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Lithium extraction from liquid resources has drawn significant attention owing to the availability of abundant deposits. However, developing highly efficient Li+ adsorbent materials is limited by the unclear chemical mechanism correlating the adsorbent material structure and ion adsorption performance, as well as the diffusion mechanism of ions in the bulk phase of the material. Here, by fabricating three kinds of adsorbent precursors Li4Ti5O12 (LTO) with different exposed planes, we reveal the internal mechanism that links the material structure and Li+ desorption performance. The LTO with the 110 planes exhibited the highest Li+ desorption efficiency of 98%, and the corresponding desorption product H4Ti5O12 (HTO) with 110 is more likely to adsorb Li+ as it delivered adsorption capacity up to 37.58 mg g−1. The structural analysis reveals that more 8a sites were exposed on the 110 planes of the material, and the density functional theory (DFT) results clarify that Li+ diffusion to the 8a sites is favored (0.40 eV). Our work not only uncovers the mechanism that connects the material structure and ion ad/desorption performance but also paves the way for designing efficient and advanced Li+ adsorbents to assist lithium resource extraction. [ABSTRACT FROM AUTHOR]

Developing highly efficient and stable electrocatalysts for oxygen reduction reaction (ORR) is a challenging task in energy conversion technologies. In this work, diverse axial ligands have been used to modify the ORR activity of transition metal and nitrogen codoped graphene (MN4-Gra). The weakening of the ORR intermediates by the axial ligand would activate these intermediates efficiently and improve the catalytic activity. Our study indicated that among the axial ligands adopted, nitrobenzene and benzene have good performance in improving the ORR activity. Several promising ORR catalysts are predicted. Among them, FeN4-Gra modified by nitrobenzene, i.e., FeN4-Gra/ben/NO2 has the best catalytic activity with a small overpotential of 0.21 V and energy barrier of 0.24 eV in the rate determining step, followed by RuN4-Gra/ben/NO2 and FeN4-Gra/benzene. These catalysts are also demonstrated to be stable by the calculated formation energies and dissolution potentials. The scaling relationships suggested that the adsorption energy of *OH and d band center would be good descriptors for predicting the highly efficient ORR catalysts. Therefore, axial ligand engineering would be a useful strategy to enhance the efficiency of ORR catalysts. [ABSTRACT FROM AUTHOR]

Phosphors emitting visible and near-infrared persistent luminescence have been extensively studied and commercialized owing to their wide applications in emergency lighting, information storage and in vivo bioimaging. However, ultraviolet (200–400 nm) persistent phosphors are rarely reported. Here, we developed a new Pr3+ activated BaLu2Al2Ga2SiO12 persistent luminescence phosphor, which could be effectively excited by a standard 254 nm mercury lamp and exhibits excellent ultraviolet (280–400 nm) persistent luminescence lasting for more than 3 h. This exciting result encouraged us to comprehensively investigate its structural information, photoluminescence and thermoluminescence properties to reveal a feasible persistent luminescence mechanism. The results show that Pr3+ ions act as both photoluminescence and persistent luminescence emitters, and the ultraviolet light emission originates from its parity allowed 4f15d1 → 4f2 inter-configurational transitions. The suitable energy location of the lowest energy 4f2 → 4f15d1 excitation transition and small Stokes shift of less than 3000 cm−1 (0.37 eV) related to the composition and crystal structure of the host lattice BaLu2Al2Ga2SiO12 ensure the occurrence of Pr3+ 4f15d1 → 4f2 transitions. Moreover, the suitable trapping levels related to Pr4+ in BaLu2Al2Ga2SiO12:Pr3+ were also investigated utilizing thermoluminescence spectra, which could be effectively filled by carriers under 254 nm light irradiation to achieve ultraviolet persistent luminescence. This study opens up new avenues for future research on ultraviolet persistent luminescence and brings new application prospects in the fields of photocatalysis and photodynamic therapy. [ABSTRACT FROM AUTHOR]

The ion-exchange process is usually influenced by the surface properties of the adsorbents. In particular, the prophase adsorption/desorption process is confined by different crystal facets. In this research, spinel Li4Ti5O12 nanosheets with an exposed (1−14) high-index facet were prepared by a hydrothermal method followed by calcination treatment. Then, a H4Ti5O12 adsorbent was obtained, covered with the same (1−14) facets, after treatment with 0.2 M HCl. This special facet-exposed H4Ti5O12 has high cycling ability, with the adsorption uptake remaining at 96.84% after four cycles, a fast adsorption equilibrium time (equilibrium time < 60 min), excellent ion adsorption selectivity for Li+ uptake (separation factor: Li+ > K+ > Ca2+ > Na+ > Mg2+), and good adsorption capacity for Li+ uptake (21.57 mg g−1). With the help of X-ray photoelectron spectroscopy analyses, the Li+ adsorption process on the H4Ti5O12 nanosheets is shown to be an ion-exchange process. In addition, the coordination relationship between lithium and oxygen ions was investigated, illustrating that the four-coordinated structure is more stable than other complexes. These results indicate that hydrogen ions are exchanged for lithium ions at tetrahedral 8a sites, leading to the H4Ti5O12 structure with high stability in the adsorption–desorption cycling process. [ABSTRACT FROM AUTHOR]

