Theoretical Understanding and Prediction of Lithiated Sodium Hexatitanates

Sodium hexatitanates (Na₂Ti₆O₁₃) with tunnelled structures have been experimentally proposed to be good candidates for anode materials of lithium ion batteries because of their low potential, small shape transformation, and good reversibility. The understanding of the properties of this lithiated titanate is significant for their development. To this end, the first-principle calculations were performed to investigate the interaction between Li ions and Na₂Ti₆O₁₃ at the atomic level. After structural optimization with various Li:Ti ratios, the Li ions are found to energetically prefer to stay at the small rhombic tunnels of Na₂Ti₆O₁₃, where the diffusion energy barrier of Li ions is also lower. Such preference is determined by the chemical environment around Li ions. Our theoretical intercalation potential and volume change on the basis of the optimized atomic structures agree with the experimental observations. The analysis of the electronic properties reveals the Burstein–Moss effect in lithiated Na₂Ti₆O₁₃ due to the heavy n-type doping. Such materials possess high conductivity, which can benefit their applications in photoelectrochemical or electrochemical areas

High-Efficiency Co/Co_<i>x</i>S_<i>y</i>@S,N-Codoped Porous Carbon Electrocatalysts Fabricated from Controllably Grown Sulfur- and Nitrogen-Including Cobalt-Based MOFs for Rechargeable Zinc–Air Batteries

Developing bifunctional oxygen electrocatalysts with superior catalytic activities of oxygen reduction reaction (ORR) and oxygen revolution reaction (OER) is crucial to their practical energy storage and conversion applications. In this work, we report the fabrication of Co/Co_<i>x</i>S_<i>y</i>@S,N-codoped porous carbon structures with various morphologies, specific surface areas, and pore structures, derived from controllably grown Co-based metal–organic frameworks with S- and N-containing organic ligands (thiophene-2,5-dicarboxylate, Tdc; and 4,4′-bipyridine, bpy) utilizing solvent effect (<i>e.g.</i>, water and methanol) under room temperature and hydrothermal conditions. The results demonstrate that Co/Co_<i>x</i>S_<i>y</i>@S,N-codoped carbon fibers fabricated at a pyrolytic temperature of 800 °C (Co/Co_<i>x</i>S_<i>y</i>@SNCF-800) from Co-MOFs fibers fabricated in methanol under hydrothermal conditions as electrocatalysts exhibit superior bifunctional ORR and OER activities in alkaline media, endowing them as air cathodic catalysts in rechargeable zinc–air batteries with high power density and good durability

Fluorescence Determination of Nitrite in Water Using Prawn-Shell Derived Nitrogen-Doped Carbon Nanodots as Fluorophores

In this work, we report the synthesis of nitrogen (N)-doped carbon nanodots (N-CNDs) with an N doping level of 3.6 at. % by hydrothermal treatment of prawn shell and their application as fluorophores for selective and sensitive fluorescence detection of NO₂^– in water. The results demonstrate that NO₂^– detection by directly fluorescent quenching at N-CNDs fluorophores can achieve an analytical detection linear range up to 1.0 mM with a detection limit of 1.0 μM. The obtained detection limit of NO₂^– using N-CNDs fluorophores is dramatically lower than the maximum limit value of 3.0 mg L^–1 (namely, 65 μM) for NO₂^– in drinking water ruled by the World Health Organization (WHO), which is very important for a practical application of the developed analytical method. The interference experiments indicate that only I^– ions among all common anions and cations investigated show very adverse influence on selective detection of NO₂^– by this developed N-CNDs based fluorescent determination method. Further, the fluorescence quenching of N-CNDs on NO₂^– concentrations under the given experimental conditions fits a linear Stern–Volmer relationship very well, indicating a dynamic quenching process in this N-CNDs/NO₂^– fluorescence sensing system. A fluorescent quenching mechanism resulted from the redox reaction between the excited oxidation state of N-CNDs under light excitation and NO₂^– was proposed based on the experimental results. The findings in this work exhibit the great potential using cheap and abundant biomass-derived N-doped carbon nanodots as fluorophores for selective and sensitive determination of environmentally harmful anions

