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Accelerated anthropogenic emission of greenhouse gases due to increasing energy demands has created a negative impact on our planet. Therefore, the replacement of fossil by renewable energy resources has become of paramount interest, both societally and scientifically. It is within this setting that organic photocatalysts have emerged as a new generation of earth-abundant catalysts for the conversion of solar radiation into chemical energy. In 2014, the first example of a covalent organic framework (COF) photocatalyst for the hydrogen evolution reaction was reported by our group, which has not only marked the beginning of COF photocatalysis for solar fuel production but also helped to accelerate research into "soft photocatalysis" based on porous polymers in general. In the last decade, significant progress has been made toward developing COFs as robust, molecularly precise platforms emulating artificial photosynthesis. This mini-review commemorates the 10th anniversary of COF photocatalysis and gives a brief historical overview of the milestones in the field since its inception in 2014. We review milestones in the development of COFs for solar fuel production and related photocatalytic transformations, including hydrogen evolution, oxygen evolution, overall water splitting, CO 2 reduction, N 2 fixation, oxygen reduction, and alcohol oxidation. We discuss lessons learned for the design of structure-property-function relationships in COF photocatalysts, and future perspectives and challenges for the field of "soft photocatalysis" are given., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

While considerable efforts have been devoted to developing functionalized covalent organic frameworks (COFs) as oxygen evolution electrocatalysts in recent years, studies related to the investigation of the true catalytically active species for the oxygen evolution reaction (OER) remain lacking in the field. In this work, the active species of a cobalt-functionalized COF (TpBpy-Co) is studied as electrochemical OER catalyst through a series of electrochemical measurements and post-electrolysis characterizations. These results suggest that cobalt oxide-based nanoparticles are formed in TpBpy-Co from Co(II) ions coordinated to the COF backbone when exposing TpBpy-Co to alkaline media, and these newly formed nanoparticles serve as the primary active species for oxygen evolution. The study thus emphasizes that caution is warranted when assessing the catalytic activity of COF electrocatalysts, as the pristine COF may act as the pre-catalyst, with the active species forming only under catalyst operating conditions. Specifically, strong coordination between COFs and metal centers under electrochemical operation conditions is crucial to avoid unintended transformation of COF electrocatalysts. This work thus contributes to the rational development of earth-abundant COF OER catalysts for the production of green hydrogen from renewable resources., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

The exchange bias phenomenon, inherent in exchange-coupled ferromagnetic and antiferromagnetic systems, has intrigued researchers for decades. Van der Waals materials, with their layered structures, offer an ideal platform for exploring exchange bias. However, effectively manipulating exchange bias in van der Waals heterostructures remains challenging. This study investigates the origin of exchange bias in MnPS 3 /Fe 3 GeTe 2 van der Waals heterostructures, demonstrating a method to modulate nearly 1000% variation in magnitude through simple thermal cycling. Despite the compensated interfacial spin configuration of MnPS 3 , a substantial 170 mT exchange bias is observed at 5 K, one of the largest observed in van der Waals heterostructures. This significant exchange bias is linked to anomalous weak ferromagnetic ordering in MnPS 3 below 40 K. The tunability of exchange bias during thermal cycling is attributed to the amorphization and changes in the van der Waals gap during field cooling. The findings highlight a robust and adjustable exchange bias in van der Waals heterostructures, presenting a straightforward method to enhance other interface-related spintronic phenomena for practical applications. Detailed interface analysis reveals atom migration between layers, forming amorphous regions on either side of the van der Waals gap, emphasizing the importance of precise interface characterization in these heterostructures., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

Covalent organic frameworks (COFs) are promising electrocatalyst platforms owing to their designability, porosity, and stability. Recently, COFs with various chemical structures are developed as efficient electrochemical CO 2 reduction catalysts. However, controlling the morphology of COF catalysts remains a challenge, which can limit their electrocatalytic performance. Especially, while porphyrin COFs show promising catalytic properties, their particle size is mostly large and uncontrolled because of the severe aggregation of crystallites. In this work, a new synthetic methodology for rationally downsized COF catalyst particles is reported, where a tritylated amine is employed as a novel protected precursor for COF synthesis. Trityl protection provides high solubility to a porphyrin precursor, while its deprotection proceeds in situ under typical COF synthesis conditions. Subsequent homogeneous nucleation and colloidal growth yield smaller COF particles than a conventional synthesis, owing to suppressed crystallite aggregation. The downsized COF particles exhibit superior catalytic performance in electrochemical CO 2 reduction, with higher CO production rate and faradaic efficiency compared to conventional COF particles. The improved performance is attributed to the higher contact area with a conductive agent. This study reveals particle size as an important factor for the evaluation of COF electrocatalysts and provides a strategy to control it., (© 2024 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

