Naked-eye lead(II) capturing from contaminated water using innovative large-pore facial composite materials

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Naked-eye lead(II) capturing from contaminated water using innovative large-pore facial composite materials Md. Rabiul Awual , Md. Munjur Hasan , Jibran Iqbal , Aminul Islam , Md. Aminul Islam , Abdullah M. Asiri , Mohammed M. Rahman PII: DOI: Reference:

S0026-265X(19)32363-X https://doi.org/10.1016/j.microc.2019.104585 MICROC 104585

To appear in:

Microchemical Journal

Received date: Revised date: Accepted date:

30 August 2019 30 November 2019 29 December 2019

Please cite this article as: Md. Rabiul Awual , Md. Munjur Hasan , Jibran Iqbal , Aminul Islam , Md. Aminul Islam , Abdullah M. Asiri , Mohammed M. Rahman , Naked-eye lead(II) capturing from contaminated water using innovative large-pore facial composite materials, Microchemical Journal (2019), doi: https://doi.org/10.1016/j.microc.2019.104585

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Highlights: 

Ligand based functional composite material was fabricated for Pb(II) capturing.



The Pb(II) ion detected in optical visualization from the sufficient color formation.



The Pb(II) detection limit was low and the maximum adsorption capacity was high.

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Naked-eye lead(II) capturing from contaminated water using innovative large-pore facial composite materials Md. Rabiul Awual a , b , c *, Md. Munjur Hasan d, Jibran Iqbal b, Aminul Islam e, Md. Aminul Islam f , Abdullah M. Asiri c, Mohammed M. Rahman c

a

Materials Science and Research Center, Japan Atomic Energy Agency (SPring–8), Hyogo

679–5148, Japan b

College of Natural and Health Sciences, Zayed University, P.O. Box 144534, Abu Dhabi,

United Arab Emirates c

Center of Excellence for Advanced Materials Research, Faculty of Science, King Abdulaziz

University, Jeddah 21589, Saudi Arabia d

Department of Applied Chemistry & Chemical Engineering, University of Dhaka, Dhaka-

1000, Bangladesh e

Department of Petroleum and Mining Engineering, Faculty of Engineering and Technology,

Jessore University of Science and Technology, Bangladesh f

Department of Arts and Sciences, Faculty of Engineering, Ahsanullah University of Science

and Technology (AUST), Dhaka-1208, Bangladesh

* Corresponding author. E–mail address: [email protected] (M.R. Awual).

ABSTRACT Detection and removal of toxic metal ions from aqueous solutions is considered among the most important environmental issues in recent years as these metals are hazardous, carcinogenic, and classified as toxic pollutants. In this study, organic ligand embedded large-

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pore facile composite material was prepared by the direct anchoring method and then, was characterized in systematic ways for understanding the lead (Pb(II)) detection and removal in naked-eye ability in an aqueous solution was evaluated. The material was exhibited the specific functionality for Pb(II) detection and removal from aqueous media with the addition of trace level of Pb(II) ion. The Pb(II) ion detection limit of the presented method was 0.44 µg/L at optimum conditions. The impact of effective Pb(II) ion removal parameters including solution pH, the initial concentration, contact time and desorption ability was studied. The results demonstrated that the addition composite material have synergistic effect on Pb(II) adsorption capacity. The data of adsorption processes clarified that with increased pH up to 5.50, the Pb(II) adsorption was suitable at pH 5.50. Moreover, the composite material exhibited the large surface area-to-volume ratios and uniformly mesostructures shaped pores that were actively working to selective capturing of Pb(II) ion. The adsorption data were well fitted to the Langmuir model and the maximum adsorption capacity was 176.66 mg/g. The material was capable to uptake the Pb(II) ion even in the presence of a high amount of coexisting metal ions. The adsorbed Pb(II) ion was completely eluted with 0.20 M HCl and simultaneously regenerated into the initial form for the next operation after washing with water without loss in its initial performances. Then the modified composite material enhanced the affinity between Pb(II) and functional surface for improving the selectivity to uses a very promising in purification of wastewater. Keywords: Composite material; Pb(II) ions; Selectivity; Naked-eye observation; Drinking water.

