Fabrication of TitaniumâTin Oxide Nanocomposite ... - ACS Publications

Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Fabrication of Titanium−Tin Oxide Nanocomposite with Enhanced Adsorption and Antimicrobial Applications Mahfooz-ur-Rehman,† Wajid Rehman,*,† Muhammad Waseem,‡ Babar Ali Shah,§ Muhammad Shakeel,*,∥ Sirajul Haq,⊥ Umber Zaman,# Irum Bibi,† and Hashmat Daud Khan∥ †

Department of Chemistry, HAZARA University, Mansehra 21120, KPK, Pakistan Department of Physics, COMSATS Institute of Information Technology, Islamabad 44000, Pakistan § Riphah International University, Islamabad 44000, Pakistan ∥ State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, P. R. China ⊥ Department of Chemistry, Azad Jammu and Kashmir University, Muzaffarabad 13100, Azad Kashmir, Pakistan # Institute of Chemical Sciences, Gomal University, D.I. Khan 29050, KPK, Pakistan

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‡

S Supporting Information *

ABSTRACT: The binary nanocomposite (BNC) was synthesized by using SnCl2·5H2O and C12H28O4Ti precursors and characterized by Brunauer− Emmett−Teller analysis, X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, Fouriertransform infrared spectroscopy, and transmission electron microscopy. The characterization results confirm the successful synthesis of binary nanocomposite with size of about 15 nm. The synthesized binary nanocomposite (BNC) was evaluated for lead ions (Pb2+) removal from aqueous solution and antimicrobial activities. The maximum adsorption capacities of 68.36, 68.81, and 70.01 mgg−1 of lead (Pb2+) ions were detected at 293, 303, and 313 K, respectively. Both the Langmuir and Freundlich models were applied to the adsorption data, and the high regression value (R2) suggests that the Langmuir model describes the adsorption data better than the Freundlich model. The qm and Kb values revealed that the binary nanocomposite exhibits good adsorption capacity for lead (Pb2+) ions. Moreover, it was also observed that the binary nanocomposite bears good antimicrobial activities against selected stains.

1. INTRODUCTION A large amount of contaminated industrial and household wastewater containing heavy metals like Cd, Cr, Cu, Ni, As, Pb, and Zn is discharged into the ecosystem. All of these metals are considered as hazardous due to their high solubility and nonbiodegradable nature. These heavy metals enter the food chain and are easily absorbed by and accumulated in the human body. When their concentration exceeds the permissible limit, heavy metals can cause serious health problems.1 Among these toxic metals, lead is considered as a very toxic pollutant introduced in the natural water system from a variety of industrial wastewater sources.2 Water pollution especially due to lead contamination is considered as a serious global concern. It is fatal for animals and human beings, causing serious damage to the kidneys, reproductive system, liver, and brain function. The symptoms of lead toxicity include headache, dizziness, muscle weakness, renal damage, and anemia.3 The main source of lead exposure to human is coal combustion, lead mining, smelting, leaded gasoline, lead-based paints, and use of lead pipes in water supply system. Therefore, it is very important to develop a system to remove lead and other heavy metals before disposal. Various techniques are being used for the removal of heavy metals from © XXXX American Chemical Society

effluents, including ion exchange, chemical precipitation, filtration, and reverse osmosis. These techniques have some serious disadvantages like incomplete removal, high energy requirement, high cost, and membrane scaling.4 Recently, various approaches have been utilized for the development of cheaper and effective methods to remove the contaminant from aqueous system. Among these methods, nanoadsorption is considered as a promising approach to remove heavy metals by using low-cost adsorbents.5 The unique properties of nanomaterials provide opportunities for the removal of toxic metals from contaminated water system. In the literature, various nanoparticles have been reported to be used for heavymetal removal from aqueous system.6−8 Among these nanoparticles, TiO2 nanoparticles were utilized to remove contaminants from water.9,10 Li et al.11 compared the adsorption of lead ion using TiO2 nanoparticles and TiO2/ cellulose fiber nanocomposites and found that hybrid material adsorbed 371.0 mgg−1 compared to TiO2, which adsorbed 20 mgg−1. These studies show that TiO2 and its composites are Received: December 23, 2018 Accepted: April 4, 2019

