Photocatalytic H2 Production Rate Research Articles

Slow Photon-Enhanced Heterojunction Accelerates Photocatalytic Hydrogen Evolution Reaction to Unprecedented Rates

Slow Photon-Enhanced Heterojunction Accelerates Photocatalytic Hydrogen Evolution Reaction to Unprecedented Rates

Recycling Spent LiCoO2 Battery as a High‐efficient Lithium‐doped Graphitic Carbon Nitride/Co3O4 Composite Photocatalyst and Its Synergistic Photocatalytic Mechanism

The ever‐increasing quantity of spent lithium‐ion batteries (LIBs) is both a potential environmental pollutant and a valuable resource. The spent LIBs recycling mainly aimed at the separation of valuable elements. Some issues still exist in these processes such as high energy consumption and complex separation procedures. This study avoided element separation and proposed a facile approach to transform spent LiCoO2 electrode into a lithium (Li)‐doped graphitic carbon nitride (g‐C3N4)/Co3O4 composite photocatalyst through one‐pot in situ thermal reduction. During the thermal process, melamine served as the reductant for LiCoO2 decomposition and the raw material for g‐C3N4 production. Li was in situ doped in g‐C3N4 and the generated Co3O4 was in situ integrated, forming a Li‐doped g‐C3N4/Co3O4 composite photocatalyst. This special composite exhibited an enhanced photocatalytic performance, and its photocatalytic H2 production and RhB degradation rates were 8.7 and 6.8 times higher than those of g‐C3N4. The experiments combined with DFT calculation revealed that such enhanced photocatalytic efficiency was ascribed to the synergy effect of Li doping and Co3O4 integrating, which extended the visible light absorption (450–900 nm) and facilitated the charge transfer and separation. This study transforms waste into a high‐efficient catalyst, realizing high‐valued utilization of waste and environmental protection.

In-situ Pt nanoparticles decorated BiOBr heterostructure for enhanced visible light-based photocatalytic activity: Synergistic effect

Advanced functional materials for photocatalytic hydrogen (H2) generation using abundant solar energy are the core of new and renewable energy research. In this paper, we report the in-situ deposition of platinum quantum-sized particles (Pt QDs) on bismuth oxybromide (BBr) 3D marigold flowers with exposed (101)/(110) facets (i.e. BBr–Pt) hierarchies prepared by a simple solvo-thermal method acting as a surfactant/structure stabilizer in the presence of CTAB. Synthesized samples were characterized by a series of analytical techniques. Intimate contact as demonstrated by HRTEM, effect of Pt loading in 3D-BiOBr nanostructure on photocatalytic H2 production and crystal violet (CV) dye degradation rate under white LED light irradiation was studied. This was greatly improved by loading Pt QDs on BBr, the latter showing the highest photocatalytic activity for BBr-2Pt nanostructure, due to the synergistic effect of quantum-sized Pt nanoparticles and exposed ((101) and (110) planes). The BBr–2Pt nanostructure photocatalysts showed highest H2 generation of 320.69 μmol g−1, which is 142 folds larger than bare BBr (2.26 μmol g−1).

Mixed-Valence Bimetallic Ce/Zr MOF-Based Nanoarchitecture: A Visible-Light-Active Photocatalyst for Ciprofloxacin Degradation and Hydrogen Evolution.

A mixed-valency bimetallic Ce/Zr MOF with Ce3+/Ce4+ ions incorporated and an oxygen vacancy-rich single-component photocatalyst have been designed through the one-step solvothermal route to harness photons from the visible-light spectrum for green energy (H2) generation and ciprofloxacin (CIP) degradation. The one-pot-engineered bimetallic Ce/Zr MOF shows visible-light-active characteristics accompanied by a narrower band gap, along with enhanced exciton separation and superior ligand-to-metal charge transfer (LMCT), due to the presence of an interconvertible Ce3+/Ce4+ ions pair in comparison to its pristine MOF counterpart. The Ce ion insertion led to increase in electron density around the Zr4+ ion, along with generation of some oxygen vacancies (OV), which cumulatively led to the rise in the photo-reaction output. The synthesized UNH (Ce/Zr 1:1) MOF displayed a boosted photocatalytic H2 production rate of 468.30 μmol h-1 (ACE = 3.51%), which is around fourfolds higher than that of pristine MOFs. Moreover, for CIP photodegradation, the UNH (Ce/Zr 1:1) shows an enhanced efficiency of 90.8% and follows pseudo-first-order kinetics with a rate constant of 0.0363. Typically, the active species involved in the photo-redox reaction of the CIP photodegradation follows the order hydroxyl radical (OH•) < superoxide radical (O2•-), as confirmed by the TA and NBT tests. Consequently, the bimetallic Ce/Zr MOF can be readily employed as a robust photocatalyst with enhanced tendencies towards CIP degradation and H2 evolution.

