Wide Interlayer Research Articles

Bonding of crown ethers to α-zirconium phosphate—Novel layered adsorbent for radioactive strontium separation

Searching for new efficient, selective, and stable, adsorbents for 90Srgenerated in the nuclear fuel cycle remains important. In the last year, 18 crown 6ether and its derivatives have been intensively studied as highly efficient ion-exchangers for removal of 90Sr. However, one of the main problems for further application of these expensive macrocyclic ligands is loss in solid-liquid media due to their solubility. To overcome this problem, in this work, we have developed a new organic – inorganic layer α-ZrP composite by intercalation of 4-amino-benzo-18 crown 6. This new α-ZrP composite (AM-ZrP) not only inherits the advantages of 4-amino-benzo-18 crown 6 and α-ZrP, exhibiting excellent stability under acid and radioactive conditions, but also efficiently decreases the loss of valuable4-amino-benzo-18 crown 6 in the adsorption process. Furthermore, the preparation process for AM-ZrP is simple and it can be easily produced on a large-scale. Remarkably, having a pore size matching4-amino-benzo-18 crown 6, AM-ZrP shows high selectivity for capturing Sr2+ from complicated mixed solutions. The maximum adsorption capacity for Sr2+ onto AM-ZrP is 320.16 mg·g−1, which is about five times that of neat α-ZrP. Itsurpasses most other inorganic adsorbents, which can be attributed to the much higher number of adsorption sites and the wide interlayer spacing of α-ZrP after interactionwith4-amino-benzo-18 crown 6. Our present work not only poses a new way to promote crown ether compounds and α-ZrP materials, furthering their application in nuclear wastewater disposal, but also develops a new way of thinking about the design and preparation of new adsorbents for removal of difficult-to-capture ions from nuclear wastewater.

A facile and cost effective synthesis of nitrogen and fluorine Co-doped porous carbon for high performance Sodium ion battery anode material

The development of cost effective, high performance, electrode materials for sodium ion batteries is of critical importance for large scale energy storage. Herein, we synthesize a novel nitrogen and fluorine co-doped porous carbon using a facile one-pot pyrolysis of three low cost components: polytetrafluoroethylene, a nitrogen-containing resin, and potassium hydroxide. The co-doped carbon comprises 3D assemblies of highly porous sheets with defects/disorders (and wide interlayer spacing of ~0.42 nm), which have a large surface area of 2040.3 m2 g−1 with hierarchical pore sizes. The advantageous combination of these structural features facilitates high sodium ion storage capacity, fast transfer kinetics and stable cycling. As a result, the co-doped carbon delivers an impressive 312.6 mAh g−1 at 0.1 A g−1 after 300 cycles and 215.3 mAh g−1 at 5 A g−1 after 5000 cycles (or 0.005% loss per cycle). Therefore, the excellent cycling performance of the carbon in combination with its convenient and low cost synthesis offers a promising sodium ion battery anode material for large scale energy storage.

Efficient removal of iodide anion from aqueous solution with recyclable core-shell magnetic Fe3O4@Mg/Al layered double hydroxide (LDH)

Magnetic Mg/Al layered double hydroxides (LDH) with three cationic ratios (Mg/Al = 2:1, 3:1, and 4:1) were successfully synthesized and utilized for the first time in an iodide adsorption study. The effects of the Mg/Al ratio of LDH on iodide adsorption were investigated, and physicochemical properties of synthetic LDHs depending on Mg/Al ratio were confirmed by XRD, TEM, ICP-OES, VSM, Zeta-potential, and BET analyses. The ferrimagnetic property was well preserved even after a coating of LDH on magnetite irrespective of the Mg/Al ratio. Among the three Mg/Al ratios, the calcined Fe3O4@4:1 Mg/Al LDH exhibited excellent performance for iodide removal with 105.04 mg/g of the maximum iodide adsorption capacity due to its wide interlayer spacing and largest BET surface area. In the presence of competing carbonate anions, the Fe3O4@4:1 LDH showed removal rate of >80% at a dosage of over 3 g/L solid to liquid ratio. The recyclability test of Fe3O4@4:1 LDH showed that the removal performance for iodide is maintained at >80% even during the first to the fourth cycles. These results demonstrated that the magnetic Mg/Al LDH adsorbent can be effectively utilized for remediation of radioactive iodide anions with high efficiency and economics.

