Comparative Study of Single and Multiple Pollutants System Using Ti

Article pubs.acs.org/jced

Comparative Study of Single and Multiple Pollutants System Using Ti−Fe Chitosan LDH Adsorbent with High Performance in Wastewater Treatment Rehab Mahmoud,*,† Samah Abdel Moaty,‡ Fatma Mohamed,§ and Ahmed Farghali∥ †

Department of Chemistry, Faculty of Science, Beni-Suef University, 62511 Beni-Suef, Egypt Materials Science Lab, Chemistry Department, Faculty of Science, Beni-Suef University, 62511 Beni-Suef, Egypt § Polymer Research Lab, Department of Chemistry, Faculty of Science, Beni-Suef University, 62511 Beni-Suef, Egypt ∥ Materials Science and Nanotechnology Department, Faculty of Postgraduate Studies for Advanced Sciences, Beni-Suef University, 62511 Beni-Suef, Egypt ‡

ABSTRACT: Ti−Fe chitosan (LDH) nanoparticles with nitrate intercalated anions as a novel adsorbent were produced via milling technique. The synthesized LDH was characterized by XRD, FT-IR, BET surface area, zeta potential, FESEM, and HRTEM. The adsorption capability of novel catalyst was under study with regard to several pollutants in the wastewater (phosphate, cadmium, and benzoquinone) in single and multiple solutions. Ti−Fe chitosan LDH demonstrated high activity toward cadmium and benzoquinone and succeeded to remove 98% of both and 63% of phosphate in wastewater at pH = 8. However, in multiple solutions, the results reached 58, 95, and 82% removal of cadmium, benzoquinone, and phosphate, respectively, at the same pH. The kinetics and mechanism of adsorption strength over the adsorbent were further studied. Furthermore, the adsorption of cadmium was confirmed by potentiometric analysis. Astonishingly, the novel LDH indicates acceptable antimicrobial activities against some species of bacteria and fungi.

1. INTRODUCTION Environmental pollution triggered by wastewater from industrial waste materials is the main problem faced by the world nowadays. Industrialization, civilization, agricultural activities, and other environmental and global changes are basic sources of water pollution.1 Organic contaminants, oxyanions, and heavy metals are regarded as the representative contaminants in the environment. Benzoquinone is one of the most toxic organic pollutants, not to mention it is present in a wide variety of benzene derivatives in the course of their oxidative degradation.2 Based upon the received reports, the Cd 2+ ions are considered the main reason for water pollution. These pollutants interact with each other in the wastewater in some cases. Consequently, more toxic substances were produced and more serious ecological problems were generated, so, the removal of harmful pollutants is of great interest and importance.3 Despite availability of many physical techniques, such as electrodialysis, crystallization, reverse osmosis, etc, the problem is still exacerbating. Despite the fact that the chemical precipitation method is still of evident effect, it generates problems for sludge handling and disposal because of chemical treatment, in addition to the fact that such techniques are high cost.4 Many researchers have executed the removal of harmful ions from wastewater using various adsorbents.5,6 Layered double hydroxides (LDH) have gained attention due to being © XXXX American Chemical Society

an alternative high capacity and low cost adsorption material for harmful pollutants. Many researchers studied the growth of E. coli, S. cerevisiae, and B. subtilis in the existence of the LDH materials containing TiO2 nanoparticles. The results affirmed there was an enhancement in the antibacterial effect, with the inhibiting bacteria growth of 80% (S. cerevisiae), 22% (S. aureus), and 81% (E. coli), respectively. Chitosan has shown the possibility to adsorb big amounts of metal ions. This, in turn, has resulted in much interest in ascertaining its potential to remove metal ions over a large range of sewage systems and types. Literatures have come out to date regarding the capability of chitosan to adsorb cations from solutions. Initially a review of the isotherms used for study is presented; and the adsorption capacities for various metal ions are briefed.7−11 Our present work studied removal for Cd2+ ion, phosphate, and benzoquinone in single and multiple contaminants system for the first time by using Ti−Fe chitosan LDH. In the present work, we synthesized and characterized Ti−Fe chitosan-layered double hydroxide composites as a novel Received: May 18, 2017 Accepted: September 21, 2017

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DOI: 10.1021/acs.jced.7b00453 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Figure 1. EDAX of Ti−Fe Chitosan layered double hydroxide.

adsorbent and checked their efficiency in competitive adsorbing phosphate, cadmium, and benzoquinone in single and multiple solutions. Investigations of the kinetics and adsorption isotherms at equilibrium of different pollutants on the Ti−Fe chitosan LDH were checked. Furthermore, the adsorption of Ti−Fe chitosan LDH for Cd2+ removals was confirmed potentiometrically; to perform accurate evaluation of the dissociation constants of chitosan which is important to understand its association and complexation reaction with Cd2+. Consequently, the equilibrium investigation of chitosan and its complex formation were carried out in aqueous solution at 298 K and 0.1 mol L−1 NaNO3. Finally, there was an investigation of the antimicrobial activity of LDH against various types of microorganisms.

