Domino Effect: Gold Electrocatalyzing Lithium Reduction to Accelerate Nitrogen Fixation.

Green production of NH3 , especially the Li-mediated electrochemical N2 reduction reaction (NRR) in non-aqueous solutions, is attracting research interest. Controversies regarding the NRR mechanism greatly impede its optimization and wide applications. To understand the electrocatalytic process, we treated Au coated carbon fibrous paper (Au/CP) as the model catalyst. In situ XRD confirmed the transformation of lithium intermediates during NRR. Au greatly improved electron transfer kinetics to catalyze metallic Li formation, and accordingly highly accelerated spontaneous NRR. The Faradaic efficiency of NRR on Au/CP reached 34.0 %, and NH3 yield was as high as 50 µg h-1 cm-2 . Our research shows that the key step of Li-mediated non-aqueous NRR is electrocatalytic Li reduction and offers a novel electrocatalyst design method for Li reduction.

A Heterobimetallic AuIII -PtII Photocatalyst for Water Reduction to Hydrogen.

A supramolecular complex, [Au(C^N^C)(C≡CC6 H4 C≡C)Pt(terpy)]+ , has been synthesized as a photocatalyst for water reduction. This compound consists of a cyclometalated alkyne-gold(III) photosensitizer and a platinum(II) terpyridine complex bridged through a central phenylethynyl group.

An all-inorganic lead halide perovskite-based photocathode for stable water reduction.

Lead halide perovskites (LHPs) have been investigated for photoelectrochemical hydrogen generation from water splitting. However, the harsh requirements in preparing the environment, i.e. isolating water and oxygen, hinder the wide applications of lead halide perovskites. Herein, an all-inorganic perovskite, i.e. a CsPbBr3-based photocathode, has been prepared to generate hydrogen. It is notable that as a valuable trial for a potential large-scale production, the whole preparation process was completed in an open-air environment. The LHP photocathode achieved the highest photocurrent of about 1.2 mA cm-2 at 0 VRHE. And the photocurrent remains around 94% after continuous illumination for 1 h with the Faradaic efficiency of 90%, illustrating a good photoelectrochemical stability. The all-inorganic LHP photocathodes are facile to prepare with a relatively good performance, and can be improved via band engineering and structure optimization, of which large-scale applications can be expected.

[Emergy analysis of four typical planting modes in Karst faulted basins of Yunnan Province, China.] / 云南断陷盆地喀斯特4ç§å ¸åž‹ç§æ¤æ¨¡å¼çš„èƒ½å€¼åˆ†æž.

Accurate evaluation of typical cropping patterns in faulted basins can provide scientific guidance for planting in the area. The planting modes of marigold, pomegranate, pomegranate+grass+sheep in Mengzi City of Yunnan Province were compared with the traditional corn planting mode. The ecological benefits and economy benefits of these rocky desertification control modes were analyzed by the method of emergy analysis. The environmental loading ratio (ELR) and emergy restoration ratio (ERR) were 13.80 and 0.41 in pomegranate planting mode, respectively, while 0.30 and -2.87 in marigold planting mode. The ecological benefits in pomegranate planting mode and marigold planting mode were lower than that of corn, and ELR and ERR were 1.30 and 4.64, respectively. However, the economic pure benefit per unit (EPBU) in pomegranate planting mode and marigold planting mode were 3.05 and 59.98 times of that in corn mode, respectively, indicating that pomegranate planting mode and marigold panting mode had higher economic benefits than that of corn. Pomegranate+pasture+sheep mode had the highest ecological and economic benefits among the four modes. The plus of forage+livestock subsystem to pomegranate planting mode had high eco-efficiency (ELR of 4.95, ERR of 0.63) and economic benefit (EPBU of 71.38 times than that of corn). Thus, we recommend that the local government should increase technical support for marigold planting mode and pomegranate+pasture+sheep mode, which including optimizing structures of fertilizer input, and crop cultivation and livestock breeding processes. Meanwhile, government could establish short-term labor markets for picking of fruits and flowers.

