Towards a win-win chemistry: extraction of C.I. orange from Kamala fruit (Mallotus philippensis), and simultaneous exercise of its peels for the removal of Methylene Blue from water

Abstract Kamala fruit (Mallotus philippensis), hereinafter MP, has been simultaneously exercised for the extraction of a natural dye, C.I. orange and its peels were converted into an efficient adsorbent for the rapid removal of methylene blue (MB) dye from aqueous solutions. The material has been characterized by Fourier Transform Infra-red (FTIR),Field Emission Scanning Electron Microscopy- Electron dispersive spectroscopy (FESEM-EDS), Brunauer–Emmett–Teller (BET) surface area, and pHZPC. FTIR suggests the presence of polyphenolic moieties responsible for adsorption, whereas FESEM confirms the porous texture. Optimization of process variables such as contact time, pH, adsorbent dose, and temperature of operation indicates that the adsorption gets modulated by the pH, with a best at 11. The Freundlich model (R2 = 0.994), and pseudo-second-order kinetics (R2 = 0.999) best describe the adsorption pathway. Dilute hydrochloric acid is sufficient to induce >66% regeneration, which ensures reusability. With the maximal uptake for MB is 30.2 mg/g at ambient conditions, the superiority over the existing materials has been confirmed. Treatment of dye containing industrial effluent suggests about a 50% reduction in one cycle. It can be concluded that both-way benefits, namely natural dye extraction and preparation of a peel-based adsorbent for methylene blue removal from aqueous solution, can be achieved using the kamala fruit peels. Novelty statement Mallotus philippensis, a seasonal fruit, commonly known as Kamala, was employed to serve a dual advantage of extracting a natural dye called C.I. orange from the peels; thereinafter, the peels were converted as an adsorbent to remove Methylene blue from water and industrial wastewater with high efficacy. From 100 g of raw material, 1.7 g of C.I. orange dye was extracted, along with 44 g of peel-based adsorbent. The maximum adsorption capacity for MB is 30.2 mg/g at ambient conditions, better and more impactful than contemporary adsorbents. The approach is firmly established in the circular economy as a dual benefit agent, generating clean and green revenue through natural dye extraction. Graphical Abstract


Introduction
Water contamination is posing a global threat to civilization (Akpomie and Conradie 2021). The major source of water pollutants is the increase in agricultural, commercial, and domestic activities. As the world's industrialization accelerates, the discharge of industrial effluent into freshwater accounts for the majority of water pollution (Zhang et al. 2021). Dyes are widely utilized as coloring agents in many sectors, including paper, textile, food processing, pharmaceuticals, cosmetics, and other industries such as leather, printing, and rubber (Kumari and Dey 2019a;Qaiyum et al. 2022). At least 3,000 different azo dyes were utilized in the paper industry, as well as printing inks and paints. More than 100,000 commercially available dyes with over 7 Â 10 5 tons of dyestuff are produced annually (Sahu and Singh 2019). So the discharge of the harmful byproducts of these dye-based industries into water bodies causes pollution as well as hampers photosynthesis of aquatic lives preventing the penetration of sunlight into water (Chung 2016). Besides, coagulation-sedimentation (Saitoh et al. 2014), flotation (Hu et al. 2020), filtration, Fenton chemical oxidation (Moradi and Ghanbari 2014), photocatalysis (Hasanpour and Hatami 2020), ion exchange treatment (Hassan and Carr 2018), aerobic and anaerobic treatment (Gisi et al. 2016), adsorption, ozonation (Ulson et al. 2010) even microorganism and enzymes have been employed for wastewater treatment.
Methylene blue is the chloride salt of 3,7-bis(dimethylamino)phenothiazin-5-ium which is used to treat many diseases (McDonagh et al. 2013). Severe eye damage, respiratory infections, vomiting, nausea, and other problems have been recorded after prolonged exposure to MB. One of the most prevalent therapeutic applications of MB in the treatment of methemoglobinemia is induced by nitrophenol overexposure from pharmaceuticals or industrial chemicals (Oz et al. 2011). MB is used for the successfully treatment of psychiatric diseases due to its pharmacological properties that prevent guanyl cyclase activation by nitric oxide. Due to its limited biodegradability, MB prevents sunlight from penetrating water, affecting not only natural photosynthesis but also lowering Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) levels. The removal of MB from wastewater is a global and environmental concern, and academicians are constantly devising economic strategies to address it. Adsorption is commonly used for dye remediation from wastewater because it is simple to operate, produces no hazardous by-products, cheap, and efficient (Kumari and Dey 2019b;Aldawsari et al. 2021).
The existence of cellulose, polyphenols, hemicelluloses, lignin, and surface functional groups such as hydroxyl, carboxyl, amino, and carbonyl groups in phytosorbents improves dye binding ability to the surface (Leng et al. 2015). Additionally, research has been performed to increase the adsorption capabilities of the material's surface.
The current research focuses on converting leftover MP fruit peels into a suitable phytosorbent for MB removal from water. Mallotus Philippens is a medium-sized tree mainly found in Asia and Australia. It is also known as the Kamala (orange colored) tree or Kumkum tree since the inner covering of the fruit generates an orange color, also known as C.I. orange. The fruit peel is abandoned postcolor production, resulting in voluminous waste. As a consequence, using leftover fruit peel as an adsorbent may be both ecologically benign and effective. The said fruit peel was demonstrated for MB removal from simulated water and industrial wastewater.