Metal-organic frameworks (MOFs) are a rapidly growing class of materials that offer great promise in various applications. However, the synthesis remains challenging: for example, a range of crystal structures can often be accessed from the same building blocks, which complicates the phase selectivity. Likewise, the high sensitivity to slight changes in synthesis conditions may cause reproducibility issues. This is crucial, as it hampers the research and commercialization of affected MOFs. Here, it presents the first-ever interlaboratory study of the synthetic reproducibility of two Zr-porphyrin MOFs, PCN-222 and PCN-224, to investigate the scope of this problem. For PCN-222, only one sample out of ten was phase pure and of the correct symmetry, while for PCN-224, three are phase pure, although none of these show the spatial linker order characteristic of PCN-224. Instead, these samples resemble dPCN-224 (disordered PCN-224), which has recently been reported. The variability in thermal behavior, defect content, and surface area of the synthesised samples are also studied. The results have important ramifications for field of metal-organic frameworks and their crystallization, by highlighting the synthetic challenges associated with a multi-variable synthesis space and flat energy landscapes characteristic of MOFs., (© 2024 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

Controlled synthesis of phase-pure metal-organic frameworks (MOFs) is essential for their application in technological areas such as catalysis or gas sorption. Yet, knowledge of their phase formation and growth remain rather limited, particularly with respect to species such as water whose vital role in MOF synthesis is often neglected. As a consequence, synthetic protocols often lack reproducibility when multiple MOFs can form from the same metal source and linker, and phase mixtures are obtained with little or no control over their composition. In this work, the role of water in the formation of the Zr-porphyrin MOF disordered PCN-224 (dPCN-224) is investigated. Through X-ray total scattering and scanning electron microscopy, it is observed that dPCN-224 forms via a metal-organic intermediate that consists of Zr 6 O 4 (OH) 4  clusters linked by tetrakis(4-carboxy-phenyl)porphyrin molecules. Importantly, water is not only essential to the formation of Zr 6 O 4 (OH) 4  clusters, but it also plays a primary role in dictating the formation kinetics of dPCN-224. This multidisciplinary approach to studying the speciation of dPCN-224 provides a blueprint for how Zr-MOF synthesis protocols can be assessed and their reproducibility increased, and highlights the importance of understanding the role of water as a decisive component in Zr-MOF formation., (© 2023 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

Multianionic metal hydrides, which exhibit a wide variety of physical properties and complex structures, have recently attracted growing interest. Here we present Sr 6 N[BN 2 ] 2 H 3 , prepared in a solid-state ampoule reaction at 800 °C, as the first combination of nitridoborate, nitride and hydride anions within a single compound. The crystal structure was solved from single-crystal X-ray and neutron powder diffraction data in space group P2 1 /c (no. 14), revealing a three-dimensional network of undulated layers of nitridoborate units, strontium atoms and hydride together with nitride anions. Magic angle spinning (MAS) NMR and vibrational spectroscopy in combination with quantum chemical calculations further confirm the structure model. Electrochemical measurements suggest the existence of hydride ion conductivity, allowing the hydrides to migrate along the layers., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The crystalline lithium oxonitridophosphate Li 8+x P 3 O 10-x N 1+x , was obtained in an ampoule synthesis from P 3 N 5 and Li 2 O. The compound crystallizes in the triclinic space group P 1 - ${\mathrel{\mathop{{\rm { 1}}}\limits^{{\rm -}}}}$ with a=5.125(2), b=9.888(5), c=10.217(5) Å, α=70.30(2), β=76.65(2), γ=77.89(2)°. Li 8+x P 3 O 10-x N 1+x is a double salt, the structure of which contains distinctive complex anion species, namely non-condensed P(O,N) 4 tetrahedra, and P(O,N) 7 double tetrahedra connected by one N atom. Additionally, there is mixed occupation of O/N positions, which enables further anionic species by variation of O/N occupancies. To characterize these motifs in detail, complementary analytical methods were applied. The double tetrahedron exhibits significant disorder in single-crystal X-ray diffraction. Furthermore, the title compound is a Li + ion conductor with a total ionic conductivity of 1.2×10 -7  S cm -1 at 25 °C, and a corresponding total activation energy of 0.47(2) eV., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

While micromachines with tailored functionalities enable therapeutic applications in biological environments, their controlled motion and targeted drug delivery in biological media require sophisticated designs for practical applications. Covalent organic frameworks (COFs), a new generation of crystalline and nanoporous polymers, offer new perspectives for light-driven microswimmers in heterogeneous biological environments including intraocular fluids, thus setting the stage for biomedical applications such as retinal drug delivery. Two different types of COFs, uniformly spherical TABP-PDA-COF sub-micrometer particles and texturally nanoporous, micrometer-sized TpAzo-COF particles are described and compared as light-driven microrobots. They can be used as highly efficient visible-light-driven drug carriers in aqueous ionic and cellular media. Their absorption ranging down to red light enables phototaxis even in deeper and viscous biological media, while the organic nature of COFs ensures their biocompatibility. Their inherently porous structures with ≈2.6  and ≈3.4 nm pores, and large surface areas allow for targeted and efficient drug loading even for insoluble drugs, which can be released on demand. Additionally, indocyanine green (ICG) dye loading in the pores enables photoacoustic imaging, optical coherence tomography, and hyperthermia in operando conditions. This real-time visualization of the drug-loaded COF microswimmers enables unique insights into the action of photoactive porous drug carriers for therapeutic applications., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

