Selective Adsorption toward Hg(II) and Inhibitory Effect on Bacterial

Research Article Cite This: ACS Appl. Mater. Interfaces 2018, 10, 40302−40316

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Selective Adsorption toward Hg(II) and Inhibitory Effect on Bacterial Growth Occurring on Thiosemicarbazide-Functionalized Chitosan Microsphere Surface Yan Wang,† Qifeng Dang,† Chengsheng Liu,*,† Dejun Yu,‡ Xiaoying Pu,† Qiongqiong Wang,† Hong Gao,† Bainian Zhang,§ and Dongsu Cha∥ †

College of Marine Life Sciences, Ocean University of China, 5 Yushan Road, Qingdao 266003, P. R. China Qingdao Marine Biomedical Research Institute, 23 Hong Kong East Road, Qingdao 266071, P. R. China § Qingdao Aorun Biotechnology Co., Ltd., Room 602, Century Mansion, 39 Donghaixi Road, Qingdao 266071, P. R. China ∥ The Graduate School of Biotechnology, Korea University, Seoul 136-701, South Korea

ACS Appl. Mater. Interfaces 2018.10:40302-40316. Downloaded from pubs.acs.org by UNIV OF WINNIPEG on 12/03/18. For personal use only.

‡

S Supporting Information *

ABSTRACT: The work presented here aims to fabricate dual-purpose adsorbent with adsorption selectivity for Hg(II) and antibacterial activity. TSC-PGMA-MACS microspheres were first constructed via esterification of malic acid (MA) with chitosan (CS) and through successively grafting glycidyl methacrylate (GMA) and thiosemicarbazide (TSC) onto MACS microsphere surfaces. Fourier transform infrared spectroscopy, elemental analysis, energy-dispersive X-ray spectrometry, X-ray diffraction, differential scanning calorimetry, thermogravimetry, differential thermogravimetry, scanning electron microscopy, and Brunauer−Emmett−Teller results provided ample evidence that new mesoporous adsorbent, with 35.340 m2 g−1 of specific surface area and abundant −NH2 and CS, was successfully fabricated and had loose crystalline, thermodynamically stable, and well-defined architectures, beneficial for Hg(II) adsorption and bacterial cell killing. Optimal adsorption parameters were determined via varying pH, time, concentrations, and temperatures, and pH 6.0 was chosen as an optimal pH for Hg(II) adsorption. Adsorption behavior, described well by pseudo-second-order kinetic and Langmuir isotherm models, and thermodynamic parameters implied a chemical, monolayer, endothermic, and spontaneous adsorption process, and the maximum adsorption capacity for Hg(II) was 242.7 mg g−1, higher than most of the available adsorbents. Competitive adsorption exhibited excellent adsorption selectivity for Hg(II) in binary-metal solutions. Besides, TSC-PGMA-MACS microspheres had outstanding reusability even after five times recycling, with adsorption capability loss 0.05), likely due to the formation of hydroxides, such as soluble Hg(OH)+ and colloidal precipitate Hg(OH)2, to restrain complex formation. Altogether, Hg(II) adsorption on TSC-PGMA-MACS microspheres greatly depended on pH within the experimental pH values, and pH 6.0 was chosen as the optimal pH for Hg(II) adsorption in the following tests. 3.2.2. Effect of Contact Time and Adsorption Kinetics. Figure 5B displays the effects of contact time. Clearly, both adsorption capacity and removal percentage curves had a similar curvilinear trend over time. Within incipiently 10 min, adsorption amount quickly reached 141 mg g−1, more than half of the saturated adsorption capacity. Then, accumulative adsorption amount increased to 205 mg g−1 at 90 min, and the removal percentage was 88%. These results were mainly because of numerous available adsorption sites and high ionconcentration gradient at liquid−solid interface, which drove TSC-PGMA-MACS microspheres to combine with Hg(II) easily. Subsequently, the adsorption amount and removal percentage increased slowly and gradually tended to plateaus, which might be caused by the following reasons: with the 40309

