Photocatalytic H2 Production Performance Research Articles

W18O49 Frameworks Decorated with Graphitic Carbon Nitride Quantum Dots for Photocatalytic Hydrogen Production

Quantum dots (QDs) have exhibited remarkable advantages for photocatalytic H2 evolution. Unfortunately, despite their unique quantum size effects and abundant catalytic active sites, many applications of QDs have been hindered in that they are prone to aggregation and easy to leach off from the substrate. Therefore, it is highly desirable to fabricate a special nanostructure with confinement effects to conquer their intrinsic drawbacks. Herein, we present a direct g-C3N4–x/W18O49 Z-scheme nanocomposite for enhanced photocatalytic H2 production. This system is composed of a W18O49 framework with several microporous slits and g-C3N4 QDs with a rich nitrogen vacancy. These several microporous slits can fix QDs and avoid their aggregation. Besides, the microporous slit surface can be functionalized by adjusting the pH value, thus ensuring intimate contact between W18O49 framework and g-C3N4–x QDs. The unique Z-scheme confinement structure facilitates photoinduced carrier transfer and improves the photocatalytic H2 production performance. The g-C3N4–x/W18O49 nanocomposite exhibits an exceedingly high H2 evolution rate and super stability because of the confinement structure and effective charge channel. This study provides a strategy to design the high-efficiency catalysts for solar H2 production.

A one-pot sealed ammonia self-etching strategy to synthesis of N-defective g-C3N4 for enhanced visible-light photocatalytic hydrogen

Photocatalytic hydrogen (H2) evolution from water is considered as a prospective approach, which can convert inexhaustible solar energy into chemical energy to alleviate energy crisis and environmental problems. Herein, the N-defective g-C3N4 with porous structure was firstly synthesized in a sealed crucible by one-step thermal polymerization method. The experimental data showed that the yield of the catalyst was obviously increased under sealing condition. Moreover, the N-defective g-C3N4 prepared from urea precursor under sealed condition reached an optimum photocatalytic H2 production rate of 597.4 μmol/h and an apparent quantum efficiency of 15.6% at wavelength of 420 nm. This enhanced photocatalytic H2 production performance is mainly ascribed to the introduction of N-defects, which not only extended of the visible light absorption, but also acted as the electron trap centers to suppress the recombination of the photogenerated electron and hole pairs. This work offers one-step facile strategy for the introduction of N-defects to prepare N-defective g-C3N4 with superior photocatalytic activity, which is also a great substitute for the high-energy consuming and complicated synthetic routes.

Boosting the photocatalytic ability of hybrid biVO4-TiO2 heterostructure nanocomposites for H2 production by reduced graphene oxide (rGO)

Fabricating heterostructures has been recognized as an effective strategy to improve visible-light photocatalytic H2 production performance. Therefore, a simple approach based on combining template-assisted liquid-phase deposition and hydrothermal techniques was introduced to synthesize BiVO4-TiO2/reduced graphene oxide (rGO) heterostructure nanocomposites. The ternary hetero-nanostructures were composed of TiO2 nanotubes, with an average diameter of 100 nm and tens micrometers in length, BiVO4 nanoparticles and various amounts of rGO nanosheets. The highest photocatalytic H2 production rate of 1427.1 μmol.h − 1g − 1 with an apparent quantum yield of 6.4% at 420 nm was achieved at optimum rGO content (3 wt.%) under visible-light irradiation, which was 2.5 and 1.5 times higher than that of TiO2 nanotubes)563.5 μmol.h − 1g − 1) and BiVO4-TiO2 (915.7 μmol.h − 1g − 1), respectively. The excellent enhancing effect of rGO on photocatalytic performance of the heterojunction formed between these materials was attributed to the large surface area, light absorption capacity due to band gap engineering, and separation of photo-generated charge carriers. It demonstrates the design of the ternary BiVO4-TiO2/rGO hetero-nanostructures that was proposed in the present strategy could effectively separate the electron-hole pairs for sustainable photocatalytic H2 production, as was verified by PL, TRF and EIS photospectroscopy measurements.