The Li + ion conductor Li 27-x [P 4 O 7+x N 9-x ]O 3 (x≈1.9) has been synthesized from P 3 N 5 , Li 3 N and Li 2 O in a Ta ampoule at 800 °C under Ar atmosphere. The cubic compound crystallizes in space group I 4 ‾ 3 d ${I\overline 4 3d}$ with a=12.0106(14) Å and Z=4. It contains both non-condensed [PO 2 N 2 ] 5- and [PO 3 N] 4- tetrahedra as well as O 2- ions, surrounded by Li + ions. Charge neutrality is achieved by partial occupancy of Li positions, which was refined with neutron powder diffraction data. Measurements of the partial ionic and electronic conductivity show a total ionic conductivity of 6.6×10 -8  S cm -1 with an activation energy of 0.46±0.02 eV and a bulk ionic conductivity of 4×10 -6  S cm -1 at 25 °C, which is close to the ionic conductivity of amorphous lithium nitridophosphate. This makes Li 27-x [P 4 O 7+x N 9-x ]O 3 an interesting candidate for investigation of structural factors affecting ionic conductivity in lithium oxonitridophosphates., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Non-crystalline lithium oxonitridophosphate (LiPON) is used as solid electrolyte in all-solid-state batteries. Crystalline lithium oxonitridophosphates are important model structures to retrieve analytical information that can be used to understand amorphous phases better. The new crystalline lithium oxonitridophosphate Li 5+x P 2 O 6-x N 1+x was synthesized as an off-white powder by ampoule synthesis at 750-800 °C under Ar atmosphere. It crystallizes in the monoclinic space group P2 1 /c with a=15.13087(11) Å, b=9.70682(9) Å, c=8.88681(7) Å, and β=106.8653(8)°. Two P(O,N) 4 tetrahedra connected by an N atom form the structural motif [P 2 O 6-x N 1+x ] (5+x)- . The structure was elucidated from X-ray diffraction data and the model corroborated by NMR and infrared spectroscopy, and elemental analyses. Measurements of ionic conductivity show a total ionic conductivity of 6.8×10 -7  S cm -1 at 75 °C with an activation energy of 0.52±0.01 eV., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms were provided to sixty-one labs, who were asked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called "BET surface identification" (BETSI), expands on the well-known Rouquerol criteria and makes an unambiguous BET area assignment possible., (© 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Covalent organic frameworks (COFs) offer vast structural and chemical diversity enabling a wide and growing range of applications. While COFs are well-established as heterogeneous catalysts, so far, their high and ordered porosity has scarcely been utilized to its full potential when it comes to spatially confined reactions in COF pores to alter the outcome of reactions. Here, we present a highly porous and crystalline, large-pore COF as catalytic support in α,ω-diene ring-closing metathesis reactions, leading to increased macrocyclization selectivity. COF pore-wall modification by immobilization of a Grubbs-Hoveyda-type catalyst via a mild silylation reaction provides a molecularly precise heterogeneous olefin metathesis catalyst. An increased macro(mono)cyclization (MMC) selectivity over oligomerization (O) for the heterogeneous COF-catalyst (MMC:O=1.35) of up to 51 % compared to the homogeneous catalyst (MMC:O=0.90) was observed along with a substrate-size dependency in selectivity, pointing to diffusion limitations induced by the pore confinement., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Carbon nitrides are among the most studied materials for photocatalysis; however, limitations arise from inefficient charge separation and transport within the material. Here, this aspect is addressed in the 2D carbon nitride poly(heptazine imide) (PHI) by investigating the influence of various counterions, such as M = Li + , Na + , K + , Cs + , Ba 2+ , NH 4 + , and tetramethyl ammonium, on the material's conductivity and photocatalytic activity. These ions in the PHI pores affect the stacking of the 2D layers, which further influences the predominantly ionic conductivity in M-PHI. Na-containing PHI outperforms the other M-PHIs in various relative humidity (RH) environments (0-42%RH) in terms of conductivity, likely due to pore-channel geometry and size of the (hydrated) ion. With increasing RH, the ionic conductivity increases by 4-5 orders of magnitude (for Na-PHI up to 10 -5 S cm -1 at 42%RH). At the same time, the highest photocatalytic hydrogen evolution rate is observed for Na-PHI, which is mirrored by increased photogenerated charge-carrier lifetimes, pointing to efficient charge-carrier stabilization by, e.g., mobile ions. These results indicate that also ionic conductivity is an important parameter that can influence the photocatalytic activity. Besides, RH-dependent ionic conductivity is of high interest for separators, membranes, or sensors., (© 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

