SPECIFICATION FIELD OF APPLICATION

The present invention refers to the removal of anions, such as arsenates, nitrates and phosphates from the drinking and industrial water, through the use of silica microparticles and/or nanoparticles with their surface modified with groups of guanidine.

BACKGROUND

During the last years, the discharge of anions as perchlorate (CKV), nitrate (NO3 ), phosphate (HPO4 ) and arsenate (HAsCV ) in surface and ground waters has had a significant impact on the quality of water and the human health.

An important contaminant of water is arsenate, which can be found at high and low concentrations as a consequence of the natural contamination of mountains or the mining industry in other cases.

Unlike domestic wastewater, the industrial effluents frequently contain chemical substances that are not eliminated through standard treatments, both by being at high concentrations or due to their chemical nature. Many of the chemical compounds already detected in industrial wastewaters are the object of special regulations due to their toxicity or long-term biological effects. Among the contaminants present in the water generated by the industries, the aforementioned inorganic anions can be found, which generate a negative impact on the health of world population. and bladder cancer, as well as neurological disorders, loss of appetite, nauseas, changes in pigmentation, and hyperkeratosis in human beings. Natural waters in general contain low levels of total arsenic, which is present in two different ionic states, pentavalent arsenate (As V) and/or trivalent arsenite (As III) within the concentration range of 1-10 pg/L.

As a result of the mining activity, in northern Chile water with high levels of arsenic can be found, this being why different technologies had to be implemented in order to provide drinking water with levels of arsenic allowed (< 0.01 ppm).

Additionally, the current advances in nanotechnology have made possible the development of new materials to be used in different areas, such as electronics, pharmaceutical, cosmetics, agriculture and environment. Due to the impact generated by this technology in the last decade, the economic investment has been increased in this are to strengthen the development, mainly, and the improvement of new materials.

Despite there are several types of nanomaterials, those generating greater interest are carbon nanotubes (CNTs) and nanoparticles (NPs) from silica metal and nonmetal oxides (S1O2), titanium (T1O2), cerium (CeC^), silver (Ag/Ag ₂ 0), among others.

The use of microparticles and nanoparticles in the environmental area, specifically in the cleanup of industrial waters, has produced great expectations, since they represent viable, nontoxic and efficient strategies. Various nanomaterials have been studied in order to be potentially used in the treatment of effluents coming from the industry, and some of the most studied ones are shown in

Table 1.

Despite the great variety of materials, the metal and nonmetal oxide NPs undoubtedly show key properties, which make them particularly attractive for their use in the treatment of residual water; they have a great surface area that can be chemically modified to increase their affinity to the compounds of interest. In addition, several studies have verified that these NPs show a great capacity to adsorb metal ions and anions in their structure.

In order to reduce the presence of oxyanions, such as arsenates and phosphates in drinking water, there are several proposals using various types of nano materials, allophane nanoclays and functionalized dendrimers, among others, which show high selectivity due to the combination of their capacity of hydrogen bond and electrostatics.

Mesoporous silica in particular has attracted significant interest due to its capacity of adsorbing compounds in a reversible way. This material provides a great surface and a great volume of properties.

The synthesis of several nanomaterials has been reported to be used in the removal of heavy metal cations from wastewaters, mainly focusing on Ni ²⁺ , Cu ²⁺ , Cd ²⁺ y Cr ⁴⁺ .

The patent document US9683163 discloses a process to remove a particle of asphaltene in a substrate; to this effect, silicate nanoparticles are used modified with a chemical group having two portions: a first part bonded to the nanoparticle and a second one having an aromatic group. The publication of Fallahi et al (Dig. J. Nanomater. Bios., Vol. 11, No. 3, 2016, p. 853-863) describes Fe ₃ 0 ₄ nanoparticles modified with guanidine and its use in the absorption of heavy metal ions, such as Pb, Cd, Zn and Cu. The results showed that the use of these modified nanoparticles was relatively selective, simple, fast, of low cost and respectful of the environment, thus a good factor of preconcentration been obtained in a wide dynamic linear range.

