Light-driven Hydrogen Generation Research Articles

Visible light driven hydrogen generation and pollutant degradation with Au loaded 2D/2D heterojunctional nanocomposite of MoS2 and g-C3N4

The growing energy crises and accumulating organics in water have caused significant threats to the economy and environment in the current time. To minimize the impact of these problem, here we established a 2D/2D interaction between MoS2 and g-C3N4 through simple hydrothermal and calcination processes and was further loaded with Au nanoparticles. The visible light driven photocatalysis was arrived by splitting water and degrading hazardous pollutant in wastewater. The large surface to surface interaction exceedingly increased the charge transfer and separation for highly speedy photocatalysis. About 220 μmol H2 was available from 2Au/9MS/CN nanocomposite in 1 h which was 24.44 times higher than the amount available from bare g-C3N4. Further, all the photocatalysts delivered acceptable eradication activity for 2-chlorphenol and 68% pollutant was removed in 1 h. The highly accelerated photocatalysis with 2Au/9MS/CN nanocomposite is related to the extended visible light purchasing due to the surface plasmon resonance of the Au metal and enhanced charge separation arrived from the well-established 2D/2D heterojunction. We hope that this work will attract major attention of the researchers towards the preparation of dimension-matched 2D/2D heterojunctional nanocomposites for energy production and eradication of organics from water.

Tuning acceptor content and molecular structure in linear donor–acceptor polymeric photocatalysts for ultrahigh-performance visible-light-driven hydrogen evolution

A series of linear conjugated polymers were synthesized by tuning the dibenzothiophene-S,S-dioxide (DBTO) content and varying their molecular structures, and applied to study the light-driven hydrogen generation from water. We found that the photocatalytic hydrogen evolution rate (HER) under visible light irradiation improved upon increasing the content of DBTO segment in donor–acceptor (D–A) structural polymers. Benefiting from the D–A structure and the high content of active centers of DBTO group, the polymer DB-Th displayed an unprecedentedly high HER of 334.50 mmol g−1h−1 under visible-light-driven and cocatalyst-free conditions (one of the most effective bare polymer photocatalysts that has been reported), which is 1.38-fold as that of the 2D–A type polymer with the lower DBTO content and 255-fold as that of the D–D structural polymer without DBTO segment, demonstrating the significance of acceptor content in D–A structures for achieving ultrahigh photocatalytic hydrogen evolution activity under visible light.

Latest avenues on solar light-driven photocatalytic hydrogen generation using surface modified nanomaterials towards sustainable environment and circular bioeconomy

The developing interest in energy has started to work to our advantage in growing clean and electrified energy sources to supplant oil-based commodities.The global use of petroleum derivatives is increasing at an alarming and unsustainable rate, resulting in environmental damage such as releasing toxic contaminants and greenhouse gases. Nanomaterials constantly changing in their configuration may be required to a transition to a green energy-based economy. The photocatalytic water splitting method holds promise for producing hydrogen quickly and effectively. Solar energy can split water to create hydrogen, making it a valuable renewable energy source.Either co-catalysts or dopants have been added to the current photocatalysts for improvement. In this article, novel nanophotocatalysts for rational hydrogen synthesis and modified photocatalysts are discussed. The results can highlight the synthesis of nanostructured materials that demonstrate favorable catalytic properties, which can be achieved as alternative and stable catalysts for efficient hydrogen production withoutmuch environmental adverseimpacts.

