## 1 Introduction  
Different types of dyes are used in various applications such as textiles, ceramics, printing, and paper production. In particular, the textile industry generates large amounts of wastewater containing dye molecules which threats humans and other living organisms [1]. Since dyes possess complex chemical structures they are non-biodegradable [2]. It is estimated that around fourteen thousand metric tons of textile dyes are thrown into the environment each year, causing serious damage to the environment [3]. A special case corresponds to the alkaline dyes. For instance, crystal violet (CV) causes eye irritation and cornea damage upon contact with the eye tissue. Further, CV ingestion generates nausea, vomiting, respiratory distress, diarrhea, and abdominal pain [4]. CV also prevents the penetration of sunlight into the water stream, reducing both the photosynthetic activity and the dissolution of oxygen [3]. The high residence time of CV in water is due to its resistance to physical,chemical, and biological degradation, and hence it is highly harmful for aquatic organisms, since just 1 ppm inhibits the photosynthesis of aquatic plants [4]. Several technologies such as electrochemical treatment, precipitation, ion exchange, reverse osmosis, and evaporation have been reported to remove dyes from water sources. However, the adsorption-based systems are one of the most attractive alternatives due to their easy implementation, versatility, and rapid kinetics [5]. Therefore, many adsorption materials have been studied for the removal of dyes. Carbon nanotubes and graphene are among the preferred adsorbents for removing pollutants from waters [6]. Nevertheless, the use of these adsorbents is inconvenient due to their high production costs. On the contrary, low cost and environmentally friendly activated charcoals can be obtained from lignocellulosic feedstock such as coconut shells and palm seeds, achieving a high carbon content and low amount of ash [7; 8]. Likewise, they could also be obtained from other sources such as minerals and lignite. Activated charcoal is an amorphous material whose main component is carbon, and it is considered macroscopically as an allotropic form of graphite. Activated charcoal has a high surface area, microporous structure, and a heterogeneous surface chemistry, mainly composed of carboxylic, phenol, ketone, quinone, hydroquinone, and aldehyde moieties. The adsorption properties in turn, depend on the source and activation method [9]. The physical or thermal activation can be carried out in presence of water vapor, CO\({}_{2}\), or air. Conversely, the chemical activation requires lower temperatures and an activation agent which inhibits the production of undesirable volatile substances. In recent years, many adsorbents have been obtained from different sources and treatments to remove alkaline dyes such as CV (Table 1). Most of these treatments imply milling, pyrolysis, and chemical methods such as oxidation and polymerization. However, the adsorption capacity of the resulting products varies depending on the source and processing employed. For instance, one of the most successful methods relies on complexation of corn cob with ethylenediaminetetraacetic acid (EDTA) improving the CV adsorption capacity to 185.2 mg g\({}^{-1}\)[10]. Another less expensive method employs natural zeolites as effective adsorbents with an adsorption capacity of 177.8 mg g\({}^{-1}\)[11]. However, other studies report very low adsorption capacities with zeolites and commercial activated charcoal of 10.7 [12] and \(<\)50.1 mg g\({}^{-1}\)[13; 14]. This suggests that the actual crystalline and chemical composition of the adsorbent impacts the adsorption process. Therefore, it is worthwhile to search for new inexpensive materials for CV adsorption. Annually, the world production of crustacean waste ranges from six to eight million tons, being China, Indonesia, Thailand, and India the countries with the highest production rate resulting in a large quantity of shrimp and crabs waste [15].