DOI: 10.1021/acsami.8b14893 ACS Appl. Mater. Interfaces 2018, 10, 40302−40316

Research Article

ACS Applied Materials & Interfaces

(Table 1) demonstrated that intraparticle diffusion was not a rate-limiting step for this adsorption. In summary, all data drew a logical conclusion that the crucial rate-limiting step was chemisorption rather than intraparticle diffusion. 3.2.3. Effect of Initial Concentration and Adsorption Isotherm. Figure 5C depicts the effects of initial Hg(II) concentrations on adsorption toward Hg(II) at 298 K. As initial Hg(II) concentrations increased, the adsorption capacity for Hg(II) gradually increased until the saturated adsorption appeared, mainly owing to the enhanced driving force for mass transfer at high initial Hg(II) concentrations. During the adsorption process, hydroxyl, amino, carboxyl, and thione groups on TSC-PGMA-MACS microspheres might be responsible for Hg(II) adsorption; besides, the thiourea group on TSC with two tautomeric forms, which can form bidentate and/or quadridentate ligand(s) to coordinate with Hg(II),37,45 should be an active participant in the adsorption process. Likely, high Hg(II) concentrations cause a high affinity between adsorption sites and absorbates. In addition, the removal percentage decreased with increase in Hg(II) concentrations because of a lack of adsorption sites on microspheres. Here, we used Langmuir and Freundlich isotherm models, which are often applied to homogeneous monolayer, heterogeneous multilayer, and reversible adsorption, to deal with the adsorption data. Two isotherm models are expressed as eqs 8 and 9.

increase in contact time, (1) the adsorption sites on microsphere surfaces were largely occupied, (2) the driving force for mass transfer in solutions continuously weakened, and (3) the void resistance to adsorption constantly increased. In addition, adsorption behavior was also related to adsorption reactions of soft bases (e.g., −OH and −NH2) with Hg(II), as well as to the migration and diffusion of Hg(II) to pores or channels in TSC-PGMA-MACS microsphere matrices. To explore potential rate-limiting steps during Hg(II) adsorption, including external film diffusion, intraparticle diffusion, and chemisorption,17 we selected several adsorption kinetic models to fit the experimental data. Pseudo-first-order and pseudo-second-order kinetic models are expressed as eqs 5 and 6, respectively. ln(qe1 − qt) = ln qe1 − k1t

(5)

t 1 t = + 2 qt qe2 k 2qe2

(6)

−1

where qt (mg g ) is the adsorption capacity at contact time t (min), qe1 and qe2 (mg g−1) are adsorption capacities at equilibrium, and k1 (min−1) and k2 (g mg−1 min−1) are equilibrium rate constants of pseudo-first-order and pseudosecond-order kinetic models, respectively. Kinetic parameters from linear fitting (Figure S2A,B) are listed in Table 1. Clearly, Table 1. Kinetic Model Parameters of TSC-PGMA-MACS Microspheres for Hg(II) Adsorption kinetic model

Qe =

parameter qeexp (mg g−1) qe1cal (mg g−1) k1 (min−1) R12 qe2cal (mg g−1) k2 (g mg−1 min−1) R22 Kid1 (mg g−1 min−1/2) Kid2 (mg g−1 min−1/2) Kid3 (mg g−1 min−1/2) C1 (mg g−1) C2 (mg g−1) C3 (mg g−1)

pseudo-first-order

pseudo-second-order

intraparticle diffusion

225.1 111.1 0.029 0.9562 234.7 5.4 × 10−4 0.9995 22.4 12.1 0.8 28.7 108.1 212.8

(8) (9)

