Photocatalytic H2 Production Rate Research Articles

The metallic 1T-phase WS2 nanosheets as cocatalysts for enhancing the photocatalytic hydrogen evolution of g-C3N4 nanotubes

Herein, we report that 2D metallic 1T-WS2 acts as co-catalyst in assisting g-C3N4 nanotubes (NTs) obtained via a simple grinding method for promoting photocatalytic H2 production. The 1T-WS2/g-C3N4 composite with optimum 27% 1T-WS2 displays a significantly improved photocatalytic H2 production rate (1021 μmol h−1 g−1), 17.6 times higher than g-C3N4 NTs. Besides, the apparent quantum efficiency (AQE) of 1T-WS2/g-C3N4 composite (27%) achieves 11.23% under light at λ = 370 nm. Meanwhile, the 1T-WS2/g-C3N4 composites present an excellent photocatalytic H2 production stability. The possible photocatalytic mechanism over 1T-WS2/g-C3N4 composites is proposed. Specifically, the photogenerated electrons from 1D g-C3N4 tubular nanostructure with open mesoporous morphology are migrated to conductive 1T-WS2 NSs quickly as electron acceptors along the 1D path. 1T-WS2 NSs can also offer abundant active sites on the edge and basal planes.

Selective formation of interfacial bonding enables superior hydrogen production in organic–inorganic hybrid cocatalyzed photocatalysts

Rational design of cocatalysts on semiconductor photocatalysts holds great promise for boosting the photo-to-electron conversion efficiency. However, constructing favorable interfacial structure facilitating the charge carriers’ transportation in photocatalyst system remains challenging. Here, we demonstrate an organic–inorganic hybrid cocatalyzed photocatalyst with tunable interfacial structure for photocatalytic hydrogen (H2) production, where polyaniline (PANI) monolayer and Pt nanoparticles cocatalyzed CdS is a proof-of-concept. The selective formation of adequate interfacial bonding at both the cocatalyst/semiconductor interfaces, and the organic/inorganic cocatalyst interface is the key to promote charge carriers’ transport. The photocatalytic H2 production rate of CdS/PANI-O/Pt-OH with adequate S-C, S-Pt and Pt-N interfacial bonding is 16 times and 84 times that of CdS/PANI-R/Pt-H with much less interfacial bonding and pristine CdS, respectively. And superior apparent quantum efficiency of 92.1% at 440 nm is achieved. This finding opens up a rational approach to understanding and engineering the interfacial structure in various energy conversion systems.

Rationalizing and controlling the phase transformation of semi-metallic 1T′-phase and semi-conductive 2H-phase MoS2 as cocatalysts for photocatalytic hydrogen evolution

In this study, we report that the 2D semi-metallic 1T′-MoS2 serves as co-catalyst in assisting 1T′-MoS2/g-C3N4 composites obtained via a one-pot hydrothermal technique for boosting photocatalytic H2 evolution, and the phase transformation from 1T′ to 2H is achieved via thermal treatment. The designed 1T′-MoS2/g-C3N4 composite exhibits significant enhancement than pure g-C3N4 and 2H-MoS2/g-C3N4. The 1T′-MoS2/g-C3N4 composite with optimum 20 wt% 1T′-MoS2 displays a significantly improved photocatalytic H2 production rate (4426 μmol·h−1·g−1), which is about 86.7 and 1.41 times of pure g-C3N4 and 20 wt%–2H-MoS2/g-C3N4 composite, along with excellent stability. Besides, the apparent quantum efficiency (AQE) of 1T′-MoS2/g-C3N4 composite (20 wt%) achieves 13.55%. 1T′-MoS2 co-catalysts not only serve as effective electron acceptors, but have the merits of the energetically more stable.

