Synthetic Leaves Based on Crystalline Olefin-Linked Covalent Organic Frameworks for Efficient CO2 Photoreduction with Water.

We report, for the first time, a new synthetic strategy for the preparation of crystalline two-dimensional olefin-linked covalent organic frameworks (COFs) based on aldol condensation between benzodifurandione and aromatic aldehydes. Olefin-linked COFs can be facilely crystallized through either a pyridine-promoted solvothermal process or a benzoic anhydride-mediated organic flux synthesis. The resultant COF leaf with high in-plane π-conjugation exhibits efficient visible-light-driven photoreduction of carbon dioxide (CO2) with water (H2O) in the absence of any photosensitizer, sacrificial agents, or cocatalysts. The production rate of carbon monoxide (CO) reaches as high as 158.1 µmol g-1 h-1 with near 100% CO selectivity, which is accompanied by the oxidation of H2O to oxygen. Both theoretical and experimental results confirm that the key lies in achieving exceptional photoinduced charge separation and low exciton binding. We anticipate that our findings will facilitate new possibilities for the development of semiconducting COFs with structural diversity and functional variability.

Highly Selective Photocatalytic Synthesis of Acetic Acid at 0-25oC.

Acetic acid (AA), a vital compound in chemical production and materials manufacturing, is conventionally synthesized by starting with coal or methane through multiple steps including high-temperature transformations. Here we present a new synthesis of AA from ethane through photocatalytic selective oxidation of ethane by H2O2 at 0-25°C. The catalyst designed for this process comprises g-C3N4 with anchored Pd1 single-atom sites. In-situ studies and computational simulation suggest the immobilized Pd1 atom becomes positively charged under photocatalytic condition. Under photoirradiation, the holes on the Pd1 single-atom of OH-Pd1Å/g-C3N4 serves as a catalytic site for activating a C-H instead of C-C of C2H6 with a low activation barrier of 0.14 eV, through a concerted mechanism. Remarkably, the selectivity for synthesizing AA reaches 98.7%, achieved under atmospheric pressure of ethane at 0°C. By integrating photocatalysis with thermal catalysis, we introduce a highly selective, environmentally friendly, energy-efficient synthetic route for AA, starting from ethane, presenting a promising alternative for AA synthesis. This integration of photocatalysis in low-temperature oxidation demonstrates a new route of selective oxidation of light alkanes.

Photo-Induced Active Lewis Acid-Base Pairs in a Metal-Organic Framework for H2 Activation.

The establishment of active sites as the frustrated Lewis pair (FLP) has recently attracted much attention ranging from homogeneous to heterogeneous systems in the field of catalysis. Their unquenched reactivity of Lewis acid and base pairs in close proximity that are unable to form stable adducts has been shown to activate small molecules such as dihydrogen heterolytically. Herein, we show that grafted Ru metal-organic framework-based catalysts prepared via N-containing linkers are rather catalytically inactive for H2 activation despite the application of elevated temperatures. However, upon light illumination, charge polarization of the anchored Ru bipyridine complex can form a transient Lewis acid-base pair, Ru+-N- via metal-to-ligand charge transfer, as confirmed by time-dependent density functional theory (TDDFT) calculations to carry out effective H2-D2 exchange. FTIR and 2-D NMR endorse the formation of such reactive intermediate(s) upon light irradiation.

Unveiling the Surface Structure of ZnO Nanorods and H2 Activation Mechanisms with 17O NMR Spectroscopy.

ZnO plays a very important role in many catalytic processes involving H2, yet the details on their interactions and H2 activation mechanism are still missing, owing to the lack of a characterization method that provides resolution at the atomic scale and follows the fate of oxide surface species. Here, we apply 17O solid-state NMR spectroscopy in combination with DFT calculations to unravel the surface structure of ZnO nanorods and explore the H2 activation process. We show that six different types of oxygen ions in the surface and subsurface of ZnO can be distinguished. H2 undergoes heterolytic dissociation on three-coordinated surface zinc and oxygen ions, while the formed hydride species migrate to nearby oxygen species, generating a second hydroxyl site. When oxygen vacancies are present, homolytic dissociation of H2 occurs and zinc hydride species form from the vacancies. Reaction mechanisms on oxide surfaces can be explored in a similar manner.

