Surface Modification of Tea-Waste-Based Biochar Adsorbent: Synthesis, Characterization, and Batch Adsorption for the Removal of Zidovudine ARV Drug and Phenol

Abstract

Domestic, agricultural, and industrial waste has been investigated as a substitute for activated carbon adsorbents. For instance, the transformation of tea waste to biochar can be utilized as a substitute for activated carbon adsorbents. In this study, tea waste-based biochar adsorbents (biochar, biochar/reduced graphene oxide (biochar/rGO), biochar/reduced graphene oxide/deep eutectic solvent-cetyltrimethylammonium bromide (biochar/rGO/DES-CTAB), and biochar/reduced graphene oxide/deep eutectic solvent-glycerol (biochar/rGO/DES-glycerol)) were synthesized by simple thermal treatment of tea waste and sucrose followed by modification with reduced graphene oxide and deep eutectic solvents. The obtained materials were characterized using a range of spectroscopy techniques, Fourier Transformed Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy–Energy-Dispersive X-ray Spectroscopy (SEM–EDS), Brunauer, Emmett, and Teller (BET) surface area analysis, and pH at point of zero charge (pH _PZC). The obtained results showed that the principal material, i.e., biochar was modified, and FTIR results confirmed the presence of added functional groups. SEM images revealed surface structural changes, and BET showed a decrease in pore size from 10.16 nm to 6.87 nm. The synthesized materials were applied for the removal of ZDV and phenol from the aqueous medium. Batch adsorption studies were conducted to optimize operating parameters such as the adsorbent dose, solution pH, contact time, and initial concentration. Pseudo-first-order (PFO), Pseudo-second-order (PSO), and intraparticle diffusion (IPD) kinetic models were determined to investigate the mechanism of the adsorption process. The coefficient of correlation, R², was used to determine the best fit of the kinetic models. The adsorption results showed that the DES-glycerol-modified adsorbent was more efficient in removing the pollutants ZDV and phenol than biochar, biochar/rGO, and biochar/rGO/DES-CTAB adsorbents. In addition, the results showed that an acidic medium of pH 2.00 and a contact time of 1 h 30 min and 30 min is sufficient for removing ZDV and phenol, respectively, from an aqueous medium.

1. Introduction

Wastewater containing organic pollutants poses a significant risk to the entire water body, human health, and aquatic life. Although various wastewater treatment methods such as osmosis, ozonation, advanced oxidation processes (AOPs), coagulation, filtration, photo-degradation, adsorption, etc., have been studied, adsorption is most preferred because it is easier to operate, cheapest amongst most methods, environmentally friendly, and has a wide range of adsorbent choices [1]. Conversely, the success of the adsorption process is solely based on the choice of the adsorbent and the intended use.

Traditionally, various adsorbents such as activated alumina, zeolites [2] silica gel, activated carbon [3], etc., are some of the adsorbent choices used during the removal of organic pollutants. However, some of these adsorbents have several disadvantages such as the removal of deposits, higher commercial costs, lower adsorbent regeneration efficiency, and lower surface area [1,4]. Tea is one of the most popular beverages worldwide, with approximately 20 billion cups of tea consumed daily [5,6,7] resulting in approximately 2 million of tea waste generated annually [8]. Tea leaves contain more iron embedded in the native leaf tissue than other biochar precursors such as wood. The heteroatom-doped porous biochar is produced without further doping or immobilization, which is advantageous for activating it with other materials to generate greater reactive oxygen species such as sulfate radicals and singlet oxygen atoms [9].

Although biochar has promising aspects of being a good adsorbent, it has a lower surface area, limiting its capabilities and efficiency [10]. Therefore, to enhance the properties of biochar as an adsorbent, biochar modification has been evaluated. The modification can be via chemical, physical, or mineral impregnation, or even engineered magnetically [10]. Modifying biochar is necessary to enhance its surface area, effectiveness, and surface activities and incorporate it with other beneficial materials [11]. Iris and colleagues noted that using modified metal/biochar composites can also improve the reaction rate [12], whereas other modifications have effects such as reduction, complexation, and enhanced sorption potential [13]. rGO is a rich carbon-containing material and a promising adsorbent. The modification of biochar with rGO will result in an increased surface area and increased carbon content that will aid in the adsorption of organic pollutants, whereas DES is a non-toxic, economically friendly adsorbent. DES has excellent properties and is easily manipulated into designer adsorbents. Hence, the introduction of DES-CTAB and DES-glycerol will aid in the incorporation of desired functional groups.

Several studies have been conducted that prove that the modification of biochar with other materials is beneficial and greatly improves biochar’s adsorption capabilities. Liakos et al., 2021 studied activated porous biochar adsorbent made from tea and plane tree leaves biomass for the removal of pramipexole dihydrochloride from aqueous solutions [14]. Sarkar et al. (2019) researched the removal of dye from wastewater using acid-modified tea leaves (AMTL) as an adsorbent [15]. Wong et al. (2018) used activated carbon made from spent tea leaves for the removal of pharmaceutical waste from contaminated aqueous solutions [16]. Kazmi et al., 2013 studied the removal of phenol compounds from contaminated water using activated tea leaves as an adsorbent [17]. These studies are evident enough to prove that biochar modification can greatly improve biochar’s overall characteristics and properties. However, the methods of modification in previous studies were not in line with green chemistry guidelines. These studies used harsh, toxic, and large quantities of chemicals to synthesize materials such as GO and rGO [18,19]. Furthermore, it is important to note that the current study used methods and chemicals that comply with green chemistry principles.

Hence, in this study, tea waste-based biochar adsorbents were obtained using simple, direct, and effortless methods for surface modification of tea waste material with sucrose by simple thermal treatment to obtain biochar/rGO and further modified with deep eutectic solvent. In addition, the modified biochar/rGO/DES-glycerol was used as an adsorbent for the first time to remove zidovudine ARV drug and phenol from aqueous solutions. This approach has never been reported elsewhere.

2. Methodology

2.1. Chemicals and Materials

Unless otherwise indicated, all the chemicals and reagents used in this study are of analytical grade, obtained from suppliers, and used without further purification. Zidovudine, phenol (purity ≥ 99), boric acid (purity ≥ 99.5), glycerol (purity ≥ 99.5), cetyltrimethylammonium bromide (CTAB, purity ≥ 98), choline chloride (purity ≥ 98), and propanoic acid (purity ≥ 96) were acquired from Sigma Aldrich, South Africa. Moreover, 0.1 M NaOH and 1 M HCl were purchased in solution form from Rochelle, South Africa.