Lithium-rich spinel lithium manganese oxide (LMO) compounds are one kind of promising adsorbents for lithium recovery from brine due to their high capacity and low Mn dissolution; Li1.6Mn1.6O4 is one of them. However, Mn3+ exists in the Li1.6Mn1.6O4 precursor due to incomplete reaction during syntheses, and the disproportionation reaction of Mn3+ inevitably results in Mn dissolution during lithium adsorption and desorption. The stable recycling and structural stability of Li1.6Mn1.6O4 were improved in aqueous lithium resources through K-gradient doping (LMO-K). The dissolution of Mn is reduced to 4.0% from 5.4% (before doping) and the adsorption capacity is kept at high capacity (31.6 mg g−1) at a low Li+ concentration of 12 mmol L−1. In addition, first-principles calculations further confirm that K substitutes for Li at 16d sites, leading to the stabilization of the Mn cations in the compound. With the help of K doping, the undesired dissolution of Mn in the cycle process is inhibited, which may be due to the reduction in the content of Mn3+ and improvement in the structural stability of the adsorbent. [ABSTRACT FROM AUTHOR]

The design of highly stable, effective, and selective electrocatalysts is essential for electrochemical reduction of carbon dioxide (CO2). Here, on the basis of density functional theory (DFT) computations, the reaction mechanisms of the reduction of CO2 over a series of bis(iminothiolato)metal (TMIT, TM = Mn, Fe, Co, Ni, Cu, Ru, Rh, and Pd) were studied. It is found that the CO2RR activity of TMIT depends on the choice of the central metal atom. Our results demonstrated that HCOOH is the main product for TMIT (TM = Mn, Fe, Co, Ni, Cu, Pd). Among them, MnIT and FeIT are promising CO2RR catalysts for the HCOOH production due to the good selectivity and catalytic activity with the low overpotential of 0.34 V and 0.35 V, respectively. For RuIT and RhIT, the main product is CO, and the strong adsorption of CO on the catalyst surfaces would poison the catalysts. This makes RhIT and RuIT not good CO2RR catalysts. We anticipate that this work may shed new light on the development of high-performance metal organic framework (MOF)-based electrocatalysts. [ABSTRACT FROM AUTHOR]

In this study, the catalytic activities of oxygen reduction reaction (ORR) on a series of transition metal–N4-graphene (M–N4-C) composites, comprising 3d (Cr–Ni), 4d (Mo–Ag) and 5d (Os–Au) transition metals have been investigated by using the density functional theory. Our results indicated that the adsorption energy of oxygen atom is the key factor to describe the catalytic activity. For ORR, the highest activity was achieved at the oxygen adsorption energy of 2.25 eV. M–N4-C (M = Co, Rh and Ir) composites with appropriate oxygen adsorption strength exhibited high ORR activity. In addition, the Co–N4-C and Rh–N4-C composites with the oxygen adsorption strength close to 2.78 eV are also predicted to have excellent performance for oxygen evolution reaction (OER). [ABSTRACT FROM AUTHOR]

The rational design of heteroatom doped graphene as a highly active and non-noble oxygen reduction reaction (ORR) electrocatalyst is significant for the commercial applications of the fuel cells. In this work, the catalytic activity for the ORR and the reaction mechanism on the surface of FeN2 doped graphene (FeN2-Gra) have been studied by using density functional theory. The results indicate that the ORR is a four-electron process on FeN2-Gra, similar to FeN3-Gra and FeN4-Gra. But FeN2-Gra shows quite different reaction mechanisms compared with FeN3-Gra and FeN4-Gra. For FeN2-Gra, the OOH hydrogenation to form OH + OH is the kinetically most favorable pathway, in which the O2 hydrogenation to form OOH is the rate-determining step with an energy barrier of 0.47 eV. This energy barrier is smaller than 0.56 eV for FeN4-Gra, and much smaller than 0.87 eV for FeN3-Gra and 0.86 eV for pure Pt. The predicted working potential is 0.18 V. FeN2-Gra also has better capability of resisting CO poisoning compared with pure Pt. Consequently, the FeN2-Gra is a good ORR catalyst. [ABSTRACT FROM AUTHOR]

