Role of Purged Air in the Synthesis of the Mesoporous NiO/C Composite and Its Application in Wastewater Treatment

In this study, two methods were used to synthesize the NiO/C composite from agricultural waste. The mesoporous composite was successfully synthesized via a novel precipitation method in the presence of dissolved gases. The morphology of the composites was differentiated by using characterization techniques such as X-ray diffraction, the point of zero charge (pHpzc), field-emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy, energy-dispersive X-ray analysis (EDAX), and vibrating sample magnetometry (VSM). Then, the mechanism of synthesis was elucidated using the above experimental characterization data. Results of FESEM and EDAX analyses of Ni(OH)2–carbon composite clearly showed the role of dissolved gases in the synthesis. Both the composites were subjected as the adsorbent to remove the toxic Pb(II) ions from the wastewater. Batch adsorption experiments were carried out to compare the Pb(II) ion removal capability of both the composite materials. The parameters such as the effect of pH, the dosage of the adsorbents, and initial concentration were studied. At the optimized conditions, isotherm studies for each of the adsorbent were also carried out. The isotherm results revealed that the maximum removal capacity qe (mg/g) was 30.78 for PJNC and 43.48 for PJGNC. The VSM analysis confirmed that both the adsorbents were soft magnetic materials. Hence, they could be competently separated from salted/treated water using a magnetic field.

wastewater are focused on various methods such as chemical precipitation, coagulation, electrofloatation, ion exchange, adsorption, photodegradation, and membrane filtration (Hua et al., 2012;Patra et al., 2020;Shaheen et al., 2018;Wan Ngah & Hanafiah, 2008). Among these, adsorption technique is more efficient, cost-effective, and eco-friendly. The economic adsorption process could be appropriately determined by the proper selection of the cheapest and the most effective adsorbent. Activated carbon is the most commonly used absorbent today as it is the most economical and efficient. This investigation focuses on the utility of the biowaste material, which is expected to perform better than the commercial activated carbon (Sud et al., 2008;Wan Ngah & Hanafiah, 2008). In this study, carbon was derived from Prosopis juliflora (PJ) wood, which is invasive to the environment. P. juliflora is usually found in abundance in the arid and semiarid continents (Chandrasekaran et al., 2020;El-Keblawy & Abdelfatah, 2014;Shackleton et al., 2015;Zachariades et al., 2011).
In the recent times, researchers have paid attention to convert nanometal oxides such as ferric oxides, aluminum oxides, manganese oxides, magnesium oxides, cerium oxides, and titanium oxides as an efficient adsorbent, as they have a large surface area and high activities with magnetic regeneration property (Bharath et al., 2021;Hua et al., 2012;Zachariades et al., 2011). Metal oxides are more effective, but they are not cost-effective. Latest studies reveal that metal oxide/carbon composites play a key role in high-power devices, electrochemical capacitors, catalysts, and adsorbents (Fu et al., 2019;Modwi et al., 2017;Wu & Hsieh, 2008) because the metal oxide/ carbon composites are efficient and cost-effective. Hence, many efforts have been directed to synthesize an efficient carbon composite. The features of the composite have been determined by the method of synthesis (Hale, 1976;Zachariades et al., 2011). In this study, NiO/carbon composite was synthesized by precipitation method using sodium hydroxide and nickel nitrate. In another way, the same precipitation was carried out with air as the predecessor. The composites prepared by the aforementioned methods were differentiated by characterization techniques such as the point of zero charge (pHpzc), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray analysis (EDAX), field-emission scanning electron microscopy (FESEM), and vibrating sample magnetometry (VSM). The mechanism of synthesis has been discussed and explored by using the abovementioned experimental characterization data. Then, those composites were subjected to purify the wastewater to determine the efficiency variance, which discusses the efficiency of two different NiO/C composites in the removal of Pb (II) ions from an aqueous solution.

Synthesis of P. juliflora Carbon
The P. juliflora (PJ) wood parts were collected from places in and around Coimbatore (11.0168° N, 76.9558° E), Tamil Nadu, India. The PJ wood was wrecked and broken into comparable similar sizes (2-3 cm) and later washed gently by using doubledistilled water. The PJ wood pieces were taken in a muffle furnace and exposed to pyrolysis with a slow heating rate (5 K/min) (Estela et al., 2018). It was kept in the furnace up to 673 K to get a high yield of carbon (Selvaraju et al., 2018). The prepared carbon (named as P. juliflora carbon; PJC) from P. juliflora was washed thoroughly using double-distilled water to remove the ash and some dissolved matter. Then, it was dried and cooled to atmospheric temperature. The PJC obtained from the above process was crushed and converted into a composite with NiO by two precipitation methods.

