Schiff based ligand containing nano-composite adsorbent for optical copper(II) ions removal from aqueous solutions

Accepted Manuscript Schiff based ligand containing nano-composite adsorbent for optical copper(II) ions removal from aqueous solutions Md. Rabiul Awual, Gaber E. Eldesoky, Tsuyoshi Yaita, Mu. Naushad, Hideaki Shiwaku, Zeid A. AlOthman, Shinichi Suzuki PII: DOI: Reference:

S1385-8947(15)00712-3 http://dx.doi.org/10.1016/j.cej.2015.05.049 CEJ 13690

To appear in:

Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

23 March 2015 13 May 2015 14 May 2015

Please cite this article as: Md. Rabiul Awual, G.E. Eldesoky, T. Yaita, Mu. Naushad, H. Shiwaku, Z.A. AlOthman, S. Suzuki, Schiff based ligand containing nano-composite adsorbent for optical copper(II) ions removal from aqueous solutions, Chemical Engineering Journal (2015), doi: http://dx.doi.org/10.1016/j.cej.2015.05.049

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Schiff based ligand containing nano-composite adsorbent for optical copper(II) ions removal from aqueous solutions

Md. Rabiul Awual a,*, Gaber E. Eldesoky b, Tsuyoshi Yaita a, Mu. Naushad b, Hideaki Shiwaku a, Zeid A. AlOthman b, Shinichi Suzuki a

a

Actinide Chemistry Research Group, Energy and Environment Materials Science Division,

Quantum Beam Science Centre, Japan Atomic Energy Agency (Spring-8), Hyogo 679-5148, Japan b

Department of Chemistry, College of Science, Bld#5, King Saud University, Riyadh 11451,

Saudi Arabia

* Corresponding author. Tel.: +81 791 58 2642; fax: +81 791 58 0311. E–mail address: [email protected], [email protected] (M. R. Awual).

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Graphical Abstract

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ABSTRACT A novel Schiff base ligand based nano-composite adsorbent (NCA) was prepared for the detection and removal of copper (Cu(II)) ions in wastewater samples. Upon the addition of Cu(II) ions to NCA at optimum conditions, the clear color was visible to the naked-eye in the detection system. This NCA exhibited an obvious color change from yellowish to dark green in the presence of Cu(II) ions in aqueous solution. The limit of detection was found to be 0.16 µg/L by optical detection. The NCA could detect the Cu(II) ions over other foreign ions with high sensitivity and selectivity. For adsorption behaviour, influences several factors such as solution pH, contact time, concentration for Cu(II) ion adsorption was investigated by batch experiment in detail. The results showed that neutral solution pH was suitable to get optimum Cu(II) ions adsorption. Also an extending contact time was favourable for improving adsorption efficiency. The adsorption process of Cu(II) ions by the NCA was followed the Langmuir adsorption isotherm model. The maximum adsorption capacity of Cu(II) ions by the NCA from the Langmuir isotherm model was 173.62 mg/g. The mesoporous NCA exhibited higher adsorption capacity compared with some other reported diverse materials. In the multi-component system, the competing ions did not significantly interfere in the adsorption of Cu(II) ions. The adsorbed Cu(II) ions was effectively eluted with 0.25 M HCl and remain the almost same functionality for many cycles use. Even in seven consecutive cycles, the NCA showed great potential in the optical Cu(II) ions removal from wastewater. Then the proposed NCA could be used a promising adsorbent for the clean-up of Cu(II) ions in wastewater treatment.

Keywords: Schiff based ligand; Nano-composite adsorbent (NCA); Copper(II) ions; Optical capturing; Wastewater treatment.

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1. Introduction Copper ions (Cu(II)) are an essential element in living organisms and play an important role in body functions [1,2]. Most of the Cu(II) ions have been discharged into the environment and human body through the food chain from diverse manufacturing, mining and casting industries [3]. An excess intake of Cu(II) ion is adversely affected and associated with a number of diseases such as hepatitis, liver cirrhosis, kidney disease, anemia, bone disorders [4,5] and Parkinson's diseases (Barnham et al., 2008). The maximum permissible limit in drinking water set by USEPA is 1.30 mg/L [6] while the WHO restricted for Cu(II) ions in drinking water is 0.05 mg/L [7]. Therefore, the detection and removal of Cu(II) ions is of great significance to keep control of water quality and human health. Many sophisticated methods have been exploited for the determination of Cu(II) ions such as atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma-mass spectroscopy, neutron activation analysis, voltammetry and electrothermal atomic absorption spectrometry [8-12]. These are highly sensitive and selective, however; these always require expensive instrumentation, laboratory setup, complicated sample preparation procedures, long detection period, skilled personnel and high operating cost, which make unsuitable for on-site or field monitoring [13]. Therefore, there is an increasing demand in the development of high sensitive, low cost, good selective and easily prepared colorimetric materials for Cu(II) ions detection that can be utilized for simple naked-eye detection without using highly sophisticated instruments and reliable for using in on-site real sample treatment [14,15]. There are numerous reports on colorimetric Cu(II) detection and most of them showed low sensitivity and poor selectivity over competing diverse ions [16-18]. In this connection, we have reported different functional group containing optical nanomaterials for diverse metal ions detection with rapid sensitivity and selectivity [19-21]. In this study, we have prepared different Schiff base ligand