The highly unfavorable thermodynamics of direct aluminum hydrogenation can be overcome by stabilizing alane within a nanoporous bipyridine-functionalized covalent triazine framework (AlH 3 @CTF-bipyridine). This material and the counterpart AlH 3 @CTF-biphenyl rapidly desorb H 2 between 95 and 154 °C, with desorption complete at 250 °C. Sieverts measurements, 27 Al MAS NMR and 27 Al{ 1 H} REDOR experiments, and computational spectroscopy reveal that AlH 3 @CTF-bipyridine dehydrogenation is reversible at 60 °C under 700 bar hydrogen, >10 times lower pressure than that required to hydrogenate bulk aluminum. DFT calculations and EPR measurements support an unconventional mechanism whereby strong AlH 3 binding to bipyridine results in single-electron transfer to form AlH 2 (AlH 3 ) n clusters. The resulting size-dependent charge redistribution alters the dehydrogenation/rehydrogenation thermochemistry, suggesting a novel strategy to enable reversibility in high-capacity metal hydrides., (© 2021 Wiley-VCH GmbH.)

The all-solid-state battery (ASSB) is a promising candidate for electrochemical energy storage. In view of the limited availability of lithium, however, alternative systems based on earth-abundant and inexpensive elements are urgently sought. Besides well-studied sodium compounds, potassium-based systems offer the advantage of low cost and a large electrochemical window, but are hardly explored. Here we report the synthesis and crystal structure of K-ion conducting T5 KSi 2 P 3 inspired by recent discoveries of fast ion conductors in alkaline phosphidosilicates. KSi 2 P 3 is composed of SiP 4 tetrahedra forming interpenetrating networks of large T5 supertetrahedra. The compound passes through a reconstructive phase transition from the known T3 to the new tetragonal T5 polymorph at 1020 °C with enantiotropic displacive phase transitions upon cooling at about 155 °C and 80 °C. The potassium ions are located in large channels between the T5 supertetrahedral networks and show facile movement through the structure. The bulk ionic conductivity is up to 2.6×10 -4  S cm -1 at 25 °C with an average activation energy of 0.20 eV. This is remarkably high for a potassium ion conductor at room temperature, and marks KSi 2 P 3 as the first non-oxide solid potassium ion conductor., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

1D photonic crystals (1DPCs) are well known from a variety of applications ranging from medical diagnostics to optical fibers and optoelectronics. However, large-scale application is still limited due to complex fabrication processes and bottlenecks in transferring 1DPCs to arbitrary substrates and pattern creation. These challenges were addressed by demonstrating the transfer of millimeter- to centimeter-scale 1DPC sensors comprised of alternating layers of H 3 Sb 3 P 2 O 14 nanosheets and TiO 2 nanoparticles based on a non-invasive chemical approach. By depositing the 1DPC on a sacrificial layer of lithium tin sulfide nanosheets and hydrophobizing only the 1DPC by intercalation of n-octylamine via the vapor phase the 1DPC can be detached from the substrate by immersing the sample in water. Upon exfoliation of the hydrophilic sacrificial layer, the freestanding 1DPC remains at the water-air interface. In a second step, it can be transferred to arbitrary surfaces such as curved glass. In addition, the transfer of patterned 1DPCs is demonstrated by combining the sacrificial layer approach with area-resolved intercalation and etching. The fact that the sensing capability of the 1DPC is not impaired and can be modified after transfer renders this method a generic platform for the fabrication of photonic devices., (© 2021 The Authors. Small published by Wiley-VCH GmbH.)

Covalent organic frameworks (COFs) are an extensively studied class of porous materials, which distinguish themselves from other porous polymers in their crystallinity and high degree of modularity, enabling a wide range of applications. COFs are most commonly synthesized solvothermally, which is often a time-consuming process and restricted to well-soluble precursor molecules. Synthesis of polyimide-linked COFs (PI-COFs) is further complicated by the poor reversibility of the ring-closing reaction under solvothermal conditions. Herein, we report the ionothermal synthesis of crystalline and porous PI-COFs in zinc chloride and eutectic salt mixtures. This synthesis does not require soluble precursors and the reaction time is significantly reduced as compared to standard solvothermal synthesis methods. In addition to applying the synthesis to previously reported imide COFs, a new perylene-based COF was also synthesized, which could not be obtained by the classical solvothermal route. In situ high-temperature XRPD analysis hints to the formation of precursor-salt adducts as crystalline intermediates, which then react with each other to form the COF., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