Visible-Light-Driven Hydrogen Production and Polymerization using Triarylboron-Functionalized Iridium(III) Complexes.

The development of novel iridium(III) complexes has continued as an important area of research owing to their highly tunable photophysical properties and versatile applications. In this report, three heteroleptic dimesitylboron-containing iridium(III) complexes, [Ir(p-B-ppy)2 (N^N)]+ {p-B-ppy=2-(4-dimesitylborylphenyl)pyridine; N^N=dipyrido[3,2-a:2',3'-c]phenazine (dppz) (1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (2), and 1,10-phenanthroline (phen) (3)}, were prepared and fully characterized electrochemically, photophysically, and computationally. Altering the conjugated length of the N^N ligands allowed us to tailor the photophysical properties of these complexes, especially their luminescence wavelength, which could be adjusted from λ=583 to 631 nm in CH2 Cl2 . All three complexes were evaluated as visible-light-absorbing sensitizers for the photogeneration of hydrogen from water and as photocatalysts for the photopolymerization of methyl methacrylate. The results showed that all of them were active in both photochemical reactions. High activity for the photosensitizer (over 1158 turnover numbers with 1) was observed, and the system generated hydrogen even after 20 h. Additionally, poly(methyl methacrylate) with a relatively narrow molecular-weight distribution was obtained if an initiator (i.e., ethyl α-bromophenylacetate) was used. The living character of the photoinduced polymerization was confirmed on the basis of successful chain-extension experiments.

High light harvesting efficiency CuInS2 quantum dots/TiO2/MoS2 photocatalysts for enhanced visible light photocatalytic H2 production.

Expanding the photoresponse range of TiO2-based photocatalysts is of great interest for photocatalytic H2 production. Herein, noble-metal-free CuInS2 quantum dots were employed as a novel inorganic dye to expand the visible light absorption of TiO2/MoS2 for solar H2 generation. The as-prepared CuInS2/TiO2/MoS2 photocatalysts exhibit broad absorption from the ultraviolet to near-infrared region. Under visible light irradiation (λ > 420 nm), the CuInS2/TiO2/MoS2 photocatalyst with 0.6 mmol g-1 CuInS2 and 0.5 wt% MoS2 showed the highest H2 evolution rate with a value of 1034 µmol h-1 g-1. Moreover, a considerable H2 evolution rate of 141 µmol h-1 g-1 was obtained under the irradiation of the optimized CuInS2/TiO2/MoS2 photocatalyst with >500 nm light. The reaction mechanism of the CuInS2/TiO2/MoS2 photocatalyst for photocatalytic H2 evolution was investigated in detail by photoluminescence decay study, and the results showed that the photoexcited electrons of CuInS2 can be transferred efficiently through TiO2 to MoS2 and then react with the absorbed protons to generate H2. The reported sensitization strategy tremendously improves the visible light absorption capacity and the photocatalytic performance of TiO2-based photocatalysts.

Bandgap-tunable black phosphorus quantum dots: visible-light-active photocatalysts.

Bandgap-tunable black phosphorus quantum dots prepared by a liquid exfoliation method in a mixture solvent of N-methylpyrrolidone and oleic acid can act as efficient photocatalysts for the degradation of rhodamine B. This is the first report on solely black phosphorus capable of destroying organic pollutants under visible light irradiation.

Synthesis of Pyridinic-Rich N, S Co-doped Carbon Quantum Dots as Effective Enzyme Mimics.

N and S co-doped carbon quantum dots (N, S-CQDs) with high N- and S-doping level were synthesized by microwave solid-phase pyrolysis within 50 s. Owing to the dominant pyridinic N injection into the conjugated framework, both high enzyme mimics catalytic activity and photoluminescence quantum yield are achieved simultaneously.

Robust, double-shelled ZnGa2O4 hollow spheres for photocatalytic reduction of CO2 to methane.

