Development Of A Catalytic Support Based On Ziziphus Spina-Christi Seed Shells, Application To The Adsorption Of Crystal Violet In Aqueous Solution

Hinimdou B, Djonga PND, Bagamla W, Nongni JPT and Harouna M

Published on: 2022-01-08


The objective of this study is the development of a natural residue and it application by the adsorption of an cationic dye know for it toxicity which is crystal Violet (C.V) contained in water. This rexperienced natural waste is the hulls of the grains of Z-Spina collected in the region of far North Cameroon (Maroua), these residues are very abundant and can compete with conventional materials: Coal, silica gel, alimin. The caracterization of the materials after physicochemical treatement has shown the possibility of its reconvery. The X-ray fluorescence technique (RFX) has shown that it is rich in carbon, oxygent and iron. While IR Spectroscopy has proven that it works well. Adsorption test have also shown that under appropriate conditions the retention rate is greater than 80%. The results also showed that pH is a very important parameter when processing colored solutions. The experimental parameters such as pH of solution, contact time, adsorbent dose, initial concentration of CV and temperature were analyzed.  To analyze the adsorption mechanism of Langmuir isotherms, freundlich models were studied Dubunin-Kaganer-Radushkevich (D-K-R) as well as the kinetic models of pseudo-first order, pseudo-second order, Elovich and Intraparticular Diffusion. The adsorbend showed good potential for adsorption at pH 3.0 with a yield of elimination of CV by active carbon was 86.93% at 30°C. Adsorption equilibrium was reached after 20min. Thermodynamic parameters such as ?H°= 12.14 Kj/mol, ?G°=-5.83.10-4 at -6.21.10-4 Kj/mol and ?S°= 1864.9 Kj/mol proved that adsorption mechanism of CV is possible, with the physisorption, spontaneouse and exothermic in the ranges of temperature 30-60°C.


Adsorption; kinetic; Characterization; Crystal violet (CV); Activated carbon; ziziphus spina-christi


Since the beginning of humanity, dyes have been appliied in practically all spheres of our daily life for painting and dyeing paper, skin and clothing. These dyes may contain functional groups, natural or else originating from chemical or synthetic reactions. The latter have numerous applications in different fields such as, for example, dyeing and printing on fibers and fabrics of all kinds, coloring of foodstuffs, dyes for medical and cosmetic uses [1]. For the most part, these dyes are difficulty biodegradable compound, they are recognized, toxcic or harmful to humans and animals [2]. Currently the primary concern is that of the aqueous discharges of dyes by industrialists which are dramatic sources of pollution, eutrophication and unaesthetic disturbance in aquatic life and therefore present a potential danger of bioaccumulation which can affect humas, by transport through the food chain [3]. There are several techniques for treating this pollution such as precipitation, ultra-filtration, electrode-deposition, solvent extract [4], electrochemical oxidation [5], the ozonation [6], and adsorption [7]. Adsorption on activated carbon, which is an efficient but expensive process and which produces delayed pollution which itself constitutes an environmental threat. Local biomass waste could that are both economical and less polluting. CV is a cationic dye of the azoic family (Figure 1). In testing the efficacy of our activated carbon for retention CV, various reaction parameters were considered (mass of the adsorbent, the pH, the initial content of adsorbate, and the model of sorption kinetics response best describes the process of sorption). The present study aims to use Activated Carbon form shells of z. spina to remove the CV in order to reduce dye pollution.

Figure 1: Chemical structure of Crystal Violet.

