High-Temperature Stable Gold Nanoparticle Catalysts for Application under Severe Conditions: The Role of TiO2 Nanodomains in Structure and Activity

Photothermal heating of titanium nitride nanomaterials for fast and uniform laser warming of cryopreserved biomaterials

Titanium nitride (TiN) is presented as an alternative plasmonic nanomaterial to the commonly used gold (Au) for its potential use in laser rewarming of cryopreserved biomaterials. The rewarming of vitrified, glass like state, cryopreserved biomaterials is a delicate process as potential ice formation leads to mechanical stress and cracking on a macroscale, and damage to cell walls and DNA on a microscale, ultimately leading to the destruction of the biomaterial. The use of plasmonic nanomaterials dispersed in cryoprotective agent solutions to rapidly convert optical radiation into heat, generally supplied by a focused laser beam, proposes a novel approach to overcome this difficulty. This study focuses on the performance of TiN nanoparticles (NPs), since they present high thermal stability and are inexpensive compared to Au. To uniformly warm up the nanomaterial solutions, a beam splitting laser system was developed to heat samples from multiple sides with equal beam energy distribution. In addition, uniform laser warming requires equal distribution of absorption and scattering properties in the nanomaterials. Preliminary results demonstrated higher absorption but less scattering in TiN NPs than Au nanorods (GNRs). This led to the development of TiN clusters, synthetized by nanoparticle agglomeration, to increase the scattering cross-section of the material. Overall, this study analyzed the heating rate, thermal efficiency, and heating uniformity of TiN NPs and clusters in comparison to GNRs at different solution concentrations. TiN NPs and clusters demonstrated higher heating rates and solution temperatures, while only clusters led to a significantly improved uniformity in heating. These results highlight a promising alternative plasmonic nanomaterial to rewarm cryopreserved biological systems in the future.

Photothermal synthesis of a CuO x &FeO y catalyst with a layered double hydroxide-derived pore-confined frame to achieve photothermal CO2 hydrogenation to CO with a rate of 136 mmol min-1 gcat -1

Solar-driven CO₂ conversion into the industrial chemical CO via the reverse water-gas reaction is an ideal technological approach to achieve the key step of carbon neutralization. The high reaction temperature is cost-free due to the photothermal conversion brought about by solar irradiation and is beneficial to the catalytic efficiency. However, the thermostability of adopted catalysts is a great challenge. Herein, we develop an in situ photothermal synthesis to obtain a CuO _x &FeO _y catalyst with a layered double hydroxide-derived pore-confined frame. The optimized sample delivers a CO generation rate of 136.3 mmol min^-1 g_cat ^-1 with the selectivity of ∼100% at a high reaction temperature of 1015 °C. The efficient catalytic activity can be attributed to the fact that the pore-confined frame substrate prevents the growth of CuO _x and FeO _y nanoparticles during the high-temperature reaction and the basic groups on the substrate promote the adsorption and activation of CO₂.

A molecular dynamics study on the thermal properties of carbon-based gold nanoparticles

Due to unique features in surface activity, thermal stability, electrical and thermal conductivity, and compatibility with biomolecules such as DNA and proteins, carbon-based nanoparticles are raised potential as a candidate for various applications such as catalytic processes, drug delivery, light, and electrical engineering. Based on this premise, thermodynamic features of pure, graphene, and carbon nanotube (CNT)-based gold nanoparticles (AuNPs) are investigated using molecular dynamics approach. Melting, heat capacity, thermal conductivity, contact angle of molten AuNPs, and phase transition are calculated as indicators of thermodynamic properties of pure and carbon-based AuNPs. Simulation results indicate that the presence of a carbon platform and its contact surface area has a significant role in the thermodynamic properties of AuNPs and leads the phononic heat capacity and thermal conductivity to decrease for AuNPs. The platform also causes the melting point temperature of AuNPs to increase. The melting of gold on the carbon base is of the first-order type. In addition, contact angle for molten AuNPs on the Graphene is significantly higher than the one on the CNT due to more contact area on the Graphene substrate.Graphical abstract .

