Electronegativity principle for hydrogen evolution activity using first-principles calculations.

The catalytic activity of a heterogeneous catalyst is routinely described by the Sabatier principle using molecule/proton adsorption energy ΔGH as the thermodynamic descriptor. This descriptor, however, fails in quantitatively tracking the reaction rate due to the lack of charge transfer information during a reaction. Herein, we use density functional theory (DFT) calculations combining both canonical and grand-canonical ensembles to report a positive correlation between reaction kinetics and interfacial charge transfer for the hydrogen evolution reaction (HER). The Sabatier relationship for the HER catalysts exhibits a large dispersion in the canonical calculation but an improved linearity under the grand-canonical ensemble, indicating that surface charges are indeed important. This charge effect can be well captured by the Mulliken electronegativity χ of a catalyst because the reaction barrier shows a linear dependence on χ for a wide range of catalysts. Specifically, a catalyst with lower electronegativity exhibits a lower barrier and thus a faster reaction rate. This electronegativity principle is reaction route and pH independent and is founded on the thermoneutral requirement on ΔGH.

Substantial impact of surface charges on electrochemical reaction kinetics on S vacancies of MoS2 using grand-canonical iteration method.

The surface charges of catalysts have intricate influences on the thermodynamics and kinetics of electrochemical reactions. Herein, we develop a grand-canonical iteration method based on density functional theory calculations to explore the effect of surface charges on reaction kinetics beyond the traditional Butler-Volmer picture. Using the hydrogen evolution reaction on S vacancies of MoS2 as an example, we show how to track the change of surface charge in a reaction and to analyze its influence on the kinetics. Protons adsorb on S vacancies in a tough and charge-insensitive water splitting manner, which explains the observed large Tafel slope. Grand-canonical calculations report an unanticipated surface charge-induced change of the desorption pathway from the Heyrovsky route to a Volmer-Tafel route. During an electrochemical reaction, a net electron inflow into the catalyst may bring two effects, i.e., stabilization of the canonical energy and destabilization of the charge-dependent grand-canonical part. On the contrary, a net outflow of electrons from the catalyst can reverse the two effects. This surface charge effect has substantial impacts on the overpotential and the Tafel slope. We suggest that the surface charge effect is universal for all electrochemical reactions and significant for those involving interfacial proton transfers.

Photoelectrocatalytic Processes of TiO2 Film: The Dominating Factors for the Degradation of Methyl Orange and the Understanding of Mechanism.

Various thicknesses of TiO2 films were prepared by the sol-gel method and spin-coating process. These prepared TiO2 films exhibit thickness-dependent photoelectrochemical performance. The 1.09-µm-thickTiO2 film with 20 spin-coating layers (TiO2-20) exhibits the highest short circuit current of 0.21 mAcm-2 and open circuit voltage of 0.58 V among all samples and exhibits a low PEC reaction energy barrier and fast kinetic process. Photoelectrocatalytic (PEC) degradation of methyl orange (MO) by TiO2 films was carried out under UV light. The roles of bias, film thickness, pH value, and ion properties were systematically studied because they are the four most important factors dominating the PEC performance of TiO2 films. The optimized values of bias, film thickness, and pH are 1.0 V, 1.09 µm, and 12, respectively, which were obtained according to the data of the PEC degradation of MO. The effect of ion properties on the PEC efficiency of TiO2-20 was also analyzed by using halide as targeted ions. The "activated" halide ions significantly promoted the PEC efficiency and the order was determined as Br > Cl > F. The PEC efficiency increased with increasing Cl content, up until the optimized value of 30 × 10-3 M. Finally, a complete degradation of MO by TiO2-20 was achieved in 1.5 h, with total optimization of the four factors: 1.0 V bias, 1.09-µm-thick, pH 12, and 30 × 10-3 M Cl ion content. The roles of reactive oxygen species and electric charge of photoelectrodes were also explored based on photoelectrochemical characterizations and membrane-separated reactors. Hydrogen peroxide, superoxide radical, and hydroxyl radical were found responsible for the decolorization of MO.

