Highest Photocatalytic Hydrogen Production Rate Research Articles

Constructing a noble-metal-free 0D/2D CdS/SnS2 heterojunction for efficient visible-light-driven photocatalytic pollutant degradation and hydrogen generation

Semiconductor photocatalysis has attracted the attention of a wide audience for its outstanding capabilities in water purification and energy conversion. Herein, a noble-metal-free nanoheterojunction is created by planting zero-dimensional (0D) CdS nanograins, of 10–20 nm in size, on the surface of 2D SnS2 nanosheets (NSs) using an in situ chemical bathing deposition process, where SnS2 NSs have an average diameter of 400 nm and thicknesses of less than 20 nm. The possible formation mechanism of the CdS/SnS2 (CS/SS) heterogeneous nanostructure is elaborated upon. The catalytic activities over CS/SS nanocomposites for the photodegradation of organic dye and hydrogen evolution from photolysis water splitting are examined under visible light irradiation. The apparent rate constant (k) of the optimal CS/SS-3 composite in the decontamination of methylene blue (MB) is up to 3.34 and 1.87 times as high as that of pristine SnS2 and pure CdS counterparts, respectively. The optimized CS/SS-3 sample consistently achieves the highest photocatalytic hydrogen production rate, at 10.3 and 5.7 folds higher than that of solo SnS2 and CdS panels, respectively. The boosted photocatalytic capacities of CdS/SnS2 heterostructures are essentially attributed to the formation of the closely interfacial incorporation of CdS and SnS2 semiconductors, resulting in the effective charge transportation and spatial separation of the photoinduced electron–hole pairs. Furthermore, the traditional type-II charge transfer pathway is proposed based on the perfect band structure and the free radical experiment results.

Constructing CdIn2S4/ZnS type-I band alignment heterojunctions by decorating CdIn2S4 on ZnS microspheres for efficient photocatalytic H2 evolution

In this study, a series of promising binary hybrid heterojunction CdIn2S4/ZnS (CIS/ZnS) were constructed via a facile hydrothermal method. Credible characterization methods including powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectra (DRS) were carried out to investigate the physicochemical properties the as-obtained photocatalysts. Photocatalytic water splitting for hydrogen evolution was performed to evaluate the photocatalytic activity of the photocatalyst. The results indicate that the light-harvesting ability could be markedly enhanced by decorating CdIn2S4 on ZnS microspheres. Compared with the pristine CdIn2S4 and ZnS, the hybrid photocatalysts present more efficient photocatalytic hydrogen production performance. Among composite photocatalysts, the 5% CIS/ZnS sample manifests the highest photocatalytic hydrogen production rate of 10.80 mmol g−1 h−1, which is 2.6 and 5.4 times higher than that of ZnS and CdIn2S4, respectively. Moreover, a type-I band alignment mechanism was prudently put forward to interpret the photocatalytic hydrogen generation activity. The boosted photocatalytic hydrogen evolution activities of CIS/ZnS can be attributed to the enhanced light-harvesting ability, efficient separation and transfer of the photo-induced charge carriers, and inhibition of electrons and holes recombination of binary hybrid CIS/ZnS photocatalysts.

NiO co-catalyst modification ZnIn2S4 driving efficient hydrogen generation under visible light

Photocatalytic hydrogen production is considered as a good countermeasure to solve the energy crisis, but the existing photocatalysts have very slow electron-hole separation efficiency. How to design a photocatalyst with high photogenerated carrier separation efficiency has become a difficult rproblem. The efficiency of photogenerated carrier separation can significantly improve by precious metal co-catalyst, but its further development is limited by high cost. In this work, non-precious metal NiO is used as a co-catalyst and formed heterojunction with ZnIn2S4 (ZIS) as a cocatalyst, which significantly enhances the efficiencies of photogenerated carrier separation. According to the results of transient photocurrent (TPR) and Photoluminescence (PL), ZnIn2S4/NiO (ZIS/NiO) has the fastest photogenerated carrier separation rate when the mass fraction of NiO is 3%, which is about 5 times than pure ZIS. At the same time, the highest photocatalytic hydrogen production rate of 5 mmolg−1 h−1 was achieved under visible-light (λ ≥ 420 nm), which was 6.2 times more than pure ZIS (0.804 mmolg−1 h−1). This work offers a new option for low cost, high performance co-catalyst.

