Amorphous Shell Research Articles

Activation of peroxymonosulfate by MnOOH/g-C3N5: Study on highly selective removal of phenolic pollutants and its non-radical pathway

In this research, the MnOOH/g-C3N5 material was successfully synthesized, demonstrating its efficacy in selectively removing phenolic organic pollutants. This material outperformed traditional free radical pathways, exhibiting higher selectivity, enhanced persulfate utilization efficiency, and strong resistance to background anions and complex organic matter. Using phenol as the target pollutant, the MnOOH/g-C3N5/PMS system achieved 81 % mineralization, a PMS utilization efficiency of 88 %, and a 75 % process unit energy consumption value in degrading phenol. This efficient degradation is attributed to the synergistic effects of high-valence metal oxides (MnV(O)/MnIV(O)), singlet oxygen (1O2), and electron transfer complexes, as confirmed by electrochemical analysis and In-situ EPR. Additionally, Transmission Electron Microscopy observations disclosed the development of an amorphous shell on the MnOOH/g-C3N5 surface post-reaction. Electrochemical Impedance Spectroscopy analysis suggested an enhanced charge transfer resistance, further affirming the role of MnOOH/g-C3N5 as an "electron transfer station" in the electron transfer process, accompanied by the formation of electron transfer complexes. This study provides crucial scientific insights and theoretical guidance for applying MnOOH/g-C3N5 materials in environmental engineering.

Formation and agglomeration of nanoparticles and carbon debris in MnO2@C/GO

Carbon-loaded manganese dioxide (MnO2) nanoparticle materials have potential applications in energy storage and conversion, environmental and sensing applications. Carbon-coated MnO2 nanoparticles can avoid particle agglomeration. However, the process of forming MnO2 nanoparticles and carbon shells is unclear when carbon material is used as a carrier. In this work, the generation and convergence processes of nanoparticles and carbon debris were probed at bulk and monolayer levels using graphene oxide as carrier. And it is deduced that MnO2 nanoparticles first nucleate and aggregate at GO plane. As the size of the nanoparticles increases, the surrounding nanoparticles further aggregate. GO is etched during the formation of nanoparticles, resulting in the formation of carbon debris. Amorphous carbon shells are mainly formed by the aggregation of carbon debris. The MnO2@C/GO obtained was tested for H2O2 detection and showed superior H2O2 reduction properties.

Seed-Assisted Hydrothermal Synthesis of Monodispersed Au@C Core–Shell Nanostructures for Enhancing Thermal Diffusivity of Water-Based Nanofluids

Au@C core–shell nanostructures (Au@C-NS) were synthesized through a low-temperature seed-assisted hydrothermal approach using glucose as carbon source. The material characterization and chemical analysis confirm that the synthesis method allows to obtain uniform core–shell nanostructures constituted by a crystalline metal core and an amorphous carbon shell. Depending on the synthesis conditions, their average size ranges from 146 nm to 342 nm with relative standard deviation as low as 7 %. It is proposed that the characteristic monodispersity results due to a high nucleation rate of the carbon phase at the liquid–solid interface. The obtained monodisperse Au@C-NS were used to prepare water-based nanofluids with superior heat transport properties. The thermal lens analysis shows that the thermal diffusivity of Au@C nanofluids is 9.5 % and 31.3 % higher than their Au nanofluids counterparts and pure water, respectively, at particle concentration of 285 × 1011 ml−1. Phonon-related interactions at the metal cores and carbon shells interfaces are proposed as the heat transport mechanism behind the thermal diffusivity enhancement of the Au@C water-based nanofluids.

Significant improvement in the removal performance of decimeter-sized zero-valent iron plates for mixed heavy metal ions in wastewater by enhancing surface sharpness