Efficient Light Responsive (UCNPs)-Pt@MOF/Au Composites for Photocatalytic Hydrogen Evolution By Harvesting from Extended UV to Near-Infrared

Photocatalytic water splitting by utilizing broadband spectral response from UV to near-infrared (NIR) region is a big challenge and yet a prime target. 50% of the solar spectrum constituted by NIR light and in this work, our target is to increase absorption range from UV-visible to NIR by using (UCNPs)-Pt@MOF/Au composites. In this context, lanthanide-doped upconversion nanoparticles (UCNPs) are able to convert NIR to UV and visible, which are then harvested by metal-organic framework (MOF) and Au. MOF and plasmonic Au nanoparticles (NPs) broaden the absorption of UV light to a visible region as well as speed up the transfer of charges considerably. For this experiment, we used MIL-125 as a MOF because it is a wide-bandgap semiconductor. The spatial separation of Pt and Au particles by the MOF further steers the charge migration and also provides access to active Pt sites for the catalytic product as a result, the optimized composite exhibits high photocatalytic H2 production rate under UV, visible and NIR regions.

Self-Activation of TiO2 Nanotubes for Photocatalytic H2 Generation

TiO2 and particularly its anatase form, is one of the most widely studied oxide semiconductors for photocatalytic production of H2 from aqueous solutions.In anatase, the conduction band is situated at an energetic position that allows the transfer of photogenerated electrons to aqueous media and thus the conversion of H+ into H2. Moreover, TiO2 provides an almost unique high resistance against chemical and photocorrosion. On the other hand, photocatalytic H2 production from aqueous electrolytes shows very slow kinetics on all TiO2 surfaces. Therefore, typically decoration of titania with co-catalysts is used to accelerate the H2 evolution kinetics. Most effective co-catalysts are costly noble metals, such as Pt, Pd, or Au. Economically it is of great interest to develop means and approaches to reduce the use of such costly co-catalyst. In the presentation, we discuss efficient noble-metal-free approaches for catalyzing photocatalytic hydrogen generation. A particularly interesting approach is provided by defined defect engineering of anatase. Specific shallow Ti3+ states can promote the generation of photocatalytic H2. Most spectacular is that these catalytic sites can be formed by photoinduced reduction. In other words, under suitable illumination conditions it is possible to create, in situ, energetically suitable Ti3+ states that then act as an intrinsic co-catalyst for photocatalytic H2 evolution. As a result, both co-catalytic formation of active sites and photocatalytic H2 formation is observed. I.e., with increasing illumination time, a light‐induced self‐amplification of the photocatalytic H2 production rate occurs. The effect is characterized by electron paramagnetic resonance (EPR) spectroscopy, reflectivity, and photoelectrochemical techniques. The origin of the self‐activation and amplification behavior observed for anatase nanoparticles and nanotubes will be discussed in the presentation.

Metal-free Z-scheme 2D/2D VdW heterojunction for high-efficiency and durable photocatalytic H2 production

Metal-free material is a kind of promising ideal candidate in application of photocatalytic hydrogen (H2) production for everlasting direct solar-to-fuel conversion, but a longstanding challenge still is how to achieve the continuously high-efficiency and stable H2 production performance. Herein, metal-free 2D/2D carbon nitride/C-doped BN (CN/BCN) Van der Waals (VdW) heterojunctions are fabricated, and the optimal photocatalytic H2 production rate over them reaches up to 3357.1 µmol h−1 g−1 that far exceeds that of single CN (1298.8 µmol h−1 g−1) under the visible light. Meanwhile, the high apparent quantum efficiency (AQE) of 16.3% at 420 nm is achieved surprisingly. Moreover, the metal-free 2D/2D CN/BCN VdW heterojunction exhibits the superior stability because H2 production rate has barely reduction when enduring 15 cycle runs with total 60 h. The boosted H2 production performance arises from the formation of Z-Scheme mechanism that dramatically accelerates interfacial transfer and separation of charge carriers. This work furnishes a demonstration model for the tailor-made design and fabrication of other challenging metal-free 2D/2D VdW heterojunctions applied to catalysis, electronics, optoelectronics, etc.