The synthesis of porous electrode materials is often linked with the generation of waste that results from extensive purification steps and low mass yield. In contrast to porous carbons, covalent triazine frameworks (CTFs) display modular properties on a molecular basis through appropriate choice of the monomer. Herein, the synthesis of a new pyridine-based CTF material is showcased. The porosity and nitrogen-doping are tuned by a careful choice of the reaction temperature. An in-depth structural characterization by using Ar physisorption, X-ray photoelectron spectroscopy, and Raman spectroscopy was conducted to give a rational explanation of the material properties. Without any purification, the samples were applied as symmetrical supercapacitors and showed a specific capacitance of 141 F g -1 . Residual ZnCl 2 , which acted formerly as the porogen, was used directly as the electrolyte salt. Upon the addition of water, ZnCl 2 was dissolved to form the aqueous electrolyte in situ. Thereby, extensive and time-consuming washing steps could be circumvented., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The electrochemical splitting of water holds promise for the storage of energy produced intermittently by renewable energy sources. The evolution of hydrogen currently relies on the use of platinum as a catalyst-which is scarce and expensive-and ongoing research is focused towards finding cheaper alternatives. In this context, 2D polymers grown as single layers on surfaces have emerged as porous materials with tunable chemical and electronic structures that can be used for improving the catalytic activity of metal surfaces. Here, we use designed organic molecules to fabricate covalent 2D architectures by an Ullmann-type coupling reaction on Au(111). The polymer-patterned gold electrode exhibits a hydrogen evolution reaction activity up to three times higher than that of bare gold. Through rational design of the polymer on the molecular level we engineered hydrogen evolution activity by an approach that can be easily extended to other electrocatalytic reactions., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The intuitive use, inexpensive fabrication, and easy readout of colorimetric sensors, including photonic crystal architectures and Fabry-Pérot interference sensors, have made these devices a successful commercial case, and yet, understanding how the diffusion of analytes occurs throughout the structure is a key ingredient for designing the response of these platforms on demand. Herein, the diffusion of amines in a periodic multilayer system composed of two-dimensional nanosheets and dielectric nanoparticles is tracked by a combination of spectroscopic measurements and theoretical modelling. It is demonstrated that diffusion is controlled by the molecular size, with larger molecules showing larger layer swelling and slower diffusion times, which translates into important sensor characteristics such as signal change and saturation time. Since the approach visualizes the analyte impregnation process in a time- and spatially resolved fashion, it directly relates the macroscopic color readout into microscopic processes occurring at the molecular level, thus opening the door to rational sensor design., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Fast sodium-ion conductors are key components of Na-based all-solid-state batteries which hold promise for large-scale storage of electrical power. We report the synthesis, crystal-structure determination, and Na + -ion conductivities of six new Na-ion conductors, the phosphidosilicates Na 19 Si 13 P 25 , Na 23 Si 19 P 33 , Na 23 Si 28 P 45 , Na 23 Si 37 P 57 , LT-NaSi 2 P 3 and HT-NaSi 2 P 3 , based entirely on earth-abundant elements. They have SiP 4 tetrahedra assembled interpenetrating networks of T3 to T5 supertetrahedral clusters and can be hierarchically assigned to sphalerite- or diamond-type structures. 23 Na solid-state NMR spectra and geometrical pathway analysis show Na + -ion mobility between the supertetrahedral cluster networks. Electrochemical impedance spectroscopy shows Na + -ion conductivities up to σ (Na + )=4×10 -4  S cm -1 . The conductivities increase with the size of the supertetrahedral clusters through dilution of Na + -ions as the charge density of the anionic networks decreases., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Graphitic carbon nitrides have emerged as an earth-abundant family of polymeric materials for solar energy conversion. Herein, a 2D cyanamide-functionalized polyheptazine imide (NCN-PHI) is reported, which for the first time enables the synergistic coupling of two key functions of energy conversion within one single material: light harvesting and electrical energy storage. Photo-electrochemical measurements in aqueous electrolytes reveal the underlying mechanism of this "solar battery" material: the charge storage in NCN-PHI is based on the photoreduction of the carbon nitride backbone and charge compensation is realized by adsorption of alkali metal ions within the NCN-PHI layers and at the solution interface. The photoreduced carbon nitride can thus be described as a battery anode operating as a pseudocapacitor, which can store light-induced charge in the form of long-lived, "trapped" electrons for hours. Importantly, the potential window of this process is not limited by the water reduction reaction due to the high intrinsic overpotential of carbon nitrides for hydrogen evolution, potentially enabling new applications for aqueous batteries. Thus, the feasibility of light-induced electrical energy storage and release on demand by a one-component light-charged battery anode is demonstrated, which provides a sustainable solution to overcome the intermittency of solar radiation., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Harvesting the properties of nanosheets is not only crucial from a fundamental perspective, but also for the development of novel functional devices based on 2D nanosheets. Herein, we demonstrate the processing of organically modified TBA x H 1-x Ca 2 Nb 3 O 10 nanosheets into photonic thin films and study their colorimetric sensing properties in response to various aqueous and organic solvent vapors. Building on the enhanced solvent accessibility of TBA-containing nanosheets and their photocatalytic activity under UV irradiation, we develop a new concept for photocatalytic lithography using TBA x H 1-x Ca 2 Nb 3 O 10 nanosheets as a negative photoresist to obtain high-fidelity micron-scale patterns of robust inorganic nanosheets. Photocatalytic nanosheet lithography (PNL) therefore adds a new resist-free, resource efficient direct patterning technique to the toolbox of photolithography., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An approach toward intercalant tunable nanosheet-based Fabry-Pérot sensors is presented. The intercalant tetrabutylammonium significantly increases the sensitivity of the photonic nose sensor to volatile organic compounds with increasing polarity, enabling polarity-driven color-coded vapor differentiation. Paired with the improved millisecond response times for polar vapors, vapor imaging with spatio-temporal resolution is within reach., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

