Simultaneous Photocatalytic Tetracycline Oxidation and Cr(VI) Reduction by Z-Scheme Multiple Layer TiO2/SnIn4S8.

Wastewater pollutants are a major threat to natural resources, with antibiotics and heavy metals being common water contaminants. By harnessing clean, renewable solar energy, photocatalysis facilitates the synergistic removal of heavy metals and antibiotics. In this paper, MXene was both a template and raw material, and MXene-derived oxide (TiO2) and SnIn4S8 Z-scheme composite materials were synthesized and characterized. The synergistic mode of photocatalytic reduction and oxidation leads to the enhanced utilization of e-/h+ pairs. The TiO2/SnIn4S8 exhibited a higher photocatalytic capacity for the simultaneous removal of tetracycline (TC) (20 mg·L-1) and Cr(VI) (15 mg·L-1). The main active substances of TC degradation and Cr(VI) reduction were identified via free radical scavengers and electron paramagnetic resonance (EPR). Additionally, the potential photocatalytic degradation route of TC was thoroughly elucidated through liquid chromatography-mass spectrometry (LC-MS).

Precisely Modulating the Photosensitization Efficiency of Transition-Metal Chalcogenide Quantum Dots toward Solar Water Oxidation.

Precisely modulating the spatial charge migration/separation constitutes the central issue in dictating the solar conversion efficiency of photoelectrochemical (PEC) cells, whereas it still remains a grand challenge. Here, we conceptually demonstrate the construction of hierarchically ordered metal oxide (MO)/transition-metal chalcogenide quantum dots (TMC QDs) multilayered heterostructured photoanodes, that is, MO/[TMC QDs(+)/TMC QDs(-)]n (TMC QDs: CdTe, CdSe, CdS), by a simple and general bottom-up self-assembly route. Tailor-made intrinsically oppositely charged TMC QDs are alternately deposited on the highly ordered MO via a generic ligand-triggered electrostatic interaction to craft heterostructured photoanodes. The charge-transfer pathway stimulated by the photosensitization of TMC QDs is finely tuned by the assembly sequence. The advantageous multilayered nanoarchitecture renders the MO/[TMC QDs(+)/TMC QDs(-)]n photoanodes exhibit substantially enhanced PEC performances under light irradiation, owing to the applicable energy-level configuration and peculiar combination fashion between building blocks and considerably boosted interfacial charge separation resulting from generating spatial tandem charge transport. Furthermore, photosensitization efficiency comparison among TMC QDs is comprehensively performed with PEC mechanisms elucidated.

Layer-by-Layer Self-Assembly of Metal/Metal Oxide Superstructures: Self-Etching Enables Boosted Photoredox Catalysis.

The capability of noble metal nanoparticles (NPs) as efficient charge transfer mediators to stimulate Schottky-junction-triggered charge flow in multifarious photocatalysis has garnered enormous attention in the past decade. Nevertheless, fine-tuning and controllable fabrication of a directional charge transport channel in metal/semiconductor heterostructures via suitable interface engineering is poorly investigated. Here, we report the progressive fabrication of a tailor-made directional charge transfer channel in Pt nanoparticles (NPs)-inlaid WO3 (Pt-WO3) nanocomposites via an efficient electrostatic layer-by-layer (LbL) self-assembly integrated with a thermal reduction treatment, by which oppositely charged metal precursor ions and polyelectrolyte building blocks were intimately and alternately assembled on the WO3 nanorods (NRs) by substantial electrostatic interaction. LbL self-assembly buildup and in situ self-etching-induced structural variation of WO3 NRs to a microsized superstructure occur simultaneously. We found that such exquisitely crafted Pt-WO3 nanocomposites exhibit conspicuously enhanced and versatile photoactivities for nonselective mineralizing of organic dye pollution and reduction of heavy metal ions at ambient conditions under both visible and simulated sunlight irradiation, demonstrating a synergistic effect. This is attributed to the imperative contribution of Pt NPs as electron traps to accelerate the directional high-efficiency electron transport from WO3 to Pt NPs, surpassing the confinement of electron transfer kinetics of WO3 owing to low conduction level. More intriguingly, photoredox catalysis can also be triggered simultaneously in the same reaction system. The primary in situ produced active species in the photocatalytic reactions were specifically analyzed, and underlying photocatalytic mechanisms were determined. Our work would provide a universal synthesis strategy for constructing various metal-decorated semiconductor nanocomposites for widespread photocatalytic utilizations.