Materials and methods
Methylene blue (99% pure, Merck, India) was used to prepare the stock solution, while hydrochloric acid (98% pure, Himedia, India) and sodium hydroxide (97% pure, Himedia, India) was employed to modify the pH. An OS 100 orbital shaking incubator was used in the overall study. For the centrifugation, a Remi Benchtop centrifuge (model R-8M) was employed. A Redline Binder oven was used to dry the samples. The Hitachi Double Beam spectrophotometer was used for all colorimetric measurements (model U-2900). Vanira LI 613 pH meter was used to measure the pH of the solution. The Fourier Transform Infra-red (FTIR) spectra were obtained using FTIR spectrum 2 (Perkin Elmer). The surface morphology Field Emission Scanning Electron Microscopy-Electron dispersive spectroscopy (FESEM-EDX) was recorded using a Zeiss optical microscope. Brunauer-Emmett-Teller (BET) surface area was measured in Nova touch 2LX using the nitrogen adsorption-desorption method.

Collection and treatment of kamala fruit (MP)
Fallen Kamala fruits (Mallotus philippensis) was obtained from our university campus (Ranchi, India, 23 26 0 30 00 N, 85 8 0 45 00 E, having a mean altitude from sea level of 2,310 ft (705 m) in the month of February-March. The maroon colored fruits were separated from their seeds first. To extract the color, the peel was refluxed eight times (8 Â 4 h) with distilled water. The peels were filtered, carefully cleaned, and oven-dried for 48 h at 65 C. A household mixer grinder was used to crush the dry fiber into powder (Lifelong Duos, LLMG92, India) and sieved to get the required particle size. Additionally, the fruit extract was centrifuged and crystallized to produce a deep crimson powder.

FTIR spectra
Figure S1 (supporting information) presents the FTIR spectra of MP before and after the adsorption of MB dye. The broad peak at 3,430 cm À1 is due to polysaccharide moieties present in the MP. The À OH unit promotes hydrogen bonding with the dye molecule. Adsorption caused such a peak to move to 3,428 cm À1 , indicating an effective hydrogen bonding interaction with the dye molecule. The peak at 2,924 cm À1 is mainly due to the presence of aliphatic carbon moieties, which are retained in the final spectrum. A peak is present at 1,715 cm À1 , which may be attributed to the presence of carbonyl groups arising from ester moieties. Such a peak was found to have diminished significantly, suggesting a major change within the structural unit. The peak at 1,628 cm À1 is due to -OH bending vibrations. Other peaks present in the fingerprint zone are mainly contributed by the organic moieties present within MP. Since a dilute solution of the dye has been used, a drastic change in peaks was not observed. This is consistent with our previous observations Dey et al. 2022b). Figure 1 represents the surface morphology of MP before and after the adsorption of MB molecules. The surface of MP contains pits and a valley-like structure with uneven pores, channels, and nonuniform structures. Pores and channels are seen, which account for better adsorption of dye molecules. Significant smothering of the surface has been observed with the disappearance of pores and uneven valleys in Figure 1b indicating the adsorption of MB onto the surface partially covers the pores, overrides ridges, and pits. Intermittent deposition of particles could be seen. In Figure S2, EDX image shows the presence of carbon and oxygen before adsorption, while additional peaks of nitrogen and sulfur have been noticed after adsorption, which appeared due to the presence of MB molecules on the surface.

