Static and dynamic filtration of nickel and lead ions by adsorptive membrane induced by POP via layer by layer technique

Layer-by-layer assembly in nanochannels: assembly mechanism and applications

Layer-by-layer (LbL) assembly is a versatile technology to construct multifunctional nanomaterials using various supporting substrates, enabled by the large selection freedom of building materials and diversity of possible driving forces. The fine regulation over the film thickness and structure provides an elegant way to tune the physical/chemical properties by mild assembly conditions (e.g. pH, ion strength). In this review, we focus on LbL in nanochannels, which exhibit a different growth mechanism compared to "open", convex substrates. The assembly mechanism in nanochannels is discussed in detail, followed by the summary of applications of LbL assemblies liberated from nanochannel templates which can be used as nanoreactors, drug carriers and transporting channels across cell membranes. For fluidic applications, robust membrane substrates are required to keep in place nanotube arrays for membrane-based separation, purification, biosensing and energy harvesting, which are also discussed. The good compatibility of LbL with crossover technologies from other fields allows researchers to further extend this technology to a broader range of research fields, which is expected to result in an increased number of applications of LbL technology in the future.

Robust cellulose-based composite adsorption membrane for heavy metal removal

Adsorptive membranes offer an effective mode to remove heavy metal ions from contaminated water, due to the synergies made possible by low-cost, high-affinity adsorbents and highly scalable filtration in one system. However, the development of adsorptive membranes is hampered by their instability in the aqueous phase and low binding affinity with a broad spectrum of heavy metals in a reasonable flux. Herein, a regenerated cellulose support membrane is strongly grafted with stable and covalent-bonded polyelectrolyte active layers synthesized by a reactive layer-by-layer (LBL) assembly method. The LBL assembled layers have been successfully tested by scanning electron microscopy, Fourier-transform infrared spectroscopy and X-ray photo-electron spectroscopy. The covalent bonding provides the membrane with long-term stability and a tunable water flux compared to a membrane assembled by electrostatic bonding. The maximum adsorption capacity of the membrane active layers can reach up to 194 mg/g, showing more efficient adsorption at lower heavy metal concentration and higher pH value of feed solution. The membrane can remove multiple ions, such as Cu, Pb, and Cd, by adsorption and is easy to be regenerated and recovered. The strong covalent bonding can extend the membrane lifetime in water purification to remove multiple heavy metals at high efficiency.

Taguchi optimization design of diameter-controlled synthesis of multi walled carbon nanotubes for the adsorption of Pb(II) and Ni(II) from chemical industry wastewater

Herein, Taguchi L₉ orthogonal array was used for the first time to optimize synthesis of diameter-controlled multi walled carbon nanotubes (MWCNTs). The nanoadsorbents, MWCNTs_5-15 nm and MWCNTs_16-25 nm were applied for Pb(II) and Ni(II) ion removal from paint, battery and electroplating wastewater. The results indicated successful synthesis of MWCNTs with diameter distribution ranges of 5-15 nm and 16-25 nm. The synthetized smaller diameter MWCNTs_5-15 nm revealed higher Brunauer-Emett-Teller (BET) surface area of 1306 ± 5 m²/g compared to larger diameter MWCNTs_16-25 nmwith the surface area of 1245 ± 4 m²/g. They demonstrated excellent adsorption of Pb(II) and Ni(II) ions within the permissible concentration proposed by WHO at pH, contact time, adsorbent dosage and temperature of 5, 60 min, 30 mg/L and 50 °C, respectively. Particularly, MWCNTs_5-15 nm possessed high adsorption capacity of 215.38 ± 0.03 mg/g for Pb(II) and 230.78 ± 0.01 mg/g for Ni(II). Again, the maximum adsorption capacity of 201.35 ± 0.02 and 206.40 ± 0.02 mg/g was achieved for Pb(II) and Ni(II) using MWCNTs_16-25 nm. All in all, the adsorption capacity of the nanoadsorbents at the investigated diameter range showed higher efficiency compared to other materials for heavy metals elimination from chemical industrial wastewater.