ZnxCd1–xS quantum dot with enhanced photocatalytic H2-production performance

H2 is an important energy carrier for replacing fossil fuel in the future due to its high energy density and environmental friendliness. As a sustainable H2-generation method, photocatalytic H2 production by water splitting has attracted much interest. Here, oil-soluble ZnxCd1–xS quantum dot (ZCS QD) with a uniform particle size distribution were prepared by a hot-injection method. However, no photocatalytic H2-production activity was observed for the oil-soluble ZCS QD due to its hydrophobicity. Thus, the oil-soluble ZCS QD was converted into a water-soluble ZCS QD by a ligand-exchange method. The water-soluble ZCS QD exhibited excellent photocatalytic H2-production performance in the presence of glycerin and Ni2+, with an apparent quantum efficiency of 15.9% under irradiation of 420 nm light. Further, the photocatalytic H2-generation activity of the ZCS QD was ∼10.7 times higher than that of the ZnxCd1–xS relative samples prepared by the conventional co-precipitation method. This work will inspire the design and fabrication of other semiconductor QD photocatalysts because QD exhibits excellent separation efficiency for photogenerated electron–hole pairs due to its small crystallite size.

Exfoliated, mesoporous W18O49/g-C3N4 composites for efficient photocatalytic H2 evolution

Rapid recombination of photogenerated carriers and lack of active sites have always been the problems for enhancing the H2 evolution performance of semiconductor-based photocatalysts, which can be solved promisingly by co-catalysis and lifting specific surface area, respectively. In this work, a simple two-step green route is developed to synthesize novel exfoliated and mesoporous W18O49/g-C3N4 composites through calcining the precursors of g-C3N4 powder impregnated with ammonium tungstate solution in a reductive atmosphere produced by the pyrolysis of polyacrylonitrile powder. With the optimal loading amount of W18O49, the obtained W18O49/g-C3N4 composite presents an excellent photocatalytic performance for H2 production in triethanolamine aqueous solution under visible light. The H2 evolution rate at 7 °C was 912.3 μmol⋅g−1h−1, 9.7-fold higher than that of pure g-C3N4. In addition, the mechanism of the H2 production over the obtained W18O49/g-C3N4 photocatalysts was also proposed. This work will provide a new strategy for improving the specific surface area of nanomaterials and constructing the heterojunctions between different nanostructures simultaneously.

Doping effect of metalloid group in graphitic carbon nitride molecular structure for significantly improved photocatalytic hydrogen production and photoelectric performance

It is a considerable research focus to introduce a new conjugate structure into the graphitic carbon nitride (g-C3N4) molecule by polymerization to improve the photocatalytic and photoelectrochemical performance. Herein, the 1,4-cyclohexadiene (CHD) group-doped g-C3N4 (CHD-g-C3N4) nanosheet photocatalyst is prepared by a simple thermal polymerization, which dramatically improves the photocatalytic H2 production and photoelectrochemical performance. Surprisingly, the optimal H2 production rate and the photocurrent density of CHD-g-C3N4 reaches up to 522.0 μmol h−1 g−1 and 31.19 μA cm−2, which is 6.29 and 6.96 times higher than that of pure g-C3N4, respectively. The high-efficiency and stable photocatalytic H2 production and photoelectrochemical performance of CHD-g-C3N4 originate from the doping effect of conjugated groups in g-C3N4 molecule, which extends the π-conjugated system to accelerate electron mobility. This work indicates that the introduction of metalloid groups with conjugation effect is of great significance for improving photocatalytic and photoelectric performance, and provides a new idea for the non-metallic modification of g-C3N4 as a highly active catalyst.

