Introduction

In the last century, the pharmaceutical industries had tremendous growth and novel inventions for the well-being of humankind. However, synthetic pharmaceutical chemicals, products, solvents etc., are discharged into water streams during synthesis or excreted in urine and feces after consumption. Many studies reported the pharmaceuticals existence in ground and drinking surface water and their impacts on the living systems and environment (Bexfield et al. 2019; González-González et al. 2022). Ibuprofen is the most prescribed anti-inflammatory medicine released in the environment through manufacturing units, hospitals, veterinary usage, etc. Ibuprofen existing in water systems ranges from 18 to 6297 ng/L and is considered an unsafe pharmaceutical for aquatic species (Ortiz de García et al. 2014; Alluhaybi et al. 2023; Rabbat et al. 2023). Therefore, using a facile, eco-friendly, low-cost advanced technique, ibuprofen-bearing wastewater must be purified before discharge into the environment.

Recently, pharmaceutical removal with adsorption technology has been explored as one of the most capable techniques due to its high efficiency and low-cost wastewater treatment processes (Oba et al. 2021; Zhang et al. 2022). The most frequently used materials used as adsorbents are activated carbons, metal oxides, zeolitic minerals biopolymers, and synthetic polymers (Oba et al. 2021; Eniola et al. 2022; Zhang et al. 2022). However, most adsorbents either have low adsorption efficiency or are costly. Therefore, new biocompatible, low-cost, promising materials are still desirable. Nanomaterials have been widely investigated for environmental applications in the last two decades. The high surface area and small size make them suitable materials for scavenging drugs from effluents (Ahmed et al. 2020). Nano carbons and polymers, i.e., carbon nanofibers, carbon nanotubes, graphene, chitosan, polyaniline etc., have been studied as advanced adsorbents with high efficiency and selectivity for scavenging pollutants such as organic dyes, pesticides, pharmaceuticals, and metals in aqueous solutions (Ahmed et al. 2020; Samadi et al. 2021; Manimegalai et al. 2023; Oba et al. 2021; Zhang et al. 2022). Graphene is a novel component of the carbon family with a very high surface area (2630 m2/g) and extraordinary two-dimensional lamellar morphology with sp2-hybridized carbon atoms. Generally, graphene interacts with the organic molecules through π–π interactions. Due to this interaction, graphene is most suitable for separating and scavenging organic pollutants from wastewater (Manimegalai et al. 2023). Graphene flakes can be produced by exfoliation of graphite using chemical wet dispersion followed by ultrasonication in water and organic solvents. Graphene oxide is generally produced from the oxidation of graphite, and the oxidation of graphite introduces an abundant functional group on its surface that can be used as an active site for binding drug molecules. Banerjee et al. (2016) investigated ibuprofen elimination capacity of GO nanoplatelets and found a poor adsorption capacity of 3.73 mg/g. Sahin et al. (2020) reported about 11.5 and 12.8 mg/g efficiency of the GO and activated carbon cannot be considered very effective. Graphene oxide is an advanced material used as a nano adsorbent for pharmaceutical scavenging, which is limited by some factors, like its small size and good dispersibility. It is challenging to complete the elimination of graphene oxide from aquatic systems. Secondly, graphene sheets usually show agglomeration in aqueous solution due to the π–π interactions, which decreases adsorption because the total surface area is reduced and there are fewer active sites for sorption (Liu and Qiu 2020). To address these problems, researchers have extensively studied the process of surface tailoring of graphene oxide nanosheets by chemical treatment, adding organic functional groups and inorganic nanoparticles onto graphene/graphene oxide surfaces. Anchoring of the GO surface enhances functionality, restricts the agglomeration of GO, and retains porosity and surface area in the nanocomposite (Liu and Qiu 2020; Manimegalai et al. 2023). The merging of GO with natural biopolymer or synthetic polymers may improve the adsorptive scavenging of pharmaceuticals (Samadi et al. 2021; Oba et al. 2021; Manimegalai et al. 2023; Zhang et al. 2022).

Chitosan (CS) is obtained by deacetylating the plentiful natural polysaccharide, chitin. It is used for various applications, including scavenging pollutants. Chitosan can be easily modified and converted into different shapes and sizes. Chitosan has several advantages compared to commercial adsorbent materials, such as low price, eco-friendliness, macromolecular structure, and high adsorption capacity. Previously reported articles revealed that chitosan is a capable biopolymer for scavenging ibuprofen from synthetic aqueous solution (Bany-Aiesh et al. 2015; Phasuphan et al. 2019). Bany-Aiesh et al. (2015) synthesized β-CD-grafted chitosan to decontaminate ibuprofen and reported about 11.23 mg/g efficiency β-CD-grafted chitosan. Phasuphan et al. (2019) developed chitosan-modified waste tire crumb rubber for ibuprofen scavenging. The results show 17.7 mg/g adsorption of ibuprofen. A novel hybrid based on oxidized graphene and chitosan can be an efficient material for separating and scavenging hazardous ibuprofen from the environment. However, some studies reported that mixing GO with chitosan showed high agglomeration due to the high viscosity of chitosan (Zuo et al. 2013; Su et al. 2021). Therefore, other materials can be added to the polymeric matrix to utilize the advantages of GO and chitosan. This will help to distribute GO sheets evenly and enhance the performance of new material. The synergetic and compatible properties of the materials may support better and faster pollutant decontamination.

