Shengyao Wang

Light-Switchable Oxygen Vacancies in Ultrafine Bi5O7Br Nanotubes for Boosting Solar-Driven Nitrogen Fixation in Pure Water

Solar-driven reduction of dinitrogen (N2 ) to ammonia (NH3 ) is severely hampered by the kinetically complex and energetically challenging multielectron reaction. Oxygen vacancies (OVs) with abundant localized electrons on the surface of bismuth oxybromide-based semiconductors are demonstrated to have the ability to capture and activate N2 , providing an alternative pathway to overcome such limitations. However, bismuth oxybromide materials are susceptible to photocorrosion, and the surface OVs are easily oxidized and therefore lose their activities. For realistic photocatalytic N2 fixation, fabricating and enhancing the stability of sustainable OVs on semiconductors is indispensable. This study shows the first synthesis of self-assembled 5 nm diameter Bi5 O7 Br nanotubes with strong nanotube structure, suitable absorption edge, and many exposed surface sites, which are favorable for furnishing sufficient visible light-induced OVs to realize excellent and stable photoreduction of atmospheric N2 into NH3 in pure water. The NH3 generation rate is as high as 1.38 mmol h-1 g-1 , accompanied by an apparent quantum efficiency over 2.3% at 420 nm. The results presented herein provide new insights into rational design and engineering for the creation of highly active catalysts with light-switchable OVs toward efficient, stable, and sustainable visible light N2 fixation in mild conditions.

Fe@Fe2O3 promoted electrochemical mineralization of atrazine via a triazinon ring opening mechanism

In this study, an electrochemical/electro-Fenton oxidation (EC/EF) system was designed to degrade atrazine, by utilizing boron-doped diamond (BDD) and Fe@Fe2O3 core-shell nanowires loaded active carbon fiber (Fe@Fe2O3/ACF) as the anode and the cathode, respectively. This EC/EF system exhibited much higher degradation rate, decholorination and mineralization efficiency of atrazine than the electrochemical (EC) and electrochemical/traditional electro-Fenton (EC/TEF) oxidation counterpart systems without Fe@Fe2O3 core-shell nanowires. Active species trapping experiment revealed that Fe@Fe2O3 could activate molecular oxygen to produce more OH through Fenton reaction, which favored the atrazine degradation. High performance liquid chromatography, high performance liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry were applied to probe the decomposition and mineralization of atrazine during this novel EC/EF process, which revealed that two intermediates of triazinons (the isomerization of hydroxylated atrazine) were generated during the electrochemical/electro-Fenton oxidation of atrazine in the presence of Fe@Fe2O3 core-shell nanowires. The experimental and theoretical calculation results suggested that atrazine might be degraded via a triazinon ring opening mechanism, while the presence of Fe@Fe2O3 notably accelerated the decholorination process, and produced more hydroxylated products to promote the generation of trazinons and the subsequent ring cleavage as well as the final complete mineralization. This work provides a deep insight into the triazine ring opening mechanism and the design of efficient electrochemical advanced oxidation technologies (EAOTs) for persistent organic pollutant removal.

Highly efficient visible light induced photocatalytic activity of a novel in situ synthesized conjugated microporous poly(benzothiadiazole)–C3N4 composite

In this study, a novel π-conjugated microporous poly(benzothiadiazole)–graphitic carbon nitride (BBT–C3N4) photocatalyst was synthesized through a facile in situ palladium-catalyzed Sonogashira–Hagihara cross-coupling polycondensation of 4,7-dibromobenzo[c][1,2,5]thiadiazole with 1,3,5-triethynylbenzene in the presence of evenly dispersed g-C3N4 using mixed DMF/TEA as solvent at 80 °C. Systematic characterization results revealed that BBT was equally dispersed on the surface of C3N4 with chemical bonds. The photocatalytic tests showed that this BBT–C3N4 composite exhibited enhanced photocatalytic removal of both sulfathiazole and Cr(VI) in comparison with the pure BBT and C3N4 as well as a mechanical mixture of BBT and C3N4, indicating that the oxidation and reduction abilities of BBT–C3N4 were simultaneously enhanced after composition under visible light irradiation. This was subsequently confirmed by radical detection, PL analysis and scavenger experiments as well. Holes and photoelectrons were demonstrated to be the main active species during the photocatalytic removal of sulfathiazole and Cr(VI), respectively. A possible photoelectron transfer mechanism for efficient photoinduced electron–hole separation of BBT–C3N4 composites is proposed based on all the results. This study provides new insight into the design of highly efficient visible light-driven photocatalysts with superior redox ability for wastewater treatment.

