In order to recover lithium from brine with a high Mg²⁺/Li⁺ ratio, a positively charged nanofiltration (NF) membrane was prepared by depositing polydopamine (PDA)-coated graphitic carbon nitride (g-C₃N₄) as the interlayer (PDA-g-C₃N₄) and the interfacial polymerization (IP) of polyethyleneimine (PEI) and trimesoyl chloride (TMC) was carried out. Under optimal conditions, the water contact angle of the composite membrane is only 55.5° and the isoelectric point (IEP) is 6.01. The final positively charged NF membrane (M5) exhibits high permeance (10.19 L·m⁻²·h⁻¹·bar⁻¹) and high rejection of Mg²⁺ (98.20%) but low rejection of Li⁺ (13.33%). The separation factor (SF) is up to 48.08, and the Mg²⁺/Li⁺ ratio of the permeate is 0.036 in the simulated brine. In conclusion, the M5 membrane shows a good separation performance for salt lake brine (SF = 12.79 and Mg²⁺/Li⁺ ratio of the permeate = 1.43) and good fouling resistance. Therefore, the positively charged M5 membrane with PDA-g-C₃N₄ as the interlayer has the potential to be used for the recovery of lithium from brine.

The ECTFE membrane with bicontinuous structure was prepared by a binary diluent via thermally induced phase separation method. The effect of binary diluent composition on membrane structure was investigated systematically. The Flory–Huggins interaction parameters between ECTFE and diluents were investigated to analyze the mechanism of phase separation. Dibutyl sebacate (DBS) was selected as the primary diluent due to the high boiling point and strong interaction with ECTFE, while triphenyl phosphite (TPP) was selected as the secondary diluent because of the good compatibility with DBS. As the weight ratio of DBS to TPP was 3/2, a uniform bicontinuous structure was obtained. A typical upper critical solution temperature behavior was displayed and the monotectic concentration was as high as approximately 50 wt.%. Finally, an ECTFE hollow fiber membrane with a bicontinuous structure was prepared by the binary diluent and revealed high mechanical strength (tensile strength of 2.40 MPa) and filtration performance (water flux of 313 L m⁻² h⁻¹ at 0.1 MPa).

To date, remarkable progress has been achieved in the fabrication of poly(vinylidene fluoride) (PVDF) membranes with high performance for applications in wastewater treatment. After a comprehensive overview of recent progress on the preparation of PVDF membranes via thermally induced phase separation (TIPS) method, this paper provided historical information about the plenty of work focused on the preparation and advanced industrialization of PVDF membranes that was carried out by Beijing Key Laboratory of Membrane Materials and Engineering of Tsinghua University (Beijing, China). The work followed the line of formula design, advanced production, and membrane module development. Firstly, an innovative PVDF membrane with good performance was prepared via TIPS (liquid–liquid, L–L) method based on exhaustive thermodynamic and dynamic researches on the membrane formation process. Secondly, advanced production of the PVDF hollow fiber membrane was achieved by an effective combination of material processing and unit operation. Additionally, different ultrafiltration (UF) modules were fabricated according to various application situations. The final step explored the possibility of using an integrated membrane solution that adopted the modules where wastewater treatment was intended for water recycling, as shown in four application cases. The application results have shown that PVDF membranes prepared via TIPS (L–L) method break through the traditional phase separation limitation and exceed performance expectation. This paper can be a useful reference for the preparation and development of polymeric membranes and modules.

A treatment consisting of room temperature stretching and subsequent annealing was utilized to regulate the morphology and performance of polyvinylidene fluoride (PVDF) hollow fiber membranes. The effects of stretching ratios and stretching rates on the crystallization behavior, morphology, and performance of the PVDF membranes were investigated. The results showed that the treatment resulted in generation of the β crystalline phase PVDF and increased the crystallinity of the membrane materials. The treatment also brought about the orientation of the membrane pores along the stretching direction and led to an increase in the mean pore size of the membranes. In addition, as the stretching ratio increased, the tensile strength and permeation flux were improved while the elongation at break was depressed. However, compared to the stretching ratio, the stretching rate had less influence on the membrane structure and performance. In general, as the stretching ratio was 50% and the stretching rate was 20 mm/min, the tensile strength was increased by 36% to 7.47 MPa, and the pure water flux was as high as 776.28 L/(m²·h·0.1bar), while the mean pore size was not changed significantly. This research proved that the room temperature stretching and subsequent annealing was a simple but effective method for regulating the structure and the performance of the PVDF porous membranes.

The emerging interest in fluoride-removal from wastewater has attracted attention to zeolite since it has been considered as a natural adsorbent. However, the fluoride-removal efficiency of natural zeolite is generally low. As part of the effort to improve the zeolite adsorption efficiency, we have produced and tested the Mn-Ti modified zeolite. In the current work, the material preparation is discussed, and prepared materials were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy, and Fourier transform infrared (FTIR) spectra. Both static and dynamic experiments were conducted to examine the effects of independent variables. In the static adsorption section, sensitivity analysis experiments were conducted for independent variables, such as adsorbent dosage, pH, temperature, and competitive ions. The maximum adsorption capacity is 2.175 mg/g, which was obtained at PH = 7, temperature = 25 °C, and initial fluoride concentration = 10 mg/L. For adsorption kinetics, both Lagergren and Pseudo-second order models predict the experiments very well, which probably demonstrates that the current process is a combination of physical sorption and chemisorption. For adsorption isotherms, the Freundlich model performs better than the Langmuir model since it is usually applied to illustrate adsorption on inhomogeneous surfaces. In the dynamic adsorption section, sensitivity analysis experiments were also conducted for independent variables, such as adsorbent thickness, flow velocity, initial fluoride concentration, and PH. Additionally, the adsorption mechanism is also discussed. The main reason is the hydrated metal fluoride precipitate formation. As we know, the current work provides the first quantified comparison of the natural zeolite and the Mn-Ti modified zeolite regarding fluoride-removal efficiency.

The non-isothermal crystallization behavior of poly(vinylidene fluoride) (PVDF) in dialkyl phthalate diluents during the thermally induced phase separation (TIPS) process was investigated by differential scanning calorimetry (DSC) at various cooling rates. Dialkyl phthalates with different alkyl chain-length, namely dimethyl phthalate (DMP), diethyl phthalate (DEP) and dibutyl phthalate (DBP), were used as the diluent. The effects of alkyl chain-length of dialkyl phthalate and cooling rate on the non-isothermal crystallization behavior as implied by the Avrami analysis modified by Jeziorny and Mo’s analysis were determined. The values of half-time, $t_{1/2}$, and the parameters $Z_c$ and $F(t)$, which characterized the kinetics of non-isothermal crystallization, showed that the crystallization rate increased with the increase of the alkyl chain-length of dialkyl phthalate due to the lower compatibility between PVDF and dialkyl phthalate. Moreover, the alkyl chain-length of dialkyl phthalate also has a great impact on the compact spherulitic structure of PVDF membranes prepared from different PVDF/dialkyl phthalate blends. With the decrease of the alkyl chain-length of dialkyl phthalate, the number of spherulites increased and the size of spherulites became smaller. This research thus not only proves the effects of alkyl chain-length of dialkyl phthalate on the non-isothermal crystallization behavior of PVDF, but also provides a systematic strategy to evaluate a single diluent during the TIPS process.