Post-modification of nanoporous silica type SBA-15 by bis(3-triethoxysilylpropyl)tetrasulfide as an efficient adsorbent for arsenic removal

Synthesis of a core-shell magnetic covalent organic framework for the enrichment and detection of aflatoxin in food using HPLC-MS/MS

A porous magnetic covalent organic framework, Fe3O4@TPBD-TPA (terephthalaldehyde (TPA) , N, N, N', N'-tetrakis(p-aminophenyl)-p-phenylenediamine (TPBD)), was synthesized using the Schiff base reaction under mild reaction conditions. This adsorbent exhibited excellent adsorption performance for aflatoxins. The adsorption capacity of Fe3O4@TPBD-TPA for aflatoxins ranged from 64.4 to 84.4 mg/g. A magnetic solid-phase extraction combined with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method based on Fe3O4@TPBD-TPA was developed for the efficient determination of four types of aflatoxins in food samples (maize, maize oil, peanut, and peanut oil). The determination coefficients (R2) were ≥0.9972. The method exhibited detection limits ranging from 0.01 to 0.06 μg/kg and spiked recoveries of 80.0 to 113.1%. The intra-day and inter-day precision were less than 6.77%, indicating good repeatability. The adsorbent showed promising prospects for the efficient enrichment of trace amounts of aflatoxins in complex food matrices.

Removal efficiency of As(III) from aqueous solutions using natural and Fe(III) modified bentonites

Contamination of water with arsenic is a major global health problem. The use of adsorbent materials for the removal of As from aqueous systems is a plausible solution to this problem. In this work, the use of commercial bentonites (purified and modified with iron (III)) for the removal of As from water was studied. The samples were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier Transformed Infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and nitrogen adsorption/desorption isotherms to determine their physicochemical properties. The arsenic removal capacities of adsorbent materials were studied from 1 mg/L solutions of As (III) using the colorimetric technique of molybdenum blue. High adsorption capacity (0.33 mg/g) of As (III) was obtained in aqueous systems after 1 h of treatment with unmodified bentonite. The incorporation of iron improved the removal performance in short times. The obtained results could be the starting point for the development of a low-cost filtration system that contributes to solve the problem of arsenic in water.

Determination of cyanide based on a dual-emission ratiometric nanoprobe using silver sulfide quantum dots and silicon nanoparticles

A novel ratiometric fluorescent nanoprobe was designed for the sensitive determination of cyanide anion (CN^-) by the electrostatic attraction between positively charged silicon nanoparticles (Si NPs) and negatively charged silver sulfide quantum dots (Ag₂S QDs). The nanoprobe exhibited two well-resolved emission peaks at 446 nm and 540 nm under a single excitation wavelength (360 nm). In the presence of CN^-, the fluorescence of Ag₂S QDs at 540 nm was remarkably quenched, while the fluorescence of the Si NPs at 446 nm remained constant, establishing the desired conditions for ratiometric fluorescence detection. Under optimal conditions, the ratiometric fluorescence assay showed good linearity (R² = 0.9921) within the range 0.05-15 μM, and the limit of detection was calculated to be 56 nM (at an S/N ratio of 3). The proposed Ag₂S QD/Si NP nanoprobe has been successfully used to determine CN^- in water and sprouting potato samples with satisfactory recoveries in the range 97-110.5%.

On-site detection of As(III) based on silver nanoparticles aggregation mediated by phosphates using surface-enhanced Raman scattering (SERS)

A portable and simple method was developed for on-site selective determination of As(III) based on the SERS signal of As(III)-O vibration. The method relies on the synergistic effect of nanoparticles aggregation and analyte adsorption. Experimental results demonstrated that phosphate replaced the ligands of HH@Ag NPs, which in turn facilitated the adsorption of As(III) on the surface of HH@Ag NPs. The phosphate was introduced as an agglomerating agent to improve the detection ability of the method for As(III). The method shows good selectivity and linear relationship between 5 × 10^-8 and 0.8 × 10^-6 M, with the detection limit of 1.8 × 10^-9 M. The method was applied to actual water samples and successfully detected As(III), indicating that the method could have application potential in actual detection scenarios.

Guanidinylated SBA-15/Fe3O4 mesoporous nanocomposite as an efficient catalyst for the synthesis of pyranopyrazole derivatives

In this study, a novel mesoporous nanocomposite was fabricated in several steps. In this regard, SBA-15 was prepared by the hydrothermal method, next it was magnetized by in-situ preparation of Fe3O4 MNPs. After that, the as-prepared SBA-15/Fe3O4 functionalized with 3-minopropyltriethoxysilane (APTES) via post-synthesis approach. Then, the guanidinylated SBA-15/Fe3O4 was obtained by nucleophilic addition of APTES@SBA-15/Fe3O4 to cyanimide. The prepared nanocomposite exhibited excellent catalytic activity in the synthesis of dihydropyrano[2,3-c]pyrazole derivatives which can be related to its physicochemical features such as strong basic sites (presented in guanidine group), Lewis acid site (presented in Fe3O4), high porous structure, and high surface area. The characterization of the prepared mesoporous nanocomposite was well accomplished by different techniques such as FT-IR, EDX, FESEM, TEM, VSM, TGA, XRD and BET. Furthermore, the magnetic catalyst was reused at least six consequent runs without considerable reduction in its catalytic activity.