1. Introduction Lead (Pb(II)) is one of the most toxic metal ions found naturally in environmental water and agricultural land according to the discharge of industrial waste effluent. According

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to its unique chemical and physical properties, considering of high malleability, low melting point, ductility, and resistance to corrosion, this metal ion is highly attractive for various industrial applications for the use in plastics, paint, automobiles, ceramics, batteries, and pesticides industries [1-5]. The Pb(II) ion is highly toxic and existed as persistent, bioaccumulative and toxic metal and expose adverse neurodevelopmental effects, including decreased cognitive function, inattention and impulsivity on children at blood lead levels [68]. Therefore, the Pb(II) ion has serious hazardous effect even to death at high exposure levels. Then the maximum allowable level of Pb(II) ion in potable water is 10 µg/L and the EPA action level is 15 µg/L [9]. This is noted that the Pb(II) ion is still found higher levels than the allowable limit in water bodies such as surface waters and groundwater [10-14]. Therefore, it is an emerging to quantify and remove excessive toxic Pb(II) from water to safeguard the public health. There are many analytical methods, including inductively coupled plasma-atomic emission spectrometry (ICP-AES), graphite furnace atomic absorption spectrometry (GFAAS), ICP-mass spectrometry (MS), atomic fluorescence spectrometry (AFS), X-ray fluorescence (XRF), cyclic voltammetry (CV) and UV–Vis spectrophotometry have been indicated for the determination of Pb(II) ions in wide variety of liquid samples [15-20]. The sophisticated instrumentation of like ICP-MS, GF-AAS, ICP-MS, AFS, XRF and CV are quite expensive, tedious and time consuming for preparation of sample to quantify the Pb(II) ions from complex sample matrixes [21-24]. However, the UV–Vis is simple and rapid technique for determination of Pb(II) ion with the color formation of the deployed reagents, however; the selectivity of the method is poor due to the use of chromophoric reagents [2527]. Then it is imperative an alternative method consisted of simplicity, high selectivity, and cost-effective for determination of Pb(II) ions from different types of aqueous samples.

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In recent years, the ligand based solid materials have been attracted the scientists and researchers around the world because of its color formation, high sensitivity, simplicity, low cost and small amount of sample is required for detection the contaminates in food, pollutants in environment and clinical diagnosis [28-32]. The composite solid material are generally coupled with organic-inorganic assembled to read out the response of chemical reaction occurred between analytes and chromophoric organic ligand, which was coated of the composite materials [33-35]. The solid composite materials offered a high surface ratio and high optical contrast for colorimetric detection of variety of metal ions based on the solution acidity and ligand field effect [36-40]. Based on the simplicity, the organic ligand based composite material was designed for naked-eye Pb(II) ion detection with high sensitivity and immense selectivity according to the pH dependent effect. Several techniques such as adsorption, precipitation, ion-exchange, electrochemical reduction, and reverse osmosis have been developed to remove Pb(II) ion as well as to reduce its pollution in the water bodies [41-47]. The precipitation has been the most popularly used in plants for a primary Pb(II) removal according to the neutralization-flocculation process. However, this method is not suitable for removing low concentration of Pb(II) to meet the request of water quality to keep safe the human health [48,49]. Among methods listed above, the adsorptions by developed diverse adsorbents have been identified to be the promising process because of their high removal efficiency and low sludge generations. The functional adsorbents has high affinity to the Pb(II) ion due to the ion-exchange mechanism and complexation ability [50-53]. Moreover, the adsorbents are reusable even after several cycles use as cost-effective material. Recently, ligand based composite materials have been introduced to the field of adsorption as it demonstrates relatively higher adsorption capacity due to its large surface area and open functionality to the specific metal ion at optimum pH condition. Many research articles have been published in the field of diverse metals removal

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from water using different ligand based composite or conjugate materials. On the other hand, some of the nanomaterial such as graphene oxide, carbon nanotubes are still expensive and difficult to prepare, reuse and dispose of safely [54,55]. Moreover, some of nanomaterials are toxic and serious threat on human life as these can leach to drinking water being treated and create a severer health hazard. To avoid such nanomaterials, the ligand based organicinorganic composite material was designed, which was environmentally friendly and easy to safe dispose [56]. In previously published reports, our group has developed alternative ligand based solid material for analytical quantification of diverse metal ions [5-7,14]. The present study aims to provide a new composite material for the detection and removal of Pb(II) ion with the additional advantages of being simpler and cheaper than the previous ones. The new composite material is based in the formation of stable complexation of Pb(II) with 4-nitro-1naphthylam evidencing a phenomenon of quenching for sensitive and selective detection and removal from waste samples in aqueous media. The organic ligand was accumulated onto mesoporous silica by non-covalent interactions, Van der Waals forces and reversible covalent bonds [20,21,33]. The mesoporous silica monolith was used for fabrication of composite material due to the high surface area, relatively low-cost and excellent mechanical properties. Several experimental parameters, including pH acidity, limit of detection, initial concentration, contact time, and foreign ion effects were systematically evaluated and addressed. The composite material responses can be defined by Pb(II) ions and also transduced measurable signals at optimum solution pH based on the cation selectivity trends. Moreover, the Pb(II) ions can be detected and adsorbed with high selectivity and immense sensitivity and the newly fabricated composite material would be cost–effective based on the reuses cycles abilities.

