Zhiping Zeng

Bridging the Gap: Electron Relay and Plasmonic Sensitization of Metal Nanocrystals for Metal Clusters.

In recent years, enormous attention has been paid to the construction of metal cluster-semiconductor nanocomposites because of the fascinating and unique properties of metal clusters; however, investigations on photoelectrochemical (PEC) and photocatalytic properties of metal cluster-semiconductor systems are still rare. Moreover, to date, intrinsic correlation between metal clusters and bulk metal nanocrystals has yet to be elucidated. In this work, a facile layer-by-layer (LbL) self-assembly strategy has been developed to judiciously and intimately integrate gold nanocrystals (Au) within the interface between gold clusters (Au(x)) and hierarchically ordered TiO2 nanotube arrays framework, by which imperative roles of Au nanocrystals as electron relay mediator and plasmonic sensitizer for Aux clusters were revealed. In addition, it was found that synergistic interaction between Au nanocrystals and Aux clusters contributed to promising visible-light-driven photocatalytical and PEC performances. It is anticipated that our work could provide a general way for rationally constructing metal and metal clusters codecorated semiconductor heterostructures and, more significantly, bridge the gap between metal clusters and metal nanocrystals for a diverse range of applications.

Graphene Oxide Quantum Dots Covalently Functionalized PVDF Membrane with Significantly-Enhanced Bactericidal and Antibiofouling Performances

Covalent bonding of graphene oxide quantum dots (GOQDs) onto amino modified polyvinylidene fluoride (PVDF) membrane has generated a new type of nano-carbon functionalized membrane with significantly enhanced antibacterial and antibiofouling properties. A continuous filtration test using E. coli containing feedwater shows that the relative flux drop over GOQDs modified PVDF is 23%, which is significantly lower than those over pristine PVDF (86%) and GO-sheet modified PVDF (62%) after 10 h of filtration. The presence of GOQD coating layer effectively inactivates E. coli and S. aureus cells, and prevents the biofilm formation on the membrane surface, producing excellent antimicrobial activity and potentially antibiofouling capability, more superior than those of previously reported two-dimensional GO sheets and one-dimensional CNTs modified membranes. The distinctive antimicrobial and antibiofouling performances could be attributed to the unique structure and uniform dispersion of GOQDs, enabling the exposure of a larger fraction of active edges and facilitating the formation of oxidation stress. Furthermore, GOQDs modified membrane possesses satisfying long-term stability and durability due to the strong covalent interaction between PVDF and GOQDs. This study opens up a new synthetic avenue in the fabrication of efficient surface-functionalized polymer membranes for potential waste water treatment and biomolecules separation.

Light-Induced In Situ Transformation of Metal Clusters to Metal Nanocrystals for Photocatalysis.

In situ transformation of glutathione-capped gold (Aux) clusters to gold (Au) nanocrystals under simulated solar light irradiation was achieved and utilized as a facile synthetic approach to rationally fabricate Aux/Au/TiO2 ternary and Au/TiO2 binary heterostructures. Synergistic interaction of Aux clusters and Au nanocrystals contributes to enhanced visible-light-driven photocatalysis.

Ultrasmall-Superbright Neodymium-Upconversion Nanoparticles via Energy Migration Manipulation and Lattice Modification: 808 nm-Activated Drug Release

Nd3+-sensitized upconversion nanoparticles are among the most promising emerging fluorescent nanotransducers. They are activated by 808 nm irradiation, which features merits such as limited tissue overheating and deeper penetration depth, and hence are attractive for diagnostic and therapeutic applications. Recent studies indicate that ultrasmall nanoparticles (<10 nm) are potentially more suitable for clinical application due to their favorable biodistribution and safety profiles. However, upconversion nanoparticles in the sub-10 nm range suffer from poor luminescence due to their ultrasmall size and greater proportion of lattice defects. To reconcile these opposing traits, we adopt a combinatorial strategy of energy migration manipulation and crystal lattice modification, creating ultrasmall-superbright Nd3+-sensitized nanoparticles with 2 orders of magnitude enhancement in upconversion luminescence. Specifically, we configure a sandwich-type nanostructure with a Yb3+-enriched intermediate layer [Nd3+]-[Yb3+-Yb3+]-[Yb3+-Tm3+] to form a positively reinforced energy migration system, while introducing Ca2+ into the crystal lattice to reduce lattice defects. Furthermore, we apply the nanoparticles to 808 nm light-mediated drug release. The results indicate time-dependent cancer cells killing and better antitumor activities. These ultrasmall-superbright dots have unraveled more opportunities in upconversion photomedicine with the promise of potentially safer and more effective therapy.

