2. Materials and methods

#### 2.1 Chemical reagents

electrolysis, are applied for the remediation of heavy metal ions from aqueous solutions [3–5]. Notwithstanding, by far, the majority of these procedures are restrained by both ecological and economic constraints. In contrast, adsorption has been qualified to be the most relevant and promising method, on account of its low cost, flexible operation, and reversibility. A wide variety of low-cost adsorbents, for example, agricultural by-products, industrial wastes, and natural mineral materials, were found to have good adsorption capacity [6]. However, these materials possess weak resistance to abrasive forces in column apply and leaching of few organics

It is well known that the substantial factors affecting the adsorption process are pore size distribution, specific surface areas, and pore surface chemistry. In this endeavor, it is imperative to search materials with enormous porous structures, high specific surface areas, and low density. In the last few decades, ordered mesoporous silica has triggered a growing interest in the field of water treatment, owing to its diverse outstanding properties. These enclose tunable pore-size, high specific surface area, large pore volume, chemical inertness, thermal stability, and

One of the basic techniques applied for fabricating organic-inorganic hybrid materials is the sol-gel method. Tetraalkoxysilanes (Si(OR)4) like tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS) are widely employed as a precursor for preparing monolithic silica, owing to their hydrophobicity and strong covalent Si-O bonding [10]. It is worthy to state that the as-prepared hybrid materials by the sol-gel route are divided into two classes on account of the interaction type between organic and inorganic components. In class I, organic and inorganic components are strongly attached by covalent or dative covalent bonds, while in the second, these two components are weakly bonded through hydrogen or Van der Waals bonds. Indeed, these materials have generated considerable interest for their potential application in multiple fields such as: adsorption [11], drug delivery systems [12, 13], biosensors [14], nanotechnology, and nanomedicine applications [15, 16] and catalysis [17]. Organic-inorganic hybrid materials displayed high efficiency and outstanding selectivity towards target pollutant than the other silica gels. Nitrogen/thiol and magnetic functionalized mesoporous silica have been at the foreground of these composites. In the same vein, Benhamou et al. have shown that amine functionalized MCM-41 and MCM-48 exhibited a higher adsorption capacity than pristine. They also evinced that both hybrid materials have a higher affinity for Cu(II) and Pb(II) than for Cd(II) and Co(II) in single and mixed cation solutions [18]. Shahbazi and co-workers grafted aminopropyl (NH2) and melamine-based dendrimer amines (MDA) to SBA-15 mesoporous silica. They observed that NH2–SBA-15 and MDA–SBA-15 were over ten-fold better than the pristine SBA-15 in the adsorption of Pb(II), Cu (II), and Cd(II) [19]. Interestingly, they also showed that in column studies, the adsorption yield was swayed by the flow rate. Apart from the fact that magnetic silica-based materials exhibited excellent adsorption affinity towards heavy metal ions, such adsorbents compared to the nitrogen and thiol designer silicates can be easily removed from aqueous solution after adsorption. In the same context, Wang et al. [20] synthesized an amino-functionalized core-shell magnetic mesoporous SBA-15 silica composite which displayed a high adsorption capacity for Pb(II) ions. This adsorbent can be readily removed and regenerated. Despite the high adsorption capacity and the extra-ordinary selectivity towards target metal, as well as the capacity for simultaneous removal of aqueous pollutants, organic-inorganic hybrid materials are still not applied for a continuous process in a fixed-bed column. Another challenge to overcome is the difficulty in their largescale production because of the complexity of synthesis methods and the control

the ability to attach a plethora of different functional groups [7–9].

throughout retention process.

Water Chemistry

128

All reagents were of analytical grade and used as received without further purification. Hydrophobic tetraethyl orthosilicate (TEOS, 99%) was utilized as a silica precursor, while ethanol was a bridging medium. Cd(NO3)2.4H2O, Cu(NO3) 2.3H2O, and Zn(NO3)2.6H2O were employed as metal sources for batch and column adsorption experiments. These reagents were supplied by Sigma-Aldrich, USA. The organic precursors 1,3,4-thiadiazole-2,5-diamine and 1,3,4-thiadiazole-2,5-dithiol were prepared according to the literature [21, 22].

#### 2.2 Methods

#### 2.2.1 Adsorbent synthesis

Pursuant to our foregoing studies, xerogels were synthesized using the following process [Helali 15 et 16]: 10 ml of deionized water, 20ml of ethanol, and 22.8 mL of TEOS were mixed under vigorous magnetic stirring. To the as-prepared mixture was added a necessary amount of organic precursor (10<sup>1</sup> M, 11.6 g of 1,3,4 thiadiazole-2,5-diamineor or 15 g of 1,3,4-thiadiazole-2,5-dithiol). Thereafter, the reactant mixture was stirred for 6 h at 78°C and at the last ripened for 48 h at 100°C; the resulting xerogels were labeled M1 and M2, and the synthesis mechanism is represented in Figure 1.

