Design
and fabrication of thin film nanocomposite (TFN) membranes
with tunable solvent permeation properties is highly required to meet
the demands of practical applications. Herein, a series of TFN membranes
are elaborately fabricated by embedding cyclodextrins (CDs) into hydrophilic
polymeric membrane (e.g., polyethylenimine, PEI). Within the active
layer, hydrophobic cavities of CDs serve as exquisite pathways for
nonpolar solvents, whereas the free volume cavities of the PEI matrix
act as efficient pathways for polar solvents, constructing a dual-pathway
nanostructure. The solvent permeation properties of these two pathways
can be accurately tuned by adjusting the cavity size of CD and the
fractional free volume (FFV) of PEI. Increasing the cavity size of
CD allows larger nonpolar solvent to permeate, meanwhile increasing
solvent flux. For instance, varying the cavity size from 0.60 to 0.75
nm elevates the toluene (0.60 nm) permeance from 0.13 to 2.52 L m–2 h–1 bar –1. Similar
behaviors are observed for polar solvents when increasing the FFV
of PEI by adjusting the PEI–CD interfacial interactions. Particularly,
the isopropyl alcohol permeance is elevated from 3.37 to 4.16 L m–2 h–1 bar –1 when
increasing FFV from 0.489% to 0.502%. Moreover, the rejection ability
and extended trial of TFN membranes are also explored.
Summary
Hazardous materials, such as heavy metals, are the major sources of health risk. Using genetically modified organisms (GMOs) to dispose heavy metals has the advantages of strong environmental compatibility and high efficiency. However, the biosecurity of GMOs used in the environment is a major concern. In this study, a self‐controlled genetic circuit was designed and carefully fine‐tuned for programmable expression in Pseudomonas putida KT2440, which is a widely used strain for environmental bioremediation. The cell behaviours were controlled by automatically sensing the variation of Hg2+ concentration without any inducer requirement or manual interventions. More than 98% Hg2+ was adsorbed by the engineered strain with a high cell recovery rate of 96% from waterbody. The remaining cells were killed by the suicide module after the mission was accomplished. The escape frequency of the engineered P. putida strain was lower than 10−9, which meets the recommendation of US NIH guideline for GMOs release (<10−8). The same performance was achieved in a model experiment by using natural lake water with addition of Hg2+. The microbial diversity analysis further confirmed that the remediation process made little impact on the indigenous ecosystem. Thus, this study provides a practical method for environmental remediation by using GMOs.
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