Showing papers by "Congjie Gao published in 2022"

Relation between tensile and fatigue strengths for a high-strength low-alloy steel

Abstract: The microstructure, tensile and fatigue strengths of the high-strength 35CrMo steel with quenched and tempered (QT) and hot-rolled (HR) states were investigated. There is not a commonly linear relation between tensile and fatigue strengths, namely, the HR steel with higher tensile strength has lower fatigue strength, which is mainly attributed to microstructural inhomogeneity of the steel and different damage mechanisms under fatigue and tensile loads. In this work, an estimation method of fatigue strength for steels with dual phase is suggested.

Preparation of anti-fouling zwitterionic nanofiltration membrane with tunable surface charge

Abstract: Anti-fouling property is of vital significance and remains a challenge in the membrane separation field. In this work, N-diethylethylenediamine (DEEDA) was incorporated into the polyamide matrix first. Then, an anti-fouling zwitterionic nanofiltration membrane with tunable surface charge was fabricated by the grafting of p-xylylene dichloride (XDC) on the membrane surface. The resulting nanofiltration membrane possessed zwitterionic groups of positively charged N+ and negatively charged COO-. Meanwhile, the surface charge could be tuned precisely by the concentration of XDC. A neutrally charged nanofiltration membrane was obtained when the concentration of XDC was 1.0 ​wt% and the preparing membrane showed permeance of 9.1 ​L·m-2·h-1·bar-1 with high rejection of CaCl2 (90.8%) and Na2SO4 (91.3%) at pH ​= ​6.5. This membrane exhibited excellent anti-fouling properties towards not only negatively charged bovine serum albumin but also positively charged lysozyme. The optimum membrane, PA-XDC-1.0, had flux recovery rates of 95.0% and 94.0% for bovine serum albumin and lysozyme, respectively, which was higher than those of PA-DEEDA-0 (86.1% and 80.7%). This work offered a facile way to fabricate an anti-fouling zwitterionic nanofiltration membrane with tunable surface charge, which had wide applications in water purification.

Recent advances in nanofiltration, reverse osmosis membranes and their applications in biomedical separation field

Abstract: In the face of human society's great requirements for health industry, and the much stricter safety and quality standards in the biomedical industry, the demand for advanced membrane separation technologies continues to rapidly grow in the world. Nanofiltration (NF) and reverse osmosis (RO) as the high-efficient, low energy consumption, and environmental friendly membrane separation techniques, show great promise in the application of biomedical separation field. The chemical compositions, microstructures and surface properties of NF/RO membranes determine the separation accuracy, efficiency and operation cost in their applications. Accordingly, recent studies have focused on tuning the structures and tailoring the performance of NF/RO membranes via the design and synthesis of various advanced membrane materials, and exploring universal and convenient membrane preparation strategies, with the objective of promoting the better and faster development of NF/RO membrane separation technology in the biomedical separation field. This paper reviews the recent studies on the NF/RO membranes constructed with various materials, including the polymeric materials, different dimensional inorganic/organic nanomaterials, porous polymeric materials and metal coordination polymers, etc. Moreover, the influence of membrane chemical compositions, interior microstructures, and surface characteristics on the separation performance of NF/RO membranes, are comprehensively discussed. Subsequently, the applications of NF/RO membranes in biomedical separation field are systematically reported. Finally, the perspective for future challenges of NF/RO membrane separation techniques in this field is discussed.

Preparation of Porous Silicate Cement Membranes via a One-Step Water-Based Hot–Dry Casting Method

Abstract: A commercial interest in the improvement in the separation performance and permeability of porous materials is driving efforts to deeply explore new preparation methods. In this study, the porous silicate cement membranes (PSCMs) were successfully prepared through an adjustable combination of hot–dry casting and a cement hydration process. The obtained membrane channel was unidirectional, and the surface layer was dense. The physical characteristics of the PSCMs including their pore morphology, porosity, and compressive strength, were diversified by adjusting the solid content and hot–dry temperature. The results indicated that with the solid content increasing from 40 wt. % to 60 wt. %, the porosity decreased by 8.07%, while the compressive strength improved by 12.46%. As the hot–dry temperature increased from 40 °C to 100 °C, the porosity improved by 23.04% and the BET specific surface area and total pore volume enlarged significantly, while the compressive strength decreased by 27.03%. The pore size distribution of the PSCMs exhibited a layered structure of macropores and mesopores, and the pore size increased with the hot–dry temperature. Overall, the PSCMs, which had typical structures and adjustable physical characteristics, exhibited excellent permeability and separation performance.

