Design and applications of hollow-structured nanomaterials for photocatalytic H2 evolution and CO2 reduction

Synergistic effect of interstitial phosphorus doping and MoS2 modification over Zn0.3Cd0.7S for efficient photocatalytic H2 production

ZnxCd1-xS photocatalysts have been widely investigated due to their diverse morphologies, suitable band gaps/band edge positions, and high electronic mobility. However, the sluggish charge separation and severe charge recombination impede the application of ZnxCd1-xS for hydrogen evolution reaction (HER). Herein, doping of phosphorus (P) atoms into Zn0.3Cd0.7S has been implemented to elevate S vacancies concentration as well as tune its Fermi level to be located near the impurity level of S vacancies, prolonging the lifetime of photogenerated electrons. Moreover, P doping induces a hybridized state in the bandgap, leading to an imbalanced charge distribution and a localized built-in electric field for effective separation of photogenerated charge carriers. Further construction of intimate heterojunctions between P-Zn0.3Cd0.7S and MoS2 accelerates surface redox reaction. Benefiting from the above merits, 1 % MoS2/P-Zn0.3Cd0.7S exhibits a high hydrogen production rate of 30.65 mmol·g-1·h-1 with AQE of 22.22 % under monochromatic light at 370 nm, exceeding most ZnxCd1-xS based photocatalysts reported so far. This work opens avenues to fabricate examplary photocatalysts for solar energy conversion and beyond.

Modulation of π-Electron Density in Ultrathin 2D Layers of Graphite Carbon Nitride for Efficient Photocatalytic Hydrogen Production

The rational design and synthesis of novel semiconductor nano-/quantum materials have been ambitiously pursued in the field of photocatalysis as the technology is promising and critical for attaining future energy and environmental sustainability. Herein, the integrity of aromatic carbon into graphitic carbon nitride (CN) at the same molecular plane with a few 2D layers is achieved by using modulated precursors of CN, forming carbon regulated ultrathin CN (CUCN) with improved charge transfer kinetics and photocatalytic hydrogen production. The grafted graphite rings adjacent to carbon nitride frameworks induce a significant rearrangement and relocalization of the overall framework, and form conjugated sp2 hybridized interfaces and internal electric fields that drive the separation and directional transfer of photogenerated electrons from CN sheets towards intralayer graphite regions, where the photocatalytic hydrogen evolution reaction occurs extensively, yielding largely increased HER rate of 2231.8 µmol g-1 h-1 by 8.2 times relative to CN, as well as a remarkable apparent quantum yield of 2.93% under monochromatic light at 420 nm. The high physicochemical stability and low synthesis cost of CUCN make it a potential benchmark photocatalyst that can be readily modified via element doping, heterojunction introduction, defect engineering, and so on, to further enhance its HER performance.

Bioengineering of one dimensional hierarchical Cu7S4 hollow nanotubes for non-enzymatic glucose sensing applications

Herein, a novel and facile eco-friendly green chemistry approach has been devised at room temperature for synthesis of 1D hierarchical Cu7S4 hollow nanotubes on Cu substrate via volatile organosulfur compounds from Allium sativum L for non-enzymatic glucose detection. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and X-ray spectroscopy (XPS) were employed to characterize the surface morphology, structural phase, compositional, and chemical states of the obtained samples, respectively. The SEM results confirm the formation of 1D hierarchical Cu7S4 hollow nanotubes. The XRD patterns are indexed to orthogonal anilite Cu7S4 crystal planes and the EDX spectra clearly reveal the presence of Cu and S elements. XPS spectra confirms peaks of Cu 2p and S 1s core levels, which are typical characteristics of Cu(i) and S(ii), respectively. The Brunauer-Emmett-Teller (BET) specific surface area for obtained Cu7S4 hollow nanotubes is 2.07 m2 g-1 with a pore size distribution of 27.90 nm. Using Cu7S4 hollow nanotubes, the detection of non-enzymatic glucose was conducted over a dynamic range of concentrations from 0.5 to 100 μmol L-1 and reveals a high sensitivity of 1058.33 μA mM-1cm-2 and a limit of detection (LOD) of 0.127 μmol L-1. The obtained results indicated that Cu7S4 hollow nanotubes are promising candidates for non-enzymatic glucose detection.

