SiO2 Spheres Research Articles

The ablation behavior and modification mechanism of SiC under different laser energy

The laser modification pretreatment method is an effective way to address the machining difficulties of silicon carbide (SiC), a typical hard-to-machine material. Therefore, the ablation behavior and modification mechanism of SiC under different laser energy were explored in this paper. A new multi-scale model of laser irradiation SiC that couples heat transfer and fluid motion is first established. Then, a series of experiments is carried out to evaluate the model's accuracy, and the interaction between laser and SiC is discussed in detail. The results show that the dominant modification mechanism changes from coulomb explosion to multiphoton absorption, incubation effect, and heat accumulation with the laser energy increase. This leads the surface topography of SiC to transition from nanoparticle formation to disorder to a melting state. In ablative state, micro/nano porous and humps are formed at the edge of ablation groove due to surface tension, generation and rupture of bubbles, respectively. Furthermore, the surface roughness is not proportional to the laser energy due to the plasma shielding effect, and the surface roughness can be reduced by enhancing the flow of the molten material. Amorphous Si–O–C, Si and spherical SiO2 exist in deposition area, leading to SiC elastic modulus decreases from 347 GPa to 103.82 GPa, and the shear strength decreases from 20.9 GPa to 17.25 GPa. The results of this study can provide references for parameters selection and theoretical support for improving the machinability of SiC.

Modified silica nanoparticles stabilized foam for enhanced oil recovery

Foam has been successfully used to improve mobility control in the process of enhanced oil recovery, yet the instability of foam limits its application. Modified nanoparticles with varying wettability were prepared by reacting 3-methacryloxypropyltrimethoxysilane (KH570) with spherical SiO2 nanoparticles in this study. Fourier transform infrared (FTIR) spectra and the measured contact angles were used to characterize the surface properties of the modified SiO2 particles, and the foam stabilization effects of wettability SiO2 were compared. Pore-scale visualization experiments were conducted using a 2D micromodel to identify the prevailing enhanced oil recovery (EOR) mechanisms of modified nano SiO2-Sodium alpha-olefin Sulfonate (AOS) foam flooding. The results indicate that modified SiO2 effectively improves foam stability by adsorbing on the bubble surface and forming a mesh-like structure. The optimum contact angle of the particles is approximately 60°, resulting in a significant increase in drainage half-life by 29.4% compared to foam stabilized only by AOS. Additionally, Foam stabilized by modified SiO2 demonstrates superior dynamic stability and deformation resistance. The modified SiO2 stabilized foam exhibits enhanced interfacial viscoelasticity and plugging and profile control performance, surpassing AOS foam in displacing more residual oil in dead-end pores. The oil recovery of the micro model was determined by ImageJ software. KH570@SiO2 (0.2wt%)-AOS (0.2wt%) foam flooding increased the recovery by 8.7% compared to AOS (0.2wt%) foam flooding.

Simultaneously quantitative and qualitative regulation of active sites of Ni-phyllosilicate for enhanced CO2 hydrogenation to methane

To address the problems of low metal utilization rate and poor low-temperature activity of the nickel phyllosilicate catalysts for CO2 methanation, this work prepared ultrathin defect-rich Ni-phyllosilicate through ball milling method in the presence of H2O2 modifier, which simultaneously created active sites with more quantity and higher quality. The instantaneous temperature and high pressure derived from the collision and friction of grinding balls provided driving force for the Ni-phyllosilicate synthesis, and the shear force destroyed the interlayer forces to construct the ultrathin layers. H2O2 molecule could insert the layers and dissociate to O2 bubbles, whose cavitation effect created holes and defects in the nickel phyllosilicate nanosheets and SiO2 spheres. H2O2 amount was crucial for the defect construction and the optimum Ni-AA-1H catalyst possessed the ultrathin nanosheet of 0.68 nm and high Ni dispersion of 15.6 %, whose TOFCO2 reached 3.76 × 10−2 s−1 at 160 °C. The in-situ DRIFTS results confirmed the enhanced low-temperature activity and the HCOO− reaction pathway over Ni-AA-1H for CO2 methanation. Nickel precursor effect was also investigated, and nickel acetylacetonate was determined as the optimal one compared with nickel acetate and nickel chloride, owing to the high steric effect of CH3COCHCOCH3− group and strong basicity environment during ball milling process.