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2. Experimental and methods 2.1. Materials All

chemicals

were

used

as

purchased

for

the

experimental

works.

Tetramethylorthosilicate (TMOS), Pluronic F108, and 4-nitro-1-naphthylamine (NNP) were purchased from Sigma–Aldrich. The other chemicals were also obtained from in analytical grade. The pH adjustments in detection operation, buffer solutions of 3–morpholinopropane sulfonic acid (MOPS), 2-(cyclohexylamino) ethane sulfonic acid (CHES) and N-cyclohexyl3-aminopropane sulfonic acids (CAPS), potassium chloride (KCl), concentrated hydrochloric acid (HCl) and sodium hydroxide (NaOH) was purchased in analytical grade. The standard Pb(II) solution (1000 mg/L) and other metal salt reagents were purchased in analytical grade.

2.2. Mesoporous silica monolith and composite material The mesoporous silica monolith was synthesized by direct template approach with slight change of the reported technique [57]. The mass ratio was 1.3:2:1 of the F108:TMOS:HCl/H2O. After mixing of F108/TMOS, the resultant mixture was heated in water bath at 65°C for until gel like product. Adding of HCl (at pH = 1.3) to the gel product, the hydrolysis was developed and the methanol was evaporated by rotary evaporator. Then the monolith was dried in the oven at 45 0C for 14 h. Then the calcination was carried out at 520 0C under the air atmosphere. The silica material was grounded properly for the systematic characterization and used as organic NNP ligand immobilization for the fabrication of the NNP coated composite material. The composite material was fabricated by direct immobilization of NNP (70 mg) in ethanol into 1.0 g grounded mesoporous silica. The anchoring operation was carried out at 40 7

0

C until the maximum saturation of NNP ligand onto the silica materials. The ethanol was

evaporated using the rotary evaporator at 45 0C, and the composite material was rinsed with water until no leaching of the ligand was observed in the washing samples in aqueous solution. Then the composite material was dried in the oven and ready for use to Pb(II) detection and removal operations at optimum experimental protocol. The NNP loading amount was calculated from the following Eq. [44,45]: Q = (Ci – Cf) V/m

(1)

Where Q is the adsorbed (mmol/g), V is the total amount (L), m represents the amount of composite material (g), Ci and Cf was the original and last amount in solution of ligand, respectively.

2.3. Detection of Pb(II) ions In the Pb(II) detection, the composite material was mixed in a mixture of specific Pb(II) concentrations (2.0 mg/L) and adjusted at appropriate pH from 2.0 to 9.50 in the specific amount of the composite material (10 mg) at constant volume (10 mL) with shaking in a temperature-controlled water bath with a mechanical shaker for 10 min at a constant agitation speed to observe significant color formation. A blank solution was also prepared, following the same procedure for comparison of color difference with the Pb(II) containing composite material. After equilibration time, the composite material was separated by suction filtration and used for color assessment and absorbance measurements by solid-state UV–vis spectrophotometer. The limit of detection (LD) for Pb(II) by the composite material was evaluated from the linear part of the calibration plot according to the following equation [43,46]:

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LD = KSb/m

(2)

Where, K value is 3, Sb is the standard deviation for the blank and m the slope of the calibration graph in the linear range, respectively.

2.4. Pb(II) removal, desorption and reuses In the adsorption system, the composite material was also immersed in Pd(II) ion concentrations and adjusted at specific pH values by adding HCl or NaOH in 20 mL solutions. The solid materials were separated by filtration system and Pb(II) concentration in before and after adsorption operation was analyzed by ICP–AES. The Pb(II) adsorption was determined according to the following equations: Mass balance qe = (C0 – Cf) V/M (mg/g) and Pb(II) ion adsorption efficiency Re =(C0 – Cf) 100/ C0 (%)

(3) (4)