Table 1. Ball Milling Conditions for Preparing Ti−Fe Chitosan DH condition

description

vessel size balls diameters materials of vessels materials of balls ball/precipitate mass ratio speed time

7.5 cm diameter ranged from 1.11 to 1.75 cm diameter stainl steel porclien 8:1 mass ratio 300 rpm 10 h

washed with distilled water completely, and dried at 80 °C for 24 h. 2.3. Batch Adsorption of Pollutants (Cadmium, Phosphate, and Benzoquinone) in Single and Multiple Contaminates System Solutions. All experiments to investigate the adsorption (single and multiple contaminants system solutions) of Cd2+, PO43−, and benzoquinone onto Ti−Fe chitosan LDH adsorbent were carried out. The adsorption of different pollutants was investigated by mixing the Ti−Fe chitosan LDH and each Cd2+, PO43−, and benzoquinone single solution. On the other hand, multiple contaminants system solutions were carried out by mixing all ions with concentrations 25, 20, and 20 mg/L for cadmium, phosphate, and benzoquinone, respectively, and added to the certain amount of adsorbent. The orbital shaker with speed of 200 rpm at room temperature was used for shaking the prepared samples were shaken with an orbital shaker at a shaking speed of 200 rpm at room temperature for 24 h. The precipitates were separated by filtration through 0.22 μm filter paper. The remaining concentration of the cadmium, phosphate ions, and benzoquinone

2. EXPERIMENTAL SECTION 2.1. Materials. Ti−Fe chitosan LDH were prepared using iron nitrate (Fe(NO 3 ) 3 ·9H 2 O), titanium isopropoxide (C12H28O4Ti), sodium hydroxide (NaOH), hydrochloric acid (HCl), chitosan with low molecular weight (161.61), and acetic acid (CH3COOH) as starting chemicals. All used chemicals were of analytical reagent grade and not further purified. Further more, all solutions used during the experiments were prepared freshly in ultrapure water obtained from a NANO Pure-ultrapure water system. 2.2. Synthesis of Ti−Fe Chitosan LDH. A solution of titanium isopropoxide was mixed with solution of iron nitrate and solution of chitosan (with percentages of 3:4:2 molar ratio, respectively, as shown in Figure 1), then sodium hydroxide solution (8 mol L−1) was added and the resulting solution was put into milling vessel, then it was allowed to mill for 10 h as shown in Table 1. The precipitate was collected by filtration, B



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(ATCC 27853) were used as Gram-negative bacteria. Aspegillus f locculosus (ATCC 13697) and Aspegillus nigricans (ATCC 10535) were examples of fungi. All different species were bought and obtained from Cairo Microbiology Research Center. All tubes were exposed to sterilization in an autoclave before conducting the experiments. Muller Hinton broth was utilized to culture E. coli, S. aureus, St.coccus, and P. aeruginosa at 37 °C for 24 h in an incubator. The liquid cultures were finally diluted; to obtain bacterial cell concentration of approximately 107 colony forming units (CFU)/ml for the following antibacterial test. 2.5.3. Minimal Inhibitory Concentration (MIC) Measurement. The MIC was deemed as the lowest concentration of

before and after adsorption were measured by atomic absorption spectrometry (Agilent Tecnologies 200 Series AA), UV spectrophotometer (UV-2600 UV−vis SPECTROPHOTOMETER), and HPLC (Agilent Technologies 1260 Infinity), respectively. In present work, various factors were utilized to optimize % removal ability of chitosan LDH, such as pH (2−10), concentration of Ti−Fe chitosan LDH (0.025−0.1 g/L), and effect of time (from 1 to 24 h). All experiments were done three times; to ascertain of their reproducibility, and the average of concentration was determined using SPSS version 16. Means and standard deviation (±SD) values were computed and P values less than 0.05 were considered as statistically significant values. The adsorption efficiency of pollutant ions onto the Ti−Fe chitosan LDH were calculated according to the following eq 1):

Q=

(Co − C t) x100 Co

(1)

Where Q is the adsorptivity (%), Co is regarded as the initial concentration of pollutants ion, and Ct is the concentration of ions in (mg/L) after adsorption at time t (min). The amount of pollutants ions adsorption at equilibrium qe (mg/g) was calculated through eq 2:

qe =

V (Co − Ce) W

(2)

It is clear that in the equation, the equilibrium adsorption capacity of adsorbent in mg·(pollutant)/g·(adsorbent) is represented by qe, while Co stands for the initial concentration of pollutants ions before adsorption in mg/L, and Ce is the equilibrium concentration of pollutants ions in mg/L. The pollutants solution volume in liters is represented by V, and W stands for the adsorbent weight in gram. 2.4. Characterization. The crystallite structure of Ti−Fe chitosan LDH before and after adsorption was recorded by PANalytical (Empyrean) X-ray diffraction. FT-IR spectra of the novel adsorbent before and after adsorption were measured by Bruker (Vertex 70 FTIR-FT Raman) spectrometer. The surface morphology of the Ti−Fe chitosan LDH was analyzed by field emission scanning electron microscopy FESEM (Gemini, Zeiss-Ultra 55, field emission high-resolution scanning electron microscope).Transmission electron microscope images were taken by JEOL-JEM 2100 (Japan). EDAX, was taken by (Quanta FEG250). BET surface area was determined from adsorption isotherms using a Quanta chrome NOVA automated gas sorption system. The stability of the suspensions of Ti−Fe chitosan LDH were examined using zeta potential on a Malvern (Malvern Instruments Ltd.) at different pH values. 2.5. Antimicrobial Activity. 2.5.1. Isolation of Bacterial Pathogens and Biochemical. E. coli strain was grown on its selective media MacConkey agar media (Oxoid; CM 0115) and Eosin Methylene Blue agar (EMB; Oxoid; CM 69) plates; whereas the other strains (Staphylococcus and Streptococcus) were determined on agar plates (Gram stain and colony morphology). The plates were exposed to incubation at 37 °C for 48 h and growth of bacteria was under observation for all of the isolates.12 Standard Kits (Biomerieux, Marcy L’etoil, France) API had been used for both physiological and biochemical identification of each bacterial isolates of both Gram-positive and -negative bacteria. 2.5.2. Test Species. The used test organisms were St. coccus (ATCC 25913), S. aureus (ATCC 49619) as examples of Gram-positive bacteria. E. coli (ATCC 25922), P. aeruginosa

Figure 2. XRD patterns of Ti−Fe Chitosan LDH, ICDD cards no 04-011-5537 for titanium, no 00-034-1266 for iron, and no 00-054-1953 for chitosan. C



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Figure 3. (a),(b) HRTEM of Ti−Fe chitosan layered double hydroxide. (c),(d) FESEM of Ti−Fe chitosan layered double hydroxide.

