Uranyl Affinity between Uranyl Cation and Different Kinds of Monovalent Anions: Density Functional Theory and Quantitative Structure-Property Relationship Model.

In order to design effective extractants for uranium extraction from seawater, it is imperative to acquire a more comprehensive understanding of the bonding properties between the uranyl cation (UO22+) and various ligands. Therefore, we employed density functional theory to investigate the complexation reactions of UO22+ with 29 different monovalent anions (L-1), exploring both mono- and bidentate coordination. We proposed a novel concept called "uranyl affinity" (Eua) to facilitate the establishment of a standardized scale for assessing the ease or difficulty of coordination bond formation between UO22+ and diverse ligands. Furthermore, we conducted an in-depth investigation into the underlying mechanisms involved. During the process of uranyl complex [(UO2L)+] formation, lone pair electrons from the coordinating atom in L- are transferred to either the lowest unoccupied molecular degenerate orbitals 1ϕu or 1δu of the uranyl ion, which originate from the uranium atom's 5f unoccupied orbitals. In light of discussion concerning the mechanisms of coordination bond formation, quantitative structure-property relationship analyses were conducted to investigate the correlation between Eua and various structural descriptors associated with the 29 ligands under investigation. This analysis revealed distinct patterns in Eua values while identifying key influencing factors among the different ligands.

Ion transport through short nanopores modulated by charged exterior surfaces.

Short nanopores find extensive applications, capitalizing on their high throughput and detection resolution. Ionic behaviors through long nanopores are mainly determined by charged inner-pore walls. When pore lengths decrease to sub-200 nm, charged exterior surfaces provide considerable modulation to ion current. We find that the charge status of inner-pore walls affects the modulation of ion current from charged exterior surfaces. For 50-nm-long nanopores with neutral inner-pore walls, the charged exterior surfaces on the voltage (surfaceV) and ground (surfaceG) sides enhance and inhibit the ion transport by forming ion enrichment and depletion zones inside nanopores, respectively. For nanopores with both charged inner-pore and exterior surfaces, continuous electric double layers enhance the ion transport through nanopores significantly. The charged surfaceV results in higher ion current by simultaneously weakening the ion depletion at pore entrances and enhancing the intra-pore ion enrichment. The charged surfaceG expedites the exit of ions from nanopores, resulting in a decrease in ion enrichment at pore exits. Through adjustment in the width of charged-ring regions near pore boundaries, the effective charged width of the charged exterior is explored at ∼20 nm. Our results may provide a theoretical guide for further optimizing the performance of nanopore-based applications, such as seawater desalination, biosensing, and osmotic energy conversion.

Colorimetric method transforms into highly sensitive homogeneous voltammetric sensing strategy for mercury ion based on mercury-stimulated Ti3C2Tx MXene nanoribbons@gold nanozyme activity.

Nanozymes were emerged as the next generation of enzyme-mimics which exhibit great applications in various fields, but there is rarely report in the electrochemical detection of heavy metal ions. In this work, Ti3C2Tx MXene nanoribbons@gold (Ti3C2Tx MNR@Au) nanohybrid was prepared firstly via a simple self-reduction process and its nanozyme activity was studied. The results showed the peroxidase-like activity of bare Ti3C2Tx MNR@Au is extremely weak, while in the presence of Hg2+, the related nanozyme activity is stimulated and improved remarkably, which can easily catalyze oxidation of several colorless substrates (e.g., o-phenylenediamine) to form colored products. Interestingly, the product of o-phenylenediamine exhibits a strong reduction current which is considerably sensitive to the Hg2+ concentration. Based on this phenomenon, an innovative and highly sensitive homogeneous voltammetric (HVC) sensing strategy was then proposed to detect Hg2+ via transforming the colorimetric method into electrochemistry since it can exhibit several unique advantages (e.g., rapid responsiveness, high sensitivity and quantificational). Compared to the conventional electrochemical sensing methods for Hg2+, the designed HVC strategy can avoid the modification processes of electrode coupled with enhanced sensing performances. Therefore, we expect the as-proposed nanozyme-based HVC sensing strategy provides a new development direction for detecting Hg2+ and other heavy metals.