Where V is the volume of the aqueous solution (L), and M is the weight of the composite material (g), C0 and Cf are the initial and final concentrations of Pb(II) ion in solutions, respectively. To define the equilibrium contact time, 5.0 mg/L Pb(II) amount of fixed volume solution was used in each fraction, and the composite material amount was fixed at 20 mg in each case. After 10 min interval, the solid material was separated and filtrate was determined by the ICP-AES. The highest adsorption amount was defined based on the different initial concentrations of Pb(II), and each sample was determined by the ICP-AES. In desorption operations, first 30 mL of 4.0 mM Pb(II) ion solution was adsorbed on the 50 mg composite material and then desorption experiments were performed using 9

different eluents. The Pb(II) ion adsorbed onto composite material was washed with deionized water several times and transferred into a 50 mL beaker. The washing solution was also analyzed by ICP-AES. The 0.20 M HCl solution was used as appropriate eluent and then the mixture was stirred for 15 min. The concentration of Pb(II) ion released from the adsorbent into aqueous phase was analyzed by the ICP–AES. Then the composite material was reused several cycles to investigate the reusability after washing with water.

2.5. Selectivity The Pb(II) and the competing ion interaction were carried out to understand the selective adsorption ability where the diverse counter-ion was used. The solution was contained 20 mg/L of each Zn(II), Cd(II), Al(III), Fe(III), Mg(II), Ca(II), Ni(II), Ag(I), K(I), Na(I), Mn(II), Hg(II), Bi(III) ion and the Pb(II) amount were 1.0 mg/L. The sample volume was to be 20 mL and composite material amount was 20 mg. Then the mixture was stirred for 1 h and separated by suction filtration method. The solution was checked using the ICP-AES.

2.6. Instrumentations The N2 adsorption-desorption isotherms were measured using the 3Flex analyzer (Micromeritics, USA) at 77 K for determining the materials morphology in terms of surface characterization. The pore size was measured based on the Barrett–Joyner–Halenda (BJH) method. Both silica and CJA were preheated at 110 0C for 3 h. The TEM micrographs were received by using JEOL (JEM-2100F). To detect the color form of Pb(II) ion by UV–vis in the solid state was utilized for color optimization and their corresponding signal intensity

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measurement. The Pb(II) ion determination was analyzed using the ICP-AES (PerkinElmer, Germany, 8300). All experimental demonstrations were duplicated at least to verify the extracted data in this study.

3. Results and discussion 3.1. The inorganic silica and composite material The porosity of the mesoporous silica and the ligand immobilized composite material was characterized by the N2 adsorption–desorption isotherms as well TEM instrumentations. According to the N2 adsorption-desorption isotherms, the hysteresis loops with type IV were observed for the as made mesoporous silica and composite material as shown in Fig. 1. The specific surface area measurement was based on the isothermal data of nitrogen adsorption and was calculated according to the standard BET model (Brunauer-Emmett-Teller), which is applicable to mesoporous and some microporous materials. However, the mesoporous silica was exhibited the highest BET specific surface areas and pore volumes compared to the composite material as the data are shown in Fig. 1 (inset). This was expected that the ligand was connected inside pore of the mesoporous silica based on the co-valent or hydrogen bonding [53,54,57]. However, the composite material was exhibited high surface area and pore size for high encapsulation of the Pb(II) ion due to open functionality at optimum experimental conditions. The ordered structure was evaluated by the TEM images capturing both of the mesoporous silica and the composite material. The images are ordered hexagonal structures showed that uniformly-sized pores and these were well-ordered channel-like pore arrays and distinctly connected each other in all direction as defined in Fig. 2. The well-defined white 11

dots-like pores along the channels confirmed the high degree of architecture ordering mesoporous silica for high amount organic ligand of NNP immobilization [10,11,34]. The uniform arrangement of pores and continuous arrays ensured the direct interaction between the NNP ligand molecule and silica into the rigid condensed pore surfaces for high accumulation of Pb(II) ions during detection and removal operations. After successful immobilization of NNP organic ligand onto mesoporous silica, the significant pores were observed as judged from Fig. 2 (C and D).

