On the coordination chemistry of a bacterial siderophore cepabactin from a theoretical perspective.

Iron is one of the essential metals required by almost all living organisms. However, nature has certain constraints in distributing this element among tissues. Since polymeric oxide-bridged Fe (III) is the prominent source of Fe (III) ions, the insolubility of Fe (III) ions in aqueous systems reduces the direct uptake by cells. Secondly, the free-Fe entities which generate .OH radicals pave the way to the destruction of the cells. Hence, a protective coordination environment via sophisticated chemical systems is required for the acquisition of Fe, its successive transport, storage, and effective utilization in various tissues. Siderophores are polydentate ligands used by bacterial cells for Fe acquisition, with a relatively high affinity for Fe (III) ions. Secreted from the bacterial cells into the external aqueous medium, they sequester Fe to give a soluble complex which re-enters the organism at a specific receptor. Once it gets inside the cell, the Fe is released from the complex and utilized for essential biochemical reactions. The medicinal applications of these natural ligands, developing progressively in various research groups, necessitate the theoretical aspects of their coordination chemistry. This research paper deals with the coordination chemistry of one of the siderophores, cepabactin (Cep). The chemical computations confirm that the FeIII(Cep)3 complex is octahedral and high spin. The oxygen atoms of Cep, which are hard and negatively charged, thus act as electron donors in the FeIII(Cep)3 complex formation. This in turn makes the siderophores relatively less attractive towards Fe (II) ions.

Solar-driven hybrid photo-Fenton degradation of persistent antibiotic ciprofloxacin by zinc ferrite-titania heterostructures: degradation pathway, intermediates, and toxicity analysis.

Present work puts forward an efficient strategy to degrade one of the persistent antibiotic contaminants, ciprofloxacin (CIP). Hybrid advanced oxidation process (HAOP) is tailored with a synergy effect between photocatalysis and photo-Fenton catalysis on zinc ferrite-titania heterostructured composite (ZFO-TiO2). The ZFO-TiO2 heterostructured composite enables heterogenous surfaces for enhanced charge separation where HAOP is implemented for CIP degradation with the aid of class AAA solar simulator. The results reveal an enhanced degradation rate of CIP (kobs = 0.255 min-1), noticeably higher than the conventional TiO2-based photocatalysis. The HAOP system strongly enhances the reaction rates showing five times higher performance as compared to TiO2-based photocatalysis. The substitution reactions for degradation of CIP into its intermediates were analyzed by LC-MS/MS, and the plausible degradation pathways have been graphically modeled identifying 3-phenyl-1-propanol and phenol molecules as less toxic end products. Toxicity of the photodegraded samples reveal 18.1 ± 1.24% inhibition of V. fischeri at the end of 60-min treatment indicating reduced toxicity of CIP contaminated samples. Antimicrobial inhibition studies on E. coli also corroborate an effective CIP removal (~ 100%) in less than 90 min. The study puts forward a novel ZFO-TiO2 composite HAOP system for efficient and rapid mineralization of an antibiotic pollutant, extendable towards wide range of pharmaceutical drug degradation studies.

Piezocatalytic Techniques in Environmental Remediation.

As a consequence of rapid industrialization throughout the world, various environmental pollutants have begun to accumulate in water, air, and soil. This endangers the ecological environment of the earth, and environmental remediation has become an immediate priority. Among various environmental remediation techniques, piezocatalytic techniques, which uniquely take advantage of the piezoelectric effect, have attracted much attention. Piezoelectric effects allow pollutant degradation directly, while also enhancing photocatalysis by reducing the recombination of photogenerated carriers. In this Review, we provide a comprehensive summary of recent developments in piezocatalytic techniques for environmental remediation. The origin of the piezoelectric effect as well as classification of piezoelectric materials and their application in environmental remediation are systematically summarized. We also analyze the potential underlying mechanisms. Finally, urgent problems and the future development of piezocatalytic techniques are discussed.

Ultra-Sensitive Impedimetric Immunosensor Using Copper Oxide Quantum Dots Grafted on the Gold Microelectrode for the Detection of Parathion.