2.2. Preparation of Tea Waste-Based Biochar Adsorbents

2.2.1. Preparation of Biochar

The tea waste bags were collected at Alberton, South Africa. The tea waste bags were washed several times with deionized water and dried in an oven at 60 °C overnight. The fanning was collected, washed with deionized water, and dried overnight. The dried fanning was crushed to powder, transferred to a crucible, and placed immediately in a heated muffle furnace in an oxygen environment at a temperature of 500 ± 10 °C for 1 h. The resulting material was labeled and stored in a desiccator until further use. Figure 1 presents the images of tea waste before pyrolysis and after pyrolysis.

2.2.2. Preparation of Reduced Graphene Oxide (rGO)

Sucrose was obtained as granulated sugar from a retail store and utilized without further purification. Exactly 2 g of granulated sugar was added to 100 mL of deionized water in a Borosil glass beaker and stirred until mixed. The solution was transferred to a crucible and placed immediately into the heated muffle furnace in an oxygen environment. The furnace was maintained at 500 ± 10 °C for 1 h. The heating causes sugar to dehydrate, resulting in black foam. The final product was gathered and stored in a desiccator until further use [20].

2.2.3. Preparation of Biochar/rGO

Equal quantities of sucrose and fanning were weighed into a beaker containing sufficient deionized water and stirred until homogeneity. The mixture was then transferred into a crucible and placed immediately into the heated muffle furnace, maintained at 500 ± 10 °C for 1 h in an oxygen environment. The resulting material was transferred into a sealable container and stored in a desiccator until further use.

2.2.4. Preparation of DES-CTAB

Deep eutectic solvents were prepared as described by [21]. A mixture of CTAB, choline chloride, and propanoic acid with a mole ratio (0.5:4:8) was placed in a round bottom flask, capped, stirred, and maintained at 75–80 °C until a homogenous clear liquid was obtained.

2.2.5. Preparation of DES-Glycerol

A mixture of glycerol, choline chloride, and boric acid with a mole ratio (1:1:1) was placed in a round bottom flask, capped, stirred, and maintained at 75–80 °C until a homogenous clear liquid was obtained.

2.2.6. Modification of Biochar Reduced Graphene Oxide Composite with DES-CTAB and DES-Glycerol

Equal amounts of the biochar/rGO composite and DES (1:1 mass: mass ratio) were mixed with 10 mL of methanol in a 250 mL conical flask. The mixture was stirred at room temperature (25 °C) for 5 h and then oven-dried overnight at 80 °C. The modified adsorbents (biochar/rGO/DES-CTAB/glycerol) were then washed with double-distilled water until a neutral pH is achieved. The mixture was filtered with a 0.45 m PTFE membrane. The DES-modified biochar/rGO/DES-CTAB/glycerol was dried at 80 °C overnight and placed in a desiccator until further use.

2.3. Characterization

Characterization was used to identify, isolate, or quantify substances or materials or characterize their physical properties, such as morphology and surface texture. All the synthesized materials (biochar, biochar/rGO, biochar/rGO/DES-CTAB, and biochar/rGO/DES-glycerol) were characterized by FTIR, XRD, EDS, SEM, AND BET.

2.3.1. Fourier-Transform Infrared Spectroscopy (FTIR)

The FTIR analyses were performed using the Nicolet IS50 analytical FTIR spectrometer (Waltham, MA, USA). A diamond accessory was used to examine the nanocomposites and nanoparticle materials. All spectra were captured using a solid-state scanning technique ranging from 400 cm⁻¹ to 4000 cm⁻¹.

2.3.2. X-ray Diffraction (XRD)

XRD analyses were performed using the Shimadzu-XRD 700, X-ray diffractometer with Cu Ka radiation (λ—1.154056 Å) to determine the crystallinity of the materials. A scan speed of 1°/min, a current of 30 mA, and a voltage of 40 kV were used in the 2-theta range of 10–90°.

2.3.3. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS)

The microstructure and surface morphology of biochar nanocomposite materials were studied using scanning electron microscopy (SEM). Images were captured using a tungsten filament source on a Zeiss 10 kV field emission scanning electron microscope (FESEM). The elemental identification and adsorbent mapping were aided by energy-dispersive X-ray spectroscopy (EDS).

2.3.4. Brunauer–Emmett–Teller (BET)

BET analyses were performed to determine the surface area, pore sizes, and diameters of the adsorbents on a Micromeritics Tristar II 3020 instrument, and the surface area was calculated by the BET method. Materials were degassed with nitrogen prior to analyses.

2.4. Batch Adsorption Studies

2.4.1. Preparation of Phenol Solution

A stock solution of 1000 ppm was prepared by weighing 1.00 g of phenol pellets and dissolving them in 1000 mL of deionized water in a volumetric flask.

2.4.2. Preparation of Zidovudine Solution

A stock solution of 20 ppm was prepared by weighing 0.02 g of ZDV and dissolving it in 1000 mL of deionized water in a volumetric flask.

2.4.3. Preliminary Adsorption Studies

The preliminary adsorption study was conducted by evaluating the effect of adsorbent dosage and pH using biochar, biochar/rGO and biochar/rGO/DES-CTAB, and biochar/rGO/DES-glycerol.

Effect of Dose

The desired experimental concentrations were determined by diluting the stock solution with deionized water. In this experiment, the dosage effect was investigated by varying the dosage in ranges of 0.001 g to 0.1 g in a 40 mL solution of 10 ppm ZDV and 50 ppm phenol. The mixture was agitated at 200 rpm at room temperature (25 °C) for 24 h. The adsorption experiments were performed in duplicate, and the data presented are the average results obtained.

The concentration of pollutants was quantified using a UV-vis spectrophotometer, with calibration curves plotted for every quantification test. ZDV and phenol were quantified at wavelengths of 276.30 nm and 268.42 nm, respectively. The adsorption capacity and percentage removal (%R) were calculated using Equations (1) and (2), respectively.

$$qe=\frac{Co-Ce}{m}(V)$$

(1)

$$\%R=\frac{Co-Ce}{Co}\times 100$$

(2)

where qe is the adsorbed ZDV/phenol on the adsorbent, m is the mass of the adsorbent (g), V is the volume of the pollutant (ZDV/phenol) solution (L), Co is the initial concentration mg/L, and Ce is the final concentration mg/L of ZDV/phenol.