While natural photosynthesis serves as the model system for efficient charge separation and decoupling of redox reactions, bio-inspired artificial systems typically lack applicability owing to synthetic challenges and structural complexity. We present herein a simple and inexpensive system that, under solar irradiation, forms highly reductive radicals in the presence of an electron donor, with lifetimes exceeding the diurnal cycle. This radical species is formed within a cyanamide-functionalized polymeric network of heptazine units and can give off its trapped electrons in the dark to yield H 2 , triggered by a co-catalyst, thus enabling the temporal decoupling of the light and dark reactions of photocatalytic hydrogen production through the radical's longevity. The system introduced here thus demonstrates a new approach for storing sunlight as long-lived radicals, and provides the structural basis for designing photocatalysts with long-lived photo-induced states., (© 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Covalent organic frameworks (COFs) are a new class of nanoporous polymeric vector showing promise as drug-delivery vehicles with high loading capacity and biocompatibility. The interaction between the carrier and the cargo is specifically tailored on a molecular level by H-bonding. Cell-proliferation studies indicate higher efficacy of the drug in cancer cells by nanocarrier delivery mediated by the COF., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A 2D nanosheet-based photonic nose for vapor identification is presented. A HSbP2 O8 nanosheet thin-film sensor with resistive readout is developed for the tracking of trace amounts of water, and a photonic HSbP2 O8 /TiO2 multilayer structure is effective at optically distinguishing between chemically similar solvent vapors through analyte-specific host-guest interactions., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Herein, the synthesis and characterization of the first mixed-valent, purely cobalt-based zeolitic imidazolate framework, Co(II)3Co(III)2(C3H3N2)12 is presented. The material adopts the cubic garnet-type structure and combines high thermal stability of up to 350 °C with excellent chemical stability. Electrochemical characterization showed that the cobalt centres are redox active and efficiently support oxygen evolution, thus rendering this framework a potential candidate for single-site heterogeneous catalysis based on earth-abundant elements., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new optical touchless positioning interface based on ultrasensitive humidity responsive 1D photonic crystals utilizing the giant moisture dependent swelling capacity of 2D phosphatoantimonate nanosheets is presented. The spatially confined, full spectral color change combined with reversible transparency switching induced by the humidity sheath of a human finger allows for real time, true color lateral finger motion tracking under touchless conditions., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this contribution, we report on novel functionalized triazines, which represent new precursors for C/N/(H) compounds or suitable building blocks for carbon-based functional networks. Our results provide insights into the structural properties of molecular carbon nitride materials and their design principles. Tris(1-propynyl)-1,3,5-triazine (C3 N3 (C3 H3 )3 ) and tris(1-butynyl)-1,3,5-triazine (C3 N3 (C4 H5 )3 ) were prepared by substitution reactions of cyanuric chloride (C3 N3 Cl3 ) with prop-1-yne and but-1-yne. The crystal structure of tris(1-propynyl)-1,3,5-triazine was solved in the orthorhombic space group Pbcn (Z=4, a=1500.06 (14), b=991.48(10), c=754.42(6) pm, V=1122.03(18)×10(6)  pm(3) ), whereas tris(1-butynyl)-1,3,5-triazine crystallized in the triclinic space group P-1 (Z=6, a=1068.36(12), b=1208.68(12), c=1599.38(16) pm, α=86.67(3), β=86.890(4), γ=86.890(4)°, V=1997.7(4)×10(6)  pm(3) ). For both structures, planar triazine units and layerlike packing of the molecules were observed. Tris(1-propynyl)-1,3,5-triazine is built up from hydrogen-bonded zig-zag strands, whereas tris(1-butynyl)-1,3,5-triazine shows parallel layered arrangements. Both compounds were investigated by NMR spectroscopy, IR spectroscopy, and differential thermal analysis/thermogravimetric analysis, which provided insights into their structural, chemical, and thermal properties. In addition, tris(1-propynyl)-1,3,5-triazine was pyrolyzed and a new polymeric triazine-based compound containing mesitylene units was obtained. Its structural features and properties are discussed in detail., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Solar-light-driven H2 production in water with a [NiFeSe]-hydrogenase (H2ase) and a bioinspired synthetic nickel catalyst (NiP) in combination with a heptazine carbon nitride polymer, melon (CN(x)), is reported. The semibiological and purely synthetic systems show catalytic activity during solar light irradiation with turnover numbers (TONs) of more than 50,000 mol H2(mol H2ase)(-1) and approximately 155 mol H2 (mol NiP)(-1) in redox-mediator-free aqueous solution at pH 6 and 4.5, respectively. Both systems maintained a reduced photoactivity under UV-free solar light irradiation (λ>420 nm)., (© 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