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DOI: 10.1021/acs.jced.8b01243 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

spectroscopy model INCA 200 (U.K.) at 20 keV. The morphology of the prepared BNC was determined by transmission electron microscopy (TEM) by using TEM Model Hitachi TEM HT7700. The specific surface area was measured by Quantachrome Quarasol SI using the nitrogen adsorption method. The thermal analysis of the sample was performed in TG/DTA analyzer PerkinElmer model 6300. Fourier transform infrared (FTIR) spectra were recorded in Shimadzu FTIR spectrophotometer model IR Affinity-1S. The equilibrium concentration of lead ions was determined by atomic absorption spectrometer PerkinElmer model AAS 800 (flame mode) with acetylene as a carrier gas. The XPS technique was used to explore the mechanism of reaction. 2.4. Adsorption of Pb2+ Ions on BNC. The working solutions of Pb2+ ions were prepared by dissolving the calculated amount of Pb(NO3)2 in DI water at different Pb2+ ion concentrations (5−200 mg L−1). The adsorption study was performed at pH 5 and at different temperatures, 293, 303, and 313 K, by varying the initial concentration of Pb2+ ions from 5 to 200 mg L−1. For each measurement, 50 mg of BNC adsorbent was taken in a flask containing 50 mL of lead ion solution and shaken in a rotary shaker at 200 rpm for 3 h at constant temperature. After equilibration time, the final pH of suspension was recorded and the filtrate was tested for Pb2+ ions on an atomic absorption spectrometer. 2.5. Antimicrobial Study. In our study, we focused on determining the antimicrobial activities of common bacterial and fungal species that cause diseases. These species include Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, and Trichophyton rubrum. S. aureus is a Gram-positive bacterium present in normal body flora, while P. aeruginosa is a Gram-negative bacterium mostly found inside living body. Both are common microorganisms responsible for diseases in plants and animals, including human beings. C. albicans is commonly found in human gut flora (gastrointestinal tract) and reproduces inside the human body. This is responsible for candidiasis developed in mouth or throat. T. rubrum is a dermatophytic fungus mostly found in the upper layer of dead skin and is responsible for fungal infections of nail and athlete foot. Antibacterial activities were determined by the well diffusion method. Mueller−Hinton agar plates (150 mm) were prepared and preincubated for 24 h at 35 °C (±2 °C) to confirm sterility. The pure cultures of microorganisms were subcultured in a Mueller−Hinton broth. The subculture was applied to preincubated plates by uniformly streaking on the plates with sterile swab. The plates were kept for 10 min so that the culture gets adsorbed. After that, 8 mm wells were produced into the plates where solvent blank and suspension of nanomaterial (≈100 μL) were poured by using a micropipette. The suspension of nanomaterials was prepared in dimethyl sulfoxide, which is further diluted in distilled water (solvent blank). A suspension of different concentrations of nanomaterials was added to wells by using a micropipette. The plates were incubated for 24 h at 35 ± 2 °C and zones were measured. Solvent blank was used as negative control, and ceftriaxone and clotrimazole were used as antibacterial and antifungal positive controls, respectively.

capable to adsorb lead ions. SnO2 is an n-type semiconductor with a wide band gap of 3.6 eV. It is reported to be used for removal of toxic dyes, as a catalyst for the oxidation of organic compounds, and as a gas sensor.12 Considering these properties, it is expected that it will serve the purpose. Similarly, the existence of microbial resistance to antibiotics in human and plants is due to the extensive use of drugs.13 To deal with this matter of serious concern, there is a great demand for novel antimicrobial agents to control microbial infections. Various techniques are being used for the fabrication of nanoparticles like sol gel, spray pyrolysis, hydrothermal, microwave-assisted, and chemical precipitation methods. Among the different methods, chemical precipitation is preferred due to its simplicity and high yield.14 Very limited literature is available for the selection and coupling of SnO2 and TiO2 nanoparticles with other metal oxides for the adsorption of heavy metals and as microbial agent. It is expected that these nanocomposite have enhanced the adsorption capability and antimicrobial activity compared to their counterparts. Moreover, both these oxides are nontoxic, inexpensive, and chemically very stable. It was reported that activities are enhanced due to the combination of different functional groups in a single compound.15,16 In present study, a novel binary nanocomposite (BNC) was fabricated by in situ coupling of TiO2 and SnO2 nanoparticles via the chemical precipitation method. The synthesized nanocomposite was used to explore the effect of coupling of nanoparticles for the adsorption of lead from aqueous medium and to investigate antimicrobial activities.