Effect of pH

The pH of the solution is a critical parameter for determining the optimal pH of organic adsorption capability onto the absorbent [19] The initial concentration of (ZDV and phenol) and the adsorbent dosages were fixed. The solutions’ pH varied from 2, 4, 6, 8, 10, and 11 using 0.1 M NaOH and 0.1 M HCl. The mixture was placed in a shaker at 200 rpm for 24 h. The samples were filtered, and the concentration of pollutants was determined using a UV-vis spectrophotometer.

2.4.4. Detailed Adsorption Studies

In this section, studies such as the point of zero charge, isotherm, kinetics, desorption, and regeneration were conducted using only the adsorbent that demonstrated better performance in preliminary adsorption studies, i.e., biochar/rGO/DES-glycerol.

Point of Zero Charge

The point of zero charge was determined by investigating the isoelectric point of the adsorbent under study over a pH range of 2–12.

Isotherm and Kinetic Studies

The isotherm and kinetics studies were conducted by investigating the effect of the initial concentration and contact time. The experiments were carried out using concentrations of 5, 10, 15, 20, 50, and 100 mg L⁻¹ at an optimum pH of 2. The mixtures were agitated at 150 rpm for 6 h at room temperature. For each concentration, small aliquots of the bulk sample were drawn at predetermined intervals and filtered for the analysis of the remaining amount of the initial pollutant concentration using UV vis.

To explore the adsorption interaction and evaluate the equilibrium, the experimental data obtained after the study of the initial concentration effect were fitted with models such as Langmuir (Equation (3)) and Freundlich (Equation (4)) equilibrium isotherms [22,23].

$$\mathrm{Langmuir} \mathrm{equation} \to q_e=\frac{q_m{b}_K{C}_e}{{\left(1+b_k{C}_e\right)}^{aK}}$$

(3)

$$\mathrm{Freundlich} \mathrm{equation} \to q_e=K_F{C}_e^n$$

(4)

where C_e is the residual ZDV/phenol concentration in the solution (mg L⁻¹), q_e is the ZDV/phenol concentration in the adsorbent (mg g⁻¹), K_F (mg/g)/(mg/L), n is the Freundlich constant, and n (dimensionless) is the heterogeneity factor. q_m is the maximum ZDV/phenol adsorption quantity per gram of adsorbent (mg g⁻¹) and KL is the Langmuir adsorption equilibrium constant (L mg⁻¹).

To determine the adsorption dynamics, rate, mechanism, and transport of the pollutants (under study) onto different adsorbents, the experimental data obtained during the studies of contact time were fitted with kinetics models such as the Pseudo-first order (PFO), Pseudo-second order (PSO) [24], and Weber–Morris intraparticle diffusion models (IPD) [25]. The adequacy of the model that explains the data was determined by the R² value of the non-linear regression analysis’ proximity to unity.

$$\mathrm{PFO} \mathrm{equation} \to q_t=q_e-e^{-k1t}$$

(5)

$$\mathrm{PSO} \mathrm{equation} \to q_t=\frac{q_e^2{k}_{2}t}{1+k_2{q}_{e}t}$$

(6)

$$\mathrm{IPD} \to q_t=k_{ld}{t}^{1/2}+C$$

(7)

Desorption and Regeneration Studies

It is vital to avoid producing secondary waste by dumping discarded (contaminated) adsorbents into the environment. The adsorbents’ reusability was examined to renew the adsorbents and isolate the contaminants. Desorption experiments were performed by introducing 0.5 g of the adsorbent (biochar/rGO/DES-glycerol) to 40 mL of 10 mg L⁻¹ ZDV and 50 mg L⁻¹ phenol. The solutions were shaken for 24 h at room temperature. The pollutant equilibrium concentration was obtained after filtering the solutions. The saturated adsorbents were dried in an oven at 80 °C. In conical flasks, 0.05 g of saturated adsorbents was weighed, 10 mL of ethanol was added, and the flasks were agitated for 30 min. The initial concentration of the pollutants (ZDV and phenol) was determined using the collected filtrates.

The following equation was used to determine the desorption efficiency:

$$\mathrm{D}\mathrm{e}\mathrm{s}\mathrm{o}\mathrm{r}\mathrm{p}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n} \mathrm{e}\mathrm{f}\mathrm{f}\mathrm{i}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{n}\mathrm{c}\mathrm{y}=\frac{\mathrm{C}\mathrm{d}\mathrm{e}\mathrm{s}}{\mathrm{C}\mathrm{a}\mathrm{d}\mathrm{s}}\times 100$$

(8)

where C_des is the concentration of ZDV/phenol adsorbed on the adsorbents (mg L⁻¹) and C_ads is the concentration of dye adsorbed on the adsorbent in the initial cycle (mg L⁻¹).

3. Results and Discussion

3.1. FTIR Analysis

FTIR spectra of the biochar, biochar/rGO, biochar/rGO/DES-CTAB, and biochar/rGO/DES-glycerol are shown in Figure 2. The results showed that biochar/rGO/DES-CTAB and biochar/rGO showed similar and consistent bands. The FTIR spectra of all the materials (biochar, biochar/rGO composite, biochar/rGO/DES-CTAB, and biochar/rGO/DES-glycerol) showed enhancement of peaks and different functional groups, which indicates that the primary material (biochar) has been modified. The DES-CTAB-modified adsorbent showed an additional peak at 2848 cm⁻¹, which collaborates with the CH₂ symmetric stretch.

The DES-CTAB modified material also showed a broad band at 3530 cm⁻¹–3151 cm⁻¹ belonging to an –OH stretching vibration. The less intense peak at 730 cm⁻¹ is attributed to C-Cl stretch by the introduction of the DES-CTAB. The biochar was successfully modified with rGO and DES-CTAB. For biochar/rGO and biochar/rGO/DES-CTAB, the peaks at 1607 cm⁻¹, 1422 cm⁻¹, 1228 cm⁻¹, and 1059 cm⁻¹ correspond to C=C, O=C-O bending, the alkoxy -CO group, and C-O functional groups, respectively. The latter, less intense peaks are attributed to the vibrations of the C-H functional groups.

