A novel two-dimensional Janus TiSiGeN4 monolayer with N vacancies for efficient photocatalytic nitrogen reduction.

The photocatalytic nitrogen reduction reaction (pNRR) is a clean technology that converts H2O and N2 into NH3 under environmental conditions using inexhaustible sunlight. Herein, we designed a novel two-dimensional (2D) Janus TiSiGeN4 structure and evaluated the pNRR performance of the structure with the presence of nitrogen vacancies at different positions using density functional theory (DFT) calculations. The intrinsic dipoles in the Janus TiSiGeN4 structure generate a built-in electric field, which promotes the migration of photogenerated electrons and holes towards the (001) and (00-1) surfaces, respectively, to achieve efficient charge separation. For the pNRR, the Si atoms exposed after the formation of top N vacancies can realize the efficient activation of N2 through the "acceptance-donation" mechanism, while the presence of middle N vacancies not only suppresses the hydrogen evolution reaction, a competition reaction, but also lowers the reaction barrier for the protonation of N atoms. The limiting potential of TiSiGeN4 with the coexistence of both top and middle N vacancies (TiSiGeN4-VN-mt) is as low as -0.44 V. In addition, the introduction of N vacancies generates defect levels, narrowing the band gap and improving the light response. This work provides theoretical guidance for the design of efficient pNRR photocatalysts under mild conditions.

Preparation of highly dispersed Ni single-atom doped ultrathin g-C3N4 nanosheets by metal vapor exfoliation for efficient photocatalytic CO2 reduction.

Single-atom photocatalysts can modulate the utilization of photons and facilitate the migration of photogenerated carriers. However, the preparation of single-atom uniformly doped photocatalysts is still a challenging topic. Herein, we propose the preparation of Ni single-atom doped g-C3N4 photocatalysts by metal vapor exfoliation. The Ni vapor produced by calcining nickel foam at high temperature accumulates in between g-C3N4 layers and poses a certain vapor pressure to destroy the interlayer van der Waals forces of g-C3N4. Individual metal atoms are doped into the structure while exfoliating g-C3N4 into nanosheets by metal vapor. Upon optimization of Ni content, the Ni single atom doped g-C3N4 nanosheets with 2.81 wt% Ni exhibits the highest CO2 reduction performance in the absence of sacrificial agents. The generation rates of CO and CH4 are 19.85 and 1.73 µmol g-1h-1, respectively. The improved photocatalytic performance is attributed to the anchoring Ni of single atoms on g-C3N4 nanosheets, which increases both carrier separation efficiency and reaction sites. This work provides insight into the design of photocatalysts with highly dispersed single-atom.

Structural stability, dihydrogen bonding, and pressure-induced polymorphic transformations in hydrazine borane.

Hydrazine borane (N2H4BH3) has attracted considerable interest as a promising solid-state hydrogen storage material owing to its high hydrogen content and easy preparation. In this work, pressure-induced phase transitions of N2H4BH3 were investigated using a combination of vibrational spectroscopy, X-ray diffraction, and density functional theory (DFT) up to 30 GPa. Our results showed that N2H4BH3 exhibits remarkable structural stability in a very broad pressure region up to 15 GPa, and then two phase transitions were identified: the first one is from the ambient-pressure Pbcn phase to a Pbca phase near 15 GPa; the second is from the Pbca phase to a Pccn phase near 25 GPa. As revealed by DFT calculations, the unusual stability of N2H4BH3 and the late phase transformations were attributed to the pressure-mediated evolutions of dihydrogen bonding frameworks, the compressibility and the enthalpies of the high-pressure polymorphs. Our findings provide new insight into the structures and bonding properties of N2H4BH3 that are important for hydrogen storage applications.

Chiral MOF Derived Wearable Logic Sensor for Intuitive Discrimination of Physiologically Active Enantiomer.