The coupling or composite of polyaniline could be a practical approach to developing new material for ibuprofen remediation application. Polyaniline is a highly stable and functional conducting polymer widely used for wastewater purification (Talukder et al. 2023). The polyaniline/GO composite (PANI/GO) has been used for heavy metals adsorption (Shao et al. 2014; Han et al. 2019), and chitosan/polyaniline composite (CS/PANI) has been applied for the removal of the dyes from the wastewaters (Sahnoun and Boutahala 2018; Minisy et al. 2019). Incorporating PANI and GO in chitosan matrix add several functional groups, which may help in ibuprofen molecules binding and enhance the mechanical strength of chitosan and stability in acidic solutions (Usman et al. 2019).

Selecting PANI and GO amount ratio in the chitosan polymeric matrix is crucial in developing a suitable material. Moreover, the handling, removal, and recovery of powdered materials is always a challenging task. Hence, novel thin films have been developed based on the rational incorporation of GO and PANI nanoparticles in chitosan (CS) matrix (CS/GO/PANI) to ibuprofen scavenge from the aqueous solution. The immobilization of GO and PANI in chitosan matrix enhanced the efficiency of ibuprofen adsorption and stability of the prepared thin films. A comparative ibuprofen scavenging study of the pure CS, CS/GO, CS/PANI, and rationally designed CS/GO/PANI thin films has been performed, and a detailed mechanism based on the surface change and interactions has been explored using FTIR and XPS analysis.

Materials and methods

Materials

Medium molecular weight chitosan (C12H24N2O9; degree of deacetylation ≥ 75%, MW- 190–310 kDa, Product: 448,877), H2SO4 (95–97%) and graphite were purchased from Sigma-Aldrich Chemie GmbH and Merck. Aniline and ibuprofen sodium were procured from Sigma, USA, and Sisco Research Laboratories Pvt. Ltd India. Hydrochloric acid (HCl) and sodium hydroxide (NaOH) were collected from Techno Pharmchem Ltd., Haryana, India, and BHD Chemical Ltd, Poole, England. Ammonium persulfate (APS) was purchased from Loba Chemie Pvt Ltd, India. H2O2 (33%) and KMO4 were obtained from Panreac AppliChem.

Synthesis of graphene oxide and polyaniline

The graphene oxide (GO) was synthesized using graphite powder using the slightly modified Hummer method, as reported earlier (Jilani et al. 2021). The detailed procedure of GO synthesis is mentioned in supplementary data. The powdered polyaniline (PANI) was synthesized using the oxidative polymerization method. Initially, 50 mL of aniline (1 M) was taken in a flask kept in an ice bath. After that, 50 mL of 1 M solution of ammonium persulfate (prepared in 1 M HCl) was added dropwise to aniline solution under sitting conditions. After 3 h, a blue-green precipitate of PANI was filtered and cleaned with water, ethanol, and acetone to remove the unreacted reagent and other impurities. PANI was soaked in 0.5 M NaOH solution for 5 h to convert the emeraldine salt to an emeraldine base. The emeraldine base of PANI was again filtered and cleaned with water, ethanol, and acetone to remove the excess NaOH and dried at 90 °C for 18 h. The dried emeraldine base of PANI was used to prepare CS/GO/PANI thin films.

Chitosan/graphene oxide/ polyaniline hydrogel thin films casting

CS/GO/PANI thin films were prepared by mixing CS with GO and PANI. The amount of CS was kept constant while the ratio of GO and PANI-EB were varied. Chitosan and PANI solutions were initially prepared in acetic acid and DMF, respectively. An aqueous solution of 1.5% (w/v) chitosan was prepared in 1.5% (v/v) acetic acid solution. At the same time, PANI solution was prepared in pure 110 mL DMF by taking 0.05 g of PANI-EB powder under continuous stirring for 18 h at 25 °C. An aqueous solution of GO (3 mg. mL−1) was used to prepare CS/GO/PANI thin films. The details of volumes and amounts of CS, GO, and PANI-EB mixed for thin-film casting are reported in Table 1. For the CS/GO/PANI thin film casting, a fixed volume of GO solution was mixed with the PANI solution and stirred for 10 min. After that, CS solution was added to GO-PANI solution after 30 min of stirring. The solution was poured onto the petri dish and left to dry at 40 °C for 48 h. An aqueous solution of 5% ethanol was poured into petri dish, and CS/GO/PANI thin films were peeled off. The obtained CS/GO/PANI thin films were washed several times with 5% ethanol and dried at 60 °C for 18 h.