Rich carbon vacancies facilitated solar light-driven photocatalytic hydrogen generation over g-C3N4 treated in H2 atmosphere

Graphite carbon nitride (g-C3N4) has caught far-ranging concern for its masses of advantages, for instance, the unique graphite-like two-dimensional lamellar structure, low cost, nontoxic, suitable bandgap of 2.7 eV and favorable stability. Whereas owing to the shortcomings of low solar absorptivity and fast recombination of photo-induced charge pairs, the overall quantum efficiency of photocatalysis for g-C3N4 is suboptimal, resulting in limited practicality of g-C3N4 (GCN). In our study, modified g-C3N4 materials (HCN) with ample carbon vacancies (CVs) were obtained through calcinating of g-C3N4 in H2 atmosphere. Higher specific surface area and more active sites of HCN were induced by roasting of g-C3N4 in H2. CVs that occurred in the N-(C3) bond lead to the reduction of electron density around N, thus narrowing the bandgap of HCN-3h and enlarging corresponding light response capability. Under the synergistic function of abundant pore construction and CVs on HCN, the photo-excited e−/h+ pairs can be memorably separated and transferred, which is favorable to photocatalytic efficiency. Among HCN, the HCN-3h sample has the highest H2 generation rate of 4297.9 μmol h−1 g−1, which achieves 2.3-fold higher than that of GCN (1291.7 μmol h−1 g−1). This paper brings forward a meaningful method of boosting the photocatalytic performance of photocatalysts by constructing abundant CVs.

Directed synthesis of a new decamolybdate-encapsulated nanocage framework by mixed-ligands for light-driven hydrogen generation

Directed synthesis of a new decamolybdate-encapsulated nanocage framework by mixed-ligands for light-driven hydrogen generation

Mechanistic insight the visible light driven hydrogen generation by plasmonic Au-Cu alloy mounted on TiO2 @B-doped g-C3N4 heterojunction photocatalyst

Designing of two dimensional surfaces and interfaces with light-active materials has been established as a versatile approach to increase their photocatalytic activity. In the present work, n-type anatase TiO 2 coupled with p-type B-doped g-C 3 N 4 nanosheet (BCN) were fabricated and Au-Cu nanoalloy with varying atomic ratio were deposited on the p-n heterojunction. The incorporation of Au-Cu on the interface of the dyad enhances light absorption over broad regime, charge separation, and migration. Au-Cu with 1:1 ratio (with an average particle size of 1.2 nm) loaded p-n hetrojunction (TBCAC-1:1) shows excellent photocurrent enhancement (approximately 4.4-folds) in the cathodic direction as compared to their monometallic plasmonic counterpart. Additionally, the catalyst shows photocurrent at zero biased potential as well as lower onset potential as compared to the other alloy. TBCAC-1:1 photocatalyst could able to produce 2150 μmol h −1 g −1 of hydrogen, which is (approximately 3-folds) as compared to their monometallic counterparts. The hydrogen evolution process for Au-Cu (1:1) system was found to be governed by the charge distribution which dictates the binding preference of the Au and Cu sites leading to the water splitting as investigated by DFT calculation. The excellent hydrogen generation by the photocatalyst links to the synergistic effect between Au and Cu associated with the hot electron photochemistry due to surface plasmon resonance phenomenon. Hot electron mediated H 2 generation by a plasmonic TiO 2 /BCN/Au-Cu photocatalyst • n-type TiO 2 with p-type B-doped g-C 3 N 4 nanosheet (BCN) were fabricated and Au-Cu nanoalloy were deposited on it. • Au-Cu on the interface of the dyad enhances light absorption over broad regime, charge separation, and migration. • Au-Cu with 1:1 ratio loaded p-n hetrojunction (TBCAC-1:1) shows excellent photocurrent enhancement in the cathodic direction as compared to other. • TBCAC-1:1 produced 2150 μmol h -1 g -1 of hydrogen (approximately 3-folds) as compared to monometallic counterparts. • The hydrogen evolution process is governed by the charge distribution between Au and Cu sites investigated by DFT calculation.