Chiral sensors have attracted growing interest due to their application in health monitoring. However, rational design of wearable logic chiral sensors remains a great challenge. In this work, a dual responsive chiral sensor RT@CDMOF is prepared through in situ self-assembly of chiral γ-cyclodextrin metal-organic framework (CDMOF), rhodamine 6G hydrazide (RGH), and tetracyanovinylindane (TCN). The embedded RGH and TCN inherit the chirality of host CDMOF, producing dual changes both in fluorescence and reflectance. RT@CDMOF is explored as a dual channel sensor for chiral discrimination of lactate enantiomers. Comprehensive mechanistic studies reveal the chiral binding process, and carboxylate dissociation is confirmed by impedance and solid-state 1 H nuclear magnetic resonance (NMR). A flexible membrane sensor is successfully fabricated based on RT@CDMOF for wearable health monitoring. Practical evaluation confirms the potential of fabricated membrane sensor in point-of-care health monitoring by indexing the exercise intensity. Based on above, a chiral IMPLICATION logic unit can be successfully achieved, demonstrating the promising potential of RT@CDMOF in design and assembly of novel smart devices. This work may open a new avenue to the rational design of logic chiral sensors for wearable health monitoring applications.

Achieving Simplified and Tunable Flexibility in Carborane-Based Emitters for Quantitative Vapochromic VOC Sensing.

Photoluminescence (PL) sensing of volatile organic compounds (VOCs) represents a convenient and economic detection method toward air pollutants. However, tetraphenylethylene (TPE)-based and recent carborane (Cb)-based sensors retained multiple sites that are responsive to VOC stimulation, making quantitative PL sensing rather challenging. Rendering the simplified and tunable flexibility in the PL sensors is key to achieve the quantitative target. In this work, we proposed a dimeric model of Cb-based emitters to deal with flexibility. Three emissive dibenzothiophene (DBT)-alkynylated carboranes (Cb-1/2/3) were designed and synthesized. Among them, Cb-3 contributed green and green-yellow emission in the crystals, as well as yellow and orange emission in the VOC-incorporated films, together unfolding its vapochromic properties. Crystallographic studies revealed that Cb-3 molecules were invariably dimerized in an interlocked fashion and the redshift in PL was caused by the successive through-space conjugation of DBT moieties. Theoretical calculations verified the thermodynamics stability of Cb-3 dimers and suggested that DBT could individually rotate different angles under the simulation of VOCs. Based on the above findings, we introduced DBT-alkynylated carboranes to detect the VOCs and established linear relationships between the photon energy at the PL maxima and the concentrations of benzene and tetrahydrofuran (THF) vapors. Aside from the successful implementation of quantitative vapochromic sensing, the fast response (6 s) and recovery (3∼5 s), as well as the good reusability, were also evidenced in the sensing of THF vapors.

Kinetics analysis of oxygen vacancies in TiO2 solar water reduction: Revealing effects and eliminating disadvantages.

A consensus is yet to be reached on the effects of oxygen vacancy (VO) on the performance of TiO2 for photocatalytic water splitting as contrasting viewpoints have been presented in the latest researches. Herein, a comprehensive set of spectroelectrochemical methods are deployed to clearly reveal the advantages and disadvantages of VO on the performance of TiO2. The results indicate that surface VO improves the photocatalytic activity while bulk VO has a negative effect on the water reduction performance of TiO2. Intensity-modulated photocurrent spectroscopy (IMPS) and UV-vis spectroscopy provide compelling evidence that the improvement of H2 evolution can be attributed to the presence of defect level, while the low interface charge transfer efficiency caused by surface VO limits the further improvement of photocatalytical H2 evolution, which can be alleviated by an organic hole transport coating. The density functional theory (DFT) and surface photovoltaic (SPV) analyses confirm that the built-in field between TiO2 and hole molecules is the reason for the interface charge transfer efficiency improvement. Our findings provide a comprehensive understanding of VO in TiO2 by carrier behavior analysis and a scheme to further promote the photocatalytic performance.

Chiral UiO-MOFs based QCM sensors for enantioselective discrimination of hazardous biomolecule.