Bio-inspired hierarchical assembly of Au/ZnO decorated carbonized spinach leaves with enhanced photocatalysis performance

Inspired by the characteristics that plant leaves are beneficial for solar light absorption, we have prepared a bio-inspired hierarchical assembly of carbonized spinach leaves@Au/ZnO (CS@Au/ZnO) for solar energy utilization. CS@Au/ZnO shows a low light reflectance of 5% and a high specific surface area of 311.41 m2/g. CS@Au/ZnO demonstrates higher photocatalytic degradation efficiency: more than 97% of Rhodamine B (RhB) and 61% of ciprofloxacin (CIP) could be degraded in 180 min under the visible light irradiation. In addition, we also tested the photocatalytic H2 production performance of CS@Au/ZnO and the H2 evolution rate is 2.384 mmol g−1 h−1 under simulated solar light. CS@Au/ZnO shows a high cycling stability in recyclable photocatalytic degradation and photocatalytic water splitting. Moreover, CS@Au/ZnO shows a swift and steady photocurrent of about 63.6 μA/cm2, illustrating a high sensitivity to solar light. The enhanced photocatalysis performance of CS@Au/ZnO could be ascribed to the naturally optimized macroporous structure of CS with high conductivity, which could enhance the light harvesting and carrier transport, simultaneously. Moreover, modification of AuNPs can broaden the light response range of ZnONRs and reduce the probability of electron-hole recombination. Due to the wide availability of plant leaves, CS@Au/ZnO assembly has broad application prospects in photocatalytic degradation of organic pollutions, photovoltaic devices, and photocatalytic H2 evolution.

Graphitic carbon nitride with thermally-induced nitrogen defects: an efficient process to enhance photocatalytic H2 production performance.

Graphitic carbon nitride (g-C3N4, CN) with nitrogen vacancies was synthesized by a controlled thermal etching method in a semi-closed air-conditioning system. The defect-modified g-C3N4 shows an excellent photocatalytic performance demonstrated by water splitting under visible light irradiation. With proper heat-treatment durations such as 2 h (CN2) and 4 h (CN4) at 550 °C, the hydrogen production rates significantly increase to 100 μmol h−1 and 72 μmol h−1, which are 11 times and 8 times the rate of the pristine CN (8.8 μmol h−1) respectively. The excellent hydrogen production performance of nitrogen defect modified CN2 is due to the synergy effect of the decreased band gap, enlarged specific surface area and increased separation/migration efficiency of photoinduced charge carriers. This simple defect engineering method provides a good paradigm to improve the photocatalytic performance by tailoring the electronic and physical structures of g-C3N4.

Synergistic effect of nitrogen-doping and graphene quantum dot coupling for high-efficiency hydrogen production based on titanate nanotubes

Highly efficient H2 production from water splitting has been achieved by N-doped titanate nanotubes (N-TNTs) decorated with graphene quantum dots (GQDs) in this work. In order to promote charge carrier transmission at the interface, a facile and environmentally friendly in situ growth method was employed to construct a strongly coupled N-TNT/GQD composite photocatalyst. The results revealed that N atoms were effectively doped into the crystal lattice of the TNTs in the form of both interstitial N and substitutional N, and the GQDs were decorated onto both the inner and outer surfaces of the N-TNTs through the formation of Ti–O–C chemical bonds. Photoelectrochemical measurements proved that, in N-TNT/GQD composite, N-doping can extend light response to the visible-light range, and the coupling with GQDs not only enhanced visible-light absorption, but also promoted interfacial charge carrier transfer. Due to the synergistic effect between N-doping and GQD coupling, the closely integrated N-TNT/GQD composite exhibits a much superior photocatalytic H2 production performance under UV–vis irradiation, being 2.1 times higher than that of pure TNTs.

