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Per- and polyfluoroalkyl substances (PFAS) have been extensively utilized in practical applications that include surfactants, lubricants, and firefighting foams due to their thermal stability and chemical inertness. Recent studies have revealed that PFAS were detected in groundwater and even drinking water systems which can cause severe environmental and health issues. While adsorbents with a large specific surface area have demonstrated effective removal of PFAS from water, their capability in desorbing the retained PFAS has been often neglected despite its critical role in regeneration for reuse. Further, they have demonstrated a relatively lower adsorption capacity for PFAS with a short fluoroalkyl chain length. To overcome these limitations, electric field-aided adsorption has been explored. In this work, reversible adsorption and desorption of PFAS dissolved in water upon alternating voltage is reported. An inexpensive graphite adsorbent is fabricated by using a simple press resulting in a mesoporous structure with a BET surface area of 132.9 ± 10.0 m2 g−1. Electric field-aided adsorption and desorption experiments are conducted by using a custom-made cell consisting of two graphite electrodes placed in parallel in a polydimethylsiloxane container. Unlike the conventional sorption process, a graphite electrode exhibits a higher adsorption capacity for PFAS with a short fluoroalkyl chain (perfluoropentanoic acid, PFPA) in comparison to that with a long fluoroalkyl chain (perfluorooctanoic acid, PFOA). Upon alternating the voltage to a negative value, the retained PFPA or PFOA is released into the surrounding water. Finally, we engineered a device module mounted on a gravity-assisted apparatus to demonstrate electrosorption of PFAS and collection of high purity water.

Effective remediation of produced water requires separating crude oil-water mixture and removing the dissolved organic pollutants. Membranes with selective wettability for water over oil enable the gravity-driven separation of an oil-water mixture by allowing water to permeate through while repelling oil. However, these membranes are often limited by their inability to remove the dissolved organic pollutants. In this work, a membrane with in-air superhydrophilic and underwater superoleophobic wettability is fabricated by thermal annealing of a stainless steel mesh. The resulting membrane possesses a hierarchical surface texture covered with a photocatalytic oxide layer composed of iron oxide and chromium oxide. The membrane exhibits chemical and mechanical robustness, which makes it suitable for remediation of crude oil and water mixture. Further, after being fouled by crude oil, the membrane can recover its inherent water-rich permeate flux upon visible light irradiation. Finally, the membrane demonstrates that it can separate surfactant-stabilized crude oil-in-water emulsion under gravity and decontaminate water-rich permeate by photocatalytic degradation of dissolved organic pollutants upon continuous irradiation of visible light.

Herein, we report electrochemically durable oxygen reduction reaction catalysts for proton exchange membrane fuel cells under conditions of hydrogen starvation. Insufficient hydrogen supply during transient conditions leads to a cell reversal state in a proton exchange membrane fuel cell, and oxidation of the carbon support severely decreases the cell performance. The use of carbon nanotubes as a support for the oxygen reduction reaction catalyst is found to suppress carbon oxidation due to the high crystallinity, low defect density, and high aspect ratio, which results in a consistent cell voltage, electrochemical surface area, and electrical resistance, even after 100 rounds of cell reversal. This study demonstrates the excellent durability of proton exchange membrane fuel cells with a Pt/Carbon nanotube electrode, as confirmed by X-ray diffraction, transmission electron microscopy, Raman spectroscopy and cyclic voltammetry analysis.

Precise control over micro- and nano-particle composition, size and shape is critical for developing the next generation of successful drug carriers. Fabrication methods also need to be able to create charged and multiphasic particles with ease in order to improve the overall efficiency of drug delivery systems. Multiple phases in a single particle allow for the delivery of multiple payloads without negative payload interactions. The addition of charged polyelectrolyte (PEL) multilayers can improve particle stability, targeting efficacy, drug-release kinetics, and increase the types of payloads that can be delivered. Many of the traditional methods for PEL functionalization of multiphasic particles are time and energy intensive which significantly limits their scalability, and therefore therapeutic potential. In this work, we combine the bulk layer-by-layer PEL application methodology with our previously developed technique of fabricating multiphasic particles on substrates with patterned wettability to synthesize biocompatible, monodisperse, Janus polymer-PEL particles.

Photoresponsive titania surfaces are of great interest due to their unique wettability change upon ultraviolet light illumination. However, their applications are often limited either by the inability to respond to visible light or the need for special treatment to recover the original wettability. Sensitizing TiO2 surfaces with visible light-absorbing materials has been utilized in photovoltaic applications. Here we demonstrate that a dye-sensitized TiO2 surface can selectively change the wettability towards contacting liquids upon visible light illumination due to a photo-induced voltage across the liquid and the underlying surface. The photo-induced wettability change of our surfaces enables external manipulation of liquid droplet motion upon illumination. We show demulsification of surfactant-stabilized brine-in-oil emulsions via coalescence of brine droplets on our dye-sensitized TiO2 surface upon visible light illumination. We anticipate that our surfaces will have a wide range of applications including microfluidic devices with customizable wettability, solar-driven oil–water clean-up and demulsification technologies., Controlling surface wettability using visible light is highly attractive for a range of liquid separation technologies. Here, Varanasi, McKinley and colleagues fabricate dye-sensitized photocatalytic TiO2 surfaces on which liquid droplet motion can be externally manipulated by visible light illumination.

Titanium dioxide (titania or TiO₂) is well known for its photocatalytic properties and its ability to remove organic contaminants under UV light illumination. It is also known to switch its surface wetting characteristics from being hydrophilic to superhydrophilic under exposure to UV light in air. However, less is known about the switching of the hydrophilicity of TiO₂ surfaces immersed in an oil medium. In this work, self-assembled TiO₂ nanoparticle surfaces are immersed in an oil environment, and the kinetics of contamination-induced hydrophobicity and photoinduced hydrophilicity are studied using in situ contact angle measurements. A simple model is developed to relate the evolution in the measured contact angle to photocatalytically induced changes on the surface of nanoporous titania by integrating the Langmuir–Hinshelwood adsorption isotherm with the Cassie–Baxter analysis of the effective contact angle of a drop sitting on a composite surface. The resulting model can be used to predict and control wetting kinetics in drop coalescence applications. Moreover, it is shown that immersed oil–water separation membranes which have been fouled by low surface tension contaminants can be rapidly recovered in situ using this underwater photocatalytic reaction without the need for backwashing or harsh chemical reagents. Keywords: oil-water; photocatalysis; self-cleaning; titanium dioxide; wetting, Center for Clean Water and Clean Energy at MIT and KFUPM (Grant R15-CW-11)

Superhydrophobic surfaces (i.e., surfaces extremely repellent to water) allow water droplets to bead up and easily roll off from the surface. While a few methods have been developed to fabricate metallic superhydrophobic surfaces, these methods typically involve expensive equipment, environmental hazards, or multi-step processes. In this work, we developed a universal, scalable, solvent-free, one-step methodology based on thermal sensitization to create appropriate surface texture and fabricate metallic superhydrophobic surfaces. To demonstrate the feasibility of our methodology and elucidate the underlying mechanism, we fabricated superhydrophobic surfaces using ferritic (430) and austenitic (316) stainless steels (representative alloys) with roll off angles as low as 4° and 7°, respectively. We envision that our approach will enable the fabrication of superhydrophobic metal alloys for a wide range of civilian and military applications.