Imprinting âNano-SiO2-Crosslinked Chitosan-Nano-TiO2â Polymeric

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Imprinting “Nano-SiO2-Crosslinked Chitosan-NanoTiO2” Polymeric Nanocomposite for Selective and Instantaneous Microwave-Assisted Sorption of Hg(II) and Cu(II) Mohamed E. Mahmoud, Gehan M. Nabil, Hany Abdel-Aal, Nesma A. Fekry, and Maher M. Osman ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b03215 • Publication Date (Web): 14 Feb 2018 Downloaded from http://pubs.acs.org on February 15, 2018

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ACS Sustainable Chemistry & Engineering

Imprinting “Nano-SiO2-Crosslinked Chitosan-Nano-TiO2” Polymeric Nanocomposite for Selective and Instantaneous Microwave-Assisted Sorption of Hg(II) and Cu(II) Mohamed E. Mahmoud*, Gehan M. Nabil, Hany Abdel-Aal, Nesma A. Fekry, Maher M. Osman Faculty of Science, Chemistry Department, Alexandria University, P.O. Box 426, Alexandria 21321, Egypt, E.mail: [email protected], Telephone number: 0020-140933009, Fax number: 00203-3911794.

Abstract An imprinting polymeric nanocomposite-like structure was synthesized by bonding of crosslinked chitosan to nano-SiO2 and nano-TiO2 simultaneously via bifunctional glutaraldehyde linker. The structure of “nano-SiO2-crosslinked chitosan-nano-TiO2” nanocomposite was confirmed and characterized by FT-IR, XRD and TGA. The surface area (6.47 cm3 g-1), porosity (0.193 cm3 g-1) and particle size (14-40 nm) were confirmed from the study of SEM, HR-TEM and surface area measurements. This nanocomposite announced selective and enhanced sorption for mercury and copper ions with high performance using microwave technique. Different factors; microwave-contact time, pH, nanocomposite dosage, temperature and initial metal concentration, affecting on the metal sorption capacity, were monitored. The maximum capacity values; 8000 and 4000 µmol g-1 for mercury and copper, respectively were observed at pH 6 using only 20 s. Thermodynamic parameters were also calculated and perfectly referred to spontaneous sorption operations. The sorption of divalent mercury and copper were successfully explained by three isotherm models; Langmuir, Freundlich and Dubinin-Radushkevich (D-R), showing favorable operations. The nanocomposite maintained its selectivity and sorption power for mercury and copper even in presence of other interfering ions. Microwave-assisted technique achieved fast effective operations for extraction of mercury with 98.0-99.5% and copper with 94.4-96.6% from different water samples.

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Keywords: Nanocomposite, Imprinting, Crosslinked chitosan, Nano-SiO2, NanoTiO2, Solid phase extraction. Introduction The scientific revolution against the significant threats of heavy metals toward both environmental and health has been broken out for many years over the world. Mercury in all forms is extremely toxic, carcinogenic and hazardous even at very low concentrations1-3. It releases to the environment from various anthropogenic activities as mining operations, tanneries and metal plating in addition to other natural processes including volcanic action, abrasion of mercury-containing sediments2. The maximum contaminant level (MCL) announced by the EPA4 of mercury was set at 0.002 mg L-1 and copper is also necessary for many metabolic operations and enzyme systems for all living systems with the MCL = 1.3 mg L-1. Copper may reach to the food through the spraying of vegetables and fruits with pesticides-contained copper that prevents fungi and algae growth. Copper toxicity "copperiedus” points out to the consequences of an excess copper in the body resulting in acute copper poisoning on Human5. Various alternative technologies were developed for heavy metals recovery from aqueous matrices. Solid-phase extraction (SPE), however, becomes the most popular technique because of its simplicity, high efficiency and low operation time6. The impact application of SPE depends on selection of the sorbent and its surface modification because it can control the sorption factors such as selectivity and sorption capacity. Latterly, several issues related to water quality have been greatly progressed using nanoparticles, nanofiltration or other techniques resulting from development of nanotechnology. Nanosized metal oxides (NMOs) can be promoted efficient nanosorbents in SPE owing to their unique physicochemical properties7. Moreover, surface modification of NMOs becomes a creative point of research by which the immobilization of some ligands with nitrogen, oxygen, sulfur 2 ACS Paragon Plus Environment

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and/or phosphorus donor-atoms onto nanoparticles is aimed to enhance and facilitate sorption and selectivity characters8-12. Based on the literature survey, many research works reported chitosan for extraction of mercury and/or copper ions. Adsorption of mercury was reported using chitosan-alginate nanoparticles13, aminated chitosan bead14, magnetic glutaminemodified-chitosan microspheres15, chitosan-poly(vinyl alcohol) hydrogel adsorbent 16 and magnetic chitosan resin modified with Schiff's base derived from thiourea and glutaraldehyde17. While adsorption of copper has been reported by using chitosan nanoparticles and alginate microparticles18. In the current study, a novel imprinting polymer-like structure was designed and fabricated via immobilization and bonding of glutaraldehyde-crosslinking chitosan onto titanium oxide and silica nanoparticles simultaneously. It is also aimed to apply the microwave-assisted sorption technique to produce higher sorption and faster operating time. Therefore, the present work is directed to; i) confirm structure and

properties

of

“nano-SiO2-crosslinked

chitosan-nano-TiO2“

polymeric

nanocomposite by various instrumental techniques, ii) evaluate and enhance its efficiency in selective extraction performance of mercury and copper using microwave-assisted sorption technique, iii) study different sorption parameters and restricting conditions and iv) investigate the potential contribution of fabricated nanocomposite and its implementation in water treatment by utilizing microwaveassisted sorption technique. Materials and Experiments Chemicals and solutions All chemicals were purchased via Sigma-Aldrich chemical company, USA. Silica nanopowder (nano-SiO2, 12 nm, 99.8%, spec. surface area 175-225 m2 g-1 BET), titanium (IV) oxide nanopowder (nano-TiO2, 21 nm, 99.7%, spec. surface area 45-55 m2 g-1 BET), glutaraldehyde (50% in H2O, molecular weight 100.12) and pure powder chitosan (poly(D-glucosamine, low molecular weight 5x104-19x104 g 3 ACS Paragon Plus Environment