Synthesis of NiO/C Composites
First, 4.6 g PJC was taken into a clean beaker along with 400 mL distilled water. After half an hour, that heterogeneous solution was constantly air purged at a flow rate of 2 × 10 −2 m 3 /h. Then, 50 mL of 1 M NiNO 3 was added to the above and the purging process continued about 30 min for even dispersion. To this mixture, 50 mL of 2.0 M NaOH gradually was added at regular intervals, which resulted in a green Ni(OH) 2 precipitate on the surface of the carbon. That mixture was kept for a whole day for the settlement of the Ni(OH) 2 /PJC composite (PJGNH) at the bottom. The filtrate was decanted and the residue was washed with double-distilled water to achieve the neutral pH. Then, the final product was kept in the muffle furnace and heated for half an hour up to 250 °C to get a black PJ shell consequential nanocomposite NiO/PJC (PJGNC) (Xing et al., 2004;Yuan et al., 2005). The synthesis procedure is shown in Fig. 1 and Eqs. (1) and (2). In addition, the NiO/PJC composite was prepared by the above-cited method without purging of the air. The obtained Ni(OH) 2 /carbon was termed as PJNH and it was calcinated to convert into the NiO/ carbon composite, which was termed as PJNC. This process is also shown in Fig. 1 and Eqs. (3) and (4).

Characterization
The morphology of PJGNC and PJNC was uniquely distinguished by using FESEM (SUPRA 55 VP-4132; Carl Zeiss), XRD analysis (SmartLab; Rigaku). The composition of the elements present in PJGNC and PJNC was differentiated and quantified by EDAX analysis. The variance in magnetic property of PJGNC and PJNC was studied using a 7410 series VSM (Lakeshore). The adsorption/ desorption nitrogen isotherm in the P/P o range at 77.3 K (ASAP 2020 V4.02 H) was used to accurately differentiate the specific surface area and pore size of the PJGNC and PJNC.

Batch Mode Adsorption Studies
Using acceptable standards and methods, a comparison of the removal capacity of the prepared adsorbents was Fig. 1 Diagrammatic procedure for the synthesis of PJGNC and PJNC (4.6 g of PJC with 400 mL of distilled water, air flow rate: 2 × 10 −2 m 3 /h, 1 M NiNO 3 and 2.0 M NaOH, calcination temperature: 250 °C) conducted by batch adsorption studies. In this study, 100 mL optimal concentrations of lead (II) ions solutions were taken with a specified amount of adsorbents in the reagent bottles. Subsequently, using a mechanical shaker, they were agitated at 180 rpm at 303 K to elucidate the optimal dosage of the adsorbents in the adsorption process and the optimum pH from initial concentrations of Pb(II) ions. The role of the pH in the adsorption process was investigated by equilibrating 100 mL of 10 mg/L Pb(II) ion solution with 1.0 g/L dried adsorbents at various pH values between 1.0 and 8.0. The adsorbents ranging from 0.5 to 1.0 g/L were studied with a specified Pb(II) ion solution to find their optimal dose. The probability of the adsorption process was studied. The finest pH and the composite doses were accurately determined as 6.0 and 1.0 g/L for both PJNC and PJGNC. All the batch experiments were carried out with the abovementioned parameters with an equilibration time of about 180 min. After each batch experiment, the supernatant solution was decanted and analyzed by using an atomic absorption spectrophotometer (AAS-WFX-130; Systronics). Therefore, the amount ( q t ) of Pb (II) ions adsorbed could be calculated by following Eq. (5) and the adsorption efficiency ( R t ) could be calculated using Eq. (6) : where C i is the metal ions concentration measured before adsorption, C e is the metal ions concentration measured after adsorption, W is the weight of the dried adsorbent, and V is the aqueous solution volume in liters.

