Volume 5, Issue 4 -

Within the last decade the combination of photoredox catalysis and other catalytic modes of activation has become a powerful tool for organic synthesis to enable transformations that are not possible using single catalyst systems and hence are complementary to traditional methodology. Especially reactions proceeding via synergistic catalysis where co-catalyst and photocatalyst simultaneously and separately activate different reaction partners greatly benefit from the special properties of molecules and transition metal complexes in their excited state being oxidizing and reducing in nature at the same time. Apart from allowing for the generation of radical (open-shell) reactive intermediates by SET under mild conditions from bench-stable, abundant precursors, the photocatalyst often acts to interweave the distinct catalytic cycles by interaction at multiple points of the reaction mechanism to provide overall redox-neutral processes by shuttling electrons within in this complex network of elementary reaction steps. Synergistic strategies moreover may allow to performing such reactions with enantioselectivity, while mostly the selectivity is achieved by the chiral co-catalyst. The merger of photocatalysis has been achieved with a broad range of alternative modes of catalysis including organocatalysis, Brønstedt and Lewis acid and base catalysis, enzyme catalysis as well as in the context of cross-coupling transition metal catalysis overcoming challenging steps in this methodology and therefore has contributed to considerably expand the repertoire of suitable coupling partners. While only selected examples will be discussed, this chapter will highlight various dual catalytic platforms focusing on the photocatalytically generated intermediates, but also illustrating the diverse roles of photocatalysts in the context of such synergistic multicatalysis reactions.

The minimum reactant concentration required to synthesize Au/M (M = Ag, Pt, Pd, Ru …) core-shell nanoparticles by the one-pot microemulsion route was calculated by a simulation model under different synthesis conditions. This minimum concentration was proved to depend on the reduction potential of the slower metal M and on the rigidity of the surfactant film composing the microemulsion. Model results were tested by comparing with Au/M nanoparticles taken from literature. In all cases, experimental data obey model predictions. From this agreement, one can conclude that the smaller the standard potential of the slower reduction metal, the lower the minimum concentration needed to obtain core-shell nanoparticles. In addition, the higher the surfactant flexibility, the higher the minimum concentration to synthesize metal segregated nanoparticles. Model prediction allows to quantify which is the best value of concentration to prepare different pairs of core-shell Au/M nanoparticles in terms of nature of M metal in the couple and microemulsion composition. This outlook may become an advanced tool for fine-tuning Au/M nanostructures. Graphical Abstract :

Conventional inorganic semiconductor quantum dots (QDs) have numerous applications ranging from energy harvesting to optoelectronic and bio-sensing devices primarily due to their unique size and shape tunable band-gap and also surface functionalization capability and consequently, have received significant interest in the last few decades. However, the high market cost of these QDs, on the order of thousands of USD/g and toxicity limit their practical utility in many industrial applications. In this context, graphene quantum dot (GQD), a nanocarbon material and a new entrant in the quantum-confined semiconductors could be a promising alternative to the conventional toxic QDs due to its potential tunability in optical and electronic properties and film processing capability for realizing many of the applications. Variation in optical as well as electronic properties as a function of size, shape, doping and functionalization would be discussed with relevant theoretical backgrounds along with available experimental results and limitations. The review deals with various methods available so far towards the synthesis of GQDs along with special emphasis on characterization techniques starting from spectroscopic, optical and microscopic techniques along with their the working principles, and advantages and limitations. Finally, we will comment on the environmental impact and toxicity limitations of these GQDs and their hybrid nanomaterials to facilitate their future prospects. Graphical Abstract: Structure of doped, functionalized and hybrid GQDs

Developments in the field of visible-light photoredox catalysis have considerably enriched toolbox of preparative organic chemists in recent years. This fast-growing area of research has emerged after seminal studies mainly by MacMillan, Yoon, and Stephenson groups were published in 2008 and 2009. This chapter focuses on the twentieth-century roots of photoredox catalysis with [Ru(bpy) 3 ] 2+ , and the key properties of this species are briefly summarized.

The X-ray Absorption Fine Structure (XAFS) with its subregions X-ray Absorption Near-edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) is a powerful tool for the structural analysis of materials, which is nowadays a standard component of research strategies in many fields. This review covers a wide range of topics related to its measurement and use: the origin of the fine structure, its analytical potential, derived from the physical basis, the environment for measuring XAFS at synchrotrons, including different measurement geometries, detection modes, and sample environments, e. g. for in-situ and operando work, the principles of data reduction, analysis, and interpretation, and a perspective on new methods for structure analysis combining X-ray absorption with X-ray emission. Examples for the application of XAFS have been selected from work with heterogeneous catalysts with the intention to demonstrate the strength of the method providing structural information about highly disperse and disordered systems, to illustrate pitfalls in the interpretation of results (e. g. by neglecting the averaged character of the information obtained) and to show how its merits can be further enhanced by combination with other methods of structural analysis and/or spectroscopy.