The bands at 1044 cm⁻¹ are assigned to alkoxy C-O-C stretching in the biochar and biochar/rGO [18]. The composite biochar/rGO had no attached functional groups between 1600 cm⁻¹ and 4000 cm⁻¹. This confirms the reduction of the most oxygen-containing functional groups by the rGO. The biochar/rGO/DES-glycerol modified adsorbent showed an additional peak at 2848 cm^−1, corresponding to the CH₂ symmetric stretch. The DES-glycerol-modified material also showed a broad band at 3530 cm⁻¹–3151 cm⁻¹ belonging to an –OH stretching resulting from the DES [19]

The less intense peak at 730 cm⁻¹ is attributed to C-Cl stretch by introducing the DES-glycerol. This confirms that biochar was successfully modified with rGO and DES-glycerol. For biochar/rGO/DES-glycerol, the peaks at 1607 cm⁻¹, 1422 cm⁻¹, 1228 cm⁻¹, and 1059 cm⁻¹ correspond to C=C, O=C-O bending, alkoxy -CO group, and C-O functional groups, respectively. The latter less intense peaks at 881 cm⁻¹ and 792 cm⁻¹ are attributed to the vibrations of the C-H functional groups.

3.2. XRD Analysis

XRD analysis was conducted to evaluate the crystallinity of the materials synthesized. Biochar, biochar/rGO, and biochar/rGO/DES-CTAB X-ray diffractograms (Figure 3) demonstrated that the biochar had been modified. The results showed that Biochar is an amorphous form of carbon with broad peaks, indicating a largely poorly crystalline structure. However, the diffractogram for biochar/rGO/DES-CTAB shows sharper peaks at the same 2ϴ values as the primary biochar material. Deep eutectic solvent, which has a more crystalline structure than biochar, is responsible for the sharpness of the peaks. The XRD profile of biochar shows a small diffraction peak at two thetas equal to 29°.

At exactly two thetas equal to 29°, the biochar/rGO composite showed a more intense peak. This sharp diffraction peak is due to the introduction of the rGO, causing a structural ordering of carbons and improved material carbon content. Furthermore, the biochar/rGO composite showed a smoother baseline than the other synthesized materials. The XRD spectra for the DES-CTAB-modified composite (biochar/rGO/DES-CTAB) resulted in a slight shift to the left of the diffraction peak previously observed in biochar and biochar/rGO composites at two thetas equal to 29° to 28° (Figure 3). A new and more intense peak is observed at two thetas equal to 24°. This could be due to the introduction of the DES-CTAB. The spectrum of the DES-CTAB-modified material was almost similar to that of the starting material, with three less intense bands observed at two thetas equal to 15°, 25°, and 45°, respectively.

X-ray diffractograms of biochar, biochar/rGO, and biochar/rGO/DES-glycerol showed a similar structural morphology. The broad diffraction peak at two thetas equal to 20° and 35° indexed as (C002) indicates an amorphous carbon structure with randomly aligned aromatic sheets [26]. The diffractogram for biochar/rGO/DES-glycerol, on the other hand, exhibits a sharper peak at the same two theta values as both materials. The diffraction peaks observed at two thetas equal to 25°, 40°, and 51° correlate to the structure’s many inorganic components from the materials, most of which are quartz [27]. The peak at 11.5° (2θ) of all the indexed materials (001) [28], is most likely connected to graphene oxide-like materials. Furthermore, the sharpness of the peaks is due to the formation of the graphene oxide-like structure upon the modification of biochar with rGO. The development of graphene oxide, which can be used as a direct indicator of the degree of oxidation of the carbonaceous structure in the biochar’s core, is particularly important for planar and extended molecules.

3.3. EDX Analysis

Elemental analyses of the adsorbents are shown in

Table 1. EDS elemental content (%) of biochar; biochar/rGO, biochar/rGO/DES-CTAB, and biochar/rGO/DES-glycerol.

Adsorbent	C	O	Si	Al	CA	Cl	O/C
Biochar	85.53	13.05	0.81	0.61	0.73	-	0.15
Biochar/rGO	89.37	9.87	0.48	0.28	0.28	-	0.11
Biochar/rGO/DES-CTAB	80.9	13.01	-	2.52	-	3.58	0.16
Biochar/rGO/DES-glycerol	84.92	13.95	-	-	0.31	0.82	0.16

. The EDS measurements focused on different areas of the composites. Biochar showed the contents of carbon, oxygen, and calcium. The O/C ratio shows the polarity and oxygen-containing surface functional groups in biochar; the higher the ratio, the more polar the functional groups [18]. The DES-CTAB and DES-glycerol-modified adsorbents showed a higher O/C ratio than the composite material (biochar/rGO), indicating that biochar/rGO/DES-CTAB and biochar/rGO/DES-glycerol are more hydrophilic. than biochar/rGO. Both materials also showed no detectable hydrogen. The composite biochar/rGO introduced silicon into the mixture and increased the carbon content by 3.84% resulting in a carbon content of 89.3%. This is due to rGO being a carbon-rich material. Further modification of the material by introducing DES-CTAB added aluminum and chlorine to the mixture.

The final modified material (biochar/rGO/DES-CTAB) contained C, O, Al, and Cl at quantities of 80.90%, 13.01%, 2.52%, and 3.58%, respectively. A slight carbon content reduction of 8.9% and an increased oxygen content of 3.14% were observed.

On the other hand, further modification occurred by introducing DES-glycerol, which added calcium and chlorine to the mixture. The final modified material contained C, O, Ca, and Cl at quantities of 84.92%, 13.95%, 0.31%, and 0.82%, respectively. A slight carbon content reduction of 4.45% and an increased oxygen content of 4.08% were noticed. This is assumed to come from the introduction of DES-glycerol. All the materials were further characterized with SEM.

3.4. SEM Analysis

SEM was used to study the surface morphology and fundamental physical properties of the synthesized adsorbents, including the tea-waste-based biochar after thermal treatment. As shown in Figure 4, post-thermal treatment of the biochar showed rough and irregular surface layers similar to a rod with many visible fractures and possible open stomata. The modification of biochar with the rGO composite formed a mesoporous structured composite. The composite showed a more defined surface area than that of biochar alone. The composite also looked like thick fractured sheets with irregular pores that were unevenly spread on the material’s surface.

The composite biochar/rGO showed more developed and well-defined porosity and unique surface characteristics than the starting biochar material. The porous surface area of an adsorbent is an essential indication of its capacity to absorb. The size of the molecule compared to the pore volume impacts the adsorption process’s efficiency.

Moreover, molecules with large particle sizes may not fit into small pores, affecting the adsorption capability [29]. In this case, the composite adsorbent (biochar/rGO) had smaller pores and larger pore volumes, making the material adopt greater characteristics and creating a range of active adsorption sites. Further modification of biochar/rGO with DES-CTAB and DES-glycerol resulted in a completely different structural morphology. The biochar/rGO/DES-CTAB resulted in irregular open cavities and pores spread out unevenly on the surface of the adsorbent. The biochar/rGO/DES-glycerol resulted in sheets of different shapes and sizes with prominent black holes and cavities, suggesting that contaminants can be trapped and absorbed into the surface of the adsorbent.