The rational design of non-noble materials as low-cost, highly efficient, and durable catalysts to improve the oxygen reduction reaction is extremely urgent and challenging. The oxygen reduction reaction is a kinetically sluggish process that greatly affects the energy conversion efficiency. In this paper, novel hierarchical heteroatoms-co-doped Fe2M/graphene (M = P, N) nanocomposites were developed by a facile strategy, including hydrothermal and subsequent calcination methods. The thermal treatment of an ionic liquid and thiourea not only supplied heteroatom sources but also promoted the formation of iron phosphide and iron nitride and enhanced their catalytic performances. The electrochemical results indicated that the as-obtained hybrid catalysts manifested enhanced electrocatalytic activity toward the oxygen reduction reaction owing to the strong synergistic effects. The high content of heteroatoms distributed on the surface and interface of the hybrids and the density functional theory calculations suggested that Fe–N–C, Fe–P–C, and Fe–S–C multiple active surface sites were formed at the hybrids interfaces. Moreover, these results demonstrated that heteroatom-doped catalysts could effectively form a charge-transfer channel and thus modify the charge distribution in the hybrids interfaces. The as-prepared heteroatoms-doped Fe2M/graphene hybrids would be developed into highly efficient catalysts as ideal alternatives for noble metal catalysts in practical applications. [ABSTRACT FROM AUTHOR]

Non-precious metal catalysts have attracted particular interest in recent years due to their promising ORR (oxygen reduction reaction) activity in fuel cells. In this work, the structural stability and ORR mechanism of CoN3 embedded graphene have been studied theoretically in acid media. The results indicate that CoN3 embedded graphene is stable thermodynamically. The kinetically most favorable reaction pathway for the ORR is a four-electron process. The process of OOH hydrogenation to generate O + H2O is the most favorable pathway. In the rate determining step, the energy barrier is 0.38 eV, much smaller than the theoretical value of ∼0.80 eV for pure Pt. The predicted working potential is 0.4 V for the most favorite pathway. Besides the lower energy barrier, the smaller Tafel slope compared with pure Pt in both low and high overpotential regions also suggests that CoN3 embedded graphene is a promising electrocatalyst for the ORR. [ABSTRACT FROM AUTHOR]

Using CO2 as a carbonyl building block to synthesize valuable chemicals is an important issue in the field of green and sustainable chemistry. Herein, the conversion of CO2 with glycerol to glycerol carbonate was investigated in the presence of 2-cyanopyridine. It was found that 2-cyanopyridine not only acts as the dehydrating agent to break the thermodynamic limit of the reaction, but also activates the carbonyl bond of CO2 to catalyze the present carbonylation as confirmed by FTIR experimental spectra. Moreover, the activation closely depends on the stereo-structure of cyanopyridine, in that 3-cyanopyridine and 4-cyanopyridine do not have such activating function. The theoretical calculation demonstrated that 2-cyanopyridine could bond CO2 through the conjugating nitrogen to form a five-membered ring, thus CO2 is activated and then reacts with glycerol to produce glycerol carbonate. The reaction parameters were examined and evaluated for the reaction catalyzed with 2-cyanopyridine in the absence of any metal catalysts and additives. With increasing CO2 pressure, the yield of glycerol carbonate increases, and under the optimum conditions an 18.7% yield is obtained which is one of the best results reported up to now. The present work provides a new way for activation of CO2. [ABSTRACT FROM AUTHOR]

The electronic structures and photophysical properties of the recently reported Ir(iii) cyclometallated complexes containing the 2-(1-phenoxy-4-phenyl)-5-methylpyridine ligand (1) were studied via density functional theory and time-dependent density functional theory calculations. To improve the performance and establish the structural–photophysical property relationships, a series of Ir(iii) complexes 2–6 with –CH3/H and t-Bu substituents have been designed according to the experimental complex 1. The calculated results demonstrate that the different substituted ligands not only modify the absorption and emission bands, but also enhance the phosphorescent quantum efficiency. The t-Bu substituent increases the energy levels of the LUMO for complexes 4, 5 and 6 and broadens the HOMO–LUMO energy gaps. When compared with 1, the emission wavelengths for 3 and 6 are red-shifted considerably, while they are slightly blue-shifted for 4 and 5. In particular, the –CH3 and t-Bu substituents in 2, 4 and 5 lead to a relatively high quantum yield. Therefore, the designed complexes 2, 4 and 5 with –CH3/t-Bu substituents are expected to be promising phosphorescence emitters with high quantum efficiency. [ABSTRACT FROM AUTHOR]