Table 1 The amount of the CS, GO, and PANI used to prepare CS/GO/PANI thin films
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Characterization

The surface topography images of gold sputtered CS, CS/GO, and CS/GO/PANI dried hydrogel structures were obtained using JSM-6700F scanning electron microscopy (JEOL, Tokyo, Japan) at 2.00 kV (CS and CS/GO) and 10.0 kV (CS/GO/PANI) using LEI detector. The XRD pattern of the CS, CS/GO, and CS/GO/PANI thin films were recorded on RIGAKU, ALTIMA-IV X-Ray Diffractometer using Cu K α radiation (λ = 0.15405 nm) at 40 kV in the range of 2θ: 5–70° (scanning rate 2°/min, step size 0.05°/step) in the continuous scanning mode. The surface functional groups and interactions between CS/GO/PANI thin film and ibuprofen were studied by Perkin Elmer Fourier Transform-Infrared Spectrometer in the 4000–400 cm−1 range. The zeta potential of the CS/GO/PANI thin film was recorded on Zetasizer Nano ZS (Malvern, USA). The analysis of ibuprofen was done on the HACH DR-6000 UV–visible spectrophotometer (Germany).

Swelling studies

The swelling of the prepared films was tested by immerging 0.25 g thin film in 25 mL di-ionized water at 24 °C. The swollen thin films were weighed at different time intervals. The degree of swelling of the prepared thin films was calculated by following equation:

$$\mathrm{Degree}\;\mathrm{of}\;\mathrm{swelling}\;\left(\%\right)=\frac{\left(Ws-W_0\right)}{W_0}\times100$$

where DS is the degree of swelling (%), W0 and Ws are the weight of films before immersing and swelling, respectively.

Ibuprofen removal and thin film regeneration experiments

Ibuprofen sorption in the static modes was performed by mixing a certain amount of the prepared biopolymeric films in a 25 mL aqueous drug solution and shaking it for a certain period to reach equilibrium. The pH of ibuprofen solution was adjusted between 3 and 9.5 using 0.1 M HCl or NaOH, and adsorption time was adjusted between 0 and 180 min to find the optimum pH and equilibrium time. The effect of the amount of ibuprofen in the solution varied from 25 to 200 mg L−1 to determine adsorption isotherm at 24, 36, and 50 °C. The role of salt on ibuprofen removal was studied by varying NaCl concentrations from 5 to 100 mg L−1. All the adsorption experiments were conducted in triplet, and average results are reported. The following equation was used to calculate ibuprofen removal capacity (qt) of the prepared biopolymeric films.

$${{\text{q}}}_{{\text{t}}}=({{\text{C}}}_{0}-{{\text{C}}}_{{\text{e}}})V/m$$
(1)

where, initial and equilibrium ibuprofen concentrations are represented as C0 and Ce (mg L−1) were analyzed by UV–visible spectrophotometer at λmax -222 nm. The calibration curve of ibuprofen is included in the supplementary file (Fig. S1). The volume of ibuprofen solution is indicated as (V) in liter, and the mass of the biopolymeric film is represented as (m) in grams.

The desorption of ibuprofen and regeneration of CS/GO/PANI-1 thin film was done by immersing the drug-saturated biopolymeric film in 25 mL pure ethanol, acetone, and 0.01 M NaOH solution. The adsorption/desorption ability of the CS/GO/PANI-1 thin film was tested up to five cycles.

Results and discussion

Synthesis, preliminary adsorption, swelling, and characterization studies of thin films

Innovative and effective biopolymeric thin films based on chitosan (CS), graphene oxide (GO), and polyaniline (PANI) have been designed for the separation and decontamination of ibuprofen from the aqueous solution. The conjugation of CS, GO, and PANI was expected to synergize the used materials better to form a multifunctional adsorbent thin film with many active sites for ibuprofen scavenging. Therefore, GO and PANI amounts were varied stoichiometrically in CS matrix to optimize the ratio of both (GO and PANI) fillers to get highly efficient thin film for the water purification application.

The ratio of GO and PANI fillers was optimized by varying their stoichiometric amounts in CS matrix to produce a highly efficient thin film for optimal water purification. A schematic scheme for preparing CS/GO/PANI-1 thin film is illustrated in Fig. 1.

Fig. 1
figure 1

Schematic diagram showing the CS/GO/PANI-1 thin film preparation

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The photograph and flexibility of the CS/GO/PANI-1 thin film is shown in Fig. 1. The CS/GO/PANI-1 thin film showed high flexibility and no cracking after several folding times. Herein, nine thin films were prepared, which included pure CS, CS/GO, CS/PANI, and six films based on CS, GO, and PANI, as shown in Table 1. The application of all prepared thin films for the scavenging of ibuprofen has been demonstrated in Fig. 2. The results indicated that the immobilization of PANI and GO into CS matrix affects the adsorption capacities of thin films. Ibuprofen scavenging capacity of CS/GO and CS/PANI film is higher than the pure CS thin film, suggesting the synergetic behavior of the GO and PANI in the binding of the drug molecules. The ternary thin film shows the increase in ibuprofen adsorption onto the film, which has the highest amount of PANI and lowest GO. As the amount of GO in CS/GO/PANI thin films increases, ibuprofen scavenging capacity reduces probability due to the agglomeration of GO in the film, which inhibits access to the active site of the thin film.