3.3. The Pb(II) ions detection The solution acidity is important parameters in color enhancing metal ion detection by the composite material to observe the color signal [6,32,34]. The proposed composite material was highly influenced by the solution acidity during trace Pb(II) ions detection. The Pb(II) ion optical detection with ligand based material was determined over a wide pH range from 2.0 to 9.50 using different buffer solutions at each pH region. The absorbance spectra of the [Pb(II)-NNP]n+ complex at λ = 478 nm was carefully measured and data are shown in Fig. 3. The results clarified that the dose amount was sufficient to achieve good color separation of “signal” between the composite material “blank” and Pb(II) ion detection “sample,” even at trace concentration of Pb(II) ions. The composite material was highly sensitive towards the Pb(II) ions with significant colo formation at pH of 5.50. The data also emphasized that the functional composite material has high functionality in terms of sensitivity to Pb(II) ions at pH 5.50. Moreover, the ligand based composite materials are exhibited high tendency to form stable complxation bonding at specific solution acidity [44,45]. The composite materials are highly sensitive in terms of its optical color intensity and signal responses to Pb(II) ions even trace concentrations levels. The design of composite

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material exhibited high physical features and textural properties in optical monitoring of Pb(II) ions. An increase of Pb(II) ion levels from 0 to 2.0 mg/L, increase in absorbance spectra corresponds to the equilibrium color formation complexes between the composite material and the Pb(II) ions as depicted in Fig. 4(A). The absorbance spectra was sharply increased with addition of wide range of Pb(II) ions levels clarifying the charge transfer (intense π-π transition) complex was happened. Fig. 4(A) also clarified that increasing the absorbance spectra corresponds to equilibrium color formation between composite material and Pb(II) ions implied the sensitive detection in low levels without using highly sophisticated instrumentations. This data presented that composite material is highly sensitive and effective optical detection of Pb(II) ions from low to high concentration levels (from μg/L to mg/L). The calibration plot during Pb(II) ion detection operation by the composite material was also evaluated based on the color optimization with the corresponding signal intensity. This is noted that the quality of the calibration methods is necessary to ensure both accuracy and precision of the Pb(II) ion detection systems [6,7,53]. The calibration plot of the composite material showed a linear correlation at low concentration levels of Pb(II) ions as defined in Fig. 4(B). The linear curves clarified that the Pb(II) ions can be analyzed with highest sensitivity even in the low concentration levels. The limit of detection (LD) of Pb(II) ions using the composite material was 0.44 µg/L based on the determination method from Eq. (2). The wastewater usually co-existed with several cations and anions [20,45,57]. The affinity of the composite material for a series of diverse metal ions at pH 5.50 was evaluated. The data revealed that the addition of Pb(II) ions with composite material induced changes in the color absorption spectrum as expected. However, the equilibrium time for complete color development with stable signal intensity was measured by kinetic evaluation to be about 10 13

min. The signal intensity change of each cation and anion according to the slight changes in absorbance spectra when its concentrations in solution was higher than the Pb(II) ions. The tolerance levels of each ion are depicted in Fig. 5. The results indicated that the diverse metal ions are not interfering with specification of color and corresponding absorbance spectra. Therefore, it is confirmed that the selective Pb(II) ions detection by the composite material is possible even with the addition of high concentrations of interfering metal ion species. Then the proposed composite material is selective towards the Pb(II) ions for efficient detection in wastewater samples.

3.4. The Pb(II) adsorption In order to optimize the specific pH for sensitive adsorption by the composite material, a wide pH range solution acidity was evaluated for Pb(II) ion adsorption. The adsorption efficiency in the function of solution pH is shown is Fig. 6(A). The data also clarified that the Pb(II) ion adsorption efficiency was increased with increasing equilibrium pH. The data was demonstrated that the maximum adsorption efficiency was attained at pH 5.50, which was adjacent to the detection experimental measurement. In addition, the organic ligand based composite materials have high adsorption tendency to the specific metal ions at optimum pH region according to the nature of chemical bonding mechanism [21,22]. Over pH neutral region, Pb(II) ions undergo a number of hydrolysis reactions leading to various species depending upon the initial Pb(II) concentration [5,7]. Several researchers also indicated that the Pb(II) adsorption onto metal oxide materials is increases above pH 7.0 due to the hydrolysis of Pb(II) ions as insoluble complexes. Then the all adsorption experiments were carried out at pH 5.50 in this adsorption experimental operation. A series of batch contact time was carried out to understand the optimum Pb(II) ion 14