The extensive use of organophosphates (OPs) pollutes the environment, leading to serious health hazards for human beings. The current need is to fabricate a sensing platform that will be sensitive and selective towards the detection of OPs at trace levels in the nM to fM range. With this discussed in the present report, an ultra-sensitive immunosensing platform is developed using digestive-ripened copper oxide quantum dots grafted on a gold microelectrode (Au-µE) for the impedimetric detection of parathion (PT). The copper oxide quantum dots utilized in this study were of ultra-small size with a radius of approximately 2 to 3 nm and were monodispersed with readily available functional groups for the potential immobilization of antibody parathion (Anti-PT). The miniaturization is achieved by the utilization of Au-µE and the microfluidic platform utilized has the sample holding capacity of about 2 to 10 µL. The developed immunosensor provided a wide linear range of detection from 1 µM to 1 fM. The lower Limit of Detection (LoD) for the developed sensing platform was calculated to be 0.69 fM, with the sensitivity calculated to be 0.14 kΩ/nM/mm2. The stability of the sensor was found to be ~40 days with good selectivity. The developed sensor has the potential to integrate with a portable device for field applications.

Measuring tuberculosis patient perceived quality of care in public and public-private mix settings in India: an instrument development and validation study.

BACKGROUND: At present, there are no validated quantitative scales available to measure patient-centred quality of care in health facilities providing services for tuberculosis (TB) patients in India and low-income and middle-income countries. METHODS: Initial themes and items reflective of TB patient's perceived quality of care were developed using qualitative interviews. Content adequacy of the items were ascertained through Content validity Index (CVI) and content validity ratio (CVR). Pilot testing of the questionnaire for assessing validity and reliability was undertaken among 714 patients with TB. Sampling adequacy and sphericity were tested by Kaiser-Meyer-Olkin and Bartlett's test, respectively. Exploratory and confirmatory factor analysis was undertaken to test validity. Cronbach's α and test-retest scores were used to test reliability. RESULTS: A 32-item tool measuring patient-perceived quality of TB distributed across five domains was developed initially based on a CVI and CVR cut-off score of 0.78 and cognitive interviews with patients with TB. Bartlett's test results showed a strong significance f (χ2=3756 and p<0.001) and Kaiser-Meyer-Olkin was measured to be 0.698 highlighting data adequacy and correlation between the variables. Exploratory factor analysis with varimax rotation extracted 4 factors related to 14 items with Eigen values >1 which accounted for 60.9% of the total variance of items. Correlation (z-value >1.96) between items and factors was highly significant and Cronbach's α was acceptable for the global scale (0.76) for the four factors. Intraclass correlation coefficient and the test retest scores for four factors were (<0.001) significant. CONCLUSION: We validated a measurement tool for patient-perceived quality of care for TB (PPQCTB) which measured the patient's satisfaction with healthcare provider and services. PPQCTB tool could enrich quality of care evaluation frameworks for TB health services in India.

Co4N-WNx composite for efficient piezocatalytic hydrogen evolution.

A dual-phase transition metal nitride (TMN) based Co4N-WNx system has been fabricated using nitridation of CoWO4. The interface between centrosymmetric Co4N and non-centrosymmetric WNx promotes charge carrier separation. This system also shows piezoelectric behavior. The piezoelectric property has been proved using piezoelectric force microscopy (PFM) measurements. In addition, modulating the non-centrosymmetric structure of Co4N-WNx allows a hydrogen production rate of about 262.7 µmol g-1 h-1 in pure water. We also show that the piezocatalytic hydrogen evolution efficiency is satisfactory. Co4N-WNx can also help achieve simultaneous piezocatalytic hydrogen production and RhB degradation. This work provides a novel strategy for designing efficient piezocatalytic materials.

Boosting Oxygen Reduction for High-Efficiency H2 O2 Electrosynthesis on Oxygen-Coordinated CoNC Catalysts.

Atomically dispersed CoNC is a promising material for H2 O2 selective electrosynthesis via a two-electron oxygen reduction reaction. However, the performance of typical CoNC materials with routine CoN4 active center is insufficient and needs to be improved further. This can be done by fine-tuning its atomic coordination configuration. Here, a single-atom electrocatalyst (Co/NC) is reported that comprises a specifically penta-coordinated CoNC configuration (OCoN2 C2 ) with Co center coordinated by two nitrogen atoms, two carbon atoms, and one oxygen atom. Using a combination of theoretical predictions and experiments, it is confirmed that the unique atomic structure slightly increases the charge state of the cobalt center. This optimizes the adsorption energy towards *OOH intermediate, and therefore favors the two-electron ORR relevant for H2 O2 electrosynthesis. In neutral solution, the as-synthesized Co/NC exhibits a selectivity of over 90% over a potential ranging from 0.36 to 0.8 V, with a turnover frequency value of 11.48 s-1 ; thus outperforming the state-of-the-art carbon-based catalysts.