Fig. 2
figure 2

a The comparative adsorption of ibuprofen onto prepared thin films from aqueous solution b Swelling behavior of prepared thin films in water. (Vol.: 25 mL, pH: 8.1, ibuprofen concentration: 100 mg/L, Temp.: 30 °C, thin film mass: 0.025 g, time: 180 min)

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Furthermore, adsorption properties of the prepared thin films can be explained on the basis of their swelling properties. The swelling behavior of the prepared thin films is shown in Fig. 2b. The results showed that pure CS and CS/GO films have the highest swelling. The swelling decreases as the amount of PANI in the thin films increases. The higher swelling of CS and CS/GO thin films is mainly due to the polar function groups like hydroxyl and carboxylic on the thin films. These functional groups make the films more hydrophilic and enhance their hydration properties (Sabzevari et al. 2018). The hydration properties of thin films decreased with the increase in the amount of PANI in the thin films. Therefore, CS/GO/PANI-1 showed the least swelling. The swelling behavior of the prepared thin films also affects their adsorption properties. The adsorption of ibuprofen onto prepared thin films decreases as the hydrophilicity and hydration properties of thin films increase due to the thin films' affinity for water molecules than ibuprofen. Therefore, CS/GO/PANI-1 showed the highest adsorption of ibuprofen. The presence of PANI in thin films enhances its hydrophobic properties, favoring the interaction with ibuprofen molecules rather than water molecules. The CS/GO/PANI films containing 1.5 mg GO, and 22.5 mg PANI (film code-CS/GO/PANI-1) showed the best performance to remove ibuprofen was selected for the characterization, and further exploration of ibuprofen decontaminating application. The CS, CS/GO, and CS/GO/PANI-1 thin films were characterized using SEM, XRD, FTIR, XPS, and zeta potential analysis.

The surface and cross-section morphology of the pure CS, CS/GO, and CS/GO/PANI-1 thin films are represented in Fig. 3. The top surface morphology of CS in Fig. 3(a and b) shows the relativity smooth surface with the thickness about 11.4 – 12 μm (Fig. 3c) compared to CS/GO (Fig. 1d-e) and CS/GO/PANI-1 (Fig. 3g-h) thin films. The CS/GO (Fig. 3d-e) thin film shows few protuberances due to the agglomeration of GO sheet in the dense CS solution. GO sheet does not mix properly in the highly viscous CS solution, resulting in GO aggregation. This aggregation behavior is reported in several GO-immobilized polymeric structures (Zuo et al. 2013; Su et al. 2021). A better distribution of GO and PANI in the CS matrix can be seen in Fig. 3e-f, indicating PANI helps better GO dispersion in CS/GO/PANI-1 thin films. The cross-section morphology of CS, CS/GO, and CS/GO/PANI-1 thin films show the continuous and uniform structure of CS (Fig. 3c). The thinness and roughness gradually increase as GO (Fig. 3f) and GO-PANI (Fig. 3i) are immobilized in CS for CS/GO and CS/GO/PANI-1 thin film formation.

Fig. 3
figure 3

SEM images of thin films (a, b) CS, (c, d) CS/GO, and (e, f) CS/GO/PANI-1 (inset- cross-section images of respective materials)

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XRD patterns of the pure CS, CS/GO, and CS/GO/PANI-1 thin films are depicted in Fig. 4. The characteristic peaks of CS are recorded at 2θ—9.75° (020), 14.3° (110), and 20.13° (200), indicating the semi-crystalline nature of CS (Aziz et al. 2017). The CS peak at 2θ – 20.13° represents crystal form II (Lou et al. 2017). The XRD pattern of GO shows a strong peak at 2θ—10.2° reflection of the (001) plane of GO sheets. After incorporating GO by the CS matrix, peaks become sharper, indicating the increases in the crystallinity due to the GO strong peak. Similar trends have also been reported by Abolhassani et al. (2017) and Rouby et al. (2018). The XRD pattern of CS/GO thin films shows a shift in the peaks at 2θ – 10.1°, 14.05° and 20.6°. However, the immobilization of GO and PANI in CS matrix shows a reduction in the crystallinity, and a shift in the position of the peaks is observed at 2θ – 9.95° (020), 10.3° (001) GO peak) 14.45° (110) and 20.5° (200). This behavior of reducing the peak intensities, changes in peak position, and peak broadening are mainly due to the structural and hydrogen bonding distortion between the polymeric chains, and a complexation occurs between the functional groups of the CS, GO, and PANI (Aziz et al. 2017; Lou et al. 2017).

Fig. 4
figure 4

XRD pattern of GO (inset), CS, CS/GO, and CS/GO/PANI-1 thin films

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Optimization of ibuprofen adsorption onto CS/GO/PANI-1 thin film

The interaction of the contaminant and adsorbent can be controlled by various parameters such as solution pH, temperature, concentration, ionic strength, etc. Therefore, the scavenging of ibuprofen onto CS/GO/PANI-1 thin film was exploded to find the optimum adsorption conditions and to determine the adsorption mechanism.