−1

−1

where Qe (mg g ) and Ce (mg L ) are the adsorption capacity and the concentration of Hg(II) at adsorption equilibrium, respectively, Qm (mg g−1) is the maximum adsorption capacity, KL (L mg−1) is an equilibrium constant for Langmuir model associated with the affinity of adsorption sites and the binding energy of adsorption, and KF (mg1−1/n L1/n g−1) and n are Freundlich constants related to adsorption capacity and intensity, respectively. Relative isotherm parameters from linear fitting (Figure S3A,B) are summarized in Table 2. Obviously, RL2 was more near to 1 than RF2, and the Table 2. Isotherm Model Parameters of TSC-PGMA-MACS Microspheres for Hg(II) Adsorption at 25 °C

adsorption capacity (qe2 ) for Hg(II) calculated from pseudosecond-order model was closer to the experimental datum (qeexp), compared to that (qe1cal) from pseudo-first-order model. Moreover, the adsorption toward Hg(II) was more consistent with the pseudo-second-order model because R22 > R12. Therefore, the rate-limiting step during Hg(II) adsorption on TSC-PGMA-MACS microspheres was chemisorption via chelation and/or electrostatic interaction(s). To further clarify the adsorption behavior, the Weber and Morris intraparticle diffusion model was employed to deal with the experimental data, and this model is given as eq 7. −1

1 + KLCe

Q e = KFCe1/ n

cal

qt = K idt 1/2 + C

Q mKLCe

isotherm model Langmuir

Freundlich

parameter qeexp (mg g−1) Qm (mg g−1) KL (L mg−1) RL2 KF (mg1−1/n L1/n g−1) n RF 2

225.1 242.7 6.71 × 10−2 0.9970 24.714 2.180 0.9404

maximum adsorption capacity (242.7 mg g−1) calculated from Langmuir isotherm model was much close to q e exp . Accordingly, Langmuir isotherm model well interpreted the adsorption toward Hg(II) on TSC-PGMA-MACS microspheres. However, Hg(II) adsorption was also considered an energetically heterogeneous and favorable process according to the Freundlich isotherm model, since the heterogeneity factor 1/n associated with the favorability of adsorption was smaller

(7) −1/2

where Kid (mg g min ) is the rate constant of intraparticle diffusion and C is the intercept of the linear fitting plot. Three linear segments were present in the linear fitting plot (Figure S2C), suggesting that more than one stage influenced the adsorption process. However, Kid1 > Kid2 > Kid3 and C ≠ 0 40310


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3.3. Selective Adsorption in Binary-Metal Solution. It is meaningful to determine whether TSC-PGMA-MACS microspheres are of selective adsorption toward Hg(II) in binary-metal solutions, since more than one metal ion, in most cases, coexists in real polluted water. We here chose Mg(II), Ca(II), Co(II), Cu(II), Pb(II), or Cd(II) as a coexisting metal ion to prepare six binary-metal solutions. Effects of coexisting metal ions on the maximum adsorption capacity for Hg(II) are displayed in Figure 6A. Although all of the relative removal ratios revealed that the divalent metal ions tested had no significant effects on adsorption toward Hg(II), there were slight changes as a result of competitive adsorption. Weak, even negligible, competition existed between Hg(II) and Mg(II) or Ca(II), and the relative removal ratio for Hg(II) was ca. 100% in Hg(II) + Mg(II) or Hg(II) + Ca(II) solution. Such a result can be well explained by HSAB theory, namely, major functional groups like thiol (soft base) on TSC-PGMAMACS microspheres in acidic surroundings are preferentially combined with Hg(II) (soft acid), rather than Mg(II) and Ca(II) (hard acids), in binary-metal solutions. As for other metal ions, the order of effects on Hg(II) removal was Pb(II) > Cu(II) > Cd(II) > Co(II). These outcomes mainly originated from three aspects: (1) theoretically, the influence of soft-acid Cd(II) on Hg(II) adsorption should be stronger than Pb(II), Cu(II), and Co(II) that belong to hard-medial-soft acids, but larger metal ions like Pb(II) are more accessible to adsorption sites on the surfaces of TSC-PGMA-MACS microspheres;12,42 (2) Pb(II) and Cu(II) have stronger affinity for −NH2 on microspheres compared to Cd(II);36 and (3) it is well illustrated that polymers with S and N atoms can readily bind Hg(II) via strong covalent bonds.16 Based on the analyses above, it was concluded that TSC-PGMA-MACS microspheres had a strong ability to selectively adsorb Hg(II) in binary-metal solutions. 3.4. Desorption and Reusability. Reusability is one of the crucial factors for evaluating whether an adsorbent has the actual application value. EDTA solution (0.5 M) was here chosen as desorbent used for eluting Hg(II) adsorbed onto TSC-PGMA-MACS microspheres. Figure 6B shows that there was a decreasing tendency for Hg(II) removal with the increase in reuse times, mainly related to the mass loss during adsorption and desorption, as well as to the loss of adsorption sites due to the strong affinity between Hg(II) and functional groups. However, the relative removal ratios within five-time consecutive cycles were 98.2, 94.5, 93.2, 88.3, and 86.0%, indicating a good reusability. Additionally, Table S5 provides the comparison of the maximum adsorption capacity of TSCPGMA-MACS microspheres for Hg(II) with adsorbents reported in journals. Obviously, TSC-PGMA-MACS microspheres presented 242.7 mg g−1 of maximum adsorption capacity, higher than most of the adsorbents reported previously. 3.5. Possible Adsorption Mechanism. To well understand the adsorption behavior toward Hg(II) on TSC-PGMAMACS microspheres and to find out as much information as possible about potential adsorption sites and bonding modes, FTIR spectra and XRD patterns before and after Hg(II) adsorption were recorded, as displayed in Figure 6C,D. As shown in Figure 6C, some characteristic absorption bands of TSC-PGMA-MACS-Hg(II) microspheres, compared to TSCPGMA-MACS microsphere spectrum, were significantly changed in intensity and/or in position. Bands at 3477 cm−1 (−OH) and 3334 cm−1 (−NH2) became weaker in intensity