adsorption by the composite material. The time was varied and other experimental condition was fixed, and the filtrate solution was analyzed by the ICP–AES after each fraction. The adsorption results are also shown in Fig. 6(B). The data also clarified that the Pb(II) ions adsorption versus time curves was single, smooth and continuous indicating monolayer Pb(II) ion adsorption onto the composite material surface. The similar trend is also reported by the ligand-based function materials [43,45]. The data also defined that the adsorption efficiency was sharply observed within first few minutes reaction time. Increasing the reaction time, increases the adsorption efficiency and the equilibrium adsorption was attained in 50 min. Then, it was estimated that the reaction time of 3 h was found to be sufficient to reach equilibrium adsorption when the initial Pb(II) ions concentration was from low to high in the determination of maximum adsorption capacity. Moreover, the complexation mechanisms are slow kinetics than the ion–exchange and hydrogen bonding reaction mechanism as reported of the ligand exchange and granular resin-based adsorbents [58]. However, the solvent extraction processes are also slow kinetics, creating another sludge problem, unable to remove low level metal ions and classified as costly method [59,60]. The maximum Pb(II) adsorption was evaluated when the initial Pb(II) concentration was varied from low to high and the data are shown in Fig. 7. The Pb(II) adsorption isotherms were measured for this composite material using an optimized condition and the results are shown in Fig. 7 (inset). Here, the adsorption data was fitted according to the Langmuir isotherm model. The Langmuir isotherm model is the best known of all isotherms describing adsorption or removal operation with monolayer coverage [46,51]. In addition, the Langmuir can predict the adsorption nature in the saturation effect by the functional material. The Langmuir equation is applicable to homogeneous adsorption, where the adsorption of each molecule on the surface has equal adsorption activation energy. Here, the Pb(II) adsorption by the composite material was carried through the Langmuir isotherm according 15

to following equation: Ce/qe = 1/(KLqm) + (1/qm)Ce (linear form)

(5)

where KL is the Langmuir adsorption equilibrium constant, Ce is the equilibrium level of Pb(II) ions, qm (mg/g) and qe (mg/g) are maximum adsorption capacity and adsorbed amount of Pb(II), respectively. In Ce/qe vs Ce, qm and KL were measured from the slope and intercept. The Langmuir plots for adsorption isotherm data are exhibited in Fig. 7 (inset). The data clarified that that Pb(II) adsorption data was highly fitted to the Langmuir adsorption isothermal equation. The correlation coefficient in the linear regression was 0.979; the maximum adsorption capacity was 176.66 mg/g and the adsorption coefficient KL is calculated to be 1.54 L/mg. The results also suggested that the composite material surface was homogenous after the NNP organic ligand anchoring onto mesoporous silica. There are several metal ions existed in water such as Ca(II), Mg(II), Al(III), Ni(II), Mn(II), Zn(II), Bi(III), Cd(II), Hg(II), Fe(III), Ba(II) and so on. Then these ions were considered as competing metal ion with 20-folds higher level than the Pb(II) ion in the selectivity evaluation. After stirring and suction filtration, the filtrate solution was analyzed by the ICP–AES. Each metal adsorption by the composite material is shown in Fig, 8 (A). The data revealed that the other metal ion adsorption was negligible compared to the Pb(II) adsorption by the composite material. As counted the mathematical data, around 96.5% Pb(II) ions was adsorbed from the multi-mixture solution by the proposed composite materials. This data confirmed that the present composite material is highly selective to Pb(II) ions even in the presence of high concentration of foreign ions.

3.5. Desorption and reuses

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From the potential application stand point, cost-effective materials are highly desired based efficient regeneration and reuses. To understand the regeneration and reuse of the material, an elution experiment using different concentrations of HCl was used. However, the 0.20M HCl was suitable eluent for complete elution to keep the remaining functionality of the composite material for several cycles use. Then the reuse study was carried out following the adsorption-elution-regeneration operations for seven cycles and adsorption efficiency in each cycle was counted. The reuses cycles are shown in Fig. 8 (B). In elution operations, the composite material was simultaneously regenerated into the initial form without damaging the structural morphology. The data also confirmed that the Pb(II) removal efficiency was slightly decreased after seven consecutive cycles, clarifying the reuses of the composite material was sufficient for wastewater treatment.

4. Conclusions This study classified the simultaneous detection and removal of Pb(II) ion in nakedeye approach by organic ligand functionalized composite material using simple one-step capturing operation. The composite material was successfully anchored onto the mesoporous silica and then quantitation of Pb(II) ion with simple, fast, reproducible, sensitive and selective feasibility. The material was captured the ultra-trace Pb(II) ions via a colorimetric signal response with naked-eye observation according to the data presentation. Moreover, the composite material enabled the detection by the [Pb(II)–NNP]n+ binding with stable complex mechanism and the detection limit was 0.44 µg/L. The adsorption data were fitted to the Langmuir model as expected from the composite material morphology with ordered structure and large-pore diameter. The isotherm data revealed that the maximum Pb(II) adsorption by the composite materials was 176.66 mg/g. The ion selectivity was measured both in single

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and multi-mixture solution in the case of detection and adsorption operation, respectively. The foreign ions were not interfered based on the color formation or adsorption by the material due to the high affinity to the organic functional group of the composite material surface. The Pb(II) desorption was complete, and the material was reused in several cycles maintaining high adsorption and recovery to comply the cost-effective material. In addition, the proposed material can be claimed that the detection and adsorption process is likely an efficient way enabling simple and fast capturing of Pb(II) from wastewater solutions.