2. EXPERIMENTAL SECTION 2.1. Chemicals. Analytical grade chemicals, including tin chloride, titanium isopropoxide, ammonium hydroxide, nheptane, hydrochloric acid, sodium hydroxide, ethanol, dioctyl sodium sulfosuccinate (SDS), Tween 80, lead nitrate, nitric acid, and Mueller−Hinton agar, were purchased from Merck. All of the solutions were prepared in deionized (DI) water, and for pH adjustment, nitric acid (0.1 M) and sodium hydroxide (0.1 M) solutions were used. 2.2. Synthesis of TiO2−SnO2 Binary Nanocomposite (BNC). For the synthesis of TiO2−SnO2 binary nanocomposite, 0.1 M solution of tin(II) chloride was prepared in deionized water and 20 mL of titanium isopropoxide was mixed with 20 mL of methanol. To prepare microemulsion, a mixture of 100 mL of n-heptane, 3 mL of deionized water, 6 g of dioctyl sodium sulfosuccinate, 12 mL of Tween 80, and 20 mL of ethanol was taken in a prewashed 500 mL pyrex reactor and mixed vigorously for 30 min to form a stable microemulsion. First, the precursor solution of tin(II) chloride was added to the microemulsion and stirred for 30 min, followed by a slow addition of prepared solution of titanium isopropoxide and agitated for further 30 min at 600 rpm. After adding 6% ammonia solution dropwise, the appearance of off-white precipitates confirms the completion of reaction, which was then cooled and aged for 24 h. The obtained precipitates of BNC were centrifuged at 5000 rpm and washed with water followed by methanol. The final product was dried at 105 °C, meshed, and stored in a polymeric bottle. 2.3. Characterization of BNC. X-ray diffraction (XRD) analysis was performed by utilizing Panalytical X’Pert Pro with copper (1.54 Å) as the X-ray generation source. The respective voltage and current were 40 kV and 30 mA. The elemental percentage was determined by energy-dispersive X-ray (EDX)

3. RESULTS AND DISCUSSION 3.1. Characterization of the Material. 3.1.1. XRD Measurements of BNC. The XRD pattern of synthesized B



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BNC (Figure 1) shows the diffraction bands at 2θ = 27.21, 35.01, 53.06, and 67.26° with corresponding hkl planes 400,

Figure 3. TEM images of BNC before (a) and after (b) Pb2+ ion adsorption.

nanoparticles and appeared as dark images with little increase in size due to deposition of Pb2+ ions compared to bare BNC. It is clearly indicated from the TEM images that lead is properly loaded onto the nanoparticles. Similar kinds of TEM images were produced by Bagbi et al. (2016)21 while studying lead adsorption on magnetite nanoparticles. Results of TEM imaging are in complete agreement with the results of FTIR spectroscopy after adsorption of lead clearly shows its deposition on the NPs surface (Figure 3b). 3.1.4. EDX Analysis. The weight percentage and atomic percentage were determined by analyzing EDX spectrum. The EDX spectrum (Figure 4) of TiO2−SnO2 exhibits peaks at 0.2,

Figure 1. X-ray diffraction pattern of BNC.

