AU2021102663A4

AU2021102663A4 - Modified nano-sio2 spike material for turbidity of water treatment unit and preparation method thereof

Info

Publication number: AU2021102663A4
Application number: AU2021102663A
Authority: AU
Inventors: Hongmei Fan; Cuiling Gao; Jie Guan; Xiangke He; Xiaohui Peng
Original assignee: Shandong Institute for Product Quality Inspection
Current assignee: Shandong Institute for Product Quality Inspection
Priority date: 2020-10-30
Filing date: 2021-05-18
Publication date: 2021-07-08
Anticipated expiration: 2029-05-18
Also published as: CN112326383B; CN112326383A

Abstract

The present disclosure belongs to the technical field of reference material preparation, and particularly relates to a modified nano-SiO2 spike material for turbidity of a water treatment unit and a preparation method thereof. The spike material is modified nano-SiO2 subjected to a modification, and the SiO2 is in a form of spherical particle and has an average particle size of 100 to 500 nm. According to the present disclosure, the modification is carried out under a synergistic action of 3-Chloropropyl trimethoxysilane and hydrochloric acid, so that an acting force between hydroxyl groups on a surface of the nano-SiO 2 is reduced, a clear particle surface is formed, the agglomeration of the nano-SiO2 is prevented, and good standing stability is achieved. There is a good linear relationship between a concentration of a modified nano-SiO 2 solution prepared in the present disclosure and turbidity, so the modified nano-SiO 2 solution has the characteristics of being used as a spike material for turbidity of a water treatment unit. Modified nano-SiO2 aqueous solution with different particle sizes may be prepared according to requirements of filter elements of different precisions, and the controllability of the particle size is high. The modified nano-SiO2 solution prepared in the present disclosure has no effect on oxygen consumption and a pH value of water. 1/5 WD 8,6 .~ M~g~ 5CO KX T~~~4WD S- W a~ S0O KX Tm:92325 (a) Unmodified SiO 2 (b) Modified SiO 2 Fig.1I 130 1o 2 100 0 so 30 10 -0 3000 2000 1000 ______________________________________Wave nmber(,r-Vl_______________________ Fig. 2

Description

1/5

WD 8,6 .~ M~g~ 5CO KX T~~~4WD S- W a~ S0O KX Tm:92325

(a) Unmodified SiO 2 (b) Modified SiO 2 Fig.1I

130

1o 2

100

0

so

30

10

-0

3000 2000 1000 ______________________________________Wave nmber(,r-Vl_______________________

Fig. 2

MODIFIED NANO-SIO2 SPIKE MATERIAL FOR TURBIDITY OF WATER TREATMENT UNIT AND PREPARATION METHOD THEREOF

Field of the Invention

The present disclosure belongs to the technical field of reference material preparation, and particularly relates to a modified nano-Si02 spike material for turbidity of a water treatment unit and a preparation method thereof.

Background of the Invention

Turbidity is an important physical indicator to characterize a turbid degree of water. The turbidity of the source water is caused by an optical scattering or absorption behavior of a suspended matter, a colloidal matter or both. Household and similar water purification devices can eliminate threats of surface water pollution, tap water disinfection by-products, and secondary pollution of water pipelines to residents' drinking water. In order to standardize the inspection of products related to drinking water hygiene safety and strengthen the supervision and management of the quality of water treatment units, the Ministry of Health formulated the "Regulations on Inspection of Products Related to Drinking Water Hygiene Safety of the Ministry of Health" in 2001. According to the regulations, in hygiene safety and hygiene function tests of water delivery and distribution equipment (pipes, pipe fittings, water storage containers, and water stop materials), protective materials (coatings, linings, etc.), water processing materials, and general water treatment units that are in contact with drinking water, test for turbidity is required. Spike tests for turbidity are required for general water treatment units such as activated carbon filter elements and membrane filter assemblies, but a spike material for turbidity and its preparation method are not specified in the regulations. Testing organizations use different spike materials in test of the turbidity of the general water treatment units according to the "Regulations on the Inspection of Products Related to Drinking Water Hygiene Safety of the Ministry of Health", which results in a great difference in test results, so it is impossible to make an objective judgment on the performance of the water treatment units. According to the national standards QB/T 4143-2019 "Household and Similar General Water Treatment Units" and QB/T 4144-2019 "Household and Similar Pure Water Treatment Units" promulgated by the Ministry of Industry and Information Technology in 2019, 25 NTU Formazin solutions are provided as spike materials for turbidity test of the water treatment units and the pure water treatment units. As a non-uniform suspension system, the Formazin suspension is in an unstable suspension state and has obvious shortcomings during use.

