From nanoparticles to single atoms for Pt/CeO2: Synthetic strategies, characterizations and applications

Single-atom nanozymes for antibacterial applications

Bacteria have always been a thorny problem that threatens human health and food safety. Conventional antibiotic treatment often leads to the emergence of drug resistance. Therefore, the development of more effective antibacterial agents is urgently needed. Single-atom nanozymes (SAzymes) can efficiently eliminate bacteria due to their high atomic utilization, abundant active centers, and good natural enzyme mimicry, providing a potential alternative choice for antibiotics in antibacterial applications. Here, the antibacterial applications of SAzymes are reviewed and their catalytic properties are discussed from the aspects of active sites, coordination environment regulation and carrier selection. Then, the antibacterial effect of SAzymes is elaborated in combination with photothermal therapy (PTT) and sonodynamic therapy (SDT). Finally, the problems faced by SAzymes in antibacterial applications and their future development potential are proposed.

Theoretical study of structure sensitivity on ceria-supported single platinum atoms and its influence on carbon monoxide adsorption

Density functional theory (DFT) calculations explore the stability of a single platinum atom on various flat, stepped, and defective ceria surfaces, in the context of single-atom catalysts (SACs) for the water-gas shift (WGS) reaction. The adsorption properties and diffusion kinetics of the metal strongly depend on the support termination with large stability on metastable and stepped CeO2(100) and (210) surfaces where the diffusion of the platinum atom is hindered. At the opposite, the more stable CeO2(111) and (110) terminations weakly bind the platinum atom and can promote the growth of metallic clusters thanks to fast diffusion kinetics. The adsorption of carbon monoxide on the single platinum atom supported on the various ceria terminations is also sensitive to the surface structure. Carbon monoxide weakly binds to the single platinum atom supported on reduced CeO2(111) and (211) terminations. The desorption of the CO2 formed during the WGS reaction is thus facilitated on the latter terminations. A vibrational analysis underlines the significant changes in the calculated scaled anharmonic CO stretching frequency on these catalysts.

Bottom-Up Synthesis of Platinum Dual-Atom Catalysts on Cerium Oxide

We present here the synthesis and performance of dual-atom catalysts (DACs), analogous to well-known single-atom catalysts (SACs). DACs feature sites containing pairs of metal atoms and can outperform SACs due to their additional binding possibilities. Yet quantifying the improved catalytic activity in terms of proximity effects remains difficult, as it requires both high-resolution kinetic data and an understanding of the reaction pathways. Here, we use an automated bubble counter setup for comparing the catalytic performance of ceria-supported platinum SACs and DACs in ammonia borane hydrolysis. The catalysts were synthesized by wet impregnation and characterized using SEM, HAADF-STEM, XRD, XPS, and CO-DRIFTS. High-precision kinetic studies of ammonia borane hydrolysis in the presence of SACs show two temperature-dependent regions, with a transition point at 43 °C. Conversely, the DACs show only one regime. We show that this is because DACs preorganize both ammonia borane and water at the dual-atom active site. The additional proximal Pt atom improves the reaction rate 3-fold and enables faster reactions at lower temperatures. We suggest that the DACs enable the activation of the water-O-H bond as well as increase the hydrogen spillover effect due to the adjacent Pt site. Interestingly, using ammonia borane hydrolysis as a benchmark reaction gives further insight into hydrogen spillover mechanisms, above what is known from the CO oxidation studies.

Local environmental engineering for highly stable single-atom Pt1/CeO2catalysts: first-principles insights

Single-atom Pt1/CeO2catalysts may cope with the high cost and durability issues of fuel cell electrocatalysts. In the present study, the stability and underlying interaction mechanisms of the Pt1/CeO2system are systematically investigated using first-principles calculations. The Pt adsorption energy on CeO2surfaces can be divided into chemical interaction and surface deformation parts. The interaction energy, mainly associated with the local chemical environment, i.e. the number of Pt-O bonds, plays a major role in Pt1/CeO2stability. When forming a Pt-4O configuration, the catalytic system has the highest stability and Pt is oxidized to Pt2+. An electronic metal-support interaction mechanism is proposed for understanding Pt1/CeO2stability. In addition, our calculations show that the Pt1/CeO2(100) system is dynamically stable, and the external O environment can promote the further oxidation of Pt to Ptn+(2 ≤n< 4). The present study provides useful guidance for the experimental development of highly stable and efficient electrocatalysts for fuel cell applications.

Acid-Base and Photocatalytic Properties of the CeO2-Ag Nanocomposites

In this work, CeO₂ nanoparticles, as well as CeO₂ nanocomposites with plasmonic silver nanoparticles, were synthesized using a simple sol-gel process. The concentration of silver in the composites varied from 0.031-0.25 wt%. Cerium hydroxide dried gel was calcined at temperatures from 125 to 800 °C to obtain CeO₂. It was shown that, at an annealing temperature of 650 °C, single-phase CeO₂ nanopowders with an average particle size in the range of 10-20 nm can be obtained. The study of acid-base properties showed that with an increase in the calcination temperature from 500 to 650 °C, the concentration of active centers with pKa 9.4 and 6.4 sharply increases. An analysis of the acid-base properties of CeO₂-Ag nanocomposites showed that with an increase in the silver concentration, the concentration of centers with pKa 4.1 decreases, and the number of active centers with pKa 7.4 increases. In a model experiment on dye photodegradation, it was shown that the resulting CeO₂ and CeO₂-Ag nanopowders have photocatalytic activity. CeO₂-Ag nanocomposites, regardless of the silver concentration, demonstrated better photocatalytic activity than pure nanosized CeO₂.