511, 800, and 844. The diffraction peaks obtained for BNC were in good agreement with standard reference card 01-0891832, which suggests the cubic geometrical shape for the synthesized BNC NPs. The average crystallite size calculated by the Debye−Scherrer formula (eq 1) was 34.57 nm Dp = Kλ /β cos θ

(1)

where Dp is the particle size in Å, K is a constant related to the Miller index of crystallographic planes (assigned a value of 0.95), λ is the wavelength of Cu Kα radiation (1.54 Å), β is the full width at half-maximum, and θ is the Bragg angle. 3.1.2. FTIR Spectroscopy. The FTIR spectrum of the BNC in the range of 4000−400 cm−1 is shown in Figure 2 as inset,

Figure 4. EDX spectra of BNC. Figure 2. FTIR spectra of BNC before and after adsorption of Pb2+ ions. Full-scan FTIR spectra of BNC before adsorption (inset).

3.2, and 4.2 keV for O, Sn, and Ti, respectively. The weight percentages found in the sample for O, Sn, and Ti are 36.56, 44.75, and 18.22 wt %, respectively. From the spectrum, it is evident that no other peak corresponding to impurities was detected, which indicates high purity of the synthesized nanoparticles. 3.1.5. Surface Area Measurements. The surface area of BNC was found to be 138 m2 g−1, with the average pore volume and pore radius of 0.192 cm3 g−1 and 25.05 Å, respectively. The value of surface area in the present study is higher than that reported by Beheshti and Irani while studying the removal of Pb2+ ions from aqueous solutions using diatomite nanoparticles.22 The reason for the high surface area is the coupling of TiO2 and SnO2 as reported earlier.23 Moreover, the high surface area of the composite can be associated to the smaller size of its counterparts. 3.1.6. Thermogravimetric Analysis (TG) of BNC. The thermogram of BNC is shown in Figure 5. The TG curve shows the first steady and sharp weight loss of 3.58% at 100.44 °C, which can be associated with the removal of physisorbed and chemisorbed water molecules, while the second gradual

which exhibits peaks in the region of 400−680 and 1254 cm−1. The presence of peaks in this region is due to bridged Sn−O− Sn, Ti−O−Ti, and Ti−O−Sn bonds of titanium and tin oxides.17 The peak at 732 cm−1 is due to the presence of O− Ti−O bonding.18 In the FTIR spectra, the broad band observed at 3348−3195 cm−1 is assigned to the stretching vibration of water molecule, while the small peak at about 1609 cm−1 is due to the vibration of the OH group.19 The FTIR spectra of Pb2+ ion-loaded nanoparticles are shown in Figure 2. The appearance of a new peak at 895 cm−1 in the FTIR spectrum confirms the presence of lead (M−O−Pb) on the surface of the nanoparticles.20 3.1.3. TEM Images. TEM images of BNC before and after Pb2+ ion adsorption are shown in Figure 3. From the TEM image in Figure 3a, it is evident that the size of BNC is 15 nm (±2), showing monodispersed appearance with slight variations in shape with distant boundaries. From the TEM image of BNC after Pb2+ ion adsorption (Figure 3b), it is clear that Pb2+ ions are uniformly distributed on the surface of the C



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q = (Co − Ce)

V M 1000

(2)

where q is the adsorption capacity in mgg−1, Co and Ce are the initial and equilibrium concentrations of Pb2+ ion, respectively, V is the volume (mL), and M is the mass of the absorbents. The results of Pb2+ ions adsorbed are reported in Table 1. From the adsorption data, it is evident that there is a slight increase in adsorption with temperature. However, it is also concluded that with increase in the concentration of Pb2+ ions in solution, percent adsorption decreases, due to the saturation of the adsorption sites on the adsorbent. 3.2.3. Mechanism for Pb2+ Ion Adsorption. Equation 3 was applied to the adsorption data and XPS analysis was performed to extract the sorption mechanism of Pb2+ ions onto BNC surface. The values of log Kd were plotted against log qm − q, and the n values obtained from the slope of the straight line, as

Figure 5. TG curve of BNC.

