The application of polyethyleneimine draw solution in a combined forward osmosis/nanofiltration system

A Generalized Polymer Precursor Ink Design for 3D Printing of Functional Metal Oxides

Three-dimensional-structured metal oxides have myriad applications for optoelectronic devices. Comparing to conventional lithography-based manufacturing methods which face significant challenges for 3D device architectures, additive manufacturing approaches such as direct ink writing offer convenient, on-demand manufacturing of 3D oxides with high resolutions down to sub-micrometer scales. However, the lack of a universal ink design strategy greatly limits the choices of printable oxides. Here, a universal, facile synthetic strategy is developed for direct ink writable polymer precursor inks based on metal-polymer coordination effect. Specifically, polyethyleneimine functionalized by ethylenediaminetetraacetic acid is employed as the polymer matrix for adsorbing targeted metal ions. Next, glucose is introduced as a crosslinker for endowing the polymer precursor inks with a thermosetting property required for 3D printing via the Maillard reaction. For demonstrations, binary (i.e., ZnO, CuO, In2O3, Ga2O3, TiO2, and Y2O3) and ternary metal oxides (i.e., BaTiO3 and SrTiO3) are printed into 3D architectures with sub-micrometer resolution by extruding the inks through ultrafine nozzles. Upon thermal crosslinking and pyrolysis, the 3D microarchitectures with woodpile geometries exhibit strong light-matter coupling in the mid-infrared region. The design strategy for printable inks opens a new pathway toward 3D-printed optoelectronic devices based on functional oxides.

Influence of the anionic structure and central atom of a cation on the properties of LCST-type draw solutes for forward osmosis

Thermo-responsive ionic compounds were synthesized to examine if they have a powerful ability to draw solutes for forward osmosis (FO). The investigated compounds were tetrabutylammonium benzenesulfonate, tetrabutylphosphonium benzenesulfonate, tetrabutylammonium 2-naphthalenesulfonate, and tetrabutylphosphonium 2-naphthalenesulfonate (abbreviated as [N₄₄₄₄][BS], [P₄₄₄₄][BS], [N₄₄₄₄][NS], and [P₄₄₄₄][NS]). The lower critical solution temperature (LCST) characteristics of the materials that formed the monocyclic aromatic compound [BS] were not confirmed; however, the LCSTs of others that formed the bicyclic aromatic compound [NS] were confirmed to be approximately 37 °C ([N₄₄₄₄][NS]) and 19 °C ([P₄₄₄₄][NS]) at 20 wt% in aqueous solutions; this is valued in reducing the energy required for recovery of the draw solute. In addition, it suggests that ammonium-based ionic compounds have a higher recovery temperature than phosphonium-based ionic compounds. When an active layer was oriented to a draw solution (AL-DS mode) and using 20 wt% aqueous [N₄₄₄₄][NS] draw solution at room temperature, water and reverse solute fluxes were about 3.07 LMH and 0.58 gMH, respectively. Thus, this is the first study to investigate structural transformations of the anion and central atom of the cation and to examine prospective draw solutes of the FO system in this series.

Thermo-responsive ionic compounds having lower critical solution temperature were utilized as a draw solute for eco-sustainable forward osmosis.

Surface chemistry of spiky silica nanoparticles tailors polyethyleneimine binding and intracellular DNA delivery

Cellular delivery of DNA using silica nanoparticles has attracted great attention. Typically, polyethyleneimine (PEI) is used to form a silica/PEI composite vector. Understanding the interactions at the silica and PEI interface is important for successful DNA delivery and transfection, especially for silica with different surface functionality. Herein, we report that a higher content of hydrogen boning formed between PEI molecules and phosphonate modified silica nanoparticles could slow down the PEI dissolution from the freeze-dried solid composites into aqueous solution than the bare silica counterpart. The pronounced PEI retention ability through phosphonation of silica nanoparticles effectively improves the transfection efficiency due to the high DNA binding affinity extracellularly, effective lysosome escape and high nuclear entry of both PEI and DNA intracellularly. Our study provides a fundamental understanding on designing effective silica-PEI-based nano-vectors for DNA delivery applications.

