Regulating CO and H2 Ratios in Syngas Produced from Photocatalytic CO2/H2O Reduction by Cu and Co Dual Active Centers on Carbon Nitride Hollow Nanospheres.

For photocatalytic CO2 reduction to produce syngas, there are challenges in achieving a high catalytic efficiency and precise control over the product ratio. In this study, two non-noble metal complexes Cobpy and Cubpy (bpy = 2,2'-bipyridine) as cocatalysts for CO2 reduction and hydrogen evolution, respectively, were in situ supported on carbon nitride hollow nanospheres to construct a hybrid system for photocatalytic syngas production. The resulting CO/H2 ratio can be precisely regulated within a wide range of 0:1-9:1 by accurately controlling the content of the two complexes. The presence of the two complexes promotes the migration of photogenerated electrons of the carbon nitride. CO2 can be reduced to CO on the photoreduced species Co(bpy)2+ of Cobpy on CNHS, and H+ can be reduced to H2 on the photoreduced species Cu(bpy)2+ of Cubpy. Furthermore, this method is also applicable to other photocatalysts, such as CdS and TiO2 for generating syngas and regulating product ratios.

Decorating Zn0.5Cd0.5S with C,N Co-Doped CoP: An Efficient Dual-Functional Photocatalyst for H2 Evolution and 2,5-Diformylfuran Oxidation.

Photocatalytic H2 evolution and biomass-derived alcohol oxidation is a cooperative way for improving the utilization of photogenerated charge carriers. Herein, a highly efficient photocatalyst was fabricated by decorating Zn0.5Cd0.5S with a C,N codoped CoP polyhedron (referred to as CoP, derived from ZIF-67), and then it was used for H2 evolution and 5-hydroxymethylfurfural (HMF) oxidation. For the optimized sample (20% CoP/Zn0.5Cd0.5S), the generated H2 rate is significantly enhanced from that of the HMF aqueous solution with 2,5-diformylfuran (DFF) as a concomitant product, about 31.7 times higher than the pristine Zn0.5Cd0.5S under visible light irradiation. The separation of photoexcited electrons (e-) and holes (h+) in the process was promoted, as both e- and h+ were involved in the desired conversions. From the results of density functional theory (DFT) calculations and in situ XPS spectra, the utilization of e- was further improved as a spontaneous transfer from Zn0.5Cd0.5S to CoP occurred due to the p-n heterojunction formed between Zn0.5Cd0.5S (n type) and CoP (p type). This work provides an efficient method to separate the photoinduced charge carriers and a new way for H2 evolution accompanied by transformation of HMF to DFF.

Fabrication of 2D/2D BiOBr/g-C3N4 with efficient photocatalytic activity and clarification of its mechanism.

Precise regulation of photoexcited charge carriers for separation and transportation is a core requirement for practical application in the photocatalysis field. Herein, a 2D/2D BiOBr/g-C3N4 heterojunction is prepared by a self-assembly method and exhibits enhanced and stable activity for photocatalytic degradation of bisphenol A (BPA) and norfloxacin (NFA) under visible light. Compared to pure g-C3N4, the kinetic constants of BPA and NFA degradation over BiOBr/g-C3N4 are enhanced by about 14.74 and 4.01 times, respectively. The separation and transportation mechanism for the photoexcited charge carriers is clarified by electron paramagnetic resonance (EPR), in situ X-ray photoelectron spectroscopy (in situ XPS), and theoretical calculations. The results show that BiOBr/g-C3N4 exhibits the feature of a relative p-n junction, in which the charges photoexcited on BiOBr/g-C3N4 with high redox potentials can be kept and spatially separated. Moreover, the built-in electric field with the direction of g-C3N4 → BiOBr and the opportune band curvature provide the driving force for charge separation and transportation. Additionally, BPA and NFA degradation intermediates are also detected by liquid chromatography-mass spectrometry. It is of great significance to fabricate efficient photocatalysts for environmental purification and other targeted reactions.

Accelerating Nickel-Based Molecular Construction via DFT Guidance for Advanced Photocatalytic Hydrogen Production.