#### 2.2.2 Characterization

Xerogel morphology was carried out using a scanning electronic microscope (Cambridge Instruments Stereoscan 120) operating at 15 kV. The textural properties of hybrid materials were determined from the N2 adsorption-desorption isotherms recorded at 77 K with a Micrometrics ASAP-2000 volumetric apparatus. The specific surface areas were computed by the multi-point analysis (BET) (Brunauer et al., 1938) in the relative pressure interval of 0.03˂P/P° ˂0.3. Howbeit pore size distribution was acquired from the adsorption-desorption branches of the isotherm

examples were centrifuged at 12000 rpm for 20min with the end goal to separate the solid from the liquid phase. The supernatant containing metal ions was evaluated employing an atomic absorption spectrophotometer (SHIMADZU AA-680, Japan). The percent adsorption of metal ion delineated is as follows (Eq. (1)):

Bi-Functionalized Hybrid Materials as Novel Adsorbents for Heavy Metal Removal from…

where Ci and Cf are the initial and final (or equilibrium) adsorbate concentra-

Dynamic adsorption trial run in the fixed-bed column was conducted in a glass column (3.5 cm length and 1.2 cm diameter), stuffed with 1 g of the xerogel. The

rate of 20 mL min�<sup>1</sup> by using a peristaltic pump (Flowtech India, model NFP01). Samples were gathered at determined time interims, and the residual adsorbate concentration (Ce) was measured spectrophotometrically (Eq. (2)). Column exploitation was ceased when the adsorbate concentration attained 95% of its initial concentration. The maximum column capacity (qc) can be reckoned as

qt ¼ A � Q � C �

qe <sup>¼</sup> qtotal

where qtotal (mg) is the total quantity of adsorbed metal ions, A is the area

) is the influent concentration, and M (g) is the mass of adsorbent.

As a means to examine the regeneration of the synthesized hybrid materials, the metal cation-loaded adsorbents are desorbed with 10 mL of HCl solution (0.5 M) for 60 minutes. Afterwards, the recovered xerogel is flushed with deionized water

Parameters Values WHO Standard pH 2.8 5.5–6.5 Temperature 40 20–30

) 720 20

) 371 280

) 90 40

) 100 5

) 10 0.2

) 2 0.1

under breakthrough curve (Ce/(C0) versus time, Q (mL.min�<sup>1</sup>

1

Ci � Cf Ci

� 100 (1)

) was pumped in a down flow mode at a flow

<sup>1000</sup> (2)

) is the flow rate,

<sup>M</sup> (3)

adsorption ð Þ¼ %

tions, respectively.

follows Eq. (3):

C0 (mg.L�<sup>1</sup>

2.2.5 Desorption studies

TSS (mg.L�<sup>1</sup>

COD (mg.L�<sup>1</sup>

BOD (mg.L�<sup>1</sup>

Zn (mg.L�<sup>1</sup>

Pb (mg.L�<sup>1</sup>

Cd (mg.L�<sup>1</sup>

Physicochemical characterization of electroplating wastewaters.

Table 1.

131

2.2.4 Fixed-bed column studies

metal ion concentration (150 mg. L�<sup>1</sup>

DOI: http://dx.doi.org/10.5772/intechopen.86802

Figure 1. Synthesis mechanism of hybrid materials M1 and M2.

through the BJH pattern. The total pore volume was evaluated at a relative pressure of P/P° = 0.99.

The experimental parameters for the 13C CP MAS NMR were 9 KHz SPIN rate, 5 s pulse delay. NMR spectroscopy was carried out on an MSL 500 Bruker Spectrometer. FT-IR spectra were collected on 550 Nicolet Magana Spectrometer in KBr pellets in the range of 4000–400 cm<sup>1</sup> . X-ray photoelectron spectroscopy (XPS) measurement was conducted on a VG ESCALAB MK II spectrometer in the pulsecount mode at a pass energy of 50 eV employing a Mg Kα (1253.6 eV) achromatic X-ray source. In order to evaluate the surface charges, the electro-kinetic potential was performed by Malvern instrument Zeta Nano ZS.

#### 2.2.3 Adsorption experiments

Stock solutions were set up by dissolving the required metal mass in 1 L of double-distilled water. Aliquots were prepared by diluting standard stock solution to the desired concentrations (5–400 mg.L<sup>1</sup> ). All experiments were done at room temperature in triplicate, and the average values were utilized for further estimation. For every essay, 0.01 g of xerogel was thoroughly blended in conical flasks containing 25 ml of test solution with various metal concentrations at a required pH adjusted prior to the experiment with 0.1 mol. L<sup>1</sup> of HNO3 or 0.1 mol. L<sup>1</sup> of NaOH solution. The flasks were shaken for the coveted contact time in an electrically thermostatic reciprocating shaker (Selecta multimatic-55, Spain) at 150 rpm. The contact time for metal ions and the hybrid materials were ranged from 10 to 100 min.

