Stability and Reversible Oxidation of Sub-Nanometric Cu5 Metal Clusters: Integrated Experimental Study and Theoretical Modeling**

Sub-nanometer metal clusters have special physical and chemical properties, significantly different from those of nanoparticles. However, there is a major concern about their thermal stability and susceptibility to oxidation. In situ X-ray Absorption spectroscopy and Near Ambient Pressure X-ray Photoelectron spectroscopy results reveal that supported Cu5 clusters are resistant to irreversible oxidation at least up to 773 K, even in the presence of 0.15 mbar of oxygen. These experimental findings can be formally described by a theoretical model which combines dispersion-corrected DFT and first principles thermochemistry revealing that most of the adsorbed O2 molecules are transformed into superoxo and peroxo species by an interplay of collective charge transfer within the network of Cu atoms and large amplitude “breathing” motions. A chemical phase diagram for Cu oxidation states of the Cu5-oxygen system is presented, clearly different from the already known bulk and nano-structured chemistry of Cu

Screening of Heterogeneous Photocatalysts for Water Splitting

In this contribution, a simple method for the screening of photocatalytic activity of catalyst materials is presented. The method is based on two steps the immobilization of the photocatalyst and the subsequent testing of their photocatalytic activity, using the gas evolution at the solid liquid interface. Up to four catalysts can be tested under the same conditions. The observed gas evolution for selected photocatalysts is consistent with trends reported in the literature from conventional photocatalytic reactor

Nitrogen and phosphorus resorption in two wetland macrophytes

Nitrogen (N) and phosphorus (P) resorption efficiency (RE) and, resorption proficiency (RP) and functional strategies in Schoenoplectus lacustris subsp. tabernaemontani and Typha latifolia occurring in Cernek Lake and Uzun Lake with different nutrient status situated in Bafra town in Central Black Sea Region of Turkey was investigated. Mass-based N and P concentrations during summer (from June to September) in both species were rather higher than those of British, European and American wetland species. However, both N- and P-limitations were found in both species during the sampling period. It has been found that transitional strategy between CS and C strategies (C/CS) was common for the two species, whilst T. latifolia individuals in Cernek Lake exhibited CS strategy. N resorption was incomplete in Cernek and Uzun Lakes in both species. P resorption was complete in Uzun Lake for both species, whereas P resorption was intermediate in Cernek Lake, but more proficient for T. latifolia. Both PRE and PRP in T. latifolia individuals in Cernek Lake were higher than those in Schoenoplectus lacustris subsp. tabernaemontani individuals and this shows that CS species has an efficient internal cycling of P

Polyoxometalate POM boosting the light harvesting ability of graphitic carbon nitride for efficient photocatalytic hydrogen production

Phosphomolybdic acid PMA was used to achieve simultaneously P doping and heterojunction construction of graphitic carbon nitride gCN . P gCN PMAx composites were obtained via post thermal annealing of bulk gCN PMAx and characterized in detail using different techniques including XRD, XPS, SEM, and DRS. As an in situ hard templating agent and doping source, the loaded PMA helps to provide porous structured materials and reinforced electronic properties whereby many transitions are enhanced resulting in the improvement of light harvesting. The electronic properties of gCN are improved strongly with the increased amount of PMA loaded, but the crystallinity becomes worse and the material becomes much more amorphous and disordered. The materials were investigated for the hydrogen evolution reaction HER showing the highest H2 evolution performance of 625 amp; 956;mol g amp; 8722;1 h amp; 8722;1 for the P gCN PMA1.5 sample, which is almost 4 times higher than that of gCN with 167 amp; 956;mol g amp; 8722;1 h amp; 8722;1. The P gCN PMA1.5 sample was investigated under long term irradiation and in recycling tests indicating the good photocatalytic stability of this material. The apparent quantum efficiency AQE exhibited by P gCN PMA1.5 0.7 is 7 times higher than the AQE measured exhibited by gCN. This is evidence of the boosting effect exhibited by the loading of PMA onto the surface of gCN 0.1 . Thus, this study aims to offer a novel strategy to improve the activity of gCN by applying polyoxometalates as modifiers for better light harvestin

Outstanding nobility observed in Cu5 clusters reveals the key role of collective quantum effects

21 pags., 5 figs.Subnanometer-sized metal clusters often feature a molecule-like electronic structure, which makes their physical and chemical properties significantly different from those of nanoparticles and bulk material. Considering potential applications, there is a major concern about their thermal stability and susceptibility towards oxidation. Cu clusters of only 5 atoms (Cu5 clusters) are first synthesized in high concentration using a new-generation wet chemical method. Next, it is shown that, contrary to what is currently assumed, Cu5 clusters display nobility, beyond resistance to irreversible oxidation, at a broad range of temperatures and oxygen pressures. The outstanding nobility arises from an unusual reversible oxidation which is observed by in situ X-ray Absorption Spectroscopy and X-ray Photoelectron Spectroscopy on Cu5 clusters deposited onto highly oriented pyrolitic graphite at different oxygen pressures and up to 773 K. This atypical property is explained by a theoretical approach combining different state-of-the-art first principles theories. It reveals the essential role of collective quantum effects in the physical mechanism responsible for the nobility of Cu5 clusters, encompassing a structural ‘breathing’ through concerted Cu–Cu elongations/contractions upon O2 uptake/release, and collective charge transfer as well. A predictive phase diagram of their reversible oxidation states is also delivered, agreeing with the experimental observations. The collective quantum effects responsible of the observed nobility are expected to be general in subanometer-sized metal clusters, pushing this new generation of materials to an upper level.This work has been partly supported by the European Union’s Horizon 2020 Research and Innovation Programme un-der Grant Agreement No. 825999; the Spanish Agencia Estatal de Investigación (AEI) and the Fondo Europeo de Desarrollo Regional (FEDER, UE) under Grant No. MAT2016-75354-P; the Austrian Science Fund (FWF) under Grant P29893-N36; the CMST COST Action CM1405 “Molecules in Motion” (MOLIM); the Xunta de Galicia, Spain (Grupos Ref. Comp.ED431C 2017/22 and AEMAT ED431E 2018/08); Obra Social Fundación La Caixa: Ref.LCF/PR/PR12/11070003; ANPCyT PICT (2017-1220 and 2017-3944) and UNLP (Project11/X790), Argentina.N