Adsorption Efficiency of Anatase TiO2 Nanoparticles

Journal of Inorganic and Organometallic Polymers and Materials https://doi.org/10.1007/s10904-018-1038-x

Adsorption Efficiency of Anatase TiO2 Nanoparticles Against Cadmium Ions Sirajul Haq1 · Wajid Rehman2 · Muhammad Waseem3 Received: 23 August 2018 / Accepted: 2 December 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018

Abstract The anatase TiO2 nanoparticles were synthesized by the reduction of titanium isopropoxide at pH 4.5. The surface area, pore size and pore volume were found to be 156.9 m2/g, 18.23 Å and 0.071 cm3/g respectively. The crystallite size calculated by Debye Sherrer’s equation was found 8.1 nm. The percent purity and the composition were studied by energy dispersive X-rays spectroscopy. The point of zero charge has been calculated from salt addition method. The point of zero charge (PZC) was calculated by salt addition method. The PZC was found to shift to higher values by increasing the concentration of background electrolyte. Batch adsorption technique has been employed for the sorption of Cd2+ ions. The adsorption data was found well fitted to Langmuir model. It was observed that the exchange of surface H+ with Cd2+ is greatly affected with temperature. A set of equations was applied to determine the possible adsorption mechanism of C d2+ ions onto T iO2 surface. Keywords Adsorption · Anatase · Pore size · PZC · Surface area

1 Introduction Chemical pollution can be manifested through the use of pesticides, chemical warfare agents (CWAs) in military actions, in case of terrorist attacks and wide use of toxic chemicals in different industries. During different industrial process i.e., mining, metal processing and electroplating, heavy metals like arsenic, cadmium, chromium, lead and mercury are released to contaminate ecosystem. The presence of heavy metals at trace level is a cause of acute or chronic toxic effect due to their accumulation and non-biodegradability in human body. Cadmium is one among these toxic metals, naturally found in a mineral greenockite (Cadmium sulfide) in abundance and little amount in sphalerite. Cadmium is heavily utilized in welding, rechargeable nickel–cadmium batteries, phosphate fertilizers, electroplating and also used in rods of nuclear reactors [1, 2]. The galvanizing pipes, * Sirajul Haq [email protected] 1

Department of Chemistry, University of Azad Jammu and Kashmir, Muzaffarabad 13100, Pakistan

2

Department of Chemistry, Hazara University, Mansehra 21300, Pakistan

3

Department of Chemistry, Comsat University Islamabad (CUI), Islamabad, Pakistan

runoff of waste batteries, fertilizers and paints are the main sources responsible for exposure of water to cadmium [3]. The reported daily intake of cadmium is 0.005 mg/L, however, according to WHO its permissible limit is 0.003 mg/L per day [1, 4]. The antagonistic health effects of cadmium accumulation in human body are causing damage to kidney and stomach while its high concentration is carcinogen [2, 5, 6]. The ingestion of cadmium may cause many diseases like cancer, breathing problems, effect reproductive hormones level and defects in birth [2, 5, 6]. In present age we need some efficient and effective methods for removal of pollutants from our environment. The pollutants may be degrade by using catalyst or adsorbed on the surface of an adsorbent. Beside other methods, adsorption is one of the most effective and economic method used for the adsorption heavy metals from its aqueous [7]. In this process we need a surface having adsorption ability such as carbon nanotubes, metal oxides and nanocomposites were used in the past [8–11]. The nanosized materials have unique physical, chemical and biological properties which may not be expect from micro and macro materials [12]. The TiO2 exists in three crystalline phases such rutile, anatase and brookite. Many methods are reported for the synthesis of anatase TiO2 nanoparticles like hydrothermal, solvothermal and sol–gel [12]. In literature it is reported that anatase phase is widely used in

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solar cell, photocatalytic reactions, also used in manufacturing of papers, paints, cosmetic and sunscreens [9, 13]. The TiO2 is one of the metal oxides used formerly for adsorption of heavy metals for its aqueous solution [13]. In the present study anatase TiO2 nanoparticles was synthesized and characterized by surface area measurements, XRD, EDX, SEM, EDX, FTIR and DRS analysis. The adsorption of C d2+ ions was monitoring by varying pH, temperature and Cd2+ ions concentration. Thermodynamic parameter were also calculated after using Langmuir model, which was fitted well to adsorption data.