Figure 4. (a) Zeta potential. (b), (c), (d) Zeta average size at different pH of Ti−Fe chitosan LDH nanoparticle suspension. D



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Figure 5. (a) N2 sorption isotherms and (b) pore size distribution of Ti−Fe chitosan LDH.

Ti−Fe chitosan LDH where the growth of microorganisms was completely inhibited for 24 h, using broth dilution method according to Clinical Laboratory Standards Institute (CLSI).4 Bacterial strains were grown overnight using MHA plates at 37 °C before being in use. The antimicrobial activity of Ti−FeLDH nanoparticles was checked by the standard broth dilution method.13 With regard to each sample, different concentrations were exposed to dilution using Muller Hinton broth; with the aim of providing a final concentration ranging from 1000 to 6.25 μg/mL. Because there is both positive and negative control tube, the isolated bacteria was subcultured on Muller Hinton Agar (M.H.A) and exposed to incubation at 37 °C for 24 h.14 Colony from the tested microorganism was suspended in 5 mL saline, and the suspension was adjusted to 0.5 McFarland standards; in order to give organism suspension of (1 × 108 CFU/mL). The bacterial suspension diluted with saline to obtain 107 CFU/mL. All tubes were incubated at 37 °C for 24 h. Results were recorded in terms of MIC, which is the lowest concentration of antimicrobial agent causing almost complete inhibition of growth or giving no tangible growth. The MIC of Ti−Fe chitosan LDH nanoparticles was measured by broth dilution test in dark condition. The tubes were incubated at 37 °C for 48 h on a rotary platform. The visual turbidity of the tubes was noted either before or after incubation. The MIC was defined as the end point; where no visible turbidity could be detected. 2.5.4. Determination of Minimum Bactericidal Concentration (MBC). After MIC calculation of the nanoparticles was tested, aliquots of 100 μL from all tubes in which no visible bacterial growth was under observation, were seeded in MHA plates and incubated for 24 h at 37 °C. The MBC end point is regarded as the lowest concentration of antimicrobial agent that kills 100% of the initial bacterial population. The number of plates without colonies was noted.13

Table 2. Surface Area Measurements for Ti−Fe Chitosan LDH surface area (m2/g)

146.5

total pore volume (cc/g) average pore diameter (nm) micro pore volume (cc/g)

0.118958 32.120 0.006458

3. RESULTS AND DISCUSSION 3.1. Ti−Fe Chitosan LDH Characterization. 3.1.1. X-ray Diffraction Examination of Synthesized LDH. The XRD patterns are reported by their ICDD cards that are no. 04-011-5537 for titanium, no. 00-034-1266 for iron, and no. 00-054-1935 for chitosan. Figure 2 illustrates the XRD structural forms of Ti−Fe chitosan LDH. Particularly, the peaks at 2θ = 14.5°, 16.30°,

Figure 6. FT-IR spectra of (a) Ti−Fe chitosan layered double hydroxide (b) chitosan. E



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functional groups. Both of acidic and basic groups which could go through dissociation and protonation,18 which clearly appear at pH= 8. Dissociation of surface functional groups, such as amino group of chitosan, causes a negative surface charge on LDH. At neutral pH, zeta potential value of Ti−Fe chitosan LDH dispersed in 10 mM NaCl solution was negative as predicted. The reduction of the zeta potential is brought about by compensation of the negative charges at the Ti−Fe chitosan LDH surface by the protons in solution.19 SEM and TEM images (Figure 3b,c) showed particle sizes smaller than 1172 nm which were calculated by DLS. The reason is that DLS measures the intensity weighted average particle size, over estimating the relative contribution of the largest particles, because these particles are the strongest scatters. Moreover, DLS checks the equivalent hydrodynamic diameter of the colloids in suspension which is larger in comparison with the diameter observed in SEM and TEM. 3.1.2. Surface Area Measurements of Ti−Fe Chitosan LDH. To understand the specific surface area and porosity of the as-prepared Ti−Fe chitosan LDH, nitrogen sorption was measured. Figure 5a displays the N2 adsorption−desorption isotherm and the Ti−Fe chitosan LDH curve relating to the pore size distribution. The curves show that the Ti−Fe chitosan LDH follows type II shape. Also, there a small closed adsorption−desorption hysteresis loop with a value of pressure above 0.4, that is related to mesopores and capillary

19.03°, 20.79°, 22.75°, 26.70°, 28.36°, 35.10°, 36.7°, 63.1° are relating to the diffraction from the (111), (200)/(121), (−211), (−122), (310)/(013), (301), (211)/(004), (400), and (020) planes of LDHs, respectively. While the peaks attributing to the titanium phase are highlighted in red, the ones attributing to the iron phase are in green, and the peaks at the chitosan phase are in blue. The size of the crystallite is calculated by the DebySherrer̀s formula and then corrected for the fwhm of the 100% peak of one phase, specifically (310) for iron phase and (013) for titanium phase indicating that the crystallite size of both layers was 49.4 nm. The dimensions and morphology of Ti−Fe chitosan LDH were examined with HRTEM and FESEM. The HRTEM micrograph (Figure 3a,b) indicated that the prepared LDHs were known as crystallites, uniformity in nature. FESEM (Figure 3c,d) shows that all layers are clustered in a plate-like morphology.15 This could be attributed to the homegenity and the slowness of the nucleation process.16 The stability of the synthesized of nanoparticles was measured by zeta potential at different pH values.17 It was valuable to adjust the native sample pH to a more relevant pH. The values of zeta potential for Ti−Fe chitosan LDH obtained at pH ∼ 3, 5, 6, 8, and 10 were 12.9, −7.13, −6.29, −17.5, and −6.08; showing the high stability of synthesized nanoparticles as illustrated in Figure 4a−d. This result explained that the surfaces of these materials contain pH-dependent ionizable

