Zhenfei Tian

Defect-Mediated Formation of Ag Cluster-Doped TiO2 Nanoparticles for Efficient Photodegradation of Pentachlorophenol

A novel strategy was designed to prepare Ag cluster-doped TiO(2) nanoparticles (Ag/TiO(2) NPs) without addition of any chemical reducing agent and/or organic additive. A defect-rich TiO(x) species was generated by laser ablation in liquid (LAL) of a Ti target. The silver ions could be reduced and deposited on the surface of TiO(2) NPs through the removal of oxygen vacancies and defects; the TiO(x) species evolved into anatase NPs in a hydrothermal treatment process. The derived Ag/TiO(2) NPs are approximately 25 nm in size, with narrow size distribution. The Ag clusters are highly dispersed inside TiO(2) and less than 3 nm in size. The doped amount can be tuned by changing the concentration of Ag(+) ions. The as-synthesized Ag/TiO(2) NPs display improved photocatalytic efficiency toward pentachlorophenol (PCP) degradation.

A novel reduction approach to fabricate quantum-sized SnO2-conjugated reduced graphene oxide nanocomposites as non-enzymatic glucose sensors

Quantum-sized SnO2 nanocrystals can be well dispersed on reduced graphene oxide (rGO) nanosheets through a convenient one-pot in situ reduction route without using any other chemical reagent or source. Highly reactive metastable tin oxide (SnO(x)) nanoparticles (NPs) were used as reducing agents and composite precursors derived by the laser ablation in liquid (LAL) technique. Moreover, the growth and phase transition of LAL-induced SnO(x) NPs and graphene oxide (GO) were examined by optical absorption, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and high-resolution transmission electron microscopy. Highly dispersed SnO(x) NPs can also prevent rGO from being restacked into a multilayer structure during GO reduction. Given the good electron transfer ability and unsaturated dangling bonds of rGO, as well as the ample electrocatalytic active sites of quantum-sized SnO2 NPs on unfolded rGO sheets, the fabricated SnO2-rGO nanocomposite exhibited excellent performance in the non-enzymatic electrochemical detection of glucose molecules. The use of LAL-induced reactive NPs for in situ GO reduction is also expected to be a universal and environmentally friendly approach for the formation of various rGO-based nanocomposites.

Zinc stannate nanocubes and nanourchins with high photocatalytic activity for methyl orange and 2,5-DCP degradation

Nanomaterials have emerged as remarkable photocatalysts. In this report, multifunctional cube-like Zn2SnO4 and urchin-like ZnSnO3 nanomaterials were successfully synthesized using zinc and tin metals as ablation targets by the combined strategy of laser ablation in liquid and hydrothermal treatment. Addition of ammonia to the hydrothermal reaction can not only tune the phase structure of the final products from cubic spinel-type Zn2SnO4 to face-centered perovskite ZnSnO3 but also control the morphology of ZnSnO3 in a concentration-dependent manner. When the ammonia concentration was set to 3.0 mol L−1, uniform urchin-like Zn-deficient ZnSnO3 with remarkable lattice distortion was obtained. Photocatalytic activity tests using methyl orange (MO) and 2,5-dichlorophenol (2,5-DCP) as probe molecules under ultraviolet light excitation demonstrated that urchin-like ZnSnO3 is highly active and effective for the degradation of high concentrations of MO (25 ppm) and 2,5-DCP (10 ppm).

Spontaneous Growth and Chemical Reduction Ability of Ge Nanoparticles

Forming colloidal solutions containing semiconductor quantum-sized nanoparticles (NPs) with clean surface has been a long-standing scientific challenge. In this contribution, we report a “top-down” method for the fabrication of Ge NPs by laser ablation of a Ge target in deionized water without adding any stabilizing reagents. The initial Ge NPs in amorphous structure showed spontaneous growth behavior by aging Ge colloids in deionized water under ambient temperature, which gradually evolved into a metastable tetragonal structure as an intermediate phase and then transformed into the stable cubic structure, being consistent with the Ostwalds rule of stages for the growth in a metastable system. The laser-induced initial Ge NPs demonstrate a unique and prominent size-dependent chemical reductive ability, which is evidenced by the rapid degradation of organic molecules such as chlorinated aromatic compounds, organic dyes, and reduction of heavy metal Cr(VI) ions.

Organization of Mn3O4 nanoparticles into γ-MnOOH nanowires via hydrothermal treatment of the colloids induced by laser ablation in water

We report a simple and green strategy to organize Mn3O4 nanoparticles into single-crystalline γ-MnOOH nanowires on the basis of hydrothermal treatment of the colloids induced by laser ablation in water. Evidence obtained from a transmission electron microscopy investigation revealed that the organization mainly involved the following steps: nanoparticles → polycrystalline nanochains → single crystalline nanowires.