Hydroxyl-Decorated Diiron Complex as a [FeFe]-Hydrogenase Active Site Model Complex: Light-Driven Photocatalytic Activity and Heterogenization on Ethylene-Bridged Periodic Mesoporous Organosilica

A biomimetic model complex of the [FeFe]-hydrogenase active site (FeFeOH) with an ethylene bridge and a pendant hydroxyl group has been synthesized, characterized and evaluated as catalyst for the light-driven hydrogen production. The interaction of the hydroxyl group present in the complex with 3-isocyanopropyltriethoxysilane provided a carbamate triethoxysilane bearing a diiron dithiolate complex (NCOFeFe), thus becoming a potentially promising candidate for anchoring on heterogeneous supports. As a proof of concept, the NCOFeFe precursor was anchored by a grafting procedure into a periodic mesoporous organosilica with ethane bridges (EthanePMO@NCOFeFe). Both molecular and heterogenized complexes were tested as catalysts for light-driven hydrogen generation in aqueous solutions. The photocatalytic conditions were optimized for the homogenous complex by varying the reaction time, pH, amount of the catalyst or photosensitizer, photon flux, and the type of light source (light-emitting diode (LED) and Xe lamp). It was shown that the molecular FeFeOH diiron complex achieved a decent turnover number (TON) of 70 after 6 h, while NCOFeFe and EthanePMO@NCOFeFe had slightly lower activities showing TONs of 37 and 5 at 6 h, respectively.

Wheel-shaped icosanuclear Cu-containing polyoxometalate catalyst: Mechanistic and stability studies on light-driven hydrogen generation

In this paper, we report the synthesis and characterization of a wheel-shaped icosanuclear-containing polyoxometalate (POM), K12Li13[Cu20Cl(OH)24(H2O)12(P8W48O184)]·22H2O (K12Li13-Cu20P8W48). The resulting cation-exchanged tetrabutylammonium salt of the polyoxoanion Cu20P8W48 (TBA-Cu20P8W48) exhibits high efficiency for visible-light-driven H2 production in the presence of an [Ir(ppy)2(dtbbpy)][PF6] photosensitizer and a triethanolamine electron donor. Under optimal conditions, the turnover number for H2 production reaches ∼2892 after 5 h of photocatalysis and thereafter continuously increases to ∼13400 in a long-term 120 h reaction, representing the best performance among all reported transition-metal-substituted POM catalysts. Mechanistic studies confirm the existence of reductive and oxidative quenching processes, of which the reductive quenching pathway is dominant. Various stability tests demonstrate that the TBA-Cu20P8W48 catalyst slowly dissociates Cu ions under turnover conditions; however, both the starting TBA-Cu20P8W48 and its molecular decomposition products are dominant active species for efficient and long-term H2 production.

High temperature hydrothermal etching of g-C3N4 for synthesis of N doped carbon quantum dots-supported CdS photocatalyst to enhance visible light driven hydrogen generation

Herein, we proposed a facile method to synthesize N doped carbon quantum dots (NCQDs) using g-C3N4 as carbon-nitrogen source, and the NCQDs-modified CdS nanocomposite catalysts for photocatalytic water splitting were synthesized by one-step hydrothermal method. The results showed that the NCQDs with a size of 3.2 nm obtained by hydrothermal etching were adsorbed on the surface of CdS particles with a size of 80 nm and induced the regulation of the surface morphology of CdS particles. There was strong interaction between NCQDs and CdS through C-S bond. The introduction of NCQDs in composite catalysts not only increased the photo-absorption performance but also suppressed the recombination of photo-generated carriers, which enabled the photo-generated electrons to transfer to NCQDs effectively and quickly and improved the photocatalytic performance of hydrogen production from water splitting. The composite photocatalysts showed good response to visible light in UV-Vis DRS and the photocatalytic water splitting experiment showed that the photocatalytic hydrogen production activity of composite catalysts was significantly improved under visible light (λ > 400 nm). And the maximum hydrogen production rate reached 2306.1 μmol/g/h, which was about 7 times the amount of unsupported NCQDs sample.

A Multi-Layer Device for Light-Triggered Hydrogen Production from Alkaline Methanol.

