Hansoo Kim

Jaesung Lee

Dal Yong Kim

Sung Joon Park

Wansuk Choi

Min Gyu Shin

Sungkwon Jeon

Jin Young Seo

Hee woong Park

Jung Ho Choi

Ju Yeon Lee

Sang U We

Chan Hyung Park

Seon Oh Hwang

Soon Jin Kwon

Sang-Hee Park

Seo been Ko

Kyung Suk Lee

Jeongmin Jang

Mina Kim

Myeongji Yun

Yeonjae Park

Gayeon Won

Daehun Kim

Seunghyun Kang

So Young Nam

Jeongeun Choi

Joon Hee Jo

Jinsuk Ku

Lee Dong Soo

Ryung Il Kim

Dong-Jun Lee

Hyunji Nam

Jinhyeong Lee

Hyo-Eun Kwon

Changjoo Sung

Sunghyun Park

Jimin Kang

Yeojin Ahn

Heseong An

We are developing advanced organic materials for securing clean water and environment and saving energy.
We are employing nanoscale architecturing techniques to fabricate ultrathin films and hybrid materials with high performance and unique functions along with elucidating the underlying fundamentals.

Improving membrane durability associated with fouling and chlorine resistance remains one of the major challenges in desalination membrane technology. Here, we demonstrate that attractive features of graphene oxide (GO) nanosheets such as high hydrophilicity, chemical robustness, and ultrafast water permeation can be harnessed for a dual-action barrier coating layer that enhances resistance to both fouling and chlorine-induced degradation of polyamide (PA) thin-film composite (TFC) membranes while preserving their separation performance. GO multilayers were coated on the PA-TFC membrane surfaces via layer-by-layer (LbL) deposition of oppositely charged GO nanosheets. Consequently, it was shown that the conformal GO coating layer can increase the surface hydrophilicity and reduce the surface roughness, leading to the significantly improved antifouling performance against a protein foulant. It …

Layer-by-layer assembly of graphene oxide nanosheets on polyamide membranes for durable reverse-osmosis applications

Growing concerns over access to clean and safe water have led to intense research on advanced materials for water purification.[1–4] To meet this challenge, seawater desalination and water treatment using reverse osmosis (RO) membranes have become one of the most energy-efficient technologies for creating sustainable water supplies. State-of-the-art commercial RO membranes utilize a thin film composite (TFC) design consisting of a highly crosslinked polyamide (PA) selective layer on a microporous polymeric support, wherein separation of water from solutes occurs through the dense PA layer.[5] The structural characteristics (eg, chemistry, molecular topology, homogeneity) of the PA layer are thus critically important in controlling the permselectivity of the TFC membrane. The PA selective layer is traditionally fabricated via interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC), which results in the formation of a highly crosslinked, fully-aromatic PA network.[5, 6] The rapid reaction rate between the diamine and triacid chloride leads to the system quickly reaching a gel point, wherein subsequent diffusion of both monomers becomes restricted.[7] Thus, interfacial polymerization produces selective layers that are highly depth-heterogeneous with limited control over film thickness and have ridge-and-valley structures, all of which confound our understanding of the membrane performance behavior and ultimately limit our ability to optimize permselectivity. We recently reported on a process for generating PA layers on nonporous substrates that can overcome the limitations of traditional interfacial polymerization …

Molecular layer‐by‐layer assembled thin‐film composite membranes for water desalination

We report a fabrication method of polyamide (PA) thin film composite reverse osmosis membranes, so-called support-free interfacial polymerization (SFIP). In contrast to conventional interfacial polymerization (IP) where a PA layer is formed in-situ on top of a support, in this SFIP method the PA layer is first formed at the interface without a support, followed by attachment onto a support. Enhancing the chemical adhesion between the PA layer and a polyacrylonitrile support through the chemical modification on the support leads to the fabrication of defect-free membranes which outperform the conventional IP-assembled membranes. Importantly, SFIP allows for the precise characterization of the PA layer and the PA-support interface by easily isolating each membrane component. SFIP produces a thinner and smoother PA structure with a more wettable and less negatively charged surface than its IP-assembled …

Fabrication of polyamide thin film composite reverse osmosis membranes via support-free interfacial polymerization

We establish and validate a measurement method based on wrinkling–cracking phenomena that allows unambiguous measurements of three fundamental mechanical properties in nanoscale thin film geometries, including elastic modulus, strength, and fracture strain. In addition to polymer and metal thin films, the method is applied to the active nanolayers of a composite reverse osmosis membrane before and after chlorination, illustrating the ability to detect a ductile-to-brittle transition in these materials indicative of “embrittlement”, a behavior that impairs long-term durability and is detrimental to membrane performance.

