Unveiling Dynamic Structure and Bond Evolutions in BiOIO3 Photocatalysts during CO2 Reduction.

We have established a correlation between photocatalytic activity and dynamic structure/bond evolutions of BiOIO3-based photocatalysts during CO2 reduction by combining operando X-ray diffraction with photoelectron spectroscopy. More specifically, the selective photo-deposition of PtOx species on BiOIO3 (010) facets could effectively promote the electron enrichment on Bi active sites of (100) facets for facilitating the adsorption/activation of CO2 molecules, leading to the formation of Bi sites with high oxidation state and the shrink of crystalline structures. With introducing light irradiation to drive CO2 reduction, the Bi active sites with high oxidation states transformed into normal Bi3+ state, accompanying with the expansion of crystalline structures. Owing to the dynamic structure, bond, and chemical-state evolutions, a significant improvement of photocatalytic activity for CO evolution has been achieved on PtOx-BiOIO3 (195.0 µmol g-1 ⋅ h-1), much higher than the pristine (61.9 µmol g-1 ⋅ h-1) as well as metal-Pt decorated BiOIO3 (70.3 µmol g-1 ⋅ h-1) samples. This work provides new insights to correlate the intrinsically dynamic structure/bond evolutions with CO2 reduction activity, which may help to guide future photocatalyst design.

Subnanometric Bismuth Clusters Confined in Pyrochlore-Bi2 Sn2 O7 Enable Remarkable CO2 Photoreduction.

The development of highly efficient photocatalysts for conversion of carbon dioxide (CO2 ) with water (H2 O) into chemical fuels is of great importance for energy sustainability and carbon resource utilization. Herein, we demonstrated a facile hydrothermal method for in situ construction of subnanometric Bi metallic clusters in pyrochlore-Bi2 Sn2 O7 frameworks, leading to the remarkable improvements of photocatalytic performances for CO2 reduction into CO in the absence of sacrificial reagent. More specifically, an outstanding CO evolution activity of 114.1 µmol g-1 h-1 has been achieved, more than 20-fold improvement compared with the pristine Bi2 Sn2 O7 (5.7 µmol g-1 h-1 ). Detailed experiments together with in situ characterizations reveal that the spatially confined Bi clusters could significantly promote charge-separation/electron-enrichment and adsorption/activation of CO2 molecules, which provides highly efficient reaction channels to facilitate the generation of *COOH intermediate as well as the subsequent desorption of *CO towards CO formation. These demonstrations provide an important knowledge for precise design and fabrication of highly efficient photocatalysts for CO2 conversion into solar fuels.

Regulating π-Conjugation in sp2 -Carbon-Linked Covalent Organic Frameworks for Efficient Metal-Free CO2 Photoreduction with H2 O.

The development of sp2 -carbon-linked covalent organic frameworks (sp2 c-COFs) as artificial photocatalysts for solar-driven conversion of CO2 into chemical feedstock has captured growing attention, but catalytic performance has been significantly limited by their intrinsic organic linkages. Here, a simple, yet efficient approach is reported to improve the CO2 photoreduction on metal-free sp2 c-COFs by rationally regulating their intrinsic π-conjugation. The incorporation of ethynyl groups into conjugated skeletons affords a significant improvement in π-conjugation and facilitates the photogenerated charge separation and transfer, thereby boosting the CO2 photoreduction in a solid-gas mode with only water vapor and CO2 . The resultant CO production rate reaches as high as 382.0 µmol g-1  h-1 , ranking at the top among all additive-free CO2 photoreduction catalysts. The simple modulation approach not only enables to achieve enhanced CO2 reduction performance but also simultaneously gives a rise to extend the understanding of structure-property relationship and offer new possibilities for the development of new π-conjugated COF-based artificial photocatalysts.

Bias-Free Solar-Driven Syngas Production: A Fe2 O3 Photoanode Featuring Single-Atom Cobalt Integrated with a Silver-Palladium Cathode.