BET surface area analysis
The surface area was evaluated by the N 2 adsorption-desorption method and found to be 1.12 m 2 /g while the pore volume of the material is 6.6 Â 10 À2 cm 3 /g. The plot follows the type III adsorption isotherm established on the assumption that a substantial number of molecules containing the same energy are present at each receptor site. (Qaiyum et al. 2022)

Adsorption experiments
Scheme 1 outlines the C.I. orange dye extraction and methylene blue removal using MP fruit peel. The batch experiments were studied in 100 mL Erlenmeyer flask. MP powder (0.15 g) was added to the desired dye solution (30 mL, 20 mg/L). The prepared dye solution has a pH of 7. At a speed of 110 ± 5 rpm, the solutions were agitated for 1 h.
Where C 0 denotes the initial concentration and C e denotes the final concentration (mg/L), m is the amount of MP powder (g) and v denotes the volume (L). The influence of temperature (308, 318, and 328 K) and pH (5-11) has been tested. Dilute HCl and dilute NaOH were used to test the regeneration of dye-loaded spent material. The adsorbent was separated by centrifugation, and the residual dye concentration was measured. The efficiency was calculated as follows: Efficiency % ¼ Dye uptake in second run Dye uptake in the first run Â 100 (3)

Equilibration time
The preliminary agitation experiments were carried out in 0-60 min Figure 2a. The absorption was found to be exceedingly quick, with 97.5% dye adsorption achieved within the first 15 min. Furthermore, as the time length grew, a flattened curve was seen, which can be attributed to active center saturation on the adsorbent. Henceforth, 15 min of contact was used for all other experiments.

Effect of pH and pH ZPC
The function of pH in dye binding to the adsorbent surface is critical. The functional groups, such as carboxyl, hydroxyl, and amine groups, are significantly affected by pH alteration. MB adsorption was studied at pH values ranging from 5 to 11 and is presented in Figure 2b. Adsorption is negligible at low pH but rises progressively with increasing pH. This is explained by considering the MP's zero point charge (pH ZPC ¼7.5). Lower pH causes protonation of the MP surface, which repels the cationic dye MB, restricting the adsorption of dye molecules onto the surface. The MP surface becomes negatively charged at higher pH (pH > pH ZPC ), due to the formation of an electric double layer onto the surface of MP which favors cationic dye binding via electrostatic attraction.

Effect of concentration
The concentration was varied from 10 to 40 mg/L while other parameters remained constant. The change in adsorption percentage as a function of concentration is presented in Figure 2c. The percentage of dye molecules adsorbing to the MP surface gets slightly reduced with an increasing concentration of dye, which could be due to the faster saturation of the MP surface due to the higher quantity of dye molecules present in a highly concentrated solution. Similar observations were reported earlier.

Kinetic study
Adsorption is better understood by developing the most accurate kinetic model that can be used to describe the adsorption mechanism. Three kinetic models were examined and presented, namely pseudo-first-order, pseudo-second-order, and intra-particle diffusion. (Figure 3a-c). The ease of adsorption is governed by the pseudo-first-order model (Equation (4)) which roughly parallel the number of available sites.
log q e À q t ð Þ ¼ log q e À k 1 t 2:303 (4) The amounts of dye adsorbed at equilibrium and at time t are represented by the symbols q e and q t (min). The rate constant is k 1 (min). The site occupancy is proportional to the square of unoccupied sites, according to the pseudosecond-order model (Equation (5)).
k 2 (g/mg.min À1 ) designates the pseudo-second-order rate constant. According to the intra-particle diffusion model (Equation (6)), mass transfer to the adsorbent surface occurs by diffusive transfer. The diffusion of liquid molecules onto the solid adsorbent occurs through three steps transfer of mass onto the external surface of the adsorbent is followed by pore diffusion of the solute, whereas in the last step equilibrium is reached. Equilibrium is reached rapidly in comparison to the former steps.
The corresponding rate constant is k 3 (mg/g.min 0.5 ). From Table 1, it is evident that multiple modes seem to operate within the adsorbent-adsorbate system. With a R 2 ¼ 0.999, MB predominately follows the pseudo-second-order model. Diffusive transfer, on the other hand, provides some assistance.

Isotherm interpretation
Adsorption isotherms show how dye interacts with the surface of the adsorbent at equilibrium. Langmuir and Freundlich isotherms were used to fit the experimental data. The Langmuir model (Equation (7)) assumes that adsorption occurs by monolayer adsorption onto a homogenous surface where intermolecular repulsion is insignificant.
Where c e (mg/L) represents the equilibrium concentration, q e (mg/g) represents the equilibrium adsorption, q max (mg/g) represents the maximum adsorption capacity, and b represents the Langmuir constant (L/g). The Freundlich isotherm model (Equation (8)) assumes multilayer, heterogeneous adsorption.
Where q e (mg/g) denotes the quantity of adsorbed dye, k f and n denote the Freundlich constants and adsorption intensity. For a good adsorption process, the value of 'n' should be between 1 and 10. Isotherm plots for MB are shown in Figure 4. The Freundlich model (R 2 ¼0.994) matches the data better than the Langmuir model and the value of 'n' in the Freundlich model is 1.08-2.03 (Table 2).

