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In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/pps Page 1 of 15 Photochemical & Photobiological Sciences Applicationsof a new type of poly(methyl methacrylate)/TiO nanocompositeas an 2 t p antibacterial agent and reducing photocatalyst i r c s u n Alireza Salabat*, Farid Mirhoseini a M Department of Chemistry, Faculty of Science, Arak University, 38156-8-8349, Arak, Iran d e *Corresponding Author:TEL: +98-86-34173400;Fax: +98-86-34173406; t p E-mail address: [email protected] e c c A Abstract s e c A new type of poly(methyl methacrylate) (PMMA)/TiO nanocomposite film sensitized by ionic 2 n liquid with low dosage of TiO nanoparticles was prepared based on microemulsion method. The e 2 i c photocatalytic activity, via the photoreduction of 4-Nitrophenole (4-NP) to 4-Aminophenole (4- S AP) by NaBH and the photocatalytic-based antibacterial activity over Escherichia coli and 4 l a Staphylococcus arouse destruction of the prepared nanocomposite film were investigated. The c i g conditions for maximum efficiencyin the present of visible light irradiation have been evaluated. o The rate constant of photoreduction of 4-NP to 4-AP was calculated and the maximum rate l o constantwas found over the 0.01wt.%of TiO content in photocatalystand solution pH of 7.5.A i 2 b o photocatalytic antibacterial maximum activity against gram negative bacterium was also t o obtainedover the 0.01 wt.% of TiO content in photocatalyst. A notable exception of this work is 2 h that PMMA/TiO nanocomposite films show efficient photocatalyst activity at very low loading P 2 of TiO in contrast of other previousreports. & 2 l a c i m e h c o t Keywords:TiO ; microemulsion; Photoreduction;4-Nitrophenole; Antibacterial activity 2 o h P 1 Photochemical & Photobiological Sciences Page 2 of 15 1. Introduction very low TiO content and to confirm the 2 t p necessity of visible light photocatalyst i Titanium dioxide (TiO ) as a popular r 2 c applicability, a very simple process based on s photocatalyst has been drawing a lot of ionic liquid-microemulsion system is u attention because of its environmental n conducted in this work to emphasis this global a applications in the decomposition of pollutants M concerns.6 By using the ionic liquid based and microbial species in water and air.1-3 Since d microemulsion system, a polymer-TiO 2 e the past two decades, much scientific attention nanocomposite can be deduced which not only t p in the field of polymer-based photocatalyst has is visible light activephotocatalyst without any e been focused owing to its advantages, such as c additive, but also improves the recombination c easy post treatment recovery.2,4 Some of A of photogenerated holes and electron as the various research works have additionally been s major limitation of polymer-TiO2 mediated e reported in the visible light active TiO c 2 photocatalysis. An important highlight as per n photocatalyst. Singh et al.2 presented a e our previous literature study is to prepare an i remarkable review that this comprehensive c economical PMMA/ionic liquid sensitized S study covers over a hundred published papers. TiO2 with very low dosage of TiO2. The l a Until today, as per other literature survey it prepared low dosage of PMMA/ TiO can be c 2 appears that the polymer-based TiO was i 2 g an effective photocatalyst in degradation of o fabricated with high loading of TiO and 2 methylene blue dye to overcome the main l o sometimes in presence of different sensitizer drawback of the previous developed i b additive such as dye and noble metals.2,5 o polymer/TiO nanocomposite that published 2 t It must be noted that the preparation of novel o by Magalhase et al.7 They prepared low h polymer-supported TiO nanocomposite with 2 density polyethylene (LDPE)/ TiO P 2 the above pleasing properties and especially & photocatalyst using various TiO contents (32, 2 low TiO contents is a utopia. As the best of 2 l 68, 82 wt.%). In progressing of our previous a knowledge, we found that still any research c research work in waste water treatment,6 in i papers have been reported on very low m this study we considered the photodegradation e concentration of TiO in polymer composites. 