Ti3C2 MXene co-catalyst assembled with mesoporous TiO2 for boosting photocatalytic activity of methyl orange degradation and hydrogen production

Photocatalytic degradation and hydrogen production using solar energy through semiconductor photocatalysts are deemed to be a powerful approach for solving environmental and energy crisis. However, the biggest challenge in photocatalysis is the efficient separation of photo-induced carriers. To this end, we report that the mesoporous TiO2 nanoparticles are anchored on highly conductive Ti3C2 MXene co-catalyst by electrostatic self-assembly strategy. The constructed mesoporous TiO2/Ti3C2 composites display that the mesoporous TiO2 nanoparticles are uniformly distributed on the surface of layer structured Ti3C2 nanosheets. More importantly, the as-obtained mesoporous TiO2/Ti3C2 composites reveal the significantly enhanced light absorption performance, photo-induced carriers separation and transfer ability, thus boosting the photocatalytic activity. The photocatalytic methyl orange degradation efficiency of mesoporous TiO2/Ti3C2 composite with an optimized Ti3C2 content (3 wt%) can reach 99.6% within 40 min. The capture experiments of active species confirm that the •O2− and •OH play major role in photocatalytic degradation process. Furthermore, the optimized mesoporous TiO2/Ti3C2 composite also shows an excellent photocatalytic H2 production rate of 218.85 μmol g–1 h–1, resulting in a 5.6 times activity as compared with the pristine mesoporous TiO2 nanoparticles. This study demonstrates that the MXene family materials can be applied as highly efficient noble-metal-free co-catalysts in the field of photocatalysis.

Surface molecule induced effective light absorption and charge transfer for H2 production photocatalysis in a carbonized polymer dots-carbon nitride system

Current sunlight-powered H2 production that employ carbonized polymer dots (CPDs)-graphitic carbon nitride (g-C3N4) systems has made significant progress. However, we still have a limited understanding of the mechanism by which CPDs contribute to the phtocatalytic efficiency. Surface molecule 1,2,3,5-tetrahydro-5-oxo-imidazo[1,2-α]pyridine-7-carboxylic acid (IPCA) has been verified to largely impact the photophysical properties of CPDs. Here, we report the design of g-C3N4, IPCA-g-C3N4 and CPDs-g-C3N4 catalysts to uncover the critical role of IPCA. The photocatalytic H2 production rates of g-C3N4 were improved by the hybridization with IPCA and CPDs (1172 ± 39; 2150 ± 92 vs. 828 ± 121 μmol g−1 h−1, respectively). The DFT calculations further unraveled that electron transfer pathway in ICPA-CN@H3O+ followed ICPA -> g-C3N4 -> H3O+ procedure. The results indicate that IPCA on CPDs is conducive to extending the light-responsive range, redistributing of photoinduced electron-hole pairs, increasing the electron density of g-C3N4, and thus improving H2 generation rates.

Boosting the photogenerated charge separation of g-C3N4 by constructing a Ni@Ni2P cocatalyst with a core–shell structure

The photocatalytic H2 production rate is significantly boosted by constructing Ni@Ni2P core–shell cocatalyst on g-C3N4 resulted from the working function gradient to improve the separation efficiency of photogenerated electrons and holes.

Confining single Pt atoms from Pt clusters on multi-armed CdS for enhanced photocatalytic hydrogen evolution

Atomically dispersed platinum clusters are developed as a novel single atom co-catalyst, which dramatically enhances the photocatalytic H2production rate.

KW-GO, a graphene-like carbon extracted from kitchen waste (KW) advances the hydrogen production of V2O5

In this paper, graphene-like carbon (KW-GO) extracted from kitchen waste (KW) is used to reduce the agglomeration of V2O5 and improve the separation rate of photogenerated electron-hole pairs from V2O5. We found that the V2O5-KW-GO composite material (VKW-GO) could significantly enhance the photocatalytic activity and H2 production rate under visible light irradiation compared to pure V2O5. To analyze the composition and morphology of the materials, XRD, SEM, BET, UV–Vis, XPS, and Raman were measured. The results showed that the addition of KW-GO reduced the aggregation of V2O5 powder. At the same time, the specific surface area of the composite sample increased providing more active sites for photocatalytic hydrogen production. In addition, the visible absorption range of the composite sample also increased. As a result, the hydrogen production rate of V2O5 increased from 247.52 mol h−1 g−1 to 354.15 mol h−1 g−1. The method using V2O5 and VKW-GO as a catalyst for H2 production is innovative, and the conclusion may provide important theoretical guidance for photocatalytic hydrogen production.