mol-1, 75-85% deacetylated degree ) were also purchased. A 0.1-M aqueous solution of mercury and copper were prepared from mercury(II)chloride, ≥99.5%, molecular weight 271.50 and copper(II) sulfate pentahydrate, ≥98.0%, molecular weight 249.69, respectively. Buffer solutions (pH 2.0-7.0) were prepared by mixing appropriate volumes of 1.0-M hydrochloric acid solution (HCl, 37%, molecular weight 36.46) and 1.0-M sodium acetate trihydrate solution (≥99.5%, molecular weight 136.08) then diluting to 1L with double-deionized water (DDW). The pHvalues of buffer solutions were controlled by utilizing an Orion pH-meter model 420A fitted with an Orion combined glass electrode. Synthesis of nanocomposites Synthesis of “nano-SiO2-crosslinked chitosan-nano-TiO2” Firstly, the synthesis of crosslinked chitosan was carried out as previously reported19. In details, 4.0 g of chitosan was dissolved in 600 mL of 0.05-M acetic acid with continuous stirring for 12 h. Subsequently, 64 mL of glutaraldehyde was quickly combined with the solution of chitosan. After addition, the mixture under gelation changed its color from dark yellow to orange. Eventually, the produced orange gel was neutralized with 0.2-M of NaOH solution, washed several times with DDW and dried in a vacuum oven (~56oC) for overnight. The dried product was grinded into powder by using mortar and pestle. Immobilization of crosslinked chitosan onto both nano-SiO2 and nano-TiO2 simultaneously was achieved by using glutaraldehyde crosslinker 20. In 250 mL round flask, 2.0 g of the dried crosslinked chitosan, 1.0 g of acid activated nano-SiO2 and 1.0 g of acid activated nano-TiO2 were combined with 50 mL of glutaraldehyde. The mixture was slightly acidified with 5.0 mL of 0.1-M HCl solution and then refluxed for about 6 h. The product was washed with DDW several times and then dried at 80oC overnight. This dried material was milled into a small powder and sieved. 4 ACS Paragon Plus Environment

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Synthesis of other nanocomposites with one type of nano-oxide A similar procedures were performed by using one type of nano-oxide support in order to produce two other nanocomposites;“nano-SiO2-crosslinked chitosannano-SiO2” and “nano-TiO2-crosslinked chitosan-nano-TiO2” then the three nanosorbents were firstly studied in a parallel manner to declare which one is more influential. Sorption studies The microwave-assisted capacities of mercury and copper were studied at different microwave-contact time periods of 5, 10, 15, 20, 25 and 30 s. Each batch experiment was performed in 25 mL flask by mixing a 1.0 mL of 0.1-M mercury or copper solutions with 10.0 mg of the dry “nano-SiO2-crosslinked chitosan-nanoTiO2” nanocomposite. The total volume was diluted by 9 mL of DDW and positioned in the microwave oven. After heating, the sorbent in the mixture was isolated by filtration and washed with 50 mL of DDW. Residual concentration in the filtrate was determined and the quantity of adsorbing metal ion of the nanocrosslinked chitosan was calculated by Eq. (1). q=

(Co −C)V m

x103

(1)

Where, Co and C (mol L-1) are the starting and residual metal ion concentrations respectively, V is the volume of solution in mL, m refers the mass of dried nanocrosslinked chitosan in gram, while q (µmol g-1) is the metal capacity that represents the quantity of adsorbing metal ion (µmol) per gram of nano-crosslinked chitosan. Impact of pH on sorption capacity was investigated at various pH values (pH 2.0-7.0) by adding 9 mL of buffer solutions and shaken for 20 s as the microwavecontact time. Similar batch experiments were performed by using various nanocrosslinked chitosan masses of 10, 20, 30, 40 and 50 mg using the optimum buffer solution (pH 6). 5 ACS Paragon Plus Environment


A digital temperature controller was employed to monitor the impact of temperature on the capacity values of mercury and copper. 10.0 mg of the nanocomposite, 1.0 mL of 0.1-M metal ion solution and 9.0 mL of the optimum buffer solution (pH 6) was shaken (5 min) at various temperatures (30, 40, 50 and 60oC). Sorption equilibrium was evaluated for mercury and copper species by using various concentrations; 0.04, 0.08, 0.12, 0.16 and 0.2-M of ions. Moreover, impact of interfering ions on the extraction operations of mercury and copper ions were examined in existence of other competing ions using equimolar concentrations. The studied solutions were provided by incorporating with a 1.0 mL of 0.1-M copper or mercury solution and a 1.0 mL of 0.1-M of a competing ion solution of either Na(I), Mg(II), Zn(II) or Ni(II). These solutions were then completed to10.0 mL of DDW in a 25 mL flask containing 10.0 mg of the dry nano-crosslinked chitosan. Reaction mixture was heated for 20 s in the microwave oven, filtered and washed several times with 50 mL of DDW. Finally, the unextracted mercury or copper was finally measured by AAS. Potential applications for extraction of mercury and copper ions from real water Three various water samples either originally contaminated or spiked with mercury and copper were collected and utilized to examine the efficiency of the designed nano-crosslinked chitosan for extraction of the two metal ions under study. The tap water, sea water and an industrial wastewater samples were accumulated and analyzed for mercury and copper contents then spiked. One liter sample passed throughout a two-stage micro-column packed with 100±1 mg of the dry nanocomposite under constant flow rate (10 mL min-1). The effluent was analyzed to identify concentrations of mercury or copper. The % extraction was calculated on the basis of duplicate analysis. Another one liter of water was contacted with 100±1 6 ACS Paragon Plus Environment

