Science China Materials最新文献

The chemical structure of covalent organic frameworks (COFs) plays a key role in their response to the surface doping strategy used for tuning their electronic character, but it is still not fully understood. To explore a rational design proposal for their chemical structure, the electronic properties of three n-doped typical COFs, including boron-containing (COF-1), triazine-based (CTF), and C–C bond-linked (GCOF) COFs, were investigated theoretically in this work. As expected, the chemical doping effects are different for these COFs. The dispersion of the frontier bands, the nuclear-independent chemical shift (NICS) aromaticity index results, distribution of the electron localization function (ELF), and Hirshfeld charge population plots show that part of the transferred electron from dopants will be offset by the intralayer charge transfer of COFs. Thus, chemical doping effects are more significant if the electron distribution in the COFs is more localized. This means the response of COFs to the surface doping strategy should be dominated by the conjugation degree of their chemical structure. Our results prove that the intrinsic conjugation degree of COFs plays a key role in such doping functionalization strategies, which are expected to provide more useful information for the initial structure design of COF materials and facilitate their practical applications as active electronic transport materials in nanoscale devices.

Emerging two-dimensional ternary transition metal dichalcogenide alloys have attracted much attention for their unique optical and optoelectronic properties, making them ideal candidates for optoelectronic applications. However, a comprehensive understanding of their quantum confinement effects and photoelectronic response characteristics remains crucial for device optimization and performance enhancement. In this study, we employed various spectroscopic techniques to investigate the optical properties and electronic band structures of molybdenum sulfide selenide (MoSSe) films with different layer numbers (4–11 layers). Our results revealed the splitting of Raman modes and shifting of phonon vibrational frequencies with increasing thickness, suggesting that MoSSe has strong interactions within the lattice. The A_1g and E_2g¹ modes were mainly shifted by internal strain and dielectric screening effect versus thickness, respectively. The redshift phenomenon of A and B excitons with increasing thickness was attributed to the leading effect of quantum confinement on exciton properties and optical band gaps. We observed a strong decrease in the direct bandgap spectral weight in photoluminescence (PL) when the layer number increased from 4 to 5. In addition, we have fabricated MoSSe photodetectors that exhibit a broadband response in the visible wavelength band of 350–800 nm. Furthermore, the observed enhancement in photocurrent and responsivity with increasing film thickness underscored the potential of MoSSe-based devices for practical optoelectronic applications. This research contributes to advancing our fundamental understanding of MoSSe materials and paves the way for the design and development of high-performance optoelectronic devices.

In this work, we report a novel one-dimensional metal-organic framework (MOF) templated for the synthesis of transition metal sulfides with excellent oxygen evolution reaction (OER) performance via a self-sulfidation process, eliminating the need for additional sulfur sources. After pyrolysis, MOFs containing Co ions as the metal nodes and 1-phenyl-5-mercaptotetrazole (PMTA) as the ligand were transformed to Co₉S₈ nanoparticles, which were encapsulated in a nitrogen and sulfur dual-doped carbon (Co₉S₈@NSC) matrix. Additionally, PMTA, as a ligand, possesses the unique advantage of forming porous coordination polymers with a wide range of metals (e.g., Fe, Ni, and Cu), enabling the versatile synthesis of transition metal sulfide electrocatalysts. Consequently, when served as the electrocatalyst for OER, the N, S co-doped Co₉S₈@NSC porous nanotubes exhibited excellent OER performance with the overpotential of only 248 mV at 10 mA cm⁻² and long-term stability. These works provide new insights and inspiration for the rational design and development of non-precious metal-based sulfides with practical potential applications.