Figure 7. Effect of different pH on the adsorption of (a),(d) phosphate; (b),(e) cadmium; and (c),(f) benzoquinone in single and multiple solution. F



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condensation was observed.20 The calculated mean of the pore diameter sample < (50 nm) shows a mesoporous structure. This result is consistent with the SEM observations (Figures 3c,d). Moreover, the results are supported by the wide distribution of pore size in Figure 5b (10−160 nm, maximum at 40 nm), resulting from the hierarchical LDH structure. As shown in Table 2, a highly particular surface area of 146 m2/g was obtained for the Ti−Fe chitosan LDHs because of the hierarchical structure.21 3.1.3. Fourier Transform-Inferared of Ti−Fe Chitosan LDH. Figure 6. Illustrates the FT-IR spectra of Ti−Fe chitosan LDH. The infrared bands were around 3389 cm−1 based upon the calculation by υ (OH) overlapped on υs (N−H).22 The band from 2380 cm−1 is calculated by υ (−CO) of the amide group CONHR of the chitosan.22 Interestingly, it is observed that the bands of the characteristic absorption become clear at 1626 cm−1 (−NH2 bending).23 The peak located at 1399 cm−1 is related to the ν3 extending vibration of the NO3 groups in the LDH interlayer. In addition, the absorption bands at 1073 cm−1

result in skeletal vibration including the COO stretching.23 The bands at approximately 674, 598, and 459 cm−1 ensue from metal−oxygen bonds M-O vibration in the brucite-like.24 3.3. Adsorption Studies. 3.3.1. Influence of Initial pH on the Adsorption of Cd2+, PO43− Ions and Benzoquinone in Single and Multiple Contaminated Systems. Adsorption experiment leads to the single (Cd2+ or PO43− or benzoquinone) and the multiple (Cd2+ or PO43− or benzoquinone) systems as a function of pH which ranges from 2.0 to 10.0 at 293 K as illustrated in Figures 7 and 8. The pH is a significant factor which has a great effect on removing the pollutant metal ions from wastewater. pH determines the metal sorption as it has association with both the chemistry of the metal in the solution and the ionization state of functional groups of the adsorbent that are accountable for the accessibility of binding sites. Figure 7b,e displays the influence of pH on Cd2+ adsorption in single or multiple solutions onto chitosan−LDH nanomaterial. The adsorption of Cd2+ ions in single solutions increased linearly along with

Figure 8. Effect of different pH on the adsorption of cadmium, phosphate, and benzoquinone in (a) single and (b) multiple solutions.

Figure 9. Representative concentration distribution curves as a function of pH calculated for chitosan system at 25 °C, I = 0.10 mol L−1 NaNO3 and CChitosan = 0.001 mol L−1. G



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and decreased the adsorption of Cd2+ ions. As pH increases above pH = 4, the adsorption increases which may be related to

pH increase. The low pH level leads to the protonation of the amino groups and their positive charges repelled the Cd2+ ions

Figure 10. FT-IR spectra of Ti−Fe chitosan layered double hydroxide (a) after adsorption with cadmium, (b) after adsorption with phosphate, (c) after adsorption with benzoquinone, in single solution, and (d) after adsorption in multiple solutions. H



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chelation through amino group because the pH increases the OH groups involved in the chelation process, as illustrated in the following equations:

The sum of adsorption declines gradually with pH increasing up to 10, in order to reach 55% of phosphate adsorbed. This could be attributed to the impact of both valence diversity of phosphate species for the adsorption sites and the growing adsorption of OH− on LDH. Also, phosphate occurs as H2PO4−, HPO42−, PO43−, with pK1= 2.15, pK2= 7.20, and pK3= 12.33, respectively, depending on the pH of the solution. The optimal pH for the adsorption of phosphate from water is deemed to vary in the range from 2 to 10. This is significant, from the environmental perspective, as the pH of most water streams ranges from neutral to slightly alkaline except for acid drainage. Phosphate adsorption was under the effect of the environmental species present in solution like Cd2+ and benzoquinone. Perhaps the interaction of phosphate and cadmium ions can be described by the following complexation mechanism:

OH − chit − NH3+ ⇌ HO − chit − NH 2 + H+ pK a1 = 6.20 ± 0.02, 6.3525

(3)

OH − chit − NH 2 ⇌− O‐chit − NH 2 + H+ pKa 2 = 12.3025

(4)

