Photosensitization Efficiency Modulation of Atomically Precise Silver Nanoclusters for Photoelectrocatalysis.

Atomically precise metal nanoclusters (NCs) have emerged as feasible alternatives to traditional photosensitizers in solar energy conversion due to the unique atomic stacking mode, quantum size effect, and abundant active sites. Despite the sporadic advancement in fabricating metal NC-based photosystems, most of which are predominantly centered on Au NCs, unleashing atomically precise silver nanoclusters as light-harvesting antennas has still been in the infant stage, with the charge transfer mechanism remaining elusive. Herein, we comprehensively demonstrate the photosensitization effect of Ag NCs in the photoelectrochemical (PEC) water-splitting reaction and strictly evaluate the correlation of photosensitization efficiency with atomic architecture. To these ends, tailor-made negatively charged l-glutathione (GSH)-capped Ag NCs [Agx, Ag9(GSH)6, Ag16(GSH)9, Ag31(GSH)19] as building blocks are controllably deposited on the metal oxide (MOs = TiO2, WO3, Fe2O3) substrate by a facile self-assembly strategy. Benefiting from the highly efficient photosensitization effect of atomically precise Ag NCs, these self-assembled MOs/Ag NC heterostructured photoanodes with an elegant charge transfer interface demonstrate significantly enhanced photoelectrochemical water oxidation performances under visible-light irradiation on account of efficient charge transport from Ag NCs to the MO substrate, substantially prolonging the charge lifetime of Ag NCs. Our work would significantly inspire ongoing interest in unlocking the generic photosensitization capability of atomically precise metal NCs for solar energy conversion.

Unexpected Boosted Solar Water Oxidation by Nonconjugated Polymer-Mediated Tandem Charge Transfer.

Conjugated polymers are deemed as conductive carrier mediators for engendering the π electrons along the molecular framework, while the role of nonconjugated insulated polymers has been generally overlooked without the capability to participate in the solar-powered oxidation-reduction kinetics and charge-transfer process. Alternatively, considering the ultrashort charge lifetime and significant deficiency of metal nanocluster (NC)-based photosystems, the fine tuning of charge migration over atomically precise ultrasmall metal NCs as novel light-harvesting antennas has so far not yet been unleashed. Here, we unlock the charge-transfer capability of a nonconjugated polymer to modulate the charge flow over metal NCs (Aux and Au25) by such a solid-state nonconductive polymer via a conceptually new chemistry strategy by which l-glutathione (GSH)-capped gold (Aux@GSH) NCs and poly(diallyl-dimethylammonium chloride) (PDDA) were alternately self-assembled on the metal oxide (MO: WO3, Fe2O3, and TiO2) substrates. The ultrathin nonconjugated PDDA interim layer periodically intercalated in-between Aux (Au25) NC layers concurrently serves as an unexpected charge-transfer mediator to foster the unidirectional electron flow from Aux(Au25) NCs to MOs by forming a tandem charge-transfer chain, hence endowing the multilayered MO/(PDDA-Aux)n heterostructures with significantly boosted photoelectrochemical water oxidation performance under light irradiation. The unanticipated role of PDDA as a cascade charge mediator is demonstrated to be universal. Our work would unlock the potential charge-transport capability of nonconjugated polymers as a novel charge mediator for solar-to-chemical conversion.

General Layer-by-Layer Assembly of Multilayered Photoanodes: Triggering Tandem Charge Transport toward Photoelectrochemical Water Oxidation.

Modulation of photoinduced charge separation/migration and construction of controllable charge transfer pathway over photoelectrodes have been attracting enduring interest in semiconductor-based photoelectrochemical (PEC) cells but suffer from sluggish charge transport kinetics. Here, we report a general approach to fabricate NP-TNTAs/(TMCs QDs/PSS)n (X = Te, Se, S) photoanodes via a facile and green electrostatic layer-by-layer (LbL) self-assembly strategy, for which transition-metal chalcogenides quantum dots (TMCs QDs) [CdX (X = Se, Te, S)] and poly(sodium 4-styrenesulfonate) (PSS) were periodically deposited on the nanoporous TiO2 nanotube arrays (NP-TNTAs) via substantial electrostatic force, resulting in the continuous charge transfer pathway. NP-TNTAs/(TMCs QDs/PSS)n photoanodes demonstrate significantly enhanced solar-driven photoelectrochemical (PEC) water oxidation activities, relative to NP-TNTAs and TMCs QDs under visible and simulated sunlight irradiation, predominantly because of the suitable energy level configuration between NP-TNTAs and TMCs QDs, unique integration mode, and high-speed interfacial charge separation rate endowed by LbL assembly. The ultrathin PSS intermediate layer functions as "molecule glue" for pinpoint and uniform self-assembly of TMCs QDs on the framework of NP-TNTAs and photosensitization effect of TMCs QDs triggers the unidirectional charge transfer cascade, synergistically boosting the charge separation/transfer efficiency. Our work offers an efficacious approach to craft multilayered photoelectrodes and spur further interest in finely tuning the spatial charge flow in PEC cell for solar-to-hydrogen conversion.