Materials and Methods

Preparation of Activated Carbon

The collected cores of z. spina are done in Maroua city, Far North region of Cameroon. After the collect, we abundantly washed with the fruit of z. spina and shells were collected. They were immersed lean fruit in the hot water for separate, the pulpe of the hulls. Once separation, the pulpe of the hulls, we used the mortar out of wooden for separate hulls of the almonds. After this operation, the hulls are then washed by distilled water then dried in the air oven at 110°C for 24 hours. The hulls are thrashed by mortar, after the sieving we have to retain only particle of seize lower than 300µm. These fraction of the hulls are impregnated by phosphoric acid (1:1) at ratio from the initial solution of 95% of phosphoric acid, a prepared solution of 25% by dilution, is then mixed with the raw material. The mixture is homogenized with magnetic stirrer for 48hours. After impregnation these samples of the hulls of z. spina are dried by the oven at 110°C during 24 hours and cooled. The activated material was carbonized at 500°C with average activation time of 2hours in a furnace [8]. With a heating rate of 10°C/min and the cooling is done gradually in a desiccator at room temperature. Once cooling we washed with distilled water until a neutral pH and we dried again in the air oven at 110°C for 24hours. Then we crushed in mortar with a porcelain pestle until a powder having a particle size less than 100µm which constitute our powdered activated carbon (CA).

Characterization of the Activated Carbon

Knowledge of the physico-chemical and structural properties of any material is necessary to contribute to the understanding of many phenomena such as adsorption or others we represent some characteristics namely DRX, SEM, fluorescence X and FTIR. The XRD makes it possible to identify the nature of the crystalline and amorphous phases present in the solid [26], the SEM is used to determine the morphology of our material the elementary composition has been carried out to determine the contents in various elements, the functional surface group of the prepared activated carbon were determined by FTIR spectroscopy.  The Iodine index gives the indication on the porosity of the prepared activated carbon [8]. Quantitative characteristic for the Activated Carbon reveals the mass loss during carbonization [8].

Preparation of PV Solution

CV is an cationic dye with a molecular formula C25H30N3Cl (Figure 1). The dye stock solution was prepared by dissolving accurately weighted PV in distilled water to with concentration of 1000ppm. Experimental solution was obtained by diluting PV in accurate proportion of required initial concentration.

The Batch Mode Adsorption Study

Adsorption studies were carried out at room temperature (25°C) in a 250 ml reactor. For each experiment, remove 0.04-0.36g of adsorbent was weighed and put in the reactor containing 20ml of concentration ranging from 2 to 14 ppm, and pH increasing from 3 to 12. The mixture was mixed by magnetic stirrer on the interval of time between 3 and 40 minutes. After agitation, the solution was filtered and the residual concentration was determined by UV-visible spectrophotometry. The absorbance was measured at 600nm for the CV, the adsorbed per unit mass of adsorbent (Qe; mg/g) in the equilibrium amount of adsorption and the percentage (%R) are given by the following relationship.

Adsorption Kinetics Studies

Pseudo first-order, pseudo second-order, intraparticle and fractional power rate equations have been used to model the kinetics adsorption of CV [9]. A nonlinear regression was used for all these models. All experiment was done in triplicate. The pseudo first-order equation [10] is generally expressed as:

Where qe is the amount of CR adsorbed at equilibrium per unit weight of the adsorbent (mg/g), qt is the amount of CR adsorbed at any time (mg/g) and k1 is the pseudo first-order rate (constant/min). The values of log (qe−qt) were correlated with t. From the plot of log (qe−qt) versus t, k1 and qe can be determined from the slope and intercept, respectively. The pseudo second-order kinetic rate equation is expressed as:

Where k2 is the rate constant of the pseudo second-order adsorption equation (g/mg.min). The constants qe and K2can be obtained by plotting t/q versus t in equation (4). Intraparticle diffusion model equation [11] is generally expressed as:

Where qt (mg/g) is the amount adsorbed at time t and Kint is the intraparticle rate constant (mg/gmin1/2), whereas the larger Kint values illustrate a better adsorption mechanism which is related to an improved bonding between ions and the adsorbent particles.