Thermodynamics study
To assess the feasibility of the solid-solute interaction, thermodynamic parameters were investigated at three different temperatures: 308, 318, and 328 K ( Table 3). The thermodynamic calculation was performed using the equations outlined below.
DG ¼ ÀRTlnK a (10) The overall interaction is observed to be spontaneous (DG ¼ À2.597 to À6.676 kJ/mol) endothermic (DH ¼13.593 to 51.380 kJ/mol), and defined by an increase in entropy (DS ¼0.052 to 0.177 kJ/mol) at the interface between the solid and liquid junctions.

Effect of co-existent ions
The effect of co-existent ions has been assessed with commonly present ions such as PO 4 3À , AsO 4 3À , Hg 2þ , and Pb 2þ ( Figure S3). Final concentrations of the co-existent ions were measured along with MB. No significant reduction in adsorption was found in all four cases.

Estimation of maximum adsorption capacity
Maximum adsorption capacity can be calculated by using Equation (9) Where 'C 0 ' is the initial concentration and 'C e ' is the final concentration of the solution. 'v' stands for volume of the solution, and 'm'stands for the mass of the adsorbent used. The q max of the MP was found to be 30.2 mg/g.

Regeneration and reuse
The Long term applicability of an adsorbent depends on its regeneration tendency. The MP was tested in four different solutions to regenerate the adsorbent, which can be used multiple times to have a larger impact. Regeneration was tested using HCl (0.1 M), NaOH (0.1 M), MeOH(0.1M), and NaCl (0.1 M) solutions; 66% regeneration was accomplished by 0.1 M HCl after which the MP was tested for second-cycle use for adsorption of MB. Regenerated material shows an adsorption capacity of 22 mg/g, with a retention of 70% activity. Methanol was also found to be a promising agent for regeneration.

Adsorption mechanism
The adsorbent surface may change with pH and other conditions. The driving adsorption mechanism may vary the adsorption of MB molecules from wastewater, and the association between MP and MB may be caused primarily by weak hydrogen bonding due to the presence of functional groups on the surface, electrostatic attraction, and p-p interaction. This is also supported by other findings in similar observations (Jawad et al. 2021). Furthermore, the pores on the surface of MP could provide the driving force for dye molecules to adhere to MP.

Industrial sample analysis
It is necessary to establish the material's efficiency using an industrial effluent to evaluate its effectiveness on an industrial scale. As a result, a batch experiment was conducted using raw sewage obtained from the industry. Filtration, centrifugation, and neutralization are the stages undertaken for wastewater pretreatment. 2 mL of effluent was taken and diluted three times. The input concentration was recorded. The initial pH of the effluent was detected to be greater than 9 (alkaline), which was reduced to 7.5 by using 0.01(M) HCl. To the diluted effluent, 0.15 g of MP powder was added and then put forth in an orbital shaker for 15 min. Then, the final concentration was calculated. The concentration reduces to approximately to half of its initial concentration, which suggests a practical application of the material on an industrial scale.

Economic viability check
A sound techno-economic approach is necessary to recommend a material as a prospective and sustainable resource. C.I. orange, a natural dye, is extracted when Kamala fruit peel is used as an adsorbent. Given that synthetic dyes are carcinogenic and mutagenic in nature, the development of organic colors could be more environmentally friendly. As a result, this strategy generates some revenue. In addition, manufacturing may be scaled to any size. We are able to achieve dye purification, trash removal management, and revenue generation at the same time. A high output/input ratio is possible as a result of this. To summarize, the procedure satisfies a portion of the green engineering requirement. Hence, it can be stated that MP powder can be an excellent solution for sustainable water treatment.

Comparative analysis
To ascertain its better applicability, MP was compared with other established adsorbents for its enhanced removal of dye molecules. Table 4 gives us an understanding of the adsorption capacity of various adsorbents with regards to the present work. It was clear that the present material is good for MB removal.

Conclusion
Kamala fruit peels were exercised for the remediation of methylene blue from wastewater. FESEM-EDX, FTIR, BET, and pH zpc suggest a porous phytosorbent, suitable for dye remediation. With an adsorption capacity of 30.2 mg/g at a dose of 0.15 g, it has better applicability in wastewater   treatment. The process follows pseudo-second-order kinetics with R 2 ¼ 0.999. The Freundlich isotherm model with a higher correlation coefficient (R 2 ¼0.994) signifies that multilayer adsorption of the dye molecule is taking place. 66% regeneration of the spent material was achieved with 0.1 (M) HCl solutions, suitable for reuse. When tested with industrial effluent containing MB dye, a 50% reduction in dye concentration was noticed, indicating its applicability in the real world samples. No significant change in adsorption pattern of dye is observed when induced with counter ions in the solution. The industrial wastewater trial has given an edge to this material for its better applicability and usage.