Surface modification of aromatic polyamide film by oxygen plasma

Ultrafast plasma method allows rapid immobilization of monatomic copper on carboxyl-deficient g-C3N4 for efficient photocatalytic hydrogen production

Transition-metal monometallic photocatalysts have received extensive attention owing to the maximization of atomic utilization efficiency. However, in previous related works, single-atom loading and stability are generally low due to limited anchor sites and mechanisms. Recently, adding transition-metal monatomic sites to defective carbon nitrides has a good prospect, but there is still lack of diversity in defect structures and preparation techniques. Here, a strategy for preparing defect-type carbon-nitride–coupled monatomic copper catalysts by an ultrafast plasma method is reported. In this method, oxalic acid and commercial copper salt are used as a carboxyl defect additive and a copper source, respectively. Carbon nitride samples containing carboxyl defects and monatomic copper can be processed within 10 min by one-step argon plasma treatment. Infrared spectroscopy and nuclear magnetic resonance prove the existence of carboxyl defects. Spherical aberration electron microscopy and synchrotron radiation analysis confirm the existence of monatomic copper. The proportion of monatomic copper is relatively high, and the purity is high and very uniform. The Cu PCN as-prepared shows not only high photo-Fenton pollutant degradation ability but also high photocatalytic hydrogen evolution ability under visible light. In the photocatalytic reaction, the reversible change of Cu⁺/Cu²⁺ greatly promotes the separation and transmission of photogenerated carriers and improves the utilization of photoelectrons. The photocatalytic hydrogen evolution rate of the optimized sample is 8.34 mmol g⁻¹·h⁻¹, which is 4.54 times that of the raw carbon nitride photocatalyst. The cyclic photo-Fenton experiment confirms the catalyst has excellent repeatability in a strong oxidation environment. The synergistic mechanism of the photocatalyst obtained by this plasma is the coordination of single-atom copper sites and carboxyl defect sites. The single copper atoms incorporated can act as an electron-rich active center, enhancing the h+ adsorption and reduction capacity of Cu PCN. At the same time, the carboxyl defect sites can form hydrogen bonds to stabilize the production of hydrogen atoms and subsequently convert them to hydrogen because of the unstable hydrogen bond structure. This plasma strategy is green, convenient, environment-friendly, and waste-free. More importantly, it has the potential for large-scale production, which brings a new way for the general preparation of high-quality monatomic catalysts.

Improving Interlayer Adhesion of Poly(p-phenylene terephthalamide) (PPTA)/Ultra-high-molecular-weight Polyethylene (UHMWPE) Laminates Prepared by Plasma Treatment and Hot Pressing Technique

Poly(p-phenylene terephthalamide) (PPTA) is a high-performance polymer that has been utilized in a range of applications. Although PPTA fibers are widely used in various composite materials, laminar structures consisting of PPTA and ultra-high-molecular-weight polyethylene (UHMWPE), are less reported. The difficulty in making such composite structures is in part due to the weakness of the interface formed between these two polymers. In this study, a layered structure was produced from PPTA fabrics and UHMWPE films via hot pressing. To improve the interlayer adhesion, oxygen plasma was used to treat the PPTA and the UHMWPE surfaces prior to lamination. It has been found that while plasma treatment on the UHMWPE surface brought about a moderate increase in interlayer adhesion (up to 14%), significant enhancement was achieved on the samples fabricated with plasma treated PPTA (up to 91%). It has been assumed that both surface roughening and the introduction of functional groups contributed to this improvement.

Physicochemical Studies on the Surface of Polyamide 6.6 Fabrics Functionalized by DBD Plasmas Operated at Atmospheric and Sub-Atmospheric Pressures

This work proposes the use of a dielectric barrier discharge (DBD) reactor operating at atmospheric pressure (AP) using air and sub-atmospheric pressure (SAP) using air or argon to treat polyamide 6.6 (PA6.6) fabrics. Here, plasma dosages corresponding to 37.5 kW·min·m-2 for AP and 7.5 kW·min·m-2 for SAP in air or argon were used. The hydrophilicity aging effect property of untreated and DBD-treated PA6.6 samples was evaluated from the apparent contact angle. The surface changes in physical microstructure were studied by field emission scanning electron microscopy (FE-SEM). To prove the changes in chemical functional groups in the fibers, Fourier transform infrared spectroscopy (FTIR) was used, and the change in surface bonds was evaluated by energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). In addition, the whiteness effect was investigated by the color spectrophotometry (Datacolor) technique. The results showed that the increase in surface roughness by the SAP DBD treatment contributed to a decrease in and maintenance of the hydrophilicity of PA6.6 fabrics for longer. The SAP DBD in air treatment promoted an enhancement of the aging effect with a low plasma dosage (5-fold reduction compared with AP DBD treatment). Finally, the SAP DBD treatment using argon functionalizes the fabric surface more efficiently than DBD treatments in air.

Remote Plasma Oxidation and Atomic Layer Etching of MoS2

Exfoliated molybdenum disulfide (MoS2) is shown to chemically oxidize in a layered manner upon exposure to a remote O2 plasma. X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and atomic force microscopy (AFM) are employed to characterize the surface chemistry, structure, and topography of the oxidation process and indicate that the oxidation mainly occurs on the topmost layer without altering the chemical composition of underlying layer. The formation of S-O bonds upon short, remote plasma exposure pins the surface Fermi level to the conduction band edge, while the MoOx formation at high temperature modulates the Fermi level toward the valence band through band alignment. A uniform coverage of monolayer amorphous MoO3 is obtained after 5 min or longer remote O2 plasma exposure at 200 °C, and the MoO3 can be completely removed by annealing at 500 °C, leaving a clean ordered MoS2 lattice structure as verified by XPS, LEED, AFM, and scanning tunneling microscopy. This work shows that a remote O2 plasma can be useful for both surface functionalization and a controlled thinning method for MoS2 device fabrication processes.

Real-time monitoring of polymer swelling on the nanometer scale by atomic force microscopy

The swelling of a polymer surface has been monitored in real time on the nanometer scale by atomic force microscopy (AFM). After modification by oxygen plasma treatment, poly(p-phenylene terephthalamide) (PPTA) displays a characteristic nanostructured surface morphology consisting of high-lying features alternating with topographically depressed areas. Selective swelling of the least cross-linked, depressed areas after the adsorption of ambient water or water from saturated humid atmospheres was observed by tapping mode AFM operated in the attractive interaction regime. The swollen areas could be distinguished from the nonswollen ones by local variations in the sample indentation made by the AFM tip when imaging in the tapping mode repulsive interaction regime. Monitoring the swelling of the plasma-treated polymer surface provided a means to reveal the nanometer-scale heterogeneity that this type of treatment creates on the polymer surface, which is something that would not be possible otherwise. Measurement of AFM tip-sample adhesion forces evidenced rapid water adsorption onto the oxygen plasma-treated surface, supporting the idea of water-induced swelling. This high hydrophilicity was interpreted as arising from the incorporation of polar oxygen functionalities, as demonstrated by X-ray photoelectron spectroscopy (XPS).