Formazin turbidity reference material is a commonly used reference material for turbidity. During preparation, different environmental temperature may lead to different particle sizes, and different storage time and temperature of the storage environment cause the particle size to change continuously, which results in uncontrollable particle size of the Formazin in the suspension. Due to the large particle size and fast settlement rate in the Formazin solution, particles in the Formazin solution will settle to form a relatively great concentration difference after a period of time, leading to poor standing stability. In the spike test of the water treatment unit, a desired spike material that can make a concentration of a spiked object meet a standard requirement without change of other physical and chemical indicators of water, and has certain stability and a reasonable turbidity removal rate is required. In the prior art, there is no relevant record of using modified silicon dioxide as a spike material for turbidity of a water treatment unit.

Summary of the Invention

Aiming at the problems existing in the prior art, the present disclosure provides a modified nano-SiO2 spike material for turbidity of a water treatment unit.

The present disclosure further provides a preparation method of a modified nano-SiO 2 spike material for turbidity of a water treatment unit.

In order to achieve the above objectives, the present disclosure adopts the following technical solutions:

the present disclosure provides a modified nano-SiO2 spike material for turbidity of a water treatment unit, wherein the SiO2 is in a form of spherical particle and has an average particle size of 100 to 500 nm.

The present disclosure further provides a preparation method of a modified nano-SiO 2 spike material for turbidity of a water treatment unit, characterized by including the following steps:

(1) weighing and dissolving nano-SiO 2 in absolute ethanol, and performing ultrasonic oscillation and then magnetic stirring on the mixture to obtain a silicon dioxide ethanol solution for later use;

(2) adding 3-Chloropropyl trimethoxysilane to the dispersed nano-SiO 2 ethanol solution for reaction in a thermostatic water bath, adding an appropriate amount of hydrochloric acid at an volume concentration of 3% to the mixture for a subsequent reaction, constantly stirring the mixture during the reaction, performing centrifugal separation on the mixture after the reaction is finished, washing the mixture 3 times with absolute ethanol, performing vacuum drying on the mixture, weighing and adding an appropriate amount of the modified nano-SiO 2 powder to level 3 water, and performing ultrasonic dispersion on the mixture for 1 hour to prepare a spiked solution.

Further, at step (1), a ratio of the nano-SiO 2 to the absolute ethanol is 1 g : 30 mL.

Further, at step (1), the time of the ultrasonic concussion and the time of the magnetic stirring are both 60 min.

Further, at step (2), a mass ratio of the 3-Chloropropyl trimethoxysilane to the nano-SiO 2 is (2-3): 1.

According to the preparation method provided by the present disclosure, reacting in the thermostatic water bath is performed at 85°C for 0.5 h.

Further, an addition amount of the hydrochloric acid is 1 mL for each 1 g of the nano-SiO 2 .

During the above reaction, the appropriate amount of hydrochloric acid at the concentration of 3% is added for the subsequent reaction for 3.5 h.

Further, the vacuum drying is drying at 55°C for 8 h.

The present disclosure further provides an application of nano-SiO 2 prepared by the above preparation method as a spike material for turbidity of a water treatment unit.