Nitrogen-doped Ti3C2 MXene quantum dots as an effective FRET ratio fluorometric probe for sensitive detection of Cu2+ and D-PA.

In this work, a ratiometric fluorescence sensing platform was established to detect Cu2+ and D-PA (d-penicillamine) based on nitrogen-doped Ti3C2 MXene quantum dots (N-MODs) that was prepared via a simple hydrothermal method and exhibited strong fluorescent and photoluminescence performance as well as excellent stability. Since the oxidation reaction between o-phenylenediamine (OPD) and Cu2+ induced the formation of 2,3-diaminophenazine (ox-OPD) which not only can emerge an emission peak at 570 nm, but also inhibit the fluorescence intensity of N-MQDs at 450 nm, a ratiometric reverse fluorescence sensor via fluorescence resonance energy transfer (FRET) was designed to sensitively detect Cu2+, where N-MQDs acted as energy donor and ox-OPD as energy acceptor. More importantly, another considerably interesting phenomenon was that their catalytic oxidation reaction can be restrained in the presence of D-PA because of the coordination of Cu2+ with D-PA, further triggering the obvious changes in ratio fluorescent signal and color, thus a ratiometric fluorescent sensor of determining D-PA was proposed also in this work. After optimizing various conditions, the ratiometric sensing platform showed rather low detection limits for Cu2+ (3.0 nM) and D-PA (0.115 µM), coupled with excellent sensitivity and stability.

Iodine-doped g-C3N4 modified zinc titanate electron transporting layer for highly efficient perovskite solar cells.

The development of excellent ternary metal oxides as electron transporting layers (ETLs) is highly challenging for perovskite solar cells (PSCs). In this study, ZnTiO3 (ZTO) nanoparticles are synthesized via a facile sol-gel method, and used as an ETL in PSCs. Furthermore, for the first time, iodine-doped g-C3N4 (ICN) is introduced into ZnTiO3-based ETL as additive via a glass-assisted annealing route. Characterizations demonstrate that the ZnTiO3-based ETL with the addition of ICN will enhance the PCE, which is attributed to the improved crystalline quality and more favorable energy level alignment. Moreover, the existence of ICN will strengthen the interfacial cohesion between perovskite layer and ETL as well as retard the perovskite crystals from decomposing, leading to the high quality capping light-harvesting layer upon ICN-modified ZnTiO3 (ZTO-ICN) film. Consequently, a champion device fabricated with ZTO-ICN ETL achieves a maximum PCE of 19.17 % with an open circuit voltage (Voc) of 1.012 V, a short-circuit current density (Jsc) of 26.32 mA cm-2 and a fill factor (FF) of 0.720 under AM 1.5 G sunlight (100 mW cm-2).

Upon DFT-D3 dispersion correction and ECD spectral confirmation, only several conformers can stably coexist for three fungal cycloaspeptides (A, D, G).

Dispersion correction in theoretical determination of cyclopeptide conformations is emphasized. Whether in gas approximation or in solvation simulation, the density functional theory with London dispersion correction (DFT-D3) demonstrates that only 2-3 conformers can stably coexist for cycloaspeptides (A, D, G) at B3LYP-D3 and CAM-B3LYP-D3. Conformational rationality is confirmed by electronic circular dichroism (ECD). Whether for Cotton effect or for excitation energy, TD-B3LYP-D3 has better performances than TD-CAM-B3LYP-D3 because the former can better reproduce the experiment. A molecular orbital analysis is used to interpret ECD, where two energy bands observed in experiment originates from the ππ* transitions other than the σπ* transitions. Long-range correction and solvent effect make H-bonds shorten, and dispersion correction makes them further shorten.

Robust Mesoporous Functional Hydrogen-Bonded Organic Framework for Hypochlorite Detection.