Unique catalytic mechanisms of methanol dehydrogenation at Pd-doped ceria: A DFT+U study.

Pd-doped ceria is highly active in promoting oxidative dehydrogenation (ODH) reactions and also a model single atom catalyst (SAC). By performing density functional theory calculations corrected by on-site Coulomb interactions, we systematically studied the physicochemical properties of the Pd-doped CeO2(111) surface and the catalytic methanol to formaldehyde reaction on the surface. Two different configurations were located for the Pd dopant, and the calculated results showed that doping of Pd will make the surface more active with lower oxygen vacancy formation energies than the pristine CeO2(111). Moreover, two different pathways for the dehydrogenation of CH3OH to HCHO on the Pd-doped CeO2(111) were determined, one of which is the conventional two-step process (stepwise pathway) with the O-H bond of CH3OH being broken first followed by the C-H bond cleavage, while the other is a novel one-step process (concerted pathway) involving the two H being dissociated from CH3OH simultaneously even with a lower energy barrier than the stepwise one. With electronic and structural analyses, we showed that the direct reduction of Pd4+ to Pd2+ through the transfer of two electrons can outperform the separated Ce4+ to Ce3+ processes with the help of configurational evolution at the Pd site, which is responsible for the existence of such one-step dehydrogenation process. This novel mechanism may provide an inspiration for constructing ceria-based SAC with unique ODH activities.

[Preadmission follow-up condition of neonates hospitalized due to severe hyperbilirubinemia after discharge from the department of obstetrics and influencing factors for follow-up compliance: a multicenter investigation]. / äº§ç§‘å‡ºé™¢åŽå› ä¸¥é‡é«˜èƒ†çº¢ç´ è¡€ç—‡ä½é™¢æ–°ç”Ÿå„¿å ¥é™¢å‰éšè®¿æƒ å†µåŠéšè®¿ä¾ä»Žæ€§å½±å“å› ç´ çš„å¤šä¸­å¿ƒè°ƒæŸ¥.

OBJECTIVES: To investigate the preadmission follow-up condition of neonates hospitalized due to severe hyperbilirubinemia after discharge from the department of obstetrics and the influencing factors for follow-up compliance. METHODS: A multicenter retrospective case-control study was performed for the cases from the multicenter clinical database of 12 units in the Quality Improvement Clinical Research Cooperative Group of Neonatal Severe Hyperbilirubinemia in Jiangsu Province of China from January 2019 to April 2021. According to whether the follow-up of neonatal jaundice was conducted on time after discharge from the department of obstetrics, the neonates were divided into two groups: good follow-up compliance and poor follow-up compliance. The multivariate logistic regression model was used to identify the influencing factors for follow-up compliance of the neonates before admission. RESULTS: A total of 545 neonates with severe hyperbilirubinemia were included in the study, with 156 neonates (28.6%) in the good follow-up compliance group and 389 (71.4%) in the poor follow-up compliance group. The multivariate logistic regression analysis showed that low gestational age at birth, ≥10% reduction in body weight on admission compared with birth weight, history of phototherapy of siblings, history of exchange transfusion of siblings, Rh(-) blood type of the mother, a higher educational level of the mother, the use of WeChat official account by medical staff to remind of follow-up before discharge from the department of obstetrics, and the method of telephone notification to remind of follow-up after discharge were associated with the increase in follow-up compliance (P<0.05). CONCLUSIONS: Poor follow-up compliance is observed for the neonates with severe hyperbilirubinemia after discharge from the department of obstetrics, which suggests that it is necessary to further strengthen the education of jaundice to parents before discharge and improve the awareness of jaundice follow-up. It is recommended to remind parents to follow up on time by phone or WeChat official account.

[Antibiotic use in very low birth weight/extremely low birth weight infants in 15 hospitals in Jiangsu Province of China: a multicenter survey]. / 江苏省15家医院极低/è¶ ä½Žå‡ºç”Ÿä½“é‡å„¿æŠ—ç”Ÿç´ ä½¿ç”¨çŽ°çŠ¶è°ƒæŸ¥.