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mg of the dry nanocomposite in the microwave for 20 s. The water sample was then filtered and analyzed to identify the contents of mercury and copper. Also, the percentage of microwave-assisted metal extraction was determined. Results and discussion Synthesis, characterization and surface morphology Scheme 1 represents the reaction between crosslinked chitosan, glutaraldehyde, nano-SiO2 and nano-TiO2 as well as the synthetic procedure of “nano-SiO2crosslinked chitosan-nano-TiO2” nanocomposite. Various instrumental techniques were used to study and evaluate the possible and simultaneous bonding of crosslinked chitosan to nano-SiO2 and nano-TiO2 via the bifunctional glutaraldehyde linker including the FT-IR, XRD, TGA, SEM, HRTEM, and surface area measurements. Figure 1a, 1d, 1c and 1d show the FT-IR spectra of nano-SiO2, nano-TiO2, crosslinked chitosan and “nano-SiO2-crosslinked chitosan-nano-TiO2”, respectively. The FT-IR spectrum of nano-SiO2 exhibited two characteristic peaks at 807 and 1106 cm-1 due to mainly the vibration of Si-OH and Si-O-Si functional groups, respectively21. These very intense peaks are corresponding to the SiO2 network. The sharp peak at 471 cm-1 is caused by the Si-O bending vibrations22. The broad absorption peak (3447 cm-1) is referred to the fundamental stretching vibrations of various types of O-H groups. Combination of the SiO2 vibrational modes is generally located at 1636 and 1383 cm-1 modes23. The FT-IR spectrum of nano-TiO2 was identified to exhibit wide ban at 3448 and 1384 cm−1 due to hydroxyl groups of Ti-OH with which physisorbed water molecules are bound by weak hydrogen bonds24. The strong absorption band centered at 675 cm−1 is the typical Ti-O-Ti vibration25. The FT-IR spectrum of crosslinked chitosan was found to show several peaks of implicit functional groups that confirm the structure. The absorption broad peak at 3429 cm−1 is caused by vibration of O-H and N-H groups. The C-H (sp3) stretching vibration is manifested through a strong peak at 7 ACS Paragon Plus Environment


2936 cm−1. It is also characterized by two other peaks centered at 1569 and 1410 cm−1 attributed to vibrational mode of C=O in O=C-NH and the N-H bending of NH2 group, respectively7. The sharp peak at 1658 cm−1, due to vibration of C=N bonds can confirm the successful crosslinking of chitosan. A number of significant peaks at 1245, 1122, 1064 and 689 cm−1 are mainly related to vibrations of C-N, CO-C, C-O in glucosamine rings and O-H out of plane bending, respectively26. However, the FT-IR spectrum of “nano-SiO2-crosslinked chitosan-nano-TiO2" involves, besides the characteristic peaks of individual components, two other peaks at 1642 and 1383 cm−1 to point out to the stretching vibrational modes of NHCO and confirm the amide formation due to the bonding of the crosslinked chitosan simultaneously to nano-SiO2 and nano-TiO2 through the bifunctional glutaraldehyde. The XRD pattern (Figure 2) was also investigated for the developed nanocomposite. Several characteristics peaks at 2θ = 24.8, 37.0, 47.4, 53.1, 54.2 and 62.0 are evident to account for a tetragonal phase as previously reported 26. Appearance of same characteristic peaks reflects the stability of the crystalline nanocomposite. Furthermore, the intense diffraction peaks at 2θ = 24.8 confirm that the synthesized “nano-SiO2-crosslinked chitosan-nano-TiO2” nanocomposite is finely crystalline. The thermal behavior of this polymeric nanocomposite was analyzed by TGA from 35 to 700°C (Figure 3). It exhibited an overall mass loss = 71.7%. In the range 35-125°C, a single process, evidenced by a broad minimum peak on the curve with the highest rate at 75°C, took place causing a first mass loss = 12.8%. This weight loss represents water desorption. The temperature of this process indicated that such water was physisorbed and loosely bound on the nanocomposite surface. In addition, the material mass remained stable to 160°C. After this temperature, a dramatic mass loss process took place with a higher rate at 180-580°C. The weight loss, in this temperature range was about 58.8% and this suggests the destruction of crosslinked chitosan and release of NH3, CO, CO2, CH4 and CH3COOH27. Above 600°C, the 8 ACS Paragon Plus Environment

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material was stable and maintained about 28.3% to indicate that the nanocomposite was finally converted into stable oxides of Si and Ti. The surface morphology and imaging of the synthesized "nano-SiO2crosslinked chitosan-nano-TiO2" were monitored and studied by SEM and TEM techniques (Figure 4a and 4b). The images obviously show the aggregated spherical nanoparticles. The particle size was found in the range from 14 to 40 nm. The aggregates formation is a property of a material when sized in nanoscale, also attributed to natural tendency of “nano-SiO2-crosslinked chitosan-nano-TiO2" to undergo clustering owing to a variety of charges on its surface of nano-crosslinked chitosan. In addition, these images show homogeneous distributions of the nanoparticles on a uniform surface. The multi-point BET method of nanocrosslinked chitosan was utilized to determine the surface area and pore size by the sorption and desorption curve. The results obtained at standard temperature and pressure (STP) indicated the surface area = 6.47 cm3 g-1, mean pore diameter = 27.38 nm and the pore volume = 0.193 cm3 g-1. All these data confirm the porous and large surface area of this nanocomposite, which enhances the sorption behaviors toward metal ions. The closed loop hysteresis pattern (Figure 5) represents two inferences, (i) the cone-shape pores and the formation of an increasingly thick film of ions whose radius would be equal to that of the cavities created within the nanocomposite, and (ii) the reversible sorption and desorption operations and the ability for recycling. Sorption studies The newly designed nanocomposite “nano-SiO2-crosslinked chitosan-nanoTiO2” is characterized by numerous binding sites into the assembled polymeric network. The ions of certain metal of complementary size and functionality can bind selectively with the electron-pair donor atoms involving in these binding-cavities. Therefore, the fabricated nanocomposite is much close to a molecular imprinting 9 ACS Paragon Plus Environment


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polymer (MIP) that introduces a template of certain molecules 28. Table 1 elucidates that “nano-SiO2-crosslinked chitosan-nano-TiO2” obtained via immobilization of cross-linked chitosan onto two types of oxides nanoparticles; SiO2 and TiO2 of different size provides more efficient nanocomposite for mercury and copper with capacity values of 8000 and 4000 µmol g-1, respectively rather than the two other nanocomposites; “nano-SiO2-crosslinked chitosan-nano-SiO2” and