This study aims to lower the work function (Wa) of a decimeter-sized zero-valent iron plate (DZVIP) by introducing surface sharpness (TDZVIP) during stirring. Sharpness was achieved by cutting isosceles triangles with heights of 1 cm and varying apex angles (α) of 10˚, 20˚, 30˚, 40˚, and 50˚. A mixed simulated wastewater containing Cu(II), Te(IV), Se(IV), As(III), Bi(III), and Pb(II) at concentrations exceeding emission standards was prepared. Results indicate that the removal process exhibits mixed kinetic behavior, and sharpness significantly enhances the removal capacity (Re), mean removal rate (Vm), recycling performance, and final discharge quality. The Vm values for Cu(II), Te(IV), Se(IV), As(III), Bi(III), and Pb(II) over TDZVIP with optimized α are 2.34, 1.97, 1.51, 1.59, 4.09, and 1.53 times higher, respectively, than those over PDZVIP (without sharpness). UPS measurements provide direct evidence of Wa reduction, while XRD offers indirect confirmation. This is the first time the Wa of the amorphous shell has been identified and verified as a critical potential barrier for core electrons transferring from the DZVIP surface to wastewater. Additionally, it has been successfully reduced by incorporating surface sharpness and stirring, leading to enhanced removal efficiency, improved recycling performance, and higher final discharge quality.

Probing the Nanonewton Mitotic Cell Deformation Force by Ion-Resonance-Enhanced Photonics Force Microscopy.

Mechanical forces are essential for regulating dynamic changes in cellular activities. A comprehensive understanding of these forces is imperative for unraveling fundamental mechanisms. Here, we develop a microprobe capable of facilitating the measurement of biological forces up to nanonewton levels in living cells. This probe is designed by coating the core of anatase titania particles with amorphous titania and silica shells and an upconversion nanoparticles (UCNPs) layer. Leveraging both antireflection and ion resonance effects from the shells, the optically trapped probe attains a maximum lateral optical trap stiffness of 14.24 pN μm-1 mW-1, surpassing the best reported value by a factor of 3. Employing this advanced probe in a photonic force microscope, we determine the elasticity modulus of mitotic HeLa cells as 1.27 ± 0.3 kPa. Nanonewton probes offer the potential to explore 3D cellular mechanics with unparalleled precision and spatial resolution, fostering a deeper understanding of the underlying biomechanical mechanisms.

Formation mechanism and luminescence properties of silicon carbide nanowires with core-shell structure

For the preparation of SiC nanowires (SiC NWs) by carbothermal reduction, it is of great significance to study the formation mechanism of sic nanowires for process optimization and the controllable preparation. Although first-principles molecular dynamics (FPMD) can simulate systems of hundreds of atoms on a picosecond time scale, the results of FPMD are still insufficient to elucidate the formation mechanism of core-shell SiC nanowires. To make up this deficiency, this article has conducted Deep Potential Molecular Dynamics (DPMD) simulation on nanoseconds timescales with near FPMD accuracy for systems containing thousands of atoms, the results more concretively show the formation process of core-shell SiC nanowires. DPMD simulation results show when CO molecules react with SiO molecules, CO molecules are wrapped by SiO molecules to form agglomerates, SiO molecules in the agglomerates that can come into contact with the wrapped CO molecules will react with wrapped CO molecules to form the SiC core, and SiO molecules that in the outer layer of the agglomerates will disproportionate into the amorphous SiO2 shell. Furthermore, the formation mechanism of SiC nanowires was validated in combination with thermodynamics and experimental methods. Thermodynamic results show that vacuum conditions are favorable for the formation of SiO and CO and lower the temperature of SiC preparation. Finally, the core-shell structure of SiC NWs with good luminescence properties were successfully prepared by carbothermal reduction method using carbon black and silicon dioxide as raw materials under the pressure of less than 5 kPa.

Room Temperature Synthesis of Tellurium by Solution Atomic Layer Deposition.

This study demonstrates the deposition of tellurium (Te) on silicon/silicon nitride substrates using solution atomic layer deposition (sALD) at ambient temperature. The process employs tellurium tetrachloride (TeCl4) and bis(triethylsilyl)-telluride ((TES)2Te) as precursors, with toluene as the solvent. Growth parameters were optimized through systematic variation of the pulse and purge times. Morphological characterization via scanning and transmission electron microscopy revealed needle-like crystallites, while X-ray diffractometry confirmed the crystalline nature of the deposited Te. Increasing the number of deposition cycles resulted in larger Te crystallites and enhanced substrate surface coverage. A thin amorphous carbon shell surrounding the crystallites and carbon inclusions was observed, likely originating from the organic solvent. X-ray photoemission spectroscopy analysis indicated high-purity Te films with minimal surface oxidation. The small chlorine signal suggested a near-complete precursor reaction and the efficient purging of byproducts. This novel sALD approach presents a promising method for depositing Te on various surfaces under mild conditions.

