Thermotolerance and Antibacterial Properties of MgO-Triclosan Nanocomposites

Available online at www.sciencedirect.com

ScienceDirect Procedia Engineering 102 (2015) 410 – 416

The 7th World Congress on Particle Technology (WCPT7)

Thermotolerance and Antibacterial Properties of MgO-Triclosan Nanocomposites Hongmei Cuia,b, Xiaofeng Wua*, Donghai Zhanga, Jingkun Zhanga, Hong Xiaoa,Yunfa Chena , a

State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, 1 Zhongguancun Road, Haidian District, Beijing 100190, P.R.China. b University of Chinese Academy of Sciences, Beijing 100049, P.R. China

Abstract Antibacterial MgO-Triclosan nanocomposites was prepared by a facile adsorption process using nano-MgO as adsorbent in a triclosan ethanol solution. Adsorption experiments showed that as-synthesized MgO nanoparticles possess high adsorptive capability towards triclosan. TG and FTIR analysis showed that the MgO-Triclosan nanocomposites performed good thermotolerance. Antibacterial tests showed that it still retained most of its active component, and exhibits high antimicrobial activity even after heat treatment for 30min at 250°C. © Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ©2015 2014The The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and peer-review under responsibility of Chinese Society of Particuology, Institute of Process Engineering, Chinese Selection and peer-review under responsibility of Chinese Society of Particuology, Institute of Process Engineering, Chinese Academy Academy of Sciences (CAS). of Sciences (CAS)

Keywords: Magnesium oxides; Nanocomposite Materials˗Antibacterial behavior.

Corresponding author. Tel: +86-10-82544900; Fax: 86-10-82544919 E-mail addresses: [email protected] (X. Wu) or [email protected] (Y. Chen)

1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and peer-review under responsibility of Chinese Society of Particuology, Institute of Process Engineering, Chinese Academy of Sciences (CAS)

doi:10.1016/j.proeng.2015.01.175

Hongmei Cui et al. / Procedia Engineering 102 (2015) 410 – 416

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1. Introduction Thermotolerance or heat-resistant capacity of antibacterial materials has great significant influence on the processability and performance of antibacterial products. Typically, the low heat-tolerant antibacterial components are decomposed towards polymer-based antibacterial products through a high-temperature twin screw extrusion, resulting in the inferior products. The development of high themotolerant antibacterial fillers is a necessary and key steps in manufacturing polymer-based antimicrobial products. Triclosan [1] is a commercially antibacterial and antifungal agent as a polychloro-phenoxy-phenol, and has found its applicable limits due to high-temperature coloration form its decomposition during the twin screw extrusion process. Therefore. It is urgent and highly desired to develop the high thermotolerant inorganic-organic antibacterial fillers utilizing in the process of polyermer-based antimicrobial products. Magnesium oxide (MgO) is widely used for catalysis, toxic waste remediation and antibacterial action due to its well-defined surface defect structures, which include low-coordinated ions and vacancies[2-7]. The novel and useful properties of MgO are further enhanced, especially in the form of a nanoscale powder. Magnesium oxide as an inorganic antibacterial agent has high heat resistance and good stability. At the same time, because a large number of defects is present on the MgO surface, it can absorb some ionic-organic or purely organic antibacterial agents to form a composite antibacterial material with improved thermal stability [8-14]. Many synthesis routes such as sol-gel, hydrothermal, aqueous wet chemical, and surfactant methods provide nanosized MgO[15-20]. Kumar[21] et al synthesized nano-sized MgO powder using magnesium nitratic hexahydrate and oxalic acid as precursors with ethanol as a solvent, presenting a potential large-scale synthetic routes in developing nanscale high heat-resistant MgO-based antibacterial composite materials. By now, few effort has been reported in develop the high thermotolerant MgO-triclosan nanocomposite antimicrobial materials as fillers. In our study, nano-sized MgO was prepared firstly and the adsorption dynamics and adsorptive capacity of MgO towards triclosan is investigated. The thermotolerance of as-prepared MgO-Triclosan nanocomposite antibacterial materials is also discussed. 2. Experimental 2.1. Synthesis of nano-sized MgO MgO nanoparticles were prepared according to the reported procedure [21]. In a typical synthesis procedure of nano-sized MgO, 0.2mol Mg(NO3)2.6H2O and 0.2 mol (COOH)2.2H2O were separately dissolved in 100mL ethanol and stirred to obtain two clear solutions. Then, the two solutions were mixed together to yield a white precursor solution and stirring continued for 30 minutes. Subsequently, the precursor was digested for 12h, and the final white precursor product was washed with ethanol, collected by filtration, and then dried at 80°C in an oven. The nanosized MgO was then prepared by calcination of the precursor in air at 500°C at 10°C /min for 2h. 2.2. Synthesis of MgO-triclosan and Sintering Treatments A quantity of 0.3g dry nanoscale MgO was added to 100mL of desired concentration triclosan solution and the suspension was kept under constant agitation (200rpm) for 24h in an incubator-shaker maintained at 25°C. Afterwards the solutions were centrifuged at 10,000 rpm for 10min. Then, the precipitate was collected, and dried at 80°C. The supernatant solution was used to determinate the adsorption capacity of nano-MgO. The absorbance of the supernatant solution was recorded using a UV-VIS-NIR spectrophotometer. The adsorption capacity was then obtained by using the following mass balance equation: V C .V ( A  Ae ) qe (C  Ce ) W W . A (1-1) The adsorption rate is determined from the following formula: (C 0  C e ) (A 0  A e ) E u 100 u 10 (1-2) C0 A0 where C0 and Ce are the initial and fixed time triclosan concentrations in solution, respectively, and Ao, Ae are the