Isotherms Analysis
The unique design of the adsorption system could be correlated by the adsorption isotherm (Hameed et al., 2008;Saravanakumar et al., 2019). It would be necessary to explain the dispersion of adsorbate on the adsorbent in the liquid phase (Yao et al., 2016). The batch adsorption results in the present study were analyzed using two major isotherm models namely Freundlich isotherm and Langmuir isotherm. The first one indicated the equilibrium distribution of Pb(II) ions between the solid and liquid phases. This isomer was valid effectively for only monolayer adsorption onto a surface with a finite quantity number of active sites. This isotherm model assumed unchanging/uniform energies of adsorption onto the surface and no drifting/transmigration of adsorbate on the surface of the adsorbent (Bouabidi et al., 2018). Langmuir isotherm could be represented by following Eq. (7): Linear form of Langmuir Eq. (8) could be represented as: where C e is the equilibrium concentration of Pb(II) ions (mg L −1 ), Q e is the amount of Pb(II) ions adsorbed per gram of the adsorbent at equilibrium (mg/g), Q o is the maximum monolayer coverage capacity (mg/g), and b L is the Langmuir isotherm constant (L/mg).
The Freundlich isotherm was used to describe the adsorption of metal ions on the heterogeneous surface. This isotherm does not necessitate limit of the adsorption when coverage is sufficient to fill a monolayer. It could be represented by following Eqs. (9) and (10) (Khozhaenko et al., 2016): where n is the adsorption intensity, k F is the Freundlich isotherm constant (mg/g), Q e is the amount of Pb (II) ions adsorbed per unit gram of the adsorbent at equilibrium (mg/g), and C e is the equilibrium concentration of adsorbate (mg/L).

Structural Variation in PJNC and PJGNC
The structural variance of the PJNH and PJGNH composites could be understood by the powder XRD pattern, which is shown in Fig. 2. The 2θ values of both PJNH and PJGNH are related to the respective Miller indices (001), (100), (101), (102), (110), (111), and (200) (Huang et al., 2007). The broadened peak of PJGNH and PJNH indicates poor crystallinity. The intensity of PJGNH is a little higher than PJNH. It shows the orientation effect of purged gases on the precipitation of nickel hydroxide. It supports high aggregation of Ni(OH) 2 with an outer layer of carbon particles. The reduced intensity peaks on PJNH indicate the domination of carbon on precipitation (Poinern et al., 2009). The crystalline structure of PJNC and PJGNC could be explained by the powder XRD analysis. Figure 3 shows the powder XRD analysis of PJNC and PJGNC. The 2θ values of both PJNC and PJGNC are matching to the corresponding (111), (200), (220), (311), and (222) Miller indices (Mahmoud et al., 2015;Suresh et al., 2016;Wu & Hsieh, 2008;Xiang et al., 2002). The observed values denote the presence of nano-NiO crystallites in the composite. The calcination of PJC-NiOH at 250 °C influences the orientation effect and changes the phase of amorphous carbon (PJC) to a crystalline composite. The peak intensity of PJGNC is higher than PJNC. It also indicates the extent of crystallinity of PJGNC (Inoue & Hirasawa, 2013). The sharp peaks of PJGNC show mesopore size enlargement. It clearly supports the formation of Ni(OH) 2 influenced by purged air. The continued purging of air tends to disperse properly of the carbon particles in the liquid phase on precipitation of Ni(OH) 2 . It also leads to the quantized effect (Jayaram & Prasad, 2009).

FTIR Spectral Analysis
The reports of the FTIR analysis of PJNC and PJGNC are shown in Fig. 4. The PJNC and PJGNC composites were derived from P. juliflora. Therefore, they showed peaks of the functional group present in PJC.
In Table 1, the observed peaks and presented functional groups are represented along with the assignments (Khalil et al., 2010;Pallarés et al., 2018;Saravanakumar et al., 2013;Shen & Gu, 2009). The wood-derived adsorbents comprised a combination of cellulose, hemicellulose, and lignin content. respectively (Khalil et al., 2010). The prominent peak around 590 cm −1 is attributed to the presence of NiO group in the composites (Suresh et al., 2016;Tang et al., 2019).

Zeta potential Studies
Generally, the pH of solution affects the surface charge on the adsorbent (Priya et al., 2018;Karthik et al. 2011). The point of zero charges (pH pzc ) of the adsorbent is one of the important factors to predict the range of pH, which shows maximum adsorption (Kosmulski 2009;Tang et al., 2019). The pH pzc can be calculated by the plot of pH vs zeta potential. According to Fig. 5, the pH pzc of PJNC and PJGNC calculated are 6.0 and 5.7, respectively. It is shown that PJNC has a neutral surface charge at pH (6.0) and a positive surface charge (zeta potential + 23 to 3 mV) at pH (< 6.0). Then, it shows a negative surface charge (zeta potential − 5 to − 29 mV) at pH > 6.0. The zeta potential style for PJGNC slightly fluctuates and differs compared to PJNC. Similarly, PJGNC had positive surface charge (zeta potential + 19 to + 4 mV) at pH < 5.7, negative surface charge (zeta potential − 2 to − 34 mV) at pH > 5.7, and neutral surface charge at pH 5.7. The pH pzc values of both PJNC and PJGNC were lower than those of pure NiO nanoparticles (pH pzc = 10.8), which confirm that the surface of NiO was impacted by PJC (Acharya et al., 2009). The high pH pzc value of PJNC confirmed the decomposition of functional groups in the carbon of the composite and led to the decrease of the negative sites on the adsorbents. Meanwhile, the dissolved gases present in the PJGNH were influenced to avoid the decomposition of the functional group during calcination (Feygenson et al., 2010). It could be confirmed by the low pH pzc of PJGNC. The negative (− ve) surface of PJGNC influenced the positively charged Pb(II) ions and generated the interactions among Pb(II) ions and showed higher removal efficiency than PJNC.