A new dimension: The doping of amorphous poly(triazine imide) (PTI) through ionothermal copolymerization of dicyandiamide with 4-amino-2,6-dihydroxypyrimidine (4AP) results in triazine-based carbon nitrides with increased photoactivity for water splitting compared to crystalline poly(triazine imide) (PTI/Li(+)Cl(-), see picture) and melon-type carbon nitrides. This family of carbon nitride semiconductors has potential as low-cost, environmentally clean photocatalysts for solar fuel production., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The transfer of supramolecular templating to the realm of metal-organic frameworks opens up new avenues to the design of novel hierarchically structured materials. We demonstrate the first synthesis of mesostructured zinc imidazolates in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB), which acts as a template giving rise to ordered lamellar hybrid materials. A high degree of order spanning the atomic and mesoscale was ascertained by powder X-ray diffraction, electron diffraction, as well as solid-state NMR and IR spectroscopy. The metrics of the unit cells obtained for the zinc methylimidazolate and imidazolate species are a=(11.43±0.45), b=(9.55±0.35), c=(27.19±0.34) Å, and a=(10.98±0.90), b=(8.95±0.95), c=(26.33±0.34) Å, respectively, assuming orthorhombic symmetry. The derived structure model is consistent with a mesolamellar structure composed of bromine-terminated zinc (methyl)imidazolate chains interleaved with motionally rigid cationic surfactant molecules in an all-trans conformation. The hybrid materials exhibit unusually high thermal stability up to 300 °C, at which point CTAB is lost and evidence for a thermally induced transformation into poorly crystalline mesostructures with larger feature sizes is obtained. Treatment with ethanol effects the extraction of CTAB from the material, followed by facile transformation into pure microporous ZIF-8 nanoparticles within minutes, thus demonstrating a unique transition from a mesostructure into a microporous zinc imidazolate., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Poly(triazine imide) with intercalation of lithium and chloride ions (PTI/Li(+)Cl(-)) was synthesized by temperature-induced condensation of dicyandiamide in a eutectic mixture of lithium chloride and potassium chloride as solvent. By using this ionothermal approach the well-known problem of insufficient crystallinity of carbon nitride (CN) condensation products could be overcome. The structural characterization of PTI/Li(+)Cl(-) resulted from a complementary approach using spectroscopic methods as well as different diffraction techniques. Due to the high crystallinity of PTI/Li(+)Cl(-) a structure solution from both powder X-ray and electron diffraction patterns using direct methods was possible; this yielded a triazine-based structure model, in contrast to the proposed fully condensed heptazine-based structure that has been reported recently. Further information from solid-state NMR and FTIR spectroscopy as well as high-resolution TEM investigations was used for Rietveld refinement with a goodness-of-fit (χ(2)) of 5.035 and wRp=0.05937. PTI/Li(+)Cl(-) (P6(3)cm (no. 185); a=846.82(10), c=675.02(9) pm) is a 2D network composed of essentially planar layers made up from imide-bridged triazine units. Voids in these layers are stacked upon each other forming channels running parallel to [001], filled with Li(+) and Cl(-) ions. The presence of salt ions in the nanocrystallites as well as the existence of sp(2)-hybridized carbon and nitrogen atoms typical of graphitic structures was confirmed by electron energy-loss spectroscopy (EELS) measurements. Solid-state NMR spectroscopy investigations using (15)N-labeled PTI/Li(+)Cl(-) proved the absence of heptazine building blocks and NH(2) groups and corroborated the highly condensed, triazine-based structure model., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report on the existence and formation of the carbon nitride precursor melam (H(2)N)(2)(C(3)N(3))NH(C(3)N(3))(NH(2))(2), thereby clarifying one of the last unresolved issues posed by the complex thermal condensation of melamine C(3)N(3)(NH(2))(3). Experimental proof is put forward that melam is a direct condensation product of melamine, but can be detected only in small amounts under special reaction conditions owing to its rapid transformation into melem. The coexistence of melamine and melem during thermal condensation yields two adduct phases with distinct compositions [C(3)N(3)(NH(2))(3)](2)[C(6)N(7)(NH(2))(3)] and [C(3)N(3)(NH(2))(3)][C(6)N(7)(NH(2))(3)](2). They may be considered as co-crystallizates of melamine and melem and can be isolated as intermediates between 590 and 650 K prior to the formation of single-phase melem C(6)N(7)(NH(2))(3). Melam (C2/c, a=1811.0(4), b=1086.7(2), c=1398.4(3) pm, beta=96.31(3) degrees, V=2735.3(9)x10(6) pm(3), T=130 K) adopts a ditriazinylamine-type structure with a twisted conformation about the bridging NH moiety and transforms into melem around 640 K. Two compounds deriving from melam have been synthesized by solution and solid-state reactions. The salt melamium diperchlorate C(6)N(11)H(11)(ClO(4))(2).2H(2)O (C2/c, a=1747.8(4), b=1148.2(2), c=993.6(2) pm, beta=118.79(3) degrees, V=1747.4(6)x10(6) pm(3), T=130 K) crystallizes as a dihydrate and exhibits a doubly protonated, planar melam core. In the neutral complex Zn[C(6)N(11)H(9)]Cl(2) (P2(1)/c, a=743.00(15), b=2233.2(5), c=762.5(2) pm, beta=99.86(3) degrees, V=1246.5(4)x10(6) pm(3), T=200 K), melam acts as a symmetrically bent bidentate ligand, which is coordinated to the Lewis acid Zn-site through two ring nitrogen atoms.

