The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.201908505.Single-atom (SA) catalysis is a novel frontline in the catalysis field due to the often drastically enhanced specific activity and selectivity of many catalytic reactions. Here, an atomic-scale defect engineering approach to form and control traps for platinum SA sites as co-catalyst for photocatalytic H 2 generation is described. Thin sputtered TiO 2 layers are used as a model photocatalyst, and compared to the more frequently used (001) anatase sheets. To form stable SA platinum, the TiO 2 layers are reduced in Ar/H 2 under different conditions (leading to different but defined Ti 3+ -O v surface defects), followed by immersion in a dilute hexachloroplatinic acid solution. HAADF-STEM results show that only on the thin-film substrate can the density of SA sites be successfully controlled by the degree of reduction by annealing. An optimized SA-Pt decoration can enhance the normalized photocatalytic activity of a TiO 2 sputtered sample by 150 times in comparison to a conventional platinum-nanoparticle-decorated TiO 2 surface. HAADF-STEM, XPS, and EPR investigation jointly confirm the atomic nature of the decorated Pt on TiO 2 . Importantly, the density of the relevant surface exposed defect centers-thus the density of Pt-SA sites, which play the key role in photocatalytic activity-can be precisely optimized.Single-atom (SA) or single-site catalysis (SACs) has over the past years become an increasingly fascinating topic in the catalysis field. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] SACs have allowed new approaches in heterogeneous catalysis, [12,13] minimized the use of precious metals, [14]

SACs) (see also reviews [11][12][13] ). SACs could offer ultimate atom economy and make every active site accessible, like homogeneous catalysts but being recyclable, which is a subject of paramount importance. [14] Major challenges in the field though encompass: i) the development of materials with precise functionalities for robust metal ion binding and ii) metal cooperativity in heterometallic and mixed-valence SACs, as identified in the recent topical perspective. [12] Meeting the first challenge could facilitate higher metal contents avoiding clustering and leaching upon reaction and catalyst recycling. This is also a prerequisite for the second challenge (metal-metal cooperation), since low metal content translates into large intermetallic distances. [6] Cooperation between two metal ions linked by a single-frame ligand has shown enormous potential in homogeneous catalysis. [15] For example, biocatalysts (metalloenzymes) use binuclear [16] and mixed-valence metal centers [17] for effective catalysis. Therefore, the development of heterogeneous catalysts with cooperativity between metal centers, keeping all the salient features of SACs, could offer a platform for the development of the next generation of catalysts.Graphene-based 2D materials have contributed to the development of SACs, [10,[12][13][14][18][19][20][21][22][23][24][25][26][27] in which metal ions are tetracoordinated in porphyrinic-like vacancies. Although only low contents of metal atoms can be achieved (up to ≈1 wt%), [10,12,14,18,[22][23][24][25][26] Single-atom catalysts (SACs) aim at bridging the gap between homogeneous and heterogeneous catalysis. The challenge is the development of materials with ligands enabling coordination of metal atoms in different valencestates, and preventing leaching or nanoparticle formation. Graphene functionalized with nitrile groups (cyanographene) is herein employed for the robust coordination of Cu(II) ions, which are partially reduced to Cu(I) due to graphene-induced charge transfer. Inspired by nature's selection of Cu(I) in enzymes for oxygen activation, this 2D mixed-valence SAC performs flawlessly in two O 2 -mediated reactions: the oxidative coupling of amines and the oxidation of benzylic CH bonds toward high-value pharmaceutical synthons. High conversions (up to 98%), selectivities (up to 99%), and recyclability are attained with very low metal loadings in the reaction. The synergistic effect of Cu(II) and Cu(I) is the essential part in the reaction mechanism. The developed strategy opens the door to a broad portfolio of other SACs via their coordination to various functional groups of graphene, as demonstrated by successful entrapment of Fe III /Fe II single atoms to carboxy-graphene. Single-Atom CatalysisThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.201900323.

Surface exposed Ti3+ and lattice embedded Ti3+ in an optimum ratio is the determining factor for optimized photocatalytic H2 evolution.

