Towards Organic Zeolites and Inclusion Catalysts: Heptazine Imide Salts Can Exchange Metal Cations in the Solid State

Highly crystalline potassium (heptazine imides) were prepared by the thermal condensation of substituted 1,2,4- triazoles in eutectic salt melts. These semiconducting salts are already known to be highly active photocatalysts, e.g. for the visible light driven generation of hydrogen from water. Herein, we show that within the solid state structure, potassium ions can be exchanged to other metal ions while the crystal habitus is essentially preserved

Triazoles : a new class of precursors for the synthesis of negatively charged carbon nitride derivatives

Carbon nitride polymers were prepared for the first time by the pyrolysis of 3,5-disubstituted-1,2,4-triazole derivatives, namely 3,5-diamino-1,2,4-triazole [1] and 3-amino-1,2,4-triazole-5-thiol [2], in bulk as well as in LiCl/KCl salt melts. The reaction of [1] and [2] in bulk yields condensed heptazine-based polymers, while in LiCl/KCl eutectics it leads to the formation of well-defined potassium poly(heptazine imides), according to the results of 13C NMR and XPS investi-gations, whose formation resembles that of emeraldine salts of polyaniline. The density functional calculations supported the structural model suggested for potassium poly(heptazine imide) polymer. Owing to the specific reaction path, the products obtained from triazoles therefore show electronic properties rather different to known carbon nitrides, such as band gap and conduction and valence bands positions. With the degree of crystallinity of the reference materials, triazole-derived carbon nitrides are characterized by almost complete absence of steady photoluminescence, charge separation and localization upon excitation seems to be improved. As a consequence, photocatalysts prepared from [2] outperform classical carbon nitrides in a model dye degradation reaction and mesoporous graphitic carbon nitride in hydrogen evolution reaction under visible light irradiation. On its turn, [1] can be conveniently used as a co-monomer in order to prepare carbon nitrides with improved visible light absorption

Tridimensional few-layer graphene-like structures from sugar-salt mixtures as high-performance supercapacitor electrodes

© 2018 Elsevier Ltd This work describes a straightforward approach to the production of highly-performing and cost-effective C-based materials for energy storage application while proposing an original and effective method to the control of the final material morphology. Indeed, robust few-layer graphene-like and highly open-cell structures have been prepared by a modified chemical activation procedure starting from costless sugar/salt mixtures. The as-prepared C-samples ensure high ion-accessible surface area and low ion transport resistance, two key features for the fabrication of effective electrochemical double layer supercapacitors. A selected sample from this series exhibits high specific capacitance (Cg) (312 and 234 F g−1 at 0.5 and 50 A g−1, respectively, in 0.5 M H2SO4), particularly at high current density values, along with excellent cycling stability and Cg retention for increasing charge–discharge rates

Biochemical applications of surface-enhanced infrared absorption spectroscopy

An overview is presented on the application of surface-enhanced infrared absorption (SEIRA) spectroscopy to biochemical problems. Use of SEIRA results in high surface sensitivity by enhancing the signal of the adsorbed molecule by approximately two orders of magnitude and has the potential to enable new studies, from fundamental aspects to applied sciences. This report surveys studies of DNA and nucleic acid adsorption to gold surfaces, development of immunoassays, electron transfer between metal electrodes and proteins, and protein–protein interactions. Because signal enhancement in SEIRA uses surface properties of the nano-structured metal, the biomaterial must be tethered to the metal without hampering its functionality. Because many biochemical reactions proceed vectorially, their functionality depends on proper orientation of the biomaterial. Thus, surface-modification techniques are addressed that enable control of the proper orientation of proteins on the metal surface. [Figure: see text

ATR-SEIRAS - an approach to probe the reactivity of Pd-modified quasi-single crystal gold film electrodes

Quasi-single crystalline gold films of 20 nm thickness and preferential (111) orientation on Si hemispheres were modified by controlled potentiostatic deposition of Pd (sub-ML, ML, multi-L) from sulphate and/or chloride-containing electrolyte. The electrochemical properties of these model electrodes were characterised for hydrogen and (hydrogen-) sulphate adsorption as well as for surface oxide formation by cyclic voltammetry. Conditions were developed to fabricate defined and stable I'd monolayers. In situ ATR-SEIRAS (Attenuated Total Reflection Surface Enhanced Infrared Reflection Absorption Spectroscopy) experiments were carried out to describe the electrochemical double layer of Pd modified gold film electrodes in contact with aqueous 0.1 M H2SO4 with focus on interfacial water and anion adsorption. Based on an analysis of the non-resonant IR background signal the potential of zero charge is estimated to 0.10-0.20 V (vs. RHE). CO was found to be weakly physisorbed in atop sites on Au(111-20 nm)/0.1 M H2SO4 only in CO saturated electrolyte. CO, deposited on a quasi-single crystal gold film modified with I NIL Pd, is chemisorbed with preferential occupation of bridge sites and atop positions at step edges. Saturated CO adlayers, as obtained by deposition at 0.10 V, contain isolated water species and are covered by a second layer of hydrogen bonded water. Potentiodynamic SEIRAS experiments of CO electro-oxidation on Pd-modified gold film electrodes demonstrate clearly the existence of a "pre-oxidation" region. They also provide spectroscopic evidence that isolated water and weakly hydrogen bonded water are consumed during the reaction and that atop CO on defect sites is a preferential reactant. The simultaneous in situ monitoring of the potential- and time-dependent evolution of characteristic vibrational modes in the OH- and CO-stretching regions are in agreement with the Gilman ("reactant pair") mechanism of CO oxidation. (C) 2004 Elsevier B.V. All rights reserved