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functionalized nanomaterial that has high selectivity for Cu(II) ions and can be applied to environmental samples treatment for efficient detection and removal operations. In the past decades, several technologies have also been developed for the removal of heavy metal ions including ion exchange, reverse osmosis, chemical precipitation, coprecipitation, oxidation, electrochemical treatment and adsorption [22-25]. It is noted that adsorption is one of the most recommended physicochemical technologies due to the fast response, cost-effective, high efficiency and simple operation [26-31]. In addition, the adsorbents are easy to remove from a purified solution and reduce the overall costs of the processes. Compared with other forms of materials, functional nanomaterials are promising absorbents because of their high adsorption performance, low secondary pollution problem and operation simplicity [32]. A series of highly ordered mesoporous silica materials [33-35] has been developed for metal ions capturing due to their high surface area, good accessibility to active sites and rapid mass transport inside the nanostructures [36]. Recently, the design and synthesis of organic–inorganic mesoporous silica for removal and sensing of enormous metal ions has become drawn the scientific interest [37,38]. From the stand point of large surface area even after ligand immobilization, mesoporous structure materials exhibited the high stability and keep the open functionality of the functional ligand capable of reacting with metal ions to enhance the efficiency and high selectivity for the target metal ions [39]. Particularly interesting is the synthesis of Schiff bases ligand containing nanomaterials in their structure make an effective functional group for metal ions capturing. In addition, the Schiff bases which contained nitrogen and oxygen donor atoms and trend to high selectivity towards complexation of transition metal ions at optimum conditions. Also the Schiff bases containing additional donor groups to form stable metal ion complexation in the case of optical signaling for simultaneous metal ions detection and removal. Therefore, this study

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will focus the Schiff base ligand containing nano-composite adsorbent (NCA) for efficient Cu(II) ions detection and removal in water samples. Ligand immobilization onto the mesoporous silica is a simple and versatile method to generate organic-inorganic based promising material [40,41]. The Schiff base ligand of N,N`di(3-carboxysalicylidene)-3,4diamino-5-hydroxypyrazole (DSDH) (Scheme 1) was successfully synthesized and then indirectly immobilized onto the mesoporous silica. The obtained NCA has potential advantages for detection and adsorption of Cu(II) ions from wastewater because of its number of interesting characteristics such as high surface area, high porosity, and high functionality at optimum conditions. Also the surface chemical properties of the NCA can be easily changed by chemical processes to improve its sensitivity and adsorption capacity. Moreover, the prepared can easily be handled and eco-friendly and it can be used of industrial wastewater treatment. The morphology of the NCA was characterized by SEM, TEM and BET studies. The detection and adsorption performance toward Cu(II) has been investigated in the batch mode. The factors affecting the Cu(II) ions detection and adsorption sorption such as the solution pH, contact time, initial concentration, competition of the diverse metals and the adsorption behavior of Cu(II) ions with adsorption isotherm model were studied systematically.

2. Materials and methods 2.1. Materials All materials and chemicals were of analytical grade and used as purchased without further purification. Tetramethylorthosilicate (TMOS), Pluronic F108 (EO141PO44EO141) and 3-formylbenzoic acid were obtained from Sigma–Aldrich Company Ltd. USA. Dilauryl dimethyl ammonium bromide (DDAB) was purchased from Tokyo Chemical Industry Co. Ltd., Japan. The standard Cu(II) ions solutions, and metal salts for the source of metal ions

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were purchased from Wako Pure Chemicals, Osaka, Japan. The buffer reagents of 3– morpholinopropane sulfonic acid (MOPS), 2-(cyclohexylamino) ethane sulfonic acid (CHES) and N-cyclohexyl-3-aminopropane sulfonic acid (CAPS) were procured from Dojindo Chemicals, Japan, and KCl, HCl, NaOH were from Wako Pure Chemicals, Osaka, Japan. Ultra-pure water prepared with a Millipore Elix Advant 3 was used throughout this work.

2.2. Preparation and characterization of Schiff base DSDH ligand The preparation of Schiff base ligand of N,N`di(3-carboxysalicylidene)-3,4diamino-5hydroxypyrazole (DSDH) is reported elsewhere [42a] and structure is shown in Scheme 1. The DSDH was prepared by the reaction of 3,4-Diamino-5-hydroxypyrazole (one mole) and 3-formylbenzoic acid (two moles) in ethanol and a small amount of acetic acid. The resultant mixture was then heated under reflux for 3 h and left to cool at room temperature. The solid formed upon cooling was collected by suction filtration. The separated product was recrystallized from the system dichloromethane/ methanol 1/1, and then dried at 50°C for 24 h. The purity of the DSDH was analyzed by CHN elemental analyses. The observed values (C19H14N4O5) were C, 60.15%; H, 3.66%; N, 14.76% and the calculated values were C, 60.32%; H, 3.70%; N, 14.81%. The product was characterized by 1H NMR spectroscopy. The 1

H NMR (400 MHz, CDCl3): δ 7.72 (H, m, benzylideminin), 8.17 (H, p, benzylideminin),

8.35 (H, CH, benzylideminin), 8.36 (H, CH, benzylideminin), 8.36 (H, o, benzylideminin), 8.68 (H, p, benzylideminin), 11.0 (H, carboxylic acid), 11.52 (H, pyrazole-OH), 12.60 (H, pyrazole).