Zero-valent iron nanoparticles (nZVI) treated by reduced sulfur compounds (i.e., sulfidated nZVI, S-nZVI) have attracted increased attention as promising materials for environmental remediation. While the preparation of S-nZVI and its reactions with various groundwater contaminants such as trichloroethylene (TCE) were already a subject of several studies, nanoparticle synthesis procedures investigated so far were suited mainly for laboratory-scale preparation with only a limited possibility of easy and cost-effective large-scale production and FeS shell property control. This study presents a novel approach for synthesizing S-nZVI using commercially available nZVI particles that are treated with sodium sulfide in a concentrated slurry. This leads to S-nZVI particles that do not contain hazardous boron residues and can be easily prepared off-site. The resulting S-nZVI exhibits a core–shell structure where zero-valent iron is the dominant phase in the core, while the shell contains mostly amorphous iron sulfides. The average FeS shell thickness can be controlled by the applied sulfide concentration. Up to a 12-fold increase in the TCE removal and a 7-fold increase in the electron efficiency were observed upon amending nZVI with sulfide. Although the FeS shell thickness correlated with surface-area-normalized TCE removal rates, sulfidation negatively impacted the particle surface area, resulting in an optimal FeS shell thickness of approximately 7.3 nm. This corresponded to a particle S/Fe mass ratio of 0.0195. At all sulfide doses, the TCE degradation products were only fully dechlorinated hydrocarbons. Moreover, a nearly 100% chlorine balance was found at the end of the experiments, further confirming complete TCE degradation and the absence of chlorinated transformation products. The newly synthesized S-nZVI particles thus represent a promising remedial agent applicable at sites contaminated with TCE.

No abstract

Cu doping in titania is usually detrimental to the material's photoconductivity, which prevents the use of this combination in photoanodes. In this work, we produce TiO 2 nanotube arrays intrinsically doped with copper and establish sufficient conductivity to use them as efficient photoanodes for methanol oxidation in a photoelectrochemical hydrogen generation setting. Firstly, Cu-doped TiO 2 nanotubes were produced by anodizing a TiÀ Cu binary alloy. By subsequent thermal reduction of the structure in an Ar/H 2 environment, conductive copper-doped TiO 2 nanotubes (TiCuTNÀ Ar/H 2 ) can be achieved with an approximately 10 3 times higher conductivity than the non-reduced material. When these reduced Cu-doped TiO 2 nanotubes are used as photoanode, copper species embedded in the TiO 2 wall catalyze the methanol oxidation reaction. As a result of the combined effect of conductivity and catalytic effect of Cu, such reduced Cu:TiO 2 nanotubes can generate a photocurrent of 0.76 mA cm À 2 at 1 V vs. RHE, under AM1.5 (100 mW/ Cm 2 ) irradiation -in a 50 : 50 MeOH/water solution -this is 33 times higher than for pristine Cu:TiO 2 nanotubes.[a] S.

Fluorescent gold nanoclusters (AuNCs) are envisaged as a novel type of fluorophores. This work reports on the first comparative study investigating the effect of presence/absence/abundance of fatty acids (namely palmitic acid, PA) or other substances (like glycoproteins and globulins) in the protein (bovine serum albumin, BSA) on synthesis and properties of the final AuNCs. The most popular template (BSA) and microwave (MW)-assisted synthesis of AuNCs have been intentionally chosen. Our results clearly demonstrate that the fluorescent characteristics (i.e., fluorescence lifetime and quantum yield) are affected by the fatty acids and/or other substances. Importantly, the as-prepared AuNCs are biocompatible, as determined by Alamar Blue assay performed on Hep G2 cell line.

Metal–metal cooperation in a solid‐state mixed‐valence single‐atom catalyst, boosts yield and selectivity in oxidative amine coupling, with uncompromised reusability, as shown by Manoj B. Gawande, Paolo Fornasiero, Radek Zbořil, and co‐workers in article number https://doi.org/10.1002/adma.201900323. The catalyst, stemming from the chemical entrapment and partial reduction of Cu(II) ions on cyanographene, lays the ground for the exploitation of the large family of covalent graphene derivatives as versatile 2D coordination ligands, beyond the porphyrin motif in nitrogen‐doped graphenes.