Efficient Visible Light Photocatalytic H2 Research Articles

(Invited) Towards Broadband Photocatalysis

Forming nanomaterials junctions and using plasmons represent two important, promising strategies for realizing broadband photocalysis in strategically important applications such as solar fuels and photocatalytic degradation of pollutants. In this talk, I will present some of our recent work on the rational design of nanohybrids and their applications in solar fuels and photocatalysis. One example is about the in situ synthesis of plasmonic Ag nanoparticles (AgNPs) and Ag-MOF. The intimate and stable interface between the AgNPs and Ag-MOF and hot electron transfer from the plasmonic AgNPs to MOF led to highly efficient visible-light photocatalytic H2 generation in aqueous solution, which surpasses most of reported MOF-based photocatalytic systems. This work sheds light on effective electronic and energy bridging between plasmonic NPs and MOF.

WO3/Cd0.5Zn0.5S heterojunction for highly efficient visible-light photocatalytic H2 evolution

The construction of heterogeneous structure is an effective measure to enhance photocatalytic hydrogen evolution. Herein, the WO3/Cd0.5Zn0.5S (WO3/CZS) heterogeneous catalyst is prepared via a simple hydrothermal method. The two-dimensional WO3 nanosheet is prepared by roasting the precipitates of sodium tungstate and hydrochloric acid. WO3 can effectively increase the absorption intensity of visible light, thereby generate more photogenerated carriers. Meanwhile, based on the universality of two-dimensional materials, the addition of WO3 nanosheet improves the stability of WO3/CZS composite catalyst. Additionally, the tight heterogeneous interface between WO3 and CZS ensures efficient electrons transport, which inhibits the recombination of electron-hole pairs. The optimized 30%-WO3/Cd0.5Zn0.5S photocatalyst shows the highest H2 production rate of 42.26 mmol g−1 h−1 under visible light, which is 3.43 times higher than the pure Cd0.5Zn0.5S photocatalyst (12.31 mmol g−1 h−1).

Silver nanoparticle enhanced metal-organic matrix with interface-engineering for efficient photocatalytic hydrogen evolution

Integrating plasmonic nanoparticles into the photoactive metal-organic matrix is highly desirable due to the plasmonic near field enhancement, complementary light absorption, and accelerated separation of photogenerated charge carriers at the junction interface. The construction of a well-defined, intimate interface is vital for efficient charge carrier separation, however, it remains a challenge in synthesis. Here we synthesize a junction bearing intimate interface, composed of plasmonic Ag nanoparticles and matrix with silver node via a facile one-step approach. The plasmonic effect of Ag nanoparticles on the matrix is visualized through electron energy loss mapping. Moreover, charge carrier transfer from the plasmonic nanoparticles to the matrix is verified through ultrafast transient absorption spectroscopy and in-situ photoelectron spectroscopy. The system delivers highly efficient visible-light photocatalytic H2 generation, surpassing most reported metal-organic framework-based photocatalytic systems. This work sheds light on effective electronic and energy bridging between plasmonic nanoparticles and organic semiconductors.

(Invited) Towards Broadband Solar Fuel Production

Combining nanomaterials of different properties into nanohybrids can potentially lead to improved properties/performance or multiple functions. In particular, forming nanomaterials junctions and using plasmons represent two important, promising strategies for realizing broadband photocalysis in strategically important applications such as solar fuels and photocatalytic degradation of pollutants in our environments. In this talk, I will present some of our recent work on the rational design and realization of nanohybrid materials as well as their applications in solar fuel and photocatalysis. For instance, the construction of homojunctions of nanoplates made of metal–organic frameworks (MOF) led to broadened light absorption and increased photoactivity. The well-defined MOF homojunction was prepared by a facile one-pot synthesis route directed by hollow transition metal nanoparticles. The homojunction is enabled by two concentric stacked nanoplates with slightly different crystal phases. The enhanced charge separation in the homojunction was visualized by in-situ surface photovoltage microscopy. The as-prepared nanostacks displayed a visible-light-driven carbon dioxide reduction with very high carbon monooxide selectivity, and excellent stability. Another example is about the in situ synthesis of plasmonic Ag nanoparticles (AgNPs) and Ag-MOM (metal organic matrix) using one-step facile approach. The intimate and stable interface between the AgNPs and Ag-MOM and hot electron transfer from the plasmonic AgNPs to MOM led to highly efficient visible-light photocatalytic H2 generation in aqueous solution, which surpasses most of reported MOF-based photocatalytic systems. This work sheds light on effective electronic and energy bridging between plasmonic NPs and metal organic matrix.Related