Understanding the nickel-based molecular catalyst structure and functional relationship is crucial for catalytic hydrogen production in aqueous solutions. Density functional theory (DFT) provides mature theoretical knowledge for efficient catalyst design, significantly reducing catalyst synthesis time and energy consumption. In the present work, three molecular catalysts, Ni(qbz)(pys)2 (qbz = 2-quinoline benzimidazole) (NQP 1), Ni(qbo)(pys)2 (qbo = 2-quinoline benzothiazole) (NQP 2), and Ni(pbz)(pys)2 (pbz = 4-chloro-2,2-pyridylbenzimidazole) (NQP 3) (pys = 2-mercaptopyridine), were designed and synthesized and exhibit a high performance for H2 generation in aqueous solution with a lamp (λ ≥ 400 nm) under visible light irradiation. Under the optimal conditions, a H2 evolution rate as high as 1190 µmol h-1 can be obtained over 25 mg of NQP 1 with the best catalytic performance. DFT has been adopted in this study to unveil the relationship between the ligand qbz and catalyst NQP 1─an efficient step in the design of catalysts with an excellent catalytic performance. We show that, in addition to the presence of the triphenyl ring increasing the overall electron density, rapid electron transfer (ET) from excited fluorescein (Fl) to NQP 1 significantly improves the chance of photogenerated electrons transferring to the active site, ultimately increasing the catalytic activity for H2 production. This work on understanding the correlation between structures and properties of complexes provides a new idea for manufacturing high-performance photocatalysts.

The Hole-Tunneling Heterojunction of Hematite-Based Photoanodes Accelerates Photosynthetic Reaction.

Single-atom metal-insulator-semiconductor (SMIS) heterojunctions based on Sn-doped Fe2 O3 nanorods (SF NRs) were designed by combining atomic deposition of an Al2 O3 overlayer with chemical grafting of a RuOx hole-collector for efficient CO2 -to-syngas conversion. The RuOx -Al2 O3 -SF photoanode with a 3.0 nm thick Al2 O3 overlayer gave a >5-fold-enhanced IPCE value of 52.0 % under 370 nm light irradiation at 1.2 V vs. Ag/AgCl, compared to the bare SF NRs. The dielectric field mediated the charge dynamics at the Al2 O3 /SF NRs interface. Accumulation of long-lived holes on the surface of the SF NRs photoabsorber aids fast tunneling transfer of hot holes to single-atom RuOx species, accelerating the O2 -evolving reaction kinetics. The maximal CO-evolution rate of 265.3 mmol g-1 h-1 was achieved by integration of double SIMS-3 photoanodes with a single-atom Ni-doped graphene CO2 -reduction-catalyst cathode; an overall quantum efficiency of 5.7 % was recorded under 450 nm light irradiation.

Construction and performance of a simple and efficient g-C3N4 photocatalytic hydrogen production system.

Surface and bulk structure modification is an effective strategy to improve the photocatalytic performance of g-C3N4 (CN). In this work, dilute NaOH solution was used in situ to regulate the CN structure for enhanced photocatalytic hydrogen evolution reaction (HER). Characterization results indicate that after treatment with dilute NaOH solution, the surface of CN was hydroxylated, resulting in the change of CN structure and the increase of BET specific surface area. Furthermore, some Na+ ions can be intercalated into the framework of CN, and form the Na-N bond. These modifications boost the HER activity of CN. The test carried out in 7.5 mM NaOH solution shows the highest activity and it is almost 3.7 times higher than that performed in water. Control tests indicate that hydroxides of other alkali and alkali earth metals such as LiOH, KOH, Ca(OH)2, and Ba(OH)2 have similar promotion effects. This work demonstrates a valid and simple way to enhance the HER activity of CN through performing the reaction in a weakly alkaline solution.

Theoretical study on the DNA interaction properties of copper(II) complexes.