Stiffness, strength, and ductility of nanoscale thin films and membranes: a combined wrinkling–cracking methodology

We present a new strategy to strongly and effectively immobilize silver nanoparticles (AgNPs) on polyamide thin film composite membranes to endow antibacterial activity. This method relies on the immobilization of relatively large silica particles (SiO 2 , ~400 nm in diameter), where AgNPs of ~30 nm in diameter are tightly and densely bound (AgNP@SiO 2 ), on the membrane surface using cysteamine as a covalent linker. The formation of multiple Ag–S chemical bonds between a “bumpy” AgNP@SiO 2 and the rough membrane surface provides a great leaching stability of AgNPs and AgNP@SiO 2 . AgNP@SiO 2 particles were well distributed over the entire membrane surface without severe aggregation. The surface coverage of the membrane by AgNP@SiO 2 was tuned by adjusting the deposition time and AgNP@SiO 2 particle concentration. The AgNP@SiO 2 -immobilized membrane showed excellent antibacterial …

Immobilization of silver nanoparticle-decorated silica particles on polyamide thin film composite membranes for antibacterial properties

This study is the first to demonstrate the capability of Cl – to markedly accelerate organic oxidation using thermally activated peroxymonosulfate (PMS) under acidic conditions. The treatment efficiency gain allowed heat-activated PMS to surpass heat-activated peroxydisulfate (PDS). During thermal PMS activation at excess Cl – , accelerated oxidation of 4-chlorophenol (susceptible to oxidation by hypochlorous acid (HOCl)) was observed along with significant degradation of benzoic acid and ClO 3 – occurrence, which involved oxidants with low substrate specificity. This indicated that heat facilitated HOCl formation via nucleophilic Cl – addition to PMS and enabled free chlorine conversion into less selective oxidizing radicals. HOCl acted as a key intermediate in the major oxidant transition based on temperature-dependent variation in HOCl concentration profiles, kinetically retarded organic oxidation upon NH 4 …

Chloride-mediated enhancement in heat-induced activation of peroxymonosulfate: New reaction pathways for oxidizing radical production

Reverse osmosis (RO) process using a thin-film composite (TFC) membrane is a current leading technology for water desalination. The polyamide permselective layer of the TFC membrane enables salt retention and water permeation, with the ultimate goal of minimizing the permselective layer thickness for maximum energy efficiency. Yet this drive towards reducing the permselective layer thickness is greatly handicapped by the interfacial polymerization (IP) approach used to fabricate TFC membranes. We present layered interfacial polymerization (LIP) as a new paradigm for fabricating TFC membranes with unprecedented nanoscale control in the permselective layer thickness and smoothness, coupled with the advantage of industrial scale manufacturability. Membranes fabricated using LIP demonstrated high NaCl rejection necessary for water desalination, with water permeance≈ 86% and permselectivity≈ …

Thin film composite reverse osmosis membranes prepared via layered interfacial polymerization

Independent control of the extrinsic and intrinsic properties of the polyamide (PA) selective layer is essential for designing thin-film composite (TFC) membranes with performance characteristics required for water purification applications besides seawater desalination. Current commercial TFC membranes fabricated via the well-established interfacial polymerization (IP) approach yield materials that are far from ideal because their layer thickness, surface roughness, polymer chemistry, and network structure cannot be separately tailored. In this work, tailor-made PA-based desalination membranes based on molecular layer-by-layer (mLbL) assembly are presented. The mLbL technique enables the construction of an ultrathin and highly cross-linked PA seletive layer in a precisely and independently controlled manner. The mLbL-assembled TFC membranes exhibit significant enhancements in performance compared …

Tailor-made polyamide membranes for water desalination

We present a facile method for fabricating polyamide (PA) nanofiltration (NF) membranes exhibiting remarkable separation performance and high acid stability via solvent activation on PA reverse osmosis (RO) membranes with strong polar aprotic solvents (dimethyl sulfoxide (DMSO), dimethylformamide and N -methyl-2-pyrrolidone). The solvents with strong solvency power for PA greatly swelled and deformed the dense RO PA layer, making the PA network more permeable and looser, which significantly improved the water permeance of the RO membrane while maintaining its high rejection to divalent salts. Consequently, the solvent-activated RO membranes exhibited remarkable NF-grade separation performance, exceeding that of the commercial NF membrane (NF270, Dow Filmtec.). Particularly, the DMSO-activated membrane showed ∼30% higher water permeance, higher salt rejection and ∼6.8 times …

High-performance and acid-resistant nanofiltration membranes prepared by solvent activation on polyamide reverse osmosis membranes