Fabrication of the SnS2/ZnIn2S4 heterojunction for highly efficient visible light photocatalytic H2 evolution

A series of SnS 2 /ZnIn 2 S 4 ( x -SS/ZIS) photocatalysts with different mass ratios of SnS 2 were prepared by a hydrothermal method. The resulted composites were used for photocatalytic hydrogen evolution under visible light excitation. All the SS/ZIS composites exhibited significantly enhanced photocatalytic activity for H 2 evolution. Obviously, the highest H 2 evolution rate of 769 μmol g −1 h −1 was observed over 2.5-SS/ZIS, which was approximately 10.5 times that of the ZnIn 2 S 4 (73 μmol g −1 h −1 ). The enhanced photocatalytic performance was attributed to the successful construction of SnS 2 /ZnIn 2 S 4 heterojunctions, leading to rapid charge separation and fast transfer of the photo-generated electrons and holes under light irradiation. On the basis of PL, electrochemical impedance spectroscopy (EIS), photocurrent measurements and the H 2 evolution tests, a plausible photocatalytic mechanism was proposed. • SnS 2 /ZnIn 2 S 4 composites were synthesized from SnS 2 nanosheets and ZnIn 2 S 4 microspheres. • SnS 2 /ZnIn 2 S 4 heterojunctions enhanced photocatalytic H 2 production under visible light. • Efficient charge separation and transfer at the heterojunctions explained the improved performance.

Well-designed NiS/CdS nanoparticles heterojunction for efficient visible-light photocatalytic H2 evolution

Heterojunction photocatalysts based on semiconducting nanoparticles show excellent performance in many photocatalytic reactions. In this study, 0D/0D heterojunction photocatalysts containing CdS and NiS nanoparticles (NPs) were successfully synthesized by a chemical precipitation method. The NiS NPs were grown in situ on CdS NPs, ensuring intimate contact between the semiconductors and improving the separation efficiency of hole-electron pairs. The obtained NiS/CdS composite delivered a photocatalytic H 2 evolution rate (7.49 mmol h −1 g −1 ), which was 39.42 times as high as that of pure CdS (0.19 mmol h −1 g −1 ). This study demonstrates the advantages of 0D/0D heterojunction photocatalysts for visible light-driven photocatalytic hydrogen production. • 0D/0D NiS/CdS heterojunction were successfully synthesized by a novel method. • Photocatalytic activity of NiS/CdS-X was related to the crystallization time of CdS. • NiS/CdS-90 showed high catalytic activity and stability for hydrogen evolution. • The possible mechanism for enhanced photocatalytic activity was proposed.

Enhancing interfacial charge transfer in mesoporous MoS2/CdS nanojunction architectures for highly efficient visible-light photocatalytic water splitting

Mesoporous MoS2-modified CdS nanojunction networks possessing advantageous electronic connectivity and charge transfer behavior at the interfaces deliver highly efficient visible-light photocatalytic H2 production activity from water splitting.

Two-dimensional ZnS (propylamine) photocatalyst for efficient visible light photocatalytic H2 production

Photocatalytic hydrogen production is recognized as a prospective technology for energy conversion to alleviate the energy shortage. Hence, we propose a convenient method to synthesize two-dimensional (2D) ZnS-propylamine (pa) hybrid complex materials with traditional solvothermal method, demonstrating prominent photocatalytivity under visible light irradiation. Meanwhile, the improvement of hydrogen production has been further investigated by controlling different in-situ ultrasonic times. The optimized hydrogen generation obtained from ZnS(pa)x was up to 1828 μmol/g under 4 h visible light irradiation. The high performance could be contributed by the inorganic-organic coordination effect on optimizing the morphology and structure, which enlarge reaction sites and accelerate carriers migration of the material. This work represents an effective approach to promote and optimize the traditional wide bandgap semiconductors for enlarging visible light photocatalytic performances.