2.3. Synthesis of mesoporous inorganic silica and nano-composite adsorbent (NCA) The highly ordered mesoporous silica was prepared following the reported methods with slight modification [42]. In typical conditions, the composition mass ratio of

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F108:TMOS:HCl/H2O was 1.3:2:1, where F108 was used as a soft template. F108 and TMOS were mixed and then shaking at 60°C until homogeneous. An acidic HCl solution (at pH = 1.3) was added to the mixture and exothermic reaction was occurred. The methanol which was condensed by TMOS was removed from the solution using a diaphragm vacuum pump connected to a rotary evaporator at 45°C. The materials were dried at 45°C for 24 h and the organic moieties were removed by calcination at 510°C for 6 h under normal atmosphere [43]. The material was ground properly and ready to use for fabrication as nano-composite adsorbent by indirect immobilization of Schiff based DSDH. The NCA was synthesized by indirect method [41a]. Firstly, the 0.20 M dilauryl dimethyl ammonium bromide (DDAB) was dissolved in ethanol solution and 1.0 g of mesoporous silica was immobilized with stirring for 1 h. Then the Schiff base DSDH (65 mg) was dissolved in ethanol solution and 1.0 g of DDAB-mesoporous silica was added into the solution. The mixture was stirred for 6 h until ligand saturation achieved. The ethanol was removed by a vacuum connected to a rotary evaporator at 45°C and the materials were washed with warm water to check the ligand stability. Then the material was dried at 45°C for 6 h and ground to fine powder for Cu(II) ions detection and removal operations. The immobilization amount of DSDH (0.10 mmol/g) was calculated from the following equation: Q = (C0– C) V/m

(1)

where Q is the adsorbed amount (mmol/g), V is the solution volume (L), m is the mass of mesoporous silica (g), C0 and C are the initial concentration and supernatant concentration of the Schiff based DSDH ligand, respectively.

2.4. Optical Cu(II) ions detection and removal The NCA was immersed in a mixture of 2.0 mg/L of Cu(II) ions and adjusted at appropriate pH of 2.01, 3.50 (0.2 M of KCl with 2.0 M HCl), 5.20 (0.2 M CH3COONa with

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1.0 M HCl), 7.01 (3-morpholinopropane sulfonic acid (MOPS) with NaOH), 9.50 (0.2 M 2– (cyclohexylamino) ethane sulfonic acid (CHES) with NaOH) and 11.01 and 12.50 (0.2 M N– cyclohexyl–3–aminopropane sulfonic acid (CAPS) with NaOH) at constant volume (10 mL) with shaking in a temperature-controlled water bath with a mechanical shaker at 25°C for 15 min at a constant agitation speed of 110 rpm to achieve good color separation. The blank solution in each pH region was also prepared for comparison of color differences. The NCA was filtered using Whatman filter paper (25 mm; Shibata filter holder) and used for color assessment by solid-state UV-Vis-NIR spectrophotometer. The limit of detection (LD) of Cu(II) ions by the NCA was calculated according to the following equation [44]: LD = KSb/m

(2)

where K value is 3, Sb and m are the standard deviation and the slope of the calibration graph, respectively. In removal operations, the stock solution was diluted and adjusted to a desired pH and 10 mg of NCA was added. The relations between the sorption properties of NCA and the pH of the solution were studied in the pH range from 2.0 to 12.50. It is noted that the solution pH was adjusted using dilute HCl and or NaOH solution as required in the removal operation. The solutions were shaking for 1 h and NCA was separated by filtration method. The filtrate solution was analyzed by ICP–AES. In contact time effect, the Cu(II) ions concentration was 10.0 mg/L and the adsorbent dose was 20 mg. Maximum sorption capacity was evaluated when the initial Cu(II) concentration was variable and the NCA amount was fixed. The Cu(II) ions sorption was calculated according to the following equations:

Mass balance q e = (C0 – Cf) V/M (mg/g)

(3)

(C0 – Cf) and metal removal efficiency R =

x 100 (%) C0

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(4)

where V is the volume of the aqueous solution (L), and M is the weight of the NCA (g), C0 and Cf are the initial and final concentrations of Cu(II) in solutions, respectively. The elution/regeneration and reusability of the NCA was examined by acid treatment. The Cu(II) loaded NCA was stirred in 5 mL of 0.25 M HCl solution for 10 h at room temperature to strip Cu(II) ions. The final Cu(II) concentration in the aqueous phase was determined by ICP-AES. The NCA was then washed with deionized water several times. Then the resulting cleaned NCA was dried at 45°C and subjected again to adsorption– desorption-regeneration process for seven cycles.