Although tremendous progress has been achieved in the field of hydrogen-bonded organic frameworks (HOFs), the low stability, small/none pores, and difficult functionality severely obstruct their development. Herein, a novel robust mesoporous HOF (HOF-FAFU-1) decorated with a high density of free hydroxy moieties has been designed and readily synthesized in the de novo synthesis. In HOF-FAFU-1, the planar building blocks are connected to each other by typical intermolecular carboxylate dimers to form two-dimensional (2D) layers with sql topology, which are further connected to their adjacent layers by face-to-face π-π interactions to obtain a three-dimensional (3D) open mesoporous framework. Owing to the high density of intermolecular hydrogen bonding and strong π-π interactions, HOF-FAFU-1 is very stable, allowing it to retain its structure in aqueous solutions with a pH range of 1-9. Benefiting from the decorated hydroxy moieties, HOF-FAFU-1 was exploited as a fluorescent sensor for hypochlorite detection in water media by a turn-off mode, which cannot be realized by its nonhydroxy groups anchoring counterpart (HOF-TCBP). The proposed sensing system is highly efficient, validated by a very broad linear range (0-0.45 mM), fast response (15 s), and small limit of detection (LOD) (1.32 µM). The fluorescent quenching of HOF-FAFU-1 toward hypochlorite was also investigated, mainly being ascribed to the transformation of building blocks from the fluorescent reduced state to the nonfluorescent oxidative state. This work not only demonstrates that HOFs integrated with high stability and large pores as well as high density of functional groups can be simultaneously realized by judicious design of building blocks but also conceptually elucidates that such HOFs can effectively extend the application fields of HOFs.

Cuttlefish ink loaded polyamidoxime adsorbent with excellent photothermal conversion and antibacterial activity for highly efficient uranium capture from natural seawater.

Owing to the abundant uranium reserves in the oceans, the collection of uranium from seawater has aroused the widespread interest. Compared to the uranium extraction from ore, uranium collection from seawater is a more environmentally friendly strategy. The amidoxime (AO) functional group has been considered as one of the most efficient chelating groups for uranium capture. In this work, by drawing upon the photothermal character and antibacterial activity of cuttlefish ink, a cuttlefish ink loaded polyamidoxime (CI-PAO) membrane adsorbent is developed. Under one-sun illumination, the CI-PAO membrane shows a high extraction capacity of 488.76 mg-U/g-Ads in 500 mL 8 ppm uranium spiked simulated seawater, which is 1.24 times higher than PAO membrane. The adsorption rate of CI-PAO membrane is increased by 32.04%. Furthermore, exhibiting roughly 75% bacteriostatic rate in composite marine bacteria, the CI-PAO shows a dramatically antibacterial activity, which effectively prevents the functional sites on the adsorbent surface from being occupied by the biofouling blocks. After immersing in natural seawater for 4 weeks, light-irradiated CI-PAO gave high uranium uptake capacity of 6.17 mg-U/g-Ads. Hence, the CI-PAO membrane adsorbent can be considered as a potential candidate for the practical application for uranium extraction from seawater.

Novel Third-Order Nonlinear Optical Materials with Craig-Möbius Aromaticity.

Electron delocalization in aromatic materials significantly impacts their third-order nonlinear optics (NLO). Despite organometallic complexes with Craig-Möbius aromaticity attracting great attention for their unusual physicochemical properties, their third-order NLO have been little studied to date. Herein, 12 Craig-Möbius aromatic organometallics with a stable structure similar to osmapentalyne, namely, carbolong complexes, are screened by DFT. They exhibit high third-order NLO responses because of the d and p electron delocalization in the organometallic ring. Furthermore, electron-hole distribution analyses draw a conclusion that extending the conjugated plane will increase the π-conjugation system to enhance the local excitation in the plane, and the introduction of typical aromatic ligands can result in the organometallic ring-to-ligand charge transfer (RLCT), which are effective methods to improve the third-order NLO response. This study opens a new window in the application of Craig-Möbius aromatic complexes and provides a new approach for third-order NLO materials design.

Tin Metal Cluster Compounds as New Third-Order Nonlinear Optical Materials by Computational Study.

It is quite appealing but challenging to predict and synthesize new nonlinear optical (NLO) materials with exceptional performance. Herein, the different Sn4 cluster core structures and third-order NLO properties are studied through electronic structure, excited hole-electron, bonding character, and aromaticity analysis. As a result, Sn4 clusters with ring core structure (Sn4-R) not only have the smallest Egap, the largest UV-vis response intensity, but also the strongest third-order NLO response in our work. As proved by natural bond orbitals' (NBO) analysis, electron localization function (ELF), and adaptive natural density partitioning (AdNDP), the Sn44+ has two in-plane four center-two electron (4c-2e) Sn-Sn σ-bonds, resulting in a good delocalization. For the first time, delocalization of metal cluster cores in tin clusters that is beneficial to the third-order NLO response is proposed, which provides a new guidance to design and prepare third-order NLO materials.