2 Materials and Methods 2.1 Materials All the chemicals used during this research work were of analytical grade. Titanium(IV) isopropoxide, cadmium nitrate, sodium nitrate, ammonium hydroxide, nitric acid and absolute ethanol were purchased from Sigma Aldrich. All the solutions were prepared in deionized water.

2.2 Synthesis of TiO2 Nanoparticles The TiO2 nanoparticles were synthesized by previously reported method with little modification [14]. In the typical synthesis of T iO2 adsorbent, 0.852 mL of titanium isopropoxide were added to the 80 mL hot deionized water and stirred for 15 min. Afterward, 20 mL absolute ethanol was added and stirred the reaction mixture for further 90 min at 55 °C. The reaction mixture were filtered, dried at 120 °C and stored in polyethylene bottle.

Journal of Inorganic and Organometallic Polymers and Materials

2.4 PZC of TiO2 Nanoparticles Salt addition method was used to perform the PZC experiment for T iO2 nanoparticles. In the typical process, 30 mL of 0.01 M NaNO3 solution were taken in 50 mL titration flask. The initial pH was adjust at 2–10 by added of H NO3 and NaOH solution and 0.05 g of adsorbent was added to this solution. After 1 h of shaking in temperature control water bath, the final pH of the mixture were measured. The ∆pH were plotted against initial pH to get the PZC of the synthesized TiO2 nanoparticles. The same procedure were repeated for 0.1 M, 1 M solutions of N aNO3 and binary solution of NaNO3 (0.1 M) and Cd (NO3)2 (50 ppm).

2.5 Adsorption Study of Cd2+ Ion on TiO2 Nanoparticles Batch technique was performed for the adsorption of Cd2+ ions on the surface of TiO2 nanoparticles. A stock solution of Cadmium nitrate was prepared by dissolving 1 g in 1000 mL of deionized water. By applying dilution formula, solutions with different concentrations ranging between 10 and 100 ppm were prepared for further process and 0.1 M Sodium nitrate solution were used as background electrolyte. In the typical experiment, a binary solution of 0.1 M solution of N aNO3 with different concentration of C d2+ ions were prepared. The initial pH of the solutions were adjust to 4 and 6 by using N H4OH and HNO3 solutions and added 0.05 g of adsorbent (TiO2). Then the flask were sealed and kept in temperature control water bath shaker for 1 h. After the 1 h the final pH of the solution were measured and filter the mixture. The filtrate were than tested for remaining C d2+ ions concentration using atomic adsorption spectroscopy.

2.3 Characterization of TiO2 Nanoparticles Micromeritics Gemini VII 2390 surface area analyzer was used to measure BET surface area and pore size whereas XRD pattern was acquired by using X-ray diffraction model Panalytical X-Pert Pro. The source for the X-ray generation was Cu (1.54 Å) at 40 kV voltage and 30 mA current. The Energy dispersive X-ray model INCA 200 (UK) was employed at 20 keV whereas the morphology of the sample was traced by using scanning electron microscopy (SEM) model JEOL 5910 (Japan). The optical property of the nanoparticles was studied by diffuse reflectance spectroscopy (DRS) model UV–VIS/NIR spectrometer lambda 950 with integrating sphere of 200–2500 nm. The FTIR spectra before and after adsorption were recorded by using Nicolet 6700 (USA) in the range 4000–400 cm−1. To determine the equilibrium concentration of C d2+ ions atomic absorption spectrophotometer model AAS 800 was used.

