PdO/SnO2 heterostructure for low-temperature detection of CO with fast response and recovery

Novel Perovskite Oxide Hybrid Nanofibers Embedded with Nanocatalysts for Highly Efficient and Durable Electrodes in Direct CO2 Electrolysis

The unique characteristics of nanofibers in rational electrode design enable effective utilization and maximizing material properties for achieving highly efficient and sustainable CO2 reduction reactions (CO2RRs) in solid oxide electrolysis cells (SOECs). However, practical application of nanofiber-based electrodes faces challenges in establishing sufficient interfacial contact and adhesion with the dense electrolyte. To tackle this challenge, a novel hybrid nanofiber electrode, La0.6Sr0.4Co0.15Fe0.8Pd0.05O3-δ (H-LSCFP), is developed by strategically incorporating low aspect ratio crushed LSCFP nanofibers into the excess porous interspace of a high aspect ratio LSCFP nanofiber framework synthesized via electrospinning technique. After consecutive treatment in 100% H2 and CO2 at 700 °C, LSCFP nanofibers form a perovskite phase with in situ exsolved Co metal nanocatalysts and a high concentration of oxygen species on the surface, enhancing CO2 adsorption. The SOEC with the H-LSCFP electrode yielded an outstanding current density of 2.2 A cm-2 in CO2 at 800 °C and 1.5 V, setting a new benchmark among reported nanofiber-based electrodes. Digital twinning of the H-LSCFP reveals improved contact adhesion and increased reaction sites for CO2RR. The present work demonstrates a highly catalytically active and robust nanofiber-based fuel electrode with a hybrid structure, paving the way for further advancements and nanofiber applications in CO2-SOECs.

Room-temperature response of MOF-derived Pd@PdO core shell/γ-Fe2O3 microcubes decorated graphitic carbon based ultrasensitive and highly selective H2 gas sensor

With the current upsurge in hydrogen economies all over the world, an increased demand for improved chemiresistive H2 sensors that are highly responsive and fast acting when exposed to gases is expected. Owing to safety concerns about explosive and highly flammable H2 gas, it is important to develop resistive sensors that can detect the leakage of H2 gas swiftly and selectively. Currently, interest in metal-organic frameworks (MOFs) for gas-sensor applications is increasing due to their open-metal sites, large surface area, and unique surface morphologies. In this research, a highly selective and sensitive H2-sensor was established based on graphitic carbon (GC) anchored spherical Pd@PdO core-shells over γ-Fe2O3 microcube (Pd@PdO/γ-Fe2O3@GC which is termed as S3) heterostructure materials. The combined solvothermal followed by controlled calcination-assisted S3 exhibited a specific morphology with the highest surface area of 79.12 m2 g-1, resulting in fast response and recovery times (21 and 29 s, respectively), and excellent sensing performance (ΔR/R0∼ 96.2 ± 1.5), outstanding long-term stability, and a 100 ppb detection limit when detecting H2-gas at room temperature (mainly in very humid surroundings). This result proves that adsorption sites provided by S3 can promote surface reactions (adsorption and desorption) for ultrasensitive and selective H2gas sensors.

Bioinspired palladium-doped manganese oxide nanocorns: a remarkable antimicrobial agent targeting phyto/animal pathogens

