Abstract:

Objective Metal-organic frameworks (MOFs) possess an exceptionally high active specific surface area and exhibit structural and functional diversity, among other characteristics. Studies have shown that MOFs have demonstrated effective degradation of chemical warfare agents. However, the crystal morphology of MOFs powders limits their practical application in catalytic degradation processes. To address this issue, the utilization of a coating modification technique becomes crucial. This technique leverages the adhesion and secondary reactivity of hydrophilic modified coatings to facilitate the in-situ growth of MOFs crystals on the modified polypropylene (PP) surface. This research aims to boost the MOFs loading on the substrate and improve the stability of the MOFs. Overall, this method is significant for developing textiles tailored for the rapid removal of chemical warfare agent simulants.

Method PP nonwovens were immersed in a mixed solution of tannic acid (TA) and aminopropyltriethoxysilane (APTES) to prepare TA-APTES coating modified PP nonwovens. The modified PP with the TA-APTES coating was sequentially submerged in the solution of zirconium tetrachloride and 2-aminoterephthalic acid, enabling the in-situ growth of zirconia-based metal-organic frameworks (UiO-66-NH₂) on the PP surface to prepare a PP/TA-APTES/UiO-66-NH₂ (PTAU) fiber-based composite. The surface morphology, composition, and structure of the composite were characterized by scanning electron microscopy, Fourier transform infrared, X-ray diffraction and X-ray photoelectron spectroscopy(XPS), respectively. The loading of MOFs in the composite was characterized by inductively coupled plasma optical emission spectrometry and the wettability of the composite was characterized by static water contact angle test. Moreover, the degradation performance of the composite on chemical warfare agent simulants was evaluated.

Results Compared with the unmodified PP, the surface of PP composite modified by TA-APTES coating became rough which is conducive to the growth of MOFs on the surface of PP. The infrared spectrum showed the characteristic peaks of the modified TA-APTES and UiO-66-NH₂. The XRD pattern of the PP after TA-APTES coating confirmed that the UiO-66-NH₂ crystalline form remained unchanged in the composite. The XPS characterization revealed the elemental valence composition of the composite surface before and after the reaction. The thermogravimetric testing suggested that the final residual mass percentage of the original PP nonwovens was 1.3%, while the residual mass percentage of PTAU composite was 17.4%, indicating that the thermal stability performance of the treated PP was improved. These results showed that the MOFs was successfully modified on the surface of TA-APTES coating on PP. Additionally, TA-APTES coatings significantly changed the wettability of PP composites and enhanced the loading capacity of MOFs on the composite surface to 20.96%. The UV spectrum of dimethyl p-nitrophenyl phosphate (DMNP) degradation catalyzed by composite demonstrated that the characteristic peak of DMNP at 270 nm gradually decreases and the characteristic peak of the hydrolysis product p-nitrophenol at 400 nm gradually increases, and the degradation rate of the composite reached 100% after 30 min. The half-life of degradation of PTAU composite was 4.8 min.

Conclusion TA-APTES coating was used to modify PP nonwoven to construct the active site of MOF nucleation, which promoted the uniform distribution and robust growth of UiO-66-NH₂ on PP surface. The inductively coupled plasma optical emission spectrometry results showed that the loading of UiO-66-NH₂ in composite was increased by TA-APTES coating, reaching up to 20.96%. The experimental results demonstrate that TA-APTES coating can effectively improve the surface wettability of PP composite material from hydrophobic to hydrophilic, and greatly improving its catalytic degradation efficiency in aqueous solution. The catalytic degradation experiment showed that the catalytic degradation efficiency of PTAU composite was further improved, the conversion rate reached 100% in approximately 30 minutes, and the degradation half-life was about 4.8 min.

Key words: metal-organic framework, chemical warfare agent, catalytic degradation, in situ growth method, coating modification, polypropylene nonwoven