Chemisorption Induced Formation of Biphenylene Dimer on Surfaces

We report an example that demonstrates the clear interdependence between surface-supported reactions and molecular adsorption configurations. Two biphenyl-based molecules with two and four bromine substituents, i.e. 2,2-dibromo-biphenyl (DBBP) and 2,2,6,6-tetrabromo-1,1-biphenyl (TBBP), show completely different reaction pathways on a Ag(111) surface, leading to the selective formation of dibenzo[e,l]pyrene and biphenylene dimer, respectively. By combining low-temperature scanning tunneling microscopy, synchrotron radiation photoemission spectroscopy, and density functional theory calculations, we unravel the underlying reaction mechanism. After debromination, a bi-radical biphenyl can be stabilized by surface Ag adatoms, while a four-radical biphenyl undergoes spontaneous intramolecular annulation due to its extreme instability on Ag(111). Such different chemisorption-induced precursor states between DBBP and TBBP consequently lead to different reaction pathways after further annealing. In addition, using bond-resolving scanning tunneling microscopy and scanning tunneling spectroscopy, we determine the bond length alternation of biphenylene dimer product with atomic precision, which contains four-, six-, and eight-membered rings. The four-membered ring units turn out to be radialene structures

Chemisorption-induced formation of biphenylene dimer on Ag(111)

We report an example that demonstrates the clear interdependence between surface-supported reactions and molecular-adsorption configurations. Two biphenyl-based molecules with two and four bromine substituents, i.e., 2,2′-dibromobiphenyl (DBBP) and 2,2′,6,6′-tetrabromo-1,1′-biphenyl (TBBP), show completely different reaction pathways on a Ag(111) surface, leading to the selective formation of dibenzo[e,l]pyrene and biphenylene dimer, respectively. By combining low-temperature scanning tunneling microscopy, synchrotron radiation photoemission spectroscopy, and density functional theory calculations, we unravel the underlying reaction mechanism. After debromination, a biradical biphenyl can be stabilized by surface Ag adatoms, while a four-radical biphenyl undergoes spontaneous intramolecular annulation due to its extreme instability on Ag(111). Such different chemisorption-induced precursor states between DBBP and TBBP consequently lead to different reaction pathways after further annealing. In addition, using bond-resolving scanning tunneling microscopy and scanning tunneling spectroscopy, we determine with atomic precision the bond-length alternation of the biphenylene dimer product, which contains 4-, 6-, and 8-membered rings. The 4-membered ring units turn out to be radialene structures.This work was financially supported by the National Natural Science Foundation of China (21773222, 51772285, 21872131, U1732272, and U1932214), the National Key R&D Program of China (2017YFA0403402, 2017YFA0403403, and 2019YFA0405601), and Users with Excellence Program of Hefei Science Center CAS (2020HSC-UE004). The work at Washington State University was primarily funded through the National Science Foundation CAREER program under Contract no. CBET-1653561. This work was also partially funded by the Joint Center for Deployment and Research in Earth Abundant Materials (JCDREAM) in Washington State. Most of the computational resources were provided by the Kamiak HPC under the Center for Institutional Research Computing at Washington State University. This research also used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under Contract no. DE-AC02-05CH11231. The work at Donostia International Physics Center was primarily funded through the Juan de la Cierva Grant (no. FJC2019-041202-I) from Spanish Ministry of Economy and Competitiveness, the European Union’s Horizon 2020 Research and Innovation program (Marie Skłodowska-Curie Actions Individual Fellowship (no. 101022150), and the MCIN/AEI/ 10.13039/501100011033 (Grant no. PID2019-107338RB-C63).Peer reviewe

MOF-Derived Ultrathin Cobalt Phosphide Nanosheets as Efficient Bifunctional Hydrogen Evolution Reaction and Oxygen Evolution Reaction Electrocatalysts

The development of a highly efficient and stable bifunctional electrocatalyst for water splitting is still a challenging issue in obtaining clean and sustainable chemical fuels. Herein, a novel bifunctional catalyst consisting of 2D transition-metal phosphide nanosheets with abundant reactive sites templated by Co-centered metal−organic framework nanosheets, denoted as CoP-NS/C, has been developed through a facile one-step low-temperature phosphidation process. The as-prepared CoP-NS/C has large specific surface area and ultrathin nanosheets morphology providing rich catalytic active sites. It shows excellent electrocatalytic performances for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic and alkaline media, with the Tafel slopes of 59 and 64 mV/dec and a current density of 10 mA/cm2 at the overpotentials of 140 and 292 mV, respectively, which are remarkably superior to those of CoP/C, CoP particles, and comparable to those of commercial noble-metal catalysts. In addition, the CoP-NS/C also shows good durability after a long-term test