Uncovering the underlying science behind dimensionality in the potassium battery regime

Compared to the significant advances in its lithium and sodium analogue, the practical application of potassium ion batteries (KIBs) has been hindered by the sluggish K ion diffusion. Electrochemical storage via insertion/de-insertion reactions in lamellar electrode materials critically rests upon the host materials with wide interlayer spacing and the sizes of the guest ions. To uncover the underlying science behind the dimensionality in the KIBs regime, we investigated MoS2/K half-cell using uniform MoS2 rod, sheet, and sphere structures synthesized by a facile and controllable method for the first time. Impressively, when MoS2 is in the shape of a hierarchical rod, there is more intercalation pseudocapacitance (74.8% at the scan rate of 1.5 mV s−1) and the optimized electrode resulted in high-rate capacity (320 and 183 mAh g−1 at 0.1 and 1 A g−1, respectively). In contrast, MoS2 sheet and sphere contribute little pseudocapacitance (69.1% and 61.4%, respectively) and therefore exhibit low-rate capacity (232 and 110 mAh g−1 for MoS2 sheet, 185 and 96 mAh g−1 for MoS2 sphere at 0.1 and 1 A g−1, respectively). Density functional theory (DFT) results uncover that the K atom is much more liable to occupy the octahedral (Oh) site. What’s more, non-destructively 3D reconstruction of MoS2 rod electrode strongly demonstrated the integrity of the rod structure after K+ insertion. The work paves a new way for the design of two dimensional (2D) materials and offers profound insights into the charge storage mechanism of KIBs.

Gas-liquid diffusion synthesis of different Ni(OH)2 nanostructures for their supercapacitive performance

The wide interlayer spacing can improve charge transfer rate and release the internal strain during the discharge-charge processes. The interlayer spacing and crystal phase of Ni(OH)2 nanocrystals are generally associated with the introduction of various anions. In this study, we have prepared four kinds of Ni(OH)2 nanocrystals with a simple gas-liquid route by simply altering the Ni salts. The crystal phases of the obtained Ni(OH)2 nanostructures can be controlled by the introduction of nitrate, chlorine, acetate and sulfate anions respectively. The electrochemical test results indicate that flake-like Ni(OH)2 prepared using nickel acetate exhibits the largest charge storage capacity and capacitance value can be reached 2018 F g−1 at 10 A g−1 current density in 2 mol L−1 KOH electrolyte.

Pressure‐Driven Solvent Transport and Complex Ion Permeation through Graphene Oxide Membranes

AbstractIn this paper, an in‐depth investigation of three graphene oxide (GO) based membranes—pure GO, Al3+ intercalated GO (Al‐GO), and poly(ethylene glycol) (PEG) modified GO (PEG‐GO)—is presented. Both Al‐GO and PEG‐GO membranes have wider interlayer d‐spacing compared to pure GO, and the d‐spacing size correlates well to the cross‐membrane water flux with JPEG‐GO > JAl‐GO > JGO. Pressure‐driven transport of water/ethanol mixtures across all three types of GO membranes is dominated by solvent viscosity—not solvent polarity showing distinctively semi‐hydrophilic membrane characteristics. Interestingly, the results suggest that both ethanol cluster size and molecular geometry contribute to preferential ethanol rejection, indicating that both GO and Al‐GO membranes possess superior size sieving capability. Further, the lower permeation of tris(1,10‐phenanthroline)ruthenium(II) (Ru(phen)32+) compared to the charge‐equivalent smaller‐sized tris(bipyridine)ruthenium(II) (Ru(bpy)32+) demonstrates the excellent steric selectivity of GO membranes. Compared to pure GO, the widened d‐spacing in PEG‐GO allows ≈100% higher ion permeation while ion flux through Al‐GO is an order of magnitude lower, suggesting the significant role of electrostatic interaction in ion transport. In conclusion, these findings ought to enrich the understanding of the GO‐based membranes and enable future rational designs for a wide range of applications, including water purification and solvent separation.

