# Graphene Oxide Adsorption Enhanced by Attapulgite to Remove Pb (II) from Aqueous Solution
## 1 Introduction  
Pb\({}^{2+}\) is a heavy metal ion found in industrial and agricultural wastewater and acidic landfill leachate [1]. Because of its high toxicity, nonbiodegradability, wide presence, and bioaccumulation, it constitutes a pollutant that threatens humans and the environment [2]. Long-term consumption of lead-ion-containing drinking water can induce serious diseases, such as anemia, reproductive diseases, genotoxicity, and nervous system effects. In particular, children bear the greatest risk of lead-induced toxicity [3]. These concerns have caused increasingly more scientists to investigate simple yet highly effective treatment methods for lead-containing wastewater [4]. Methods that have been used to date in the removal of lead ions from wastewater include chemical precipitation [5], coprecipitation [6], cloud-point extraction [7], electrochemical reduction [8], flocculation [9], ion exchange [10], membrane filtration [11; 12], and adsorption [2; 3; 4; 13; 14; 15; 16]. Among these methods, adsorption offers the advantages of simple operation, high efficiency, and economic feasibility, and environmental friendliness [17]. However, it is essential to identify high-efficiency adsorbents that are easy to prepare, inexpensive, and easy to regenerate. Most studies have focused on the search for these high-efficiency adsorbents.  
Graphene oxide (GO) is typically obtained by oxidation or sonication of graphite, and it possesses oxygen-containing functional groups, including hydroxyl groups (-OH), epoxy groups (-C=O), and carboxyl groups (-COOH). In addition, GO also possesses a high specific surface area [18]. Compared to other carbon-based materials, GO exhibits better environmental compatibility and biocompatibility [19]. Oxygen-containing functional groups can be used as the adsorption sites for heavy metal ions in wastewater [20]. Through interaction with these oxygen-containing functional groups, heavy metal ions can be removed from wastewater, thus enabling purification [21]. In addition, the presence of these functional groups enables the stable dispersion of GO in water and other polar organic solvents [22]. However, pure GO or GO-based adsorbents reported in the literature have suffered from limitations such as toxic preparation conditions, complex preparation methods, difficulty in separation, and high cost. As a result, inorganic clay minerals with excellent adsorptionand separation properties are selected here to create a composite with GO to fabricate Pb\({}^{2+}\) adsorbents with excellent properties at a low cost.  
Attapulgeite (ATP) is a water-containing magnesium aluminum phyllosilicate, which is an inorganic mineral that exhibits high cation exchange capacity, rapid hydration [23], and environmental compatibility. Research has shown that the as-prepared GO composites exhibit excellent adsorption to heavy metal ions such as Pb\({}^{2+}\), Zn\({}^{2+}\), Cu\({}^{2+}\), Cd\({}^{2+}\)[24], and Ni\({}^{2+}\)[25]. ATP can be regenerated after adsorption saturation. In addition, because of its low cost and easy access [26], ATP exhibits wide application potential and practical value in the removal of heavy metal ions in wastewater due to its cheapness, abundance, and chemical stability [27].  
Although there are abundant studies of GO composite materials [28], there are no reports on facile composite materials combining GO and the inorganic clay material ATP. GO exhibits a two-dimensional layer structure [29], whereas the ATP single crystal exhibits a fine fibrous morphology [30]. The present study aimed to graft ATP to the GO surface, forming a novel composite material with a \"plane-needle\" structure, thus achieving improved GO properties and decreased cost in the treatment of lead-containing wastewater. The already large specific surface area of GO was further increased to improve the separation performance, thus avoiding the loss of GO nanoparticles in lead-containing wastewater and achieving more efficient and economical treatment of heavy metal lead ions in wastewater.