m-Phenylenediamine, also known as  meta phenylenediamine, has the molecular formula C?H?N?. It consists of two amino groups linked at the meta positions of the benzene ring. This kind of material is chemically reactive; its amino groups can undergo acylation, diazotization, and condensation reactions. It serves as an important intermediate in the production of dyes, aramids, epoxy resin curing agents, and rubber additives, and is also commonly used in hair dyes and fur dyeing processes.

Nanofiller-confined spatial fluctuation synthesizing membranes

Thin-film composite (TFC) membranes, which are quintessential representatives of RO membranes, are widely employed for water filtration due to their cost-effectiveness, operational simplicity, and scalability for industrial applications. Nevertheless, a persistent trade-off between permeability and selectivity remains a critical constraint limiting their performance. A key strategy in pursuing ultrafast water transport in TFC membranes involves creating thin polyamide (PA) active layers to minimize the transport distance for water molecules. Traditional TFC membranes are fabricated through interfacial polymerization (IP) reactions between aqueous-phase m-phenylenediamine (MPD) and organic-phase trimesoyl chloride (TMC) at the aqueous-organic interface. Moreover, recent studies have revealed that the separation performance is not solely dictated by thickness, but also critically by its molecular-scale heterogeneity and surface topology. While inhibiting m-Phenylenediamine diffusion can yield a thinner and smoother selective layer, substantial experimental evidence has demonstrated that nanoscale heterogeneity, such as surface wrinkling and microstructural diversity, also plays a vital role in enhancing water transport, potentially facilitating ultrafast permeation. For example, lignin and its derivative, sodium lignosulfonate (SL), have been shown to promote the cross-interface diffusion of m-Phenylenediamine, thereby increasing the surface irregularity. Coupled with abundant hydrophilic functional groups (i.e., hydroxyl or –OH, and sulfonic or –SO3?), which can establish extensive hydrogen-bonding networks, the resulting membrane exhibits significantly enhanced permeability.[1]

A more detailed analysis using height distribution histograms confirms that the 2LDH-1SL TFN membrane possesses significantly greater peak-to-valley distances, which directly contribute to an increased effective surface area for water transport. This disparity is attributed to the role of LDH-SL in modulating m-Phenylenediamine diffusion at the aqueous-organic interface. By creating localized free energy minima, LDH-SL accelerates the reaction rate between MPD and TMC, substantially increasing interfacial instability. In summary, the fabrication of highly wrinkled TFN membranes is intricately associated with the dynamic equilibrium between the facilitated diffusion of m-Phenylenediamine at the aqueous-organic interface and its inhibited diffusion within the organic bulk phase. This equilibrium process is substantially regulated by the amphiphilic nature of SL: at lower concentrations of SL, nanoparticles predominantly distribute within the organic phase, where steric hindrance impedes the mass transfer of m-Phenylenediamine. This restriction significantly reduces the interfacial reaction kinetics with TMC, stabilizing the interface and favoring the development of a smooth, thin PA layer. Conversely, as SL concentration escalates, the directional enrichment of nanoparticles at the aqueous-organic interface generates localized minima in free energy, which thermodynamically favors the transport of m-Phenylenediamine across the interface, subsequently resulting in the formation of a PA layer characterized by increased surface roughness and thickness. An optimal balance between these two contrasting mechanisms enables the precise modulation of IP dynamics with an ideal doping ratio of SL, ultimately facilitating the controlled fabrication of highly wrinkled TFN membranes with enhanced structural and transport properties.

Catechol/m-Phenylenediamine Modified Sol–Gel

To extend the corrosion resistance and service life of sol–gel coatings, modification methods must be employed. For example, Santana et al. prepared SiO? sol coatings modified with cerium nitrate and clay particles on low-carbon steel, demonstrating that both modifications could improve the corrosion resistance of the substrate sol–gel coating. Previous researchers prepared a series of modified sol–gel coatings applied to AZ31 magnesium alloys. Recently, Qiu et al. discovered that catechol/m-phenylenediamine (CA/MPD) could achieve coprecipitation through the Michael addition reaction. The combination of CA/MPD can form a uniform and dense coating on the surface of the substrate, and this coating can effectively fill the nano-defects of the sol–gel structure to increase the barrier effect. Inspired by these studies, this research designed and prepared a new environmentally friendly catecholamine-modified sol–gel coating to extend the corrosion protection effect and duration on 3003 aluminum alloy. Catechol (CA) and m-phenylenediamine (MPD) were used to synthesize catecholamine substances to modify the sol–gel system. The corrosion protection effect of the modified coating in a 3.5 wt% NaCl aqueous solution was evaluated using electrochemical impedance spectroscopy (EIS) and potentiometric polarization tests.[2]

Scientists designed and prepared an innovative, green Catechol / m-phenylenediamine -modified sol–gel coating with a thickness of approximately 6.8 μm. The corrosion protection performance and stability of the CA/MPD@sol–gel coating were significantly improved compared to the unmodified sol–gel coating. Long-term EIS tests on the modified coating showed that after 30 days of testing, the catecholamine-modified sol–gel coating still maintained good protective performance. This result indicates that the catechol / m-phenylenediamine @sol–gel-modified coating significantly improves the coating’s stability and low-frequency impedance in EIS tests, enhancing the sol–gel coating’s protective performance. The modification effect of CA/MPD on the sol–gel changes with increasing concentration, initially rising and then falling. Very low or very high concentrations of CA/MPD are unfavorable for the coating’s protective performance. Therefore, an appropriate concentration of CA/MPD should be selected for modifying the coating. The catechol / m-phenylenediamine @sol–gel material was characterized using ultraviolet-visible absorption spectroscopy (UV-Vis), Fourier transform infrared absorption spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The catechol / m-phenylenediamine adsorbed on the sol–gel surface and diffused into the sol–gel coating, forming chemical bonds. By filling the microporous or nanoporous structure inside the sol–gel, the modification filled the microstructural defects of the coating, enhancing its compactness and effectively inhibiting the diffusion of solvent molecules and corrosive particles, such as chloride ions, to the aluminum alloy surface, thereby enhancing the corrosion protection performance of the sol–gel coating.

References

[1]Lin, R., Zhao, Q., Chu, H. et al. Nanofiller-confined spatial fluctuation in monomer diffusion synthesizing ultrafast reverse osmosis membranes driven by hydrogen-bonding networks. Nat Commun 16, 9978 (2025). https://doi.org/10.1038/s41467-025-64959-x

[2]Huang K, Huang X, Wang L, Tu S, Yang Z, Guo H, Lei B, Feng Z, Meng G. Catechol/m-Phenylenediamine Modified Sol-Gel Coating with Enhanced Long-Lasting Anticorrosion Performance on 3003 Al Alloy. Molecules. 2024 Sep 30;29(19):4644. doi: 10.3390/molecules29194644. PMID: 39407574; PMCID: PMC11478023.