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.

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.

Partially Self-Transformed Transition-Metal Chalcogenide Interim Layer: Motivating Charge Transport Cascade for Solar Hydrogen Evolution.

Directional and high-efficiency charge transport to the target active sites of photocatalyst is central to boost the solar energy conversion but is retarded by the sluggish charge transfer kinetics and deficiency of active sites. Here, we report the elaborate design of cascade unidirectional charge transfer channel over spatially multilayered CdS@CdTe@MoS2 dual core-shell ternary heterostructures by partial transformation of CdS to CdTe interim layer followed by seamless encapsulation with an ultrathin MoS2 layer. The suitable energy-level alignment and unique coaxial multilayered assembly mode among the building blocks accelerate the interfacial charge separation and transport, endowing the CdS@CdTe@MoS2 heterostructures with conspicuously enhanced visible-light-driven photocatalytic hydrogen generation performances along with good photostability. The integrated roles of ultrathin CdTe intermediate layer in passivating the defect sites of CdS NWs framework, mediating the unidirectional charge transfer cascade and prolonging the charge lifetime, were ascertained. Besides, the crucial role of the outermost MoS2 layer as the metal-free cocatalyst in enriching the surface active sites for hydrogen evolution was also determined. Our work would provide new alternatives for finely tuning the charge flow toward promising solar-to-hydrogen conversion efficiency.

[Mangiferin protects rats against chronic bronchitis via regulating NF-kappaB (P65) and IkappaBalpha expression in mononuclear cells].

This study is to investigate the protective effect of mangiferin on NF-kappaB (P65) and IkappaBalpha expression in peripheral blood mononuclear cell (PBMC) in rats with cigarette smoke induced chronic bronchitis. The rat model with chronic bronchitis was established by cigarette smoke. Real-time fluorescence RT-PCR was executed for evaluating the NF-kappaB (P65) and IKkappaBalpha gene expression in mononuclear cell, and flow cytometry for their protein expression. The serum hs-CRP (high-sensitivity C-reactive proteins) and TNF-alpha (tumor necrosis factor-alpha) were detected by enzyme-linked immunosorbent assay. The histopathological score was obtained from lung tissue HE staining slides of lung tissue. The results showed that mangiferin could markedly suppress the NF-kappaB (P65) mRNA and protein expression in mononuclear cell, while promote the IkappaBalpha mRNA and protein expression. Furthermore, mangiferin could lower serum hs-CRP and TNF-alpha level, and reduce the chronic inflammatory damage of bronchiole. These results suggested that mangiferin could notably ameliorate chronic bronchiole inflammation induced by cigarette smoke, and this protective effect might be linked to the regulation of NF-kappaB (P65) and IkappaBalpha expression in mononuclear cell.

Maneuvering Intrinsic Instability of Metal Nanoclusters for Boosted Solar-Powered Hydrogen Production.

Atomically precise metal nanoclusters (NCs) have recently been unleashed as novel photosensitizers but inevitably suffer from light-induced self-transformation to metal nanocrystals (NYs), leading to substantially reduced photoredox activities. Herein, we conceptually demonstrate how to manipulate the intrinsic instability of metal NCs for smartly crafting long-range cascade charge transfer chain assisted by an ultrathin poly(dialyldimethylammonium chloride) (PDDA) layer that was intercalated at the interface of metal NCs and semiconductor. The unidirectional electron flow endowed by Schottky-type self-transformed metal NYs and unexpected electron-withdrawing capability of PDDA layer concurrently foster the charge transfer cascade, resulting in the markedly enhanced net efficiency of photocatalytic hydrogen evolution performances under visible light irradiation. Our work opens new frontiers for judiciously harnessing the inherent detrimental instability of metal NCs for boosted charge transfer toward solar-to-hydrogen conversion.

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.