Ready-to-use room temperature one-pot synthesis of surface-decorated gold nanoparticles with targeting attributes

Gold nanoparticles (AuNPs) can be used in diagnostic and therapeutic applications. The development of facile and fast synthetic approaches is accordingly desirable towards ready-to-use biomedical materials. We report a practical one-pot method for the synthesis in aqueous media and room temperature of surface-decorated AuNPs with enhanced biological responses. The gold ions could be reduced using only polyethyleneimine (PEI) derivatives containing sugar and-or alkyl chains acting simultaneously as reducing and stabilizing agent, without the aid of any other mediator. The process is possibly potentialized by the presence of the amino groups in the polymer chains which further confer colloidal stability. The kinetics of AuNPs nucleation and growth depends on the chemical nature of the polymer chains. Particularly, the presence of lactose moieties conjugated to the PEI chains conducted to surface-decorated AuNPs with low cytotoxicity that are remarkably faster uptaken by HepG2 cells. These cells overexpress asialoglycoprotein (ASGP-R), a galactose receptor. These findings may kick off significant advances towards the practical and ready-to-use manufacturing of functionalized AuNPs towards cell-targeting since the methodology is applicable for a large variety of other ligands that can be conjugated to the same polymer chains.

Ultrasonic degradation of selected dyes using Ti3C2Tx MXene as a sonocatalyst

MXene, a new family of two dimensional materials, was utilized as a sonocatalyst in an ultrasonic treatment (US) process for removal of methylene blue (MB) and acid blue 80 (AB). The physico-chemical properties of MXene were characterized using scanning electron microscopy, transmission electron microscopy, porosimetry, and a zeta potential analyzer. Degradation of dyes by US was systemically investigated under several experimental conditions including: power density of US (45, 90, 135, and 180 W L^-1), frequency of US (28 and 970 kHz), pH of dye solution (3.5, 7, and 10.5), solution temperature (293, 303, and 313 K), and addition of hydroxyl radical promotor (H₂O₂) and scavenger (t-BuOH) to concentrations of 25 mM. Based on the experimental results, the quantity of H₂O₂, which was used as an indicator of hydroxyl radical concentration, was an important factor in determining the degradation rate of MB and AB in this US study. Additionally, synergetic indices for removal of both dyes were higher than 1.0 in all cases, indicating the outstanding efficiency of MXene as a sonocatalyst in the US reactor for removal of both, due to an increase in both (i) the quantity of H₂O₂ in the US reactor and (ii) active sites for adsorbates from dispersion effects. A stability test on MXene in the US process was conducted using X-ray diffraction and five-cycle recycling performance tests. Based on our experimental data, MXene can be utilized as a sonocatalyst in the US process for a high removal rate for dyes (e.g., MB).

Comprehensive evaluation on removal of lead by graphene oxide and metal organic framework

Graphene oxide (GO) and metal-organic framework (MOF) as adsorbents were applied to removal of Pb(II) with comprehensive characterizations and various experimental conditions. Various characterizations were conducted to clarify the physico-chemical properties of adsorbents. The analyses of adsorption experiments included (i) dosage amounts, (ii) isotherm and kinetic studies, and (iii) several factors related to water chemistry (i.e., solution pH, background ions, and humic acid). The maximum equilibrium adsorption capacity (q_e) for Pb(II) using the GO and MOF was 555 and 108 mg g^-1, respectively, as determined in the optimum dosage experiments. Although the surface area of the MOF (629 m² g^-1) was much larger than that of the GO (19.8 m² g^-1), the adsorption capacity of the MOF was five times lower due to electrical repulsion. Thus, the MOF was utilized as the control group for comparison with the GO to evaluate the adsorption mechanisms in the experiments related to surface charge (i.e., under various pH and humic acid conditions). The adsorption isotherms and kinetics model determined using GO followed the Langmuir model (R² > 0.99) and pseudo-second-order model (R² > 0.99), respectively. Additionally, three adsorption-desorption cycles were conducted with the GO adsorbent to evaluate the maintenance of the removal ratio after regeneration and the equilibrium adsorption capacity was determined. Finally, the adsorption of other heavy metals (i.e., Cu(II), Cd(II), and Zn(II)), separately and in mixtures, was also evaluated to determine the selectivity of the adsorbents.