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initial and fixed time absorbance values. V is the solution volume (in L) and W is the weight (in g) of dry MgO used. In order to determine the thermotolerance of the samples, the nanoscale MgO-Triclosan was respectively calcined in air at 200 °C, 250°C and 300°C at 15°C /min for 30min, denoted as “MgO-Tri-T”, where “tri”denotes “Triclosan”and “T” is the “calcination temperature”. 2.3. Antimicrobial Assay The antimicrobial effects of MgO-Triclosan powder were determined by using a disk diffusion assay with E.coli (ATCC 2385) as a model bacterium. A quantity of 0.1g MgO-Triclosan powder was added to a 10mL buffer solution to prepare a suspension, then 20PL of the suspension was added dropwise onto sterilized paper of 5×5mm in size and drid. Agar (20mL ) was poured into a sterilized dish and solidified. The freshly prepared E.coli (0.1mL) with a concentration of 105 CFU/mL was uniformly inoculated in the solidified agar gel. Each MgO-Triclosan paper was placed on an agar plate, then incubated at 37ºC for 24h. The antimicrobial activity of the specimens was compared by measuring the diameters of the zone of inhibition around each paper. 2.4. Characterization Thermogravimetric analysis (TGA) were conducted in a flow of N2 at a ramp rate of 5°C/min on a SDT Q600 instrument. The crystal structures of the as-prepared samples was characterized by X-ray diffraction (XRD). The size and morphology of the samples were examined by transmission electron microscopy (TEM). FTIR spectra of samples were collected on a Bruker Vector 22 FT-IR spectrometer ( as KBr discs ). Absorbance data were collected on a Varian UV-vis-NIR spectrophotometer at 282nm.

3. Results and discussion 3.1. Characterization of MgO nanoparticles The XRD patterns of the MgO products synthesized is shown in Fig.1a. All the diffraction peaks match well with the face centered cubic structure in JCPDS 45-0946. The morphology of the product was studied using TEM analysis. As shown in Fig.1b, the MgO particles are about 20 nm in size. The particles appear to be agglomerated, but one can still see particle edges. The BET anaslysis results reveal that the specific surface area of nano-sized MgO is 145.4 m2/g.

Figure 1. XRD patterns of nano-sized MgO samples (a); TEM images of nano-sized of MgO samples (b). 3.2. Adsorption time and optimal concentration of triclosan solution Adsorption experiments [22-24] were carried out in batch mode by combining 100 mL of 60mg/L and 80mg/L triclosan solutions with 0.3g MgO. An aliquot (10mL) sample was withdrawn from the flask at regular time intervals, centrifuged and the triclosan concentration in the supernatant solution was analyzed by measuring the absorbance. Fig. 2a shows nano-sized MgO with different initial concentrations of triclosan adsorption. As seen in

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the Fig.2a and Table 1, for the 60mg/L and 80mg/L concentrations of triclosan, the nano-sized MgO adsorption shows similar dynamics. In the initial 5h, the triclosan adsorption capacity increases rapidly, and then levels off. In addition, the higher the initial concentration of triclosan, the higher the equilibrium adsorption capacity. Adsorption capacity and triclosan concentration experiments were carried out separately as batch tests. The experiments were carried out in batch mode by taking 100 mL of 20mg/L-100mg/L triclosan solution with 0.3g MgO. The temperature was 25°C and the maximum adsorption capacity (q max) of the adsorbent was measured after constant agitation for 24h. Fig.2b shows a plot of q max versus triclosan concentration. At first, the adsorption rate increases with increasing concentration and then decreases when the concentration is greater than 80mg/L. The adsorption rate is greater than 72% in the 40-80 mg/L range. For lower triclosan concentrations, the maximum adsorption capacity qmax increased with the concentration of the triclosan solution, but when the initial concentration was higher than 80mg/L, the maximum adsorption capacity remained almost unchanged. So, the optimum concentration of triclosan solution was 80 mg/g, adsorption time was 24h.

