During recent years, pharmaceuticals and their metabolites have been increasingly found in water bodies and diclofenac is one of the pharmaceuticals residues most frequently detected thus far. The aim of this work was to evaluate the Moringa oleifera seeds as an alternative for diclofenac (DCF) removal in water samples. The batch procedure for DCF removal at the optimized conditions (25 mL of 10.0 mg L−1 DCF, pH 5.0, extraction time of 30 min and M. oleifera mass of 2.0 grams) achieved adsorption of 100% of DCF in real water samples. The pseudo-second-order kinetic described the adsorption rate-controlling step. The adsorption isotherms were fitted by Langmuir, Freundlich and Sips models and the sorption capacity of the biosorbent is spontaneously favourable. The maximum adsorptive capacity was estimated at 32.05 mg g−1 and 32.85 mg g−1 by Langmuir and Sips models, respectively. The advantages of this procedure include good reproducibility in the removal of DCF even at low concentrations in real samples and does not require an additional step of pre-treatment of the adsorbent. The results highlight the potential of M. oleifera seeds as a cheap, environmentally friendly alternative for the removal of DCF from polluted water.

  • Moringa oleifera seeds were efficient in the adsorption of diclofenac obtaining removals greater than 95%.

  • The adsorptive capacity of moringa was sufficient for remediation of contaminated water without any structural change of the adsorbent.

  • The adsorption rate is determined by the chemical interactions.

  • Adsorption equilibrium is reached spontaneously.

  • The procedure was satisfactorily applied to real environmental samples.

Graphical Abstract

Graphical Abstract
Graphical Abstract

The presence of emerging contaminants in the aquatic environment has been subject of increasing concerning due to their effects on the environment and on the human health even at low concentrations ( ≤ μg L−1). In this category, pharmaceuticals are the contaminants most frequently detected due to its widespread use (Izadi et al. 2020). Diclofenac (DCF) is a nonsteroidal anti-inflammatory drug that is widely prescribed in human and veterinary medicine with analgesic and anti-pyretic properties (Naghipour et al. 2018; Xu et al. 2020). Although the DCF's ecotoxicity is relatively low, if it interacts with other drugs present in water, the toxicological potential increases considerably (Xu et al. 2020). Surface and ground water contaminated by DCF can cause extensive damage to biota, e.g., feminization of fish (Medina et al. 2021); therefore, this compound has been recently included in the List of Priority Contaminants, regulated by 2013/39/EU Directive (Medina et al. 2021).

Previous studies demonstrated that DCF is not removed or is partially eliminated in conventional water treatment plants (Xu et al. 2020; Medina et al. 2021). Therefore, it is necessary innovative and alternative technologies to removal DCF and other drugs in contaminated water. Advanced oxidation process (AOP) is innovative alternative to removal organic contaminants in water (Alkhuraiji 2019). However, the efficiency of these processes is considerably improved by the addition of chemical species, and additional techniques such as ultrasound radiation (Zhuan & Wang 2020). In addition, such procedures should be aware to the formation of degradation by-products with unknown toxicity. Also, considerable attention has been given to use of activated carbon (AC) for the adsorption of pharmaceuticals from aqueous solutions (Naghipour et al. 2018). Despite the efficiency of these procedures, they involve the use of chemical reagents, which may make them economically unfeasible. A promising alternative for the treatment of effluents that contain pharmaceuticals are natural adsorbents as a substitute for AC. Studies involving the use of biomass for the adsorption of pharmaceuticals are still scarce in the literature.

Moringa oleifera is a fast-growing tree that can reach 12 meters high found mainly in semiarid, tropical, and subtropical areas. Several applications have been proposed for M. oleifera, as its use in malnutrition and animal feed (Gopalakrishnan et al. 2016). The seeds have been used for the treatment of turbid water due to their flocculation properties (Baptista et al. 2017) and applied to textile effluent treatment (Agarwal et al. 2019). Other studies describe their use for the treatment of aqueous solutions containing silver (Araújo et al. 2010a), nickel (Marques et al. 2012) and chromium (Matouq et al. 2021) ions. However, there are still few reports available on the use of M. oleifera seeds, in their entirety, without the need for any structural change, for the adsorption of pharmaceuticals as DCF.