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3 Results and Discussions 3.1 Physiochemical Properties The BET surface area of T iO2 nanoparticles was detected to 2 be 156.9 m /g with average pore width is 18.23 Å and single point adsorption total pore volume of pores was 0.071 cm3/g. The XRD pattern of nanosize anatase T iO2 (Fig. 1) showed diffraction peaks at 2 theta values with hkl planes 25.35° (101), 37.78° (004), 48.07° (200), 62.72° (204), match with JCPDS card no. 00-004-00477, 54.86° (211) and 73.50° (107) match with JCPDS card no. 01-071-1168 and one peak at 69.95° (116) match with JCPDS card no. 10-075-1537. All the diffraction peak were assigned to anatase crystalline phase with tetragonal geometry. The crystallite size was calculated from the full width and half maxima (FWHM) of

Journal of Inorganic and Organometallic Polymers and Materials 250

detected, showing the synthesized particle are pure, with no impurities. These results are also supported the XRD data. The Fig. 3 represents the UV visible reflectance spectrum of TiO2. The band gap reflectance edge of TiO2 was determined at 375 nm, giving direct band gap 3.30 eV, which is slightly higher than reported earlier [16].

101

200

Intensity

150

100

3.2 PZC of TiO2 Nanoparticles

004

200

211 204

50

107 116

0

20

25

30

35

40

45

50

55

60

65

70

75

Position (2 ) Fig. 1 XRD pattern of TiO2 (inset: SEM) nanoparticles

diffraction peaks using Scherer equation [15]. The average crystallite size of the TiO2 nanoparticles found was 8.1 nm having 1.95% lattice strain. The SEM micrograph of anatase T iO2 nanoparticles are given in the inset of Fig. 1, which shows clear nanostructure having distinct boundaries with nearly uniform geometry. The SEM micrograph confirm the porosity of T iO2 nanoparticles with small grain size ranging from 32.14 to 42.85 nm with average grain size 38.09 nm. The grain size obtained from SEM micrograph are 4–5 time larger than the crystallite size calculated for XRD. Thus it is clear that TiO2 nanoparticles (grain) showed in SEM micrograph are composed several crystallites as calculated by the XRD data. The Energy dispersive X-ray (Fig. 2) of T iO2 nanoparticles shows that the % weight of titanium is 53.07% and that of oxygen is 46.92%. In this spectrum no other peak has been

The surface charge of the anatase T iO2 nanoparticles was determined in NaNO3 solution with different concentration (Fig. 4). The PZC of TiO2 in different solution was found to lie at 6.4 in 0.01 M, 6.6 in 0.1 M, 6.9 in 1 M and 6.8 in binary solution of 0.1 M and 50 ppm C d2+ ions solution. The PZC of the TiO2 was increase with increasing concentration of electrolyte. The PZC of T iO2 was nearly same in 1 M and binary solutions.

3.3 Adsorption Study The adsorption behavior of T iO2 nanoparticles was studied by changing various experimental parameters like pH, temperature and adsorbate ( Cd2+) ions concentration. The initial pH selected for adsorption study was 4 and 6 and temperature were ranging between 293 and 232 K while the adsorbate ions concentration were varied between 10 and 100 ppm. The adsorption isotherm for Cd2+ ions on the TiO2 at pH 4 (a) and 6 (b) are given in Table 1. It is clear that with the increase in temperature, pH and initial Cd2+, adsorption of C d2+ ions on the surface of TiO2 nanoparticles also increases. Similarly percent adsorption also increases with increasing temperature and pH, however it was decreased with increasing initial concentration and this may be due to the unsaturation of available surface sites as well as due to the adsorbate–adsorbate interaction.

Fig. 2 EDX spectrum of T iO2 nanoparticles before (inset: after) adsorption

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% Reflectance

75

Table 1 Adsorption data (mg/g) at pH 4 and 6

TiO2 X=375

60

Temperature (K)

pH 4 X (mg/g)

pH 6 X (mg/g)

293

5.4 9.30 14.56 18.26 26.55 6.05 10.02 15.58 19.38 27.86 6.76 11.62 16.63 20.93 29.89 7.75 12.36 18.36 21.94 31.55

7.36 14.52 21.43 29.77 46.53 9.67 16.03 25.34 35.29 52.16 10.22 16.64 28.39 37.81 57 10.72 18.48 31.48 41.41 63.42

45

303 30

15

345

360

375

390

405

313

420

Wavelenght (nm) Fig. 3 UV–Vis diffuse reflectance spectra of TiO2 nanoparticles 323