“nano-TiO2-

crosslinked chitosan-nano-TiO2” included one type of oxide nanoparticles that displayed lower capacity. The higher selectivity and capacity of “nano-SiO2crosslinked chitosan-nano-TiO2” nanocomposite may be attributed to suitable distribution of binding sites and comparable cavity size resulting from bonding the crosslinked-chitosan by bifunctional linker “glutaraldehyde” with nano-SiO2 and nan-TiO2 together29. Effect of microwave-contact time The effect of microwave reaction contact time on the efficiency of “nanoSiO2-crosslinked chitosan-nano-TiO2” nanocomposite for removal of mercury and copper metal ions is performed in Figure 6. The interaction between either mercury or copper and the imprinting nanocomposite was generally found to occur by two successive steps. 1st step exhibited fast increasing the percentage extraction. 2 nd step predicts a saturation of active sites on the surface with the target adsorbed metal ion. It was clearly demonstrated that the removal processes of mercury and copper by the prepared nanocomposite were proceed with high rate judging from the high metal capacity values after 5s of microwave-contact time and reached the maximum within only 20s. The very rapid reaction equilibrium and high capacity confirm that the microwave-assisted SPE can provide numerous advantages over other batch techniques11. Effect of pH


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The most important parameter that manipulates the sorption behavior of metals from solutions is the hydrogen ion concentration expressed in pH value. The variation of hydrogen ion concentration impacts the chemistry, solubility of ions and the electron density of donor atoms of crosslinked chitosan throughout nanocomposite. In Figure 7, was found that the sorption capacities of mercury and copper were significantly impacted and increased with elevation the aqueous solution pH value till attained to the maximum (pH 6) for mercury and copper ions. The observed trend was obtained as expected and simply explained owed to lone pair of electrons on nitrogen and oxygen atoms of crosslinked chitosan, which are fit to form the coordinated bond with mercury or copper ions. At low pH, most of the active functional groups of “nano-SiO2-crosslinked chitosan-nano-TiO2" are protonated and become positively charged sites to produce an electrostatic repulsion with ions and hence impediment of mercury and copper ions sorption onto crosslinked chitosan nanocomposite. However, increasing pH resulted in deprotonation of the active functional groups and facilitated the chelation with metal ions thus increasing the capacity30. The highest capacity values for mercury and copper were found 800 and 400 µmol g-1, respectively. Effect of adsorbent dosage The number and accessibility of binding sites within the crosslinked chitosan and on the overall surface of nanocomposite that are already bonded with ions were illustrated by studying mass impact on the metal sorption process. The capacity values and percentage of metal extraction were determined via utilizing different masses of the designed nanocomposite (10-50 mg) as compiled in Table 2. The % extraction values of mercury and copper were found to increase with increasing dosage due to larger surface area and greater number of active binding sites. Whereas, the highest extraction percentages of mercury (98.7%) and copper (92.5%) were obtained (50 mg). The capacity values of both mercury and copper were progressively lowered with increasing nanocomposite dosage. This observation may 11 ACS Paragon Plus Environment


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be assigned to the formulation of aggregates during sorption operations causing a direct reduction in the exposed surface area and the number of vigorous binding sites7. Effect of temperature and thermodynamic studies Temperature impact on the extraction of mercury and copper was also investigated and found to display a gradual diminish in the quantity adsorbed of both ions with increasing the temperature (Figure 8). This behavior obviously suggests an exothermic process31. The thermodynamic parameters; ΔGo, ΔHo, and ΔSo for adsorptive uptake of the two metal ions at different temperatures were determined and listed out (Table 3). The standard free energy ΔGo can be calculated from Eq. (2). ΔG° = −𝑅𝑇 𝑙𝑛𝐾𝐷

(2)

Whereas, R (8.314 J mol-1 K-1) is the real gas constant, T(K) is the temperature. The KD value is the sorption partition constant which is defined as the ratio of (metal ion) onto the solid phase to its amount in solution at equilibrium and this parameter is commonly determined from Eq. (3). q

KD = C

e

(3)

Where, q and Ce represent metal concentrations on the nanocomposite and in solution at equilibrium (mg L-1), respectively. The entropy (ΔSo) and enthalpy (ΔHo) of sorption can be determined using Van't Hoff Eq. (4). lnK D =

Δ S° R

−

Δ H° RT

(4)

The plot of lnKD against 1/T (Figure 9) gives a straight line with an acceptable coefficient of determination (R2 = 1.0 for mercury and 0.99 for copper ions) with slope = - ΔHo/R and Intercept = ΔSo/R. The negative ΔGo values obtained and outlined (Table 3) refer to spontaneous sorption operations for extraction of mercury and copper ions. The less negative values are indicating to the less favorable 12 ACS Paragon Plus Environment

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sorption operations. The observed decline in reaction spontaneity at a higher temperature may be imputed to (i) an increment in the adsorbate solubility and (ii) decreasing the chemical potential; both of these factors decrease the metal sorption12. The ΔHo values are -41.35 and -10.46 kJ mol-1 for sorption of mercury and copper, respectively. These large negative values substantially predict exothermic processes and strong chemical interactions between metal ions and nanocomposite32. The more negative value for mercury than copper indicates the chemical binding of mercury with the nanocomposite is stronger than copper. The negative value of ΔSo in case of mercury and copper metal ions suggests a declining randomness at the solid/liquid connect during the sorption and this trend refers that the sorption is unfavorable at higher T. Effect of metal concentration and isotherm studies for mercury and copper The sorption isotherm is an important operation for designing sorption system. Three models of sorption were studied for microwave-assisted extraction of mercury and copper namely Langmuir, Freundlich, and Dubinin-Radushkevich isotherms by variation the concentration of mercury and copper ions solutions (0.04 - 0.2 M), and results are illustrated in Figure 10. Based on the collected data, it was found that the higher concentration produced the higher capacity values. The capacity values observed at a high metal concentration of 0.2-M were found 561.7 mg g-1 for mercury and 279.4 mg g-1 for copper. Eq. (5) is defined the Langmuir isotherm model, and stated that the sorption behavior is related to a homogenous surface forming monolayer without interaction between the adsorbing species33. 𝐶𝑒 𝑞𝑒

1

= 𝑏.𝑞

𝑚𝑎𝑥

+𝑞

𝐶𝑒

(5)

