Dameng Wang

Laser-ablation-induced synthesis of porous ZnS/Zn nano-cages and their visible-light-driven photocatalytic reduction of aqueous Cr(VI)

A novel and versatile technique for the facile synthesis of porous ZnS/Zn nano-particles is developed by laser ablation Zn metal in solution containing thioacetamide (TAA), hydrochloric acid (HCl) and hexadecyl trimethyl ammonium bromide (CTAB). The acid plays a critical role in the formation of porous surface structures, due to the acid-decomposition of Zn and S ions in the early stage of the nucleation process. Compared with core-shell ZnS/Zn nano-particles, the as-prepared ZnS/Zn porous structures have enhanced activity in visible-light-driven photocatalytic reduction of extremely toxic aqueous Cr(VI), because of the increased surface area and higher pore volume. The present results have opened up a new paradigm to obtain superior photo-catalyst in reduction of aqueous Cr(VI) under visible light.

Laser induced fabrication of mono-dispersed Ag 2 S@Ag nano-particles and their superior adsorption performance for dye removal

A novel and versatile strategy for the convenient synthesis of mono-dispersed Ag2S@Ag hybrid nano-particles is developed by simply using laser ablation of Ag target in thioaetamide (TAA) solution. The as-prepared Ag2S@Ag nano-particles exhibit superior adsorption performance for the removal of methyl blue (MB) and methyl orange (MO) from wastewater. Most importantly, without any centrifugal process, the new adsorbents can be removed from solutions easily by filters after adsorbing dyes, since the Ag2S@Ag nano-particles are agglomerated and deposited on the bottom. We demonstrated that the excellent features are highly related to Ag structures in the Ag2S@Ag nano-particles. The unique excited and polarized Ag species with positive charge regions enable the Ag2S@Ag nano-particles to have much more active sites as adsorption sites. Then, it will result in the generation of strong ionic bounds via electron-static interaction between positive active site of the adsorbent and negative charge of the dye molecules. Our results provide a breakthrough in the complicated process including the removal of adsorbents that arises from the separate process after adsorption of organic contaminants. Thus, these findings are of great significance for the practical application in water purification.

Laser-induced photochemical synthesis of branched Ag@Au bimetallic nanodendrites as a prominent substrate for surface-enhanced Raman scattering spectroscopy

The project of wielding laser light as a versatile tool for sculpting branched Ag@Au bimetallic nanocrystals with mean size of ~50 nm has been developed in this work. The moderate overgrowth of Ag species with negligible damage effect on the branched Ag@Au nanostructures was achieved by laser-induced photo-oxidation. The final Ag@Au nanodendrites exhibit superior surface enhanced Raman scattering (SERS) activities with an enhancement factor up to ~1011 and a detection limit as low as ~10-14 M. The pronounced feature should be attributed to the noticeable small-sized branches (<10 nm) and unique pronounced inter-metallic synergies. Our results have a promising potential for developing SERS-based ultrasensitive probes in biomedical application.

Ultra-small Sn2S3 porous nano-particles: an excellent photo-catalyst in the reduction of aqueous Cr(VI) under visible light irradiation

We present the direct conversion of bulk Sn metal to sub-10 nm Sn2S3 porous nano-particles based on pulsed-laser ablation of a Sn target in solution. The as-prepared ultra-small porous structures exhibit superior photocatalytic activity and excellent stability in the reduction of aqueous Cr(VI) under visible light irradiation.

Direct synthesis of size-tailored bimetallic Ag/Au nano-spheres and nano-chains with controllable compositions by laser ablation of silver plate in HAuCl4 solution

The direct conversion of bulk silver metal to size-tailored bimetallic silver–gold (Ag/Au) nano-spheres and nano-chains with controllable compositions has been achieved by laser ablation of an Ag target in HAuCl4 solution. Taking advantage of the replacement reaction between Ag and Au ions, the average sizes of the bimetallic Ag/Au nano-particles substantially decreased from tens of nanometers to sub-2 nm with the increase in HAuCl4 concentration (0.12–4.59 mM). Meanwhile, the relative ratio of Ag and Au elements in individual Ag/Au nano-particles has been systematically changed from about 9 : 1 to 1 : 9. The UV-visible absorption spectra of the Ag/Au nano-particles significantly red shifted from about 400 nm to 785 nm. The designed simplistic, single-step, versatile strategy does not require seed preparations, intermediate workup processes or any potential toxic surfactants. This will offer a convenient and valuable new way to fabricate bimetallic nano-particles with desired structures and functions.

Laser-induced fabrication of single crystal zinc hydroxyl dodecylsulfate nano-sheets with excellent fluorescence emission

An attractive strategy to convenient synthesis of free-standing single-crystal zinc hydroxyl dodecylsulfate (ZHDS) nano-sheets has been developed by simply using laser ablation of a bulk Zn metal target in a liquid medium containing deionized water and enough/excess sodium dodecylsufate (SDS). Taking advantage of enough/an excess amount of sodium dodecylsulfate (SDS), tightly packed and highly ordered layers of DS functional groups were generated and resulted in the crystallization of metallo–organic ZHDS nano-sheets over the plasma created by laser ablation of the Zn target. The experimental results confirm that the ZHDS nano-sheets are indeed softer materials and intercalated with numerous DS functional groups in crystal structures. The novel free-standing two-dimensional ZHDS nano-sheets exhibit excellent fluorescence emission at 417 nm. It has been proved that the hydroxyl (–OH) groups should play the main role in the outstanding photoluminescence in the blue-band region. Moreover, the strong blue emission can be changed to bright green-band emission (vacancy oxygen-related PL emission in ZnO) centered at about 516 nm after annealing the ZHDS nano-sheets at 400 °C for 3 hours. The excellent performances will be of great significance for ZHDS nano-sheets in low-cost metallo/organic light-emitting material and photo-electro-chemical bio-analysis in the future. Based on pulse laser fabrication in liquid, the new conjugation of metal complexes and organic compounds has opened up exciting classes of hybrid materials for applications spanning optoelectronics, energy conversion, photodynamic therapy, etc.