For asserting such behavior, we started to study the equilibrium of dissociation of chitosan and its formation of binary complex with Cd2+ metal ions using potentiometric technique. The protonation constants (pKas) were in use in metal binary complex studies, with the aim of predicting the level of the pH at which pH the ligand is detached and forms complexes with metal ions. Then, the dissociation constant of chitosan was checked at 25 °C and 0.1 mol·L−1 NaNO3 in the aqueous solution. To analyze the potentiometric titration curves, HYPERQUAD 2008 software appropriate for one protonation constant was used. Accordingly, the values of the hydroxyl group are not indicated due to inability to be assessed via potentiometric titration. The obtained pKa value of chitosan is comparable to those reported in the literature,25 after putting into consideration both the different experimental conditions: medium × ionic strength and the calculation methods. Also, the protonation constants were evaluated by the protonated nitrogen of the amino group and the hydroxyl of C-6, −OH was reported from the literature. This is also displayed in the curves of the species distribution (Figure 9) of the chitosan ligand as a function of pH indicating that chitosan first exists 100% in the fully protonated form below pH < 5 in acidic solution. By increasing pH, the ligand misses the first proton. As the pH rises, the second proton starts deprotonation of the free ligand anion which reach the peak percentage of 99.70% at pH 11.70. The knowledge of stability constant is of much significance in many fields.26 Also, the stability constants help us to collect significant information regarding the affinity of Cd2+ metal ion for a particular ligand like chitosan which is of much significance for adsorption process. The values of stability constant of binary complex reported was (9.40 ± 0.02) showing the affinities of chitosan for chelation with Cd2+ metal ions under investigations. This affinity may be ascribed to the structure of chitosan and consequently no steric hindrance in the formed 1:1 complexes. There is an expectation that the selective adsorption and removal of cadmium metal ions can be reached at pH ≈5. In competitive environments, Cd2+ ions may precipitate as CdHPO4 at pH higher than 5 and as Cd10(PO4)6(OH)2 at pH 7.5−8.027 (Figure 7b,e. On the other hand, the adsorption of phosphate on Ti−Fe chitosan LDH was investigated at varied pH (2−10) solutions. The impact of the initial pH on phosphate adsorption is displayed in Figure 7a,d. At pH 2, 79.9% of phosphate is adsorbed, which may be ascribed to the interaction between chitosan and phosphate ions and that can be shown via the following pathways (eqs 5−7):28 −CH 2OH + PO4 −3 → CH 2O − PO3−2

(5)

−NH 2 + PO4 −3 → NH − PO3−2

(6)

+

−NH3 + PO4

−3

+

→ NH3 PO4

−3

Cd(II) + HPO4 −2 → Cd(HPO4 )

(8)

Which may give an explanation for the decrease of phosphate adsorption and that behavior around pH= 6. In addition, the increase beyond pH= 6 may be interpreted based upon the interaction between the benzoquinone and phosphate [eq 8] facilitating the adsorption under the effect of intermolecular force like hydrogen bond.29 Ti−Fe chitosan LDH is deemed as a unique adsorbent to benzoquinone whether in a single system or in a multiple single at wide ranges of pH. Figure 7c displayed the single system at acidic medium. It became evident when pH values increased that there was an increase in the adsorption of benzoquinone.

Figure 11. Adsorption % at different concentration of catalyst (a) cadmium, (b) phosphate, and (c) benzoquinone in single solution on the Ti−Fe chitosan LDH.

(7) I



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spectrum after adsorption as compared with the spectra of chitosan−LDH before adsorption can be counted on with regard to confirming the interaction processes during adsorption which is indicative of deprotonation of the functions group. Figure 10a−d illustrated the different FTIR bands for pollutants at different pH. The band at 3389 cm−1 declined to 2989 cm−1 after adsorption of Cd2+, suggesting that the bonded OH groups exerted a significant role in Cd2+ adsorption. Appearance of some new peaks at 2881 and 1487 cm−1 for cadmium and 831 cm−1 for phosphate refers to presence of aliphatic groups, specifically CH2 and CH in cadmium adsorption and P−O peak at 831 cm−1 can be observed as the assistant of the more intense peak at 787 cm−1 which typically becomes evident for phosphorylated chitosan in phosphate adsorption.30 Disappearance of characteristic peak 1399 cm−1 is because of the replacement between cadmium ion, phosphate, or benzoquinone with the interlayer nitrate in Ti−Fe chitosan LDH. 3.3.2. Effect of Initial Concentration of Adsorbent on Adsorption of Cd2+, PO43−, and Benzoquinone in Single Contaminants Systems. The effect of the adsorbent concentrations from 0.025 to 0.1 g/L on the adsorption of Cd2+ metal ions, phosphate, and benzoquinone pollutants were deemed as a function of the initial cadmium metal ions, phosphate and benzoquinone concentrations were 25 mg/L for

This was attributed to benzoquinone being protonated to hydroquinone and being considered as an H-bond donor, while the LDH chitosan was considered as H-bond acceptor. The interaction may have been via H-bonding interaction but there was a weak interaction between benzoquinone and LDH. In neutral medium or in basic medium, it was favorable to take up benzoquinone, where its predominant species are expected to be anionic. Therefore, the strong interaction between it and LDH was attributed to both of hydrophilic−ionic interactions between the −CO and −O− groups of benzoquinone and NH3+ of chitosan and hydrophobic−hydrophobic interactions between the nonpolar groups of benzoquinone and nonpolar group of LDH. Moreover the adsoritivity of benzoquinone in a mixed system (containing PO43− and Cd2+) increases with pH value increase (basic medium). Benzoquione uptake was clear in acid medium due to formation of benzoyl phosphate which forms electrostatic attraction with NH3+ of chitosan in LDH. After that the adsorbitivity increases in basic medium. But at pH 6, we noticed that the adsorpitivity decreased at pH 6 and 6.5. The decrease was attributed to the soluble−insoluble transition phase of chitosan. Figure 10a−d displayed FTIR spectra of Ti−Fe chitosan LDH before and after adsorption for single and multiple contaminants system at different pH, furthermore, the shifts and changes in the intensity of characteristic bands of the LDH

Figure 12. Plots of effect of contact time on Cd2+, PO43−, and benzoquinone adsorption (a), (b), (c) in single solutions and (d), (e), (f) in multiple solutions on Ti−Fe chitosan LDH. J