Developments of enantioselective devices for discriminating bio-enantiomers is of significant importance. Due to the vital role of Cysteine (Cys) in biological processes and the hazardous effect of its D-enantiomer, discriminating Cys enantiomers without auxiliary enzyme is highly wanted. In this work, a pair of UiO-MOF enantiomers (UiO-tart) have been fabricated through post-modification, which could be further fabricated into enantiomeric sensing devices (UiO-tart@Au). By employing the Quartz Crystal Microbalance (QCM) technology, gravimetric discrimination of Cys enantiomers could be achieved. UiO-tart@Au is highly enantioselective, and the afforded enantioselective factor (5.97 ± 0.54) represents the best performance reported ever. In the fabricated device, MOF layer acts as the chiral selector for specific Cys enantiomer, and the reaction between the captured Cys enantiomer and Au results in the mass growth of the system. Solid-phase extraction (SPE) gives an e.e. value of 71.6 ± 3.8%, substantially confirming the chiral-selector role of UiO-tart. DFT calculations indicate that enantiomeric H-bonding effect and greater reaction enthalpy should be the reason. To the best of our knowledge, this work represents the first example of chiral tartaric acid derived MOF sensors for enantioselective discrimination of Cys, suggesting a promising potential of developing chiral MOFs based devices for enhanced enantioselective application.

Recovering the Thermally Activated Delayed Fluorescence in Aggregation-Induced Emitters of Carborane.

The aggregation-induced emission (AIE) behaviors of carborane-based hybrid emitters have been extensively reported, while their combinations with the thermally activated delayed fluorescence (TADF) are still scarce. We designed and synthesized three Janus carboranes (the chemical structures resemble the double-faced god, Janus) Cb-1/2/3 with different carbazole moieties. All of the Janus carboranes exhibited quenched emission in solution with ΦPL (quantum efficiency of photoluminescence (PL)) lower than 0.01. The PL performance was improved by proceeding to the aggregates in THF/water (ΦPL 0.17-0.35) and further improved in the crystals or solid with ΦPL up to 0.99 for Cb-1, 0.85 for Cb-2, and 0.61 for Cb-3, which agreed with the AIE enhancement. Although the PL of solid Cb-1/2/3 showed non-TADF properties with lifetimes only at several nanoseconds, the crystallographic studies have shown a root cause of π···π stacking that quenched the TADF, and the theoretical calculations forecasted small singlet-triplet energy gaps (ΔES-T) therein. According to these findings, TADF was recovered in Cb-1/2/3 by doping into 1,3-bis(carbazol-9-yl)benzene (mCP). The 10 wt % doped films of Cb-1/2/3 have achieved a trade-off of ΦPL (0.84 in Cb-3 and 0.83 in Cb-1) and delayed lifetime (up to 8 µs). The doped devices of organic light-emitting diodes incorporating Cb-1/2/3 achieved the highest external quantum efficiency at 10.1% and the maximized luminance of 5920 cd/m2 at a driving voltage of 8 V.

Selective dual detection of H2S and Cu2+ by a post-modified MOF sensor following a tandem process.

Fabrication of metal-organic frameworks (MOFs) based multifunctional sensors for various environmental pollutants represents a promising solution to the development of novel monitoring technologies. In this work, a dual responsive sensor of UiO-66-MA has been efficiently fabricated via post-modification of the UiO-66-MOF with maleic anhydride (MA), and dual detection of H2S and Cu2+ in aquatic environments has been achieved tandemly. UiO-66-MA could selectively undergo Michael addition with H2S accompanying a linear fluorescence turn-on behavior. The sensing is highly sensitive and selective, and the detection limit value of 3.3 nM represents the lowest record among all MOF-based H2S sensing researches. Moreover, an alternative sensor for Cu2+ could be further tandemly afforded after the H2S sensing. The H2S added product of UiO-66-MA/H2S exhibits selective fluorescence quenching towards Cu2+ with a detection limit as low as 2.6 nM. UiO-66-MA exhibits dual sensing functions for H2S and Cu2+ following a tandem process based on combinatorial principles of Michael addition and S-Cu coordination. Evaluation studies suggest the promising potentials of UiO-66-MA in determining the level of H2S and Cu2+ in aquatic environment, and the tandemly derived dual sensing functions demonstrate the advantages of developing multifunctional MOF sensors based on combinatorial principles.