Sinter-Resistant Nanoparticle Catalysts Achieved by 2D Boron Nitride-Based Strong Metal-Support Interactions: A New Twist on an Old Story

Strong metal-support interaction (SMSI) is recognized as a pivotal strategy in hetereogeneous catalysis to prevent the sintering of metal nanoparticles (NPs), but issues including restriction of supports to reducible metal oxides, nonporous architecture, sintering by thermal treatment at >800 °C, and unstable nature limit their practical application. Herein, the construction of non-oxide-derived SMSI nanocatalysts based on highly crystalline and nanoporous hexagonal boron nitride (h-BN) 2D materials was demonstrated via in situ encapsulation and reduction using NaBH₄, NaNH₂, and noble metal salts as precursors. The as-prepared nanocatalysts exhibited robust thermal stability and sintering resistance to withstand thermal treatment at up to 950 °C, rendering them with high catalytic efficiency and durability in CO oxidation even in the presence of H₂O and hydrocarbon simulated to realistic exhaust systems. More importantly, our generic strategy offers a novel and efficient avenue to design ultrastable hetereogeneous catalysts with diverse metal and support compositions and architectures.

Role of the Support in Gold-Containing Nanoparticles as Heterogeneous Catalysts

In this review, we discuss selected examples from recent literature on the role of the support on directing the nanostructures of Au-based monometallic and bimetallic nanoparticles. The role of support is then discussed in relation to the catalytic properties of Au-based monometallic and bimetallic nanoparticles using different gas phase and liquid phase reactions. The reactions discussed include CO oxidation, aerobic oxidation of monohydric and polyhydric alcohols, selective hydrogenation of alkynes, hydrogenation of nitroaromatics, CO₂ hydrogenation, C–C coupling, and methane oxidation. Only studies where the role of support has been explicitly studied in detail have been selected for discussion. However, the role of support is also examined using examples of reactions involving unsupported metal nanoparticles (i.e., colloidal nanoparticles). It is clear that the support functionality can play a crucial role in tuning the catalytic activity that is observed and that advanced theory and characterization add greatly to our understanding of these fascinating catalysts.

Nanocomposite structure of two-line ferrihydrite powder from total scattering

Ferrihydrite is one of the most important iron-containing minerals on Earth. Yet determination of its atomic-scale structure has been frustrated by its intrinsically poor crystallinity. The key difficulty is that physically-different models can appear consistent with the same experimental data. Using X-ray total scattering and a nancomposite reverse Monte Carlo approach, we evaluate the two principal contending models-one a multi-phase system without tetrahedral iron(III), and the other a single phase with tetrahedral iron(III). Our methodology is unique in considering explicitly the complex nanocomposite structure the material adopts: namely, crystalline domains embedded in a poorly-ordered matrix. The multi-phase model requires unphysical structural rearrangements to fit the data, whereas the single-phase model accounts for the data straightforwardly. Hence the latter provides the more accurate description of the short- and intermediate-range order of ferrihydrite. We discuss how this approach might allow experiment-driven (in)validation of complex models for important nanostructured phases beyond ferrihydrite.

Boosting the catalysis of gold by O2 activation at Au-SiO2 interface

Supported gold (Au) nanocatalysts have attracted extensive interests in the past decades because of their unique catalytic properties for a number of key chemical reactions, especially in (selective) oxidations. The activation of O₂ on Au nanocatalysts is crucial and remains a challenge because only small Au nanoparticles (NPs) can effectively activate O₂. This severely limits their practical application because Au NPs inevitably sinter into larger ones during reaction due to their low Taman temperature. Here we construct a Au-SiO₂ interface by depositing thin SiO₂ layer onto Au/TiO₂ and calcination at high temperatures and demonstrate that the interface can be not only highly sintering resistant but also extremely active for O₂ activation. This work provides insights into the catalysis of Au nanocatalysts and paves a way for the design and development of highly active supported Au catalysts with excellent thermal stability.

The development of sintering resistant supported Au catalysts with high activity still remains a challenge. Here the authors construct a Au-SiO₂ interface by depositing SiO₂ thin layer onto Au/TiO₂ catalyst which shows very high activity in CO oxidation even after calcination at 800 °C.