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pollutants were determined as illustrated before (experimental part). There is an increase in adsorption with the increase of contact time, not to mention the maximum adsorption takes place at 4 h. After this time, there was no further adsorption for single and multiple systems. 3.3.4. Kinetics Analysis in Single and Multiple Contaminants Systems. The kinetics of adsorption reveals the uptake rate of the solute and displays the efficiency of adsorption process for the adsorbent and then determines its potential applications. The adsorption mechanism counts on the chemical and physical properties of the adsorbent and on the mass transfer process as well.31 Furthermore, kinetics study of the adsorption process is significant for adsorbents design as the kinetics provides key resources to the mechanisms and the pollutants uptake rate. Pollutants removal process, from an aqueous phase by adsorbent, could be interpreted by applying kinetic models and investigating the rate-controlling mechanism, like chemical reaction, mass transfer, and diffusion control. The kinetic parameters are good predictors of the adsorption rate that is utilized to design and propose a model for the adsorption process. Literature showed that pollutants removal kinetics process is explicitly explained by applying pseudo-first-order, second-order, and intraparticle diffusion kinetic models. To examine the mechanisms of the metal

cadmium and 20 mg/L for both phosphate and benzoquinone at a pH ≈ 8. The adsorption beach time was set at 24 h in order to attain an equilibrium state. As indicated in Figure 11, the pollutants adsorption is on increase with the increase of initial adsorbents concentration to certain limit reaches 98% at 0.05 mg/L for both cadmium and benzoquinone ions, and reaches 63% at 0.05 mg/L for phosphate. This may be attributed to the increase in the driving force from the active sites and concentration gradient in the adsorbents which lead to the distinctively increased adsorpitivity to 0.05 mg/L. After that, it is worth mentioning any further increase in LDH adsorbent leads to decrease in adsorptivity; owing to an increase in negative charge (which is confirmed by zeta potential analysis as illustrated in Figure 4 that rises electrical repulsion causing decrease in removal). 3.3.3. Contact Time Effect on Adsorption of Cd2+, PO43−, and Benzoquinone in Single and Multiple Contaminated Systems. The contact time effect on the adsorption of Cd2+, PO43− ions, and benzoquinone at initial concentration were 25 for cadmium, and 20 mg/L for both phosphate and benzoquinone at a pH value of 8 as was illustrated in Figure 12. The contact time varied from 1 to 24 h during the experiment, The analysis of batch adsorption of pollutants were conducted in 60 min, while steps and the residual concentrations for

Figure 13. Regressions of kinetic plots for cadmium ions in (a,b,c) single solution and (d,e,f) multiple solutions on the Ti−Fe chitosan LDH. (a,d) Pseudo-first-order model, (b,e) pseudo-second-order model, and (c,f) intraparticle diffusion model. K



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Figure 14. Regressions of kinetic plots for phosphate ions in (a,b,c) single solution and (d,e,f) multiple solutions on the Ti−Fe chitosan LDH. (a,d) Pseudo-first-order model, (b,e) pseudo-second-order model, and (c,f) intraparticle diffusion model.

the first adsorption rate h (mg/g min) is calculated from h = k2qe2. In addition, the kinetic results will be analyzed, using the intraparticle diffusion model, to explain the diffusion mechanism. This model is conveyed in eq 11 as

adsorption process, the linear equations of the three kinetic models were applied (see Figures 13, 14, and 15). The pseudofirst-order model proposes that the binding generated from physical adsorption and is interpreted by eq 9 as ln(qe − qt) = ln(qe) − k1t

qt = k it 0.5 + C

(9)

where qt and qe are considered the amounts of pollutants adsorbed on the LDH adsorbent in mg (adsorbate)/ g(adsorbent) at equilibrium and at time t, respectively, k1 is regarded the rate constant of the pseudo-first-order model (min−1).32 The values of qe and k1 are calculated from the intercept and the slope of the linear plot of ln (qe − qt) versus t. The pseudo-second-order model is rooted in chemical adsorption (chemisorptions) and presented by eq 10 as t 1 t = + q qe k 2qe2

(11)

where C is the intercept and ki is the intraparticle diffusion rate constant (mg/g min1/2) and determined by the slope of the linear plot of q versus t 0.5.33 With regard to cadmium and phosphate ions adsorption in single and multiple systems, the results were illustrated in Figures 13 and 14a−f, respectively. Three models of kinatic, pseudo-first, second-order mode,l and intraparticle diffusion model for single and multiple solutions, were compared for their fit of goodness. Each linear plot of ln (qe − qt) versus t, (t/qt) versus t, and qt versus t0.5 were calculated for the three model, respectively. Table 3 provided the coefficients of the models. Comparing the regression coefficients for each expression, results showed that both the first-order rate expression and the intraparticle diffusion model are not completely valid for the present system. This could be

(10)

where qe and qt follow the same description as the pseudo-firstorder model and k2 is the rate constant of the pseudo-secondorder model (g/mg min), the slope and intercept of the linear plot of t/qt against t yielded the values of qe and k2. Moreover, L



Article

Figure 15. Regressions of kinetic plots for benzoquinone in (a,b,c) single solution and (d,e,f) multiple solutions on the Ti−Fe chitosan LDH. (a,d) Pseudo-first-order model, (b,e) pseudo-second-order model, and (c,f) intraparticle diffusion model.