weight loss of 4.58% at 488.79 °C may be associated with the decomposition of organic groups present in the surfactant molecules.24 3.2. Optimization of Experimental Conditions for Sorption of Pb2+ Ion on BNC. 3.2.1. Selection of pH, Concentrations, Temperature, and Adsorbent Dose. The pH value of media plays an important role in the adsorption process.25 We have optimized our experimental conditions at pH 5 by considering various studies of researchers regarding the effect of pH on lead adsorption. Moradi et al. studied the impact of pH on lead adsorption and reported that in acidic pH, the H+ ions compete with the Pb2+ ions to reach the functional group of nanocomposites, resulting in low adoption of Pb2+ ions.26 It is reported that at higher pH, Pb precipitation takes place and lowers the availability of Pb contents in aqueous medium. Under basic conditions, when lead is electrically neutral and has poor solubility in the form of [Pb(OH)2]°, precipitation predominates.27 At pH 5, the amount of lead ion sorption increases due to decreased competition between hydrogen ions and metal ions. Rajput studied that at pH 5, lead removal remained constant.20 Further, Jin and Gao reported maximum adsorption of lead on TiO2 nanoparticles at pH 5.28 The working solutions of Pb2+ ions were prepared by dissolving the calculated amount of Pb(NO3)2 in deionized water at different Pb2+ ion concentrations (5−200 mg L−1). The adsorption study was performed at different temperatures, 293, 303, and 313 K, by varying the initial concentration of Pb2+ ions from 5 to 200 mg L−1. For each measurement, 50 mg of BNC adsorbent was taken in a flask containing 50 mL of lead ions solution and was shaken in rotary shaker at 200 rpm for 3 h at constant temperature. After equilibration time, the final pH of the suspension was recorded and the filtrate was tested for Pb2+ ions on an atomic absorption spectrophotometer. 3.2.2. Batch Studies. A batch adsorption experiment was conducted to calculate the amount of metal ion adsorbed onto BNC. The amount of metal ions adsorbed onto the adsorbent was calculated by the following equation

Figure 6. Plot of log qm − q versus log Kd.

shown in Figure 6, represent the number of hydrogen ions released to solution as a result of Pb2+ ion adsorption log Kd = log K + n log⌈qm − q⌉

(3)

where Kd refers to the distribution coefficient, K is the exchange constant, and n represents the H+/Mz+ stoichiometry of an ion-exchange reaction. The n values in the present study were close to unity, which shows 1:1 exchange ratio between H+ and Pb2+ ions according to the following reaction, where R represents the adsorption sites. RH + PbOH+ F RPbOH + H+

(4)

It was noted that the uptake of Pb2+ ions resulted in a decrease in equilibrium pH of the solution from 5.00 to 4.75. The decrease in the pH value confirms the release of H+ ions into the solution during the sorption process. 3.2.3.1. XPS Analysis. Wide-range XPS images (survey scans) of TiO2−SnO2 before and after Pb2+ ion adsorption are shown in Figure 7a,b. The survey scans demonstrate the presence of all expected elements, and the presence of Pb confirms the adsorption of Pb2+ ions onto the surface of binary NPs. To get detailed information about the oxidation state of

Table 1. Langmuir and Freundlich Parameters for the Adsorption of Lead Ions by BNC Langmuir parameters −1

Freundlich constants −1

2

temp. (K)

qm (mgg )

Kb (L g )

R

293 303 313

68.36 68.81 70.07

10.56 10.98 11.20

0.990 0.993 0.995 D

dimensionless constant 2

1/n

Kf

R

2.62 2.74 3.22

1.23 1.66 1.78

0.951 0.948 0.946

RL 0.0185−0.0005 0.0178−0.0005 0.0175−0.0005 DOI: 10.1021/acs.jced.8b01243 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


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site of Sn and Ti. The Pb 4f doublet consists of Pb 4f7/2 (138.45 eV) and Pb 4f5/2 (143.32 eV) peaks and confirms the presence of Pb in +2 state. Pb peaks at similar binding energies have already been observed elsewhere.31 Thus, from the XPS results, it can be concluded that the surface of nanoparticles is rich in hydroxyl group, which is responsible for lead adsorption on surface. 3.3. Isotherm Models. Langmuir and Freundlich models were used to explain the equilibrium data of the Pb2+ ion adsorption onto BNC. 3.3.1. Langmuir Model. The Langmuir equation (eq 5) was used to illustrate the relationship between the equilibrium concentration in the solution and the amount of metal ions sorbed