2.5. Analyses The N2 adsorption-desorption isotherms were measured using the 3Flex analyzer (Micromeritics, USA) at 77 K. The pore size distribution was measured from the BJH adsorption. Mesoporous silica was pre-treated at 100°C for 3 h under vacuum until the pressure was equilibrated to 10–5 Torr before the N2 adsorption-desorption analysis. The specific surface area (SBET) was measured by using multi-point adsorption data from the linear segment of the N2 adsorption isotherms using Brunauer–Emmett–Teller (BET) theory. The TEM images were obtained by using a JEOL (JEM-2010) and operated at the accelerating voltage of the electron beam at 200 kV. The TEM samples were prepared by dispersing the powder particles in ethanol solution using an ultrasonic bath and then dropping them onto copper grids. The SEM analysis was performed on Hitachi S–4300 operated at 16 keV. The NMR spectra was obtained on a Varian NMR System 400 MHz Spectrometer. The absorbance spectra was measured by UV–Vis–NIR spectrophotometer (Shimadzu-3700). The metal ions concentrations were determined by ICP–AES (SII NanoTechnology Inc.), and the instrument was calibrated using five standard solutions containing 0, 0.5, 1.0, 1.5 and 2.0 mg/L (for each element), and the correlation coefficient of the calibration curve was higher

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than 0.9999. Also sample solutions having complicated matrices were not used and no significant interference of matrices was observed. All the experiments were duplicated at least and the mean value was used in all cases. The maximum variation with batch sorption data was 5.0%. Moreover, the data presented in the Figures are average values.

3. Results and discussion 3.1. Mesoporous silica and nano-composite adsorbent A typical N2 adsorption-desorption isotherm of a mesoporous silica monolith is shown in Fig. 1 (a). The mesoporous silica showed a typical Type IV isotherm according to the IUPAC classification method [45]. The disappearance of saturation limit with a hysteresis indicates that the obtained material is mesoporous. The hysteresis can be classified as H2 type where a vapor-percolation threshold was involved of the boundary curve occurring at P/P0 of approximately 0.44. The corresponding pore size distribution curve indicated that the prepared mesoporous silica had a large pore size around 7.7 nm. According to the SBET data, the mesoporous silica showed a very high specific surface area of 555 m2/g and a relatively large pore volume of 0.68 cm3/g, which were benefit for their further applications of Schiff base organic ligand immobilization for metal ions separation. Noticeable changes were found in the pore structures of mesoporous silica after successful Schiff base ligand immobilization, although the N2 adsorption-desorption isotherms exhibited a typical IV-type of ordered mesoporous materials. The surface area, pore volume and pore sizes were sharply decreased as the organic ligand of DSDH was embedded onto the meso-structure channel (Fig. 1 (b)) and the data were summarized in Fig. 1 (inset). The structures and morphology of the mesoporous silica and Schiff base ligand immobilized NCA samples were characterized by SEM and TEM techniques. SEM images in

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Fig. 2 (A and B) confirmed the mesospheres had a relative large particle size distribution, and most of them were intact with an average pore diameter and well-ordered mesoporous structures. The TEM images of mesoporous silica clearly show that the mesoporous silica was composed of ordered mesopores and apparently possesses larger pores for densely organic ligand immobilization as judged from Fig. 2 (C and D). In preparation of NCA by using silica monoliths carrier, the hydrogen bonding might occur between the abundant hydroxyl groups of pore silica surface and the heteroatoms of the Schiff base ligand [35]. Moreover, the TEM images showed well-organized parallel channels and clarified as a typical hexagonal with ordered mesopore structure [41]. The TEM images are also shown in Fig. 2 (E and F) after Schiff based DSDH ligand immobilized onto the mesoporous silica and also exhibited the appreciable mesopores of the composite materials.

3.2. Optical Cu(II) ions detection The Cu(II) ions detection by the Schiff based ligand immobilized materials is related to the several parameters such as pH of buffer solutions, concentrations of Cu(II) ions, limit of detection and ions selectivity. Therefore, these factors were optimized for Cu(II) ion detection by the NCA. Also the difference in the color intensity values of the NCA before and after the addition of Cu(II) ions was determined to evaluate the optimum conditions. The influence of the solution pH on this system was investigated in pH range of 2.012.5 from the stand point of environmental application. Over the wide pH ranges, the absorbance intensities of the [Cu(II)-DSDH]n+ complex displayed strong pH dependence and high absorption intensity with significant color formation at pH 7.0 (Fig. 3); this warrant the NCA application in Cu(II) ions detection by naked-eye. The data also indicated that there was no sharp color difference was observed in the other pH region as depicted from Fig. 3. The