Resurfacing of InAs Colloidal Quantum Dots Equalizes Photodetector Performance across Synthetic Routes.

The synthesis of highly monodispersed InAs colloidal quantum dots (CQDs) is needed in InAs CQD-based optoelectronic devices. Because of the complexities of working with arsenic precursors such as tris-trimethylsilyl arsine ((TMSi)3As) and tris-trimethylgermyl arsine ((TMGe)3As), several attempts have been made to identify new candidates for synthesis; yet, to date, only the aforementioned two highly reactive precursors have led to excellent photodetector device performance. We begin the present study by investigating the mechanism, finding that the use of the cosurfactant dioctylamine plays a crucial role in producing monodispersed InAs populations. Through quantitative analysis of ligands on the surface of InAs CQDs, we find that (TMGe)3As leads to In-rich characteristics, and we document the presence of an amorphous In-oleate shell on the surface. This we find causes surface defects, and thus, we develop materials processing strategies to remove the surface shell with a view to achieving efficient charge transfer in CQD solids. As a result, we develop resurfacing protocols, tailored to each dot synthesis, that produce balanced In-to-As stoichiometry regardless of synthetic input, enabling us to fabricate NIR photodetectors that achieve best-in-class EQEs at 940 nm excitons (25-28%, biased), independent of the synthetic pathway.

Colloidal TiO2 nanocrystals with engineered defectivity and optical properties.

Partially reduced forms of titanium dioxide (sometimes called "black" titania) have attracted widespread interest as promising photocatalysts of oxidation due to their absorption in the visible region. The main approaches to produce it rely on postprocessing at high temperatures (up to 800 °C) and high pressures (up to 40 bar) or on highly reactive precursors (e.g., TiH2), and yield powders with poorly controlled sizes, shapes, defect concentrations and distributions. We describe an approach for the one-step synthesis of TiO2 colloidal nanocrystals at atmospheric pressure and temperatures as low as 280 °C. The temperature of the reaction allows the density of oxygen vacancies to be controlled by nearly two orders of magnitude independently of their size, shape, or colloidal stability. This synthetic pathway appears to produce vacancies that are homogeneously distributed in the nanocrystals, rather than being concentrated in an amorphous shell. As a result, the defects are protected from oxidation and result in stable optical properties in oxidizing environments.

Enhanced solar urea synthesis from CO2 and nitrate waste via oxygen vacancy mediated-TiOx support lead-free perovskite

The nitrogen fertilizer industry, particularly urea production, notably contributes to greenhouse gas emissions and energy consumption. Urea synthesis via solar energy encounters several challenges. Specifically, solar urea synthesis methods often exhibit low efficiency and yield, primarily stemming from inefficient energy conversion processes and intricate reaction pathways. Moreover, the kinetics of the urea synthesis reaction may be sluggish, thereby impacting the overall production rate. Therefore, in this study, we introduce a novel electron-reserve-enhanced Cs2CuBr4/TiOx-Ar (CCBT-Ar) structure for the photocatalytic synthesis of urea from CO2 and nitrate waste. Theoretical calculations and spectroscopic analysis underscore the critical role of oxygen vacancies (Ov) within the amorphous TiOx shell, enhancing reactant adsorption and catalyzing the rate-determining step (*OCONH2→*HOCONH2). However, the presence of Ov also results in significant carrier recombination, acting as trapping centers and reducing urea production activity. Importantly, we demonstrate that in-situ-grown carbon nanosheets, in conjunction with TiOx, function as efficient electron reservoirs, markedly mitigating trapping-induced recombination and facilitating electron redistribution. These reserved electrons can then actively participate in the urea synthesis process. As a result, the electron-reserve-enhanced structure exhibits robust solar urea yield and selectivity, even in challenging wastewater conditions. This work provides a rational and innovative approach to catalyst development in complex solar synthesis, offering promising avenues for the sustainable production of value-added chemicals while concurrently reducing carbon emissions.