Microbial pathogens are known for causing great environmental stress, owing to which emerging challenges like lack of eco-friendly remediation measures, development of drug-resistant and mutational microbial strains, etc., warrants novel and green routes as a stepping stone to serve such concerns sustainably. In the present study, palladium (Pd) doped manganese (II, III) oxide (Mn3O4) nanoparticles (NPs) were synthesized using an aqueous Syzygium aromaticum bud (ASAB) extract. Preliminary phytochemical analysis of ASAB extract indicates the presence of polyphenolics such as phenols, alkaloids, and flavonoids that can act as potential capping agents in NPs synthesis, which was later confirmed in FTIR analysis of pure and Pd-doped Mn3O4 NPs. XRD, Raman, and XPS analyses confirmed the Pd doping in Mn3O4 NPs. FESEM and HRTEM study reveals the mixed morphologies dominated by nanocorns appearance. Zeta potential investigation reveals high stability of the synthesized NPs in colloidal solutions. The developed Pd-doped Mn3O4 NPs were tested against two fungal phytopathogens, i.e., Sclerotinia sclerotiorum and Colletotrichum gloeosporioides, known for causing great economic losses in yield and quality of different plant species. The antifungal activity of synthesized Pd-doped Mn3O4 NPs displayed a dose-dependent response with a maximum of ~92%, and ~72% inhibition was recorded against S. sclerotiorum and C. gloeosporioides, respectively, at 1000 ppm concentration. However, C. gloeosporioides demonstrated higher sensitivity to Pd-doped Mn3O4 NPs upto 500 ppm) treatment than S. sclerotiorum. The prepared NPs also showed significant antibacterial activity against Enterococcus faecalis. The Pd-doped Mn3O4 NPs were effective even at low treatment doses, i.e., 50-100 ppm, with the highest Zone of inhibition obtained at 1000 ppm concentration. Our findings provide a novel, eco-benign, and cost-effective approach for formulating a nanomaterial composition offering multifaceted utilities as an effective antimicrobial agent.

High production of furfural by flash pyrolysis of C6 sugars and lignocellulose by Pd-PdO/ZnSO4 catalyst

Furfural (C₅H₄O₂) is an important platform chemical for the synthesis of next-generation bio-fuels. Herein, we report a novel and reusable heterogeneous catalyst, Pd-PdO/ZnSO₄ with 1.1 mol% palladium (Pd), for the production of furfural by flash pyrolysis of lignocelluloses at 400 °C. For both dry and wet C6 cellulose and its monomers, the furfural yields reach 74-82 mol%, relative to 96 mol% from C5 xylan and 23-33 wt% from sugarcane bagasse and corncob. The catalyst has a well-defined structure and bifunctional property, comprising a ZnSO₄ support for the dehydration and isomerization of glucose, and a local core-shell configuration for metallic Pd⁰ encapsulated by an oxide (PdO) layer. The PdO layer is active for the Grob fragmentation of formaldehyde (HCHO) from glucose, which is subsequently in-situ steam reformed into syn-gas (i.e. H₂ and CO), whereas the Pd⁰ core is active in promoting the last dehydration step for the formation of furfural.

Conductometric ppb-Level CO Sensors Based on In2O3 Nanofibers Co-Modified with Au and Pd Species

Carbon monoxide (CO) is one of the most toxic gases to human life. Therefore, the effective monitoring of it down to ppb level is of great significance. Herein, a series of In₂O₃ nanofibers modified with Au or Pd species or simultaneous Au and Pd species have been prepared by electrospinning combined with a calcination process. The as-obtained samples are applied for the detection of CO. Gas-sensing investigations indicate that 2 at% Au and 2 at% Pd-co-modified In₂O₃ nanofibers exhibit the highest response (21.7) to 100 ppm CO at 180 °C, and the response value is ~8.5 times higher than that of pure In₂O₃ nanofibers. More importantly, the detection limit to CO is about 200 ppb with a response value of 1.23, and is obviously lower than that (6 ppm) of pure In₂O₃ nanofibers. In addition, the sensor also shows good stability within 19 days. These demonstrate that co-modifying In₂O₃ nanofibers with suitable amounts of Pd and Au species might be a meaningful strategy for the development of high-performance carbon monoxide gas sensors.

Synthesis of a Spatially Confined, Highly Durable, and Fully Exposed Pd Cluster Catalyst via Sequential Site-Selective Atomic Layer Deposition

Bottom-up synthesis based on site-selective atomic layer deposition is a powerful atomic-scale processing approach to fabricate materials with desired functionalities. Typical selective atomic layer deposition (ALD) can be achieved using selective activation of a growth area or selective deactivation of a protected area. In this work, we explored the site selectivity based on the difference of the inherent surface reactivity between different materials and within the same materials. By sequentially applying two site-selective atomic layer deposition, the ALD Pd catalyst is spatially confined on ALD SnO₂ modified h-BN substrate Pd/SnO₂/h-BN shows improved catalytic activity and stability due to strong metal-support interactions and spatial confinement. The results reveal that sequential site-selective ALD is a feasible and effective synthesis strategy that provides an attractive path toward designing and developing highly stable catalysts.