Developing highly efficient heterostructural photocatalysts for direct CO₂ reduction coupled with water oxidation remains challenging, the key to which is to establish an efficient interfacial charge transport channel. Herein, we present a Cs₃Sb₂Br₉/Sb–C₃N₄ Z-scheme heterojunction prepared with an in-situ growth method based on the Sb atomic pinning effect. As revealed by the analysis of experimental and theoretical calculation results, the introduction of Sb anchors on C₃N₄ leads to the formation of an Sb–N charge transfer bridge between Cs₃Sb₂Br₉ and C₃N₄, promoting interfacial charge communication over Cs₃Sb₂Br₉/Sb–C₃N₄ heterojunction. Moreover, it can induce the heterojunction interfacial charge transfer pathway between Cs₃Sb₂Br₉ and C₃N₄ to change from type II to the type Z-scheme, enabling the change of the catalytic site from C₃N₄ to Cs₃Sb₂Br₉, thus promoting the CO₂ activation. As a result, Cs₃Sb₂Br₉/Sb–C₃N₄ achieves efficient CO₂ to CO photocatalytic conversion using water as the electron source under simulated solar light irradiation (100 mW·cm⁻²), with the yield of 198.4 µmol·g⁻¹·h⁻¹, which is nearly 3-fold and 9-fold over the counterpart synthesized catalyst without Sb anchors (Cs₃Sb₂Br₉/g–C₃N₄) and pure g–C₃N₄, respectively. This work provides a new alternative solution for the design of highly efficient heterojunction photocatalysts.

Utilizing plasmonic non-noble metal nanoparticles (NPs) for photocatalytic hydrogen evolution reaction is a significant step toward green energy production. However, optimizing the interface between non-noble metal NPs and semiconducting materials in metal-semiconductor composites remains challenging owing to the inevitable surface oxide layers of non-noble metal NPs because the surface oxide layers of non-noble metal NPs can suppress the transfer of photoinduced carriers, leading to poor photocatalytic performance. Herein, we propose a photoinduced interface activation strategy to reduce the number of oxide layers based on a dynamic charge-transfer mechanism under illumination conditions, with Bi NPs and a Ni-based metal-organic framework (MOF) selected as model materials. Under light illumination, the photoinduced charges and plasmonic hot electrons heavily pooled at the interface between the Bi NPs and Ni-MOF, resulting in the reduction of the oxide layer on the surface of Bi, thus attenuating its hindering effect on charge transfer. This phenomenon led to a dynamically enhanced carrier concentration in the Bi/Ni-MOF composite, with an outstanding photocatalytic hydrogen evolution rate of 5822 µmol g⁻¹ h⁻¹ achieved with the composite. The results of this study indicate that our strategy provides a new method for optimizing plasmonic non-noble metal Bi NPs with oxide layers.

High performance thermal insulation materials are urgently demanded for energy saving and thermal protection applications. Organic aerogels are considered as promising and highly efficient thermal insulation materials, but high shrinkage has been a major obstacle to limit their development and application. Herein, by a co-polymerization of formaldehyde (F) and benzoxazine prepolymers, polybenzoxazine with increased crosslink density and thus enhanced gel strength was formed, leading to low shrinkage polybenzoxazine (PBOF) aerogels with hierarchical micro/nanostructures. The hierarchical porous nanoskeleton of PBOF aerogels, composed of stacked thick-united spherical nanoparticles, was formed due to the different solubility of the reactants in N,N-dimethylformamide and F aqueous solution. Benefitting from the low shrinkage (13.22%, exceeding 60% reduction), the PBOF aerogels exhibit a low thermal conductivity of 0.0397 W m⁻¹ K⁻¹ at room temperature and outstanding thermal protection ability at high temperature. A 13 mm thick sample could resist a butane flame of 1300°C for 90 s, and the hand was not burn when touching the back. This strategy enables PBOF aerogels with a new perspective for their applications in civil and military fields.