According to the present disclosure, a nano-silicon oxide powder with a controllable particle size is taken as a substrate, the dispersity and stability of the nano-silicon oxide powder in an aqueous solution are improved by modification of organic silane, a Formazin spike material is compared with the modified nano-SiO2 , influence of a SiO 2 aqueous solution on oxygen consumption and a pH value of water is discussed and the modified nano-SiO 2 has better performance as a spike material for turbidity of a water treatment unit.

Beneficial effects of the present disclosure are as follows:

(1) According to the present disclosure, under a synergistic action of 3-Chloropropyl trimethoxysilane and hydrochloric acid, a modifier is successfully covalently bound to a surface of nano-SiO2, so an acting force between hydroxyl groups on the surface of the nano-SiO 2 is reduced, a clear particle surface is formed, the agglomeration of the nano-SiO 2 is prevented, and high standing stability is achieved.

(2) There is a good linear relationship between a concentration of the modified nano-SiO 2

solution prepared in the present disclosure and turbidity, and a correlation coefficient R2 is 0.9995; and the modified nano-SiO2 solution has relatively high dilutability, and a linear correlation coefficient R2 is 0.9979. The modified nano-SiO 2 aqueous solution has relatively high stability and dilutability, its concentration has a good linear relationship with turbidity, and the modified nano-SiO2 has the characteristics of being used as a spike material for turbidity of a water treatment unit. Modified nano-SiO2 aqueous solutions with different particle sizes may be prepared according to requirements of different filter films, and the controllability of the particle size is high.

(3) The modified nano-SiO 2 solution prepared in the present disclosure has no influence on oxygen consumption and a pH value of water.

Brief Description of the Drawings

Fig. 1 is an SEM diagram of nano-SiO 2 before and after modification of 3-Chloropropyl trimethoxysilane prepared in Embodiment 1;

wherein, (a) is unmodified nano-SiO 2 , and (b) is modified nano-SiO 2 .

Fig. 2 is an infrared spectroscopy diagram of nano-SiO 2 before and after modification of 3-Chloropropyl trimethoxysilane;

wherein, 1: unmodified; 2: modified by only 3-Chloropropyl trimethoxysilane; and 3: modified by 3-Chloropropyl trimethoxysilane and hydrochloric acid (HCL).

Fig. 3 is a particle size distribution diagram of the nano-SiO2 prepared in Embodiment 1.

Fig. 4 is a particle size distribution diagram of a Formazin solution.

Fig. 5 is a diagram of changing trend of Day of a Formazin solution versus time.

Fig. 6 is a diagram of changing trend of Xav of a modified nano-SiO 2 solution versus time.

Fig. 7 shows a turbidity value of a modified nano-SiO2 aqueous solution.

Fig. 8 is a dilutability diagram of a modified nano-SiO 2 aqueous solution.

Fig. 9 is a standing diagram of a modified nano-SiO2 solution (412 NTU) and a Formazin solution (400 NTU).

Fig. 10 shows changes of turbidity of a modified nano-SiO 2 solution and a Formazin solution.

Detailed Description of the Embodiments

The technical solutions of the present disclosure will be further explained and illustrated below through specific embodiments.

Reagents and instruments used in the present disclosure are as follows:

the reagents: nano-SiO2 (Shanghai Changbei Nano Master Technology Co., Ltd., an average particle size is 100 to 500 nm), 3-Chloropropyl trimethoxysilane (Shanghai Aladdin Biochemical

Technology Co., Ltd.), absolute ethanol (Sinopharm Chemical Reagent Co., Ltd, an analytical reagent (AR)), and hydrochloric acid (Sinopharm Chemical Reagent Co., Ltd, a guaranteed reagent (GR));

