Graphdiyne Based Ternary GD-CuI-NiTiO3 S-Scheme Heterjunction Photocatalyst for Hydrogen Evolution

Gas-Template Synthesis of Ultrathin Porous Carbon Nitrides for Photocatalytic Redox Reactions

Graphitic carbon nitride (g-C3N4) has emerged as a promising metal-free photocatalyst but is plagued by its low activity owing to a high electron-hole recombination rate and small specific surface area. A specialized gas-template method was successfully employed to synthesize an ultrathin porous carbon nitride (UPCN) photocatalyst containing nitrogen vacancies. This thermally induced exfoliation and polycondensation approach can be modulated using different gas templates. Compared with bulk g-C3N4, UPCNs feature an optimized ultrathin structure, larger surface area, weaker fluorescence intensity, lower impedance, and higher photocurrent response. These properties contribute to more exposed active sites, shorter diffusion paths for both ions and electrons, and improved carrier separation. Consequently, UPCNs exhibit considerably enhanced photocatalytic performance in both the hydrogen evolution reaction (HER) and the photooxidation of 2,6-dimethyl-1,4-dihydro-3,5-pyridinedicarboxylic ester (1,4-DHP) under visible light. Among UPCNs, TPA-UPCN (tetrapropylammonium chloride as the gas template) exhibits the highest photocatalytic activity, surpassing NH4Cl-templated carbon nitrides (2747 vs 2092 μmol·g-1·h-1) in HER. Moreover, TPA-UPCN achieves unprecedented photocatalytic oxidation efficiency for 1,4-DHP. This study provides a new approach for the preparation of UPCN materials with enhanced photocatalytic performance.

Graphdiyne Preparation and Application in Photocatalytic Hydrogen Evolution

Graphdiyne (GDY) is a new two-dimensional carbon network material composed of sp2 hybrid carbon and sp hybrid carbon conjugation. It has unique physical and chemical properties, such as high porosity, good electrical conductivity, high carrier mobility, adjustable band gap, and so on. The preparation of GDY and GDY derivatives by adjusting physical and chemical methods and changing monomers has become the key material in the fields of photocatalysis, energy storage, life science, and so on. In this paper, new methods for controllable growth of GDY are reviewed, including liquid phase chemical classical total synthesis, chemical vapor deposition, the interface method, the explosion method, and the mechanically driven ball milling method. FT-IR, Raman, NMR, and XAS are the main means to characterize the structure of GDY. Finally, the representative application of GDY in the field of photocatalytic hydrogen evolution is summarized, and its future development has been explored.

Porous carboxymethyl cellulose nanocrystalline imprinted composite aerogels for selective adsorption of gadolinium

Gadolinium is widely applied in medical and high-tech materials because of special magnetic properties. Recovery of gadolinium from waste rare earth products has both economic and environmental value. In this experiment, honeycomb porous composite aerogels were constructed using sericin and sodium alginate mixed with functionally modified carboxymethylated cellulose nanocrystals for the adsorption and separation of gadolinium ions. There were large numbers of carboxyl groups as well as hydroxyl groups on the surface of sodium alginate and filamentous protein, which provided more sites for the adsorption of gadolinium ions. Besides, a stable honeycomb structure appeared on the surface of composite aerogels when the mixture of filamentous protein and sodium alginate was 1:1, which increased the specific surface area of materials to 140.65 m2 g-1. Additionally, the imprinted composite aerogels Ic-CNC/SSA were prepared by virtue of the imprinting technology, enhancing the adsorption selectivity of composite aerogels for gadolinium. The adsorption experiments revealed that the maximum adsorption capacity of Ic-CNC/SSA reached 93.41 mg g-1 at pH 7.0, indicating good selective adsorption of gadolinium ions. In summary, such composite aerogels provide great potential and reference value for the selective adsorption of gadolinium ions in industry.

Graphdiyne (CnH2n-2)-Based GDY/CuI/MIL-53(Al) S-Scheme Heterojunction for Efficient Hydrogen Evolution

Graphdiyne (g-C_nH_2n-2) is a new carbon material composed of sp and sp² hybrid carbon atoms. Since the synthesis by Li's team, graphdiyne has been widely studied in other fields because of its excellent properties. In this paper, graphdiyne was synthesized from copper-containing materials and the composite GDY/CuI/MIL-53(Al) S-scheme heterojunction is prepared for photocatalytic cracking of water to produce hydrogen. First, GDY/CuI was prepared by organic synthesis, and then GDY/CuI was anchored on the surface of MIL-53(Al) by in situ ultrasonic stirring. After the continuous optimization of experimental conditions, the final hydrogen evolution rate is much higher than that of MIL-53(Al). This efficient photocatalytic performance can be attributed to the S-scheme heterojunction formed by the unique energy band arrangement. At the same time, the mechanism of charge transfer was demonstrated by in situ irradiation X-ray photoelectron spectroscopy. The strong interaction among the three strongly promotes the separation and transfer of photogenerated electron-hole pairs.