Precise Tuning of Coordination Positions for Transition-Metal Ions via Layer-by-Layer Assembly To Enhance Solar Hydrogen Production.

Finely tuning the charge transfer constitutes a central challenge in photocatalysis, yet exquisite control of the directional charge transfer to the target reactive sites is hindered by the rapid charge recombination. Herein, dual separated charge transport channels were fabricated in a one-dimensional transition-metal chalcogenide (TMC)-based system via an elaborate layer-by-layer (LbL) self-assembly approach, for which oppositely charged metal-ion-coordinated branched polyethylenimine (BPEI) and MoS2 quantum dots (QDs) were alternately integrated to fabricate the multilayered TMC@(BPEI/MoS2 QDs)n heterostructures with controllable interfaces. Photocatalytic hydrogen generation performances of such ternary heterostructures under visible light irradiation were evaluated, which unravels that the BPEI layer not only behaves as "molecule glue" to enable the electrostatic LbL assembly with MoS2 QDs in an alternate stacking fashion on the TMC frameworks but also acts as a unidirectional hole-transfer channel. More significantly, transition-metal ions (Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) coordinated on the outmost BPEI layer are able to function as interfacial electron transfer mediators for accelerating the interfacial cascade electron transport efficiency. These simultaneously constructed dual high-speed electron and hole-transfer channels are beneficial for boosting the charge separation and enhancing the photocatalytic hydrogen evolution performances.

Charge Transport Surmounting Hierarchical Ligand Confinement toward Multifarious Photoredox Catalysis.

Metal nanoparticles (NPs) have been deemed an imperative sector of nanomaterial for triggering the Schottky-junction-driven electron flow in photoredox catalysis, but they suffer from sluggish charge-transfer kinetics, rendering efficient charge flow difficult. Here, we report the construction of unidirectional charge-transfer channel in a metal/semiconductor heterostructure via a ligand-triggered self-assembly method, by which hierarchically branched ligands (DMAP)-capped Pd NPs were controllably attached on the WO3 nanorods (NRs) scaffold, resulting in the well-defined Pd@DMAP/WO3 NRs heterostructures. The pinpointed deposition of Pd@DMAP on the WO3 NRs endows the Pd@DMAP/WO3 NRs heterostructure with conspicuously improved photoactivities for organic pollutant mineralization, as well as the capacities for photocatalytic selective oxidation of aromatic alcohols to aldehydes and photoreduction of chromium ions under the irradiation of simulated sunlight and visible light, far surpassing the applicability of blank WO3 NRs. This is due to the imperative contribution of Pd@DMAP as efficient electron reservoir in accelerating the unidirectional flow of electrons from Pd@DMAP to WO3 NRs, overcoming the confinement of spatially hierarchically branched ligand and interface configuration. Moreover, interfacial charge transport efficiency is finely tuned by the interface configuration engineering. The active species in the multifarious photoreactions were unveiled, and a linker-triggered photoredox catalysis mechanism was put forward. It is hoped that our current work would afford new strategies for strategically constructing metal/semiconductor heterostructures for versatile photocatalytic applications.

Self-transformation of ultra-small gold nanoclusters to gold nanocrystals toward boosted photoreduction catalysis.

Glutathione-protected Aux nanoclusters uniformly and intimately embedded at the interface of CdSe QDs and graphene were in situ self-transformed to Au nanocrystals (NCs) via a facile thermal reduction strategy. The inlaid Au NPs substantially accelerate the interfacial directional charge transfer toward multifarious photoreduction catalysis under visible light irradiation.

Ligand-triggered electrostatic self-assembly of CdS nanosheet/Au nanocrystal nanocomposites for versatile photocatalytic redox applications.

