Fabrication Of Gold Nanohybrids And The Activities For Pollutant Detection And Removal

With the industrial development and population growth, the uncontrolled discharge of industrial and domestic waste results in the detection of the chemical pollutants or biological contaminants (such as aniline, nitrophenol and Escherichia coli) in ecological environment, which have threatened ecosystems and human health seriously. Their ultrasensitive detection and efficient control have emerged as hot issues in the pollutant removal and environmental detection.The gold nanomaterials have been widely used for the applications in environmental detection and catalysis due to their unique localized surface plasmon resonance (LSPR) and catalytic activities. The detection and catalytic activity of gold nanomaterials are limited by their morphology and dimention, which could be addressed by morphological or structural design. In addition, the lack of correlation between the structure and the activity and complex environmental requirements also limit the applications of the gold nanomaterials. To address the above challenges, this thesis presents the following efficient structure control and design methods for the environmental applications:(1) Hollow Au nanorod@nanoshells (AuNR@NSs) have been synthesized by galvanic replacement reaction. AuNR@NSs are single crystals in nature and exhibit broadband LSPR property that can be tuned to near-infrared regions by adjusting structural parameters. Redshift can be realized by increasing the length, whereas blueshift can be achieved by increasing either the width or the thickness of nanoshells. The surface enhanced Raman spectra (SERS) based detection of AuNR@NSs has been investigated by using 4-aminothiophenol (4-ATP) as the target molecule. AuNR@NSs exhibit excellent SERS activity for 4-ATP detection using the excitation lasers with wavelengthes ranging from 514 nm to 830 nm due to their broadband LSPR properties. The SERS enhancement factor can be tuned to 2.8×105.(2) AuNR@NS-AuNPs core-satellites nanoassemblies have synthesized by the electrostatic attraction using AuNR@NSs as cores and AuNPs as satellites. The numerical results by the frequency-domain finite element method (FEM) indicate that AuNR@NS-AuNPs nanoassemblies display two dominant plasmonic modes, corresponding to high-energy dipolar resonance mode of AuNPs and low-energy coupling mode between AuNR@NSs and AuNPs. The high-energy mode isn't sensitive to structures but the frequency of low-energy mode is highly dependent on sizes and numbers of AuNPs and distances between the core and satellites. Engineering these structural parameters can precisely program strength and distribution of "hot spots" to maximize the overall SERS activity for 4-ATP detection. The enhancement factor can be up to 2.88×106 with 1nm distance between cores and 13 nm AuNPs with numbers of 22 per core.(3) AuNR@NSs are prepared by using AuNRs with high aspect ratio, which exhibit strong surface plasmon resonance in the near-inferrad (NIR) region. Efficient drug-loading in hollow AuNR@NSs is facilitated by employing a phase-change material of 1-tetradecanol. Remote controlled release of drugs can be triggered by photothermal effect originated from the AuNR@NSs. The drug-loaded AuNR@NSs enable combined chemotherapy and photothermal effects in killing tumor cells upon NIR laser irradiation, therefore, enhance the killing efficiency with the inactivation rate of 40% in 15 min NIR laser irradiation.(4) Multilayered AuNR@NSs (mAuNR@NSs) were successfully synthesized to improve the catalytic activity. The number of layers was controlled by tuning the cycle times of silver coating and galvanic replacement reaction. Broadening and red-shifting plasmonics and enhanced catalytic activity were observed with the increasing of the shell numbers. Hexa-AuNR@NSs exhibited highest catalytic activity, with 97% conversion in 2 min after adsorption and specific kinetic constant of 3.7x104 min-1 g-1. The photothermal effect of mAuNR@NSs can also enhance the catalytic performance obviously. With the support of the polyurethane foam, the mAuNR@NSs can act as recyclable efficient heterogeneous catalysts for the reduction of the 4-nitrophenol.(5) Multifunctional Co-Fe2O3@PDA-Au was fabricated via coating polydopamine (PDA) through self-polymerization and further loading gold nanoparticles by in situ reduction for the detection and removal of dyes. The Co-Fe2O3@PDA-Au shows strong adsorptivity up to 37.1 mg g-1 for methylene blue and photodegradation for dyes with 41 times than Co-Fe2O3. The presence of gold nanoparticle in the Co-Fe2O3@PDA-Au system promotes SERS activity with an impressive detection limit of 1 ?M. The hybrids have been supported by polyurethane foam to improve the separation efficiency, which demonstrate the excellent stability and reusability as the adsorbent and photocatalyst.In summary, the structure and size tunability of gold nanomaterials can enhance the SERS based sensing and catalytic activity efficiently. The decoration of semiconductor by gold nanoparticles can improve the photocatalytic degradation for the pollutant. This thesis provides a feasible approach to design gold nanohybrids, which would promote the applications of gold nanomaterials in environmental detection and pollution control.