二维层间距可控的GOF复合膜的合成方法和分子筛分性能的研究

Graphene oxide (GO) membranes have an excellent molecule-sieving performance for many kinds of mixtures. However, the performance of GO membrane was limited by their low mechanical stability while the improve method is still lacking. Literature and our previous research showed that it is desirable to retain the regular 2D channels of the GO with an appropriate inter-space when intensifying the strength of GO based membranes.Graphene oxide frameworks (GOFs), the new rising porous materials, are well meeting the above requirements of stocking GO in short-range order because the interlamellar spacing of GO is well defined by the linking units. By choosing the linkers with various sizes and functionality, the interlamellar spacing as well as physicochemical properties can be controlled to some extent. In this proposal, we plan to synthesize a serial of GOF materials from the small size molecules with dual-active terminal groups and GO nanosheets by solvthermal method. We will develope synthesis method to accurately control the size of 2D interlamellar spacing of GOF in the range of 0.25-0.45 nm by adjusting the density of oxygen-contained groups of GO and chosing dual-active terminal molecules with different size. With the new GOF materials, we will investigate the synthesis method of GOF hybrid membranes and the separation performance and stability of these GOF membranes for the separation of small size gas molecules, dehydration of solvents and ions rejection. Effects of the interaction between permeate molecules and GOF on the microstructure and chemical state of GOF membrane will be investigated by atmosphere adjustable scan electron microscope and near atmosphere pressure X-ray photoelectron spectroscopy. This investigation will provide an efficient, cheap, energy-saving and eco-friendly new method for the separation of small size molecules. It will not only extend the fundamental knowledge of the chemical modification of GO based materials, but also highly match the market's requirement of high efficient membrane separation.

氧化石墨烯（GO）膜具有优异的分子筛分性能，却受制于其较差的机械性能，且缺乏有效地改进手段。文献和我们的研究表明，在增强机械强度时要保持尺寸合适的2D通道和至少短程有序的GO层叠形态。新兴的氧化石墨烯框架（GOFs）契合这种需求。本课题将通过溶剂热方法系统研究新型GOF的合成，通过分子大小和GO含氧基团密度的调节实现GOF的层间距在0.25-0.45nm间精确可控。开发超薄、高稳定性的GOF复合膜制备工艺，并研究GOF膜在气体、溶剂脱水和脱盐中的分离性能和稳定性能。将利用原位SEM和近常压XPS等手段渗透介质和GOF复合膜相互作用对微观结构和化学态信息的影响规律。本课题的研究将为小分子混合物膜分离提供一个高效、廉价、节能、绿色的新途径。不仅有利于拓展和丰富对石墨烯基材料的化学改性和分离过程的基础认知，而且契合高效膜分离的社会实践需求。

单层氧化石墨烯（GO）堆垛形成二维层间纳米通道可用于尺寸筛分。GO基膜因材料易得、制备简单和性能优越等特点，已迅速成为当今膜科学与技术前沿的一大重要和热门课题，分离对象涵盖了气体、液体和脱盐等领域。然而，随着研究深入，GO基膜凸显两个主要问题：一是如何精确调控二维通道大小以适应不同对象（特别是小分子）的分离需求；二是如何有效增强层间作用力和强度，提升膜的可用性。本项目致力于解决这些问题，并取得重要进展，在项目期间以通讯作者身份在Nature Communications, Advanced Materials, Journal of Materials Chemistry A (2篇), Chem Eng J, Chem Commu和Journal of Membrane Science等知名国际期刊发表文章10篇，1篇入选ESI高引论文。.与分子筛膜等具有内部强相互作用不同，GO基膜体相主要为pi-pi键和氢键等弱作用力，膜机械强度低，并且客体分子在分离时可以轻易扩大层间距，从而影响分离性能和稳定性。增强碳层间的作用力最直接有效的办法是以GO含氧基团为 “锚点”通过交联分子对GO碳层进行共价桥连，从而形成层间距均一的氧化石墨烯框架（GOFs）。为了同时达到控制层间距满足小分子筛分的目的，交联分子除拥有多活性基团外，尺寸越小越有利于层间距控制。.经广泛研究选择硫脲（TU）作为交联分子，因为TU有双NH2-和C=S-多活性终端，分子骨架仅有3原子，且具有弱还原性。为获得均质连续的GOF复合膜，该团队首次实现层层自组装：首先通过载体表面嫁接的活性基团与GO反应在载体上固定单层GO，再由TU和GO经脱水缩合和亲核加成反应在载体上实现周期性组装形成均质TU-GOF复合膜（图1）。通过条件控制，TU-GOF膜的层间距可精确调控，膜厚可控制在数十纳米。表征结果证实TU对碳层的固定作用极大地抑制了膜在分离介质中的溶胀变形，显著增强了膜的机械稳定性。分离结果表明TU-GOF膜对H2具有高选择性，如H2/CO2，H2/N2和H2/CH4理想选择性达~200，H2渗透速率10-7mol/m2/s/Pa。这是GO基膜首次基于二维层间筛分实现H2高效分离，且性能远高于聚合物膜的Robeson上限，也优于大部分无机膜。