Table 3. Coefficients of Pseudo-First- and Second-Order Adsorption Kinetic Models and Intraparticle Diffusion Modela PO43−

Cd2+ order models pseudo-first-order

pseudo-second-order

intraparticle diffusion model

a

benzoquinone

parameters

single

mixed

single

mixed

single

mixed

qe cal. (mg/g) qe exp. (mg/g) K1 (min−1) R2 qe cal. (mg/g) qe exp. (mg/g) K2 (g/mg min) R2 ki (mg/g min0.5) C (mg/g) R2

1.99 53 4.3965 e−3 0.799 55.5 53 0.05 0.99 0.54 38.9 0.70

2.36 12.4 1.6 e−3 0.5 12.5 12.4 1.7 0.999 5.7 e−3 12.3 0.61

23.14 22.5 2.98 e−3 0.699 25 22.5 1 0.9892 0.55 8.1 0.68

1.9 1.66 4.38 e−3 0.799 0.3 1.66 0.007 0.497 0.05 1.1 0.89

14 9.8 4.798 e−3 0.58 10 9.8 0.1 0.999 0.164 5.7 0.78

14.59 9.6 6.167 e−3 0.687 10 9.6 0.1 0.999 0.154 5.7 0.77

Cd2+ metal ions = 25 mg/L, phosphate and benzoquinoe 20 mg/L for both, Ti−Fe chitosan layered double hydroxide 0.05g.

an indication that the sorption of phosphate ions in single solutions by chitosan LDH catalyst is controlled kinetically by the second-order reaction compared to the first-order process that asserted chemical adsorption. On the other hand, in multiple solutions, the intraparticle diffusion model fits well with the experimental data as shown in Figure 14f. The adsorption kinetics of phosphate ion in multiple solutions onto solid particles goes through two distinct steps. Thus, analyzing the

explained by the low correlation coefficients in single solutions. On the other hand, the second-order kinetic model showed a fit of goodness to the experimental data as illustrated by the adsorbate in Figure 14b. Also, using the pseudo-second-order model for the linear plots showed strong correlation coefficients (in most cases >0.99). This shows that both the theoretical and experimental qe values go in line with each other. Consequently, this provides M



Article

Figure 16. Adsorption % at different concentration of pollutants cadmium, phosphate, and benzoquinone in single and multiple solutions on the Ti−Fe chitosan LDH (a) represented as curve shape and (b) represented as column chart.

Table 4. Isotherm Parameters for Removal of Harmful Ions by Ti−Fe Chitosan Layered Double Hydroxide PO43−

Cd2+ isotherms Langmuir

Freundlich

benzoquinone

parameters

single

multi

single

multi

single

multi

q0 (mg/g) KL (l/mg) RL R2 KF 1/n R2

869 0.11 0.05 0.05 81.45 0.9 0.97

250 0.4 0.016 0.56 91.835 0.78 0.97

40 0.04 0.13 0.95 4.953 0.42 0.96

50 0.05 0.11 0.98 9.025 0.34 0.99

71.4 0.20 0.03 0.89 18.17 0.34 0.9

69.4 0.49 0.02 0.92 36.5 0.08 0.12

experimental data may be carried out depending on the intraparticle diffusion model (eq 11), which gives a description for a two stage adsorption process onto and within the adsorbent model.34−36 Adsorption of benzoquinone onto Ti−Fe chitosan LDH adsorbent in single and multiple solutions were optimally depicted using the pseudo-second-order model. Figure 15b,e displays straight lines of t/qt versus adsorption time that validates the pseudo-second-order reaction kinetics model explained in eq 10).This goes in line with the latest data on the kinetics of benzoquinone adsorption onto metal oxide/ hydroxide adsorbents in aqueous solutions.37 3.3.5. Adsorption Isotherm in Single and Multiple Contaminant Systems. There was an increase in the adsorption abilities of Ti−Fe chitosan LDH toward pollutants increased in synchronization with increase in contaminants

concentration to a certain limit, and then any further increase in concentration leads to decrease in adsorption % as shown in Figure 16 and Table 4. This trend in experimental data is ascribed to increase in negative charge (which is confirmed by zeta potential analysis as exhibited in Figure 4) that raises the electrical repulsion causing a decrease in removal percentage. Besides, the equilibrium adsorption isotherms are significant for deciding the adsorption capacity of pollutants and detecting the nature of adsorption onto the LDH adsorbent. The equilibrium adsorption potential of adsorbent was investigated by the eq 2, where Ce was assessed for first concentration of each ion which ranges from 20 to 100 mg/L after equilibrium time. Figures 17, 18, and 19 display the adsorption isotherms of Cd2+, PO43−, and benzoquinone, respectively, on Ti−Fe chitosan LDH. Furthermore, in these Figures, it was found that the equilibrium increased with concentration of pollutant. N



Article

Figure 17. (a) Adsorption isotherms of Cd2+ ions in (a,b,c) single solution and (d,e,f) multiple solutions on the Ti−Fe chitosan LDH. (a, d) Adsorption isotherm, (b,e) Langmuir, (c,f) Freundlich isotherms.

qo and KL are the Langmuir constants related to the adsorption capacity and the rate of adsorption, respectively. Plotting Ce/qe against Ce showed a straight line with a slope of 1/qe. The Langmuir constants KL and qo were determined from this isotherm. The other significant parameter, RL, known as the equilibrium parameter or the separation factor. In the current study, this is assessed from the relation RL, and calculated by eq 13.39

This is attributed to the increase in the driving force from the concentration gradient. The current results are consistent with literature that showed that most widespread models used to investigate the adsorption isotherm are Langmuir and Freundlich equations. First, the Langmuir model depicts qualitatively the formation of a monolayer adsorbate on the outer surface of the adsorbent, after which further adsorption does not occur.38 The model provides the equilibrium distribution of the adsorbate between the liquid and solid stages. Second, the Langmuir equation assumes a structurally homogeneous adsorbent where all sorption sites are similar and energetically equivalent. The Langmuir adsorption isotherm was employed to equilibrium adsorption assuming monolayer adsorption onto a surface with a finite number of identical sites, and provided by eq 12 as follows:38 Ce 1 1 = + Ce qe (qoKL) (qo)

RL =

1 [1 + KLCo]

(13)

