Visible Light Driven Photoelectrochemical Water Oxidation by Zn- and Ti-Doped Hematite Nanostructures

The electrodeposition method was used for modification of a nanostructured hematite photoanode with Ti and Zn to improve the photoelectrocatalytic performance of hematite in the water splitting reaction. The photoelectrocatalytic activity of the hematite electrodes modified with Ti⁴⁺ and Zn²⁺ was optimized through the controlled variation of the dopant ion concentration in the electrodeposition solution. Under optimized conditions, for standard illumination of AM 1.5G (100 mW cm^–2), the photocurrent density at the Ti/Zn-modified hematite anode reached 1.5 mA cm^–2 at 1.23 V vs RHE that was 2.5-times higher than that observed with the pristine hematite electrode, the photoelectrocatalysis onset potential being 63 mV reduced. Effects of Ti and Zn doping on the photoelectrochemical activity of pristine hematite were studied by scanning electron microscopy, UV–vis spectroscopy, elemental analysis, and electrochemical impedance spectroscopy. On the basis of the obtained results, the improved performance of the Ti/Zn-modified hematite stemmed from the combination of the enhanced electrical conductivity along with the facilitated charge transport in the bulk phase and at the surface of hematite. The effect of Zn-doping decreasing the overpotential of the reaction by 218 mV (solely Zn-doped compared to that of the pristine hematite) was correlated with the Zn contribution to the interfacial catalysis of water oxidation

Simultaneous Electrosynthesis of Syngas and an Aldehyde from CO₂ and an Alcohol by Molecular Electrocatalysis

A tandem cell for artificial photosynthesis with CO2 and water as the oxidants and an organic alcohol as the reductant is described. The use of molecular catalysts with high activity and selectivity, in an appropriate cell configuration, leads to electrochemical reduction of CO2 and water to CO and H2 (syngas) in tandem with benzyl alcohol oxidation to benzaldehyde. A faradaic efficiency (FE) of ∼70% for the formation of benzaldehyde was obtained with simultaneous syngas generation with varying ratios of H2 and CO at the cathode. The maximum energy efficiency obtained for the electrochemical cell was 17.6%

Monitoring and Modeling Endosulfan in Chinese Surface Soil

Endosulfan is a currently used organochlorine pesticide in China, with annual usage of 2300 t between 1994 and 2004. Concentrations of endosulfan (including α- and β-isomers and their metabolite endosulfan sulfate) were reported for surface soil collected in 2005 at 141 sites (6 background, 95 rural, and 40 urban) across China. The concentrations of total endosulfan (sum of α-endosulfan, β-endosulfan, and endosulfan sulfate) at all sites ranged from BDL (below detection limit) to 19000 pg/g dry weight (dw), with geometric mean (GM) 120 pg/g dw. Rural soils had the highest total endosulfan concentrations, with GM 160 pg/g dw, followed by urban soils (GM = 83 pg/g dw) and background soils (GM = 38 pg/g dw). The observed soil concentrations of α-endosulfan (GM = 6.5 pg/g dw) were much lower than those of β-endosulfan (GM = 49 pg/g dw) and endosulfan sulfate (GM = 47 pg/g dw). The fractional abundance of α-endosulfan Fα-endo [α-endosulfan/(α-endosulfan + β-endosulfan)] for all soils ranged from 0.00040 to 0.91, with GM 0.10, much lower than those in technical products (ranged from 0.67 to 0.7), which most likely reflects that α-endosulfan is more volatile and degrades faster than β-endosulfan in soil. Consequently, half-life of β-endosulfan in soil is expected longer than α-endosulfan. Significant correlation between endosulfan sulfate and its parent isomers suggested that the presence of endosulfan sulfate originated from its parent isomers. Based on multiple linear regression model, inventories of endosulfan sulfate in Chinese agricultural soil in 2004 with a 1/4° longitude × 1/6° latitude resolution are established. Comparison between field measurements and modeling results showed significant correlations between the modeled and measured endosulfan concentrations, and 89%, 83%, and 70% of monitoring data fell between the lowest and the highest modeled concentrations for α- and β-endosulfan and endosulfan sulfate, respectively. The good agreement lends credibility to modeled soil concentrations of endosulfan. To our knowledge, this is the first soil concentration inventory for endosulfan sulfate, which paves the way for further study on its environmental behavior

Uniform Doping of Titanium in Hematite Nanorods for Efficient Photoelectrochemical Water Splitting

Doping elements in hematite nanostructures is a promising approach to improve the photoelectrochemical (PEC) water-splitting performance of hematite photoanodes. However, uniform doping with precise control on doping amount and morphology is the major challenge for quantitatively investigating the PEC water-splitting enhancement. Here, we report on the design and synthesis of uniform titanium (Ti)-doped hematite nanorods with precise control of the Ti amount and morphology for highly effective PEC water splitting using an atomic layer deposition assisted solid-state diffusion method. We found that Ti doping promoted band bending and increased the carrier density as well as the surface state. Remarkably, these uniformly doped hematite nanorods exhibited high PEC performance with a pronounced photocurrent density of 2.28 mA/cm² at 1.23 V vs reversible hydrogen electrode (RHE) and 4.18 mA/cm² at 1.70 V vs RHE, respectively. Furthermore, as-prepared Ti-doping hematite nanorods performed excellent repeatability and durability; over 80% of the as-fabricated photoanodes reproduced the steady photocurrent density of 1.9–2.2 mA/cm² at 1.23 V vs RHE at least 3 h in a strong alkaline electrolyte solution

