[en] We demonstrated CdS quantum dot-sensitized solar cells (QDSSCs) based on anatase TiO₂ nanosheets with exposed {001} and {100} facets. Under the illumination of one Sun (AM 1.5 G, 100 mW cm⁻²), the photovoltaic conversion efficiencies were 2.29% for a QDSSC based on {001}-TiO₂ nanosheets, 2.18% for a QDSSC based on {100}-TiO₂ nanosheets, and 1.46% for a QDSSC based on commercial Degussa P25. It was found that the exposed highly reactive facets of TiO₂ nanosheets had a remarkable influence on the QDSSCs due to their better adsorption abilities for QDs, leading to the high short current density and the enhanced photovoltaic performance. (paper)

[en] Doping a graphene sheet with different atoms is a promising method for tuning its electronic properties. We report a first-principle investigation on the electronic properties of N, B, S, Al, Si or P doped graphene. It is revealed that the doped graphene can show an interesting physical regularity, which can be described by a simple 3N rule: a doped graphene has a zero gap or a neglectable gap at the Dirac point when its primitive cell is 3N × 3N (N is an integer), otherwise there is a gap tunable by the dopant concentration. This unique 3N rule provides a useful guideline for the design of doped graphene for electronic applications. (paper)

[en] Electrochemical study of the decorated Pt-Au catalyst synthesized by Cu underpotential deposition (UPD)-Pt redox replacement technique has been conducted in this work. The parameters affecting the Cu UPD on Au/C nanoparticles in sulfuric acid electrolyte, including the UPD potential, deposition time and potential sweep rate, were investigated in detail. Anode stripping method was used to calculate the charge of the deposited Cu adlayers. Results showed that Pt-Au catalyst prepared by this UPD-redox replacement approach is not a core-shell structure but a decorated structure. A series of decorated Pt-Au/C catalysts with various Pt coverages were synthesized and examined for formic acid oxidation (FAO). It is found that the specific activity of Pt atoms increases with the decrease of Pt surface coverage on Au. Life test showed that better stability was pertained for this decorated Pt-Au/C catalyst compared to Pt/C towards FAO

[en] Highly active Pt-decorated Au nanoparticles on carbon support with Pt:Au mole ratio ranging from 1:10 to 1:2 was successfully synthesized based on successive reduction strategy. The successful formation of this structure was suggested by transmission electron microscopy, UV-vis and voltammetry analyses. The electrocatalytic activity of this decorated structure toward formic acid oxidation surprisingly increases despite the low amount of Pt being used. At 0.1 V, the specific activity of PtAu/C with Pt/Au mole ratio 1:8 was more than one order of magnitude higher than the conventional Pt/C. The enhancement was attributed to the less Pt ensemble sites that the decorated structure possesses (ensemble effect) and the increase in the Pt atom reactivity on Au nanocrystal. The formic acid oxidation mechanism on this decorated structure was also elucidated using electrochemical impedance spectroscopy technique. It is proposed that besides the dehydrogenation reaction pathway happening on clean Pt sites, the reactive intermediate i.e. formate species could also be oxidized by the adsorbed water species on Pt at higher potential.

[en] Highlights: • MPPAs have an excellent adsorption capacity for CO₂. • DFT and GCMC methods were used to investigate the substituent groups effect on MPPAs. • MPPA-SO₃H exhibits excellent potential for separating CO₂ from the CO₂/N₂ mixture. To improve the performance of nitrogen-rich melamine-based porous polyamides (MPPAs) for CO₂ adsorption and separation, density functional theory and grand canonical Monte Carlo simulations were conducted to study the influence of the substitution position and functional groups. First, the fluorine atom was employed to assess the effect of the substitution position. The simulations revealed the best substitution position in the MPPA framework. Four oxygen-containing substituents were then introduced to further improve the CO₂ selectively. The simulations revealed that sulfonic acid group modified MPPA has the greatest potential CO₂ adsorption capacity and CO₂/N₂ selectivity.