Tunneling Interlayer for Efficient Transport of Charges in Metal Oxide Electrodes

Due to the limited electronic conductivity, the application of many metal oxides that may have attractive (photo)-electrochemical properties has been limited. Regarding these issues, incorporating low-dimensional conducting scaffolds into the electrodes or supporting the metal oxides onto the conducting networks are common approaches. However, some key electronic processes like interfacial charge transfer are far from being consciously concerned. Here we use a carbon-TiO2 contact as a model system to demonstrate the electronic processes occurring at the metal-semiconductor interface. To minimize the energy dissipation for fast transfer of electrons from semiconductor to carbon scaffolds, facilitating electron tunneling while avoiding high energy-consuming thermionic emission is desired, according to our theoretical simulation of the voltammetric behaviors. To validate this, we manage to sandwich ultrathin TiO2 interlayers with heavy electronic doping between the carbon conductors and dopant-free TiO2. The radially graded distribution of the electronic doping along the cross-sectional direction of carbon conductor realized by immobilizing the dopant species on the carbon surface can minimize the energy consumption for contacts to both the carbon and the dopant-free TiO2. Our strategy provides an important requirement for metal oxide electrode design.

Layer-by-layer assembly of nitrogen-doped graphene quantum dots monolayer decorated one-dimensional semiconductor nanoarchitectures for solar-driven water splitting

A layer-by-layer (LbL) assembly of highly ordered nitrogen-doped graphene quantum dots (N-GQDs)/ZnO nanowire (NW) heterostructures was demonstrated as a high performance photoanode in photoelectrochemical (PEC) hydrogen generation for the first time. The nitrogen doping of GQDs was achieved by a facile synthesis strategy under ambient conditions, based on which N-GQDs were uniformly and intimately deposited on the ZnO NW framework via pronounced electrostatic interaction. The deposited amount of N-GQDs and PEC water splitting performances of N-GQDs/one-dimensional (1D) semiconductor heterostructures can be tuned by the assembly layer. The integrative roles of nitrogen doping and photosensitization of GQDs in conjunction with intimate interfacial integration between the photoanode components afforded by the LbL assembly strategy were found to collaboratively contribute to enhanced PEC water splitting. It is anticipated that our work could afford a facile and general strategy for steering toward the rational design of a large variety of N-GQDs/1D semiconductor nanoarchitectures for extensive photocatalytic or PEC applications.

Unraveling the cooperative synergy of zero-dimensional graphene quantum dots and metal nanocrystals enabled by layer-by-layer assembly

Recent years have witnessed a cornucopia of synthetic methods for fabricating carbon–metal nanocomposites. Nonetheless, achieving a cooperative synergy of zero-dimensional carbon nanomaterials and metal nanocrystals is still uncommon. To this end, we performed a controllable structural design comprising customizable alternating layers of active and functional zero-dimensional nanomaterials, which were intimately assembled together. This unique highly-ordered multilayer configuration was afforded by a judicious layer-by-layer (LbL) assembly strategy, enabling the rational and tunable construction of a series of well-defined metal/graphene quantum dots (M/GQDs)n (M = Au, Ag, Pt) multilayers. This strategy allows the direct assembly of customized units of positively-charged graphene quantum dots (GQDs) and negatively-charged metal nanocrystals (NCs), which were integrated in an alternating stacked fashion under a pronounced electrostatic attractive interaction. Moreover, these multilayer thin films demonstrate remarkably efficient and versatile catalytic performance toward the selective organic transformation of aromatic nitro compounds, electrocatalytic methanol oxidation and photoelectrochemical water splitting under simulated solar light irradiation under ambient conditions, attributed to the cooperative synergy of the metal NC and GQD building blocks. More significantly, the catalytic performances of the (M/GQDs)n (M = Au, Ag, Pt) multilayer thin films are tunable via the assembly cycle and sequence, as well as by selecting different metal NC types. This work highlights the significance of the customizable design of GQDs–metal-based systems for various advanced chemical-to-energy conversion applications.

Insight into the charge transport correlation in Aux clusters and graphene quantum dots deposited on TiO2 nanotubes for photoelectrochemical oxygen evolution

In recent years, metal clusters-based photoelectrocatalysis has elicited considerable attention; nonetheless, the exploitations of high efficiency metal clusters–semiconductor heterostructured photoelectrodes are still in the infant stage. Herein, by judiciously capitalizing on glutathione-capped gold (Aux) nanoclusters and graphene quantum dots (GQDs) as building blocks and spatially hierarchically ordered nanoporous TiO2 nanotube arrays (NP-TNTAs) as a conceptual semiconductor platform, GQDs and Aux clusters were rationally and closely integrated on the framework of NP-TNTAs through a progressive electrostatic self-assembly strategy. It was unraveled that Aux clusters play a decisive role in triggering the cascade interfacial charge transfer from GQDs to NP-TNTAs owing to their cooperative synergy, thereby affording conspicuously enhanced solar-powered photoelectrochemical (PEC) water splitting performances under simulated solar light irradiation. Furthermore, the specific PEC water splitting mechanism was unambiguously determined, which for the first time bridges the gap between metal clusters and carbon materials in terms of intrinsic correlations in the charge transfer pathway. It is anticipated that our work would spur further interest in exploring metal cluster-based PEC systems for solar energy conversion.