Noble-metal-free CdS/Ni-MOF composites with highly efficient charge separation for photocatalytic H2 evolution

Constructing semiconductor-based photocatalysts with high-performance and excellent stability is a promising approach to achieve optimum photocatalytic H2 production rate from water splitting. In this study, a novel effective visible-light-driven catalyst, namely, CdS/Ni-MOF, has been successfully synthesized by in-situ growth of CdS nanoparticles on the surface of hollow Ni-based metal-organic framework (Ni-MOF) spheres. The heterogeneous interface contact and matched band position promote charge separation. As a noble-metal-free catalyst, the obtained CdS/Ni-MOF composite having an optimal CdS loading of 40 wt.% exhibits a remarkable H2 production rate of 2508 μmol/g/h under visible light, which is about eight times higher than that of single CdS. Ni-MOF serves as a station for the rapid transfer of photo-induced electrons, leading to the high photocatalytic performance. Meanwhile, Ni-MOF comprising highly dispersed Ni2+ catalytic sites also acts as co-catalyst, which is beneficial for hydrogen evolution. Therefore, Ni-MOF functions as both an electron acceptor and a co-catalyst in the photocatalytic H2 production from water. This work highlights the advantages of combining semiconductor and MOF functionalities to fabricate a photocatalyst with enhanced catalytic activity.

Microwave heating preparation of phosphorus doped g-C3N4 and its enhanced performance for photocatalytic H2 evolution in the help of Ag3PO4 nanoparticles

This paper synthesized a novel Ag3PO4/P-g-C3N4 via a two-step chemical route i.e. microwave-assisted heating and ion-exchange procedures. The as-synthesized hybrid presented high efficiency for photocatalytic hydrogen production. Systematic investigation indicated that phosphorus was successfully doped into the g-C3N4 framework through microwave heating the mixture of melamine and NH4H2PO4 for 40 min, which increases the BET surface area, broadens the visible light response region, and elevates the separation efficiency of electron-hole pairs. The Ag3PO4 nanoparticles were decorated on the optimal P-g-C3N4 sample via an ion-exchange process. Due to the instability of Ag3PO4, the formed composite is actually Ag/Ag3PO4/P-g-C3N4 photocatalyst. The introduced Ag3PO4 nanoparticles further improves the charge separation efficiency of P-g-C3N4, but slightly affects the surface area and optical property, which highlights the key role of the separation efficiency of electron-hole pairs in photocatalytic reaction. The best Ag3PO4/P-g-C3N4 hybrid shows a photocatalytic H2 production rate of 1221 and 90.2 μmol g−1 h−1 under simulated sunlight and visible light, respectively. This value is 2.1 and 1.4 times greater than that of g-C3N4 and P-g-C3N4, respectively. Meanwhile, the Ag3PO4/P-g-C3N4 displayed high photocatalytic stability. A probable photocatalytic mechanism of the hybrid was also suggested.

Supramolecular electrostatic self-assembly of mesoporous thin-walled graphitic carbon nitride microtubes for highly efficient visible-light photocatalytic activities

For efficient solar energy conversion, the morphology engineering of hollow graphitic carbon nitride (g-C3N4) is one of the promising approachs benefiting from abundant exposed active sites and short photocarrier transport distances, but is difficult to control on account of easy structural collapse. Herein, a facile supramolecular electrostatic self-assembly strategy has been developed for the first time to fabricate mesoporous thin-walled g-C3N4 microtubes (mtw-CNT) with shell thickness of ca. 13 nm. The morphological control of g-C3N4 enhances specific surface area by 12 times, induces stronger optical absorption, widens bandgap by 0.18 eV, improves photocurrent density by 2.5 times, and prolongs lifetimes of charge carriers from bulk to surface, compared with those of bulk g-C3N4. As a consequence, the transformed g-C3N4 exhibits the optimum photocatalytic H2-production rate of 3.99 mmol·h−1·g−1 (λ > 420 nm) with remarkable apparent quantum efficiency of 8.7% (λ = 420 ± 15 nm) and long-term stability. Moreover, mtw-CNT also achieves high photocatalytic CO2-to-CO selectivity of 96% (λ > 420 nm), much better than those on the most previously reported porous g-C3N4 photocatalysts prepared by the conventional hard-templating and soft-templating methods.