Robust, double-shelled ZnGa2O4 hollow spheres were successfully fabricated by hydrothermally treating an aqueous solution containing Zn(ii), Ga(iii), and citric acid, followed by annealing at 600 °C, 700 °C, or 800 °C in air to remove the carbon species. The hollow structure is expected to trap incident photons to enhance the light absorbance. The sample annealed at 700 °C exhibited the optimized photocatalytic performance in the reduction of CO2 in the presence of water vapor to methane. This property is ascribed to the improved crystallinity of the sample, which has fewer defect centers for the recombination of electron-hole pairs compared with that annealed at 600 °C. The reduced performance of the sample done at 800 °C relative to the one annealed at 700 °C is attributed to the formation of additional impurities besides ZnGa2O4, possibly due to partial Zn(ii) evaporation at higher temperature leading to segregation of potential Ga-based oxides. RuO2 and Pt were loaded onto the sample surface to greatly enhance the photocatalytic performance. The best photocatalytic performance was observed in the sample co-loaded with Pt and RuO2.

Metal-complex chromophores for solar hydrogen generation.

Solar H2 generation from water has been intensively investigated as a clean method to convert solar energy into hydrogen fuel. During the past few decades, many studies have demonstrated that metal complexes can act as efficient photoactive materials for photocatalytic H2 production. Here, we review the recent progress in the application of metal-complex chromophores to solar-to-H2 conversion, including metal-complex photosensitizers and supramolecular photocatalysts. A brief overview of the fundamental principles of photocatalytic H2 production is given. Then, different metal-complex photosensitizers and supramolecular photocatalysts are introduced in detail, and the most important factors that strictly determine their photocatalytic performance are also discussed. Finally, we illustrate some challenges and opportunities for future research in this promising area.

Evaluation of bis-cyclometalated alkynylgold(iii) sensitizers for water photoreduction to hydrogen.

Well-defined gold sensitizers for hydrogen production from water remain extremely rare despite decades of interest, and are currently limited to systems based on ruthenium, iridium or platinum complexes. This report details the synthesis and characterization of a series of neutral cyclometalated gold(iii) complexes of the type [(RC^N^CR)Au(C[triple bond, length as m-dash]C-R')] (R = H or tert-butyl group; R' = aryl groups) that have been found to be good candidates to function as harvesting materials in light-induced electron transfer reactions. We established the efficacy of systems with these gold(iii) complexes as photosensitizers (PSs) in the production of renewable hydrogen in the presence of [Co(2,2'-bipyridine)3]Cl2 or [Rh(4,4'-di-tert-butyl-2,2'-bipyridine)3](PF6)3 as a H2-evolved catalyst and triethanolamine (TEOA) as a sacrificial electron donor in acetone-water solution. All complexes are active, and there is a more than threefold increase over other candidates in photocatalytic H2 generation activity. Under the optimal reaction conditions, hydrogen evolution took place through a photochemical route with the highest efficiency and with a turnover number (TON) of up to 1441.5 relative to the sensitizer over 24 hours. In the initial photochemical path, the reductive quenching of the excited gold(iii) complex by TEOA due to the latter's greater concentration in the system followed by electron transfer to the catalyst species is proposed to be the dominant mechanism. A photo-to-H2 quantum yield of approximately 13.7% was attained when illuminated with monochromatic light of 400 nm. Such gold(iii) complexes have demonstrated significant utility in solar-to-hydrogen reactions and thus represent a new effective class of light-harvesting materials. These results open possibilities for pursuing more efficient photosensitizers featuring gold(iii) complexes in photocatalytic solar energy conversion.

Osmium(ii) complexes for light-driven aerobic oxidation of amines to imines.

Herein, we describe the synthesis and characterization of three Os(ii) complexes (i.e., [Os(fptz)2(PPhMe2)2] (1, fptzH = 3-trifluoromethyl-5-pyridyl-1,2,4-triazole), [Os(fptz)2(CO)(L1)] (2, L1 = PPh3; 3, L1 = pyridine)) that have been successfully utilized as good photocatalysts to promote aerobic oxidative coupling of amines to imines with molecular oxygen in air as a green oxidant. Complex 1 is the most effective catalyst for the oxidative coupling of benzylamine with molecular O2 (air) as the oxidant because of the complex's strong absorption of visible light and long-lived triplet state. The application of a low catalyst loading (0.06 mol%) of complex 1 to the oxidative coupling of a wide range of amines affords the corresponding imines efficiently and selectively in most cases. The reaction mechanism was investigated via relevant control and quenching experiments. The results indicated that the reaction occurs via an active (1)O2-involved pathway. The (1)O2-generating ability of complex 1 as a photosensitizer was evaluated using 9,10-dimethylanthracene (DMA) as a chemical trap for (1)O2.

