Growth of 1D Nanorod Perovskite for Surface Passivation in FAPbI3 Perovskite Solar Cells.

The regulation of perovskite crystallization and nanostructure have revolutionized the development of high-performance perovskite solar cells (PSCs) in recent years. Yet the problem of stably passivating perovskite surface defects remains perplexing. The 1D perovskites possess superior physical properties compared with bulk crystals, such as excellent moisture stability, self-healing property, and surface defects passivation. Here, 4-chlorobenzamidine hydrochloride (CBAH) is developed as spacer to form orientationally crystallized nanorod-like 1D perovskite on the top surface of 3D perovskite for surface passivation of FAPbI3 perovskite. Further structure characterizations indicate the coexistence of 1D-3D hybrid perovskite lattices in nanorod-like perovskite passivation layer, which regulates the crystallization and morphology effectively and assists in promoting charge extraction, and suppressing charge recombination. As a result, the CBAH treated FAPbI3 -based PSCs exhibit a boosted power conversion efficiency of 21.95%. More importantly, the resultant unencapsulated devices display improved thermal, moisture, and illumination stability, and high reproducibility in terms of device performance. These results indicate the potential of organic halide salts for regulation of perovskite crystallization, offering a promising route of utilizing 1D perovskites nanorods in photovoltaic fields.

Janus (Mo/ß-Mo2C)@C heterostructure as an efficient electrocatalyst for the hydrogen evolution reaction in acidic and alkaline media.

To explore low-cost, high-efficiency, and noble-metal-free catalysts for electrocatalytic water splitting in both acidic and alkaline media, the metal-metal carbide Janus hierarchical structure comprising Mo andß-Mo2C embedded on a carbon layer (Mo/ß-Mo2C)@C is synthesized by a hydrothermal reaction and subsequent low-temperature magnesium thermic process. Systematic characterization by XRD, XPS, Raman scattering, and SEM/TEM reveals the successful formation of metallic Mo andß-Mo2C nanoparticles. The synthesized (Mo/ß-Mo2C)@C has a large specific surface area and boasts highly efficient hydrogen evolution reaction activity including low overpotentials of 152 and 171 mV at a current density of 10 mA cm-2and small Tafel slopes of 51.7 and 63.5 mV dec-1in acidic and alkaline media, respectively. In addition, the catalyst shows outstanding stability for 48 h in both acidic and alkaline media. The excellent catalytic activity originates from more active sites and greater electron conductivity bestowed by the carbon layer, which also improves the long-term stability in both acidic and alkaline solutions.

Enhanced photocatalytic degradation of 4-chlorophenol under visible light over carbon nitride nanosheets with carbon vacancies.

Two-dimensional graphitic carbon nitride (g-C3N4, GCN) is considered as one of the promising visible light-responsive photocatalysts for energy storage and environmental remediation. However, the photocatalytic performance of pristine GCN is restricted by the inherent shortcomings of rapid charge carrier recombination and limited absorption of visible light. Vacancy engineering is widely accepted as the auspicious approach for boosting the photocatalytic activity of GCN-based photocatalysts. Herein, a magnesium thermal calcination method has been developed to reconstruct GCN, in which magnesium serves as a carbon etcher for introducing carbon vacancies and pores into GCN (Vc-GCN). The fabricated Vc-GCN demonstrates excellent photocatalytic performances of degrading hazardous 4-chlorophenol under visible light irradiation benefiting from the improved carrier separating and light absorption ability as well as rich reactive sites. The optimal Vc-GCN sample delivers 2.3-fold enhancement from the pristine GCN. The work provides a tactic to prepare GCN photocatalysts with controllable carbon vacancies and for a candidate for the degradation of organic pollutants from the environment.

Graphdiyne as a Host Active Material for Perovskite Solar Cell Application.

This work demonstrates a novel photovoltaic application in which graphdiyne (GD) can be employed as a host material in a perovskite active layer for the first time. In the device fabrication, the best molar ratio for active materials is verified as PbI2/MAI/GD being 1:1:0.25, yielding a peak power-conversion efficiency of 21.01%. We find that graphdiyne, as the host material, exerts significant influence on the crystallization, film morphology, and a series of optoelectronic properties of the perovskite active layer. A uniform MAPbI3 film with highly crystalline qualities, large domain sizes, and few grain boundaries was realized with the introduction of graphdiyne. Moreover, the current-voltage hysteresis was negligible, and device stability was significantly improved as well. The results indicate that graphdiyne as the host active material presents great potential for the enhancement of the performance of perovskite solar cells.

