Impact of the ethylene content on poly (ethylene-co-vinyl alcohol) membrane morphology and performance via immersion precipitation for lithium extraction

Synthesizing LiFePO4 by phosphate & iron recovered from sludge-incinerated ash and Li extracted from concentrated brines

Phosphorus (P) recovered from sludge-incinerated ash (SIA) could be applied to synthesize highly added-value products (FePO4 and LiFePO4) with in situ Fe in SIA. Indeed, LiFePO4 is a future of rechargeable batteries, which makes lithium (Li) highly needed. Alternatively, Li could also be extracted from concentrated brines to face a potential crisis of Li depletion on lands. Based on H3PO4 and Fe3+ co-extracted from the acidic leachate of SIA by tributyl phosphate (TBP), FePO4 (31.2 wt% Fe, 17.6 wt% P and the molar ratio of Fe/P = 0.98) was easily formed only adjusting pH of the stripping solution to 1.6. Interestingly, the organic phase from the first-stage co-extraction process of Fe3+ and H3PO4 could be utilized for Li-extraction from salt-lake brine, based on the TBP-FeCl3-kerosene system, and a good performance (78.7%) of Li-extraction and separation factors (β) (186.0-217.4) were obtained. Furthermore, the compounds with Li-extraction are complex, possibly LiFeCl4∙2TBP, in which Li+ could be stripped to form Li2CO3 by 4.0 M HCl (with a stripping rate up to 83%). Besides, Li2CO3 could also be obtained from desalinated brine by adsorption with manganese oxide ion sieve (HMO) and desorption with HCl. In the two cases, almost pure Li2CO3 products were obtained, up to 99.7 and 99.5 wt% Li2CO3 respectively, after further purification and concentration. Finally, recovered FePO4 and extracted Li2CO3 were synthesized for producing LiFePO4 that had a similar electrochemical property (69.5 and 77.8 mAh/g of the initial discharge capacity) to those synthesized from commercial raw materials.

Electrospun EVOH/AST-120 hybrid nanofiber membranes for removal of indoxyl sulfate from blood

Nanofibers containing activated carbon using poly(ethylene-co-vinyl alcohol) (EVOH) were prepared to remove indoxyl sulfate (IS) from the blood. IS is a urinary toxin that is highly toxic and triggers the progression of chronic kidney disease (CKD). Here, nanofibers containing activated carbon (AST-120), which has been used practically as an adsorbent for indole (a precursor of IS), were fabricated via electrospinning for the adsorption and removal of IS from the blood. EVOH containing different ethylene ratios was used as the nanofiber material; moreover, the effect of the ethylene ratio on various properties of the nanofibers, such as surface wettability and the IS adsorption rate, was investigated. As a result, EVOH/AST-120 nanofibers comprising EVOH with a low ethylene ratio exhibited faster IS adsorption behavior. This adsorption behavior agreed well with the pseudo-second-order model, suggesting that the diffusion of IS into the nanofibers is the rate-limiting step of the process of adsorption. Furthermore, the nanofibers successfully reduced the IS concentration in the blood under circulating conditions. Therefore, these EVOH/AST-120 nanofibers are expected to greatly improve the prognosis of patients with CKD when used in combination with the current hemodialysis therapy as an IS-adsorbing filter.

Novel Near-Infrared Light-Induced Triple-Shape Memory Composite Based on Poly(ethylene-co-vinyl alcohol) and Iron Tannate

Remote controllability and multiple-shape memory performance are two important functions for shape memory polymers (SMPs) in engineering applications, which are still a challenge to achieve via a facile approach. Herein, we synthesized a shape memory composite with near-infrared (NIR) light-induced triple-shape memory performance by in situ formation of iron tannate (FeTA) nanoparticles in cross-linked poly(ethylene-co-vinyl alcohol) (EVOH). EVOH possessed two transition temperatures enabling the composites with triple-shape memory behavior, while FeTA nanoparticles served as the photothermal conversion factor for NIR light-induced responsiveness. Because the light-induced triple-shape memory performance of the composite is highly dependent on its photothermal conversion property, the control of FeTA doping would also be an effective solution to prepare light-induced multiple-SMPs with various shape transformations. Moreover, the composites exhibited high light-driving recovery stress, which could lift burdens 1600 times heavier than their own weight, indicating their great potential as a smart soft actuator for various applications.

Fabrication of a PVDF membrane with tailored morphology and properties via exploring and computing its ternary phase diagram for wastewater treatment and gas separation applications

We report a simple approach for tailoring the morphology of poly(vinylidene fluoride) (PVDF) membranes fabricated using a nonsolvent induced phase separation (NIPS) method that sustains both the hydrophilic and hydrophobic properties. Various membrane structures, i.e. skin layers and whole membrane structures as well, were obtained via an experimental method based on the obtained and computed ternary phase diagram. The nonsolvent interactions with polymer solution resulted in the different forms and properties of a surface layer of fabricated membranes that affected the overall transport of solvent and nonsolvent molecules inside and outside the bulk of the fabricated membranes. The resulting morphology and properties were confirmed using the 3D optical profiler, SEM, FT-IR and XRD methods. The effect of binary interaction parameters on the morphology of the fabricated membranes and on their separation performance was tested using water/oil mixture and gas separation. Both hydrophobic and hydrophilic properties of PVDF showed the excellent durable separation performance of the prepared membranes with 92% of oil separation and the maximum flux of 395 L h^-1 m^-2 along with 120 min of long-term stability. CO₂ separation from H₂, N₂, CH₄ and SF₆ gases was performed to further support the effect of tuned PVDF membranes with different micro/nanostructured morphologies. The gas performance demonstrated ultrahigh permeability and a several-fold greater than the Knudsen separation factor. The results demonstrate a facile and inexpensive approach can be successfully applied for the tailoring of the PVDF membranes to predict and design the resulting membrane structure.

Fabricating PES/SPSF membrane via reverse thermally induced phase separation (RTIPS) process to enhance permeability and hydrophilicity

A new method was presented to prepare hydrophilic PES/SPSF flat-sheet membrane by a reverse thermally induced phase separation (RTIPS) method to enhance permeability and hydrophilicity. SPSF was self-made and was blended to improve the hydrophilicity of PES flat-sheet membrane. The performance of PES/SPSF flat-sheet membrane, which varied with SPSF content and coagulation water bath temperature, was investigated by SEM, FTIR, AFM, pure water flux, BSA rejection rate, water contact angle and long-term testing. FTIR results proved the successful blending of SPSF with PES membrane, SEM images showed that dense skin surface and finger-like structure emerged in the membrane fabricated by NIPS method, while a porous top surface and sponge-like structure emerged in the membrane fabricated by RTIPS. The pure water flux and BSA rejection rate of the membrane for RTIPS were both higher than those for NIPS. AFM images revealed that surface roughness increased with the addition of SPSF. The water contact angle decreased with the increase of SPSF, which illustrated better hydrophilicity with the addition of SPSF. The flat-sheet PES membrane prepared with 2 wt% SPSF by RTIPS method exhibited decent properties, reaching maximum pure water flux (966 L m⁻² h⁻¹) and at the same time the BSA rejection rate was 79.2%. The long-term test proved that the anti-fouling performance of PES/SPSF membrane was better than that of PES membrane.

A new method is presented to prepare hydrophilic PES/SPSF flat-sheet membrane by a reverse thermally induced phase separation (RTIPS) method to enhance permeability and hydrophilicity.