Polyvinyl alcohol hydrogel-supported forward osmosis membranes with high performance and excellent pH stability

Viability of Total Ammoniacal Nitrogen Recovery Using a Polymeric Thin-Film Composite Forward Osmosis Membrane: Determination of Ammonia Permeability Coefficient

Total ammoniacal nitrogen (TAN) occurs in various wastewaters and its recovery is vital for environmental reasons. Forward osmosis (FO), an energy-efficient technology, extracts water from a feed solution (FS) and into a draw solution (DS). Asymmetric FO membranes consist of an active layer and a support layer, leading to internal concentration polarization (ICP). In this study, we assessed TAN recovery using a polymeric thin-film composite FO membrane by determining the permeability coefficients of NH4+ and NH3. Calculations employed the solution-diffusion model, Nernst-Planck equation, and film theory, applying the acid-base equilibrium for bulk concentration corrections. Initially, model parameters were estimated using sodium salt solutions as the DS and deionized water as the FS. The NH4+ permeability coefficient was 0.45 µm/s for NH4Cl and 0.013 µm/s for (NH4)2SO4 at pH < 7. Meanwhile, the NH3 permeability coefficient was 6.18 µm/s at pH > 9 for both ammonium salts. Polymeric FO membranes can simultaneously recover ammonia and water, achieving 15% and 35% recovery at pH 11.5, respectively.

Enhanced water treatment performance of ceramic-based forward osmosis membranes via MOF interlayer

Forward osmosis (FO) membrane processes could operate without hydraulic pressures, enabling the efficient treatment of wastewaters with mitigated membrane fouling and enhanced efficiency. Designing a high-performance polyamide (PA) layer on ceramic substrates remains a challenge for FO desalination applications. Herein, we report the enhanced water treatment performance of thin-film nanocomposite ceramic-based FO membranes via an in situ grown Zr-MOF (UiO-66-NH2) interlayer. With the Zr-MOF interlayer, the ceramic-based FO membranes exhibit lower thickness, higher cross-linking degree, and increased surface roughness, leading to higher water flux of 27.38 L m-2 h-1 and lower reverse salt flux of 3.45 g m-2 h-1. The ceramic-based FO membranes with Zr-MOF interlayer not only have an application potential in harsh environments such as acidic solution (pH 3) and alkaline solution (pH 11), but also exhibit promising water and reverse salt transport properties, which are better than most MOF-incorporated PA membranes. Furthermore, the membranes could reject major species (ions, oil and organics) with rejections ＞94 % and water flux of 22.62-14.35 L m-2 h-1 in the treatment of actual alkaline industrial wastewater (pH 8.6). This rational design proposed in this study is not only applicable for the development of a high-quality ceramic-based FO membrane with enhanced performance but also can be potentially extended to more challenging water treatment applications.

Thin Film Composite Membranes as a New Category of Alkaline Water Electrolysis Membranes

Alkaline water electrolysis (AWE) is considered a promising technology for green hydrogen (H2 ) production. Conventional diaphragm-type porous membranes have a high risk of explosion owing to their high gas crossover, while nonporous anion exchange membranes lack mechanical and thermochemical stability, limiting their practical application. Herein, a thin film composite (TFC) membrane is proposed as a new category of AWE membranes. The TFC membrane consists of an ultrathin quaternary ammonium (QA) selective layer formed via Menshutkin reaction-based interfacial polymerization on a porous polyethylene (PE) support. The dense, alkaline-stable, and highly anion-conductive QA layer prevents gas crossover while promoting anion transport. The PE support reinforces the mechanical and thermochemical properties, while its highly porous and thin structure reduces mass transport resistance across the TFC membrane. Consequently, the TFC membrane exhibits unprecedentedly high AWE performance (1.16 A cm-2 at 1.8 V) using nonprecious group metal electrodes with a potassium hydroxide (25 wt%) aqueous solution at 80 °C, significantly outperforming commercial and other lab-made AWE membranes. Moreover, the TFC membrane demonstrates remarkably low gas crossover, long-term stability, and stack cell operability, thereby ensuring its commercial viability for green H2 production. This strategy provides an advanced material platform for energy and environmental applications.