Figure 7. Wide-range survey spectra of TiO2−SnO2 BNC (a) before and (b) after Pb adsorption.

elements and the type of Pb adsorption (surface adsorption or bulk), narrow-range XPS images were obtained for TiO2− SnO2 and Pb for pure and Pb-adsorbed nanoparticles. The narrow-range XPS images of the Sn 3d region before and after Pb adsorption are shown in Figure 8a,b. The Sn 3d

Ce C 1 = + e q qmKb q

(5) −3

where Ce (mmol dm ) is the equilibrium concentration of metal ions in the solution, q (mmol g−1) is the amount of Pb2+ ion adsorbed per unit weight of the adsorbent, Kb (L g−1) is the binding energy constant, and qm (mmol g−1) is the maximum value of metal-ion adsorption per unit weight of adsorbent related to monolayer adsorption capacity of the adsorbent.32 The high regression value of 0.994 proposed that the Langmuir model fitted well to adsorption data (Figure 9a).

Figure 9. Adsorption isotherms for Pb2+ sorption: (a) Langmuir model (b) Freundlich model on BNC.

The values of qm and Kb are calculated from the slope and intercept. The adsorbent used in this study shows good adsorption capacity. The reason for this high capacity is the high surface area and small particle size. It is further concluded that adsorption is favored at high temperature and the adsorption process is endothermic in nature. El-Sayed reported that increase in Pb2+ ion adsorption with increase in temperature is expected due to the diffusion and increase in the surface area of the adsorbent, which ultimately results in an increase in the number of adsorption sites resulting from breaking of some internal bonds.33 A similar adsorption trend was reported while studying the removal of Pb2+ ions from aqueous solutions using diatomite nanoparticles.23 3.3.2. Freundlich Model. The Freundlich model is described by isotherm based on distribution of sorption sites and energies. The Freundlich equation is given below 1 log qe = log K f + × log Ce (6) n

Figure 8. Narrow-range spectra of lead ions before and after adsorption: (a, b) Sn 3d and (c, d) Ti 2p. Narrow-range spectrum of Pb 4f after adsorption on TiO2−SnO2 BNC (inset).

spectrum consists of a symmetrical doublet corresponding to Sn 3d5/2 (486.43 eV) and Sn 3d3/2 (494.86 eV), indicating that Sn is present in +4 state in SnO2.28,29 No shift in binding energies of Sn 3d spectrum has been observed for Pb-absorbed system. Narrow-range XPS images in the Ti 2p region before and after Pb adsorption are shown in Figure 8c,d, respectively. The Ti 2p spectrum consists of a Ti 2p3/2 (458.48 eV) and Ti 2p1/2 (464.27) doublet. The peaks are consistent with Ti in +4 states in TiO2 lattice.30 Moreover, another small peak at 459.53 eV may be corresponding to a fraction of Ti ions in +3 states. A similar spectrum in the Ti 2p region was observed for Pb-adsorbed samples without any notable shift in binding energies. The narrow-range scan in the Pb 4f region for Pb-adsorbed TiO2−SnO2 nanoparticle is shown in the inset of Figure 8d. As we noted, no shift in binding energies has been observed in Sn 3d and Ti 2p binary spectra after Pb adsorption. This confirms that Pb is only present on the surface and is not replacing any

where qe is the amount of lead species adsorbed at equilibrium in mgg−1, Ce is the solute equilibrium concentration in mg L−1, Kf and n are Freundlich constants, and Kf represents the quantity of ions adsorbed onto adsorbent at equilibrium concentration. It was observed that Kf varied from 1.23 to 1.78 E



