Patterned-MOF-Functionalized Nanofiltration Membranes for Selective Removal of Selenium and Arsenic from Fracking Wastewater

水力压裂法或“水力压裂法”将岩层中的石油和天然气释放出来，会产生大量废水，通常通过将其抽回地下来处理。这一过程有一个不幸的副作用，那就是处置区域的地震活动增加。能够去除废水中返回的任何有害成分，以便在水力压裂过程中或用于其他目的(如灌溉)时重复使用，将最大限度地减少水力压裂对当地社区的有害影响。在水力压裂废水中发现的有害物质中，有有毒的重金属，如硒和砷。该项目将开发一种使用纳滤膜从水力压裂废水中去除硒和砷的新方法。纳滤膜是半透性的，这意味着某些小分子或离子(如氯化钠)穿过膜，而其他组分则被困在膜后面。当处理水力压裂废水时，纳滤膜容易受到油污的影响，换句话说，废水中残留的油污物质会聚集在膜表面，直到水和小分子不能再通过。因此，本项目将利用表面图案和防污染金属有机物骨架(MOF)来防止膜油污。MOF是一类由金属离子和有机连接物形成的高孔性晶体材料。由于MOF可以选择性地从大量流体中捕获溶解的分子和离子，因此在膜合成中是一种有吸引力的改性剂。这种分离的有效性源于MOF对分子或离子的亲和力、材料的极高孔隙率以及将材料的吸着剂性能调节到感兴趣的分子的能力。MOF上的工程表面图案预计将产生局部混合，从而使污染材料不太可能粘在膜表面上。整个研究工作旨在通过去除有毒重金属来实现水力压裂废水的可持续处理方案。拟议的研究将由研究生和本科生进行，他们将合作制定研究计划，指导其他学生，并向来自代表性不足群体的当地K-12学生进行STEM外联。此外，水处理和膜设计的概念将被纳入研究团队的课程，使本科生和研究生接触水处理的当前主题和挑战。该项目旨在通过表面图案和防污染金属-有机骨架来缓解油污和吸附能力的减少，以保持MOF对硒和砷的选择性，同时将其结合在纳滤膜中以处理水力压裂废水。研究人员推测，表面微图案化和防污染氧化石墨烯(GO)修饰的MOF将减轻石油引起的膜污染，从而防止膜在采油废水中的容量和选择性损失。该方法将检查三种不同尺寸的微图案和两种类型的GO装饰MOF，以量身定制防污能力、选择性和渗透性。该项目将从根本上理解图案尺寸和合成过程如何影响MOF的容量、选择性和油污阻力。该项目将产生关于GO装饰的MOF，特别是GO-铜和GO-Fe-MOF是否比非GO-装饰的MOF提高防污性能的新知识。最终，这项拟议的研究有望通过去除有毒重金属来实现可持续的生产水处理方案。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Hydraulic fracturing or "fracking" of rock layers to release the oil and gas trapped within produces a substantial amount of wastewater that is typically disposed of by pumping it back underground. This process has the unfortunate side-effect of increasing seismic activity in disposal areas. The ability to remove any hazardous components returned in the wastewater, so that it can be reused in the fracking process or for other purposes such as irrigation, would minimize the detrimental impact of fracking in local communities. Toxic heavy metals, such as selenium and arsenic, are among the hazardous materials found in fracking wastewater. This project will develop a new approach to remove selenium and arsenic from fracking wastewater using nanofiltration (NF) membranes. NF membranes are semi-permeable, meaning certain small molecules or ions (i.e., sodium chloride) pass through the membrane while other components are trapped behind the membrane. NF membranes are susceptible to oil-fouling when treating fracking wastewater, or in other words, oil contaminants remaining in the wastewater collects at the membrane surface until water and small molecules can no longer pass through. Therefore, this project will utilize surface patterns and anti-fouling metal organics frameworks (MOFs) to prevent membrane oil-fouling. MOFs are a class of highly porous crystalline materials formed from metal ions and organic linkers. MOFs are an attractive modifier in membrane synthesis since they can selectively capture dissolved molecules and ions from large volumes of fluid. The effectiveness of this separation arises from the affinity of the MOF for the molecule or ion, the extraordinarily high porosity of the material, and the ability to tune the sorbent properties of the material to the molecule of interest. Engineering surface patterns on the MOF is expected to create localized mixing such that foulant materials are less likely to stick to a membrane surface. The overall research effort aims to enable sustainable treatment schemes for fracking wastewater by removing toxic heavy metals. The proposed research will be carried out by graduate and undergraduate students, who will collaboratively develop research plans, mentor other students, and perform STEM outreach to local K-12 students from underrepresented groups. Additionally, water treatment and membrane design concepts will be incorporated into the research team’s classes to expose undergraduate and graduate students to current topics and challenges in water treatment.This project aims to mitigate oil-fouling and adsorption capacity reduction using surface patterns and anti-fouling metal-organic frameworks to maintain MOF selectivity for selenium and arsenic while incorporated in an NF membrane to treat fracking wastewater. The investigators hypothesize that surface micro-patterning and anti-fouling graphene oxide (GO)-decorated MOFs will mitigate oil-induced membrane fouling, thereby preventing capacity and selectivity loss of thin-film nanocomposite membranes in produced water service. The approach will examine three different sized micro-patterns and two types of GO-decorated MOFs to tailor anti-fouling ability, selectivity, and permeance. The project will yield fundamental understanding of how pattern size and synthesis procedure affect the MOF capacity, selectivity, and oil-fouling resistance. This project will generate new knowledge on whether GO-decorated MOFs, specifically GO-Cu- and GO-Fe-MOFs, improve anti-fouling performance over non-GO-decorated MOFs. Ultimately, the proposed research is expected to enable sustainable produced water treatment schemes through the removal of toxic heavy metals.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.