Postmodified Dual Functional UiO Sensor for Selective Detection of Ozone and Tandemly Derived Sensing of Al3.

Development of highly sensitive and selective fluorescent sensors toward hazardous analytes represents great progress in fabricating sensing devices for practical applications. In this work, a highly selective sensor with dual functions has been fabricated via facile postmodification of the UiO-MOF. Butene modified salicylaldehyde is covalently linked to the UiO-66 scaffold via an efficient Schiff-base reaction, resulting in a highly fluorescent ozone sensor of UiO-66-butene. Ozonolysis of the terminal olefin followed by ß-elimination could significantly quench the bright blue fluorescence of UiO-66-butene, and linear turn-off detection of ozone in the range of 0-100 µM is well established. The detection is highly sensitive and selective, and a detection limit of 73 nM was calculated. Remarkably, the ozonolysis afforded product could further act as a selective sensor for Al3+ via turn-on fluorescence with a detection limit of 142 nM, representing a second potential sensing function. The chemically selective sequential ozonolysis/ß-elimination and remarkable dual functions offer the exclusive detection of ozone over other oxidative species as well as Al3+ over other cations following a tandem process, representing the first example of a direct MOF sensor for dual sensing of ozone and Al3+. This work demonstrates the potential of employing combinatorial principles for fabricating highly selective sensors, and postmodification of MOFs represents a promising facile strategy for developing various functional sensors.

QCM based enantioselective discrimination of enantiomers by a pair of serine derived homochiral coordination polymers.

Decoding enantioselective molecular interactions between sensors and guests into readable signal represents a great challenge in developing selective sensing technology. In this work, a pair of serine derivatives based homochiral coordination polymer (HCP) enantiomers, (L)-SA-Cd and (D)-SA-Cd, were synthesized and explored as enantioselective sensors towards guest enantiomers. Quartz crystal microbalance (QCM) technology was employed to indicate the gravimetric change of (L)- and (D)-SA-Cd towards variable chiral guests, and an enantioselective factor of 1.72 ±â€¯0.15, 1.81 ±â€¯0.08, 1.37 ±â€¯0.03 and 2.89 ±â€¯0.09 were achieved for lactic acid, menthol, valinol and 1-phenylethylamine (PEA), respectively. PEA was further selected to comprehensively study the enantioselectivity via electrochemical tests, HPLC analysis and theoretical calculations. By comparison with state-of-art works, the enantioselective discrimination for PEA enantiomers is better than a vast majority of similar reports. (L)- and (D)-form of SA-Cd exhibited mirror behaviors towards guest enantiomers, and control experiments indicated the role of HCP construction in enhancing enantioselectivity. H-bonding effect was found to be the binding force between SA-Cd and PEA, as verified by FT-IR and UV-Vis titration studies. Further DFT calculations revealed the existence of conformation oriented H-bonding between the chiral -OH groups of serine fragment and -NH2 group of PEA. The findings indicate that HCP construction represents an effective strategy for promoting enantioselectivity, and monitoring gravimetric change could be a promising general method in decoding most of the enantioselective recognition process.

Zirconium based metal-organic framework in-situ assisted hydrothermal pretreatment and enzymatic hydrolysis of Platanus X acerifolia exfoliating bark for bioethanol production.

Metal-organic framework (MOF) assisted hydrothermal pretreatment and co-catalysis strategy based on UiO-66 MOF is developed for the first time. The Planetree exfoliating bark was pretreated with or without UiO-66 assisted hydrothermal method at a temperature ranging from 160 to 240 °C for 1-3 h residence. With the rise of pretreatment severity, the total reducing sugar (TRS) was increased till reached maximum, 180 mg g-1, in the presence of UiO-66. The fitting models validate the optimal hydrothermal condition was at 180 °C and 1 h, which was characterized with high TRS and very low yield of furfural and HMF. The TRS from enzymatic hydrolysis reaches maximum, 391 mg g-1, in the presence of MOF co-catalysis and the maximum ethanol yield achieved was 73%. Altered morphology, higher surface area and porosity are noticed after MOF assisted hydrothermal pretreatment. This study insights the MOFs' application in lignocellulose biomass processing.