Photoelectrochemical syngas production from aqueous CO2 is a promising technique for carbon capture and utilization. Herein, we demonstrate the efficient and tunable syngas production by integrating a single-atom cobalt-catalyst-decorated α-Fe2 O3 photoanode with a bimetallic Ag/Pd alloy cathode. A record syngas production activity of 81.9 µmol cm-2 h-1 (CO/H2 ratio: ≈1 : 1) was achieved under artificial sunlight (AM 1.5 G) with an excellent durability. Systematic studies reveal that the Co single atoms effectively extract the holes from Fe2 O3 photoanodes and serve as active sites for promoting oxygen evolution. Simultaneously, the Pd and Ag atoms in bimetallic cathodes selectively adsorb CO2 and protons for facilitating CO production. Further incorporation with a photovoltaic, to allow solar light (>600 nm) to be utilized, yields a bias-free CO2 reduction device with solar-to-CO and solar-to-H2 conversion efficiencies up to 1.33 and 1.36 %, respectively.

Correction: Fabrication and behaviors of CdS on Bi2MoO6 thin film photoanodes.

[This corrects the article DOI: 10.1039/C6RA28323C.].

Reversing electron transfer in a covalent triazine framework for efficient photocatalytic hydrogen evolution.

Covalent triazine-based frameworks (CTFs) have emerged as some of the most important materials for photocatalytic water splitting. However, development of CTF-based photocatalytic systems with non-platinum cocatalysts for highly efficient hydrogen evolution still remains a challenge. Herein, we demonstrated, for the first time, a one-step phosphidation strategy for simultaneously achieving phosphorus atom bonding with the benzene rings of CTFs and the anchoring of well-defined dicobalt phosphide (Co2P) nanocrystals (∼7 nm). The hydrogen evolution activities of CTFs were significantly enhanced under simulated solar-light (7.6 mmol h-1 g-1), more than 20 times higher than that of the CTF/Co2P composite. Both comparative experiments and in situ X-ray photoelectron spectroscopy reveal that the strong interfacial P-C bonding and the anchoring of the Co2P cocatalyst reverse the charge transfer direction from triazine to benzene rings, promote charge separation, and accelerate hydrogen evolution. Thus, the rational anchoring of transition-metal phosphides on conjugated polymers should be a promising approach for developing highly efficient photocatalysts for hydrogen evolution.

Anchoring Black Phosphorus Quantum Dots on Fe-Doped W18 O49 Nanowires for Efficient Photocatalytic Nitrogen Fixation.

Herein, we demonstrate that the surface anchoring of black phosphorus quantum dots (BPQDs) and bulk iron-doping in W18 O49 nanowires significantly promotes the photocatalytic activity toward N2 fixation into NH3 . More specifically, a NH3 production rate of up to 187.6 µmol g-1 h-1 could be achieved, nearly one order of magnitude higher than that of pristine W18 O49 (18.9 µmol g-1 h-1 ). Comprehensive experiments and density-functional theory calculations reveal that Fe-doping could enhance the reducing ability of photo-generated electrons by decreasing the work function and elevating the defect band (d-band) centers. Additionally, the surface BPQDs anchoring could facilitate the N2 adsorption/activation owing to the increased adsorption energy and advantaged W-P dimer bonding-mode. Therefore, synergizing the surface BPQD anchoring and bulk Fe-doping remarkably enhanced the photocatalytic activity of W18 O49 nanowires for NH3 production.

Highly sensitive and selective photoelectrochemical aptasensing of di-2-ethylhexyl phthalate based on graphene quantum dots decorated TiO2 nanotube arrays.

A photoelectrochemical (PEC) sensing platform for di-2-ethylhexyl phthalate (DEHP) was constructed using graphene quantum dots decorated TiO2 nanotube arrays (GQDs-decorated TiO2 NTs) as the transducer species and the anti-DEHP aptamer as the biological recognition element. GQDs were synthesized using the alkali-mediated hydrothermal method, and then anchored onto the TiO2 NTs uniformly and intimately via pronounced electrostatic interaction. Coupling GQDs with TiO2 NTs not only enhanced visible-light absorption, but promoted charge separation and transportation, exhibiting excellent photocurrent response, and PEC activity. Various means were conducted to explore morphologies, optical, structural and PEC properties of the materials. As an identification unit, the anti-DEHP aptamer molecules were immobilized on GQDs-decorated TiO2 NTs using a cross-linking coupling method. The developed PEC sensing platform exhibits excellent sensing behavior for DEHP, and provides a low detection limit of 0.1 ng/L, high selectivity and stability. Meanwhile, its application in real environmental samples was evaluated and satisfying results were achieved. Thus, the established sensing platform provides a promising tool to detect DEHP in the environment.

