# Adsorption of Cadmium and Methylene Blue Using Highly Porous Carbon from Hemp Seeds
## 1 Introduction  
Water systems globally are constantly compromised when wastewater contaminated with toxic metals and dyes enters the environment, threatening the ecosystem and human health [1]. It is vital to seek suitable methods to analyze water contaminants [2]. Several toxic metal ions, such as cadmium (Cd), and dyes, including methylene blue (MB), are discharged into surface water [3]. Cadmium is a corrosion-protective coating for steel and iron, batteries, solar cells, alloys, plastic stabilizers and pigments [4, 5]. Cadmium and its compounds are dangerous, causing cardiovascular, neurological, renal, reproductive, gastrointestinal and respiratory cancer [1]. It is released from the body very slowly and has coactive toxicity with other metal ions, making it very dangerous [1]. [PERSON] and [PERSON] (2022) [1] used carbonized coconut shells to absorb cadmium. Their results indicated a maximum capacity of 44.67 mg/g. [PERSON] et al. (2022) [6] used phosphate-modified clay to remove cadmium, showing a maximum adsorption capacity of 198.34 mg/g. [PERSON] et al. (2022) [7] removed cadmium, lead and copper from water by bleaching ethylene tetramethylene phosphonic acid into UiO-66. Their adsorbent had a large adsorption capacity with good stability and was considered new. All the adsorbentsmentioned above still had some flaws in their adsorption processes, such as poor thermal and chemical stability, low adsorption capacity and sorption rate, poor recyclability and high process cost. Methylene blue is one of the organic dyes used for dyeing wool, silk and cotton fabrics [8]. When untreated pigments are released into the environment, they cloud the water, decrease aquatic plants' photosynthetic activity and interrupt the ecosystem [9]. Pollutants from methylene blue are highly toxic and cause mutagenic, allergenic and carcinogenic effects [10]. Therefore, it is essential to eliminate methylene blue from wastewater. [PERSON] et al. (2023) [11] used fly ash as a biomass adsorbent for removing methylene blue. Their results indicated that raw fly ash had a low methylene blue adsorption capacity of 71.22 mg/g compared to that of biochar fly ash, which was 139.93 mg/g. Biochar fly ash is easily dispersed in the adsorption system and has low reusability [12]. [PERSON] et al. (2022) [13] prepared porous biochar from wood and bamboo-derived heavy bio-oil to absorb methylene blue. Their results showed that the methylene blue adsorption capacity increased and then decreased when the carbonization temperature was raised to 800 \({}^{\circ}\)C for 2 h. Although a highly porous adsorbent was obtained in that study, a high temperature of 800 \({}^{\circ}\)C was not favorable for the sorption of methylene blue. Activated carbon has been used as an adsorbent in treating many toxic ions and dyes and can be produced from different materials. However, using activated carbon involves high costs and difficulty in regeneration [14; 15]. The use of low-cost raw materials may alleviate these problems. This study highlights hemp seeds as an alternative for water treatment. Although many studies have reported on cadmium and methylene blue adsorption, there is little information regarding removing these pollutants using hemp seeds. This work attempts to contribute to solving environmental pollution challenges by utilizing hemp seeds. Most studies to date emphasize the adsorption of a single pollutant at a time. Few studies have been published on the simultaneous adsorption of different contaminants [16]. However, wastewater effluents are composed of mixtures of pollutants, and the challenge of simultaneously removing them remains [17]. Several studies have used different parts of hemp as an adsorbent for various pollutants. [PERSON] et al. (2009) [18] wrote on the adsorption of Pb(II), Cd(II) and Zn(II) using hemp fibers. [PERSON] et al. (2014) [19] described the uptake of Zn(II), and [PERSON] et al. (2015) [20] studied the adsorption of Ni(II), using hemp fibers. Few studies have reported on hemp seeds as potential adsorbents.