Hydrolysis of cellulose using cellulase physically immobilized on highly stable zirconium based metal-organic frameworks.

Developing a new cellulase-MOF composite system with enhanced stability and reusability for cellulose hydrolysis was aimed. Physical adsorption strategy was employed to fabricate two cellulase composites, and the activity of composite was characterized by hydrolysis of carboxymethyl cellulose. The NH2 functionalized UiO-66-NH2 MOF exhibited higher protein loading than the precursor UiO-66, due to the extra anchor sites of NH2 groups. The immobilized cellulase showed enhanced thermostability, pH tolerance and lifetime. The maximum activity attained at 55 °C could be kept 85% when used at 80 °C, and the residual activities were 72% after ten cycles and 65% after 30 days storage. The abundant NH2 and COOH groups of MOF adsorb cellulase and enhance its stability, and the resulted heterogeneity offered the opportunity of recovering composite via mild centrifuge. The findings suggest the promising future of developing cellulase-MOF composite with ultrahigh activities and stabilities for practical application.

A multifunctional Co-based metal-organic framework: heterogeneous catalysis, chemiluminescence sensing and moisture-dependent solvatochromism.

Crystalline materials with multi-catalytic applications are of great value to both fundamental research and practical applications. The platform of metal-organic frameworks (MOFs) is utilized to fabricate a microporous versatile catalyst with high stability. Self-assembly of a flexible ligand, 4-(4-carboxybenzylamino)benzoic acid (H2CBBA), with Co(ii) resulted in a 3D framework, CBBA-Co, with Co3O clusters exposed in the zigzag channels. Upon in situ activation, CBBA-Co exhibited multiple heterogeneous catalytic activities. Theoretical calculations were carried out to give insights into the catalytic process. In addition, CBBA-Co also showed promising potential in optical sensing by virtue of its catalytic activity. The luminol chemiluminescence was greatly enhanced by CBBA-Co, and linear determination of the concentration of H2O2 in the range of 0-30% was established. The successful implementation of CBBA-Co indicates the feasibility and promising future of employing MOFs as an efficient platform for the fabrication and study of multifunctional catalysts, both experimentally and theoretically.

Metabolomics profiling reveals the mechanism of increased pneumocandin B0 production by comparing mutant and parent strains.

Metabolic profiling was used to discover mechanisms of increased pneumocandin B0 production in a high-yield strain by comparing it with its parent strain. Initially, 79 intracellular metabolites were identified, and the levels of 15 metabolites involved in six pathways were found to be directly correlated with pneumocandin B0 biosynthesis. Then by combining the analysis of key enzymes, acetyl-CoA and NADPH were identified as the main factors limiting pneumocandin B0 biosynthesis. Other metabolites, such as pyruvate, α-ketoglutaric acid, lactate, unsaturated fatty acids and previously unreported metabolite γ-aminobutyric acid were shown to play important roles in pneumocandin B0 biosynthesis and cell growth. Finally, the overall metabolic mechanism hypothesis was formulated and a rational feeding strategy was implemented that increased the pneumocandin B0 yield from 1821 to 2768 mg/L. These results provide practical and theoretical guidance for strain selection, medium optimization, and genetic engineering for pneumocandin B0 production.

Preparation of Paraffin@Poly(styrene-co-acrylic acid) Phase Change Nanocapsules via Combined Miniemulsion/Emulsion Polymerization.