1.0 0.5

pHeq

0.0 -0.5 -1.0

capacity, K b is the binding energy constant calculated from the slope and intercept of the plot Ce/X versus Ce plot respectively. The Langmuir parameter Xm, Kb and including r2 values at pH 4 and 6 are listed in Table 2 was increased with increasing temperature. However, the effect of temperature was more on Kb values as compared to Xm values. The increasing pattern of Kb values with temperature suggesting that the system are thermodynamically favored. Moreover, the higher value of Kb at higher temperature and pH showed greater stability of Cd2+ ions with absorbent [17]. The RL is an important feature of Langmuir isotherm and is expressed as dimensionless constant separation which is defined by the following equation.

0.01M NaNO3

-1.5

0.1M NaNO3

-2.0

Cd + NaNO3

1M NaNO3 2+

2

4

6

8

10

pHi Fig. 4 PZC of T iO2 NPs in the absence and presence of Cd2+ ions

3.4 Modeling Langmuir model was applied in order to calculate sorption maxima and binding energy constant. The sorption data was fitted to the linear form of Langmuir model with r2 values ranging from 0.849 to 0.899 and 0.855 to 0.911 at pH 4 (a) and pH 6 (b) respectively, as shown in Fig. 5. The linear Langmuir equation are given below.

Ce C 1 + e = X Xm Kb Xm

(1)

where Ce is equilibrium concentration of C d2+ ions in solution, X is the maximum amount of Cd2+ absorbed per unit weight of absorbent, Xm is the maximum absorption

13

(2) where “b” is the Langmuir constant and Co is the initial concentration (mg/L). The RL values calculated for different initial concentration used during adsorption experiment at different temperature at pH 4 and 6 are listed in Table 3. As it clear from the Table 3 that at pH 4 the RL is ranging from 0.057 to 0.006 at 293 K, 0.048 to 0.005 at 303 K, 0.039 to 0.004 at 313 K and 0.032 to 0.003 at 323 K. Similarly RL values at pH 6 are ranging from 0.050 to 0.005 at 293 K, 0.0339 to 0.0035 at 303 K, 0.0332 to 0.0034 at 313 K and 0.030 to 0.0030 at 323 K. The RL decreases with increase in temperature of the system. The low RL values at pH 6 than 4 points towards the favorable adsorption.

RL = 1∕1 + bCo

Journal of Inorganic and Organometallic Polymers and Materials 4.0 3.5

y = 2.4552x + 1.5051(R² = 0.849) y = 2.5695x + 1.3024(R² = 0.853) y = 2.5704x + 1.0485(R² = 0.886) y = 2.6012x + 0.8732(R² = 0.899)

293 K 303 K 313 K 323 K

2.0

a

1.6

3.0

b

y = 1.4241x + 0.7521(R² = 0.855) y = 1.4607x + 0.5136 (R² = 0.894) y = 1.325x + 0.456 (R² = 0.902) y = 1.2004x + 0.383 (R² = 0.911)

1.4

Ce/X (L/g)

Ce/X (L/g)

293 K 303 K 313 K 323 K

1.8

2.5 2.0

1.2 1.0 0.8

1.5 0.6

1.0

0.4 0.2

0.5 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Ce (mmol/L)

Ce (mmol/L)

Fig. 5 Langmuir plots at a pH 4 and b pH 6

Table 3 RL values at pH 4 and 6 at different temperatures

Table 2 Langmuir parameters at different pH and temperatures pH

4

6

Temperature (K)

Langmuir parameters X m (mmol/g)

K b (L/g)

293 303 313 323 293 303 313 323

0.357 0.355 0.359 0.359 0.702 0.684 0.754 0.833

1.631 1.973 2.451 2.978 1.893 2.844 2.905 3.134

Temperature (K)

pH 4

pH 6

R2

20

0.849 0.853 0.886 0.899 0.855 0.894 0.902 0.911

30

0.057 0.044 0.015 0.010 0.006 0.048 0.024 0.012 0.008 0.005 0.039 0.019 0.010 0.006 0.004 0.032 0.016 0.008 0.005 0.003