Ultrathin Pd metallenes as novel co-catalysts for efficient photocatalytic hydrogen production

Photocatalytic hydrogen production as a green and pollution-free technology plays an important role in alleviating the fossil fuel crisis, but remains a great challenge. Herein, an ultrathin two-dimensional (2D) palladium metallene (Pd-ene) is first developed as hydrogen evolution co-catalysts for g-C3N4 nanosheets. The Pd-ene and Pd-ene/g-C3N4 photocatalysts were fabricated by a hydrothermal method and deposition method using acetylacetonate palladium as Pd source, and the Pd-ene with a size of 100 nm uniformly distributed on the surface of g-C3N4 nanosheets forming a 2D/2D structure. The Pd-ene/g-C3N4 with 2 wt% Pd-ene showed the highest photocatalytic hydrogen production rate with 31,292 μmol/h/ g, which was>98 times that of the pure g-C3N4 and superior to the PdNC/g-C3N4 loading with Pd nanocluster. The unique 2D/2D structure of the Pd-ene/g-C3N4 catalyst, which promotes the transfer and separation of photogenerated charge carriers, is credited with the improved photocatalytic performance. In additions, the 2D structure of Pd-ene makes it expose more reaction sites for the photocatalytic reduction reaction, promoting the hydrogen production of the photocatalysts. This study demonstrates that the development of structurally matched 2D metallene co-catalysts for 2D photocatalysts is a promising strategy to obtain the photocatalysts with high hydrogen production performance.

Plasmonic Ag-nanoparticles decorated phosphorus and boron co-doped g-C3N4 for enhanced photocatalytic H2 production

Solar water splitting by semiconductor photocatalysts has emerged as a favorable approach for green hydrogen production. Graphitic carbon nitride (g-C3N4) has gained substantial recognition amongst numerous semiconductor photocatalysts as a metal-free semiconductor with suitable band gap, appropriate band edge positions, and satisfactory photocatalytic activity for hydrogen production. However, its practical application is severely affected by high charge carrier recombination rate and inefficient visible light absorption. Introducing non-metal dopants into the g-C3N4 structure could suppress charge carrier recombination and tune the electronic property. Also, metal nanoparticles exhibit surface plasmon resonance (SPR) upon light interaction increasing the visible light absorption by the transport of hot electrons into the g-C3N4 framework. In this work, we report hybrid photocatalytic materials containing Ag-plasmonic metal and non-metal (B/P) dual heteroatom-doped g-C3N4 prepared via in-situ thermal polycondensation and succeeded by the photodeposition of Ag NPs. The structure of the prepared materials was studied through PXRD and FTIR spectroscopy; XPS was used for chemical analysis; SEM was used to study the morphology; and optical characteristics were studied through UV–Vis and PL spectroscopic techniques. The synergistic effects of SPR and heteroatom co-doping exhibit superior photocatalytic hydrogen production compared to pristine, B or P individual-doped, and B/P co-doped g-C3N4 samples. The optimized 1Ag/PBCN photocatalyst has demonstrated the highest photocatalytic hydrogen production rate of 1825 μmolh-1g−1, 18.3 times greater than g-C3N4. The modified hybrid material shows better activity due to the efficient charge carriers separation and extended visible light absorption. This work indicates that elemental co-doping and loading plasmonic nanoparticles on g-C3N4 to form hybrid nanocomposites may be a potential strategy to achieve better photocatalytic hydrogen evolution. The proposed methodology and outcomes will be helpful in the design and development of plasmon-enhanced hybrid photocatalysts for solar-driven green hydrogen production from water splitting.

Surface-assisted synthesis of biomass carbon-decorated polymer carbon nitride for efficient visible light photocatalytic hydrogen evolution

Template is frequently studied as a structure-directing agent to tune the nanomorphology of photocatalysts. However, the influences of template on the polymerization of precursors and compositions of the resulting samples are rarely considered. Herein, a biomass carbon-modified graphitic carbon nitride (CCNx) with a thin-layer morphology is synthesized via one-pot surface-assisted polymerization of melamine precursor on organic yeast. The formation of the hydrogen bond between melamine and yeast induces a strong interfacial confinement, giving rise to small-sized CCNx. In addition, the carbon materials derived from yeast dramatically broaden n → π* visible light harvesting, improve electron delocalization, and greatly enhance charge carrier separation. The optimized CCNx presents a much higher photocatalytic hydrogen production rate of 2704 μmol g-1h−1 under visible light irradiation (λ ≥ 420 nm), which is nearly 11-fold that of its pristine counterpart. This work realizes the synergistic effect between morphology tunning and composition tailoring by using biomass template, which shows a great potential in developing efficient metal-free photocatalysts.