Developing highly active non-noble metal oxygen reduction reaction (ORR) catalysts is crucial for a variety of renewable energy applications including fuel cells and metal–air batteries. Heteroatom doped carbon materials, known as metal-free catalysts, show potential applications in the ORR, and may be promising replacement candidates for expensive, scarce platinum catalysts. Despite the inspiring progress made, the performance of the current metal-free carbon catalysts is still far from satisfactory for large-scale applications. Herein, we introduce an effective and robust ORR catalyst based on N, S co-doped carbon materials with abundant surface active sites. Electrochemical results indicate that the incorporation of sulfur into nitrogen-doped carbon (S-NCx) can dramatically improve the stability of the catalyst by improving the selectivity of O2 electro-reduction to H2O. Density functional theory calculations reveal that sulfur doping lowers the energy barrier of O2(ads) hydrogenation to form OOH(ads), thus leading to enhanced intrinsic activity. In particular, the correlation between ORR activity and nitrogen and sulfur species in these materials is studied in-depth, and it is found the ORR performance of S-NCx catalysts is significantly affected by pyridinic N and C–S–C contents. [ABSTRACT FROM AUTHOR]

The non-precious metal graphene catalyst doped with Fe–Px are recently proposed as a promising candidate in substituting Pt for catalyzing oxygen reduction reaction (ORR) in fuel cells. Systematic DFT calculations are performed to investigate the catalytic activity and the ORR mechanism on the Fe–Px (x = 1–4) system in acid medium in this work. Our results indicated that the configuration with one Fe and two P atoms codoped at zigzag edge site (Fe–P2–zig-G) is the most stable, in excellent agreement with the experimental observation that the ratio of Fe and P is nearly 1 : 2. The four-electron reduction mechanism for ORR on the Fe–P2–zig-G is via the competing OOH hydrogenation pathways (to form either OH + OH or O + H2O). The rate determining step is the O2 hydrogenation with an energy barrier of 0.43 eV, much smaller that of calculated 0.80 eV for pure Pt. In addition, the highest energy barrier of the studied ORR mechanism is the O2 dissociation with an energy barrier of 0.70 eV, a value also smaller than that of pure Pt. This demonstrated that the zigzag edge site of the Fe–P2 codoped graphene should be active for the ORR. [ABSTRACT FROM AUTHOR]

The mechanisms of the oxygen reduction reaction (ORR) on Pt/Cu(111) and Pt/Cu(100) have been investigated by using density functional theory. Compared with pure Pt(111) and Pt(100), the adsorptions of ORR intermediates are weakened on both Pt/Cu(111) and Pt/Cu(100) surfaces. The ORR follows the oxygen dissociation mechanism on Pt/Cu(100) which is the same as that on pure Pt(100). However, the ORR mechanism is the peroxyl dissociation mechanism on pure Pt(111), hydrogen peroxide dissociation on Pt/Cu(111). The rate determining step is OH + H+ + e−→ H2O on Pt/Cu(100) and pure Pt(100), O + H+ + e−→ OH on pure Pt (111) and OOH + H+ + e−→ H2O2 on Pt/Cu(111). Compared with the energy barrier of the rate determining step on pure Pt(111) (0.86 eV) and Pt(100) (0.76 eV), the ORR reaction activity is improved on Pt/Cu(111) and hindered on Pt/Cu(100), with the barriers of 0.40 and 0.85 eV, respectively. For the effects of electric potential, OH protonation is favorable thermodynamically at a broad electrode potential (from 0 to 1.23 V) on the Pt/Cu(111) surface, in agreement with the high durability of Pt/Cu observed in experiments. The working potentials of Pt/Cu(111) and Pt/Cu(100) are predicted to be 0.39 and 0.73 V, respectively. [ABSTRACT FROM AUTHOR]

A DFT/TDDFT investigation was performed on the electronic structures, absorption and emission properties, as well as the phosphorescence efficiency of the recently synthesized Ir(iii) complexes SOFIrpic (1a) and POFIrpic (2a) with sulfonyl/phosphoryl substituted 2-(2,4-difluorophenyl)pyridine (dfppy) as the cyclometalated ligand. The calculated absorption and emission wavelengths are in agreement with experimental data. The higher quantum yield of experimental observation for 1a compared with 2a was explained by its smaller energy separation between the singlet S1 and the triplet T3 states. Based on these experimental structures, a series of cyclometalated Ir(iii) complexes (1b, 1c, 1d and 2b, 2c, 2d) have been designed by introduction of different ancillary ligands. The calculated results reveal that the different ancillary ligands not only tune the energy gap but also enhance the photoluminescence quantum efficiency. It is expected that the designed complexes 1b, 2b and 2c could be potential candidates as blue-emitting materials with high quantum efficiency. [ABSTRACT FROM AUTHOR]