A Review of Conductive Carbon Materials for 3D Printing: Materials, Technologies, Properties, and Applications.

Carbon material is widely used and has good electrical and thermal conductivity. It is often used as a filler to endow insulating polymer with electrical and thermal conductivity. Three-dimensional printing technology is an advance in modeling and manufacturing technology. From the forming principle, it offers a new production principle of layered manufacturing and layer by layer stacking formation, which fundamentally simplifies the production process and makes large-scale personalized production possible. Conductive carbon materials combined with 3D printing technology have a variety of potential applications, such as multi-shape sensors, wearable devices, supercapacitors, and so on. In this review, carbon black, carbon nanotubes, carbon fiber, graphene, and other common conductive carbon materials are briefly introduced. The working principle, advantages and disadvantages of common 3D printing technology are reviewed. The research situation of 3D printable conductive carbon materials in recent years is further summarized, and the performance characteristics and application prospects of these conductive carbon materials are also discussed. Finally, the potential applications of 3D printable conductive carbon materials are concluded, and the future development direction of 3D printable conductive carbon materials has also been prospected.

In situ synthesis of g-C3N4 by glass-assisted annealing route to boost the efficiency of perovskite solar cells.

TiO2-based electron transport layers (ETLs) show tremendous advantages in constructing efficient perovskite solar cells (PSCs), but the power conversion efficiency (PCE) needs further improvements. Thus, in this study, graphitic carbon nitride (g-C3N4), a typical two-dimensional material, was synthesized in-situ and introduced into TiO2-based ETLs as an additive via a facile glass-assisted annealing route. The results demonstrated that the addition of g-C3N4 positively influenced the crystalline quality of the perovskite layers, as well as the conductivity and photovoltaic properties of the devices. Furthermore, favorable energy level alignment facilitated rapid migration of electrons and suppressed charge recombination at the interfaces. Consequently, the champion device fabricated using the g-C3N4-modified ETL achieved a maximum PCE of 20.46% owing to the remarkable improvement in the Voc, Jsc, and fill factor. The PCE is approximately 20% higher than that obtained for the pristine device, i.e., 17.18%.

Dual-emissive metal-organic framework: a novel turn-on and ratiometric fluorescent sensor for highly efficient and specific detection of hypochlorite.

Hypochlorite (ClO-) is widely used as a disinfectant, whose residue content in water should be strictly controlled due to the potential threat to human health in an inappropriate concentration. Herein, dual-emissive metal-organic frameworks with a UiO-66 prototype structure, PDA/Eu/PDA-UiO-66-NH2(x), were elegantly designed and prepared by a mixed ligand assembly and sequential post-synthesis strategy. Since blue emission is sensitive to ClO-, PDA/Eu/PDA-UiO-66-NH2(40) was selected as a model nanosensor for ratiometric and turn-on sensing of ClO- while red emission acts as a reference signal. Remarkably, PDA/Eu/PDA-UiO-66-NH2(40) shows high efficiency and specificity toward ClO- detection, as verified by a very short response time of 15 s, a wide linear range of 0.1-60 µM, a low detection limit of 0.10 µM, and excellent selectivity toward common competing ions. The recovery experiments show that the recoveries of spiking ClO- in tap water range from 96 to 103%. The rigidification of the coordinated H2N-BDC2- ligands should be responsible for the turn-on fluorescence of PDA/Eu/PDA-UiO-66-NH2(40). This work not only shows a highly efficient and specific fluorescent nanosensor for ClO- detection but also presents the first MOF-based fluorescent probe for turn-on and ratiometric sensing of ClO-.

Anion-directed assemblies of europium(III) coordination polymers based on 1H-benzimidazole-5,6-dicarboxylate: structures and luminescence properties.