than 1.0. Therefore, both monolayer and multilayer adsorptions should coexist in the Hg(II) adsorption process, whereas monolayer adsorption was more dominant during this process. Figure 5C also depicts the nonlinear regression for Langmuir and Freundlich isotherms, further illustrating that the Langmuir model fitted better with the experimental data than the Freundlich model because the correlation coefficient for the former (0.9921) was larger than that for the latter (0.9864). To study the affinity between Hg(II) and microspheres, we calculated RLa closely related to the Langmuir model. All RLa values (Table S4) were within 0−1, indicating that the adsorption process was favorable. Altogether, all results suggested that the adsorption toward Hg(II) on TSCPGMA-MACS microspheres was monolayer adsorption, with finite identical adsorption sites. 3.2.4. Effect of Temperature and Thermodynamic Analysis. Figure 5D shows the effects of temperatures on adsorption toward Hg(II). Both adsorption capacity and removal percentage increased with increase of temperature, indicating that the increase in temperature promoted Hg(II) adsorption. Thermodynamic parameters, changes in Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS), were calculated according to eqs 10, 11, and 12. Kv =

Qe Ce

ln K v =

(10)

ΔS ΔH − R RT

(11) (12)

ΔG = ΔH − T ΔS −1

where Kv (L g ) is the equilibrium adsorption constant obtained from Langmuir isotherm; R (8.314 J mol−1 K−1) is an ideal gas constant; T (K) is the absolute temperature; ΔH (kJ mol−1) and ΔS (J mol−1 K−1) denote the changes in enthalpy and entropy obtained from Figure S3C, respectively; and ΔG (kJ mol−1) is the change in Gibbs free energy. As presented in Table 3, positive ΔS implied the increase in randomness and Table 3. Thermodynamic Parameters of Adsorption toward Hg(II) on TSC-PGMA-MACS Microspheres thermodynamic parametera temperature (K) 278 288 298 308 318

ΔS (J mol−1 K−1)

64.82

ΔH (kJ mol−1)

ΔG (kJ mol−1)

17.19

−0.83 −1.48 −2.13 −2.77 −3.42

a ΔS, change in entropy; ΔH, change in enthalpy; ΔG, change in Gibbs free energy.

disorder at the solid−solute interface during Hg(II) adsorption, further indicating that Hg(II) adsorption was an entropy-driven process. Positive ΔH showed that Hg(II) adsorption was endothermic in nature, consistent with the fact that the removal percentage of Hg(II) increased with the increase of temperature.9 Moreover, the negative values of ΔG at different temperatures implied the spontaneous nature and feasibility of Hg(II) adsorption. Overall, the adsorption toward Hg(II) on TSC-PGMA-MACS microspheres was an endothermic and spontaneous process. 40311