2 of a phenolic compound and also photocatalyst h This makes a promising research area to be c antibacterial activity by using a very low TiO2 o explored and developed further. In order to t contents (0.008-0.014 wt.%) immobilized in o providing a novel route for fabrication of a h PMMA. P buoyant polymer-TiO nanocomposite with 2 2 Page 3 of 15 Photochemical & Photobiological Sciences Phenolic compounds such as 4-Nitrophenol, candidate to use in the health care industry and t p which is one of the organic pollutants listed by environment materials.17,18 Ratova et al.3 i r c EPA in U.S.A, are carcinogenic and harmful produced LDPE/ TiO films by an extrusion 2 s for the environment. These types of method and tested photocatalytic antibacterial u n compounds are extensively used in plastic activity, via the destruction of Escherichia coli a M industries, petrochemical, agrochemical and so at the same time as TiO contents was 5 and 30 2 forth.8 The selective reduction of aromatic wt.%. They also investigated the d e nitro compounds to the corresponding photodecomposition of methylene blue dye t p aromatic amines which are widely utilized in under UV illumination by the same (LDPE)– e c the dyes, photographic, agricultural, and TiO films. Hence, in continuation of our c 2 A pharmaceutical industries, is one of the research works on microemulsion systems as s fundamental transformation with reducing soft template for nanomaterials synthesis19,20, e c agents in organic synthesis.9 Photodegradation the chief object of the present examination is n e of p-nitrophenol (PNP) has been investigated to focus on the some environmental i c by Chen at different conditions, in aqueous applications of PMMA/TiO nanocomposite, 2 S suspension of P25 TiO2 nanoparticles and also prepared by ionic liquid based microemulsion l a over immobilized P25 TiO nanoparticles.10 system. An interesting feature of advanced c 2 i g They reported pseudo firs-order kinetics that it innovative microemulsion systems is effective o respects for all of parent compounds. Indeed, and sustainable synthesis route with very low l o we underline to the role of TiO as a concentration of ionic liquid and TiO i 2 2 b o photocatalytic antibacterial material that has nanoparticles in composite. In our previous t o considerable beneficial properties such as bio- report, PMMA/TiO /IL nanocomposite as a 2 h compatibility, high potential for self-cleaning highly efficient visible light photocatalyst was P and high antibacterial activity11,12 and is now synthesized and characterized.6 In the current & l the basis for a number of commercial work, the application of the prepared a c antibacterial products.13-16 PMMA/TiO /IL nanocomposite with very low 2 i m Surprisingly, there is an increasing interest in dosage of TiO for photoreduction of 4-NP has 2 e combining photocatalytic activity of TiO and been investigated. The effects of TiO dosage, h 2 2 c hydrophobic polymer for preparation of pH and light intensity of lamp on the rate o t polymer supported TiO in bacteriological constant of photoreduction process have been o 2 h study.3 So, polymeric materials are a good determined. As a second application the P 3 Photochemical & Photobiological Sciences Page 4 of 15 antibacterial effect of the nanocomposite was TX-100 (6.56 wt.%) and1-buthnol (2.24 wt.%) t p also tested on the destruction of clinical strain was prepared. Then, different amounts of TiO 2 i r c of Escherichia coli (Gram-negative) and nanoparticles were loaded into this s Staphylococcus arouse (Gram-positive) in microemulsion system. Benzoyl peroxide u n visible light. (BPO) as an initiator (0.2 wt.% based on the a M weight of MMA) was added to the above d 2. Experimental stabilized TiO colloidal systems to start 2 e polymerization process at 60°C. For labeling t p Materials purposes, the resultant transparent nanohybrid e c Hydrophilic ionic liquid, ([bmim][BF ]),and films of PMMA/TiO were termed as S1, S2, c 4 2 A the nonionic surfactant of Triton X-100 were S3, and S4 referring to the amounts of TiO 2 s purchased from Sigma-Aldrich. The titanium nanoparticles corresponding to 0.008, 0.01, e c dioxide TiO nanoparticles used in this study 0.012 and 0.014 wt.