Two europium(III) coordination polymers (CPs), namely, poly[[diaquabis(µ4-1H-benzimidazole-5,6-dicarboxylato-κ6N3:O5,O5':O5,O6:O6')(µ2-oxalato-κ4O1,O2:O1',O2')dieuropium(III)] dihydrate], {[Eu2(C9H4N2O4)2(C2O4)(H2O)2]·2H2O}n (1), and poly[(µ3-1H-benzimidazol-3-ium-5,6-dicarboxylato-κ5O5:O5',O6:O6,O6')(µ3-sulfato-κ3O:O':O'')europium(III)], [Eu(C9H5N2O4)(SO4)]n (2), have been synthesized via the hydrothermal method and structurally characterized. CP 1 shows a three-dimensional network, in which the oxalate ligand acts as a pillar, while CP 2 has a two-dimensional network based on a europium(III)-sulfate skeleton, further extended into a three-dimensional framework by hydrogen-bonding interactions. The structural diversity in the two compounds can be attributed to the different acidification abilities and geometries of the anionic ligands. The luminescence properties of 1 display the characteristic europium red emission with CIE chromaticity coordinates (2/3, 0.34). Interestingly, CP 2 shows the characteristic red emission with CIE chromaticity coordinates (0.60, 0.34) when excited at 280 nm and a near-white emission with CIE chromaticity coordinates (0.38, 0.29) when excited at 340 nm.

First-principles study of structural stability, electronic and optical properties of GA-doped MAPbI3.

Organic-inorganic hybrid halide perovskites have been considered as potential photoconductive materials for photovoltaic applications. Through first-principles calculations, we have investigated the structural stability, electronic and optical properties of GA-doped MAPbI3. Our calculated results reveal that 25% GA doping slightly reduce the structural stability of MAPbI3. The band gap of GA-doped MAPbI3 is increased from 1.49 to 1.60 eV. The optical absorption of GA-doped MAPbI3 is weaken than that of MAPbI3 in the visible light region. Moreover, our calculated results can explain available experiments well. These finding can perovide a light on the development of efficient perovskite solar cells.

Computational analysis of non-heme iron-oxo formation by direct NO release in nitrite reduction.

A direct NO-releasing reaction of nitrite catalyzed by [N(afaCy)3Fe(OTf)]+ (afa (azafulvene-amine); OTf (trifluoromethanesulfonate); Cy (cyclohexyl)) was investigated using density functional theory (DFT) with D3 dispersion correction. The complex featured a secondary coordination sphere that facilitated the formation of the iron-oxo product [N(afaCy)3FeO]+ with three (Fe)OH-N hydrogen bonds. As a high-spin iron(ii), the O-binding initial intermediate Fe(O)-nitrito was thermodynamically favorable in the S = 2 state. The cleavage of the (Fe)O-NO bond was performed by a ß-electron shift to produce Fe(iii)-O by electron rearrangement in the S = 5/2 state. The different electron configurations are responsible for the structural properties, the valence of iron in the complexes, and the pathways of the reactions. Moreover, the two different H-bonds, (Fe)OH-N and (Fe)O-HN (by O-protonation), in the product complexes played a role in determining the reaction channels by impacting the N-H bond rotation. Thus, an exothermic sequence of conversions Fe(ii) → Fe(iii)-O → Fe(iii)-OH → Fe(iii)-O was established for the targeted product formation. This process provided a clue to build two key intermediates, iron-oxo and iron-hydroxo, in a variety of biological and synthetic systems. The results of this study are in agreement with experimental observations and describe the roles of H-bonding in nitrite reduction catalyzed by the non-heme iron complex.

Pressure-induced effects in the inorganic halide perovskite CsGeI3.

Perovskite photovoltaic materials are gaining significant attention due to their excellent photovoltaic properties. In this study, density functional theory calculations were performed to investigate the structure and electronic and optical properties of CsGeI3 under hydrostatic strain. The results show that the band gap of CsGeI3 can be tuned from 0.73 eV to 2.30 eV under different strain conditions. The results indicate that the change in the band gap under strain is likely to be determined by the Ge-I-Ge bond angle. Interestingly, the length of the short Ge-I bond remains unchanged, whereas that of the long Ge-I bond exhibits an evident increment with strain ranging from -4% to 4%. A suitable band gap (1.36 eV) of CsGeI3 can be obtained under a strain of -1%. Both the calculated elastic constants and the phonon spectrum imply that this structure is stable under the abovementioned condition. Bandgap narrowing induces a red shift of the light absorption spectrum of CsGeI3 by extending the onset light absorption edge. These results are important for understanding the effects of strain on the halide perovskites and guiding the experiments to improve the photovoltaic performance of the perovskite solar cells.