In Situ Construction of Hollow Coral-Like Porous S-Doped g-C3N4/ZnIn2S4 S-Scheme Heterojunction for Efficient Photocatalytic Hydrogen Evolution

The rational design of visible-light-responsive catalysts is crucial for converting solar energy into hydrogen energy to promote sustainable energy development. In this work, a C─S─C bond is introduced into g-C3N4 (CN) through S doping. With the help of the flexible C─S─C bond under specific stimuli, a hollow coral-like porous structure of S-doped g-C3N4 (S-CN) is synthesized for the first time. And an S-doped g-C3N4/ZnIn2S4 (S-CN/ZIS) heterojunction catalyst is in situ synthesized based on S-CN. S0.5-CN/ZIS exhibits excellent photocatalytic hydrogen evolution (PHE) efficiency (19.25 mmol g-1 h-1), which is 2.7 times higher than that of the g-C3N4/ZnIn2S4 (CN/ZIS) catalyst (8.46 mmol g-1 h-1), with a high surface quantum efficiency (AQE) of 34.43% at 420 nm. Experiments and theoretical calculations demonstrate that the excellent photocatalytic performance is attributed to the larger specific surface area and porosity, enhanced interfacial electric field (IEF) effect, and appropriate hydrogen adsorption Gibbs free energy (ΔGH*). The synergistic effect of S doping and S-scheme heterojunction contributes to the above advancement. This study provides new insights and theoretical basis for the design of CN-based photocatalysts.

Novel hollow core-shell Zn0.5Cd0.5S@ZnIn2S4/MoS2 nanocages with Z-scheme heterojunction for enhanced photocatalysis of hydrogen generation

The development of low-cost and efficient metal sulfide photocatalysts through morphological and structural design is vital to the advancement of the hydrogen economy. However, metal sulfide semiconductor photocatalysts still suffer from low carrier separation and poor solar-to-hydrogen conversion efficiencies. Herein, two-dimensional ZnIn2S4 nanosheets were grown on Zn0.5Cd0.5S hollow nanocages to construct Zn0.5Cd0.5S@ZnIn2S4 hollow nanocages for the first time. Novel hollow core-shell Zn0.5Cd0.5S@ZnIn2S4/MoS2 nanocages with Z-scheme heterojunction structures were obtained by incorporating MoS2 nanosheet co-catalyst via the solvothermal method. The resulting Zn0.5Cd0.5S@ZnIn2S4/MoS2 exhibited unique structural and compositional advantages, leading to remarkable photocatalytic hydrogen evolution rates of up to 8.5 mmol·h-1·g-1 without the use of any precious metal co-catalysts. This rate was 10.6-fold and 7.1-fold higher compared to pure ZnIn2S4 and Zn0.5Cd0.5S, respectively. Moreover, the optimized Zn0.5Cd0.5S@ZnIn2S4/MoS2 photocatalyst outperformed numerous reported ZnIn2S4-based photocatalysts and some ZnIn2S4-based photocatalysts based on precious metal co-catalysts. The exceptional photocatalytic performance of Zn0.5Cd0.5S@ZnIn2S4/MoS2 can be attributed to the Z-scheme heterojunction of core-shell structure that enhanced charge carrier separation and transport, as well as the co-catalytic action of MoS2. Overall, the proposed Zn0.5Cd0.5S@ZnIn2S4/MoS2 with heterojunction structure is a promising candidate for the preparation of efficient photocatalysts for solar-to-hydrogen energy conversion.

Rich oxygen vacancies in confined heterostructured TiO2@In2S3 hybrid for boosting solar-driven CO2 reduction

Solar energy driving CO2 reduction is a potential strategy that not only mitigates the greenhouse effect caused by high CO2 level in atmosphere, but also yields carbon chemicals/fuels at the same time. Herein, a facile way to design the heterogeneous TiO2@In2S3 hollow structures possessing robust light harvesting in both ultraviolet and visible regions is proposed and exhibits a higher generation rate of 25.35 and 1.24 μmol·g-1·h-1 for photocatalytic CO2 reduction to CO and CH4, respectively. The excellent photocatalytic catalytic performance comes from i) the confined heterostructured TiO2@In2S3 possesses a suitable band structure and a broadband-light absorbing capacity for CO2 photoreduction, ii) the rich interfaces between nanosized TiO2 and In2S3 on the shell can significantly reduce the diffusion length of carriers and enhance the utilization efficiency of photogenerated electron-hole pairs, and iii) enriched surface oxygen vacancies can provide more active sites for CO2 adsorption.

A rationally designed 3DTiO2@CdZnS heterojunction photocatalyst for effectively enhanced visible-light-driven hydrogen evolution

Hydrogen production with higher efficiency and lower cost is of great significance for the sustainable development of energy. Zinc cadmium sulfide (CZS) is gaining more attention owing to its excellent photocatalytic properties. However, its development is greatly limited due to photogenerated charge recombination. In this work, an innovative design with a unique 3D morphology was introduced by integrating 3DTiO2 into CZS to form a novel 3DTiO2/CZS heterojunction photocatalyst. As a result, the optimized composite achieved a very high hydrogen production rate of 75.38 mmol h-1 g-1 under visible light, which is 2.4 times higher than that of the original CZS. It can also be greatly demonstrated through photoelectrochemical tests that this unique 3D morphology contributes to the effective separation of electrons and holes, thus dramatically improving the photocatalytic activity of 3DTiO2/CZS composites. The 3DTiO2/CZS composite has a rational energy band structure, which makes it more favorable for the hydrogen precipitation reaction. It is believed that such a modification strategy based on 3DTiO2 can be applied to other similar photocatalysts as well for boosting hydrogen evolution.