%. No apparent visible 2 n e was Degussa P25 (ca. 80% anatase, 20% phase separation was observed during i c rutile, with a BET surface area of 50 m2/g and polymerization process for all samples. Pure S particle size of less than 15 nm). Methyl PMMA was also prepared under the same l a methacrylate (MMA) monomer (AR grade), condition and identically formulated c i g benzoyl peroxide (BPO), 1-butanol, sodium microemulsion without TiO loading. The 2 o borohydride and 4-nitrophenol as a pollutant nanocomposite films were obtained using an l o model were prepared from Merck. All aqueous automatic film applicator (ELCOMETER). i b o solutions were prepared with deionized water The set-up of the automatic film applicator is t o (0.055 µΩ) which was produced in our lab shown in Fig. S1†. All of the produced h with PKA (Smart two pure) instrument. transparent films had the uniform thickness P & with an average central thickness of 100 μm, l as measured by a micrometer. Techniques a c Preparation of the modified PMMA/TiO such as UV-Vis diffuse reflectance spectra 2 i m nanocomposite (DRS), TEM, FT-IR and TGA were used to e characterize the resulting modified h In order to synthesis modified PMMA/TiO2 c nanocomposite and reported in our previous o nanocomposite a microemulsion system t paper.6 The UV-Vis transmittance was also o consisting of hydrophilic ionic liquid h P [bmim][BF ] (2.26 wt.%), MMA (88.94wt.%), 4 4 Page 5 of 15 Photochemical & Photobiological Sciences used to claim transparency of the fabricated heterogeneously placed into a 20 mL of total t p film. aqueous solution containing 4-nitrophenol i r c (0.144 mM) and excesses amount of 1.2M UV-Vis transmittance s sodium borohydride solution in the presenceof u n The UV-Vis transmittance spectrum of the visible light irradiation. During the reduction a M prepared nanocomposite for S2 as a typical process the UV−visible spectra of the reaction d sample was obtained in air at room mixture was recorded at intervals of 60 min. e temperature in the wavelength range of 200– Before analyzing with a double beam UV-vis t p 600 nm by using a UV/Vis/NIR spectrophotometer (Perkin Elmer lambda 15), e c spectrophotometer (JASCO, V-670 (190-2700 the nanocomposite film was removed from all c A nm). solutions to stop reaction. The temperature of s the reaction solution was kept constant at e Photocatalytic activitytest c 25°C. Three following control samples were n Photoreactor and Photoreduction of 4-NP employed: blank (1), a solution of 4-NP e i c without the photocatalyst and sodium S All the nanocomposites and pure PMMA films borohydride, blank (2), a solution of 4-NP in l were initially assessed for the photoreduction a the presence of the photocatalyst without c of 4-NP at normal laboratory environmental i g sodium borohydride, and blank (3), a solution conditions. The photoreduction experiment o of 4-NP with sodium borohydride and without l was carried out in a glass beaker as the o the photocatalyst. The removal efficiency was i b reaction vessel. The assembled photocatalytic o measured by applying the following equations: activity test system was described elsewhere.6 t o In this system there is a sun-light fluorescent h P lamp attached vertically at the top. The (cid:2885)(cid:3116)(cid:2879)(cid:2885)(cid:3178) % Photocatalytic efficiency = (cid:2885)(cid:3116) ×(110)0 & distance between the light and the reactor was l a fixed at 10 cm. The assembled system was where Ao (at 400 nm) is the initial absorbance c placed inside a wooden box coloured black so of 4-NP at zero time and At the absorbance of mi that no stray light can inter the reactor. The 4-NP at ttime. e h reduction of 4-nitrophenol to a beneficial c o compound, 4-aminophenol, by sodium Antibacterial activity test (Kirby-Bauer t o borohydride was chosen as a model reaction. h method) P A thin film of the nanocomposite was 5 Photochemical & Photobiological Sciences Page 6 of 15 The photocatalytic-based antibacterial activity t p of each of the produced nanocomposite films i 3. Results and discussion r c and pure PMMA film were evaluated