The fast development of solid-liquid phase change materials calls for nanomaterials with large specific surface area for rapid heat transfer and encapsulation of phase change materials to prevent potential leakage. Here we report a combined miniemulsion/emulsion polymerization method to prepare poly(styrene-co-acrylic acid)-encapsulated paraffin (paraffin@P(St-co-AA)) nanocapsules. The method could suppress the shortcomings of common miniemulsion polymerization (such as evaporation of monomer and decomposition of initiator during ultrasonication). The paraffin@P(St-co-AA) nanocapsules are uniform in size and the polymer shell can be controlled by the weight ratio of St to paraffin. The phase change behavior of the nanocapsules is similar to that of pure paraffin. We believe our method can also be utilized to synthesize other core-shell phase change materials.

Novel CO2 Fluorescence Turn-On Quantification Based on a Dynamic AIE-Active Metal-Organic Framework.

Traditional CO2 sensing technologies suffer from the disadvantages of being bulky and cross-sensitive to interferences such as CO and H2O, these issues could be properly tackled by innovating a novel fluorescence-based sensing technology. Metal-organic frameworks (MOFs), which have been widely explored as versatile fluorescence sensors, are still at a standstill for aggregation-induced emission (AIE), and no example of MOFs showing a dynamic AIE activity has been reported yet. Herein, we report a novel MOF, which successfully converts the aggregation-caused quenching of the autologous ligand molecule to be AIE-active upon framework construction and exhibits bright fluorescence in a highly viscous environment, resulting in the first example of MOFs exhibiting a real dynamic AIE activity. Furthermore, a linear CO2 fluorescence quantification for mixed gases in the concentration range of 2.5-100% was thus well-established. These results herald the understanding and advent of a new generation in all solid-state fluorescence fields.

Metal-Organic Framework Photosensitized TiO2 Co-catalyst: A Facile Strategy to Achieve a High Efficiency Photocatalytic System.

A 3D metal-organic framework (ADA-Cd=[Cd2 L2 (DMF)2 ]⋅3 H2 O where H2 L is (2E,2'E)-3,3'-(anthracene-9,10-diyl)diacrylic acid) constructed from diacrylate substituted anthracene, sharing structural characteristics with some frequently employed anthraquinone-type dye sensitizers, was introduced as an effective sensitizer for anatase TiO2 to achieve enhanced visible light photocatalytic performance. A facile mechanical mixing procedure was adopted to prepare the co-catalyst denoted as ADA-Cd/TiO2 , which showed enhanced photodegradation ability, as well as sustainability, towards several dyes under visible light irradiation. Mechanistic studies revealed that ADA-Cd acted as the antenna to harvest visible light energy, generating excited electrons, which were injected to the conduction band (CB) of TiO2 , facilitating the separation efficiency of charge carriers. As suggested by the results of control experiments, combined with the corresponding redox potential of possible oxidative species, . O2- , generated from the oxygen of ambient air at the CB of TiO2 was believed to play a dominant role over . OH and h+ . UV/Vis and photoluminescence technologies were adopted to monitor the generation of . O2- and . OH, respectively. This work presents a facile strategy to achieve a visible light photocatalyst with enhanced catalytic activity and sustainability; the simplicity, efficiency, and stability of this strategy may provide a promising way to achieve environmental remediation.

Template-Free Synthesis of Monoclinic BiVO4 with Porous Structure and Its High Photocatalytic Activity.

Monoclinic BiVO4 photocatalysts with porous structures were synthesized by a two-step approach without assistance of any templates. The as-prepared samples were characterized by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy (DRS), photocurrent responses, and electrochemical impedance spectra (EIS). It is found that the as-prepared BiVO4 samples had a porous structure with aperture diameter of 50-300 nm. Moreover, the BET specific surface area of the porous BiVO4-200 °C sample reaches up to 5.69 m²/g, which is much higher than that of the sample of BiVO4 particles without porous structure. Furthermore, a possible formation mechanism of BiVO4 with porous structure was proposed. With methylene blue (MB) as a model compound, the photocatalytic oxidation of organic contaminants in aqueous solution was investigated under visible light irradiation. It is found that the porous BiVO4-200 °C sample exhibits the best photocatalytic activity, and the photocatalytic rate constant is about three times of that of the sample of BiVO4 particles without porous structure. In addition, the photocurrent responses and electrochemical impedance spectra strongly support this conclusion.