Accelerating charge transfer for highly efficient visible-light-driven photocatalytic H2 production: In-situ constructing Schottky junction via anchoring Ni-P alloy onto defect-rich ZnS

The development of efficient and stable photocatalysts is fundamentally required for sunlight-driven water splitting. Herein, Ni-P alloy is controllably anchored onto the surface of defect-rich ZnS (DR-ZnS) nanospheres through in-situ photodeposition strategy. The optimized Ni-P/DR-ZnS nanocomposite displays superior visible-light photocatalytic H2 production rate (69.92 μmol h−1), which is about 29 times and 3.6 times higher than that of the bare DR-ZnS and 1 wt% Pt/DR-ZnS, respectively, and a notable apparent quantum yield of 2.4 % at 420 nm. The existence of rich defects endows the DR-ZnS with visible-light absorption capability. The constructed Schottky junction between the Ni-P alloy and DR-ZnS accelerates the transfer of photogenerated electrons from DR-ZnS to Ni-P, thus boosting the photocatalytic performance. Moreover, the charge transfer process and underlying photocatalytic mechanism are unravelled by multiple in-depth characterizations. This research sheds novel light on rationally fabricating high-efficient and low-cost photocatalysts through integrating defect engineering and Schottky junction design.

Excellent photoelectrochemical hydrogen evolution performance of FeSe2 nanorod/ZnSe 0D/1D heterostructure as efficiency carriers migrate channel

In the photoelectrochemistry reaction, the electrode is most important. As a common electrode material, the metal oxide has a large band gap and high internal resistance, which is disadvantageous for photocatalytic hydrogen production. Metal selenide generally has a narrow band gap and low internal resistance, which is a promising new type of photocatalyst. A FeSe2/ZnSe heterojunction photocatalyst is constructed by loading ZnSe nanoparticles on FeSe2 nanorods. In this heterostructure, ZnSe is uniformly supported on the surface of FeSe2 to form a 0D/1D structure. Experiments have confirmed that the photoelectrochemical activity and photocatalytic H2 production rate of this heterojunction photocatalyst is greatly improved, and its optimum performance is three times of ZnSe in photoelectrochemical activity and 2.3 times in photocatalytic H2 production rate. Further analysis reveals that the internal resistance of the composite photocatalyst is greatly reduced due to the compositing of FeSe2, and the carrier separation efficiency is also improved. In this FeSe2/ZnSe heterojunction, the conduction band of ZnSe is more negative than that of FeSe2, and the photogenerated electrons generated on the conduction band of ZnSe can be transferred to that of FeSe2, thereby prolonging the carrier lifetime and improving photoelectrochemical activity. This work confirms that FeSe2/ZnSe is a very effective heterostructure, which avoids the addition of precious metals and rare earth metals and shows great application prospects.

Layer-by-layer assembly into bulk-like g-C3N4via artificial manipulation of electrostatic forces.

For the first time, bulk-like g-C3N4 was achieved through initiating layer-by-layer assembly, which involves the important process of artificially manipulating protonated and oxygen doped g-C3N4 nanosheets. When acting as a photocatalyst under UV-visible light irradiation, bulk-like g-C3N4 exhibited an excellent photocatalytic H2 production rate of 1538 μmol h-1 g-1, about 8 times higher than that of the bulk g-C3N4 counterpart.

Synergetic effect of defects rich MoS2 and Ti3C2 MXene as cocatalysts for enhanced photocatalytic H2 production activity of TiO2

The biggest challenging issue in photocatalytic hydrogen production is to efficiently separate the photoinduced electron-hole pairs and requires the enrichment of photoinduced electrons on the surface of photocatalysts. Herein, TiO2 nanosheets (NSs) are in situ grown on highly conductive Ti3C2 MXene and then MoS2 rich in molybdenum vacancies are uniformly distributed on TiO2@Ti3C2 composite through a two-step hydrothermal method. Thus, a unique structure of MoxS@TiO2@Ti3C2 composite with molybdenum vacancies and double co-catalysts (Ti3C2 and MoS2) is achieved. The photocatalytic H2 production rate of MoxS@TiO2@Ti3C2 composite with an optimized hydrothermal treatment temperature (160 °C) is nearly 193 and 6 times higher than that of pure TiO2 NSs and MoS2@TiO2@Ti3C2 composites (160 °C). A large number of active sites with the enhanced specific activity for H2 generation are induced by the introduction of molybdenum vacancies to MoS2 in MoxS@TiO2@Ti3C2 composites. The presence of molybdenum vacancies can suppress carrier recombination, which is beneficial to the reaction. Besides, the presences of Ti3C2 MXene and MoS2 are found to as double co-catalysts to enhance the electronic conductivity, resulting in an increase in efficiency for electron transfer.