OBJECTIVES: To investigate the current status of antibiotic use in very low birth weight/extremely low birth weight infants in Jiangsu Province of China, and to provide a clinical basis for the quality and improvement of antibiotic management in the neonatal intensive care unit (NICU). METHODS: A retrospective analysis was performed on the data on general conditions and antibiotic use in the very low birth weight/extremely low birth weight infants who were admitted to 15 hospitals of Jiangsu Province from January 1, 2019 to December 31, 2020. A questionnaire containing 10 measures to reduce antibiotic use was designed to investigate the implementation of these intervention measures. RESULTS: A total of 1 920 very low birth weight/extremely low birth weight infants were enrolled, among whom 1 846 (96.15%) were treated with antibiotic, and the median antibiotic use rate (AUR) was 50/100 patient-days. The AUR ranged from 24/100 to 100/100 patient-days in the 15 hospitals. After adjustment for the confounding factors including gestational age, birth weight, and neonatal critical score, the Poisson regression analysis showed that there was a significant difference in the adjusted AUR (aAUR) among the hospitals (P<0.01). The investigation results showed that among the 10 measures to reduce antibiotic use, 8 measures were implemented in less than 50% of these hospitals, and the number of intervention measures implemented was negatively correlated with aAUR (rs=-0.564, P=0.029). CONCLUSIONS: There is a high AUR among the very low birth weight/extremely low birth weight infants in the 15 hospitals of Jiangsu Province, with a significant difference among hospitals. The hospitals implementing a relatively few measures to reduce antibiotic use tend to have a high AUR. It is expected to reduce AUR in very low birth weight/extremely low birth weight infants by promoting the quality improvement of antibiotic use management in the NICU.

Clinical effect of different maintenance doses of caffeine citrate in the treatment of preterm infants requiring assisted ventilation: a pilot multicenter study. / ä¸åŒç»´æŒå‰‚é‡æž¸æ©¼é ¸å’–å•¡å› å¯¹è¾ åŠ©é€šæ°”æ—©äº§å„¿çš„ç–—æ•ˆè¯„ä¼°ï¼šä¸€é¡¹åˆæ­¥å¤šä¸­å¿ƒç ”ç©¶.

OBJECTIVES: To explore the optimal maintenance dose of caffeine citrate for preterm infants requiring assisted ventilation and caffeine citrate treatment. METHODS: A retrospective analysis was performed on the medical data of 566 preterm infants (gestational age ≤34 weeks) who were treated and required assisted ventilation and caffeine citrate treatment in the neonatal intensive care unit of 30 tertiary hospitals in Jiangsu Province of China between January 1 and December 31, 2019. The 405 preterm infants receiving high-dose (10 mg/kg per day) caffeine citrate after a loading dose of 20 mg/kg within 24 hours after birth were enrolled as the high-dose group. The 161 preterm infants receiving low-dose (5 mg/kg per day) caffeine citrate were enrolled as the low-dose group. RESULTS: Compared with the low-dose group, the high-dose group had significant reductions in the need for high-concentration oxygen during assisted ventilation (P=0.044), the duration of oxygen inhalation after weaning from noninvasive ventilation (P<0.01), total oxygen inhalation time during hospitalization (P<0.01), the proportion of preterm infants requiring noninvasive ventilation again (P<0.01), the rate of use of pulmonary surfactant and budesonide (P<0.05), and the incidence rates of apnea and bronchopulmonary dysplasia (P<0.01), but the high-dose group had a significantly increased incidence rate of feeding intolerance (P=0.032). There were no significant differences between the two groups in the body weight change, the incidence rates of retinopathy of prematurity, intraventricular hemorrhage or necrotizing enterocolitis, the mortality rate, and the duration of caffeine use (P>0.05). CONCLUSIONS: This pilot multicenter study shows that the high maintenance dose (10 mg/kg per day) is generally beneficial to preterm infants in China and does not increase the incidence rate of common adverse reactions. For the risk of feeding intolerance, further research is needed to eliminate the interference of confounding factors as far as possible.

Responses of Defect-Rich Zr-Based Metal-Organic Frameworks toward NH3 Adsorption.