Uniform and well-crystallized YPO4·0.8H2O and YPO4·0.8H2O : Tb3+, Eu3+ nanocrystals have been successfully synthesized by a facile hydrothermal method using trisodium citrate (Cit3−) as a “shape modifier”. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectra were used to characterize the samples. It was found that the pH of the initial solution was responsible for determining the shape of the final products. In addition, the YPO4·0.8H2O samples prepared by Cit3−-assisted hydrothermal synthesis exhibited an intense and bright blue emission. Characterized with Fourier transform infrared (FT-IR) spectra and electron paramagnetic resonance (EPR) spectra, the carbon-related impurities induced by trisodium citrate (Cit3−) in the hydrothermal process were confirmed and confirmed that the paramagnetic defects relating to the luminescence properties existed in the luminescent YPO4·0.8H2O nanocrystals. More interestingly, the YPO4·0.8H2O : Tb3+, Eu3+ samples could be effectively excited with 380 nm and the luminescence colors of YPO4·0.8H2O : Tb3+, Eu3+ nanocrystals can be easily tuned by changing the concentration of Eu3+ ions due to an efficient energy transfer from Tb3+ to Eu3+. These results revealed that the combination of the defect luminescence and rare earth-doping emission in YPO4·0.8H2O : Tb3+, Eu3+ nanocrystals could result in tunable emission in a large color gamut, which may be potentially applied in fields such as solid state lighting and field emission displays. [ABSTRACT FROM AUTHOR]

DFT/TDDFT calculations were carried out to investigate the electronic structures, absorption and emission spectra, and phosphorescence efficiency of recent synthesized Ir(iii) complexes [Ir(tfmppy)2(tpip)] (1), [Ir(dfppy)2(tpip)] (2) (tfmppy = 4-trifluoromethylphenylpyridine; dfppy = 4,6-difluorophenylpyridine; tpip = tetraphenylimidodiphosphinate). The calculated absorption and emission wavelengths are in agreement with experimental data. The electron transition properties have been analyzed. Compared with 2, the higher quantum yield of experimental observation for 1 was explained by its larger separation between 3MLCT/π→π* and 3MC d–d states. Based on these experimental structures, a series of cyclometalated Ir(iii) complexes have been designed by substituting “CH” groups with the N atom at 1-, 2-, 3-, and 4-positions on the pyridine moiety in C^N ligands of 1 and 2, respectively. The calculated results reveal that the N substitution not only tunes the emitting color of 1 and 2 but also enhances photoluminescence quantum efficiency. It is hoped that the designed 1a, 2a and 2c could be potential candidates as blue-emitting materials with high quantum efficiency. Moreover, the effects of different functionals on emission properties were also investigated. [ABSTRACT FROM AUTHOR]

A series of polynuclear superalkali cations C3X3Li3+, C3(NCN)3Li3+, C3X(NCN)2Li3+, C3[C(CN)2]3Li3+, C3(NCN)[C(CN)2]2Li3+, C3X[C(CN)2]2Li3+ (X = O, S, Se) and their corresponding neutral species were investigated by using the density functional theory. Except for C3Se3Li3, the ionization potentials for the studied neutral species are in the range of 2.52–3.75 eV, which are lower than the ionization potential of Cs atom (3.89 eV). For C3Se3Li3, although it has larger IP value of 4.51 eV than 3.89 eV of Cs, it is still less than IP = 5.39 eV of Li atom. Hence, they can be classified as superalkalies. In addition, the calculated results also indicated that besides the hyperlithiated configuration and segregated configuration, the excess electron may fully delocalize over various atoms (both center and ligands) in superalkalies. The present investigation gives hints to scientists that the search to a superatom can be extended by using more complicated cyclic (pseudo)oxocarbons as the central core of polynuclear superalkalies. [ABSTRACT FROM AUTHOR]

The ground and excited state geometries of several red-emitting phosphors (N∧N)2Os(P∧P) [where N∧N = 5-(1-isoquinolyl)-1,2,4-triazoles, P∧P = bis(dimethylphosphino)methylene(dmpm) (1); P∧P = cis-1,2-bis-(dimethylphosphino)ethene(dmpe) (2); P∧P = 1,2-bis(dimethylphosphino)benzene(dmpb) (3); P∧P = 1,2-bis(dimethylphosphino)naphthalene(dmpn) (4); P∧P = 1,2-bis(dimethylphosphino)-4-cyano-benzene(dmpcb) (5)] have been investigated by using the density functional theory (DFT) methods. The calculated results indicate that, for the studied complexes, the electron-transporting performance is better than the hole-transporting performance. The alteration of cis-P∧P ancillary ligands with different conjugation lengths and substituents has an impact on the optoelectronic properties of these complexes, especially the electron-withdrawing group –CN in 5. The calculated energy gaps are nearly the same for complexes 1to 4(3.34 eV), while for 5, the HOMO and LUMO energies are lowered and the energy gap increases (3.42 eV). The absorption of 1is red shifted, while that of 5is blue shifted compared with the absorptions of 2, 3, and 4, which have similar absorptions. Complexes 2, 3, and 4have almost identical emission wavelength 699 nm, while 1(715 nm) and 5(735 nm) are red shifted. The calculated electron affinities and reorganization energies indicate that complex 5is the easiest for electron injection and has the best electron-transporting performance. [ABSTRACT FROM AUTHOR]

