Selective Ion Transport in Two-Dimensional Ti3C2Tx Nanochannel Decorated by Crown Ether.

Ion sieving is a critical process employed in various applications, such as desalination and ion extraction. Nevertheless, achieving rapid and accurate ion sieving remains an exceptionally difficult task. Drawing inspiration from the effective ion sieving capabilities of biological ion channels, we present the development of two-dimensional Ti3C2Tx ion nanochannels incorporating 4-aminobenzo-15-crown-5-ether molecules as specific ion binding sites. These binding sites had a significant influence on the ion transport process and improved ion recognition. Permeation of both Na+ and K+ was facilitated because their ion diameters are compatible with the cavity in the ether ring. Moreover, owing to the strong electrostatic interactions, the permeation rate for Mg2+ increased by a factor of 55 compared to that for the pristine channels, which was higher than those of all monovalent cations. Furthermore, the transport rate for Li+ was relatively lower than those of Na+ and K+, which was attributed to difficult binding of the Li+ to the oxygens in the ether ring. Consequently, the ion selectivities of the composite nanochannel were up to 7.6 for Na+/Li+ and 9.2 for Mg2+/Li+. Our work presents a straightforward approach to creating nanochannels exhibiting precise ion discrimination.

Unlocking osmotic energy harvesting potential in challenging real-world hypersaline environments through vermiculite-based hetero-nanochannels.

Nanochannel membranes have demonstrated remarkable potential for osmotic energy harvesting; however, their efficiency in practical high-salinity systems is hindered by reduced ion selectivity. Here, we propose a dual-separation transport strategy by constructing a two-dimensional (2D) vermiculite (VMT)-based heterogeneous nanofluidic system via an eco-friendly and scalable method. The cations are initially separated and enriched in micropores of substrates during the transmembrane diffusion, followed by secondary precise sieving in ultra-thin VMT laminates with high ion flux. Resultantly, our nanofluidic system demonstrates efficient osmotic energy harvesting performance, especially in hypersaline environment. Notably, we achieve a maximum power density of 33.76 W m-2, a 6.2-fold improvement with a ten-fold increase in salinity gradient, surpassing state-of-the-art nanochannel membranes under challenging conditions. Additionally, we confirm practical hypersaline osmotic power generation using various natural salt-lake brines, achieving a power density of 25.9 W m-2. This work triggers the hopes for practical blue energy conversion using advanced nanoarchitecture.

Fouling behavior of typical organic foulants in polyvinylidene fluoride ultrafiltration membranes: characterization from microforces.

To further unravel the organic fouling behavior of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes, the adhesion forces of membrane-foulant and foulant-foulant were investigated by atomic force microscopy (AFM) in conjunction with self-made PVDF colloidal probe and foulant-coated colloidal probe, respectively. Fouling experiments with bovine serum albumin, sodium alginate, humic acid, and secondary wastewater effluent organic matter (EfOM) were carried out with PVDF UF membrane. Results showed a positive correlation between the membrane-foulant adhesion force and the flux decline rate and extent in the initial filtration stage, whereas the foulant-foulant interaction force was closely related to the pseudostable flux and the cake layer structure in the later filtration stage. For each type of foulant used, the membrane-foulant adhesion force was much stronger than the foulant-foulant interaction force, and membrane flux decline mainly occurred in the earlier filtration stage indicating that elimination of the membrane-foulant interaction force is important for the control of membrane fouling. Upon considering the foulant-foulant interaction force and the membrane flux recovery rate of fouled membranes, it was evident that the main contributor to physically irreversible fouling is the foulant-foulant interaction force.

Study of antifouling modified ultrafiltration membrane based on the secondary treated water of urban sewage.

Mixtures of polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA) containing hydrophilic ultrafiltration membranes were prepared by adding PVA (5 to 30%) to PVDF by the phase inversion method. The hydrophilic contact angle (CA), equilibrium water content, pure water flux and bovine serum albumin retention were studied to assess the membrane performance. The anti-fouling performance of modified membrane to the secondary treated water was evaluated by flux decline, washing recovery rate and fouling resistance analysis. Scanning electron microscopy showed that the cross-section structure of the membranes had finger-like pores, which were well developed and uniformly distributed, and the sub-layer structure was looser and more porous with the increasing content of PVA. The CA gradually decreased. The steady flux was 800 L/m(2) h from P15 to P30, and the BSA retention sharply declined. The ultrafiltration tests for secondary treated water indicated that the main fouling source of the modified membrane was the concentration polarization and cake layer resistance. After physical flushing, the flux recovery ratio of the membrane could reach 100% when the PVA content was 5-15%, which shows excellent anti-pollution performance and good prospects for use in processing wastewater from urban sewage.