Nitrogen-incorporation activates NiFeOx catalysts for efficiently boosting oxygen evolution activity and stability of BiVO4 photoanodes.

Developing low-cost and highly efficient catalysts toward the efficient oxygen evolution reaction (OER) is highly desirable for photoelectrochemical (PEC) water splitting. Herein, we demonstrated that N-incorporation could efficiently activate NiFeOx catalysts for significantly enhancing the oxygen evolution activity and stability of BiVO4 photoanodes, and the photocurrent density has been achieved up to 6.4 mA cm-2 at 1.23 V (vs. reversible hydrogen electrode (RHE), AM 1.5 G). Systematic studies indicate that the partial substitution of O sites in NiFeOx catalysts by low electronegative N atoms enriched the electron densities in both Fe and Ni sites. The electron-enriched Ni sites conversely donated electrons to V sites of BiVO4 for restraining V5+ dissolution and improving the PEC stability, while the enhanced hole-attracting ability of Fe sites significantly promotes the oxygen-evolution activity. This work provides a promising strategy for optimizing OER catalysts to construct highly efficient and stable PEC water splitting devices.

A highly sensitive photoelectrochemical aptasensor based on BiVO4 nanoparticles-TiO2 nanotubes for detection of PCB72.

In this work, a simple and highly sensitive photoelectrochemical (PEC) aptasensor has been developed for detecting PCB72 based on TiO2 nanotubes (NTs) decorated with BiVO4 nanoparticles (NPs). The BiVO4 NPs-TiO2 NTs composites prepared through a simple hydrothermal method exhibit good visible-light adsorption ability, high PEC response and perfect photo-excited stability. The synthesized composites were explored as the photoactive sensing materials for development of a PEC sensing platform for the first time. Here, Au nanoparticles (NPs) were first deposited the composites, and the anti-PCB72 aptamer molecules were immobilized on the Au NPs-deposited BiVO4 NPs-TiO2 NTs. The developed PEC aptasensor exhibits high sensitivity and specificity for PCB72 with a wide linear range from 1 ng/L to 500 ng/L and a low detection limit of 0.23 ng/L. The application of the aptasensor was evaluated by determining PCB 72 in the environment water samples. Thus, a simple and efficient PEC sensing platform was established for detecting the content of PCBs in the environment.

Visible-light-driven photoelectrochemical sensing platform based on BiOI nanoflowers/TiO2 nanotubes for detection of atrazine in environmental samples.

In this work, a visible-light-driven photoelectrochemical (PEC) sensing platform was developed based on BiOI nanoflowers/TiO2 nanotubes (BiOI NFs/TiO2 NTs) for detection of atrazine (ATZ). The BiOI NFs/TiO2 NTs p-n heterojunctions synthesized by decorating BiOI NFs on TiO2 NTs via simple hydrothermal approach exhibit strong visible-light absorption ability, high photocurrent response and PEC activity. Thus BiOI NFs/TiO2 NTs heterostructures were first explored to act as the photoelectrode for the immobilization of the anti-ATZ aptamer to develop a PEC sensing platform. The design PEC aptasensing platform exhibits prominent analytical performance for determination of ATZ with a low detection limit of 0.5 pM under visible-light irradiation, and displays good selectivity for ATZ in the control experiments. The superior behavior of the sensing platform could be ascribed to the design of the appropriate sensing material with tubular microstructure, excellent PEC response of the photoelectrode, and the large loading amount of aptamer. Meanwhile, the PEC sensing platform was used to determine ATZ in environmental samples and a satisfied result was obtained.

Unveiling the Activity and Stability Origin of BiVO4 Photoanodes with FeNi Oxyhydroxides for Oxygen Evolution.

Understanding the origin of formation and active sites of oxygen evolution reaction (OER) cocatalysts is highly required for solar photoelectrochemical (PEC) devices that generate hydrogen efficiently from water. Herein, we employed a simple pH-modulated method for in situ growth of FeNi oxyhydroxide ultrathin layers on BiVO4 photoanodes, resulting in one of the highest currently known PEC activities of 5.8 mA cm-2 (1.23 VRHE , AM 1.5 G) accompanied with an excellent stability. More importantly, both comparative experiments and density functional theory (DFT) studies clearly reveal that the selective formation of Bi-O-Fe interfacial bonds mainly contributes the enhanced OER activities, while the construction of V-O-Ni interfacial bonds effectively restrains the dissolution of V5+ ions and promotes the OER stability. Thereby, the synergy between iron and nickel of FeNi oxyhydroxides significantly improved the PEC water oxidation properties of BiVO4 photoanodes.