𝑚𝑎𝑥

Where Ce (mg L-1) is the concentration at equilibrium, qe (mg g-1) is the quantity of mercury or copper adsorbed onto nano-SiO2-crosslinked chitosan-nano-TiO2 nanocomposite at equilibrium, b and qmax are Langmuir model parameters, which are referred to the energy of sorption and highest capacity, respectively. A straight 13 ACS Paragon Plus Environment


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line was obtained when plotting Ce/qe against Ce, with R2 values 0.992 and 0.993 for mercury and copper, respectively. This implies that the sorption operations of both metal ions are well accepted to Langmuir isotherm model (Figure 11a). The Langmuir constants qmax and b of mercury and copper sorption are collected in Table 4. The separation factor (RL) is given by Eq. (6). R L = 1 ⁄ (1 + b. Co )

(6)

Where, the value of RL points out the nature of the sorption operation if RL > 1 as this operation is unfavorable, RL = 1 this indicates linearity, if 0 < RL < 1, the operation is favorable and if RL= 0, it indicates that the operation is irreversible. As shown from Table 4 the values of RL corresponds to 1.0 to refer to a linear sorption behavior between mercury or copper and designed nanocomposite. The Freundlich model represented by Eq. (7), is based on a heterogeneous sorption surface to provide equal available sites with different energies of sorption 34. 1

lnq e = lnK F + n lnCe

(7)

Where, KF is the Freundlich constant which is defined as the sorption or distribution related to the bond energy and represents the quantity of mercury or copper adsorbed on "nano-SiO2- crosslinked chitosan-nano-TiO2" as a measure of capacity, mg g−1, n is the intensity of the adsorbents. A straight line is obtained when plotting lnq e versus lnCe (Figure 11b) with a slope = 1/n and intercept = lnKF. In Table 4, the Freundlich parameters of "Nano-SiO2-crosslinked chitosan-nano-TiO2" nanocomposite are collected. The value of sorption intensity "n" for the studied nanocomposite is greater than unity and this trend indicates that mercury and copper are favorably adsorbed by this adsorbent. The Dubinin-Radushkevich (D-R) isotherm model35 was chosen to estimate the characteristic porosity of the nanocomposite surface and sorption mean free energy. The linearized D-R form is presented by Eq. (8). lnqe = ln qs – ( Kad Ɛ2 ) 14 ACS Paragon Plus Environment

(8)

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Where, qs is the theoretical saturation capacity (mg g−1), ε is the Polanyi potential which is determined by Eq. (9) and Kad is the Dubinin-Radushkevich isotherm constant which is acquainted with the mean free energy of sorption (J mol-1). Ԑ =RT ln (1 + 1⁄Ce)

(9)

A straight line is obtained when plotting lnq e versus ε2 (Figure 12a and 12b). The qs value was calculated and found to correspond to 487.8 and 280.9 mg g−1 for mercury and copper, respectively. While the Kad values were 8.39 and 0.19 mol2.J-2 for mercury and copper, respectively (Table 4). The energy (Es, kJ mol−1) can be calculated by Eq. (10) 𝑬𝒔 =

𝟏 √𝟐𝑲𝒂𝒅

(10)

The obtained ES; 0.244 and 1.62 kJ mol−1 for extraction mercury and copper, respectively by the “nano-SiO2-crosslinked chitosan-nano-TiO2” indicate nonspecific sorption mechanism that proceeds via physisorption, chemisorption and ion exchange10. Effect of interfering ion The legitimacy of “nano-SiO2-crosslinked chitosan-nano-TiO2" as a selective nanocomposite for extraction of either mercury or copper ions was investigated by exploring their capacity values and extraction percentages in the existence of other competing metal ions. The collected results in Table 5 articulate that the existence of contending ions was found to exhibit limited interference behaviors. The percentage selectivity of mercury coexisting with an equimolar concentration of sodium(I), magnesium(II), zinc(II) and nickel(II) was identified as 100, 100, 95 and 90%, respectively, while those for copper were 100, 95, 95 and 80%, respectively. The variable affinities of different interfering ions in competitive sorption are due to difference in their ionic charges and radius of ions and the nature of functional groups involved in the crosslinked chitosan36. The outlined results manifest 15 ACS Paragon Plus Environment


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achieving our aim to promote a high-performance nanocomposite for selective SPE of mercury and copper ion. Potential applications for mercury and copper extraction from real samples The application and validity of “nano-SiO2-crosslinked chitosan-nano-TiO2” nanocomposite were explored and examined in the direct extraction of mercury and copper from different real water samples. Two parallel procedures were achieved in this study. Table 6 summarizes the data and results obtained by the two techniques. The first procedure involves passing mercury or copper-containing water sample through an extraction micro-column packed with 100 mg of "nano-SiO2- crosslinked chitosan-nano-TiO2". The micro-column extraction of mercury or copper was based on 2-stage analysis. Following up the extraction percentages in each stage confirmed high efficiency and greatly improving the removal of both metal ions. The second extraction procedure was performed by the microwave-assisted technique that shows much higher removal efficiency and shorter operating time 11. The extraction percentages determined by microwave-assisted sorption of mercury from the tap water, sea-water and industrial water samples were 99.5, 98.8 and 98.0%, respectively, while those for copper are 96.6, 95.2, 94.4%, respectively. These results declare the advantages of microwave-assisted sorption method that provides instantaneous extraction of mercury and copper ion from aqueous matrices. Conclusion The

“nano-SiO2-crosslinked

chitosan-nano-TiO2”

nanocomposite

was

successfully synthesized and its structure was confirmed by various instrumental techniques. This nanocomposite was designed as an imprinting polymeric nanosorbent for selective SPE of mercury and copper. The adsorptive extraction was highly enhanced by utilizing microwave-assisted sorption technique. The maximum capacity values; 8000 and 4000 µmol g-1 for mercury and copper, respectively were obtained within the 20s at optimum buffering condition (pH 6). The percentage of 16 ACS Paragon Plus Environment

