Nanoclays‐Incorporated Thin‐Film Nanocomposite Membranes for Reverse Osmosis Desalination

Thin-film nanocomposite membranes incorporated with defective ZIF-8 nanoparticles for brackish water and seawater desalination

Thin film nanocomposite (TFN) membranes contain nanoparticles in the thin polyamide (PA) top layer, resulting in a remarkable increase in water permeability without compromising the salt rejection. Mesoporous silica nanoparticles (MSN) have gained much attention as nanofillers for improved performance PA TFN membranes. However, aggregation of MSN inside the PA layer and their tendency to fast dissolution in aqueous solutions are serious challenges which strongly affect the separation performance of MSN-based TFN membranes. In this work, these challenges were addressed by controlling the functionalization of MSN with hydrophobic organo-silane, such as octadecyltrichlorosilane (OTS) or methyltrichlorosilane (MTS), before incorporating in the PA layer. MSN were synthesized first by sol-gel process and then functionalized using post-grafting method during silanization reaction. The functionalization was tuned in order to allow the hydrophobic alkyl group of the silane molecule to graft both the external surface of MSN as well as their interior pores or to modify only their external surface depending on the functionalization procedure and the silane concentration. The model of functionalization and the amount of OTS or MTS grafted on the surface were estimated through the nitrogen adsorption measurement and thermogravimetric analysis. The functionalized MSN with a particle diameter of ≈ 80 nm were thereafter easily dispersed in the organic solvent during the TFN membrane preparation via interfacial polymerization method. The membrane performance was then assessed based on water permeability and salt rejection measurements. Several parameters were found to have a strong influence on the membrane performance such as concentration of grafted OTS or MTS and the NPs loading inside the PA layer. The low aggregation and good integration of the functionalized nanofillers inside the PA layer produced TFN membranes with superior initial water permeability. The results revealed that the initial water permeability of the TFN membranes with OTS functionalized MSN achieved ≈ 65% higher initial permeability than the reference TFC membrane at the optimum OTS amount and NPs loading, without sacrificing the membrane selectivity. Whereas the corresponding TFN membranes with MTS functionalized MSN achieved ≈ 130% higher permeance but with 2% less salt rejection than the reference TFC membrane at the same conditions. The controlled functionalization of MSN nanofillers not only can improve membrane performance but also can provide a deeper understanding of the role of porous structure of MSN on the separation mechanism. This work clearly emphasizes the direct relationship between the internal pores of MSN inside the PA barrier layer and increasing or decreasing the water permeability of resulting TFN membranes. Furthermore, it was investigated, how hydrophobic functionalization of MSN can improve the stability of MSN in aqueous solutions and improve the stability of the respective TFN membranes over prolonged filtration time at different pH values. The results showed that TFN membranes containing the OTS-functionalized MSN had only ≈ 6% (or 7.5% for MTS-functionalized MSN) decline in salt rejection compared to 34.5% decline for the membrane containing unfunctionalized nanofillers accompanied by increasing in water permeability after 240 h filtration time (120 h at pH 5 then 120 h at pH 9). According to these results, it was concluded that the functionalized MSN have low dissolution tendency due to the formation of a protective organic layer leading to enhanced long-time stability of the TFN membranes. Finally, the durability of the barrier layer after a prolonged use for desalination performance of PA TFN membranes was also investigated.

The role of sheet-like TiO2 in polyamide reverse osmosis membrane for enhanced removal of endocrine disrupting chemicals

The membrane technology is still considered a costly method to produce potable water. In view of this, RO membrane with enhanced water permeability without trade-off in salt rejection is desirable as it could further reduce the cost for water desalination. In this study, thin film nanocomposite (TFN) membranes containing 0.05 or 0.10 w/v% hydrophilic nanofillers in polyamide layer were synthesized via interfacial polymerization of piperazine and trimesoyl chloride monomers. The resultant TFN membranes were characterized and compared with a control thin film composite (TFC) membrane. Results from the filtration experiments showed that TFN membranes exhibited higher water permeability, salt rejection and fouling resistance compared to that of the TFC membrane. Excessive amount of nanofillers incorporated in the membrane PA layer however negatively affected the cross-linking in the polymer matrix, thus deteriorating the membrane salt rejection. TFN membrane containing 0.05 w/v% of nanofillers showed better performances than the TFC membrane, recording a pure water flux of 11.2 L/m2∙h, and salt rejection of 95.4%, 97.3% and 97.5% against NaCl, Na2SO4 and MgSO4, respectively.

