Dynamic manipulation of crystallization is pivotal to the quality of polycrystalline films. A molten-salt-assisted crystallization (MSAC) strategy is presented to improve grain growth of the all-inorganic perovskite films. Compared with the traditional solvent annealing, MSAC enables more intensive mass transfer by means of convection and diffusion, which is beneficial to the interaction among the precursor colloids and to inducing in-plane growth of perovskite grains, resulting in the formation of high-quality perovskite films with suppressed pinhole and crack formation. Additionally, the introduction of molten salt alters the intermediate phases, and thus changes the crystallization pathways by reducing the energy barrier to produce films with desired optical and electrical properties. As a result, the MSAC strategy endows the devices with champion steady-state output efficiency of 19.83% and open-circuit voltage (Voc ) as high as 1.2 V, among the highest for this type of solar cell, thanks to its effectively reduced Voc deficit.

Molten-Salt-Assisted CsPbI3 Perovskite Crystallization for Nearly 20%-Efficiency Solar Cells

A new composite of the metal-azolate framework (MAF-6) and phosphomolybdic acid (PMA), named PMA(x)@MAF-6, was prepared. Well-dispersed (size: ∼4 nm) Mo2N, on porous carbon, was prepared without external nitrogen sources firstly via carbonization of the PMA(x)@MAF-6. The prepared catalyst was applied in oxidative desulfurization (ODS) with H2O2 as a greenoxidant and showed remarkable performance. A selected catalyst Mo2N@C-3 had the highest turnover frequency (30 h-1, around 2–3 times of the best catalyst so far) with the lowest activation energy (27.8 kJ·mol−1) in ODS (with H2O2) among any molybdenum-based catalysts. The ODS over Mo2N@C was explained by a non-radical mechanism via active Mo-peroxo species. Moreover, the high activity of the catalyst is partly because of the contribution of nitrogen in Mo2N. The studied catalyst could be easily recycled by solvent washing. Therefore, Mo2N, especially supported on carbon (like Mo2N@C), could be firstly suggested as a promising catalyst in ODS.

Molybdenum nitride@porous carbon, derived from phosphomolybdic acid loaded metal-azolate framework-6: A highly effective catalyst for oxidative desulfurization

Plasmon-free surface-enhanced Raman scattering (SERS) substrates have attracted tremendous attention for their abundant sources, excellent chemical stability, superior biocompatibility, good signal uniformity, and unique selectivity to target molecules. Recently, researchers have made great progress in fabricating novel plasmon-free SERS substrates and exploring new enhancement strategies to improve their sensitivity. This review summarizes the recent developments of plasmon-free SERS substrates and specially focuses on the enhancement mechanisms and strategies. Furthermore, the promising applications of plasmon-free SERS substrates in biomedical diagnosis, metal ions and organic pollutants sensing, chemical and biochemical reactions monitoring, and photoelectric characterization are introduced. Finally, current challenges and future research opportunities in plasmon-free SERS substrates are briefly discussed.

The origin of ultrasensitive SERS sensing beyond plasmonics

Semiconductor-based surface enhanced Raman spectroscopy (SERS) platforms take advantage of the multifaceted tunability of semiconductor materials to realize specialized sensing demands in a wide range of applications. However, until quite recently, semiconductor-based SERS materials have generally exhibited low activity compared to conventional noble metal substrates, with enhancement factors (EF) typically reaching 103, confining the study of semiconductor-based SERS to purely academic settings. In recent years, defect engineering has been proposed to effectively improve the SERS activity of semiconductor materials. Defective semiconductors can now achieve noble-metal-comparable SERS enhancement and exceedingly low, nano-molar detection concentrations towards certain molecules. The reason for such success is that defect engineering effectively harnesses the complex enhancement mechanisms behind the SERS phenomenon by purposefully tailoring many physicochemical parameters of semiconductors. In this perspective, we introduce the main defect engineering approaches used in SERS-activation, and discuss in depth the electromagnetic and chemical enhancement mechanisms (EM and CM, respectively) that are influenced by these defect engineering methods. We also introduce the applications that have been reported for defective semiconductor-based SERS platforms. With this perspective we aim to meet the imperative demand for a summary on the recent developments of SERS material design based on defect engineering of semiconductors, and highlight the attractive research and application prospects for semiconductor-based SERS. 