The phase stability and mechanical properties of tungsten borides W2B, WB, WB2, W2B5and WB4were extensively studied by first-principles calculations within density functional theory. The thermodynamic and mechanical stabilities were examined. Our calculations on the enthalpy–pressure relationship and convex hulls have demonstrated that at zero pressure, the experimentally observed W2B–W2B (W2B–W2B represents W2B in W2B structure type, the same hereinafter) and WB–WB, and assumed WB2–ReB2phases are stable against decomposition into other components. The estimated hardness of WB2–ReB2is 39.4 GPa, suggesting that it is a potentially hard compound. At 60 GPa, the most stable phases are WB–WB and WB2–WB2. WB–WB, WB2–AlB2and WB4are the ground state phases at 100 GPa. The phase transition mechanism for WB2was discussed. The synthesis of WB2–AlB2could be conducted at high pressures. [ABSTRACT FROM AUTHOR]

H 2 TiO 3 (HTO) is considered to be one of the most promising adsorbents for lithium recovery from aqueous lithium resources duo to its highest theoretical adsorption capacity. However, its actual adsorption capacity is much lower owing to its unknown structure and incomplete leaching of lithium. After Al is doped into H 2 TiO 3 (HTO-Al), the adsorption capacity of HTO-Al is 32.12 mg g -1 and the dissolution of Ti is 2.53%. HTO-Al has good adsorption selectivity, and all the separation factors α are ≫1. Furthermore, HTO-Al also exhibits good cyclic stability and solubility resistance. After 5 cycles, the adsorption capacity remains 29.3 mg g -1 and the dissolution rate is 1.7%. Therefore, HTO-Al has potential application value for recovering Li + from aqueous lithium resources., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The ion-exchange process is usually influenced by the surface properties of the adsorbents. In particular, the prophase adsorption/desorption process is confined by different crystal facets. In this research, spinel Li4Ti5O12 nanosheets with an exposed (1-14) high-index facet were prepared by a hydrothermal method followed by calcination treatment. Then, a H4Ti5O12 adsorbent was obtained, covered with the same (1-14) facets, after treatment with 0.2 M HCl. This special facet-exposed H4Ti5O12 has high cycling ability, with the adsorption uptake remaining at 96.84% after four cycles, a fast adsorption equilibrium time (equilibrium time < 60 min), excellent ion adsorption selectivity for Li+ uptake (separation factor: Li+ > K+ > Ca2+ > Na+ > Mg2+), and good adsorption capacity for Li+ uptake (21.57 mg g-1 ). With the help of X-ray photoelectron spectroscopy analyses, the Li+ adsorption process on the H4Ti5O12 nanosheets is shown to be an ion-exchange process. In addition, the coordination relationship between lithium and oxygen ions was investigated, illustrating that the four-coordinated structure is more stable than other complexes. These results indicate that hydrogen ions are exchanged for lithium ions at tetrahedral 8a sites, leading to the H4Ti5O12 structure with high stability in the adsorption-desorption cycling process.

The adsorption method is a promising route to recover Li + from waste lithium batteries and lithium-containing brines. To achieve this goal, it is vital to synthesize a stable and high adsorption capacity adsorbent. In this work, Li 4 Ti 5 O 12 nanorods are prepared by two hydrothermal processes followed by a calcination process. Then the prepared Li 4 Ti 5 O 12 nanorods are treated with different HCl concentrations to obtain a H 4 Ti 5 O 12 adsorbent with 5 μm length along the [100] direction. The maximum amount of extracted lithium can reach 90% and the extracted titanium only 2.5%. The batch adsorption experiments indicate that the H 4 Ti 5 O 12 nanorod maximum adsorption capacity can reach 23.20 mg g -1 in 24 mM LiCl solution. The adsorption isotherms and kinetics fit a Langmuir model and pseudo-second-order model, respectively. Meanwhile, the real adsorption selectivity experiments show that the maximum Li + adsorption capacity reaches 1.99 mmol g -1 , which is far higher than Mg 2+ (0.03 mmol g -1 ) and Ca 2+ (0.02 mmol g -1 ), implying these nanorods have higher adsorption selectivity for Li + from Lagoco Salt Lake brine. The adsorption capacity for Li + remains 91% after five cycles. With the help of XPS analyses, the adsorption mechanism of Li + on the H 4 Ti 5 O 12 nanorods is an ion exchange reaction. Therefore, this nanorod adsorbent has a potential application for Li + recovery from aqueous lithium resources., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