Synthesis and application of a novel monomer 5-(1-Pyrrolidinyl)-1,3-benzenedicarbonyl dichloride in membranes

Abstract: Developing novel monomers used for aromatic polyamide membranes is one of the promising modifications to tailor the membranes more efficient. Acyl chloride-based compound as the organic phase reactive monomer is vital to the fabrication of membranes. This study focuses on designing and synthesizing a novel acyl chloride monomer 5-(1-pyrrolidinyl)-1,3-benzenedicarbonyl dichloride (PIPC) based on the purpose of improving membrane permeability and anti-fouling, and preliminarily verify its feasibility for the synthesis of aromatic polyamide membranes. PIPC monomer with a rigid pyrrolidinyl group (–NC4H8) was synthesized from three steps of N-alkylation, ester hydrolysis and acylation reaction successively. IR and 1HNMR spectra were employed to demonstrate the successful synthesis of PIPC. The application of PIPC in the membrane field was also implemented via using PIPC alone as the organic phase reactive monomer, the first/second organic phase reactive monomer, and PIPC and trimesoyl chloride (TMC) together act as the organic phase reactive monomer to react with m-phenylenediamine (MPD) by interfacial polymerization (IP). The MPD-PIPC-TMC membrane prepared by PIPC as the first organic phase reactive monomer exhibited the highest water flux (27.89 ​L ​m−2 ​h−1), with the increase of 36.8% than the MPD-TMC membrane (20.38 ​L ​m−2 ​h−1), while maintaining similar salt rejection. The PIPC with a rigid pyrrolidinyl group was demonstrated to be a promising organic phase monomer for further synthesizing high permeability aromatic polyamide membrane, which showed great application prospects in the field of membrane industry.

Amino-functionalization of hydroxylated SBA-15 for enhanced uranium adsorption from seawater

Abstract: Uranium extraction from seawater is a strategic deployment to the sustainable development of nuclear energy. However, challenges exist in uranium enrichment because of the extremely low U(VI) concentration and the complexity of seawater. Herein, a novel NH2-functionalized mesoporous hydroxylated SBA-15 (NH2-H-SBA-15), synthesized via post-grafting method was used as the adsorbent in uranium adsorption field. The adsorbent was prepared by reacting between aminosilane and the surface silanol groups of hydroxylated SBA-15. It shows stable adsorption properties in a wider applicable pH range (6-8) because amino groups have better adaptability both in weakly acidic and alkaline environment. Moreover, adsorption kinetic data better fitted pseudo-second-order model, which indicated that the uranium adsorption process belongs to chemical adsorption. Isothermal data better followed the Langmuir model, suggesting a monolayer coverage adsorption mode. Additionally, the adsorption capacity of the NH2-H-SBA-15 is approximatively 115 mg·g-1 within 7 days at pH = 8.1 and 25 ℃ in uranium-spiked natural seawater. Therefore, the NH2-H-SBA-15 shows the excellent selectivity of uranium in the natural seawater (αU/M > 1) which provides a promising prospect in extracting uranium from seawater.

High Flux Nanofiltration Membranes with Double-Walled Carbon Nanotube (DWCNT) as the Interlayer

Abstract: Nanofiltration (NF) membranes with a high permeability and rejection are of great interest in desalination, separation and purification. However, how to improve the permeation and separation performance still poses a great challenge in the preparation of NF membranes. Herein, the novel composite NF membrane was prepared through the interfacial polymerization of M-phenylenediamine (MPD) and trimesoyl chloride (TMC) on a double-walled carbon nanotube (DWCNT) interlayer supported by PES substrate. The DWCNT interlayer had a great impact on the polyamide layer formation. With the increase of the DWCNT dosage, the XPS results revealed an increase in the number of carboxyl groups, which decreased the crosslinking degree of the polyamide layer. Additionally, the AFM results showed that the surface roughness and specific surface area increased gradually. The water flux of the prepared membrane increased from 25.4 L/(m2·h) and 26.6 L/(m2·h) to 109 L/(m2·h) and 104.3 L/(m2·h) with 2000 ppm Na2SO4 and NaCl solution, respectively, under 0.5 MPa. Meanwhile, the rejection of Na2SO4 and NaCl decreased from 99.88% and 99.38% to 96.48% and 60.47%. The proposed method provides a novel insight into the rational design of the multifunctional interlayer, which shows great potential in the preparation of high-performance membranes.