Reduced graphene oxide anchored magnetic ZnFe2O4 nanoparticles with enhanced visible-light photocatalytic activity

We report a facile approach to immobilize magnetic ZnFe2O4 nanoparticles (NPs) onto a reduced grapheme oxide (rGO) network by using highly reactive ZnOx(OH)y and FeOx colloids as precursors, which were respectively obtained by laser ablation of metallic zinc (Zn) and iron (Fe) targets in pure water. A microstructure investigation of such nanocomposites (NCs) revealed that ZnFe2O4 NPs are well-dispersed onto rGO sheets. Such a structure was helpful for separating the photoexcited electron–hole pairs and accelerating the electrons transfer. Electrochemical impedance measurements indicated the remarkable decrease of the interfacial layer resistance of the composite structure compared to that of pure ZnFe2O4 NPs. As a result of these advantages, such NCs present a prominent enhancement in the photodegradation efficiency for methylene blue dye. Besides, the excellent magnetic properties of the ZnFe2O4 NPs allow the catalysts to be easily separated from the solution by a magnet for recycling. This effort not only provided a new approach to fabricate ZnFe2O4–rGO NCs, also expanded the application of ZnFe2O4 NPs used as visible-light excited photocatalysts in application of organic pollutants degradation.

In situ growth of lamellar ZnTiO3 nanosheets on TiO2 tubular array with enhanced photocatalytic activity

We report a self-sacrificed in situ growth design toward preparation of ZnTiO3-TiO2 heterojunction structure. Highly reactive zinc oxide colloidal particles derived by laser ablation in liquids can react with TiO2 nanotubes to form a lamellar ZnTiO3 nanosheet structure in a hydrothermal-treatment process. Such hybrid structural product was characterized by X-ray diffraction, scanning and transmission electron microscopy, UV-vis diffuse reflection spectroscopy and X-ray photoelectron spectroscopy. The enhanced photocatalytic activity of the hybrid structure toward degradation of methyl orange (MO) and pentachlorophenol (PCP) molecules was demonstrated and compared with single phase TiO2, as a result of the efficient separation of light excited electrons and holes at the hetero-interfaces in the two semiconductors.

Synthesis of Mn-doped α-Ni(OH)2 nanosheets assisted by liquid-phase laser ablation and their electrochemical properties

We designed a new strategy, namely, the laser ablation of a target material in an aqueous ionic solution, to prepare Mn-doped Ni(OH)2 nanosheets based on reactions between the pulsed laser-induced plasma plume of Mn and the surrounding NiCl2 solution. The crystalline phase, morphology and structure of the as-derived products are characterised by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Results indicate the hierarchical assembly of numerous tiny nanosheet building blocks into a Mn-doped α-Ni(OH)2 spherical structure. Importantly, the positive electrode made of Mn-doped α-Ni(OH)2 nanosheets exhibits a high specific capacitance of ~1000 F g(-1) under a current density of 5 A g(-1), concurrently possessing excellent cycling ability. This novel strategy may offer researchers an alternative for designing interesting solid targets and ionic solutions towards the fabrication of other new nanostructures for fundamental research and potential applications.

Layered mesoporous Mg(OH)2/GO nanosheet composite for efficient removal of water contaminants

A layered magnesium hydroxide (Mg(OH)2) nanosheet/graphene oxide (GO) composite was synthesized through laser ablation of the Mg target in an aqueous solution with GO. Its mesoporous structure and application as an adsorbent for the removal of methylene blue (MB) and heavy metal ions from water were investigated. Mg(OH)2 nanosheets were organized in situ from the strong reaction between the laser-ablated Mg species and water molecules. The GO nanosheet served as a heterogeneous nucleation and growth site for sheet-like Mg(OH)2 nanocrystals. The resulting porous Mg(OH)2/GO nanosheet composite had a high specific surface area of 310.8 m2 g−1 and a pore volume of 1.031 cm3 g−1. These characteristics show that the composite could be an excellent adsorbent. The composite exhibited a maximum adsorption capacity of 532 mg g−1 at 298 K for typical contaminants of MB, and over 300 mg g−1 for heavy metal ions Zn2+ and Pb2+.

Core–shell TaxO@Ta2O5 structured nanoparticles: laser ablation synthesis in liquid, structure and photocatalytic property

Monodispersed, homogeneous core–shell TaxO@Ta2O5 (x = 1, 2) composite nanoparticles (NPs) are successfully synthesized via one-step liquid phase laser ablation (LPLA) of a tantalum metal plate in ethanol. The morphology, phase structure, and surface states of the core–shell NPs are investigated by scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The LPLA-derived spherical-like NPs consist of well-crystallized TaxO cores with diameters of 10–40 nm and amorphous-like Ta2O5 shells with a thickness of ca. 5 nm. A possible formation pathway for TaxO@Ta2O5 core–shell NPs is proposed on the basis of LPLA and subsequent reactive quenching processes. Photocatalytic degradation of methylene blue in the liquid phase serves as a probe reaction to evaluate the activity of the as-prepared core–shell NPs under the irradiation of UV light. Theoretical calculation based on density functional theory indicated the metallic nature of the core TaO phase. Interestingly, compared with pure Ta2O5 powders, the incorporation of suboxide TaxO cores into the shell of Ta2O5 contributes to an enhancement in photocatalytic activity. This work provides new information that may be used for the design and novel application of homogeneous core–shell nanostructures.