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extraction of mercury and copper metal ions was significantly increased with increasing pH and nanocomposite dose while decreasing with rising temperature. The large negative values of ΔHo and ΔGo indicated the spontaneity of sorption operations. The sorption operations of copper and mercury were further explained and studied by three isotherm models showing favorable sorption processes with low required energy and high effectiveness. This nanocomposite exhibited excellent ability to selectively extract mercury and copper compared to other previously reported adsorbents (Table 7) even in existence of other competing metal ions with high percentage near to 100% within only 20s. References (1) Mahmoud, M. E.; Yakout, A. A.; Hussein, K. H.; Osman, M. M. Magnetic accumulation and extraction of Cd(II), Mercury and Pb(II) by a novel nano Fe3O4-coated-dioctylphthalate-immobilizedhydroxylamine. J. Environ. Chem. Eng. 2015, 3, 843–851. DOI: .org/10.1016/j.jece.2015.03.024 (2) Vieira, R. S.; Oliveira, M. L. M.; Guibal, E.; Rodriguez-Castell, E.; Beppu, M. M. Copper, mercury and chromium adsorption on natural and crosslinked chitosan films: An XPS investigation of mechanism. Colloids and Surf. A. 2011, 374, 108–114. DOI: 10.1016/j.colsurfa.2010.11.022 (3) Rocha, C. G.; Zaia, D. A. M.; Alfaya, R. V. Use of rice straw as biosorbent for removal of Copper, Zn(II), Cd(II) and Mercury ions in industrial effluents. J. Hazard. Mater. 2009, 166, 383–388. DOI: org/10.1016/j.jhazmat.2008.11.074 (4) Barringer, J.L.; Szabo, Z.; Schneider, D.; Atkinson, W.D.; Gallagher, R.A. Mercury in ground water,

septage, leach-field effluent, and soils in residential areas, New Jersey coastal plain, Sci. Total Environ. 2006, 361, 144–162. doi:10.1016/j.scitotenv.2005.05.037 (5) Gonzalez-Estrella J.; Li, G.; Neely, S.E.; Puyol, D.; Sierra-Alvarez, R.; Field, J.A. Elemental copper

nanoparticle toxicity to anaerobic ammonium oxidation and the influence of ethylene diamine-tetra acetic acid (EDTA) on copper toxicity, Chemosphere 2017, 184, 730-737. DOI: org/10.1016/j.chemosphere.2017.06.054 (6) Mashhadizadeh, M. H.; Karami, Z. Solid phase extraction of trace amounts of Ag, Cd, Cu, and Zn in environmental samples using magnetic nanoparticles coated by 3-(trimethoxysilyl)-1-propantiol and modified with 2-amino-5-mercapto-1,3,4-thiadiazole and their determination by ICP-OES. J. Hazard. Mater. 2011, 190, 1023–1030. DOI: 10.1016/j.jhazmat.2011.04.051 (7) Mahmoud, M. E.; Yakout, A. A.; Abdel-Aal, H.; Osman, M. M. High performance SiO2-nanoparticlesimmobilized-Penicillium funiculosum for bioaccumulation and solid phase extraction of lead. Bioresour. Technol. 2012, 106, 125–132. DOI: 10.1016/j.biortech.2011.11.081



Page 18 of 34

(8) Mahmoud, M. E.; Amira, M. F.; Zaghloul, A. A.; Ibrahim, G.A. Microwave-enforced sorption of heavy metals from aqueous solutions on the surface of magnetic iron oxide-functionalized-3aminopropyltriethoxysilane. Chem. Eng. J. 2016, 293, 200–206. DOI: org/10.1016/j.cej.2016.02.056 (9) Mahmoud, M. E.; Yakout, A. A.; Elserw, M. I.; Osman, M. M. Adsorption Behavior of Solvent-Free Microwave Assisted Nanosilica-Functionalized Carboxylic Acids for the Removal of Cobalt (II) from Water. Clean – Soil, Air, Water 2016, 44, 909-1084. DOI: 10.1002/clen.201500012 (10) Zhang, Z.; Cui, H. Biodegradability and Biocompatibility Study of Poly(Chitosan-g- lactic Acid) Scaffolds. Molecules 2012, 17, 3243–3258 DOI: 10.3390/molecules17033243 (11) Radwan, A. A.; Alanazi, F. K.; Alsarra, A. I. Microwave irradiation-assisted synthesis of a novel crown ether crosslinked chitosan as a chelating agent for heavy metal ions (M+n). Molecules 2010, 15, 6257– 6268. DOI: 10.3390/molecules15096257 (12) Kyzas, G. Z.; Deliyanni, E. A. Mercury (II) Removal with Modified Magnetic Chitosan Adsorbents. Molecules 2013, 18, 6193-6214. DOI: 10.3390/molecules18066193 (13) Dubey, R.; Bajpai, J.; Bajpai, A. K. Chitosan-Alginate Nanoparticles (CANPs) as Potential Nanosorbent for Removal of Hg (II) Ions, Environ. Nanotech. Monit. Manag. 2016, 6, 32–44. DOI. org/10.1016/j.enmm.2016.06.008 (14) Jeon, C.; Park, K. H. Adsorption and desorption characteristics for mercury ions using aminated chitosan bead. Water Res. 2005, 39, 3938–3944. DOI. org/10.1016/j.watres.2005.07.020 (15) Tao, X.; Li, K.; Yan, H.; Yang, H.; Li, A. Simultaneous removal of acid green 25 and mercury ions from aqueous solutions using glutamine modified chitosan magnetic composite microspheres. Environ. Pollut. 2016, 209, 21-29. DOI. org/10.1016/j.envpol.2015.11.020 (16) Wang, X.; Deng, W.; Xie, Y.; Wang, C. Selective removal of mercury ions using a chitosan–poly(vinyl alcohol) hydrogel adsorbent with three-dimensional network structure. Chem. Eng. J. 2013, 228, 232– 242. DOI.org/10.1016/j.cej.2013.04.104 (17) Donia, A. M.; Atia, A. A.; Elwakeel, K. Z. Selective separation of mercury(II) using magnetic chitosan resin modified with Schiff’s base derived from thiourea and glutaraldehyde. J. Hazard. Mater. 2008, 151, 372–379. https:// doi:10.1016/j.jhazmat.2007.05.083 (18) Yu, K.; Ho, J.; Mc Candlish, E.; Buckley, B.; Patel, R.; Li, Z.; Shapley, N. C. Copper ion adsorption by chitosan nanoparticles and alginate microparticles for water purification applications. Colloids Surf. A: 2013, 425, 31– 41. DOI.org/10.1016/j.colsurfa.2012.12.043 (19) Nagireddi, S.; Katyar, V.; Uppaluri, R. Pd(II) adsorption characteristics of glutaraldehyde cross-linked chitosan copolymer resin. Int. J. Biol. Macromol. 2017, 94, 72–84. DOI.org/10.1016/j.ijbiomac.2016.09.088 (20) Cahyaningrum, S; Sianita, M. Immobilization of Pepsin onto Chitosan Silica Nanobeads with Glutaraldehyde as Crosslink Agent. Bull. Chem. React. Eng. Cat. 2014, 9, 263-269. DOI.org/10.9767/bcrec.9.3.7060.263-269 (21) Mahmoud, M.E.; Fekry, N.A.; El-Latif M.M.A. Nanocomposites of nanosilica-immobilized-

