Experimental study on the effect of hydrophilic/hydrophobic SiO2 nanofluids on the wettability of coal samples with different surface roughnesses

Coal sample wettability shows a negative correlation with surface roughness. [Display omitted] •Hydrophilic/hydrophobic SiO2 nanofluids demonstrate excellent effectiveness in altering coal wettability.•Hydrophilic SiO2 nanofluids improve wettability of coal samples compared to deionized water solution.•Hydrophobic SiO2 nanofluids attenuate the wettability of coal samples compared to alcohol solution. Coal, as one of the most important energy sources, is constrained by coal dust in safe mining operations, where the wettability of coal plays a crucial role in dust control. To investigate the impact of different nature nanofluids on coal wettability, this study proposes a method using hydrophilic/hydrophobic SiO2 nanofluids to modify coal wettability. The effect of SiO2 nanofluid on the water absorption of coal samples was investigated using moisture content measurement experiments. The wettability and modification effect of coal samples with different roughness surfaces before and after the experiments were analyzed by using the contact angle and the Relative Enhancement Value (REV) of the contact angle, and the mechanism of the SiO2 nanofluid to change the wettability of the coal samples was revealed by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The research results indicate that the modification effects of SiO2 nanofluids on the wettability of coal samples are significant. After treatment with hydrophilic SiO2 nanofluids, the moisture content of coal samples increased by 66.7%, demonstrating enhanced water absorption capacity, with the contact angle rapidly decreasing to below 70°, indicating stronger hydrophilicity. After treatment with hydrophobic SiO2 nanofluids, the moisture content of coal samples decreased by 41.7%, indicating reduced water absorption capacity, with the contact angle remaining above 123°, indicating increased hydrophobicity. Moreover, as surface roughness increases, the average contact angle of coal samples increases by 14%, indicating a gradual decrease in wettability. The primary reason for the change in coal wettability is the formation of SiO2 nanoparticle aggregates on the coal surface, where the functional groups within aggregates exhibit varying attraction to water molecules, thereby altering coal wettability. This study contrasts the modification effects of hydrophilic/hydrophobic SiO2 nanofluids, providing insights into their wetting behavior on coal surfaces. The findings serve as an experi