Construction of a 3D/2D g-C3N4/ZnIn2S4 hollow spherical heterostructure for efficient CO2 photoreduction under visible light

Abstract: The development of high-efficiency photocatalysts is of great importance to realize robust solar-driven CO₂ conversion; however, the low carrier separation efficiency and poor light absorption ability usually limit the performance of the photocatalysts. Herein, a hollow In₂S₃/polymeric carbon nitride (IS/CN) heterojunction was prepared via electrostatic self-assembly and in situ sulfidation under solvothermal conditions. The intimate interfacial contact between the IS and CN facilitates the construction of an effective heterojunction, as demonstrated by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The optimized IS/CN-5 sample exhibits a high CO evolution rate of 483.4 μmol g–¹ h–¹, which is 99 and 6 times as high as that of IS and CN, respectively. The improved charge separation and transfer efficiency, the hollow nanotube structure, and the enhanced CO₂ adsorption ability are the reasons for the excellent photocatalytic activity. Besides, a possible photocatalytic mechanism of CO₂ reduction by the IS/CN heterojunction was proposed on the basis of the band structures. This work provides an effective and facile strategy to construct hollow semiconductor heterojunctions for photocatalytic applications.

Abstract: In the photocatalytic water splitting hydrogen production system, the key to efficient use of solar energy is to choose a suitable photocatalyst. As an important ternary sulfide, ZnIn2S4 (ZIS) has attracted wide attention because of its narrow band gap (Eg = 2.3–2.8 eV) and wide light absorption range. However, further modification was still needed. Therefore, in this work, the unique C/ZIS hollow tubes with nano-flakes were prepared by a simple solvothermal method. To a large extent, this unique structure increased the utilization of light and active sites. Moreover, the dissolution of PAN during the solvothermal process caused the carbon element to be uniformly doped into the hollow tube framework. After a series of characterization results, C/ZIS-3.0 has the best hydrogen release rate (1241.94 μmol g−1 h−1) and good cyclability under visible light irradiation (λ ≥ 420 nm). And its unique morphology and possible catalytic mechanism were further discussed.

Abstract: Photocatalytic CO2 reduction to CH4 is a promising strategy to solve the greenhouse effect and energy shortage problems. However, its application has been restricted by its low efficiency and poor selectivity. Herein, atomically thin defective TiO2 is modified with iron tetraphenylporphyrin (FeTPP) to reinforce the selectivity of CO2 reduction. The synthesized Fe-TiO2-x photocatalyst exhibits a CH4 production rate of 20.48 μmol g−1 h−1 and a CH4 selectivity of 56.1% under visible light irradiation. Oxygen vacancies (OVs) of defective TiO2 contributed to visible light absorption and FeTPP dispersion. The presence of FeTPP enhances the adsorption of CO intermediates, promoting the CH4 selectivity. The conduction band of Fe-TiO2-x lowers, inhibiting the CO generation. During the photoconversion process, CO2˙− and COOH− intermediate products were detected by in situ DRIFTS. The synergistic effect of OVs and FeTPP improves the efficiency and selectivity of CO2 photoreduction to CH4. This work offers a new insight towards designing a photocatalyst for photoreduction of CO2 to CH4.

Abstract: Structure design of photocatalysts is highly desirable for taking full advantage of their abilities for H2 evolution. Herein, the highly-efficient TiO2{001}/g-C3N4 (TCN) heterostructures have been fabricated successfully via an in situ ethanol-thermal method. And the structure of g-C3N4 in the TCN heterostructures could be exfoliated from bulk g-C3N4 to nanosheets, nanocrystals and quantum dots with the increase of the synthetic temperature. Through detailed characterization, the structural evolution of g-C3N4 could be attributed to the enhanced temperature of the ethanol-thermal treatment with the shear effects of HF acid. As expected, the optimal TCN-2 heterostructure shows excellent photocatalytic H2 evolution efficiency (1.78 mmol h−1 g−1) under visible-light irradiation. Except for the formed built-in electric field, the significantly enhanced photocatalytic activity of TCN-2 could be ascribed to the enhanced crystallinity of TiO2{001} nanosheets and the formed g-C3N4 nanocrystals with large surface area, which could extend the visible light absorption, and expedite the transfer of photo-generated charge carriers further. Our work could provide guidance on designing TCN heterostructures with the desired structure for highly-efficient photocatalytic water splitting.

Abstract: A facile synthetic strategy for nitrogen-deficient graphitic carbon nitride (g-C3 Nx ) is established, involving a simple alkali-assisted thermal polymerization of urea, melamine, or thiourea. In situ introduced nitrogen vacancies significantly redshift the absorption edge of g-C3 Nx , with the defect concentration depending on the alkali to nitrogen precursor ratio. The g-C3 Nx products show superior visible-light photocatalytic performance compared to pristine g-C3 N4 .

Abstract: Photocatalysts and Photoelectrodes James L. White,† Maor F. Baruch,† James E. Pander III,† Yuan Hu,† Ivy C. Fortmeyer,† James Eujin Park,† Tao Zhang,† Kuo Liao,† Jing Gu,‡ Yong Yan,‡ Travis W. Shaw,† Esta Abelev,† and Andrew B. Bocarsly*,† †Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States ‡Chemical and Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States

Abstract: As a promising two-dimensional conjugated polymer, graphitic carbon nitride (g-C3 N4 ) has been utilized as a low-cost, robust, metal-free, and visible-light-active photocatalyst in the field of solar energy conversion. This Review mainly describes the latest advances in g-C3 N4 photocatalysts for water splitting. Their application in CO2 conversion, organosynthesis, and environmental purification is also briefly discussed. The methods to modify the electronic structure, nanostructure, crystal structure, and heterostructure of g-C3 N4 , together with correlations between its structure and performance are illustrated. Perspectives on the challenges and opportunities for the future exploration of g-C3 N4 photocatalysts are provided. This Review will promote the utilization of g-C3 N4 materials in the fields of photocatalysis, energy conversion, environmental remediation, and sensors.

Abstract: Photocatalytic reduction of CO2 into hydrocarbon fuels, an artificial photosynthesis, is based on the simulation of natural photosynthesis in green plants, whereby O2 and carbohydrates are produced from H2 O and CO2 using sunlight as an energy source. It couples the reductive half-reaction of CO2 fixation with a matched oxidative half-reaction such as water oxidation, to achieve a carbon neutral cycle, which is like killing two birds with one stone in terms of saving the environment and supplying future energy. The present review provides an overview and highlights recent state-of-the-art accomplishments of overcoming the drawback of low photoconversion efficiency and selectivity through the design of highly active photocatalysts from the point of adsorption of reactants, charge separation and transport, light harvesting, and CO2 activation. It specifically includes: i) band-structure engineering, ii) nanostructuralization, iii) surface oxygen vacancy engineering, iv) macro-/meso-/microporous structuralization, v) exposed facet engineering, vi) co-catalysts, vii) the development of a Z-scheme system. The challenges and prospects for future development of this field are also present.

Abstract: O-doped g-C3N4 was synthesized for the first time by a facile H2O2 hydrothermal approach. The O-doping in the g-C3N4 lattice could induce intrinsic electronic and band structure modulation, resulting in its absorbance edge up to 498 nm and enhanced visible-light photoactivity, consequently.