In this study, M. oleifera seeds were evaluated as a new low-cost adsorbent to remove DCF from the public potable water supply, river water and groundwater. The parameters that affect DCF adsorption (adsorbent dosage, pH, extraction time) were evaluated. Several models were carried out to determine the most suitable kinetic model and isotherm to explain the results. The use of M. oleifera seeds has certain advantages from both economic and environmental points of view, such as availability, the renewable nature of the adsorbent material, easy operation and their low cost.

Instrumentation

Determination of diclofenac was performed using high-performance liquid chromatography – HPLC (Shimadzu, Kyoto, Japan) equipped with C18 column (150 × 4.6 mm, 5 μm diameter) and UV/VIS SPD-10A detector set at 282 nm. Acetonitrile and 0.10% (v/v) acetic acid (1:1) mixture was used as mobile phase.

Reagents and solutions

All solutions were prepared using ultrapure water (18 MΩ cm), analytical grade reagents and HPLC grade solvents. Diclofenac sodium (DCF) (molecular weight = 318.1 g mol−1; chemical formula = C14H10Cl2NNaO2; pKa = 4.2) was purchased from Sigma Aldrich (Rome, Italy). Working solutions (0.5–100.0 mg L−1) were prepared from the dilution of the 1,000 mg L−1 DCF. Acetonitrile used as mobile phase was purchased from Sigma Aldrich. Prior to use, all glassware was kept overnight in 10% (v/v) aqueous nitric acid solution, followed by ultrasonication for 1 hour and finally washed with deionized water. Samples and solvents were filtrated in cellulose acetate membranes (Chrom filter) with 0.45 μm pores.

Preparation of adsorbent material

The M. oleifera seeds used as adsorbent material were collected in the city of Uberlândia-Brazil (latitude 18 °55′07″ S and longitude 48 °16′38″ W). After collecting the material, the pods were shelled and the seeds were washed twice with deionized water and left in an ultrasound bath for 10 minutes. Then, the seeds were dried in the open air (24–28 °C) for 8 hours in a dust-free environment. The dried seeds were ground in a commercial blender. Seed powders were separated according to particle size, using a sieve shaker with defined granulometry meshes. A particle size range of 0.5–1.0 mm was selected for further experiments. The material characterization was presented in previous works (Araújo et al. 2010b).

Batch adsorption procedure

DCF removal studies were performed by adding the prepared biosorbent in 10 mg L−1 diclofenac solutions. The mixture was shaken for 30 min in a magnetic stirrer and then the suspension was filtered through filter paper (Whatman N°42). The filtrate was diluted with mobile phase before HPLC analysis. DCF was quantified before and after the removal experiments. In order to achieve the optimum conditions in terms of diclofenac removal, the following variables were evaluated: adsorbent mass (0.5 to 2.0 g) and stirring time (5 to 1,440 min). The pH was maintained at 5.0 during all experiments. DCF removal percentage was estimated by the following equation:
formula
(1)
where Co and Cf (mg L−1) are DCF concentration before and after the adsorption process, respectively.

Adsorption kinetic models and isotherms

The experiments to investigate the adsorption kinetics were carried out in the temperature range of 25–28 °C using 0.5 g of M. oleifera seeds powder, 25 mL of 10.0 mg L−1 DCF solution at pH 5.0, and stirring time up to 30 min. These same conditions were applied to adsorption isotherm experiments, except that the concentration of DCF varied from 0.5 to 100.0 mg L−1. In both experiments, these conditions were applied to ensure the achievement of the equilibrium state; mixtures were then filtered and DCF quantified by HPLC.

In both studies, the DCF concentration after the adsorption (Cf) was used to calculate the adsorption capacity of DCF at equilibrium (qe) in milligrams per gram of adsorbent, through Equation (2):
formula
(2)
where V is the volume of the DCF solution in liters and m is the mass of the adsorbent material in grams.

