Charged Layered Boron Nitride‐Nanoflake Membranes for Efficient Ion Separation and Water Purification

Abstract

most intensively studied research areas in the development of high-performance separation membranes.Most 2D materials typically have a layered geometry where the atoms are linked by strong in-plane covalent bonds, while the two adjacent layers are held together by van der Waals forces. [7] Exfoliated nanosheets typically show a high surface-area-tothickness ratio, which is instrumental in improving the adsorption capacity or the ion selectivity, both of which can lead to a better separation performance. In addition to highly effective ion-rejection properties, 2D membranes are also known to possess excellent water permeability. Due to these properties, many 2D materials such as nm-thick graphitic carbon nitride (g-C 3 N 4 ) nanosheets, [8] MoS 2 sheets, [9] WS 2 nanosheets, [6] graphene, [10] Mxene nanosheets, [11] and graphene oxide (GO), [12] have been recently used as the building blocks for fabricating ultrathin layered membranes for separation applications. These 2D membranes have shown highly efficient size-selective ion separation and high water permeance.Hexagonal boron nitride (h-BN), so-called "white graphene," is however one of the promising 2D materials that has not been utilized to its full potential in ion-separation applications. For efficient ion separation, the membrane should show high ion selectivity, which is primarily dependent on the channel size and surface charge on the membrane. The h-BN material is known to have a high surface charge density resulting from the adsorption of the hydroxyl ions on the surface defect sites. [13] It also shows excellent oxidation and corrosion resistance, which is an important property for wastewater treatment applications. The high chemical stability of h-BN also enables it to be resistant to chemical cleaning, which is frequently needed during separation processes. Qin et al. reported high ionic conductivities for h-BN nanofluidic channels, prepared by the one-step BN exfoliation method and amine functionalization. [14] More recently, Chen et al. developed a 2D h-BN membrane by functionalizing h-BN flakes (h-BNF) with amino groups to overcome its poor water dispersibility. The functionalized h-BNF membranes demonstrated fast solvent transport and good ion-rejection properties, based on molecular sieving mechanism. [15] However, these membranes do not show charge-based (Donnan) exclusion, due to the amine functionalization of the 2D layered nanomaterials have attracted considerable attention for their potential for highly efficient separations, among other applications. Here, a 2D lamellar membrane synthesized using hexagonal boron nitride nanoflakes (h-BNF) for highly efficient ion separation is reported. The ion-rejection performance and the water permeance of the membrane as a function of the ionic radius, ion valance, and solution pH are investigated. The nonfunctionalized h-BNF membranes show excellent ion rejection for small sized salt ions as well as for anionic dyes (>97%) while maintaining a high water permeability, ≈1.0 × 10 −3 L m m −2 h −1 bar −1...

Green synthesis of copper oxide nanoparticles using extracts of Solanum macrocarpon fruit and their redox responses on SPAu electrode

“…In addition, it is apparent that the SPAuE/CuO(m) with the lowest current response in the (Fe(CN) 6 ) 3−/4− demonstrated the highest Cu 2+ peak current magnitude in the KCl medium. Hence, the suppressed current response observed for SPAuE/CuO(m) could be attributed to the electrostatic repulsion between the positive ions of Fe 2+/3+ in the (Fe(CN) 6 ) 3−/4− probe and the highly electroactive Cu 2+ radical of CuO(m) NPs [ 31 , 32 ]. Similar observation has been reported in studies related to (Fe(CN) 6 ) 3−/4− probe [ 33 , 34 , 35 ].…”

“…Additionally, the magnitude of the peak to peak potential separation (ΔEp) for the bare and modified electrodes in both (Fe(CN) 6 ) 3−/4− and KCl media, was more than 59 mV (a theoretical value for a perfect redox system), while the redox peak ratios showed deviation from unity ( Table 1 ). This suggests that the redox behaviours of the electrodes in both solutions are characteristic of a quasi-reversible system (25 mV/s scan rate) [ 31 ]. However, in KCl media, the peak to peak separations (ΔEp) for both electrodes were less in magnitude compared to that of the (Fe(CN) 6 ) 3−/4− , and further confirms the removal of the electrostatic repulsive effect in (Fe(CN) 6 ) 3−/4− media.…”

“…3 mV to 378.4, and 157.5 mV–527.7 mV/s at the scan rate of 10 mV/s to 200 mV/s for the bare, SPAuE/CuO(h), and SPAuE/CuO(m) respectively. The ΔEp, was broader in the SPAuE/CuO(h), and SPAuE/CuO(m), which could be attributed to ohmic drop or slower rate of electron transfer in the (Fe(CN) 6 ) 3−/4− medium [ 31 ]. Also, the redox peak current ratios increased with an increase in scan rate as shown in Figure 6 d.

Figure 6 The variation of the redox cordinates with scan rate for (a) Bare in (Fe(CN) 6 )3 −/4− , (b) SPAuE/CuO(h) in (Fe(CN) 6 ) 3−/4− , (c) SPAuE/CuO(m) in (Fe(CN) 6 ) 3−/4− (d) Redox peaks variation with scan rate (inset: ΔEp with scan rate) in (Fe(CN) 6 ) 3−/4− (e) SPAuE/CuO(h) in KCl, and (f) SPAuE/CuO(m) in KCl.

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Tree‐Inspired Ultralong Hydroxyapatite Nanowires‐Based Multifunctional Aerogel with Vertically Aligned Channels for Continuous Flow Catalysis, Water Disinfection, and Solar Energy‐Driven Water Purification

“…[5][6][7][8][9][10][11][12] Among them, the membrane filtration and adsorption have been implemented to effectively remove organic and bacterial contaminants. Many functionalized materials were investigated for this purpose, for example, amyloid fibrils aerogel, [13] boron nitride nanoflake membrane, [14] metal-organic framework, [15] and hydrogel spheres. [16] However, the insufficient efficiency and potential fouling concern hinder the long-term service and repeat usage.…”

Ion‐Selective MXene‐Based Membranes: Current Status and Prospects

“…Separation techniques play a major role in our daily lives and in many industries owing to their use in applications such as purification, concentration, and fractionation. Separation can be achieved by using conventional separation processes such as crystallization, condensation, and distillation, which are energy intensive (they use 10-15% of the amount of energy that hexagonal boron nitride, [63][64][65][66][67] graphene, [68] and graphene oxide [69,70] have been used. Only a few materials that can separate ions based on their charges and sizes have been investigated.…”