晶体硅金刚线切割废料制备高纯氮化硅

以晶体硅金刚线切割废料为原料,通过氮化反应制得氮化硅,既回收了金刚线切割废料,又解决了环境污染的问题。 通过X射线衍射仪(XRD)、扫描电子显微镜(SEM)和X射线能量色谱仪(EDS)等技术手段研究了原料经HCl和HF酸洗净化后制备氮化产物的物相组成、组分质量分数和微观形貌的影响。 结果表明,HCl酸洗后切割废料制备的氮化产物中主要物相为Si₂N₂O和Si₃N₄,而HF酸洗后切割废料制备的氮化产物中主要物相为Si₃N₄。 氮化产物中Si₂N₂O的形成与切割废料中SiO₂的质量分数有关,降低原料中SiO₂的质量分数是切割废料经过高温氮化制得氮化硅的前提。     

氮化硅纳米线制备过程中反应条件的影响

采用X 射线衍射和扫描电子显微镜技术, 考察了溶胶-凝胶法制备氮化硅纳米线过程中反应条件(添加剂种类和含量、反应时间以及反应温度)对碳热还原产物组成和形貌的影响. 结果表明, 碳化后铁含量为5%(w)的凝胶, 在1300 ℃下反应10 h, Si₃N₄纳米线产率较高. 添加剂的种类和含量不同, 所得产物的组成和形貌也不相同.随着反应温度的升高或反应时间的延长,产物经历了一个从SiO_x到Si₂N₂O 再到Si₃N₄的转变过程. 在有金属组分存在时, Si₃N₄纳米线由气-液-固过程形成.     

Preparation and characterization of a supported Si3N4 membrane via a non-aqueous sol–gel process

We report a novel fabrication process of a mesoporous Si₃N₄ membrane on an Al₂O₃ support via a non-aqueous sol–gel technique. The membrane was prepared by dipping an -Al₂O₃ support disk into a silicon diimide sol that was synthesized by catalytic ammonolysis of tris(dimethylamino)silylamine, H₂NSi(NMe₂)₃. The SEM image and nitrogen adsorption analysis indicate that amorphous Si₃N₄ layers with nano-sized pores have formed on the surface and also inside the pores of the Al₂O₃ support disk. The new membrane demonstrates high selective absorption of NO₂, suggesting a potential application as a selective filter for gas sensors.     

Direct Determination of Trace Impurities in Silicon Nitride by Fluorinating ETV-ICP-AES with the Slurry Sampling Technique

Silicon nitride (Si₃N₄) ceramics are of great technological importance as high-density. corrosion-and heat-resistant materials for use in high-temperature and in reactor technology.     

胍盐离子液体对Si3N4/钢摩擦副的摩擦性能

两种具有较高热稳定性的胍盐离子液体用于Si₃N₄/钢摩擦副摩擦学性能的研究,在扫描电子显微镜下观察了磨斑表面形貌,并与烷基咪唑离子液体进行对比。 用X射线光电子能谱仪(XPS)分析了润滑机理。 结果表明,胍盐离子液体对Si₃N₄/钢摩擦副具有非常好的润滑作用,其承载能力强,摩擦系数小,磨痕浅。 摩擦过程中,Si₃N₄/钢摩擦副界面发生了复杂的摩擦化学反应并形成了边界润滑膜,起到减摩抗磨的作用。     

New trend of radiation application to polymer modification — irradiation in oxygen free atmosphere and at elevated temperature

Polycarbosilane (PCS) fiber as a precursor for ceramic fiber of silicon carbide was cured by electron beam (EB) irradiation under oxygen free atmosphere. Oxygen content in the cured PCS fiber was scarce and the obtained silicon carbide (SiC) fiber with low oxygen content showed high heat resistance up to 1973 K and tensile strength of 3 GPa. Also, the EB cured PCS fiber with very low oxygen content could be converted to silicon nitride (Si₃N₄) fiber by the pyrolysis in NH₃ gas atmosphere, which was the new processing to produce Si₃N₄ fiber. The process of SiC fiber synthesis was developed to the commercial plant.

