G-C3N4 sheet nanoarchitectonics with island-like crystalline/amorphous homojunctions towards efficient H2 and H2O2 evolution

Photocatalystic evolution of H2O2 from water and oxygen has attracted significant attention because of environmentally friendly. The absorption in visible and hydrophilic feature of graphitic carbon nitride (g-C3N4) make it a good candidate. In this paper, a rapid post-treatment at high temperature was developed to obtain g-C3N4 nanosheets with abundant crystalline/amorphous interfaces to form homojunctions, which optimized uniplanar carrier mobility dynamics. The conversion from bulk to two-dimensional g-C3N4 resulted from the breakage of interplanar hydrogen bonds and interlayer Van der Waals force. The unique morphology not only rendered photocatalyst with larger specific surface area but also inhibited the robust volume recombination of charge carriers. The accelerated charge carriers flow at the interface, interplane and interlayer together ameliorated the separation and transfer of electrons and holes. A new-emerged n→π* transition ameliorated the poor light utilization efficiency. Beyond the increased photocatalytic H2 evolution property (779.2 μmol g-1 h-1), optimized sample displayed a H2O2 evolution activity as high as 4877.1 μM g-1 h-1 under visible light illumination, which was ∼5.8 times of that of bulk g-C3N4. Detailed photocatalytic mechanism investigation manifested that the two-step single-electron oxygen reduction process occupied the dominant status in H2O2 evolution. This work proposed a novel strategy for obtaining g-C3N4 homojunctions as a promising bi-functional metal-free catalyst to be applied in clean energy production field.

Z-scheme WOx/Cu-g-C3N4 heterojunction nanoarchitectonics with promoted charge separation and transfer towards efficient full solar-spectrum photocatalysis

Construction of Z-scheme heterojunctions has been considered one superb method in promoting solar-assisted charge carrier separation of carbon-based materials to achieve efficient utilization of solar energy in hydrogen production and CO₂ reduction. One interesting concept in nanofabrication that has become trend recent years is nanoarchitectonics. A heterostructure photocatalyst constructed based on the idea of nanoarchitectonics using the combination of g-C₃N₄, metal and an additional semiconducting nanocomposite is investigated in this paper. Z-scheme tungsten oxide incorporated copper modified graphitic carbon nitride (WO_x/Cu-g-C₃N₄) heterostructures are fabricated via immobilization of WO_x on Cu nanoparticles modified superior thin g-C₃N₄ nanosheets. Mechano-chemical pre-reaction and a two-step high-temperature thermal polymerization process are the keys in attaining homogeneous distribution of Cu nanoparticles in g-C₃N₄ nanosheets. The horizontal growth of homogeneously distributed WO_x nanobelts on Cu modified g-C₃N₄ (Cu-g-C₃N₄) base via solvothermal synthesis is achieved. The photocatalytic performances of the heterostructures are evaluated through water splitting and CO₂ photoreduction measurements in full solar spectrum irradiation condition. The presence of Cu nanoparticles in the composite system improves charge transport between g-C₃N₄ and WO_x and thus enhances the photocatalytic performances (H₂ generation and CO₂ photoreduction) of the composite material, while the presence of WO_x nanocomposites enhances light absorption of the composite material in the near infrared range. The synthesized heterostructure with optimized WO_x to Cu-g-C₃N₄ ratio and in case of no co-catalyst addition exhibits enhanced photocatalytic H₂ evolution (4560 μmolg^-1h^-1) as well as excellent CO₂ reduction rate (5.89 μmolg^-1h^-1 for CO generation).

Interface Nanoarchitectonics of TiO2/g-C3N4 2D/2D Heterostructures for Enhanced Antibiotic Degradation and Cr(VI) Reduction

Mixed-phase TiO₂ nanosheets were loaded on superior thin g-C₃N₄ nanosheets by a one-step solvothermal synthesis to form unique two-dimensional (2D)/2D heterostructures, which increased the interface area between TiO₂ and g-C₃N₄, resulting in the easy migration of photogenerated carriers between two components. The rate of photocatalytic reactions increased significantly. Ciprofloxacin, tetracycline hydrochloride, and oxytetracycline hydrochloride were selected as target substances to test the photocatalytic degradation properties of the sample. The photoreduction performance of Cr(VI) was also tested. The results indicate that the photocatalytic degradation rate of antibiotics using TiO₂/g-C₃N₄ heterostructures under visible light irradiation was twice that of g-C₃N₄. It took only 30 min to remove Cr(VI) (20 mg/L) under full solar spectrum irradiation; the photoreduction rate of Cr(VI) is also nearly twice that of pure TiO₂. The improved performance was attributed to the rich active sites brought by mixed-phase TiO₂ nanosheets. The extensive interface made the rapid migration of photogenerated carriers possible. The heterostructures revealed a band gap of 2.81 eV, which is less than that of TiO₂ (3.2 eV), resulting in the increased absorption of visible light. Meanwhile, the mixed phase of TiO₂ was beneficial for the separation of photogenerated carriers.

