In recent years, the removal of dyes from wastewater has attracted considerable attention due to their harmful effects to ecosystem and human health. Adsorption as a facile and effective technique has been widely used to eliminate a large variety of dyes from aqueous solutions. Activated carbon is the most preferred adsorbent to treat wastewater but its use is limited because of high cost. Therefore, several low-cost and natural materials and wastes have been used as precursors for the preparation of alternative adsorbents. Among them, sawdust as an abundant and low-cost by-product has been explored as adsorbent for the removal of dyes from wastewater. This review focuses on the various sawdust used as a precursor for the preparation of activated carbons. Extensive literature information about sawdust, its compositions, activation methods, its efficiency for dyes removal, and environmental conditions effects has been reviewed. The applicability of various adsorption kinetic models and adsorption isotherm models for dye removal by sawdust-derived activated carbons has been also reported. Finally, this paper highlights the use of sawdust as base material for various composites and mixture which can be used as granular activated carbon.

Batch adsorption experiments have been conducted to investigate the removal of methyl orange from aqueous solution by an activated carbon prepared from prickly pear seed cake by phosphoric acid activation. The adsorption process has been described by using kinetic and isotherm models. The kinetic of adsorption was examined by pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. Adsorption isotherm was modeled using Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms. The adsorption process of methyl orange was well explained by the pseudo-second-order model and Freundlich isotherm. Also, pseudo-n-order model has been applied to estimate the order of adsorption kinetic and it was found equal to 2 which confirm the good accuracy of the pseudo-second order. Moreover, Dubinin–Radushkevich isotherm reveals that the adsorption of methyl orange onto activated carbon was a physisorption process in nature. The adsorption capacity of activated carbon was found to be 336.12 mg/g at temperature 20°C and pH∼7. These results demonstrated that the prickly pear seed cake is a suitable precursor for the preparation of appropriate activated carbon for dyes removal from aqueous solution.

In the present study, the experimental design method was used to optimize the preparation conditions of an activated carbon from prickly pear seed cake by phosphoric acid activation. The parameters studied include impregnation ratio, carbonization temperature, and carbonization time. The optimal conditions for the preparation of the activated carbon with high adsorption capacity for methylene blue were identified to be an impregnation ratio of 2.9, carbonization temperature of 541°C, and carbonization time of 88 min. The obtained activated carbon was characterized by SEM/EDX, FTIR, pHpzc, and its capacity to adsorb methylene blue. FTIR analysis and pHPZC showed the acidic character of the activated carbon surface. The adsorption capacity of the optimal activated carbon was found to be 260 mg·g−1 for methylene blue. The adsorption equilibrium of methylene blue was well explained by the pseudo-second-order model and Freundlich isotherm. Furthermore, the performance of the produced activated carbon was examined by the methyl orange removal.

In the present study, batch adsorption experiments were carried out to investigate the removal of methyl orange (MO) from aqueous solution using sugar scum powder as an effective inorganic adsorbent which is a cheap precursor and abundant. The characteristics of this material were determined using XRD, SEM/EDX, and FTIR. The adsorption performance of sugar scum powder was evaluated using MO as the model adsorbate. Effects of various parameters such as initial dye concentration, contact time, and adsorbent dose were studied. The adsorption process can be best described by the pseudo-second-order kinetic and Langmuir adsorption isotherm models. Maximum monolayer adsorption capacity for MO removal was found to be 15.24 mg/g at temperature 22°C and pH 7.2. Moreover, thermodynamic parameters suggested that the adsorption of MO onto sugar scum powder was a spontaneous and exothermic process. The results demonstrated that sugar scum is a suitable precursor for the preparation of efficient adsorbent for dye removal from wastewater.

A novel and inexpensive adsorbent was prepared from sugar scum for the removal of methylene blue as an organic pollutant from aqueous solutions. The response surface methodology was used to study the effects of the calcination temperature and time on the yield and the methylene blue adsorption. In order to determine the optimal conditions of the preparation, the Doehlert design and desirability function were applied. The increase in calcination temperature increases the methylene blue adsorption and induces a reduction in yield. The optimal conditions have been identified to be a calcination temperature of 986°C and calcination time of 61 min. The characteristics of the obtained adsorbent were determined using SEM/EDX, and surface functions were obtained based on FTIR and pHpzc. The produced adsorbent had a porous structure and a pHpzc of 12.5. The results showed that the yield was 49.74% and the adsorption of methylene blue was 24.52 mg·g−1 with a contact time of 10 h determined by kinetic test. The sugar scum was found to be an effective material for the preparation of appropriate adsorbent for dye removal from wastewater.