A dimethyl disulfide gas sensor based on nanosized Pt-loaded tetrakaidecahedralα-Fe2O3nanocrystals.

Surface modification by employing precious metals is one of the most effective ways to improve the gas-sensing performance of metal oxide semiconductors. Pureα-Fe2O3nanoparticles and Pt-modifiedα-Fe2O3nanoparticles were prepared sequentially using a rather simple hydrothermal synthesis and impregnation method. Compared with the originalα-Fe2O3nanomaterials, the Pt-α-Fe2O3nanocomposite sensor shows a higher response value (Ra/Rg = 58.6) and a shorter response/recovery time (1 s/168 s) to 100 ppm dimethyl disulfide (DMDS) gas at 375 °C. In addition, it has better selectivity to DMDS gas with the value of more than 9 times higher than the other target gases at 375 °C. This study indicates that the Pt-α-Fe2O3nanoparticle sensor has good prospects and can be used as a low-cost and effective DMDS gas sensor.

Enhanced photo-fenton and photoelectrochemical activities in nitrogen doped brownmillerite KBiFe2O5.

Visible-light-driven photo-fenton-like catalytic activity and photoelectrochemical (PEC) performance of nitrogen-doped brownmillerite KBiFe2O5 (KBFO) are investigated. The effective optical bandgap of KBFO reduces from 1.67 to 1.60 eV post N-doping, enabling both enhancement of visible light absorption and photoactivity. The photo-fenton activity of KBFO and N-doped KBFO samples were analysed by degrading effluents like Methylene Blue (MB), Bisphenol-A (BPA) and antibiotics such as Norfloxacin (NOX) and Doxycycline (DOX). 20 mmol of Nitrogen-doped KBFO (20N-KBFO) exhibits enhanced catalytic activity while degrading MB. 20N-KBFO sample is further tested for degradation of Bisphenol-A and antibiotics in the presence of H2O2 and chelating agent L-cysteine. Under optimum conditions, MB, BPA, and NOX, and DOX are degraded by 99.5% (0.042 min-1), 83% (0.016 min-1), 72% (0.011 min-1) and 95% (0.026 min-1) of its initial concentration respectively. Photocurrent density of 20N-KBFO improves to 8.83 mA/cm2 from 4.31 mA/cm2 for pure KBFO. Photocatalytic and photoelectrochemical (PEC) properties of N-doped KBFO make it a promising candidate for energy and environmental applications.

Integrating trace amounts of Pd nanoparticles into Mo3N2 nanobelts for an improved hydrogen evolution reaction.

Significant efforts have been directed towards the use of transition metal nitrides as electrocatalysts for the hydrogen evolution reaction (HER). Molybdenum nitride, despite its potential for scalable production, suffers from the bottleneck of poor catalytic activity. Furthermore the kinetics of the water dissociation process ought to be improved for enhancing its potential. Here, we report a facile method for the incorporation of a trace amount of Pd nanoparticles into Mo3N2 nanobelts (0.75 Pd/Mo3N2) for an enhanced HER in both acidic and alkaline solutions. When employed for the HER, the 0.75 wt% Pd/Mo3N2 nanobelt delivers excellent catalytic activity with overpotentials of 45 and 65 mV in 0.5 M H2SO4 and 1 M KOH at a current density of 10 mA cm-2. As-prepared 0.75 wt% Pd/Mo3N2 displays a smaller Tafel slope and offers substantial stability in both acidic and alkaline media under the same operating conditions. The improved performance of the as-prepared 0.75 wt% Pd/Mo3N2 points to fast charge transfer, higher electrical conductivity and synergistic effects between Pd and Mo. This work displays a direct method for reducing the use and cost associated with the use of platinum-group metals while also delivering superior HER catalytic performance.

Mesoporous Ti0.5Cr0.5N for trace H2S detection with excellent long-term stability.

Efficient, accurate and reliable detection and monitoring of H2S is of significance in a wide range of areas: industrial production, medical diagnosis, environmental monitoring, and health screening. However the rapid corrosion of commercial platinum-on-carbon (Pt/C) sensing electrodes in the presence of H2S presents a fundamental challenge for fuel cell gas sensors. Herein we report a solution to the issue through the design of a sensing electrode, which is based on Pt supported on mesoporous titanium chromium nitrides (Pt/Ti0.5Cr0.5N). Its desirable characteristics are due to its high electrochemical stability and strong metal-support interactions. The Pt/Ti0.5Cr0.5N-based sensors exhibit a much smaller attenuation (1.3%) in response to H2S than Pt/C-sensor (40%), after 2 months sensing test. Furthermore, the Pt/Ti0.5Cr0.5N-based sensors exhibit negligible cross response to other interfering gases compared with hydrogen sulfide. Results of density functional theory calculation also verify the excellent long-term stability and selectivity of the gas sensor. Our work hence points to a new sensing electrode system that offers a combination of high performance and stability for fuel-cell gas sensors.