Surface modification induced construction of core-shell homojunction of polymeric carbon nitride for boosted photocatalytic performance

Surface modification has been considered a simple and effective strategy to enhance the photocatalytic activity of polymeric carbon nitride (CN), but resultant difference of energy band structures between the modified surface layer and the unmodified inside in the sample has always been neglected. Herein, maleoyl-modified CN (MaCN) was simply prepared via a dehydration reaction between CN and maleic acid, and exhibits enhanced charge separation, optical absorption, and thus photocatalytic hydrogen evolution activity, relative to the bulk CN. The surface modification causes variation of the band structure, suggesting the difference of band levels between the surface layer with maleoyl-modification and the inside without any modification in MaCN, and the surface layer and the inside with matched band levels form type-II core-shell homojunction to enhance the charge separation. This work expounds a conceptual framework of core-shell homojunction in surface-modified CN photocatalysts.

Pt nanoparticles embedded spine-like g-C3N4 nanostructures with superior photocatalytic activity for H2 generation and CO2 reduction

Conventional two-dimensional (2D) graphitic carbon nitride, 2D g-C₃N₄ with its layered structures and flat and smooth 2D surface possesses certain disadvantages that is affecting their photocatalytic performances. In this paper, new nanostructured spine-like three-dimensional (3D) g-C₃N₄ nanostructures are created for the first time via a new three-step synthesis method. In this method, self-assembly of layered precursors and H⁺ intercalation introduced by acid treatment play an important role for the unique nanostructure formation of 3D g-C₃N₄ nanostructures. The spine-like 3D g-C₃N₄ nanostructures show a superior photocatalytic performance for H₂ generation, achieving 4500 μmol·g^-1·h^-1, 8.2 times higher than that on conventional 2D g-C₃N₄. Remarkably spine-like 3D g-C₃N₄ nanostructures demonstrate a clear photocatalytic activity toward CO₂ reduction to CH₄ (0.71 μmol·g^-1·h^-1) in contrast to the negligible photocatalytic performance of conventional 2D g-C₃N₄ for the reaction. Adding Pt clusters as co-catalysts substantially enhance the CH₄ generation rate of the 3D g-C₃N₄ nanostructures by 4 times (2.7 μmol·g^-1·h^-1). Spine-like 3D g-C₃N₄ caged nanostructure leads to the significantly increased active sites and negatively shifted conduction band position in comparison with conventional 2D g-C₃N₄, favorable for the photocatalytic reduction reaction. This study demonstrates a new platform for the development of efficient photocatalysts based on nanostructured 3D g-C₃N₄ for H₂ generation and conversion of CO₂ to useful fuels such as CH₄.

The pivotal role of defects in fabrication of polymeric carbon nitride homojunctions with enhanced photocatalytic hydrogen evolution

Fabrication of homojunctions is a cost-effective efficient way to enhance the photocatalytic performance of polymeric carbon nitride (CN), but the generation of defects upon synthesizing CN homojunctions and their roles in the homojunction fabrication were hardly reported. Herein, nitrogen-deficient CN homojunctions were simply synthesized by calcining dicyandiamide-loaded CN (prepared from urea and denoted as UCN) with dicyandiamide polymerizing into CN (denoted as DCN) and simultaneous formation of nitrogen vacancies in the surface of UCN. Fabrication of the nitrogen-deficient UCN (dUCN)/DCN homojunction depends on the nitrogen vacancy content in dUCN which can tune the energy band structure of dUCN from not matching to matching with that of DCN. The dUCN/DCN homojunction exhibits extended optical absorption and remarkably enhanced charge separation and photocatalytic H₂ evolution, compared with UCN and DCN. This work illustrates the pivotal role of defects in fabricating CN homojunctions and supplies a new facile way to synthesize nitrogen-deficient CN.

Interface chemistry of two-dimensional heterostructures - fundamentals to applications

Two-dimensional heterostructures (2D HSs) have emerged as a new class of materials where dissimilar 2D materials are combined to synergise their advantages and alleviate shortcomings. Such a combination of dissimilar components into 2D HSs offers fascinating properties and intriguing functionalities attributed to the newly formed heterointerface of constituent components. Understanding the nature of the surface and the complex heterointerface of HSs at the atomic level is crucial for realising the desired properties, designing innovative 2D HSs, and ultimately unlocking their full potential for practical applications. Therefore, this review provides the recent progress in the field of 2D HSs with a focus on the discussion of the fundamentals and the chemistry of heterointerfaces based on van der Waals (vdW) and covalent interactions. It also explains the challenges associated with the scalable synthesis and introduces possible methodologies to produce large quantities with good control over the heterointerface. Subsequently, it highlights the specialised characterisation techniques to reveal the heterointerface formation, chemistry and nature. Afterwards, we give an overview of the role of 2D HSs in various emerging applications, particularly in high-power batteries, bifunctional catalysts, electronics, and sensors. In the end, we present conclusions with the possible solutions to the associated challenges with the heterointerfaces and potential opportunities that can be adopted for innovative applications.

