Inherent poor stability of perovskite nanocrystals (NCs) is the main impediment preventing broad applications of the materials. Here, TiO 2 shell coated CsPbBr 3 core/shell NCs are synthesized through the encapsulation of colloidal CsPbBr 3 NCs with titanium precursor, followed by calcination at 300 °C. The nearly monodispersed CsPbBr 3 /TiO 2 core/shell NCs show excellent water stability for at least three months with the size, structure, morphology, and optical properties remaining identical, which represent the most water-stable inorganic shell passivated perovskite NCs reported to date. In addition, TiO 2 shell coating can effectively suppress anion exchange and photodegradation, therefore dramatically improving the chemical stability and photostability of the core CsPbBr 3 NCs. More importantly, photoluminescence and (photo)electrochemical characterizations exhibit increased charge separation efficiency due to the electrical conductivity of the TiO 2 shell, hence leading to an improved photoelectric activity in water. This study opens new possibilities for optoelectronic and photocatalytic applications of perovskites-based NCs in aqueous phase.

The introduction of dopants plays a key role in the physical properties of semiconductors for optoelectronic applications. However, doping is generally challenging for nanocrystals (NCs), especially for two-dimensional (2D) NCs, due to the self-annealing effect and high surface energies required for dopant addition. Here, we report an efficient doping strategy for Mn-doped 2D CsPbCl3 (i.e., Mn:CsPbCl3) nanoplatelets (NPLs) through a postsynthetic solvothermal process. While the original lightly doped 2D Mn:CsPbCl3 NPLs were obtained from growth doping, higher Mn doping efficiencies were achieved through diffusion doping under pressure-mediated solvothermal conditions, resulting in enhanced Mn photoluminescence (PL). Surprisingly, a new CsMnCl3 phase with complete dopant substitution by spinodal decomposition was observed with extended solvothermal treatment, which is confirmed by powder X-ray diffraction, X-ray absorption  fine structure, and electron paramagnetic resonance. Compared with Mn:CsPbCl3 NPLs, the pure CsMnCl3 NPLs give rise to shorter Mn PL lifetime, which is consistent with the short Mn–Mn distance within CsMnCl3 NPLs. This work provides an efficient strategy for doping inside NCs as well as new insights on the dopant concentration-dependent structural and optical properties of perovskite NCs.

Manganese-doped cesium lead chloride (CsPbCl3) perovskite nanocrystals (NCs) have recently garnered attention because of their unique magneto-optical properties, giving them potential in a variety of optoelectronic applications. One common method to dope Mn2+ into host CsPbCl3 NCs is through a postsynthetic ion exchange reaction. However, most ion exchange strategies utilize a Mn2+-containing precursor solution, which adds limitations to the reaction due to compatibility and stability issues. Here, we report a new method of cation exchange in CsPbCl3 NCs where Pb2+ cations are partially replaced by Mn2+ cations using a solid Mn2+–precursor source, resulting in a quasi-solid-solid cation exchange at ambient conditions. The ability to perform the cation exchange without the addition of any external solvents allowed for a systematic study on the NC doping. The reaction takes place at the interface between the Mn2+-containing solid precursor and the NC surface. Electron paramagnetic resonance and optical characterizations including a shortened Mn2+ photoluminescence lifetime immediately following the exchange indicated initial heterogeneous doping with the Mn2+ dopants localized on the NC surface. Spatial distribution of dopants within the NCs is observed by inward diffusion over time. Additionally, dopant concentration can be controlled through engineering starting ligand compositions, which not only changes the ligands present at the Mn2+–precursor–NC interface but also leads to varying degrees of precursor activation. This study not only provides a clean and facile doping method without the need for additional solvents but also a cation exchange strategy which can be closely studied to improve the understanding of doping processes at the molecular level in perovskite NC systems.

Selective cleavage of C−C bonds can be a valuable tool for various applications including polymer degradation and biomass utilization. Performing chemical transformations involving C−C bond cleavage steps under mild conditions and ambient temperature remains challenging due to the high dissociation energies of the C−C bond. This fundamental challenge can be solved by coupling a dye-sensitized photoelectrochemical cell (DSPEC) system, that generally targets the water splitting reaction, with a hydrogen atom transfer (HAT) mediator (HAT-DSPEC). Here, we report the solar-driven selective cleavage of the C(aryl)− C(alkyl) σ-bond in lignin at ambient temperature using an HAT-DSPEC under redox-neutral conditions. The photocatalyst (bis-2,2′-bipyridine)(2,2′-bipyridine-4,4′-dicarboxylic acid)Ru(II) (RuC) adsorbed onto a TiO 2 nanorod array with the length of ∼1.6 μm and a rod diameter of 100 nm atop fluorine-doped tin oxide (FTO|TiO 2 NRAs|RuC) film was prepared and investigated with an HAT mediator, 4-acetamido 2,2,6,6tetramethylpiperidine-1-oxyl (ACT), in solution. Photophysical and electrochemical studies of RuC and ACT with a lignin model compound, 1-(4-hydroxy-3,5-dimethoxyphenyl)-2-(2-methoxyphenoxy) propane-1,3-diol (LMC) reveal that the metal-toligand charge transfer (MLCT) excited states from the RuC are efficiently quenched in the presence of ACT with LMC. The HAT-DSPEC photoanode, containing the surface-bound photocatalyst RuC at the photoanode with ACT and LMC in solution, sustained an excellent photocurrent density, significantly outperforming that with the photocatalyst RuC alone. Moreover, the chemoselective cleavage of the C(aryl)−C(alkyl) bond in the LMC at the ambient temperature was demonstrated in the HAT-DSPEC system with a remarkable photocatalytic turnover number (>3000) leading to excellent selectivity (>90%) of C−C bond cleavage under AM1.5G irradiation (1 sun, 100 mW cm −2 ). These results were obtained over short reaction times and mild, redox-neutral reaction conditions without the need for extended reaction time (e.g., >24 h) or high temperature that is typical of homogeneous catalytic systems. This is the first report to demonstrate that an HAT-DSPEC can serve as a viable method for performing visible-light-driven selective C−C bond cleavage at ambient temperature.

