Separating molecules or ions with sub-Angstrom scale precision is important but technically challenging. Achieving such a precise separation using membranes requires Angstrom scale pores with a high level of pore size uniformity. Herein, we demonstrate that precise solutesolute separation can be achieved using polyamide membranes formed via surfactantassembly regulated interfacial polymerization (SARIP). The dynamic, self-assembled network of surfactants facilitates faster and more homogeneous diffusion of amine monomers across the water/hexane interface during interfacial polymerization, thereby forming a polyamide active layer with more uniform sub-nanometre pores compared to those formed via conventional interfacial polymerization. The polyamide membrane formed by SARIP exhibits highly size-dependent sieving of solutes, yielding a step-wise transition from low rejection to near-perfect rejection over a solute size range smaller than half Angstrom. SARIP represents an approach for the scalable fabrication of ultra-selective membranes with uniform nanopores for precise separation of ions and small solutes.
Single-site
catalysts (SSCs) have drawn considerable attention,
because of their superior behaviors in catalysis. However, the origin
of promoting the effect of a single site is not well understood. Here,
we take the single-atom Ni1/Mg(100) and single-site Ni4/Mg(100) catalysts as a case study to elucidate their behaviors
under the complex dry reforming of methane (DRM, CO2 +
CH4→ 2CO + 2H2) reaction by combining
theoretical modeling (density functional theory and kinetic Monte
Carlo simulation) and experimental studies. The synergy between single
Ni atom and MgO is found to improve the binding property of MgO; yet,
it is not enough to dissociate CO2 and CH4.
It can be achieved by the single-site Ni4/MgO(100) catalyst,
enabling the formations of CO, H2, and H2O under
the DRM conditions. During this process, coking, as observed for bulklike
Ni particles, is eliminated. By confining the reaction to occur at
the isolated Ni sites in the SSC, the Ni4/MgO(100) catalyst
is able to balance the CO2 and CH4 activations,
which is identified as the key for tuning the DRM activity and selectivity
of Ni/MgO catalysts. The theory-identified promotion introduced by
increasing the size of MgO-supported Ni clusters from Ni1 to Ni4 and the MgO-introduced site confinement of single-site
catalysts are verified by corresponding experimental studies, highlighting
the essential roles of confined sites in tuning the performance of
SSCs during complex catalytic processes.
The finite-element approach of absolute nodal coordinate formulation (ANCF) is a possible way to simulate the deployment dynamics of a large-scale mesh reflector of satellite antenna. However, the large number of finite elements of ANCF significantly increases the dimension of the dynamic equations for the deployable mesh reflector and leads to a great challenge for the efficient dynamic simulation. A new parallel computation methodology is proposed to solve the differential algebraic equations for the mesh reflector multibody system. The mesh reflector system is first decomposed into several independent subsystems by cutting its joints or finite-element grids. Then, the Schur complement method is used to eliminate the internal generalized coordinates of each subsystem and the Lagrange multipliers for joint constraint equations associated with the internal variables. With an increase of the number of subsystems, the dimension of simultaneous linear equations generated in the numerical solution process will inevitably increase. By using the multilevel decomposition approach, the dimension of the simultaneous linear equations is further reduced. Two numerical examples are used to validate the efficiency and accuracy of the proposed parallel computation methodology. Finally, the dynamic simulation for a 500 s deployment process of a complex AstroMesh reflector with over 190,000 generalized coordinates is efficiently completed within 78 hrs.
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