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Figure 6. (A) Effects of coexisting metal ions on Hg(II) adsorption in binary-metal solutions. (B) Adsorption and desorption toward Hg(II) on TSC-PGMA-MACS microspheres within five-time consecutive cycles. (C) FTIR spectra and (D) XRD patterns of TSC-PGMA-MACS microspheres before and after Hg(II) adsorption (initial concentration of each metal ion, 250 mg L−1; contact time, 180 min; pH 6.0; temperature, 298 K; dosage, 1 g L−1; stirring speed, 160 rpm).

Figure 7. Probable bonding modes and adsorption sites for Hg(II) on TSC-PGMA-MACS microspheres.

and were combined into a single broad band at 3446 cm−1, and the band at 1063 cm−1 (C−O on C3−OH ) shifted to 1055 cm−1 because O and N atoms donated their lone-pair electrons to Hg(II), weakening or changing the vibration intensity of

−OH and −NH2. Strong vibrations at 1732 cm−1 (CO) and 1387 cm−1 (COO−) were largely weakened and shifted to 1722 and 1384 cm−1, indicating the interaction of −COOH with Hg(II).11 Primary characteristic bands at 1575 cm−1 (N− 40312


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Figure 8. MICs of (A) TSC-PGMA-MACS and (B) TSC-PGMA-MACS-Hg(II) microspheres against E. coli and S. aureus. (C) Inhibitory rates of CS powder, TSC-PGMA-MACS and TSC-PGMA-MACS-Hg(II) microsphere suspensions, and Hg(II) solutions against E. coli and S. aureus. (D) Growth of E. coli and S. aureus in LB agar plates after being treated with samples (MICs, minimum inhibitory concentrations; temperature, 37 °C; sterile nutrient broth, 5 mL; absorbent, 5 mg; pH 6.0; stirring speed, 160 rpm; Hg(II) solution, 250 mg L−1).

H) and 649 cm−1 (CS) almost completely disappeared after Hg(II) adsorption, and a new band appeared at 1635 cm−1, demonstrating that N and S atoms on TSC moieties participated in the formation of Hg(II) complexes.16 FTIR analyses above were well supported by some literature data, e.g., Li et al. report that the band at ∼3437 cm−1 identified as −OH and −NH2 shifts to 3450 cm−1, after interactions between −OH or −NH2 and HMIs;36 and Chauhan et al. find that N−H vibrations at 1607 and 1557 cm−1 move to 1640 and 1547 cm−1 after the complex generation between sensing material and Hg(II).16 As shown in Figure 6D, the diffraction peak at 17.4° in TSC-PGMA-MACS-Hg(II) microsphere pattern became broader and weaker than that in TSCPGMA-MACS microsphere pattern, and the crystallinity after Hg(II) adsorption greatly decreased, indicating the possibility of reactions between adsorbent and Hg(II), which destroyed the symmetry and stereoregularity of polysaccharide molecules, leading to incomplete decrystallization. Similar findings are also reported by other researchers, e.g., Zhang and Kyzas find that crystallinity significantly compromises after HMI adsorption.28,46 More importantly, as documented in previous studies,2,12,15−17 high selectivity and affinity of TSC-PGMAMACS microspheres with Hg(II) might be mainly owing to strong interactions between S- or N-containing ligands and Hg(II), which have been proved by phenylthiourea-, thiocarbamoyl-, and thiourea-modified adsorbents.2,12,17

