Microscopic mechanism of SiO2-H2O nanofluids to enhance the wettability of coal dust

doi:10.11949/0438-1157.20230557

Abstract

Abstract:

Coal dust pollution is one of the problems that the world’s coal industry needs to solve urgently. Exploring green and efficient new coal dust wetting agents has potential application value in this field. In this study, the mechanism of the effect of SiO₂-H₂O nanofluid on the wettability of coal dust was investigated by the Wender model using Materials Studio molecular simulation software and physical experiments. The results show that the reactivity of SiO₂ nanoparticles (NPs) is high, and their surface hydroxyl groups can easily form hydrogen bonds with coal molecules and water molecules, thus affecting the wetting properties of coal dust. NPs have a strong ability to interact with coal molecules, and their adsorption on the surface of coal dust can adsorb more water molecules. When the adsorption number of NPs was 0—5, the interaction energies between coal and NPs, NPs and water, and the number of hydrogen bonds between solid-liquid molecules in the adsorption system tended to increase with the increase in the number of NPs. The g(r) curves between hydrogen and oxygen atoms in coal and NPs have the largest values and higher peaks, while the g(r) curves between hydrogen and oxygen atoms in coal and water are the opposite. With the increase of the adsorbed number of NPs, the water molecule mean square displacement and diffusion coefficient tended to increase, which accelerated the wetting of coal dust. Compared with water, the nanofluids have lower surface tension, and when the particle concentration is 2.0%(mass), the decrease rate of contact angle of modified coal dust reaches about 52.85%—61.51%, while the adsorption and agglomeration of NPs on the surface of nanofluid-treated coal dust is obvious. In this study, the molecular simulation results were verified with the experimental results, which elucidated the microscopic mechanism of NPs to enhance the wettability of coal dust, obtained the influence law of NPs on the wettability of coal dust, revealed the adsorption characteristics of NPs on the surface of coal dust, and laid a theoretical foundation for the enhancement of the wettability of coal dust by SiO₂-H₂O nanofluids.

Key words: SiO₂-H₂O nanofluids, coal dust, wettability, molecular simulation

摘要：

煤尘污染是世界煤炭行业亟需解决的难题之一，探索绿色高效的新型煤尘润湿剂对于该领域来说具有潜在的应用价值。以Wender模型为研究对象，借助Materials Studio分子模拟软件与物理实验探究了SiO₂-H₂O纳米流体对煤尘润湿性的影响机制。研究表明：SiO₂纳米颗粒(NPs)的反应活性较高，其表面羟基容易与煤分子和水分子形成氢键，从而影响煤尘的润湿特性。NPs与煤分子的相互作用能力较强，其吸附在煤尘表面后能吸附更多的水分子。当体系中NPs的吸附数量为0~5时，随NPs数量的增加，吸附体系中煤和NPs、NPs和水之间的相互作用能以及固-液分子间氢键的数量呈增大的趋势。煤和NPs中氢、氧原子之间的g(r)曲线值最大，峰值较高，而煤和水中氢、氧原子之间的g(r)曲线与之相反。随着NPs吸附数量的增加，水分子均方位移与扩散系数呈增大的趋势，加速了对煤尘的润湿。与水相比，纳米流体具有较低的表面张力，当颗粒浓度为2.0%(质量)时，改性煤尘接触角下降率达到了52.85%~61.51%，同时纳米流体处理后的煤尘表面NPs吸附集聚现象明显。本研究分子模拟结果与实验结果相互验证，阐明了NPs强化煤尘润湿性的微观机理，获得了NPs对煤尘润湿性的影响规律，揭示了NPs在煤尘表面的吸附特征，为SiO₂-H₂O纳米流体强化煤尘润湿性奠定了理论基础。

关键词: SiO₂-H₂O纳米流体, 煤尘, 润湿性, 分子模拟

CLC Number:

TD 714

Jiajia ZHAO, Shixiang TIAN, Peng LI, Honggao XIE. Microscopic mechanism of SiO₂-H₂O nanofluids to enhance the wettability of coal dust[J]. CIESC Journal, 2023, 74(9): 3931-3945.

赵佳佳, 田世祥, 李鹏, 谢洪高. SiO₂-H₂O纳米流体强化煤尘润湿性的微观机理研究[J]. 化工学报, 2023, 74(9): 3931-3945.

Figures/Tables 18

Fig.1 Surface morphology characterization of SiO2 NPs

Table 1 Maceral content and vitrinite reflectance of coal samples

编号	显微组分含量/%			$R ¯ m a x / %$
编号	镜质组	惰质组	壳质组	$R ¯ m a x / %$
RB	56.9	37.9	5.2	0.46
HY	54.7	40.1	5.2	0.56
SM	60.3	31.7	8.0	0.58
JP	63.5	30.3	6.2	0.63

Table 1 Maceral content and vitrinite reflectance of coal samples

编号	显微组分含量/%			$R ¯ m a x / %$
编号	镜质组	惰质组	壳质组	$R ¯ m a x / %$
RB	56.9	37.9	5.2	0.46
HY	54.7	40.1	5.2	0.56
SM	60.3	31.7	8.0	0.58
JP	63.5	30.3	6.2	0.63

Fig.2 Molecular model

Fig.3 Molecular dynamics model

Fig.4 “Two-step” preparation of nanofluids

Fig.5 Distribution of surface charge

Fig.6 Adsorption configuration of system

Table 2 Interaction energy of the molecular

NPs数量	相互作用能 (kcal/mol)
NPs数量	W&C	N&C	N&W	W&C-N
0	-411.15	—	—	—
1	-418.20	-56.02	-25.91	-444.11
2	-415.45	-100.86	-55.32	-470.77
3	-392.47	-124.25	-75.59	-468.06
4	-344.58	-170.64	-123.19	-467.77
5	-265.84	-167.99	-162.17	-428.01

Fig.7 Hydrogen bonding effect in coal/NPs/water system

Fig.8 Number of hydrogen bonds in the coal/NPs/water system

Fig.9 Radial distribution function curves of H and O atoms among coal, water and NPs

Fig.10 Relationship between lgt and lgMSD

Fig.11 Mean square displacement of water molecules

Table 3 Linear fitting parameters and diffusion coefficients of mean square displacement of water molecules

NPs数量	拟合方程	R²	D_c/(Å²/ps)
0	y=1.132x+1.297	0.9995	0.1887
1	y=1.253x+7.265	0.9991	0.2088
2	y=1.322x+4.610	0.9998	0.2203
3	y=1.371x+5.423	0.9996	0.2285
4	y=1.473x+2.898	0.9998	0.2455
5	y=1.586x+0.363	0.9999	0.2643

Fig.12 Characterization of nanofluid

Fig.13 Surface tension parameters of nanofluids

Fig.14 Change of contact angle

Fig.15 SEM and EDS spectra of coal dust surface

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Microscopic mechanism of SiO₂-H₂O nanofluids to enhance the wettability of coal dust

SiO₂-H₂O纳米流体强化煤尘润湿性的微观机理研究

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