Photocatalytic nitrogen fixation from N2 provides an alternative strategy for ammonia (NH3) production, but it was limited by the consumption of a sacrificial electron donor for the currently reported half-reaction system. Here, we use naturally abundant and renewable cellulose as the sacrificial reagent for photocatalytic nitrogen fixation over oxygen-vacancy-modified MoO3 nanosheets as the photocatalyst. In this smartly designed photocatalytic system, the photooxidation of cellulose not only generates value-added chemicals but also provides electrons for the N2 reduction reaction and results in the production of NH3 with a maximum rate of 68 µmol·h-1·g-1. Also, the oxygen vacancies provide efficient active sites for both cellulose oxygenolysis and nitrogen fixation reactions. This work represents useful inspiration for realizing nitrogen fixation coupled with the generation of value-added chemicals from N2 and cellulose through a photocatalysis strategy.
Solar-driven photothermal catalytic H2 production from lignocellulosic biomass was achieved by using 1T-2H MoS2 with tunable Lewis acidic sites as catalysts in an alkaline aqueous solution, in which the number of Lewis acidic sites derived from the exposed Mo edges of MoS2 was successfully regulated by both the formation of an edge-terminated 1T-2H phase structure and tunable layer number. Owing to the abundant Lewis acidic sites for the oxygenolysis of lignocellulosic biomass, the 1T-2H MoS2 catalyst shows high photothermal catalytic lignocellulosic biomass-to-H2 transformation performance in polar wood chips, bamboo, rice straw corncobs, and rice hull aqueous solutions, and the highest H2 generation rate and solar-to-H2 (STH) efficiency respectively achieves 3661 µmol·h-1·g-1 and 0.18% in the polar wood chip system under 300 W Xe lamp illumination. This study provides a sustainable and cost-effective method for the direct transformation of renewable lignocellulosic biomass to H2 fuel driven by solar energy.
The conversion of lignocellulosic biomass to chemical fuel can achieve the sustainable use of lignocellulosic biomass, but it was limited by the lack of an effective conversion strategy. Here, we reported a unique approach of photothermal catalysis by using MoS2-reduced graphene oxide (MoS2/RGO) as the catalyst to convert lignocellulosic biomass into H2 fuel in alkaline solution. The RGO acting as a support for the growth of MoS2 results in the high exposed Mo edges, which act as efficient Lewis acidic sites for the oxygenolysis of lignocellulosic biomass dissolved in alkaline solution. The broad light absorption capacity and abundant Lewis acidic sites make MoS2/RGO to be efficient catalysts for photothermal catalytic H2 production from lignocellulosic biomass, and the H2 generation rate with respect to catalyst under 300 W Xe lamp irradiation in cellulose, rice straw, wheat straw, polar wood chip, bamboo, rice hull, and corncob aqueous solution achieve 223, 168, 230, 564, 390, 234, and 55 µmol·h-1·g-1, respectively. It is believed that this photothermal catalysis is a simple and "green" approach for the lignocellulosic biomass-to-H2 conversion, which would have great potential as a promising approach for solar energy-driven H2 production from lignocellulosic biomass.
TiO2 nanoparticles grown on MoS2/N-doped graphitic carbon were demonstrated to be efficient noble-metal-free photocatalysts for H2 production from lignocellulosic biomass, and the H2 generation rate from wheat straw, corncob, polar wood chip, bamboo, rice hull, corn straw and rice straw aqueous solution respectively reaches 4.9, 6.7, 11.7, 14.5, 8.4, 7.3 and 6.2 µmol g-1 h-1.
