A new technique of zero-valent zinc coupled with ascorbic acid (ZVZ/AA) was developed and applied to debrominate the 2,2′,4,4′-Tetrabromodiphenyl ether (BDE-47), which achieved high conversion and rapid debromination of BDE-47 to less- or non-toxic forms. The reaction conditions were optimized by the addition of 100 mg/L ZVZ particles and 3 mmol/L AA at original solution pH = 4.00 using the solvent of methanol/H 2 O (v:v = 4:6), which could convert approximately 94% of 5 mg/L BDE-47 into lower-brominated diphenyl ethers within a 90 min at the ZVZ/AA system. The high debromination of BDE-47 was mainly attributed to the effect of AA that inhibits the formation of Zn(II)(hydr)oxide passivation layers and promotes the corrosion of ZVZ, which leads to increase the reactivity of ZVZ. Additionally, ion chromatography and gas chromatography mass spectrometry analyses revealed that bromine ion and lower-debromination diphenyl ethers formed during the reduction of BDE-47. Furthermore, based on the generation of the intermediates products, and its concentration changes over time, it was proposed that the dominant pathway for conversion of BDE-47 was sequential debromination and the final products were diphenyl ethers. These results suggested that the ZVZ/AA system has the potential for highly efficient debromination of BDE-47 from wastewater.
Min Chen,Jiangzhou Luo,Jun Hu,Yuxuan Zhao,Honglei Ling,Xueping Zong,Song Xue
The network polyimide (PI) precursor is a promising candidate to fabricate the advanced carbon molecular sieve (CMS) membrane since its robust crosslinked structure could prevent pore structure collapse during CMS formation. Exploring the relationship between network PI precursor structure and CMS membrane is highly significant. Herein, a novel brominated network PI precursor was fabricated via in-situ cross-linking technique firstly, and then the thermally induced bromination/debromination process was applied to tune the microporosity and gas transport properties of network PI precursor and its derived CMS membranes. After the bromination/debromination and carbonization at 550 °C, the resultant CMS membrane exhibited both high gas permeability and gas selectivities compared to its un-brominated network PI precursor derived CMS membrane. This is due to the bromination/debromination and carbonization enable the CMS membrane possesses large d -spacing values (11.06 Å), high BET surface areas (538.57 m 2 /g), and high percentage (∼71 %) of ultra-micropores. For instance, 6F-TA/TA-Br-550/30 membrane exhibits great CO 2 /CH 4 separation ability, with a CO 2 permeability of 6300 Barrer and a CO 2 /CH 4 selectivity of 46.11, which is suppressed the latest 2019 trade-off curves. We anticipate that the present bromination/debromination and carbonization could provide a fresh perspective on the rational design of network PI precursor and its derived CMS membrane with excellent gas separation performance.
Jun Hu,Jiangzhou Luo,Yuxuan Zhao,Min Chen,Honglei Ling,Xiaoting Zhou,Song Xue
Constructing membranes that possess both exceptional gas transport property and strong resistance to CO 2 -induced plasticization is a crucial need in membrane separation , yet it still stands as an ongoing challenge. In present study, we firstly added the bromine atom into the 2, 2′-bis(trifluoromethyl)benzidine (TF) to synthesis two new bromine substituted diamines, and subsequently one of the brominated diamines was employed as a comonomer alongside commercial tris(4-aminophenyl)amine (TAPA) and dianhydride 6FDA to prepare the network polyimide (PI) membrane via copolymerization . Following this, these new brominated PIs would undergo debromination process during the subsequent heating treatment. As a result, the bromination/debromination effect created new microporosity , which increased the d-spacing and BET surface area of the membrane, thereby largely enhancing the crosslinked PI membrane’s gas separation performance. Moreover, the robust network structures achieved through in-situ crosslinking way, derived from a segment of trifunctional TAPA monomers , enhance the resultant membrane's resistance to CO 2 plasticization issue. An exemplified membrane referred to as 6 F-TA/TF-dBr-450 membrane displays outstanding CO 2 /CH 4 separation capabilities, with a CO 2 permeability of 1420.56 Barrer and a CO 2 /CH 4 selectivity of 39.67, surpassing the 2008 Roberson upper bound by a considerable margin. Besides, this membrane demonstrates outstanding durability against CO 2 -induced plasticization, showcasing its strength under pressures of at least 35 Bar.
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