as a UV-Vis transmittance s series of photocatalytic experiments. A clinical u The UV-Vis transmittance spectrum of the n isolates Escherichia coli bacterium (from a prepared PMMA and PMMA/TiO 2 M Gram-negative) and Staphylococcus arouse nanocomposite (S2) is illustrated in ESI (Fig. d (from Gram-positive) were used for this study. S2†). As expected, the UV-VIS spectrum of e Agar well diffusion method21 was used for t p PMMA sample exhibit a transmittance of 60% determination of the degree of photocatalytic e and higher at or above 260 nm. The UV-Vis c destruction of Escherichia coli and c spectrum of PMMA/TiO2 is also revealed an A Staphylococcus arouse. The pH was fixed at increase in the transmittance at above 400 nm s 7.3. Briefly, sterile molten Mueller-Hinton e due to the presence of TiO nanoparticles as 2 c agar (20 ml) was poured into sterile petri n can be seen in Fig. S2†. e dishes and allowed to solidify at room i c temperature. Pyre cultures of pathogenic S bacteria as 0.5 McFarland (108 CFU/ml) was Effect of TiO2 contents of nanocomposites l a swabbed on the Muller-Hinton agar plates. on the4-NP photoreduction c i g Further 5 mm thin film disk of pure PMMA as In order to study the kinetic of the o a control sample and all of nanocomposite l o photoreduction process by UV-visible method, films with different dosage of TiO (samples i 2 b a time-dependent spectra for 4-NP/sodium o S1 to S4) were situated onto 5 mm paper disk borohydride reaction mixture containing t o on the inoculated surface of Mueller-Hinton nanocomposite (S2) was obtained and shown h agar plates. Inoculated plates were incubated P in Fig.1. As can be seen, the absorption band & for 24 h at 37 °C in a thermostatic light of the nitrophenolate ions at ca. 400 nm is l incubator under visible light irradiation (lamp a decreased, while the absorption band at ca. c 60 W). The substrates were kept 20 cm away i 300 nm increased due to the formation of m from the light source. The zone of inhibition aminophenolateions.22 e was measured and the results were expressed h c as mm compared to control pure PMMA. This o t procedure was repeated three times. o h P 6 Page 7 of 15 Photochemical & Photobiological Sciences t p i r c s u n a M d e t p e c c A s e c n e i c Fig 1. Spectral patterns of 4-NP solution during the photocatalytic reduction process in the presence of S2 S nanocomposite sample, under visible-light irradiation for 6 h. l a c i g o The photocatalytic activity of the prepared electron transfer from donor (BH -) to acceptor 4 l o nanocomposites was tested in photoreduction (4-NP). UV−visible spectrophotometric i b of 4-NP by sodium borohydride in aqueous analysis substantiated that the modified o t solution. Fig. 2 shows the photoreduction PMMA/TiO served as a photocatalyst for the o 2 h process of 4-NP at different conditions. The photoreduction reaction. P nitrophenolate ion as an intermediate forms in & (2) the aqueous solution of sodium borohydride l (cid:2913)(cid:2911)(cid:2930)(cid:2911)(cid:2922)(cid:2935)(cid:2929)(cid:2930) a from nitrophenol. The nitrophenolate ion can 4−NP+NaBH(cid:2872)(cid:4657)⎯⎯⎯⎯(cid:4654) 4−AP c A reduction test on 4-NP as a blank (3) i m be reduced to aminophenolate ion in the (without photocatalyst) shows that, without e presence of desired PMMA/TiO photocatalyst 2 addition of a photocatalyst, the photoreduction h c and the reducing agent by equation (2). of 4-NP by NaBH4 is slow and the o Actually, visible light active TiO in this new t 2 photoreduction efficiency, which was o type of nanocomposite is acted to expedite h calculated by equation (1), is less than 9% P 7 Photochemical & Photobiological Sciences Page 8 of 15 after 6h of visible light illumination. No absorbance and initial absorbance, t p remarkable change was also observed for respectively. The result of plotting ln(A /A) 0 t i r c blank (1) and (2) solutions. As can be seen versus the reaction time exhibits a good linear s from Fig. 2, the concentration of 4-NP correlation. The calculated rate constants of u n decreased as a function of irradiation time. photoreduction and the linear regression a M Pure PMMA as S0 sample was also tested