| dc.description.abstract | Due to increasing concern over the shortage of freshwater, there is a dire need to remediate unconventional water sources such as agricultural, industrial, or municipal wastewater beyond what is obtainable from the hydrologic water cycle. With the advances in surface science, wastewater remediation technologies, including membrane-based and adsorption-based technologies, have been preferred due to their resilience and effectiveness. This dissertation aims to improve the existing membrane-based and adsorption-based technologies by modulating the solid-liquid interaction parameters like photocatalysis, wettability, and electrostatic force of attraction.The first part of the dissertation discusses the fabrication of superhydrophilic and oleophobic coating, which can be utilized to separate and desalinate an oil and saline water mixture, and photocatalytically degrade the organic substances. The photocatalytic surface is coated on a commercial membrane with an ultraviolet (UV) light-curable adhesive. A mixture of photocatalytic nitrogen-doped titania (N-TiO2) and perfluoro silane-grafted silica (F-SiO2) nanoparticles is coated successively. The membrane resulted in a chemically heterogeneous surface with intercalating high and low surface energy regions (i.e., N-TiO2 and F-SiO2, respectively) that were securely bound to the commercial membrane surface. The coated membrane was then utilized for continuous separation and desalination of an oil-saline water mixture and for simultaneous photocatalytic degradation of the organic substances adsorbed on the membrane surface upon visible light irradiation. In the second part, a photocatalytic mesh that can selectively permeate water while repelling oil was fabricated by coating a mixture of nitrogen-doped TiO2 (N-TiO2) and perfluoro silane-grafted SiO2 (F-SiO2) nanoparticles on a stainless-steel mesh. Utilizing the photocatalytic mesh, the time-dependent evolution of the water-rich permeate flux as a result of photocatalytic degradation of the oil was studied under the visible light illumination is studied. A mathematical model was then developed that can relate the photocatalytic degradation of the organic substances deposited on a mesh surface to the evolution of the permeate flux. This model was established by integrating the Langmuir–Hinshelwood kinetics for photocatalysis and the Cassie–Baxter wettability analysis on a chemically heterogeneous mesh surface into a permeate flux relation. Consequently, the time-dependent water-rich permeate flux values are compared with those predicted by using the model. It is found that the model can predict the evolution of the water-rich permeate flux with a goodness of fit of 0.92. In the following part, a robust in-air oleophobic hydrophilic coating for a filter was fabricated utilizing poly(ethylene glycol)diacrylate (PEGDA) and 1H,1H,2H,2H-heptadecafluorodecyl acrylate (F-acrylate). Methacryloxypropyl trimethoxysilane (MEMO) was utilized as an adhesion promoter to enhance the adhesion of the coating to the filter. The filter demonstrates robust oil repellency preventing oil adhesion and oil fouling. Utilizing the filter, gravity-driven and continuous separations of surfactant-stabilized oil-water emulsions are demonstrated. Finally, we demonstrate that the filter can be reused multiple times upon rinsing for further oil-water separations. The fourth part of the dissertation focuses on the remediation of dissolved contaminants like PFAS. For this, electric field-aided adsorption has been explored. 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 to a gravity-assisted apparatus to demonstrate electrosorption of PFAS and collection of high purity water. In the last part, we demonstrate electrosorption of PFAS with varied fluoroalkyl chains by utilizing MXene-PEDOT:PSS absorbent. Intercalation of PEDOT:PSS to the MXene help enhance the capacitive property of MXene, increasing the electrosorption of PFAS. Using the adsorbent, we demonstrate electrosorption of PFAS with varied fluoroalkyl chain lengths from water upon applying a voltage of V = 1.0 V. Also, the adsorbent can desorb the PFAS from its surface when applying a voltage of V = - 1.0 V, which regenerates the adsorbent for further operations. Finally, a pseudo-second-order kinetic model that describes the reversible electrosorption of PFAS from MXene-PEDOT:PSS adsorbent is proposed. | |
