Lead adsorption behaviours on nanoscale zero valent irons (nZVI) coupled with rice husk MCM-41

The aims of this work were to investigate the characteristics of nanoscale zero valent irons (nZVI) coupled with mesoporous materials (RH-MCM-41) adsorbent and to study the removal mechanisms of Pb (II) from synthetical solutions using full pictorial design batch experiments. Synthetic nZVI coupled with RH MCM-41 as Pb (II) adsorbent were characterized by XRD, TEM, BET and XANES. The results of XANES analyses confirmed the ability of RH-MCM-41 to prevent oxidations of Fe0 to Fe2+ and Fe3+. XANES results also verified the oxidation states of Pb (II). The solution pH was the most significant positive effect in controlling Pb (II) adsorption. The equilibrium and kinetic adsorption isotherms well fitted with the Langmuir isotherm. The pseudo-second order kinetic adsorption indicated that the adsorption process is the rate limiting step for Pb (II) removal. Furthermore, Langmuir-Hinshelwood confirmed the obvious Pb (II) adsorption at the active site of adsorbents. The reduction rate constant (kr = 5,000 mg/L.min) was higher than the adsorption rate constant (Kad = 0.0002 L/mg). Regarding the research results, four pathways including: reduction process, adsorption on FeOOH, adsorption on RH-MCM-41 and complex reaction between Fe and Pb ions were suggested for Pb (II) removal by nZVI coupled with RH-MCM-41

The influence of CeF₃ on radiation hardness and luminescence properties of Gd₂O₃–B₂O₃ glass scintillator

The effect of CeF3 concentration and γ-irradiation on the physical, optical and luminescence properties of Gd2O3–B2O3–CeF3 glasses were studied in this work. Before irradiation, the addition of CeF3 in glass degraded the network connectivity observed from FTIR and possibly created the non-bridging oxygen (NBO) in glass structure. This NBO caused the reduction of Ce3+/Ce4+ ratio in XANES, the red-shift in transmission spectra and the raise of refractive index with addition of CeF3 content. Such red-shift also was influenced by 4f–5d transition of Ce3+ dopant. This ion generated the strongest photoluminescence (PL) and radioluminescence (RL) in 0.3 mol% CeF3-doped glass with nanoseconds decay time. The irradiation with γ-rays damaged the glass structure, broke the chemical bonds, and created color center in the glass network. The non-bridging oxygen hole center (NBOHC), that absorbed photons in the visible light region, caused the darkening, color change and increment of refractive index. These irradiation effects on glass were mitigated by the addition of CeF3 that the electron donation of Ce3+ decreased the number of NBOHC. The Ce3+/Ce4+ ratio in most glasses after irradiation then reduced compared to them before irradiation, resulting to the decrease in PL and RL intensity. Our results confirm that CeF3 can enhance the radiation hardness of glass and the 0.3 mol% CeF3-doped glass is a promising glass scintillator.Kaewnuam E., Wantana N., Ruangtaweep Y., et al. The influence of CeF₃ on radiation hardness and luminescence properties of Gd₂O₃–B₂O₃ glass scintillator. Scientific Reports 12, 11059 (2022); https://doi.org/10.1038/s41598-022-14833-3

Identification of Barium-Site Substitution of BiFeO3-Bi0.5K0.5TiO3 Multiferroic Ceramics: X-ray Absorption Near Edge Spectroscopy

In this work, the effects of barium substitution on the local structure, dielectric and magnetic properties of the polycrystalline ceramics 0.6BiFeO3–0.4(Bi0.5K0.5)TiO3 (0.6BFO–0.4BKT) system was investigated. A solid-state reaction technique was used to synthesize the materials with barium (Ba) doping of 1, 3, 5, 7, and 10 mol%. XRD analysis reveals the coexistence between tetragonal and rhombohedral phases of single-phase perovskite in pure 0.6BFO–0.4BKT and the rhombohedral reach phase was found with increasing Ba content. XANES simulations indicate that the majority of Ba atoms occupy A-site in BKT lattice of Ba-doped 0.6BFO-0.4BKT, the oxidation state of Fe, Ti, and Ba ions are +3, +4 and +2, respectively. At 5 mol% of Ba doping content, the dielectric measurement shows the morphotropic phase boundary (MPB) and the maximum value of ferromagnetic characteristic were observed, indicating an optimum composition, properties and production conditions