A broom-like tube-in-tube bundle O-doped graphitic carbon nitride nanoreactor that promotes photocatalytic hydrogen evolution

Metal-free graphite carbon nitride (g-C3N4) is an ideal catalyst in the field of photocatalytic hydrogen evolution due to its visible light response, thermochemical stability and low cost. However, limited by the high photogenerated electron-hole recombination rate and poor light trapping ability of bulk g-C3N4 prepared by thermal condensation, it remains a great challenge in boosting the photocatalytic hydrogen (H2) evolution performance. Herein, a broom-like O-doped g-C3N4 nanoreactor (O-CN-NTs) oriented by tube-in-tube was developed for the first time through the “calcination-hydrothermal-calcination” method. The tube-in-tube nanoreactor not only can facilitate the scattering of incident light inside the cavity to enhance the utilization of light, but also can reduce the transport distance of carriers from the bulk to the surface to facilitate electron-hole separation. The morphology design of the tube-in-tube nanoreactor plays a very important role in improving the performance of photocatalytic H2 production. Furthermore, the density functional theory (DFT) calculation results manifest that the charge redistribution around the doped oxygen atoms accelerates the separation of electron-hole. The doping of oxygen atoms in g-C3N4 nanoreactor further enhanced the photocatalytic H2 production performance. Attributed to above advantages, the visible-light-driven (≥420 nm) photocatalytic H2 production rate of O-CN-NTs can achieve 13.61 mmol g-1h−1, which is approximately 71.63 times that of bulk g-C3N4 (CN550).

CdS-Cu1.81S heteronanorods with continuous sublattice for photocatalytic hydrogen production

Photocatalytic hydrogen (H2) production is a cascade reaction that involves multiple limiting steps, such as light-harvesting, charge separation and transfer, redox reaction rate, and so on. Thus, there is a need to optimize each reaction node to promote the photocatalytic H2 production efficiency for the commercial application of sustainable energy. Herein, we report integrally designed CdS-Cu1.81S heteronanorods (HNRs) for photocatalytic H2 production driven by near-infrared to ultraviolet irradiation. The intraparticle p-n junction and the well-constructed heterointerface result in highly efficient charge separation and transfer between the heterogeneous domains. Further adjusting the redox reaction sites on the surface of CdS-Cu1.81S HNRs leads to a high photocatalytic H2 production rate of 2.714 mmol·h−1·g−1, representing 150-fold and 108-fold improvements compared with pristine Cu1.81S and CdS nanorods (NRs), respectively. Our work provides an alternative entry point for boosting the performance of noble-metal-free photocatalyst and highlights the importance of synergetic design.

Ni(OH)2 Nanosheets Modified Hexagonal Pyramid CdS Formed Type II Heterojunction Photocatalyst with High-Visible-Light H2 Evolution

CdS has a wide visible-light response range and suitable energy band structure; it has been spotlighted in the field of photocatalysis. Nevertheless, its poor photogenerated carriers separation efficiency leads to dissatisfying photocatalytic H2 production activity. In this work, we prepared a hexagonal pyramid CdS-Ni(OH)2 hybrid photocatalyst. The maximal photocatalytic H2 production rate of CdS-Ni(OH)2 hybrid photocatalyst was 29.51 mmol/h/g, which was 5.6 times and 1.9 times higher than the hexagonal pyramid CdS and CdS-Pt. A type II heterojunction can be formed between CdS and Ni(OH)2. The separation efficiency of photogenerated carriers can be improved effectively. Furthermore, it has been confirmed that photogenerated holes can transfer from CdS to Ni(OH)2, which effectively improved the photogenerated holes transfer and accelerated the oxidation of the sacrifice agent. Finally, the photocatalytic H2 production activity can be significantly promoted.