On the Sensitivity to Density-Functional Approximations for CO Binding Energies of Single-Atom Catalysts in Nitrogen-Doped Graphene.

Density functional theory (DFT) methods are the working horse in screening new catalytic materials. They are widely used to predict trends in binding energies, which are then used to compare the activity of different materials. The binding strength of CO is an important descriptor to the CO2 reduction catalytic activity of the single transition metal atoms embedded on nitrogen-doped graphene (TM/NG). In this work, however, we show that CO binding strengths in different TM/NG has very different sensitivity to DFT methods. Specifically, Fe/NG CO binding energy changes dramatically with the percentage of exact exchange in the functional; Co/NG does less so, while Ni/NG nearly has no change. Such varying behaviors is a direct result of different local spin configurations, similar to the performance of DFT methods for metal porphyrin complexes. Therefore, caution should be exercised when using DFT binding energies for quantitative predictions in TM/NG single atom catalysis.

Inversely Tuning the CO2 Electroreduction and Hydrogen Evolution Activity on Metal Oxide via Heteroatom Doping.

Tuning the electronic states near the Fermi level can effectively facilitate the reaction kinetics. However, elucidating the role of a specific electronic state of metal oxide in simultaneously regulating the CO2 electroreduction reaction (CO2 RR) and competing hydrogen evolution reaction (HER) is still rare, making it difficult to accurately predict the practical CO2 RR performance. Herein, replacing the Zn site by heteroatoms with different outer electrons (Mo and Cu) is found to tune both occupied and unoccupied orbitals near the Fermi level of ZnO. Moreover, the different electronic states significantly modulate both CO2 RR and HER activity with a totally inverse trend, thus dramatically tuning the practical CO2 RR performance. In parallel, the correlation between electronic states, reaction free energies and practical activity is demonstrated. This work provides a possibility for engineering efficient CO2 RR eletrocatalysts through tunable composition and electronic structures.

Optimal Geometrical Configuration of Cobalt Cations in Spinel Oxides to Promote Oxygen Evolution Reaction.

MgCo2 O4 , CoCr2 O4 , and Co2 TiO4 were selected, where only Co3+ in the center of octahedron (Oh), Co2+ in the center of tetrahedron (Td), and Co2+ in the center of Oh, can be active sites for the oxygen evolution reaction (OER). Co3+ (Oh) sites are the best geometrical configuration for OER. Co2+ (Oh) sites exhibit better activity than Co2+ (Td). Calculations demonstrate the conversion of O* into OOH* is the rate-determining step for Co3+ (Oh) and Co2+ (Td). For Co2+ (Oh), it is thermodynamically favorable for the formation of OOH* but difficult for the desorption of O2 . Co3+ (Oh) needs to increase the lowest Gibbs free energy over Co2+ (Oh) and Co2+ (Td), which contributes to the best activity. The coexistence of Co3+ (Oh) and Co2+ (Td) in Co3 O4 can promote the formation of OOH* and decrease the free-energy barrier. This work screens out the optimal geometrical configuration of cobalt cations for OER and gives a valuable principle to design efficient electrocatalysts.

Is ceramsite the last straw for sewage sludge disposal: a review of sewage sludge disposal by producing ceramsite in China.

With the rapid development of urbanization, the amount of urban sewage treatment is increasing. Waste activated sludge (WAS) is a by-product of sewage treatment, and its output is increasing year by year. How to properly handle WAS is related to the sustainable development of the sewage treatment industry. The production of ceramsite from WAS is an effective way to realize the utilization of sludge. This paper comprehensively describes the use of WAS as raw material, adding clay, cement, glass powder, shale, coal gangue, river sediment, pulverized fly ash and other auxiliary materials (AM) to produce sintered sewage sludge ceramsite and non-sintered sludge ceramsite. This paper analyzes the advantages and disadvantages of the process of making ceramsite from WAS. The research points out the development prospect of ceramsite from WAS.

Rhodococcus gannanensis sp. nov., a novel endophytic actinobacterium isolated from root of sunflower (Helianthus annuus L.).