Understanding structural responses of metal-organic frameworks (MOFs) to external stimuli such as the inclusion of guest molecules and temperature/pressure has gained increasing attention in many applications, for example, manipulation and manifesto smart materials for gas storage, energy storage, controlled drug delivery, tunable mechanical properties, and molecular sensing, to name but a few. Herein, neutron and synchrotron diffractions along with Rietveld refinement and density functional theory calculations have been used to elucidate the responsive adsorption behaviors of defect-rich Zr-based MOFs upon the progressive incorporation of ammonia (NH3) and variable temperature. UiO-67 and UiO-bpydc containing biphenyl dicarboxylate and bipyridine dicarboxylate linkers, respectively, were selected, and the results establish the paramount influence of the functional linkers on their NH3 affinity, which leads to stimulus-tailoring properties such as gate-controlled porosity by dynamic linker flipping, disorder, and structural rigidity. Despite their structural similarities, we show for the first time the dramatic alteration of NH3 adsorption profiles when the phenyl groups are replaced by the bipyridine in the organic linker. These molecular controls stem from controlling the degree of H-bonding networks/distortions between the bipyridine scaffold and the adsorbed NH3 without significant change in pore volume and unit cell parameters. Temperature-dependent neutron diffraction also reveals the NH3-induced rotational motions of the organic linkers. We also demonstrate that the degree of structural flexibility of the functional linkers can critically be affected by the type and quantity of the small guest molecules. This strikes a delicate control in material properties at the molecular level.

Interaction of Hydrogen with Ceria: Hydroxylation, Reduction, and Hydride Formation on the Surface and in the Bulk.

The study reports the first attempt to address the interplay between surface and bulk in hydride formation in ceria (CeO2 ) by combining experiment, using surface sensitive and bulk sensitive spectroscopic techniques on the two sample systems, i.e., CeO2 (111) thin films and CeO2 powders, and theoretical calculations of CeO2 (111) surfaces with oxygen vacancies (Ov ) at the surface and in the bulk. We show that, on a stoichiometric CeO2 (111) surface, H2 dissociates and forms surface hydroxyls (OH). On the pre-reduced CeO2-x samples, both films and powders, hydroxyls and hydrides (Ce-H) are formed on the surface as well as in the bulk, accompanied by the Ce3+ ↔ Ce4+ redox reaction. As the Ov concentration increases, hydroxyl is destabilized and hydride becomes more stable. Surface hydroxyl is more stable than bulk hydroxyl, whereas bulk hydride is more stable than surface hydride. The surface hydride formation is the kinetically favorable process at relatively low temperatures, and the resulting surface hydride may diffuse into the bulk region and be stabilized therein. At higher temperatures, surface hydroxyls can react to produce water and create additional oxygen vacancies, increasing its concentration, which controls the H2 /CeO2 interaction. The results demonstrate a large diversity of reaction pathways, which have to be taken into account for better understanding of reactivity of ceria-based catalysts in a hydrogen-rich atmosphere.

[Contributing factors for the withdrawal from treatment in neonates with respiratory failure].

OBJECTIVE: To investigate the factors contributing to the withdrawal from treatment in neonates with respiratory failure. METHODS: The medical data of 2 525 neonates with respiratory failure were retrospectively studied, who were reported in 30 hospitals of Jiangsu Province from January to December, 2019. According to whether a complete treatment was given, they were divided into a complete treatment group with 2 162 neonates and a withdrawal group with 363 neonates. A multivariate logistic regression analysis was used to investigate the factors contributing to the withdrawal from treatment in neonates with respiratory failure. RESULTS: The multivariate logistic regression analysis showed that small-for-gestational-age birth, congenital abnormality, gestational age < 28 weeks, living in the rural area or county-level city, and maternal age < 25 years were risk factors for the withdrawal from treatment in neonates with respiratory failure (P < 0.05), while a higher 5-minute Apgar score and cesarean section were protective factors (P < 0.05). Furthermore, 176 answers were obtained from 160 parents of the neonates who were willing to tell the reason for the withdrawal from treatment, among which severe sequelae (44.9%, 79/176) had the highest frequency, followed by uncontrollable disease condition (24.4%, 43/176), family financial difficulties (18.2%, 32/176), and dependence on mechanical ventilation (12.5%, 22/176). CONCLUSIONS: Small-for-gestational-age birth, congenital abnormality, gestational age, living area, maternal age, Apgar score at birth, and method of birth are contributing factors for the withdrawal from treatment in neonates with respiratory failure. A poor prognosis and a low quality of life in future might be major immediate causes of withdrawal from treatment in neonates with respiratory failure, which needs to be confirmed by further studies.