Figure 2. The adsorption capacity of MgO against the contact time in 60mg/L and 80mg/L triclosan solution (a); The maximum adsorption capacity(qmax) versus initial concentration of triclosan (inset: Adsorption rate versus initial concentration of triclosan (b) Table 1 The pesudo-first-order and pseudo-second-order kinetic parameters for the adsorption of different concentrations of triclosan onto MgO nanoparticles Concentation (mg/L)

qe-e (mg/g)

60 80

14.01 20.45

Pseudo-first-order model qe-a1 (mg/g) 7.57 30.2

Pseudo-second-order model

k1 (min-1)

R2

qe-a2 (mg/g)

k2 (g/mg/min)

6.27×10-3 6.56×10-3

0.967 0.987

14.15 20.44

3.13×10-3 2.80×10-4

R2 0.998 0.967

3.3. TG analysis of composite sample The results of a DSC-TG analysis of the sample is shown in Fig.3. The TG results indicate that there are two main stages of weight loss. In the first stage, a weight loss of 9% occurs in the temperature range of 30-250°C, corresponding to an endothermic reaction. The first exothermic peak is probably due to the thermal decomposition of triclosan. Since the triclosan molecule contains two benzene rings, it is possible that thermal decomposition of the complex formed by dehydrogenation of the fused ring compound occurs, and then possibly even graphitization occurs. In the second stage, a weight loss of 11% occurs over the temperature range of 250-400°C, corresponding to an endothermic reaction. The exothermic peak that appears at 358°C is likely due to the fused ring compound that corresponds to the thermal decomposition. The composite sample does not exhibit significant thermal decomposition or loss at 200°C, and the aforementioned FTIR spectrum exhibits better consistency. Therefore, it

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can be deduced that this material can be used for heat treatment at temperatures near 200°C with plastics and powder coatings.

Figure 3. TG and DTG patterns of MgO-Tri composite antibacterial materials. The temperature was raised at the rate of 5°C/min in N2. 3.4. IR absorption of MgO powder and MgO-Tri powder Fig.4a shows the FTIR spectra for Triclosan, MgO and MgO-Tri, which were heated to temperatures of 200,250, and 300°C for 30min in air. The MgO spectrum shows that water molecules have been adsorbed on the surface of the sample as proven by the presence of a broad band at 3200-3600cm-1 and a band at 1639cm-1. This behavior occurs because of the special characteristic of MgO, in which it adsorbs moisture from the enviroment[25,26]. The O-H bending band with Mg appears as a sharp peak at 1465cm-1. The O-H stretching vibration peaks with phenol at 3300cm-1 are masked by the strong absorption peak of MgO at 3500cm-1. The strong absorption peak of MgO at 1465-1639cm-1 masks the benzene absorption at 1305-1505cm-1. A comparison of the IR spectra of Fig. 4a shows that the absorption peaks at 1000-1300cm-1 have not been overshadowed by the MgO absorption peaks. As can be seen from Fig.4b, the absorption peak at 1100cm-1 is the absorption peak of chlorinated aryl, and the absorption peaks at 1180cm-1, 1230cm-1, and 1255cm-1 are significantly reduced as the temperature increases. The absorption peaks at 1180, 1130, and 1255cm-1 in the MgO-Tri-300 sample almost disappeared, thus when the sample was calcined at 300°C for 30min, the triclosan apparently decomposed or evaporated, so that the intensity of the infrared absorption peaks at 1180, 1130, and 1255cm-1 decreased significantly.

Figure 4. Fourier transform infrared (FTIR) spectra of MgO powder, triclosan, and MgO-Tri-T powder 3.5. Antibacterial performance analysis of different samples Fig. 5 illustrates how the antimicrobial activity decreases with calcination temperature, because high temperature burning of triclosan having antimicrobial activity releases volatile components and thermal decomposition takes

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place. With an increase in calcination temperature, the antimicrobial activity of the samples is decreased, because the high temperature makes triclosan volatile and results in thermal decomposition. The average inhibition zone size of MgO-Tri is 18.7mm. After calcination at 200°C for 30min, the average size of the inhibition zone decreased to 17.1mm; after calcination at 250°C, the average inhibition zone was 17.3mm. After calcination at 300°C for 30min, the antibacterial rings become very small and almost disappeared.

Figure5 Photos of bacterial inhibition rings of MgO-Tri samples calcined at various temperatures (a. MgO-Tri ;b. MgO-Tri-200; c. MgO-Tri-250; d. MgO-Tri-300)

4. Conclusions Magnesium oxide nanoparticles were synthesized and successfully employed in the adsorption of triclosan. The XRD results showed that the MgO products possess a cubic structure. The TEM images showed that the MgO nanoparticles were about 10-20 nm in size, and the BET measurements revealed that MgO has a specific surface area of 145m2/g. As an adsorbent MgO can adsorb triclosan forming a MgO-Tri composite material. As the triclosan concentration increases, the maximum adsorption increased. A maximum adsorption of 20.44 mg/g was achieved with an 80mg/L triclosan solution at 25°C. The antibacterial and thermal stability properties of triclosan/MgO were characterized by FTIR and DSC-TG. Studies have shown that the composite antibacterial material has good heat resistance. Even at 250°C, 30min after heat treatment, the material still retained most of its antibacterial activity, and exhibited excellent antimicrobial dissolution.

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Acknowledgements This work was supported by GF Science and Technology Innovation Fund of Chinese Academy of Sciences ( No.CXJJ-11-M44 ), National High Technology Research and Development Program 863(NO.2010AA064903) of China, and National Natural Science Foundation of China ( No.51002154 and No.51272253 ).

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