The other application was the crosslinking of polytetrafluoroethylene (PTFE). PTFE, which had been recognized to be a typical chain scission polymer, could be induced to crosslinking by irradiation at the molten state in oxygen free atmosphere. The physical properties such as crystallinity, mechanical properties, etc. changed much by crosslinking, and the radiation resistance was much improved.     

Hydrothermal Syntheses,Crystal Structures and Thermal Properties of Two New Organically Templated Open-framework Gallium Phosphites

Two new open-framework gallium phosphites formulated as (C₂N₂H₁₀)_0.5Ga₂(OH)(H₂O)(HPO₃)₃(1) and (C₃N₂H₅)₂(C₃N₂H₆)Ga₈(H₂O)₆(HPO₃)₁₄(2) were hydrothermally synthesized in the presence of ethylenediamine(en) and imidazole as structure directing agents(SDA), respectively. Structural analyses reveal that the 3D structures of compounds 1 and 2 are both built up from the linkage of GaO₆, GaO₅(H₂O) and HPO₃^2? units by sharing vertices. The structure of compound 2 is constructed from well-known 4.6.12-net connecting layers in the AAAA stacking sequence, which are penetrated by the 1D Ga-O-P chains to form a 3D pillared-layered structure.     

类石墨烯C3N4纳米片光催化分解水制氢中的量子限域效应

从层状化合物获得的纳米片是一类新型纳米结构材料,这种二维各向异性的纳米甚至亚纳米级的材料具有独特的物理化学性能,其中最好的一个例证就是从石墨烯C₃N₄到石墨烯C₃N₄纳米片的转变。通过高温氧化热刻蚀方法将体相g-C₃N₄剥离成g-C₃N₄纳米片,应用于染料敏化可见光分解水产氢,表现出了较体相g-C₃N₄高于2.6倍的产氢速率。通过X射线衍射（XRD）、傅里叶变换红外（FTIR）光谱、扫描电子显微镜（SEM）、Brunauer-Emmett-Teller（BET）、荧光光谱和光电化学等表征研究了g-C₃N₄纳米片的结构及曙红（EY）和g-C₃N₄纳米片之间的电子迁移过程。热剥离后的g-C₃N₄纳米片具有较高的比表面积,不仅可以更为有效地吸附染料分子,还因其量子限域效应大大增强了光生电荷的分离效率和电子转移效率,改善了电子沿平面方向的传输能力以及光生载流子的寿命,从而显著提高g-C₃N₄纳米片的光催化产氢活性。     

Two New Inorganic-organic Hybrid Compounds Constructed from Different Polymolybdates and Transition Metal-amine Subunits

Two new polyoxometalate(POM)-based hybrid compounds, [Cu(en)][H₄Mo₄O₁₆]_0.5(1)(en=ethylene- diamine) and [Ag(3-C₅H₆N₂)₂][H₂PMo₁₂O₄₀](2)(3-C₅H₆N₂=3-aminopyridine), containing different transition metal-amine subunits were hydrothermally synthesized and characterized by elemental analyses, infrared spectroscopy and single-crystal X^-ray diffraction. For compound 1, each [H₄Mo₄O₁₆]^4-(Mo₄O₁₆) cluster was linked to four neighboring Mo₄O₁₆ clusters through four [Cu(en)]²⁺ subunits to yield a (2,4)-connected 2D layer, which was further extended to a 3D supramolecular network via hydrogen bonding interactions. For compound 2, the adjacent [H₂PMo₁₂O₄₀]^- clusters were bridged by [Ag(3-C₅H₆N₂)₂]⁺ subunits to generate a 1D chain. The electrochemical behaviors and the photocatalytic activities of compounds 1 and 2 were studied in detail.     