Template-Free Synthesis of Hematite Photoanodes with Nanostructured ATO Conductive Underlayer for PEC Water Splitting

Hematite is a promising semiconductor candidate for PEC water splitting. However, hematite is far well short of the theoretical value of solar-to-fuel conversion efficiency because of the fast recombination of photogenerated carriers. To address this limitation, a facile template-free preparation of hematite photoanode with nanostructured ATO (antimony-doped tin oxide) conductive underlayer served as a scaffold to transport photogenerated electron was developed to decrease the recombination opportunities of the carriers. Furthermore, the constructed ATO scaffold could also increase the light absorption of hematite and the number of the carriers, resulting in better PEC performance of hematite

Inner Layer Control of Performance in a Dye-Sensitized Photoelectrosynthesis Cell

Interfacial charge transfer and core-shell structures play important roles in dye-sensitized photoelectrosynthesis cells (DSPEC) for water splitting into H2 and O2. An important element in the design of the photoanode in these devices is a core/shell structure which controls local electron transfer dynamics. Here, we introduce a new element, an internal layer of Al2O3 lying between the Sb:SnO2/TiO2 layers in a core/shell electrode which can improve photocurrents by up to 300%. In these structures, the results of photocurrent, transient absorption, and linear scan voltammetry measurements point to an important role for the Al2O3 layer in controlling internal electron transfer within the core/shell structure

Levels and Isomer Profiles of Dechlorane Plus in Chinese Air

The highly chlorinated flame retardant, Dechlorane Plus (DP), was measured in air across 97 Chinese urban and rural sites. DP was detected in 51 of these sites, with a mean air concentration in urban centers (15.6 ± 15.1 pg m−3) approximately 5 times greater than those measured in rural areas (3.5 ± 5.6 pg m−3). These DP levels were likely attributable to local sources rather than trans-boundary influences. Elevated urban levels were measured along the southeastern coast and in south-central China; the highest concentration was observed in the city of Kunming (66 pg m−3). Few of the urban samples (7%) and a majority of the rural samples (62%) were below the method detection limit, notably areas in rural central and northeastern China. The mean fractional abundance of the syn-DP isomer (fsyn) in all samples was 0.33 ± 0.10, values indistinguishable from that of a commercial mixture (fsyn = 0.35). This paper represents the first report on DP levels in Chinese air, together with isomeric ratio profiles from urban and rural sites

Enhanced Reducibility via Altering Exciton Binding Energy of Conjugated Microporous Polymers for Photocatalytic Reduction

Visible-light-driven organic transformations, such as photocatalytic reductive dehalogenation, are highly significant but remain challenging to implement because of the insufficient charge separation. Herein, we report a facile strategy to realize heterogeneous and high-efficiency photocatalytic dehalogenation under mild conditions via tuning the exciton binding energy of conjugated microporous polymers (CMPs) with an alternating electron donor (D)–acceptor (A) structural motif. The integration of acceptors, especially strong ones (sA), into the conjugated polymer scaffolds minimized the exciton binding energy, suppressed charge carrier recombination, and facilitated the charge transfer effectively. CMP-CSU11, featuring an alternative D–sA skeleton with the lowest exciton binding energy, exhibited a superior photocatalytic dehalogenation efficiency over 99% in only 50 min, surpassing the state-of-the-art photoreductive dehalogenation catalysts, enabling a broad scope of substrates (14 examples), and possessing extraordinary recyclability. This work provides an effective strategy based on intramolecular charge transfer engineering to develop heterogeneous photocatalysts for task-specific organic transformation

Light-Driven Water Splitting by a Covalently Linked Ruthenium-Based Chromophore–Catalyst Assembly

The preparation and characterization of new Ru­(II) polypyridyl-based chromophore–catalyst assemblies, [(4,4′-PO₃H₂-bpy)₂Ru­(4-Mebpy-4′-epic)­Ru­(bda)­(pic)]²⁺ (<b>1</b>, bpy = 2,2′-bipyridine; 4-Mebpy-4′-epic = 4-(4-methylbipyridin-4′-yl-ethyl)-pyridine; bda = 2,2′-bipyridine-6,6′-dicarboxylate; pic = 4-picoline), and [(bpy)₂Ru­(4-Mebpy-4′-epic)­Ru­(bda)­(pic)]²⁺ (<b>1</b>′) are described, as is the application of <b>1</b> in a dye-sensitized photoelectrosynthesis cell (DSPEC) for solar water splitting. On SnO₂/TiO₂ core–shell electrodes in a DSPEC configuration with a Pt cathode, the chromophore–catalyst assembly undergoes light-driven water oxidation at pH 5.7 in a 0.1 M acetate buffer, 0.5 M in NaClO₄. With illumination by a 100 mW cm^–2 white light source, photocurrents of ∼0.85 mA cm^–2 were observed after 30 s under a 0.1 V vs Ag/AgCl applied bias with a faradaic efficiency for O₂ production of 74% measured over a 5 min illumination period