It usually requires high temperature and high pressure to reform methanol with water to hydrogen with high turnover frequency (TOF). Here we show that hydrogen can be produced from alkaline methanol on a light‐triggered multi‐layer system with a very high hydrogen evolution rate up to ca. 1 μmol s−1 under the illumination of a standard Pt‐decorated carbon nitride. The system can achieve a remarkable TOF up to 1.8×106 moles of hydrogen per mole of Pt per hour under mild conditions. The total turnover number (TTN) of 470 000 measured over 38 hours is among the highest reported. The system does not lead to any COx emissions, hence it could feed clean hydrogen to fuel cells. In contrast to a slurry system, the proposed multi‐layer system avoids particle aggregation and effectively uses light and Pt active sites. The performance is also attributed to the light‐triggered reforming of alkaline methanol. This notable performance is a promising step toward practical light‐driven hydrogen generation.

High photocatalytic performance of hydrogen evolution and dye degradation enabled by CeO2 modified TiO2 nanotube arrays

The environment remediation and new energy development are the investigation focus of scientists, and the photocatalytic technology could simultaneously achieve the goal by solar energy conversion. In this paper, the hybrid photocatalysts were synthesized by the deposition of CeO2 nanospheres on TiO2 nanotube arrays (TiO2 NTs) by the solvothermal/annealing treatment, and the operation order displayed vital influences on the photocatalytic capacity. The Sample 4 prepared with annealing-solvothermal-annealing treatment showed the improved light response and low photoelectron recombination. The high visible light-driven photocurrent and hydrogen generation were obtained, and the photocatalytic removal of RhB, MB and Cr(VI) was also attractive. The hybrid TiO2 NTs/CeO2 photocatalyst displayed the high photostability toward the H2 generation and dye degradation, and the mechanism was proposed to explain the outstanding photocatalytic ability. Consequently, it could be recognized that the TiO2 NTs/CeO2 photocatalyst would exhibit excellent potential in dyeing and electroplating wastewater purification and new energy development because of the attractive photocatalytic capacity.

Enhanced light-driven hydrogen generation in carbon nitride photocatalysts by interfacial electron-transfer cascade

This work aims at depositing high-crystallinity NiOx nanoparticles on the surface of graphitic carbon nitride (g-CN) nanosheets to improve light-driven hydrogen (H2) generation. Notably, assisted by transmission electron microscopy (TEM), we can discover that the solvothermal-processed NiOx nanoparticles attached over g-CN possess a great crystallinity with a diameter size of approx. 3–5 nm. As a result, the NiOx-nanoparticle loading can obviously enhance the H2 evolution rate (HER) of g-CN from 0 to 307 μmol h−1 g−1 under irradiation of AM1.5 spectra. Meanwhile, the apparent quantum efficiencies (AQE) at 400 nm can even approach the superior 1.5%. What’s more, X-ray photoelectron spectroscopy (XPS) and transient absorption (TA) spectra contribute to propose that the photogenerated electrons can first reduce Ni3+ into metallic nickel (Ni0), and then the H+ prefers to be reduced on the surface of Ni2+/Ni0 sites.

Ultrafast Electron Transfer from CdSe Quantum Dots to an [FeFe]-Hydrogenase Mimic.

The combination of CdSe nanoparticles as photosensitizers with [FeFe]-hydrogenase mimics is known to result in efficient systems for light-driven hydrogen generation with reported turnover numbers in the order of 104-106. Nevertheless, little is known about the details of the light-induced charge-transfer processes. Here, we investigate the time scale of light-induced electron transfer kinetics for a simple model system consisting of CdSe quantum dots (QDs) of 2.0 nm diameter and a simple [FeFe]-hydrogenase mimic adsorbed to the QD surface under noncatalytic conditions. Our (time-resolved) spectroscopic investigation shows that both hot electron transfer on a sub-ps time scale and band-edge electron transfer on a sub-10 ps time scale from photoexcited QDs to adsorbed [FeFe]-hydrogenase mimics occur. Fast recombination via back electron transfer is observed in the absence of a sacrificial agent or protons which, under real catalytic conditions, would quench remaining holes or could stabilize the charge separation, respectively.

