Linlin Xu

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.

Laser-induced construction of multi-branched CuS nanodendrites with excellent surface-enhanced Raman scattering spectroscopy in repeated applications

We report on the successful fabrication of multi-branched CuS nanodendrites with average branch length of about 20 nm by laser ablation of bulk Cu target in thioacetamide (TAA) solution. During the nucleation of Cu and S species, the accurate anisotropic growth should be attributed to an ultra-rapid acid etching process by laser-induced TAA hydrolyzing reaction. Interestingly, the semiconductor CuS nanodendrites provide pronounced surface enhanced Raman scattering (SERS) properties with noble-metal comparable activity and a detection limit as low as ~10-10 M, approaching the requirement (~nM) for single molecule detection. More importantly, after SERS analysis, the crystal violet (CV) probe molecules can be effectively removed from the substrate by 1064nm laser irradiation-induced moderate thermal treatment. Therefore, the unique and distinctive advantage is that the as-prepared CuS nanodendrites exhibit excellent reusability for 60 cycles of repeated SERS analyses. The low-cost CuS semiconductor nanodendrites with enhanced SERS properties should be established as a prominent SERS-based ultrasensitive probe in the repeated applications.

Self-assembled monolayers of bimetallic Au/Ag nanospheres with superior surface-enhanced Raman scattering activity for ultra-sensitive triphenylmethane dyes detection

The bimetallic Au/Ag self-assembled monolayers (SAMs) were constructed by using mono-dispersed Au/Ag nanospheres (Ag: 4.07%-34.53%) via evaporation-based assembly strategy. The composition-dependent surface-enhanced Raman scattering (SERS) spectroscopy revealed that the Au/Ag (Ag: 16.83%) SAMs provide maximized activity for triphenylmethane dyes detection. With the inter-metallic synergy, the optimized SAMs enable the Raman intensity of crystal violet molecules to be about 223 times higher than that of monometallic Au SAMs. Moreover, the SERS signals with excellent uniformity (<5% variation) are sensitive down to 10-13  M concentrations because of the optimal matching between bimetallic plasmon resonance and the incident laser wavelength.

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.

Photochemical synthesis of ZnO@Au nanorods as an advanced reusable SERS substrate for ultrasensitive detection of light-resistant organic pollutant in wastewater

The prospect of wielding surface-enhanced Raman spectroscopy (SERS) as a powerful technique for ultrasensitive detection of organic molecules in wastewater has received extensive attention in environmental surveillance. Based on ultraviolet (UV, 405 nm) laser irradiation of ZnO nanorods in HAuCl4 solution, ZnO@Au nanorods with controllable Au nanoparticles were successfully fabricated and established as an advanced SERS-based substrate. The reduction of Au ions was driven by the generation of electron-hole pairs via UV laser excitation of semiconductor-based nanomaterials, resulting in the moderate overgrowth of Au nanoparticles on the ZnO nanorods. The Au composition-dependent SERS analysis of crystal violet (CV) molecules revealed that the ZnO@Au nanorods with 16.21% Au contents exhibited optimized SERS activity in comparison with other nano-substrates in this paper. Furthermore, the detection limit of light-resistant methyl blue (MB) dye molecules was achieved at nanomole (nM) level of 10-9 M (0.8 μg/L), providing ultrasensitive detection of organic pollution in wastewater. Even after twenty recycles, the excellent reusability of this novel substrate with 65% original SERS intensity was achieved by subsequently eliminating the residual MB molecules via photocatalytic degradation. Therefore, the as-prepared ZnO@Au nanorods can serve as a cost-effective, clean, reusable and active SERS substrate for ultrasensitive monitoring of light-resistant organic pollutant in natural ecosystems.

Laser irradiation-induced construction of Pt/Ag bimetallic nanourchins with improved electrocatalytic properties