A polyamide (PA) thin film composite (TFC) reverse osmosis (RO) membrane having high permselectivity and excellent mechanical/chemical durability was prepared using a polyethylene (PE) support. Although the PE support's uniform pores and high surface porosity are beneficial for enhancing membrane permselectivity, its intrinsic hydrophobicity makes the fabrication of a PA selective layer challenging. An oxygen plasma treatment on the PE support, combined with using a sodium dodecyl sulfate (SDS) during interfacial polymerization, allowed a PA layer to be formed on the support due to by enhancing its water wettability. The systematic optimization of the membrane fabrication parameters ( e.g. , plasma pretreatment, monomer and SDS compositions and post-heat treatment) achieved high membrane performance. The fabricated PE-supported membrane (TFC-PE) showed ~30% higher water flux with ~0.4 …

Polyethylene-supported high performance reverse osmosis membranes with enhanced mechanical and chemical durability

We report on the facile preparation of highly scattering metal-coated polystyrene (PS) latex beads by using solvent-controlled heterocoagulation. Starting with an aqueous dispersion of PS beads and poly(vinyl pyrrolidone)-capped metal nanoparticles (NPs), homogeneous and dense metal coatings were obtained by the controlled addition and removal of tetrahydrofuran (THF). Different sizes (30, 60, and 80 nm), chemistries (gold and silver), and shapes (sphere and cube) of NPs were successfully incorporated on commercially available PS beads. The resulting metal coated-PS microspheres exhibited highly enhanced scattering and tunable optical characteristics useful for biomedical imaging, sensors, and opto-electronic devices. The fabricated composite beads were stable, with no loss of metal coating, during long-term water storage. The morphology and coverage of the metal coating, and the bead’s optical …

Facile preparation of highly-scattering metal nanoparticle-coated polymer microbeads and their surface plasmon resonance

We present a facile method to enhance separation performance of polyamide (PA) reverse osmosis (RO) membranes via solvent activation with a new type of organic solvent, benzyl alcohol (BA). Activation with BA remarkably improved water permeance (up to ∼140% increase) while maintaining high NaCl rejection (∼99.6%) of the pristine RO membrane, thereby overcoming the flux-rejection trade-off limitation. Thus, the water permeance and permselectivity of the BA-activated RO membrane significantly exceeded those of commercial RO membranes. This significant performance enhancement was attributed to the appropriate solvency power of BA (determined based on Hansen solubility parameters), which led to the balanced structural deformation of the PA selective layer; BA activation produced a less dense and highly permeable PA structure by greatly swelling PA, while simultaneously healing loosened …

Facile performance enhancement of reverse osmosis membranes via solvent activation with benzyl alcohol

Biofouling is a pervasive problem for any materials that are exposed to aquatic environments. Especially, it is a dire problem for the desalination membranes used to sustainably supply clean water, necessitating development of the methods to mitigate membrane biofouling. We present a topological modification approach to achieve ultralow fouling of water desalination membranes by realizing the sharkskin-mimetic (Sharklet) surface patterns and identify their unique antifouling mechanism based on computational fluid dynamics simulation. Our approach relies on a newly developed layered interfacial polymerization that can produce a conformal selective layer on patterned porous supports prepared by phase separation micromolding. The Sharklet-patterned membrane exhibited remarkably low biofouling compared to the conventional membranes with irregular roughness and topologically modulated membranes …

Sharkskin-mimetic desalination membranes with ultralow biofouling

In this study, we prepared poly(acryloyl hydrazide) (PAH)-grafted cellulose nanocrystal (CNC-PAH) particles via the atom transfer radical polymerization method for application to Cr(VI) adsorption. The closely-packed PAH chains grafted on the cellulose nanocrystal (CNC) surface provide a high density of amine groups that can adsorb Cr(VI) through strong electrostatic, hydrogen bonding and chelating interactions. CNC-PAH exhibited the optimum Cr(VI) adsorption capacity at the solution pH = 3, where its electrostatic attraction with Cr(VI) was maximized. Cr(VI) was chemisorbed in CNC-PAH by following the Langmuir isotherm mechanism (homogeneous monolayer adsorption). The Cr(VI) adsorption kinetics of CNC-PAH was controlled predominantly by intra-particle diffusion resistance imparted by the PAH shell layer. Thermodynamic analysis revealed that Cr(VI) adsorption of CNC-PAH is a spontaneous and …

Poly (acryloyl hydrazide)-grafted cellulose nanocrystal adsorbents with an excellent Cr (VI) adsorption capacity

The elastic modulus, fracture strength, and onset fracture strain of supported glassy polystyrene films with a thickness ranging from 250 to 9 nm were quantitatively determined by a recently developed wrinkling–cracking method. Films with a thickness below about 40 nm showed a decrease in both elastic modulus and fracture strength with decreasing film thickness, whereas the onset fracture strain was shown to increase. The observed variations in mechanical properties with respect to the bulk counterparts support the notion that a mechanically soft thin layer having a loosely entangled chain network exists in the near-surface region of polymeric materials, whose contribution becomes more pronounced in thinner films.

