# Effect of Washing Temperature on Adsorption of Cationic Dyes by Raw Lignocellulosic Biomass
## 1 Introduction  
Water is essential for the survival of humanity, as well as for all animal and plant species on Earth, and it is vital for the overall health of the environment. Indeed, all biological processes in the biosphere depend on the availability of water, and no other liquid can fulfill its role [1]. The rapid growth in population, along with increased urbanization, industrialization, and intensified agricultural practices, has led to a substantial rise in water consumption. This trend has also been accompanied by a corresponding increase in agricultural, industrial, and household waste, which contains detergents, cleaning agents,and other contaminants, leading to the infiltration of harmful substances into groundwater reserves [2]. Dyes are among the pollutants that can pose serious problems. Most of dyes are synthetic, and they now represent a large group of chemical compounds [3]. The global production of synthetic dyes is estimated at 800,000 tonnes per year. Approximately 120,000 tonnes of these dyes are released annually during the fabric manufacturing and dyeing stages [4]. These compounds are known to be toxic, mainly due to their complex structures, non-biodegradability, and high molecular weight, which make them resistant to destruction by certain physico-chemical treatment methods [5; 6; 7; 8; 9]. Dyes cause short-term hazards such as eutrophication, under-oxygenation, color, turbidity, and odor, as well as long-term hazards including persistence, bioaccumulation, and diseases [2; 10; 11]. The treatment of water polluted by dyes has, therefore, become a priority in our modern world. Developing methods and optimizing existing processes to be both effective and inexpensive have been the focus of many studies [12]. Among the pollution control processes, adsorption remains a relatively common technique that is highly effective and easy to implement [13; 14; 15]. Commercial activated carbon is the most widely used adsorbent due to its high adsorption capacity, but it is expensive and requires regeneration [16; 17; 18]. Recently, significant research has been conducted to test adsorption on alternative natural materials, known as replacement materials. These natural materials are advantageous due to their biodegradability, low commercial value, non-toxic nature, and renewable origin [19; 20; 21]. Previous work has examined the feasibility of pollutant removal using a variety of biosorbents in their raw state, such as _orange peels_[22], _pine cones_[10], _cockle shells_[23; 20], _artichoke leaves_[24], Huai _Flos chrysanthemum_[25], _sago waste_[26], and cones of _Pinus brutia_[27]. Other research has aimed to improve the retention capacity of these biosorbents through chemical treatments, for example, _ coconut shells_[28] and _cupressum semipervirens_ treated with sulfuric acid [16]; _Maclura pomerira_[2] and _durian leaves_[29] treated with sodium hydroxide; _bamboo_ treated with sodium carbonate [30]; and _Sargassum_ sp. treated with hydrochloric acid [31]. Additionally, some research has focused on the synthesis of activated carbon from economic precursors, such as chitosan-based carbons [32], _olive-stone-_based activated carbon [33], _wild-carob-_based activated carbon [6], and activated carbon prepared from _date stones_. However, none of the previous studies have examined the impact of the wash water temperature on biosorbents used in their raw state--a parameter that could influence their performance. The washing conditions vary from one study to another without clear justification: some researchers have used hot water [34; 35; 36], while others have preferred water at room temperature [22; 25; 26]. In this study, we focused on valorizing two abundant solid wastes, wild carob and _Maclura pomerira_, by simultaneously examining the effect of washing water temperature (cold, warm, or hot) on the adsorption performance of these raw biosorbents for the removal of two cationic dyes, methylene blue and crystal violet, from aqueous solutions.