ABSTRACT
Molybdenum disulfide (MoS2) has recently emerged as one of the most promising water nano-based adsorbent materials for heavy metal removal with the potential to provide an alternative to conventional water decontamination technologies. In this study, we demonstrate the trade-off between mercuric removal capacity and overall MoS2 adsorbent stability, both driven by MoS2 synthesis parameters. A bottom-up hydrothermal synthesis setup at various growth temperatures was employed to grow flower-like MoS2 films onto planar alumina supports. A thorough material characterization suggests that an increase in growth temperature from 150 to 210 °C results in higher MoS2 crystallinity. Interestingly, elevated growth temperatures resulted in poor mercuric removal (525 mg g-1, K = 2.2 × 10-3 h-1), yet showed enhanced chemical stability (i.e., minimal molybdenum leaching during exposure to mercury). On the other hand, low growth temperatures produce amorphous supported MoS2, exhibiting superb mercuric removal capabilities (5158 mg g-1, K = 36.1 × 10-3 h-1) but displaying poor stability, resulting in substantial byproduct molybdate leaching. Mercuric removal by crystalline MoS2 was accomplished by adsorption and electrostatic attraction-based removal mechanisms, whereas redox reactions and HgS crystallization-based removal mechanisms were more dominant when using amorphous MoS2 for mercury removal. Overall, our study provides essential insights into the delicate balance between MoS2 mercuric removal capabilities and MoS2 degradation, both related to material synthesis growth conditions. Employment of nano-enabled water treatments in general, and MoS2 for heavy metal removal in particular, requires us to better understand these important fundamental trade-off behaviors to achieve sustainable, effective, and responsible implementation of nanotechnologies in large scale systems.
ABSTRACT
External forces are an important factor in tissue formation, development, and maintenance. The effects of these forces are often studied using specialized in vitro stretching methods. Various available systems use 2D substrate-based stretchers, while the accessibility of 3D techniques to strain soft hydrogels, is more restricted. Here, we describe a method that allows external stretching of soft hydrogels from their circumference, using an elastic silicone strip as the sample carrier. The stretching system utilized in this protocol is constructed from 3D-printed parts and low-cost electronics, making it simple and easy to replicate in other labs. The experimental process begins with polymerizing thick (>100 µm) soft fibrin hydrogels (Elastic Modulus of ~100 Pa) in a cut-out at the center of a silicone strip. Silicone-gel constructs are then attached to the printed-stretching device and placed on the confocal microscope stage. Under live microscopy the stretching device is activated, and the gels are imaged at various stretch magnitudes. Image processing is then used to quantify the resulting gel deformations, demonstrating relatively homogenous strains and fiber alignment throughout the gel's 3D thickness (Z-axis). Advantages of this method include the ability to strain extremely soft hydrogels in 3D while executing in situ microscopy, and the freedom to manipulate the geometry and size of the sample according to the user's needs. Additionally, with proper adaptation, this method can be used to stretch other types of hydrogels (e.g., collagen, polyacrylamide or polyethylene glycol) and can allow for analysis of cells and tissue response to external forces under more biomimetic 3D conditions.