Based on FTIR and XRD analyses, it was reasonable to conclude that −OH, −COOH, −NH2, and CS groups on TSC-PGMA-MACS microsphere surfaces were involved in chemical reactions during Hg(II) adsorption. Namely, S, N, and O on TSC-PGMA-MACS microspheres in slightly acidic surroundings contributed lone-pair electrons to empty orbits of Hg(II) to form complexes through coordinate covalent bonds. A series of potential adsorption sites and binding modes were here proposed, which were that Hg(II) was bonded to (1) two CS (or S−H), (2) two −NH2 (or N−H), (3) one −NH2 and one −OH, (4) two −COOH, (5) two C3−OH, (6) two GMA−OH, (7) two O on GMA−OH and C3−OH, and (8) four S and/or N. The schematic adsorption sites and binding modes are illustrated in Figure 7. 3.6. Antibacterial Evaluation and Mechanism. Inhibitory effects of materials against Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria, which are the main representatives of the most common pathogenic strains associated with water contamination, were estimated by an MIC assay method. Figure 8A,B shows antibacterial activity curves of TSC-PGMA-MACS and TSC-PGMA-MACS-Hg(II) microspheres in acidic media with various concentrations. Clearly, both TSC-PGMA-MACS and TSC-PGMA-MACSHg(II) microspheres showed a certain degree of antibacterial activity against E. coli and S. aureus, and the antibacterial activity of the former, as well as of the latter, against two tested 40313


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MACS-Hg(II) microspheres reacted easily with −NH2, −COOH, and −SH on proteins and nucleic acids to hinder the growth of bacteria. Notably, −NH2 and CS on TSCPGMA-MACS microspheres might be protonated, to a lower degree, in slightly acidic media at pH 6.0; however, the acidic components produced during the growth of bacteria could promote the protonation of certain moieties, largely enhancing antibacterial activity. Altogether, the graft of TSC imparted high antibacterial activity to TSC-PGMA-MACS microspheres, and the antibacterial activity after adsorption toward Hg(II) was greatly enhanced.

bacteria did not show obvious differences. Most strikingly, the latter showed antimicrobial activity superior to the former, in view of much lower Abs 600 values at the same concentrations of 1.0 mg mL−1 of antiseptics. The MIC values of the former against both bacteria were all equal to 2.0 mg mL−1, whereas the counterparts of the latter were all equivalent to 0.25 mg mL−1. To confirm the reliability of the above findings, we also determined the MICs through the colony counting method, and the results (Figure S4) were consistent with the counterparts obtained via the turbidimetric method. Such an equivalent MIC of each tested sample against both E. coli and S. aureus, unlike our previous studies on water-soluble CS derivatives,22−25 might be because bacterial activity occurring on solid interfaces was dependent not only on antimicrobials’ concentration but also on contact probability and affinity between antimicrobials and bacteria in liquid media. As shown in Figure 8C, the order of inhibitory rates of materials against two bacteria was TSC-PGMA-MACS-Hg(II) microspheres > TSC-PGMA-MACS microspheres > CS powders at the same concentration (1.0 mg mL−1), which was verified by Figure 8D. Moreover, Figure 8C,D reveals that both tested bacteria could not survive in nutrient broth medium containing 250 mg L−1 Hg(II) that was also the concentration used in batch adsorption experiments, indicating high toxic effects of Hg(II) on bacterial cells. Also, the inhibitory rate remained at a high level when Hg(II) concentration decreased to 56.3 mg L−1, which was equivalent to the Hg(II) concentration of 0.25 mg mL−1 of TSC-PGMA-MACS-Hg(II) microsphere suspension, implying that the higher antibacterial activity of TSC-PGMAMACS-Hg(II) microspheres might be mainly derived from the participation of Hg(II). Undeniably, antibacterial activity was greatly compromised upon the change from free Hg(II) to Hg complexes, which is illustrated in Figures 8B and S5. More recently, researchers have proposed several possible antibacterial mechanisms for acid- or water-soluble CS derivatives,22,23,25,47,48 but the most approved one is that CS derivatives bind to bacterial cytomembranes via electrostatic interactions, altering membrane permeability and further causing the death of bacteria. In the present work, newly prepared TSC-PGMA-MACS microspheres were insoluble in neutral and acidic solutions; however, antibacterial experiments showed that TSC-PGMA-MACS microspheres were of high antibacterial activity against E. coli and S. aureus, and antibacterial activity of the microspheres after adsorption toward Hg(II) was much higher than that before adsorption. As for such desirable findings, several possible explanations are summarized below: (1) coordination atoms S, N, and O on TSC-PGMA-MACS microspheres readily chelated with Hg(II) to inhibit the growth of microorganisms; (2) functional groups (e.g., −NH2 and CS) on TSC-PGMA-MACS microsphere surfaces could be protonated in acidic media, binding to negatively charged bacterial membranes via electrostatic interactions, changing cytomembrane permeability, and further resulting in the death of bacteria; (3) the introduction of TSC containing −NH2 and CS onto PGMA-MACS microsphere surfaces not only increased the species of moieties that can be protonated in acidic solutions but also enhanced the positive charge density on microsphere surfaces, leading to stronger antibacterial activity superior to CS powders; (4) the positive charge density on microsphere surfaces after Hg(II) adsorption was higher than before, endowing TSC-PGMA-MACS-Hg(II) microspheres with higher antibacterial activity superior to TSC-PGMA-MACS microspheres; and (5) TSC-PGMA-

