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Vishwakarma, Niraj K.,Hwang, Yoon-Ho,Adiyala, Praveen Reddy,Kim, Dong-Pyo American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.49
<P>Many efforts have been made on stimuli-responsive switchable catalysis to trigger catalytic activity over various chemical reactions. However, the reported light-, pH- or chemically responsive organocatalysts are mostly incomplete in the aspects of shielding efficiency and long-term performance. Here, we advance the flow-assisted switchable catalysis of metal ions in a microenvelope system that allows the on-off catalysis mode on demand for long-lasting catalytic activity. Various metal-ion catalysts can be selectively embedded in a novel polymeric core-shell of the heteroarm star copolymer of poly(styrene) and poly(4-vinylpyridine) emanated from a polyhedral oligomeric silsesquioxane center. The immobilized core-shell polymer on the inner wall of a poly(dimethylsiloxane) envelope microreactor shows on-off switching catalysis between the expanded active mode and contracted protective mode under continuous flow of solvents or subsequent dry conditions. In particular, the preserved catalytic activity of toxic Hg<SUP>2+</SUP> for oxymercuration was demonstrated even for 2 weeks without leaching, whereas the activity of moisture-sensitive Ru<SUP>3+</SUP> ions for polymerization of methyl methacrylate was maintained even after 5 days from an open atmosphere. It is practical that the tight environment of the enveloped microfluidic system facilitates cyclic switching between the reaction-“on” and -“off” modes of such toxic, sensitive/expensive catalysts for long-term prevention and preservation.</P> [FIG OMISSION]</BR>
Singh, Vikram,Jang, Seungwook,Vishwakarma, Niraj K,Kim, Dong-Pyo Nature Publishing Group 2018 NPG Asia Materials Vol.10 No.1
<P>Covalent organic frameworks (COFs) are two-dimensional/three-dimensional crystalline polymeric materials with diverse molecular backbones and topologies and are strong candidates for numerous applications. However, the ready availability of these materials is a challenge. The key issues are slow production rates, harsher and longer reaction conditions, and a need for post-synthetic modification to obtain desired molecular functionalities. Only a few studies, including those using microfluidic techniques, have focused on refining these factors, but these reports lack synthetic continuity and scalability. Herein, we present a fast, intensified and continuous synthesis and post-synthetic modification of beta-ketoenamine-linked COFs by confining organic building units into moving microdroplets in a transparent capillary. This study introduces a one-step, facile approach to serially modify NO2- to NH2-substituted COFs in a fraction of the time, effort and cost of traditional methods. These results may stimulate the development of novel COFs with unique chemistries and functions for various applications.</P>
Ramanjaneyulu, Bandaru T.,Vishwakarma, Niraj K.,Vidyacharan, Shinde,Adiyala, Praveen Reddy,Kim, Dong-Pyo Korean Chemical Society 2018 Bulletin of the Korean Chemical Society Vol.39 No.6
In the past decade, microreaction technology has been attracted much attention to the scientific community as one of the subareas in chemical synthesis. The microreactor improves the yield with higher selectivity, and also facilitates the reactions by simple, safe, fast, and green approaches. This review gives an overview on our contributions to develop versatile continuous-flow syntheses and process technology by exampling gas-liquid binary phase in modified PDMS microreactors, and process intensification for safe operation of toxic/hazardous chemistry by generating hazardous chemicals to end utilization via various separation techniques in newly devised systems as well as ordinary capillary reactors. Furthermore, it covers process technology for ultrafast organic synthesis such as submillisecond control of short-lived intermediates in a polyimide chip reactor. These works provide outlooks for integrated and automated flow chemistry via one-flow/feed to end concept, i.e., useful in pharmaceutical industry, toward enabling new and innovative chemistry beyond limits of a batch reactor.