Enhanced Visible-light Photocatalytic Activity of g-C3N4/Nitrogen-doped Graphene Quantum Dots/TiO2 Ternary Heterojunctions for Ciprofloxacin Degradation with Narrow Band Gap and High Charge Carrier Mobility

Limited visible-light absorption and high recombination rate of photogenerated charges are two main drawbacks in g-C₃N₄-based photocatalysts. To solve these problems, g-C₃N₄/nitrogen-doped graphene quantum dots (NGQDs)/TiO₂ ternary heterojunctions were facilely prepared via a one-step calcining method. The morphology, structure, optical and electrochemical properties of g-C₃N₄/NGQDs/TiO₂ were characterized and explored. The optimal g-C₃N₄/NGQDs/TiO₂ composite exhibits enhanced photocatalytic degradation performance of ciprofloxacin (CIP) compared with the as-prepared g-C₃N₄, TiO₂(P25) and g-C₃N₄/TiO₂ heterojunction under visible light irradiation. The apparent rate constant of the composite is around 6.43, 4.03 and 2.30 times higher than those of g-C₃N₄, TiO₂ and g-C₃N₄/TiO₂, respectively. The enhanced photocatalytic efficiency should be mainly attributed to the improvement of light absorption and charge separation and transfer efficiency, originating from the narrow band gap and high charge carrier mobility. The active species trapping experiments results showed that the h⁺ and ^·O₂^- were the main active species in the degradation process. A possible photocatalytic reaction mechanism of the g-C₃N₄/NGQDs/TiO₂ composite for the enhanced degradation of CIP under visible light irradiation was also proposed.     

理论计算研究二维/二维BP/g-C3N4异质结的光催化CO2还原性能

Photocatalytic reduction of CO₂ to hydrocarbon compounds is a promising method for addressing energy shortages and environmental pollution. Considerable efforts have been devoted to exploring valid strategies to enhance photocatalytic efficiency. Among various modification methods, the hybridization of different photocatalysts is effective for addressing the shortcomings of a single photocatalyst and enhancing its CO₂ reduction performance. In addition, metal-free materials such as g-C₃N₄ and black phosphorus (BP) are attractive because of their unique structures and electronic properties. Many experimental results have verified the superior photocatalytic activity of a BP/g-C₃N₄ composite. However, theoretical understanding of the intrinsic mechanism of the activity enhancement is still lacking. Herein, the geometric structures, optical absorption, electronic properties, and CO₂ reduction reaction processes of 2D/2D BP/g-C₃N₄ composite models are investigated using density functional theory calculations. The composite model consists of a monolayer of BP and a tri-s-triazine-based monolayer of g-C₃N₄. Based on the calculated work function, it is inferred that electrons transfer from g-C₃N₄ to BP owing to the higher Fermi level of g-C₃N₄ compared with that of BP. Furthermore, the charge density difference suggests the formation of a built-in electric field at the interface, which is conducive to the separation of photogenerated electron-hole pairs. The optical absorption coefficient demonstrates that the light absorption of the composite is significantly higher than that of its single-component counterpart. Integrated analysis of the band edge potential and interfacial electronic interaction indicates that the migration of photogenerated charge carriers in the BP/g-C₃N₄ hybrid follows the S-scheme photocatalytic mechanism. Under visible-light irradiation, the photogenerated electrons on BP recombine with the photogenerated holes on g-C₃N₄, leaving photogenerated electrons and holes in the conduction band of g-C₃N₄ and the valence band of BP, respectively. Compared with pristine g-C₃N₄, this S-scheme heterojunction allows efficient separation of photogenerated charge carriers while effectively preserving strong redox abilities. Additionally, the possible reaction path for CO₂ reduction on g-C₃N₄ and BP/g-C₃N₄ is discussed by computing the free energy of each step. It was found that CO₂ reduction on the composite occurs most readily on the g-C₃N₄ side. The reaction path on the composite is different from that on g-C₃N₄. The heterojunction reduces the maximum energy barrier for CO₂ reduction from 1.48 to 1.22 eV, following the optimal reaction path. Consequently, the BP/g-C₃N₄ heterojunction is theoretically proven to be an excellent CO₂ reduction photocatalyst. This work is helpful for understanding the effect of BP modification on the photocatalytic activity of g-C₃N₄. It also provides a theoretical basis for the design of other high-performance CO₂ reduction photocatalysts.      