A novel Gram-positive, aerobic, non-motile strain, designated strain M1T, was isolated from sunflower root (Helianthus annuus L.) and characterised using a polyphasic taxonomic approach. The morphological and chemotaxonomic properties of the isolate were typical of those of members of the genus Rhodococcus. Phylogenetic analyses based on 16S rRNA gene sequence showed that strain M1T belongs to the genus Rhodococcus and clustered with Rhodococcus canchipurensis MBRL 353T (99.1%, sequence similarity) and Rhodococcus pedocola UC12T (98.7%). However, the DNA-DNA hybridizations between strain M1T and R. canchipurensis MBRL 353T and R. pedocola UC12T were found to be 52.8 ± 0.7 and 41.8 ± 0.2%, respectively. The optimal growth temperature and pH for strain M1T was found to be at 28 °C and at pH 7.0. The peptidoglycan was found to contain meso-diaminopimelic acid; galactose, glucose and arabinose were detected as diagnostic sugars. The main polar lipids were identified as diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannoside; MK-8(H2) was found to be the dominant menaquinone. The major fatty acids were identified as C16:0, 10-methyl C18:0 and C18:1 ω9c. Mycolic acids were found to be present. The G+C content of the genomic DNA was determined to be 69.5 mol%. Based on a comparative analysis of phenotypic and genotypic characteristics, in combination with DNA-DNA hybridization results, the isolate is concluded to represent a novel species of the genus Rhodococcus, for which the name Rhodococcus gannanensis sp. nov. is proposed. The type strain is M1T (=CGMCC 1.15992T = DSM 104003T).

Tuning the hydrogen evolution activity of MS2 (M = Mo or Nb) monolayers by strain engineering.

Strain engineering is an effective strategy to tune the electronic, magnetic and optical properties of atomically thin materials like graphene and monolayer transition-metal dichalcogenides (m-TMDs). Using first-principles calculations, we show that strain is also effective for tuning the catalytic activity of m-MS2 (M = Mo or Nb) towards the hydrogen evolution reaction (HER), which is essential for electrochemical hydrogen generation from water splitting. A wide strain range covering both compressive (0-6%) and tensile (0-10%) regions is considered. It is found that biaxial tensile strain can enhance the HER activity more effectively than uniaxial tensile strain, while compressive strain deteriorates the HER activity. Compared with monolayer 1T-NbS2, monolayers 1T-MoS2 and 1H-NbS2 exhibit better strain tunability towards their HER activities since more active sites can be induced with increasing strain. In contrast, monolayer 1H-MoS2 is catalytically inert in the considered strain range because H adsorption is too weak. We demonstrate that tensile strain can lead to decrease of the adiabatic proton affinity but simultaneously a larger magnitude of increase of the adiabatic electron affinity, thus enhancing the catalytic activity. Electronic structure calculations show that tensile strain can activate the relatively inert inner valence electrons and enlarge the d-band exchange splitting, both of which induce destabilization of the system and enhancement of catalytic activity.

Dual-doping to suppress cracking in spinel LiMn2O4: a joint theoretical and experimental study.

Electrochemical cycling stabilities were compared for undoped and Al/Co dual-doped spinel LiMn2O4 synthesized by solid state reactions. We observed the suppression of particle fracture in Al/Co dual-doped LiMn2O4 during charge/discharge cycling and its distinguishable particle morphology with respect to the undoped material. Systematic first-principles calculations were performed on undoped, Al or Co single-doped, and Al/Co dual-doped LiMn2O4 to investigate their structural differences at the atomistic level. We reveal that while Jahn-Teller distortion associated with the Mn(3+)O6 octahedron is the origin of the lattice strain, the networking -i.e. the distribution of mixed valence Mn ions - is much more important to release the lattice strain, and thus to alleviating particle cracking. The calculations showed that the lattice mismatching between Li(+) intercalation and deintercalation of LiMn2O4 can be significantly reduced by dual-doping, and therefore also the volumetric shrinkage during delithiation. This may account for the near disappearance of cracks on the surface of Al/Co-LiMn2O4 after 350 cycles, while some obvious cracks have developed in undoped LiMn2O4 at similar particle size even after 50 cycles. Correspondingly, Al/Co dual-doped LiMn2O4 showed a good cycling stability with a capacity retention of 84.1% after 350 cycles at a rate of 1C, 8% higher than the undoped phase.