Facile synthesis of nano-si/graphite-carbon anode through microwave-induced carbothermal shock for lithium-ion batteries

We present a cost-effective synthesis process for producing a carbon-coated nano-Si@Graphite (n-Si@G-C) anode, in which nano-sized Si (n-Si) particles (∼50 nm in size) are anchored onto natural graphite particles by a carbothermal shock through microwave induction. During the carbothermal shock process, graphite undergoes a fast increase in temperature resulting in micron-sized Si (m-Si) particles (∼4 μm in size) to undergo stress fractures due to rapid thermal expansion. This process leads to the formation of abundant n-Si particles onto graphite particles. Subsequently, a thin carbon shell is introduced by a wet-coating process combined with a thermal decomposition of coal-tar pitch. The amorphous carbon shell offers multiple functionalities: i) preventing direct exposure of n-Si particles to the electrolyte, ii) accommodating their volume expansion, and iii) maintaining electron conduction pathways. The resulting n-Si@G-C anode allows a high reversible capacity (500.8 mAh g−1) as well as fast-charging characteristics. When utilized in a full-cell configured with a commercial-grade LiNi0.8Co0.1Mn0.1O2 cathode, it achieves a notable reduction in charging time (approximately 10.1 min@80 % state of charge). After 300 cycles, a high capacity retention (71.3 %) can be retained under 3C charging. Moreover, the distinctive structural features of the n-Si@G-C anode effectively suppress undesirable Li plating.

Predicting buckling regimes during first lithiation of a crystalline silicon cylindrical anode particle: Influence of size and charging rate

A mathematical model for buckling analysis during the first lithiation of cylindrical crystalline silicon (c-Si) anode particles is presented using the finite deformation framework. A reaction–diffusion model that incorporates a reversible alloying–dealloying reaction (ADR) captures the lithiation in the expanding amorphous zone, while an addition reaction models the dynamics of the crystalline-amorphous silicon interface. A “movable” lithium part and an “immovable” lithium part make up the full lithium. In sharp contrast to the case of amorphous silicon (a-Si), the axial force evolution in c-Si is found to show two different peaks during the initial and final stages of lithiation, respectively. These peaks form the basis of two different buckling criteria, which, in turn, are shown to be sensitively influenced by the influx of lithium and a crucial size-dependent parameter. This framework gives an insight towards investigating the buckling phenomena for lithiation with an evolving amorphous silicon zone due to the interface movement, which is still absent in the present literature. Additionally, the present model enables us to obtain a quantitative and mechanistic insight into and capture the previous experimental observation that the mechanical stability of a cylindrical silicon particle may be improved by maintaining a crystalline silicon core inside the amorphous shell through controlled first lithiation. It is shown that such a crystalline-amorphous core–shell structure can be advantageous to more complicated designs involving carbon fiber as the core. It is thus hoped that this model will contribute towards improving the theoretical underpinnings of an improved design of mechanically robust electrodes for next-generation batteries.

Preparation and anti-oxidation performance of TaC-SiC nanocomposites by precursor-derived ceramic method

As a kind of ultra-high temperature ceramic, TaC is widely used in aerospace field. In order to improve its high temperature oxidation resistance, SiC is usually added as a second phase. TaC-SiC nanocomposites prepared by precursor-derived ceramic method have the advantages of low pyrolysis temperature, small particle size and uniform phase composition. Some studies have used solid polycarbosilane (PCS) as the precursor of SiC. However, it has problems such as high cost and need to add solvent. In this work, TaC-SiC nanocomposites were prepared by precursor-derived ceramic method with polytantaloxane (PTO) and vinyl-containing liquid polycarbosilane (LPVCS) instead of PCS as raw materials after 2 h pyrolysis at 1600 °C. The obtained TaC-SiC nanocomposites have a particle size of about 200 nm and a grain size of 15–40 nm, wrapped by 1–2 nm amorphous carbon shells, which is beneficial to inhibit grain growth. By analyzing the oxidation mechanism of TaC-SiC nanocomposites, it was found that higher SiC content was conducive to antioxidant, because the SiO2 protective layer formed by oxidation insulated O2 diffusion.

Insights into the nature of Zr-species in MFI-type Zr-metallosilicates by using bulk and surface techniques

The purpose of this study is to prepare Zr-metallosilicates with MFI-type framework via direct hydrothermal approach, by varying Si and Zr precursors. First, a set of routine characterization techniques was applied to confirm the presence of the targeted structure as well as their intrinsic properties. Results suggest the formation of MFI-type materials with large specific surface areas (up to 421 m2 g−1). Then, a combination of advanced spectroscopic techniques (XPS, ToF-SIMS, EPR), high-resolution microscopy, and periodic Density Functional Theory (DFT) calculations were applied to study their bulk and surface properties as well as the nature and localization of Zr-species. It appears that the insertion of zirconium atoms within a MFI framework is energetically unfavorable, leading to the formation of an amorphous silica-zirconia shell coating the zeolite crystals.