High-efficiency fabrication of uniform photonic crystals by a vertical deposition method from multiple glass slides of simple moulds and their application in isomer recognitions

Vertical deposition method is a simple, cheap and common method for fabricating photonic crystals (PCs). However, a majority of PCs are obtained based on the traditional vertical deposition method from one glass slide, the method is low efficiency. Herein, it is proposed to efficiently fabricate uniform PCs by an optimized vertical deposition method from double or multiple glass slides of simple moulds. Amounts of SiO2 spheres, distances of two glass slides of moulds, preparation temperatures and different diameters of SiO2 spheres are investigated for obtaining uniform PCs. And different types of PCs (the bottom-middle-top 3D PCs, bilayer 2D PCs and amorphous PCs) are also fabricated based on the optimized vertical deposition method. The above method is a simple, cheap and high-efficiency way for mass production of uniform PCs. Meanwhile, the chemicals with similar refractive indices (isomers and cis-trans isomers) can be easily distinguished under high humidity based on dynamic reflection spectra of the PCs. For example, the difference in the refractive indices of m-xylene and p-xylene is only 0.002, the difference of desorption balance time of PCs is 263 s. The PCs have potential applications in visual detections, isomer recognitions and monitoring of volatilization rates of trace liquids.

Aminated Spherical SiO2 Synthesized from Fly Ash and Its Application for Pb2+ and Cu2+ Sorption

Fly ash was utilized as raw material for the preparation of spherical SiO2 (SS), which was subsequently ammonified using APTES (H2NCH2CH2CH2Si(OC2H5)3) to obtain aminated spherical SiO2 (SSN). The physicochemical properties of SS and SSN were systematically characterized. Notably, SS exhibited a remarkable specific surface area and pore volume, enabling it to accommodate abundant nitrogen-containing groups. These functional groups served as crucial active sorption sites, significantly enhancing the sorption capacity of SiO2 for Pb2+ and Cu2+ ions. Thus, the removal efficiency was above 99.9% when using dosages of 4 and 6 g/L SSN in solutions containing 200 mg/L of Pb2+ and Cu2+, respectively. Additionally, SSN showed a higher theoretical maximum sorption capacity for Pb2+ and Cu2+ ions, as determined by the Langmuir isotherm model, with values of 185.2 mg/g and 86.2 mg/g, respectively. These results surpass those reported in previous studies on adsorbents derived from fly ash. The chemical reactions that occurred between the aqueous cations and nitrogen-containing groups were identified as the pivotal factors governing the sorption of Pb2+ and Cu2+. This study presents a practical approach to fly ash utilization, along with the effective removal of Pb2+ and Cu2+ from water.

Green synthesized SiO2/Bi2O3 nanocomposite sensor for catechol and hydroquinone detection in water

A new sensitive and selective electrochemical was constructed by modification of the carbon paste electrode (CPE) with SiO2/Bi2O3 nanocomposite (SiO2/Bi2O3/CPE) to quantify catechol (CT) and hydroquinone (HQ). The green synthesized SiO2 and Bi2O3 nanoparticles were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron (SEM) and transmission electron (TEM) microscopy. Results indicated the formation of amorphous spherical SiO2 NPs and crystalline spherical Bi2O3 NPs with particle sizes of 6 and 25 nm, respectively. Cyclic voltammetry results showed the greater electrochemical activity of SiO2/Bi2O3/CPE compared with CPE, SiO2/CPE, and Bi2O3/CPE. This is due to the synergistic effect of SiO2/Bi2O3 nanocomposite leading to larger electroactive surface area. CT and HQ were determined using differential pulse voltammetry (DPV) in phosphate buffer solution at pH 7.2 in the linear ranges of 8.0 ×10−9 - 5.0 ×10−6 M and 5.0 ×10−9 - 5.0 ×10−6 M with the detection limits of 7.0 ×10−10 M and 7.5 ×10−10 M, respectively. The diffusion coefficients of CT and HQ were calculated by chronoamperometry as 1.2 × 10−6 cm2/s and 7 × 10−6 cm2/s, respectively. The sensor demonstrated excellent repeatability and stability allowing the estimation of CT and HQ in Nile river, tap and bottled real water samples with high recoveries.