0.050 0.025 0.013 0.008 0.005 0.034 0.017 0.008 0.005 0.004 0.033 0.016 0.009 0.006 0.003 0.030 0.015 0.007 0.005 0.003

40

3.5 Adsorption Mechanism The adsorption mechanism of C d2+ ions on the surface of T iO2 nanoparticles was explore by using Eqs. 3 and 4. The possible adsorption mechanism of Cd2+ ions were extract from the number of hydrogen ions released to solution, calculated from the slope of straight line obtained by plotting log Kd versus log Xm − X and log Kd versus pHeq (Fig. 6) [18, 19]. The plot log Kd versus log Xm − X (Fig. 6 a and b) gives a straight line with slope “n” equal to the number of hydrogen released during the exchange reaction. At both pH, the n was found around 1 at low temperatures (393 and 303 K) while increased to 2 at high temperatures (313 and 323 K). Thus the exchange of surface H+ with Cd2+ ions is greatly affected with temperature. The greater values of n further suggests higher affinity of Cd2+ ions toward adsorbent.

log Kd = log K + n log Xm − X

(3)

log Kd = log Kex − npHeq

(4)

50

The adsorption of Cd2+ ions on surface of TiO2 nanoparticles, accompanied the changes in initial pH. It was due the adsorption of Cd2+ ions, H+ ions released to the aqueous solution case a decrease in p Heq. Thus a famous kurbatov equation (Eq. 4) was used to verify the adsorption mechanism suggested by Eq. 3 [2, 19]. The plot of log Kd versus pHeq shown in Fig. 6c, d, gives nearly same stoichiometric exchange ratio as that obtained from the log Kd versus log

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0.1

0.5 0.4

0.0

0.3

-0.1

0.2

log Kd

log Kd

a

293 K 303 K 313 K 323 K

0.2

-0.2

0.1

-0.3

0.0

-0.4

-0.1

-0.80

-0.75

-0.70

-0.65

-0.60

-0.55

-0.5

-0.50

b

293 K 303 K 313 K 323 K

-0.4

0.1

0.5

-0.2

-0.1

293K 303K 313K 323K

0.4

0.0

0.3

-0.1

0.2

logKd

logKd

c

293K 303K 313K 323K

0.2

-0.3

log Xm-X

log Xm-X

-0.2 -0.3

d

0.1 0.0

-0.4

-0.1

-0.5

-0.2 3.15

3.20

3.25

3.30

3.35

3.40

3.45

3.50

3.55

5.3

pHeq

5.4

5.5

5.6

5.7

5.8

pHeq

Fig. 6 Plots of K d versus X m − X and pHeq at pH 4 (a and c) and pH 6 (b and d)

Xm − X. The “n” values obtained from the plot of log Kd versus pHeq at both pH have same increasing pattern with temperature as given by the plot of log Kd versus log Xm − X. At high temperature the pHeq had more acidic values proposed greater number of H+ ions was released to solution. d2+ The proposed exchange mechanism between H + and C are given by the reactions as: At lower temperature

TiOH + Cd2+ → (TiO)Cd + 1H At higher temperature Ti(OH)2 + Cd2+ → (TiO2 )Cd + 2H iO 2 surface was The adsorption of C d 2+ ions onto T also confirmed by EDX analysis of the T iO 2 nanoparticles before and after adsorption. The EDX spectrum

13

(inset in Fig. 2) of TiO 2 nanoparticles after adsorption possess a sharp band around 3 keV, confirm the presence of the Cd in the samples. The uptake of C d 2+ ions was also investigated by FTIR analysis. The FTIR spectrum of TiO2 nanoparticles before and after adsorption shows different behavior (Fig. 7). A broad band at in the range of 3600–3400 cm−1 is due to the O–H stretching while the band at 1637 cm−1 was slightly shifted to wavenumber 1627 cm−1 after Cd2+ sorption. The bands at 1149 cm −1 is due to the presence of NO3−3 as Cd(NO3)3 was used as Cd source and the two bands at 1114 and 1074 cm −1 are shifted to 1080 and 1025 cm−1 are due to Ti–O–Cd complex formation [20, 21]. The intensity of these transmittance bands increases with increasing the initial Cd2+ ion concentration of electrolyte solution, suggesting the maximum adsorption of Cd2+ ions at high initial concentration.