Phosphorus-modified two-dimensional graphdiyne (CnH2n-2)/ZnCdS forms S-scheme heterojunctions for photocatalytic hydrogen production

Graphdiyne (GDY) is a new type of carbon allotrope material with a network structure composed of sp- and sp²-hybridized carbon, and its excellent photoelectrochemical properties have an extraordinary impact on energy materials. In this work, a graphite alkyne material was calcined and used as an anchor substrate to fix bimetallic sulfide-zinc-cadmium sulfide to form a phosphorus-doped graphdiyne (GDY-P)/zinc-cadmium sulfide (ZnCdS) heterojunction photocatalyst. The close contact between the 2D/0D binary heterojunction interfaces produced a strong interfacial force, and the final hydrogen evolution rate of the GDY-P/ZnCdS structure reached 10 395.57 μmol g^-1 h^-1, which was 2.57 and 240 times those of ZnCdS and GDY, respectively. The S-scheme heterojunction constructed by GDY-P and ZnCdS accelerates the formation of electron-hole pairs, improves the utilization of strongly reduced electrons, and overcomes the self-agglomeration of ZnCdS, ensuring the high hydrogen evolution activity of the binary structure. This work provides a new application paradigm for the construction of S-scheme heterojunctions for hydrogen evolution using new carbon materials in the field of photocatalysis.

Emerging S-Scheme Photocatalyst

Photocatalysis is a green technology to use ubiquitous and intermittent sunlight. The emerging S-scheme heterojunction has demonstrated its superiority in photocatalysis. This article covers the state-of-the-art progress and provides new insights into its general designing criteria. It starts with the challenges confronted by single photocatalyst from the perspective of energy dissipation by borrowing the common behaviors in the dye molecule. Subsequently, other problems faced by single photocatalyst are summarized. Then a viable solution for these problems is the construction of heterojunctions. To overcome the problems and mistakes of type-II and Z-scheme heterojunctions, S-scheme heterojunction is proposed and the underlying reaction mechanism is summarized. Afterward, the design principles for S-scheme heterojunction are proposed and four types of S-scheme heterojunctions are suggested. Following this, direct characterization techniques for testifying the charge transfer in S-scheme heterojunction are presented. Finally, different photocatalytic applications of S-scheme heterojunctions are summarized. Specifically, this work endeavors to clarify the critical understanding on curved Fermi level in S-scheme heterojunction interface, which can help strengthen and advance the fundamental theories of photocatalysis. Moreover, the current challenges and prospects of the S-scheme heterojunction photocatalyst are critically discussed.

Interface engineering: Synergism between S-scheme heterojunctions and Mo-O bonds for promote photocatalytic hydrogen evolution

Simple high-temperature calcination and hydrothermal methods were followed to synthesize CeO₂ and Mo-S, respectively. The efficient photocatalytic hydrogen evolution activity exhibited by the composite catalysts can be attributed to the edge active sites in Mo-S. The Mo-O bonds formed between CeO₂ and Mo-S could further accelerate the processes of separation and migration of electrons between the catalyst interfaces. The hybrid catalyst 10%-CeO₂/Mo-S exhibiting the best hydrogen generation ability (4.3 mmol h^-1g^-1) was obtained by optimizing the content of CeO₂ in CeO₂/Mo-S. Analysis of the PL spectral profile and photocurrent response recorded for the system revealed that 10%-COMS exhibited excellent photogenerated carrier separation ability. Analysis of the LSV and EIS curves revealed that 10%-COMS exhibited the optimal hydrogen production potential. The charge migration resistance provided by the systems was lower than the charge migration resistance provided by CeO₂ and Mo-S. The synergism between the S-scheme heterojunctions and the Mo-O bonds helped accelerate the separation and migration of photo-induced carriers at the catalyst interfaces. The introduction of covalent bonds in the S-scheme heterojunctions and the results presented herein can potentially help develop a new method to realize photocatalytic hydrogen evolution.