Ternary CuZnS Nanocrystals: Synthesis, Characterization, and Interfacial Application in Perovskite Solar Cells.

Ternary CuZnS nanocrystals (NCs) are synthesized via a facile, scalable, noninjection method at low temperatures for the first time, wherein sodium ascorbate plays the dual roles of reducing agent and capping ligand in the preparation process. These NCs can be dispersed well in a polar solvent like dimethyl sulfoxide, and the average size is ∼4 nm as measured by transmission electron microscopy. The results of X-ray diffraction and X-ray photoelectron spectroscopy indicate that the crystal structure of CuZnS NCs displays covellite CuS-like structure and the Zn element partly occupies the Cu position. Also, the crystal structure of CuZnS NCs is completely converted from a covellite CuS structure into a digenite Cu9S5 structure when the NCs are treated above 350 °C. Moreover, CuZnS NCs demonstrate favorable hole transport properties. When it is employed in MAPbI3-based perovskite solar cells as a hole transport layer, a peak power conversion efficiency of 18.3% is achieved. Simultaneously, the devices based on CuZnS exhibit a remarkably reduced J-V hysteresis. The results indicate that CuZnS is a promising hole transport layer for enhancing perovskite solar cell performance and presents great potential for optoelectronic applications, as well.

A photoelectrochemical aptasensor for thrombin based on the use of carbon quantum dot-sensitized TiO2 and visible-light photoelectrochemical activity.

A photoelectrochemical (PEC) aptasensor for the highly sensitive and specific detection of thrombin is described. This aptasensor is based on an indium tin oxide (ITO) support that is covered with carbon quantum dot (CQD)-sensitized TiO2 and acts as a photoactive matrix. The ITO/TiO2/CQD electrode was prepared by impregnation assembly. It displays an enhanced and steady photocurrent response under irradiation by visible light. A carboxyl-functionalized thrombin-binding aptamer was covalently immobilized on the modified ITO to obtain a PEC aptasensor whose photocurrent decreases with increasing concentration of thrombin. Under 420 nm irradiation at a bias voltage of 0 V, the aptasensor has a linear response in the 1.0 to 250 pM thrombin concentration range, with a 0.83 pM detection limit. Conceivably, this approach can be extended to numerous other PEC aptasensors for the detection of targets for which appropriate aptamers are available. Graphical abstract Schematic of a PEC aptasensor for thrombin. It is based on the use of CQD as the sensitizer, TiO2/CQDs as the photoactive matrix, and the thrombin aptamer as the recognition element.

An Exceptionally Water Stable Metal-Organic Framework with Amide-Functionalized Cages: Selective CO2 /CH4 Uptake and Removal of Antibiotics and Dyes from Water.

As the main organic pollutants in wastewater, antibiotics and organic dyes are harmful to the environment and public health, and their removal is important but challenging. In this work, highly porous 3D metal-organic frameworks (MOFs) [M2 (PDAD)(H2 O)]n (PCN-124-stu; M=Cu, Zn; H4 PDAD = 5,5'-(pyridine-3,5-dicarbonyl)bis(azanediyl)diisophthalic acid) were synthesized, and PCN-124-stu(Cu) shows excellent chemical and thermal stability. PCN-124-stu(Cu) was used as a host for efficient extraction of various organic dyes, especially the large-molecule dye Coomassie brilliant blue, and fluoroquinolones from water, in comparison with five common MOFs, zeolite 13X, and activated carbon. PCN-124-stu(Cu) exhibits absolute predominance for fluoroquinolone adsorption among these microporous materials because of the H-bonds between fluoroquinolone molecules and the amide groups in the frameworks, except for MIL-100(Cr), which is a mesoporous MOF. Moreover, PCN-124-stu(Cu) could release fluoroquinolones slowly in physiological saline and retained its framework structure after four adsorption/desorption cycles. In addition, PCN-124-stu(Cu) can be used as a platform for selective adsorption of CO2 /CH4.

Highly efficient electron transport obtained by doping PCBM with graphdiyne in planar-heterojunction perovskite solar cells.