Application of the proposed method

The method was applied using the biosorbent for to evaluated adsorption of diclofenac from potable water (public supply), river water, and groundwater. The sample of potable water treated by a local sanitation company was collected from a tap in a research laboratory in the city of Uberlândia (Brazil), and river samples were collected from three different locations along the Uberabinha River, which runs through an urban zone in the city of Uberlândia. In these samples, diclofenac was not detected. Thus, to assess the performance of the adsorbent material in these systems, the samples were spiked with 10.0 mg L−1 DCF. The samples were filtered through filter paper and the pH was adjusted to 5.0 using 0.1 mol L−1 HCl. The samples (25 mL) were then treated with 0.5 g of adsorbent and using a stirring time of 5 min. The DCF was quantified using HPLC before and after the removal experiments.

Optimization of adsorption process

The adsorption efficiency of the biosorbent depends on parameters as pH, material amount and contact time. The initial concentration of DCF (10 mg L−1) was selected in such a way that the lowest concentration expected after adsorption was within the limit of quantification of the equipment (0.37 mg L−1). Regarding the particle size, the selected size range (0.5–1.0 mm) was for presenting the largest contact surface without the occurrence of agglomerations in the solution.

The pH of DCF solutions was set at 5.0 for all experiments based on characterization studies of the M. oleifera seeds presented by Araújo and collaborators (Araújo et al. 2010b). Its pH value of the point of zero charge is in the range of 6 to 7. Thus, below this pH range, the surface of the sorbent is positively charged and it is able to adsorb diclofenac as its anionic form that is predominant close to pH 5.0.

The effect of contact time on removal percentage of DCF sodium is shown in Figure 1. The adsorbed amount of DCF onto M. oleifera seeds increases with the increase of contact time and the equilibrium state is reached in about 120 min. Adsorption capacity presented a rapid increase during the first 60 min. This high adsorption capacity at the initial stage indicated higher driving force that made fast transfer of diclofenac to the surface of adsorbent particles. From Figure 1 the DCF removal efficiency was ca. 90%.
Figure 1

Effect of the variation of the adsorption time. Conditions: Volume of the solution = 25.0 mL, pH = 5.0, Diclofenac concentration = 10.0 mg L−1, Mass = 2.0 g of the adsorbent.

Figure 1

Effect of the variation of the adsorption time. Conditions: Volume of the solution = 25.0 mL, pH = 5.0, Diclofenac concentration = 10.0 mg L−1, Mass = 2.0 g of the adsorbent.

Close modal
The effect of biosorbent mass on DCF removal was evaluated in the range of 0.5–2.0 g using an adsorption time of 30 min. The results are summarized in Figure 2. Removal efficiency increased up to 2.0 g of M. oleifera seeds. It is observed that the availability of adsorption sites is higher by employing more biosorbent mass, until a saturation trend is observed, which results in higher DCF removal.
Figure 2

Effect of varying the mass of the adsorbent. Conditions: Volume of the solution = 25.0 mL, pH = 5.0, DCF concentration = 10.0 mg L−1, stirring time = 30 minutes.

Figure 2

Effect of varying the mass of the adsorbent. Conditions: Volume of the solution = 25.0 mL, pH = 5.0, DCF concentration = 10.0 mg L−1, stirring time = 30 minutes.

Close modal

Adsorption kinetics study

The study of adsorption kinetics provides important information regarding its mechanism and the limiting step that controls the adsorption rate (Ho & McKay 1999). The models used to assess the kinetics of the adsorption process that best fit the data are the pseudo-first-order models of Lagergren, the pseudo-second order of Ho & McKay (1999) and the intraparticle diffusion model (Weber & Morris 1963).

The equations that describe the kinetic models of pseudo-first order, pseudo-second order and intraparticle diffusion, respectively, are represented by Equations (3)–(5):
formula
(3)
formula
(4)
formula
(5)
where qe: adsorption capacity of DCF per gram of adsorbent at equilibrium (mg g−1); qt: adsorption capacity of DCF per gram of adsorbent at time t (mg g−1); k1: pseudo-first-order velocity constant (min-1); k2: pseudo-second order velocity constant (g mg−1 min−1) and kd: intraparticle diffusion coefficient (mg g−1 min−0.5).

The parameter values obtained from the linear fit for the pseudo-first order and pseudo-second order models are summarized in Table 1.