CdS nanorods decorated with ultrathin MoS2 nanosheets for efficient visible-light photocatalytic H2 production

A binary composite photocatalyst MoS2/CdS was synthesized by a modified solvothermal method. The composites show higher photogenerated electron transfer rate and stronger photocatalytic performance. The structure and morphology were characterized by different methods. It was found that the composites consist of by core–shell structure. And the MoS2 nanosheets are ultrathin and exposed to a large number of edge positions, which is beneficial to improve carrier transport efficiency. Further findings show that the more reactive sites are on the nannosheets, the more hydrogen will be produced. UV–Vis, PL and transient photocurrent analysis showed that the catalyst effectively inhibit the recombination of photogenerated electrons and holes. Hydrogen production experiment indicates the best photocatalytic performance appears when the loading of MoS2 is 8wt%, and the rate of hydrogen production is about 5200 μmol g−1 h−1.

Noble-Metal-Free CdS Decorated Porous NixCo1–xO Skeleton Derived from Metal–Organic Framework for Efficient Visible-Light H2 Production

Noble-metal-free CdS@NixCo1–xO photocatalyst was synthesized for the first time using a metal–organic framework (MOF) to serve as the template for efficient visible-light photocatalytic H2 producti...

Orthorhombic WP co-catalyst coupled with electron transfer bridge UiO-66 for efficient visible-light-driven H2 evolution

The abundant transition metal phosphides co-catalysts on the earth can satisfy the sustainable and clean solar H2 production through photocatalytic water splitting, which is promising to replace the rare precious metals, such as Pt, Au, Pd, Ru and so on. In this paper, we use the temperature-programmed solid phase method to prepare WP nanoparticles. Based on the Density Functional Theory (DFT) calculations, we demonstrate that the WP nanoparticles possess outstanding electrical conductivity and excellent capability to transport electrons. WP nanoparticles are loaded onto the surface of UiO-66 via the ultrasound-assisted impregnation method to induce a highly efficient visible-light photocatalytic H2 production activity of 384 µmol in 5 h, which is 10.67 times than that of pure UiO-66. The catalytic performance is attributed to the excellent metallic conductivity and the favourable Fermi level position of WP nanoparticles. Further studies of PL, TRPL and Mott-Schottky curves, we can not only know that the modification of WP nanoparticles do improve the electron transfer ability, but also that the matched work functions between the EY and UiO-66 provides a feasible thermodynamic path for the transmission of electrons. Our work demonstrates that the earth-abundant transition metal phosphides material have the potential to construct cheaper and high catalytic performance photocatalysts.

Fabrication of a NiCo2O4/Zn0.1Cd0.9S p-n heterojunction photocatalyst with improved separation of charge carriers for highly efficient visible light photocatalytic H2 evolution

Photocatalytic hydrogen (H2) evolution is a greatly promising strategy for solar to H2 conversion. However, photocatalytic activity of single photocatalyst is limited due to the fast recombination of photogenerated charge carriers. Recently, various heterojunction photocatalysts have been constructed to improve photocatalytic activity. Herein, a novel NiCo2O4/Zn0.1Cd0.9S (NCO/ZCS) p-n heterojunction photocatalyst was fabricated via a simple calcination method. The optimized NiCo2O4 content is 3 wt%, and corresponding NCO/ZCS shows the maximum H2 evolution rate of 34.4 mmol g−1 h−1 under visible light irradiation, which is over 4.9 times higher than that of pure ZCS, and has the apparent quantum efficiency of 58.8% at 420 nm. The improved photoactivity of NCO/ZCS can be attributed to the construction of NCO/ZCS p-n heterojunction. In addition, a possible mechanism for photocatalytic H2 evolution of NCO/ZCS p-n heterojunction was proposed.

Strong organic acid-assistant synthesis of holey graphitic carbon nitride for efficient visible light photocatalytic H2 generation

A facile and cost-effective method was developed for the synthesis of holey N-deficient graphitic carbon nitride nanosheets (FCN) using trifluoroacetic-acid-treated urea as a precursor. The role of trifluoroacetic acid on the composition, structure and photocatalytic performance of the prepared catalysts was carefully investigated. The obtained samples displayed laminated porous morphology with nitrogen defects, larger specific surface areas, extended range of spectral response and enhanced electron mobility of charge carriers. Consequently, the optimized catalyst FCN-400 exhibited superb photocatalytic performance and excellent cycling stability for hydrogen evolution. The hydrogen evolution rate over FCN-400 reached 309.3 μmol/h under visible light irradiation, which is 11.3-fold of that of urea-derived graphitic carbon nitride (27.3 μmol/h).