nanopolyaniline and crosslinked nanopolyaniline for removal of heavy metals, Chem. Eng. J. 2016, 304, 679–691. DOI.org/10.1016/j.cej.2016.06.110 18 ACS Paragon Plus Environment

Page 19 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering (22) Carmona, V.B.; Oliveira, R.M.; Silva, W.T.L.; Mattoso, L.H.C; Marconcini J.M. Nanosilica from rice husk:

Extraction

and

characterization,

Ind.

Crops

Prod.

2013,

43,

291–296.

DOI.org/10.1016/j.indcrop.2012.06.050 (23) Guibal, E.; Roulph, C.; Cloirec, P.L. Infrared spectroscopic study of uranyl biosorption by fungal biomass and materials of biological origin. Environ. Sci. Technol. 1995, 29, 2496–2502. DOI: 10.1021/es00010a007 (24) Mahmoud, M.E.; Abdou, A.E.H.; Sobhy, M.E.; Fekry N.A. Solid–solid crosslinking of carboxymethyl

cellulose nanolayer on titanium oxide nanoparticles as a novel biocomposite for efficient removal of toxic heavy metals from water, Int. J. Biol. Macromol. 105 (2017) 1269–1278. DOI.org/10.1016/j.ijbiomac.2017.07.156 (25) Jiang, D.; Xu, Y.; Hou, B.; Wu D.; Sun, Y. H. Synthesis of visible light-activated TiO2 photocatalyst via surface organic modification. J. Solid State Chem. 2007, 180, 1787-1791. DOI: 10.1016/j.jssc.2007.03.010 (26) Mahmoud, M. E.; Abou Ali, S. A. A.; Nassar, A. M. G.; Elweshahy, S. M. T.; Ahmed, S. B. Immobilization of chitosan nanolayers on the surface of nano-titanium oxide as a novel nanocomposite for efficient removal of La(III) from water. Inter. J. Biol. Macromol. 2017, 101, 230–240. DOI.org/10.1016/j.ijbiomac.2017.03.049 (27) Corazzari, I.; Nistic, R.; Turci, F.; Faga, M. G.; Franzoso, F.; Tabasso, S.; Magnacca, G. Advanced physicochemical characterization of chitosan by means of TGA coupled on-line with FTIR and GCMS: Thermal degradation and water adsorption capacity. Polym. Degrad. Stability 2015, 112, 1-9. DOI.org/10.1016/j.polymdegradstab.2014.12.006 (28) Zhang, Y. G.; Song, D.; Lanni, L.M.; Shimizu, K.D. Importance of functional monomer dimerization in the molecular imprinting process. Macromol. 2010, 43, 6284-6294. DOI: 10.1021/ma101013c (29) Zhang, M.; Helleur, R.; Zhang, Y. Ion-Imprinted Chitosan Gel Beads for Selective Adsorption of Ag+ from Aqueous Solution. Carbohydr. Polym. 2015, 130, DOI.org/10.1016/j.carbpol.2015.05.038

206-212.

(30) Mahmoud, M.E.; Hassan, S.S.M.; Kamel, A.H.; Elserw, M.I.A. Development of microwave-assisted functionalized nanosilicas for instantaneous removal of heavy metals, Powder Technol. 326, 454-466. https://doi.org/10.1016/j.powtec.2017.12.001 (31) El-Hamshary, H.; El-Sigeny, S. Removal of phenolic compounds using (2-hydroxyethyl methacrylate/ acrylamidopyridine) hydrogel prepared by gamma radiation, Sep. Purif. Technol. 2007, 57, 329–337. DOI:10.1016/j.seppur.2007.04.013 (32) Alkan, M.; Demirbas, O.; Elikcapa, S.; Dogan, M. Sorption of acid red 57 from aqueous solution onto sepiolite. J. Hazard. Mater. 2004, 116, 135–145. DOI: 10.1016/j.jhazmat.2004.08.003 (33) Langmuir, I. The adsorption of gases on plane surfaces of glass, mica and platinum. J. Am. Chem. Soc. 1918, 40, 1361–1403. DOI: 10.1021/ja02242a004 (34) Freundlich, H. Über die adsorption in Lösungen. Z. Phys. Chem. 1906, 57, 385–470. (35) Masoud Jahandar Lashaki, Mohammadreza Fayaz, Saeid Niknaddaf, Zaher Hashisho Effect of the

adsorbate kinetic diameter on the accuracy of the Dubinin–Radushkevich equation for modeling 19 ACS Paragon Plus Environment


Page 20 of 34

adsorption of organic vapors on activated carbon, Journal of Hazardous Materials 241–242 (2012) 154–163. DOI:.org/10.1016/j.jhazmat.2012.09.024 (36) Mahmoud, M. E.; Yakout, A. A.; Abdel-Aal, H.; Osman, M. M. Enhanced biosorptive removal of cadmium from aqueous solutions by silicon dioxide nano-powder, heat inactivated and immobilized Aspergillus ustus. Desalination 2011, 279, 291-197. DOI:10.1016/j.desal.2011.06.023


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Scheme 1. Synthetic procedures of "nano-SiO2-crosslinked chitosan-nano-TiO2"



Page 22 of 34

Table 1. Mercury and Copper capacity values for the three synthesized nanocompositesat pH 6 and 20 s microwave contact time Metal sorption capacity (µmol g-1)

Nanocomposite

Mercury

Copper

Nano-SiO2-crosslinked chitosan-nano-SiO2

3200

3500

Nano-TiO2-crosslinked chitosan-nano-TiO2

5600

3100

Nano-SiO2-crosslinked chitosan-nano-TiO2

8000

4000

Table 2. Effect of dosage on Mercury and Copper capacity values at pH 6 and 20 s microwavecontact time.