Two-dimensional (2D) semiconductors for photocatalysis are more advantageous than the other photocatalytic materials since the 2D semiconductors generally have large specific surface area and abundant active sites. Phosphorus silicon (SiP), with an indirect bandgap in bulk and a direct bandgap in the monolayer, has recently emerged as an attractive 2D material because of its anisotropic layered structure, tunable bandgap, and high charge carrier mobility. However, the utilization of SiP as a photocatalyst for photocatalysis has been scarcely studied experimentally. Herein, we reported the synthesis of SiP nanosheets (SiP NSs) prepared from bulk SiP by an ultrasound-assisted liquid-phase exfoliation approach which can act as a metal-free, efficient, and visible-light-responsive photocatalyst for photocatalytic H2 production and nitrogen fixation. In a half-reaction system, the maximal H2 and NH3 generation rate under visible light irradiation achieves 528 and 35 µmol·h-1·g-1, respectively. Additionally, the apparent quantum yield for H2 production at 420 nm reaches 3.56%. Furthermore, a Z-scheme photocatalytic overall water-splitting system was successfully constructed by using Pt-loaded SiP NSs as the H2-evolving photocatalyst, Co3O4/BiVO4 as the O2-evolving photocatalyst, and Co(bpy)33+/2+ as an electron mediator. Notably, the highest H2 and O2 generation rate with respect to Pt/SiP NSs achieves 71 and 31 µmol·h-1·g-1, respectively. This study explores the potential application of 2D SiP as a metal-free visible-light-responsive photocatalyst for photocatalysis.
Visible-light-driven photocatalytic cellulose-to-H2 conversion system was successfully designed by using MoS2 /ZnIn2 S4 as the photocatalyst and cellulase as the enzyme catalyst. At first, the cellulose was converted to glucose by cellulase. The generated glucose acted as an efficient hole trapper and electron donor, which was further converted into H2 through photocatalytic reaction over MoS2 /ZnIn2 S4 under visible light irradiation. The optimum H2 generation rate achieved under visible light irradiation (λ>420â nm) was 12.2â µmol â h-1 â g-1 in the presence of 100â mg of 3 % MoS2 /ZnIn2 S4 , 100â mg cellulase and 2â g poplar wood chip. These results open up a new possibility for the development of efficient visible-light-responding photocatalytic cellulose to H2 conversion system that combine photocatalysis and enzyme technology.
Cellulase , Molybdenum , Molybdenum/radiation effects , Hydrogen , Cellulose , Light , Glucose
Herein, we present a stable water-soluble cobalt complex supported by a dianionic 2,2'-([2,2'-bipyridine]-6,6'-diyl)bis(propan-2-ol) ligand scaffold, which is a rare example of a high-oxidation species, as demonstrated by structural, spectroscopic and theoretical data. Electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility measurements revealed that the CoIV center of the mononuclear complex in the solid state resides in the high spin state (sextet, S=5/2). The complex can effectively catalyze water oxidation via a single-site water nucleophilic attack pathway with an overpotential of only 360â mV in a phosphate buffer with a pH of 6. The key intermediate toward water oxidation was speculated based on theoretical calculations and was identified by in situ spectroelectrochemical experiments. The results are important regarding the accessibility of high-oxidation state metal species in synthetic models for achieving robust and reactive oxidation catalysis.
Cobalt , Water , Catalysis , Cobalt/chemistry , Electron Spin Resonance Spectroscopy , Oxidation-Reduction , Water/chemistry
A Z-scheme system was successfully constructed for visible-light-driven photocatalytic H2 production from lignocelluloses, the highest H2 evolution rate of this Z-scheme system is 5.3 and 1.6 µmol h-1 in α-cellulose and poplar wood chip aqueous solutions, respectively, under visible light irradiation.
As an alternative strategy for H2 production under ambient conditions, solar-driven lignocellulose-to-H2 conversion provides a very attractive approach to store and utilize solar energy sustainably. Exploiting efficient photocatalyst for photocatalytic lignocellulose-to-H2 conversion is of huge significance and remains the key challenge for development of solar H2 generation from lignocellulose. Herein, 2D-2D MoS2 /TiO2 photocatalysts with large 2D nanojunction were constructed for photocatalytic lignocellulose-to-H2 conversion. In this smart structure, the 2D nanojunctions acted as efficient channel for charge transfer from TiO2 to MoS2 to improve charge separation efficiency and thus enhance photocatalytic lignocellulose-to-H2 conversion activity. The 2 % MoS2 /TiO2 photocatalyst showed the highest photocatalytic lignocellulose-to-H2 conversion performance with the maximal H2 generation rate of 201 and 21.4â µmol h-1 g-1 in α-cellulose and poplar wood chip aqueous solution, respectively. The apparent quantum yield at 380â nm reached 1.45 % for 2 % 2D-2D TiO2 /MoS2 photocatalyst in α-cellulose aqueous solution. This work highlights the importance of optimizing the interface structures of photocatalyst for solar-driven lignocellulose-to-H2 conversion.