Mo-activated VC as effective cocatalyst for an enhanced photocatalytic hydrogen evolution activity of CdS

Seeking an efficient and stable cocatalyst is of importance for semiconductor-based photocatalytic water splitting to produce hydrogen. In this sense, Mo-activation of VC for better cocatalytic properties was proposed for the first time, aiming to attain improved hydrogen generation of CdS. Our novel, yet facile physical preparation method permits intimate coupling of Mo-activated VC cocatalyst to CdS (through electrostatic attraction force), thereby promises drastic activity enhancement for hydrogen generation. Results indicate the best VC-activating competency of Mo against other transition metals (Co, Fe, Ni, Zn and Cu), which induces highest H2 productivity of CdS after modifying with Mo-activated VC. Under optimum setting, CdS/Mo(0.38)-VC(5 wt%) manifested highest photocatalytic hydrogen production rate of 2267 μmol h−1 g−1, associated to 300 % and 440 % improvement as compared to that of CdS/VC(5 wt%) and pure CdS, respectively. Such activity also outperformed those that yielded by MoSx- or noble metals(Pt, Au or Ag)-co-catalyzed CdS, attributed to the promoted interfacial charges transfer and lowered overpotential of CdS/Mo(0.38)-VC(5 wt%) in hydrogen generation. Correspondingly, high apparent hydrogen production quantum efficiency of 4.3 % was also recorded by the same photocatalyst at 420 nm. In term of stability test, CdS/Mo(0.38)-VC(5 wt%) manifested excellent longevity in 24 h continuous photoreaction and fair recyclability over five consecutive photoreaction cycles. This work provides a new insight to cocatalysts design and synthesis, thereby realizing economic alternatives to precious metal (Pt, Au, Ag) in solar-derived H2 production.

The charge transfer pathway of g-C3N4 decorated Au/Ni3(VO4)2 composites for highly efficient photocatalytic hydrogen evolution

The photocharge carrier separation and migration within the heterostructure interface plays a pivotal role in the photoelectrocatalytic hydrogen production and the photocatalytic degradation activity. Herein, a series of the 2D/3D g-C3N4/Ni3(VO4)2 photocatalyst were successfully fabricated via a facile hydrothermal method. The prepared samples were characterized by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), ultraviolet‐visible (UV‐vis), Brunauer‐Emmett‐Teller (BET) surface area, and photoluminescence spectroscopy (PL) emission spectroscopy. The highest photocatalytic hydrogen production rate of g-C3N4/Au/Ni3(VO4)2 was about 3345 μmol g−1 h−1, which largely beyond that obtained of g-C3N4/Ni3(VO4)2 (501 μmol g−1 h−1), and pristine g-C3N4 (14 μmol g−1 h−1). The optimal apparent quantum efficiency was counted to be 6.8 % at λ = 420 nm and 1.1 % at λ = 600 nm. Moreover, the photocatalytic property of g-C3N4/Au/Ni3(VO4)2 could remain unchanged almost with 50 h in 5 cycles. The improvement of photocatalytic H2 yield is attributed to the result of rapid separation of photogenic carriers in space and surface plasmon resonance effect of Au nanoparticles.