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color intensity of the NCA was high at pH 7.0 in the presence Cu(II) ions and pH 7.0 was selected as the optimal value for all experiments to define the other parameters. The color optimization properties of NCA with Cu(II) ions were studied to understand the Cu(II) ions concentration for optimum color formation. On the gradual addition of Cu(II) ions, the color intensity was also increased as judged from Fig. 4 (A). The data also clarified that the absorbance intensity at 515 nm significantly increased. This can be explained through the charge-transfer transudation of the Schiff base molecule [46]. Therefore, the absorbance increment of [Cu(II)-DSDH]n+ complex was induced by the change of charge-transfer and the dramatic color change from yellowish to dark green. This evaluation is indicated that Schiff base ligand immobilized NCA could be served as sensitive chromogenic materials for Cu(II) ions detection in water samples. To determine the limit of detection, the calibration curves were evaluated based on the relationship between R–R0 (at λmax = 515 nm) according to the absorbance intensity difference of different Cu(II) ions concentration onto the NCA. The calibration curve is shown in Fig. 4 (B). It is also noted that the calibration plot is linear correlation by the NCA when the Cu(II) ions concentrations are low ranges from 0.002 mg/L to 0.05 mg/L (Fig. 4 (B)). The correlation coefficient value was 0.99 as depicted in the inset in Fig. 4 (B). The data indicated that a wide range of low-concentration Cu(II) ions can be detected in water samples. The detection limit was determined at 0.16 µg/L even in presence of the several matrices (calibration curve with dotted lines). The relative standard deviation is approximately 3.2% for the analytical data of three replicate analyses. In order to check the selectivity of the colorimetric assay for the detection of Cu(II) ions by the NCA, the other coexistent metallic ions such as K+, Na+, Ag+, Ca2+, Mg2+, Cd2+, Zn2+, Ni2+, Mn2+, Pd2+, Ba2+, Fe3+ and Al3+ were investigated under optimum conditions. The results obtained by measurement of the existing common ion did not interfere with signaling

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any remarkable color change as judged from Fig. 5. Also the diverse anions were tested, and no color was detected by the NCA. These data are indicated that the proposed NCA could be an excellent chromogenic material for Cu(II) ions detection with high selectivity in aqueous solution.

3.3. Cu(II) ions adsorption parameters The aqueous solution pH plays an important factor for affecting the surface charge of the adsorbents and the degree of speciation of adsorbate during investigating the adsorption capacity of the adsorbent [47]. To understand the effect of pH on adsorption by NCA, the initial solution pH was varied within the range of 2.0–12.5. The effect of pH on Cu(II) ions adsorption on the NCA is shown in Fig. 6 (A). Fig. 6 (A) clarified that the Cu(II) ions adsorption was strongly affected by the pH solution. In the acidic region, the protons were strongly competed with Cu(II) ions by the NCA active sites and no significant adsorption were possible in this area. Increasing the pH range reduced the protons for competing with Cu(II) ions the adsorption efficiency increases. The adsorption efficiency was possible at the neutral pH region by the NCA and pH 7.0 was selected for further Cu(II) adsorption operation in this study. To determine the equilibrium Cu(II) ions adsorption, the effect of contact time on the NCA was investigated along with 20 mg of adsorbent dose, 10 mg/L of the initial Cu(II) ions concentration and the solution pH of 7.0 at room temperature. A series of adsorption experiments for contact times ranging from 0 to 80 min was carried out in this study and the data were presented in Fig. 6 (B). The Cu(II) ions adsorptions increased within contact times range from 0 to 50 min and then remain constant with further increasing of contact time as judged from Fig. 6 (B). Also it is clarified that the Cu(II) ions adsorption on the NCA is rapid within the first 10 min, more than 68% of Cu(II) ions could be adsorbed, and then increased

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slowly and reached adsorption equilibrium around 50 min. The initial adsorption was rapid because the Cu(II) ions was contacted quickly with the available active sites on the surface of NCA. Further increasing the contact time, the available active sites gradually decreased and the adsorption process was slow process and taking time to achieve adsorption equilibrium [48]. This trend is very similar to our previous where organic-inorganic materials are conjugated [49]. In ion-exchange adsorption, adsorption processes are very rapid to take the ions from the aqueous solution [50,51]. However, we have chosen 2 h as the optimum contact time to determine the maximum adsorption capacity by the NCA. In order to understand the adsorption process, scientists were considered several different isotherm models. Adsorption isotherms are used to describe the adsorption process under the equilibrium conditions. However, the fitting experimental data is an important parameter to comply the isotherm model due to the interactions of solutes with the adsorbent surface [18,21,36,52]. The adsorbent surface forms complex with Cu(II) ions using Schiff base groups as defined in the Scheme 2. Also Fig. 7 shows the relationships between the equilibrium concentration of Cu(II) ions and the amount of Cu(II) ions adsorbed on the NCA. The adsorption rate was rapid at low concentrations of Cu(II) ions and starting from a certain concentration value it reaches to a plateau. Among different sorption isotherm models, the Langmuir model is the most widely used model for metal ions adsorption. Then the Langmuir model was used to interpret and check the adsorption data. The linear form of Langmuir isotherm is as follows:

Ce/q e = 1/(KLqm) + (1/qm)Ce

(linear form)

