Switchable gas separation membranes are intriguing systems for regulating the transport properties of gases. However, existing stimuli-responsive gas separation membranes suffer from either very slow response times or require high energy input for switching to occur. Accordingly, herein, we introduced light-switchable polymeric carbon nitride (pCN) gas separation membranes with fast response times prepared from melamine precursor through in-situ formation and deposition of pCN onto a porous support using chemical vapor deposition. Our systematic analysis revealed that the gas transport behavior upon light irradiation is fully governed by the polarizability of the permeating gas and its interaction with the charged pCN surface, and can be easily tuned either by controlling the power of the light and/or the duration of irradiation. We also demonstrated that gases with higher polarizabilities such as CO2 can be separated from gases with lower polarizability like H2 and He effectively with more than 22% increase in the gas/CO2 selectivity upon light irradiation. The membranes also exhibited fast response times (<1 s) and can be turned “on” and “off” using a single light source at 550 nm.

With regard to the development of single atom catalysts (SACs), non-noble metal–organic layers combine a large functional variability with cost efficiency. Here, we characterize reacted layers of melamine and melem molecules on a Cu(111) surface by noncontact atomic force microscopy (nc-AFM), X-ray photoelectron spectroscopy (XPS) and ab initio simulations. Upon deposition on the substrate and subsequent heat treatments in ultrahigh vacuum (UHV), these precursors undergo a stepwise dehydrogenation. After full dehydrogenation of the amino groups, the molecular units lie flat and are strongly chemisorbed on the copper substrate. We observe a particularly extreme interaction of the dehydrogenated nitrogen atoms with single copper atoms located at intermolecular sites. In agreement with the nc-AFM measurements performed with an O-terminated copper tip on these triazine- and heptazine-based copper nitride structures, our ab initio simulations confirm a pronounced interaction of oxygen species at these N–Cu–N sites. To investigate the related functional properties of our samples regarding the oxygen reduction reaction (ORR), we developed an electrochemical setup for cyclic voltammetry experiments performed at ambient pressure within a drop of electrolyte in a controlled O2 or N2 environment. Both copper nitride structures show a robust activity in irreversibly catalyzing the reduction of oxygen. The activity is assigned to the intermolecular N–Cu–N sites of the triazine- and heptazine-based copper nitrides or corresponding oxygenated versions (N–CuO–N, N–CuO2–N). By combining nc-AFM characterization on the atomic scale with a direct electrochemical proof of performance, our work provides fundamental insights about active sites in a technologically highly relevant reaction.

Because of appealing material properties and ease of fabrication, organic semiconductors have found a variety of applications in integrated photonics, including optical waveguiding in broadband communication systems, use as amplifiers and modulators in signal processing, and for realizing optical detectors and sensors. Polymeric carbon nitride thin films have emerged as a valuable alternative to currently employed inorganic materials in light manipulation and waveguiding owing to their structural flexibility, transparency over a wide wavelength range, and accessible synthesis from sustainable and cost-effective materials. Here, we demonstrate organic polymeric carbon nitride-based nanophotonic devices for telecommunication wavelengths. The high ordinary refractive index of the polymer of 2 or higher, covering both visible and near-infrared wavelength ranges, enables a small device footprint, strong mode confinement, and efficient fiber-to-chip coupling via grating couplers. Proof-of-concept experiments with photonic waveguides and microring resonators show broadband transmission in the visible wavelength range and quality factors exceeding 104 for a wavelength of 1550 nm. The outstanding material properties of polymeric carbon nitride will open new perspectives for polymeric photonic devices for a broad wavelength range.

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