Experimental Study on Tailings Deposition Distribution Pattern and Sedimentation Characteristics.

Tailings pond accidents frequently occur during an extended period, resulting in loss of life and property, wastage of resources, and environmental pollution. Relying on tailings pond engineering, this paper carried out sample particle fragmentation experiments and settling column experiments to explore the deposition distribution pattern of tailings in both horizontal and vertical directions as well as the impact of particle size distribution on the sedimentation stratification effect. The results show that the median particle size on the dry beach surface in the horizontal direction slowly decreased with the increase in the distance from the subdam. The particle size of tailings showed great fluctuations in the vertical direction, which gradually became finer with the increase in the depth overall. At the same time, saturated sedimentation experiments suggested the inconsistent variation rule with the field test, namely, coarse on the bottom and fine at the top, and the change in particle size greatly affected the tailing sedimentation stratification effect. With the increase in fine particle content in tailings, the appearance time of the water-sand interface was shortened to within 30 min, but the sedimentation and consolidation completion times were delayed to about 1400 min. The settling column results indicate that the increase in fine particle content gradually weakened the sedimentation stratification effect, and the sedimentation pattern transformed from independent sedimentation to floc-type average sedimentation, which led to the enhanced water-retaining property of the settled layer. This may lead to an increase in the saturation line and a decrease in the length of the dry beach, seriously affecting the safe operation of the tailings pond. The research results provide some theoretical guidance and basic data for analyzing the consolidation efficiency of tailings and the stability of the tailings pond.

Electrochemistry-assisted in-situ regeneration of oxygen vacancies and Ti(III) active sites for persistent uranium recovery at a low potential.

Electrochemical uranium extraction (EUE) from seawater is a very promising strategy, but its practical application is hindered by the high potential for electrochemical system, as well as the low selectivity, efficiency, and poor stability of electrode. Herein, we developed creatively a low potential strategy for persistent uranium recovery by electrochemistry-assisted in-situ regeneration of oxygen vacancies and Ti(III) active sites coupled with indirect reduction of uranium, finally achieving high selectivity, efficient and persistent uranium recovery. As-designed titanium dioxide rich in oxygen vacancies (TiO2-VO) electrode displayed an EUE efficiency of ∼99.9 % within 180 min at a low potential of 0.09 V in simulated seawater with uranium of 5∼20 ppm. Moreover, the TiO2-VO electrode also showed high selectivity (89.9 %) to uranium, long-term cycling stability and antifouling activity in natural seawater. The excellent EUE property was attributed to the fact that electrochemistry-assisted in-situ regeneration of oxygen vacancies and Ti(III) active sites enhanced EUE cycling process and achieved persistent uranium recovery. The continuous regeneration of oxygen vacancies not only reduced the adsorption energy of U(VI)O22+ but also serve as a storage and transportation channel for electrons, accelerating electron transfer from Ti(III) to U(VI) at solid-liquid interface and promoting EUE kinetic rate.

Correlating the crystal structure and facet of indium oxides with their activities for CO2 electroreduction.

Constructing structure-function relationships is critical for the rational design and development of efficient catalysts for CO2 electroreduction reaction (CO2RR). In2O3 is well-known for its specific ability to produce formic acid. However, how the crystal phase and surface affect the CO2RR activity is still unclear, making it difficult to further improve the intrinsic activity and screen for the most active structure. In this work, cubic and hexagonal In2O3 with different stable surfaces ((111) and (110) for cubic, (120) and (104) for hexagonal) are investigated for CO2RR. Theoretical results demonstrate that the adsorption of reactants on cubic In2O3 is stronger than that on hexagonal In2O3, with the cubic (111) surface being the most active for CO2RR. In experiments, synthesized cubic In2O3 nanosheets with predominantly exposed (111) surfaces exhibited a high HCOO- Faradaic efficiency (87.5%) and HCOO- current density (-16.7 mA cm-2) at -0.9 V vs RHE. In addition, an aqueous Zn-CO2 battery based on a cubic In2O3 cathode was assembled. Our work correlates the phases and surfaces with the CO2RR activity, and provides a fundamental understanding of the structure-function relationship of In2O3, thereby contributing to further improvements in its CO2RR activity. Moreover, the results provide a principle for the directional preparation of materials with optimal phases and surfaces for efficient electrocatalysis.