Table 1

Results of the kinetic parameters of the adsorption process of DCF by moringa seeds

Pseudo-first order
Pseudo-second order
r2qe (mg g−1)k1 (min−1)χ2r2qe (mg g−1)k2 (mg−1 g min−1)χ2
0.9772 0.06994 0.1287 0.04176 0.999 0.0962 13.4386 0.0001086 
Pseudo-first order
Pseudo-second order
r2qe (mg g−1)k1 (min−1)χ2r2qe (mg g−1)k2 (mg−1 g min−1)χ2
0.9772 0.06994 0.1287 0.04176 0.999 0.0962 13.4386 0.0001086 

qe, exp = 0.1060 mg g−1.

The pseudo-first-order adsorption kinetics plot of the DCF on the moringa is shown in Figure 3(a). The coefficient of determination is relatively low. Furthermore, the experimental qe value does not agree with the one calculated using this model, indicating that adsorption does not is controlled only by the number of active sites available in the adsorbent.
Figure 3

Linear fit applied to (a) pseudo-first-order and (b) pseudo-second-order adsorption kinetic models.

Figure 3

Linear fit applied to (a) pseudo-first-order and (b) pseudo-second-order adsorption kinetic models.

Close modal

As can be seen in Table 1, the coefficient of determination for the pseudo-second-order kinetic model is the one that best fit, indicating that the adsorption process fits the pseudo-second-order mechanism. The pseudo-second-order adsorption kinetics plot of the drug DCF on the moringa is shown in Figure 3(b). This model assumes that the determining step of the adsorption rate depends on the physicochemical interactions between the adsorbent and the available groups on the surface of the adsorbent in its entirety. In addition, the adsorption process on the surface of the adsorbent is proportional to the number of sites occupied (Ho & McKay 1999; Ahmad et al. 2005).

The intra-particle diffusion model was also tested to obtain more information about the mechanism involving the formation of a permeable film, which can diffuse into the pores of the adsorbent (Weber & Morris 1963).

As can be seen in Figure 4, the data plotted in relation to intra-particle diffusion does not represent a satisfactory linear fit; therefore, it cannot be elucidated mathematically by a single equation. The curve obtained does not pass through the origin and the graph is not linear throughout the process, suggesting that the intraparticle diffusion mechanism is not dominant. Thus, the data are better represented by two linear phases. The initial phase representing the effect of the boundary layer, with external mass transfer. In this case, DCF is rapidly adsorbed by moringa seeds. After some time, the equilibrium is observed, resulting in the second phase. In this case, due to the low concentration of solute in the solution as well as a lower availability of sites for adsorption, the effect of intraparticle diffusion is decreased.
Figure 4

Plot of data obtained from the application to the intra-particle diffusion kinetic model.

Figure 4

Plot of data obtained from the application to the intra-particle diffusion kinetic model.

Close modal
To evaluate the fit of the parameters obtained in the tested linear regression models for the pseudo-first-order and pseudo-second-order kinetics, the experimental qe values were compared with the respective fitted values for each contact time until reaching the equilibrium (120 min). The comparison profile is shown in Figure 5, the raw results of which are shown in Table 1 of the supplementary data. The pseudo-second order model presents values ​​of qe that are closest to the experimental results. The obtaining a smaller magnitude of the error function (χ2) in relation to the pseudo-first order confirms the adequacy of the performed fit.
Figure 5

Comparison profile between the experimental results and the kinetic models tested.

Figure 5

Comparison profile between the experimental results and the kinetic models tested.

Close modal

The performance of moringa seeds as an alternative adsorbent has presented similar conditions for satisfactory removal of other drugs. In a similar work, pseudo-second-order kinetics was also shown to be adequate to describe the limiting step of paracetamol adsorption, as reported by Ogunmodede et al. (2021).

Adsorption isotherms

Figure 6 shows the adsorption isotherm for DCF adsorption onto M. oleifera seeds. Among the isotherm models found in the literature, the primary ones are the Langmuir (Langmuir 1918) and Freundlich (Freundlich 1906).
Figure 6

Adsorption isotherm of DCF onto moringa seeds. Conditions: pH = 5.0; diclofenac concentration = 0.5 to 100.0 mg L−1, Stirring time = 30 minutes and the adsorbent mass = 0.5 mg.