Tuning Molecular Chromophores of Isoreticular Covalent Organic Frameworks for Visible Light‐Induced Hydrogen Generation

AbstractThe functions of covalent organic frameworks (COFs) can be tailored by covalently reticulating advanced molecular modules into well‐defined porous ordered materials. Herein, four COFs, USTB‐7–USTB‐10, are prepared from the solvothermal reaction of photoactive tetraaldehydes, 5,5″‐(benzo[c]‐[1,2,5]thiadiazole‐4,7‐diyl)diisophthalaldehyde and 5,5″‐(naphtho[2,3‐c][1,2,5]thiadiazole‐4,9‐diyl)diisophthalaldehyde, with p‐phenylenediamine and benzidine, respectively. Comprehensive studies of powder X‐ray diffraction, theoretical simulation, and pore size distribution disclose their isoreticular 2D dual porous structures. In contrast to benzo[c][1,2,5]thiadiazole‐based chromophore, employment of naphtho[2,3‐c][1,2,5]thiadiazole‐based tetraaldehyde enables enlarged conjugation systems for USTB‐9 and USTB‐10, rather than USTB‐7 and USTB‐8. This, in combination with the longer benzidine unit, endows USTB‐10 with a porous structure with bigger pore size than that of USTB‐9, resulting in the highest photocatalytic hydrogen production rate of 21.8 mmol g−1 h−1 with the help of a Pt cocatalyst. Experimental and theoretical studies reveal the outstanding photocatalytic activity for USTB‐10 among the four COFs associated with the narrowed bandgap and increased charge‐carrier separation efficiency.

Bi@H-TiO2/B-C3N4 heterostructure for enhanced photocatalytic hydrogen generation activity under visible light

Herein, a ternary Bi@H-TiO2/B-C3N4 type II heterostructure is successfully designed and prepared via metal Bi as cocatalyst for photocatalytic H2 generation. As expected, under λ > 300 nm light, the highest photocatalytic hydrogen production rate (HPR) of Bi@H-TiO2/B-C3N4 is up to 223.08 μmol g−1 h−1. Excitingly, under visible light (λ > 400 nm), the highest HPR of Bi@H-TiO2/B-C3N4 is increased to 18.84 μmol g−1 h−1, which is about 67.3 times, 37.7 times and 6.8 times as high as that of H-TiO2, B-C3N4 and H-TiO2/B-C3N4 under the same conditions, respectively. Moreover, the electrochemical impedance spectroscopy and transient photocurrent tests manifest that the interface resistance of Bi@H-TiO2/B-C3N4 composite decreases and the photocurrent density increases after loading metal Bi. These results indicate that loading metal Bi as cocatalyst (providing more electron trapping sites) is beneficial to improve photocatalytic activity in the type II heterostructure composite. And the electron transfer directions (B-C3N4 → H-TiO2 → Bi or B-C3N4 → Bi) are proved by ultraviolet photoelectron spectroscopy test. Therefore, the Bi@H-TiO2/B-C3N4 photocatalyst with strong visible light absorption is expected to be a promising candidate in photocatalytic fields under visible light.

Construction of ternary Z-scheme covalent triazine framework@Au@TiO2 for enhanced visible-light-driven hydrogen evolution activity

One key challenge in photocatalytic hydrogen production is how to construct high-performance photocatalyst. Covalent triazine framework (CTF) based polymers as photocatalysts show great application potential because of their good photocatalytic activity, high chemical stability, tunable electronic and optical properties, and easy synthesis process. In this paper, we designed the ternary Z-scheme heterojunction Au@TiO2-X%TrTh based on CTF polymer TrTh, TiO2 and Au nanoparticle, which exhibit higher photocatalytic hydrogen production rate compared with the corresponding binary heterojunction Au@TiO2 and TiO2-12%TrTh. The results of photocatalytic hydrogen production show that the optimized Au@TiO2-12%TrTh has a remarkable hydrogen production rate of 4288.54 μmol g−1 h−1, which is about 312.3 times of Au@TiO2 and 9.1 times of the TiO2-12%TrTh. The enhanced hydrogen production activity of the ternary heterojunction comes from the local surface plasmonic resonance effect of Au nanoparticle, lower recombination efficiency of photogenerated electron-holes pairs and Z-scheme electron transfer pathway of Au@TiO2-12%TrTh. The work provides a new strategy for designing efficient and practical photocatalyst.