Tailoring Advanced N-Defective and S-Doped g-C3 N4 for Photocatalytic H2 Evolution

Although challenges remain, synergistic adjusting various microstructures and photo/electrochemical parameters of graphitic carbon nitride (g-C₃ N₄ ) in photocatalytic hydrogen evolution reaction (HER) are the keys to alleviating the energy crisis and environmental pollution. In this work, a novel nitrogen-defective and sulfur-doped g-C₃ N₄ (S-g-C₃ N₄ -D) is designed elaborately. Subsequent physical and chemical characterization proved that the developed S-g-C₃ N₄ -D not only displays well-defined 2D lamellar morphology with a large porosity and a high specific surface area but also has an efficient light utilization and carriers-separation and transfer. Moreover, the calculated optimal Gibbs free energy of adsorbed hydrogen (ΔG_H* ) for S-g-C₃ N₄ -D at the S active sites is close to zero (≈0.24 eV) on the basis of first-principle density functional theory (DFT). Accordingly, the developed S-g-C₃ N₄ -D catalyst shows a high H₂ evolution rate of 5651.5 µmol g^-1  h^-1 . Both DFT calculations and experimental results reveal that a memorable defective g-C₃ N₄ /S-doped g-C₃ N₄ step-scheme heterojunction is constructed between S-doped domains and N-defective domains in the structural configuration of S-g-C₃ N₄ -D. This work exhibits a significant guidance for the design and fabrication of high-efficiency photocatalysts.

Fabrication of Noble-Metal-Free Mo2C/CdIn2S4 Heterojunction Composites with Elevated Carrier Separation for Photocatalytic Hydrogen Production

Molybdenum-based cocatalyst being used to construct heterojunctions for efficient photocatalytic H2 production is a promising research hotspot. In this work, CdIn2S4 was successfully closely supported on bulk Mo2C via the hydrothermal method. Based on their matching band structures, they formed a Type Ⅰ heterojunction after the combination of Mo2C (1.1 eV, −0.27 V, 0.83 V) and CdIn2S4 (2.3 eV, −0.74 V, 1.56 V). A series of characterizations proved that the heterojunction composite had higher charge separation efficiency compared to a single compound. Meanwhile, Mo2C in heterojunction could act as an active site for hydrogen production. The photocatalytic H2 production activity of the heterojunction composites was significantly improved, and the maximum activity was up to 1178.32 μmmol h−1 g−1 for 5Mo2C/CdIn2S4 composites. 5Mo2C/CdIn2S4 heterojunction composites possess excellent durability in three cycles (loss of 6%). Additionally, the mechanism of increased activity for composites was also investigated. This study provides a guide to designing noble-metal-free photocatalyst for highly efficient photocatalytic H2 evolution.

Simultaneous Loading of Ni2 P Cocatalysts on the Inner and Outer Surfaces of Mesopores P-Doped Carbon Nitride Hollow Spheres for Enhanced Photocatalytic Water-Splitting Activity

Promoting charge separation, constructing active sites, and improving the utilization of metal atoms are very important for the design of efficient photocatalysts. A simultaneous loading of Ni₂ P cocatalysts on the inner and outer surfaces of mesoporous P-doped carbon nitride hollow nanospheres (PCNHS) to construct a Ni₂ P@PCNHS@Ni₂ P photocatalyst is reported. Ni₂ P cocatalysts loading provides enough active sites on both the inner and outer surfaces for proton reduction, and the formed heterojunctions simultaneously promote the migration and separation of the photogenerated charges on the inner and outer surfaces. The photocatalytic reaction proceeds simultaneously on the inner and outer surfaces of Ni₂ P@PCNHS@Ni₂ P, which leads to a significantly improved photocatalytic water splitting performance and enhanced atomic utilization. Notably, the hydrogen evolution rate of Ni₂ P@PCNHS@Ni₂ P is 2.4 times higher than that of Pt-loaded PCNHS. The findings guide the design of hollow nanostructured composites with high-boosting photocatalytic performance.

Doping regulates pyro-photo-electric catalysis to achieve efficient water splitting in Ba1−xSrxTiO3 through solar energy and thermal resources

The effect of Sr2+ doping concentration in Ba1−xSrxTiO3 photoelectrodes on pyro-photo-electric catalysis was discussed. The main reason for the performance improvement is that doping broadens the response range of the semiconductor to visible light.