# Effect of Washing Temperature on Adsorption of Cationic Dyes by Raw Lignocellulosic Biomass
## 4 Conclusions  
This study investigated the adsorption of methylene blue (MB) and crystal violet (CV) onto raw _Maclura pomifera_ and wild carob washed with cold, warm, or hot water. The physicochemical characterization of the raw biomass revealed that the temperature of the washing water negatively impacts the texture of the biosorbents, reduced their acidic nature, and diminishes the intensity of active functional groups on the surface of both materials. The results show that the maximum adsorption capacity for MB and CV is dependent on the type of biosorbent, with _Maclura pomifera_ exhibiting a higher capacity than wild carob. The wash water temperature adversely affects the adsorption performance of _Maclura pomifera_, while it has no significant effect on the adsorption capacity of wild carob, indicating that the impact of washing water temperature is material-specific.  
The adsorption of MB and CV on raw biosorbents is positively influenced by increasing pH, contact time, or initial dye concentration and is negatively affected by increasing adsorbent dose or ionic strength. The thermodynamic analysis revealed that the biosorption process of MB and CV on raw biosorbents is physical, favorable, and spontaneous. It is exothermic in the case of MB adsorption on _Maclura pomifera_ washed with cold, warm, and hot water, while it is endothermic in other cases. The dye adsorption kinetics for wild carob are slower compared to those of _Maclura pomifera_. Equilibrium was achieved after 240 min of contact for both MB and CV adsorption on wild carob, after 120 min for CV adsorption on _Maclura pomifera_, and after 60 min for MB adsorption on _Maclura pomifera_. The analysis of the kinetic data indicated that intraparticle diffusion is not the rate-limiting step in the adsorption of MB and CV on MPC and CC; it occurs concurrently with second-order kinetics. The Sips and Redlich-Peterson models were found to be the most reliable in describing the adsorption isotherms for MB and CV on MPC and CC across the different studied temperatures.  
Conceptualization, M.B., A.B. ([PERSON]), D.C. and K.D.; methodology, M.B., A.B. ([PERSON]), D.C., K.D., A.B. ([PERSON]) and A.P.; formal analysis, M.B. and A.B. ([PERSON]); investigation, D.C. and K.D.; data curation, M.B., A.B. ([PERSON]), D.C. and A.P.; writing--original draft preparation, M.B., A.B. ([PERSON]), K.D., A.B. ([PERSON]) and A.P.; writing--review and editing, K.D. and A.P.; supervision, K.D., M.B. and A.P.; project administration, M.B. and K.D. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Polytechnical School of Constantine (Algeria).  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors declare no conflicts of interest.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Adsorbent** & **Adsorbat** &
\begin{tabular}{c} **Adsorption Capacity** \\ **(mg g\({}^{-1}\))** \\ \end{tabular} & **Reference** \\ \hline Waste coir with & CV & 2.56 & [104] \\ Sugarcane dust & CV & 13.9 & [105] \\ _Coniferous pinus_ bark & CV & 32.8 & [106] \\ Kaolinite clay & CV & 44.2 & [107] \\ Almond skin waste & CV & 85.5 & [108] \\ Coffee waste & CV & 125.0 & [109] \\ Wild carob & CV & 108.7 & This study \\ Wood apple shell & CV & 129.9 & [103] \\ _Maclura pomifera_ & CV & 149.2 & This study \\ Royal palm leaf sheath & CV & 344.8 & [110] \\ \hline \end{tabular}
\end{table}
Table 10: _Cont._