the instruments: a magnetically controlled stirring heater (Tianjin Saidelisi Test and Analytical Instrument Manufacturer), an analytical balance (Sartorius Scientific Instrument (Beijing) Co., Ltd.), a fourier transform infrared microspectrometer (Thermo Scientific), a scatterometer (Shanghai Xinrui Instrument and Apparatus Co., Ltd.), a centrifuge (Cence Centrifuge Co., Ltd in National High-tech Industrial Development Zone of Changsha), a vacuum drying oven (Shanghai Boxun Industrial Co., Ltd), a digital thermostatic water bath (Changzhou Noki Instrument Co., Ltd.), a standard light box (SDL Atlas Co., Ltd.), a nanometer particle size analyzer Winner802 (Jinan Winner Particle Technology Co., Ltd.), a laser particle size analyzer Winner2000ZD (Jinan Winner Particle Technology Co., Ltd.), and a thermal field emission scanning electron microscopy SUPPATM55 (Germany Zeiss company).

Embodiment 1

2 g of nano-Si0 2 was weighed and dissolved in 60 mL of absolute ethanol, and the mixture was subjected to ultrasonic oscillation for 60 min and then magnetic stirring for 1 h. 4.324 g of 3-Chloropropyl trimethoxysilane was added to the dispersed nano-Si02 ethanol solution for reaction in a thermostatic water bath at 85°C for 0.5 h, 2 mL of 3% hydrochloric acid was added to the mixture for a subsequent reaction for 3.5 h, the mixture was constantly stirred during the reaction, the mixture was subjected to centrifugal separation after the reaction was finished, and the mixture was washed 3 times with absolute ethanol. The mixture was dried in a vacuum drying oven at 55°C for 8 h, and was ground into powder, an appropriate amount of the modified nano-Si02 powder was weighed and added to level 3 water, and the mixture was subjected to ultrasonic dispersion for 1 h to prepare a spiked stock solution with certain turbidity of about 400 NTU.

Control 1

2 g of nano-Si02was weighed and dissolved in 60 mL of absolute ethanol, and the mixture was subjected to ultrasonic oscillation for 60 min and then magnetic stirring for 1 h. 4 mL of 3-Chloropropyl trimethoxysilane was added to the dispersed nano-Si02 ethanol solution for reaction in a thermostatic water bath at 85°C for 4 h, and was constantly stirred during the reaction, the mixture was subjected to centrifugal separation after the reaction was finished, and the mixture was washed 3 times with absolute ethanol. The mixture was dried in a vacuum drying oven at 55°C for 8 h, and was ground into powder, an appropriate amount of the modified nano-SiO2 powder was weighed and added to level 3 water, and the mixture was subjected to ultrasonic dispersion for 1 h to prepare a spiked solution with certain turbidity.

Results and Conclusions

(I) An SEM diagram of the nano-SiO 2 modified by the 3-Chloropropyl trimethoxysilane that is prepared in Embodiment is shown in Fig. 1. From Fig. 1, it can be seen that unmodified nano-SiO2 particles were in the form of agglomeration due to a strong acting force of hydroxyl groups between the particles, resulting in unsharp particle surfaces. Hydrophobic groups were introduced into the SiO 2 modified by 3-chloropropyltrimethoxysilane and hydrochloric acid, so the acting force between the hydroxyl groups on the surface of the nano-SiO 2 was reduced, and a clear particle surface was formed.

(II) The modified SiO 2 was characterized by using the fourier infrared transform infrared spectrometer, the number of scans was 32, a resolution was 4cm- , and a wave number range was 4000 to 400 cm- .

An infrared spectroscopy diagram of the nano-SiO 2 before and after modification of 3-Chloropropyl trimethoxysilane is shown in Fig. 2. Absorption peaks near 3446 cm-' and 1634 cm-1 in a curve respectively corresponded to an antisymmetric vibration and a bending vibration of water-OH; an absorption peak at 1103 cm was an antisymmetric stretching vibration of a Si-O-Si bond; and absorption peaks near 799 cm-1 and 471 cm-I respectively corresponded to a symmetric stretching vibration and a bending vibration of the Si-O-Si bond. Characteristic absorption peaks of methylene (-CH2-) and methyl (-CH3) in 3-chloropropyl trimethoxysilane appear at 2925 cm-1 and 2853cm-1, which indicates that the 3-chloropropyl trimethoxysilane used in the modification is covalently bound to the surface of the nano-silicon oxide, so a modifier is successfully covalently bound to the surface of the nano-silicon oxide. From Curve 3, it can be seen that the addition of hydrochloric acid solution is beneficial to enhancement of a modification effect.