Co3Mo3N-An efficient multifunctional electrocatalyst.

Efficient catalysts are required for both oxidative and reductive reactions of hydrogen and oxygen in sustainable energy conversion devices. However, current precious metal-based electrocatalysts do not perform well across the full range of reactions and reported multifunctional catalysts are all complex hybrids. Here, we show that single-phase porous Co3Mo3N prepared via a facile method is an efficient and reliable electrocatalyst for three essential energy conversion reactions; oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) in alkaline solutions. Co3Mo3N presents outstanding OER, ORR, and HER activity with high durability, comparable with the commercial catalysts RuO2 for OER and Pt/C for ORR and HER. In practical demonstrations, Co3Mo3N gives high specific capacity (850 mA h gZn -1 at 10 mA cm-2) as the cathode in a zinc-air battery, and a low potential (1.63 V at 10 mA cm-2) used in a water-splitting electrolyzer. Availability of Co and Mo d-states appear to result in high ORR and HER performance, while the OER properties result from a cobalt oxide-rich activation surface layer. Our findings will inspire further development of bimetallic nitrides as cost-effective and versatile multifunctional catalysts that will enable scalable usage of electrochemical energy devices.

Nitrogen, sulfur co-doped carbon coated zinc sulfide for efficient hydrogen peroxide electrosynthesis.

Oxygen electroreduction (ORR) via a two-electron pathway is a promising alternative for hydrogen peroxide (H2O2) synthesis in small-scale applications. In this work, nitrogen and sulfur co-doped carbon coated zinc sulfide nanoparticles (ZnS@C) are synthesized using facile high-temperature annealing. In an alkaline electrolyte, the presence of ZnS suppresses the reduction of H2O2 during the ORR and contributes to high H2O2 selectivity (∼90%) over a wide potential range (0.40-0.80 V). Continuous generation of H2O2 is in turn achieved at an outstanding rate of 1.485 mol gcat.-1 h-1 with a faradaic efficiency of 93.7%.

Oxygen Coordination on Fe-N-C to Boost Oxygen Reduction Catalysis.

The coordination environments of iron (Fe) in Fe-N-C catalysts determine their intrinsic activities toward oxygen reduction reactions (ORR). The precise atomic-level regulation of the local coordination environments is thus of critical importance yet quite challenging to achieve. Here, atomically dispersed Fe-N-C catalyst with O-Fe-N2C2 moieties is thoroughly studied for ORR catalysis. Advanced synchrotron X-ray characterizations, along with theoretical modeling, explicitly unraveled the penta-coordinated nature of the Fe center in the catalytic domain and the energetically optimized ORR pathways on the well-tailored O-Fe-N2C2 moieties. The combined structure identification from both experiments and theory provides an opportunity to understand the role of the coordination environments in directing the catalytic activity of single-atom or single-site catalysts; not only the center metal atom but also the whole coordinating atoms participate in the catalytic cycle.

Surface Functionalized Sensors for Humidity-Independent Gas Detection.

Semiconducting metal oxides (SMOXs) are used widely for gas sensors. However, the effect of ambient humidity on the baseline and sensitivity of the chemiresistors is still a largely unsolved problem, reducing sensor accuracy and causing complications for sensor calibrations. Presented here is a general strategy to overcome water-sensitivity issues by coating SMOXs with a hydrophobic polymer separated by a metal-organic framework (MOF) layer that preserves the SMOX surface and serves a gas-selective function. Sensor devices using these nanoparticles display near-constant responses even when humidity is varied across a wide range [0-90 % relative humidity (RH)]. Furthermore, the sensor delivers notable performance below 20 % RH whereas other water-resistance strategies typically fail. Selectivity enhancement and humidity-independent sensitivity are concomitantly achieved using this approach. The reported tandem coating strategy is expected to be relevant for a wide range of SMOXs, leading to a new generation of gas sensors with excellent humidity-resistant performance.

Dual-Metal Interbonding as the Chemical Facilitator for Single-Atom Dispersions.