Synthesis of spherical SiO2 powders from water glass and colloidal Sol through ultrasonic spray pyrolysis

Synthesis of spherical SiO2 powders from water glass and colloidal Sol through ultrasonic spray pyrolysis

Preparation of millimeter-sized spherical SiO2–Al2O3 with various acid catalysts for the acetalization of glycerol with acetone

Preparation of millimeter-sized spherical SiO2–Al2O3 with various acid catalysts for the acetalization of glycerol with acetone

Towards the understanding of the unusual rheological response of polymer nanocomposites

It is well known that the properties of polymers can be improved by the incorporation of nano-additives in the polymeric matrix, forming nanocomposite materials that often possess innovative physicochemical properties compared to the initial materials and / or the respective conventionally filled systems. In this work, we investigate the rheological response of different series of poly(ethylene oxide) / silica, PEO/SiO2, nanocomposites by shear rheology. More specifically, spherical SiO2 nanoparticles of two different radii are dispersed in PEOs of different molecular weights covering the regime from unentangled to highly-entangled systems. Nanocomposites over a wide range of compositions were developed in order to investigate both the effect of the size and concentration of the nanoparticles and the effect of the molecular weight of the polymer matrix, on the rheological properties of the nanocomposite materials. For all systems three different concentration regimes are observed with distinctly different rheological response; a ‘polymer-like’ regime, where the behavior resembles the one of the respective polymers, a ‘weak gel-like’ regime at higher nanoparticle content, where enhanced polymer / particle interactions modify the behavior, and a ‘strong gel-like’ one characterized by percolated networks of nanoparticles formed within the polymer matrices. The ‘polymer-like’ regime is especially interesting since a significant reduction of the melt viscosity is observed, which is attributed to a dilution of the entanglement network of the polymer chains due to the presence of the nanoparticles.

Laser ablation behavior and mechanism of Cf/C–SiC composites under different laser energy densities

Ceramic matrix composite (CMC) is typical difficult-to-machine material, laser assisted machining (LAM) is an effective method to solve the problem of poor machinability, and a deep understanding of the interaction between laser and material can lay a foundation for LAM. Aiming at the unclear mechanism of microstructure formation, crack propagation and material hardness evolution of laser-irradiated CMC, laser ablation behavior and mechanism of Cf/C–SiC composites under different laser energy densities were studied in this paper. The results show that Cf/C–SiC presents two different states of modification and ablation under irradiating. In modified state, fiber interface in central area is oxidized, and crystal transformation occurs. Amorphous Si–O–C, Si and spherical SiO2 exist in edge deposition area, and continuous phase disappears in heat affected zone. In ablative state, carbon nanosheets and clusters are formed in ablation groove. Surface of convex and deposition area are composed of sedimentary basement and clusters, and there are recast layer and heat affected zone in cross section. When thermal stress exceeds interfacial bond strength and critical matrix stress, the fiber interface debonding and matrix cracking occur, and both transgranular and intergranular fracture exist in the matrix. When laser scanning direction is perpendicular to fiber extension, crack propagation can be inhibited. The propagation and intersection of cracks and coarsening of SiC crystal phase in heat affected zone lead to the decrease of matrix microhardness. The results of this study can be used to provide references for parameters selection and theoretical support for LAM of CMC.

Controlled Growth of Large SiO2 Shells onto Semiconductor Colloidal Nanocrystals: A Pathway Toward Photonic Integration.

The growth of SiO2 shells on semiconductor nanocrystals is an established procedure and it is widely employed to provide dispersibility in polar solvents, and increased stability or biocompatibility. However, to exploit this shell to integrate photonic components on semiconductor nanocrystals, the growth procedure must be finely tunable and able to reach large particle sizes (around 100 nm or above). Here, we demonstrate that these goals are achievable through a design of experiment approach. Indeed, the use of a sequential full-factorial design allows us to carefully tune the growth of SiO2 shells to large values while maintaining a reduced size dispersion. Moreover, we show that the growth of a dielectric shell alone can be beneficial in terms of emission efficiency for the nanocrystal. We also demonstrate that, according to our modeling, the subsequent growth of two shells with increasing refractive index leads to an improved emission efficiency already at a reduced SiO2 sphere radius.