NiO nanoparticles dotted TiO2 nanosheets assembled nanotubes P-N heterojunctions for efficient interface charge separation and photocatalytic hydrogen evolution

The low charge separation efficiency of semiconductor photocatalyst is still a stumbling block to improve photocatalytic performance. The p-n heterojunction with built-in electric field usually favors the spatial charge separation. Herein, NiO nanoparticles dotted TiO2 nanotubes p-n heterojunction photocatalysts (NiO/TNs) are fabricated through hydrothermal and wet-impregnation strategies. The resultant NiO/TNs with relatively large surface area of 102.8 m2 g−1 shows excellent photocatalytic H2 production rate of 228 μmol h−1 g−1, which are four times higher than that of TNs (50 μmol h−1 g−1) under AM 1.5G irradiation without any cocatalyst. The high photocatalytic activity can be ascribed to the uniform growth NiO nanoparticles on surface of TNs enhancing the photoresponse to visible light region, and the formation of p-n heterojunctions induced built-in electric field promoting photogenerated electrons transmission from NiO to TNs through the heterogeneous interface, thus enhanced the charge carriers migration and separation efficiently.

MOF-mediated fabrication of coralloid Ni2P@CdS for enhanced visible-light hydrogen evolution

Ni2P is an efficient cocatalyst to improve the photoelectric properties of CdS. In consideration of this, we designed a coralloid Ni2P@CdS photocatalyst (C-Ni2P@CdS) via a MOF-mediated tandem pyrolysis strategy for enhanced photocatalytic hydrogen evolution. Benefiting from the unique synergistic effect between coralloid Ni2P and CdS, C-Ni2P@CdS shown a high photocatalytic H2 production rate of 28 391 μmol h−1 g−1, nearly 11 times higher than CdS. Compared with CdS, the absorption intensity of C-Ni2P@CdS was drastically extended in the visible-light region (λ > 540 nm). Meanwhile, PL spectra, EPR and photoelectric responsiveness etc. were further employed to study the synergistic effect between Ni2P and CdS. From Density Functional Theory (DFT), strong electronic coupling effect induced electrons to accumulate on adsorbed H2O and the most energetically favorable configuration indicated that Ni-P bridges were the active sites for water dissociation. Lastly, a viable mechanism of C-Ni2P@CdS heterojunction for photocatalytic hydrogen evolution was proposed.

Defect-rich cobalt pyrophosphate hybrids decorated Cd0.5Zn0.5S for efficient photocatalytic hydrogen evolution: Defect and interface engineering

Photocatalysts with highly efficient charge separation are of critical significance for improving photocatalytic hydrogen production performance. Herein, a cost-effective and high-performance composite photocatalyst, cobalt-phosphonate-derived defect-rich cobalt pyrophosphate hybrids (CoPPi-M) modified Cd0.5Zn0.5S is rationally devised via defect and interface engineering, in which the co-catalyst CoPPi-M delivers a strong interaction with host photocatalyst Cd0.5Zn0.5S, rendering Cd0.5Zn0.5S/CoPPi-M with a remarkably improved efficiency of charge separation and migration. Besides, Cd0.5Zn0.5S/CoPPi-M exhibits a hydrophilic surface with ample access to electrons and a strong reduction ability of electrons. Benefiting from these advantages, the integration of defect-rich cobalt pyrophosphate and Cd0.5Zn0.5S enables Cd0.5Zn0.5S/CoPPi-M−5% with high photocatalytic H2 production rate of 6.87 mmol g−1h−1, which is 2.46 times higher than that of pristine Cd0.5Zn0.5S, and the notable apparent quantum efficiency (AQE) is 20.7% at 420 nm. This work provides a promising route for promoting the photocatalytic performance of non-precious hybrid photocatalyst via defect and interface engineering, and advances energy-generation and environment-restoration devices.

Significantly Raised Visible‐Light Photocatalytic H2 Evolution on a 2D/2D ReS2/In2ZnS4 van der Waals Heterostructure (Small 32/2021)

2D/2D van der Waals Heterostructures In article number 2100296, Shi-Zhang Qiao and co-workers present a ReS2/In2ZnS4 2D/2D van der Waals hetero-junction (vdWH) that exhibits a highly-promoted visible-light photocatalytic H2-production rate of 2515 mmol h−1 g−1. This is 2266% times that for In2ZnS4. The outstanding performance is attributed to efficient interfacial electron-hole dissociation/transportation, and substantial atomic-level S active sites on ReS2. Results will be of immediate benefit in the rational design/synthesis of vdWHs for solar hydrogen generation.