/pdf/defect-engineering-in-semiconductor-based-sers-9mcwh0c9.pdf

Defect engineering in semiconductor-based SERS

In-situ design of porous vanadium nitride@carbon nanobelts: A promising material for high-performance asymmetric supercapacitors

Molybdenum nitride (δ–MoN) is an important functional material due to its impressive catalytic, energy storage, and superconducting properties. However, the synthesis of δ–MoN usually requires extremely harsh conditions; thus, the insight into δ−MoN is far behind that of oxides and sulfides of molybdenum. Herein, we report that ultrathin δ−MoN nanosheets are prepared at 270 °C and 12 atm. WN, VN, and TiN nanosheets are also synthesized by this method. The δ−MoN nanosheets show strong surface plasmon resonance, high conductivity, excellent thermal and chemical stability as well as a high photothermal conversion efficiency of 61.1%. As a promising surface enhanced Raman scattering substrate, the δ−MoN nanosheets exhibit a 8.16 × 106 enhanced factor and a 10−10 level detection limit for polychlorophenol. Molybdenum nitride is promising for catalysis, energy storage and Raman scattering, but it is synthesized under harsh conditions. Here the authors synthesize highly crystalline molybdenum nitride nanosheets using a relatively mild, non-aqueous solvothermal approach that can be extended to other nitrides.

/pdf/low-temperature-synthesis-of-plasmonic-molybdenum-nitride-5gk3q76xzr.pdf

Low temperature synthesis of plasmonic molybdenum nitride nanosheets for surface enhanced Raman scattering.

Although mesocrystals with ordered building units have great potential in many fields because of the large amount of organic molecules used as structure-directing agents during their synthesis process, severe matrix interference makes their surface-enhanced Raman scattering (SERS) properties rarely understood. Herein, a rapid (20 s) and green microwave synthetic route is developed for the 100 g scale preparation of plasmonic W18O49 mesocrystals with no additives. The ultrathin (1.5 nm) and oxygen vacancy-rich W18O49 nanowires as a building unit greatly improve the interface charge transfer, while the periodic mesocrystal structure significantly enhances the localized surface plasmon resonance effect and creates high-density electromagnetic hot spots among the nanowires. An outstanding enhancement factor of 1.2 × 107 and an ultralow detectable limit of 10-11 M are achieved, and the single-molecule imaging is also realized on this mesocrystal-based SERS substrate. Moreover, the relative standard deviation of the fabricated large-area (2.2 cm2) SERS substrate is only 6.8%.

Highly Sensitive W18O49 Mesocrystal Raman Scattering Substrate with Large-Area Signal Uniformity.

Transition metal nitrides have been widely studied due to their high electrical conductivity and excellent chemical stability. However, their preparation traditionally requires harsh conditions because of the ultrahigh activation energy barrier they need to cross in nucleation. Herein, we report three-dimensional porous VN, MoN, WN, and TiN with high surface area and porosity that are prepared by a general and mild molten-salt route. Trace water is found to be a key factor for the formation of these porous transition metal nitrides. The porous transition metal nitrides show hydrophobic surface and can adsorb a series of organic compounds with high capacity. Among them, the porous VN shows strong surface plasmon resonance, high conductivity, and a remarkable photothermal conversion efficiency. As a new type of corrosion- and radiation-resistant surface-enhanced Raman scattering substrate, the porous VN exhibits an ultrasensitive detection limit of 10−11 M for polychlorophenol. Fabrication of transition metal nitrides generally requires harsh conditions due to the high activation energy barrier for nucleation. Here, the authors report a mild molten-salt route for the synthesis of three-dimensional porous metal nitrides, VN, MoN, WN, and TiN.

/pdf/general-molten-salt-route-to-three-dimensional-porous-2kxz9i80oc.pdf

Haomin Guan

Papers

Low temperature synthesis of plasmonic molybdenum nitride nanosheets for surface enhanced Raman scattering.

Highly Sensitive W18O49 Mesocrystal Raman Scattering Substrate with Large-Area Signal Uniformity.

General molten-salt route to three-dimensional porous transition metal nitrides as sensitive and stable Raman substrates

Vanadium dioxide nanostructures with remarkable surface-enhanced Raman scattering activity