(III) The modified nano-SiO 2 was prepared into an aqueous solution, the aqueous solution was placed in the laser particle size analyzer, and its tested particle size distribution is shown in Fig. 3. An average particle size Xav of the modified nano-SiO 2 after modification was 304.71 nm. A 400 NTU Formazin standard solution was placed in the laser particle size analyzer, its particle size distribution was tested and a result was shown in Fig. 4. An average particle size Day of the Formazin standard solution was 0.998 nm.

In tests, it was found that the nano-SiO 2 powder before modification was easy to agglomerate in the aqueous solution under the action of the hydroxyl groups on the surface of the silicon oxide, and its particle size changed and increased rapidly, and was difficult to achieve stability; and due to the introduction of the hydrophobic groups on the surface of the modified nano-SiO2 , the acting force of the hydroxyl groups on the surface of the nano-SiO 2 was reduced, the agglomeration of the modified nano-SiO2 in the aqueous solution was reduced, and the stability of the solution was improved.

The samples were placed in the analyzer, and the particle sizes of the samples were recorded every five minutes in the static state. Changing particle sizes of the Formazin standard solution and the modified nano-SiO2 solution versus time are shown in Table 1, and change trends are shown in Fig. 5 (a change trend diagram of a Formazin particle size in the Formazin standard solution) and Fig. 6 (a change trend diagram of a SiO 2 particle size in the modified nano-SiO2 solution). From Fig. 3, it can be seen that the Formazin standard solution appeared agglomeration in the static state and its particle size gradually increased; in the test state, its particle size reached the maximum value at about 100 min, and then decreased sharply. This is because the agglomeration leaded to the precipitation of the Formazin solution, and the particle size of the Formazin remaining in the water was small. Compared with the Formazin standard solution, the modified nano-SiO2 with gradually increasing particle size had relatively high particle size stability (Fig. 4); as time went on, the SiO 2 particles with a larger particle size slightly settled due to the action of gravity, and a particle size change rate of the modified nano-SiO2 was 2.3%, which indicates that the modified nano-SiO 2 has relatively high stability.

Table 1 Changing particle size of a Formazin standard solution and a modified nano-SiO 2

solution versus time

Formazin solution Day ([pm) modified nano-SiO2 solution Xav (nm) min 0.998 304.71 min 1.004 304.48

min 1.168 304.28 min 1.559 304.25 min 2.169 304.39 min 2.267 304.55 min 2.387 303.98 min 2.480 303.85 min 2.551 303.21

min 2.615 303.45 min 2.631 303.12

min 2.731 302.95 min 2.808 302.58

min 2.835 301.56

min 2.929 300.48 min 3.004 299.36

min 2.989 298.32 min 3.020 298.95 min 3.124 298.76 min 3.173 298.67 100 min 3.445 298.38

105 min 3.057 297.58 110 min 2.361 297.56

115 min 2.062 297.40 120 min 1.668 297.26

(IV) A linear relationship between a concentration of the modified silicon dioxide solution and turbidity: there is no strict conversion relationship between a nephelometric turbidity unit (NTU) and a mass concentration unit (mg/L), so turbidity of water was quantitatively characterized according to a scattering or attenuation degree of light caused by suspended particles in the water. The scattered light will change due to different microscopic shapes and particle size distributions of different suspended particles An existing empirical formula is that a nephelometric turbidity unit (NTU)=0.13xa particle concentration (mg/L). The empirical formula was modified through tests in the present disclosure. Different amounts of modified silicon dioxide were weighed and added into level 3 water to prepare aqueous solutions with different turbidity. The scatterometer was calibrated by using the Formazin standard solution, a correlation curve was drawn by taking a concentration (mg/L) of the modified nano-SiO 2

aqueous solution as an x-axis and a measured turbidity value (NTU) as a y-axis, as shown in Fig. 7, a linear relationship equation of y=0.1361x-2.2126 between the concentration (mg/L) and the turbidity (NTU) was obtained, and a correlation coefficient R2 was 0.9995.