Facile fabrication of oxygen and carbon co-doped carbon nitride nanosheets for efficient visible light photocatalytic H2 evolution and CO2 reduction.

In this study, to overcome the low charge transportation efficiency and poor visible light absorption ability, and achieve highly efficient photocatalytic applications, carbon nitride nanosheets with oxygen and carbon co-doping were successfully designed and fabricated. The resultant carbon nitride nanosheets exhibited efficient photocatalytic H2 evolution and CO2 reduction performance, highlighting the efficacy of such a strategy. The highest H2 evolution rate could reach 698.43 μmol g-1 h-1, higher than that for graphitic carbon nitride (GCN). For CO2 reduction, the photocatalytic system shows a high CO selectivity, and MG3.0 achieves the largest CO generation amount of 55.2 μmol g-1. This enhanced photocatalytic reduction performance could be attributed to oxygen and carbon co-doping, which achieves fast electron extraction and transfer, and improved visible light absorption ability. It should be noted that the excessive addition of glucose in the synthesis process could enhance conductivity and promote visible light absorption of carbon nitride, but suppress the H2 evolution and CO2 reduction ability. Simultaneously, the photocatalytic reduction mechanism is discussed. This work confirms that a carbon nitride semiconductor with oxygen and carbon co-doping could be easily prepared by this strategy, achieving efficient photocatalytic applications.

Enhanced photoexcited carrier separation in CdS–SnS2 heteronanostructures: a new 1D–0D visible-light photocatalytic system for the hydrogen evolution reaction

CdS–SnS2 1D–0D core–shell heteronanostructures were designed for an efficient visible-light photocatalytic H2 evolution reaction.

Highly efficient Cu induced photocatalysis for visible-light hydrogen evolution

Coinage metal (Au, Ag, Cu) induced photocatalysis has emerged as a promising strategy in developing visible-light responsive photocatalysts. Though much progress has been made, yet researchers in this field faced great challenges from both low efficiency and rigorously relying on noble metal Au. In this work, a series of Cu/SrTiO3 with gradually increased Cu particle size from 2.8 to 7.7 nm were successfully prepared with in situ multistep photodeposition method. A highly efficient visible-light photocatalytic H2 evolution is achieved over 0.5 wt% Cu/SiTiO3 with an average Cu particle size of 3.9 nm, which reaches 5 fold as compared with its counterpart Au. As far as we know, it is the first time that Cu induced visible-light photocatalytic water splitting show prominently superior activity than that of Au under the same conditions. Further study reveals that the increase of Cu particle size effectively mitigates Fano interference between interband transition and localized surface plasmon resonance (LSPR), which extends the photo-induced carriers lifetime. The discovery here is supposed to ignite great research interests in exploring efficient and nonprecious Cu induced visible-light photocatalysis.

A New and stable Mo-Mo2C modified g-C3N4 photocatalyst for efficient visible light photocatalytic H2 production

Design and preparation of highly efficient and stable cocatalysts are critical to the improvement of photocatalyst performance. A traditional cocatalyst consists of metal nanoparticles for the separation of photo-induced electron-hole pairs and for the reduction of protons. In this research we report a metal-semiconductor composite cocatalyst to increase light adsorption and to effectively enhance proton reduction capacity. A molybdenum rich molybdenum carbide (Mo-Mo2C) based noble-metal-free metal/semiconductor cocatalyst was loaded onto graphitic carbon nitride (g-C3N4) for highly efficient photocatalytic H2 evolution from water. The Mo-Mo2C was synthesized via a temperature-programmed reaction using (NH4)6Mo7O24·4H2O as a precursor. The cocatalyst loaded 2.0 wt.% Mo-Mo2C/g-C3N4 composite photocatalyst has demonstrated excellent photocatalytic performance. The hydrogen evolution rate for the 2.0 wt.% Mo-Mo2C/g-C3N4 nanocomposites can be as high as 219.7 μmol h−1 g−1, which is 440 times higher than that of g-C3N4 alone and 90% as high as 0.5 wt.% Pt/g-C3N4 photocatalyst (244.1 μmol h−1 g−1). Due to strong synergetic effects between Mo and Mo2C nanoparticles, this rate is 11.47 and 3.60 times higher than those for 2.0 wt.% Mo/g-C3N4 (19.1 μmol h−1 g−1) and 2.0 wt.% Mo2C/g-C3N4 (60.9 μmol h−1 g−1) photocatalysts respectively. Moreover, the 2.0 wt.% Mo-Mo2C/g-C3N4 catalyst is significantly stable for application in photocatalytic hydrogen evolution, with an apparent quantum efficiency of 8.3%—one of the highest noble-metal-free efficiencies reported in literature. All results indicate that metal/semiconductor composites can serve as highly efficient cocatalysts for photocatalytic hydrogen evolution from water reduction.