Switching g-C3N4 morphology from double-walled to single-walled microtubes induced high photocatalytic H2-production performance

It is a huge challenge to find a green, simple and template-free strategy to construct metal-free graphitic carbon nitride (g-C3N4) with a special morphology to improve its performance in photocatalytic hydrogen evolution (PHE). In this study, we discover a facile method to switch the g-C3N4 morphology from bulk (Bg-C3N4) to tubes (Tg-C3N4) by melamine and cyanuric acid self-assembly to improve the PHE performance. Scanning electronic microscopy (SEM) images clearly show switching the Tg-C3N4 morphology from double-walled to single-walled microtubes. In addition, the experimental results suggest that compared to the Bg-C3N4, Tg-C3N4 not only has a large specific surface area but also exhibits a fast separation of charge carriers. Meanwhile, relative to Bg-C3N4, Tg-C3N4 can effectively improve the absorption of light and adjust the bandgap energy of g-C3N4. Excitedly, the obtained Tg–C3N4–0.2 displays the best PHE performance (967.93 μmol h−1 g−1 λ＞420 nm), which is approximately 20.95-fold greater than that of Bg-C3N4. This work offers a promising idea for developing high-efficiency photocatalysts by switching the morphology.

Highly efficient photocatalytic hydrogen evolution from 0D/2D heterojunction of FeP nanoparticles/CdS nanosheets

In this study, a novel zero-dimensional (0D)/two-dimensional (2D) heterojunction photocatalyst consisting of cadmium sulfide (CdS) nanosheets (NSs) decorated with FeP nanoparticles (NPs) was fabricated using an in situ phosphorisation method. 0D FeP NPs were tightly attached to the surfaces of 2D CdS NSs to achieve highly efficient photocatalytic hydrogen generation. The greatest H2 production was 1.39 mmol within 5 h, which is 35 times the generation of pristine CdS NSs. Additionally, the fabricated 0D/2D heterojunction photocatalyst demonstrated excellent stability, and the external quantum efficiency of the optimised photocatalyst was calculated to be 18.63% at 450 nm. The enhancement mechanisms resulting in high activity and stability were investigated using various characterisation techniques, which revealed that the construction of 0D/2D heterojunctions with close interfacial contact between 0D FeP NPs and 2D CdS NSs can accelerate photoexcited e−-h+ pairs transfer and separation, thereby enhancing photocatalytic H2 production performance and stability. This study offers new insights into the design of 0D/2D heterojunction photocatalysts for applications in the field of photocatalysis.

Atomically Dispersed Single Co Sites in Zeolitic Imidazole Frameworks Promoting High-Efficiency Visible-Light-Driven Hydrogen Production.

As photocatalysis technology could transform renewable and clean solar energy into green hydrogen (H2 ) energy through solar water splitting, it is regarded as the "Holy Grail" in chemistry field in the 21st century. Unfortunately, the bottleneck of this technique still lies in the exploration of highly active, cost-effective, and robust photocatalysts. This work reports the design and synthesis of a novel zeolitic imidazole framework (ZIF) coupled Zn0.8 Cd0.2 S hetero-structured photocatalyst for high-performance visible-light-induced H2 production. State-of-the-art characterizations and theoretical computations disclose that the interfacial electronic interaction between ZIF and Zn0.8 Cd0.2 S, the high distribution of Zn0.8 Cd0.2 S on ZIF, and the atomically dispersed coordinately unsaturated Co sites in ZIF synergistically arouse the significantly improved visible-light photocatalytic H2 production performance.

Ti3C2 nanosheets modified Zr-MOFs with Schottky junction for boosting photocatalytic HER performance

As newly-developing non-noble metallic co-catalysts, MXenes have attracted intensive attention as an ideal candidate to promote the photocatalytic H2-production activity. In this study, Ti3C2 nanosheets prepared by intercalation were further attached to porous MOFs (UiO-66-NH2) via one-pot hydrothermal method to form face-to-face intimate contact. The obtained TU10 presented the highest photocatalytic H2-evolution rates in TU series, exceeding that of pure UiO-66-NH2 by approximately 8 times. The speculation revolving about enhanced photocatalytic H2-production performance was proposed as the presence of exposed active sites at the edge of Ti3C2 nanosheets and spatial separation and transfer of charge carriers introduced by the Schottky junction at TU series interface, which accumulated the photo-induced electrons on the surface of Ti3C2 nanosheets and improved its electron-donating ability. The DFT calculations revealed that O-terminated Ti3C2 possessed the most positive Fermi level and the lowest Gibbs free energy (|ΔGH*| = 0.08 ≈ 0). This work may provide new insights for constructing MXenes/MOFs structure based on Schottky junction effect to achieve high photocatalytic H2-production performance.