3.5. BET Analysis

The adsorbent materials biochar, biochar/rGO/DES-CTAB, and biochar/rGO/DES-glycerol showed lower surface areas and pore volumes than biochar/rGO (

Table 2. BET surface analyses for biochar; biochar/rGO, biochar/rGO/DES-CTAB, and biochar/rGO/DES-glycerol.

Parameter	Biochar	Biochar/rGO	Biochar/rGO/DES-CTAB	Biochar/rGO/DES-Glycerol
BET Surface Area (m2/g)	2.806	84.969	1.059	2.506
Pore volume (cm3/g)	0.007	0.031	0.004	0.004
Pore size (nm)	10.16	1.44	13.04	6.87

). The decrease in surface area and pore volume following modification can be attributed to the introduction of DES, resulting in surface modification and blocking of the pores [21]. Nonetheless, biochar/rGO/DES-glycerol still showed higher adsorption of ZDV and phenol from wastewater.

3.6. Batch Desorption Studies

3.6.1. Preliminary Studies

Effect of Dose

The preliminary adsorption study was conducted by evaluating the effect of adsorbent dosage and pH solution. The dosage effect of the adsorbents (biochar, biochar/rGO and biochar/rGO/DES-CTAB, and biochar/rGO/DES-glycerol) between the ranges of 0.001 g to 0.1 g with a constant concentration of 10 mg L⁻¹ and 50 mg L⁻¹ of ZDV and phenol, respectively, and a volume of 40 mL pollutant solution in a 50 mL centrifuge tube was investigated. The samples were wrapped with foil and left in a shaker overnight at room temperature (25 °C) at a speed of 200 rpm. The ZDV and phenol’s percentage removal efficiency was plotted against the adsorbent dose (g), as shown in Figure 5.

The adsorption efficiency of both ZDV and phenol increased as the adsorbent dosages increased. Adsorption peaked at 0.1 g, achieving 49% and 63% removal for ZDV and phenol, respectively (Figure 5). It was also observed that once adsorption reached equilibrium, the number of organic pollutants adsorbed remained constant as the adsorbent dosage was increased. This is due to increased particle interactions and aggregation, decreasing the total surface area of the adsorbent’s active sites. Biochar showed 0% removal across all adsorbent dosages for both organic pollutants. In both experiments for the adsorption of ZDV and phenol, biochar/rGO performed better than biochar/rGO/DES-CTAB.

The removal efficiency and capacity of ZDV and phenol increased as the adsorbent dosage increased (Figure 6). This is due to the increased adsorbent surface area and the vast number of available active sites for adsorption [30]. Choosing a suitable adsorbent dosage requires careful consideration. Since biochar/rGO/DES-glycerol performed better than biochar, biochar/rGO, and biochar/rGO/DES-CTAB, only biochar/rGO/DES-Glycerol will be considered for further studies and to determine the detailed effect on pH solution for the adsorption of ZDV and phenol.

Effect of pH

Due to its impact on the probable ionic formation of the adsorbate species, adsorbent surface charge, and influence of the analyte characteristics, the adsorption system’s pH is a significant parameter in any adsorption study. The hydrophobic neutral adsorbate molecules could dissociate into other molecules when the pH of the adsorbate increases or decreases [31]. Increased electrostatic repulsion when the adsorbate pH is varied leads to reduced electrostatic interactions between oppositely charged adsorbate and adsorbent. An increase or decrease in pH may also positively affect the ability of the adsorbate to donate π-electrons, improving the π−π electron donor–acceptor interaction [32]. The effect of pH was determined with an initial concentration of 10 mg L⁻¹ and 50 mg L⁻¹ ZDV and phenol, respectively, between pH 2.00 and 11.0 at a constant adsorbent dosage of 0.1 g biochar/rGO/DES-glycerol. The samples were left in a shaker overnight at a speed of 200 rpm.

The influence of the pH solution on the adsorption efficiency showed that the maximum adsorption for ZDV and phenol occurred at pH 2.00 and gradually declined as the pH tended towards an alkaline medium. These demonstrate that acidic mediums have higher ZDV and phenol dissociation rates. Due to the activities of the functional groups on the adsorbent surface and the presence of DES, positively charged ions dominate the adsorbent surface at low pH levels. Furthermore, an increased electrostatic attraction–ion interaction mechanism between the adsorbate and adsorbent results in higher removal efficiency. This can be explained further by the adsorbent’s pH (pzc).

Additionally, the study of the pH effect (Figure 7) was conducted to further confirm the performance of the different adsorbents under study. The pH is a very crucial factor affecting the adsorption capacity of an adsorbent. From the results obtained, the influence of pH solution on the adsorption efficiency showed that maximum adsorption for ZDV and phenol occurred at pH 2.00 and gradually declined as the pH tended towards an alkaline medium. These demonstrate that acidic mediums have higher ZDV and phenol dissociation rates. Due to the activities of the functional groups on the adsorbent surface and the presence of DES, positively charged ions dominate the adsorbent surface at low pH levels. Furthermore, an increased electrostatic attraction–ion interaction mechanism between the adsorbate and adsorbent results in higher removal efficiency.

Therefore, the results obtained in Figure 7 confirm that biochar/rGO/DES-glycerol possesses better adsorption performance for the removal of ZDV and phenol. Hence, only biochar/rGO/DES-glycerol will be used for further optimization and detailed adsorption experiments.

3.6.2. Detailed Adsorption Studies

Point of Zero Charge (PZC)

The point of zero charge (PZC) is typically defined as the pH at which the net charge of the total particle surface (i.e., the adsorbent’s surface) equals zero [33]. The term proposed in colloidal flocculation research explains how pH affects the phenomena. The properties of an adsorbent determine the PZC value. For example, the surface charge of an adsorbent is characterized by the ion that resides on the surface of the particle (adsorbent) structure. At a lower pH, more hydrogen ions (protons, H+) would be adsorbed than other cations (adsorbate). If, on the other hand, the surface is positively charged and the pH is raised, fewer anions will be adsorbed as the concentration of hydroxide ions rises. If the pH is less than the PZC value, the adsorbent’s surface charge will be positive, allowing the anions to be absorbed. If the pH is higher than the PZC value, the surface charge will be negative, allowing cations to be adsorbed [33].

