## 1 Introduction
Their unique crystalline structure, composed of interconnected AlO\({}_{4}\) and SiO\({}_{4}\) tetrahedra, forms a network of micropores with a size range from 0.3 to 1 nm [24], providing a large specific surface area and excellent cation exchange capacity [18]. Over 50 natural zeolite minerals have been identified, of which analcime, chabazite, clinoptilolite, heulandite, natrolite, phillipsite, and stillbite occur in significant quantities [24]. Clinoptilolite, one of the most abundant zeolites on earth, has a 2D channel system featuring two parallel channels (a 10-membered ring of 7.2 A \(\times\) 4.4 A and an 8-membered ring of 4.7 A \(\times\) 4.1 A) intersecting with a third 8-membered ring channel (5.5 A \(\times\) 4.0 A) [23; 25]. Its framework consists of SiO\({}_{4}\) and AlO\({}_{4}\) tetrahedra with charge-balancing cations (Na\({}^{+}\), K\({}^{+}\), Ca\({}^{2+}\), Mg\({}^{2+}\)) [25]. It is commonly employed in wastewater treatment, though it exhibits limited adsorption efficiency for cationic contaminants [22]. This limitation is attributed to its low ion exchange capacity, intrinsic to its crystalline structure with a Si/Al ratio generally ranging from 4 to 6. Since the above alkaline and earth alkaline cations affect its adsorption capacity, acid treatments can be used to reduce its cation content, thereby improving the adsorption capacity [26]. However, they can generate hazardous waste that poses a significant threat to the environment. On the other hand, graphene oxide has shown promising results as an adsorbent for pollutant removal due to its high adsorption capacity. This capacity is attributed to its exceptional physicochemical properties, such as its large specific surface area and the presence of various oxygen-containing functional groups in its structure [27]. The Hummers method, introduced in the 1950s, remains one of the most widely used techniques for synthesizing graphene oxide (GO) [28]. This process involves the strong oxidation of graphite in a highly concentrated acidic medium, using a reactive mixture of sulfuric acid, potassium permanganate, and hydrogen peroxide [29]. This oxidation introduces oxygenated functional groups (carboxyl, hydroxyl, and epoxy groups) into the graphene structure, facilitating its exfoliation into monolayers or few-layered sheets [30]. However, the corrosive and toxic nature of the reagents employed generates harmful gases and ionic waste, posing a significant environmental concern. To address this environmental challenge, we previously reported [31] a scalable and environmentally friendly method for producing GO, suitable for industrial-scale water treatment. The integration of graphene oxide with other materials has proven to be a highly effective strategy for enhancing its adsorption capacity [22; 32]. This improvement arises from the synergy between the complementary properties of the different components, resulting in composite materials with optimized physical and chemical characteristics. Specifically, the combination with porous materials, such as silica or activated carbons, significantly increases the available surface area, thereby enhancing the adsorption capacity for contaminants [11; 22; 33]. Different materials can exhibit varied adsorption mechanisms (physical, chemical, or ion exchange), allowing for a more efficient interaction with a broader range of contaminants. Furthermore, the functionalization of graphene oxide through the addition of specific functional groups or the incorporation of other materials can fine-tune the adsorbent's selectivity towards certain dyes or metals. Additionally, these combinations can improve the chemical and mechanical stability of the adsorbent, increasing its durability and facilitating its reuse [34; 35]. This research aims to enhance the adsorption capacity of clinoptiolite zeolite by combining it with graphene oxide, a material known for its high adsorption capacity.