Enhanced photocatalytic activities of CdS-BiOCl/PAN composites towards photocatalytic hydrogen evolution

In this work, we successfully synthesized a series of CdS-BiOCl/PAN composites by two-step method including electrospinning process and hydrothermal process. The CdS-BiOCl/PAN composites showed great photocatalytic performance and chemical stability for H2 production under UV–vis light irradiation due to the synergistic effect among CdS, BiOCl and PAN. Meanwhile, the content of CdS in CdS-BiOCl/PAN composites plays an important role in photo-catalytic abilities. In addition, according to the analysis about the photocatalyst, the possible photocatalytic mechanism and synergistic interaction were further discussed.

Enhanced photocatalytic performance in preyssler-type P5W30CdS nanohybrids synthesized by l-cystine-mediated hydrothermal assembly

Abstract Nanohybrids of P5W30 CdS with intimate contact have been synthesized via a facile hydrothermal strategy in presence of l -cystine as sulfur precursor, chelating and anchoring linker molecule. In this process, nanosized CdS can be positively-charged by anchoring NH2 groups in l -cystine structure. Through the electrostatic interaction between the positively-charged amine-functionalized CdS and the negatively-charged Preyssler-type [NaP5W30O110]14− (denoted as P5W30), P5W30 CdS nanohybrids with intimate contact are achieved, which is verified with XRD, IR, TEM, HRTEM, EDS, XPS and UV–Vis spectra. Of particular importance is that P5W30 CdS nanohybrids demonstrate better photocatalytic performance for H2 production and RhB degradation than unhybridized CdS and P5W30 under visible light irradiation. The H2-production activity of CdS is further increased up to 59 times with 8 wt% P5W30 and 0.75 wt% NiS co-loaded, which is attributed to the facilitated charge-transfer between CdS, P5W30 and NiS. The mild, efficient and eco-friendly self-assembly method is versatile and promising for developing photocatalytic hybrid materials.

Non-noble metal Co as active sites on TiO2 nanorod for promoting photocatalytic H2 production

Non-noble metal Co was decorated on TiO2 nanorod by a photodeposition method to improve photocatalytic H2 production. Co particles with ca. 7 nm diameter dispersed well onto the TiO2 nanorods. Photocatalytic H2 production performance of Co/TiO2 was tested and the results showed that the photocatalytic activity was promoted by Co loading. The H2 evolution rate of 2.0 wt% Co/TiO2 (839.8 μmol ⋅ h−1) is 8.9 times of that of bare TiO2 (95 μmol ⋅ h−1), reaching 77.8% of that of 1.0 wt% Pt/TiO2 (1080μmol⋅h−1). Photoelectrochemical and PL measurements indicated that, like Pt cocatalyst, the loading of Co particles reduces the overpotential of H2 evolution as well as facilitates the transfer of photoinduced electrons from TiO2 to Co cocatalyst, thus improving the photocatalytic H2 evolution activity. The study not only provides a way to cut the cost of photocatalysts but gives an in-depth understanding of the effect of cocatalysts on enhancing photocatalytic H2 evolution activity.

Bimetallic Manganese Cobalt Phosphide Nanodots–Modified Graphitic Carbon Nitride for High‐Performance Hydrogen Production

It is a huge challenge for exploiting new photocatalysts with low‐cost cocatalysts in place of precious metals to realize high‐efficiency H2 production from water. Herein, a new photocatalyst with a high H2 production activity is prepared via modification of bimetallic manganese cobalt phosphide (Mn0.67Co1.33P) nanodots on graphitic carbon nitride (g‐C3N4). Moreover, the largest H2 production rate of 113.1 μmol h−1 is obtained over the Mn0.67Co1.33P/g‐C3N4‐5 sample, which is about 2.75 times than that of Pt/g‐C3N4‐5 (41.2 μmol h−1). The high‐performance H2 production suggests page a page down that the modification effect of Mn0.67Co1.33P nanodots improves the visible harvest ability and separation efficiency of charge carriers. A typical example to improve the photocatalytic H2 production performance by fabricating heterostructures using bimetallic phosphide to modify graphitic carbon nitride is provided.