Here, KL is the Langmuir constant (1/mg) and Co (mg/L) is the greatest pollutant ions concentration. The value of RL determines whether the type of the isotherm is not either unfavorable (RL > 1), linear (RL = 1), favorable (0500 >500

250 500

500 1000

Q



Article

Scheme 1. Antimicrobial Activity of Ti−Fe Chitosan LDH as a Novel Catalyst

bacterial cytoplasmic membrane and DNA, (2) protein denaturation.42 Scheme 1 indicates antimicrobial mechanism of Ti−Fe chitosan LDH. The existence of positive charges of Ti−Fe chitosan LDH was supported during liberating metal ions which affects greatly fungi and bacteria. This shows that it binds to the microorganisms membranes like what takes place in the mammalian cell, not to mention the presence of positive metal ions brought about transportation of the system from the key metal ions to the cell where they could collect and apply toxic effects at great concentrations. Figure 20 displays more moderate antimicrobial activity toward Gram-positive bacteria than Gram-negative bacteria. This is due to the cell wall of Gram-positive bacteria that fully consisted of peptide polyglycogene and sufficient amount of pores that permit foreign molecules to easily access the cell. However, cell wall structures of Gram-negative bacteria are composed of a lipopolysaccharide outer membrane and a plasma inner membrane which are too difficult for disinfectants to cross through. The mechanisms of antifungal effects of metal ions in fungi help evaluate the antifungal effects on white rot fungi. Presumably, the fungi growth was inhibited by the metal ions emitted from the LDH. The LDH structure plays a key role in antibacterial activity as bacteria might attach separately on the LDH surface. As a result, the LDH surface could possibly

Figure 20. Show the antimicrobial activity, MIC, and MBC of Ti−Fe chitosan LDH.

kill 99% of the germ. It was found that our novel catalyst has antimicrobials activity toward many species of microorganisms. This is attributed to the emergence of hydroxyl ions in an aqueous environment, which are greatly oxidant free radicals indicating excessive reactivity with biomolecules. According to Siqueira and Lopes, the high and indiscriminate reactivity41 causes this free radical to seldom diffuse away from sites of generation. Their toxic effects on bacterial cells possibly own the following mechanisms: (1) the potential damage to the R



Article

Table 6. Reported compeitive adsorption capacities of some adsorbents for different pollutants pollutants concentration used (mg/L) absorbent Mg−Al−CO3−LDH magnetic Fe3O4/Mg−Al−CO3−LDH Co−Fe LDH nanoparticle carbon nanotubes prepared on the Co−Fe LDH surface Zn−Fe LDH FeO(OH) Zn−Fe LDH Mg−Al LDH Iron (Fe+3) oxide/hydroxide nanoparticles activated carbon fibers calix 4 arene-tri acid monoquinone

adsorption capacity (mg/g) 61.40−70.20 45.60−54.70 65−94 at 6 hours 70−94 at 3 hours 90 at 4 hours

cadmium

phosphate

12 mg/L

42 45 1

0.8 M 50 mg/L 50 mg/L 10 mg/L

88−94% single 25 mg/L 98%

source 8 8 44

100% 24%

Ti−Fe chitosan LDH

benzoquinone

100 mg/L 100 mg/L 12 mg/L

mixed 25 mg/L 58%

single 20 mg/L 63%

mixed 20 mg/L 82%

150 mg/L not determined single mixed 20 mg/L 20 mg/L 98.8% 95.8%

37 46 47 this study

decrease the adsorption and adhesion of the bacteria to the host. Metallic ion-exchange LDH spread in water and attract bacteria by electrostatic forces which indicated good antibacterial activities. Furthermore, the electrostatic forces between the protonated NH3+ groups of chitosan and the negatively charged microbial cell membranes mediated the interaction.43 In addition, chitosan binds with DNA and inhibits mRNA synthesis during the diffusion of chitosan into the nuclei of the microorganisms and blocking the synthesis of mRNA and proteins. The last interpretation breaks down to that microorganisms carry a negative charge while metal ions in LDH carry a positive charge creating an “‘electrostatic”’ attraction between the treated surface and microbe. It was elicited from the aforementioned that once connected, the microbe was oxidized and died immediately.

ORCID

CONCLUSION Novel adsorbent Ti−Fe chitosan LDH intercalated with the nitrate ions was used for removing Cd2+, PO43−, and benzoquinone from wastewater in single and multiple solutions with agreeable results compared with the previous studies as illustrated in Table 6. The adsorption process was conducted at different contact times in different pHs with different contaminant concentrations and catalyst doses. Adsorption of these pollutants took place fundamentally through ion exchange and complex formation. Furthermore, the adsorption isotherms exhibited a high adsorption of cadmium and benzoquinone in comparison with phosphate in single solution experiments. However, in multiple solutions, the results were higher in benzoquinone and phosphate than in cadmium. The kinetics studies concluded that the adsorption of cadmium and benzoquinone in single and multiple solutions and phosphate in single solutions by Ti−Fe chitosan LDH followed the second-order kinetics form, where phosphate in multiple solutions followed intraparticle diffusion. In addition, the LDH efficiency in vitro was assessed against some Gram-positive, Gram-negative, and fungi. The fabricated LDH showed moderated antimicrobial potency with MIC values ranging from 62.5 to 700 μg/mL as antibacterial agents

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Rehab Mahmoud: 0000-0003-2274-2016 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Special acknowledgment for Dr. Wessam A. Mohamed for her editing and proofreading of the manuscript. The work was supported by the Faculty of Science, Materials Science Lab, Chemistry Department and Faculty of Postgraduate Studies for Advanced Sciences, Materials Science and Nanotechnology Department Beni-Suef University, Egypt.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. S

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Comparative Study of Single and Multiple Pollutants System Using Ti

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