Lithium-rich spinel lithium manganese oxide (LMO) compounds are one kind of promising adsorbents for lithium recovery from brine due to their high capacity and low Mn dissolution; Li1.6Mn1.6O4 is one of them. However, Mn3+ exists in the Li1.6Mn1.6O4 precursor due to incomplete reaction during syntheses, and the disproportionation reaction of Mn3+ inevitably results in Mn dissolution during lithium adsorption and desorption. The stable recycling and structural stability of Li1.6Mn1.6O4 were improved in aqueous lithium resources through K-gradient doping (LMO-K). The dissolution of Mn is reduced to 4.0% from 5.4% (before doping) and the adsorption capacity is kept at high capacity (31.6 mg g-1) at a low Li+ concentration of 12 mmol L-1. In addition, first-principles calculations further confirm that K substitutes for Li at 16d sites, leading to the stabilization of the Mn cations in the compound. With the help of K doping, the undesired dissolution of Mn in the cycle process is inhibited, which may be due to the reduction in the content of Mn3+ and improvement in the structural stability of the adsorbent.

The rational design of non-noble materials as low-cost, highly efficient, and durable catalysts to improve the oxygen reduction reaction is extremely urgent and challenging. The oxygen reduction reaction is a kinetically sluggish process that greatly affects the energy conversion efficiency. In this paper, novel hierarchical heteroatoms-co-doped Fe 2 M/graphene (M = P, N) nanocomposites were developed by a facile strategy, including hydrothermal and subsequent calcination methods. The thermal treatment of an ionic liquid and thiourea not only supplied heteroatom sources but also promoted the formation of iron phosphide and iron nitride and enhanced their catalytic performances. The electrochemical results indicated that the as-obtained hybrid catalysts manifested enhanced electrocatalytic activity toward the oxygen reduction reaction owing to the strong synergistic effects. The high content of heteroatoms distributed on the surface and interface of the hybrids and the density functional theory calculations suggested that Fe-N-C, Fe-P-C, and Fe-S-C multiple active surface sites were formed at the hybrids interfaces. Moreover, these results demonstrated that heteroatom-doped catalysts could effectively form a charge-transfer channel and thus modify the charge distribution in the hybrids interfaces. The as-prepared heteroatoms-doped Fe 2 M/graphene hybrids would be developed into highly efficient catalysts as ideal alternatives for noble metal catalysts in practical applications.

Non-precious metal catalysts have attracted particular interest in recent years due to their promising ORR (oxygen reduction reaction) activity in fuel cells. In this work, the structural stability and ORR mechanism of CoN 3 embedded graphene have been studied theoretically in acid media. The results indicate that CoN 3 embedded graphene is stable thermodynamically. The kinetically most favorable reaction pathway for the ORR is a four-electron process. The process of OOH hydrogenation to generate O + H 2 O is the most favorable pathway. In the rate determining step, the energy barrier is 0.38 eV, much smaller than the theoretical value of ∼0.80 eV for pure Pt. The predicted working potential is 0.4 V for the most favorite pathway. Besides the lower energy barrier, the smaller Tafel slope compared with pure Pt in both low and high overpotential regions also suggests that CoN 3 embedded graphene is a promising electrocatalyst for the ORR.

The electronic structures and photophysical properties of the recently reported Ir(iii) cyclometallated complexes containing the 2-(1-phenoxy-4-phenyl)-5-methylpyridine ligand (1) were studied via density functional theory and time-dependent density functional theory calculations. To improve the performance and establish the structural-photophysical property relationships, a series of Ir(iii) complexes 2-6 with -CH3/H and t-Bu substituents have been designed according to the experimental complex 1. The calculated results demonstrate that the different substituted ligands not only modify the absorption and emission bands, but also enhance the phosphorescent quantum efficiency. The t-Bu substituent increases the energy levels of the LUMO for complexes 4, 5 and 6 and broadens the HOMO-LUMO energy gaps. When compared with 1, the emission wavelengths for 3 and 6 are red-shifted considerably, while they are slightly blue-shifted for 4 and 5. In particular, the -CH3 and t-Bu substituents in 2, 4 and 5 lead to a relatively high quantum yield. Therefore, the designed complexes 2, 4 and 5 with -CH3/t-Bu substituents are expected to be promising phosphorescence emitters with high quantum efficiency.