The surface charge of ibuprofen and CS/GO/PANI-1 thin film is the most influential factor. Therefore, a brief study has been conducted to determine the role of the surface charge of ibuprofen and CS/GO/PANI-1 thin film on the attainment of the equilibrium and determination of the rate of the drug adsorption process. Figure 5a shows the scavenging of ibuprofen at different pH solutions and reaction times. The results indicate that ibuprofen adsorption capacity is not the same at different pH, and the equilibrium time also varied with the change in the solution pH. The fast and optimum ibuprofen adsorption was observed at pH 4. The fastest equilibrium was attained at pH 4 and 90 min. The higher ibuprofen adsorption and faster saturation of the active sites on CS/GO/PANI-1 thin film was below pH 5. Beyond pH 5, a reduction in adsorption of ibuprofen and delayed equilibrium was recorded. These results revealed that solution pH and saturation of active sites on CS/GO/PANI-1 thin film are directly related to each other, which can be explained based on the pKa of ibuprofen and zeta potential analysis of CS/GO/PANI-1 thin film. The pKa of ibuprofen is 4.9 and present in the non-ionic form below pKa 4.9 and anion over its pKa value (Cho et al. 2011). The point of zero charge (pHzpc) of CS/GO/PANI-1 thin film was observed at pH 5.4. The zeta potential of the CS/GO/PANI-1 thin film between pH 2 and 5 is 36.5 to 15.5 mV, indicating a positive surface charge. Between pH 5 and 6, the zeta potential values become negative, and pHzpc is 5.4 (Fig. 5b). The results revealed that the optimum adsorption of ibuprofen occurred in its non-ionic form. Beyond the pKa value of ibuprofen, the interaction between the anionic ibuprofen molecules and negatively charged CS/GO/PANI-1 thin film reduces due to electrostatic repulsion. However, good adsorption of ibuprofen was observed in the basic medium due to the strong anti-pH interference ability of the CS/GO/PANI-1 thin film Zhang et al. (2023). Oxygen-containing functional groups (–OH, C = O, and –COOH) on the CS/GO/PANI-1 act as a buffer, allowing reasonable adsorption to occur at both acidic and basic pH levels. Based on the pH studies, it can be concluded that non-covalent adsorption forces were involved in the scavenging and binding of ibuprofen onto CS/GO/PANI-1 thin film. These results agree with the literature, indicating that most drug molecules are adsorbent in non-ionic form rather than ionic ones (Alluhaybi et al. 2023; Rabbat et al. 2023; Streit et al. 2021).

Fig. 5
figure 5

a Equilibrium time analysis for ibuprofen adsorption onto CS/GO/PANI-1 thin film at varying solution pH, (Vol.: 25 mL, ibuprofen concentration: 100 mg/L, Temp.: 30 °C, thin film mass: 0.025 g,) b zeta potential analysis of the CS/GO/PANI-1 thin film

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Figure 5a demonstrates that the equilibrium time of ibuprofen adsorption onto CS/GO/PANI-1 thin film varied with the change in the solution pH. The rate of ibuprofen adsorption onto CS/GO/PANI-1 thin film at various pH levels was investigated by fitting the equilibrium data to pseudo-first-order, pseudo-second-order and Elovich (kinetic models. The equations and details of the kinetics parameters are depicted in Table 2. The kinetics plot for ibuprofen adsorption onto CS/GO/PANI-1 thin film at different pH is shown in Fig. 6, and kinetic parameters values along the root mean square error (RMSE) and chi-square (χ2) are depicted in Table 2. The lowest RMSE, χ2, and higher R2 represent the best-fitted model for ibuprofen decontamination. The error functions and kinetic parameter values in Table 2 revealed that the Elovich model is most suited to ibuprofen decontamination of all the studied pH ranges. Moreover, the value of \(\alpha\) obtained at pH 4 is 30.374 mg g−1 min−1, much higher than those found at the other pH (Guedidi et al. 2017). Moreover, ibuprofen adsorption energies demonstrated by the Elovich equation indicate the heterogenous nature and sharing or exchange of the electrons may involve the interaction of ibuprofen with CS/GO/PANI-1 thin film pH (Guedidi et al. 2017; Rabbat et al. 2023). Based on the solution pH and kinetic studies, further ibuprofen adsorption experiments were conducted at pH 4 and 90 min equilibrium time.

Table 2 The values of kinetics parameters of ibuprofen adsorption onto CS/GO/PANI-1 thin film at different pH solutions
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Fig. 6
figure 6

Kinetics plots for ibuprofen adsorption onto CS/GO/PANI-1 thin film at different pH solutions

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The variation in the velocity of ibuprofen molecules and solution viscosity under the influence of the solution temperature and concentrations may affect the separation and decontamination of the drug by CS/GO/PANI-1 thin film. The adsorption of ibuprofen on CS/GO/PANI-1 thin film at different ibuprofen concentrations and solution temperatures is depicted in Fig. 7a. Ibuprofen concentration gradient positively impacted the decontamination process. The adsorption of ibuprofen increases gradually while the rise in solution temperature decreases ibuprofen amount onto CS/GO/PANI-1 thin film. The increase in temperature from 24 to 50 °C may create the mass transfer resistance of drug molecules at the solution/thin film interface (Guedidi et al. 2017; Iovino et al. 2015).

Fig. 7
figure 7

a Adsorption of ibuprofen adsorption onto CS/GO/PANI-1 thin film at different solution temperatures, and adsorption isotherm plots at b 24 °C, c 35 °C and d 50 °C

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Moreover, the higher reaction temperature may facilitate the reduction in solution viscosity and fast mobility of ibuprofen molecules, resulting in less interaction of drug molecules with the CS/GO/PANI-1 thin film. The deformation of the active sites and pores on the CS/GO/PANI-1 thin film surface at higher temperatures may be the reason for the lower adsorption of ibuprofen (Arivoli et al. 2009).

