Air vortex flow can induce small amplitude vibration of aerostatic bearings on the order of nanometers, which is known to be harmful to positioning accuracy of aerostatically supported devices in ultra-precision applications. In this paper, in order to suppress the vortex flow and reduce vibration of aerostatic bearings, a novel design of arrayed microhole restrictor (AMR) is proposed, and its effects are numerically and experimentally investigated. By computational fluid dynamics analysis, the transient flow features are studied for aerostatic bearings with AMR and conventional restrictors, and static performances of the bearings are also compared. Vibration strength of the bearing is measured experimentally to validate the effectiveness of AMR. The results show that vortex shedding in the recess is suppressed and the vibration can be effectively reduced by AMR, while load capacity and stiffness of the bearing remain unchanged.

Vortex suppression and nano-vibration reduction of aerostatic bearings by arrayed microhole restrictors

Porphyrin-based materials are excellent chromophores because they strongly absorb visible light and their relatively low-energy lowest unoccupied molecular orbitals thermodynamically favor photoinduced electron transfer. They can generate charge-transfer excited states with and without cocatalyst(s) and ease energy transfer and ultrafast excitation energy migration. Combined with synthetic accessibility, these qualities make them ideal building blocks for porous metal–organic framework (MOF)- and covalent–organic framework (COF)-based photocatalysts to produce solar fuels. This review first describes the structures of the most common porphyrinic MOFs and COFs and their excited-state properties and semiconducting behavior as well as that of derived composites. The generally accepted mechanisms of formation of H2, CH4 and derivatives, and N2 are then reviewed, followed by the detailed examples of nano-MOFs and nano-COFs used for the said purpose: characteristic parameters such as rates of production, turnover numbers (TONs), turnover frequencies (TOFs), and apparent quantum efficiencies are described and compared. This shows that porphyrin-based MOFs and COFs are efficient solar-fuel-producing photocatalysts, with characteristics comparable to those of nonporphyrinic MOF and COF photocatalysts, although, on some occasions, the rates of production fall short of record values. Conversely, porphyrinic MOFs and COFs exhibit the greatest TONs and TOFs of any solar-fuel-producing MOFs or COFs but still face shortcomings concerning selectivity in CH4 production because of the many possible side products. Importantly, while the best rate of photoproduction of solar fuels has been observed from nanoscale photocatalysts, there seem to be no drastic differences in the rate (within μmol–1 h–1 and mmol g–1 h–1) between nanoscale and microscale heterogeneous photocatalysts. This observation suggests that the more active sites are mostly located at or near the surface of the particles. Overall, nanosized porphyrin-based MOFs and COFs show rich and promising photocatalytic properties for generating solar fuels but still have room for improvement. 

Visible-Light-Driven Production of Solar Fuels Catalyzed by Nanosized Porphyrin-Based Metal–Organic Frameworks and Covalent–Organic Frameworks: A Review

In this work, an atomic-layer Fe2O3-modified two-dimensional (2D) porphyrinic metal-organic framework (MOF) was prepared (2D MOF-Fe2O3), which exhibits unique interfacial electron-withdrawing effect via charge transfer pathways from Zn2O8 and C-O bonds to Fe-O bonds. Concretely, the atomic-layer Fe2O3 is deposited on 2D porphyrinic MOF (ZnTCPP) by atomic layer deposition technique to enhance the photocatalytic performance and the subsequent bacteria-killing efficacy. After 20 min light irradiation, the photocatalytic antibacterial efficacy of 2D MOF-Fe2O3 can reach up to 99.9%. The underlying mechanism of enhanced photocatalytic activity is that the heterointerface between 2D MOF and Fe2O3 can facilitate the transfer of lots of photogenerated electrons from 2D MOF to Fe2O3, where 2D MOF and Fe2O3 act as electronic donator and receptor, respectively. This work provides an insight into developing highly effective photocatalysts by using electron-withdrawing modulator to optimize charge transfer pathway. 