Direct Observation of Dynamic Bond Evolution in Single-Atom Pt/C3 N4 Catalysts.

Single-atom catalysts are promising platforms for heterogeneous catalysis, especially for clean energy conversion, storage, and utilization. Although great efforts have been made to examine the bonding and oxidation state of single-atom catalysts before and/or after catalytic reactions, when information about dynamic evolution is not sufficient, the underlying mechanisms are often overlooked. Herein, we report the direct observation of the charge transfer and bond evolution of a single-atom Pt/C3 N4 catalyst in photocatalytic water splitting by synchronous illumination X-ray photoelectron spectroscopy. Specifically, under light excitation, we observed Pt-N bond cleavage to form a Pt0 species and the corresponding C=N bond reconstruction; these features could not be detected on the metallic platinum-decorated C3 N4 catalyst. As expected, H2 production activity (14.7 mmol h-1 g-1 ) was enhanced significantly with the single-atom Pt/C3 N4 catalyst as compared to metallic Pt-C3 N4 (0.74 mmol h-1 g-1 ).

Label-free and highly selective electrochemical aptasensor for detection of PCBs based on nickel hexacyanoferrate nanoparticles/reduced graphene oxides hybrids.

In consideration of the urgent need to determine polychlorinated biphenyls (PCBs) in the environment, a label-free and highly selective electrochemical aptasensor was constructed for determining PCBs based on nickel hexacyanoferrate nanoparticles (NiHCF NPs)/reduced graphene oxides (rGO) hybrids. NiHCF NPs/rGO hybrids with small size of about 5 nm NiHCF NPs were synthesized for the first time by in situ co-deposition of NiHCF NPs on rGO surface. In the hybrids, rGO with large area and good conductivity can supply more space for loading NiHCF NPs and improve the conductivity of the hybrids. NiHCF NPs that can be used to be act as a signal probe exhibit a couple of well-defined peaks with highly reversible redox ability and good stability. Here, PCB77 as a model molecule, the anti-PCB77 aptamer was anchored on the NiHCF NPs/rGO hybrids by covalent bonding reaction. The design aptasensor for detecting PCB77 exhibits a favorable linear response from 1.0 to 100.0 ng/L with a low detection limit of 0.22 ng/L. Meanwhile, it displays good selectivity for PCB77 detection due to the specificity and high affinity of aptamer to PCB77. Additionally, the application of the aptasensor was evaluated in real environmental samples.

Direct Observation of Oxygen Vacancy Self-Healing on TiO2 Photocatalysts for Solar Water Splitting.

Oxygen vacancy (Vo) on transition metal oxides plays a crucial role in determining their chemical/physical properties. Conversely, the capability to directly detect the changing process of oxygen vacancies (Vos) will be important to realize their full potentials in the related fields. Herein, with a novel synchronous illumination X-ray photoelectron spectroscopy (SI-XPS) technique, we found that the surface Vos (surf-Vos) exhibit a strong selectivity for binding with the water molecules, and sequentially capture an oxygen atom to achieve the anisotropic self-healing of surface lattice oxygen. After this self-healing process, the survived subsurface Vos (sub-Vos) promote the charge excitation from Ti to O atoms due to the enriched electron located on low-coordinated Ti sites. However, the excessive sub-Vos would block the charge separation and transfer to TiO2 surfaces resulted from the destroyed atomic structures. These findings open a new pathway to explore the dynamic changes of Vos and their roles on catalytic properties, not only in metal oxides, but in crystalline materials more generally.

Design of a facile and label-free electrochemical aptasensor for detection of atrazine.

