Synthesis of Alkoxysilylated Humic Derivatives with Different Modification Rate Capable of Self-Adhering to Mineral Surfaces (original) (raw)
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Attachment of two distinct humic acids onto a silica gel surface
Colloids and Surfaces A-physicochemical and Engineering Aspects, 2004
A method for the attachment of two different humic acids onto silica gel has been developed. In the first step, the precursor was prepared by reacting the silylant agent 3-aminopropyltrimethoxysilane (APTS) with silica gel. Elemental analysis of the product showed the presence of 1.23 mmol of silylant agent per gram of support. Humic acid extracted from peat soil, HA PS , and commercial humic acid, HA FL , were connected by hydrogen bonds to the amine groups previously anchored onto silica gel, producing new materials named SiHA PS and SiHA FL , with 84.7 ± 0.04 and 101.7 ± 0.04 mg of humic acid per gram of modified silica for SiHA PS and SiHA FL , respectively. Thermogravimetry, infrared, 13 C and 29 Si CP/MAS-NMR spectra have confirmed the success of the attachment and the scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) technique showed a good dispersion of the humic acids onto modified silica surface for both materials.
ACS applied materials & interfaces, 2016
Humic acids (HAs) are ubiquitous macromolecules in the environment. Due to their high contents of oxygenated functional groups, they can interact with contaminants present in the natural environment and therefore influence the behavior of pollutants. However, a pH of 2 or lower is required to maintain HAs in the solid form. To increase the stability of HAs and their capacity to bind to contaminants, this work proposes the development of new hybrid materials based on alkoxysilanes and HAs for environmental applications such as dye adsorption. Three different materials with new functional groups were prepared by employing the following alkoxysilanes: tetraethyl orthosilicate, (3-aminopropyl)triethoxysilane, and N-[3-(trimethoxylsilyl)propyl]ethylenediamine. The final materials were denoted HWA, HOA, and HTA, respectively, and they were characterized by elemental analysis, diffuse reflectance Fourier-transform infrared spectroscopy (DRIFT), small-angle X-ray scattering (SAXS), scanning...
Alkoxysilylated humic derivatives were used to create covalently bound humic coatings on silica gel. The corresponding reaction was conducted in an aqueous milieu that was feasible due to the water solubility of these derivatives. The alkoxysilylated humic derivatives were obtained by alkoxysilylation of leonardite humic acid (HA) and hydroquinone-modified HA (HQ) with enhanced redox properties. The silica gel coated with covalently bound HA and HQ was tested for sequestration of aqueous Np(V) and Pu(V) under anaerobic conditions. Greater sequestration with respect to Pu(V) (up to 97%) as compared to Np(V) (up to 60%) was demonstrated for samples of silica gel coated with HA and HQ, whereas sorption of both actinides on pure silica gel did not exceed 20%. Results provide bench-scale proof that alkoxysilylated humic derivatives can be used as reagents for the in situ installation of permeable reactive barriers designed to remediate actinide-contaminated groundwater.
Synthesis, Metal-Binding Properties and Detoxifying Ability of Sulphonated Humic Acids
The complexing properties of humic substances are of primary importance for their application as detoxifying agents and microfertilizers. The promising approach for enhancing solubility of metal-humics complexes is incorporation of SO3H-groups into the structure of humics. The water soluble sulphonated humic materials can be used as flushing agents for heavy metal polluted sites and as chelating agents for production of microfertilizers. The objectives of this study were: 1) to synthesize sulphonated humic materials; 2) to evaluate solubility and stability of their complexes with Fe(III) and Hg(II); 3) to assess potential toxicity and detoxifying properties of the sulphoderivatives with respect to Hg(II) and Cu(II). Humic acids (HA) from leonardite and peat were used for modification. Concentrated sulphuric acid and chlorosulphonic acid were used as sulphonating agents. Chlorosulphonic acid was found to be much more efficient sulphonating agent causing introduction of 1.6 and 0.4 mm...
Chemical immobilisation of humic acid on silica
Immobilisation of purified Aldrich humic acid (PAHA) on aminopropyl silica and glutaraldehyde-activated aminopropyl silica has been investigated. In general the humic acid is bound to the solid by both physical and chemical bonds. The physically adsorbed HA can be released to a large extent at high pH. To minimise physical adsorption, the samples are thoroughly washed using a 1 M sodium chloride solution of pH 10 and the free amino groups of the aminopropyl silica are end-capped. The amounts of PAHA bound, the charge density-pH curves, isoelectric points (ieps), FT-IR spectra and the stability-pH curves of the products are determined. The amounts of PAHA bound to the aminopropyl silica range from 42 to 72 mg HA (g SiO 2 )-1, depending on the method of preparation. The products have low ieps and are stable in a wide range of pH. The amount of PAHA bound on the glutaraldehyde-activated aminopropyl silica is 16 mg HA (g SiO 2 )−1 and the product has an iep value at pH 7.3, which is rather different from that of naturally occurring HA.
