Fast, efficient and clean adsorption of bisphenol-A using renewable mesoporous silica nanoparticles from sugarcane waste ash.

Even with all the biological problems associated with bisphenol-A (BPA), this chemical is still being widely used, especially in thermal paper receipts. In this study, renewable mesoporous silica nanoparticles (MSN), obtained from sugarcane ash, functionalized with hexadecyltrimethylammonium (CTAB) were applied as an adsorbent in the removal of BPA from the aqueous solution. The versatility of this material and its BPA adsorption capacity were tested at different pH values, being practically constant at pH between 4 and 9, with a slight increase in pH 10 and a greater increase in pH 11. The removal time evaluation indicates a very fast adsorption process, removing almost 90% of BPA in the first 20 min of contact. The kinetic model indicates a monolayer formation of BPA molecules on the MSN-CTAB surface. The maximum adsorption capacity (Q max) was 155.78 mg g-1, one of the highest found in literature, and the highest for material from a renewable source.

Selecting the Mechanism of Surface-Enhanced Raman Scattering Effect using Shell Isolated Nanoparticles and an Oxo-Triruthenium Acetate Cluster Complex.

After more than 40 years, surface-enhanced Raman spectroscopy (SERS) stills attract much attention from chemists, not only because of the synthesis of plasmonic nanostructures but also due to the several simultaneous mechanisms which still remain unclear. One of the possibilities for a better understanding of the SERS mechanisms is the utilization of suitable inorganic complexes. The use of inorganic complexes makes it possible to observe the two main SERS mechanisms (electromagnetic and chemical) and to observe the intensification of Raman scattering due to the resonance Raman effect. In this publication, the observation of these mechanisms was possible utilizing an unpublished and very interesting complex with two oxo-triruthenium acetate clusters and an iron bis(terpyridine) in its structure (seven metals) and which interacted with bare gold nanoparticles and shell-isolated gold nanoparticles (SHIN), with a 1 nm silica shell. The utilization of SHIN allowed to quench the SERS chemical mechanism and led to a spectrum where iron-terpyridine peaks are absent and only the modes related to [Ru3O] center were observed (due to enhancement by resonance Raman, SERRS); it can be said that the the shell-isolated nanoparticles enhanced resonance Raman spectroscopy (SHINERRS) is observed. This approach led to a perfect selection of SERS mechanisms never seen before with any other molecule/complex. As can be seen in the UV-vis spectrum, this complex has a strong band around 700 nm, which suggests that silica shell enhances only surface-enhanced resonance Raman scattering, a long-distance phenomenon, different from chemical enhancement (a short-distance phenomenon). Additionally, along with the Raman spectroscopy results, cyclic voltammetry, UV-vis spectroelectrochemistry, resonance Raman (using 568 and 676 nm lasers), and density functional theory calculations of this new ruthenium cluster are presented.

Spectroscopic and electrophoresis study of substitution on the surface of gold nanoparticles by different mercaptoalkyl carboxylic acids and bioconjugation with bovine serum albumin.

To develop bioconjugated materials, it is necessary to understand how the various elements present in a conjugate interact with one another. To gain insights into nanoparticle-capping agent-protein interactions, gold nanoparticles (AuNPs) measuring 30 nm in diameter were coated with different molecules bearing a thiol group: 3-mercaptopropionic acid, 6-mercaptohexanoic acid, and 11-mercaptoundecanoic acid. The covalent conjugation of AuNPs to the protein bovine serum albumin (BSA) via a cross-linker reaction with N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide was systematically investigated under different reaction conditions with variation of the concentrations of the mercaptoalkyl carboxylic acid (MA) and BSA. All the products were analyzed by UV-vis spectroscopy, gel electrophoresis, and Raman spectroscopy in every modification step. From analysis of the UV-vis results, it is possible at low concentrations of MA to see strong coupling among AuNPs, observed when they are aggregated by KCl, which does not happen at higher concentration of MA, indicating an AuNP-to-MA ratio of 1:130,000 is best for bioconjugation purposes. Agarose gel electrophoresis, a classic technique for biomolecule characterization, indicated that BSA is capable of altering the mobility of AuNPs when it modifies completely the surface of AuNPs because of its high molecular mass (around 66 kDa). Principal component analysis of surface-enhanced Raman spectroscopy data was successfully used as a chemometric tool to assist the characterization of the nanoparticle modification with linker molecules in the absence and presence of different BSA concentrations, making it possible to clearly evaluate the gradual substitution/modification of AuNPs (1:13,000 < 1:65,000 < 1:130,000 AuNP-to-MA ratio) and the conjugation with BSA, which is homogenous at a concentration of 0.01 g L-1. Graphical abstract.

Highly Pure Silica Nanoparticles with High Adsorption Capacity Obtained from Sugarcane Waste Ash.