Further information about the role of the solution temperatures on the interaction between ibuprofen and CS/GO/PANI-1 thin film surface could be assessed by fitting ibuprofen adsorption data to the Langmuir, Freundlich, Temkin, Redlich-Peterson (R-P) and Sips isotherm equations and isotherm equations are in depicted in Table 3. The isotherm models can provide insight into the chemical and physical interactions and the formation of monolayers or multilayers on the homogeneous or heterogeneous surface of CS/GO/PANI-1 thin films. The plots for ibuprofen isotherm adsorption at different temperatures are shown in Fig. 7b-d, which show the isotherm plots of type-I indicating the gradual increase in ibuprofen adsorption onto CS/GO/PANI-1 thin film active sites. The isotherm parameter values are included in Table 3, demonstrating that two parameters of isotherm equations (Langmuir, Freundlich, and Temkin) poorly describe ibuprofen adsorption onto CS/GO/PANI-1 thin film (Rabbat et al. 2023). The calculated adsorption capacities for two parameters isotherm are far from the experimental values. RMSE and χ2 values are higher for the R-P and Sips isotherm equations. However, the values of n are greater than one for all the temperatures, suggesting favorable ibuprofen scavenging. Moreover, the values of the Freundlich constant (n) decrease 2.582 (24 °C) > 2.186 (35 °C) > 1.134 (50 °C), implying that increasing solution temperature is not supportive of the adsorption process. According to the error function values presented in Table 3, R-P and Sips models significantly described the equilibrium data (Yoo et al. 2023). The R-P model fitted better than the sips model at all the studied temperatures. The value of the KRP constant gradually decreased from 2.754 to 0.735 L mg−1 with the rise in the reaction temperature. Moreover, the values of the Redlich-Peterson constant (β) are greater than the one indicating that ibuprofen adsorption onto CS/GO/PANI-1 approaches towards the Freundlich model rather than the Langmuir isotherm (Abin-Bazaine et al. 2022). These results demonstrated that ibuprofen adsorption onto the heterogeneous surface of CS/GO/PANI-1 was mainly controlled by physical forces and less contributed by chemical adsorption.

Table 3 The values of isotherm parameters for ibuprofen adsorption onto CS/GO/PANI-1 thin film at different temperatures
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Competitive adsorption study

The existence of co-ions on ibuprofen scavenging using CS/GO/PANI-1 was studied in the presence of NaCl, and the results are depicted in Fig. 8. The results revealed that the presence of Na+ and Cl– ions significantly reduce the adsorption of ibuprofen adsorption onto CS/GO/PANI-1. The ionic strength alteration can initiate interactive impacts like the reduction in interaction, the salting out effect, clustering of adsorbents, and competition between the ions and ibuprofen for the same binding sites, which may result in the lower separation and adsorption drug molecules (Jun et al. 2019). Similar results were reported by Van Tran et al. (2019). A study conducted by Wang et al. 2017, used NaCl solution to regenerate CNT and reported that NaCl as an eluent showed 13.2% desorption of ibuprofen. The authors concluded that Na+ and Cl– ions replace ibuprofen molecules from the surface of CNT (Wang et al. 2017). However, few previous studies reported that the effect of salt on ibuprofen removal is not the same and varies from case to case. Xiong et al. (2021) and Alkhathami et al. (2023) did not observe any change in the scavenging of ibuprofen in the presence of salt. In contrast, Njaramba et al. (2023) reported a positive impact of NaCl presence in ibuprofen adsorption by Gelatin-MOF-sepiolite from an aqueous solution. These results demonstrated that the adsorption of ibuprofen in the presence of salt depends on the adsorbent rather than the solution conditions (Oba et al. 2021).

Fig. 8
figure 8

Adsorption of ibuprofen onto CS/GO/PANI-1 thin film in the presence of NaCl (Vol.: 25 mL, ibuprofen concentration: 200 mg/L pH: 4, Temp.: 24 °C, thin film mass: 0.025 g, time: 180 min)

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Adsorption mechanism

The XPS and FTIR analysis investigated the interaction of ibuprofen with CS/GO/PANI-1 surface. The XPS analysis of CS/GO/PANI-1 thin film before and after ibuprofen adsorption was performed to find the elemental compositional and interactions between the thin film and drug (Fig. 9a). The wide scan survey of CS/GO/PANI-1 thin film shows the existence of C, O, and N with ratios of 71.91%, 22.2%, and 4.81%, respectively. The peaks for C1s, N1s, and O1s were detected at 285.39, 399.39, and 532.83 eV. The deconvoluted spectra of C1s consist of four peaks at 284.58, 285.1, 286.17, and 287.66 eV in CS/GO/PANI-1 thin film, signifying C-O, C–C, C-NH, and C–O–C = O (Fig. 9b) (Selvam and Yim 2021). Three peaks were observed at 398.18, 399.30 and 400.42 eV belonged to -N = , NH, and NH2+ of PANI and CS in thin film (Fig. 9c). Moreover, O1s peak (Fig. 9d) can be deconvoluted into two components peaks appeared at 531.80 and 532.58 eV are assigned to C = O, O-C, and C–O–C of CS and GO in CS/GO/PANI-1 thin film (Daniyal et al. 2021).