(5)

where K (L/ mg) is the Langmuir binding equilibrium constant, q m (mg/g) is the maximum amount of Cu(II) ions adsorbed with the NCA, Ce (mg/L) is the equilibrium concentration of Cu(II) ions, and qe (mg/g) is the amount of Cu(II) ions adsorbed at the concentration Ce. The 15

qm and KL can be obtained from the slope and intercept of the linear plot when Ce/qe versus Ce gives a fairly good linear curve. The experimental adsorption for Cu(II) is shown in Fig. 7. As judged from Fig. 7, when the initial concentration of Cu(II) ion was higher, the equilibrium adsorption amount was also higher. This is due to the higher adsorption rate and also the utilization of all available active sites of the NCA. The maximum adsorption capacity for Cu(II) ions by the NCA was 173.62 mg/g, and the correlation coefficients value was also significant (R2 = 0.9821). It is also clarified that the maximum adsorption values was more closed to experimental result in the Langmuir adsorption isotherm model. Then the adsorption process could be described as a monolayer adsorption process due to homogenous and negligible interaction between adsorbed surfaces [15,19,38,43,53]. Moreover, the Langmuir constant KL has a positive value, indicating the favorable sorption system. The comparison of the maximum adsorption capacity with some recent different adsorbents toward Cu(II) ions is shown in Table 1. The maximum sorption capacity of the present Schiff base ligand immobilized NCA is comparable with the listed others form of materials. This data clearly clarified that the NCA can be used as a very efficient adsorbent to take up Cu(II) ions with high adsorption capacity. The competitive effects of co-existing metal ions such as Cu 2+, Na+, K+, Ag+, Ca2+, Zn2+, Ni2+, Mg2+, Cd 2+, Ba2+, Mn2+, Pd2+, Fe3+ and Al3+ on each other in multicomponent solutions and the adsorption efficiencies of NCA for the above indicated metal in a monocomponent and in the multi-component solutions were studied at pH 7.0. The results are shown in Fig. 8 (A) in the multi-component solution system. The results for the multicomponent systems show that the presence of diverse metal ions has a negligible influence on the adsorption of Cu(II) ions by the NCA at optimum conditions. It is assumed that Cu(II) ions could displace others metal ions with a weaker affinity in the multi-component solutions where metals compete for the same adsorption sites of the adsorbent metals with a greater

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affinity [54,55]. The data clarified that Cu(II) ions could be adsorbed more than 94% even in the presence of multi-component metal ions. Then the possible complex mechanism is shown in Scheme 2. The elution and regeneration of the adsorbent are an important parameter from the stand point of investment and operation costs [56,57]. Therefore, the NCA used for adsorption of Cu(II) ions must be capable of elution/regeneration for reusing without loss of functionality. The total elution rates for NCA for Cu(II) ions is high as judged from Fig. 8 (B). After seven cycles, the NCA still retained 92% of its initial adsorption capacity. Therefore, 0.25 M HCl can effectively elute Cu(II) ions from NCA after successful Cu(II) ions adsorption operation. The high reusability suggested that the NCA would be a promising material to detect and adsorb of Cu(II) ions from wastewater.

4. Conclusions In this study, a new Schiff base ligand immobilized nano-composite adsorbent (NCA) was prepared for optical sequential detection and removal of Cu(II) ions from wastewater. The NCA exhibited the porous structure with high surface area. The optimum condition was optimized and the detection/adsorption operation was carried out accordingly. The data clarified that the Cu(II) ions could be detected with a significant low-level concentration level in the presence of foreign ions. The detection and adsorption operations were carried out at the neutral pH region at room temperature. However, the sophisticated equipment and skills are not required to detect and remove of Cu(II) ions. Then the Schiff base ligand based material could be guidance to the development of a new type of the sequential recognition of Cu(II) using specific color change. From the batch studies, the mesopprous NCA exhibited considerable adsorption efficiency for Cu(II) ions compared to the other spherical molecular sieves. The NCA exhibited an excellent adsorption capacity for Cu(II) ions with good

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chemical stability. The equilibrium data confirm that the Cu(II) ions adsorption onto the NCA was fitted well with the Langmuir model and the adsorption capacity was 173.62 mg/g. Moreover, the data confirmed the monolayer adsorption behavior by the NCA. With excellent elution, regeneration and reuse performance, the NCA could be a promising in the excellent detection and removal of Cu(II) ions in water samples. Moreover, the mesoporous NCA is not only low-cost, convenient, environmental friendly, but also have a good potential to detect and remove of Cu(II) ions from aqueous solution in industry.

Acknowledgments This research was partially supported by the Grant-in-Aid for Research Activity Startup (24860070) from the Japan Society for the Promotion of Science. The authors also extended their appreciation to the Deanship of Scientific Research at King Saud University for funding the work through the research group project No. RGP-VPP-130. The authors also wish to thank the anonymous reviewers and editor for their helpful suggestions and enlightening comments.