Hierarchical Bi2WO6 nanostructures self-assembled with planar arranged nanosheets and dispersed Bi2WO6 nanosheets were synthesized with different dosages of EG via a simple hydrothermal route. The Bi2WO6 photocatalysts were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). A control experiment was conducted to test the effect of EG dosage on the growth mechanism and behavior of the highly (010) exposed hierarchical lamellar nanostructures and dispersed nanosheets. The photocatalytic nitrogen fixation rate of the hierarchical Bi2WO6 nanostructures was estimated to be 948 µmol g-1 h-1 across the full spectrum, which was 23% higher than that of the dispersed nanosheets (770 µmol g-1 h-1) due to chemisorption on the hierarchical structures and enhanced surface oxygen vacancies (OVs).
Design and synthesis of non-noble electrocatalyst with controlled structure and composition for hydrogen evolution reaction (HER) are significant for large-scale water electrolysis. Here, an elegant multi-step templating strategy is developed for the fabrication of vertically aligned CoP@Ni2P nanowire-nanosheet architecture on Ni foam. Cobalt-carbonate hydroxides nanowires grown on Ni foam are first synthesized as the self-template. Afterward, a layer of amorphous Ni(OH)2 nanosheets is grown on the Co-based precursors through a chemical bath process, which is then transformed into the hierarchical CoP@Ni2P nanoarrays by a co-phosphatization treatment. Owing to the synergistic effect of the compositions and the advantages of the hierarchical heterostructures, the resulting hybrid electrocatalyst with dense heterointerfaces is revealed as an excellent HER catalyst, with a low overpotential of 101 mV at the current density of 10 mA cm-2, a relatively small Tafel slope of 79 mV dec-1, and favorable long-term stability of at least 20 h in 1 M KOH.
BiOCl has been identified to be a promising photocatalyst for the rapid photodegradation of organic pollutants, but its practical application was restricted by its limited photocatalytic activity. In this work, a highly reactive BiOCl decahedron photocatalyst with an exposed (001) facet was successfully hydrothermally synthesized via a simple hydrothermal method using bismuth nitrate (Bi(NO3)3·5H2O) and ammonium chloride (NH4Cl) as raw materials. By adjusting the dosage of NH4Cl, the BiOCl nanoplates transformed from hexahedra with quadrilateral {110} oblique facets to decahedra with octagonal {110} and {100} oblique facets. As compared to the original BiOCl nanoplates, decahedral BiOCl possesses much more oxygen-enriched surfaces and a narrowed bandgap, resulting in enhanced photocatalytic performance. The decahedral BiOCl photocatalyst achieves a high degradability of 98% for the photodegradation of RhB after 6 min of irradiation, which is much faster than that of a hexahedral BiOCl sample.
Exploiting an appropriate strategy to prepare fine crystal quality black phosphorus nanosheet (BPNS) catalyst is a major challenge for its practical application in catalysis. Herein, we address this challenge by developing a rapid electrochemical expansion strategy for scale preparation of fine crystal quality BPNSs from bulk black phosphorus, which was demonstrated to be an active cocatalyst for photocatalytic nitrogen fixation in the presence of CdS as a photocatalyst. The transient photocurrent and charge density studies show that the BPNSs can efficiently accelerate charge separation of CdS, leading to the enhanced photocatalytic activities of BPNS/CdS nanocomposites for nitrogen fixation. The 1.5% BPNS/CdS photocatalyst exhibits the highest photocatalytic activity for nitrogen fixation with an NH3 evolution rate of 57.64 µmol·L-1·h-1. This study not only affords a rapid and simple strategy for scale synthesis of fine crystal quality BPNSs but also provides new insights into the design and development of black phosphorus-based materials as low-cost metal-free cocatalysts for photocatalytic nitrogen fixation.
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.
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 631â 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 1158â turnover numbers with 1) was observed, and the system generated hydrogen even after 20â 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.
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 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.
Noble-metal-free, visible-light-responsive and "green" MoS2 nanosheet modified-InVO4 heterostructures were synthesized as efficient photocatalysts for photocatalytic H2 production. The positive effect of intimate nanojunctions formed between MoS2 and InVO4 resulted in the excellent activity of MoS2/InVO4 which is even higher than that of Pt-loaded InVO4.
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.
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.