(V) Dilutability of the modified silicon dioxide solution: in order to test the dilutability of the modified nano-SiO2 solution, modified nano-SiO2 solutions with turbidity of 813.7 NTU were prepared and then diluted according to different proportions, and turbidity of the diluted solution was respectively measured by using turbidimeters of the same mode. A correlation curve was drawn by taking a calculated value of the proportionally diluted aqueous solution as an x-axis and a measured turbidity value (NTU) as a y-axis, as shown in Fig. 8, an equation of y=1.Olx+5.6076 of the dilutability of the modified nano-SiO 2 aqueous solution was obtained, and a correlation coefficient R2 was 0.9979. It can be seen that the modified nano-SiO 2 has relatively high dilutability.

(VI) Study on the standing stability of the Formazin solution and the modified SiO 2 solution

In order to compare the stability of the modified nano-SiO2 solution and the stability of the Formazin solurtion, a 412 NTU modified nano-SiO2 solution was prepared, and placed together with a 400 NTU Formazin solution (No. 2) into the standard light box to ensure the stability of a light source, the static states of the two solutions at 0 min, 30 min, 60 min, 90 min, 120 min, 150 min, and 180 min were respectively recorded, and a result is shown in Fig. 9.

As shown in the result at 0 min, the No. 1 and No. 2 samples that were subjected to thorough oscillation were both in the form of uniform suspension. After standing for 30 min, obvious delamination occurred at an upper part of the No. 2 Formazin standard solution. As time went on, a height of a transparent part of the No. 2 solution gradually increased, and precipitates appeared at the bottom of the No. 2 colorimetric tube at 120 min, and floccules could be observed from the upper solution. After standing for 180 min, the upper part of the No. 2 solution was a clear solution and the precipitates were at the bottom, while the No. 1 solution was still a uniformly dispersed suspension. It can be seen that the standing stability of the modified nano-SiO2 solution is higher than that of the Formazin solution.

Changes of turbidity values of a 400 NTU Formazin standard solution and a 412 NTU modified nano-SiO2 solution with different standing time were respectively measured, and a result is shown in Table 2.

Table 2 Changes of turbidity of a modified SiO 2 solution and a Formazin standard solution

turbidity (NTU) Remaining rate (%)

Formazin modified Formazin Modified SiO2

SiO2 solution solution solution solution

0 min 399.9 412 / /

10 min 399.9 412 100.0 100

20 min 399.9 412 100.0 100 30 min 391.6 393.4 97.9 97.6

40 min 393.2 391.4 95.8 95.5 50 min 366.5 387.1 91.6 94.0

60 min 362.4 381.5 90.6 92.6 70 min 358.2 381.5 89.6 92.6

80 min 323.1 377.2 70.8 91.6

90 min 281.7 375.1 70.4 91.0

100 min 191.0 374.2 47.8 90.8

110 min 128.4 374.2 32.1 90.8

120 min 102.0 374.2 25.5 90.8

From the data in Table 2 and Fig. 10, it can be seen that the turbidity of the two solutions could be kept stable and unchanged in the first 20 min, the two solutions had equivalent stability within 60 min, and the turbidity of the Formazin solution decreased sharply after 60 min, which is consistent with that shown in Fig. 9. When the Formazin standard solution stood for 100 min, its remaining turbidity value was 47.8%, which was less than 50%. When the Formazin standard solution stood for 120 min, its turbidity value was only 25.5% of the initial state, while the turbidity value of the modified SiO2 solution was 90.8% of the initial state. It can be seen that the modified SiO 2 solution has relatively high standing stability.

