RESUMO
The recycling and utilization of precious metals have emerged as a critical research focus in advancing the development of the circular economy. Among numerous methods for recovering precious metals such as gold, adsorbents with both high adsorption selectivity and capacity have become key technologies. This article incorporated the N-phenylpyrrolidine into a flexible porous polynorbornene backbone to create a class of distinctive porous organic polymers, named BIT-POP-14-BIT-POP-17. Through a reductive capture mechanism, the reductive adsorption sites of N-phenylpyrrolidine coordinate selectively with precious metals, the reduced metal is captured by the hierarchically porous polymers with flexible backbone. This approach leads to remarkable gold recovery efficiency, achieving a record of 2321 mg g-1 at ambient conditions, and 3020 mg g-1 under UV light, surpassing the theoretical limit. The porous polymers are filled in a column for a continuous uptake of gold from waste printed circuit boards (PCBs), showing recovery efficiency toward gold as high as 95% after 84 h. Overall, this work offers a new perspective on designing novel adsorbents for precious metal recovery, providing inspiration for researchers to explore novel adsorption modes and contribute to the advancement of the circular economy.
RESUMO
Although side-chain polyazobenzenes have been extensively studied, main-chain polyazobenzenes (abbreviated MCPABs) are rarely reported due to the challenges associated with difficulty in synthetic chemistry and photoisomerization of azo bonds in MCPABs. Thus, it is highly demanded to develop new mechanisms other than photoisomerization of azo bonds in MCPABs to extend their applications. In this work, we created a new series of N-linked MCPABs via fast NaBH4-mediated reductive coupling polymerization on N-substituted bis(4-nitrophenyl)amines. The structure of MCPABs has been characterized by comprehensive solid-state NMR experiments such as CPMAS 13C NMR with long and short contact times, cross-polarization polarization-inversion (CPPI), and cross-polarization nonquaternary suppressed (CPNQS). The azo bonds in MCPABs were found to be promising for acid vapor sensing, being acidified to form azonium ion with significant color change from red to green. And the azonium of MCPABs turned from green to red when exposed to base vapor, thus suitable for base vapor sensing.
RESUMO
It is demonstrated that difluoromethyl diazomethane (HCF2CHN2) can react with a broad range of carboxylic acids. The reaction is convenient, operationally simple, mild, and tolerant of a variety of different functional groups. In sharp contrast, trifluoromethyl diazomethane (CF3CHN2) fails to react with carboxylic acids in most solvents, and in acetonitrile this reagent instead undergoes an interrupted esterification (a Mumm reaction) to yield N-trifluoroethyl imides. This striking example of the ability of a single F-for-H substitution to alter a reaction pathway was rationalized through a DFT study.