Edge engineering of platinum nanoparticles via porphyrin-based ultrathin 2D metal–organic frameworks for enhanced photocatalytic hydrogen generation

Edge-doping engineering in metal nanoparticles (MNPs) is always hard to achieve due to the high surface energy of the hybrid MNPs, while porphyrin-based ultrathin two-dimensional (2D) metal–organic framework (MOF) is demonstrated the positive role in stabilize this structure. Herein, a bottom-up method was developed to prepare platinum nanoparticles (PtNPs)-decorated 2D MOF nanosheets, where a porphyrin ligand of Pd-metalized tetrakis(4-carboxyphenyl)porphyrin (PdTCPP) was applied to synthesize ultrathin MOF nanosheets as Zr-TCPP(Pd) in high yield. Attributing to the high superficial area of ultrathin Zr-TCPP(Pd) nanosheets, Pt NPs can well anchor uniformly with small nanoparticle size to obtain 2% Pt/Zr-TCPP(Pd) hybrid nanosheets, which showed a higher photocatalytic hydrogen production rate of 3348 μmol g-1h−1. This is attributed to the coordination between Zr4+ and C = O of PVP, which promotes the contact between PtNPs and Zr-TCPP(Pd) nanosheets. As a result, the long-life electrons of PdTCPP photosensitizers are rapidly transferred to the electron capture center PtNPs, and the photoelectron-hole recombination is effectively inhibited. The apparent quantum efficiency of 2% Pt/Zr-TCPP(Pd) reaches up to 1.56% at 420 nm. The density functional theory (DFT) calculations revealed the Pd-doped position in Pt79 nanoparticle is important that the Pt78Pdsurf. model (Pd atom was doped on the surface of Pt nanoparticle) showed the highest activity with abundant exposed active region.

Structural Engineering of Covalent Organic Frameworks Comprising Two Electron Acceptors Improves Photocatalytic Performance.

Covalent organic frameworks (COFs) have recently attracted much attention as potential photocatalysts for hydrogen production. The effective separation of photogenerated charges is a key objective to improve the photocatalytic activity of COFs. Here, four COFs were synthesized through the Schiff-base reaction to investigate whether the presence (simultaneous or not) of triazine and ketone as acceptors in COFs improved electron-hole separation efficiency. Evidence indicated that charge separation was more efficient when triazine and ketone were simultaneously present in the COF. The COF comprising two acceptors displayed the highest photocatalytic hydrogen production rate (31.43 μmol h-1 ; 41.2 and 3.4 times as large as those of the COFs containing only triazine or ketone, respectively). Moreover, the effect of the distance between the two acceptors on the electron-hole separation was investigated by changing the length of a bridging biphenyl ring. It turned out that the transport distance of a single phenyl group was more favorable for the catalytic reaction. This work affords insight and support for the design of efficient COF photocatalysts.

Preparation of TiO2-Based Photocatalysts Synergistically Modified with Fe3+–Graphene and Their Visible-Light-Catalyzed Hydrogen Production from Ammonia Borane

TiO2-based photocatalysts are promising materials that show great potential in the field of catalysis due to their excellent properties including nontoxicity, high photocatalytic performance, and outstanding thermal and chemical stability. However, several challenges exist regarding TiO2 applications for catalytic hydrogen production. In this work, Fe- and graphene-comodified TiO2 (Fe–rGO/TiO2) was synthesized via a two-step solvothermal method. In addition, the effect of Fe3+ and graphene addition upon the catalytic performance of TiO2 was investigated based on the ammonia borane hydrogen production reaction, and the catalysts were characterized by SEM, XRD, XPS, UV–vis, FT-IR, and Raman methods. Batch experiments showed that the synthesized Fe–rGO/TiO2 composites exhibited high photocatalytic performance for hydrogen production from ammonia borane under visible-light irradiation. Moreover, the highest photocatalytic hydrogen production rate (1235.32 μmol·min–1·gcat–1) of 2%Fe–1%rGO/TiO2 was observed under visible-light irradiation at 25 °C, and the photocatalytic activity of the sample remained almost unchanged after the fifth cycle. The XRD, XPS, FT-IR, and Raman analyses showed that Fe and graphene successfully modified TiO2 and the presence of Ti4+. In addition, the extended visible-light absorption range and a reduction of the band gap of Fe–rGO/TiO2 were demonstrated by UV–vis diffuse reflectance spectra and calculation of the band gap. Also, the preparation of hydrogen from the hydrolysis of ammonia borane photocatalyzed by TiO2 composites was discussed. These findings are crucial for designing TiO2-based photocatalysts with high performance for photocatalytic hydrogen production.