Fig. 9
figure 9

XPS analysis of CS/GO/PANI-1 thin films before and after ibuprofen adsorption (a) wide scan survey spectra, (b-d) deconvoluted C1s, N1s and O1s spectra before ibuprofen adsorption, (e–g) deconvoluted C1s, N1s and O1s spectra after ibuprofen adsorption

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The XPS analysis of ibuprofen adsorbed CS/GO/PANI-1 thin film shows an evident change in the peak position and intensity (Fig. 9a). The composition of C, O, and N in ibuprofen absorbed CS/GO/PANI-1 thin film differs from as-synthesized CS/GO/PANI-1 thin film. The elemental ratio of C, O, and N in ibuprofen adsorbed CS/GO/PANI-1 thin film is 81.15%, 18.14% and 0.83%, respectively. The XPS analysis showed a reduction in the nitrogen percentage in ibuprofen adsorbed thin film compared to the before adsorption analysis. This can be explained based on the XPS analysis nature. The XPS can analyze about 5 nm depth thin layer of the sample and the upper layer of thin film having surface adsorbed ibuprofen molecules. Since nitrogen is not present in ibuprofen molecular structure (C13H18O2), the N% is reduced after ibuprofen adsorption. Similarly, the amount of oxygen reduced after the adsorption of ibuprofen due to a low amount in its molecular structure. The amount of C% decreases after ibuprofen adsorption due to higher ratio. The peaks for C1s, N1s, and O1s appeared at 284.72, 399.92, and 531.72 eV. The shift in binding energy is due to the binding of ibuprofen on CS/GO/PANI-1 thin film. Moreover, deconvoluted C1s spectra (Fig. 9e) show that several peaks belong to C–C/C-H, C-NH, C = O, O-C = O at 284.8, 285.38, 286.49, and 288.35 eV. The N1s spectrum shows only two peaks centered at 398.65 and 399.84 eV assigned to –N = /C = N–C and –N–H (Fig. 9f). The peaks appeared at 400.42 eV in as-synthesized CS/GO/PANI-1 thin film disappeared after the binding of drug indicating that strong interaction between adsorbent and adsorbate. Additionally, a peak at 329.33 eV is observed in the deconvoluted O1s spectrum beside 531.39 and 532.38 eV (Fig. 9g). The new peaks belong to C = O (–COOH groups) of ibuprofen while the other two peaks indicate the presence of O-C and O = C–OH/O-COO groups. The above results indicate the successful adsorption of ibuprofen onto CS/GO/PANI-1 thin film.

Moreover, FTIR spectrum was further recorded to study the modifications and interaction between thin film and ibuprofen. Figure 10 shows the FTIR spectrum of CS and CS/GO/PANI-1 thin film before and after adsorption of ibuprofen. The CS spectrum (Fig. 10a) has strong peaks at 3464, 1662, 1381, and 1083 cm−1 belonging to OH and NH stretching vibrations, NH deformation vibrations, and C–OH stretching vibrations, respectively (Kumar and Jiang 2016). The FTIR spectra of CS/GO thin film is shown in Fig. 10b. Most of CS/GO spectra peaks showed a downshift compared to the pure CS spectra due to the hydrogen bonding between the functional groups of CS and GO. The bread peak appeared at 3464 cm−1 in CS and shifted to 3448 cm−1 (-OH peak). The C = O stretching band (amide I) observed at 1662 cm−1 indicates α-Chitin structure (Sikorski et al. 2009), shifted to 1647 cm−1 due to interaction between C = O and NH groups. The vibration of N–H bending peak appeared at 1566 cm−1 in the CS/GO spectrum. The strong peaks appeared at around 1083 in CS spectrum, became broader in CS/GO spectrum, and shifted to 1091 cm−1 due to stretching vibration of C–O–C of GO and C-O of the secondary alcohol (Zuo et al. 2013). A noticeable change in FTIR spectrum of CS/GO/PANI-1 thin film is recorded after incorporation with GO and PANI. Since CS, GO, and PANI have common chemical groups, a similar FTIR spectrum with a slight change in intensity of the peaks and peaks position is recorded, as shown in Fig. 10c. The transmittance bands at 1154, 1083, 1025, and 613 cm−1 indicate the C–O–C, C-O–H stretching vibrations (Lee et al. 2020). The new peak that appeared at 1558 cm−1 and 1462 cm−1 is C = N stretching of the quinoid ring characteristic band of PANI and the C = C stretching of the benzenoid ring (Rathore et al. 2020). The peaks assigned for –NH, -OH, and C-O show significant changes in the intensity and wavelength after coupling CS with GO and PANI. These results reveal that NH, -OH, and C-O groups are involved in the binding and forming of new bonds in the CS/GO/PANI-1 thin film. Although, significant changes are also observed in CS/GO/PANI-1 thin film FTIR spectrum after ibuprofen adsorption (Fig. 10d). The peaks appeared at 3360 cm−1, 1647 cm−1, 1558 cm−1, 1025 cm−1, and 934 cm−1 were shifted to 3300 cm−1, 1672 cm−1, 1510 cm−1, 1223 cm−1 and 881 cm−1, respectively. The shifting in the bands after ibuprofen adsorption can be assigned to the hydrogen bonding, π–π bonding, etc. forces involved in adsorption between the functional groups of ibuprofen and CS/GO/PANI-1 thin film (Minisy et al. 2019).

