Sulfonated Sub-1-nm Metal–Organic Framework Channels with Ultrahigh Proton Selectivity
Authors: Chen Zhao
Xingya Li
Yinlong Zhu
Ranwen Ou
Christopher D Easton
Tianyue Qian
Matthew R Hill
Huanting Wang
Cordelia Selomulya
Huacheng Zhang
Jue Hou
Journal: Journal of the American Chemical Society (2020)
Discipline: CHEMISTRY
Keywords: Biological proton channels; artificial proton channels; sulfonated metal-organic frameworks; UiO-66-X; ion conductance
Affiliations: Department of Chemical Engineering, Monash University, Clayton, Victoria 3800, Australia., Manufacturing, CSIRO, Clayton, 3168, Australia., School of Chemical Engineering, UNSW, Sydney, NSW 2052, Australia.

Abstract:  Biological proton channels are sub-1-nm protein pores with ultrahigh proton (H+) selectivity over other ions. Inspired by biological proton channels, developing artificial proton channels with biological-level selectivity is of fundamental significance for separation science. Herein we report synthetic proton channels fabrication based on sulfonated metal-organic frameworks (MOFs), UiO-66-X, X = SAG, NH-SAG, (NH-SAG)2 (SAG: sulfonic acid groups), which have sub-1-nm windows and a high density of sulfonic acid groups mimicking natural proton channels. The ion conductance of UiO-66-X channels follows the sequence: H+ ≫ K+ &gt; Na+&gt; Li+, and the sulfonated UiO-66 derivative channels show proton selectivity much higher than that of the pristine UiO-66 channels. Particularly, the UiO-66-(NH-SAG)2 channels exhibit ultrahigh proton selectivities, H+/Li+ up to ∼100, H+/Na+ of ∼80, and H+/K+ of ∼70, which are ∼3 times of that of UiO-66-NH-SAG channels, and ∼15 times of that of UiO-66@SAG channels. The ultrahigh proton selectivity in the sulfonated sub-1-nm MOF channels is mainly attributed to the narrow window-cavity pore structure functionalized with nanoconfined high-density sulfonic acid groups that facilitate fast proton transport and simultaneously exclude other cations. Our work opens an avenue to develop functional MOF channels for selective ion conduction and efficient ion separation. 

Retracted: No

PubPeer comments:
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 I have received two emails on the above topics and have provided the necessary explanations in response to those emails. I think it would be better to mention my answer to the second email here: Dear Petra van Steenbergen, I hope this email finds you well. I try my best to elaborate the problems you asked for in your previous email here: First: The main reason why we did not cite our two papers interactively was that the two papers were published somehow simultaneously. Explicitly our paper on NMCE, published in the March 2019 issue, was actually accepted in December 2019. The mentioned journal (NMCE) was a little behind the actual schedule because they had not enough papers to publish their issues on time. As a result, they had to change our paper timeline accordingly (receive, revise, and accept dates). Hence we could not cite our articles (NMCE) in GEGE; because both were under review at the same time. If you need any proof in this regard, you may contact the journal s editor-in-chief. Second: As mentioned before, some pictures, tables, method explanations, and primary tools for solving the reliability-related issues were similar in our studies. However, the conceptual problem that we wanted to deal with was different. This is why you notice some similar introductory stuff in our papers. Moreover, we assume that the knowledgeable reviewers who reviewed our published articles (in NMCE, IJCE, and GEGE) have already verified and admitted the contribution and novelties of our original works. Third: As you may aware, I am a university professor myself, working on scientific articles both as an author and a reviewer (for Springer journals as well) within the last 30 years. What I always had in my mind and emphasized to my students was complying with copyright that I believed was fulfilled by citing the used material in our works. This may be the first time I hear about the written permission of the copyright owner other than citing the article, adding the fact that this is also the first time I use a figure from a published work in my papers. Moreover, if we presume such unintentional ignorance by the author, some controls are expected to be done by the journals to prevent the probable copyright violation; however, I, as a member of some journal s editorial board, assume it strict both to cite a work and to have the written permission at the same time. By the way, I am determined to take any action you deem necessary to solve the problem. Thanks again for your kind attention and good will. Best Regards, Dr. Faradjollah Askari , 
 An important point that I need to mention is that we do not have access to the PubPeer site in Iran, and after about a week, I was able to enter the site with difficulty and with a special VPN; So in future, if you do not receive my reply in some cases, the reason may be the problem in Iran in accessing the PubPeer. Best Regards, ,