Showing papers by "Dongshi Zhang published in 2017"

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

Abstract: Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...

Recent Advances in Surfactant-Free, Surface Charged and Defect-Rich Catalysts Developed by Laser Ablation and Processing in Liquids

Abstract: In light of the talent in synthesis of highly active metal and oxide catalysts, a newly emerging technique ― laser synthesis and processing in liquids (LSPC) ― is gaining increasing attention for catalytic applications, such as water splitting, fuel cells and photodegradation of organic pollutants. The advantages of using LSPC-synthesized metal catalysts have been reviewed elsewhere [Chem. Rev. 2017, 117, 3990-4113]. In this review, we discuss the current challenging issues about the material properties (surface chemistry and particle evolution) of the LAL/LPL-synthesized metal catalysts. Main focus is put on the advantages of LSPC in surfactant-free defect engineering of oxide NPs. Compared to other techniques (e.g., hydrogenation), LSPC provides a unique platform to simultaneously introduce oxygen vacancies and surface disorders to oxide (e.g., TiO2) nanomaterials, thus allowing the band gap narrowing from both conduction band (CB) and valence band (VB) directions. The defect-rich oxides have versatile uses, such as either directly applied as photocatalysts and as building blocks to construct supported, doped and ternary oxide photocatalysts for electrochemical and photocatalytic applications. The LSPC-synthesized catalysts are promising to be applied as the commercial catalysts in light of their higher activities than those of the current Pt/C and P25 TiO2 commercial catalysts.

Perspective on how laser-ablated particles grow in liquids

Abstract: Laser ablation in liquids has emerged as a new branch of nanoscience for developing various nanomaterials with different shapes However, how to design and control nanomaterial growth is still a challenge due to the unique chemical-physical process chain correlated with nanomaterial nucleation and growth, including plasma phase (generation and rapid quenching), gas (bubble) phase, and liquid phase In this review, through summarizing the literature about this topic and comparing with the well-established particle growth mechanisms of the conventional wet chemistry technique, our perspective on the possible nanoparticle growth mechanisms or routes is presented, aiming at shedding light on how laser-ablated particles grow in liquids From the microscopic viewpoint, the nanoparticle growth contains six mechanisms, including LaMer-like growth, coalescence, Ostwald ripening, particle (oriented) attachment, adsorbate-induced growth and reaction-induced growth For each microscopic growth mechanism, the vivid growth scenes of some representative nanomaterials recorded by TEM and SEM measurements are displayed Afterwards, the scenes from the macroscopic viewpoint for the large submicro- and micro-scale nanospheres and anisotropic nanostructures formation and evolution from one nanostructure into another one are presented The panorama of how diverse nanomaterials grow during and after laser ablation in liquids shown in this review is intended to offer a overview for researchers to search for the possible mechanisms correlated to their synthesized nanomaterials, and more expectation is desired to better design and tailor the morphology of the nanocrystals synthesized by LAL technique

Germanium Sub-Microspheres Synthesized by Picosecond Pulsed Laser Melting in Liquids: Educt Size Effects

Abstract: Pulsed laser melting in liquid (PLML) has emerged as a facile approach to synthesize submicron spheres (SMSs) for various applications. Typically lasers with long pulse durations in the nanosecond regime are used. However, recent findings show that during melting the energy absorbed by the particle will be dissipated promptly after laser-matter interaction following the temperature decrease within tens of nanoseconds and hence limiting the efficiency of longer pulse widths. Here, the feasibility to utilize a picosecond laser to synthesize Ge SMSs (200~1000 nm in diameter) is demonstrated by irradiating polydisperse Ge powders in water and isopropanol. Through analyzing the educt size dependent SMSs formation mechanism, we find that Ge powders (200~1000 nm) are directly transformed into SMSs during PLML via reshaping, while comparatively larger powders (1000~2000 nm) are split into daughter SMSs via liquid droplet bisection. Furthermore, the contribution of powders larger than 2000 nm and smaller than 200 nm to form SMSs is discussed. This work shows that compared to nanosecond lasers, picosecond lasers are also suitable to produce SMSs if the pulse duration is longer than the material electron-phonon coupling period to allow thermal relaxation.

Formation Mechanism of Laser‐Synthesized Iron–Manganese Alloy Nanoparticles, Manganese Oxide Nanosheets and Nanofibers

Abstract: Laser ablation in liquids (LAL) has emerged as a versatile approach for the synthesis of alloy particles and oxide nanomaterials. However, complex chemical reactions often take place during synthesis due to inevitable atomization and ionization of the target materials and decomposition/hydrolysis of solvent/solution molecules, making it difficult to understand the particle formation mechanisms. In this paper, a possible route for the formation of FeMn alloy nanoparticles as well as MnOx nanoparticles, -sheets, and -fibers by LAL is presented. The observed structural, compositional, and morphological variations are clarified by transmission electron microscopy (TEM). The studies suggest that a reaction between Mn atoms and Fe ions followed by surface oxidation result in nonstoichiometric synthesis of Fe-rich FeMn@FeMn2O4 core–shell alloy particles. Interestingly, a phase transformation from Mn3O4 to Mn2O3 and finally to Ramsdellite γ-MnO2 is accompanied by a morphology change from nanosheets to nanofibers in gradually increasing oxidizing environments. High-resolution TEM images reveal that the particle-attachment mechanism dominates the growth of different manganese oxides.