Organic-inorganic perovskite solar cells have recently emerged at the forefront of photovoltaics research. Here, for the first time, graphdiyne (GD), a novel two dimension carbon material, is doped into PCBM layer of perovskite solar cell with an inverted structure (ITO/PEDOT:PSS/CH3NH3PbI(3-x)Cl(x)/PCBM:GD/C60/Al) to improve the electron transport. The optimized PCE of 14.8% was achieved. Also, an average power conversion efficiency (PCE) of PCBM:GD-based devices was observed with 28.7% enhancement (13.9% vs 10.8%) compared to that of pure PCBM-based ones. According to scanning electron microscopy, conductive atomic force microscopy, space charge limited current, and photoluminescence quenching measurements, the enhanced current density and fill factor of PCBM:GD-based devices were ascribed to the better coverage on the perovskite layer, improved electrical conductivity, strong electron mobility, and efficient charge extraction. Small hysteresis and stable power output under working condition (14.4%) have also been demonstrated for PCBM:GD based devices. The enhanced device performances indicated the improvement of film conductivity and interfacial coverage based on GD doping which brought the high PCE of the devices and the data repeatability. In this work, GD demonstrates its great potential for applications in photovoltaic field owing to its networks with delocalized π-systems and unique conductivity advantage.

Boron nitride nanomaterials for thermal management applications.

Hexagonal boron nitride nanosheets (BNNs) are analogous to their two-dimensional carbon counterparts in many materials properties, in particular, ultrahigh thermal conductivity, but also offer some unique attributes, including being electrically insulating, high thermal stability, chemical and oxidation resistance, low color, and high mechanical strength. Significant recent advances in the production of BNNs, understanding of their properties, and the development of polymeric nanocomposites with BNNs for thermally conductive yet electrically insulating materials and systems are highlighted herein. Major opportunities and challenges for further studies in this rapidly advancing field are also discussed.

Novel design constructed In2S3@SnO2 hollow heterojunctions by insufficiently etched MOFs as framework for photoelectrochemical bioanalysis.

Compared to sufficiently etched MOFs materials, insufficiently etched MOFs materials tend to display unsatisfactory performance due to their immature structure and have been eliminated from scientific research. Herein, this work reported a novel In2S3@SnO2 heterojunction (In2S3@SnO2-HSHT) materials, which were stably synthesized in high temperature aqueous environment and equipped extraordinary photoelectrochemical (PEC) properties, fabricated by a succinct hydrothermal synthesis method using insufficiently etched MIL-68 as a self-sacrificing template. Compared with the control groups and In2S3@SnO2 heterojunctions with collapse morphology synthesized by sufficiently etched MIL-68 in high temperature aqueous environment, In2S3@SnO2-HSHT synthesized from insufficiently etched MIL-68 as a template had a massively enhanced light-harvesting capability and generated more photoinduced charge carriers due to its well-preserved hollow structure. Therefore, based on outstanding PEC performance of In2S3@SnO2-HSHT, the established PEC label-free signal-off immunosensor to detect CYFRA 21-1, revealing vivid selectivity, stability, and reproducibility. This novel strategy adopted the insufficient chemical etching method neglected by the mainstream chemical etching approaches, which solved the challenge that the stability of the sufficient etched MOFs with hollow structure cannot be maintained under the subsequent high temperature aqueous reaction conditions, and was further applied to the design of hollow heterojunction materials for photoelectrochemical fields.

Metal-Organic Framework-Derived ZnO, N Dually Doped Nanocages as an Efficient Host for Stable Li Metal Anodes.

The drastic volume expansion and dendrite growth of lithium metal anodes give rise to poor electrochemical reversibility. Herein, ZnO, N dually doped nanocages (c-ZNCC) were synthesized as the host for lithium metal anodes using the zeolitic imidazolate framework-8 (ZIF-8). The synthesis is based on a two-step core@shell evolution mechanism, which could guide lithium deposition rapidly and offer a fast lithium-ion diffusion during the cycling process. Benefiting from the unique design, the as-obtained c-ZNCC can render a record short lithium infusion as low as 1.5 s, a stable lithium stripping/plating capability as long as 3000 h, and a voltage hysteresis of 95 mV when cycling at 10 mA cm-2 to 10 mA h cm-2. A low Tafel slope of 3.45 mA cm-2 demonstrates the efficient charge transfer of c-ZNCC-Li, and the galvanostatic intermittent titration technique measurement shows high diffusion coefficient of c-ZNCC-Li during the charging process. In addition, the LNMO||c-ZNCC-Li cell exhibits a capacity retention as high as 93.7% at 1 C after 200 cycles. This work creates a new design for deriving nanocages with dual lithiophilic spots using a metal-organic framework and carbon cloth for favorable Li metal anodes.