Soluble polyfluorene dots as photocatalyst for light-driven methylene blue degradation and hydrogen generation

The soluble Pdots based on poly(9,9-dioctylfluorene) were introduced as a photocatalyst for photodegradation activity and light-driven hydrogen generation.

Enhanced light-driven hydrogen generation on carbon quantum dots with TiO2 nanoparticles.

Solar to hydrogen (H2) conversion systems based on carbon nanomaterials have shown great potentials in the clean energy field recently. However, for most systems, energy level alignments and light-induced redox processes are still unclear, which hinder artificial designing for higher efficiency of solar energy conversion and further applications. Here we report 77% enhancement in the light-driven H2 generation efficiency of N,S co-doped carbon quantum dot (N,S-CQD) aqueous system by adding TiO2 nanoparticles. Using steady-state and transient spectroscopy, four specific energy levels of CQDs are confirmed with the band gaps of 3.55 eV (X4), 2.99 eV (X3), 2.76 eV (X2) and 1.75 eV (X1), respectively. The X2 energy band is highly active for H+ reduction with a longer lifetime of 13.38 ns. Moreover, the observed low efficiency of intrinsic transition from X3 to X2 band of N,S-CQDs accounts for the poor performance of solar to H2 conversion for pure N,S-CQDs based on H2 generation and detailed time-resolved spectroscopic results. The mechanism of H2 generation enhancement can be explained by multiple electron transfer processes between N,S-CQDs and TiO2 NPs where TiO2 NPs act as electron intermediates that efficiently transfer electrons from the inert band (X3) to the active band (X2) for H2 generation. This study enriches the fundamental understanding of N,S-CQDs and provides a new pathway toward high-performance N,S-CQD-based solar to H2 conversion systems.

Influence of Surface Ligands on Charge-Carrier Trapping and Relaxation in Water-Soluble CdSe@CdS Nanorods

In this study, the impact of the type of ligand at the surface of colloidal CdSe@CdS dot-in-rod nanostructures on the basic exciton relaxation and charge localization processes is closely examined. These systems have been introduced into the field of artificial photosynthesis as potent photosensitizers in assemblies for light driven hydrogen generation. Following photoinduced exciton generation, electrons can be transferred to catalytic reaction centers while holes localize into the CdSe seed, which can prevent charge recombination and lead to the formation of long-lived charge separation in assemblies containing catalytic reaction centers. These processes are in competition with trapping processes of charges at surface defect sites. The density and type of surface defects strongly depend on the type of ligand used. Here we report on a systematic steady-state and time-resolved spectroscopic investigation of the impact of the type of anchoring group (phosphine oxide, thiols, dithiols, amines) and the bulkiness of the ligand (alkyl chains vs. poly(ethylene glycol) (PEG)) to unravel trapping pathways and localization efficiencies. We show that the introduction of the widely used thiol ligands leads to an increase of hole traps at the surface compared to trioctylphosphine oxide (TOPO) capped rods, which prevent hole localization in the CdSe core. On the other hand, steric restrictions, e.g., in dithiolates or with bulky side chains (PEG), decrease the surface coverage, and increase the density of electron trap states, impacting the recombination dynamics at the ns timescale. The amines in poly(ethylene imine) (PEI) on the other hand can saturate and remove surface traps to a wide extent. Implications for catalysis are discussed.