Interfacing Photosynthetic Membrane Protein with Mesoporous WO3 Photoelectrode for Solar Water Oxidation

Photosynthetic biocatalysts are emerging as a new class of materials, with their sophisticated and intricate structure, which promise improved remarkable quantum efficiency compared to conventional inorganic materials in artificial photosynthesis. To break the limitation of efficiency, the construction of bioconjugated photo-electrochemical conversion devices has garnered substantial interest and stood at the frontier of the multidisciplinary research between biology and chemistry. Herein, a biohybrid photoanode of a photosynthetic membrane protein (Photosystem II (PS II)), extracted from fresh spinach entrapped on mesoporous WO3 film, is fabricated on fluorine-doped tin oxide. The PS II membrane proteins are observed to communicate with the WO3 electrode in the absence of any soluble redox mediators and sacrificial reagents under the visible light of the solar spectrum, even to 700 nm. The biohybrid electrode undergoes electron transfer and generates a significantly enhanced photocurrent compared to previously reported PS II-based photoanodes with carbon nanostructures or other semiconductor substrates for solar water oxidation. The maximum incident photon-to-current conversion efficiency reaches 15.24% at 400 nm in the visible light region. This work provides some insights and possibilities into the efficient assembly of a future solar energy conversion system based on visible-light-responsive semiconductors and photosynthetic proteins.

Perfluorinated substance assessment in sediments of a large-scale reservoir in Danjiangkou, China

The occurrence of eight perfluorinated compounds (PFCs) in the surface sediments from 10 sampling sites spread across the Danjiangkou Reservoir was investigated by isotope dilution ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) after solid-phase extraction (SPE). All the sediments from the 10 sites contained detectable levels of PFCs. The total concentration of the target PFCs in each sediment sample (C∑PFCs) ranged from 0.270 to 0.395xa0ngxa0g−1 of dry weight, and the mean value of C∑PFCs was 0.324u2009±u20090.045xa0ngxa0g−1 of dry weight for the whole reservoir. For each perfluorinated compound in one sediment, perfluorooctane sulfonate (PFOS) or perfluoro-n-butanoic acid (PFBA) consistently had a higher concentration than the other six PFCs, while perfluoro-n-octanoic acid (PFOA) was always undetectable. In terms of spatial distribution, the total and individual concentrations of PFCs in sediment from downstream sites of the Danjiangkou Reservoir were higher than those from upstream sites. Factor analysis revealed that PFCs in the sediment samples originated from electroplating and anti-fog agents in industry, food/pharmaceutical packaging and the water/oil repellent paper coating, and the deposition process. The quotient method was utilized to assess the ecological risk of PFCs in the sediments of the Danjiangkou Reservoir, which showed that the concentrations of PFCs were not considered a risk. In this study, detailed information on the concentration level and distribution of PFCs in the sediments of the Danjiangkou Reservoir, which is the source of water for the Middle Route Project of the South-to-North Water Transfer Scheme in China, was reported and analyzed for the first time. These results can provide valuable information for water resource management and pollution control in the Danjiangkou Reservoir.

Simple fabrication of Fe3O4/C/g-C3N4 two-dimensional composite by hydrothermal carbonization approach with enhanced photocatalytic performance under visible light

The construction of a multifunctional two-dimensional (2D) composite photocatalyst is of great significance because such a composite can exhibit enhanced catalytic performance and improved practical usability in contrast to a single component catalyst. Herein, a ternary photocatalyst composed of g-C3N4, a carbon layer (C), and Fe3O4 nanoparticles was successfully synthesized by a facile one-pot hydrothermal carbonization (HTC) method from g-C3N4, glucose, and FeCl3. The resultant composite, Fe3O4/C/g-C3N4, had an ordered 2D heterostructure and exhibited enhanced visible-light-driven photocatalytic performances and good magnetic recyclability. The kobs for Cr(VI) photoreduction (or dimethoate photodegradation) over Fe3O4/C/g-C3N4 was 20.9-fold (or 2.1-fold) of that over g-C3N4. Comparative study of Fe3O4/C/g-C3N4, C/g-C3N4, and g-C3N4 on their optoelectronic properties revealed that this enhanced photocatalytic activity was mainly due to rapid photogenerated electron transport from the g-C3N4 component to carbon and/or Fe3O4, which effectively suppressed the recombination of photogenerated electrons and holes. In addition, the good surface adsorption capacity of the carbon component towards Cr(VI) also contributed to Cr(VI) photoreduction over Fe3O4/C/g-C3N4. Finally, a reasonable photocatalytic reaction mechanism of Fe3O4/C/g-C3N4 was proposed based on the results of trapping experiments. This study is not only limited to developing a high-performance g-C3N4 based photocatalyst, but also expected to provide a green, facile, and cost-efficient strategy to combine 2D materials with a carbonaceous layer and other functional components for a multifunctional system.

Doping β-CoMoO4 Nanoplates with Phosphorus for Efficient Hydrogen Evolution Reaction in Alkaline Media

Mass production of hydrogen by electrolysis of water largely hinges on the development of highly efficient and economical electrocatalysts for hydrogen evolution reaction (HER). Though having the merits of high earth abundance, easy availability, and tunable composition, transition-metal oxides are usually deemed as poor electrocatalysts for HER. Herein, we demonstrate that doping β-CoMoO4 nanoplates with phosphorus can turn them into active electrocatalysts for HER. Theoretical calculation and experimental studies unravel that enhanced electrical conductivity and optimized hydrogen adsorption free energy are major causes for the improvement of intrinsic activity. As a result, only an overpotential of 138 mV is required to drive hydrogen evolving at a current density of 10 mA cm-2 in 1 M KOH for P-doped β-CoMoO4, which outstrips many recently reported transition-metal oxides and is just slightly inferior to commercial Pt/C. This work opens a new route to tune the HER performance of transition-metal oxides.