Youngbin Baek

High-Performance Reverse Osmosis CNT/Polyamide Nanocomposite Membrane by Controlled Interfacial Interactions

Polyamide reverse osmosis (RO) membranes with carbon nanotubes (CNTs) are prepared by interfacial polymerization using trimesoyl chloride (TMC) solutions in n-hexane and aqueous solutions of m-phenylenediamine (MPD) containing functionalized CNTs. The functionalized CNTs are prepared by the reactions of pristine CNTs with acid mixture (sulfuric acid and nitric acid of 3:1 volume ratio) by varying amounts of acid, reaction temperature, and reaction time. CNTs prepared by an optimized reaction condition are found to be well-dispersed in the polyamide layer, which is confirmed from atomic force microscopy, scanning electron microscopy, and Raman spectroscopy studies. The polyamide RO membranes containing well-dispersed CNTs exhibit larger water flux values than polyamide membrane prepared without any CNTs, although the salt rejection values of these membranes are close. Furthermore, the durability and chemical resistance against NaCl solutions of the membranes containing CNTs are found to be improved compared with those of the membrane without CNTs. The high membrane performance (high water flux and salt rejection) and the improved stability of the polyamide membranes containing CNTs are ascribed to the hydrophobic nanochannels of CNTs and well-dispersed states in the polyamide layers formed through the interactions between CNTs and polyamide in the active layers.

A carbon nanotube wall membrane for water treatment

Various forms of carbon nanotubes have been utilized in water treatment applications. The unique characteristics of carbon nanotubes, however, have not been fully exploited for such applications. Here we exploit the characteristics and corresponding attributes of carbon nanotubes to develop a millimetre-thick ultrafiltration membrane that can provide a water permeability that approaches 30,000 l m(-2) h(-1) bar(-1), compared with the best water permeability of 2,400 l m(-2) h(-1) bar(-1) reported for carbon nanotube membranes. The developed membrane consists only of vertically aligned carbon nanotube walls that provide 6-nm-wide inner pores and 7-nm-wide outer pores that form between the walls of the carbon nanotubes when the carbon nanotube forest is densified. The experimental results reveal that the permeance increases as the pore size decreases. The carbon nanotube walls of the membrane are observed to impede bacterial adhesion and resist biofilm formation.

The improvement of antibiofouling properties of a reverse osmosis membrane by oxidized CNTs

Polyamide reverse osmosis (RO) membranes with deposited carbon nanotubes (CNTs) coated with poly(vinyl alcohol) (PVA) on the surface were prepared by interfacial polymerization followed by the deposition of oxidized CNTs and the coating of PVA on the surface. The polyamide membrane with the oxidized CNTs and PVA coating (PA–CNT–PVA membrane) showed much improved mechanical properties and durability compared with the polyamide membrane without CNTs (PA membrane). The PA–CNT–PVA membrane also exhibited much better antifouling properties than the PA membrane and the commercial RO membrane (LFC-1). The improved durability and antibiofouling performances of the PA–CNT–PVA membrane were possible when the CNTs were well-dispersed on the top of the polyamide active layers and stabilized by the thin crosslinked PVA coatings.

Autonomous Graphene Vessel for Suctioning and Storing Liquid Body of Spilled Oil

Despite remarkable strides in science and technology, the strategy for spilled oil collection has remained almost the same since the 1969 Santa Barbara oil spill. The graphene vessel devised here can bring about an important yet basic change in the strategy for spilled oil collection. When it is placed on the oil-covered seawater, the graphene vessel selectively separates the oil, then collects and stores the collected oil in the vessel all by itself without any external power inputs. Capillarity and gravity work together to fill this proto-type graphene vessel with the spilled oil at a rate that is higher than 20,000 liters per square meter per hour (LMH) with oil purity better than 99.9%, and allow the vessel to withstand a water head of 0.5 m. The vessel also has a superb chemical stability and recyclability. An expanded oil contact area, considerably greater than the thickness of the oil layer, forms at the reduced graphene oxide (rGO) foam interface upon contact with the spilled oil. This expanded contact area does not change much even when the oil layer thins out. As a result, the high oil collection rate is maintained throughout the recovery of spilled oil.