The effect of the pH solution can be explained further by the adsorbent’s pH (pzc). The pH (pzc) (Figure 8) test is used to determine the pH at which the surface of the adsorbent is zero [34] and can adsorb contaminants easily. This means that the adsorbent biochar/rGO/DES-glycerol is positively charged below pH < pH_pzc and negatively charged above pH < pH_pzc. The adsorbent’s surface charge is predominantly positively charged at pH values below their pH (pzc) [35,36], making it more effective at absorbing anionic adsorbates at lower pH mediums. Since the pH (pzc) values are positive, it demonstrates the relevance and significance of the surface charge and solution pH during adsorption.

ZDV has a pka of 9.80 [37], making the ZDV molecule negatively charged below its neutral pH of 9.80 and positively charged above pH 9.80. Since the adsorbent biochar/rGO/DES-glycerol is predominantly positively charged below the pH medium of 7.40, a few mechanisms can be assumed between the negatively charged ZDV molecules and positively charged adsorbent surface in acidic media. Furthermore, ZDV is a thymidine analogue that contains a 3′-azide group rather than a 3′-hydroxyl functional group. It is believed that the 3′-azide group on the ZDV molecule and the surface charge of biochar/rGO/DES-glycerol in an acidic medium drives the reaction to the highest adsorption affinity of the drug achieving almost 100% removal (Figure 7). As the system’s pH increased to become more basic, adsorption dropped consistently until pH 11.00, when no adsorption occurred between the ZDV molecules and the adsorbent.

The adsorption of weak electrolytes, such as phenol compounds, from aqueous solutions on a porous amphoteric solid adsorbent’s surface depends primarily on two crucial factors. One is the degree of electrolyte dissociation and the dominant charge on the adsorbent surface. Both factors depend on the aqueous solution’s pH. The first consideration can be predicted qualitatively by the weak electrolyte’s pKa (activity constant); the electrolyte will remain unaffected at a pH less than the pKa. The second factor, however, is more difficult to determine [38]. At pH = 2.00 (Figure 7), adsorbate molecules are easily combined with the positively charged surface of biochar/rGO/DES-glycerol via electrostatic attraction. Phenol has a dissolution constant (pKa) of 10.0 [39]. It ionizes more easily and has a greater polarity. As a result, phenolic molecules have increased electrostatic sensitivity. Furthermore, increasing the ionic strength of the sorbate solution appears to have a considerable influence on phenol adsorption. Unionized phenol molecules would be attracted by physical force as well. In general, phenol adsorption is most effective at lower pH values; the same trend was reported by other researchers [40,41,42].

There is no significant increase in the phenol’s adsorption rate at pH 4.0 to 8.0. Electrostatic forces had little effect at this stage, and adsorption can be due to any mechanism other than electrostatic interactions. Nonetheless, the study of the impact of pH showed an adsorption capacity between 50 and 60 per cent from pH 4 to 8, which is still very significant.

The percentage removal of phenol reached 31% at pH = 11.00. Interfering ions may have outcompeted phenolic molecules for adsorption sites at higher pH values, resulting in the observed adsorption trend. The reduced adsorption capacity towards pH 11.00 is due to the negatively charged adsorbent surface of biochar/rGO/DES-glycerol, which repels phenoxide ions. At pH 10.0, the surface of the biochar/rGO/DES-glycerol and phenol molecules was negatively charged, resulting in an increasing electrostatic repulsion; hence, the reduced adsorption capacity was observed.

Isotherm Studies

The relationship between the number of organic pollutants adsorbed onto biochar/rGO/DES-glycerol and an adsorption isotherm presents the pollutant’s concentration at the equilibrium state. The adsorption isotherm investigation also reveals the distribution of adsorbate molecules in the solid and liquid phases at equilibrium. For design and operating purposes, selecting a suitable isotherm model is critical. The models that best describe equilibrium data are found to be suitably derived from the regression analysis with the highest degree of unison.

Furthermore, the adsorption isotherm provides critical information about the adsorption process’s capabilities for wastewater purification applications. Multiple isotherm models describe equilibrium curves and extract system information from the literature. Freundlich and Langmuir’s isotherms were used in this study to describe equilibrium adsorption, and investigated parameters are shown in

Table 3. Investigated isotherm parameters for the adsorption of ZDV and phenol onto biochar/rGO/DES-glycerol.

Model	Parameter	ZDV	Phenol
Langmuir	qe (mg g−1)	20.192	61.653
	KL (L mg−1)	0.400	0.007
	R2	0.999	0.992
	RL	0.288	0.984
Freundlich	KF (mg/g)/(mg/L)n	7.448	4.01
	n	0.331	0.535
	R2	0.958	0.986

. The R² closest to 1 indicated that Langmuir was the best-fit model for the experimental data during the adsorption of ZDV and phenol onto biochar/rGO/DES-glycerol. According to empirical models and theoretical evidence, ZDV and phenol adsorption onto biochar/rGO/DES-glycerol were primarily monolayer adsorption.

The Langmuir model implies that (i) the adsorption is monolayer and occurs on the adsorbent surface with an equal number of adsorption sites, and (ii) the adsorbed molecules do not interact.

The model is appropriate for the adsorption of contaminants in various sites with comparable energies [43].

The maximum ZDV and phenol adsorption capacity on biochar/rGO/DES-glycerol obtained from the Langmuir model is 20.192 mg/g and 61.653 mg/g, respectively. A crucial element of the Langmuir isotherm may be described by a dimensionless constant known as the equilibrium parameter R_L.

R_L is expressed by the following equation:

$$R_L=\frac{1}{1+K_L{C}_i}$$

(9)

K_L is the Langmuir constant, while C_i denotes the initial pollutant concentration. Unfavorable adsorption circumstances are indicated by R_L values larger than one, and RL values between one and zero characterize favorable adsorption conditions. An R_L value of 1 or 0 indicates either linear or irreversible adsorption. The degree of favorability is strongly associated with the irreversibility of the system, offering a qualitative assessment of the interactions between the adsorbent and adsorbate. Table 3 shows that the process has R_L values of 0.984, indicative of favorable adsorption [44]. These findings suggest that the experimental adsorption system is better represented by the Langmuir isotherm (Figure 9A,B), implying that adsorption sites are energetically homogenous. Furthermore, Freundlich R² values for both the adsorption of ZDV and phenol were greater than 0.9, indicating that the Freundlich model may be applied to describe the experimental results. The Freundlich model implies that the pollutant molecules are adsorbed into multilayers on a non-uniform surface that involves several mechanisms, and the adsorption capacity rises endlessly with increasing concentration. As per Table 3, the K_F values of ZDV and phenol were 7.448 (mg/g)/(mg/L)ⁿ and 4.01 (mg/g)/(mg/L)ⁿ. Furthermore, the value of n < 1 indicates that the adsorption of ZDV and phenol onto biochar/rGO/DES-glycerol was favorable.

