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Solar-driven photocatalysis has attracted significant attention in water splitting, CO 2 reduction and organic synthesis. The syntheses of valuable azo- and azoxyaromatic dyes via selective photoreduction of nitroaromatic compounds have been realised using supported plasmonic metal nanoparticles at elevated temperatures (≥90 °C); however, the high cost, low efficiency and poor selectivity of such catalyst systems at room temperature limit their application. Here we demonstrate that the inexpensive graphitic C 3 N 4 is an efficient photocatalyst for selective syntheses of a series of azo- and azoxy-aromatic compounds from their corresponding nitroaromatics under either purple (410 nm) or blue light (450 nm) excitation. The high efficiency and high selectivity towards azo- and azoxy-aromatic compounds can be attributed to the weakly bound photogenerated surface adsorbed H-atoms and a favourable N-N coupling reaction. The results reveal financial and environmental potential of photocatalysis for mass production of valuable chemicals. The synthesis of azo- and azoxy-aromatic dyes via photoreduction of nitroaromatics is hindered by high costs and low catalytic efficiencies and selectivities. Here the authors demonstrate the facile synthesis of these important dyes from their corresponding nitroaromatic precursors by using an inexpensive graphitic C 3 N 4 photocatalyst.

Hydrogen peroxide (H2O2) is an important chemical in synthetic chemistry with huge demands. Photocatalytic synthesis of H2O2 via oxygen reduction and water oxidation reactions (ORR and WOR) is considered as a promising and desirable solution for on‐site applications. However, the efficiency of such a process is low due to the poor solubility of molecular oxygen and the rapid reverse reaction of hydroxyl radicals (•OH) with hydrogen atoms (H). Here, a strategy is proposed to boost the H2O2 evolution via oxidation of water by employing a H acceptor (A, nitrocyclohexane), an •OH mediator (M, dioxane), and a photocatalyst (CdS nanosheets). While •OH radicals are stabilized by dioxane to produce ketyl radicals prior to the formation of H2O2, H atoms are effectively utilized in the generation of cyclohexanone oxime, an important intermediate in the production of Nylon 6. The system displays a rapid kinetic accumulation of H2O2 (0.13 min−1) to a high concentration (6.6 mM). At optimum reaction conditions, a high quantum efficiency (16.6%) and light‐to‐chemical conversion efficiency (4.9%) can be achieved under 410 nm irradiation. Photocatalytic partial water oxidation promoted by a hydrogen acceptor (A) and a hydroxyl mediator (M) couple on CdS nanosheets. While the photogenerated •OH radicals can be stabilized by M to produce ketyl radicals prior to the formation of H2O2, H atoms are transferred to A. This strategy enables a rapid evolution of H2O2 with a high quantum efficiency (16.6%) under visible light irradiation.

Chain reactions on a surface offer an important route to linear nanopatterning. We recently reported cooperative reactions on a silicon surface in which the reaction of one halogen atom with a silicon atom of a silicon dimer induced the halogenation of its neighbouring silicon atom through surface-mediated charge transfer. The reaction was unable to propagate further but here we describe how, by chemically bridging the gaps between the rows of these silicon dimers, this mechanism is able to form extended chains. The agents for chain growth are CH 3 Cl molecules that dissociatively attach CH 3 groups and chlorine atoms to silicon atoms from different dimers. By means of charge transfer through the surface, this gives rise to dangling bonds adjacent to the CH 3 groups and chlorine atoms (in effect, ‘free radicals’) that dissociate further incoming CH 3 Cl molecules, thereby providing the growing points for chains of indefinite length. This versatile mechanism of chain growth is examined in experiments and using ab initio theory. Chain-reactions could provide an alternative method for surface patterning. Now the chain reaction of CH 3 Cl molecules on a silicon surface has been observed to create lines that are made up of alternating CH 3 groups and Cl atoms. The reactions are propagated through surface-mediated charge-transfer and have been studied using microscopy and ab initio theory.

