## 1 Introduction
Therefore, adsorption is a powerful, versatile and simple method for removing environmental pollutants from water streams [14; 15; 16]. The adsorption effect of the adsorbent on the adsorbate depends on several factors, including the crystalline structure, particle size, pore dimensions, pore volume, specific surface area of the adsorbent and the type of adsorbate [17]. Among them, the specific surface area and particle size have the most significant influences on the adsorption effect. The smaller the particle size is, the larger the specific surface area, and the larger the equilibrium adsorption capacity. Based on the above advantages, it is considered to be an effective technology for the treatment of volatile organic compounds, such as TCE and PCE [18]. In general, various artificial and natural porous materials are often used as adsorbents in typical adsorption methods, and the most effective adsorbent is activated carbon [19]. Activated carbon is widely used in wastewater treatment and has received industrial attention because of its high surface area, high adsorption capacity and good porosity [12; 20]. [PERSON] et al. [21] showed that different types of activated carbon have the largest adsorption capacity for ethanol, as high as 1900 mg g\({}^{-1}\) and 1650 mg g\({}^{-1}\). [PERSON] and [PERSON] [15] pointed out that the adsorption capacity of activated carbon for naphthalene (naphthalene) is 73.01 mg g\({}^{-1}\). [PERSON] et al. [22] and [PERSON] and [PERSON] [23] showed that the adsorption capacity of activated carbon for 2,4-dichlorophenol is 46.74 mg g\({}^{-1}\) and 258.71 mg g\({}^{-1}\), respectively. However, due to some shortcomings of adsorbents, such as pore blockage, short service life and high regeneration cost, their further industrial applications are limited [18]. Traditional activated carbon is expensive to manufacture and is not easy to recycle. Therefore, its application in industry has gradually developed. Before activated carbon is used to treat polluted water, other kinds of adsorbents are added for treatment to reduce the consumption of activated carbon. Silica gel is a kind of environmentally friendly and porous silica hydrate with good thermal conductivity and specific surface area [24]. Therefore, silica gel is often used as an adsorbent for various substances. For example, [PERSON] et al. [25] found that the adsorption capacity of two kinds of silica gel for dichromate is 24.03 mg g\({}^{-1}\) and 16.52 mg g\({}^{-1}\), respectively. In addition, a study by [PERSON] et al. [26] showed that the adsorption capacity of silica gel for Mn(II) is 3.3 mg g\({}^{-1}\). In addition to removing heavy metal pollution from the environment, silica gel can also be used to remove organic substances. A study by [PERSON] et al. [27] indicated that the adsorption capacity of octamethylcyclotetrasiloxane with silica gel for volatile organic silicon compounds (VOSiCs) is 250 mg g\({}^{-1}\). [PERSON] et al. [18] found that the adsorption capacity of silica gel for toluene is 325 mg g\({}^{-1}\). In the above studies, silica gel was used as an adsorbent, and it was found that the adsorption capacity of silica gel for organic substances is better than that for heavy metals. In addition, silica gel is rarely used to adsorb chlorine-containing organic compounds (such as TCE and PCE). Therefore, in this study, we selected a silica gel gel with a good adsorption capacity for organic substances and a low price to carry out the TCE and PCE adsorption experiments. According to the experimental results of [PERSON] et al. [28] on the activated-carbon adsorption of TCE, the Freundlich and Dubinin-Astakhov models can be used to analyze and interpret experimental data at a confidence level of 95%. Between them, the Dubinin-Astakhov model shows greater statistical uncertainty but is more suitable for high concentration ranges. Therefore, under the condition of a low solute concentration, the Freundlich model shows better affinity and applicability for adsorption mechanisms and experimental data [29].