Facile synthesis and improved Li-storage performance of Fe-doped MoS2/reduced graphene oxide as anode materials

MoS2 nanosheets have been widely explored as LIB anode materials due to higher theoretical capacity and weak interlayer interactions, but limited by their low conductivity and ease of stacking. Herein, we reported a novel Fe doped MoS2/reduced graphene oxide (Fe-MoS2/rGO) composite as LIB anode material and its one-step synthesis method. The results show that the synthesized Fe-MoS2/rGO composite has unique porous heterostructure, where networked Fe-MoS2 nanosheets of several nm thickness grow upon crumpled rGO sheets with high specific area. Due to the Fe doping as well as the mild synthesis conditions, the resulting Fe-MoS2 upon rGO sheets has wide interlayer spacing, abundant lattice defects and lower inner resistance. As a result, the Fe-MoS2/rGO electrode exhibits significant improvement in electrochemical performance relative to the non-doped MoS2/rGO electrode. The reversible capacities of Fe-MoS2/rGO electrode reach 1255 mAh/g (2nd circle) and 946 mAh g−1 (100th circle) with a retention of 75.4%. By comparison, the reversible capacities of MoS2/rGO electrode are only 654.1 mAh g−1 (2nd circle) and 429 mAh g−1 (100th circle) with a low retention of 64.1%.

Two-dimensional V4C3 MXene as high performance electrode materials for supercapacitors

Two-dimensional (2D) MXenes such as Ti3C2, Ti2C, Mo2C, and Mo1.33C have shown excellent electrochemical performances as supercapacitor electrodes, and the exploration of new and/or high-capacity MXene-based supercapacitor electrode materials is an active field. In this work, 2D multi-layered V4C3 MXene has been synthesized by selectively etching Al from V4AlC3 and it shows a high capacitance of 209 F g−1 at 2 mV s−1, good rate performance, and stable long cyclic performance with capacitance retention rate of 97.23% after 10000 cycles at 10 A g−1 in 1 M H2SO4. Importantly, the pseudocapacitance (∼100.1 F g−1) accounts for about 37% of the total capacity (∼268.5 F g−1) for V4C3 MXene electrode. Therefore, the high specific capacitance of V4C3 MXene is not only due to their wide interlayer spacing (∼0.466 nm), large specific surface areas (∼31.35 m2 g−1) and pore volumes (∼0.047 cm3 g−1), and good hydrophilicity but also attributed to the abundant valence states of vanadium (+2, +3, and +4). The high rate performance and excellent cycling stability of V4C3 MXene electrodes are mainly attributed to the high electronic conductivity (1137 S m−1 at 300 K). The present work provides another promising MXene-based supercapacitor electrode material.

Triazine-graphdiyne: A new nitrogen-carbonous material and its application as an advanced rechargeable battery anode

Existing methodological strategies for the doping of nitrogen (N) atoms in carbon materials usually contain more than one species with indefinite N content, which made it difficult to study the role of each type of N atoms played duing the doping and severely restrict the wide application. Herein, we reported a developed synthetic strategy for preparing carbonous materials contained with specific N atoms. The well-defined carbonous network triazine-graphdiyne (TA-GDY), which comprising merely one type of N atoms with fixed amount, has been prepared through bottom-up way with triethynyltriazine as the starting molecule. TA-GDY is an unique two-dimensional (2D) carbonous material, including sp- and sp2-hybridized carbon atoms, as well as quantitative pyridine-like sp2-hybridized N atoms. All the N atoms are placed on the plane of the carbon skeleton, and the high N content provides plenty of active heteroatom sites decorated uniformly in the hexagonal honeycomb-like pores. Based on theoretical prediction, the wide interlayer spacing and large amount of pyridinic-N as well as uniform honeycomb-like pores are favorable for Li-ion storage and diffusion. As expected, the TA-GDY-based electrodes exhibit outstanding Li-ion storage performance, such as superior rate capability, larger capacity, and excellent stability.