in values are reported in Table 1. The rate d photoreduction reaction and the obtained result constant toward the S2 sample of the e was same as the blank (3). The maximum photocatalyst was calculated as 3.3 × 10−3 t p photoreduction efficiency, calculated by min−1, which was the maximum value. As e c equation (1), was 78.25 %, belonging to shown in the results of Table 1, the rate c A sample S2, after 6 h irradiating. As we constant was increased with the increasing s expressed in our previous work,which was the dosage of TiO2 and approaching a limiting e c photocatalytic degradation of MB dye, it is value at high loading of nanoparticles. This n e clearly found that the ionic liquid sensitized behaviour may be due to aggregation of i c TiO supported PMMA could be an effective nanoparticles in polymer matrix which causing 2 S catalyst for the water treatment.6 For this a decrease in the number of surface active l a catalyst a noticeable effect of IL on the sites. c i g catalytic activity under visible light was o 1.2 established and a suitable mechanism was l o proposed. 1 i b o Since the sodium borohydride was used in 0.8 t o excess, the rate of photoreduction process can 0 A 0.6 h bedescribed by the following equation22: A/t Blank (1) P Blank (2) 0.4 Blank (3) & S0 (3) S1 0.2 S2 al (cid:2914)[(cid:2872)(cid:2879)(cid:2898)(cid:2900)] (cid:2961) S3 c (cid:2914)(cid:2930) = −(cid:1863)[4−NP] S4 where k is the rate constant of the 0 i m 0 200 400 photoreduction. The concentration of 4-NP time (min) e h was calculated based on the absorbance at 400 c Fig 2. Effect of TiO nanoparticles concentration of 2 o nm. The rate constant could be determined PMMA/TiO photocatalyst on 4-NP photoreduction t 2 o from the slope of the plot of ln(A /A) versus 0 t under visible light irradiation. h time. A and A are the time-dependent P t 0 8 Page 9 of 15 Photochemical & Photobiological Sciences Table 1The calculated pseudo first-order rate constants h++ H O → ·OH + H+ (4) 2 (ads) (ads) t p of 4-NP photoreduction and the linear regression values i Sample k× 10-3(min-1) R2 This reaction would increase the cr Blank(1) 0.0900 0.7319 photoreduction of 4-NP by electron and holes s Blank(2) 0.8000 0.8818 u mechanismat neutral pH. n Blank (3) 0.2000 0.9976 a S0 0.2000 0.9800 M S1 1.4001 0.9984 100 S2 3.3310 0.9995 on d S3 1.7000 0.9831 cti e u 80 S4 1.2011 0.9926 ed t r p o Effect of pH hot 60 e f p c y o c The pH value of the reaction medium during nc 40 A e ci photoreduction reactions plays a very fi s Ef 20 % e significant role in the process design and c 0 n control photocatalysts.6,23 To evaluate the 3 4 5 6 7 8 9 10 11 e photocatalytic activity at different pH, the S2 pH ci S sample was used. The higher efficiencies were Fig 3.Effect of solution pH on the 4-NP photoreduction l a observed at pH value of about 7.5 (Fig.3). It is over S2 nanocomposite sample under visible light c clear that the change in the solution pH has a irradiation. i g o critical effect on the 4-NP photoreduction, Effect of light intensity l o which directly affects the surface charge i b The kinetics of the 4-NP photoreduction by properties of the photocatalyst and the o adsorption of pollutants.6 As can be seen any (S2) sample, under three various visible light ot lamps was studied. Table 2 contains a h further decrease or increase of pH less than 7 P summary of first order rate constants and or more than 8, significantly decrease the & linear regression values of kinetic data. The photocatalytic reduction efficiency. Therefore, l a emission spectrum and the total radiation data we suggest that a pH of 7.5 is optimum for the c i reduction of 4-NP with S2 sample of the fluorescence lamps (18, 36 and 60 W), m nanocomposite.As Islam et al.23expressed the obtained using Avaspec 2048 TEC instrument e h effect of pH on degradation of 4-NP against at the same condition of the photocatalysis c o test,areshown in Fig.S3† and reported in table TiO2 at neutral condition, the following t o reaction is possible for generation of ·OH: 2. It can be seen that the rate constant value of h P 4-NP photoreduction under 60 W irradiating 9
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