Holli

Despite intensive research on photochemical activation of sol–gel metal oxide materials, the relatively long processing time and lack of deep understanding of the underlying chemical courses have limited their broader impact on diverse materials and applications such as thin-film electronics, photovoltaics, and catalysts. Here, in-depth studies on the rapid photochemical activation of diverse sol–gel oxide films using various spectroscopic and electrical investigations for the underlying physicochemical mechanism are reported. Based on the exhaustive chemical and physical analysis, it is noted that deep ultraviolet-promoted rapid film formation such as densification, polycondensation, and impurity decomposition is possible within 5 min via in situ radical-mediated reactions. Finally, the rapid fabrication of all-solution metal oxide thin-film-transistor circuitry, which exhibits stable and reliable electrical performance with a mobility of >12 cm² V⁻¹ s⁻¹ and an oscillation frequency of >650 kHz in 7-stage ring oscillator even after bending at a radius of <1 mm is demonstrated.

The general physicochemical mechanisms underlying photoactivated sol–gel reactions are described, with comprehensive chemical and structural analysis inducing rapid (<5 min) fabrication of various metal oxide films at low temperatures (<150 °C), and all-solution processed high-performance electronic devices and circuitry on ultrathin polymeric substrates are demonstrated. This will open new possibilities to prepare future electronic materials in a fast, scalable, and economic manner.

The 2D semiconductor MoS₂ in its mono- and few-layer form is expected to have a significant exciton binding energy of several 100 meV, suggesting excitons as the primary photoexcited species. Nevertheless, even single layers show a strong photovoltaic effect and work as the active material in high sensitivity photodetectors, thus indicating efficient charge carrier photogeneration. Here, modulation spectroscopy in the sub-ps and ms time scales is used to study the photoexcitation dynamics in few-layer MoS₂. The results suggest that the primary photoexcitations are excitons that efficiently dissociate into charges with a characteristic time of 700 fs. Based on these findings, simple suggestions for the design of efficient MoS₂ photovoltaic and photodetector devices are made.

Few-layer MoS₂ flakes are intermediates between conventional semiconductors and excitonic nanomaterials. By femtosecond optical pump–probe spectroscopy it is shown that photoexcitation creates excitons as the primary species. The excitons efficiently dissociate into charge carriers with a time constant of 700 fs, making few-layer MoS₂ an excellent candidate for efficient photodetectors and photovoltaic devices.

The front cover demonstrates the fabrication of sol–gel derived metal oxide electronic devices and circuits by low-temperature photochemical activation via in-situ radical-mediated reactions. On page 2807, M.-H. Yoon, S. K. Park, and colleagues show that the rapid photoactivation process enables the conversion of the sol–gel precursors into metal oxide electronic materials directly on ultra-flexible plastic substrates, which will serve as a general methodology in a rapid, scalable, and economic manner.

Copper-exchanged SSZ-13 is a very efficient material in the selective catalytic reduction of NO_x using ammonia (deNO_x-SCR) and characterizing the underlying distribution of copper sites in the material is of prime importance to understand its activity. The IR spectrum of NO adsorbed to divalent copper sites are modeled using ab initio molecular dynamics simulations. For most sites, complex multi-peak spectra induced by the thermal motion of the cation as well as the adsorbate are found. A finite temperature spectrum for a specific catalyst was constructed, which shows excellent agreement with previously reported data. Additionally these findings allow active and inactive species in deNO_x-SCR to be identified. To the best of our knowledge, this is the first time such complex spectra for single molecules adsorbed to single active centers have been reported in heterogeneous catalysis, and we expect similar effects to be important in a large number of systems with mobile active centers.

Theory and practice: The IR spectra of NO adsorbed on Cu centers in a copper-containing zeolite were modeled using molecular dynamics simulations. The spectra are complex, which is due to the thermal motions of the cations and the adsorbates, and are in excellent agreement with the experimental spectra.

Poly(triazine imides) intercalated with Li⁺ and X⁻ (PTI/X, X=Cl or Br), which are described widely as crystalline polymeric carbon nitrides, were synthesized in a facile manner by heating a mixture of melamine and LiX. This method has the advantages of low cost, scalable production, and high efficiency. Importantly, both PTI/Cl and PTI/Br exhibit an enhanced photocatalytic performance compared to conventional graphitic polymeric carbon nitride in the degradation of rhodamine B under visible-light irradiation because of their higher visible-light-harvesting ability and charge carrier separation efficiency.

Easy does it: Crystalline polymeric graphitic carbon nitrides with an enhanced visible-light-driven photocatalytic performance are prepared by heating a mixture of melamine and lithium halides.

The cover picture shows effective hydrogen production from an aqueous solution of ammonia-borane (NH₃-BH₃, AB) by bimetallic FeNi nanoparticles supported on CeO₂. In their Full Paper, K. Mori, T. Taga, and H. Yamashita show highly dispersed and partially oxidized amorphous FeNi NPs stabilized by strong interaction with the CeO₂ is active for the catalytic dehydrogenation of AB. The advantages of this catalytic system, such as the facile preparation method, free of noble metals, and high recyclability are particularly desirable for a hydrogen vector in terms of potential industrial application in fuel cells. The article highlighted by this cover can be found on p. 1285 ff. of Issue 8, 2015.

On the surface: The reaction kinetics of CO₂ photocatalytic reduction to formic acid on graphitic carbon nitride polymers can be promoted by surface organometallic chemistry. C.B.=Conduction band, V.B.=Valance band, D=electron donor.