Theoretical studies on DNA-cleavage and DNA-binding properties of a series of Cu(II) complexes [Cu(bimda)(diimine)] 1-5 have been carried out by density functional theory (DFT). The optimized structures of Cu(II) complexes were docked into parallel, antiparallel and mixed G-quadruplexes, with which the binding energies of complexes 1-5 were obtained. The cytotoxicities of these complexes can be predicted preliminarily by the binding energies. To explore the energy changes of Cu(II) complexes in duplex DNA, the optimized structures of these complexes were docked into the duplex DNA, and the obtained docking models were further optimized using QM/MM method. The DNA-cleavage abilities of complexes 1-5 can be predicted accurately and explained reasonably by the computed intra-molecular reorganization energies of these complexes. This work reported here has implications for the understanding of the interaction Cu(II) complexes with the DNA, which might be helpful for the future directing the design of novel anticancer Cu(II) complexes.

Rational synthesis of MnxCd1-xS for enhanced photocatalytic H2 evolution: Effects of S precursors and the feed ratio of Mn/Cd on its structure and performance.

Rational synthesis of photocatalytic materials is an effective way to improve their performance. In this work, to optimize the S precursors, a series of MnxCd1-xS (MCS) were first hydrothermally synthesized with the prevalent thiourea (TA), thioacetamide (TAA) and L-cysteine (L-Cys) as the S sources. The optimum feed ratio of Mn/Cd was then determined based on the optimized S precursor. The effects of S precursors and the feed ratio of Mn/Cd on the phase structure, absorption, morphology, band structure, and the photocatalytic hydrogen evolution reaction (HER) performance of MCS were investigated systematically. The hexagonal phase structures of MnS, CdS, and MCS are favored by TA and L-Cys as the S sources, while their cubic phases are benefited by TAA. TAA is the preferred S source for the preparation of highly active MCS and the solid solution is formed through the consolidation of cubic α-MnS into cubic CdS. The activity of MCS can be improved with the increase of Mn content from x = 0-0.6. The sample with x = 0.6 shows the highest HER activity (2253 µmol·h-1·g-1) and the performance is almost 6 times higher than CdS (416 µmol·h-1·g-1). The enhanced activity can be attributed to the improved separation efficiency of photo-induced charge carriers and the negative-shifts of Ecb, which are induced by the introduction of Mn. A segregation of inert α-MnS from MCS is occurred when Mn content is >0.6, resulting in a decay of the HER activity. A change of the semiconductivity from n-type to bipolar type is occurred in MCS due to the uneven sulfidation of Mn in MCS.

Noble metal-free 0D-1D NiSx/CdS nanocomposites toward highly efficient photocatalytic contamination removal and hydrogen evolution under visible light.

The development of stable noble metal-free photocatalysts with efficient separation and transportation of the photogenerated electrons-holes is of crucial importance for promoting the application of photocatalysis technology. Herein, we propose an electron transfer strategy by reasonable design and fabrication of novel 0D NiSx nanosheets as a co-catalyst on the surface of 1D CdS nanorods (CdS-NRs) to enhance photocatalytic hydrogen evaluation and contamination (Cr(vi), rhodamine B and bisphenol A) removal in water. Under visible light irradiation, the 0D-1D NiSx/CdS-NR nanocomposite with 1.5% NiSx loading gave a hydrogen evolution rate of 5.98 mmol h-1 g-1, which is about 5.3 times and 1.9 times higher than that of the native CdS-NRs and the optimal 1% Pt/CdS-NRs, respectively. Notably, good stability in the recycling test and a high apparent quantum efficiency of about 69.9% at 420 nm were also obtained. The 1.5% NiSx/CdS-NRs exhibited enhanced photocatalytic contamination degradation efficiency of about 2 times higher than pure CdS-NRs. In this hybrid photocatalyst, 0D NiSx nanosheets came into intimate interfacial contact with the surface of 1D CdS-NRs and played a similar role as noble metals, which could effectively improve the separation, transportation efficiencies and lifetime of photogenerated charge, and thus enhance the photocatalytic performance of CdS-NRs with more efficient conversion of solar energy. This work shows not only a possibility for the utilization of noble metal-free NiSx as a co-catalyst in the photocatalysis, but also provides new insight into the design and fabrication of high-performance composite photocatalysts (such as NiSx/g-C3N4 and NiSx/Zn3In2S6).

Ultra-low content of Pt modified CdS nanorods: Preparation, characterization, and application for photocatalytic selective oxidation of aromatic alcohols and reduction of nitroarenes in one reaction system.