Fabricating Robust Pt Clusters on Sn-Doped CeO2 for CO Oxidation: A Deep Insight into Support Engineering and Surface Structural Evolution

The size effect on nanoparticles, which affects the catalysis performance in a significant way, is crucial. The tuning of oxygen vacancies on metal-oxide support can help reduce the size of the particles in active clusters of Pt, thus improving catalysis performance of the supported catalyst. Herein, Ce-Sn solid solutions (CSO) with abundant oxygen vacancies have been synthesized. Activated by simple CO reduction after loading Pt species, the catalytic CO oxidation performance of Pt/CSO was significantly better than that of Pt/CeO₂ . The reasons for the elevated activity were further explored regarding ionic Pt single sites being transformed into active Pt clusters after CO reduction. Due to more exposed oxygen vacancies, much smaller Pt clusters were created on CSO (ca. 1.2 nm) than on CeO₂ (ca. 1.8 nm). Consequently, more exposed active Pt clusters significantly improved the ability to activate oxygen and directly translated to the higher catalytic oxidation performance of activated Pt/CSO catalysts in vehicle emission control applications.

Synergistic Effect of Pt and Dual Ni/Co Cations in Hydrotalcite-Derived Pt/Ni1.5Co0.5AlO Catalysts for Promoting Soot Combustion

In this article, the catalysts of hydrotalcite-derived Ni_1.5Co_0.5AlO nanosheet-supported highly dispersed Pt nanoparticles (Pt_n/Ni_1.5Co_0.5AlO, where n% is the weigh percentage of the Pt element in the catalysts) were elaborately fabricated by the gas-bubble-assisted membrane--reduction method. The specific porous structure formed by the stack of hydrotalcite-derived Ni_1.5Co_0.5AlO nanosheets can increase the transfer mass efficiency of the reactants (O₂, NO, and soot) and the strong Pt-Ni_1.5Co_0.5AlO interaction can weaken the Ni/Co-O bond for promoting the mobility of lattice oxygen and the formation of surface-oxygen vacancies. The Pt_n/Ni_1.5Co_0.5AlO catalysts exhibited excellent catalytic activity and stability during diesel soot combustion under the loose contact mode between soot particles and catalysts. Among all the catalysts, the Pt₂/Ni_1.5Co_0.5AlO catalyst showed the highest catalytic activities for soot combustion (T₅₀ = 350 °C, TOF = 6.63 × 10^-3 s^-1). Based on the characterization results, the catalytic mechanism for soot combustion is proposed: the synergistic effect of Pt and dual Ni/Co cations in the Pt/Ni_1.5Co_0.5AlO catalysts can promote the vital step of catalyzing NO oxidation to NO₂ in the NO-assisted soot oxidation mechanism. This insight into the synergistic effect of Pt and dual Ni/Co cations for soot combustion provides new strategies for reducing the amounts of noble metals in high-efficient catalysts.

Single-Atom Catalysts: A Review of Synthesis Strategies and Their Potential for Biofuel Production

Biofuels have been derived from various feedstocks by using thermochemical or biochemical procedures. In order to synthesise liquid and gas biofuel efficiently, single-atom catalysts (SACs) and single-atom alloys (SAAs) have been used in the reaction to promote it. SACs are made up of single metal atoms that are anchored or confined to a suitable support to keep them stable, while SAAs are materials generated by bi- and multi-metallic complexes, where one of these metals is atomically distributed in such a material. The structure of SACs and SAAs influences their catalytic performance. The challenge to practically using SACs in biofuel production is to design SACs and SAAs that are stable and able to operate efficiently during reaction. Hence, the present study reviews the system and configuration of SACs and SAAs, stabilisation strategies such as mutual metal support interaction and geometric coordination, and the synthesis strategies. This paper aims to provide useful and informative knowledge about the current synthesis strategies of SACs and SAAs for future development in the field of biofuel production.

Migration of Silver and Copper Nanoparticles from Food Coating

Packaging containing nanoparticles (NPs) can increase the shelf life of products, but the presence of NPs may hazards human life. In this regard, there are reports regarding the side effect and cytotoxicity of nanoparticles. The main aim of this research was to study the migration of silver and copper nanoparticles from the packaging to the food matrix as well as the assessment techniques. The diffusion and migration of nanoparticles can be analyzed by analytical techniques including atomic absorption, inductively coupled plasma mass spectrometry, inductively coupled plasma atomic emission, and inductively coupled plasma optical emission spectroscopy, as well as X-ray diffraction, spectroscopy, migration, and titration. Inductively coupled plasma-based techniques demonstrated the best results. Reports indicated that studies on the migration of Ag/Cu nanoparticles do not agree with each other, but almost all studies agree that the migration of these nanoparticles is higher in acidic environments. There are widespread ambiguities about the mechanism of nanoparticle toxicity, so understanding these nanoparticles and their toxic effects are essential. Nanomaterials that enter the body in a variety of ways can be distributed throughout the body and damage human cells by altering mitochondrial function, producing reactive oxygen, and increasing membrane permeability, leading to toxic effects and chronic disease. Therefore, more research needs to be done on the development of food packaging coatings with consideration given to the main parameters affecting nanoparticles migration.