(VII) Influence of a Formazin spike material and a modified SiO 2 spike material on physical and chemical properties of water:

in a hygiene function test of a general water treatment unit, test items such as oxygen consumption, turbidity, and trichloromethane in a spike test of a filter element or a filter assembly may be carried out at the same time, so a spike material for turbidity is required to not affect indicators such as a pH value, oxygen consumption, volatile phenol, and trichloromethane of water. Because no organic matter such as volatile phenol and trichloromethane was added in the preparation of the Formazin spike material and the modified nano-SiO 2 , only the pH value and the oxygen consumption were measured and taken as influence factors of the spike material on water in present disclosure. pH values and oxygen consumption of tap water, a Formazin-spiked solution (25 NTU), and a modified SiO 2-spiked solution (25 NTU) were measured, and data is shown in Table 3:

Table 3 Influence of a Formazin spike material and a modified SiO 2 spike material on a pH value and oxygen consumption of water

tap water Formazin-spiked modified

solution SiO 2-spiked

solution

pH values(/) 7.55 7.61 7.57

oxygen 0.80 466.4 1.34

consumption

(mg/L)

From the data in Table 3, it can be seen that the pH value and the oxygen consumption of the modified SiO 2-spiked solution did not change significantly, while the Formazin could be oxidized by potassium permanganate to produce an oxidation reaction, so that the oxygen consumption of the Formazin-spiked water changed greatly. The Formazin-spiked solution and the modified SiO2 -spiked solution had a slight influence on the pH value of water. It can be seen that the Formazin spike material is not suitable for being used as a spike material for a spike test of a water treatment unit.

Claims

1. A modified nano-SiO 2 spike material for turbidity of a water treatment unit, characterized in that the SiO 2 is in a form of spherical particle and has a particle of 100 to 500 nm.

2. A preparation method of the modified nano-SiO 2 spike material for turbidity of a water treatment unit according to claim 1, characterized by comprising the following steps: (1) weighing and dissolving nano-SiO 2 in absolute ethanol, performing ultrasonic oscillation and then magnetic stirring on the mixture to obtain a silicon dioxide ethanol solution for later use. (2) adding 3-Chloropropyl trimethoxysilane to the dispersed nano-SiO 2 ethanol solution for reaction in a thermostatic water bath, adding an appropriate amount of hydrochloric acid at a volume concentration of 3% to the mixture for a subsequent reaction, constantly stirring the mixture during the reaction, performing centrifugal separation on the mixture after the reaction is finished, washing the mixture 3 times with absolute ethanol, performing vacuum drying on the mixture, weighing and adding an appropriate amount of the modified nano-SiO 2 powder to level 3 water, and performing ultrasonic dispersion on the mixture to prepare a spiked solution.

3. The preparation method according to claim 2, characterized in that at step (1), a ratio of the nano-SiO2 to the absolute ethanol is 1 g : 30 mL.

4. The preparation method according to claim 2 or 3, characterized in that at step (1), the time of the ultrasonic oscillation and the time of the magnetic stirring are both 60 min.

5. The preparation method according to claim 2, characterized in that at step (2), a mass ratio of the 3-Chloropropyl trimethoxysilane to the nano-SiO 2 is (2-3): 1.

6. The preparation method according to claim 2 or 5, characterized in that the reaction in the thermostatic water bath is performed at 85°C for 0.5 h.

7. The preparation method according to claim 1, 5 or 6, characterized in that an addition amount of the hydrochloric acid is 1 mL for each 1 g of the nano-SiO 2 .

8. The preparation method according to claim 7, characterized in that the appropriate amount of the hydrochloric acid at the concentration of 3% is added for the subsequent reaction for 3.5 h.

9. The preparation method according to claims 2 to 8, characterized in that the vacuum drying refers to drying at 55°C for 8 h.

10. An application of a nano-SiO 2 prepared by the preparation method according to any one of claims 2 to 9 as a spike material for turbidity of a water treatment unit.