WO3-x horizontally-grown on TiO2(B) nanosheets for enhanced photo- and electro-chemical activity

WO3-x was deposited on TiO2(B) nanosheets prepared using TiCl4 to form layered heterostructures via a two-step solvothermal synthesis, in which the horizontal growth of WO3-x on TiO2(B) nanosheets was carried out using WCl6 and ascorbic acid as a reducer. Optimized preparation conditions allowed WO3-x/TiO2(B) layered heterostructures to be formed. The photo- and electro-chemical properties of layered heterostructures depended strongly on the amount of WO3-x. The WO3-x/TiO2(B) heterostructures demonstrated perfect catalytic performance in full solar-spectrum light and a fast degradation effect for dye and organic colorless pollutant. All target chemicals were degraded within 10 min using WO3-x/TiO2(B) samples as a photo-catalyst in the full solar-spectrum. The photo-assisted production kinetic of Cr(VI) ions were tested. The results indicate that the reproduction rate of Cr(VI) ions using WO3-x/TiO2(B) sample is three times higher than the initial TiO2 nanosheets. The result of the photo current and Mott-Shottky curve indicates that enhanced catalysis activity is ascribed to the surface of the metastable TiO2(B) with Ti3+ defects and oxygen vacancies as active sites for photocatalytic reaction. In addition, the loading of WO3-x greatly broadened the light absorption range of TiO2(B), meaning that the product responded in the full solar spectrum.

Nanosheet-assembled hierarchical flower-like g-C3N4 for enhanced photocatalytic CO2 reduction activity

Nanosheet-assembled hierarchical flower-like g-C₃N₄ prepared by a molecular self-assembly and ethanol insertion strategy shows enhanced photocatalytic CO₂ reduction activity.

Enhanced Kinetics over VS4 Microspheres with Multidimensional Na+ Transfer Channels for High-Rate Na-Ion Battery Anodes

Developing 3 D self-assembled nanoarchitectures with well-defined crystal structures is an effective strategy to enhance the electrochemical performances of electrode materials. (1 1 0)-oriented and bridged-nanoblocks self-assembled VS₄ microspheres are controllably synthesized by a facile one-step hydrothermal method. The (1 1 0)-bridged structure sets up open pathways for Na⁺ diffusion among nanoblocks, and the (1 1 0)-oriented structure provides unobstructed pathways for Na⁺ diffusion in the nanoblocks, which collectively constructs multidimensional Na⁺ transfer channels in the VS₄ microspheres, promoting the electrochemical kinetics. As an anode for Na-ion batteries (SIBs), this material exhibits pseudocapacitive Na⁺ storage and excellent rate capability, delivering high capacities of 339 and 270 mAh g^-1 at rates of 0.1 and 2.0 A g^-1 , respectively, with a capacity retention of 79 % in the voltage window of 0.5-3.0 V. In particular, the reversible capacity reaches 575 mAh g^-1 after 300 cycles even at 1.0 A g^-1 in the voltage window of 0.05-3.0 V, outperforming those of the ever-reported VS₄ -based anode materials. This work presents an effective strategy to the exploration and design of high-performance anodes for SIBs.

A general strategy via chemically covalent combination for constructing heterostructured catalysts with enhanced photocatalytic hydrogen evolution

A general strategy via chemically covalent combination was reported to fabricate heterostructured catalysts of carbon nitride/covalent organic frameworks (CNFs), which show superior photocatalytic activity and higher stability as compared to the conventional heterostructures of CN and COFs connected via van der Waals forces.

Retracted Article: Fabrication of hollow CoS1.097 prisms toward supercapactior performance

The controlled synthesis of a variety of microstructures is valuable for understanding the relationship between morphology and properties and exploring potential applications. In this paper, hollow CoS1.097 prisms were prepared by prismatic Co-precursors using thioacetamide (TAA) as a sulfidation treatment reagent. A plausible mechanism was proposed for the formation of the hollow prism structure. S2- comes from TAA to displace the anions in Co-precursors by adjusting temperature and pressure. The original prism morphology of the Co-precursor was maintained and a hollow prismatic structure was formed by an anion exchanging process. Interestingly, the composition of samples after sulfidation treatment can be controlled by changing the diffusion to obtain Co3O4/CoS1.097 and CoS1.097 materials. As electrode materials for supercapacitors, hollow CoS1.097 prisms revealed ideal electrochemical performance.