BET Analysis and Particle Size of Adsorbents
The composite synthesis method was used to study the surface properties of the material. The Brunauer-Emmett-Teller (BET) model precisely revealed how metal oxide had combined with PJ carbon. The mean pore diameter (d) values, total pore volume (P/P o ), and specific surface area (A BET ) were calculated and the values are given in Table 2. The results show that the surface area and pore volume of PJNC are lower than those of PJGNC. The dioxygen in PJGNH at calcination increased the mean pore diameter of PJGNC. The average particle sizes of PJNC and PJGNC were calculated using a particle size analyzer (SZ100; Horiba, Japan) and reported as 71 ± 5 and 89 ± 5 nm, respectively. The particle sizes of both composites were higher than those of PJC (37 nm), which confirmed the aggregation of NiO with PJC.

SEM-EDAX Analysis
The scanning micrographs (FE-SEM) precisely differentiated the morphology of PJNH and PJGNH. Figure 6a and b show the aggregation of Ni(OH)2 with PJC. It reveals a high accumulation of Ni(OH)2 taking place in PJGNH due to the accessibility of more available active sites, which were influenced by the dissolved oxygen. The micrograph of Fig. 6c visibly confirms the gases between Ni(OH)2 and PJC. It is intentionally caused to increase the surface  (Kloss et al. 2012) area and pore diameter of the PJGNC composite throughout the calcination process (Mahmoud et al., 2015). The micrographs in Fig. 6d and f show the structures of PJNC and PJGNC, respectively. Figure 6f shows the mesoporous structure of PJGNC, which is created by purged gases. Figure 6e and g show PJNC and PJGNC after adsorption of Pb(II) ions. It reveals that the high amount of Pb (II) ions adsorbed on the surface of PJGNC is due to the influence of the high surface area, pore diameter, and more active sites on the adsorbent (Tang et al., 2019). The SEM-EDAX elemental dot maps of PJNH and PJGNH are shown in Fig. 7 a. The light green, violet, and brown dots in the figure indicate the concentrations of O, C, and Ni, respectively. The presence of a higher luminous intensity of dots indicates a significant concentration of the element. In this mapping, the light green dots indicate that the quantity of oxygen distribution is highly abundant in PJGNH compared to PJNH. The EDAX analysis in Fig. 7b and c also confirmed the presence of a high quantity of dioxygen in PJGNH.

VSM Analysis
Generally, the potential removal of powder adsorbent from the effluent after treatment is very difficult. It could be made easy by using a magnetic adsorbent. The magnetic properties of nanocomposites were characterized using a VSM graph (Ahilandeswari et al., 2020;Gupta et al., 2011). From  Fig. 8, the hysteresis loop of both the adsorbents reveals an antiferromagnetic character . This type of small hysteresis loops are meant to be the soft type magnets and complete magnetization enhances their low squareness shape. The magnetization values of PJGNC (87 × 10 −3 emu/g) and PJNC (14 × 10 −2 emu/g) were found to be decreased compared to pure NiO (65 emu/g) due to the presence of nonmagnetic carbon. It confirmed   (Cai et al., 2015;Feygenson et al., 2010;Fu et al., 2019). The very low value of retentivity also signposted/ indicated easier demagnetization of the prepared  (Ghaemi et al. 2017;Indhu & Muthukumaran, 2018). Hence, both could act as good adsorbents in the effluent remediation field.

Reverberation of Synthesis Process
Generally, the composite properties are influenced by the synthesis method. In this study, NiO/C composite was synthesized in two ways. Initially, carbon and NiNO 3 solution were purged with air. The dioxygen present in the air was dissolved in this solution and combined on the surfaces and micropores of the carbon in the liquid phase. It was influenced to combine the Ni 2+ ions with PJ carbon. After adding NaOH solution, the Ni 2+ precipitated along with dioxygen entrapped between Ni(OH) 2 and carbon.