CdTe QDs@SiO2 composite material for efficient photocatalytic degradation of tetracycline composites

In the contemporary context, tetracycline is widely utilized as a prevalent antibiotic in various facets of life. However, the excessive use of antibiotics has caused visible environmental consequences. Henceforth, the scientific community has increasingly focused on developing catalysts that exhibit exceptional efficacy in the proficient degradation of tetracycline. In this study, a novel nanomaterial was developed to encapsulate CdTe quantum dots (QDs) with a SiO2 shell. The distinct synthesis approach generated a composite material that showed heterogeneity and considerably increased the contact area with contaminants. Consequently, the transfer of photoelectron to the SiO2 spheres was significantly improved, leading to a more efficient separation during the catalytic process. The study investigated how different factors, such as the loading of the catalyst, the initial concentration of tetracycline, pH levels, and the wight ratio of CdTe QDs (SiO2 + CdTe QDs) affected the effectiveness of photocatalytic tetracycline degradation. The findings indicated that the optimal degradation efficiency was observed at a catalyst concentration of 0.25 g/L and a solution pH of 9, leading to an impressive degradation rate of 96% within a mere 2 h timeframe.

Synergistic action of highly-active porous carbon-based bifunctional electrocatalysts and neutral electrolyte: endowing zinc–air batteries with ultra-long cycle stability

A honeycomb N/S co-doped Co9S8 nanoparticle material loaded with porous carbon skeleton (N/SdCF-OIM/Co9S8) as cathode catalyst was designed by using Co-MOF and SiO2 spheres. The ZABs based on N/SdCF-OIM/Co9S8 in neutral electrolyte have longer cycle stability than in alkaline electrolytes.

Engineering semiconductor quantum dots for co-upcycling of CO2 and biomass-derived alcohol

A heterointerface engineering strategy of immobilizing core–shell CdSe/CdS quantum dots onto SiO2 spheres was realized to efficiently integrate CO2 photoreduction with the oxidation of furfuryl alcohol in one system.

Colloidal synthesis of metallodielectric Janus matchsticks.

We present a gram-scale synthesis of metallodielectric Janus matchsticks, which feature a gold-coated silica sphere and a silica rod. SiO2 Janus matchsticks are synthesized in one batch by growing amine-functionalized SiO2 spheres at the end of SiO2 rods. Gold deposition on the spheres produces Au-SiO2 Janus matchsticks with an aspect ratio controlled by the rod length. The metallodielectric Janus matchsticks, produced by scalable colloidal synthesis, hold great potential as functional colloidal materials.

An ordered mesoporous carbon-silica hybrid for the detection of the antiviral drug ribavirin in clinical samples.

Ribavirin (RIB) is widely used for the treatment of viral diseases such as herpes, hepatitis C, and Lassa fever. Moreover, to control the spread of COVID-19, the consumption of antiviral medicines, including RIB, has increased significantly worldwide. By combining ordered mesoporous carbon with silica nanoparticles via ultrasound, we synthesized silica/ordered mesoporous carbon (SiO2-OMC) hybrid composites that show excellent electrochemical performance. The hybrid composite was found to contain spherical SiO2 nanoparticles having diameters ranging from 21 to 29 nm. A sensor comprising a carbon paste electrode and SiO2-OMC (SiO2-OMC/CPE) facilitated the ultrasensitive and selective detection of RIB at an oxidation potential of 0.71 V, having a linear range of 0.1-40 μmol L-1, limit of detection of 0.067 μmol L-1, and sensitivity of 1.969 μA μmol-1 L. Furthermore, the results indicate that charge transfer at the interface of the SiO2-OMC hybrid results in a synergistic effect compared to OMC and SiO2 alone. The advantages include the potential for regenerating the sensor surface, rapid and facile production, and suitability for the detection of RIB in capsule, human plasma, and urine samples, making SiO2-OMC/CPE a promising interface for bioelectrochemical applications.

Simulating and Analyzing the Electronic Structure of a Spherical Amorphous SiO2 Nanoparticle of Finite Radius

This study focuses on the electronic structure and properties of amorphous SiO2 nanoparticle with a radius of 18 Å using Density Functional Theory and the Orthogonalized Linear Combination of Atomic Orbital method. Through employing appropriate statistical techniques, three distinct models (I, II, and III) of amorphous SiO2 nanoparticle with an 18 Å radius are generated based on the continuous random network structure incorporating periodic boundaries. The calculated Total Density of States and Partial Density of States reveal insights into the electronic interactions within the nanoparticle. The band gap values are assessed at both less accurate and more accurate potentials such that the band gap increases from 2 eV to 4.2 eV with higher potentials for Model I, where surface atoms has dangling bonds stabilized by hydrogen atoms. Model II, consisting of all surface silicon atoms bonded to four oxygen atoms, exhibits a band gap of 1 eV, increasing to 1.8 eV with higher potentials. Model III, saturated with hydrogen atoms, shows a band gap of 4 eV, decreasing to 3.75 eV at higher potentials. The introduction of the more accurate potential serves to minimize the gap states initially observed with the less accurate potential. The electronic structure calculations provide crucial information for understanding the electronic interactions within the amorphous SiO2 nanoparticle with implications for their applications in various fields such as biomedicine, catalysis, electronics, and nanotechnology.