A facile and efficient ligand-triggered electrostatic self-assembly strategy has been developed to fabricate a series of Au/CdS nanosheet (Ns) (Au-CdS Ns) nanocomposites with varied weight addition ratios of Au nanoparticles (NPs) by judiciously utilizing the intrinsic surface charge properties of assembly units, through which uniform dispersion and controllable deposition of Au NPs on the CdS Ns were achieved. Versatile probe reactions including photocatalytic oxidation of an organic dye pollutant, selective photocatalytic reduction of aromatic nitro compounds and photocatalytic hydrogen production reactions under visible light irradiation and ambient conditions were used to systematically evaluate the photoredox performances of the as-assembled well-defined Au-CdS Ns nanocomposites. It was unveiled that the photoactivities of Au-CdS Ns nanocomposites strongly depend on the weight addition ratio of Au NPs and the addition of an excess amount of Au NPs is detrimental to the separation of photogenerated charge carriers from CdS Ns. With the optimum addition amount of Au NPs (1 wt%), it was found that spontaneous assembly of Au NPs on the CdS Ns remarkably prolonged the lifetime of the photogenerated charge carriers from CdS Ns under visible light irradiation, thus resulting in significantly enhanced photocatalytic redox activities of Au-CdS Ns nanocomposites compared with those of CdS Ns. The crucial role of Au NPs in the photoredox reactions as efficient electron traps rather than plasmonic sensitizers was determined. Moreover, predominant active species responsible for the photocatalytic process were unambiguously determined and a possible photocatalytic mechanism was elucidated. It is anticipated that our work could open up a new avenue to rationally prepare various 2D semiconductors-metal nanocomposites by utilizing such a simple and efficient self-assembly strategy for extensive photocatalytic applications in a myriad of fields.

[Study on Electroencephalogram Recognition Framework by Common Spatial Pattern and Fuzzy Fusion].

Common spatial pattern (CSP) is a very popular method for spatial filtering to extract the features from electroencephalogram (EEG) signals, but it may cause serious over-fitting issue. In this paper, after the extraction and recognition of feature, we present a new way in which the recognition results are fused to overcome the over-fitting and improve recognition accuracy. And then a new framework for EEG recognition is proposed by using CSP to extract features from EEG signals, using linear discriminant analysis (LDA) classifiers to identify the user's mental state from such features, and using Choquet fuzzy integral to fuse classifiers results. Brain-computer interface (BCI) competition 2005 data sets IVa was used to validate the framework. The results demonstrated that it effective ly improved recognition and to some extent overcome the over-fitting problem of CSP. It showed the effectiveness of this framework for dealing with EEG.

Self-assembly of a Ag nanoparticle-modified and graphene-wrapped TiO2 nanobelt ternary heterostructure: surface charge tuning toward efficient photocatalysis.

In recent years, tremendous research efforts have been made towards developing graphene (GR)-based nanocomposites for photocatalytic applications. In this work, surface-coarsened TiO2 nanobelts (SC-TNBs) closely enwrapped with monodispersed Ag nanoparticles (NPs) and GR nanosheets (i.e. Ag/GR/SC-TNBs) were fabricated using a facile self-assembly strategy followed by photoreduction. It was found that the as-prepared Ag/GR/SC-TNBs ternary heterostructure exhibited significantly improved photocatalytic performances under irradiation with UV light in comparison with blank SC-TNBs and its binary counterparts owing to the formation of double heterojunctions among the components. The intimate integration of Ag NPs and GR with SC-TNBs achieved by the self-assembly buildup exerts a profound effect on the transfer of photogenerated electrons over the SC-TNBs substrate in which Ag NPs serve as an efficient "electron reservoir" and GR as an electron transporter and collector, thus concurrently prolonging the lifetime of the photogenerated electron-hole pairs and resulting in the remarkably enhanced photoactivity over the Ag/GR/SC-TNBs ternary nanocomposite. In addition, the underlying photocatalytic mechanism was elucidated and the primary active species were determined.

Rapid microwave hydrothermal synthesis of GaOOH nanorods with photocatalytic activity toward aromatic compounds.

GaOOH nanorods were synthesized from Ga(NO(3))(3) via a facile microwave hydrothermal method. The obtained sample was characterized by x-ray diffraction, N(2) sorption-desorption, UV-vis diffuse reflectance spectroscopy, transmission electron microscopy, electron spin resonance, and x-ray photoelectron spectroscopy. The results revealed that the as-synthesized sample was consisted of rod-like particles. It possessed a surface area of 14.3 m(2) g(-1), and a band gap of 4.75 eV. The photocatalytic property of GaOOH nanorods was evaluated by the degradation of aromatic compounds (such as benzene and toluene) in an O(2) gas stream under ultraviolet (UV) light illumination. The results demonstrated that GaOOH nanorods exhibited superior photocatalytic activity and stability as compared to commercial TiO(2) (P25, Degussa Co.) in both benzene and toluene degradation. In the extended (35 h) reaction test toward benzene, GaOOH maintained a high activity, and no obvious deactivation was observed. A possible mechanism of the photocatalysis over GaOOH is proposed.