## 2 Hybrid Graphene-Based Materials (Hybrid GBMs)
### Graphene-Based Biosorbents
#### 2.5.1 Graphene-Based Materials Immobilized with Chitosan  
A significant challenge in utilizing GO, especially in water matrices, is the substantial aggregation stemming from \(\pi\)-\(\pi\) interactions among GO sheets and their inadequate dispersion in aqueous environments [66]. These drawbacks result in a considerable decline in adsorption efficiency by constricting the accessible surface area for molecular interaction. To address these challenges, using CS is a promising strategy for immobilizing  
Figure 3: Schematic illustration of the N-GQDs/Fe\({}_{3}\)O\({}_{4}\) synthesis approach @SiO\({}_{2}\)/IRMOF-1/MIP adsorbent. Reproduced with permission [37] Copyright © 2024 Elsevier. graphene-derived materials [66; 67]. CS, a biopolymer endowed with notable biodegradability, non-toxicity, and intriguing physicochemical attributes, presents a compelling solution for graphene-based materials. Its functional groups, including -OH and -NH\({}_{2}\), facilitate the activation of adsorption sites while enhancing electrostatic interactions and hydrogen bonding with functional groups inherent in GO, for example [66; 68]. Despite the CS's intrinsic limitations in thermal stability and mechanical properties, these shortcomings are mitigated through synergistic interactions upon integration with graphene-based materials. Consequently, CS serves as a stabilizing agent for GO sheets, effectively mitigating aggregation issues [66]. Graphene oxide/chitosan (GO/CS) immobilized sorbents are synthesized through various methods, including sol-gel [69] processing and chemical crosslinking [70]. However, the conventional approach typically entails dissolving chitosan in an acetic acid aqueous solution (1-3% \(v/v\)). This process yields a yellowish-colored homogeneous solution obtained from the solubilization of chitosan. Moreover, the solution of graphene-based material is combined with the CS solution, followed by sonication until a homogeneous mixture is achieved. This amalgamation forms the basis of the GO/CS material, which can be utilized directly or subjected to subsequent processes, such as freeze drying [66]. Due to its inherent simplicity, this synthesis procedure has been widely used to produce various sorbent materials, primarily for application in microextraction protocols, as discussed in this section. [PERSON] et al. [40] reported the fabrication of a GO/CS aerogel for the extraction of hydrophobic pollutants. The authors employed a blend of ethanol and the cross-linking agent terephthalaldehyde in their synthesis approach, followed by vacuum freeze-drying for 24 h. Key findings underscored the superior analytical performance of the resultant GO/CS sorbent compared to conventional sorbent phases, such as polydimethylsiloxane/divinylbenzene (PDMS/DVB). This enhancement was primarily attributed to the robust hydrophobic, \(\pi\)-\(\pi\), halogen bond, and hydrogen bond interactions between the coating and the analytes. While using cross-linkers in the synthesis of GO/CS has garnered considerable attention, conventional procedures outlined in the literature remain relevant. [PERSON], [PERSON], and [PERSON] [71] demonstrated the synthesis of GO/CS material via the traditional method, as previously described, followed by filtration and drying steps. In pollutant detection, incorporating cross-linking agents into GO/CS sorbent materials has been extensively documented in the literature for their significant impact on the abundance of functional groups available for binding with these compounds. As has been previously reported by [PERSON] et al. [66], the authors stated that the hydrolysis reaction of borax leads to the formation of tetrahydroborate ions B(OH)\({}^{4-}\) upon interaction with the -OH groups inherent in CS and GO. This reaction results in the formation of orthoborate chemical bonds, thereby exerting a notable influence on the ultimate adsorption characteristics of the GO/CS material. As previously mentioned, [PERSON] et al. [40] the use of terephthalaldehyde as a cross-linking agent.