高活性氮化碳纳米片的制备策略

Layered graphitic carbon nitride (g-C₃N₄) is a typical polymeric semiconductor with an sp² π-conjugated system having great potential in energy conversion, environmental purification, materials science, etc., owing to its unique physicochemical and electrical properties. However, bulk g-C₃N₄ obtained by calcination suffers from a low specific surface area, rapid charge carrier recombination, and poor dispersion in aqueous solutions, which limit its practical applications. Controlling the size of g-C₃N₄ (e.g., preparing g-C₃N₄ nanosheets) can effectively solve the above problems. Compared with the bulk material, g-C₃N₄ nanosheets have a larger specific surface area, richer active sites, and a larger band gap due to the quantum confinement effect. As g-C₃N₄ has a layered structure with strong in-plane C-N covalent bonds and weak van der Waals forces between the layers, g-C₃N₄ nanosheets can be prepared by exfoliating bulk g-C₃N₄. Alternatively, g-C₃N₄ nanosheets can otherwise be obtained through the anisotropic assembly of organic precursors. Nevertheless, some of these methods have various limitations, such as high energy consumption, are time consuming, and have low yield. Accordingly, developing green and cost-effective exfoliation and preparation strategies for g-C₃N₄ nanosheets is necessary. Herein, the research progress of the exfoliation and preparation strategies (including the thermal oxidation etching process, the ultrasound-assisted route, the chemical exfoliation, the mechanical method, and the template method) for two-dimensional C₃N₄ nanosheets are introduced. Their features are systematically analyzed and the perspectives and challenges in the preparation of g-C₃N₄ nanosheets are discussed. This study emphasizes the following: (1) The preparation method of g-C₃N₄ nanosheets should be properly selected according to the practical application needs. Additionally, various strategies (such as chemical method and ultrasonic method) can be combined to exfoliate nanosheets from bulk g-C₃N₄; (2) More reasonable nano- or even subnanostructured g-C₃N₄ nanosheets should be continuously explored; (3) Novel modification strategies, such as defective engineering, heterojunction construction, and surface functional group regulation, should be introduced to improve the reactivity and selectivity of the g-C₃N₄ nanosheets; (4) The application of in situ characterization techniques (such as in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), electron spin resonance (ESR) spectroscopy, and Raman spectroscopy) should also be strengthened to monitor the detailed catalytic process and investigate the g-C₃N₄ nanosheet structure-efficiency relationship. (5) To gain a deeper understanding of the relationship between the macroscopic properties and the microscopic structure, the combination of theoretical calculations and experimental results should be strengthened, which will be beneficial for exploiting high-quality g-C₃N₄ nanosheets.      

基于2-氨基吡啶的两个簇基超分子化合物的合成、 结构及催化性能

以磷钼酸、 2-氨基吡啶、 五氧化二钒、 氯化锌和氯化镍等为主要原料, 采用水热方法合成了2个簇基超分子化合物[H₃PMo₁₂O₄₀]₂[C₅H₆N₂]₆(1)和[H₂PMo₁₂V₂O₄₂][C₅H₆N₂]₅·3H₂O(2)(C₅H₆N₂=2-氨基吡啶). 通过元素分析、 红外光谱、 紫外-可见光谱、 X射线光电子能谱、 热重分析、 X射线单晶衍射及X射线粉末衍射等手段对化合物进行了结构表征. 结构分析显示, 簇单元不同的2个超分子化合物以各自独特的堆积方式形成三维超分子网络. 利用苯乙烯的环氧化反应研究了2个化合物的催化性能.     

Coupled Hartree-Fock calculations of the electric dipole polarizability and first hyperpolarizability of some “inorganic benzenes”

Extended basis sets of gaussian functions were used to calculate near Hartree-Fock estimates of the electric dipole polarizabilities, , and first hyperpolarizabilities, β, of the “inorganic benzenes” B₃N₃H₆, B₃O₃H₃, B₃P₃H₃ and Al₃N₃H₆. Assuming that electron delocalization is responsible for the enhanced polarizabilities of aromatic systems, an aromaticity scale can be set up according to the trend of theoretical polarizabilities obtained in this work, i.e. (B₃O₃H₃) < (B₃N₃H₆ ) < (C₆H₆ ), which is consistent with previous calculations of the degree of delocalization in these compounds.     

