propionic, valeric and enanthic) show a certain affinity to the liquid–gas, solid–liquid and solid–gas interfaces, being the relative adsorption on them competitive. The adsorption behavior of these carboxylic acids is experimentally investigated combining pendant drop tensiometry, contact angle measurements on α-Al2O3 polycrystalline ceramics and adsorption on particles in aqueous suspensions, as a function of the hydrocarbon chain length of the acids and their bulk concentration, at pH equal to the acids’ pKa. The hydrophilic character of the coated alumina decreases with the acids concentration upon a certain concentration beyond that, it increases. The minimum of hydrophilicity is reached right before bi-layer arrangements on the adsorption pattern of the acids on the solid substrates take place.