Acid–Base Polymeric Foams for the Adsorption of Micro-oil Droplets from Industrial Effluents

Abstract

Separation of toxic organic pollutants from industrial effluents is a great environmental challenge. Herein, an acid-base engineered foam is employed for separation of micro-oil droplets from an aqueous solution. In acidic or basic environments, acid-base polymers acquire surface charge due to protonation or dissociation of surface active functional groups. This property is invoked to adsorb crude oil microdroplets from water using polyester polyurethane (PESPU) foam. The physicochemical surface properties of the foam were characterized using X-ray photoelectron spectroscopy, inverse gas chromatography, electrokinetic analysis, and micro-computed tomography. Using the surface charge of the foam and oil droplets, the solution pH (5.6) for maximum separation efficacy was predicted. This optimal pH was verified through underwater wetting behavior and adsorption experiments. The droplet adsorption onto the foam was governed by physisorption, and the driving forces were attributed to electrostatic attraction and Lifshitz-van der Waals forces. The foam was regenerated and reused multiple times by simple compression. The lowest trace oil content in the retentate was 3.6 mg L, and all oil droplets larger than 140 nm were removed. This work lays the foundation for the development of a new class of engineered foam adsorbents with the potential to revolutionize water treatment technologies.

Adsorptive Recovery of Crude Oil Microdroplets from Wastewater Using Surface Engineered Sponges

“…In this work, PESPU sponge with pore size of 200-1100 µm and porosity of ~97% was used as a 3D substrate due to its complementary acid-base surface groups and high porosity. 9 Facile dip-coating was selected as the technique to functionalize the sponge surface with organic groups, to incorporate nanoroughness, and to manipulate the surface energy. Among currently available nanomaterials for coating the sponge, silica-based nanomaterials are favorable due to their earth abundancy and nontoxicity.…”

“…The raw and emulsified properties of the crude oil are described elsewhere. 9 The polyester polyurethane sponge was purchased from a local vendor. The sponge films for AFM were prepared by pressing the sponge in a compression mold at 160 °C.…”

“…where, the crude oil interfacial tension with water ( − ), measured using axisymmetric drop shape analysis (ADSA) method, is ~14 mJ m -2 . 9 Since the binding between the droplets and the sponge is high, the adsorbed crude oil recovery by the established method of mechanical compression was not effective. 9 Therefore, surface chemical displacement principles 49 were applied to regenerate the SEnS and rapidly recover adhered crude oil film by using a solvent at ambient conditions.…”

Adsorptive Recovery of Crude Oil Microdroplets from Wastewater Using Surface Engineered Sponges

“…The effect of pH on the temporal removal efficiency can be further understood from the zero charge points of the SEnS and crude oil microdroplets. 9 As shown in Figure 4b, the zero charge points of the SEnS and crude oil occur at pH 6.3 and 4.9, respectively. Therefore, at pH 5.6, a positive charge exists on the SEnS and a negative charge exists on the oil microdroplet surfaces.…”

“…The adsorption experiments were performed using crude oil-in-water emulsions with a droplet size below 10 μm. 9 Based on surface charge characterization, the best adsorption occur at pH 5.6. As such, this pH is compared with a more acidic condition (3.6), neutral (pH 7.0), and more basic condition (pH 9.6).…”