Reactivity and mass loss are considered mutually exclusive in conventional zero-valent metal (ZVM) technology to treat environmental contaminants. Here, we report the outstanding performance of Co-based metallic glass (MG) in degrading an aqueous solution of azo dye, thus eliminating this trade-off. Ball-milled Co-based MG powders completely degrade Acid Orange II at an ultrafast rate. The surface-area-normalized rate constant of Co-based MG powders was one order of magnitude higher than that of Co-based crystalline counterparts and three orders of magnitude higher than that of the widely studied Fe0 powders. The coordinatively unsaturated local structure in Co-based MG responds to the catalysis for degradation, resulting in very low mass loss. Wide applicability and good reusability were also present. Co-based MG is the most efficient material for azo dye degradation reported thus far, and will promote the practical application of MGs as functional materials.
Asymmetric epoxidation of allylic alcohols is an important reaction in synthetic organic chemistry. [1] Sharpless and Katsuki [2] have provided an excellent homogeneous catalytic system for this reaction which consists of titanium tetraisopropoxide and a chiral dialkyl tartrate. Heterogeneous systems have tremendous advantages over homogeneous catalytic systems. [3] One of the most attractive advantages is the easy separation of the product from the catalyst without tedious experimental work-up.Different approaches have been used in the preparation of heterogeneous Sharpless-type catalytic systems for the asymmetric epoxidation of allylic alcohols. An early attempt to develop a polymer-supported system employed a single tartrate ester unit bound to a polystyrene resin; [4a] in this case, the chiral induction was only modest (ca. 50 ± 60 % ee). Choudary et al. [4b] reported the asymmetric epoxidation of allylic alcohols with a heterogeneous titanium-pillared montmorillonite catalyst in the presence of chiral tartrate ester. However, the preparation of the solids seems to be difficult to reproduce. [5] Hormi and co-workers [4c, 4d] synthesized insoluble branched/crosslinked poly(tartrate ester)s and investigated their use as optically active ligands in the heterogeneous asymmetric epoxidation of allylic alcohols with titanium tetraisopropoxide and tert-butyl hydroperoxide. These geltype polymeric ligands swell during the catalytic reaction. Basset and co-workers [4e] reported silica-supported tantalum catalysts for the enantioselective epoxidation of allylic alcohols in the presence of chiral tartrate derivatives. Their result is comparable to that obtained in the homogeneous Sharpless reaction. However, the organometallic tantalum compound used in the synthesis is not easy to prepare. [6] The preparation of organic ± inorganic hybrid materials is of growing interest. [7, 8] In contrast to organic polymers, organic ± inorganic hybrid materials do not swell or dissolve in organic solvents, and have many advantages over most organic polymers because of their superior mechanical and thermal stabilities. Moreover, any leaching could be avoided as the organic moieties are covalently attached to the inorganic supports. For hybrid materials, the design and synthesis of chiral catalytic materials [8] with high enantioselectivities are especially attractive. [8c±e] Highly efficient and enantioselective transition metal complexes have been reported in the literature. The design and synthesis of chiral hybrids with activity and enantioselectivity similar to that of homogeneous catalysts remain a challenge. Few reports have appeared on the synthesis of organic ± inorganic hybrid chiral materials and on their use as heterogeneous catalysts in enantioselective reactions. [8c±e] We report herein the synthesis of organic ± inorganic hybrid chiral materials by grafting a chiral tartaric acid derivative onto the surface of silica and in the mesopores of MCM-41 material (Scheme 1 b), and provide the first example of their su...
To reduce the surface figure error induced by mechanical strains during the integration process of a high-precision mirror, a cost-efficient compensation method by spring preloads is proposed. The study is based on the primary mirror of a Ritchey–Chrétien space telescope with a focal length of 1200 mm. First, the surface figure degradation of the mirror during the assembly process is expressed and analyzed. Then, a finite element model of the mirror and its mounting structure is established, and surface deformations caused by different preloading forces are simulated. An optimized combination of different preloads was obtained through data fitting, and the influence of the combined preload on the mirror was analyzed. The simulation results show that ring preloads mainly affect spherical aberration and high-order spherical aberrations, while quadrupole preloads mainly affect astigmatism, and the optimized preload can compensate for the surface figure error from
0.120
λ
RMS to
0.088
λ
RMS. Last, the surface figure error of the mirror is measured by experiments under optimized preloads, and the result is
0.084
λ
RMS, which verifies the correctness of the analysis process and effectiveness of the compensation method.
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