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Okamoto, Selective cesium removal from radioactive liquid waste by crown ether immobilized new class conjugate adsorbent, J. Hazard. Mater. 278 (2014) 227–235. [42] (a) M.R. Awual, T. Yaita, H. Shiwaku, S. Suzuki, Ultimate selenium(IV) monitoring and removal from water using a new class of organic ligand based composite adsorbent. J. Hazard. Mater. 291 (2015) 111–119; (b) M.R. Awual, M.A. Khaleque, M. Ferdows, A.M.S. Chowdhury, T. Yaita, Rapid recognition and recovery of gold(III) with functional ligand immobilized novel mesoporous adsorbent, Microchem. J. 110 (2013) 591–598. [43] (a) M.R. Awual, M.A. Khaleque, Y. Ratna, H. Znad, Simultaneous ultra-trace palladium(II) detection and recovery from wastewater using new class mesoadsorbent, J. Ind. Eng. Chem. 21 (2015) 405–413; (b) M.R. Awual, T. Yaita, H. Shiwaku, Design a novel optical adsorbent for simultaneous ultra-trace cerium(III) detection, sorption and recovery, Chem. Eng. J. 228 (2013) 327–335; (c) M.R. Awual, T. Yaita, H. Shiwaku, S. Suzuki, A sensitive ligand embedded nano-conjugate adsorbent for effective cobalt(II) ions capturing from contaminated water, Chem. Eng. J. 276 (2015) 1–10. [44] (a) M.R. Awual, Investigation of potential conjugate adsorbent for efficient ultra-trace gold(III) detection and recovery, J. Ind. Eng. Chem. 20 (2014) 3493–3501; (b) 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. [45] (a) S.A. El-Safty, M.A. Shenashen, M. Ismael, M. Khairy, M.R. Awual, Optical mesosensors for monitoring and removal of ultra-trace concentration of Zn(II) and Cu(II) ions from water, Analyst, 137 (2012) 5278–5290; (b) S.A. El-Safty, A. Shahat, M.R. Awual, M. Mekawy, Large three-dimensional mesocage pores tailoring silica

25

nanotubes as membrane filters: nanofiltration and permeation flux of proteins, J. Mater. Chem. 21 (2011) 5593–5603; (c) S.A. El-Safty, M.A. Shenashen, M. Ismael, M. Khairy, M.R. Awual, Mesoporous aluminosilica sensors for the visual removal and detection of Pd(II) and Cu(II) ions, Micropor. Mesopor. Mater. 166 (2013) 195– 205. [46] T. Gunnlaugsson, J.P. Leonard, N.S. Murray, Highly selective colorimetric naked-eye Cu(II) detection using an azobenzene chemosensor, Org. Lett. 6 (2004) 1557-1560. [47] L. Mihaly-Cozmuta, A. Mihaly-Cozmuta, A. Peter, C. Nicula, H. Tutu, D. Silipas, E. Indrea, Adsorption of heavy metal cations by Na-clinoptilolite: equilibrium and selectivity studies, J. Environ. Manage. 137 (2014) 69–80. [48] T. Jiang, W. Liu, Y. Mao, L. Zhang, J. Cheng, M. Gong, H. Zhao, L. Dai, S. Zhang, Q. Zhao, Adsorption behavior of copper ions from aqueous solution onto graphene oxide–CdS composite, Chem. Eng. J. 259 (2015) 603–610. [49] Y. Wu, H.J. Luo, H. Wang, C. Wang, J. Zhang, Z.L. Zhang, Adsorption of hexavalent chromium

from

aqueous

solutions

by

grapheme

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with

cetyltrimethylammonium bromide, J. Colloid Interf. Sci. 394 (2013) 183–191. [50] (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, 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, A. Jyo, S.A. El-Safty, M. Tamada, N. Seko, A weak-base fibrous anion exchanger effective for rapid phosphate removal from water, J. Hazard. Mater. 188 (2011) 164–171; (d) M.R. Awual, A. Jyo, M. Tamada, A. Katakai, Zirconium(IV)

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loaded bifunctional fiber containing both phosphonate and sulfonate as arsenate adsorbent, J. Ion Exchange 18 (2007) 422–427. [51] (a) M.R. Awual, A. Jyo, Assessing of phosphorus removal by polymeric anion exchangers, Desalination 281 (2011) 111–117; (b) 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; (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. Naushad, M.R. Khan, Z.A. ALOthman, M.R. Awual, Bromate removal from water samples using strongly basic anion exchange resin Amberlite IRA-400: Kinetics, isotherms and thermodynamic studies, Desalination and Water Treat. (2015) DOI: 10.1080/19443994.2015.1005157. [52] M. Ceglowski, G. Schroeder, Preparation of porous resin with Schiff base chelating groups for removal of heavy metal ions from aqueous solutions, Chem. Eng. J. 263 (2015) 402–411. [53] Q. Tao, Z.Y. Xu, J.H. Wang, F.L. Liu, H.Q. Wan, S.R. Zheng, Adsorption of humic acid to aminopropyl functionalized SBA-15. Micropor. Mesopor. Mater. 131 (2010) 177– 185. [54] F. Qin, B. Wen, X.Q. Shan, Y.N. Xie, T. Liu, S.Z. Zhang, S.U. Khan, Mechanisms of competitive adsorption of Pb, Cu, and Cd on peat, Environ. Pollut. 144 (2006) 669– 680. [55] M.A. Gonzalez, I. Pavlovic, R. Rojas-Delgado, C. Barriga, Removal of Cu 2+, Pb 2+ and Cd2+ by layered double hydroxide–humate hybrid: Sorbate and sorbent comparative studies, Chem. Eng. J. 254 (2014) 605–611.