A multicenter retrospective study on survival rate and complications of very preterm infants. / æžæ—©äº§å„¿å­˜æ´»çŽ‡å’Œå¹¶å‘ç—‡çš„å¤šä¸­å¿ƒå›žé¡¾æ€§ç ”ç©¶.

OBJECTIVES: To study the survival rate and the incidence of complications of very preterm infants and the factors influencing the survival rate and the incidence of complications. METHODS: The medical data of the very preterm infants with a gestational age of <32 weeks and who were admitted to the Department of Neonatology in 11 hospitals of Jiangsu Province in China from January 2018 to December 2019 were retrospectively reviewed. Their survival rate and the incidence of serious complications were analyzed. A multivariate logistic regression analysis was used to evaluate the risk factors for death and serious complications in very preterm infants. RESULTS: A total of 2 339 very preterm infants were enrolled, among whom 2 010 (85.93%) survived and 1 507 (64.43%) survived without serious complications. The groups with a gestational age of 22-25+6 weeks, 26-26+6 weeks, 27-27+6 weeks, 28-28+6 weeks, 29-29+6 weeks, 30-30+6 weeks, and 31-31+6 weeks had a survival rate of 32.5%, 60.6%, 68.0%, 82.9%, 90.1%, 92.3%, and 94.8% respectively. The survival rate tended to increase with the gestational age (P<0.05) and the survival rate without serious complications in each gestational age group was 7.5%, 18.1%, 34.5%, 52.2%, 66.7%, 75.7%, and 81.8% respectively, suggesting that the survival rate without serious complications increased with the gestational age (P<0.05). The multivariate logistic regression analysis showed that high gestational age, high birth weight, and prenatal use of glucocorticoids were protective factors against death in very preterm infants (P<0.05), and 1-minute Apgar score ≤3 was a risk factor for death in very preterm infants (P<0.05); high gestational age and high birth weight were protective factors against serious complications in very preterm infants who survived (P<0.05), while 5-minute Apgar score ≤3 and maternal chorioamnionitis were risk factors for serious complications in very preterm infants who survived (P<0.05). CONCLUSIONS: The survival rate is closely associated with gestational age in very preterm infants. A low 1-minute Apgar score (≤3) may increase the risk of death in very preterm infants, while high gestational age, high birth weight, and prenatal use of glucocorticoids are associated with the reduced risk of death. A low 5-minute Apgar score (≤3) and maternal chorioamnionitis may increase the risk of serious complications in these infants, while high gestational age and high birth weight may reduce the risk of serious complications.

[Clinical features of preterm infants with a birth weight less than 1 500 g undergoing different intensities of resuscitation: a multicenter retrospective analysis].

OBJECTIVE: To evaluate the clinical features of preterm infants with a birth weight less than 1 500 g undergoing different intensities of resuscitation. METHODS: A retrospective analysis was performed for the preterm infants with a birth weight less than 1 500 g and a gestational age less than 32 weeks who were treated in the neonatal intensive care unit of 20 hospitals in Jiangsu, China from January 2018 to December 2019. According to the intensity of resuscitation in the delivery room, the infants were divided into three groups:non-tracheal intubation (n=1 184), tracheal intubation (n=166), and extensive cardiopulmonary resuscitation (ECPR; n=116). The three groups were compared in terms of general information and clinical outcomes. RESULTS: Compared with the non-tracheal intubation group, the tracheal intubation and ECPR groups had significantly lower rates of cesarean section and use of antenatal corticosteroid (P < 0.05). As the intensity of resuscitation increased, the Apgar scores at 1 minute and 5 minutes gradually decreased (P < 0.05), and the proportion of infants with Apgar scores of 0 to 3 at 1 minute and 5 minutes gradually increased (P < 0.05). Compared with the non-tracheal intubation group, the tracheal intubation and ECPR groups had significantly higher mortality rate and incidence rates of moderate-severe bronchopulmonary dysplasia and serious complications (P < 0.05). The incidence rates of grade Ⅲ-Ⅳ intracranial hemorrhage and retinopathy of prematurity (stage Ⅲ or above) in the tracheal intubation group were significantly higher than those in the non-tracheal intubation group (P < 0.05). CONCLUSIONS: For preterm infants with a birth weight less than 1 500 g, the higher intensity of resuscitation in the delivery room is related to lower rate of antenatal corticosteroid therapy, lower gestational age, and lower birth weight. The infants undergoing tracheal intubation or ECRP in the delivery room have an increased incidence rate of adverse clinical outcomes. This suggests that it is important to improve the quality of perinatal management and delivery room resuscitation to improve the prognosis of the infants.