Nitrogen‐Doped Graphdiyne as High‐capacity Electrode Materials for Both Lithium‐ion and Sodium‐ion Capacitors

AbstractNitrogen‐doped graphdiyne (N‐GDY) is prepared through the nitriding of graphdiyne (GDY) under ammonia. This material possesses excellent ability for the fast diffusion and storage of lithium and sodium ions due to its high conductivity, wide interlayer distance, unique three‐dimensional porous structure, and associated defects from nitrogen doping. The lithium‐ion capacitor (LIC) and sodium‐ion capacitor (SIC) fabricated with N‐GDY as the negative electrode show outstanding electrochemical performance, especially having both high power density and energy density. Besides exhibiting an energy density of 174 Wh kg−1, the N‐GDY‐based LIC can still offer an energy density of 107 Wh kg−1 even at a power density of 11250 W kg−1, whereas the N‐GDY‐based SIC can retain an energy density of 119 Wh kg−1 at a power density of 22500 W kg−1. The energy densities of N‐GDY‐based LIC and SIC are higher than those of pure GDY and many other carbon materials.

Graphdiyne for Electrochemical Energy Storage Devices

Electrochemical energy storage devices are becoming increasingly important in modern society for efficient energy storage. The use of these devices is mainly dependent on the electrode materials. As a newly discovered carbon allotrope, graphdiyne (GDY) is a two-dimensional full-carbon material. Its wide interlayer distance (0.365 nm), large specific surface area, special three-dimensional porous structure (18-C hexagon pores), and high conductivity make it a potential electrode material in energy storage devices. In this paper, based on the facile synthesis method and the unique porous structure of GDY, the applications of GDY in energy storage devices have been discussed in detail from the aspects of both theoretical predictions and recent experimental developments. The Li/Na migration and storage in mono-layered and bulk GDY indicate that GDY-based batteries have excellent theoretical Li/Na storage capacity. The maximal Li storage capacity in mono-layered GDY is LiC3 (744 mAh.g(-1)). The experimental Li storage capacity of GDY is similar to theoretical predictions. The experimental Li storage capacity of a thick GDY film is close to that of mono-layered GDY' (744 mAh.g(-1)). A thin GDY film with double-side storage model has two-times the Li storage capacity (1480 mAh.g(-1)) of mono-layered GDY. Powder GDY has lower Li storage capacity than GDY film. The maximal Na storage capacity in GDY corresponds to NaC5.14 (316 mAh.g(-1)), and mono-layered GDY possesses higher theoretical Na storage capacity (NaC2.57). The experimental Na storage capacity (261 mAh.g(-1)) is similar to its theoretical value. Besides, GDY as electrode material, applied in metal-sulfur batteries, presents excellent electrochemical performance (in Li-S battery: 0.1C, 949.2 mAh.g(-1); in Mg-S battery: 50 mA.g(-1), 458.9 mAh.g(-1)). This ingenious design presents a new way for the preparation of carbon-loaded sulfur. GDY electrode material is also successfully used in supercapacitors, including the traditional supercapacitor, Li-ion capacitors, and Na-ion capacitors. The traditional supercapacitor with GDY as the electrode material shows good double layer capacitance and pseudo-capacitance. Both Li-ion capacitor (100.3 W.kg(-1), 110.7 Wh.kg(-1)) and Na-ion capacitor (300 W.kg(-1), 182.3 Wh.kg(-1)) possess high power and energy densities. Moreover, the effects of synthesis of GDY nanostructure, heat treatment of GDY, and atom-doping in GDY on the performance of electrochemical energy storage will be introduced and discussed. The results indicate that GDY has great potential for application in different energy storage devices as an efficient electrode material.