Birnbaum et al (Birnbaum, E. R.; Rau, K. C; Sauer, N. N. Selective Anion Binding from Water Using Soluble Polymers. Separation Science and Technology 2003, 38, 389-404) have described use of amino-terminated nanoparticles (dendrimers) for recovery anions such as FlAsCU , CrCU and HPO ₄ . Diallo also reported the characterization of amino-terminated dendrimers on binding of perchlorate (CIO ₄ ) anions (13) (Diallo, M. S.; Falconer, K.; Johnson, J. H., Jr; Goddard, W. A., 3rd Dendritic anion hosts: perchlorate uptake by G5-NH2 poly(propyleneimine) dendrimer in water and model electrolyte solutions. Environ. Sci. Technol. 2007, 41, 6521-6527). Those evidence support the conjugation of nanoparticles with positively charged groups to remove anions.

However, the development of nanomaterials allows being efficient for the removal of anions is still an emerging field. There is the need of having new systems allowing the removal of this kind of compounds efficiently and at low cost in turn. The present invention provides a method and device for the cleanup of waters focused on the removal of anions, such as arsenates, nitrates and phosphates.

The device comprises the incorporation of functionalized particles with guanidine groups on its surface.

BRIEF DESCRIPTION OF FIGURES

Figure 1: Infrared spectrum of: a) 4-guanidinobutyric acid; b) Np Si0 ₂ -propylamine; c) NpSiC bisguanidine; d) Np S monoguanidine.

Figure 2: ¹ H-N R spectrum of S1O2 nanoparticle functionalized with guanidine dissolved in

D ₂ 0.

Figure 3: a) (outside) SEM micrograph of S1O2 mono-guanidine nanoparticle; b) (inside) EDX spectrum analyzed in the box.

Figure 4: a) (outside) SEM micrograph of S1O2 bisguanidine nanoparticle; b) (inside) EDX spectrum analyzed in the box.

DETAILED DESCRIPTION OF THE INVENTION

The present invention refers to nanoparticles and microparticles of silica modified on their surface with one or more guanidine groups.

Specifically, these modified particles are formed by a silica dioxide (S1O2) core having guanidine groups functionalized in first and second generation dendrons on the surface.

The first generation dendrons correspond to molecules with just one branching, and the second generation ones show a second branching over the first one.

The structures (I) and (II) represent a first generation and a second generation dendron respectively.

(D The incorporation of these surface groups provides selectivity to nanoparticles and to microparticles before the toxic oxianions mentioned above.

The selection of the guanidine group is based on studies showing the interaction existing between the arginine aminoacid and the DNA phosphates and other nucleotides.

The interaction between inorganic and organic compounds through the physical force and the chemical bond is important as a method to control the structure and properties of the inorganic- organic meso structured materials. The modification of the terminal groups is a technique used to change the structural or physical-chemical properties of nanoparticles, such as the size of the internal cavities and the protonation states, among others. In particular, the bonding of a molecule to a nanoparticle can be attributed to several aspects, such as the formation of hydrogen bonds, free energy, cavities in the nanoparticle, electrostatic interactions, among others.

The present invention refers to the functionalization method of the surface of inorganic microparticles and nanoparticles using organic compounds that modify it in the desired way in order to provide affinity thereof to the arsenic species.

The functionalization of the surface is performed on nanoparticles and microparticles of S1O2 propylamine, which in turn contribute with an internal cavity of the mesoporous silica housing anionic and hydrophobic species.

Likewise, the present invention refers to the method of preparation of these functionalized microparticles and nanoparticles. from drinking water and industrial waters by using said functionalized particles.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention refers to silica particles with functionalized surface comprising the incorporation of at least one guanidine group.

In one embodiment of the invention, the functionalized silica particles comprise the incorporation of a guanidine group.

In another embodiment of the invention, the functionalized silica particles comprise the incorporation of two guanidine groups (bisguanidine).

In a preferred embodiment of the invention, the functionalized silica particles have a particle size within the range of 200 nm to 1.25 pm.

The present invention also refers to a method of preparation of functionalized silica particles with a guanidine group comprising the stages of:

i) providing particles of aminopropylated S1O2;

ii) suspending the particles in organic solvent;

iii) adding 4-guanidine butyric acid to the suspension;

iv) adding dicyclicohexylcarbodiimide dissolved in organic solvent;

v) stirring the suspension for at least 24 hours;

vi) centrifuging the suspension obtained, settling the supernatant, washing the functionalized particles and drying.