Figure 6

Adsorption isotherm of DCF onto moringa seeds. Conditions: pH = 5.0; diclofenac concentration = 0.5 to 100.0 mg L−1, Stirring time = 30 minutes and the adsorbent mass = 0.5 mg.

Close modal
The Langmuir model assumes that adsorption is limited to the monolayer; a maximum adsorption indicates the saturation of this monolayer. The fitting of the experimental data to the Langmuir linear equation can be expressed by the following equation:
formula
(6)
where Ce (mg L−1) is the equilibrium concentration of the DCF, qe (mg g−1) is the adsorption capacity of DCF adsorbed per unit mass of the adsorbent at equilibrium, qmax (mg g−1) is the maximum adsorptive capacity, and KL (L mg−1) is the Langmuir constant related to the adsorption capacity.
The value of KL was used to calculate the RL parameter according to Equation (7). This admission constant RL is called the equilibrium parameter, being a measure of favoring adsorption. RL values between 0 and 1 represent a favorable adsorption process explained by the Langmuir isotherm (Rao et al. 2006).
formula
(7)
Figure 7(a) presents the data according to Equation (6). The correlation coefficient obtained was 0.9991 and qmax was estimated at 32.05 mg g−1, which is similar the experimental qmax (31.71 mg g−1) value, thus showing that the data fit the Langmuir model as observed in the Figure 4(a).
Figure 7

Langmuir (a), Freundlich (b) and Sips (c) isotherm plots for the sorption of diclofenac onto Moringa oleifera seeds.

Figure 7

Langmuir (a), Freundlich (b) and Sips (c) isotherm plots for the sorption of diclofenac onto Moringa oleifera seeds.

Close modal
The Freundlich isotherm is an empirical expression that takes into account the heterogeneity of the surface and multilayer adsorption onto the binding sites located on the surface of the sorbent. The Freundlich model is expressed as follows:
formula
(8)
where Ce (mg L−1) is the equilibrium concentration of the metal, qe (mg g−1) is the adsorption capacity of DCF adsorbed per unit mass of the adsorbent at equilibrium, and n and KF (mg g−1) are the Freundlich constants related to the biosorption intensity and adsorption equilibrium constant, respectively.

Figure 7(b) was plotted according to Equation (8) and the values of n, and KF are 1.0785 and 0.2894 respectively. The determination coefficient (r2) obtained was 0.9943, thus showing that the experimental data provide a good fitted with the Freundlich model, as observed in Figure 4(b). The value of n was greater than 1, suggesting relatively strong adsorption of DCF onto the surface of moringa seeds.

The isotherm evaluation showed that the experimental data for adsorption of DCF onto moringa seeds provided a good fit to the two isotherm models. Despite that linear correlation (r2) value of the Langmuir model is slightly higher than that of the Freundlich model (Table 2), it is reasonable to assume that DCF adsorption behavior onto biosorbent may take place in monolayer on the surface of the adsorbent. However, based on satisfactory correlation coefficients, the data are also consistent with a model in which the multilayers adsorption takes place on the adsorbent materials. This result is somewhat expected, bearing in mind the complexity of the structure and composition of the biosorbent.

Table 2

Equilibrium parameters of DCF adsorption onto M. oleífera seeds

Langmuir 
qmax (mg g−1RL KL (L mg−1KL (L mol−1r2 χ2 
32.05 0.0086 1.1528 366 702.72 0.9991 0.1074 
Freundlich 
KF (mg g−1)(L g−1)1/n n r2 χ2   
0.2894 1.0785 0.9943 0.0977   
Sips 
qmax (mg g−1Ks (μg L−1)−1/n n r2 χ2  
32.85 0.00772 1.03156 0.9961 0.4433  
Langmuir 
qmax (mg g−1RL KL (L mg−1KL (L mol−1r2 χ2 
32.05 0.0086 1.1528 366 702.72 0.9991 0.1074 
Freundlich 
KF (mg g−1)(L g−1)1/n n r2 χ2   
0.2894 1.0785 0.9943 0.0977   
Sips 
qmax (mg g−1Ks (μg L−1)−1/n n r2 χ2  
32.85 0.00772 1.03156 0.9961 0.4433  