Physical and Electrochemical Properties of Transition Metal Oxides with Hollow Structure As Sulfur Host Material for Lithium-Sulfur Batteries

INTRODUCTION Because of its high theoretical energy density, possibly low cost, and environmental friendliness, lithium-sulfur (Li-S) batteries have received a lot of interest. However, the principal disadvantage impeding the success of Li–S batteries lies in the severe leakage and migration of soluble lithium polysulfide intermediates out of cathodes upon cycling caused “shuttle effect”. The loss of active sulfur species incurs significant capacity decay and poor battery lifespans which has prevented it from commercial realization.Several researches have been conducted with an attempt to improve capacity of batteries while maintaining life of the Li-S cellใ including an introduction of nanostructured cathode host materials. Two main approaches have currently been explored a. chemical confinement and b. physical confinement to anchor the lithium poly-sulfide (LiPSs) reaction products durin the charging process. Transition metal oxides such as TiO2 and SnO2 has been studied with a potential material to anchor polysulfides via Lewis acid–base interactions and thus maybe able to chemically confine LiPSs within or on the transition metal oxide. Physical confinement may also be possible by trapping LiPSs within a transition metal oxide host structure e.g. hollow structure and thus help impedes polysulfide dissolution into the electrolyte. In this study, TiO2 and SnO2 are focused to understand the physical and electrochemical properties of sulfur host material with hollow structures. The in situ XAS is also conducted to understand the behavior of the dissolution and migration of long-chain LiPSs intermediates (Li2S x , 4 ≤ x ≤ 8) in the sulfur cathode upon discharge. EXPERIMENTAL The transition metal oxide, TiO2 and SnO2, were successfully synthesized by a templated method. The synthesis process involved four steps, preparation of SiO2 spheres, synthesis of SiO2@transition metal oxide core-shell structure by coating transition metal oxide shell on SiO2 and crystallization by calcination and etching the SiO2@transition metal oxide to form hollow transition metal oxide spheres. Structural properties of the synthesized samples were studied by X-ray diffraction (XRD) using Cu-Kα (λ=1.5418 Å) radiation. Particle morphologies and size of the resulting compounds were observed using a field emission scanning electron microscope. Composite electrodes for electrochemical studies were prepared by doctor blade coating of a slurry compound onto carbon-coated aluminium foil current-collectors. The transition metal oxide and sulfur composite, conductive carbon and PVDF binder were mixed in the ratio of 80:10:10 by weight. Electrochemical characterizations were performed by in 2032 coin cells and Galvanostatic charge-discharge cycling was done between 1.8-3.0 V at 0.1C using a MACCOR Series 4000 at room temperature. RESULTS AND DISCUSSIONS Based on the XRD results, single phase anatase TiO2 and tetragonal SnO2 were both successfully synthesized by the templated method. SEM images (Fig. 1a and 1b) demonstrate that TiO2 and SnO2 are generally spherical structures with nanometer scale dimensions ranging from 250-350 nm and 450-500 nm, respectively. The interior hollow region can be seen clearly in the images of broken spheres. The shelled surface of the synthesized powders is hierarchically made up of interconnected nanocrystals providing a possibly porous structure. Hence, the hierarchically porous and hollow structure has a large surface area for adsorbing the LiPSs distributed in the electrolyte.Fig. 1c shows the charge and discharge voltage profiles of SnO2 and sulfur composite electrode cathode in the first five cycles. Two discharge plateaus were clearly observed, which might be attributed to the two-step sulfur-lithium reaction process. The initial plateau, centered about 2.30 V, was commonly attributed to the reduction of the S8 ring and the formation of S8 2−. The second discharge plateau at 2.10 V was attributed to further reduction of the higher polysulfides (Li2S n , 4 ≤ n ≤ 8) to the lower polysulfides (Li2S n , n ≤ 3). There exhibited two plateaus in the charge process at about 2.25 and 2.35 V, respectively. Electrochemical performance in relations to capacity retention and the in situ XAS to understand the behavior of the dissolution and migration of LiPSs will be discussed in the meeting. Figure 1

