Benzotrithiophene-based Covalent Organic Framework Photocatalysts with Controlled Conjugation of Building Blocks for Charge Stabilization

Covalent organic frameworks have recently shown high potential for photocatalytic hydrogen production. However, their structure-property-activity relationship has not been sufficiently explored to identify a research direction for structural design. Herein, we report the design and synthesis of four benzotrithiophene (BTT)-based covalent organic frameworks (COFs) with different conjugations of building units, and their photocatalytic activity for hydrogen production. All four BTT-COFs had slipped parallel stacking patterns with high crystallinity and specific surface areas. The change in the degree of conjugation was found to rationally tune the rate of photocatalytic hydrogen evolution. Based on the experimental and calculation results, the tunable photocatalytic performance could be mainly attributed to the electron affinity and charge trapping of the electron accepting units. This study provides important insights for designing covalent organic frameworks for efficient photocatalysts.     

Inertial-microfluidic radial migration in solid/liquid two-phase flow through a microcapillary: Particle equilibrium position

Although equilibrium of spherical particles under radial migration has been extensively investigated, mostly in macroscale flows with characteristic lengths on the order of centimeters, it is not fully characterized at relatively small Reynolds numbers, 1 ≤ Re ≤ 100. This paper experimentally studies “inertial microfluidic” radial migration of spherical particles in circular Poiseuille flow through a microcapillary. Microparticle tracking experiments are performed to obtain the spatial distribution of the particles by adopting a depth-resolved measurement technique. Through the analysis of the radial distribution of particles, inertial microfluidic circular Poiseuille flow is shown to induce a strong radial migration of particles at substantially small Re, which is quite in contrast to the pipe flows at large Re previously reported. This particle migration phenomenon is so prominent that particle equilibrium positions are formed even at small Re. However, it turns out that there exists a certain critical Re below which particle equilibrium position is almost fixed, but above which it seems to drift toward the channel wall.     

Polymerization and copolymerization of ethene initiated with disiloxane-bridged biscyclopentadienylzirconium complexes and methylaluminoxane

The disiloxane-bridged zirconocene complexes, tetramethyldisiloxanediylbis (cyclopentadienyl)zirconium dichloride and tetramethyldisiloxanediylbis(cyclopentadienyl) dimethylzirconium initiate the homopolymerization of ethene as well as the copolymerization of ethene and α-olefin with a modified methylaluminoxane as cocatalyst. The catalyst systems give resonable activity but the molecular weight of polyethene decreases drastically with increasing polymerization temperature.     

Polymerization of ethene initiated with a mixture of siloxane-bridged mono- and dinuclear zirconocenes

In the polymerization of ethene cocatalyzed with modified methylaluminoxane, the catalyst activities of the siloxane-bridged dinuclear zirconocenes, tetramethyldisiloxanediylbis(cyclopentadienylindenylzirconium dichloride) ( 3 ) and hexamethyltrisiloxanediylbis(cyclopentadienylindenylzirconium dichloride) ( 4 ) were lower than that obtained with the siloxane-bridged mononuclear zirconocene, tetramethyldisiloxanediyldicyclopentadienyldimethylzirconium ( 1 ). On the other hand, weight-average molecular weight M̄_w and ratio of weight- to number-average molecular weights M̄_w/M̄_n of polyethene (PE) obtained with 3 or 4 were higher than those of PE obtained with 1. For a binary mixture of 1/3 or 1/4 , it was found that the obtained PE exhibits a bimodal molecular weight distribution for an appropriate composition of the mixed zirconocenes. M̄_w/M̄_n of PE could be adjusted by changing the relative concentrations of the two zirconocenes.