Recent advances in thin film nanocomposite membranes containing an interlayer (TFNi): fabrication, applications, characterization and perspectives.

Polyamide (PA) reverse osmosis and nanofiltration membranes have been applied widely for desalination and wastewater reuse in the last 5-10 years. A novel thin-film nanocomposite (TFN) membrane featuring a nanomaterial interlayer (TFNi) has emerged in recent years and attracted the attention of researchers. The novel TFNi membranes are prepared from different nanomaterials and with different loading methods. The choices of intercalated nanomaterials, substrate layers and loading methods are based on the object to be treated. The introduction of nanostructured interlayers improves the formation of the PA separation layer and provides ultrafast water molecule transport channels. In this manner, the TFNi membrane mitigates the trade-off between permeability and selectivity reported for polyamide composite membranes. In addition, TFNi membranes enhance the removal of metal ions and organics and the recovery of organic solvents during nanofiltration and reverse osmosis, which is critical for environmental ecology and industrial applications. This review provides statistics and analyzes the developments in TFNi membranes over the last 5-10 years. The latest research results are reviewed, including the selection of the substrate and interlayer materials, preparation methods, specific application areas and more advanced characterization methods. Mechanistic aspects are analyzed to encourage future research, and potential mechanisms for industrialization are discussed.

New insight into the adsorption behaviour of effluent organic matter on organic-inorganic ultrafiltration membranes: a combined QCM-D and AFM study.

Adsorption of organic matter on membranes plays a major role in determining the fouling behaviour of membranes. This study investigated effluent organic matter (EfOM) adsorption behaviour onto poly(vinylidene fluoride) (PVDF) membrane blended with SiO2 nanoparticles using quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). The QCM-D results suggested that low adsorption of EfOM and an EfOM layer with a non-rigid and open structure was formed on SiO2-terminated membrane surfaces. Conformational assessment showed that EfOM undergoes adsorption via two steps: (i) in the initial stage, a rapid adsorption of EfOM accumulated onto the membrane; (ii) the change in dissipation was still occurring when the adsorption frequency reached balance, and the layer tended towards a more rearranged or organized secondary structure upon adsorption onto the more hydrophilic surface. For the AFM force test, when a self-made EfOM-coated probe approached the membrane, a 'jump-in' was observed for the hydrophobic membrane after repulsion at a small distance, while only repulsive forces were observed for PVDF/SiO2 membranes. This study demonstrated that the PVDF/SiO2 membrane changed the entire filtration process, forming a 'soft' open conformation in the foulant layer.

[Adsorption Mechanisms Analysis of EfOM on PVDF Ultrafiltration Membranes Modified by SiO2 Using QCM-D and AFM].

To further unravel adsorption mechanisms of effluent organic matter (EfOM) on the PVDF ultrafiltration membranes modified by nano-silica particles from micro perspective during different filtration phases, the membranes were prepared by adjusting the dosage of nano-silicon. The adsorption of EfOM on the surface of the membranes and the interaction between EfOM and the membranes were measured by quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM).The QCM-D results suggested that adsorbing capacity and adsorption rate of EfOM on the hydrophilic surfaces were lower than on the hydrophobic surfaces. Meanwhile, it was found that EfOM underwent adsorption via two steps: In the initial 15 min stage, a rapid adsorption of EfOM accumulated onto the membrane surface; The change in dissipation still occurred when the EfOM adsorption frequency reached balance, which demonstrated that the adsorption of EfOM remained unchanged on the membrane surfaces, and changes in the conformation of adsorption layer still occurred. For the AFM force test, it was found that the EfOM-membranes and EfOM-EfOM interactions declined with the increase of hydrophily, which revealed the essential reason for the decrease of adsorbing capacity and adsorption rate. The combined utilization of QCM-D and AFM effectively explained the effect of modified membranes on adsorption mechanisms of EfOM.

[Adhesion Force Analysis of Protein Fouling of PVDF Ultrafiltration Membrane Using Atomic Force Microscope].