Fig. 7 a EDAX elemental dot maps of PJNH and PJGNH. b EDAX analysis of PJNH and PJGNH
The entrapped oxygen is clearly shown in the FESEM micrographs (Fig. 6c). The EDAX analysis also supported the presence of high dioxygen content in PJGNH compared to PJNH by showing high luminous intensity and weight percentage of O 2 . At calcination, the entrapped gases would leave in the form of CO, CO 2 , and O 2 . The released gases enlarged the micropores of the composite to mesopores. It was confirmed by the BET analysis. At the same time, it avoided the decomposition of the active functional group present in the PJ carbon. The functional group present in PJGNC enhanced the negative surface charge on the composite, which was also confirmed by the zeta potential study.

Effect of pH
The adsorption efficiency of an adsorbent usually depends on the pH of the solution (Gupta et al., 2011). The impact of pH on the adsorption efficiency was examined in a range of pH values, from 2 to 9. Figure 9 clearly shows that the removal efficiency of both adsorbents has decreased after pH 7 due to precipitation of Pb(II) ions . Below pH 2, PJNC and PJGNC did not perceive the significant amount of Pb(II) ions. It specifies the Pb(II) ion adsorption on adsorbent active sites entered by the hydrogen (H +) ions (Gerçel & Gerçel, 2007;Ghaemi et al., 2017). On increasing the pH, the adsorption efficiency of both the adsorbents increased due to decrease in the hydrogen ion concentration. On increasing the pH from 2 to 6, the removal percentage of PJNC and PJGNC adsorbents increased from 34 to 83% and from 36 to 93%, respectively. The adsorption capacity of PJNC and PJGNC attained a maximum at pH 6 due to the availability of the negative surface charge on the adsorbents. However, the efficiency of PJGNC was found to be significantly higher than PJNC due to the presence of more dynamically active sites on PJGNC.

Effect of Adsorbent Dosage
The impact of adsorbent dosage on the removal of Pb (II) ions is shown in Fig. 10. It denotes that the removal efficiency of both the adsorbents had increased abruptly with the increase in the adsorbent dosage. It was found that on increasing the adsorbent dose, the number of availability of active sites also increased. Therefore, it favorably helped to increase the adsorption efficiency (Acharya et al., 2009). While increasing the weight of adsorbents from 0.5 to 10.0 g/L, the removal efficiency of PJNC for 10, 20, 30, and 40 mg/L Pb(II) concentration ions, respectively, with the increase in the adsorbent doses from 0.5 to 10.0 g/L at constant temperature (303 K) and at pH 6.0. Figure 10 shows that PJGNC has a higher adsorption efficiency due to the influence of the high surface area, pore diameter, and pore volume of PJGNC (Jaiswal et al., 2015).

Effect of Initial Concentration
The removal efficiency of the adsorbent varied depending on the concentrations of the adsorbate (Jaiswal et al., 2015). The effect of concentration on modification was assessed in the concentration ranges from 4 to 40 mg/L. The outcomes in Fig. 11a and b demonstrate that change in the concentration of adsorbate exerted a significant influence on the adsorption. The Pb(II) ion removal efficiencies (mg/g) of PJNC and PJGNC were improved on increasing the metal ion concentration, at the optimized pH and 1.0 g/L dosage. While using the initial concentration from 4 to 40 mg/L, the adsorption capacities (mg/g) of PJNC and PJGNC were increased from 3.65 to 25.18 mg/g and 3.86 to 33.58 mg/g, respectively. The increasing trend of both the adsorbents confirmed that the absorption of Pb(II) ions on adsorbent was simply physical adsorption. At the same time, the removal percentage of Pb(II) ions decreased with the increase in concentration (Fig. 11a). Thus, it showed the presence of the specific/precise limit of adsorption sites on the surface of adsorbent (Ahrouch et al., 2019;Fig. 9 Effect of pH on the adsorption capacities of Pb(II) ions (initial concentration of metal ions: 10 mg/L, temperature: 303 K, adsorbent dose: 1 g/L contact time: 3 h) Goel et al., 2005;Khandanlou et al., 2015). The presence of a higher number of significant active sites and large pore diameter had significantly influenced the removal capacity of PJGNC than PJNC.