Acknowledgments The research was partially supported by the RIF grant (R19052) from Zayed University, Abu Dhabi, United Arab Emirates. Also, the research was partially supported by the Grant-in-Aid for Research Activity Start-up (24860070) from the Japan Society for the Promotion of Science. The part of the experimental works was carried out at Japan Atomic Energy Agency. The author also wishes to thanks to the anonymous reviewers and editor for their helpful suggestions and enlightening comments.

Conflict of Interest: None

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S.H. Teo, A. Islam, E.S. Chan, S.Y.T. Choong, N.H. Alharthi, Y.H. Taufiq-Yap, M.R. Awual, Efficient biodiesel production from Jatropha curcus using CaSO4 /Fe2 O3-SiO2 core-shell magnetic nanoparticles, J. Clean. Prod. 208 (2019) 816–826; (c) R.M. Kamel, A. Shahat, W.H. Hegazy, E.M. Khodier, M.R. Awual, Efficient toxic nitrite monitoring and removal from aqueous media with ligand based conjugate materials, J. Mol. Liq. 285 (2019) 20–26; (d) M.R. Awual, M.M. Hasan, A novel fine-tuning mesoporous adsorbent for simultaneous lead(II) detection and removal from wastewater, Sensor. Actuat. B: Chem. 202 (2014) 395–403. [54] A.A. Alqadami, M. Naushad, Z.A. ALOthman, Ayman A. Ghfar, Novel Metal–Organic Framework (MOF) Based Composite Material for the Sequestration of U (VI) and Th (IV) Metal Ions from Aqueous Environment, ACS Applied Mat. Interf. 9 (2017) 36026−36037. [55] E. Daneshvar, A. Vazirzadeh, A. Niazi, M. Kousha, M. Naushad, A. Bhatnagar, Desorption of Methylene blue dye from brown macroalga: Effects of operating parameters, isotherm study and kinetic modeling, J. Clean. Prod. 152 (2017) 443–453. [56] I. Mironyuk, T. Tatarchuk, M. Naushad, H. Vasylyeva, I. Mykytyn, Highly efficient adsorption of strontium ions by carbonated mesoporous TiO2, J. Mol. Liq. 285 (2019) 742–753. [57] (a) S.A. El-Safty, A. Shahat, M.R. Awual, Efficient adsorbents of nanoporous aluminosilicate monoliths for organic dyes from aqueous solution, J. Colloid Interf. Sci. 359 (2011) 9–18; (b) M.R. Awual, T. Yaita, Y. Okamoto, A novel ligand based dual conjugate adsorbent for cobalt(II) and copper(II) ions capturing from water, Sensor. Actuat. B: Chem. 203 (2014) 71–80; (c) H. Znad, K. Abbas, S. Hena, M.R. Awual, Synthesis a novel multilamellar mesoporous TiO2/ZSM-5 for photo-catalytic degradation of methyl orange dye in aqueous media, J. Environ. Chem. Eng. 6 (2018) 218–227; (d) M.R. Awual, M. Ismael, T. Yaita, Efficient detection and extraction of cobalt(II) from lithium ion batteries and wastewater by novel composite adsorbent, Sensor. Actuat. B: Chem. 191 (2014) 9–18. [58] (a) A. Shahat, H.M.A. Hassan, H.M.E. Azzazy, M. Hosni, M.R. Awual, Novel nanoconjugate materials for effective arsenic(V) and phosphate capturing in aqueous media, Chem. Eng. J. 331 (2018) 54–63; (b) M.R. Awual, M.A. Hossain, M.A. Shenashen, T. Yaita, S. Suzuki, A. Jyo, Evaluating of arsenic(V) removal from water by weak-base anion exchange adsorbents, Environ. Sci. Pollut. Res. 20 (2013) 421– 430; (c) M.R. Awual, M.A. Shenashen, T. Yaita, H. Shiwaku, A. Jyo, Efficient arsenic(V) removal from water by ligand exchange fibrous adsorbent, Water Res. 46 (2012) 5541–5550; (d) M.R. Awual, A. Jyo, Assessing of phosphorus removal by polymeric anion exchangers, Desalination 281 (2011) 111–117. [59] (a) M.R. Awual, A. Jyo, T. Ihara, N. Seko, M. Tamada, K.T. Lim, Enhanced trace phosphate removal from water by zirconium(IV) loaded fibrous adsorbent, Water Res. 45 (2011) 4592–4600; (b) M.R. Awual, A. Jyo, S.A. El-Safty, M. Tamada, N. Seko, A 27