Polymeric Carbon Nitride-based Single Atom Photocatalysts for CO2 Reduction to C1 Products

Photocatalytic CO₂ reduction to C₁ fuels is considered to be an important way for alleviating increasingly serious energy crisis and environmental pollution. Due to the environment-friendly, simple preparation, easy formation of highly-stable metal-nitrogen(M-N_x) coordination bonds, and suitable band structure, polymeric carbon nitride-based single-atom catalysts(C₃N₄-based SACs) are expected to become a potential for CO₂ reduction under visible-light irradiation. In this review, we summarize the recent advancement on C₃N₄-based SACs for photocatalytic CO₂ reduction to C₁ products, including the reaction mechanism for photocatalytic CO₂ reduction to C₁ products, the structure and synthesis methods of C₃N₄-based SACs and their applications toward photocatalytic CO₂ reduction reaction(CO₂RR) for C₁ production. The current challenges and future opportunities of C₃N₄-based SACs for photoreduction of CO₂ are also discussed.     

Theoretical study of tricyclo[3,3,1,1]decane, tricyclo[3,3,1,1]decsilane molecules and their halogen derivatives, C10H12X4 and Si10H12X4 (X=F, Cl, Br, I)

The B3LYP/3-21G* ab initio molecular orbital method from the program package was applied to study tricyclo[3,3,1,1^3,7]decane and tricyclo[3,3,1,1^3,7]decsilane molecules and their halogen derivatives (1,3,5,7-tetrahalotricyclo[3,3,1,1^3,7]decane and 1,3,5,7-tetrahalotricyclo[3,3,1,1^3,7]decsilane, C₁₀H₁₂X₄ and Si₁₀H₁₂X₄ respectively). The optimized structures of these compounds were obtained. Ionization potentials, HOMO and LUMO energies, energy gaps, heats of formation, atomization energies and vibration frequencies were calculated. The calculations indicate that these molecules are stable and have T_d symmetry. Tricyclo[3,3,1,1^3,7]decsilane and its halogen derivatives (Si₁₀H₁₂X₄) are found to have higher conductivity than tricyclo[3,3,1,1^3,7]decane and its halogen derivatives (C₁₀H₁₂X₄). 1,3,5,7-Tetrafluorotricyclo[3,3,1,1^3,7]decane (C₁₀H₁₂F₄) and 1,3,5,7-tetrafluorotricyclo[3,3,1,1^3,7]decsilane (Si₁₀H₁₂F₄) were found to be the easiest compounds to form and the most difficult to dissociate of all 1,3,5,7-tetrahalotricyclo[3,3,1,1^3,7]decane and 1,3,5,7-tetrahalotricyclo[3,3,1,1^3,7]decsilane compounds, respectively.     

Cu2+改性g-C3N4光催化剂的光催化性能

Photocatalytic technology can effectively solve the problem of increasingly serious water pollution, the core of which is the design and synthesis of highly efficient photocatalytic materials. Semiconductor photocatalysts are currently the most widely used photocatalysts. Among these is graphitic carbon nitride (g-C₃N₄), which has great potential in environment management and the development of new energy owing to its low cost, easy availability, unique band structure, and good thermal stability. However, the photocatalytic activity of g-C₃N₄ remains low because of problems such as wide bandgap, weakly absorb visible light, and the high recombination rate of photogenerated carriers. Among various modification strategies, doping modification is an effective and simple method used to improve the photocatalytic performance of materials. In this work, Cu/g-C₃N₄ photocatalysts were successfully prepared by incorporating Cu²⁺ into g-C₃N₄ to further optimize photocatalytic performance. At the same time, the structure, morphology, and optical and photoelectric properties of Cu/g-C₃N₄ photocatalysts were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, UV-Vis diffuse reflectance spectroscopy (DRS), and photoelectric tests. XRD and XPS were used to ensure that the prepared photocatalysts were Cu/g-C₃N₄ and the valence state of Cu was in the form of Cu²⁺. Under visible light irradiation, the photocatalytic activity of Cu/g-C₃N₄ and pure g-C₃N₄ photocatalysts were investigated in terms of the degradation of RhB and CIP by comparing the amount of introduced copper ions. The experimental results showed that the degradation ability of Cu/g-C₃N₄ photocatalysts was stronger than that of pure g-C₃N₄. The N₂ adsorption-desorption isotherms of g-C₃N₄ and Cu/g-C₃N₄ demonstrated that the introduction of copper had little effect on the microstructure of g-C₃N₄. The small difference in specific surface area indicates that the enhanced photocatalytic activity may be attributed to the effective separation of photogenerated carriers. Therefore, the enhanced photocatalytic degradation of RhB and CIP over Cu/g-C₃N₄ may be due to the reduction of carrier recombination rate by copper. The photoelectric test showed that the incorporation of Cu²⁺ into g-C₃N₄ could reduce the electron-hole recombination rate of g-C₃N₄ and accelerate the separation of electron-hole pairs, thus enhancing the photocatalytic activity of Cu/g-C₃N₄. Free radical trapping experiments and electron spin resonance indicated that the synergistic effect of superoxide radicals (O₂^•−), hydroxyl radicals (•OH) and holes could increase the photocatalytic activity of Cu/g-C₃N₄ materials.     