Effect of Contact Time and Kinetic Studies

Tests of the effect of contact time and kinetic experiments were conducted to assess the adsorption rate, efficiency, durability, and mechanisms of the adsorbents. Rapid pollutant removal is critical in wastewater treatment processes. Across all concentrations, the best contact time for biochar/rGO/DES-glycerol to absorb ZDV and phenol was approximately 1 h and 30 min and 60 min, respectively (Figure 10). Due to unoccupied sorption sites on the adsorbent, adsorption of the adsorbate molecules was fast at first, indicating that diffusion might be the regulating element in the pollutant’s adsorption process [17] onto biochar/rGO/DES-glycerol.

Then the sluggish rate of the flattening observed might be attributed to the controlled-attachment process, as sorption sites had become occupied at this point. Mesoporosity and multiple functional groups on the modified biochar/rGO/DES-glycerol adsorbent are responsible for the exceptionally fast kinetics. The adsorption efficiency was evaluated using kinetic models such as the Pseudo-first-order (PFO), Pseudo-second-order (PSO), and intra-particle diffusion models. The PSO model is commonly used to represent the adsorption of pollutants from aqueous systems in wastewater treatment processes that occur via chemisorption in relation to the number of sites available for the exchange process at the solution-solid interface. It is assumed that there is bimolecular interaction between the adsorbent and the solvent [24].

Table 4. Kinetic parameters for pseudo-first-order, pseudo-second-order, and intra-particle diffusion models for the adsorption of ZDV and phenol onto biochar/rGO/DES-glycerol.

	Conc	PFO qe (mg g−1)	K1 (min−1)	R2	PSO qe (mg g−1)	K2 (g (mg min)−1)	R2	IPD Kdiff (mg g−1h−1/2)	C (mg g−1)	R2
ZDV	5	8.881	0.044	0.961	10.324	0.005	0.983	0.686	1.121	0.963
	10	14.941	0.041	0.742	17.327	0.003	0.763	0.900	1.590	0.954
	15	14.368	0.051	0.714	16.480	0.004	0.765	0.884	4.353	0.988
	20	12.471	0.066	0.854	14.064	0.005	0.888	0.815	3.486	0.977
Phenol	5	2.504	0.125	0.981	2.586	0.006	0.982	0.118	0.565	0.765
	10	3.241	0.798	0.967	3.331	0.385	0.986	0.059	2.343	0.588
	50	19.261	0.107	0.840	20.421	0.008	0.908	0.867	7.922	0.842
	100	35.687	0.048	0.449	37.354	0.006	0.578	0.1.550	6.838	0.940

shows the results of fitting experimental data into the models to generate kinetic parameter values. The model that best describes the experimental data was chosen based on its R² closest to unity.

The results in Table 4 show that PSO best fits the experimental data for the adsorption of ZDV and phenol onto the biochar/rGO/DES-glycerol. The PSO model is commonly used to simulate the adsorption of pollutants from an aqueous system in the wastewater treatment process, which mostly occurs via chemisorption. Compared to the number of sites that may be accessed for the exchange process at the solution–solid interface, PSO assumes that bimolecular contact between the adsorbent and the adsorbate molecules in the solution causes adsorption. The organic pollutant molecules and the adsorbent exchange and share electrons during this process [18]. This supports the concept that the adsorption of ZDV and phenol onto biochar/rGO/DES-glycerol resulted from several adsorption processes involving simultaneous reactions such as hydrophobic, π–π interactions, and H-bonding between the adsorbate molecules and the adsorbents.

The rate-controlling step of the adsorption process was determined using the intra-particle diffusion model (IPD). In addition, the rate-controlling step is generally the slowest step in the sorption process, and this stage can be attributed to external mechanisms or to the sorption process itself. The result obtained from Figure 11 reveals that the plot did not pass through the origin, and it is nonlinear. As a result, this confirms that intra-particle diffusion was not the only rate-controlling step [18]. This demonstrates that the sorption of ZDV and phenol onto biochar/rGO/DES-glycerol might be a multistep and heterogeneous process.

Regeneration/Desorption Studies

It is critical to prevent secondary waste generation by dumping (contaminated) adsorbents into the environment. The reusability of adsorbents was investigated to renew and isolate the pollutants. The regeneration study was conducted for five cycles of adsorption and desorption tests. This experiment was carried out by adding 0.50 g of the adsorbent Biochar/rGO/DES-glycerol to 40 mL of 10 mg L⁻¹ of ZDV and 100 mg L⁻¹ phenol solutions, respectively. The solutions were agitated for 24 h at room temperature on an orbital shaker at a speed of 200 rpm. After filtering the solutions, the pollutant’s equilibrium concentration was determined. The saturated adsorbents were dried in an oven at 80 °C. Exactly 0.05 g of saturated adsorbents were weighed in conical flasks, 10 mL of ethanol (desorbing solvent) was added, and the flasks were stirred for 30 min. The starting concentration of the contaminants desorbed was calculated using the collected filtrates. The desorption efficiency was calculated using Equation (2).

The regeneration test achieved 96% to 49% efficiencies for the recovery of Biochar/rGO/DES-glycerol using ZDV and 93% to 50% using phenol, respectively (Figure 12). These percentage desorption results prove that the recovery of biochar/rGO/DES-glycerol by ZDV and phenol can be achieved. The adsorbent can be reused for up to five cycles during the adsorption of ZDV and four cycles for the adsorption of phenol.

The characterization of biochar/rGO/DES-glycerol by FTIR showed a difference between the original material before and after adsorption/regeneration. As shown in Figure 13A for the adsorption of ZDV, the previously observed peak at 2848 cm⁻¹ corresponding to the CH₂ functional group appeared less intense after adsorption and post-regeneration of the adsorbent material. The broad bands at 1422 cm⁻¹ and 3530 cm⁻¹–3151 cm⁻¹ belonging to O=C-O alkoxy and –OH functional groups, respectively, have been completely removed from the surface of the adsorbent post-adsorption and regeneration.

