Effect of Mn2+ substitution on the structure, properties and HER activity of cadmium phosphochlorides.

Cadmium phosphochlorides, Cd4P2Cl3 and Cd7P4Cl6, possess cadmium atoms differently bonded to chlorine and phosphorus ligands. A combined experimental and theoretical study has been carried out to examine the effect of manganese substitution in place of cadmium in these compounds. Experimentally it is found that manganese prefers the Cd7P4Cl6 phase over Cd4P2Cl3. First-principles calculations reveal, stabilization of Cd7P4Cl6 upon Mn-substitution with a significant reduction in the formation energy when Mn2+ is substituted at Cd-sites coordinated octahedrally by Cl-ligands. Substitution of Mn2+ at two different Cd-sites in these compounds not only alters their formation energy differently but also causes a notable change in the electronic structures. In contrast to n-type conductivity in pristine Cd7P4Cl6, Mn2+ substituted Cd7-y Mn y P4Cl6 analogues exhibit p-type conductivity with a remarkable enhancement in the photochemical HER activity and stability of the system. Photochemical properties of pristine and substituted compounds are explained by studying the nature of charge carriers and their dynamics.

Structural Features and HER activity of Cadmium Phosphohalides.

We have carried out a combined experimental and theoretical investigation of the structures and properties of a family of cadmium phosphochlorides with varying Cl/Cd and P/Cd ratios, Cd2 P3 Cl, Cd4 P2 Cl3 , Cd3 PCl3, and Cd7 P4 Cl6 . Their optical band gaps are in the visible region and the values are sensitive to the Cl/Cd and P/Cd ratios, leading to an increase and decrease, respectively. First-principles calculations were used to understand the bonding and electronic structures. All phosphochlorides except Cd2 P3 Cl possess direct band gaps. The calculated dielectric constants and Born effective charges illustrate the bonding, hybridization, and ionic character in these compounds. The band positions indicate the thermodynamic feasibility to perform water splitting. All systems can be used in the hydrogen evolution reaction (HER), where Cd7 P4 Cl6 has the highest activity and Cd3 PCl3 the lowest. The apparent quantum yield is highest in Cd7 P4 Cl6 (20.1 %) even without the assistance of a co-catalyst. The HER activity can be understood on the basis of photoelectrochemical measurements.

Photochemical and Photoelectrochemical Hydrogen Generation by Splitting Seawater.

Producing hydrogen from water in an efficient manner could significantly reduce consumption of fossil fuels. In this regard the abundant presence of water in oceans offers an important alternative approach for water splitting using seawater. Direct use of seawater for the generation of hydrogen is a difficult and complex process due to the presence of various ions in seawater, which affect the activity of the catalysts and makes the selectivity towards efficient water splitting a challenging task. Herein various ways are reported to efficiently reduce seawater to hydrogen under visible light irradiation by various catalysts already reported by this group. A better performance than pure water was observed in some cases, and in a few cases the opposite was observed, implying that with a proper approach seawater can be efficiently reduced to generate hydrogen.

Unique Features of the Photocatalytic Reduction of H2O and CO2 by New Catalysts Based on the Analogues of CdS, Cd4P2X3 (X = Cl, Br, I).

Photochemical reduction of H2O and CO2 has been investigated with a new family of catalysts of the formula Cd4P2X3 (X= Cl, Br, I), obtained by the complete aliovalent substitution of the sulfide ions in CdS by P and X (Cl, Br, I). Unlike CdS, the Cd4P2X3 compounds exhibit hydrogen evolution and CO2 reduction from water even in the absence of a sacrificial agent or a cocatalyst. Use of NixPy as the cocatalyst, enhances hydrogen evolution, reaching 3870 (apparent quantum yield (AQY) = 4.11) and 9258 (AQY = 9.83) µmol h-1 g-1, respectively, under artificial and natural (sunlight) irradiation, in the case of Cd4P2Br3/NixPy. Electrochemical and spectroscopic studies have been employed to understand the photocatalytic activity of this family of compounds. Unlike most of the semiconductor-based photocatalysts, Cd4P2X3 catalysts reduce CO2 to CO and CH4 in the absence of sacrificial-agent or cocatalyst using water as the electron source. CO, CH4, and H2 have been obtained with these catalysts under artificial as well as sun-light irradiation. First-principles, calculations have been carried out to understand the electronic structure and catalytic features of these new catalysts.