For the adsorption isotherm contemplates, the initial metal concentration was run from 10 to 400 mg. L<sup>1</sup> . After each adsorption procedure, the gathered

Bi-Functionalized Hybrid Materials as Novel Adsorbents for Heavy Metal Removal from… DOI: http://dx.doi.org/10.5772/intechopen.86802

examples were centrifuged at 12000 rpm for 20min with the end goal to separate the solid from the liquid phase. The supernatant containing metal ions was evaluated employing an atomic absorption spectrophotometer (SHIMADZU AA-680, Japan). The percent adsorption of metal ion delineated is as follows (Eq. (1)):

$$\text{adsorption } (\text{\textquotedblleft} 6\text{\textquotedblright}) = \frac{\left(\text{C}\_{i} - \text{C}\_{f}\right)}{\text{C}\_{i}} \times 100 \,\tag{1}$$

where Ci and Cf are the initial and final (or equilibrium) adsorbate concentrations, respectively.

#### 2.2.4 Fixed-bed column studies

Dynamic adsorption trial run in the fixed-bed column was conducted in a glass column (3.5 cm length and 1.2 cm diameter), stuffed with 1 g of the xerogel. The metal ion concentration (150 mg. L�<sup>1</sup> ) was pumped in a down flow mode at a flow rate of 20 mL min�<sup>1</sup> by using a peristaltic pump (Flowtech India, model NFP01). Samples were gathered at determined time interims, and the residual adsorbate concentration (Ce) was measured spectrophotometrically (Eq. (2)). Column exploitation was ceased when the adsorbate concentration attained 95% of its initial concentration. The maximum column capacity (qc) can be reckoned as follows Eq. (3):

$$q\_t = A \times Q \times \mathcal{C} \times \frac{1}{1000} \tag{2}$$

$$q\_{\epsilon} = \frac{q\_{\text{total}}}{M} \tag{3}$$

where qtotal (mg) is the total quantity of adsorbed metal ions, A is the area under breakthrough curve (Ce/(C0) versus time, Q (mL.min�<sup>1</sup> ) is the flow rate, C0 (mg.L�<sup>1</sup> ) is the influent concentration, and M (g) is the mass of adsorbent.

#### 2.2.5 Desorption studies

through the BJH pattern. The total pore volume was evaluated at a relative pressure

measurement was conducted on a VG ESCALAB MK II spectrometer in the pulsecount mode at a pass energy of 50 eV employing a Mg Kα (1253.6 eV) achromatic X-ray source. In order to evaluate the surface charges, the electro-kinetic potential

Stock solutions were set up by dissolving the required metal mass in 1 L of double-distilled water. Aliquots were prepared by diluting standard stock solution

temperature in triplicate, and the average values were utilized for further estimation. For every essay, 0.01 g of xerogel was thoroughly blended in conical flasks containing 25 ml of test solution with various metal concentrations at a required pH adjusted prior to the experiment with 0.1 mol. L<sup>1</sup> of HNO3 or 0.1 mol. L<sup>1</sup> of NaOH solution. The flasks were shaken for the coveted contact time in an electrically thermostatic reciprocating shaker (Selecta multimatic-55, Spain) at 150 rpm. The contact time for metal ions and the hybrid materials were ranged from

For the adsorption isotherm contemplates, the initial metal concentration was

. After each adsorption procedure, the gathered

The experimental parameters for the 13C CP MAS NMR were 9 KHz SPIN rate, 5 s pulse delay. NMR spectroscopy was carried out on an MSL 500 Bruker Spectrometer. FT-IR spectra were collected on 550 Nicolet Magana Spectrometer in KBr

. X-ray photoelectron spectroscopy (XPS)

). All experiments were done at room

of P/P° = 0.99.

Water Chemistry

Figure 1.

10 to 100 min.

130

run from 10 to 400 mg. L<sup>1</sup>

pellets in the range of 4000–400 cm<sup>1</sup>

Synthesis mechanism of hybrid materials M1 and M2.

2.2.3 Adsorption experiments

was performed by Malvern instrument Zeta Nano ZS.

to the desired concentrations (5–400 mg.L<sup>1</sup>

As a means to examine the regeneration of the synthesized hybrid materials, the metal cation-loaded adsorbents are desorbed with 10 mL of HCl solution (0.5 M) for 60 minutes. Afterwards, the recovered xerogel is flushed with deionized water


Table 1.

Physicochemical characterization of electroplating wastewaters.

and parched in the air for the forthcoming experiment. Successive sorptiondesorption cycles are rehashed 10 times to build up the genuine application and the high stability of the adsorbent.
