Mei-Juan Han

Preparation and evaluation of thiol-functionalized activated alumina for arsenite removal from water

Arsenic species such as arsenite [As(III)] and arsenate [As(V)] are known human carcinogens. Though lots of metal oxide adsorbents have been developed for removal of As(V), they are much less effective for As(III) adsorption. In this study, various inorganic-organic hybrid adsorbents bearing thiol groups have been prepared by modifying activated alumina (AA) with mercaptopropyl-functionalized silica under different experiment conditions. Raman spectra demonstrated the successful functionalization of AA and verified the formation of As-S complexes after As(III) adsorption. Batch experiments were applied to evaluate the As(III) adsorption performance of the hybrid adsorbents. Compare with AA, the hybrid adsorbents exhibited enhanced adsorption abilities for As(III) due to the introduction of thiol groups, and as the thiol loading increased, the uptake of As(III) increased. Experimental results indicated that the hybrid adsorbents still maintained the merit of the AA for As(V) adsorption. Based on the results, one hybrid adsorbent referred to as BL(AA)(30)(MPTS)(3.3) has been selected by consideration of not only the adsorption capacity but also its environmentally friendly and cost-effective production. The investigation has indicated that the hybrid adsorbents are very promising for As(III) removal from water.

Fabrication and evolution of multilayer silver nanofilms for surface-enhanced Raman scattering sensing of arsenate

Surface-enhanced Raman scattering (SERS) has recently been investigated extensively for chemical and biomolecular sensing. Multilayer silver (Ag) nanofilms deposited on glass slides by a simple electroless deposition process have been fabricated as active substrates (Ag/GL substrates) for arsenate SERS sensing. The nanostructures and layer characteristics of the multilayer Ag films could be tuned by varying the concentrations of reactants (AgNO3/BuNH2) and reaction time. A Ag nanoparticles (AgNPs) double-layer was formed by directly reducing Ag+ ions on the glass surfaces, while a top layer (3rd-layer) of Ag dendrites was deposited on the double-layer by self-assembling AgNPs or AgNPs aggregates which had already formed in the suspension. The SERS spectra of arsenate showed that characteristic SERS bands of arsenate appear at approximately 780 and 420 cm-1, and the former possesses higher SERS intensity. By comparing the peak heights of the approximately 780 cm-1 band of the SERS spectra, the optimal Ag/GL substrate has been obtained for the most sensitive SERS sensing of arsenate. Using this optimal substrate, the limit of detection (LOD) of arsenate was determined to be approximately 5 μg·l-1.

SERS detection of arsenic in water: A review

Arsenic (As) is one of the most toxic contaminants found in the environment. Development of novel detection methods for As species in water with the potential for field use has been an urgent need in recent years. In past decades, surface-enhanced Raman scattering (SERS) has gained a reputation as one of the most sensitive spectroscopic methods for chemical and biomolecular sensing. The SERS technique has emerged as an extremely promising solution for in-situ detection of arsenic species in the field, particularly when coupled with portable/handheld Raman spectrometers. In this article, the recent advances in SERS analysis of arsenic species in water media are reviewed, and the potential of this technique for fast screening and field testing of arsenic-contaminated environmental water samples is discussed. The problems that remain in the field are also discussed and an outlook for the future is featured at the end of the article.

Surface-enhanced Raman scattering for arsenate detection on multilayer silver nanofilms.

Surface-enhanced Raman scattering (SERS) has recently emerged as a promising method for chemical and biomolecular sensing. SERS quantification analysis of arsenate (As(V)) was investigated using multilayer Ag nanofilms deposited on glass slides as SERS-active substrates (Ag/GL substrates) by an electroless deposition process. The As(V) limit of detection (LOD) was determined to be ∼5 μg L(-1) or lower with or without coexisting multiple background electrolytes (Na(+), K(+), Ca(2+), Mg(2+), Cl(-), NO(3)(-), SO(4)(2-) and H(2)PO(4)(-)). The presence of the background electrolytes at low concentrations was observed to enhance the SERS sensitivity of the substrate towards As(V) more than twofold. Standard calibration curves were prepared in the absence and presence of the background electrolytes. Excellent linear relationships between the peak heights of the As(V) SERS band at ∼780 cm(-1) and the As(V) concentrations were obtained in a concentration range of 0-250 μg L(-1). The selectivity of the Ag nanofilm towards oxyanions was examined to be in the order of As(V)≫phosphate≫nitrate, sulphate. A low sample-to-sample relative standard deviation (RSD) of 5.2% was also determined, suggesting the Ag/GL substrate was uniform and highly reproducible. Experimental results indicated that the SERS method could be used for quantitative analysis of As(V) in groundwater samples.

Surface modification of silver nanofilms for improved perchlorate detection by surface-enhanced Raman scattering.

Surface-enhanced Raman scattering (SERS), as one of the most sensitive spectroscopic analysis methods, has been investigated extensively for the detection of environmental contaminants in recent years. In this work, we reported the new development of robust SERS substrates for rapid and sensitive sensing of aqueous perchlorate, a widespread environmental contaminant. The fabrication of the substrates consisted of two simple steps: (a) formation of Ag nanofilms on Cu and surface-roughened Cu foils (Ag/Cu and Ag/rCu nanofilms) using a controllable and inexpensive one-step electroless plating process, and (b) surface modification of the Ag nanofilms with cysteamine (Cys) self-assembly monolayer (SAM) (Cys-Ag/Cu and Cys-Ag/rCu substrates). Due to the strong affinity of -NH(3)(+) groups of the Cys molecules for perchlorate ions, the rapid SERS detection of perchlorate has been realized with a limit of detection (LOD) down to 5 μg L(-1) (ppb) for aqueous samples without need for drying. Various calibration curves with good linear relationships were obtained, indicating the quantification potential of SERS analysis of perchlorate using these new substrates. It was found that the neutral pH yielded the maximum SERS signals, and 85% of original sensitivity was remained in 5 days of storage time in the air, indicating the substrates are fairly stable. Within 10 regeneration-reuse cycles, the SERS signals of perchlorate kept in the range of 85-105% of the original value, verifying its reusability.

Surface-enhanced Raman scattering of perchlorate on cationic-modified silver nanofilms - Effect of inorganic anions.

Surface-enhanced Raman scattering (SERS) has emerged as one of the most sensitive spectroscopic analysis methods for the detection of environmental contaminants in water, including perchlorate (ClO4(-)). However, as with other commonly used analytical techniques, analysis of realistic environmental samples by SERS presents a challenge due to complex chemical components coexisting in the samples. In this work, we investigated the influence of inorganic anions (particularly oxyanions) on SERS spectra of ClO4(-) using a cationic thiol modified silver nanofilm substrate (Cys-Ag/rCu). The results show that the anions present in the samples did not shift the ClO4(-) characteristic band positions, but did decrease signal intensities due to their competitive binding with the -NH3(+) groups of cationic thiol molecules immobilized on the substrates. The pH changes caused by both the dissociation of H2PO4(-) and the hydrolysis of HCO3(-) may also play a non-negligible role. The selectivity of the Cys-Ag/rCu substrate towards these anions was determined to be in the following order: ClO4(-)>SO4(2-)>HCO3(-), NO3(-)>Cl(-)>H2PO4(-), indicating preferential adsorption of ClO4(-) ions. In the solutions with multiple anions present, the ClO4(-) SERS spectra were affected simultaneously by all the coexisting anions. Calibration curves with very good linear relationships were successfully obtained, demonstrating the great potential of quantitative detection of aqueous ClO4(-) in the matrix.