Atomic-layer Fe2O3-modified 2D porphyrinic metal-organic framework for enhanced photocatalytic disinfection through electron-withdrawing effect

Atomic-Layer Fe2o3-Modified 2d Porphyrinic Metal-Organic Framework for Enhanced Photocatalytic Disinfection Through Electron-Withdrawing Effect

The nature and degree of defects can fine-tune the light absorption energy (Eabs) and charge transfer energy (ELMCT) of metal-organic frameworks (MOFs), which are important for photocatalytic reactions. Herein, a...

Tailoring Defect-Type and Ligand-Vacancy in Zr(IV) Frameworks for CO2 Photoreduction

Obtaining high-value-added products like C2+ hydrocarbons from CO2 reduction in a photocatalytic system has always remained a great challenge. Herein we fabricated a π-π stacking hybrid photocatalyst by combining two two-dimensional (2D) materials of g-C3N4 and Cu-porphyrin metal-organic framework (MOF). This hybrid photocatalyst exhibited the excellent capability to reduce CO2 into C2H6 in a selectivity of 44% and the selectivity of total hydrocarbons (C2H6 and CH4) was as high as 71%, as one of the best performances among the reported photocatalytic systems. The node sites of 2D-MOF were identified to be critical for the generation of C2H6, and a self-reconstruction during photocatalysis was clarified: the initial paddle-wheel CuII2(COO)4 node was reconstructed to the partially reduced Cu1+δ2(COO)3. Such reconstruction strengthened the trapping of in-situ generated CO and the synergistic action of the dual-Cu-site, therefore, achieved the efficient C-C coupling to form C2H6. 

Self-reconstruction of paddle-wheel copper-node to facilitate the photocatalytic CO2 reduction to ethane

In Fenton or Fenton-like reactions, ·OH obtained by the reductive activation of H2O2 is regarded as the major reactive oxygen species (ROS); however, the generation of other ROS like O2·– and 1O2 cannot be negligible. Since the degradation capability of a certain ROS would be varied to distinctive pollutants, the regulation of ROS production from H2O2 activation should be applicable for a more targeted pollutant degradation. Herein, a series of carbon nitride (C3N4)-supported Fe catalysts with the state of Fe ranging among single-atom, oxide-cluster, and nanoparticle catalysts were fabricated and their activities in photo-Fenton reactions were evaluated. It was uncovered that the single-atom catalyst favored the generation of O2·– and 1O2 via the oxidative activation of H2O2 and the selectivity of 1O2 toward ·OH dynamically increased with the proceeding of H2O2 activation, while the catalysts with an abundance of oxide clusters exhibited a significantly higher conversion of H2O2 to ·OH. In situ FT-IR studies demonstrated that during the H2O2 activation, the single-atom catalyst underwent a more significant surface hydroxylation than the oxide-cluster catalyst. Such a result was further consolidated by the theoretical calculation that the adsorption energy of surface hydroxyl was remarkably higher on the single-atom catalyst. Thereafter, distinctive from the easy desorption of hydroxyl during the reduction of H2O2 to ·OH in oxide-cluster catalysts, the in situ surface hydroxylation on the single-atom catalyst alters the adsorption mode of H2O2 to a H-bonded structure, which steers the selectivity of ROS generation to a more favored oxidative transformation of H2O2 to O2·–/1O2. This work uncovers the decisive role of surface hydroxyl in regulating ROS generation in a heterogeneous Fenton reaction. 

In Situ Hydroxylation of a Single-Atom Iron Catalyst for Preferential 1O2 Production from H2O2

Air bearings had been widely used in ultra-precision machine tools. In order to suppress the micro-vibration caused by air bearing, an effective way is keeping the air flow in laminar state. Porous bearing to control the micro-vibration was proposed in this paper, and the related experiments show that it can meet the requirement of decreasing the micro-vibration to less than 1nm, and the surface of diamond surface can be improved.

B.H. Sheng

Papers

Self-reconstruction of paddle-wheel copper-node to facilitate the photocatalytic CO2 reduction to ethane

In Situ Hydroxylation of a Single-Atom Iron Catalyst for Preferential 1O2 Production from H2O2

Improvement of Diamond-Cutting Surface by Means of Porous Bearing Laminar Flow