In situ one-pot fabrication of g-C3N4 nanosheets/NiS cocatalyst heterojunction with intimate interfaces for efficient visible light photocatalytic H2 generation

Constructing high-quality earth-abundant semionconductor/cocatalyst heterojunction remains a grand challenge in the promising fields of photocatalytic solar fuel H2 production. Herein, an intimate g-C3N4 nanosheet/NiS cocatalyst heterojunction is fabricated by in situ one-step calcination of urea, thiourea and nickel acetate. Interestingly, thiourea could act as both the precursor of g-C3N4 and the sulfur source of NiS. The H2-evolution activity of as-obtained photocatalysts was tested in a triethanolamine (TEOA) scavenger solution under visible light irradiation. Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) mapping analysis clearly demonstrated that the NiS catalyst nanoparticles could be in situ fabricated and homogeneously distributed on the surface of g-C3N4 nanosheets without an obvious aggregation. The maximum H2-production rate of 29.68μmolh−1 could be achieved, which is nearly comparable to that of 0.5wt% Pt loaded sample. It is believed that the intimate heterojunction interfaces between NiS nanoparticles and g-C3N4 nanosheets could be in situ constructed by high temperature calcination, which achieved the improved charge separation, the enhanced oxidation ability of TEOA and the accelerated the sluggish H2-evolution kinetics, thus resulting in the remarkably enhanced hydrogen evolution. Therefore, our study provides insights into constructing high-quality robust g-C3N4-based heterojunction material for photocatalytic applications by using a simple one-step in-situ calcination technique.

Multi-node CdS hetero-nanowires grown with defect-rich oxygen-doped MoS2 ultrathin nanosheets for efficient visible-light photocatalytic H2 evolution

Developing low-cost and high-efficiency photocatalysts for hydrogen production from solar water splitting is intriguing but challenging. In this study, unique one-dimensional (1D) multi-node MoS2/CdS hetero-nanowires (NWs) for efficient visible-light photocatalytic H2 evolution are synthesized via a facile hydrothermal method. Flower-like sheaths are assembled from numerous defect-rich O-incorporated {0001} MoS2 ultrathin nanosheets (NSs), and {1120}-facet surrounded CdS NW stems are grown preferentially along the c-axis. Interestingly, the defects in the MoS2 NSs provide additional active S atoms on the exposed edge sites, and the incorporation of O reduces the energy barrier for H2 evolution and increases the electric conductivity of the MoS2 NSs. Moreover, the recombination of photoinduced charge carriers is significantly inhibited by the heterojunction formed between the MoS2 NSs and CdS NWs. Therefore, in the absence of noble metals as co-catalysts, the 1D MoS2 NS/CdS NW hybrids exhibit an excellent H2-generation rate of 10.85 mmol·g–1·h–1 and a quantum yield of 22.0% at λ = 475 nm, which is far better than those of Pt/CdS NWs, pure MoS2 NSs, and CdS NWs as well as their physical mixtures. Our results contribute to the rational construction of highly reactive nanostructures for various catalytic applications.

Synthesis and efficient visible light photocatalytic H2 evolution of a metal-free g-C3N4/graphene quantum dots hybrid photocatalyst

In this work, we report a systematic study of the relationship between photocatalytic properties of hydrogen evolution and structures and morphologies of g-C3N4 prepared by different precursors (urea, melamine and dicyandiamide). The photocatalytic performances of H2 production are affected by the method and degree of polymerization, the degree of protonation, and the morphology of g-C3N4 prepared by different precursors. Furthermore, a novel metal-free N-GQDs/g-C3N4 catalyst was designed and synthesized, which shows much better photocatalytic activity for H2 evolution from water splitting than that of g-C3N4 due to the unique and multiple roles of N-GQDs. A mechanism is put forth to explain the roles of N-GQDs and the detailed enhancement of photocatalytic performance of the N-GQDs/g-C3N4.