Carbon dots (CDs) are a fascinating new class of fluorescent nanomaterials, yet the understanding of the fluorescent origin of CDs still lags well behind their applications. The key challenges for unveiling the fluorescent mechanism of CDs relate to the insufficient basis for structural evaluation. This work presents a temperature-gradient route to control the bottom-up approach of CDs, enabling the precise structural characterization of intermediates and the establishment of definite structure-property relationships, akin to the domino reaction synthesis of complex natural products from small organic molecules. Taking the binary components citric acid and meta-dimethylaminophenol generated CDs as a case study, their emissive mechanism, particularly the unique excitation-dependent fluorescence behavior, is reasonably explained and supported by structural evaluation through retrosynthetic analysis. The formation process of CDs is investigated using a combination of spectroscopic, thermal, and theoretical calculation techniques, demonstrating the significant potential of the temperature-gradient route in the exploration structure-property relationships and guiding the rational design of advanced CD applications.

While the “amorphous to crystalline” transformation process, which has significant potential for application, has been widely studied, the microscopic mechanism on the nanometer scale is not fully understood. In contrast to common heat-driven phase transformations, the present study demonstrated the force-driven moisture-mediated nanocrystallization of perovskite CsPbBr₃ precipitated from a glass matrix. In the present case, the breakage of the glass network under shearing force produces high-energy sites to absorb H₂O molecules/clusters from ambient moisture, and the hydration process promotes the crystallization process. Microscratch analysis combined with confocal laser scanning microscopy revealed that the distribution of CsPbBr₃ nanocrystals almost reproduced that of the localized stress field and clearly reflected the crack propagation pathways. The potential applications of perovskite glass in the optical sensing of force and moisture are also explored. Our findings provide insight into crystal nucleation/growth in glass, as well as understanding the dynamics of crack propagation during the brittle fracture process.

As the first carbon-free double helical semiconductor at an atomic scale, tin phosphide iodide (SnIP) has garnered growing interest due to its high structural flexibility, band gap in the visible spectrum range, and non-toxicity. Herein, we report the chemical vapor transport synthesis of SnIP nanowires (NWs). The photocatalytic activity of SnIP NWs was evaluated through the degradation of two representative toxic dyes, methylene blue (MB) and malachite green (MG), under visible light irradiation (λ > 400 nm). These NWs exhibited notable photocatalytic efficiency, achieving degradation rates over 97% for MB and 95% for MG within 100 min of visible light exposure. The degradation data align well with a pseudo-first-order reaction kinetics model for both dyes, with rate constants of 0.0347 and 0.0295 min⁻¹. Furthermore, the synthesized catalyst demonstrated exceptional stability and recyclability, maintaining its efficient performance till six duplicate operations cycles. Scavenger testing indicated that holes and OH radicals were the main active species driving the dye’s photodegradation. The unusual photocatalytic efficiency can be attributed to their favorable band gap within the visible spectrum range and unique one-dimensional structure. The results demonstrate that the SnIP NWs offer a promising choice for eco-friendly dye photodegradation.

Delivering excellent carrier separation through ferroelectric polarization is desirable to achieve effective solar hydrogen conversion. Here, Bi_0.9Dy_0.1FeO₃/g-C₃N₄ (BDFO/GCN) Z-scheme photocatalyst was constructed by loading BDFO nanoparticles onto sheet-like GCN, in which BiFeO₃ (BFO) was doped with the rare-earth element Dy to narrow the optical bandgap and enhance the ferroelectric property. Residual polarization effectively promoted the separation and transport of photo-generated carriers in BFO, and the Z-scheme exhibited stable reaction activity during photocatalytic degradation and photocatalytic hydrogen evolution. Through electric polarization, the heterojunction photocatalyst achieves 100% degradation of Rhodamine B (RhB) under simulated sunlight. The evolution rate of hydrogen was improved from approximately 742.5 to 1084.0 µmol·g⁻¹·h⁻¹ after polarization. This remarkable activity is attributed to the improved carrier separation facilitated by the internal polarization field. This work offers novel insights into the rational design of efficient ferroelectric photocatalysts.