Thin film nanocomposite hollow fiber membranes comprising Na+-functionalized carbon quantum dots for brackish water desalination

Thin-film nanocomposite membranes incorporated with UiO-66-NH2 nanoparticles for brackish water and seawater desalination

MXenes and other 2D nanosheets for modification of polyamide thin film nanocomposite membranes for desalination

Both brackish water desalination and seawater desalination processes are well established and in common use around the globe to create new water supply sources. The farther the location of the source water from the ocean or seashore, the lower the salinity (TDS) of the water and the lower the osmotic pressure that needs to be overcome when desalinated water is produced. This is one of the major reasons that brackish desalination is often considered less costly than seawater desalination. A number of project considerations, however, indicate that seawater desalination can be beneficial and more cost-effective than brackish water desalination. To make a fair comparison, we need to properly compare all major aspects of both types of projects to define the best and most appropriate desalination technology. While brackish water has less feed water TDS, it is more challenging to dispose of the produced concentrate. Also, although brackish water desalination needs less energy to overcome osmotic pressure, it usually requires more energy to draw the water from the well than it takes to pump seawater from the open ocean intake. Another factor is that the temperature of the brackish well water may be lower than the temperature of ocean water, giving seawater desalination an advantage in energy demand. In comparing brackish to seawater desalination, these major aspects should be evaluated: (1) Locations of seawater and brackish water plants, relative to the major consumers of the desalinated water, (2) Transportation (pumping and disposal) costs of the feed water and produced water, (3) Potential colocation of a seawater plant with a large industrial user (e.g., power plant) of the seawater for cooling or other purposes, (4) Produced quality of brackish water and seawater desalination in terms of major minerals and emerging contaminants, (5) Sustainability of the water source: capacity and depth of the brackish water wells, as well as the type of soil. (6) Technical and economic aspects of produced concentrate disposal, (7) Permitting process costs for brackish and seawater desalination, and (8) The economics of both brackish and seawater desalination treatment processes: capital costs, operational and maintenance (O&M) costs, lifetime water cost, and total water cost (TWC). This paper discusses the major evaluation criteria and considerations involved in properly comparing the economic and technical aspects of brackish and seawater desalination to determine the more favorable desalination technology for a given desalination project.

Thin-film composite (TFC) membranes incorporated with hydrophilic additives and layered double hydroxides (LDHs) for effective brackish water (BW) desalination

Efforts have been rendered by researchers to address water purification and desalination challenges through membrane separation processes. However, the trade-off phenomenon in permeability and selectivity constrained the membranes’ usage. Recent advances made in fabricating membranes, especially thin film nanocomposite (TFN) membranes using functionalized nanofillers, have high performance in water purification and desalination. In this review, state-of-the-art thin film composite (TFC) membranes in water purification and desalination along with their drawbacks are discussed. The urgent demands as an alternative of TFC membranes are highlighted for high-performance membranes. Then, the fabrication and development of high permeability and selectivity of TFN membranes are discussed. Thin film nanocomposite membranes manufactured using rational nanofillers are systematically summarized. Finally, the applications of TFN membranes in water purification and desalination are reported.

Thin-film nanocomposite reverse osmosis membranes incorporated with citrate-modified layered double hydroxides (LDHs) for brackish water desalination and boron removal

Sulfonated graphene oxide incorporated thin film nanocomposite nanofiltration membrane to enhance permeation and antifouling properties

In-situ growth of layered double hydroxides (LDHs) onto thin-film composite membranes for enhanced reverse osmosis performance

Fabrication of defect-free thin-film nanocomposite (TFN) membranes for reverse osmosis desalination

Post-synthetic modification of MOFs to enhance interfacial compatibility and selectivity of thin-film nanocomposite (TFN) membranes for water purification