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with increase in temperature, which represented that the adsorption quantity increased at higher temperature, indicating an increased adsorbent−adsorbate interaction, as shown in Figure 9b. The Kf values reported by Poursani et al.27 while studying TiO2 NPs for removal of lead shows a similar trend. A similar kind of trend in values was also reported by Mahapatra et al.34 The 1/n value describes the adsorption intensity, which ranged from 2.62 to 3.22, indicating cooperative adsorption.35 The low regression value (0.93) obtained in the Freundlich model is an indication that the Freundlich model did not fit well on the sorption data. The corresponding Langmuir and Freundlich model results are provided in Table 1. 3.4. Thermodynamics of the Sorption Process. Thermodynamic parameters like change in free energy ΔG°, enthalpy ΔH°, and entropy ΔS° that were associated with the adsorption process were calculated using the following equations log Kb =

ΔS ΔH − 2.303 R 2.303 RT

Table 2. Comparison of Maximum Adsorption Capacity with Other Nano Oxide Adsorbent qm (mgg−1)

references

Fe3O4 MnO2 CeO2 Fe2O3Al2O3 manganese oxide-coated zeolite DZ-SBA-15 GO-DPA TiO2−SnO2

29.0 0.030 9.2 23.75 60.09 30 360 70.07

49 50 51 32 52 53 54 present work

in millimeter (mm) and are presented in Table 3. A significant difference in the activity was seen with increasing concentration of the sample in the wells. It was observed that BNC was a good inhibitor of different bacterial and fungal species, while it was also noted that the activity was comparatively greater against Gram-positive bacteria than against Gramnegative bacterial and fungal species. This was due to the differences in the cell wall compositions of these microorganisms.43 Earlier studies also indicate that Gram-negative bacteria are less sensitive than Gram-positive bacteria. The mechanism for the inhibitory effect of BNC is not exactly known. However, it is believed that the BNC surface generates reactive oxygen species (ROS), which is converted to hydrogen peroxide that interacts with the cell membrane proteins and kills them.44 These ROS can include hydroxyl groups, superoxide anions, and hydrogen peroxide.45 Moreover, metal nanoparticles carry positive charge and microbes have a negative charge that results in attraction between microbes and nanoparticle. Ultimately, microbes get oxidized and die.46 The antibacterial properties of TiO2 nanoparticles reported by Matsunaga et al.47 are attributed to the high redox potential of the surface species resulting in oxidation of bacteria. Similar types of antibacterial activities were observed by Amininezhad et al.48 while evaluating the antibacterial properties of SnO2 NPs.

(7) (8)

ΔG° = ΔH − T ΔS

nanomaterial

−1

The positive value of ΔH (22.49 kJ mol ) indicates that the adsorption process was endothermic in nature, which is evident from the qm values that showed increase with increase in temperature. Therefore, high temperature is favored for adsorption of Pb2+ ions onto BNC. The positive ΔS (27.29 J mol−1 K−1) values described the affinity of nanoparticles toward Pb2+ ions, and it is also revealed that dehydration of Pb2+ ions takes place before adsorption.36−38 Similar positive values of ΔH and ΔS were reported by Pathak and Choppin et al.39 for Ni2+ adsorption on silica. The negative value of ΔG° (−10.2 to −11.6 kJ mol−1) suggests that the adsorption process is spontaneous and the decrease with increase in temperature indicates that the adsorption process is favorable at high temperature (Figure 10). The values of ΔG° reported by Waseem et al. are very close to our values.40 A similar decrease in the values of ΔG° was also reported by Xu et al.41 and Bhattacharya et al.42

4. CONCLUSIONS In the present study, BNC were successfully synthesized, characterized, and used for the removal of lead ions from aqueous solution and as antibacterial agent. The geometrical shape and crystallite size were confirmed by XRD, while the morphology of the NPs was determined by TEM analysis. The surface area measured by Brunauer−Emmett−Teller methods from the N2 adsorption method was found to be quite high, having potential for adsorption. Both the Langmuir and Freundlich models were applied, and the former model with high regression value fitted well with the adsorption equilibrium data. The adsorption of Pb2+ ions increased with increasing initial concentration, and the temperature of the electrolyte solution was due to the high surface area of the BNC. The increase of qm and Kb values with increasing temperature shows that the adsorption process was more favorable at high temperature. The qe and Kf values have similar increasing trends with increasing temperature, and it was proposed that the BNC has more adsorption potential at high temperature. The thermodynamic study indicates that the adsorption process was endothermic in nature and was more spontaneous at high temperature. The BNC possesses significant activity against both Gram-positive and Gramnegative bacteria, and its activity was higher against Gram-

Figure 10. Arrhenius plots for Pb2+ sorption on BNC.