Adsorption Isotherms

The adsorption isotherm indicates how the molecules distribution occurred between the liquid phase and the solid phase until this process reaches an equilibrium. Analysis of equilibrium adsorption data by fitting different linear isotherm models is an important step to find the suitable model that can be used for design purposes. The studies of adsorption isotherms are carried out by two well-known isotherms, the Langmuir and the Freundlich adsorption isotherm models. The Langmuir isotherm assumes monolayer adsorption onto a surface containing a finite number of adsorption sites of uniform strategies of adsorption with no transmigration of adsorbate in the plane of surface. While, the Freundlich isotherm model assumes heterogeneous surface energies, in which the energy term in the Langmuir equation varies as a function of the surface coverage [11].The applicability of the isotherm equation is compared by judging the correlation coefficients, R2.

Langmuir Isotherm

The linear form of the Langmuir isotherm model is given by the following equation:

Where Ce is the equilibrium concentration of the adsorbate (PV) (ppm), qe, the amount of adsorbed per unit mass of adsorbate (mg/g), and Qmax and KL are the Langmuir constants related to the monolayer adsorption capacity and affinity of adsorbent towards adsorbate, respectively. Where Ce/qe was plotted against Ce, a straight line with slope of 1/Qmax was obtained, indicating that the adsorption of the PV on treated z. spina produced from treated z-spina follows the Langmuir isotherm. The Langmuir constants KL and Qmax were calculated from this isotherm and their values are given in (Table 3).

Freundlich Isotherm

The well-known logarithmic form of the Freundlich model is given by the following equation:

Where qe is the amount adsorbate quilibrium (mg.g–1), Ce the equilibrium concentration of the adsorbate (PV) and KF and n are the Freundlich constants, n giving an indication of how favourable the adsorption process and KF is the adsorption capacity of the adsorbent. KF can be defined as the adsorption or a distribution coefficient and represents the quantity of dye adsorbed onto treated hulls adsorbent for a unit equilibrium concentration. The slope 1/n ranging between 0 and 1 is a measure of adsorption intensity or surface heterogeneity, becoming more heterogeneous as its value gets closer to zero [12]. A value for 1/n be low one indicates a normal Langmuir isotherm while 1/n above one is indicative of cooperative adsorption. The plot of log qe versus log Ce gives straight lines with slope of 1/n which shows that the adsorption of the PV also follows the Freundlich isotherm. Accordingly, the constants (KF and n) were calculated and recorded in results.

Results And Discussion

Characterization of the Activated Carbon

DRX of Adsorbent

Figure 2: DRX Spectrum of Activated Carbon.

SEM Of Adsorbent

Figure 3: SEM Photography of Activated Carbon.

Infrared Spectroscopy of Adsorbent: Interpretation of the IR spectrum (Figure 4) shows a vibration pic at 1731.42 cm-1 corresponding to the stretching vibration of C = O bond of ketones. There is also a pic at 1661.09 cm-1 which indicates the presence of the C = C bond of the aromatic nuclei characteristic and the pic at 1471 cm-1 indicates the presence of the stretching vibration of CH2 bond alkanes. The pic at 1691.45 cm-1 corresponding the stretching vibration of C-O bond of the carboxylic acids. We observe a pic at 3647.19 cm-1, corresponding to the pic of stretching of the hydroxyl grouping - OH and the hydrogen bonds of alcohols. The pic located at 1505.20 cm-1 indicates the presence of the stretching of N–H bond of secondary amine. Thus, the spectrum suggests the presence of the groupings like phenol, carbonyl, amine, ether and carboxylic.

Figure 4: IR Spectrum of Activated Carbon.

Values of Some Parameters of the Characterization of the Activated Carbon

(Table 1) presents values of methylene blue index, iodine index and pH as characteristics of the activated carbon from the hulls of z-spina.

Table 1: Characteristics of the activated carbon from the hulls of z-spina.



