Selective removal of Cr(VI) by tannic acid and polyethyleneimine modified zero-valent iron particles with air stability.

In this study, a new composite adsorbent for Cr(VI) removal was developed by immobilizing polyethyleneimine (PEI) on the surface of zero-valent iron (ZVI) particles with tannic acid (TA) as a stabilizer. The adsorbent (denoted as Fe-TA-PEI-10) was easy to prepare and regenerate, requiring no conditions for storage. It was found to be particularly effective for Cr(VI) removal from wastewater via reduction and adsorption. Electrochemical analysis revealed that TA significantly reduced the electron transfer resistance of Fe-TA-PEI-10 and reduced the highly toxic Cr(VI)to the less toxic Cr(III). In addition, PEI endowed amino groups to Fe-TA-PEI-10, raising the zero charge point (pHpzc) of Fe-TA-PEI-10 (pHpzc= 7.80), allowing it to adsorb Cr(VI) from the solution rapidly under electrostatic forces and chelating effects. The adsorption process was consistent with the pseudo-first-order model (R2 >0.99) and the Langmuir isotherm model (R2 >0.99), and the maximum adsorption capacity could reach 161.6 mg/g. In particular, this study presented for the first time that TA-modified Fe(0) had excellent stability in the air, and the adsorbent showed no decrease in performance for Cr(VI) removal even after exposure to the air for 30 days. When tested with a simulated electroplating rinsing wastewater, the Fe-TA-PEI-10 showed very high selectivity for Cr(VI) removal. The mechanism of Cr(VI) removal with Fe-TA-PEI-10 was found to be based on adsorption and reduction. This work provided a new scheme for developing efficient and long-lasting reactive adsorbent for Cr(VI) removal.

Nanocomposite membranes for organic solvent nanofiltration: Recent advances, challenges, and prospects.

Organic solvent nanofiltration (OSN) is an emerging technology for the separation of organic solvents that are relevant to the petrochemical, pharmaceutical, food and fine chemical industries. The separation performance of OSN membranes has continued to push the boundary up through advanced membrane fabrication techniques and novel materials for fabricating the membranes. Despite the many advantages, OSN membranes still face such challenges as low solvent permeability and durability in harsh organic solvent conditions. To overcome these limitations, attempts have been made to incorporate nanomaterial fillers into OSN membranes to improve their overall performance. This review analyzes the potential and use of nanomaterials for OSN membranes, including covalent organic frameworks (COFs), metal-organic frameworks (MOFs), metal oxides (MOs) and carbon-based materials (CBMs). Recent advances in the state-of-the-art nano-based OSN membranes, in the form of thin-film nanocomposite (TFN) membranes and mixed matrix membranes (MMMs), are reviewed. Moreover, the separation mechanisms of OSN with nano-based membranes are discussed. The challenges faced by these OSN membranes are also elaborated, and recommendations for further research in this field are provided.

Preparation and characterization of attapulgite-supported phase change energy storage materials.

Phase change materials (PCMs) for the charge and discharge of thermal energy at a nearly constant temperature are of interest for thermal energy storage and management, and porous materials are usually used to support PCMs for preventing the liquid leakage and shape instability during the phase change process. Compared with commonly used polymer matrices and porous carbons, mineral materials with naturally occurring porous structures have obvious advantages such as cost-saving and abundant resources. Attapulgite (ATP) is a clay mineral with natural porous structures, which can be used to contain PCMs for thermal energy storage. However, the poor compatibility between ATP and PCMs is a significant defect that has rarely been studied. Herein, a facile one-step organic modification method of ATP was developed and the chlorosilane-modified ATP (Si-ATP) possesses great hydrophobic and lipophilic properties. Three types of ATP with different compatibility and pore volumes were used as the supports and paraffin as the energy storage units to fabricate a series of form-stable PCMs (FSPCMs). The results showed that the shape-stabilized ability of Si-ATP for paraffin was significantly enhanced, and the Si-ATP supported FSPCM yielded an optimal latent heat of 83.7 J g-1, which was 64.4% higher than that of the pristine ATP based composite. Meanwhile, the thermal energy storage densities of the resulting FSPCMs were gradually increased with an increase in the pore volumes of the three supporting materials. These results may provide a strategy for preparing porous materials as containers to realize the shape stabilization of PCMs and improve the thermal energy storage densities of the resulting FSPCMs.

Unexpectedly Strong Size-Sieving Ability in Carbonized Polybenzimidazole for Membrane H2/CO2 Separation.