[Bacterial profiles in conjunctival sac of dry eyes and normal eyes in middle- and old-aged Yi populations].

OBJECTIVE: To compare the bacterial profiles in conjunctival sac of dry eyes and normal eyes in Yi people aged 40 years or old. METHODS: A cross-sectional survey was conducted with standardized training and protocol. A total of 140 dry eyes of 70 individuals from Yi people in Jiulong county underwent ophthalmological examinations. The secretions of the inferior palpebral conjunctival sac were embrocated and inoculated on blood plates for 48 hours. The bacteria were separated and identified. Another 132 normal eyes from 66 Yi individuals were examined as controls. RESULTS: Bacterial positive cultivations were found in 72.1% (101/140) of dry eyes and 67.4% (89/132) of normal eyes, respectively. The difference was not statistically significant (P = 0.397). No gender difference in the bacterial positive rates was found either. Gram-positive bacteria were the main bacteria in both dry eyes (95.2%, 98/103) and normal eyes (91.1%, 82/90), predominantly staphylococcus epidemids and corynebacterium. There were no statistical differences in the constituents of bacteria in Gram classification and numbers of bacteria between dry eyes and normal eyes (P > 0.05). CONCLUSION: The bacterial profile in conjunctival sac of dry eyes is similar to that of normal eyes in Yi people aged 40 years or over. Gram-positive bacteria are the main bacteria.

Vacancy and strain engineering of Co3O4 for efficient water oxidation.

Co3O4 has been widely explored in electrocatalysis but seriously limited by its poor intrinsic ability. Defect engineering is an effective method to improve the electrocatalytic ability of catalysts by regulating electronic structure and optimizing the binding energy with surface adsorbates. Herein, in this work we have successfully integrated metal vacancies and tensile strain into Co3O4. With the formation of metal vacancies, the electronic structure of Co3O4 has been regulated. Moreover, the d-band center of Co3O4 has been modulated with the presence of tensile strain. The electrochemical oxygen evolution reaction (OER) ability of the obtained electrocatalyst was improved dramatically. The overpotential to reach 10 mA cm-2 was only 327 mV. Reaction kinetics was rapidly facilitated as indicated by smaller Tafel slope and charge transfer resistance. Density Functional Theory (DFT) calculations revealed that the relocated atoms induced the formation of tensile strain and made d-band center of electrocatalyst near to Fermi level leading to enhanced the adsorption to reaction intermediates. What's more, the free energy barrier of rate-determining step (RDS) has been decreased with the integration of metal vacancies and tensile strain. This work provides an efficient strategy to develop defective and effective electrocatalysts.

Molten salt-induced vertical CoP/Co nanosheets array coupled with carbon for efficient water splitting.

The exploration of high-efficiency non-noble metal catalysts for improving the intrinsic activity and active sites for overall water splitting persists as a bottleneck issue. Herein, a facile heterogeneous molten salt strategy has been proposed to fabricate CoP/Co nanosheets array that is vertically attached to a carbon matrix. Such a hierarchical structure endows the hybrid with abundant active sites and favorable reaction kinetics. Experimental results reveal that the molten salt determines the final shape of metallic Co, which is not sensitive to the organic sources. After optimization of the molten salt mass, the CoP/Co/C-6 shows the best bifunctional performance, requiring an overpotential of 132 mV and 320 mV at 10 mA cm-2 for hydrogen evolution reaction and oxygen evolution reaction, respectively. Theoretical simulation results manifest the CoP/Co heterostructure alters the electronic structure of Co and CoP, and reduces the adsorption free energy of intermediates, thus further boosting the electrocatalysis activity. This work proposes a molten salt-assisted method for the rational design of novel two-dimensional nano-hybrids for energy conversion applications.