Precursor-reforming strategy induced g-C3N4 microtubes with spatial anisotropic charge separation established by conquering hydrogen bond for enhanced photocatalytic H2-production performance

Precursor-reforming strategy induced graphitic carbon nitride (g-C3N4) with different morphologies for enhanced photocatalytic hydrogen (H2) evolution activity is highly desirable. Herein, g-C3N4 microtubes (mg-C3N4) with adjustable closure degree of microtube orifice and spatial anisotropic charge separation are established by conquering hydrogen bond during thermally exfoliate precursor. Compared to the bulk g-C3N4 (bg-C3N4) and ultrathin g-C3N4 (ug-C3N4), the tubular structure endows mg-C3N4 with spatial anisotropic charge separation that accelerates transfer of charge carriers. As expected, the photocatalytic H2 evolution (PHE) activity of mg-C3N4 has been obviously enhanced. Particularly, the mg-C3N4-24 shows the best PHE activity (957.9 μmol h−1 g−1), which is over 18.72 and 3.77 times higher than the bg-C3N4 and ug-C3N4, respectively. In addition, selective photo-deposition experiment results reveal a charge carriers migration behavior that photoproduction electrons migrate to the outer shell and holes prefer to move onto the inner shell of mg-C3N4, thus achieving efficient spatial anisotropic charge separation. We firmly believe that the work presents significant advancement for the design of other materials by precursor-reforming strategy.

Orderly designed functional phosphide nanoparticles modified g-C3N4 for efficient photocatalytic hydrogen evolution

The synthesis of highly efficient and stable photocatalysts has always been one of the key research objects in the field of photocatalysis. Increasing the efficiency of charge separation is an important aspect of improving photocatalytic activity. In this work, the Co-W-P cocatalysts were loaded on g-C3N4, synthesized for the first time and the electron transport routes were appropriately adjusted, which extremely improved efficiency of photocatalytic decomposition of water for hydrogen evolution. A composite photocatalyst with high-efficiency photocatalytic H2 production performance under visible light was obtained by loading the Co-W-P composites on a g-C3N4 nanosheet. It was ascribed to the efficient interfacial electron transfer routes. This has contributed to the synthesis of high-priority and stable photocatalysts. Besides, the composite catalysts were characterized by SEM, TEM, XRD, XPS, UV-vis, BET, transient photocurrent, and FT-IR etc. And a mechanism of photocatalytic hydrogen production was hypothesized.

Hierarchical microsphere of MoNi porous nanosheets as electrocatalyst and cocatalyst for hydrogen evolution reaction

In industrial water electrolysis cell, the electrocatalyst has a sluggish water dissociation kinetics leading to low electrocatalytic activity for the generation of H2 from water splitting. This work reports a hierarchical microsphere constructed by MoNi porous nanosheets derived from NiMoO4 microsphere, as a rapid Tafel-step-decided electrocatalyst towards hydrogen evolution reaction (HER). Consequently, the synthesized MoNi hierarchical microsphere (MoNi HM) electrocatalyst exhibits an onset potential of as small as −7 mV vs. RHE, an operating potential of 72 mV for 10 mA cm−2, and a low Tafel slope of 36.6 mV per decade in 1.0 M KOH. Furthermore, MoNi HM as cocatalyst and CdS nanowires as photocatalyst are physically mixed (MoNi HM/CdS NWs) and presentes a champion photocatalytic performance for H2 production with a prominent H2 generation rate of as high as 151.7 μmol mg-1 h−1 at λ > 420 nm light illumination. The large contact area between MoNi nanosheets and CdS nanowires endows the fast separation of photogenerated charge carriers to significantly facilitate the photocatalytic H2 production.