Molecular separation of ions from aqueous solutions using modified nanocomposites

Herein, two novel porous polymer matrix nanocomposites were synthesized and used as adsorbents for heavy metal uptake. Methacrylate-modified large mesoporous silica FDU-12 was incorporated in poly(methyl methacrylate) matrix through an in-situ polymerization approach. For another, amine-modified FDU-12 was composited with Nylon 6,6 via a facile solution blending protocol. Various characterization techniques including small-angle X-ray scattering, FTIR spectroscopy, field emission-scanning electron microscopy, transmission electron microscopy, porosimetry, and thermogravimetric analysis have been applied to investigate the physical and chemical properties of the prepared materials. The adsorption of Pb(II) onto the synthesized nanocomposites was studied in a batch system. After study the effect of solution pH, adsorbent amount, contact time, and initial concentration of metal ion on the adsorption process, kinetic studies were also conducted. For both adsorbents, the Langmuir and pseudo-second-order models were found to be the best fit to predict isotherm and kinetics of adsorption. Based on the Langmuir model, maximum adsorption capacities of 105.3 and 109.9 mg g-1 were obtained for methacrylate-modified FDU-12/poly(methyl methacrylate) and amine-modified FDU-12/Nylon 6,6, respectively.

Response surface methodological optimization of batch Cu(II) sorption onto succinic acid functionalized SiO2 nanoparticles

Functionalizing nanosilica (n-SiO2) particles with suitable active organic moiety leads to the formation of surfaces with precisely controlled physical and chemical characteristics. In this work, a novel nanosorbent (31 ± 2.4 nm), namely succinic acid functionalized nanosilica (n-SiO2@SA), was synthesized via a simple protocol using microwave irradiation to remove Cu(II) ions from aqueous media. The successful functionalization of n-SiO2 was confirmed by FTIR, and the thermal stability of n-SiO2@SA was investigated by TGA study. Other techniques, including HRTEM, DLS and zeta-potential, were utilized to investigate the chemical, surface, and morphological properties of the fabricated n-SiO2@SA. The response surface methodology (RSM) combined with three-level, three-factorial Box–Behnken design (BBD) was applied to optimize the multivariable sorption system using data obtained from 17 batch runs to reach 98.9% of Cu(II) ion removal. The predicted optimal conditions were as follows: contact time = 30 min, pH = 7.1, initial Cu(II) concentration = 317.5 mg L−1, and sorbent dose = 15 mg at which the maximum sorption capacities for n-SiO2 and n-SiO2@SA were 209.3 and 386.4 mg g−1, respectively, at 25 °C, thus supporting the validity of functionalization process. Non-linear regression and linear least-squares methods confirm the suitability of Langmuir model to describe the experimental endothermic, feasible, and chemisorption data, whereas the normalized standard deviation Δq% recommends the pseudo second-order kinetic model to represent the kinetic data. Real Cu-contaminated wastewaters were used to examine n-SiO2@SA nanosorbent for removing Cu(II) ions.

Applications of SBA-15 supported Pd metal catalysts as nanoreactors in C-C coupling reactions

Nanoreactors are material structures with engineered internal cavities which create exclusive confined nanoscale surroundings for chemical reactions. The cavities of mesoporous silica SBA-15 can be used as nanoreactors for incorporating catalytic species such as metal nanoparticles, complexes etc. Since SBA-15 silica has a neutral framework, organic functional groups and heteroatoms have been embedded by direct or post-synthesis approaches in order to modify their functionality. Palladium is the most used transition metal for C-C bond formations. Because of the great importance of C-C coupling reactions, this review article aims at providing a deep insight into the state of art in the field of the synthesis and the application of mesoporous SBA-15 silica-supported Pd catalysts in C-C coupling transformations. In most cases, synthesis and modification of the catalyst, time and yield of reactions, recyclability and leaching of the Pd species from the SBA-15 support are discussed to reveal the role of SBA-15 in C-C coupling reactions.

Pre-concentration of Zn(II) ions from aqueous solutions using meso-porous pyridine-enrobed magnetite nanostructures

A simple, cheap and efficient method for pre-concentrating and separating Zn(II) ions from aqueous solutions and real samples has been designed. The method was implemented in a prototype featuring interchangeable chromatography-column-like cartridges, filled with meso-porous silica nanostructures, allowing easy exchange of the type and quantity of the sorbent. The adsorbents inside the column are held in place by means of porous polymer nano-fibre membranes. The effects of various parameters on the adsorption of Zn(II) ions from aqueous solutions were investigated. Maximal adsorption (∼99%) was found for Zn(II) ions amongst a mixture of Cu(II), Co(II), Ni(II), Ag(I), Au(III), Pd(II) and Pb(II) in aqueous solution. The procedure was tested for pre-concentrating and determining traces of zinc in real samples of meat, fish and hen marketed in Tehran. A desorption process using 0.5 mol L-1 HCl as eluent, showed ∼97% recovery of the Zn(II) ions adsorbed on the MSMPP sorbent.

Palladium‐anchored multidentate SBA‐15/di‐urea nanoreactor: A highly active catalyst for Suzuki coupling reaction

Modification of mesoporous silica was carried out by reaction of SBA‐15 with di‐urea‐based ligand. Next, with the help of this ligand, palladium ions were anchored within the multidentate SBA‐15/di‐urea pore channels with high dispersion. The SBA‐15/di‐urea/Pd catalyst was characterized using various techniques. Theoretical calculations indicated that each palladium ion was strongly interacted with one nitrogen and two oxygen atoms from the multidentate di‐urea ligand located in SBA‐15 channels and these interactions remained during the catalytic cycle. These results are in good agreement with those of hot filtration test: the palladium ions have very high stability against leaching from the SBA‐15/di‐urea support. The catalytic performance of SBA‐15/di‐urea/Pd nanostructure was examined for the Suzuki coupling reaction of phenylboronic acid and electronically diverse aryl halides under mild conditions with a minimal amount of Pd (0.26 mol%). Compared to previous reports, this protocol afforded some advantages such as short reaction times, high yields of products, catalyst stability without leaching, easy catalyst recovery and preservation of catalytic activity for at least six successive runs.