Polymers with high permeability and strong size-sieving ability are needed for H2/CO2 separation at temperatures ranging from 100 to 300 °C to enable an energy-efficient precombustion CO2 capture process. However, such polymers usually suffer from a permeability/selectivity tradeoff, that is, polymers with high permeability tend to exhibit a weak size-sieving ability and thus low selectivity. Herein, we demonstrate that carbonization of a suitable polymer precursor (i.e., polybenzimidazole or PBI) generates microcavities (leading to high H2 permeability) and ultramicroporous channels (leading to strong size-sieving ability and thus high H2/CO2 selectivity). Specifically, carbonization of PBI at 900 °C (CMS@900) doubles H2 permeability and increases H2/CO2 selectivity from 14 to 80 at 150 °C. When tested with simulated syngas-containing equimolar H2 and CO2 in the presence of water vapor for 120 h, CMS@900 exhibits stable H2 permeability of ≈36 barrer and H2/CO2 selectivity of ≈53 at 150 °C, above Robeson's 2008 upper bound and demonstrating robustness against physical aging and CO2 plasticization.

Formation of a thin and continuous MOF membrane with 2-D MOF nanosheets as seeds via layer-by-layer growth.

Current MOF composite membranes usually suffer from unduly thick MOF layers and poor adhesion with the polymer substrate. We prepared a thin MOF film (440 nm) on a polymer support with 2-D MOF nanosheets as seeds via a layer-by-layer growth. These 2-D MOF seeds not only provided bonding between the MOF film and the polymer substrate but also facilitated the formation of a continuous and defect-free MOF membrane, which demonstrated excellent performance in gas separation.

Superlight Adsorbent Sponges Based on Graphene Oxide Cross-Linked with Poly(vinyl alcohol) for Continuous Flow Adsorption.

In this study, superlight adsorbent sponges (bulk density 0.016-0.049 g·cm-3) were developed based on graphene oxide (GO) cross-linked with poly(vinyl alcohol) (PVA). The interlayer spacing of the GO nanosheets was increased by the insertion of PVA, and good mechanical integrity was attained by the cross-linked structure. They showed excellent continuous flow adsorption capacity (CFAC) when methylene blue (MB) was used as a model contaminant; a water flux of 396 L·m-2·h-1 through a 2 cm thick adsorbent sponge was achieved at a hydraulic head of only 10 cm water, with an almost complete retention of MB. They corresponded to a water permeability of 4.0 × 105 L·m-2·h-1·MPa-1, which was several orders of magnitudes higher than GO-based membranes for similar applications reported in the literature. The GO nanosheets were completely immobilized in the sponge by cross-linking with PVA, and thus, there was no GO nanoparticle leaching or flushing out into the treated permeate water, which was another advantage over direct use of GO powders in water treatment. Because of the high water permeability and CFAC, the cross-linked GO/PVA sponges have a great potential for wastewater treatment.

Novel affinity membranes with macrocyclic spacer arms synthesized via click chemistry for lysozyme binding.

Affinity membrane has great potential for applications in bioseparation and purification. Disclosed herein is the design of a novel affinity membrane with macrocyclic spacer arms for lysozyme binding. The clickable azide-cyclodextrin (CD) arms and clickable alkyne ethylene-vinyl alcohol (EVAL) chains are designed and prepared. By the azide-alkyne click reaction, the EVAL-CD-ligands affinity membranes with CD spacer arms in three-dimensional micro channels have been successfully fabricated. The FT-IR, XPS, NMR, SEM and SEM-EDS results give detailed information of structure evolution. The abundant pores in membrane matrix provide efficient working channels, and the introduced CD arms with ligands (affinity sites) provide supramolecular atmosphere. Compared with that of raw EVAL membrane, the adsorption capacity of EVAL-CD-ligands membrane (26.24mg/g) show a triple increase. The study indicates that three effects (inducing effect, arm effect, site effect) from CD arms render the enhanced performance. The click reaction happened in membrane matrix in bulk. The effective lysozyme binding and higher adsorption performance of affinity membranes described herein compared with other reported membranes are markedly related with the proposed strategy involving macrocyclic spacer arms and supramolecular working channels.

Modification of poly(vinylidene fluoride) ultrafiltration membranes with poly(vinyl alcohol) for fouling control in drinking water treatment.

A commercial poly(vinylidene fluoride) flat sheet membrane was modified by surface coating with a dilute poly(vinyl alcohol) (PVA) aqueous solution followed by solid-vapor interfacial crosslinking. The resulting PVA layer increased membrane smoothness and hydrophilicity and resulted in comparable pure water permeation between the modified and unmodified membranes. Fouling tests using a 5 mg/L protein solution showed that a short period of coating and crosslinking improved the anti-fouling performance. After 18 h ultrafiltration of a surface water with a TOC of approximately 7 mg C/L, the flux of the modified membrane was twice as high as that of the unmodified membrane. The improved fouling resistance of the modified membrane was related to the membrane physiochemical properties, which were confirmed by pure water permeation, X-ray photoelectron spectroscopy, and contact angle, zeta potential and roughness measurements.