SiO2 Nanoparticle Coating to Enable Polyethylene-Based Na-Ion Battery Separators

The increasing demand for Li-ion batteries (LIBs), pushed even more by the electrical vehicle industry, has highlighted the concern with the scarcity and uneven distribution of LIB raw materials. Electrochemical energy storage based on alternative chemistries, once properly developed, may provide sufficient energy density to partly supply that demand, reducing the dependence on Li natural reserves. Among the studied chemistries, Na-ion-based storage is currently attracting a lot of research attention. This is partly due to the similarities between Li and Na, which allow for the utilisation of analogous materials and methods already in place for LIBs. However, not every component of LIBs can be directly applied to Na-ion batteries (SIB).[1] This is the case for battery separators, the membranes used to avoid physical contact between the two battery electrodes to prevent short circuiting while conducting ions from one battery pole to the other. Porous polyolefin films, such as polyethylene (PE) and polypropylene (PP), have been successfully used in LIBs, but are not compatible with SIB electrolytes. In the latter case, issues arise from the poor wettability of the separator with the electrolyte, which leads to low ionic conductivity, and creates an uneven flux of ions that can cause cell failure. To address this issue, previous reports have shown that the presence of inorganic oxides such as ZrO2 [2] and SiO2 [3] on polyolefin films can increase the affinity of the separator with commonly used LIB and SIB electrolytes. Moreover, ceramic-modified films also show higher thermal stability and hindered thermal shrinkage, which improves battery safety.In this work, we investigated PE coated with spherical SiO2 particles (designed by Glantreo, Ireland) with different sizes of 85 and 200 nm. The coatings were made by tape casting both sides of a PE film with slurries containing SiO2 particles and a binder. Binder type, SiO2 concentration and SiO2/binder ratio were optimized for each particle size. The obtained films were characterized by scanning electron microscopy and infrared spectroscopy, and were compared regarding their wettability, thermal stability, and ionic conductivity. The films were tested as separators in hard-carbon half-cells with 1 mol/L NaClO4 in either diethylene glycol dimethyl ether (DEGDME) or ethylene carbonate (EC)/ propylene carbonate (PC) electrolyte. With carbonate-based electrolyte, PE has very low wettability and cells short circuit within the first cycle. However, SiO2-PE samples showed higher wettability, which allowed for cycling at low current densities. In DEGDME-based electrolyte, cells with PE separator presented capacity fade, with 50% capacity loss after 250 cycles at 400 mA/g. On the other hand, cells with SiO2-PE separator had stable cycling for more than 300 cycles and no short-circuiting was observed, even when high active mass loading electrodes (8 mg/cm2) were used. These are promising results showing that a surface layer of SiO2 particles can make PE a viable option for SIB separators.

Precise arrangement of metal atoms at the interface by a thermal printing strategy.

The kinetics and pathway of most catalyzed reactions depend on the existence of interface, which makes the precise construction of highly active single-atom sites at the reaction interface a desirable goal. Herein, we propose a thermal printing strategy that not only arranges metal atoms at the silica and carbon layer interface but also stabilizes them by strong coordination. Just like the typesetting of Chinese characters on paper, this method relies on the controlled migration of movable nanoparticles between two contact substrates and the simultaneous emission of atoms from the nanoparticle surface at high temperatures. Observed by in situ transmission electron microscopy, a single Fe3O4 nanoparticle migrates from the core of a SiO2 sphere to the surface like a droplet at high temperatures, moves along the interface of SiO2 and the coated carbon layer, and releases metal atoms until it disappears completely. These detached atoms are then in situ trapped by nitrogen and sulfur defects in the carbon layer to generate Fe single-atom sites, exhibiting excellent activity for oxygen reduction reaction. Also, sites' densities can be regulated by controlling the size of Fe3O4 nanoparticle between the two surfaces. More importantly, this strategy is applicable to synthesize Mn, Co, Pt, Pd, Au single-atom sites, which provide a general route to arrange single-atom sites at the interface of different supports for various applications.