Role of Adsorption Phenomena in Cubic Tricalcium Aluminate Dissolution

The workability of fresh Portland cement (PC) concrete critically depends on the reaction of the cubic tricalcium aluminate (C₃A) phase in Ca- and S-rich pH >12 aqueous solution, yet its rate-controlling mechanism is poorly understood. In this article, the role of adsorption phenomena in C₃A dissolution in aqueous Ca-, S-, and polynaphthalene sulfonate (PNS)-containing solutions is analyzed. The zeta potential and pH results are consistent with the isoelectric point of C₃A occurring at pH ∼12 and do not show an inversion of its electric double layer potential as a function of S or Ca concentration, and PNS adsorbs onto C₃A, reducing its zeta potential to negative values at pH >12. The S and Ca <i>K</i>-edge X-ray absorption spectroscopy (XAS) data obtained do not indicate the structural incorporation or specific adsorption of SO₄^2– on the partially dissolved C₃A solids analyzed. Together with supporting X-ray ptychography and scanning electron microscopy results, a model for C₃A dissolution inhibition in hydrated PC systems is proposed whereby the formation of an Al-rich leached layer and the complexation of Ca–S ion pairs onto this leached layer provide the key inhibiting effect(s). This model reconciles the results obtained here with the existing literature, including the inhibiting action of macromolecules such as PNS and polyphosphonic acids upon C₃A dissolution. Therefore, this article advances the understanding of the rate-controlling mechanism in hydrated C₃A and thus PC systems, which is important to better controlling the workability of fresh PC concrete

An oxalate cathode for lithium ion batteries with combined cationic and polyanionic redox

Authors acknowledge financial support from the National Natural Science Foundation of China (51822210), the Australian Research Council (ARC) for its support through Discover Project (DP 140100193),Shenzhen Peacock Plan (KQJSCX20170331161244761), the Program for Guangdong Innovative and Entrepreneurial Teams (No. 2017ZT07C341), and the Development and Reform Commission of Shenzhen Municipality for the development of the “Low-Dimensional Materials and Devices” discipline.The growing demand for advanced lithium-ion batteries calls for the continued development of high-performance positive electrode materials. Polyoxyanion compounds are receiving considerable interest as alternative cathodes to conventional oxides due to their advantages in cost, safety and environmental friendliness. However, polyanionic cathodes reported so far rely heavily upon transition-metal redox reactions for lithium transfer. Here we show a polyanionic insertion material, Li2Fe(C2O4)2, in which in addition to iron redox activity, the oxalate group itself also shows redox behavior enabling reversible charge/discharge and high capacity without gas evolution. The current study gives oxalate a role as a family of cathode materials and suggests a direction for the identification and design of electrode materials with polyanionic frameworks.Publisher PDFPeer reviewe

Surface confinement of atomically thin Pt nanoclusters on 2D -MoN for durable pH-universal hydrogen evolution

Engineering precious metals’ sub-nanometer cluster on 2D earth-abundant supports provides a promising approach for the development of high-efficient electrocatalysts in pursuit of green hydrogen. Herein, a novel solid phase deposition approach is demonstrated for the homogenous confinement of atomically thin Pt nanoclusters on 2D delta-MoN as a viable catalyst for pH-universal hydrogen evolution reaction. Notably, the optimized material (MoN-5% Pt) exhibits excellent catalytic performance as evidenced by low overpotentials required, excellent mass activity exceeding 20 A mgPt−1 at 100 mV overpotential, and outstanding stability with negligible activity degradation. The enhanced performance is attributed to (1) novel nanostructure, constituting atomically thin Pt nanoclusters confined on 2D δ-MoN substrate, thus rendering high atomic utilization and seamless surface mass transfer, and (2) influence of strong metal-support interaction that effectively limits structural deformation and performance degradation. Theoretical simulations reveal that the strong metal-support interaction induces substantial charge redistribution across the heterointerface, initiating an energy-favorable multi-active site microkinetics in which Pt atoms with an optimal hydrogen adsorption energy making way for enhanced H2 evolution, while Mo atoms situated at the heterointerface enhance water absorption/dissociation steps, enriching the catalytic surface with adsorbed hydrogen atoms.Ministry of Education (MOE)This work was financially supported by the AcRF Tier 1 (grant RG105/19) provided by the Ministry of Education in Singapore

Surface activation of atomically thin metal nitride by confined nanoclusters to trigger pH-universal hydrogen evolution

Transition metal nitrides hold great potential for electrochemical conversion by virtue of metal-like electrical conductivity and robust electrochemical stability. Their applications, however, are still limited due to the sluggish kinetics stemming from the unfavorable surface electron properties. Herein, we demonstrate that the confinement of atomically thin Os nanoclusters onto 2D δ-MoN can favorably optimize the surface electron configurations, thereby boosting the material's catalytic performance. MoN-5% Os catalyst with optimal Os loading exhibits high catalytic performance, surpassing that of commercial Pt/C. The enhanced hydrogen evolution performance is attributed to (1) the unique 2D atomically thin nanoarchitecture exposing abundant active sites and (2) the strong electronic interaction between Os nanoclusters and δ-MoN nanosheets, which favorably modulates the surface microenvironment. Theoretical investigation reveals that the confined Os nanoclusters function as surface activators, efficiently modulating the electron properties of MoN, thereby accelerating the sluggish water adsorption and dissociation processes and triggering favorable hydrogen adsorption.Ministry of Education (MOE)This work was financially supported by the AcRF Tier 1 (grant RG105/19) provided by the Ministry of Education in Singapore. X.W. greatly acknowledge the startup grant by City University of Hong Kong (grant no. 9020005) and Hong Kong Branch of National Precious Metals Material Engineering Research Center - ITC Fund