单层石墨相氮化碳负载Pt4团簇吸附O2的第一性理论研究

采用第一性原理密度泛函理论结合周期性平板模型模拟研究了Pt₄团簇吸附单层石墨相氮化碳(g-C₃N₄)的几何结构和电子性质,以及氧气在其表面上的吸附行为。同时,对比分析了氧气在纯净的石墨相氮化碳和Pt₄团簇上的吸附行为。计算结果表明, Pt₄团簇吸附在3-s-三嗪环石墨相氮化碳表面,并与四个边缘氮原子成键,形成两个六元环时为最稳定构型。Pt₄团簇倾向于吸附在三嗪环石墨相氮化碳的空位并与邻近三个氮原子成键。由于Pt与N原子较强的杂化作用,以及金属与底物之间较多电子转移增强了Pt₄团簇吸附g-C₃N₄的稳定性。另外,对比分析了氧气在纯净的g-C₃N₄和金属吸附的g-C₃N₄上吸附行为,发现金属原子的加入促进了电子转移,同时拉长了O―O键长。Pt₄吸附3-s-三嗪环g-C₃N₄比Pt₄吸附三嗪环g-C₃N₄表现出微弱的优势,表现出明显的基底扭曲以及较大的吸附能。这些结果表明,化学吸附通过调节电子结构和表面性质增强催化性能的较好方法。     

Ni,Co基硒化物修饰g-C3N4光催化产氢研究

Developing novel and efficient catalysts is a significant way to break the bottleneck of low separation and transfer efficiency of charge carriers in pristine photocatalysts. Here, two fresh photocatalysts, g-C₃N₄@Ni₃Se₄ and g-C₃N₄@CoSe₂ hybrids, are first synthesized by anchoring Ni₃Se₄ and CoSe₂ nanoparticles on the surface of well-dispersed g-C₃N₄ nanosheets. The resulting materials show excellent performance for photocatalytic in situ hydrogen generation. Pristine g-C₃N₄ has poor photocatalytic hydrogen evolution activity (about 1.9 μmol·h^-1) because of the rapid recombination of electron-hole pairs. However, the hydrogen generation activity is well improved after growing Ni₃Se₄ and CoSe₂ on the surface of g-C₃N₄, owing to the unique effect of these selenides in accelerating the separation and migration of charge carriers. The hydrogen production activities of G-C₃N₄@Ni₃Se₄ and g-C₃N₄@CoSe₂ are about 16.4 μmol·h^-1 and 25.6 μmol·h^-1, which are 8-fold and 13-fold that of pristine g-C₃N₄, respectively. In detail, coupling Ni₃Se₄ and CoSe₂ with g-C₃N₄ greatly improves the light absorbance density and extends the light response region. The photoluminescence intensity of the photoexcited Eosin Y dye in the presence of g-C₃N₄@Ni₃Se₄ and g-C₃N₄@CoSe₂ is weaker than that in the presence of pure g-C₃N₄. On the other hand, the upper limit of the electron-transfer rate constants in the presence of g-C₃N₄@Ni₃Se₄ and g-C₃N₄@CoSe₂ is greater than that in the presence of pure g-C₃N₄. Among the g-C₃N₄@Ni₃Se₄@FTO, g-C₃N₄@CoSe₂@FTO, and g-C₃N₄@FTO electrodes, the g-C₃N₄@FTO electrode has the lowest photocurrent density and the highest electrochemical impedance, implying that the introduction of CoSe₂ and Ni₃Se₄ onto the surface of g-C₃N₄ enhances the separation and transfer efficiency of photogenerated charge carriers. In other words, the formation of two star metals selenide based on g-C₃N₄ can efficiently inhibit the recombination of photogenerated charge carriers and accelerate photocatalytic water splitting to generate H₂. Meanwhile, the right shift of the absorption band edge effectively reduces the transition threshold of the photoexcited electrons from the valence band to the conduction band. In addition, the more negative zeta potential for the g-C₃N₄@Ni₃Se₄ and g-C₃N₄@CoSe₂ catalysts as compared with that for pure g-C₃N₄ leads to a notable enhancement in the adsorption of protons by the sample surface. Moreover, the results of density functional theory calculations indicate that the hydrogen adsorption energy of the N sites in g-C₃N₄ is -0.22 eV; further, the hydrogen atoms are preferentially adsorbed at the bridge site of two selenium atoms to form a Se―H―Se bond, and the adsorption energy is 1.53 eV. In-depth characterization has been carried out by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, transient photocurrent measurements, and Fourier transform infrared spectroscopy; the results of these experiments are in good agreement with one another.     

