In pursuit of cleaner air and more sustainable chemical processes, scientists are constantly exploring new materials capable of efficiently separating volatile organic compounds (VOCs) from industrial gas streams. Among these VOCs, toluene—a common solvent and pollutant—is particularly difficult to remove due to its chemical stability and strong affinity for organic matter. Now, a research team led by Professor Jiang Zhongyi and Professor Pan Fusheng at Tianjin University has developed a high-performance hybrid membrane that achieves significant efficiency in the separation of toluene and nitrogen (N₂). Their research was recently published in the journal *Advanced Membranes*, titled "Introduction of polyvinylpyrrolidone-modified HOF-101 into Pebax membranes for efficient toluene/nitrogen separation."
Challenge: How to improve the performance of hybrid membranes
Membrane separation is a green and energy-efficient VOCs recovery technology. However, achieving both high permeability and high selectivity simultaneously in a single membrane has long been a challenge. A key reason is the poor compatibility between inorganic packing materials that enhance adsorption and organic polymers that provide mechanical strength. When the two phases are not mixed uniformly, microscopic defects form, leading to gas leakage and reduced separation performance.
A clever solution: Polyvinylpyrrolidone-modified HOF-101
To address this problem, a research team at Tianjin University introduced a novel filler called HOF-101 (Hydrogen-bonded Organic Framework-101). HOF-101 is a crystalline porous material with a large specific surface area and a strong affinity for aromatic compounds such as toluene. They modified HOF-101 using polyvinylpyrrolidone (PVP). PVP is a polymer capable of forming hydrogen bonds and intertwining with the main membrane material, polyether block amide (Pebax® 1657).
This modification resulted in significant improvements:
The PVP chains grafted onto HOF-101 intertwine with Pebax segments, improving the interfacial compatibility between the filler and the polymer matrix.
The π-conjugated aromatic rings of HOF-101 interact strongly with toluene molecules, thereby enhancing the adsorption and separation efficiency of toluene.
The resulting PVP@HOF-101 composite membrane possesses a dense and uniform surface structure with virtually no interfacial defects.
Working Principle of the Composite Membrane
In this membrane system, toluene molecules preferentially dissolve and diffuse through the HOF-enhanced channels, while nitrogen molecules are effectively blocked. This difference in intermolecular interactions leads to selective permeation—toluene permeates much faster than nitrogen.
The research team tested the membrane's performance under various conditions, including variations in feed concentration, temperature, and pressure. The hybrid membrane achieved optimal performance when the PVP@HOF-101 loading was 1 wt%:
Toluene permeability: 1.51 × 10⁻⁶ mol·μm·m⁻²·s⁻¹·Pa⁻¹
Selectivity (toluene/N₂): 954
Operating stability: Performance remained stable after continuous operation for over 120 hours.
These results far surpass the performance of traditional membranes, demonstrating that the PVP modification strategy successfully balances permeability and selectivity.
Importance
This research represents a significant advancement in the field of environmentally friendly VOCs recovery. By combining the molecular precision of hydrogen-bonded organic frameworks with the flexibility of polymers, this study provides a new blueprint for designing advanced hybrid membranes.
This membrane can be used not only for toluene recovery in the petrochemical industry but also for the separation of other aromatic volatile organic compounds (VOCs), thereby contributing to emission reduction, the recovery of valuable chemicals, and support for cleaner production technologies.
Looking ahead, researchers are dedicated to optimizing the structural design of HOF materials and exploring new functional modification methods to further improve their performance and scalability. Their work highlights the increasingly important role of materials innovation in achieving sustainable industrial practices—where chemistry, engineering, and environmental science converge to build a greener future.
References:
Jiating Liu, Jiashhuai Zhao, Yuhan Wang, et al., "Incorporating Polyvinylpyrrolidone modified HOF-101 into Pebax membranes for efficient toluene/N₂ separation," Advanced Membranes, 5 (2025) 100127. DOI: 10.1016/j.advmem.2025.100127