A Carbonaceous Membrane based on a Polymer of Intrinsic Microporosity (PIM-1) for Water Treatment

As insufficient access to clean water is expected to become worse in the near future, water purification is becoming increasingly important. Membrane filtration is the most promising technologies to produce clean water from contaminated water. Although there have been many studies to prepare highly water-permeable carbon-based membranes by utilizing frictionless water flow inside the carbonaceous pores, the carbon-based membranes still suffer from several issues, such as high cost and complicated fabrication as well as relatively low salt rejection. Here, we report for the first time the use of microporous carbonaceous membranes via controlled carbonization of polymer membranes with uniform microporosity for high-flux nanofiltration. Further enhancement of membrane performance is observed by O2 plasma treatment. The optimized membrane exhibits high water flux (13.30 LMH Bar−1) and good MgSO4 rejection (77.38%) as well as antifouling properties. This study provides insight into the design of microporous carbonaceous membranes for water purification.

Experimental analysis of transport characteristics for vertically aligned carbon nanotube membranes

Abstract Membranes utilizing carbon nanotubes (CNTs) as their pores have been emerged as a novel technique for water and wastewater treatment. CNTs are nanometer–diameter cylinders, allowing fast transport of water molecular and other fluid due to their strong hydrophobic characteristics. A few studies have been done for developing membranes embedding single-wall or multiwall nanotubes and simulating their performance theoretically using molecular dynamics. Nevertheless, only a limited number of experimental works were attempted to analyze the transport phenomena inside the CNT membranes due to lack of techniques for quantitative interpretation of the experimental results. Accordingly, this study aimed at developing protocols to quantify the efficiency of CNT membranes and apply them for better understanding of transport mechanisms of the CNT membranes. Membranes made of vertically aligned CNTs, which has 3–5 nm inner diameter and 150∼250 μm length, were used. Special experimental techniques were applied ...

Feasibility of supercritical CO2 treatment for controlling biofouling in the reverse osmosis process

Physical cleaning and/or chemical cleaning have been generally used to control biofouling in the reverse osmosis (RO) process. However, conventional membrane cleaning methods to control biofouling are limited due to the generation of by-products and the potential for damage to the RO membranes. In this study, supercritical carbon dioxide (SC CO2) treatment, an environmentally friendly technique, was introduced to control biofouling in the RO process. SC CO2 (100 bar at 35°C) treatment was performed after biofouling was induced on a commercial RO membrane using Pseudomonas aeruginosa PA01 GFP as a model bacterial strain. P. aeruginosa PA01 GFP biofilm cells were reduced on the RO membrane by >8 log within 30 min, and the permeate flux was sufficiently recovered in a laboratory-scale RO membrane system without any significant damage to the RO membrane. These results suggest that SC CO2 treatment is a promising alternative membrane cleaning technique for biofouling in the RO process.

Evaluation of thin-film nanocomposite RO membranes using TiO2 nanotubes and TiO2 nanoparticles: a comparative study

AbstractThin-film nanocomposite (TFN) reverse osmosis (RO) membranes have gained attention due to their enhanced membrane performances in permeate flux and salt rejection. The structural shape of nanocomposites, such as particles and nanotubes, has been thought to have critical roles in improving their performances. However, the effects of the structural properties on membrane performance have yet to be verified. Herein, we reported the structural effects of nanocomposites on the performance of TFN RO membranes fabricated with TiO2 nanotubes (TNT) and TiO2 nanoparticles (TNP). The TFN RO membranes containing TNT or TNP exhibited similar high hydrophilicities and enhanced water permeability compared with a conventional RO membrane. In terms of membrane performance, the TNT TFN RO membranes had better water permeability than the TNP TFN RO membranes. Compared with non-porous TNP, 80-nm diameter nanochannels of TNT provided additional enhanced water permeability by serving as water transport passageways.