## 1 Introduction  
According to recent United Nations projections, the world's population will increase by more than a third by 2050. Currently, many countries worldwide suffer from a shortage of water, and therefore, achieving sustainable water management is a major challenge for such countries. Sustainable water management contains industrial wastewater treatment [1, 2]. In recent decades, industrial wastewater treatment has become increasingly complex. Increased population growth has led to an increase in industrialization and, consequently, an increase in the release of pollutants into wastewater, which threatens health and the environment [3, 4, 5, 6, 7]. Among these pollutants are dyes that are widely used in the most common industries, such as textiles, paper, and plastics [8, 9, 10, 11]. Dyes are considered as one of the major pollutants because of their complex molecular structure, stability, and effect on plant photosynthesis, as well as having low biodegradability, high toxicity, and cancerous properties [12; 13; 14]. Most dyes can be positively or/and negatively charged and could change regarding the pH. Moreover, they can also combine with metal ions in wastewater to form complex pollutants. Several methods are used to remove these complex structures such as precipitation [15], membrane filtration [16; 17], photocatalytic reduction [18], electrocoagulation [19], biological treatment [20], electrochemical removal [21], and adsorption [22; 23; 24; 25; 26; 27; 28]. In the past few decades, great attention has been paid to the adsorption process due to its ease of application on a large scale and its efficiency [29; 30; 31; 32; 33; 34]. Recently, several conventional adsorbents (e.g., activated carbons [35], ordered mesoporous carbons [36], metal-organic frameworks [37], carbon nanotubes [38], graphene-based nanocomposites [39], activated carbons [40] and natural clay [41] have been used for the removal of dyes from contaminated water solutions. However, most of these solid adsorbents are not widely practiced due to poor selectivity, high cost, difficult disposal, and complex preparation processes. Therefore, it is of great importance to find an adsorbent that is highly efficient, economic, and selective toward organic dyes. Mesoporous silica nanoparticles (MSNs) are one of the most widely used adsorbent materials in water purification due to their non-toxicity, high adsorption capacity, tunable pore structures, pore size, shorter equilibrium time, and abundant surface functional groups [42; 43]. To increase the adsorption efficiency of the porous silica particles, their surfaces have been modified with different functional groups such as amine, carboxyl, thiol, and epoxy [44; 45; 46]. The contaminants are often removed through electrostatic interactions between the target analytes and the functional groups present on the surface of the nanoparticles. To bind these functional groups on the surface of the silica, the self-assembly technique has been widely applied [47; 48]. The density of these functional groups on the surface is the crucial factor to increase the efficiency of adsorption. Furthermore, in order to improve the active sites available on the surface of the nanoparticles, surface modification with polymer brushes has been proposed [49]. Polymer brushes (surface-confined macromolecular architectures) are being increasingly used for a variety of applications and consist of a linear backbone densely grafted with polymeric side chains [50]. The confined and compact structure of the polymer brushes can provide the nanoparticle surface with remarkable properties such as stimuli responsiveness, in which the polymer can change its conformation structure by changing the surrounding environment, such as pH and temperature [51; 52; 53]. A variety of polymer brushes were applied to the surface of silica nanoparticles such as poly(2-(tert-butylamino) ethyl methacrylate) and poly(2-diethyl aminoethyl methacrylate) to study their responsive behaviors [54; 55].