Exceptional Antisintering Gold Nanocatalyst for Diesel Exhaust Oxidation

The poor thermodynamic stability of gold nanoparticles (NPs) makes it very challenging to stabilize them in small sizes at elevated temperatures. Herein, we report the preparation of antisintering Au nanocatalyst by rationally selecting the sublattice matched MgGa₂O₄ spinel as support based on theoretical predictions. Au/MgGa₂O₄ retains Au NPs of 2-5 nm even after aging over the melting temperature of bulk gold (1064 °C)! By identifying the stable structure, the extraordinary stability is found to arise from the formation of a new phase structure, namely Au-MgGa₂O₄ metal-oxide "hetero-bicrystal" that remains as crystallite without melting even at 1100 °C. More than 80% of the loaded Au can be efficiently stabilized so that the catalysts can exhibit excellent low-temperature activities for diesel exhaust (CO and C₃H₆) oxidation after severely thermal and hydrothermal aging. These results may pave ways for constructing antisintering gold nanocatalysts for industrial applications.

A sinter-resistant catalyst using an alumina support recycled from AlP fumigation residue: trash to treasure

Sintering is a long-standing issue especially in high temperature catalytic applications. In this paper, we report an effective method to slow down metal particle migration and coalescence (PMC) by using a thermally stable alumina support. Noteworthily, the alumina sample was developed from AlP fumigation residue, which is a very dangerous substance for living creatures and environment protection. By optimizing the heated hydrolysis and ball-milling conditions, we recycled a phosphate-stabilized alumina material that retained a 117 m² g^-1 surface area after 1050 °C hydrothermal aging. The catalyst using this newly developed alumina support had Pd dispersion 1.7 times higher than that using a commercial alumina support after aging. The kinetics and XPS experiments showed that phosphate neither participated in the catalytic reaction process nor changed the active sites. This catalyst also exhibited extraordinary water tolerance and durability, making it a promising material in automotive exhaust purification and other catalytic applications.

Graphene oxide/silver nanohybrid: Optimization, antibacterial activity and its impregnation on bacterial cellulose as a potential wound dressing based on GO-Ag nanocomposite-coated BC

Recently, bacterial cellulose (BC) based wound dressing have raised significant interests in medical fields. However, to our best knowledge, it is apparent that the BC itself has no antibacterial activity. In this study, we optimized graphene oxide-silver (GO-Ag) nanohybrid synthesis using Response Surface Methodology and impregnate it to BC and carefully investigate their antibacterial activities against both the Gram-negative bacteria Escherichia coli and the Gram-positive bacteria Staphylococcus aureus. We discover that, compared to silver nanoparticles, GO-Ag nanohybrid with an optimal GO suspension's pH and [ G O ] [ A g N O 3 ] ratio is much more effective and shows synergistically enhanced, strong antibacterial activities at rather low dose. The GO-Ag nanohybrid is more toxic to E. coli than that to S. aureus. The antibacterial and mechanical properties of BC/GO-Ag composite are further investigated.

Investigating the Hybrid-Structure-Effect of CeO2 -Encapsulated Au Nanostructures on the Transfer Coupling of Nitrobenzene

Due to the obvious distinctions in structure, core-shell nanostructures (CSNs) and yolk-shell nanostructures (YSNs) exhibit different catalytic behavior for specific organic reactions. In this work, two unique autoredox routes are developed to the fabrication of CeO₂ -encapsulated Au nanocatalysts. Route A is the synthesis of well-defined CSNs by a one-step redox reaction. The process involves an interesting phenomenon in which Ce³⁺ can act as a weak acid to inhibit the hydrolysis of Ce⁴⁺ under the condition of OH^- shortage. Route B is the fabrication of monodispersed YSNs by a two-step redox reaction with amorphous Co₃ O₄ as an in situ template. Furthermore, the transfer coupling of nitrobenzene is chosen as a probe reaction to investigate their catalytic difference. The CSNs can gradually achieve the conversion of nitrobenzene into azoxybenzene, while the YSNs can rapidly convert nitrobenzene into azobenzene. The different catalytic results are mainly attributed to their structural distinctions.

Remarkable thermal stability of gold nanoparticles functionalised with ruthenium phthalocyanine complexes

A gold nanoparticle (AuNP) ruthenium phthalocyanine (RuPc) nanocomposite has been synthesised that exhibits high thermal stability. Electrical resistance measurements revealed that the nanocomposite is stable up to ∼320 °C. Examination of the nanocomposite and the RuPc stabiliser complex using thermogravimetric analysis and differential scanning calorimetry show that the remarkable thermal stability is due to the RuPc molecules, which provide an effective barrier to sintering of the AuNPs.