Metabonomics analysis of flavonoids in seeds and sprouts of two Chinese soybean cultivars.

A popular food in China, soybean seeds and sprouts contained many biologically active substances which are beneficial to the human body, such as flavonoids. Northeast of China is the main producing area of soybean. The experimental materials came from the main soybean producing areas in Northeast China, this study compared flavonoids of two China cultivars of soybeans, Heinong52(HN52) and Heinong71(HN71). Here, we also considered the effects of germination on the chemical profile of flavonoids. Using a LC-ESI-MS/MS system, 114 differential flavonoid metabolites were identified. A total of 18 metabolites were significantly different between the two soybean varieties before germination, of which 14 were up-regulated and 4 were down-regulated. After germination, 33 significantly different metabolites were found in the two soybean sprouts, of which 19 were up-regulated and 14 were down-regulated. These experimental results revealed significant up-regulation of metabolites in soybean sprouts compared with soybean seeds, thus suggesting that soybean germination may increase content of flavonoid metabolites. There are six main pathways for the synthesis of flavonoids: isoflavonoid biosynthesis, flavonoid biosynthesis, flavone and flavonol biosynthesis, biosynthesis of secondary metabolites, and biosynthesis of phenylpropanoids. Soybean seeds lack flavone and flavanol biosynthesis and develop the capacity for this biosynthetic pathway after germination as sprouts. Isoflavonoid biosynthesis is the most abundantly utilized pathway.

Defective Bimetallic Selenides for Selective CO2 Electroreduction to CO.

CO2 electroreduction (CO2 RR) to CO is promising for the carbon cycle but still remains challenging. Au is regarded as the most selective catalyst for CO2 RR, but its high cost significantly hinders its industrial application. Herein, the bimetallic CuInSe2 is found to exhibit an Au-like catalytic feature: i) the interaction of Cu and In orbitals induces a moderate adsorption strength of CO2 RR intermediates and favors the reaction pathway; and ii) the hydrogen evolution is energetically unfavorable on CuInSe2 , as a surface reconstruction along with high energy change will occur after hydrogen adsorption. Furthermore, the Se vacancy is found to induce an electron redistribution, slightly tune the band structure, and optimize the CO2 RR route of bimetallic selenide. Consequently, the Se-defective CuInSe2 (V-CuInSe2 ) achieves a highly selective CO production ability that is comparable to noble metals in aqueous electrolyte, and the V-CuInSe2 cathode shows a satisfactory performance in an aqueous Zn-CO2 cell. This work demonstrates that designing cost-effective catalysts with noble-metal-like properties is an ideal strategy for developing efficient electrocatalysts. Moreover, the class of transition bimetallic selenides has shown promising prospects as active and cost-effective electrocatalysts owing to their unique structural, electronic, and catalytic properties.

Histological classification of melasma with reflectance confocal microscopy: a pilot study in Chinese patients.

OBJECTIVE: To investigate the histological classification of melasma with reflectance confocal microscopy (RCM) in vivo. METHODS: Two hundred and ten cases with facial melasma lesions were enrolled. After informed consent, the target melasma lesion of 10 patients were imaged with RCM and then biopsied as well. Under the RCM scanning, the distribution of the melanin determined the histological types, and then, the results of RCM images were compared with those of the histopathology. The other 200 cases were tested only with RCM. RESULTS: For the 10 cases imaged and biopsied, compared with that of the perilesional normal skin, the amount of melanin was significantly increased in the epidermis in all lesions under RCM, while three cases also found melanin in the dermis. Thus, seven of the 10 patients were categorized as the epidermal type while the other three as mixed ones, and the results were well correlated with those of the histopathology. Of the other 200 patients, 143 cases 71.5%) were categorized as the epidermal type while the other 57 (28.5%) cases as mixed ones. LIMITATIONS: If more melasma cases are biopsied, the data will be more convincing. CONCLUSION: RCM in vivo analysis shows complete coherence with histopathology results, which could be an alternative for the classification of melasma, and based on the results of RCM imaging, melasma is classified into two major types: the epidermal type and mixed type.