Nanocomposites

10

20

30

40

50

%Extraction

66.7

80

90

96

98.7

Capacity (µmol g-1)

8000

4800

3600

2880

2368

%Extraction

50

66.25

81.25

87.5

92.5

Capacity (µmol g-1)

4000

2650

2166.7

1750

1480

dosage (mg) Mercury

Copper


Page 23 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 3. Standard thermodynamic parameters for sorption of Mercury and Copper ions at different reaction temperatures, 5 min shaking time and pH 6. Sorption Thermodynamic Parameters Metal ion

Mercury

Copper

T (K)

KD

298

9.00

-5.499

303 313 323 333

7.33 4.00 2.44 1.63

-4.897 -3.694 -2.492 -1.288

298

2.33

-2.087

303 313 323 333

2.12 1.94 1.63 1.50

-1.947 -1.666 -1.385 -1.104

Δ G° (kJ mol-1)

R2

Δ H° (kJ mol-1)

ΔS° (kJ mol-1 K-1)

-41.35

-0.120

1.00

-10.46

-0.028

0.99

Table 4. Isotherm parameters of different isotherm models for sorption of Mercury and Copper Metal ion Isotherm model

Langmuir

Freundlich

Dubinin-Radushkevich

Isotherm parameters

Mercury

Copper

qmax ( mg g-1)

1515.2

333.3

b (L mg-1 )

1.75 x 10-5

0.72 x 10-5

RL

1

1

R2

0.992

0.993

n

1.27

2.89

KF (L. mg-1 )

0.152

0.075

R2

0.994

0.883

qs(mg g-1)

487.8

280.9

Kad (mol2 j-2 )

8.39

0.19

Es

0.244

1.62

R2

0.900

0.994



Table 5. Effect of interfering ion on capacity values and selectivity percentage of Mercury and Copper Interfering ion

Na(I)

Mg(II)

Zn(II)

Ni(II)

Mercury capacity (µmol g-1)

8000

8000

7600

7200

% Mercury selectivity

100

100

95

90

Copper capacity (µmol g-1)

4000

3800

3800

3200

%Copper selectivity

100

95

95

80

Table 6. Extraction of Mercury and Copper from tap water, sea water and industrial wastewater samples Industrial Wastewater

Sea water

Copper

Mercury

Copper

Mercury

Copper

Mercur y

Metal content (ppm) before spiking

1.0

0.4

ND

ND

ND

ND

Metal content (ppm) after spiking

5.0

5.0

5.0

5.0

5.0

5.0

1ststage

79.8

88.1

86.5

92.7

87.6

94.1

2nd stage

87.4

93.3

90.5

95.1

92.0

96.6

94.4

98.0

95.2

98.8

96.6

99.5

Water Samples

% Metal extraction

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 34

Tap Water

Column technique

Microwave-assisted extraction technique


Page 25 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47


Table 7. Comparison with some other previously published works Chitosan

adsorbent Metal ion

Crosslinked chitosan Magnetic crosslinked chitosan

Mercury

Optimum pH

Optimum time

qmax (mg/g)

5

200 min

6

Thermodynamic parameters ΔH0 (kJ/mol)

ΔS0 (kJ/mol. K)

145

+6.1

+0.023

200 min

152

+6.2

+0.024

Ref.

12

Chitosan-alginate

Mercury

5

90 min

217.4

̶

̶

13

Aminated chitosan

Mercury

7

100 min

476

-12.3

+1.2

14

Glutamine-modified chitosan magnectic composite

Mercury

5

20 min

141

̶

̶

15

Chitosan-poly(vinyl hydragel

Mercury

5.5

24 h

585.9

̶

̶

16

Schiff’s base-modified magnetic chitosan

Mercury

5

70 min

561.7

-16.4

+2.11

17

Chitosan nanoparticles

Copper

3.5

20-30 min

112.4

̶

̶

18

Nano-SiO2-crosslinked chitosan-nano-TiO2

Mercury

6

20 S

1515.2

-41.35

-0.120

Copper

6

20 S

333.3

-10.46

-0.028

alcohol)


This study


Figure 1. FT-IR spectra of (a) nano-SiO2, (b) nano-TiO2, (C) crosslinked chitosan and (d) “nanoSiO2-crosslinked chitosan-nano-TiO2“


Page 26 of 34

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Figure 2. XRD of “nano-SiO2-crosslinked chitosan-nano-TiO2”

Figure 3. TGA of “nano-SiO2-crosslinked chitosan-nano-TiO2”



Figure 4. (a) SEM and (b) TEM of “nano-SiO2-crosslinked chitosan-nano-TiO2”

Figure 5. Sorption/desorption BET isotherm of “nano-SiO2-crosslinked chitosan-nano-TiO2”


Page 28 of 34

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Figure 6. Effect of Microwave-contact time (s) on mercury and copper capacity values

Figure 7. Effect of pH on mercury and copper capacity values at 20 s microwave-contact time



Figure 8. The effect of temperature on the capacity values of mercury and copper at 5 min shaking and pH 6.

Figure 9. The Van't Hoff plot for the extraction of mercury and copper at different reaction temperature, 5 min shaking time and pH 6.


Page 30 of 34

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Figure 10. Effect of initial metal concentration on capacity values of mercury and copper at pH 6 and 20 s microwave-contact time



Figure 11. (a) Langmuir and (b) Freundlich, isotherm models for sorption of mercury and copper at pH 6 and 20 s microwave-contact time


Page 32 of 34

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Figure 12. Dubinin–Radushkevich isotherm model for sorption of (a) mercury and (b) copper at pH6 and 20 s microwave-contact time



Page 34 of 34

TOC Graphic An imprinting polymeric nanocomposite was designed from chitosan, nano-SiO2 and nano-TiO2 to remove Copper and Cd(II) using microwave sorption technique


Imprinting âNano-SiO2-Crosslinked Chitosan-Nano-TiO2â Polymeric

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