Journal of Inorganic and Organometallic Polymers and Materials Table 4 Thermodynamic parameters at different pH and temperatures

100

pH

Thermodynamic parameters

4

99

60

% Transmittance

% Transmittance

80

40

20

96 93 90 87 84

Before Adsorbtion 60ppm 100ppm

0 4000

3500

3000

2500

6 Before Adsorbtion 60ppm 100ppm

1200 1150 1100 1050 1000

950

900

-1

Wave number (cm )

2000

1500

1000

Fig. 7 FTIR spectra of T iO2 nanoparticles before and after cadmium adsorption

3.6 Thermodynamic Study Thermodynamic parameters such as entropy (∆S°), enthalpy (∆H°) and Gibbs free energy (∆G°) are calculated by using the following Eqs. 5 and 6.

ΔS ΔH − R RT

∆H (KJ/mol)

∆S (J/K mol)

− 26,246.9 − 26,725.4 − 27,203.8 − 27,682.3 − 29,307.4 − 29,840.9 − 30,374.3 − 30,907.8

12.228

47.845

13.676

53.347

500

-1

Wave number (cm )

ln Kb =

∆G (KJ/mol)

(5)

ΔG = ΔH − TΔS (6) where ∆H° is change in enthalpy of the system, ∆S° is change in entropy and ∆G° is change in free energy. The plot of lnKb versus T −1 (K−1) for pH 4 and 6 are shown in Fig. 8 and the values for thermodynamic parameters are summarized in Table 4. The ∆H° value was positive at both

pH, showed that the reaction was endothermic in nature [22]. The higher ∆H° value at pH 4 than pH 6, suggested that the system at pH 6 was more endothermic. It was suggested that the Cd2+ were first hydrated in aqueous solution and then dehydrated before adsorption. The positive ∆S° showed affinity of absorbent (TiO2) toward adsorbate (Cd2+ ions) [22, 23]. The higher value of ∆S° at pH 6, indicated that the affinity of adsorbent toward adsorbate are higher at pH 6 than pH 4. Similar positive ∆H° and ∆S° values were reported by Waseem et al. on by silica, iron hydroxide [24]. The spontaneity of the adsorption reaction was confirmed by the negative ∆G° values [25]. A decrease occur in the ∆G° with increase in temperature of the system, advocated that the reaction favored at high temperature as earlier study by Waseem and et al. while studying Cd(II) sorption of silica [19]. The small ∆G° values at pH 4 proposed that the adsorption process was more favor at pH 6.

Fig. 8 Plot of ln Kb versus T −1

1.4

ln Kb

1.2

1.0

0.8

0.6 0.0030

pH 4 y = -1470.8x + 5.7548 (R² = 0.781) pH 6 y = -1645x + 6.4166 (R² = 0.995) 0.0031

0.0032

0.0033

T

0.0034

0.0035

-1

13

4 Conclusions Anatase TiO2 nanoparticles are synthesized by chemical precipitation method by the reduction of titanium isopropoxide. The BET surface area was 156.9 m2/g with pore width 18.23 Å and pore volume was 0.071 cm3/g. the crystallite size calculated from XRD was 8.1 nm and SEM shows that particles are in the range of 32.14–42.86 nm. The composition and purity of nanoparticles was of T iO2 was confirmed by EDX while the band gap 3.30 eV are slightly greater than the previously reported. The adsorption of C d2+ ions were increases with increasing temperature, pH and initial concentration however % adsorption decreases may be due to adsorbate–adsorbate interaction. Langmuir model is applicable to adsorption data with (r2= 0.85–0.90 at pH 4 and 0.86–0.91 at pH 6). The values for thermodynamic parameters suggest that the adsorption process is spontaneous and endothermic in nature. The H+ and Cd2+ ions exchanged mechanism is varies with pH and temperature. At low temperatures the exchange ratio was 1:1 while reached to 2:1 at higher temperature, suggesting that temperature has a pronounced effect in shifting the exchange mechanism. Furthermore, it has been shown that pH 6 is more suitable for the efficient adsorption of Cd2+ ions onto TiO2 nanoparticles.

