Superhydrophobic, Surfactant‐doped, Conducting Polymers for Electrochemically Reversible Adsorption of Organic Contaminants

Abstract

Polymeric adsorbents show great potential for the replacement of activated carbon for removing a wide range of toxic organic pollutants from wastewater streams since they do not suffer from costly regeneration needs and high attrition rates. Herein, an electrochemically regenerable polymeric adsorbent based on an intrinsically conducting polymer (CP), polypyrrole (PPy), doped with anionic surfactant dioctylsulfosuccinate (AOT), denoted PPy(AOT), for mitigating organic pollutants in wastewater is reported. A facile electropolymerization protocol to synthesize highly porous PPy(AOT) is developed, with an adsorption capacity of greater than 570 mg pollutant/g polymer in its superhydrophobic oxidized state. It is demonstrated that the hydrophobicity of PPy(AOT) and hence its affinity for organics can be modulated electrochemically through the re-orientation of AOT dopants, which can be exploited to regenerate the adsorbent and use it repeatedly for multiple adsorption/desorption cycles. It also explores the interactions between the adsorbed organic molecules and the surfactant-doped CP adsorbent using a combined density functional theory and molecular dynamics approach to elucidate the mechanism of electrochemical modulations of hydrophobicity and affinity of the material. The physicochemical insights are significant for developing broader applications of such material in drug delivery, sensing, self-cleaning surfaces, microfluidics, and artificial muscles.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201801466. negative effects on aquatic ecosystems and human health. [3][4][5] Adsorption is a common technology for removing organic pollutants from wastewater, and activated carbon (AC) is one of the most widespread adsorbents due to its high specific surface area and strong interactions with target compounds. [6][7][8] Methods for AC regeneration have drawbacks, however, thermal desorption is energy-intensive, while solvent regeneration may lead to substantial loss of AC and result in secondary pollution. [7][8][9][10] To overcome recyclability problems such as observed with AC, our group has previously developed a redox-responsive polymer gel with tunable hydrophobicity that reversibly adsorbs and releases organics in the presence of water. [11] However, in this case, the redox switching relied on the addition of chemicals, which introduced additional chemical agents to the remediation process, and the efficacy of the chemical stimuli was hampered by mass transfer limitations. [11,12] Therefore, it is desirable to design new adsorbent materials whose redox-responsive hydrophobicity can be tuned using mild electrical stimuli, thereby eliminating the use of chemicals in the regeneration process, and ultimately reducing the material waste and operating cost of adsorption technology for wastewater remediation. We have addressed this problem by developing two different methods for electrochemical control of the hydrophobic environment within the adsorb...

Energetically efficient electrochemically tunable affinity separation using multicomponent polymeric nanostructures for water treatment

“…For instance, on-going work from our group develops an electrochemically responsive adsorbent based on surfactant-doped conducting polymers, in which the change in the surfactant orientation relative to the polymer backbone upon electrical stimulation is studied in detail with combined experimental and molecular modelling approaches. 45 More broadly, the method proposed here for quantifying the energetic cost and the effect of operating conditions offers a useful, general framework for evaluating the overall efficacy of electrically modulated separation processes beyond ETAS, such as ion concentration polarization and capacitive deionization. Furthermore, the electrically responsive polymeric interfaces developed here could be used for molecular systems wherein the controllability of surface hydrophobicity is important, such as lubricants, biosensors, actuators, and drug delivery systems, with broad implications for diverse areas of inquiry, ranging from devising high-performance electrochemical systems to rationalizing fundamental electrostatic interactions in biologically relevant environments.…”

Surface hydrophobicity and oleophilicity of hierarchical metal structures fabricated using ink-based selective laser melting of micro/nanoparticles

“…Janus particles were used to form aggregates with hierarchical structures, ranging from the nanometer-scale up to hundreds of micrometers, which exhibited ultrahydrophobic behavior [13]. Porous conducting polymers were synthesized on carbon fiber cloth by electrochemical polymerization of pyrrole with bipyrrole and doping of the polymer with surfactant anions, showing superhydrophobic behavior [14]. Chen et al [15] synthesized 3D interconnected porous CN/copper composites using precompression, chemical vapor deposition, and spark plasma sintering.…”

An Asymmetric Electrochemical System with Complementary Tunability in Hydrophobicity for Selective Separations of Organics

“…Electrodes functionalized with redox-active materials have been developed to remove ionic species and charged biomacromolecules from aqueous solutions in a reversible manner, 3,19−23 and we have shown recently that electrically conductive materials with immobilized redox-responsive moieties can be applied also to the separation of neutral organic species from solution. 2,24 We used polypyrrole (PPy) deposited on carbon substrates as the adsorbent and adopted two different approaches to modulate its hydrophobicity and hence affinity toward organic solutes in water: incorporation of a polyvinylferrocene (PVF) redox-responsive polymer in the PPy electrode coating 2 and doping of the PPy with the amphiphilic surfactant dioctyl sulfosuccinate (AOT). 24 We refer here to the two types of material as PVF–PPy and PPy(AOT), respectively.…”

“…2,24 We used polypyrrole (PPy) deposited on carbon substrates as the adsorbent and adopted two different approaches to modulate its hydrophobicity and hence affinity toward organic solutes in water: incorporation of a polyvinylferrocene (PVF) redox-responsive polymer in the PPy electrode coating 2 and doping of the PPy with the amphiphilic surfactant dioctyl sulfosuccinate (AOT). 24 We refer here to the two types of material as PVF–PPy and PPy(AOT), respectively. Building on the previous efforts on material design, we explore the synergistic properties of PVF–PPy and PPy(AOT) in electrochemically mediated separations of organics by pairing them as opposing electrodes in an asymmetric electrochemical cell.…”