Preparation of cyano-functionalized multiwalled carbon nanotubes as solid-phase extraction sorbent for preconcentration of phenolic compounds in environmental water.

In the present work, we showed a novel method to synthesize cyano-functionalized multiwalled carbon nanotubes (MWCNTs-CN) and utilize it as a solid-phase extraction sorbent for preconcentration of phenolic compounds in environmental water samples. MWCNTs-CN was synthesized through surface functionalization of multiwalled carbon nanotubes (MWCNTs). The functional groups on the surface of modified MWCNTs were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. The analytical procedure was based on a conventional solid-phase extraction step for which 100 mg of MWCNTs-CN were packed in a 3 mL polypropylene cartridge. Analytes were thus isolated and preconcentrated from the pretreated samples and subsequently detected on high-performance liquid chromatography-ultraviolet detection. The results showed the proposed method exhibited good sensitivity and precision for the extraction and elution of analytes. The limit of detections (S/N = 3) of the method were 0.45, 0.09, 0.08, and 3.00 ng mL(-1) for p-chlorophenol, 1-naphthol, 2-naphthol, and 2,4-dichlorophenol, respectively. The mean relative recoveries (n = 3) were between 80.28 and 103.13%, and the repeatability (RSD ≤ 5.10%) and reproducibility (RSD ≤ 7.68%) were accepted. This developed method was applied to determine phenolic compounds in environmental water samples. There is a positive result only for 2-naphthol with concentration of 0.38 ng mL(-1) in seawater sample.

Rationally constructed ZnCdS-HDCs@In2S3-HNRs double-hollow heterojunction with promoted light capture capability for photoelectrochemical biosensing.

The construction of novel heterojunction is regarded as an operative scheme to promote the transport of photogenerated carriers and reduce electron-hole pair recombination to enhance the photoelectrochemical (PEC) performances. Herein, ZnCdS hollow dodecahedral nanocages (ZnCdS-HDCs) and In2S3 hollow nanorods (In2S3-HNRs), which were derived from two different of metal-organic frameworks (MOFs) by solvothermal sulfidation method and were constructed an original double-hollow heterostructure ZnCdS-HDCs@In2S3-HNRs. The intrinsic mechanism of In2S3-HNRs benefiting from unique morphology to boost the photochemical properties under visible light irradiation was illustrated. Meanwhile, the mechanism of the novel type II heterojunction with staggered matching levels was revealed, which could effectively restrict electron-hole pair reassociation separation, and accelerated charge separation and transfer. Therefore, based on the excellent PEC performance of ZnCdS- HDCs@In2S3-HNRs double-hollow heterostructure, a signal-off PEC biosensor platform without labeled was constructed for the detection of CA15-3, which manifested acceptable specificity, reproducibility and stability. Additionally, the expected PEC biosensors showed a linear response range from 1.0 × 10-5 to 10 U·mL-1 in addition to an ultralow detection limit of 3.78 × 10-6 U·mL-1. This study innovatively constructed and prepared a new double-hollow heterojunction material with superior PEC nature for the application of PEC biosensing, which exhibits a broad application prospect.

Highly Durable and Efficient Ni-FeOx/FeNi3 Electrocatalysts Synthesized by a Facile In Situ Combustion-Based Method for Overall Water Splitting with Large Current Densities.

Ni-/Fe-based materials are promising electrocatalysts for the oxygen evolution reaction (OER) but usually are not suitable for the hydrogen evolution reaction (HER). Herein, a durable and bifunctional catalyst consisting of Ni-FeOx and FeNi3 is prepared on nickel foam (Ni-FeOx/FeNi3/NF) by in situ solution combustion and subsequent calcination to accomplish efficient alkaline water splitting. Density functional theory (DFT) calculation shows that the high HER activity is attributed to the strong electronic coupling effects between FeOx and FeNi3 in the Janus nanoparticles by modulating ΔGH* and electronic states. Consequently, small overpotentials (η) of 71 and 272 mV in HER and 269 and 405 mV in OER yield current densities (j) of 50 and 1000 mA cm-2, respectively. The catalyst shows outstanding stability for 280 and 200 h in HER and OER at a j of ∼50 mA cm-2. Also, the robustness and mechanical stability of the electrode at an elevated j of ∼500 mA cm-2 are excellent. Moreover, Ni-FeOx/FeNi3/NF shows excellent water splitting activities as a bifunctional catalyst as exemplified by j of 50 and 500 mA cm-2 at cell voltages of 1.58 and 1.80 V, respectively. The Ni-FeOx/FeNi3/NF structure synthesized by the novel, simple, and scalable strategy has large potential in commercial water electrolysis, and the in situ combustion method holds great promise in the fabrication of thin-film electrodes for different applications.