One-step synthesis CdS/single crystal ZnO nanorod heterostructures with high photocatalytic H2 production ability

CdS/single crystal ZnO nanorod heterostructure (CdS/ZnO) was fabricated via microwave synthesis method, and the structural, morphological and photocatalytic hydrogen generation was tested. Studied results demonstrated that CdS particles were decorated on the surface of single crystal ZnO nanorod with crystallite size about 43 nm, and CdS nanoparticle significantly enhanced the photocatalytic hydrogen generation ability of the heterostructure by increasing the specific surface area, promoting the separation, migration of photoinduced carriers and increasing the light absorption. Pure ZnO exhibits bandgap energy of 3.09 eV, while the CdS/ZnO sample possessed a more narrow band gap (2.62 eV) than ZnO nanorod. Under the irradiation of visible light, the highest photocatalytic hydrogen production rate of 4076 µmolg−1h−1 is observed over the CdS/ZnO with the content of CdS is 38 wt%, which is about 13.59 and 76.91 times more active than pure ZnO nanorod and CdS nanoparticle. In addition, the specific surface area of the composite sample reaches 43.375 m2/g, and the instantaneous photocurrent reaches 130 μA /cm2. The present microwave radiation method is simple, easy to control, and timesaving, thereby providing a efficient route for the preparation of metal oxide-based photocatalytic material with high hydrogen evolution activity.

Solid solutions of CdS and ZnS: Comparing photocatalytic activity and photocurrent generation

The series of Cd1-xZnxS (x = 0–1.0) photocatalysts and Cd1-xZnxS/FTO thin film photoelectrodes were prepared. The obtained samples were studied by X-ray diffraction method (XRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and N2 low temperature adsorption. The photocatalysts were tested in the reaction of hydrogen production from Na2S/Na2SO3 solution under visible light irradiation. The photocurrents were measured in aqueous solution of Na2Sn and NaCl. It was shown that the target properties in the hydrogen evolution and photocurrent production are changed differently dependent on the composition of the mixed solid solutions. The highest photocatalytic hydrogen production rate was observed over Cd0.3Zn0.7S while the most effective photoelectrode was Cd0.8Zn0.2S/FTO. The Cd1-xZnxS/FTO samples were studied by the electrochemical methods in details. The factors affecting the photocatalytic activity and the photocurrent generation were found and listed for the first time. Conduction band potential (or flat band potential) and electron lifetime play a crucial role for effective photocatalytic hydrogen production over Cd1-xZnxS. Optimal photoelectrochemical characteristics were obtained in case of high values of electron lifetime. If the electron lifetimes of the tested samples have similar values, the high concentration of charge carriers is required for high photocurrent generation over Cd1-xZnxS/FTO photoelectrodes.

Nanoscale Multidimensional Pd/TiO2/g-C3N4 Catalyst for Efficient Solar-Driven Photocatalytic Hydrogen Production

Solar-to-fuel conversion is an innovative concept for green energy, attracting many researchers to explore them. Solar-driven photocatalysts have become an essential solution to provide valuable chemicals like hydrogen, hydrocarbon, and ammonia. For sustainable stability under solar irradiation, titanium dioxide is regarded as an acceptable candidate, further showing excellent photocatalytic activity. Incorporating the photo-sensitizers, including noble metal nanoparticles and polymeric carbon-based material, can improve its photoresponse and facilitate the electron transfer and collection. In this study, we synthesized the graphitic carbon nitride (g-C3N4) nanosheet incorporated with high crystalline TiO2 nanofibers (NF) as 1D/2D heterostructure catalyst for photocatalytic water splitting. The microstructure, optical absorption, crystal structure, charge carrier dynamics, and specific surface area were characterized systematically. The low bandgap of 2D g-C3N4 nanosheets (NS) as a sensitizer improves the specific surface area and photo-response in the visible region as the incorporated amount increases. Because of the band structure difference between TiO2 and g-C3N4, constructing the heterojunction formation, the superior separation of electron-hole is observed. The detection of reactive oxygen species and photo-assisted Kelvin probe microscopy are conducted to investigates the possible charge migration. The highest photocatalytic hydrogen production rate of Pd/TiO2/g-C3N4 achieves 11.62 mmol·h−1·g−1 under xenon lamp irradiation.

