## 1 Introduction  
Organic dyes are useful chemicals, which are widely applied in industry including textiles, paper, plastics, tannery, and paints, etc. [1]. The industrial effluents containing organic dyes cause environmental crises because of their high biotoxicity and potentially mutagenic and carcinogenic effects [2; 3]. Considerable efforts have been exerted to remove dye contaminants by using methods such as adsorption [4], photocatalytic degradation [5], precipitation and microbiological coagulation [6], and biosorption [7]. Adsorption is considered as one of the most promising avenues for treating dye pollutants [1]. Various materials have been investigated as adsorbents for treating dye pollutants, among which carbon materials have shown good adsorption performance because of their superior characteristics of large surface areas and structure properties. However, complicated and time-consuming procedures are required to recover these adsorbents from wastewater, thereby prohibiting their recyclability and enhancing the cost of adsorbent regeneration [8]. Hence, developing new types of adsorbents with high adsorption capacity and removal efficiency remains challenging.  
Magnetic materials have shown promise as adsorbents for remedying environmental pollutions from organic dyes because of the remarkable feature of magnetic separation compared with the abovementioned methods [9; 10; 11]. Until now, Fe\({}_{3}\)O\({}_{4}\) based magnetic carbon materials have attracted considerable research interest for treating cationic dyes. For instance, [PERSON] and co-workers developed a solvothermal method for the synthesis of RGO/Fe\({}_{3}\)O\({}_{4}\) composite as an adsorbent for methylene blue (MB) adsorption. Although the separation problem was effectively overcome, the removal efficiency was not satisfied enough because of the low surface area of reduced graphene oxide(RGO) produced by a chemical oxidation-exfoliation-reduction process and the relatively large particle size of Fe\({}_{3}\)O\({}_{4}\) (200 nm) [11]. They further discovered that the maximum adsorption capacity toward MB removal could be improved to 48.06 mg g\({}^{-1}\) when the matrix RGO was replaced by multi-walled carbon nanotubes (MWCNTs) (Fe\({}_{3}\)O\({}_{4}\)/MWCNTs) [8]. Despite these advances, the location of micro-sized Fe\({}_{3}\)O\({}_{4}\) particles on these carbon materials significantly reduces the specific surface area, thereby reducing the original adsorption capacities and removal efficiencies. To solve the abovementioned problems, exploring carbon materials with large surface areas and deposition of nano-sized Fe\({}_{3}\)O\({}_{4}\) are expected to be a promising pathway to enhance adsorption performance toward MB removal.  
Herein, porous carbon (PC) with large surface area was synthesized and explored as a matrix for depositing nano-sized Fe\({}_{3}\)O\({}_{4}\) through a solvothermal reaction. The achieved magnetic porous carbon (MPC) was employed for MB adsorption in aqueous solution. Effects of contact time, solution pH, and initial dye concentration on the adsorption property of MPC for MB removing were investigated. The kinetics and thermodynamics of MB adsorption on MPC were further studied in detail. The highest adsorption capacity of 214.4 mg g\({}^{-1}\) with the solution pH of 11 was obtained at 25 \({}^{\circ}\)C, outperforming most of the reported magnetic adsorbent for MB adsorption. The strong magnetic sensitivity of MPC favors the recovery of the adsorbent from the aqueous solution and used for the next adsorption experiment.