Methylene blue Index


Iodine Index






Effect of Agitation Time

In oder to determne the contact time necessary to reach the adsorption equilibrium of a pollutant by a porous support, it is essential to determine the adsorption kinetics beforehand [13]. For this we followed the adsorption kinetics of crystal violet in aqueous solution on our activated carbon in order to determine the equilibruim time necessary to apply for the rest of the study. (Figure 5) shows the evolution of the retention rate of our pollutant. We notice a rapid change in the retention rate ranging from 0 to 10 minutes followed by a slow phase before reaching equilibruim. Indeed after 5 minutes of reaction the rate 82,8% well reaches 86,83% at early 20 minutes and stabilizes. The rapid adsorption of the dye observed et the start of the reaction be explained by the availability of adsorption sites on the surface of our adsorbent material but this could also be linked to the physicochemical characteristics and especially to the nature of the porosity material [14]. The slow phase which follow and which lead to equilibrium results in an increasing occupation of the adsorption sites, making them less available. Equilibrium being reached, the maximum values adsorbed remain constant whatever the increase in time. This result is similar to those obtained by [15, 16]. But this equilibrium time is less than that obtained by [14].

Figure 5: The effects of contact time on sorbent-sorbate interaction time.

Modeling of Adsorption Kinetics

The adsorption process in general strongly depends on the contact time between adsorbent and the adsorbate. Figure 5 corresponding to the percentages of elimination of CV which increases with time. The graphical representation of the pseudo first order, pseudo second order, intraparticle and Elovich equations are given by (Figure 6, 7, 8 and 9). The parameters of the graphical representations of the equation in (Table 2).


Figure 6: Plot for First-order for CV.  

Figure 7: Plot for Second-order for CV.

Figure 8: Plot for intrapraticle CV.


Figure 9: Plot for Elovich for CV.

Table 2: Constant Speed and Correlation Coefficients of Kinetic Models.


Pseudo First Order

Pseudo First Order





























In emerges from this table that the adsorption takes place in two stages:

  • The diffusion of pollutant molecules on the surface of the adsorbent.
  • The interaction between the pollutant solution and the adsorbent.

The pseudo-second order model is the most suitable with a correlation coefficient close to 1 and very similar theoretical and experimental adsorbed quantities. These results are in agreement with those of [14,17,18]. The type of mechanism is generally used to describe the chemisorption phenomena [19].

Effect of the Amount of Adsorbent

In order to evaluate the influence of the mass of the activated carbon used for the adsorption of the dye, we studied the evolution of the retention rate of our dye represented by (Figure 10). This graph shows that efficiency of the elimination of the dye increases with the increase in the dose of the adsorbent. This result is attributed to the fact that greater the quantity of the adsorbent, the more the contact surface increases and therefore a greater availability of adsorption sites. These results are similar to those obtained by [20]. However, increasing the mass of the adsorbent rater decreases the amounts adsorbed. This is explained by the saturation and clogging of the adsorption sites [21, 22].



Figure 10: The effect of carbon dose for the uptake of CV.

Effect of pH of Solution

pH is a very important parameter in the adsorption process since it affects both the load of the adsorbent and the adsorbate. (Figure 11) shows the influence of the pH of the dye solution on the retention rate of our adsorbent. It emerges from this graph that he adsorption of the crystal violet dye by our activated carbon increases at pH greater than the pH at zero load point (3,95). This is due to electrostatic attractions because our dye being of the adsorbent [23, 24].

Figure 11: The effect of pH on CV adsorption by Activated Carbon from.

Effect of Initial Concentration

In order to determine the types of isotherms involved and the maximum adsorption capacities of our adsorbent, we have studied the evolution of the retention rate of our dye as a function of its equilibrium concentration. The adsorption isotherm of the dye on adsorbent is worked on by (Figure 12). The graph obtained shows that the adsorption yield increases with the concentration of the pollutant. The limit quantity of pollutant adsorbed does not seem to be reached within the range of concentrations studied. These results are similar to those obtained by [25, 26]. The shape of the isotherm show that it is of type C, which indicates a constant relative affinity between crystal violet and the activated carbon used. These results are in agreement with those obtained by [27].