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[56] (a) 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; (b) M.R. Awual, A. Jyo, Rapid column-mode removal of arsenate from water by crosslinked poly(allylamine) resin, Water Res. 43 (2009) 1229–1236; (c) 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. [57] C. Ling, F.Q. Liu, C. Long, T.P. Chen, Q.Y. Wu, A.M. Li, Synergic removal and sequential recovery of acid black 1 and copper (II) with hyper-crosslinked resin and inside mechanisms, Chem. Eng. J. 236 (2014) 323–331.

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Table 1 Comparison of adsorption capacities of Cu(II) ions with different forms of materials

Maximum adsorption capacity (mg/g)

Ref.

Composite adsorbent

182.15

[13a]

Facial composite adsorbent

176.27

[15a]

Meso-adsorbent

175.75

[18a]

Graphene oxide–chitosan

25.40

[22]

Magnetic graphene oxide composite

62.73

[23]

111.11

[24]

11.70

[31]

Titanate nanotubes

121.92

[32]

Dodecylamine-48A

222.89

[33]

Schiff based ligand based silica gel

41.31

[34]

Herbaceous peat

4.84

[35]

137.17

[48]

Poly(MVE-alt-MA-1)

81.72

[52]

Danish peat

34.03

[54]

Layered double hydroxide–humate hybrid

47.63

[55]

Nano-composite adsorbent

173.62

This study

Used functional materials

Maghemite nanotubes Tree fern

Graphene oxide–CdS composite

29

Fig. 1. Materials surface characterization by N2 adsorption-desorption isotherms of (a) mesoporous inorganic silica and (b) Schiff based DSDH ligand immobilized nano-composite adsorbent (NCA).

30

Fig. 2. SEM images of the as prepared mesoporous inorganic silica (A and B); TEM micrographs of the mesostructured containing ordered mesoporous silica (C and D) and Schiff base ligand containing NCA (E and F).

31

Absorbance (a.u.)

1.5

1.0

0.5

0.0 2

4

6

8

10

12

Solution pH

Fig. 3. Optimization of pH effect for the detection of Cu(II) ions by NCA while the solution concentration was 2.0 mg/L of Cu(II) ions. The RSD value was >3.0% for the analytical data of duplicate analyses.

32

(A)

(B)

Fig. 4. Color optimization of the NCA while the Cu(II) ions concentration was in variable (A) and calibration profiles with correspondence to the absorbance intensity in different Cu(II) concentration at 515 nm (B). The linear fit data are shown in the inlets in graphs (B) and the dotted line represents the calibration of the Cu(II) ions in the presence of diverse metals ions.

33

Fig. 5. Ion selective profile of the NCA with significant color formation in the presence and absence of diverse metal ions. The listed diverse ions are (15 mg/L): (1) Ag+, (2) Na+, (3) K+, (4) Ca2+, (5) Cd2+, (6) Pd2+, (7) Mg2+, (8) Zn2+, (9) Ba2+, (10) Mn2+, (11) Ni2+, (12) Al3+ and (13) Fe3+. The Cu(II) ions concentration was 2.0 mg/L.

34

104

78

Efficiency (%)

Efficiency (%)

(B)

100

(A)

52

26

80 60 40 20

0 2

4

6

8

10

0

12

0

pH

20

40

60

Reaction time (min.)

Fig. 6. Effect of pH in Cu(II) adsorption by the NCA in the different pH solutions area (A) and the optimum Cu(II) ions adsorption in the effect of contact time for Cu(II) ions when the NCA amount was 20 mg and the Cu(II) ions concentration was 10.0 mg/L (B). 35

80

Fig. 7. Langmuir adsorption isotherm for Cu(II) ions by the NCA with linear form of the Langmuir equation (initial concentration: 2-75 mg/L; shaking time: 2 h; NCA amount: 10 mg).

36

(A)

(B)

100

Initial

100

Extraction

80

Efficiency (%)

Efficiency (%)

75

Sorption

50

25

60

40

20

0

0 Fe

Al

Ni Mn Mg Pd Ba Zn Cd Cu

K

Ca Na Ag

Ions

1st

2nd

3rd

4th

5th

6th

No. of cycles

Fig. 8. Selective Cu(II) ions adsorption by the NCA in the presence of diverse competing ions (A) and elution-regeneration-reuses study of the NCA with seven consecutive cycles when eluting agent was 0.25 M HCl (B).

37

7th

Scheme 1. The synthetic route of N,N`di(3-carboxysalicylidene)-3,4diamino-5-hydroxypyrazole (DSDH) Schiff based organic ligand.

38

Scheme 2. Possible complexation mechanism of Cu(II) ion with the Schiff base ligand of DSDH in the optical detection and removal operations and elution/regeneration for next uses with 0.25 M HCl acid.

39

Research highlights:


Schiff base ligand was synthesized and immobilized for nano-composite adsorbent.
Nano-composite adsorbent (NCA) was used for optical Cu(II) ions detection/removal.
The NCA exhibited the high sensitivity and selectivity for Cu(II) ions capturing.
The NCA can easily be handled and able to use of industrial wastewater treatment.

40