Laser-induced convenient synthesis of porous Cu_2O@CuO nanocomposites with excellent adsorption of methyl blue solution

We design a simple and versatile strategy to synthesize pure Cu2O@CuO nanoporous materials with pores the size of 4~8 nm based on the laser irradiation of CuO powders in distilled water. In the presence of 1.8 mg Cu2O@CuO nanocomposites, the adsorption of a nearly 99.69% MB solution (80 mg/L, 3 mL) can be achieved after 1 min, while 95.35% via 200 mg original CuO powders. The porous structures and the abundant hydroxyl (-OH) groups formed on the surfaces enable the Cu2O@CuO nanocomposites to have many more adsorption sites. Our results have opened up a novel green paradigm of wielding laser light as a versatile tool for sculpting porous nanocomposites without any residual reagents.

Laser-induced fabrication of highly branched Au@TiO2 nano-dendrites with excellent near-infrared absorption properties

In this report, highly branched Au@TiO2 nano-dendrites with a tailored surface topography have been conveniently fabricated via a novel and effective laser-induced strategy. The TiO2 nanospheres fabricated by laser ablation of the Ti target in H2O2 solution are characterized by abundant oxygen vacancies (OVs) on the (110) surface. Then, the hydroxyl radical (OH−) groups will be easily formed on the OVs in terms of water dissociation by UV laser irradiation of the TiO2 nano-spheres at the liquid interface. With the aid of OH− groups, the formation of Au@TiO2 nano-dendrites is based on the overgrowth of gold on the TiO2 nano-spheres through the reduction of HAuCl4. The absorption spectra of Au@TiO2 nano-dendrites show that localized surface plasmon resonance (LSPR) peaks can be effectively modulated from the visible region (∼545 nm) to the near-infrared region (NIR ∼ 1090 nm). The as-prepared Au@TiO2 nano-dendrites with excellent NIR absorption properties have a promising potential for developing important novel sensors and super photo-catalysts.

Ultraviolet light-induced photochemical reaction for controlled fabrication of Ag nano-islands on ZnO nanosheets: an advanced inexpensive substrate for ultrasensitive surface-enhanced Raman scattering analysis

The fascinating nanocomposites of semiconductors coupled with noble metals have a promising potential to develop a low-cost substrate for surface-enhanced Raman scattering (SERS) applications. Herein, the controlled construction of Ag nano-islands on ZnO nanosheets (Ag@ZnO nanocomposites) was successfully achieved by a green and effective strategy based on ultraviolet light induced-photochemical reaction. It was found that the Ag content in Ag@ZnO nanocomposites linearly increases to 4.62% by simply increasing the irradiation time (0~10 min). More importantly, increasing the Ag content (0~4.62%) in the nanocomposites results in enhanced SERS activities with an enhancement factor up to 107 and a detection limit as low as 10−9 M. Compared with the complete noble metal substrate, the novel Ag@ZnO nanocomposites (<5% Ag compositions) were cost-effective and possessed high biocompatible properties; which can be established as an advanced inexpensive substrate for ultrasensitive SERS analysis, particularly for food safety and biomedical applications.

Laser-induced modification of dog-bone-like Au nanorods for accurate growth of well-defined cylindrical structures

Gold nanorods (Au NRs) with regular cylindrical structures can be prepared by the conventional seed-mediated growth method. But for every success, there are dozens of failures. In most cases, a significant fraction of irregular Au NRs with dog-bone-like structures are also frequently formed. Therefore, a complementary way (the reshaping of irregular rods, etc.) to reduce the defective rate in the fabrication of regular Au NRs is urgently desired. In this paper, a novel and effective strategy for accurate growth of well-defined cylindrical Au NR structures with fairly good uniformity is developed by laser-induced shape-modification of dog-bone-like Au NRs. In the first step, large-scale irregular shaped Au NRs with dog-bone-like structures were prepared by the standard seed-mediated growth approach. Subsequently, highly mono-dispersed perfect Au NRs with ultra-smooth surfaces can be obtained by non-focused laser irradiation of the irregular Au NR solution. The irradiation parameters such as laser power density, irradiation time and laser wavelength play an important role in the accurate growth of Au NRs. At optimum conditions (∼5 W cm−2, <100 s, 1064 nm), a laser-induced reshaping process in the growth solution can also be employed to grow the cylindrical Au NRs into longer structures with aspect ratios ranging from about 2.3 to 5.6. After laser irradiation, the absorption spectra of the Au NRs show that longitudinal localized surface plasmon resonance (LSPR) peaks can be effectively modulated from about 750 nm to 810 nm. On the other hand, by adding some H2PtCl6 in the as-prepared Au NR growth solution, laser irradiation will lead to a guided growth behavior of a Pt–Ag structure, resulting in the fabrication of Pt–Ag nano-islands on Au NRs. Thus, it can be seen that the laser-induced modification is a simple, low-cost and high-throughput strategy to prepare noble metal perfectly cylindrical nano-structures with multiple structural controlling capabilities.