Platinum (Pt)-based nanomaterials with rough surfaces are regarded as promising catalysts in fuel cells. Herein, we report a versatile and green strategy to synthesize Pt/Ag (Pt : Ag ∼ 9 : 1) bimetallic nanourchins with mean size of ∼70 nm by laser irradiation of Ag2S/Ag nanoparticles in a potassium chloroplatinate (K2PtCl4) water solution. The distinctive advantages of this novel anisotropic synthesis are as follows: (I) the enhanced anisotropic replacement reaction derived by laser-induced photothermal effect on the nanoseeds gives rise to the anisotropic deposition of Pt atoms and then the formation of rugged intermediate precursors, and (II) the subsequent anisotropic overgrowth of Pt and Ag atoms via enhanced co-reduction reaction motivated by laser-induced surface plasmon resonance will preferentially occur at protrusion surfaces on the intermediate precursors. Without any binder/stabilizer/capping additives, the pure Pt/Ag bimetallic nanourchins exhibit excellent long-term stability during repeated cyclic voltammogram (CV) tests. Electrochemically active surface area (ECSA) tests illustrate that the novel catalysts exhibit a negligible loss of 0.2% after 1500 repeated applications, while that of commercial Pt/C catalyst is 78.7% after 1000 cycles. Moreover, the ECSA-normalized CV curve and chronoamperometric (CA) measurements reveal that Pt/Ag bimetallic nanourchins possess enhanced electrocatalytic activity and stability in the methanol oxidation reaction. Correspondingly, the mass-normalized (mass of Pt) CVs show that the peak of mass current is about 302.35 mA mgPt−1, which is 5.2 times higher than that of commercial Pt/C catalyst. For the entire time course (2000 s), the CA curves show that the current density is about 0.38 mA cmPt−2, while that of commercial Pt/C electrocatalyst is 0.014 mA cmPt−2. Thus the Pt/Ag bimetallic nanourchins should be established as an advanced electrocatalyst for direct methanol fuel cell application. These findings will also stimulate the investigation of using laser light as an effective tool for sculpting pure functional metal-based nanomaterials.

Controlled synthesis of hollow Ag@Au nano-urchins with unique synergistic effects for ultrasensitive surface-enhanced Raman spectroscopy

Ideally, taking advantage of synergistic effects, coinage-metallic nanocomposites combining obvious inner hollow structures and exterior unique dendritic shell architectures have a promising potential to provide unprecedented opportunity for ultrasensitive surface-enhanced Raman scattering spectroscopy (SERS) application. Herein, we report a convenient and robust synthesis of hollow Ag@Au nano-urchins with both obvious inner voids and exterior multi-antennas by employing galvanic replacement reaction between Au3+ ions and Ag nanospheres and then concomitant reduction of Au3+ ions onto precursors. The stable Ag nanospheres play an important role in the seed-mediated growth process, which were fabricated by pulsed laser ablation of Ag target in liquid. Superior to traditional chemical synthesis, the distinctive advantage is that ultra-rapid laser sintering/quenching of Ag nanoseeds enable the Ag outside surfaces to become more stable than those of core regions. The fascinating hollow Ag@Au nano-urchins obtained by adding 6 mL, 0.5 mM HAuCl4 exhibit excellent chemical stability in ionic or oxidative condition. More importantly, the obtained products provide enhanced SERS activity by using 4-Aminothiophenol (4-ATP) as the probe molecules. The obvious inner hollow structure and exterior immense antennas as well as pronounced inter-metallic synergies are integrated to provide ultrasensitive SERS signals with an enhancement factor (EF) up to ~1012. Interestingly, the SERS signals are also clearly distinguishable even the concentration of 4-ATP was decreased to ~10−13 M. The pronounced features are better than many previous works, especially those of smooth-shaped nanocomposites, monometallic nanodendrites or single-phase hollow structures. The superiorities of the hollow Ag@Au nano-urchins will make them become a prominent SERS-based substrate for ultra-trace detection of biomolecules in pathological cell diagnostics, environmental surveillance, and food safety supervision.

Laser-induced photochemical synthesis of fibrous-shaped CuO@CuS nanoporous structures for enhanced electrostatic adsorption of negatively charged contaminants from wastewater

Various nanomaterials have been established as versatile adsorbents for the removal of organic or heavy metal pollutants from wastewater. Unfortunately, the subsequent cleaning of the suspended nano-adsorbents is very difficult and costly. Herein, we report a novel synthetic route to fabricate fibrous-shaped CuO@CuS nanoporous structures by the laser irradiation of CuO powders in sodium sulfide (Na2S) liquid. Superior to conventional chemical approaches, 532 nm laser beam irradiation will lead to the formation of rich- O and S vacancy defect states in the final products. Zeta-potential experiments confirm that the positive surface charges of CuO@CuS nanomaterials significantly increase from 2 to 70 mV with an increase of laser irradiation time (0~30 min). As for the methyl blue (MB) and hexavalent chromium Cr(VI) solution, the CuO@CuS nanocomposites adsorbed with these adsorbates can be significantly self-agglomerated, due to the positive electrostatic adsorption effect on negatively charged pollutants. After the adsorption of MB molecules and Cr(IV) ions, the absorption spectra of two supernatant liquids confirm that 99.6% and 98.9% CuO@CuS nano-adsorbents can be deposited on the bottom of the pool, respectively. Without the aid of the centrifugation process or an external magnetic field in complicated nano-adsorbent separation procedures, the unique adsorption-deposition process is a significant breakthrough in the wastewater purification.

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.