During the past decades, academics and practitioners have been extensively focusing on corporate philanthropy as an important part of corporate social responsibility and a vast number of papers have ...been published on this topic in various disciplines. To have a better understanding of the evolution of corporate philanthropy, this paper critically reviews some 60 years of research covering 228 corporate philanthropy documents (including 214 journal articles, 5 dissertations, and 9 books and book chapters) across and between disciplines, and analyzes their content in a systematic and comprehensive manner. A multi‐level and multidisciplinary theoretical framework that synthesizes and integrates the corporate philanthropy literature at micro‐, meso‐, and macro‐levels of analysis is offered. Specifically, the framework presents antecedents, intermediaries (moderators and mediators), consequences of corporate philanthropy, and the underlying mechanisms of the corporate philanthropy–firm performance relationship. This paper helps bridge important knowledge gaps of corporate philanthropy and its relation with firm performance by studying corporate philanthropy at a multi‐level of analysis and applying diverse theoretical frameworks of corporate philanthropy. The paper concludes by offering several suggestions for future research on corporate philanthropy.
Oxidation of magnetite (Fe
O
) has broad implications in geochemistry, environmental science and materials science. Spatially resolving strain fields and defect evolution during oxidation of ...magnetite provides further insight into its reaction mechanisms. Here we show that the morphology and internal strain distributions within individual nano-sized (~400 nm) magnetite crystals can be visualized using Bragg coherent diffractive imaging (BCDI). Oxidative dissolution in acidic solutions leads to increases in the magnitude and heterogeneity of internal strains. This heterogeneous strain likely results from lattice distortion caused by Fe(II) diffusion that leads to the observed domains of increasing compressive and tensile strains. In contrast, strain evolution is less pronounced during magnetite oxidation at elevated temperature in air. These results demonstrate that oxidative dissolution of magnetite can induce a rich array of strain and defect structures, which could be an important factor that contributes to the high reactivity observed on magnetite particles in aqueous environment.
Polycrystalline material properties depend on the distribution and interactions of their crystalline grains. In particular, grain boundaries and defects are crucial in determining their response to ...external stimuli. A long-standing challenge is thus to observe individual grains, defects, and strain dynamics inside functional materials. Here we report a technique capable of revealing grain heterogeneity, including strain fields and individual dislocations, that can be used under operando conditions in reactive environments: grain Bragg coherent diffractive imaging (gBCDI). Using a polycrystalline gold thin film subjected to heating, we show how gBCDI resolves grain boundary and dislocation dynamics in individual grains in three-dimensional detail with 10-nanometer spatial and subangstrom displacement field resolution. These results pave the way for understanding polycrystalline material response under external stimuli and, ideally, engineering particular functions.
Abstract Photocatalysis is a promising technique due to its capacity to efficiently harvest solar energy and its potential to address the global energy crisis. However, the structure–activity ...relationships of photocatalyst during wavelength-dependent photocatalytic reactions remains largely unexplored because it is difficult to measure under operating conditions. Here we show the photocatalytic strain evolution of a single Au nanoparticle (AuNP) supported on a TiO 2 film by combining three-dimensional (3D) Bragg coherent X-ray diffraction imaging with an external light source. The wavelength-dependent generation of reactive oxygen species (ROS) has significant effects on the structural deformation of the AuNP, leading to its strain evolution. Density functional theory (DFT) calculations are employed to rationalize the induced strain caused by the adsorption of ROS on the AuNP surface. These observations provide insights of how the photocatalytic activity impacts on the structural deformation of AuNP, contributing to the general understanding of the atomic-level catalytic adsorption process.
Strain is known to enhance the activity of the oxygen reduction reaction in catalytic platinum alloy nanoparticles, whose inactivity is the primary impediment to efficient fuel cells and metal–air ...batteries. Bragg coherent diffraction imaging (BCDI) was employed to reveal the strain evolution during the voltammetric cycling in Pt–Ni alloy nanoparticles composed of Pt2Ni3, Pt1Ni1, and Pt3Ni2. Analysis of the 3D strain images using a core–shell model shows that the strain as large as 5% is induced on Pt-rich shells due to Ni dissolution. The composition dependency of the strain on the shells is in excellent agreement with that of the catalytic activity. The present study demonstrates that BCDI enables quantitative determination of the strain on alloy nanoparticles during electrochemical reactions, which provides a means to exploit surface strain to design a wide range of electrocatalysts.