The present invention also discloses a method of preparation of functionalized silica particles with a bisguanidine group comprising the stages of:

i) providing particles of aminopropylated S1O2;

ii) suspending the particles in organic solvent;

iii) adding 2,2-bis(hydroximethyl) propanoic acid to the suspension; v) stirring the suspension for at least 24 hours;

vi) centrifuging the suspension obtained, settling the supernatant, washing the functionalized particles and drying.

Likewise, the present invention provides a method to remove anions from drinking water or industrial waters comprising getting the functionalized silica particle in contact with the water to be treated.

In one embodiment of the invention, in the method to remove anions from effluents, the anions are selected from arsenates, phosphates, nitrates and perchlorates.

In another preferred embodiment of the invention, in the method to remove anions from drinking water or industrial waters, the contact is performed inside a device where the functionalized silica particles are arranged.

Additionally, the present invention discloses a device to remove anions from drinking water or industrial waters comprising the functionalized silica particles arranged inside, preferably the device is any matrix or water filtration unit.

Finally, the present invention refers to the use of functionalized silica particles for the removal of anions from drinking water or industrial waters.

EXAMPLES

1) Preparation of the functionalized mesoporous nanoparticles with guanidine groups For the performance of the synthesis, aminopropylated SiCL nanoparticles (0.5 g) were used as starting point, which size can be found within the range of 200 nm to 1.25 pm. These nanoparticles were suspended with dimethylformamide (DMF) (10 mL) at a stirring speed of 600 rpm (magnetic stirrer). Then, 4-guanidine butyric acid (4GB A) was added (0.290 g) and diaminepropylpyridine p-toluenesulfonate (DPTS) (0.235 g). Dicyclicohexylcarbodiimide (DCC) was added to the suspension drop by drop (0.454 g) dissolved in DMF (5 mL). The tightly closed.

The suspension obtained in the previous reaction was centrifuged at 8000 rpm for 5 minutes. The supernatant was discarded by settling, the solid suspended in 15 mL of DMF, and centrifuged at 800 rpm again for 5 minutes, repeating this operation in order to suspend the solid in 15 mL of ethanol and centrifuge at 8000 rpm for 15 minutes; this operation was repeated three times. The nanoparticles obtained are dried in a vacuum furnace at room temperature.

Scheme 1 shows the synthesis:

2) Preparation of the functionalized mesoporous nanoparticles with hydroxyl groups

The same procedure of the preceding example was performed, but using the following reagents in the amounts indicated for each case: functionalized nanoparticles of aminopropyl (0.500 g),

2,2-bis(hydroximethyl) propanoic acid (bisMPA) (0.348 g), DPTS (0.235 g) and DCC (0.454 g).

Scheme 2 shows the reaction involved: 3) Preparation of the functionalized mesoporous nanoparticles with bisguanidine groups

The same procedure of the first example was performed using the following reagents and amounts: nanoparticles functionalized with hydroxyl (0.300 g), 4GBA (0.300 g), DPTS (0.235 g) and DCC (0.230 g).

Scheme 3 shows the synthesis:

Characterization of functionalized nanoparticles

The structures of mesoporous nanoparticles and microparticles of S1O2 functionalized with a guanidine group and a bisguanidine group were characterized by ATR-FT-IR, RMN 1H, RMN

13C and MEB. Table 1 shows the signals in the infrared spectrum giving account of the incorporation of guanidine groups.

Table 1

Figure 1 shows the representative signals of the incorporation of guanidine groups to Si0 ₂ nanoparticles and microparticles.

