A full monolayer of superoxide: oxygen activation on the unmodified Ca3Ru2O7(001) surface

Oxygen-Mediated (0D) Cs4PbX6 Formation during Open-Air Thermal Processing Improves Inorganic Perovskite Solar Cell Performance

The desire to commercialize perovskite solar cells continues to mount, motivating the development of scalable production. Evaluations of the impact of open-air processing have revealed a variety of physical changes in the fabricated devices─with few changes having the capacity to be functionalized. Here, we highlight the beneficial role of ambient oxygen during the open-air thermal processing of metastable γ-CsPbI3-based perovskite thin films and devices. Physiochemical-sensitive probes elucidate oxygen intercalation and the formation of Pb-O bonds in the CsPbI3 crystal, entering via iodine vacancies at the surface, creating superoxide (O2-) through electron transfer reactions with molecular oxygen, which drives the formation of a zero-dimensional Cs4PbI6 capping layer during annealing (>330 °C). The chemical conversion permanently alters the film structure, helping to shield the subsurface perovskite from moisture and introduces lattice anchoring sites, stabilizing otherwise unstable γ-CsPbI3 films. This functional modification is demonstrated in γ-CsPbI2Br perovskite solar cells, boosting the operational stability and photoconversion efficiency of champion devices from 12.7 to 15.4% when annealed in dry air. Such findings prompt a reconsideration of glovebox-based perovskite solar cell research and establish a scenario where device fabrication can in fact greatly benefit from ambient oxygen.

Indirect daylight oxidative degradation of polyethylene microplastics by a bio-waste modified TiO2-based material

Microplastics are recognized as an emerging critical issue for the environment. Here an innovative chemical approach for the treatment of microplastics is proposed, based on an oxidative process that does not require any direct energy source (irradiation or heat). Linear low-density polyethylene (LLDPE) was selected as target commodity polymer, due to its widespread use, chemical inertness and inefficient recycling. This route is based on a hybrid material coupling titanium oxide with a bio-waste, rosin, mainly constituted by abietic acid, through a simple sol-gel synthesis procedure. The ligand-to-metal charge transfer complexes formed between rosin and Ti4+ allow the generation of reactive oxygen species without UV irradiation for its activation. In agreement with theorical calculations, superoxide radical ions are stabilized at ambient conditions on the surface of the hybrid TiO2. Consequently, an impressive degradation of LLDPE is observed after 1 month exposure in a batch configuration under indirect daylight, as evidenced by the products revealed by gas chromatography-mass spectrometry analysis and by chemical and structural modifications of the polymer surface. In a context of waste exploitation, this innovative and sustainable approach represents a promising cost-effective strategy for the oxidative degradation of microplastics, without producing any toxic by-products.

Bimetallic Zeolitic Imidazole Frameworks for Improved Stability and Performance of Intrusion-Extrusion Energy Applications

Hydrophobic flexible zeolitic imidazole frameworks (ZIFs) represent reference microporous materials in the area of mechanical energy storage, conversion, and dissipation via non-wetting liquid intrusion-extrusion cycle. However, some of them exhibit drawbacks such as lack of stability, high intrusion pressure, or low intrusion volume that make them non-ideal materials to consider as candidates for real applications. In this work, we face these limitations by exploiting the hybrid ZIF concept. Concretely, a bimetallic SOD-like ZIF consisting of Co and Zn ions was synthesized and compared with Co-ZIF (ZIF-67) and Zn-ZIF (ZIF-8) showing for the first time that the hybrid ZIF combines the good stability of ZIF-8 with the higher water intrusion volume of ZIF-67. Moreover, it is shown that the hybrid-ZIF approach can be used to tune the intrusion/extrusion pressure, which is crucial for technological applications.

Substitutional Coinage Metals as Promising Defects for Adsorption and Detection of Gases on MoS2 Monolayers: A Computational Approach