A facile and label-free electrochemical aptasensor for detection of atrazine (ATZ) was designed based on nickel hexacyanoferrate nanoparticles (NiHCF NPs) and electrochemically reduced graphene oxide (ERGO). Because of ERGO perfect electrochemical conductivity and large surface area, it was first modified on glassy carbon electrode (GCE) surface by electrochemical reduction. NiHCF NPs were immobilized on ERGO/GCE as a signal probe with well-defined peaks and good stability. Subsequently, gold nanoparticles (Au NPs) were electrodeposited on NiHCF NPs/ERGO to anchored aptamer and increase the conductivity and stability of the electrode. When ATZ was added, ATZ-aptamer complexes generated with poor conductivity on the sensor surface increased the hindrance of electron transfer, leading to electrochemical signal decrease. The signal change was used to detect ATZ quantitatively. The designed aptasensor exhibited good analytical performance for determining ATZ. A linear curve was obtained in the range of 0.25-250 pM with a low detection limit of 0.1 pM, and it showed perfect selectivity for ATZ in the presence of diverse interferents. Meanwhile, the electrochemical aptasensor was employed to evaluate ATZ content in the samples.

Retraction: Dual Effects of Nanostructuring and Oxygen Vacancy on Photoelectrochemical Water Oxidation Activity of Superstructured and Defective Hematite Nanorods.

Small 2018, 14, 1704464 The above article, published online on February 27, 2018 in Wiley Online Library (https://onlinelibrary.wiley.com), has been retracted by agreement between the corresponding authors, the journal Editor-in-Chief, José Oliveira, and Wiley-VCH Verlag GmbH & Co. KGaA. Although the authors stand by the scientific content of the paper, the retraction has been agreed upon due to material (Figures 1j and 1k) collected by the first author in an external lab being included in the publication without the consent of the third party. L. Wang, K. Marcus, X. Huang, Z. Shen, Y. Yang, Y. Bi, Small 2018, 14, 1704464; https://doi.org/10.1002/smll.201704464.

Dual Effects of Nanostructuring and Oxygen Vacancy on Photoelectrochemical Water Oxidation Activity of Superstructured and Defective Hematite Nanorods.

An Ar atmospheric treatment is rationally used to etch and activate hematite nanoflakes (NFs) as photoanodes toward enhanced photoelectrochemical water oxidation. The formation of a highly ordered hematite nanorods (NRs) array containing a high density of oxygen vacancy is successfully prepared through in situ reduction of NFs in Ar atmosphere. Furthermore, a hematite (104) plane and an iron suboxide layer at the absorber/back-contact interface are formed. The material defects produced by a thermal oxidation method can be critical for the morphology transformation from 2D NFs to 1D NRs. The resulting hematite NR photoanodes show high efficiency toward solar water splitting with improved light harvesting capabilities, leading to an enhanced photoresponse due to the artificially formed oxygen vacancies.

High-efficiency SrTiO3/TiO2 hetero-photoanode for visible-light water splitting by charge transport design and optical absorption management.

Herein, a two-pronged approach to obtain excellent visible-light performance of SrTiO3/TiO2 photoelectrodes for water oxidation is presented. More specifically, the combination of hetero-constructing SrTiO3 nanocubes and Cr3+/Ti3+ dual-doping has been demonstrated for achieving high efficiency of charge separation and extending photoresponse of TiO2 nanotube arrays from the UV to visible light region. As expected, this unique Cr-SrTiO3-x/Cr-TiO2-x photoanode exhibited remarkably improved PEC performance for water splitting (4.05 mA cm-2) under visible light irradiation, which is more than 100 times higher than that of pristine TiO2 nanotube arrays. Additionally, the photocurrent intensity as well as water splitting behavior remain constant even after long time irradiation, revealing its high PEC as well as structure stability. Thereby, the rational design of the interface charge transport and precise management of optical absorption endow the TiO2-based PEC system with excellent and stable visible-light performance for water splitting.

Ultrathin FeOOH Nanolayers with Abundant Oxygen Vacancies on BiVO4 Photoanodes for Efficient Water Oxidation.

Photoelectrochemical (PEC) water splitting is a promising method for storing solar energy in the form of hydrogen fuel, but it is greatly hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Herein, a facile solution impregnation method is developed for growing ultrathin (2 nm) highly crystalline ß-FeOOH nanolayers with abundant oxygen vacancies on BiVO4 photoanodes. These exhibited a remarkable photocurrent density of 4.3 mA cm-2 at 1.23 V (vs. reversible hydrogen electrode (RHE), AM 1.5 G), which is approximately two times higher than that of amorphous FeOOH fabricated by electrodeposition. Systematic studies reveal that the excellent PEC activity should be attributed to their ultrathin crystalline structure and abundant oxygen vacancies, which could effectively facilitate the hole transport/trapping and provide more active sites for water oxidation.