Silica nanoparticles (SiO2NPs) from renewable sources can be used in very different materials, such as paints, membranes for fuel cells, Li-ion batteries, adsorbents, catalysts, and so on. Brazil is the world's largest producer of sugarcane and generates huge amounts of sugarcane waste ash (SWA), which is a Si-rich source. This study investigates a method to produce highly pure SiO2NPs from SWA. The SiO2NPs were characterized by inductively coupled plasma optical emission spectroscopy, scanning and transmission electron microscopy (TEM), X-ray diffraction analyses, specific surface area and pore distribution, UV and Fourier transform infrared spectroscopy, and thermogravimetric analyses and applied as an adsorbent material in the removal of acid orange 8 (AO8) dye from aqueous solution. The SiO2 content was 88.68 and 99.08 wt % for SWA and SiO2NPs, respectively. TEM images of SWA and SiO2NPs exhibit drastic alterations of the material size ranging from several micrometers to less than 20 nm. The SiO2NPs showed a specific surface area of 131 m2 g-1 and adsorption capacity of around 230 mg g-1 for acid orange 8 dye. Furthermore, the recycling of the SiO2NPs adsorbent after AO8 adsorption was very satisfactory, with reuse for up to five cycles being possible. The results indicate that it was possible to obtain highly pure silica in a nanosize from the waste material and produce an adsorbent with high adsorption capacity and the possibility of reuse.

Detection of Plasmon Coupling between Silver Nanowires Based on Hyperspectral Darkfield and SERS Imaging and Supported by DDA Theoretical Calculations.

We report the unprecedented observation of plasmon coupling between silver nanowires, showing how the surface-enhanced Raman scattering depends upon this interaction and how the spectrum can be shaped by the hot spot. Such observations were accomplished by Raman spectroscopy mapping of silver nanowires modified with rhodamine. The local spectra on the hot spots were measured by darkfield hyperspectral microscopy, a powerful but uncommonly used technique that is capable of determining the location, structure, and spectra of the hot spots. The result obtained by the simulation of two parallel nanowires based on the discrete dipole approximation (DDA) method was in excellent agreement with the results obtained experimentally.

Surface enhanced Raman spectroelectrochemistry of a µ-oxo triruthenium acetate cluster: an experimental and theoretical approach.

Surface enhanced Raman spectroelectrochemistry (SERS) spectroelectrochemistry provides a very sensitive technique to investigate the vibrational characteristics of coordination compounds and their particular behavior under the influence of plasmonic surfaces, concomitant with the exploitation of their redox properties and electronic spectra. The results, however, depend upon the mechanisms involved in the intensification of Raman spectra associated with the electromagnetic, resonance Raman and charge-transfer excitation at the Fermi levels. By probing the model complex [(Ru3O)(CH3COO)6(4,4'-bipy)3](n) (n = 1, 0, -1) adsorbed onto rough gold electrode surfaces, contrasting SERS profiles were obtained at several successive redox potentials and oxidation states, which enables a critical discussion on the role of the complex interaction with the gold surface, and the influence of the specific electronic bands in the triruthenium acetate cluster. Density functional theory (DFT) and time-dependent DFT calculations were carried out for the complex bound to an Au20 cluster to show the participation of active lowest unoccupied molecular orbital levels centered on the gold atoms. The corresponding charge-transfer band was predicted around 1200 nm, which supports a charge-transfer interpretation for the SERS response observed at λexc = 1064 nm. The selective enhancement of the vibrational modes was discussed based on the Raman theoretical calculations.

Pushing the surface-enhanced Raman scattering analyses sensitivity by magnetic concentration: a simple non core-shell approach.

A simple and accessible method for molecular analyses down to the picomolar range was realized using self-assembled hybrid superparamagnetic nanostructured materials, instead of complicated SERS substrates such as core-shell, surface nanostructured, or matrix embedded gold nanoparticles. Good signal-to-noise ratio has been achieved in a reproducible way even at concentrations down to 5×10(-11) M using methylene blue (MB) and phenanthroline (phen) as model species, exploiting the plasmonic properties of conventional citrate protected gold nanoparticles and alkylamine functionalized magnetite nanoparticles. The hot spots were generated by salt induced aggregation of gold nanoparticles (AuNP) in the presence of those analytes. Then, the aggregates of AuNP/analyte were decorated with small magnetite nanoparticles by electrostatic self-assembly forming MagSERS hybrid nanostructured materials. SERS peaks were enhanced up to 100 times after magnetic concentration in a circular spot using a magnet in comparison with the respective dispersion of the nanostructured material.

Exploring the coordination chemistry of isomerizable terpyridine derivatives for successful analyses of cis and trans isomers by travelling wave ion mobility mass spectrometry.

The photochemical cis-trans isomerization of the 4-{4-[2-(pyridin-4-yl)ethenyl]phenyl}-2,2':6',2''-terpyridine ligand (vpytpy) was investigated by UV-vis, NMR and TWIM-MS. Ion mobility mass spectrometry was performed pursuing the quantification of the isomeric composition during photolysis, however an in-source trans-to-cis isomerization process was observed. In order to overcome this inherent phenomenon, the isomerization of the vpytpy species was suppressed by complexation, reacting with iron(II) ions, and forming the [Fe(vpytpy)(2)](2+) complex. The strategy of "freezing" the cis-trans isomerizable ligand at a given geometric conformation was effective, preventing further isomerization, thus allowing the distinction of each one of the isomers in the photolysed mixture. In addition, the experimental drift times were related to the calculated surface areas of the three possible cis-cis, cis-trans and trans-trans iron(II) complex isomers. The stabilization of the ligand in a given conformation also allows us to obtain the cis-cis and cis-trans complexes exhibiting the ligand in the metastable cis-conformation, as well as in the thermodynamically stable trans-conformation.