## 1 Introduction  
As an eco-friendly material, bamboo can reach its full growth rapidly in a few months, which is one of the most abundant renewable cellulose resources [1]. Owning to its non-toxicity, cost-effectiveness, and environmentally friendly process, bamboo is widely used in construction and reinforcing fibers, paper, textiles, board, furniture, flooring tiles, food, transportation, and packaging industries, combustion, and other bioenergy applications. However, the overall processing efficiency is relatively low [2]. In recent years, progress has been made in the preparation of bamboo charcoal [3], pulp and cellulose nanofiber [4], bamboo-plastic composite materials [5], antioxidants and immunositulants [6], and metal ion sensor [7] from bamboo processing residues. This progress shows good prospects for the development and application of bamboo waste [1]. Bamboo is a promising regeneration adsorbent for heavy metal adsorption from an aqueous solution [8]. Thus, bamboo-based bio-adsorbents for removing metal ions in an aqueous solution have been developed [9]. Bamboo charcoal and activated carbon are widely used for contaminated wastewater purification [10]. These reports show bamboo has good adsorption capacity for heavy metal ions. Some efforts have developed an efficient adsorbent by increasing the number of pores [11], or by increasing the number of accessible functional groups [12; 13; 14]. However, the selected precursor and synthetic conditions influenced the microstructure of bamboo charcoal and activated carbon, thus affecting target ions' removal efficiency [14]. Additionally, bamboo charcoal and activated carbon show poor selective adsorption. Chemically modified bamboo shows a higher adsorption capacity for heavy metals than for activated carbon [8]. The bamboo surface is rich in hydroxyl groups because the main components of bamboo are cellulose and hemicellulose, which account for about 50% of the dry matter [9]. Chemical modification of the hydroxyl group can prepare an adsorbent with higher binding capacity for target ions [8]. Functional groups, especially amino groups chemically grafted onto cellulose, can increase their adsorption performance [15; 16]. Some papers focus on the chemical modification of bamboo cellulose and their adsorption performance to heavy metal ions [9; 17; 18], dyes [12]s and CO\({}_{2}\)[19]. However, few papers have investigated the adsorption of modified bamboo to anions. The amine groups, which can be protonated or quaternized to form positive groups such as R-NH\({}_{3}\)\({}^{+}\) and R-NHH\({}_{2}\)\({}^{+}\), are often used for anionic contaminants adsorption through electrostatic interaction [20; 21; 22]. R-NH\({}_{2}\) can be protonated at acidic pH and de-protonated at a high pH, so that the amine group can adsorb anions at an acidic pH. However, the quaternized amine can adsorb anions at a wide pH range even in alkaline conditions [21]. Adsorption commonly occurred at the interface between the adsorbent and the adsorbate in an aqueous solution. More functional groups onto the adsorbent surface can obtain high adsorption capacity and velocity. Radiation-induced graft polymerization (RIGP) is often used to increase functional groups and the capacity to bond anions. RIGP was widely used to modify cellulose biomass because RIGP generates radicals and thus form grafting, which are relevant for subsequent chemical modification and processing. The high grafting yield of RIGP can be achieved quickly and without heating [23]. The functional groups or the intermediate monomer were introduced onto the polymer's surface, so the adsorbents had a high adsorption velocity [24]. Phosphate is the only phosphorus available for plant uptake and is a key limiting nutrient in aquatic ecosystems [25]. The massive discharge of phosphate from human activities and agricultural and industrial production causes eutrophication of waterbodies. It is widely known that the control of phosphate in waterbodies can prohibit eutrophication [26].