Figure 13 shows that the adsorbent after regeneration during the adsorption of phenol had no detectable functional groups attached to the material’s surface. After the adsorption of phenol, only the -OH functional group was eliminated. The elimination of functional groups showed an interaction between the adsorbent’s surface functional groups and the pollutants molecules. Functional group elimination methods included π–π interactions, hydroxyl and C-O group precipitations, and complexation with functional groups. These processes affect whether chemisorption or physisorption predominates. As a result, the strong chemical connections in chemisorption cause regenerated biochar/rGO/DES- glycerol to lose part of its active sites every cycle, which adversely affects the regeneration process [40].

Moreover, solution pH, biochar/rGO/DES- glycerol pHpzc, and contaminant pKa affect how functional groups function. Pollutants chemically interact with the active adsorbent sites to form complexes or precipitate on the adsorbent surface, which might not be reversible during desorption. As the adsorbent pores become clogged, the adsorbent progressively loses its active sites with each cycle. This might cause the biochar/rGO/DES- glycerol to decompose with the adsorption/desorption cycles, losing its properties and characteristics [45].

Comparison Studies between the Developed Modified Biochar Nanocomposite and Other Biochar-Based Composite Adsorbent Materials

Table 5. Comparison of biochar with other adsorbents for phenol removal.

Pollutant	Qe Max (mg/g)	Adsorption Conditions	Adsorbent	Author
Phenol	134.01	Column adsorption, optimum pH = 2, contact time = 180 min	Activated waste tea leaves	[17]
	9.49	Batch adsorption, optimum pH = 7, adsorbent dose = 15 mg/L	Tea waste biomass	[46]
	5.80	Batch adsorption, optimum pH = 5.48, adsorbent dosage = 2.4 g, and contact time = 8 h	Tea waste biochar	[47]
	30.31	Batch adsorption, optimum pH = 6, and contact time = 360 min	Hizikia fusiformis, biochar	[48]
	14.61	Batch adsorption, optimum pH = 6, and contact time = 120 min	Food waste, biochar	[49]
	10.84	Batch adsorption, optimum pH = 8, dosage = 0.6 g and contact time = 60 min	Magnetic palm kernel, biochar	[50]
	49.5	Batch adsorption, optimum pH = 2.5 & 3, dosage = 1 g and contact time = 25 min	Ferric chloride green tea waste biochar	[51]
	71.94	Batch adsorption, optimum pH = neutral, dosage = 13 g and contact time = 240 min	Delonix regia biochar	[52]
	61.65	Batch adsorption, optimum pH = 2, dosage = 1.0 g and contact time = 60 min	Modified tea waste	Current study

shows previous studies that used biochar nanocomposites and other biochar-derived composites to absorb phenols from wastewater. The data show that unmodified tea waste biochar had lower absorption capacities than modified tea waste-based biochar. This is because biochar has a lower surface area, limiting its adsorption capabilities and efficiency [10]. This biochar disadvantage led to biochar modification, which can be achieved by chemical, physical, magnetic, and mineral impregnation. Biochar modification aims to increase surface area and increase its adsorption capability. As seen in Table 5, modified biochar showed higher adsorption efficiencies than unmodified biochar. The current study uses timeless adsorbent synthesis, easy modification methods, and inexpensive chemicals. In this study, the adsorption capacity of synthesized novel modified tea waste biochar was comparable to the other reported studies listed below, with the highest adsorption capacity of 61.65 mg/g. The current study also reports on the rapid pollutant uptake and ease of separating the adsorbate and adsorbent.

Table 5 reveals that most studies are based only on the quantification of ARVs in wastewater rather than remediation. South Africa has the largest ARV drug consumption in the world. ARV drugs easily find their way into the environment and main water streams. Several of these drugs and their derivatives have been quantified in tap and wastewater [53,54,55,56,57]. These findings are disturbing and strongly indicate that more reliable wastewater treatment methods are needed to remove these pharmaceutical wastes. Techniques such as photolysis [37], electro-Fenton [52], UV photolysis and advanced oxidation processes [58], and photo-catalytic degradation [36] have been used for the removal of ARV drugs from wastewater. However, adsorption is the easiest and simplest technique for the remediation of ARVs from water sources. Although some studies have reported the removal of ARVs from contaminated water, most are vague and very broad. The current research focuses on the simple and effective removal of the ARV, ZDV (a commonly used ARV drug in South Africa for mother-to-child prevention of the spread of the virus) from wastewater using a modified tea waste adsorbent. It also reports on the parameters such as the effect of pH solution, adsorbent dose, equilibrium characteristics, and mechanisms involved during adsorption.

4. Conclusions

The modified biochar adsorbents were successfully synthesized, optimized, and characterized. FTIR analysis showed greater peak enhancement and the presence of added functional groups, which indicates that the primary material (biochar) has been modified. XRD analysis confirmed that the poorly crystalline biochar had been modified to a more crystalline structure by rGO and DES. Furthermore, SEM-EDX analyses confirmed the surface morphology and elemental composition of the modified adsorbents. The modification of the biochar nanomaterial resulting in a new composite material with well-defined porosity presents unique surface characteristics, open cavities, and pores spread out unevenly on the surface of the adsorbent. BET analysis of the modified biochar (biochar/rGO/DES-glycerol) showed a decrease in surface area and pore volume, perhaps due to the introduction of DES, resulting in surface modification and blocking of pores. Additionally, a preliminary adsorption test was conducted by assessing the dose effect. The results obtained from this preliminary adsorption test proved that biochar/rGO/DES-glycerol is a better adsorbent than biochar, biochar/rGO, and biochar/rGO/DES-CTAB for the removal of zidovudine and phenol from wastewater. Hence, biochar/rGO/DES-glycerol was used in detailed adsorption experiments. The adsorption was highly reliant on several variables, including the adsorbent dose, pH, contact time, and adsorbate concentration. The overall removal of ZDV and phenol by the DES-modified adsorbent (biochar/rGO/DES-glycerol) was satisfactory, achieving the highest percentage of removals for ZDV of 98% and 75% for phenol in an acidic medium. The adsorption of ZDV and phenol followed a pseudo-second-order kinetics model, in which adsorption assumes that pollutant molecules and the adsorbent exchange and share electrons during this process. The equilibrium data fitted well with the Langmuir isotherm revealing the monolayer adsorption process for ZDV, and phenol is primarily preferred. Regeneration showed that ion exchange is the predominant mechanism, followed by the chemisorption process. Overall, biochar/rGO/DES-glycerol has shown to be a good choice for removing ZDV and phenol from an aqueous medium.