Solar photochemical and thermochemical splitting of water.

Artificial photosynthesis to carry out both the oxidation and the reduction of water has emerged to be an exciting area of research. It has been possible to photochemically generate oxygen by using a scheme similar to the Z-scheme, by using suitable catalysts in place of water-oxidation catalyst in the Z-scheme in natural photosynthesis. The best oxidation catalysts are found to be Co and Mn oxides with the e(1) g configuration. The more important aspects investigated pertain to the visible-light-induced generation of hydrogen by using semiconductor heterostructures of the type ZnO/Pt/Cd1-xZnxS and dye-sensitized semiconductors. In the case of heterostructures, good yields of H2 have been obtained. Modifications of the heterostructures, wherein Pt is replaced by NiO, and the oxide is substituted with different anions are discussed. MoS2 and MoSe2 in the 1T form yield high quantities of H2 when sensitized by Eosin Y. Two-step thermochemical splitting of H2O using metal oxide redox pairs provides a strategy to produce H2 and CO. Performance of the Ln0.5A0.5MnO3 (Ln = rare earth ion, A = Ca, Sr) family of perovskites is found to be promising in this context. The best results to date are found with Y0.5Sr0.5MnO3.

Extraordinary Changes in the Electronic Structure and Properties of CdS and ZnS by Anionic Substitution: Cosubstitution of P and Cl in Place of S.

Unlike cation substitution, anion substitution in inorganic materials such as metal oxides and sulfides would be expected to bring about major changes in the electronic structure and properties. In order to explore this important aspect, we have carried out first-principles DFT calculations to determine the effects of substitution of P and Cl on the properties of CdS and ZnS in hexagonal and cubic structures and show that a sub-band of the trivalent phosphorus with strong bonding with the cation appears in the gap just above the valence band, causing a reduction in the gap and enhancement of dielectric properties. Experimentally, it has been possible to substitute P and Cl in hexagonal CdS and ZnS. The doping reduces the band gap significantly as predicted by theory. A similar decrease in the band gap is observed in N and F co-substituted in cubic ZnS. Such anionic substitution helps to improve hydrogen evolution from CdS semiconductor structures and may give rise to other applications as well.

Reduction of the internal capsule in families affected with schizophrenia.

BACKGROUND: The anterior limb of the internal capsule (ALIC), connecting cortical and subcortical structures, is involved in functional important circuits. To detect volumetric changes in ALIC, including the influence of genetic factors, a magnetic resonance imaging (MRI) study of families affected with schizophrenia was performed. METHODS: The study sample comprised 22 family members with schizophrenia (FM-SZ), 34 family members without schizophrenia (FM-NSZ), and 43 control subjects. In addition to manual tracing of ALIC, subjects underwent proton magnetic resonance spectroscopy in the left prefrontal cortex, psychopathological rating, and neuropsychological assessment of frontal lobe function. RESULTS: Compared with controls, a significant reduction of right ALIC volume was seen in all family members (12%-16% reduction, p < .01) and a reduction of left ALIC volume in FM-NSZ (10% reduction, p = .028) was also observed. Both groups of family members showed a bilateral reduction in maximal cross sectional area of the ALIC. FM-SZ performed significantly worse on neurocognitive measures (Subject Ordered Pointing Task [SOPT] and Wisconsin Card Sorting Test), and performance correlated negatively with the ALIC volume (SOPT, r = -.6, p = .03). CONCLUSIONS: A reduced volume of ALIC in affected families supports the hypothesis of disturbed frontothalamic connectivity in schizophrenia and demonstrates functional relevance by an association with reduced neurocognitive performance.