Enhanced sodium storage capability enabled by super wide-interlayer-spacing MoS2 integrated on carbon fibers

Developing advanced electrode materials for effective pseudocapacitive charge storage is one of effective strategies to enhance the rate capability and cycling stability of sodium ion storage devices. Herein, we fabricate MoS2 nanoflowers with super wide interlayer spacing (nearly twice as large as that of the original MoS2) supported on carbon fibers (named as E-MoS2/carbon fibers) and demonstrate its superior electrochemical performances as flexible and binder-free anodes for sodium-ion batteries (SIBs) and sodium-ion hybrid capacitors (SIHCs). Grafting MoS2 nanoflowers onto the carbon fiber networks not only ensures the fast electron transfer, but also endows it with flexible feature. The super wide interlayer spacing of MoS2 nanoflowers can not only decrease the ion diffusion pathways and resistance, but also increase their available and accessible active surface area, thus guaranteeing the rapid mass transport. Also, it can accommodate the large internal strain during discharge/charge processes. Benefiting from these combined structure merits, the E-MoS2/carbon fibers electrodes deliver an ultralong cycling stability up to 3000 cycles and the superior rate capacity of 104mAhg−1 at 20Ag−1, which just takes ca. 18.7s to fully charge/discharge. When further employed as the anode for SIHCs, it delivers high energy and power densities due to the high pseudocapacitive charge storage of the super wide interlayer spacing E-MoS2/carbon fibers.

Oxidation-induced electron barrier enhancement at interfaces of Ge-based semiconductors (Ge, Ge1 − xSnx, SiyGe1 − x − ySnx) with Al2O3

Experiments on internal photoemission of electrons at interfaces of SiyGe1−x−ySnx binary and ternary alloys (0≤x≤0.11; 0≤y≤0.19) with amorphous insulating Al2O3 reveal that the application of an additional oxidation step (5min in dry O3 at 300°C) after atomic layer deposition of first ≈1nm of alumina results in a significant increase of the electron barrier height (by ≈0.4–0.5eV) as compared to the conventionally grown Al2O3 layers. Furthermore, this supplemental oxidation step facilitates the removal of Ge sub-oxides from the interface. The observed electron barrier enhancement is suggested to be caused by formation of a wide gap germanate interlayer between the Ge-based semiconductors and alumina.

Nanocellulose-assisted low-temperature synthesis and supercapacitor performance of reduced graphene oxide aerogels

Abstract Here, we have synthesized reduced graphene oxide (rGO) aerogels using a nanocellulose-assisted low temperature (less than 500 °C) thermal treatment route where nanocelluloses promote the gelation of graphene oxide (GO) solution that benefits the fabrication of GO aerogels from low concentration dispersion (2.85 mg mL−1), and after their thermal decomposition the residual nanofibers act as spacer both prevent the re-stacking of graphene sheets and integrate with rGO sheets to give a particular kind of carbon-based aerogel along with numerous defects (holes). Thermal decomposition of nanocellulose appears to be complete beyond 350 °C thus its presence in form of amorphous carbon nanofibers in rGO sheets. The rGO aerogels synthesized at 350 °C provide the best balance in terms of wide interlayer spacing, high content of CO-type functional groups, and high defects content. This translates into a high discharge capacitance of 270 F g−1 at a current rate of 1 A g−1 for compressed rGO aerogels without any binder or conductive additive. Detailed electrochemical tests using 6 M KOH electrolyte establish the fact that pseudocapacitance component has substantial contribution towards the overall capacitance; closely approaching the contribution of the double layer capacitance that is the most dominant capacitance component.

Corrugated graphene layers for sea water desalination using capacitive deionization.

The effect of the electric field and surface morphology of corrugated graphene (GE) layers on their capacitive deionization process is studied using molecular dynamics simulations. Deionization performances are evaluated in terms of water flow rate and ion adsorption and explained by analysing the water density distribution, radial distribution function and distribution of the ions inside the GE layers. The simulation results reveal that corrugation of GE layers reduces the water flow rate but largely enhances ion adsorption in comparison to the flat GE layers. Such enhancement is mainly due to the adsorption of ions on the GE layers due to the anchoring effect in the regions with wide interlayer distances. Moreover, it reveals that the entrance configuration of the GE layers also has a significant effect on the performance of deionization. Overall, the results from this study will be helpful in designing effective electrode configurations for capacitive deionization.