Fig. 10
figure 10

FTIR spectrum of (a) CS, (b) CS/GO, (c) CS/GO/PANI-1 thin film and (d) CS/GO/PANI-1 thin film after ibuprofen adsorption

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The results in Fig. 5 demonstrated that non-electrostatic forces controlled the adsorption of ibuprofen onto CS/GO/PANI-1 thin film, and the non-ionic form of ibuprofen showed the highest interaction with thin film. Although anionic ibuprofen showed good adsorption onto CS/GO/PANI-1 thin film due to the electron donor–acceptor interaction, hydrophobic interaction, ibuprofen (π-acceptors) and GO-PANI benzene ring (π-donors), and pore-filling at the whole range of pH (Iovino et al. 2015). The establishment of hydrogen bonding between O and N containing groups of ibuprofen and CS/GO/PANI-1 via dipole–dipole interactions. The shifting in the C-NH, C = O, O-C = O, –N = /C = N–C, and –N–H peaks binding energies (Fig. 9e-f) after ibuprofen onto CS/GO/PANI-1 suggesting a good interaction between them (Yoo et al. 2023). A schematic mechanism for the interaction of ibuprofen onto the CS/GO/PANI-1 surface is shown in Fig. 11.

Fig. 11
figure 11

A schematic mechanism for the interaction of ibuprofen onto CS/GO/PANI-1 surface

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Desorption and regeneration

Desorption and regeneration of the thin films are more manageable than powder materials due to easy separation and recovery from the solution. Desorption of ibuprofen and regeneration of used CS/GO/PANI-1 thin film was investigated in acetone, ethanol, and 0.01 M NaOH, and the results are demonstrated in Fig. 12. The results showed that organic solvents proved higher efficiency compared to the basic solvent. The lower efficacy of NaOH solution can be explained based on the adsorption forces and the effect of pH as depicted in Fig. 5a. As shown in Fig. 5a, CS/GO/PANI-1 thin film shows good adsorption in the basic medium and non-electrostatic forces were involved in ibuprofen binding on thin film surface. Therefore, NaOH was less effective and showed lower regeneration of CS/GO/PANI-1 due to incomplete desorption of ibuprofen. In contrast, acetone has better CS/GO/PANI-1 regeneration due to the higher solubility of ibuprofen in the organic solvent than water (Filippa and Gasull 2013). The organic solvent reduces the polarity and hydrophobic interaction between ibuprofen and CS/GO/PANI-1. Therefore, organic solvent showed better desorption of ibuprofen and indicated that CS/GO/PANI-1 is an efficient adsorbent for reuse (Wang et al. 2017).

Fig. 12
figure 12

Regeneration of the CS/GO/PANI-1 thin film

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Comparison of results with literature

The comparison of the various materials used for ibuprofen scavenging is summarized in Table 4. Ibuprofen decontamination efficacy of CS/GO/PANI-1 thin film is much higher than that of several adsorbents. The results depicted in Table 4 showed that ibuprofen scavenging capacities of chitosan, graphene oxide, and polyaniline-based adsorbents are low compared to CS/GO/PANI-1 thin film. Moreover, CS/GO/PANI-1 thin film showed much faster removal of ibuprofen and with a lesser mass of thin film. An accurate comparison of this work with the literature is challenging due to the differences in the experimental conditions, adsorbent properties, and composition of CS/GO/PANI-1 thin film.

Table 4 Comparison of ibuprofen adsorption results with the literature
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Conclusion

This article reported the rational immobilization of GO and PANI in chitosan (CS) to prepare the effective biopolymeric hydrogel thin films to scavenge ibuprofen. The preliminary results demonstrated that optimized 1.5 mg GO and 22.5 mg PANI immobilized in 150 mg of CS matrix showed the highest decontamination of ibuprofen from the aqueous system. As the amount of GO increases in the thin film, adsorption capacity of the thin films reduces while vice-versa results were obtained for PANI. The results demonstrated that solution pH controls the adsorption of ibuprofen and saturation time of CS/GO/PANI-1 thin film. The fastest equilibrium was attained within 90 min at pH 4, and non-ionized ibuprofen molecules showed better adsorption than the anionic ibuprofen (pKa: ~ 4.9), and non-electrostatic forces were mainly responsible for the binding of ibuprofen onto thin film. The interaction and scavenging of ibuprofen reduced with the rise in the solution temperature due to the exothermic process, and favorable adsorption occurred at 24 °C. Ibuprofen adsorption kinetics and isotherm modeling can be explained by the Elovich model and Redlich-Peterson equation, suggesting the heterogenous surface of CS/GO/PANI-1 thin film and adsorption was controlled mainly by physical forces and less contributed by chemical adsorption. Desorption studies showed acetone was a more effective eluent than ethanol and NaOH. The results demonstrated that CS/GO/PANI-1 thin film can be successfully regenerated without significant loss in efficiency after five cycles. The comparison of the results of this study with the literature showed that CS/GO/PANI-1 thin film is efficient for decontaminating ibuprofen.