Chen Michael A, Kocar Benjamin D
Civil and Environmental Engineering, MIT, 15 Vassar Street, Cambridge, MA 02139, USA.
J Synchrotron Radiat. 2021 Mar 1;28(Pt 2):461-471. doi: 10.1107/S1600577520016239. Epub 2021 Jan 15.
The study of in situ microscale biogeochemical processes represents a major challenge in the environmental sciences. The combination of microfluidic devices with X-ray fluorescence microprobe spectroscopy may address this need, but typical materials used in these devices attenuate the X-rays needed to analyze key elements of interest, such as Fe or As. In this work, a method is presented for fabricating an etched silicon microfluidic device that is sealed with a 30 µm thin glass window that is sufficiently transparent for X-ray fluorescence microprobe spectroscopy. The capabilities of these devices for X-ray microprobe spectroscopy are demonstrated using an Fe (hydr)oxide solid that is loaded with As and then infused with sulfide, on beamline 4-BM at NSLS-II, resulting in time-variant Fe precipitation reactions and As sorption. Key results include in situ X-ray fluorescence time-series maps of Fe, As and a Br flow tracer, as well as spot XANES at both the Fe K edge and As K edge. Additionally, multiple energy mapping is used to examine the spatial speciation of As over time. The results of this work clearly demonstrate the capabilities of this novel microfluidic system that can be analyzed using X-ray fluorescence microprobe spectroscopy and can be made to study a wide range of complex microscale geochemical systems.
原位微观尺度生物地球化学过程的研究是环境科学中的一项重大挑战。微流控装置与X射线荧光微探针光谱学的结合或许能满足这一需求，但这些装置中使用的典型材料会衰减用于分析诸如铁或砷等关键感兴趣元素所需的X射线。在这项工作中，提出了一种制造蚀刻硅微流控装置的方法，该装置用一个30微米厚的薄玻璃窗密封，该玻璃窗对X射线荧光微探针光谱学具有足够的透明度。在NSLS-II的4-BM光束线上，使用负载了砷然后注入硫化物的铁（氢）氧化物固体，展示了这些装置用于X射线微探针光谱学的能力，从而导致随时间变化的铁沉淀反应和砷吸附。关键结果包括铁、砷和一种溴流动示踪剂的原位X射线荧光时间序列图，以及铁K边和砷K边的点X射线吸收近边结构。此外，利用多能量映射来研究砷随时间的空间形态。这项工作的结果清楚地展示了这种新型微流控系统的能力，该系统可以使用X射线荧光微探针光谱学进行分析，并且可用于研究广泛的复杂微观地球化学系统。