A series of Pt nanoparticles (with size of 3-4 nm) decorated CdS nanorods were prepared via a simple solvothermal method. The samples were then used for photocatalytic selective oxidation (SO) of aromatic alcohols and reduction (SR) of nitroarenes in one reaction system. The platinized samples showed enhanced activity for the conversions than pristine CdS as Pt can serve as e- trapping and reaction sites, by which the recombination of photoinduced charge carriers can be suppressed and the adsorption of reactants and the SR of nitroarenes can be promoted. The sample loaded with only of 0.03% Pt showed the highest performance and, after irradiation for 4 h, the conversions of p-methoxybenzyl alcohol and nitrobenzene are as high as 92.7% and 94.8%, while the yields of p-methoxybenzaldehyde and aniline are 80.5% and 36.0%. The activities are about 2.0 times higher than that of CdS. The coupling reaction mechanism for the SO of aromatic alcohols to aldehydes and SR of nitroarenes to anilines in the reaction system was finally proposed.

Theoretical Studies on DNA-Cleavage Mechanism of Copper(II) Complexes: Probing Generation of Reactive Oxygen Species.

Theoretical studies on DNA-cleavage properties of [Cu(bba)(diimine)] 1-4 have been carried out using density functional theory (DFT) and docking methods. The optimized structures of Cu(II) complexes were docked into DNA, glutathiones (GSH), and ascorbic acids (VC) so that the corresponding docking models were obtained. To explore DNA-cleavage properties of Cu(II) complexes, the docking models of complexes with GSH and VC were further optimized using DFT method, while the docking models of complexes with DNA were optimized using QM/MM method because DNA is a supramolecular system. The rate constants ket between complexes and DNA, GSH, and VC, oxidation-reduction potentials of complexes, and binding energies of complexes with GSH and VC were computed. The DNA-cleavage abilities of Cu(II) complexes in the presence VC, GSH, and H2O2 were explored and the experimental results could be reasonably explained. Finally, the DNA-cleavage mechanism of Cu(II) complexes was described in detail, which would contribute to future design of novel anticancer Cu(II) complexes.

Optimizing the precursor of sulfur source for hydrothermal synthesis of high performance CdS for photocatalytic hydrogen production.

Although the CdS photocatalyst has been extensively investigated, a rational hydrothermal synthesis route is still required to prepare highly active CdS for H2 evolution reaction (HER). To optimize the precursor of the sulfur source, three prevalent organic sulfur sources of thiourea (TA), thioacetamide (TAA) and l-cysteine (l-Cys) were used for hydrothermal synthesis of CdS. Their effects on the crystallographic structure, morphology, optical property, band structure, and photocatalytic HER performance of the products were then investigated systematically. The results indicated that hexagonal branched dendritic structure CdS (S-TA) could be produced in TA solution and showed the highest HER activity due to the branched 1D structure, the smallest interfacial electron transfer resistance and the most negative conduction band bottom (E cb). Whereas in TAA, spherical CdS (S-TAA) with a mixed phase of hexagonal and cubic was obtained. The mixed phase structure and the more positive E cb of S-TAA lead to a considerably lower HER activity than that of S-TA. Poorly crystallized hexagonal CdS nanoparticles (S-Cys) were prepared in l-Cys and showed the lowest HER performance as its E cb is very near to H+ reduction potential. Thus, compared to T-AA and l-Cys, TA is a more suitable sulfur source for hydrothermal preparation of highly active CdS for HER.

Solvothermal synthesis of CdIn2S4 photocatalyst for selective photosynthesis of organic aromatic compounds under visible light.

Ternary chalcogenide semiconductor, cadmium indium sulfide (CdIn2S4), was prepared by a simple solvothermal method using ethylene glycol as a solvent, as well as indium chloride tetrahydrate (InCl3.4H2O), cadmium nitrate tetrahydrate [Cd(NO3)2.4H2O], and thiacetamide (TAA) as precursors. The resulted sample was subject to a series of characterizations. It is the first time to use CdIn2S4 sample as a visible light-driven photocatalyst for simultaneous selective redox transformation of organic aromatic compounds. The results indicate that the as-synthesized CdIn2S4 photocatalyst not only has excellent photocatalytic performance compared with pure In2S3 and CdS for the selective oxidation of aromatic alcohols in an oxygen environment, but also shows high photocatalytic redox activities under nitrogen atmosphere. A possible mechanism for the photocatalytic redox reaction in the coupled system was proposed. It is hoped that our current work could extend the applications of CdIn2S4 photocatalyst and provide new insights for selective transformations of organic compounds.

