表面酸素の機能性が酸化グラフェン膜を介した金属イオンの選択的輸送を制御する(Surface Oxygen Functionality Controls the Selective Transport of Metal Ions through Graphene Oxide Membranes)

2024-07-16

2024-07-15 パシフィック・ノースウェスト国立研究所(PNNL)

グラフェン酸化物（GO）膜は、サイズに基づいて混合溶液からイオンを分離する有望な手段とされています。最近の研究で、紫外線（UV）照射によりGO膜の酸素官能基が変化し、サイズではなく電荷に基づく分離メカニズムが生じることが発見されました。この変更により、カルシウムのような大きな二価カチオンがリチウムのような小さな一価カチオンよりも速く透過します。この技術は、クリーンエネルギー技術や国内供給チェーンの課題解決に向けて、効率的で選択的かつスケーラブルな分離方法の開発を促進します。UV-rGO膜は従来のサイズ排除メカニズムとは異なり、より高い選択性を持ち、特定の金属カチオンと強く相互作用します。

＜関連情報＞

酸化グラフェン膜と紫外線照射した還元酸化グラフェン膜のイオン輸送挙動に違いが見られる Distinct ion transport behavior between graphene oxide and UV-irradiated reduced graphene oxide membranes

Yiming Yin, Shuai Tan, Difan Zhang, Richard C. Shiery, Manh-Thuong Nguyen, Vaithiyalingam Shutthanandan, Venkateshkumar Prabhakaran, Grant E. Johnson
Chemical Engineering Journal Available online: 18 May 2024
DOI:https://doi.org/10.1016/j.cej.2024.152304

Highlights

Faster divalent ion transport in ultraviolet-irradiated graphene oxide membranes.
Removal of specific oxygen functional groups improves selective ion transport.
A chromatography-like transport mechanism is proposed for irradiated membranes.

Abstract

Graphene oxide (GO) membranes are promising materials for achieving selective ion permeation in aqueous solutions. However, the swelling of GO laminates, caused by the affinity of water molecules for oxygen-containing groups (OCGs) on GO, significantly limits the practical prospects of GO membranes for selective ion transport and separation applications. Selectively removing OCGs from GO has been shown to decrease the interlayer distance between individual GO sheets, thereby improving the ability of laminate membranes to discriminate between different ions based on a size-exclusion mechanism. In this work, GO reduced through exposure to ultraviolet light (UV-rGO) is shown to display ion transport behavior that raises questions about size-exclusion as the dominant mechanism determining selective ion transport in GO membranes. Notably, smaller monovalent Li⁺ cations are found to permeate more slowly through UV-rGO membranes than larger divalent metal cations such as Ca²⁺ and Mg²⁺. This unexpected behavior results in a 3 – 4 fold improvement in the separation selectivity between these representative cations with UV-rGO compared to pristine GO membranes. Through a joint experimental and theoretical study, we identified the factors influencing selective ion transport through the nanochannels in UV-rGO membranes. We demonstrate that the selective removal of hydroxyl (–OH) groups from the basal planes of GO enhances the interactions of metal cations with functional groups located at the edges of GO, thereby resulting in a lower ratio of free Li⁺ in solution, rather than stationary Li⁺ adsorbed onto the surface GO, compared to Ca²⁺ cations. Based on these results, we propose a separation mechanism analogous to chromatography, which emphasizes the crucial role of different OCGs on GO surfaces in controlling selective ion transport through GO membranes.