Rutile {111} Faceted TiO₂ Film with High Ability for Selective Adsorption of Aldehyde

Selective adsorption is an important approach to separate organic molecules. In this study, an extraordinary selective adsorption capability of the rutile TiO₂ (111) surface toward aldehyde over alcohol and carboxylic acid has been demonstrated on the basis of <i>in situ</i> photoelectrochemical (PEC) measurements. The adsorption strength of benzaldehyde on the rutile (111) surface has been investigated through the analysis of thermodynamic and kinetic properties of photodegradation processes using <i>ex situ</i> PEC measurements. The comparative results with rutile {111} and anatase {101} faceted electrodes demonstrate that there is a strong adsorption of benzaldehyde on the rutile (111) surface. The high ability of the rutile (111) surface for selective adsorption of aldehyde can therefore be utilized as a new approach to separate and purify aldehyde in industry

Synthesis of Carbon Nanotube–Anatase TiO₂ Sub-micrometer-sized Sphere Composite Photocatalyst for Synergistic Degradation of Gaseous Styrene

The carbon nanotube (CNT)–sub-micrometer-sized anatase TiO₂ sphere composite photocatalysts were synthesized by a facile one-step hydrothermal method using titanium tetrafluoride as titanium source and CNTs as structure regulator. Various technologies including X-ray diffraction, UV–visible absorption spectra, N₂ adsorption–desorption, scanning electron microscopy, and transmission electron microscopy were employed to characterize the structure properties of the prepared composite photocatalysts. The results indicated that the composite photocatalysts consisted of CNTs wrapping around the sub-micrometer-sized anatase TiO₂ spheres with controllable crystal facets and that the aggregated particles with average diameter ranged from 200 to 600 nm. The fabricated composite photocatalysts were used to degrade gaseous styrene in this work. As expected, a synergistic effect that remarkably enhancing the photocatalytic degradation efficiency of gaseous styrene by the prepared composite photocatalysts was observed in comparison with that the degradation efficiency using pure anatase TiO₂ and the adsorption of CNTs. Similar results were also confirmed in the decolorization of liquid methyl orange. Further investigation demonstrated that the synergistic effect in the photocatalytic activity was related to the structure of the sub-micrometer-sized anatase TiO₂ spheres and the significant roles of CNTs in the composite photocatalysts. By controlling the content of CNTs, the content of TiO₂ or the temperature during the hydrothermal synthesis process, anatase TiO₂ spheres with controllable crystallite size and dominant crystal facets such as {001}, {101}, or polycrystalline could be obtained, which was beneficial for the increase in the synergistic effect and further enhancement of the photocatalytic efficiencies

Size Modulation of Zirconium-Based Metal Organic Frameworks for Highly Efficient Phosphate Remediation

Eutrophication of water bodies caused by the excessive phosphate discharge has constituted a serious threat on a global scale. It is imperative to exploit new advanced materials featuring abundant binding sites and high affinity to achieve highly efficient and specific capture of phosphate from polluted waters. Herein, water stable Zr-based metal organic frameworks (MOFs, UiO-66) with rational structural design and size modulation have been successfully synthesized based on a simple solvothermal method for effective phosphate remediation. Impressively, the size of the resulting UiO-66 particles can be effectively adjusted by simply altering reaction time and the amount of acetic acid with the purpose of understanding the crucial effect of structural design on the phosphate capture performance. Representatively, UiO-66 particles with small size demonstrates 415 mg/g of phosphate uptake capacity, outperforming most of the previously reported phosphate adsorbents. Meanwhile, the developed absorbents can rapidly reduce highly concentrated phosphate to below the permitted level in drinking water within a few minutes. More significantly, the current absorbents display remarkable phosphate sorption selectivity against the common interfering ions, which can be attributed to strong affinity between Zr–OH groups in UiO-66 and phosphate species. Furthermore, the spent UiO-66 particles can be readily regenerated and reused for multiple sorption–desorption cycles without obvious decrease in removal performance, rendering them promising sustainable materials. Hence, the developed UiO-66 adsorbents hold significant prospects for phosphate sequestration to mitigate the increasingly eutrophic problems

