Mixed transition metal oxides (MTMOs) have enormous potential applications in energy and environment. Their use as catalysts for the treatment of environmental pollution requires further enhancement ...in activity and stability. This work presents a new synthesis approach that is both convenient and effective in preparing binary metal oxide catalysts (CeCuOx) with excellent activity by achieving molecular‐level mixing to promote aliovalent substitution. It also allows a single, pure MTMO to be prepared for enhanced stability under reaction by using a bimetallic metal–organic framework (MOF) as the catalyst precursor. This approach also enables the direct manipulation of the shape and form of the MTMO catalyst by controlling the crystallization and growth of the MOF precursor. A 2D CeCuOx catalyst is investigated for the oxidation reactions of methanol, acetone, toluene, and o‐xylene. The catalyst can catalyze the complete reactions of these molecules into CO2 at temperatures below 200 °C, representing a significant improvement in performance. Furthermore, the catalyst can tolerate high moisture content without deactivation.
A mixed transition metal oxide catalyst is prepared via the thermal transformation of a bimetallic metal–organic framework precursor. The as‐synthesized CeCuOx catalyst exhibits unique properties with high aliovalent substitution, abundant oxygen vacancies, and exposed active crystal planes, leading to high reactivity and moisture tolerance for the complete oxidation of various volatile organic compounds (i.e., toluene, o‐xylene, acetone, and methanol).
The scope of hydrogel applications can be greatly expanded by the improvement of mechanical properties. However, enhancement of nanocomposite hydrogels (NC gels) has been severely limited because the ...size of crosslinking nanoparticles is too large, at least in one dimension. Here we report a new strategy to synthesize non-aggregated spherulite nanoparticles, with diameters <5 nm, in aqueous solution, and their enhancement to hydrogel. The stress and stretch ratio at rupture of our NC gel are 430 and 121 KPa with only 40-p.p.m. nanoparticle content. The NC gel containing 200-p.p.m. nanoparticles can revert to 90% of its original size after enduring 100-MPa compressive stress. Our results demonstrate that the suppression of nanoparticle size without aggregation helps to establish a super stretchable and high-toughness hydrogel network at very low inorganic content.
Clean surface of graphene was obtained at 500 °C and characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). In the XPS C1s spectrum of ...graphene, besides an asymmetric sp2 carbon peak and a π-π∗ shake-up peak appeared, an additional sp3 carbon peak representing sp3 defects was also present. In the ToF-SIMS positive ion spectrum of graphene, a series of CxH2+ ions originated from the defects of graphene was found. To determine the origin of the CxH2+ ions, defects were created on the surface of nearly defect-free highly oriented pyrolytic graphite (HOPG) by bombarding it with a Cs+ ion beam at various sputtering doses. A detailed examination of the positive ion spectra of ion-bombarded HOPG surfaces reveals the presence of the CxH2+ ions, confirming that these CxH2+ ions, which came from the defects created on the sputtered HOPG surfaces, are similar to the defects present on graphene surface. A sp3 carbon peak at 285.3 eV, representing sp3 defects appeared in the XPS spectra of sputtered HOPG samples, confirms that the surface of the sputtered HOPG is similar to that of graphene. Fragmentation mechanisms of selected ions in the ToF-SIMS spectra of graphene and HOPG were proposed.
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Luminescent defects in hexagonal boron nitride (hBN) have emerged as promising single photon emitters (SPEs) due to their high brightness and robust operation at room temperature. The ability to ...create such emitters with well‐defined optical properties is a cornerstone toward their integration into on‐chip photonic architectures. Here, an effective approach is reported to fabricate hBN SPEs with desired emission properties in distinct spectral regions via the manipulation of boron diffusion through copper during atmospheric pressure chemical vapor deposition (CVD)—a process termed gettering. Using the gettering technique the resulting zero‐phonon line is deterministically placed between the regions 550 and 600 nm or from 600 to 650 nm, paving the way for hBN SPEs with tailored emission properties. Additionally, rational control over the observed SPE density in the resulting films is demonstrated. The ability to control defect formation during hBN growth provides a cost effective means to improve the crystallinity of CVD hBN films, and lower defect density making it applicable to hBN growth for a wide‐range of applications. The results are important to understand defect formation of quantum emitters in hBN and deploy them for scalable photonic technologies.
Controlling the emission frequency of single photon emitters (SPEs) in hexagonal boron nitride has been a critical goal since their discovery in 2016. This work demonstrates a robust chemical vapor deposition method for producing SPEs of a preselectable frequency and density, based on modification of the catalytic behavior of copper using a gettering effect during growth.
The surface properties of polymer blends are important for many industrial applications. The physical and chemical properties at the surface of polymer blends can be drastically different from those ...in the bulk due to the surface segregation of the low surface energy component. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary mass spectrometry (ToF-SIMS) have been widely used to characterize surface and bulk properties. This review provides a brief introduction to the principles of XPS and ToF-SIMS and their application to the study of the surface physical and chemical properties of polymer blends.
A unique strategy is reported to constrain the nucleation centers for multilayer graphene (MLG) and, later, single‐crystal graphene domains by gettering carbon source on backside of the flat Cu foil, ...during chemical vapor deposition. Hitherto, for a flat Cu foil, the top‐surface‐based growth mechanism is emphasized, while overlooking the graphene on the backside. However, the systematic experimental findings indicate a strong correlation between the backside graphene and the nucleation centers on the top‐surface, governed by the carbon diffusion through the bulk Cu. This understanding steers to devise a strategy to mitigate the carbon diffusion to the top‐surface by using a carbon “getter” substrate, such as nickel, on the backside of the Cu foil. Depth profiling of the nickel substrate, along with the density functional theory calculations, verifies the gettering role of the nickel support. The implementation of the backside carbon gettering approach on single‐crystal graphene growth results in lowering the nucleation density by two orders of magnitude. This enables the single‐crystal domains to grow by 6 mm laterally on the untreated Cu foil. Finally, the growth of large‐area polycrystalline single layer graphene, free of unwanted MLG domains, with significantly improved field‐effect mobility of ≈6800 cm2 V−1 s−1 is demonstrated.
A backside carbon gettering approach is implemented to manipulate top‐surface CVD graphene growth on Cu foil using a Ni support substrate. This strategy limits the nucleation centers for multilayer and single‐crystal graphene domains at the top‐surface through gettering the carbon source at backside of the Cu foil, resulting in high quality uniform single‐crystal graphene.
Defects were created on the surface of highly oriented pyrolytic graphite (HOPG) by sputtering with an Ar+ ion beam, then characterized using X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight ...secondary ion mass spectrometry (ToF‐SIMS) at 500°C. In the XPS C1s spectrum of the sputtered HOPG, a sp3 carbon peak appeared at 285.3 eV, representing surface defects. In addition, 2 sets of peaks, the Cx− and CxH− ion series (where x = 1, 2, 3...), were identified in the ToF‐SIMS negative ion spectrum. In the positive ion spectrum, a series of CxH2+• ions indicating defects was observed. Annealing of the sputtered samples under Ar was conducted at different temperatures. The XPS and ToF‐SIMS spectra of the sputtered HOPG after 800°C annealing were observed to be similar to the spectra of the fresh HOPG. The sp3 carbon peak had disappeared from the C1s spectrum, and the normalized intensities of the CxH− and CxH2+• ions had decreased. These results indicate that defects created by sputtering on the surface of HOPG can be repaired by high‐temperature annealing.
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