One-dimensional nanostructures at silicon surfaces have potential applications in nanoscale devices. Here we propose a mechanism of dipole-directed assembly for the growth of lines of physisorbed dipolar molecules. The adsorbate chosen was a halide, in preparation for the patterned imprinting of halogen atoms. Using scanning tunnelling microscopy, physisorbed 1,5-dichloropentane on Si(100)-2×1 was shown to self-assemble at room temperature into molecular lines that grew predominantly perpendicular to the Si-dimer rows. Line formation was triggered by the displacement of surface charge by the dipolar adsorbate. Experimental and simulated scanning tunnelling microscopy images were in agreement for a range of positive and negative bias voltages. The geometry of the physisorbed molecules and nature of their binding were evident from the scanning tunnelling microscopy images, as interpreted by scanning tunnelling microscopy simulation.

Solar-driven photocatalysis has attracted significant attention in water splitting, CO reduction and organic synthesis. The syntheses of valuable azo- and azoxyaromatic dyes via selective photoreduction of nitroaromatic compounds have been realised using supported plasmonic metal nanoparticles at elevated temperatures (≥90 °C); however, the high cost, low efficiency and poor selectivity of such catalyst systems at room temperature limit their application. Here we demonstrate that the inexpensive graphitic C N is an efficient photocatalyst for selective syntheses of a series of azo- and azoxy-aromatic compounds from their corresponding nitroaromatics under either purple (410 nm) or blue light (450 nm) excitation. The high efficiency and high selectivity towards azo- and azoxy-aromatic compounds can be attributed to the weakly bound photogenerated surface adsorbed H-atoms and a favourable N-N coupling reaction. The results reveal financial and environmental potential of photocatalysis for mass production of valuable chemicals.

Scanning Tunneling Microscopy (STM) has been used to study the physisorption and chemisorption behaviour for three simple organic haloalkanes; 1,5-Dichloropentane (DCP), Bromomethane (CH3Br) and Chloromethane (CH3Cl)) on Si(100)-2x1, at temperatures ranging from 270 K to room temperature. The results were interpreted by Density Functional Theory (DFT) performed by collaborators at McGill University and the University of Liverpool. Physisorbed molecules of DCP were found to self-assemble into stable lines aligned predominantly perpendicular to the Si-dimer-pair rows on the surface. A novel mechanism for line formation of Dichloropentane, termed, Dipole-Directed Assembly (DDA), was elucidated by DFT calculations. For CH 3Br three different patterns of dissociative attachment of reaction products (CH3 and Br/Cl) were observed, and assigned to three reaction pathways. These experimentally determined relative yields were used to obtain differences in reaction activation energy, ΔEa, between the reaction pathways. These, in turn, were compared with computed differences in reaction barriers, ΔEb, obtained ab initio for the same pathways by DFT. For CH3Cl, two single-molecule patterns of attachment were found, and a new reaction pathway for attaching CH3Cl in long chains of alternating CH3 and Cl was discovered. The mechanisms for chain growth were determined experimentally by examination of single molecular steps. This mechanism was explained ab initio by DFT to be the result of relative barrier heights for the possible chain-growth pathways.

Doping of silicon via phosphene exposures alternating with molecular beam epitaxy overgrowth is a path to Si:P substrates for conventional microelectronics and quantum information technologies. The technique also provides a new and well-controlled material for systematic studies of two-dimensional lattices with a half-filled band. We show here that for a dense (\\(n_s=2.8\\times 10^{14}\\)\\,cm\\(^{-2}\\)) disordered two-dimensional array of P atoms, the full field angle-dependent magnetostransport is remarkably well described by classic weak localization theory with no corrections due to interaction effects. The two- to three-dimensional cross-over seen upon warming can also be interpreted using scaling concepts, developed for anistropic three-dimensional materials, which work remarkably except when the applied fields are nearly parallel to the conducting planes.