Defective molybdenum disulfide (MoS₂) monolayers (MLs) modified with coinage metal atoms (Cu, Ag and Au) embedded in sulfur vacancies are studied at a dispersion-corrected density functional level. Atmospheric constituents (H₂, O₂ and N₂) and air pollutants (CO and NO), known as secondary greenhouse gases, are adsorbed on up to two atoms embedded into sulfur vacancies in MoS₂ MLs. The adsorption energies suggest that the NO (1.44 eV) and CO (1.24 eV) are chemisorbed more strongly than O₂ (1.07 eV) and N₂ (0.66 eV) on the ML with a cooper atom substituting for a sulfur atom. Therefore, the adsorption of N₂ and O₂ does not compete with NO or CO adsorption. Besides, NO adsorbed on embedded Cu creates a new level in the band gap. In addition, it was found that the CO molecule could directly react with the pre-adsorbed O₂ molecule on a Cu atom, forming the complex OOCO, via the Eley-Rideal reaction mechanism. The adsorption energies of CO, NO and O₂ on Au_2S2, Cu_2S2 and Ag_2S2 embedded into two sulfur vacancies were competitive. Charge transference occurs from the defective MoS₂ ML to the adsorbed molecules, oxidizing the later ones (NO, CO and O₂) since they act as acceptors. The total and projected density of states reveal that a MoS₂ ML modified with copper, gold and silver dimers could be used to design electronic or magnetic devices for sensing applications in the adsorption of NO, CO and O₂ molecules. Moreover, NO and O₂ molecules adsorbed on MoS₂-Au₂s₂ and MoS₂-Cu₂s₂ introduce a transition from metallic to half-metallic behavior for applications in spintronics. These modified monolayers are expected to exhibit chemiresistive behavior, meaning their electrical resistance changes in response to the presence of NO molecules. This property makes them suitable for detecting and measuring NO concentrations. Also, modified materials with half-metal behavior could be beneficial for spintronic devices, particularly those that require spin-polarized currents.

Oxidation and Storage Mechanisms for Nitrogen Oxides on Variously Terminated (001) Surfaces of SrFeO3-δ and Sr3Fe2O7-δ Perovskites

The Ruddlesden-Popper (RP)-type layered perovskite is a candidate material for a new nitrogen oxide (NO_x) storage catalyst. Here, we investigate the adsorption and oxidation of NO_x on the (001) surfaces of RP-type oxide Sr₃Fe₂O_7-δ for all of the terminations by comparing to those of simple perovskite SrFeO_3-δ by the density functional theory (DFT) calculations. The possible (001) cleavages of Sr₃Fe₂O₇ generate two FeO₂- and three SrO-terminated surfaces, and the calculated surface energies indicated that the SrO-terminated surface generated by the cleavage at the rock salt layer is the most stable one. The oxygen of the FeO₂-terminated surfaces could be removed with significantly low energy because the process involves the favorable reduction of the Fe⁴⁺ site. Consequently, the surface oxygen at the FeO₂ site could easily oxidize adsorbed NO to NO₂ by the Mars-van Krevelen mechanism. The resulting oxygen vacancy in the surface would be filled easily with lattice oxygen in bulk. The oxidation of NO with adsorbed molecular O₂ was unfavorable by both the Langmuir-Hinshelwood and Eley-Rideal mechanisms because this process does not involve the reduction of the Fe⁴⁺ site. The oxygen of the SrO-terminated surfaces was tightly bound and acted as the adsorption site of NO and NO₂. An electron transfer strengthened the NO_x binding to the surface by forming nitrite (NO₂^-) or nitrate (NO₃^-) species. The DFT calculations revealed that the RP-type structure promoted NO_x oxidation and storage properties by forming active oxygen due to the Jahn-Teller distortion and by exposing SrO-terminated surfaces due to the cleavage at the rock salt layer.

Metal-free activation of molecular oxygen by covalent triazine frameworks for selective aerobic oxidation

Oxygen activation is a critical step in ubiquitous heterogeneous oxidative processes, most prominently in catalysis, electrolysis, and pharmaceutical applications. We present here our findings on metal-free O₂ activation on covalent triazine frameworks (CTFs) as an important class of N-rich materials. The O₂ activation process was studied for the formation of aldehydes, ketones and imines. A detailed mechanistic study of O₂ activation and the role of nitrogen heteroatoms were comprehensively investigated. The electron paramagnetic resonance (EPR) and control experiments provide strong evidence for the reaction mechanism proving the applicability of the CTFs to activate oxygen into superoxide species. This report highlights the importance of a self-templating procedure to introduce N functionalities for the development of metal-free catalytic materials. The presented findings reveal an important step toward the use of CTFs as inexpensive and high-performance alternatives to metal-based materials not only for catalysis but also for biorelated applications dealing with O₂ activation.

Adsorbate-induced structural evolution changes the mechanism of CO oxidation on a Rh/Fe3O4(001) model catalyst

The structure of a catalyst often changes in reactive environments, and following the structural evolution is crucial for the identification of the catalyst's active phase and reaction mechanism. Here we present an atomic-scale study of CO oxidation on a model Rh/Fe₃O₄(001) "single-atom" catalyst, which has a very different evolution depending on which of the two reactants, O₂ or CO, is adsorbed first. Using temperature-programmed desorption (TPD) combined with scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), we show that O₂ destabilizes Rh atoms, leading to the formation of Rh_xO_y clusters; these catalyze CO oxidation via a Langmuir-Hinshelwood mechanism at temperatures as low as 200 K. If CO adsorbs first, the system is poisoned for direct interaction with O₂, and CO oxidation is dominated by a Mars-van-Krevelen pathway at 480 K.