Defects can affect all aspects of a material by altering its electronic properties and controlling its chemical reactivity. At defect sites, preferential adsorption of reactants and/or formation of ...chemical species at active sites are observed in heterogeneous catalysis. Understanding the structural response at defect sites during catalytic reactions provides a unique opportunity to exploit defect control of nanoparticle-based catalysts. However, it remains difficult to characterize the strain and defect evolution for a single nanocrystal catalyst in situ. Here, we report Bragg coherent X-ray diffraction imaging of defect dynamics in an individual Pt nanoparticle during catalytic methane oxidation. We observed that the initially tensile strained regions of the crystal became seed points for the development of further strain and subsequent disappearance of diffraction density during oxidation reactions. Our detailed understanding of the catalytically induced deformation at the defect sites and observed reversibility during the relevant steps of the catalytic oxidation process provide important insights of defect control and engineering of heterogeneous catalysts.
Developing new methods that reveal the structure of electrode materials under polarization is key to constructing robust structure–property relationships. However, many existing methods lack the ...spatial resolution in structural changes and fidelity to electrochemical operating conditions that are needed to probe catalytically relevant structures. Here, we combine a nanopipette electrochemical cell with three-dimensional X-ray Bragg coherent diffractive imaging to study how strain in a single Pt grain evolves in response to applied potential. During polarization, marked changes in surface strain arise from the Coulombic attraction between the surface charge on the electrode and the electrolyte ions in the electrochemical double layers, while the strain in the bulk of the crystal remains unchanged. The concurrent surface redox reactions have a strong influence on the magnitude and nature of the strain changes under polarization. Our studies provide a powerful blueprint to understand how structural evolution influences electrochemical performance at the nanoscale.
Dealloying is a process whereby selective dissolution results in a porous, strained structure often with new properties. The process is of both intrinsic and applied interest, and recently has been ...used to make highly active catalysts. The porosity has been studied using electron microscopy while the dealloying‐induced strain has been studied at the ensemble level using X‐ray diffraction. Despite the importance of local, for example, at the individual particle or grain level, strain in controlling the properties of the dealloyed material, it remains unresolved due to the difficulty of imaging 3D strain distributions with nanometer resolution in reactive environments. This information could play an integral role in understanding and controlling lattice strain for a variety of applications. Here, 3D strain distributions in individual nanoparticles and thin film grains in silver–gold alloys undergoing nitric acid‐induced dealloying are imaged by Bragg coherent diffractive imaging. Particles exhibit dramatic changes in their local strains due to dealloying but grains do not. The average lattice in both grains and particles contracts during dealloying. In general, the results reveal significant dealloying‐induced strain heterogeneity at the nanoscale in both isolated and extended samples, which may be utilized to develop advanced nanostructures for a variety of important applications.
The strain distribution in nanomaterials can significantly impact their properties. Using Bragg coherent diffractive imaging, the strain evolution due to dealloying in nanocrystals and grains is investigated. It is found that nanoparticles change their strain dramatically compared to their grain counterparts. These results have implications for strain tuning nanomaterials for a variety of applications.
High catalytic efficiency in metal nanocatalysts is attributed to large surface area to volume ratios and an abundance of under-coordinated atoms that can decrease kinetic barriers. Although overall ...shape or size changes of nanocatalysts have been observed as a result of catalytic processes, structural changes at low-coordination sites such as edges, remain poorly understood. Here, we report high-lattice distortion at edges of Pt nanocrystals during heterogeneous catalytic methane oxidation based on in situ 3D Bragg coherent X-ray diffraction imaging. We directly observe contraction at edges owing to adsorption of oxygen. This strain increases during methane oxidation and it returns to the original state after completing the reaction process. The results are in good agreement with finite element models that incorporate forces, as determined by reactive molecular dynamics simulations. Reaction mechanisms obtained from in situ strain imaging thus provide important insights for improving catalysts and designing future nanostructured catalytic materials.
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