To determine the fouling behavior of bovine serum albumin (BSA) on differet hydropniic PVDF ultrafiltration membrane over a range of pH, atomic force microscopy (AFM) and self-made colloidal probes were used to detect the microscopic adhesion forces of membrane-BSA and BSA-BSA, respectively. The results showed a positive correlation between the flux decline extent and the membrane-foulant adhesion force in the initial filtration stage, whereas the foulant-foulant interaction force was closely related to the membrane fouling in the later filtration stage. Moreover, the membrane-BSA adhesion interaction was stronger than the BSA-BSA adhesion interaction, which indicated that the fouling was mainly caused by the adhesion interaction between membrane and foulant. At the same pH, the adhesion force between PA membrane-BSA was smaller than that of PP membrane-BSA, illustrating the more hydrophilic the membrane was, the better the antifouling ability it had. The adhesion force between BSA-BSA fouled PA membrane was similar to that between BSA-BSA fouled PP membrane. These results confirmed that elimination of the membrane-BSA adhesion force is important to control the protein fouling of membranes.

[Efficacy of A2/O-MBR Combined Process in Wastewater Treatment and the Characteristics of Membrane Fouling].

The hydrophilic modification of PVA composite membrane was applied in the reversed A2/O-MBR process to treat wastewater, the removal efficacy of COD, NH4(+) -N, TN, TP, turbidity and performance of composite membrane were investigated. The results indicate that the average removal rates of COD, NH4(+) -N and TP were higher than 90%, 95% and 80% under different reflux ratio, respectively. The reflux ratio had large impact on TN removal rate: when the reflux ratio was 100%, the removal rate was low; when the reflux ratio increases the range from 100% to 300%, the removal rate was correspondingly increased. Under the efficient interception of membrane, water turbidity was always less than 0.05NTU, and the composite film was controlled at (12 ± 0.5) L x (m2 x h)(-1) flux, the operation was uninterrupted for 52 days without any cleaning process of the membrane, the average rate of membrane fouling is 13.22 Pa x h(-1) and the process of membrane fouling was very slow. After FTIR analysis, we confirmed that polysaccharide and protein is a main composition of organic pollutants. LB is further proved to be the main pollutants from micro acting force between the membrane and the pollutants, which is consistent with FTIR analysis.

[Experimental study of adhesion properties between membrane surface and humic acid during microfiltration].

To further unravel the humic acid (HA) fouling mechanism during microfiltration under different conditions, such as pH, ionic strength, the concentration of calcium ions, atomic force microscopy (AFM) combined with self-made PVDF colloidal probe was applied to determine the relationship between the adhesion forces of membrane-HA or HA-HA and the flux decline of membrane. The results indicate adhesion forces were the main reason of membrane fouling. With the decrease of pH or increase of the ionic strength, due to the electrical neutralization caused by pH and electrical shielding effect of ionic strength, the adhesion forces of membrane-HA and HA-HA increased. Because of the comprehensive effect of "salt bridge" and electrical neutralization, there was a transition from increase to decrease for the adhesion forces of membrane-HA and HA-HA as the doses of calcium ions increased. In all cases, both of membrane-HA and HA-HA adhesion forces had the same variation tendency, which displayed a good correlation with the flux decline trends during fouling experiments, respectively, and provided certain theoretical support to further understand the formation mechanism of membrane fouling.

Identifying polyvinylidene fluoride ultrafiltration membrane fouling behavior of different effluent organic matter fractions using colloidal probes.

The interaction forces between effluent organic matter (EfOM) fractions and membrane were measured by atomic force microscopy in conjunction with self-made membrane material colloidal probes. The inter-EfOM-fraction and intra-EfOM-fraction interactions were investigated using corresponding EfOM-fraction-coated colloidal probe. We combined this analysis with corresponding fouling experiments to identify the EfOM fractions responsible for polyvinylidene fluoride (PVDF) ultrafiltration membrane fouling. Results show that hydrophilic and hydrophobic fractions were the dominant fractions responsible for membrane fouling and flux decline in the initial and later filtration stages, respectively, which was mainly attributed to the stronger PVDF-hydrophilic fraction and intra-hydrophobic-fraction interaction forces. This phenomenon, in conjunction with the fact that each interaction force of PVDF-EfOM fraction was stronger than corresponding intra-EfOM-fraction force, suggests that the elimination of the PVDF-hydrophilic fraction interaction force is the best strategy for controlling EfOM fouling. Moreover, the inter-EfOM-fraction interaction force was mainly controlled by the corresponding intra-EfOM-fraction interaction forces. And, while the membrane-EfOM fraction and intra-EfOM-fraction interactions for each type of EfOM fraction are equivalent, the EfOM fractions with the molecular weight smaller than the molecular weight cutoff of the membranes used were mainly responsible for membrane fouling rather than the relatively high-molecular-weight fractions.