Lollipop-shaped Co9S8/CdS nanocomposite derived from zeolitic imidazolate framework-67 for the photocatalytic hydrogen production

The unlimited consumption of traditional fossil fuels prompted an urgent need for the new H2 production strategies to provide green and sustainable energy resources. In this context, Co9S8 has emerged as a potent photocatalyst due to its narrow bandgap. Herein, we describe the synthesis of a recyclable lollipop-shaped Co9S8/CdS nanocomposite via direct annealing of zeolitic imidazolate framework-67 (ZIF-67) and CdS, as the template and sulfur source, respectively. The close contact of these two materials promotes the electron transfer and enhances the number of active sites toward the desired redox reaction. The special structure of Co9S8/CdS results in a high photocatalytic H2 production rate of 1852 μmol h−1 g−1 under visible-light illumination, which is ~200 times higher than that of pure ZIF-67 and Co9S8. Therefore, this study provides a new method for the preparation of Co9S8 that concomitantly improves the photocatalytic performance of pure ZIF-67 in the H2 production technology.

Suppressing photocarrier recombination in anatase TiO2 nanoplates via thickness optimization for enhanced photocatalytical H2 generation

Exposure of a specific crystal facet is critical to maximizing the photocatalytic performance of catalysts, which makes two-dimensional (2D) materials an attractive candidate for photocatalysis. Optimizing the 2D microstructure such as thickness to suppress the photocarrier recombination is essential to develop high performance photocatalysts. Recently developed nanosheet-seeding technique enables to synthesize 2D materials with a specific crystal facet exposed, which offers an opportunity to optimize the structural configuration of materials. In this study, anatase TiO2 nanoplates with different thickness from ~25 to ~ 120 nm were fabricated by using the nanosheet-seeding technique, and effect of the thickness on the photocatalytic H2 generation was investigated. The results demonstrate that the thickness mainly influences the charge separation process, and there exists a volcano-shaped correlation between the thickness and the photocatalytic H2 production rate. The optimal TiO2 nanoplates with the thickness of ca. 50 nm exhibit the best photocatalytic H2 evolution activity.

Ammonia-assisted fabrication of Cr1.3Fe0.7O3@amine-containing carbon quantum dot core-shell architectures with ultrathin shell for broad-spectrum-driven photocatalytic hydrogen evolution

To make the efficient spatial charge separation and exploration of broad spectrum-driven H2 evolution remains a pivot challenge. Here, a novel core@shell Cr1.3Fe0.7O3@amine-containing carbon quantum dots (S1@NCQD) composite was successfully prepared by a facile bottom-up self-assembly route. An ordinary contact structure of carbon quantum dots (CQD) modified Cr1.3Fe0.7O3 was also prepared. The photocatalytic H2 production rate of Cr1.3Fe0.7O3 composite has not been improved only through the modification of CQD. Remarkably, the as-obtained S1@NCQD composite illustrated the highest photocatalytic H2 production activity under visible light illumination, which is approximately 5.5 and 7.9 times higher than that of S1 and CQD/S1 composite, respectively. Importantly, the new class of S1@NCQD composite can also exploit broad spectrum light to trigger H2 production (3.12 μmol). Effective photoinduced electron transfer is derived from a powerful interaction between shell and core, which was characterized by using photoluminescence, time-resolved PL spectroscopy, and photocurrent measurement.

Dual‐Z‐Scheme Heterojunction for Facilitating Spacial Charge Transport Toward Ultra‐Efficient Photocatalytic H2 Production

Solar‐driven water splitting has aroused considerable interest for developing renewable and clean energies. Recently, although Z‐scheme systems greatly improve the photocatalytic H2 production rate, the photoconversion efficiency is still far from the requirement for practical applications. Herein, based on direct Z‐scheme system photocatalysts, a direct CdS/W18O49/g‐C3N4 (CWOCN) dual‐Z‐scheme system is designed and fabricated. It is found that a dual‐Z‐scheme CWOCN system can efficiently regulate photoinduced carrier transfer by constructing two direct Z‐scheme charge transfer channels in the interior of the catalyst. Accordingly, the CWOCN dual‐Z‐scheme system shows an outstanding H2 production activity of 11 658 μmol g−1 h−1 without any sacrificial agents, which is about three times higher than that of CdS/W18O49 Z‐scheme nanosheets. In addition, this dual‐Z‐scheme system exhibits a high apparent quantum efficiency of 26.73% and good stability, which can keep the H2 production rate unchanged for 24 h. The design of the dual‐Z‐scheme system ensures the efficient transmission of photogenerated carriers and further optimizes the structure of the Z‐scheme system.