Facile synthesis of silicon-doped polymeric carbon nitride with enhanced photocatalytic performance

Non-metal doping is an effective strategy to enhance the photocatalytic performance of polymeric carbon nitride (CN), but silicon (Si) doping in CN has never been realized yet. Herein, Si-doped CN (CNSi) was firstly prepared via a simple calcination process, by using (NH4)2SiF6 as the Si source, and exhibits prominently enhanced photocatalytic activity in H2 evolution from water splitting and for environmental purification. Its photocatalytic H2 production rate under visible light irradiation is 2.24 mmol g−1 h−1 which is ∼3 times that of CN, with an apparent quantum yield reaching ∼7% at 420 nm. The photoactivity improvement of CNSi arises from its prominent increase in photoinduced charge separation and transfer efficiencies. The doping mechanism of Si in CN is well illustrated. CNSi exhibits a high chemical stability and also great potential for application in solar energy conversion and environmental remediation. This work provides a novel way to modify CN and paves an avenue for synthesizing other Si-containing CN photocatalysts.

Enhanced photocatalytic hydrogen evolution over semi-crystalline tungsten phosphide

Increasing the separation efficiency and transfer rate of photogenerated charges is the dominant factor for improving photocatalytic activity. Herein, we successfully prepared semi-crystalline WP (SC-WP) with good optical properties and as a cocatalyst to modify CdS nanorods (CdS NRs) to construct SC-WP/CdS (PD) composite catalyst by simple electrostatic self-assembly method for photocatalytic hydrogen evolution. Two high-efficiency and stable photocatalytic hydrogen evolution systems were constructed with 1.0 M ammonium sulfite solution and 10 vol% lactic acid solution as sacrificial agents, respectively. Surprisingly, the maximum photocatalytic H2 production rate of 15446.21 μmol h−1 g−1 is obtained over 10PD composite, which is 10.58 times greater than that of pure CdS. The improved photocatalytic activity can be attributed to the fact that the SC-WP nanoparticles provides a large number of exposed active sites on the surface of CdS for hydrogen evolution reaction, which can efficiently capture photogenerated electrons from CdS nanorods and promotes the transport and separation of light-induced charges. And the introduction of SC-WP nanoparticles with excellent optical properties can efficiently improve the visible light absorption range and the utilization rate of the absorbed light of the PD composite. In addition, the SC-WP nanoparticles show semi-crystalline state, which is also conducive to enhancing the photocatalytic activity.

Enhanced visible-light photocatalytic H2 production of hierarchical g-C3N4 hexagon by one-step self-assembly strategy

Herein, self-assembly of hierarchical multihole g-C3N4 hexagon with excellent specific surface area (129 m2/g) and nitrogen vacancies were accomplished via a one-step polymerization of hydrothermal-treated dicyandiamide and ethylene-diamine-tetra-acetic acid (EDTA). The special chelate structure of EDTA efficiently enlarged a broad visible light response range, and the concentrations of EDTA promoted the self-assembly formation of different surface morphology. The photocatalytic H2 production rate under visible light for the optimal g-C3N4 hexagon (CN-20E) reaches 5839 μmol·g−1·h−1 and its apparent quantum efficiency reaches up to 7.3% at 420 nm, which has a 102 times higher for H2 production rate than that of bulk g-C3N4 (57 μmol·g−1·h−1). Special structure of the multihole hexagon endows them with remarkably visible light absorption, fast separation of photo-induced charge carriers, large surface areas as well as the exposure of potential photocatalytic active sites, thereby dramatically improved the H2 production property. Moreover, the forming process for the specific structure and the reaction mechanism of the enhanced photocatalytic activity were proposed according to the experimental results and theoretical calculations. This work exhibits a new avenue to rehandle graphitic carbon nitride precursor to build a grafted structure for developing highly efficient g-C3N4 in the practical photocatalytic application.