Single-layer crystalline phases of antimony: Antimonenes

The pseudolayered character of 3D bulk crystals of antimony has led us to predict its 2D single-layer crystalline phase named antimonene in a buckled honeycomb structure like silicene. Sb atoms also form an asymmetric washboard structure like black phospherene. Based on an extensive analysis comprising ab initio phonon and finite-temperature molecular dynamics calculations, we show that these two single-layer phases are robust and can remain stable at high temperatures. They are nonmagnetic semiconductors with band gaps ranging from 0.3 eV to 1.5 eV, and are suitable for 2D electronic applications. The washboard antimonene displays strongly directional mechanical properties, which may give rise to a strong influence of strain on the electronic properties. Single-layer antimonene phases form bilayer and trilayer structures with wide interlayer spacings. In multilayers, this spacing is reduced and eventually the structure changes to 3D pseudolayered bulk crystals. The zigzag and armchair nanoribbons of the antimonene phases have fundamental band gaps derived from reconstructed edge states and display a diversity of magnetic and electronic properties depending on their width and edge geometry. Their band gaps are tunable with the widths of the nanoribbons. When grown on substrates, such as germanene or Ge(111), the buckled antimonene attains a significant influence of substrates.

Photoluminescence features and carrier dynamics in InGaN heterostructures with wide staircase interlayers and differently shaped quantum wells

We present a comprehensive study of photoexcited carrier dynamics in differently grown InGaN/InGaN multiple quantum well (MQW) structures, modified by insertion of a wide interlayer structure and subsequent growth of differently shaped quantum wells (rectangular, triangular, trapezoidal). This approach of strain management allowed the reduction of dislocation density due to gradually increasing In content in the interlayer and shaping the smooth quantum well/barrier interfaces. A set of c-oriented MQW structures emitting at 470 nm were grown at Vilnius University, Institute of Applied Research, using a closed coupled showerhead type MOCVD reactor. Photoluminescence (PL) spectra of MQW structures were analysed combining continuous wave and pulsed PL measurements. Reactive ion etching of the structures enabled discrimination of PL signals originated in the InGaN interlayer structure, underlying quantum wells, and quantum barriers, thus providing growth-related conditions for enhanced carrier localization in the wells. Time-resolved PL and differential transmission kinetics provided carrier lifetimes and their spectral distribution, being the longest in triangular-shape QWs which exhibited the highest PL intensity. The light-induced transient grating (LITG) technique was used to determine the spatially averaged carrier lifetime in the entire heterostructure, in this way unravelling the electronic quality of the LED internal structure at conditions similar to device performance. LITG decay rates at low and high excitation energy densities revealed increasing with photoexcitation nonradiative recombination rate in the triangular and trapezoidal wells.

Solvent Effect on the Supramolecular Patterns and Luminescent Properties of Organic Salts Comprising Naphthalene-1,5-disulfonic Acid and Triphenylmethylamine

The solvent reaction of naphthalene-1,5-disulfonic acid and triphenylmethylamine gives rise to nine organic salts, namely, 2(HTPMA)+·(NDS)2–·2(MeOH) (1), 2(HTPMA)+·(NDS)2–·6(EtOH) (2), 2(HTPMA)+·(NDS)2–·4(n-PrOH) (3), 2(HTPMA)+·(NDS)2–·4(n-BuOH) (4), 2(HTPMA)+·(NDS)2–·2(n-PeOH) (5), 2(HTPMA)+·(NDS)2–·3(DO)·2(H2O) (6), 2(HTPMA)+·(NDS)2–·4(DMF) (7), 2(HTPMA)+·(NDS)2–·4(DMSO) (8), and 2(HTPMA)+·(NDS)2–·4(H2O) (9) (H2NDS = naphthalene-1,5-disulfonic acid, TPMA = triphenylmethylamine, DO = 1,4-dioxane), which have been characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, photoluminescence (PL), and powder and single-crystal X-ray diffraction (XRD). Structural analyses indicate that the nature of the solvent molecules can effectively influence the hydrogen bonding modes of the −SO3– and −NH3+ groups, which then result in diverse architectures. The HTPMA+ cations and NDS2– anions in salts 1, 3, and 4 are alternately arranged to form column motifs, which then pack with each other to form lamellar structures with a wide interlayer space. The NDS2– anions in salts 2 and 5 adopt standing and recumbent positions and act as pillars to extend adjacent double layers formed by HTPMA+ cations into pillared layered supramolecular networks. In comparison, pairs of HTPMA+ cations in salt 6 act as pillars and extend the layers formed by two kinds of NDS2– anions to generate pillared layered frameworks. Salts 7 and 8 exhibit a similar packing diagram, in which adjacent monolayers of HTPMA+ cations are pillared by the NDS2– anions in a recumbent position. Salt 9 is a porous hydrogen-bonding organic framework assembled from the alternate arrangement of HTPMA+ cations and NDS2– anions, and its products at 50 and 120 °C exhibit different structures after being immersed in aqueous solution with the composition of 2(HTPMA)+·(NDS)2–·4(H2O) (10) and 2(HTPMA)+·2(TPMA)·(NDS)2– (11). Luminescent investigation reveals that the emission maximum of salts 1–9 varies from 382 to 393 nm. Moreover, the detailed chemical behaviors for salt 9, such as thermal stability, temperature-dependent infrared spectroscopy, powder XRD, PL, are carefully studied.