The rare-earth tricyanomelaminates, [NH(4)]Ln[HC(6)N(9)](2)[H(2)O](7)xH(2)O (LnTCM; Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy), have been synthesized through ion-exchange reactions. They have been characterized by powder as well as single-crystal X-ray diffraction analysis, vibrational spectroscopy, and solid-state (1)H, (13)C, and (15)N MAS NMR spectroscopy. The X-ray powder pattern common to all nine rare-earth tricyanomelaminates LnTCM (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy) indicates that they are isostructural. The single-crystal X-ray diffraction pattern of LnTCM is indicative of non-merohedral twinning. The crystals are triclinic and separation of the twin domains as well as refinement of the structure were successfully carried out in the space group P1 for LaTCM (LaTCM; P1, Z=2, a=7.1014(14), b=13.194(3), c=13.803(3) A, alpha=90.11(3), beta=77.85(3), gamma=87.23(3) degrees , V=1262.8(4) A(3)). In the crystal structure, each Ln(3+) is surrounded by two nitrogen atoms from two crystallographically independent tricyanomelaminate moieties and seven oxygen atoms from crystal water molecules. The positions of all of the hydrogen atoms of the ammonium ions and water molecules could not be located from difference Fourier syntheses. The presence of [NH(4)](+) ions as well as two NH groups belonging to two crystallographically independent monoprotonated tricyanomelaminate moieties has only been confirmed by subjecting LaTCM to solid-state (1)H, (13)C, and (15)N{(1)H} cross-polarization (CP) MAS NMR and advanced CP experiments such as cross-polarization combined with polarization inversion (CPPI). The (1)H 2D double-quantum single-quantum homonuclear correlation (DQ SQ) spectrum and the (15)N{(1)H} 2D CP heteronuclear-correlation (HETCOR) spectrum have revealed the hydrogen-bonded (N--HN) dimer of monoprotonated tricyanomelaminate moieties as well as H-bonding through [NH(4)](+) ions and H(2)O molecules. The structures of the other eight rare-earth tricyanomelaminates (LnTCM; Ln=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy) have been refined from X-ray powder diffraction data by the Rietveld method. Photoluminescence studies of [NH(4)]Eu[HC(6)N(9)](2)[H(2)O](7)xH(2)O have revealed orange-red (lambda(max)=615 nm) emission due to the (5)D(0)-(7)F(2) transition, whereas [NH(4)]Tb[HC(6)N(9)](2)[H(2)O](7)xH(2)O has been found to show green emission with a maximum at 545 nm arising from the (5)D(4)-(7)F(5) transition. DTA/TG studies of [NH(4)]Ln[HC(6)N(9)](2)[H(2)O](7)xH(2)O have indicated several phase transitions associated with dehydration of the compounds above 150 degrees C and decomposition above 200 degrees C.

Poly(aminoimino)heptazine, otherwise known as Liebig's melon, whose composition and structure has been subject to multitudinous speculations, was synthesized from melamine at 630 degrees C under the pressure of ammonia. Electron diffraction, solid-state NMR spectroscopy, and theoretical calculations revealed that the nanocrystalline material exhibits domains well-ordered in two dimensions, thereby allowing the structure solution in projection by electron diffraction. Melon ([C(6)N(7)(NH(2))(NH)](n), plane group p2 gg, a=16.7, b=12.4 A, gamma=90 degrees, Z=4), is composed of layers made up from infinite 1D chains of NH-bridged melem (C(6)N(7)(NH(2))(3)) monomers. The strands adopt a zigzag-type geometry and are tightly linked by hydrogen bonds to give a 2D planar array. The inter-layer distance was determined to be 3.2 A from X-ray powder diffraction. The presence of heptazine building blocks, as well as NH and NH(2) groups was confirmed by (13)C and (15)N solid-state NMR spectroscopy using (15)N-labeled melon. The degree of condensation of the heptazine core was further substantiated by a (15)N direct excitation measurement. Magnetization exchange observed between all (15)N nuclei using a fp-RFDR experiment, together with the CP-MAS data and elemental analysis, suggests that the sample is mainly homogeneous in terms of its basic composition and molecular building blocks. Semiempirical, force field, and DFT/plane wave calculations under periodic boundary conditions corroborate the structure model obtained by electron diffraction. The overall planarity of the layers is confirmed and a good agreement is obtained between the experimental and calculated NMR chemical shift parameters. The polymeric character and thermal stability of melon might render this polymer a pre-stage of g-C(3)N(4) and portend its use as a promising inert material for a variety of applications in materials and surface science.