Adjusting the Crystallinity of Mesoporous Spinel CoGa2O4 for Efficient Water Oxidation.

Effective and stable electrocatalysts (ECs) are of great importance for the modification of semiconductor (SC) photoanodes, to achieve efficient photoelectrochemical (PEC) water splitting. Herein we demonstrate that the low-crystallinity mesoporous spinel CoGa2O4 oxygen evolution catalyst (OEC), exhibiting excellent bulk electrocatalytic stability and activity for oxygen-evolving reaction (OER), obviously improved water oxidization on a-Fe2O3 photoanode. Low crystallinity not only balances the stability and activity for ECs themselves but facilitates formation of adjustable Schottky junctions between ECs and SCs. Those would contribute to surface state passivation and photogenerated hole extraction, leading to lower onset potential and larger photocurrent. Thus, our finding suggests that low crystallinity could serve as a beneficial feature of ECs to achieve efficient PEC water splitting, owing to its preponderant tendency for the improvement of interface reaction kinetics.

MoS2 Nanosheet-Modified CuInS2 Photocatalyst for Visible-Light-Driven Hydrogen Production from Water.

Exploiting photocatalysts respond to visible light is of huge challenge for photocatalytic H2 production. Here, we synthesize a new composite material consisting of few-layer MoS2 nanosheets grown on CuInS2 surface as an efficient photocatalyst for solar H2 generation. The photocatalytic results demonstrate that the 3 wt % MoS2 /CuInS2 photocatalyst exhibits the highest H2 generation rate of 316 µmol h(-1) g(-1) under visible light irradiation, which is almost 28 times higher than that of CuInS2 . Importantly, the MoS2 /CuInS2 photocatalyst shows a much higher photocatalytic activity than that of Pt-loaded CuInS2 photocatalyst. The enhanced photocatalytic activities of MoS2 /CuInS2 photocatalysts can be attributed to the improved charge separation at the interface of MoS2 and CuInS2, which is demonstrated by the significant enhancement of photocurrent responses in MoS2 /CuInS2 photoelectrodes. This work presents a noble-metal-free photocatalyst that responds to visible light for solar H2 generation.

Neutral nickel(II) phthalocyanine as a stable catalyst for visible-light-driven hydrogen evolution from water.

Neutral nickel(ii) phthalocyanine was found to be an efficient and stable catalyst for photocatalytic H2 evolution from water when coupled with an iridium complex as the photosensitizer and triethanolamine as the sacrificial electron donor. The result shows that the Ni-N sigma bond can enhance the stability of the catalyst.

Noble-Metal-Free Molybdenum Disulfide Cocatalyst for Photocatalytic Hydrogen Production.

Photocatalytic water splitting using powered semiconductors as photocatalysts represents a promising strategy for clean, low-cost, and environmentally friendly production of H2 utilizing solar energy. The loading of noble-metal cocatalysts on semiconductors can significantly enhance the solar-to-H2 conversion efficiency. However, the high cost and scarcity of noble metals counter their extensive utilization. Therefore, the use of alternative cocatalysts based on non-precious metal materials is pursued. Nanosized MoS2 cocatalysts have attracted considerable attention in the last decade as a viable alternative to improve solar-to-H2 conversion efficiency because of its superb catalytic activity, excellent stability, low cost, availability, environmental friendliness, and chemical inertness. In this perspective, the design, structures, synthesis, and application of MoS2 -based composite photocatalysts for solar H2 generation are summarized, compared, and discussed. Finally, this Review concludes with a summary and remarks on some challenges and opportunities for the future development of MoS2 -based photocatalysts.