A DFT/TDDFT investigation was carried out on a series of homoleptic triphenylamine-featured Ir(iii) complexes [: (fac-tris[2-phenyl-4-(2-(N,N-diphenylamino)phenyl)pyridine]iridium(iii)); : (fac-tris[2-phenyl-4-(3-(N,N-diphenylamino)phenyl)pyridine]iridium(iii)); : (fac-tris[2-phenyl-4-(4-(N,N-diphenylamino)phenyl)pyridine]iridium(iii))] with one triphenylamine unit in the 2-phenylpyridine (ppy) ligand and [: (fac-tris[2,4-bis(2-(N,N-diphenylamino)phenyl)pyridine]iridium(iii)); : (fac-tris[2,4-bis(3-(N,N-diphenylamino)phenyl)pyridine]iridium(iii)); : (fac-tris[2,4-bis(4-(N,N-diphenylamino)phenyl)pyridine]iridium(iii))] with two triphenylamine units in the ppy ligand, respectively, aiming to gain insight into the influence of number and ligation position of triphenylamine units on the photophysical and electronic properties of the studied complexes. Complexes have been synthesized recently. For comparison, the parent complex Ir(ppy)3 was also investigated. The calculated results reveal that the introduction of the triphenylamine unit leads to enhanced charge-injection abilities and a balanced charge-transfer process compared with Ir(ppy)3. The different ligation positions of triphenylamine unit have an obvious effect on the absorption intensities for these complexes. The emissions of and undergo significant red shift with the introduced triphenylamine unit in ppy ligands compared with that of Ir(ppy)3, while the extent of red shift shows an apparent dependence on the number of triphenylamine units. The factors that might affect the quantum yield have been discussed.

La2VMnO6 is an insulating ferrimagnet experimentally. By substituting La with Sr, La2-xSrxVMnO6 (x = 0.5, 1.0, 1.5, 2.0) was investigated using the density functional theory. Our results indicated that half metallic properties are obtained for x = 0.5, 1.5, 2.0. For x = 1.0, it is insulating. With the increase of hole doping, the holes initially go to V 3d orbitals for x = 0.5, 1.0, and after that, the holes go to the Mn 3d orbitals for x = 1.5, 2.0. Ferrimagnetic coupling between V and Mn is found to be the ground state for x = 0.5, 1.5, while for x = 1.0 and 2.0, ferromagnetic and antiferromagnetic couplings between Mn and Mn are competitive for the ground state.

Trivalent rare-earth (RE(3+) = Eu(3+), Tb(3+)) ion activated KLa(MoO4)2 microspheres have been synthesized at 180 °C via a facile hydrothermal route without using any templates, surfactant, or other organic additives. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), photoluminescence (PL), and photoluminescent excitation spectra (PLE) were employed to characterize the samples. It is found that the pH value in the initial solution is responsible for crystal phase, shape determination and emission intensity of final products. The possible formation mechanism for products with uniform spheres has been presented. Furthermore, a systematic study on the photoluminescence of RE(3+) (RE(3+) = Eu(3+), Tb(3+)) doped KLa(MoO4)2 samples has been explored in order to obtain the multicolor tunable emission by varying the Tb(3+)/Eu(3+) ratio. The tunable luminescence may be potentially applied in fields such as solid state lighting and field emission displays.

Uniform and well-crystallized calcium fluorapatite [Ca5(PO4)3F, FAP] microrods have been successfully synthesized by a facile one-step hydrothermal synthesis method using sodium citrate as the crystal modifier. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), photoluminescent excitation spectra (PLE) and decay studies were employed to characterize the samples. The electronic structure and orbital population of FAP were also determined by means of density functional theory calculations. Under ultraviolet irradiation, the FAP:Tb(3+),Eu(3+) samples exhibit a blue-light emission of the host matrix, as well as the typical green emission band of the Tb(3+) ions, and a red-light emission of Eu(3+). The highly intense red emission bands of the Eu(3+) ions were attributed to the effective energy transfer from the Tb(3+) to Eu(3+) ions, which has been justified through the luminescence spectra and the fluorescence decay dynamics. The luminescence colors of FAP:Tb(3+),Eu(3+) microrods can be easily tuned by changing the concentration of Eu(3+) ions. The results reveal that the combination of the self-activated luminescence and rare earth-doping emission in FAP:Tb(3+),Eu(3+) microrods could result in tunable emission in a large color gamut, which can be used as a potential candidate for white-light-emitting diodes and other display devices.