References 1. R. Kumar, J. Chawla, Water Qual. Expo. Health 5, 215 (2014) 2. S. Haq, W. Rehman, M. Waseem, M. Shahid, M.U. Rehman, K.H. Shah, M. Nawaz, Mater. Res. Express 3, 1 (2016) 3. B.A. Fowler, Toxicol. Appl. Pharmacol. 238, 294 (2009) 4. S. Madala, S.K. Nadavala, S. Vudagandla, V.M. Boddu, K. Abburi, Arab. J. Chem. 10, S1883 (2017)

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Journal of Inorganic and Organometallic Polymers and Materials 5. M. Waseem, S.T. Muntha, M. Nawaz, W. Rehman, M.A. Rehman, K.H. Shah, Mater. Res. Express 4, 015017 (2017) 6. U. Garg, M.P. Kaur, G.K. Jawa, D. Sud, V.K. Garg, J. Hazard. Mater. 154, 1149–1157 (2008) 7. V.K. Gupta, P.J.M. Carrott, M.M.L. Ribeiro Carrott, Suhas, Crit. Rev. Environ. Sci. Technol. 39, 783 (2009) 8. N.B. Hartmann, S. Legros, F. Von der Kammer, T. Hofmann, A. Baun, Aquat. Toxicol. 118–119, 1 (2012) 9. Y. Gao, R. Wahi, A.T. Kan, J.C. Falkner, V.L. Colvin, M.B. Tomson, Langmuir 2004, 9585 (2004) 10. M. Hua, S. Zhang, B. Pan, W. Zhang, L. Lv, Q. Zhang, J. Hazard. Mater. 211–212, 317 (2012) 11. X. Zhao, L. Lv, B. Pan, W. Zhang, S. Zhang, Q. Zhang, Chem. Eng. J. 170, 381 (2011) 12. M. Králik, A. Biffis, J. Mol. Catal. A 177, 113 (2001) 13. K.E. Levine, R.A. Fernando, M. Lang, A. Essader, B.A. Wong, Anal. Lett. 36, 563 (2003) 14. S. Mahata, S.S. Mahato, M.M. Nandi, B. Mondal, AIP Conf. Proc. 1461, 225 (2011) 15. S. Haq, W. Rehman, M. Waseem, M. Shahid, K.H. Shah, M. Nawaz, Mater. Res. Express 3, 105019 (2016) 16. C. Wang, B.Q. Xu, X. Wang, J. Zhao, J. Solid State Chem. 178, 3500 (2005) 17. K.H. Shah, S. Mustafa, M. Waseem, A. Naeem, J. Iran. Chem. Soc. 9, 895 (2012) 18. M. Ur Rehman, W. Rehman, M. Waseem, S. Haq, K.H. Shah, P. Kang, Mater. Res. Express 5, 025512 (2018) 19. M. Waseem, S. Mustafa, A. Naeem, K.H. Shah, I. Shah, Chem. Eng. J. 169, 78 (2011) 20. S. Mustafa, M. Waseem, A. Naeem, K.H. Shah, T. Ahmad, S.Y. Hussain, Chem. Eng. J. 157, 18 (2010) 21. M. Waseem, S. Mustafa, K.H. Shah, A. Naeem, S.S. Shah, K. Mehmood, S.U. Din, Sep. Purif. Technol. 107, 238 (2013) 22. M. Waseem, S. Mustafa, A. Naeem, G.J.M. Koper, K.H. Shah, Desalination 277, 221 (2011) 23. R.S. Juang, J.Y. Chung, J. Colloid Interface Sci. 275, 53 (2004) 24. S. Mustafa, M. Waseem, A. Naeem, K.H. Shah, T. Ahmad, Desalination 255, 148 (2010) 25. T.K. Naiya, A.K. Bhattacharya, S.K. Das, J. Colloid Interface Sci. 333, 14 (2009)