What is the transfer mechanism of photogenerated carriers for the nanocomposite photocatalyst Ag3PO4/g-C3N4, band-band transfer or a direct Z-scheme?

The separation mechanisms of photoexcited carriers for composite photocatalysts are a hot point in the photocatalytic field. In this paper, the Ag3PO4/g-C3N4 nanocomposites with different main parts (Ag3PO4 or g-C3N4) were synthesized using a facile in situ precipitation method. The photocatalysts were characterized by X-ray powder diffraction, UV-vis diffuse reflection spectroscopy, transmission electron microscopy and Brunauer-Emmett-Teller methods. The photocatalytic performance was evaluated by the degradation of methylene blue under visible light irradiation. When the main part of the Ag3PO4/g-C3N4 photocatalyst is Ag3PO4, the transfer mechanism of photogenerated electron-hole takes generic band-band transfer, and the photocatalytic activity is decreased. However, when the primary part of the Ag3PO4/g-C3N4 photocatalyst is g-C3N4, the migration of photogenerated electron-hole exhibits a typical Z-scheme mechanism, and the photocatalytic activity is increased greatly. The separation mechanisms of photogenerated carriers were investigated by the electron spin resonance technology, the photoluminescence technique and the determination of reactive species in the photocatalytic reactions. It is hoped that this work could render guided information for design and application of Z-scheme photocatalysts with excellent photocatalytic performance.

Design of a direct Z-scheme photocatalyst: preparation and characterization of Bi2O3/g-C3N4 with high visible light activity.

A direct Z-scheme photocatalyst Bi2O3/g-C3N4 was prepared by ball milling and heat treatment methods. The photocatalyst was characterized by X-ray powder diffraction (XRD), UV-vis diffuse reflection spectroscopy (DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface areas, photoluminescence technique (PL), and electron spin resonance (ESR) technology. The photocatalytic activity was evaluated by degradation of methylene blue (MB) and rhodamine B (RhB). The results showed that Bi2O3/g-C3N4 exhibited a much higher photocatalytic activity than pure g-C3N4 under visible light illumination. The rate constants of MB and RhB degradation for Bi2O3(1.0wt.%)/g-C3N4 are about 3.4 and 5 times that of pure g-C3N4, respectively. The migration of photogenerated carriers adopts a Z-scheme mechanism. The photoexcited electrons in the CB of Bi2O3 and photogenerated holes in the VB of g-C3N4 are quickly combined, so the photoexcited electrons in the CB of g-C3N4 and holes in the VB of Bi2O3 participate in reduction and oxidation reactions, respectively. O2(-), OH and h(+) are the major reactive species for the Bi2O3/g-C3N4 photocatalytic system.

One-pot synthesis of ZnO2/ZnO composite with enhanced photocatalytic performance for organic dye removal.

The ZnO2/ZnO photocatalysts with various ZnO2 contents were prepared by one-pot synthesis method using ZnO and H2O2 as raw materials. The photocatalysts were characterized by XRD, UV-vis DRS, SEM, EDS, FT-IR spectra, fluorescence emission spectra, and BET specific area. The photocatalytic performance of the photocatalyst was evaluated by photocatalytic degradation of methyl orange (MO) and rhodamine B (RhB). The results showed that the photocatalytic activity of the ZnO2/ZnO was much higher than that of single-phase ZnO or ZnO2. The optimum ZnO2 content was 1.0 wt.%. The maximal degradation rate constant of MO and RhB was 4.1 times and 2.2 times that observed for pure ZnO, respectively. The stability of the prepared photocatalyst in the photocatalytic process was also investigated. The active species in dye degradation were examined by adding a series of scavengers. The possible mechanisms involved in the photocatalytic degradation of dye were also discussed.