In-situ synthesis of CdS quantum dots on CdCO3 cubic structure for enhanced photocatalytic hydrogen production performance

Abstract The CdCO3 cubic structure was firstly synthesized by hydrothermal method. Then CdS quantum dots (QDs) were in-situ deposited on the CdCO3 to form CdCO3/CdS QDs composite photocatalyst to explore its photocatalytic hydrogen production performance. Physical characterization results show that cubic CdCO3 consists of nanoflake structures, and CdS QDs are uniformly dispersed on the surface of CdCO3 nanoflakes to form heterostructures. Under visible light irradiation, CdCO3/CdS QDs photocatalyst exhibits excellent photocatalytic performance with the photocatalytic H2 production rate of 1.93 mmol·h−1·g−1. The cubic CdCO3 can provide a large number of activity sites for CdS QDs, which is conducive to the photocatalytic hydrogen production process.

Switching on the Photocatalysis of Metal-Organic Frameworks by Engineering Structural Defects.

Defect engineering is a versatile approach to modulate band and electronic structures as well as materials performance. Herein, metal-organic frameworks (MOFs) featuring controlled structural defects, namely UiO-66-NH2 -X (X represents the molar equivalents of the modulator, acetic acid, with respect to the linker in synthesis), were synthesized to systematically investigate the effect of structural defects on photocatalytic properties. Remarkably, structural defects in MOFs are able to switch on the photocatalysis. The photocatalytic H2 production rate presents a volcano-type trend with increasing structural defects, where Pt@UiO-66-NH2 -100 exhibits the highest activity. Ultrafast transient absorption spectroscopy unveils that UiO-66-NH2 -100 with moderate structural defects possesses the fastest relaxation kinetics and the highest charge separation efficiency, while excessive defects retard the relaxation and reduce charge separation efficiency.

Switching on the Photocatalysis of Metal–Organic Frameworks by Engineering Structural Defects

AbstractDefect engineering is a versatile approach to modulate band and electronic structures as well as materials performance. Herein, metal–organic frameworks (MOFs) featuring controlled structural defects, namely UiO‐66‐NH2‐X (X represents the molar equivalents of the modulator, acetic acid, with respect to the linker in synthesis), were synthesized to systematically investigate the effect of structural defects on photocatalytic properties. Remarkably, structural defects in MOFs are able to switch on the photocatalysis. The photocatalytic H2 production rate presents a volcano‐type trend with increasing structural defects, where Pt@UiO‐66‐NH2‐100 exhibits the highest activity. Ultrafast transient absorption spectroscopy unveils that UiO‐66‐NH2‐100 with moderate structural defects possesses the fastest relaxation kinetics and the highest charge separation efficiency, while excessive defects retard the relaxation and reduce charge separation efficiency.

Redox couple mediated charge carrier separation in g-C3N4/CuO photocatalyst for enhanced photocatalytic H2 production

Graphitic carbon nitride (g-C3N4) is one of the promising two-dimensional metal-free photocatalysts for solar water splitting. Regrettably, the fast electron-hole pair recombination of g-C3N4 reduces their photocatalytic water splitting efficiency. In this work, we have synthesized the CuO/g-C3N4 heterojunction via wet impregnation followed by a calcination method for photocatalytic H2 production. The formation of CuO/g-C3N4 heterojunction was confirmed by XRD, UV–vis and PL studies. Notably, the formation of heterojunction not only improved the optical absorption towards visible region and also enhanced the carrier generation and separation as confirmed by PL and photocurrent studies. The photocatalytic H2 production results revealed that CuO/g-C3N4 photocatalyst demonstrated the increased photocatalytic H2 production rate than bare g-C3N4. The maximum H2 production rate was obtained with 4 wt % CuO loaded g-C3N4 photocatalyst. Importantly, the rate of H2 production was further improved by introducing simple redox couple Co2+/Co3+. Addition of Co2+ during photocatalytic H2 production shuttled the photogenerated holes by a reversible conversion of Co2+ to Co3+ with accomplishing water oxidation. The effective shuttling of photogenerated holes decreased the election-hole pair recombination and thereby enhancing the photocatalytic H2 production rate. It is worth to mention that the addition of Co2+ with 4 wt % CuO/g-C3N4 photocatalyst showed ∼7.5 and ∼2.0 folds enhanced photocatalytic H2 production rate than bare g-C3N4/Co2+ and CuO/g-C3N4 photocatalysts. Thus, we strongly believe that the present simple redox couple mediated charge carrier separation without using noble metals may provide a new idea to reduce the recombination rate.