4. CONCLUSIONS Dual-purpose TSC-PGMA-MACS microspheres with adsorption selectivity for Hg(II) and antibacterial activity were first fabricated via elaborate three-step reactions for polluted water scavenging. Newly prepared adsorbents with 35.340 m2 g−1 of specific surface area, 7.933 nm of pore diameter, 0.158 cm3 g−1 of pore volume, and abundant −NH2 and CS groups were characterized by FTIR, EA, XRD, EDX, DSC, TG, DTG, SEM, and BET methods, confirming successful fabrication, unambiguous crystallinity, good thermostability, and well-defined mesoporous structures, beneficial for Hg(II) adsorption and antibacteria. Batch adsorption experiments demonstrated that the optimal pH was 6.0 and the maximum adsorption capacity for Hg(II) was 242.7 mg g−1 calculated on the basis of Langmuir isotherm model, higher than most of the available adsorbents. Kinetic studies showed that the adsorption process was well described by pseudo-second-order kinetic model, implying a monolayer and chemical adsorption process. Thermodynamic parameters revealed that Hg(II) adsorption was spontaneous and endothermic in nature. Competitive adsorption tests exhibited that TSC-PGMA-MACS microspheres had selective adsorption toward Hg(II) in binary-metal solutions. The adsorption capability after five cycles was maintained >86.0% of the initial saturated adsorption capacity, showing outstanding reusability of the adsorbent. FTIR and XRD analyses confirmed that S, N, and O atoms participated in coordination reactions. Besides, the order of inhibitory rates of materials against E. coli and S. aureus was TSC-PGMAMACS-Hg(II) microspheres > TSC-PGMA-MACS microspheres > CS powders, and the MIC values of TSC-PGMAMACS and TSC-PGMA-MACS-Hg(II) microspheres against both bacteria were 2.0 and 0.25 mg mL−1, respectively. Overall, TSC-PGMA-MACS microspheres with high adsorption capacity, adsorption selectively, good reusability, and antibacterial activity might serve as new adsorbent for wastewater purification.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b14893. Materials and chemicals used; characterization of materials; characteristic parameters during the thermal degradation; surface parameters; surface morphology; statistical microsphere diameters; adsorption modes on CS; linear fitting plots of kinetic and isotherm models; calculated RLa values; comparison of maximum adsorption capacity; MICs of samples; and inhibitory effects of Hg(II) solutions (PDF) 40314


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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone/Fax: +86 0532 82032586. ORCID

Chengsheng Liu: 0000-0002-1454-0193 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS C. Liu and Q. Dang received funding from Applied Basic Research Program for Youngster of Qingdao Grant 15-9-1-42jch, National Natural Science Foundation of China (NSFC) Grant 31400812, Natural Science Foundation of Shandong Province Grant ZR2014CQ052, and Science and Technology Development Funds of Qingdao Shinan Grant 2014-14-003SW and 2015-5-015-ZH.

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Selective Adsorption toward Hg(II) and Inhibitory Effect on Bacterial

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