Boosting Interfacial Charge-Transfer Kinetics for Efficient Overall CO2 Photoreduction via Rational Design of Coordination Spheres on Metal-Organic Frameworks.

The recombination of electron-hole pairs severely detracts from the efficiency of photocatalysts. This issue could be addressed in metal-organic frameworks (MOFs) through optimization of the charge-transfer kinetics via rational design of structures at atomic level. Herein, a pyrazolyl porphyrinic Ni-MOF (PCN-601), integrating light harvesters, active catalytic sites, and high surface areas, has been demonstrated as a superior and durable photocatalyst for visible-light-driven overall CO2 reduction with H2O vapor at room temperature. Kinetic studies reveal that the robust coordination spheres of pyrazolyl groups and Ni-oxo clusters endow PCN-601 with proper energy band alignment and ultrafast ligand-to-node electron transfer. Consequently, the CO2-to-CH4 production rate of PCN-601 far exceeds those of the analogous MOFs based on carboxylate porphyrin and the classic Pt/CdS photocatalyst by more than 3- and 20-fold, respectively. The reaction avoids the use of hole scavengers and proceeds in a gaseous phase which can take full advantage of the high gas uptake of MOFs. This work demonstrates that the rational design of coordination spheres in MOF structures not only reconciles the contradiction between reactivity and stability but also greatly promotes the interfacial charge transfer to achieve optimized kinetics, providing guidance for the design of highly efficient MOF photocatalysts.

Interactions of Oxide Surfaces with Water Revealed with Solid-State NMR Spectroscopy.

Hydrous materials are ubiquitous in the natural environment and efforts have previously been made to investigate the structures and dynamics of hydrated surfaces for their key roles in various chemical and physical applications, with the help of theoretical modeling and microscopy techniques. However, an overall atomic-scale understanding of the water-solid interface, including the effect of water on surface ions, is still lacking. Herein, we employ ceria nanorods with different amounts of water as an example and demonstrate a new approach to explore the water-surface interactions by using solid-state NMR in combination with density functional theory. NMR shifts and relaxation time analysis provide detailed information on the local structure of oxygen ions and the nature of water motion on the surface: the amount of molecularly adsorbed water decreases rapidly with increasing temperature (from room temperature to 150 °C), whereas hydroxyl groups are stable up to 150 °C, and dynamic water molecules are found to instantaneously coordinate to the surface oxygen ions. The applicability of dynamic nuclear polarization for selective detection of surface oxygen species is also compared to conventional NMR with surface selective isotopic-labeling: the optimal method depends on the feasibility of enrichment and the concentration of protons in the sample. These results provide new insight into the interfacial structure of hydrated oxide nanostructures, which is important to improve performance for various applications.

Methanol Synthesis at a Wide Range of H2 /CO2 Ratios over a Rh-In Bimetallic Catalyst.

There is increasing interest in capturing H2 generated from renewables with CO2 to produce methanol. However, renewable hydrogen production is expensive and in limited quantity compared to CO2 . Excess CO2 and limited H2 in the feedstock gas is not favorable for CO2 hydrogenation to methanol, causing low activity and poor methanol selectivity. Now, a class of Rh-In catalysts with optimal adsorption properties to the intermediates of methanol production is presented. The Rh-In catalyst can effectively catalyze methanol synthesis but inhibit the reverse water-gas shift reaction under H2 -deficient gas flow and shows the best competitive methanol productivity under industrially applicable conditions in comparison with reported values. This work demonstrates a strong potential of Rh-In bimetallic composition, from which a convenient methanol synthesis based on flexible feedstock compositions (such as H2 /CO2 from biomass derivatives) with lower energy cost can be established.

Metal doping in cerium metal-organic frameworks for visible-response water splitting photocatalysts.