Cu1−Fe Dual Sites for Superior Neutral Ammonia Electrosynthesis from Nitrate

AbstractThe electrochemical nitrate reduction reaction (NO3RR) is able to convert nitrate (NO3−) into reusable ammonia (NH3), offering a green treatment and resource utilization strategy of nitrate wastewater and ammonia synthesis. The conversion of NO3− to NH3 undergoes water dissociation to generate active hydrogen atoms and nitrogen‐containing intermediates hydrogenation tandemly. The two relay processes compete for the same active sites, especially under pH‐neutral condition, resulting in the suboptimal efficiency and selectivity in the electrosynthesis of NH3 from NO3−. Herein, we constructed a Cu1‐Fe dual‐site catalyst by anchoring Cu single atoms on amorphous iron oxide shell of nanoscale zero‐valent iron (nZVI) for the electrochemical NO3RR, achieving an impressive NO3− removal efficiency of 94.8 % and NH3 selectivity of 99.2 % under neutral pH and nitrate concentration of 50 mg L−1 NO3−−N conditions, greatly surpassing the performance of nZVI counterpart. This superior performance can be attributed to the synergistic effect of enhanced NO3− adsorption on Fe sites and strengthened water activation on single‐atom Cu sites, decreasing the energy barrier for the rate‐determining step of *NO‐to‐*NOH. This work develops a novel strategy of fabricating dual‐site catalysts to enhance the electrosynthesis of NH3 from NO3−, and presents an environmentally sustainable approach for neutral nitrate wastewater treatment.

Cu1-Fe Dual Sites for Superior Neutral Ammonia Electrosynthesis from Nitrate.

The electrochemical nitrate reduction reaction (NO3RR) is able to convert nitrate (NO3 -) into reusable ammonia (NH3), offering a green treatment and resource utilization strategy of nitrate wastewater and ammonia synthesis. The conversion of NO3 - to NH3 undergoes water dissociation to generate active hydrogen atoms and nitrogen-containing intermediates hydrogenation tandemly. The two relay processes compete for the same active sites, especially under pH-neutral condition, resulting in the suboptimal efficiency and selectivity in the electrosynthesis of NH3 from NO3 -. Herein, we constructed a Cu1-Fe dual-site catalyst by anchoring Cu single atoms on amorphous iron oxide shell of nanoscale zero-valent iron (nZVI) for the electrochemical NO3RR, achieving an impressive NO3 - removal efficiency of 94.8 % and NH3 selectivity of 99.2 % under neutral pH and nitrate concentration of 50 mg L-1 NO3 --N conditions, greatly surpassing the performance of nZVI counterpart. This superior performance can be attributed to the synergistic effect of enhanced NO3 - adsorption on Fe sites and strengthened water activation on single-atom Cu sites, decreasing the energy barrier for the rate-determining step of *NO-to-*NOH. This work develops a novel strategy of fabricating dual-site catalysts to enhance the electrosynthesis of NH3 from NO3 -, and presents an environmentally sustainable approach for neutral nitrate wastewater treatment.

Stöber method to amorphous metal-organic frameworks and coordination polymers

The Stöber method is a widely-used sol-gel route for synthesizing amorphous SiO2 colloids and conformal coatings. However, the material systems compatible with this method are still limited. Herein, we have extended the approach to metal-organic frameworks (MOFs) and coordination polymers (CPs) by mimicking the Stöber method. We introduce a general synthesis route to amorphous MOFs or CPs by making use of a base-vapor diffusion method, which allows to precisely control the growth kinetics. Twenty-four different amorphous CPs colloids were successfully synthesized by selecting 12 metal ions and 17 organic ligands. Moreover, by introducing functional nanoparticles (NPs), a conformal amorphous MOFs coating with controllable thickness can be grown on NPs to form core-shell colloids. The versatility of this amorphous coating technology was demonstrated by synthesizing over 100 core-shell composites from 20 amorphous CPs shells and over 30 different NPs. Besides, various multifunctional nanostructures, such as conformal yolk-amorphous MOF shell, core@metal oxides, and core@carbon, can be obtained through one-step transformation of the core@amorphous MOFs. This work significantly enriches the Stöber method and introduces a platform, enabling the systematic design of colloids exhibiting different level of functionality and complexity.