Density Functional Studies of Stoichiometric Surfaces of Orthorhombic Hybrid Perovskite CH₃NH₃PbI₃

Organic/inorganic hybrid perovskite materials are highly attractive for dye-sensitized solar cells as demonstrated by their rapid advances in energy conversion efficiency. In this work, the structures, energetics, and electronic properties for a range of stoichiometric surfaces of the orthorhombic perovskite CH₃NH₃PbI₃ are theoretically studied using density functional theory. Various possible spatially and constitutionally isomeric surfaces are considered by diversifying the spatial orientations and connectivities of surface Pb–I bonds. The comparison of surface energies for the most stable configurations identified for all surfaces shows that the stabilities of stoichiometric surfaces are mainly dictated by the coordination numbers of surface atoms, which are directly correlated with the number of broken bonds. Additionally, Coulombic interactions between I anions and organic countercations on the surface also contribute to the stabilization. Electronic properties are compared between the most stable (100) surface and the bulk phase, showing generally similar features except for the lifted band degeneracy and the enhanced bandgap energy for the surface. These studies on the stoichiometric surfaces serve as a first step toward gaining a fundamental understanding of the interfacial properties in the current structural design of perovskite based solar cells, in order to help facilitate further breakthroughs in solar conversion efficiencies

Efficient Synthesis of Furfuryl Alcohol from H₂‑Hydrogenation/Transfer Hydrogenation of Furfural Using Sulfonate Group Modified Cu Catalyst

A copper-based catalyst, which was supported by sulfonate group (−SO₃H) grafted active carbon (AC), was prepared and activated simultaneously by liquid phase chemical reduction method. The modified copper catalyst, Cu/AC–SO₃H, displayed an enhanced catalytic performance for selective hydrogenation of furfural (FAL) to furfuryl alcohol (FOL) in liquid phase, in which almost 100% FOL yield was obtained at 378 K and 0.4 MPa of hydrogen pressure after 120 min reaction. The effect of −SO₃H was evaluated and illustrated by the combination of reaction performance and physicochemical characterizations, such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectrometer (XPS) measurements. Through grafting sulfonate group on the support, better dispersion of nanoparticles, higher reduction degree of Cu, and stronger adsorption of FAL can be attained to contribute high hydrogenation performance. In addition, the effects of reaction conditions (such as reaction temperature, H₂ pressure, reaction time, solvent, and catalyst to FAL mass ratio) were evaluated intensively. Also, the Cu/AC–SO₃H catalyst showed an excellent catalytic performance for transfer hydrogenation of FAL, in which 2-propanol was utilized as the solvent and hydrogen donor concurrently. Cycling test proved the prepared catalyst could be recycled and reused for several times without noticeably reduced catalytic activity of hydrogenation

Selective Determination of Cr(VI) by Glutaraldehyde Cross-Linked Chitosan Polymer Fluorophores

Selective determination of aquatic chromium is critically important because of the dramatic differences in health and environment impacts by trivalent and hexavalent forms of chromium; however, it is challenging. In this work, for the first time, a nonconjugated polymer fluorophore (GCPF) was synthesized by cross-linking chitosan with glutaraldehyde via Schiff base reactions and systematically investigated for selective determination of Cr­(VI). The results revealed that the synthesized GCPF exhibited excellent photostability and water solubility. More importantly, GCPF possessed dramatically enhanced fluorescence intensity originated from the n−π* transitions of the Schiff base subfluorophore groups (e.g., CN) that can be selectively and sensitively quenched by Cr­(VI) through oxidative damages to CN group. An effective EDTA masking agent approach was employed to minimize ionic interferences. In the presence of high concentration of interference ions including Cr­(III), the quenching GCPF fluorescence is capable of selectively determining Cr­(VI) within a concentration range up to 50 μM and a detection limit of 0.22 μM. The analytical performance of GCPF was also confirmed by analyzing real surface water and industrial samples