Post-Treatment of Nanofiltration Polyamide Membrane through Alkali-Catalyzed Hydrolysis to Treat Dyes in Model Wastewater

This research focused on the influence of post-treatment using alkali-catalyzed hydrolysis with a full-aromatic nanofiltration (NF) polyamide membrane and its application to the efficient removal of selected dyes. The post-treated membranes were characterized through Fourier transform infrared spectroscopy, goniometry, and zeta-potential analysis to analyze the treatment-induced changes in the intrinsic properties of the membrane. Furthermore, the changes in permeability induced by the post-treatment were evaluated via the measurement of water flux, NaCl rejection, and molecular weight cutoff (MWCO) under different pH conditions and post-treatment times. Major changes induced by the post-treatment in terms of physicochemical properties were the enhancement of permeability, hydrophilicity, and negative charge due to the hydrolysis of the membrane’s amide bonds. Four different dyes were selected as representative organic pollutants considering the MWCO of the post-treated membranes. Compared with the pristine NF membrane, membranes post-treated at pH 13.5 showed better water flux with similar rejection of the target dyes. On the basis of these results, the proposed post-treatment method for NF membranes can be applied to the removal of organic pollutants of various size.

Application of volume-retarded osmosis and low-pressure membrane hybrid process for water reclamation

A new concept of volume-retarded osmosis and low-pressure membrane (VRO-LPM) hybrid process was developed and evaluated for the first time in this study. Commercially available forward osmosis (FO) and ultrafiltration (UF) membranes were employed in a VRO-LPM hybrid process to overcome energy limitations of draw solution (DS) regeneration and production of permeate in the FO process. To evaluate its feasibility as a water reclamation process, and to optimize the operational conditions, cross-flow FO and dead-end mode UF processes were individually evaluated. For the FO process, a DS concentration of 0.15 g mL^-1 of polysulfonate styrene (PSS) was determined to be optimal, having a high flux with a low reverse salt flux. The UF membrane with a molecular weight cut-off of 1 kDa was chosen for its high PSS rejection in the LPM process. As a single process, UF (LPM) exhibited a higher flux than FO, but this could be controlled by adjusting the effective membrane area of the FO and UF membranes in the VRO-LPM system. The VRO-LPM hybrid process only required a circulation pump for the FO process. This led to a decrease in the specific energy consumption of the VRO-LPM process for potable water production, that was similar to the single FO process. Therefore, the newly developed VRO-LPM hybrid process, with an appropriate DS selection, can be used as an energy efficient water production method, and can outperform conventional water reclamation processes.

New concept of pump-less forward osmosis (FO) and low-pressure membrane (LPM) process

We tested the possibility of energy-saving water treatment methods by using a pump-less forward osmosis (FO) and low-pressure membrane (LPM) hybrid process (FO-LPM). In this pump-less FO-LPM, permeate migrates from the feed solution (FS) to the draw solution (DS) through the FO membrane by use of osmotic pressure differences. At the same time, within the closed DS tank, inner pressure increases as the DS volume increases. By using the DS tank’s internal pressure, the LPM process works to re-concentrate the diluted DS, maintaining the DS concentration and producing clean water. In this study, a polymer - polystyrene sulfonate (PSS) was used as a draw solute. Based on the results of each individual portion of the process, the optimal range of the PSS DS was determined. The performance of the pump-less FO-LPM process was lower than that of a single process; however, we observed that the hybrid process can be operated without a pump for regeneration of a diluted DS. This research highlights the feasibility and applicability of pump-less FO-LPM processes using a polymeric DS for water treatment. Additionally, it is suggested that this novel process offers a breakthrough in FO technology that is often limited by operation and management cost.

Thermoresponsive Acidic Microgels as Functional Draw Agents for Forward Osmosis Desalination

Thermoresponsive microgels with carboxylic acid functionalization have been recently introduced as an attractive draw agent for forward osmosis (FO) desalination, where the microgels showed promising water flux and water recovery performance. In this study, various comonomers containing different carboxylic acid and sulfonic acid functional groups were copolymerized with N-isopropylacrylamide (NP) to yield a series of functionalized thermoresponsive microgels possessing different acidic groups and hydrophobicities. The purified microgels were examined as the draw agents for FO application, and the results show the response of water flux and water recovery was significantly affected by various acidic comonomers. The thermoresponsive microgel with itaconic acid shows the best overall performance with an initial water flux of 44.8 LMH, water recovery up to 47.2% and apparent water flux of 3.1 LMH. This study shows that the incorporation of hydrophilic dicarboxylic acid functional groups into the microgels leads to the enhancement on water adsorption and overall performance. Our work elucidates in detail on the structure-property relationship of thermoresponsive microgels in their applications as FO draw agents and would be beneficial for future design and development of high performance FO desalination.