Enhanced solar light driven hydrogen generation and environment remediation through Nd incorporated ZnIn2S4

Visible-light-driven hydrogen production is a promising pathway to realize efficient solar energy utilization. Here, Nd3+ incorporated ZnIn2S4 (Nd-ZIS) was synthesized via facile one step hydrothermal method. Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS) confirm the successful incorporation of Nd3+ in ZnIn2S4. Optical studies reveal the reduction of effective bandgap from 2.7 eV to 2.54 eV upon incorporation of Nd3+ with improved charge carrier life time of 3.12 ns. Electronic properties of ZIS and Nd-ZIS were investigated from first principle calculations. An attempt to improve photocatalytic activity of ZIS by modification with Nd3+ ions resulted in degradation of organic pollutant up to 98% under natural sunlight and decrease in life time of trap states up to a nominal value of 200 ms (as evident from photoelectrochemical measurements). The mechanism behind enhancement of photocatalytic activity of ZIS post Nd3+ integration has been proposed. Nd-ZIS was also utilized for water splitting activity exhibiting a considerable H2 generation ∼3415 μmol g−1. To the best of our knowledge, activity of Nd3+ incorporated ZIS has been explored for the first time in present work. It is believed that an in-depth understanding of photoactivity of ZIS would be significantly important for designing materials with desired photocatalytic performance in future.

Hybridization of g-C3N4 quantum dots with 1D branched TiO2 fiber for efficient visible light-driven photocatalytic hydrogen generation

The hybrid 1D branched TiO2 loaded with g-C3N4 QDs was successfully fabricated that plays a significant role in photocatalysis. The 1D branched TiO2 prepared by electrospinning followed by alkali-hydrothermal process, and g-C3N4 QDs were grafted over it by a chemical vapor deposition method. The composite display enhancement in photocatalytic hydrogen evolution is about 10.57 mmol. g−1.h−1 in comparison to the g-C3N4 sample that only produces 0.32 mmol. g−1.h−1 while the HBTiO2 sample evolved a negligible amount of hydrogen under visible light. The composite sample shows quantum efficiency for HER at 420 nm light is 18.6% that is much higher than the other two samples. The specific surface area of the composite sample is 92.39 m2g-1 that is about 13 times more than bulk g-C3N4. The bandgap of HBTiO2/g-C3N4 QDs, g-C3N4, and HBTiO2 samples calculated as 2.71 eV, 2.67eV, and 3.24eV, respectively. The TRPL spectra imply that the duration of the lifetime of composite becomes longer which effectually overwhelm the electron-hole recombination. The 1D branched TiO2 fiber reduces the charge recombination by fast transfer of electron while g-C3N4 QDs facilitate the visible light absorption by improving the optical properties. The formation of the type II heterostructure system remarkably promotes the separation and transfer of electron holes and facilitates the photo-reduction reaction.

How Eosin Y/Graphene Oxide-Based Materials Can Improve Efficiency of Light-Driven Hydrogen Generation: Mechanistic Aspects

We have demonstrated that the photocatalytic system, containing Eosin Y (EY) as a sensitizer, triethanolamine (TEOA) as a sacrificial electron donor, CoSO4 as a catalyst, and graphene oxide (GO), e...

Building Oxime-Ni2+ Complex on Polymeric Carbon Nitride: Molecular-Level Design of Highly Efficient Hydrogen Generation Photocatalysts.

We report an effective strategy to in situ construct the oxime-Ni2+ complex unit on polymeric carbon nitride (PCN) as a molecular catalyst for the highly efficient hydrogen evolution reaction (HER). The PCN was functionalized with oxime groups that allowed for immobilizing Ni2+ to form oxime-Ni2+ complex units on the PCN surface with uniform distribution. The electrochemical characterizations reveal that these oxime-Ni2+ units can effectively capture photogenerated electrons from PCN and serve as active catalytic sites for proton reduction. Notably, the oxime-Ni2+ enriched PCN showed even higher activities for photocatalytic hydrogen evolution than the Pt-loaded PCN. This work provides a new way to synthesize low-cost photocatalysts with surface grafting of noble-metal-free molecular HER catalysts for efficient light-driven hydrogen generation.