With the interest in elucidating more clearly if there is a predominant adsorption mechanism, a new isotherm model Langmuir-Freundlich (or Sips isotherm) was tested. This isotherm can be representative of the characteristics predicted by the Langmuir or Freundlich isotherm in materials of heterogeneous composition, such as the moringa seeds. In this way, the Sips isotherm combines both isotherms in the same mathematical relationship, as shown by Equation (9) (Foo & Hameed 2010):
formula
(9)

For low initial concentrations of adsorbate this model assumes the Freundlich form, while at high concentrations, the Equation (9) assumes a form similar to the Langmuir isotherm, in monolayers. In the Sips isotherm model, the constant Ks is associated with the adsorption energy and the parameter n which also represents the degree of heterogeneity. If n= 1 the system is homogeneous, equating to the Langmuir model, and for values of n increasingly smaller than 1, an increase in heterogeneity has been characterized. In the case of n > 1, it is indicative of the formation of more than one layer of adsorbate on the adsorbent (Foo & Hameed 2010). The results were plotted in the Figure 7(c).

The results present a satisfactory fit for the Sips isotherm, through the good value of the coefficient of determination 0.9961. The value of qe predicted by the Sips (32.85 mg g−1) model is appreciably close to that determined by the Langmuir isotherm. However, the highest value of the error function obtained in relation to the respective values ​​for the Langmuir and Freundlich isotherms is notorious (Table 2). The Figure 8 illustrates the comparison profile between the experimental qe values ​​for each Ce, in relation to the tested isotherm models, the raw results of which are shown in Table 2 of the supplementary data.
Figure 8

Comparison profile between the experimental results and the tested adsorption isotherm models.

Figure 8

Comparison profile between the experimental results and the tested adsorption isotherm models.

Close modal

The good agreement of the experimental data with the Langmuir model suggests that the mechanism of adsorption of DCF onto moringa seeds occurs in a way defined by specific interactions at individual active sites. The parameters calculated by the Langmuir model are reasonable to indicate the reach of the adsorption equilibrium by the saturation of the active sites. The influence of material heterogeneity is related to the variation of the spatial orientation of the organic adsorbate on the surface, which may cause π-π interactions between the DCF molecules (Viotti et al. 2019). This explains the value of parameter n obtained in the Sips isotherm, slightly greater than 1.0.

Organic molecules such as diclofenac are limited to diffusing inside micropores, due to the size of molecules being relatively larger than micropores. As solid surfaces are rarely homogeneous, in addition to chemical reactions between the adsorbent and the adsorbate, the effects of the transport phenomenon in the inner portion of the adsorbate must be considered (Ho & McKay 1999), which is consistent with the experimental results obtained in this work, taking into account that the Langmuir and Freundlich isotherms obtained very similar and satisfactory coefficient of determination values.

The constant KL was used to calculate the change in the standard Gibbs free energy (Δads) for the adsorption of DCF by moringa seeds using Equation (10):
formula
(10)
where, R is the ideal gas constant (8.314 J K−1 mol−1), T is the absolute temperature (298 K), and Ka is the thermodynamic equilibrium constant (dimensionless), which can be calculated from the Langmuir constant, KL, as discussed by Liu 2009. Since the adsorbate is an organic specie with weak charge, under these adsorption conditions, KL was used as an estimate of the value of Ka (Liu 2009). The value obtained of Δads for the adsorption of DCF by moringa seeds was −32.7 KJ mol−1, where the negative value indicated that the adsorption process was spontaneous, which is consistent with favoring the adsorptive process predicted by the Langmuir model.

Application

The method was applied using the biosorbent for evaluated adsorption of DCF in potable water (public supply) and river water. In these samples DCF was not detected, and thus, they were spiked at a concentration of 10.0 mg L−1. The samples were subsequently treated with the adsorbent material and the diclofenac removal efficiency was estimated as shown in Table 3. The results achieved indicate the potentiality of the M. oleifera seeds as an effective tool for DCF removal from water samples.