On-Surface Synthesis

On‐surface synthesis represents a chemical approach whereby molecular building blocks holding adequate functional groups are dosed onto surfaces that support or even drive their covalent linkage. The new environment created by the surface confinement and the frequent lack of solvents (most commonly being performed under vacuum conditions) makes this approach fully complementary to conventional chemistry. Among the many differences that this brings, one can find original reaction mechanisms, as well the absence of solubility or chemical instability problems when working under vacuum, each opening new doors to the synthesis of novel materials. Examples thereof include the linear polymerization of alkanes, access to an increasingly large pool of differently structured graphene nanoribbons with atomic precision, or elusive molecules like higher acenes or triangulene

MIL-100(Al) Gels as an Excellent Platform Loaded with Doxorubicin Hydrochloride for pH-Triggered Drug Release and Anticancer Effect

Slow and controlled release systems for drugs have attracted increasing interest recently. A highly efficient metal-organic gel (MOGs) drug delivery carrier, i.e., MIL-100(Al) gel, has been fabricated by a facile, low cost, and environmentally friendly one-pot process. The unique structure of MIL-100(Al) gels has led to a high loading efficiency (620 mg/g) towards doxorubicin hydrochloride (DOX) as a kind of anticancer drug. DOX-loaded MOGs exhibited high stability under physiological conditions and sustained release capacity of DOX for up to three days (under acidic environments). They further showed sustained drug release behavior and excellent antitumor effects in in vitro experiments on HeLa cells, in contrast with the extremely low biotoxicity of MOGs. Our work provides a promising way for anticancer therapy by utilizing this MOGs-based drug delivery system as an efficient and safe vehicle

Effect of Different Combustion Modes on the Performance of Hydrogen Internal Combustion Engines under Low Load

Detailed hydrogen–air chemical reaction mechanisms were coupled with the three-dimensional grids of an experimental hydrogen internal combustion engine (HICE) to establish a computational fluid dynamics (CFD) combustion model based on the CONVERGE software. The effects of different combustion modes on the combustion and emission characteristics of HICE under low load were studied. The simulation results showed that, with the increase in excess hydrogen, the equivalent combustion and excessive hydrogen combustion modes with medium-cooled exhaust gas recirculation (EGR) dilution could improve the intensity of the in-cylinder combustion of HICE, increase the peak values of pressure and temperature in the cylinder, and then improve the indicated thermal efficiency of HICE under low load. However, larger excessive hydrogen combustion could weaken the improvement in performance; therefore, the performance of HICE could be comprehensively improved by the adoption of excessive hydrogen combustion with a fuel–air ratio below 1.2 under low load. The obtained conclusions indicate the research disadvantages in the power and emission performances of HICE under low load, and they are of great significance for the performance optimization of HICE. Furthermore, a control strategy was proposed to improve the stability of HICE under low load

Low-Temperature Dissociation of CO₂ on a Ni/CeO₂(111)/Ru(0001) Model Catalyst

The adsorption of CO₂ on CeO_2‑<i>x</i>(111) and Ni/CeO_2‑<i>x</i>(111)/Ru­(0001) surfaces has been studied with reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). On the maximal-oxidized CeO₂(111) surface physisorbed linear CO₂ and a CO₂^– species are identified at 97 K. The reduced CeO_2‑<i>x</i>(111) surface exhibits higher reactivity toward adsorbed CO₂, which leads to higher coverages of CO₂^– and promotes CO₂ dissociating into CO and an active oxygen species at higher temperature, reoxidizing the reduced CeO_2‑<i>x</i>(111) films. Deposition of Ni on the maximal-oxidized CeO₂ thin films leads to slight reduction of ceria films. Adsorption of CO₂ on Ni/CeO_2‑<i>x</i>(111) films causes dissociation at 97 K and leads to Ni-CO adsorbates plus partial oxidation of Ni nanoparticles. This process is inhibited when Ni nanoparticles on CeO₂ are fully oxidized. In contrast to the results reported for CO₂ adsorption on Ni single-crystals, where the dissociation temperature was found to be higher than 240 K, the much lower dissociation temperature (∼97 K) for CO₂ on Ni nanoparticles supported on CeO₂(111) suggests that the Ni/CeO₂ catalyst exhibits high activity toward CO₂ activation