CATENA, 2016
In this study we successfully enhanced surface activity of natural humic substances (HS) with respect to mineral surfaces by functionalization with organosilanes. Of particular importance was that modification was conducted in water. Humates from coal and peat and 3-aminopropyl-triethoxysilane (APTES) were used as starting materials. Atomic force microscopy showed silanized HS produced self-assembled adsorption monolayers at the water-solid interface. These adlayers caused an increase in the surface hydrophobicity with contact angles equaling 56°. Application of silanized HS for treatment of different soil compartments including mineral soil separates and soil aggregates revealed an efficacy with respect to both re-assembly of soil aggregates and restoration of their water stability. Furthermore, field trials on the treatments of native sod-podzolic soil with silanized HS indicated improvements in soil structure as compared to non-treated soil or treatment with the non-functionalized humate. Results demonstrating the use of silanized HS as ecologically-safe, nature-inspired soil conditioners were promising.
Aminopropyl-Silica Hybrid Particles as Supports for Humic Acids Immobilization
Materials, 2016
A series of aminopropyl-functionalized silica nanoparticles were prepared through a basic two step sol-gel process in water. Prior to being aminopropyl-functionalized, silica particles with an average diameter of 549 nm were prepared from tetraethyl orthosilicate (TEOS), using a Stöber method. In a second step, aminopropyl-silica particles were prepared by silanization with 3-aminopropyltriethoxysilane (APTES), added drop by drop to the sol-gel mixture. The synthesized amino-functionalized silica particles are intended to be used as supports for immobilization of humic acids (HA), through electrostatic bonds. Furthermore, by inserting beside APTES, unhydrolysable mono-, di-or trifunctional alkylsilanes (methyltriethoxy silane (MeTES), trimethylethoxysilane (Me 3 ES), diethoxydimethylsilane (Me 2 DES) and 1,2-bis(triethoxysilyl)ethane (BETES)) onto silica particles surface, the spacing of the free amino groups was intended in order to facilitate their interaction with HA large molecules. Two sorts of HA were used for evaluating the immobilization capacity of the novel aminosilane supports. The results proved the efficient functionalization of silica nanoparticles with amino groups and showed that the immobilization of the two tested types of humic acid substances was well achieved for all the TEOS/APTES = 20/1 (molar ratio) silica hybrids having or not having the amino functions spaced by alkyl groups. It was shown that the density of aminopropyl functions is low enough at this low APTES fraction and do not require a further spacing by alkyl groups. Moreover, all the hybrids having negative zeta potential values exhibited low interaction with HA molecules.
Metal-modified silica adsorbents for removal of humic substances in water
Journal of Colloid and Interface Science, 2005
As novel adsorbents for humic substances, Fe-, Mg-, and Ca-modified silica gels SiO 2-Fe, SiO 2-Mg, and SiO 2-Ca were prepared, and their adsorbabilities to humic and fulvic acids were evaluated in water at 25 • C for 20 h. Among these adsorbents, SiO 2-Fe indicated the highest adsorbability, in which removing humic substances in water was accomplished to 80-97%. By calcination at 600 • C and washing with water, adsorbabilities of the silica adsorbents deteriorated except for the case of calcination of SiO 2-Ca. This is due to changing metal modification structures and losing chlorine, judging from elemental analysis, TG-DTA, and XPS. Especially, the modifier Fe was tightly fixed on the silica surface of SiO 2-Fe, since the metal content was almost constant even after the calcination and water washing unlike the other adsorbents. Therefore, we found that SiO 2-Fe is the most useful adsorbent among the silica adsorbents and that its modification structure is composed of Si-O-Fe, Fe-Cl, and Fe-OH. In addition, the adsorption mechanism is explained by an interaction between Fe and humic substance molecule having carboxylate and phenolate groups, accompanied with anion exchange of chloride ion Cl − for the humic substance molecule via the silica pores. SiO 2-Fe may be applied to an adsorbent alternative for charcoal in water purification plants, and the used SiO 2-Fe may be further reused as a fertilizer since humic substances have plant-glowing ability and silica strengthens plant parts.