[en] Highlights: • Fourteen Salen–M were screened to find the best one for the separation of C₂H₂. • Salen–Mn (II) showed the largest adsorption energy difference of C₂H₂ and C₂H₄. • 3D–Salen–COF–Ni (II) showed an outstanding C₂H₂/C₂H₄ selectivity. C₂H₄ is an essential industrial organic chemical. Efficiently removing C₂H₂ from C₂H₂/C₂H₄ mixtures is a significant challenge. Introducing a Salen–metal unit into porous materials is a practical way to separate gas mixtures. In this work, we used density functional theory (DFT) and grand canonical Monte Carlo (GCMC) method investigated the performances of different Salen–metal complexes in separating C₂H₂ from C₂H₄. The gas adsorption energies of fourteen Salen–metal complexes were systemically studied. Two complexes, Salen–Mn (II) and Salen–Ni (II), exhibited superior adsorptive selectivity in capturing C₂H₂ and C₂H₄. This result will be helpful for developing porous materials for the efficient removal of C₂H₂ from C₂H₂/C₂H₄ mixtures.

[en] Hybrid Pt-CdSe nanocomposite was fabricated by a two-step chemical route. Cadmium selenide (CdSe) quantum rods (QRs) were prepared by a one-pot approach with tunable size. After ligand exchange, CdSe QRs were loaded with monodisperse 1.9 nm Pt nanopaticles in aqueous solution. Transmission electron microscopy (TEM) revealed the morphology of the Pt-CdSe nanostructure, and the decreased photoluminescence (PL) intensity demonstrated that electron and hole separation can be enhanced after loading Pt on CdSe QRs. X-ray photoelectron energy spectrum (XPS) was applied to confirm the existence of Pt and detect the Pt mass concentration of 3%.

[en] Lead-based perovskite nanocrystals (NCs) have outstanding optical properties and cheap synthesis conferring them a tremendous potential in the field of optoelectronic devices. However, two critical problems are still unresolved and hindering their commercial applications: one is the fact of being lead-based and the other is the poor stability. Lead-free all-inorganic perovskite Cs_3Bi_2X_9 (X=Cl, Br, I) NCs are synthesized with emission wavelength ranging from 400 to 560 nm synthesized by a facile room temperature reaction. The ligand-free Cs_3Bi_2Br_9 NCs exhibit blue emission with photoluminescence quantum efficiency (PLQE) about 0.2 %. The PLQE can be increased to 4.5 % when extra surfactant (oleic acid) is added during the synthesis processes. This improvement stems from passivation of the fast trapping process (2-20 ps). Notably, the trap states can also be passivated under humid conditions, and the NCs exhibited high stability towards air exposure exceeding 30 days. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] Thermally activated delayed fluorescence (TADF) is generally observed in solid-state organic molecules or metal-organic complexes. However, TADF in all-inorganic colloidal nanocrystals (NCs) is rare. Herein, we report the first colloidal synthesis of an air-stable all-inorganic lead-free Cs${}_2$ZrCl${}_6$ perovskite NCs. The Cs${}_2$ZrCl${}_6$ NCs exhibit long-lived triplet excited state (138.2 µs), and feature high photoluminescence (PL) quantum efficiency (QY=60.37 %) due to TADF mechanism. The emission color can be easily tuned from blue to green by synthesizing the mixed-halide Cs${}_2$ZrBr${}_x$Cl${}_{6-<!--\; ???\; -->x}$ (0≤x≤1.5) NCs. Femtosecond transient absorption and temperature dependent PL measurements are performed to clarify the emission mechanism. In addition, Bi${}^{3+}$ ions are successfully doped into Cs${}_2$ZrCl${}_6$ NCs, which further extends the PL properties. This work not only develops a new lead-free halide perovskite NCs for potential optoelectronic applications, but also offers unique strategies for developing new inorganic phosphors. (© 2020 Wiley‐VCH GmbH)

[en] Zero-dimensional (0D) lead-free perovskites have unique structures and optoelectronic properties. Undoped and Sb-doped all inorganic, lead-free, 0D perovskite single crystals $A_{2}InC{l}_5(H_{2}O)$ (A=Rb, Cs) are presented that exhibit greatly enhanced yellow emission. To study the effect of coordination $H_{2}O$, Sb-doped $A_{3}InC{l}_6$ (A=Rb, Cs) are also synthesized and further studied. The photoluminescence (PL) color changes from yellow to green emission. Interestingly, the photoluminescence quantum yield (PLQY) realizes a great boost from <2 % to 85-95 % through doping $S{b}^{3+}$. We further explore the effect of $S{b}^{3+}$ dopants and the origin of bright emission by ultrafast transient absorption techniques. Furthermore, Sb-doped 0D rubidium indium chloride perovskites show excellent stability. These findings not only provide a way to design a set of new high-performance 0D lead-free perovskites, but also reveal the relationship between structure and PL properties. (© 2020 Wiley‐VCH Verlag GmbH and Co. KGaA, Weinheim)