Isotherm Pattern
The efficiency of adsorption is usually determined by affinity and surface properties of the adsorbents toward the adsorbate. The nature of the surface of the adsorbent in the adsorption process could be effectively determined by isotherm patterns (Goel et al., 2005;Mousa et al., 2016). In this study, Langmuir and Freundlich isotherms were applied to show the nature of adsorption with the schematic mechanism of Pb(II) ions on the PJNC and PJGNC adsorbents. The isotherm marks can be derived from Fig. 12a and b and Fig. 13a and b. These are also illustrated in Table 3. It clearly exhibits that the removal of Pb(II) ions followed the Freundlich model more reasonably Su et al., 2009). The maximum removal efficiency values of PJNC and PJGNC at 303 K were 30.78 and 43.48 mg/g, respectively.
The correlation coefficient (R2) of both the isotherms existed between 0.97 and 0.99. However, the Freundlich isotherm was more fitted over the entire temperature (Yang et al., 2018). The hexagonal Pb(II) ions on adsorbents in the SEM micrograph (Fig. 6g) also supported the multilayer formation. Thus, the following were demonstrated from the Freundlich isotherm: • The multilayer exposure coverage was outward between the adsorbate and adsorbent at a persistent constant temperature  • 1/n value was below one (1/n < 1), which showed reversible physisorption (Dada et al., 2012), and • The superior adsorption capacity of PJGNC was confirmed by a higher K f value (Shahnaz et al., 2021).
The nature of the reactions was specified by using the R L value, which was obtained from Langmuir isotherm. It also specified the shape of the isotherm to be irreversible (R L = 0) or unfavorable (R L > 1) or favorable (0 < R L < 1) and linear (R L = 1). In this study, R L values were placed between 0 < R L < 1, which also confirmed that the adsorption was a favorable process (Habtegebrel & Khan, 2018). Comparing the isotherms models, this collegial adsorption process involved both monolayer and multilayer adsorption with a fraction of active sites (Yang et al., 2018). These results concluded that PJGNC was a more favorable adsorbent than PNC in the removal of Pb(II) ions from the aqueous solutions.

Conclusions
The surface enhancement of PJNC and PJGNC composite was evidently investigated in this study. Fig. 12 a Langmuir isotherm of PJNC (temperature: 303 K, 313 K, and 323 K; adsorbent dose: 1 g/L contact time: 3 h, pH: 6). b Langmuir isotherm of PJGNC (temperature: 303 K, 313 K, and 323 K; adsorbent dose: 1 g/L contact time: 3 h, pH: 6) Pb(II) ion removal efficiency of adsorbents synthesized using two processes was investigated. The novel preparation of the composite gave a higher pore diameter, pore volume, and surface area. In addition, carbon derived from agricultural invasive Fig. 13 a Freundlich isotherm of PJNC (temperature: 303 K, 313 K, and 323 K; adsorbent dose: 1 g/L contact time: 3 h, pH: 6). b Freundlich isotherm of PJGNC (Temperature: 303 K, 313 K, and 323 K; adsorbent dose: 1 g/L contact time: 3 h, pH: 6) PJ wood was converted into a cost-effective nanocomposite. The XRD peak intensity revealed the extent of crystallinity and porous nature of PJGNC. At calcination of PJGNH, surface decomposition of the functional group was avoided by the presence of purged dissolved oxygen. It was visibly observed in the EDAX analysis. The anionic active -NH, C = C, -OH, C-O sites, and phenolic and aromatic groups of both adsorbents were confirmed by the FTIR analysis. The FESEM micrographs of PJGNH confirmed the existence of gas molecules in between Ni(OH) 2 and carbon. The mesoporous nano-PJGNC was evidently identified by FESEM micrographs. The FESEM micrographs also specified the addition of the excessive amount of Pb(II) ions onto the PJGNC compared to PJNC. The mechanism of synthesis was found to prove the surface enhancement of the PJGNC. The VSM analysis also confirmed the highly soft magnetic character of PJGNC. The Langmuir and Freundlich isotherms were studied to investigate the surface nature of the adsorbents. The isotherm results revealed that the maximum removal q e capacity was 30.78 mg/g for PJNC and 43.48 mg/g for PJGNC. The Langmuir and Freundlich isotherm equations were studied and it was found that they jointly supported the multilayer physical adsorption existing between Pb(II) ions and the adsorbent. PJGNC gave high removal capacity compared to PJNC due to the high surface area, pore diameter, and pore volume. This study revealed that PJGNC could be used to treat the wastewater for efficient removal of Pb(II) ions.