Exfoliation-induced exposure of active sites for g-C3N4/N-doped carbon dots heterojunction to improve hydrogen evolution activity

Photocatalysis is a surface catalytic process in which photogenerated electrons are transferred to the surface of the catalyst for water reduction. In this paper, we described a novel two-step calcination strategy that not only realizes the integrating of N-doped carbon dots (NCDs) with g-C3N4 nanosheets, but also can the g-C3N4/NCDs heterojunction provide more catalytic active sites and shortens the distance of charges transport to the surface of materials. The first thermal treatment in the air lead to the formation of bulk g-C3N4 while NCDs was loaded in it. The subsequent secondary calcination was conducive to the exfoliation of bulk g-C3N4 into thinner nanosheets with thickness of 1 nm. Meanwhile, more NCDs insetted in the pristine g-C3N4 were exposed to the surface of materials and more catalytic active site were formed, thus promoting the hydrogen evolution. Electron paramagnetic resonance (EPR) tests certified that the g-C3N4 nanosheet/NCDs composites can generate more OH radical compared with bulk g-C3N4 and bulk g-C3N4/NCDs, which further validated that photogenerated electron-hole was effective separated due to more exposure of NCDs and shorter distance of electron transport to the surface. Impressively, results showed that modification of g-C3N4 with NCDs (1.0 wt % loading) exhibited the highest photocatalytic hydrogen production rate (3319.3 μmol g−1 h−1) and an apparent quantum yield of 29.8 % at 420 nm, which was 13 folds of bulk g-C3N4. Our work illuminates a new method for high activity g-C3N4/carbon dots photocatalyst in the field of photocatalysis.

In-situ construction of Mo3S4/Cd0.5Zn0.5S heterojunction: An efficient and stable photocatalyst for H2 evolution

In this work, Mo3S4/Cd0.5Zn0.5S heterojunction with abundant porosity was in-situ synthesized by one-step hydrothermal method. Characterization results clearly indicate that the composite material are composed of nanoparticles with an average particle diameter about 65 nm and abundant inter-particle pores are present in between. The XPS analysis found that when Mo3S4 was introduced, the XPS peak positions of Cd2+ and Zn2+ were shifted from the XPS peak positions of Cd2+ and Zn2+ in pristine Cd0.5Zn0.5S, which indicates that there is an interaction between Mo3S4 and Cd0.5Zn0.5S at the interface. Subsequently, the Mo3S4/Cd0.5Zn0.5S (72.1 mmol h−1 g−1) heterojunction can achieve much higher photocatalytic hydrogen production rate than the pristine Cd0.5Zn0.5S (7.54 mmol h−1 g−1), and even higher than Cd0.5Zn0.5S (56.44 mmol h−1 g−1) loaded with the noble metal Pt (2.0%), indicating that heterojunction can effectively enhance photocatalytic activity. In addition, the improvement in photocatalytic activity of Mo3S4/Cd0.5Zn0.5S is highly related with enhanced absorption and utilization of light due to the presence of the inter-particle pores which inhibit recombination of electron-hole pairs, promote charge separation and accelerate the migration of photogenerated carriers.

MoS2/Zn3In2S6 composite photocatalysts for enhancement of visible light-driven hydrogen production from formic acid

Enhancing the separation efficiency of photogenerated carriers is propitious for the promotion of photocatalytic hydrogen production from formic acid decomposition. Herein, MoS2/Zn3In2S6 (MoS2/ZIS6) composite photocatalysts containing varying mass percentages of MoS2 were obtained by a straightforward synthetic method. The results confirmed that MoS2, as a cocatalyst, markedly promoted the photogenerated charge separation efficiency and visible light-driven hydrogen production activity of ZIS6 (λ > 400 nm). Specifically, the as-prepared 0.5% MoS2/ZIS6 photocatalyst exhibited the highest photocatalytic hydrogen production rate (74.25 µmol·h−1), which was approximately 4.3 times higher than that of ZIS6 (17.47 µmol·h−1). The excellent performance of the 0.5% MoS2/ZIS6 photocatalyst may be due to the fact that MoS2 has a low Fermi energy level and can thus enrich photogenerated electrons from ZIS6, and furthermore reduce H+ derived from formic acid, to form hydrogen. The structure and morphology of the MoS2/ZIS6 photocatalysts and the reactive species were determined by X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy, among others; a plausible mechanistic rationale is discussed based on the results.