Effect of confinement on stiffness and fracture of thin amorphous polymer films

We report an aromatic solvent-assisted interfacial polymerization (IP) method to prepare high performance thin film composite reverse osmosis (RO) membranes based on a polyacrylonitrile support. The use of toluene and xylene as an organic solvent phase led to excellent water flux and unprecedentedly high NaCl rejection (∼99.9%), exceeding both the control membrane prepared using a conventional aliphatic solvent ( n -hexane) and commercial RO membranes. The membrane prepared using n -hexane had a thick and moderately dense PA layer, due to the limited amine monomer diffusion, accounting for its relatively low performance. In contrast, the membranes fabricated using toluene/xylene had roof-like structures covering a thin and highly dense basal PA layer, which was formed by increased amine diffusion and an expanded miscible interface zone resulting from the enhanced miscibility of toluene …

Aromatic solvent-assisted interfacial polymerization to prepare high performance thin film composite reverse osmosis membranes based on hydrophilic supports

By combining surface wrinkling and nanopatterned polymer films, we create anisotropic, hierarchical surfaces whose larger length-scale (wrinkling wavelength) depends intimately on the geometry and orientation of the smaller length-scale (nanopattern). We systematically vary the pattern pitch, pattern height, and residual layer thickness to ascertain the dependence of the wrinkling wavelength on the nanopattern geometry. We apply a composite mechanics model to gain a quantitative understanding of the relationship between the geometric parameters and the anisotropy in wrinkling wavelength. Additionally, these results shed light on the effect of surface roughness, as represented by the nanopattern, on the metrology of thin films via surface wrinkling.

Anisotropic, hierarchical surface patterns via surface wrinkling of nanopatterned polymer films

We report on a new technique that incorporates silver nanoparticles (AgNPs) onto polyamide (PA) thin film composite (TFC) reverse osmosis membranes via arc plasma deposition (APD) to impart antibacterial properties and simultaneously improve membrane performance. APD allows the direct deposition of AgNPs under vacuum dry condition, overcoming the drawbacks of the conventional wet-chemical methods. AgNPs (~7.6 nm in diameter) were uniformly distributed without aggregation throughout the PA selective layer with some partially implanted into the PA matrix. Ag loading could be tuned by simply adjusting the number of APD purse shots. The deposited AgNPs exhibited good leaching stability, presumably due to the strong Ag-PA chemical interaction and partially buried AgNP morphology. The resulting Ag-incorporated TFC (Ag-TFC) membrane showed the strong and long-lasting antibacterial …

Direct incorporation of silver nanoparticles onto thin-film composite membranes via arc plasma deposition for enhanced antibacterial and permeation performance

Origins of the irreversible capacity loss were addressed through probing changes in the electronic and structural properties of hollow-structured Co 3 O 4 nanoparticles (NPs) during lithiation and delithiation using electrochemical Co 3 O 4 transistor devices that function as a Co 3 O 4 Li-ion battery. Additive-free Co 3 O 4 NPs were assembled into a Li-ion battery, allowing us to isolate and explore the effects of the Co and Li 2 O formation/decomposition conversion reactions on the electrical and structural degradation within Co 3 O 4 NP films. NP films ranging between a single monolayer and multilayered film hundreds of nanometers thick prepared with blade-coating and electrophoretic deposition methods, respectively, were embedded in the transistor devices for in situ conduction measurements as a function of battery cycles. During battery operation, the electronic and structural properties of Co 3 O 4 NP films in the bulk, Co …

Additive-Free Hollow-Structured Co 3 O 4 Nanoparticle Li-Ion Battery: The Origins of Irreversible Capacity Loss

Trace organic compounds (TOrCs) have emerged as a critical concern for securing high-quality and safe water resources. Advanced water treatment using reverse osmosis (RO) and nanofiltration (NF) membranes has proven to be a promising technology for removing TOrCs. In this context, identifying the TOrC rejection mechanisms of RO/NF membranes is of paramount importance for the effective design of membrane processes and materials to improve the efficiency of TOrC treatment. However, the characteristic TOrC removal mechanisms of RO/NF membranes remain unclear, presumably due to the vast differences in the membrane structures and the limited number of TOrCs that have been investigated in past studies. Hence, the present article comprehensively reviews, analyzes and elucidates TOrC rejection mechanisms by characterizing key rejection-governing solute parameters for fully-aromatic …

Sustainable & Environmental Materials Lab

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Recent Advances in Membranes for Water Electrolysis

Self-propelling shuttles for radioactive caesium adsorption

Critical review and comprehensive analysis of trace organic compound (TOrC) removal with polyamide RO/NF membranes: mechanisms and materials

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