1H RMN and 13C RMN spectroscopy

Figure 2 shows the 1H-NMR spectrum of S1O2 functionalized nanoparticles with guanidine dissolved in D2O. The hydrogens of methylene groups of C3 and C8 carbons are observed as triplets at 3.10-3.14 ppm and are integrated for 4 hydrogens, while the doublet observed at 2.20- 2.17 ppm (J = 8.0 Hz, J = 4.0 Hz) corresponds to 4 hydrogens of Cl and C6 methylene groups. The hydrogens of C2 and C7 are observed as coupled doublets integrated for 4 hydrogens at C5 group is observed at 174.44 ppm, as well as CIO carbon of C=N group at 99.88 ppm, the carbons of C3 and C8 methylene at 40.76 ppm; the signal appearing at 33.90 ppm corresponds to Cl and C6 carbons, while the carbons of C2 methylene appear within the range of 20 ppm.

Additionally, in the ¹ H-RMN spectrum of S1O2 nanoparticles with two guanidine groups, the hydrogens of the guanidine groups are observed at 6.67 ppm and are integrated for 11 hydrogens; the hydrogens of the methylene groups of C30 and C24 carbons are observed as multiples at 3.12 ppm and are integrated for 4 hydrogens, while the singlet observed at 2.92 ppm corresponds to 2 C17 hydrogens; at 2.85 ppm there appears another singlet integrated for 2 hydrogens and corresponds to C13 methylene. The hydrogens of the methylene groups of C22 and C28 carbons are observed as multiples at 2.28-2.14 ppm and are integrated for 4 hydrogens. At 1.70, there appears an integration multiple for two hydrogens associated with C7; at 1.22 ppm there is a“gown” integrated for 6 signals of hydrogen overlapped with the three hydrogens of C21 methyl group. The hydrogens of C23 and C29 methylene are observed as a multiple integrated for 4 hydrogens at 0.81 ppm. In the spectrum of 13C RMN, the carbonyls of the esther groups are observed at 195.49 ppm and 195.04 ppm and correspond to C19 and C15 carbons, respectively; the carbonyl of the CIO amide group is observed at 174.44 ppm, while the C26 and C32 carbons of the C=N groups of the guanidine groups are observed at 100.0 ppm.

Morphology of nanoparticles

The image from a scanning electron microscope (SEM) of functionalized S1O2 nanoparticles with one or two guanidine groups provides information on the morphology of the surface, the form, the size distribution and the presence of amorphous material.

In this case, the micrography through SEM shows that the synthesis method used allows obtaining nanoparticles and microparticles with a mainly spherical morphology, at a scale of 5 mih have a spherical structural form.

Figure 3 b) (inside) shows an energy-dispersive X-ray spectroscopy (EDX) spectrum that indicates the percentage of elements present on the surface, observing that this functionalized nanoparticle is made up by 46% carbon, 32.8% oxygen, 11.4% silicon, and 8.2% nitrogen.

Figure 4 a) shows the box where the SEM analysis of SiCF with two guanidine groups has been made, with the scale having been increased up to 2.5 pm in order to better observe the variation of the spherical morphology, preferably agglomerated.

In the semi-quantitative analysis of the elements of this modified nanoparticle, it is observed that the surface is made up by 39.9% carbon, 37.7% oxygen, 8.2% silicon, and 13.9% nitrogen, which gives account of the increased presence of nitrogen and oxygen, this indicating the incorporation of bisguanidine to the S1O2 nanoparticle.

Arsenate removal method

The experimental design considered the removal of arsenic at three different pH (3, 7 and 10), considering three different times of adsorption (1, 14 and 28 hours), using a fixed mass of 10 mg and a fixed volume of 10 mL, with each sample made in duplicate for the functionalized silicon nanoparticle with one guanidine group.

The presence of arsenic in all samples was determined using the ICP-MS (Inductively Coupled Plasma Mass Spectrometry) technique and it was determined as total arsenic.

The results obtained for each sample are shown in Table 2.

The results shown in Table 2 demonstrate that nanoparticles functionalized with guanidine groups have a high affinity for arsenate.

The removal of arsenic from the samples is always greater than or equal to 99.5%, regardless of the pH of the sample. economic solution to remove anions as arsenates, phosphates and nitrates present in industrial effluents.

The preceding specification is provided for illustrative purposes only and is not intended to describe all possible aspects of the present invention. While the invention has been herein shown and described in detail as regards several exemplary embodiments, the experts of the art will note that minor changes to the description and several other modifications, omissions and additions can be made without departing from the spirit and scope thereof.