3.5. Comparison with Other Adsorbents. The adsorption capacity of adsorbent under study is compared to that of other nanoadsorbents reported in the literature, and the results are presented in Table 2. The qm value obtained from the experimental data in our study is higher than other adsorbents. 3.6. Antimicrobial Activities. The antibacterial activities of BNC were examined against selected strains of bacteria shown in Figure 11, and the zone of inhibitions were measured F



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Figure 11. Zone of inhibition of BNC NPs for antimicrobial activities.

Notes

Table 3. Antimicrobial Activity of BNC NPs

The authors declare no competing financial interest.

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bacteria Gram +ve bacteria

Gram −ve bacteria

samples

S. aureus

P. aeruginosa

C. albican

Trichophytons

BNC-75 BNC-100 PC-20 NC

16 19 23 0

14 17 21 0

13 15 20 0

12 14 20 0

ACKNOWLEDGMENTS Dr. W.R. acknowledges Chinese Academy of Sciences for research support under President’s International Fellowship Initiative (2017VSB0001).

fungi

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(1) Babel, S.; Kurniawan, T. A. Cr (VI) removal from synthetic wastewater using coconut shell charcoal and commercial activated carbon modified with oxidizing agents and/or chitosan. Chemosphere 2004, 54, 951−967. (2) Dönmez, G.; Aksu, Z. Removal of chromium (VI) from saline wastewaters by Dunaliella species. Process Biochem. 2002, 38, 751− 762. (3) Naseem, R.; Tahir, S. Removal of Pb (II) from aqueous/acidic solutions by using bentonite as an adsorbent. Water Res. 2001, 35, 3982−3986. (4) Eccles, H. Treatment of metal-contaminated wastes: why select a biological process? Trends Biotechnol. 1999, 17, 462−465. (5) Leung, W. C.; Wong, M. F.; Chua, H.; Lo, W.; Yu, P.; Leung, C. Removal and recovery of heavy metals by bacteria isolated from activated sludge treating industrial effluents and municipal wastewater. Water Sci. Technol. 2000, 41, 233. (6) Savage, N.; Diallo, M. S. Nanomaterials and water purification: opportunities and challenges. J. Nanopart. Res. 2005, 7, 331−342. (7) Ponder, S. M.; Darab, J. G.; Mallouk, T. E. Remediation of Cr (VI) and Pb (II) aqueous solutions using supported, nanoscale zerovalent iron. Environ. Sci. Technol. 2000, 34, 2564−2569. (8) Diallo, M. S.; Christie, S.; Swaminathan, P.; Johnson, J. H.; Goddard, W. A. Dendrimer enhanced ultrafiltration. 1. Recovery of Cu (II) from aqueous solutions using PAMAM dendrimers with ethylene diamine core and terminal NH2 groups. Environ. Sci. Technol. 2005, 39, 1366−1377.

a

PC = positive control; NC = negative control; 20, 75, and 100 = weight (μg) of sample per mL.

positive bacteria compared to Gram-negative bacteria. Thus, it is concluded that the BNC reported in the present study can be used as an absorbent for easy, convenient, and efficient removal of Pb2+ ions from aqueous solution contaminated with Pb2+ ions and can be used as an antimicrobial agent.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b01243. Experimentally measured adsorption isotherm data obtained in this study (c vs q) (Tables S1−S3) (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (W.R.). *E-mail: [email protected] (M.S.). ORCID

Muhammad Shakeel: 0000-0002-0853-0749 G



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