Unlocking the secrets of Al-tobermorite in Roman seawater concrete

Ancient Roman syntheses of Al-tobermorite in a 2000-year-old concrete block submerged in the Bay of Pozzuoli (Baianus Sinus), near Naples, have unique aluminum-rich and silica-poor compositions relative to hydrothermal geological occurrences. In relict lime clasts, the crystals have calcium contents that are similar to ideal tobermorite, 33 to 35 wt%, but the low-silica contents, 39 to 40 wt%, reflect Al 3+ substitution for Si 4+ in Q 2 (1Al), Q 3 (1Al), and Q 3 (2 Al) tetrahedral chain and branching sites. The Al-tobermorite has a double silicate chain structure with long chain lengths in the b [020] crystallographic direction, and wide interlayer spacing, 11.49 Å. Na + and K + partially balance Al 3+ substitution for Si 4+ . Poorly crystalline calcium-aluminum-silicate-hydrate (C-A-S-H) cementitious binder in the dissolved perimeter of relict lime clasts has Ca/(Si+Al) = 0.79, nearly identical to the Al-tobermorite, but nanoscale heterogeneities with aluminum in both tetrahedral and octahedral coordination. The concrete is about 45 vol% glassy zeolitic tuff and 55 vol% hydrated lime-volcanic ash mortar; lime formed <10 wt% of the mix. Trace element studies confirm that the pyroclastic rock comes from Flegrean Fields volcanic district, as described in ancient Roman texts. An adiabatic thermal model of the 10 m 2 by 5.7 m thick Baianus Sinus breakwater from heat evolved through hydration of lime and formation of C-A-S-H suggests maximum temperatures of 85 to 97 °C. Cooling to seawater temperatures occurred in two years. These elevated temperatures and the mineralizing effects of seawater and alkali- and alumina-rich volcanic ash appear to be critical to Al-tobermorite crystallization. The long-term stability of the Al-tobermorite provides a valuable context to improve future syntheses in innovative concretes with advanced properties using volcanic pozzolans.

Phosphorescent white organic light-emitting devices with color stability and low efficiency decay by using wide band-gap interlayer

High-performance phosphorescent white organic light-emitting devices (PhWOLEDs) with color stability and low efficiency decay are demonstrated by inserting wide band-gap materials between emitting layers. The two devices with N,N′-dicarbazolyl-3,5-benzene (mCP) and p-bis(triphenylsilyl)benzene (UGH2) as the interlayer exhibit both slight Commission Internationale del’Eclairage (CIE) coordinates variations of (± 0.010, ± 0.005) and (± 0.013, ± 0.006) in a wide voltage range, and low decay in current efficiency which shifts from the peak value 35.4 cd·A−1 and 27.4 cd·A−1 to 28.8 cd·A−1 and 23.5 cd·A−1 at 40000 cd·m−2, respectively. The improvements are attributed to the charge carriers balance and the elimination of energy transfer loss by confining the carrier accumulation at the exciton formation interface through the interlayer.