weak-base fibrous anion exchanger effective for rapid phosphate removal from water, J. Hazard. Mater. 188 (2011) 164–171; (c) M.R. Awual, S.A. El-Safty, A. Jyo, Removal of trace arsenic(V) and phosphate from water by a highly selective ligand exchange adsorbent, J. Environ. Sci. 23 (2011) 1947–1954; (d) M.R. Awual, A. Jyo, Rapid column-mode removal of arsenate from water by crosslinked poly(allylamine) resin, Water Res. 43 (2009) 1229–1236. [60] (a) M.R. Awual, S. Urata, A. Jyo, M. Tamada, A. Katakai, Arsenate removal from water by a weak-base anion exchange fibrous adsorbent, Water Res. 42 (2008) 689–696; (b) M.R. Awual, M.A. Shenashen, A. Jyo, H. Shiwaku, T. Yaita, Preparing of novel fibrous ligand exchange adsorbent for rapid column–mode trace phosphate removal from water, J. Ind. Eng. Chem. 20 (2014) 2840–2847; (c) M.R. Awual, Efficient phosphate removal from water for controlling eutrophication using novel composite adsorbent, J. Clean. Prod. 228 (2019) 1311–1319; (d) M.R. Awual, M.M. Hasan, A.M. Asiri, M.M. Rahman, Cleaning the arsenic(V) contaminated water for safeguarding the public health using novel composite material, Compos. Part B-Eng. 171 (2019) 294–301.

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Fig. 1. The N2 adsorption and desorption isotherms for the determination of surface area, pore size and pore volume to the (a) porous silica monolith and (b) ligand anchoring composite material.

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Fig. 2. Determination of high ordered porosity using TEM images of (A, B) porous silica as carrier material and (C, D) ligand functionalized composite with uniform channels in all directions.

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Fig. 3. Effect of pH in order to evaluate the naked-eye Pb(II) detection using functionalized composite material when equilibrated individually at different pH areas with 2.0 mg/L concentration level in 10 mL volume. The standard deviation was >3.0% for the analytical data of duplicate analyses.

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Fig. 4. (A) Color enhancement according to the signal intensity with enhancement of Pb(II) ion at pH 5.50; (B) Calibration profile with signal intensity measured at 478 in accordance with Pb(II) amount. The insets in the graph (B) define the trace level of Pb(II) ion detection with a linear fit line in the linear level range before saturation the calibration plot.

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Fig. 5. Effect of foreign ions for the selectivity of Pb(II) ions by the composite material. The interfering cations (20.0 mg/L) are listed in order (1 to 13): (1) Ca(II), (2) Mg(II), (3) Al(III), (4) Ni(II), (5) Mn(II), (6) Bi(III), (7) Cd(II), (8) Hg(II), (9) Fe(III), (10), Ba(II), (11) Zn(II), (12) Blank and (13) 1.0 mg/L Pb(II) ion. The interfering (150 mg/L) anions are listed in order (7 to 13): (7) chloride, (8) nitrate, (9) sulfate, (10) bicarbonate, (11) carbonate, (12) phosphate and (13) perchlorate.

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Fig. 6. Effect of solution pH for the Pb(II) ion adsorption by the composite material (A) and equilibrium Pb(II) adsorption with the effect of contact time where Pb(II) concentration was constant (B).

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Fig. 7. Evaluation of adsorption capacity in the variation of initial concentration of Pb(II) ion by the composite material. The experimental data were fitted to the Langmuir adsorption isotherm model. The experimental conditions are: initial concentrations: 1.0 to 90.0 mg/L; stirring period: 3 h; amount of composite material: 10 mg.

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Fig. 8. The ion selectivity in the adsorption operation by the composite material where Pb(II) ion concentration was 1.0 mg/L and other listed metal ion concentration was 20 mg/L at optimum experimental protocol (A) and the desorption and subsequent regeneration of composite material with 0.20 M HCl eluent for subsequent reuses in seven cycles operations.

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Graphical Abstract

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