Separated metallic and semiconducting single-walled carbon nanotubes: opportunities in transparent electrodes and beyond.

Ever since the discovery of single-walled carbon nanotubes (SWNTs), there have been many reports and predictions on their superior properties for use in a wide variety of potential applications. However, an SWNT is either metallic or semiconducting; these properties are distinctively different in electrical conductivity and many other aspects. The available bulk-production methods generally yield mixtures of metallic and semiconducting SWNTs, despite continuing efforts in metallicity-selective nanotube growth. Presented here are significant advances and major achievements in the development of postproduction separation methods, which are now capable of harvesting separated metallic and semiconducting SWNTs from different production sources with sufficiently high enrichment and quantities for satisfying at least the needs in research and technological explorations. Opportunities and some available examples for the use of metallic SWNTs in transparent electrodes and semiconducting SWNTs in various device nanotechnologies are highlighted and discussed.

Effective purification of single-walled carbon nanotubes with reversible noncovalent functionalization.

An effective purification method for single-walled carbon nanotubes (SWNTs) based on a combination of oxidative acid treatment and reversible noncovalent functionalization with 1-pyreneacetic acid is reported. The functionalization was selective toward the nanotubes, allowing a nearly complete removal of residual metal catalysts and carbonaceous impurities. The resulting highly pure SWNTs remained solvent-dispersible, a valuable feature to potential applications that require solvent-based processing. The functionalization agent could be recovered quantitatively and reused. Effects of the purification process on the composition and properties of the nanotube sample were evaluated.

Carbon dots for optical imaging in vivo.

It was found and recently reported that small carbon nanoparticles can be surface-passivated by organic or biomolecules to become strongly fluorescent. These fluorescent carbon nanoparticles, dubbed "carbon dots", can be successfully used for in vitro cell imaging with both one- and two-photon excitations, as already demonstrated in the literature. Here we report the first study using carbon dots for optical imaging in live mice. The results suggest that the carbon dots remain strongly fluorescent in vivo, which, coupled with their biocompatibility and nontoxic characteristics, might offer great potential for imaging and related biomedical applications.

Photoinduced electron transfers with carbon dots.

The photoluminescence in carbon dots (surface-passivated small carbon nanoparticles) could be quenched efficiently by electron acceptor or donor molecules in solution, namely that photoexcited carbon dots are both excellent electron donors and excellent electron acceptors, thus offering new opportunities for their potential uses in light energy conversion and related applications.

Polymer functionalization and solubilization of carbon nanosheets.

Few-layer graphene materials or "carbon nanosheets" were covalently functionalized with poly(vinyl alcohol) via ester linkages, and the resulting functionalized sample became soluble, allowing solution-phase processing for various purposes such as the fabrication of polymer-carbon nanosheets composites containing no dispersion agents or any other foreign substances.

Synthesis and Applications of Graphdiyne-Based Metal-Free Catalysts.

The development of carbon materials offers the hope for obtaining inexpensive and high-performance alternatives to substitute noble-metal catalysts for their sustainable application. Graphdiyne, the rising-star carbon allotrope, is a big family with many members, and first realized the coexistence of sp- and sp2 -hybridized carbon atoms in a 2D planar structure. Different from the prevailing carbon materials, its nonuniform distribution in the electronic structure and wide tunability in bandgap show many possibilities and special inspirations to construct new-concept metal-free catalysts, and provide many opportunities for achieving a catalytic activity comparable with that of noble-metal catalysts. Herein, the recent progress in synthetic methodologies, theoretical predictions, and experimental investigations of graphdiyne for metal-free catalysts is systematically summarized. Some new perspectives of the opportunities and challenges in developing high-performance graphdiyne-based metal-free catalysts are demonstrated.