Ball milled h-BN: an efficient holes transfer promoter to enhance the photocatalytic performance of TiO2.

High activity hexagonal-BN (h-BN)/TiO(2) composite photocatalysts were prepared by ball milling method. The structural and optical properties of the samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (DRS), and fluorescence emission spectra. The effect of the loading amount of h-BN and the ball milling time on the photocatalytic degradation of Rhodamine B (RhB) and methylene blue (MB) was investigated. The results indicated that the photocatalytic activity of TiO(2) could be improved substantially by coupling with a proper amount of milled h-BN. The optimal loading amount of h-BN was found to be 0.5 wt% and the milling time was 30 min. Under this condition, the photocatalytic removal efficiencies of TiO(2) for RhB and MB could be increased as high as 15 and 8 times. The role of the milling process and the mechanism for the enhancements was finally discussed in terms of creation of negatively charged h-BN surface and promotion the separation of photoinduced holes, respectively.

In situ preparation of novel p-n junction photocatalyst BiOI/(BiO)2CO3 with enhanced visible light photocatalytic activity.

Novel p-n junction photocatalysts BiOI/(BiO)2CO3 with different contents of BiOI were in situ synthesized by etching (BiO)2CO3 precursor with hydroiodic acid (HI) solution. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectrometry (FT-IR), energy-dispersive spectroscopy (EDS) and UV-vis diffuse reflectance spectroscopy (DRS) were employed to study the structures, morphologies and optical properties of the as-prepared samples. Under visible light (λ>420 nm), BiOI/(BiO)2CO3 hybrid displayed much higher photocatalytic activity than pure (BiO)2CO3 and BiOI for the degradation of methyl orange (MO). The increased photocatalytic activity of BiOI/(BiO)2CO3 could be attributed to the formation of the p-n junction between p-BiOI and n-(BiO)2CO3, which effectively suppresses the recombination of photoinduced electron-hole pairs. Moreover, the tests of radical scavengers confirmed that •O2- and h+ were the main reactive species for the degradation of MO.

Hydrogen production over titania-based photocatalysts.

Because of their relatively high efficiency, high photostability, abundance, low cost, and nontoxic qualities, titania-based photocatalysts are still the most extensively studied materials for the photocatalytic production of hydrogen from water. The effects of the chemical and physical properties of titania, including crystal phase, crystallinity, particle size, and surface area, on its photoactivity towards hydrogen generation have been identified by various investigations. The high overpotential for hydrogen generation, rapid recombination of photogenerated electrons and holes, rapid reverse reaction of molecular hydrogen and oxygen, and inability to absorb visible light are considered the most important factors that restrict the photoactivity of titania, and strategies to overcome these barriers have been developed. These issues and strategies are carefully reviewed and summarized in this Minireview. We aim to provide a critical, up-to-date overview of the development of titania-based photocatalysts for hydrogen production, as well as a comprehensive background source and guide for future research.

Urea-based hydrothermal growth, optical and photocatalytic properties of single-crystalline In(OH)3 nanocubes.

Nearly monodisperse single-crystalline In(OH)(3) nanocubes were successfully synthesized using In(NO(3))(3) x 4.5 H(2)O as indium source in the presence of urea and cetyltrimethyl ammonium bromide (CTAB) by a two-step hydrothermal process: the stock solution was heated at 70 degrees C for 24 h and then at 120 degrees C for 12 h. The structure and morphology of the resultant In(OH)(3) samples were determined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results revealed that most of as-synthesized In(OH)(3) nanocubes were uniform in size, with the average edge length of approximately 700 nm. The influences of the reaction temperature, the reaction time, the mineralizer, and the surfactant on the morphology of the obtained products were discussed in detail. Room-temperature photoluminescence (PL) spectrum of the In(OH)(3) nanocubes showed a peculiar strong emission peak centered at 480 nm. Furthermore, the photocatalytic properties of the In(OH)(3) nanocubes were tested. It was found that In(OH)(3) exhibited not only higher activity for benzene removal, but also better H(2) evolution from water than the commercial Degussa P25 TiO(2).