Preparation and Characterization of Graphite-SiO2 Composites for Thermal Storage Cement-Based Materials.

Thermal storage cement-based materials, formed by integrating phase change materials into cementitious materials, exhibit significant potential as energy storage materials. However, poor thermal conductivity severely limits the development and application of these materials. In this study, an amorphous SiO2 shell is encapsulated on a graphite surface to create a novel thermally modified admixture (C@SiO2). This material exhibits excellent thermal conductivity, and the surface-encapsulated amorphous SiO2 enhances its bond with cement. Further, C@SiO2 was added to the thermal storage cement-based materials at different volume ratios. The effects of C@SiO2 were evaluated by measuring the fluidity, thermal conductivity, phase change properties, temperature change, and compressive strength of various thermal storage cement-based materials. The results indicate that the newly designed thermal storage cement-based material with 10 vol% C@SiO2 increases the thermal conductivity coefficient by 63.6% and the latent heat of phase transition by 11.2% compared to common thermal storage cement-based materials. Moreover, C@SiO2 does not significantly impact the fluidity and compressive strength of the thermal storage cement-based material. This study suggests that C@SiO2 is a promising additive for enhancing thermal conductivity in thermal storage cement-based materials. The newly designed thermal storage cement-based material with 10 vol% C@SiO2 is a promising candidate for energy storage applications.

Purification of carbon nanotubes for dissolution in chlorosulfonic acid

Carbon nanotubes (CNTs) can be scalably processed into high-performance fiber with a low environmental footprint by solution spinning from chlorosulfonic acid (CSA). CNTs are produced by numerous manufacturers, but CNTs typically need to undergo purification to improve solubility in CSA. For over two decades, oxidative techniques have been used to remove amorphous carbon species to improve CNT dissolution in acid. However, more recent work has attributed the improved solubility after single-walled carbon nanotube (SWCNT) oxidation to the inclusion of oxygen groups in the sidewall of the SWCNT. Here, we refute the recent claim that oxidation incorporates oxygen into the sidewall of CNTs to improve CNT dissolution to CSA. Instead, we provide experimental evidence in support of classical purification literature: at the appropriate time and temperature, oxidation removes amorphous carbon shells and defective SWCNTs without oxidizing the SWCNT sidewall. Once these amorphous carbon shells are removed, CSA can access and protonate the sp2-bonded carbon sites, which results in SWCNT dissolution. Additionally, we explore how oxidation conditions impact SWCNT aspect ratio (length of CNT divided by CNT diameter), which directly controls macroscale fiber properties.

Microstructure characterization and growth mechanism of ZrC whiskers prepared by precursor transformation method

ZrC whiskers were prepared on graphite through precursor transformation method. Effects of heat treatment temperature, catalyst concentration and heat treatment time on phase composition and microstructure of the ZrC whiskers were investigated. Growth mechanism of the ZrC whisker was analyzed. Results indicated that as heat treatment temperature increasing, catalyst activity increased and energy barrier for the carbothermal reduction reaction reduced, resulting in a gradual increase of both production and diameter of the ZrC whiskers. Catalyst could provide nucleation points for the ZrC whiskers, production and diameter of the ZrC whiskers firstly increased as the catalyst concentration increasing. While, when catalyst concentration was over high, length-diameter ratio of the ZrC whiskers decreased and some whiskers were agglomerated. Heat treatment time affected extent of the carbothermal reduction reaction. Production and length-diameter ratio of the ZrC whiskers increased firstly and then decreased with the increase of heat treatment time. When heat treatment temperature was 1600 °C, catalyst concentration was 0.4 mol/L, heat treatment time was 2 h, the ZrC whiskers with diameter of around 130 nm and length of tens of microns were synthesized. The whiskers were composed of a single-crystal ZrC core and an amorphous ZrO2 shell. Growth of the ZrC whiskers was controlled by solid-liquid-solid (S-L-S) mechanism and the Ostwald ripening mechanism.