Compatibility between Activity and Selectivity in Catalytic Oxidation of Benzyl Alcohol with Au-Pd Nanoparticles through Redox Switching of SnOx

A balance between catalytic activity and product selectivity remains a dilemma for the partial oxidation processes because the products are prone to be overoxidized. In this work, we report on the partial oxidation of benzyl alcohol using a modified catalyst consisting of nanosized Au-Pd particles (NPs) with tin oxide (SnO_x) deposited on a mesoporous silica support. We found that the SnO_x promotes the autogenous reduction of PdO to active Pd⁰ species on the Au-Pd NP catalyst (SnO_x@AP-ox) before H₂ reduction, which is due to the high oxophilicity of Sn. The presence of active Pd⁰ species and the enhancement of oxygen transfer by SnO_x led to high catalytic activity. The benzaldehyde selectivity was enhanced with the increase of SnO_x content on catalyst SnO_x@AP-ox, which is ascribed to the modulated affinity of reactants and products on the catalyst surface through the redox switching of Sn species. After H₂ reduction, SnO_x was partially reduced and Au-Pd-Sn alloy was formed. The formation of Au-Pd-Sn alloy weakened both the catalytic synergy of Au-Pd alloy NPs and the adsorption of benzyl alcohol on the reduced catalyst, thus leading to low catalytic activity.

Phosphine-Built-in Porous Organic Cage for Stabilization and Boosting the Catalytic Performance of Palladium Nanoparticles in Cross-Coupling of Aryl Halides

Herein, we report first a novel phosphine-containing porous organic cage (PPOC) from a [2 + 3] self-assembly of triphenyl phosphine-based trialdehyde and (S,S)-1,2-diaminocyclohexane via dynamic imine chemistry, which was employed as a porous material for the controlled growth of palladium nanoparticles (NPs) due to the strong affinity of Pd to the phosphine ligand based on the principle of hard and soft acids and bases. Comprehensive characterizations including X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, NMR, and X-ray absorption spectroscopy reveal that ultrafine Pd NPs with narrow size distribution (1.7 ± 0.3 nm) and enhanced surface electronic density via a strong interaction between NPs and phosphine were homogeneously dispersed in the PPOC. The resultant catalyst Pd@PPOC exhibits remarkably superior catalytic activities for various cross-coupling reactions of aryl halides, for example, Sonogashira, Suzuki, Heck, and carbonylation. The catalytic activity of Pd@PPOC outperforms the state-of-the-art Pd complexes and other Pd NPs supported on N-containing porous cages under identical conditions, owing to the enhanced surface electronic density of Pd NPs and their high stability and dispersibility in solution. More importantly, Pd@PPOC is highly stable and easily recycled and reused without loss of their catalytic activity. This work provides a new functional POC with extended potentials in catalysis and material science.

Palladium-Doped Tin Oxide Nanosensor for the Detection of the Air Pollutant Carbon Monoxide Gas

The exhaust gases from various sources cause air pollution, which is a leading contributor to the global disease burden. Hence, it has become vital to monitor and control the increasing pollutants coming out of the various sources into the environment. This paper has designed and developed a sensor material to determine the amount of carbon monoxide (CO), which is one of the major primary air pollutants produced by human activity. Nanoparticle-based sensors have several benefits in sensitivity and specificity over sensors made from traditional materials. In this study, tin oxide (SnO2), which has greater sensitivity to the target gas, is selected as the sensing material which selectively senses only CO. Tin oxide nanoparticles have been synthesized from stannous chloride dihydrate chemical compound by chemical precipitation method. Palladium, at the concentration of 0.1%, 0.2%, and 0.3% by weight, was added to tin oxide and the results were compared. Synthesized samples were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) techniques. XRD revealed the tetragonal structure of the SnO2 nanoparticles and FESEM analysis showed the size of the nanoparticles to be about 7-20 nm. Further, the real-time sensor testing was performed and the results proved that the tin oxide sensor, doped with 0.2% palladium, senses the CO gas more efficiently with greater sensitivity.