Atomically dispersed catalysts, with maximized atom utilization of expensive metal components and relatively stable ligand structures, offer high reactivity and selectivity. However, the formation of atomic-scale metals without aggregation remains a formidable challenge due to thermodynamic stabilization driving forces. Here, a top-down process is presented that starts from iron nanoparticles, using dual-metal interbonds (RhFe bonding) as a chemical facilitator to spontaneously convert Fe nanoparticles to single atoms at low temperatures. The presence of RhFe bonding between adjacent Fe and Rh single atoms contributes to the thermodynamic stability, which facilitates the stripping of a single Fe atom from the Fe nanoparticles, leading to the stabilized single atom. The dual single-atom Rh-Fe catalyst renders excellent electrocatalytic performance for the hydrogen evolution reaction in an acidic electrolyte. This discovery of dual-metal interbonding as a chemical facilitator paves a novel route for atomic dispersion of chemical metals and the design of efficient catalysts at the atomic scale.

Nickel-Iron Nitride-Nickel Sulfide Composites for Oxygen Evolution Electrocatalysis.

Advance applications like water splitting system and rechargeable metal-air battery are highly dependent on efficient electrocatalyst for the oxygen evolution reaction (OER). Heterostructured materials, with a high active surface area and electron effect, accomplish enhanced catalytic performance. Here, a nitride-sulfide composite (FeNi3N-Ni3S2) has been prepared by a simple hydrothermal process coupled with nitridation. The prepared composite electrocatalyst FeNi3N-Ni3S2 possesses lower electron densities compared to those of FeNi3N and Ni3S2, lessening the activation energy (Ea) toward the OER. Consequently, the prepared FeNi3N-Ni3S2 exhibits excellent OER performance with a low overpotential (230 mV) and a small Tafel slope (38 mV dec-1). Highly stable FeNi3N-Ni3S2 composite delivers lower charging voltage and extended lifetime in rechargeable Zn-air battery, compared with IrO2.

A Surface-Oxide-Rich Activation Layer (SOAL) on Ni2 Mo3 N for a Rapid and Durable Oxygen Evolution Reaction.

The oxygen evolution reaction (OER) is key to renewable energy technologies such as water electrolysis and metal-air batteries. However, the multiple steps associated with proton-coupled electron transfer result in sluggish OER kinetics and catalysts are required. Here we demonstrate that a novel nitride, Ni2 Mo3 N, is a highly active OER catalyst that outperforms the benchmark material RuO2 . Ni2 Mo3 N exhibits a current density of 10 mA cm-2 at a nominal overpotential of 270 mV in 0.1 m KOH with outstanding catalytic cyclability and durability. Structural characterization and computational studies reveal that the excellent activity stems from the formation of a surface-oxide-rich activation layer (SOAL). Secondary Mo atoms on the surface act as electron pumps that stabilize oxygen-containing species and facilitate the continuity of the reactions. This discovery will stimulate the further development of ternary nitrides with oxide surface layers as efficient OER catalysts for electrochemical energy devices.

Nitridation of CoWO4/CdS Nanocomposite Formed Metal Nitrides Assisting Efficiently Photocatalytic Hydrogen Evolution.

Nitridation of CoWO4/CdS nanocomposite results in the formation of metal nitrides on the surface of CdS. The high electrical conductivity, appropriate binding energy for hydrogen, and Pt-like properties of the surface nitrides promote the H2 evolution performance. Therefore, the optimal performance of nitrided CoWO4/CdS (CoWO4/CdS-N, 3650 µmol·h-1·g-1) is higher than that of Pt/CdS (2948 µmol·h-1·g-1).

Geometric Structure and Electronic Polarization Synergistically Boost Hydrogen Evolution Kinetics in Alkaline Medium.

Efficient electrocatalysts for the hydrogen evolution reaction (HER) are significant for the utilization of hydrogen as a fuel, particularly under alkaline conditions. However, the sluggish kinetics of HER remains a challenge. Here we demonstrate an efficient HER catalyst comprising Ru and AgCl nanoparticles anchored on Ag nanowires (Ru/AgCl@Ag), which delivers a low overpotential of 12 mV at 10 mA cm-2 and a Tafel slope of 38 mV decade-1. A high mass activity of 214 mA mg-1 at an overpotential of 25 mV and a long-term durability in 1.0 M KOH are observed. In combination with computational simulations, we find that the high electronegativity of chlorine in AgCl and d-band electrons from Ru synergistically destabilize the water molecule and modulate H adsorption/desorption on the surface of Ru/AgCl@Ag, respectively. This work opens a promising avenue for the facile design and application of highly active and stable composite electrocatalysts toward water splitting.