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Microporous materials, which are materials with small pores (<2 nm) and very high surface areas, have found widespread applications in diverse technological areas, such as gas storage, separation, or catalysis. Zeolites or activated carbons are the traditional choice for these purposes, but more recently metalorganic frameworks also showed promising properties to complement carbon and silica in certain fields of application. This is due to the valuable combination of high surface area and low density, with control over the chemical and physical properties of the pore walls. While metal-organic frameworks combine tunable porosities with organic functionalities, their coordination-bond-based architecture severely limits the conditions under which these materials can be applied. This deficit should be possible to overcome with the use of covalently bonded analogues, which can enhance the range of applications to more realistic conditions (e.g., heat, water, acid/base, or oxygen), where most coordination bonds start to dissolve. Thus, it is not surprising that several groups recently attempted to prepare new porous materials on a covalently bonded, purely organic base.So far, three main strategies can be distinguished for the preparation of microporous polymer networks. First, additional cross-linking of swollen polystyrene [1][2][3][4] and, more recently, polyaniline networks [5] generate so-called hyper-cross-linked polymers (HCP), with surface areas up to 2000 m 2 g À1

Strukturell ähnlich zu Liebigs Melon (Poly(aminoimino)heptazin) sind Kohlenstoffnitrid‐Photokatalysatoren (siehe Formel), die durch direkte Copolymerisation von Dicyandiamid mit Barbitursäure erhalten werden können. Das Bild zeigt, wie sich die optische Absorption der Produkte bei steigendem Barbitursäure‐Anteil in der Copolymerisationsmischung (Pfeile) weiter in die sichtbare Region ausdehnt, was von Vorteil für Solarenergieanwendungen ist.

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Potassium poly(heptazine imide) (PHI) is a photocatalytically active carbon nitride material that was recently prepared from substituted 1,2,4-triazoles. Here we show that the more acidic precursors, such as commercially available 5-aminotetrazole, upon pyrolysis in LiCl/KCl salt melt yield PHI with the greatly improved structural order and thermodynamic stability. Tetrazole-derived PHIs feature long range crystallinities and unconventionally small layer-stacking distances leading to the altered electronic band structures as shown by Mott-Schottky analyses. Under the optimized synthesis conditions, visible light driven hydrogen evolution rates reach twice the rate provided by the previous golden standard, mesoporous graphitic carbon nitride having much higher surface area. More interestingly, the up to 0.7 V higher valence band potential of crystalline PHI compared to the ordinary carbon nitrides makes it an efficient water oxidation photocatalyst which works even in the absence of any metal-based co-catalysts under visible light. To our knowledge, this is the first case of a metal free oxygen liberation from water as such