Table 3

Determination of DCF in water samples and experimental recovery of DCF in water samples spiked with 10.0 mg L−1 DCF

SamplesDCF found (mg L−1)DCF added (mg L−1)DCF after removal (mg L−1)Removal (%)
Groundwater 0.20 ± 0.01 — — 101.02 
0.20 ± 0.01 10.00 1.72 ± 0.02 83.14 
Tap water 0.28 ± 0.04 — — 100.8 
0.28 ± 0.04 10.00 1.83 ± 0.05 82.20 
River water n.d. — — — 
n.d 10.00 1.70 ± 0.01 83.05 
Lake water n.d. — — — 
n.d. 10.00 1.88 ± 0.01 81.20 
Rain water n.d. — — — 
n.d. 10.00 1.86 ± 0.01 81.40 
Wastewater 0.12 ± 0.01 — — 100.31 
0.12 ± 0.01 10.00 1.62 ± 0.09 83.80 
SamplesDCF found (mg L−1)DCF added (mg L−1)DCF after removal (mg L−1)Removal (%)
Groundwater 0.20 ± 0.01 — — 101.02 
0.20 ± 0.01 10.00 1.72 ± 0.02 83.14 
Tap water 0.28 ± 0.04 — — 100.8 
0.28 ± 0.04 10.00 1.83 ± 0.05 82.20 
River water n.d. — — — 
n.d 10.00 1.70 ± 0.01 83.05 
Lake water n.d. — — — 
n.d. 10.00 1.88 ± 0.01 81.20 
Rain water n.d. — — — 
n.d. 10.00 1.86 ± 0.01 81.40 
Wastewater 0.12 ± 0.01 — — 100.31 
0.12 ± 0.01 10.00 1.62 ± 0.09 83.80 

N.D.: not detectable. (n = 3).

DCF removal efficiencies were greater than 95% under the experimental employed conditions (25 mL of 10.0 mg L−1 DCF, pH of 5.0, contact time 30 min and 2.0 mg of M. oleifera seeds). The results showed satisfactory reproducibility to removal low concentrations of DCF in the samples tested.

The adsorption efficiency of moringa seeds as a natural biosorbent, without any structural modification, as reported here, is comparable to other more expensive adsorption procedures. In a study involving the adsorption of DCF in fixed bed columns, using AC as a synthetic material, a maximum adsorptive capacity of 36.25 mg g−1 (298 K) was observed (Franco et al. 2018). In a similar work, Viotti et al. (2019), achieved good adsorptive capacity (60.805 mg g−1) using M. oleífera pods for DCF removal in distilled water. However, a pre-treatment step of the adsorbent with HCl 0.1 mol L−1 was necessary. Satisfactory results could only be obtained by heating the system to 328 K. The authors concluded that under such conditions, the adsorption of DCF it is not spontaneous (Viotti et al. 2019).

Compared to other previously presented materials for DCF removal as hybrid inorganic materials (Thanhmingliana & Tiwari 2015) or amended iron micro particles (Ghauch et al. 2010), the biosorbent based on M. oleifera seeds has advantages in high availability, easy material preparation, good adsorption capacity, cheap cost and potential applicability to removal of other organic and inorganic contaminants.

The evaluation of M. oleifera seeds as a biosorbent for DCF removal from potable water supplies demonstrated the high potential of this material as a cheap and environmentally friendly alternative for pharmaceutical remediation in water. DCF removal efficiencies were greater than 95% from water samples under the optimum experimental conditions. The use of moringa seeds without any structural change in their natural composition represented an advantage of this procedure. The results indicated that the rate-determining step of adsorption is controlled by specific interactions of an electrostatic nature between the DCF and the surface of the adsorbent, through pseudo-second-order kinetics. The Langmuir model proved to be adequate for adjusting the adsorption isotherm. The maximum adsorptive capacity was estimated at 32.05 mg g−1, which is consistent with the theoretical value. The satisfactory maximum adsorption capacity obtained and negligible cost of biosorbent means that moringa seeds can be considered as a reliable natural material for the removal of DCF from aqueous effluents.

The authors are grateful for financial support from the Brazilian governmental agencies Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), from the MG state governmental agency Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) and GO state governmental agency Fundação de Amparo à Pesquisa do Estado de Goiás (FAPEG).

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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