A Noble-Metal-Free Nickel(II) Polypyridyl Catalyst for Visible-Light-Driven Hydrogen Production from Water.

The complex [Ni(bpy)3](2+) (bpy=2,2'-bipyridine) is an active catalyst for visible-light-driven H2 production from water when employed with [Ir(dfppy)2 (Hdcbpy)] [dfppy=2-(3,4-difluorophenyl)pyridine, Hdcbpy=4-carboxy-2,2'-bipyridine-4'-carboxylate] as the photosensitizer and triethanolamine as the sacrificial electron donor. The highest turnover number of 520 with respect to the nickel(II) catalyst is obtained in a 8:2 acetonitrile/water solution at pH 9. The H2 -evolution system is more stable after the addition of an extra free bpy ligand, owing to faster catalyst regeneration. The photocatalytic results demonstrate that the nickel(II) polypyridyl catalyst can act as a more effective catalyst than the commonly utilized [Co(bpy)3 ](2+). This study may offer a new paradigm for constructing simple and noble-metal-free catalysts for photocatalytic hydrogen production.

Energy Transfer in a Hybrid Ir(III) Carbene-Pt(II) Acetylide Assembly for Efficient Hydrogen Production.

A new heterometallic supramolecular complex, consisting of an iridium carbene-based unit appended to a platinum terpyridine acetylide unit, representing a new Ir(III) -Pt(II) structural motif, was designed and developed to act as an active species for photocatalytic hydrogen production. The results also suggested that a light-harvesting process is essential to realize the solar-to-fuel conversion in an artificial system as illustrated in the natural photosynthetic system.

Significant enhancement in photocatalytic hydrogen evolution from water using a MoS2 nanosheet-coated ZnO heterostructure photocatalyst.

A novel MoS2 nanosheet-coated ZnO heterostructure photocatalyst was successfully synthesized via a simple hydrothermal method. Two-dimensional MoS2 nanosheets were intimately deposited onto ZnO surface to form an intimate function, which favors the charge-transfer and suppresses the recombination of the photogenerated electron-hole pairs between MoS2 and ZnO, resulting in a significantly enhanced photocatalytic activity for hydrogen evolution. The photocatalytic activities of the MoS2-ZnO composite photocatalysts with different MoS2 contents for hydrogen production were systematically evaluated. The 1.00 wt% MoS2-ZnO photocatalyst shows the highest H2 production rate of 768 µmol h(-1) g(-1) in the presence of Na2S and Na2SO3 as the sacrificial reagents, which is 14.8 times higher than that of pure ZnO. The photocatalytic activity of MoS2 as a cocatalyst for H2 evolution reaction is considerably higher than many noble metals such as Pt, Rh, Ru and Au, suggesting that MoS2 could act as a potential substitute for noble metals in photocatalytic H2 production systems. This work presents a noble-metal-free, highly-efficient, and stable MoS2 cocatalyst to suppress the recombination of electron-hole pairs of ZnO, resulting in an enhanced photocatalytic hydrogen production activity.

Hydrogen photogeneration promoted by efficient electron transfer from iridium sensitizers to colloidal MoS2 catalysts.

We report the utilization of colloidal MoS2 nanoparticles (NPs) for multicomponent photocatalytic water reduction systems in cooperation with a series of cyclometalated Ir(III) sensitizers. The effects of the particle size and particle dispersion of MoS2 NPs catalyst, reaction solvent and the concentration of the components on hydrogen evolution efficiency were investigated. The MoS2 NPs exhibited higher catalytic performance than did other commonly used water reduction catalysts under identical experiment conditions. The introduction of the carboxylate anchoring groups in the iridium complexes allows the species to be favorably chem-adsorbed onto the MoS2 NPs surface to increase the electron transfer, resulting in enhancement of hydrogen evolution relative to the non-attached systems. The highest apparent quantum yield, which was as high as 12.4%, for hydrogen evolution, was obtained (λ = 400 nm).