Shape control is critical and offers an efficient way to tune the properties of nanocrystals (NCs). Here we present the growth of two-dimensional (2-D) all-inorganic CsPbX3 (X = Cl, Br, I) perovskite NCs through the assembly of corresponding 1-D nanorods (NRs) under solvothermal conditions. Both 2-D CsPbX3 perovskite nanoplatelets (NPLs) and nanosheets (NSs) with a wide lateral size range from ∼100 nm to ∼1 μm and thickness of a few unit cells can be obtained by the control of the solvothermal reaction time. The present work provides a general strategy for rational fabrication of 2-D CsPbX3 (X = Cl, Br, I) perovskite NCs without the assistance of anion exchange. The obtained fluorescent 2-D all-inorganic perovskite NCs have great potential in practical photovoltaic applications.

The ability to dope transition-metal ions into semiconductor nanocrystals (NCs) allows for the introduction and exploitation of new extrinsic properties in the original intrinsic material. Although the synthesis of doped zero-dimensional quantum dots and one-dimensional nanorods/nanowires has been widely reported, transition-metal ion-doped two-dimensional (2D) NCs have been less explored. In this study, we developed a one-pot synthesis of Mn 2+ -doped 2D CdS (i.e., Mn:CdS) nanoplatelets (NPLs). Successful Mn doping inside the CdS NPL lattice was confirmed by electron paramagnetic resonance and X-ray diffraction measurements. Surprisingly, only CdS photoluminescence (PL), without contribution from Mn PL, was observed in the Mn:CdS NPLs, regardless of Mn doping concentration. To address the issue of poor thermal stability and improve the optical properties of the 2D Mn:CdS NPLs, we synthesized ZnS shell-passivated Mn:CdS/ZnS core/shell NPLs using a single-source shelling precursor method, which allows for ZnS surface passivation of NPLs at relatively low temperatures, while being thermally adaptable to ensure minimal NPL degradation. An extremely large exciton red shift (∼420 meV), upon ZnS shell passivation, was observed because of the increased effective thickness of the CdS core NPLs. Steady-state and time-resolved emission measurements indicate that the host−dopant energy-transfer efficiency and Mn−Mn interactions within the 2D Mn:CdS/ZnS core/shell NPLs can be fine-tuned via the dopant concentration, resulting in an intense Mn PL as well as tunable dual-band emission from the host NPLs and Mn dopants. Magnetic measurements indicate intrinsic spin states in the 2D NPLs and complex magnetic interactions at high doping concentrations, including antiferromagnetic exchange between dopants and possible dopant−surface state interaction.

Objectives: To gain a better understanding of electronic cigarette (e-cigarette) use behavior and experience among adult e-cigarette users, with the goal of informing development of future e-cigarette use measures. Methods: Between August and October 2014 six focus groups were conducted in Seattle. Participants (63% male; 60% >35 years old; 60% White): e-cigarette users who used combustible tobacco products either currently or in the past. E-cigarette discussion topics covered: their daily use pattern (eg, frequency), product-related characteristics (eg, nicotine levels), and perceptions about health risks and benefits. Results: Participants' descriptions of daily use were so varied that no common "unit" of a "session" easily summarized frequency or quantity of typical e-cigarette use. Most users had difficulty in tracking their own use. Participants reported nicotine craving relief when using e-cigarettes, but described e-cigarettes use as less satisfying than combustible cigarettes. Valued characteristics included "ready availability" and the possibility of using indoors. A unique aspect of the e-cigarette use experience is the option of adding flavors and having the ability to exhale "big clouds" of vapor/aerosol. Most perceived e-cigarettes as a better and safer alternative to conventional cigarettes, yet still sought further information about health consequences and safety of e-cigarettes from trusted sources. Conclusions: E-cigarettes users are far from homogeneous in their behavior and motivation for adopting e-cigarettes. A range of use patterns arising from both hedonic and utilitarian factors, along with product characteristics (eg, variable nicotine levels and flavors) extending beyond those of conventional cigarettes, suggest that new, specific e-cigarette use measures must be developed. Implications: The current study provides timely information on adult e-cigarette use behavior, which is a crucial step in measuring this new phenomenon and assessing the risks associated with using e-cigarette products. Our findings reveal that vaping is not a mere replacement for combustible cigarette smoking and that many users of e-cigarettes enjoy product characteristics such as flavors and "clouds" that are unavailable in combustible cigarettes. Therefore, commonly available cigarette smoking measures are not well suited to measurement of e-cigarette use behavior, and indication that new measures need to be developed to accurately track e-cigarette use.

A family of DyXM(12-MC-4) compounds were synthesized and magnetically characterized (X = salicylate, acetate, benzoate, trimethylacetate, M = Na or K). The bridging ligands were systematically varied while keeping the remainder of the MC-geometry constant. The type of monovalent cation, necessary for charge balance, was also altered. The dc magnetization and susceptibility of all compounds were similar across the series. Regardless of the identity of the countercation, the Dy(Hsal)M 12-MC-4 compounds were the only compounds to show frequency-dependent ac magnetic susceptibility, a hallmark of single-molecule magnetism. This indicates that the nature of the bridging ligand in the 12-MC-4 compounds strongly affects the out-of-phase magnetic properties. The SMM behavior appears to correlate with the pK of the bridging ligand.