Cerium metal-organic frameworks (Ce-MOFs) show great promise for photocatalytic water splitting as they have low-lying unoccupied 4f orbitals with energies lower than the unoccupied linker orbitals to drive the ligand-to-metal charge transfer (LMCT) of the photo-generated electron at the linker to separate the photo-excited charges. Nevertheless, the large and negative LMCT energies of Ce-MOFs are often accompanied by high photon-absorption energies, which then limit the application of Ce-MOFs as visible-light-driven water splitting photocatalysts. In this work, we propose that metal (Zr or Ti) doping can raise the very negative LMCT energies of Ce-MOFs, consequently leading to the decrease of the absorption energy and promoting the response of Ce-MOFs to visible light. By functionalizing the linker of the mixed-metal MOFs, we found two possible visible-response photocatalysts for water splitting using a single photocatalyst.

Cerium Metal-Organic Framework for Photocatalysis.

Ligand-to-metal charge transfer (LMCT) can bring about the separation of photogenerated charges. Here we calculate the electronic structures of metal-organic frameworks (MOFs) having the UiO-66 architecture and M6O4(OH)4 inorganometallic nodes with M = Zr, Hf, Th, Ti, U, or Ce. We find that LMCT is favorable only in the Ce case, where it is promoted by the low-lying empty 4f orbitals of Ce4+. We therefore propose that incorporating Ce4+ into the node is an effective way to facilitate LMCT in a MOF. In addition, we show that by functionalizing the linker, it should be possible to engineer the electronic structure of the Ce-MOF for a desired reaction (e.g., water splitting) while preserving favorable LMCT. We also find that linker functionalization with electron donating or withdrawing groups allows tuning of the LMCT energy, and increasing the number of functional groups on each linker enhances the tuning; these findings are encouraging for applying Ce-MOFs for visible-response photocatalytic water splitting.

Combined quantum mechanical and molecular mechanical method for metal-organic frameworks: proton topologies of NU-1000.

Metal-organic frameworks (MOFs) are materials with applications in catalysis, gas separations, and storage. Quantum mechanical (QM) calculations can provide valuable guidance to understand and predict their properties. In order to make the calculations faster, rather than modeling these materials as periodic (infinite) systems, it is useful to construct finite models (called cluster models) and use subsystem methods such as fragment methods or combined quantum mechanical and molecular mechanical (QM/MM) methods. Here we employ a QM/MM methodology to study one particular MOF that has been of widespread interest because of its wide pores and good solvent and thermal stability, namely NU-1000, which contains hexanuclear zirconium nodes and 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy4-) linkers. A modified version of the Bristow-Tiana-Walsh transferable force field has been developed to allow QM/MM calculations on NU-1000; we call the new parametrization the NU1T force field. We consider isomeric structures corresponding to various proton topologies of the [Zr6(µ3-O)8O8H16]8+ node of NU-1000, and we compute their relative energies using a QM/MM scheme designed for the present kind of problem. We compared the results to full quantum mechanical (QM) energy calculations and found that the QM/MM models can reproduce the full QM relative energetics (which span a range of 334 kJ mol-1) with a mean unsigned deviation (MUD) of only 2 kJ mol-1. Furthermore, we found that the structures optimized by QM/MM are nearly identical to their full QM optimized counterparts.

Parametrization of Combined Quantum Mechanical and Molecular Mechanical Methods: Bond-Tuned Link Atoms.

Combined quantum mechanical and molecular mechanical (QM/MM) methods are the most powerful available methods for high-level treatments of subsystems of very large systems. The treatment of the QM-MM boundary strongly affects the accuracy of QM/MM calculations. For QM/MM calculations having covalent bonds cut by the QM-MM boundary, it has been proposed previously to use a scheme with system-specific tuned fluorine link atoms. Here, we propose a broadly parametrized scheme where the parameters of the tuned F link atoms depend only on the type of bond being cut. In the proposed new scheme, the F link atom is tuned for systems with a certain type of cut bond at the QM-MM boundary instead of for a specific target system, and the resulting link atoms are call bond-tuned link atoms. In principle, the bond-tuned link atoms can be as convenient as the popular H link atoms, and they are especially well adapted for high-throughput and accurate QM/MM calculations. Here, we present the parameters for several kinds of cut bonds along with a set of validation calculations that confirm that the proposed bond-tuned link-atom scheme can be as accurate as the system-specific tuned F link-atom scheme.