通过g-C3N4担载MNi12 (Fe,Co, Cu,Zn)纳米团簇调节甲烷化

As a unique two-dimensional material, graphitic carbon nitride (g-C₃N₄) has received significant attention for its particular electronic structure and chemical performance. Its instinctive defect can provide a stable anchoring site for metals, potentially improving the surface reactivity. Ni-based catalysts are economical but their activity for CO₂ methanation is lower than that of noble metal catalysts. Ni nanoparticles (NPs) supported on a substrate can further enhance the stability and activity of catalysts. Based on the principles of strong metal-support interaction (SMSI) and the synergistic effect on an alloy, MNi₁₂/g-C₃N₄ composites as novel catalysts are expected to improve stability and catalytic performance of Ni-based catalysts. The configurations are established with core-shell structures of MNi₁₂ (M = Fe, Co, Cu, Zn) nanoparticles (NPs) supported on g-C₃N₄ in this work. In the CO₂ methanation reaction, the reactivity of CO on slab (E_CO) is a critical factor, which is relative to the catalytic activity. Thus, the catalytic reactivity of these complexes via CO adsorption were explored using density functional theory (DFT). The values of cohesive energy (E_coh) for MNi₁₂ NPs range from -39.90 eV to -34.82 eV, suggesting that the formation of these NPs is favored as per thermodynamics, and E_coh and partial density of state (PDOS) reveal that the central M atom with the less filled d-shell interacts more strongly with surface Ni atoms. Therefore, ZnNi₁₂ is the most unstable structure among all the studied alloy, and the synergistic effect is also the weakest among them. When MNi₁₂ NPs are supported on the g-C₃N₄ substrate, the binding energies (E_b) vary from -9.40 eV to -8.39 eV, indicating that g-C₃N₄ is indeed a good material for stabilizing these NPs. The PDOS analysis of pure g-C₃N₄ suggests the sp² dangling bonds of N atoms in g-C₃N₄ can stabilize these transition metal NPs. Furthermore, the results of CO adsorbed on MNi₁₂ NPs and MNi₁₂/g-C₃N₄ composites show that E_CO and d_CO reduced with the introduction of g-C₃N₄. According to the results of the analysis of the Hirshfeld charges and electrostatic potential (ESP), the reason is that CO obtains less electrons from MNi₁₂ NPs after deposition on the g-C₃N₄ substrate, which lowers the reactivity of CO on catalysts. Additionally, the deformation charge density is analyzed to investigate the interaction between the NPs and g-C₃N₄. With the introduction of g-C₃N₄, charge redistribution indicates the strong metal-support interaction, which further reduces the CO adsorption energy. In summary, MNi₁₂ supported on g-C₃N₄ exhibit not only high stability but also tunable reactivity in CO₂ methanation. These changes are beneficial for CO₂ methanation reaction.