Ethylammonium as an alternative cation for efficient perovskite solar cells from first-principles calculations.

Mixed-cation lead halide perovskites have emerged as a new class of promising photovoltaic materials for perovskite solar cells. Formamidinium (FA), methylammonium (MA), and Cs cations are widely studied in the field of mixed-cation hybrid halide perovskites. In this work, we have investigated ethylammonium (CH3CH2NH3, EA) as an alternative cation to explore the stabilities and electronic properties of mixed MA1-x EA x PbI3 perovskites. The results indicate that replacing MA with EA is a more effective way to improve the stabilities of the mixed MA1-x EA x PbI3 perovskites except for MA0.75EA0.25PbI3. The band gap of MA1-x EA x PbI3 slightly increases with x from 0.25 to 1.00, which is quite different from the MA-FA mixed-cation perovskites. The results indicate that the c axis distortion of the Pb-I-Pb bond angles can play a greater role in tuning the band gap. Moreover, the mixed MA1-x EA x PbI3 perovskites show comparable absorption abilities in the visible light region to the pure MAPbI3 structure. We hope that our study will be greatly helpful for further experiments to find more efficient perovskite materials in the future.

A highly hydrolytically stable lanthanide organic framework as a sensitive luminescent probe for DBP and chlorpyrifos detection.

Organic pollutants have attracted increasing attention due to their strong persistence and extensive diffusivity. Plasticizers (PAEs) and organophosphorus pesticides (OPs), as the vital part of organic pollutants, have made extensive damage to the environment with the rapid development of modern agriculture and industry. Therefore, we have, for the first time, carried out a quantitative analysis of the PAEs and OPs by fluorescence recognition. A series of isostructural lanthanide organic frameworks, [Ln(tftpa)1.5(2,2'-bpy)(H2O)] (Ln = Gd 1, Eu 2 and Tb 3, H2tftpa = tetrafluoroterephthalic acid), were hydrothermally synthesized, of which 3 exhibited excellent hydrolytic resistance to both boiling acidic and basic aqueous solutions. Moreover, luminescence investigations show that 3 can be used as a highly sensitive and recyclable luminescence sensor for the detection of DBP (di-n-butyl phthalate) in simulated seawater and chlorpyrifos in ethanol with the detection limits of 2.07 and 0.14 ppb, respectively.

Synergistic Effect of Doping and Compositing on Photocatalytic Efficiency: A Case Study of La2Ti2O7.

Charge generation and separation are two key issues in developing a high-efficiency semiconductor for the visible-light-driven photocatalysis. Here, we use the layered perovskite-type wide-gap semiconductor La2Ti2O7 (LTO) as a model to systematically explore the synergistic effect of doping (with sulfur or nitrogen) and heterojunction (with graphitic C3N4) on improving visible light absorption and photoexcited charge separation by means of density functional theory calculations. It is found that the anion (N or S) doping into the LTO(010) surface can not only shift the optical absorption edge to the visible region, but also creates some partially occupied or unoccupied states in the band gap that would facilitate the formation of recombination centers. For the purpose of promoting electron-hole separation, the (N or S-doped) LTO(010) surfaces were hybridized with the monolayer g-C3N4. Interestingly, we found that the (S-doped) LTO/g-C3N4 heterostructure forms a type-II heterojunction, with the valence band maximum residing in the (S-doped) LTO and the conduction band minimum in g-C3N4, respectively. This band alignment feature facilitates efficient electron-hole separation. Moreover, we found that the S-doped LTO/g-C3N4 composite has a short interfacial distance (about 2.1 Å), implying that the interfacial interaction of this composite might be a chemical bond rather than a weak van der Walls interaction. The chemical bonding can enhance charge separation. Our theoretical findings provide design principles for optimizing the photocatalytic performance of the wide-gap photocatalysts and demonstrate that the S-doped LTO/g-C3N4 composite would be a potential candidate for the photocatalysis of water splitting.