Zeolitic Imidazolate Framework-67-Derived P-Doped Hollow Porous Co3O4 as a Photocatalyst for Hydrogen Production from Water

As a part of photocatalytic water splitting, the design of low-cost, high-activity catalysts plays an essential role in the development of photocatalytic water splitting. Metal oxides have the advantages of a wide range of sources, many varieties, and easy preparation. Doping engineering on their surface can construct new active sites and adjust their catalytic activity. In this work, a new strategy was developed through anion hybridization to regulate electron delocalization. Using one of the cobalt-based zeolitic imidazole skeletons (ZIF-67) as a precursor material, a two-step calcination method was used to prepare a P-doped Co₃O₄ mixed anion composite photocatalyst. The hydrogen production rate of P@Co₃O₄ is 39 times that of ZIF-67 and 6.8 times that of Co₃O₄. Through density functional theory (DFT) calculations, the electron delocalization state of the sample surface is predicted and the reaction energy barrier is reduced to promote the process of the hydrogen evolution reaction (HER). The special O(δ-)-Co(δ+)-P(δ-) surface bonding state promotes the bridging of isolated electronic states and provides active sites for the adsorption and activation of reaction substrates. The improved electron transport pathway and the synergy between the catalytic sites under the high electron transport rate are the main reasons for the enhanced photocatalytic hydrogen evolution activity. This strategy, including changing the surface bond state and optimizing the structure and composition of the catalyst not only provides a new method for preparing other MOF-derived nanomaterials with porous structures but also inspires the reasonable development of other MOF-based advanced photocatalysts.

Fabrication of novel Cu2WS4/NiTiO3 heterostructures for efficient visible-light photocatalytichydrogen evolution and pollutant degradation

The design and development of efficient and durable catalysts with visible-light response for photocatalytic hydrogen production and pollutants degradation is considered as one of the most challenging tasks. In present work, a novel Cu₂WS₄/NiTiO₃ (abbreviated as × CWS/NTO; x  = 0.25, 0.50, 0.75 and 1.00) composite was prepared via a facile electrospinning/calcination technique along with a convenient hydrothermal method. The as-prepared CWS/NTOcomposite was composed of 2D CWS nanosheets and 1D NTO nanofibers manifested by SEM and TEM images. The results of XPS verified the interfacial interaction between CWS and NTO, confirming the heterojunction formation in CWS/NTOcomposite. Photocatalytic tests demonstrated as-prepared CWS/NTO catalysts exhibited outstanding and stable photocatalytic performances for H₂ production and pollutants degradation under visible light (λ > 420 nm) irradiation. Specially, 0.50 CWS/NTO sample displayed the highest H₂-evolution activity of 810 μmol·g^-1·h^-1 with the apparent quantum efficiency (AQE) value of 1.65 % at 420 nm. Additionally, it also exhibited the optimal photodegradation properties with the rate constants of 0.030, 0.413 and 0.028 min^-1 for TC, RhB and Cr(VI), respectively. The excellent catalytic activities could be attributed to the enhanced visible-light adsorption, high specific surface area and efficient separation of photogenerated charge carriers. The ESR tests and free radicals capturing experiments confirmed that ·O₂^- and h⁺ were primary active species for TC/RhB degradation. Eventually, the probable catalytic mechanism was put forward and detailly analysed. The present work provides perspectives of rational design on NiTiO₃-based catalysts with superior photocatalytic performance for energy regeneration and environmental remediation.

Engineering of g-C3N4-based photocatalysts to enhance hydrogen evolution

The technology of photocatalytic hydrogen production that converts abundant yet intermittent solar energy into an environmentally friendly alternative energy source is an attractive strategy to mitigate the energy crisis and environmental pollution. Graphitic carbon nitride (g-C₃N₄), as a promising photocatalyst, has gradually received focus in the field of artificial photosynthesis due to its appealing optical property, high chemical stability and easy synthesis. However, the limited light absorption and massive recombination of photoinduced carriers have hindered the photocatalytic activity of bare g-C₃N₄. Therefore, from the perspective of theoretical calculations and experiments, many valid approaches have been applied to rationally design the photocatalyst and ameliorate the hydrogen production performance, such as element doping, defect engineering, morphology tuning, and semiconductor coupling. This review summarized the latest progress of g-C₃N₄-based photocatalysts from two perspectives, modification of pristine g-C₃N₄ and interfacial engineering design. It is expected to offer feasible suggestions for the fabrication of low-cost and high-efficiency photocatalysts and the photocatalytic mechanism analyses assisted by calculation in the near future. Finally, the prospects and challenges of this exciting research field are discussed.