Figure 12: Influence of Initial Concentration of CV.

The modeling of the adsorption isotherms is done by resorting to the isotherms of Langmuir, Freundlich, Temkin and D.R.K which are the four models most used for the interpretation of the results obtained during an adsorption on active carbon in solution watery. The curves obtained are shown in (Figure 13,14,15 and 16). (Table 3) shows the adsorption parameters of the four models studies.     


Figure 13: Langmuir plot for the CV.

Figure 14: Freundlich plot for the CV.

        Figure 15: Temkin plot for the CV.

Figure 16: D.R.K plot for the CV.

Table 3: Correlation Coefficients and Constants of Langmuir, Freundlich, Temkin and D.R.K.



































It emerge from the table obtained that two models, satisfactorily describe the adsorption of our dye on the activated carbon, with correlation coefficients greater than 0, 95. According to the Langmuir model, the adsorption takes place with the formation of the monolayer, the adsorption of the dye is localized on well-defined sites likely to bind only on dye molecule in this case we are in the presence of chemisorption. The Freundlich model tells us that the adsorption takes place on heterogeneous sites, with the formation of multilayer on the surface of our materials in this case the adsorption is physical. The adsorption of crystal violet on our activated carbon is both physical and chemical because for Freundlich, n ? 1 showing that the adsorption is favorable and for Langmuir, 0 < RL < 1, the adsorption is physical. These results are similar to those obtained by [27]. The Freundlich constant b is positive for the reaction carried out with leads to say that the adsorption process would be endothermic.

Effect of Temperature

In order to determine the thermodynamic parameters of our materials, we studied the evolution of the retention rate of the dye as a function of temperature. The results obtained are shown in (Figure 17). The curve obtained shows that the more the temperature increases, the more the retention rate increases, we can say that the process is endothermic. This is explained by the fact that the rise in temperature decreases the viscosity of our polluting solution thus promoting the diffusion of the molecules of this pollutant towards the internal pores of our adsorbent materials. These results are similar to those obtained by [28, 29].  The thermodynamic parameters are show in (Table 4).

Figure 17: Effect of temperature on the adsorption of PV by the activated carbon.

Table 4: Kinetic parameters for adsorption CV onto activated carbon.

T0 C






















It emerges from this table that the free energy is negative in all the processes. This indicates that the adsorption of the dye on our materials is spontaneous [30, 31]. Whatever the temperature, the adsorption process is physical since the free energy is less than 20 KJ/mol [32]. The free enthalpy is positive, indicating that the adsorption process is endothermic as well as an increase in temperature facilitates the phenomenon of adsorption. The standard entropy is positive, which means that the molecules our pollutant remain less ordered on the solid/solution interface during the adsorption process.


The objective of our work is to reduce crystal violet by adsorption on activated carbon based on the husks of Ziziphus spina-Christi grains in aqueous solution. Activated carbon is prepared by chemical activation with phosphoric acid. Elemental analysis shows that the activated carbon produced contain two major elements: carbon and oxygen. Observation with a scanning electron microscope shows a highly developed porosity over the entire surface of the prepared support. The X-ray diffractogram shows that the activated carbon has an amorphous structure with low cristallinity. The pH at zero charge is acidic. Observation on the IRTF spectrum shows vibration of the hydrogen of the hydroxyl groups O-H (carbonyl, phenol or alcohol), O-H of cellulose and lignin. The activated carbon produced with a specific surface area of the order of 893,6 m²/g. the study of the adsorption kinetics show that the reaction is rapid with an equilibrium time of 20 minutes. The retention percentage of our dye at equilibrium is: 86,93%. The pseudo-second order model is the model established in this study to simulate the kinetics of adsorption on activated carbon produced with a high correlation factor. The adsorption isotherms are simulated by the linear model of Langmuir and Freundlich. This value of n of the Freundlich model is greater than 1 which indicates that the adsorption is favorable and physical.    


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