Metal Nanoparticle Loaded Magnetic-Chitosan Microsphere: Water

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Metal Nanoparticle Loaded Magnetic-Chitosan Microsphere: Water Dispersible and Easily Separable Hybrid Metal Nano-Biomaterial for Catalytic Applications Thanusu Parandhaman, Nagaraju Pentela, Baskaran Ramalingam, Debasis Samanta, and Sujoy K. Das ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b01862 • Publication Date (Web): 05 Dec 2016 Downloaded from http://pubs.acs.org on December 5, 2016

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ACS Sustainable Chemistry & Engineering

Metal Nanoparticle Loaded Magnetic-Chitosan Microsphere: Water Dispersible and Easily Separable Hybrid Metal Nano-Biomaterial for Catalytic Applications Thanusu Parandhaman,a,c Nagaraju Pentela,b,c Baskaran Ramalingam,a Debasis Samanta,b,c and Sujoy K. Das*,a,c a

Biological Materials Laboratory, bPolymer Science Division, Council of Scientific and Industrial Research (CSIR)-Central Leather Research Institute (CLRI), Chennai-600020, India, c Academic of Scientific and Innovative Research (AcSIR), New Delhi-110001, India.

Abstract: We report a green synthesis of magnetically separable hybrid metal nano-biomaterial as water dispersible and recyclable catalysts. The hybrid nano-biomaterial was prepared in three step process. The magnetic nanoparticles were initially synthesized by biomineralization process and coated with chitosan followed by binding and reduction of metal ions, which led to the formation of magnetically separable hybrid nano-biomaterial (Fe3O4@Ch-MNPs, M=Au and Pd). The chemical composition, morphology, thermal stability and magnetic behaviour of the hybrid nano-biomaterial were characterized with Zeta potential, FTIR, XPS, XRD, VSM, FESEM, and TEM analysis. The FESEM measurement demonstrated formation of highly dispersed Au and PdNPs on the surface of nano-biomaterial, while TGA and VSM analyses indicated high thermal stability and superparamagnetic behaviour of the hybrid nano-biomaterial. The XPS studies revealed formation of pure metallic nanoparticles on the surface of the hybrid nano-biomaterial. The as-synthesised hybrid nano-biomaterial were tested for several model reactions such as photocatalytic reduction of dye, hydrogenation of p-nitrophenol and Suzuki coupling reaction at ambient temperature and in aqueous solution. The catalytic efficiencies varied with the type of MNPs and Fe3O4@Ch-PdNPs exhibited superior catalytic activities in all chemical reactions. In addition the hybrid nano-biomaterial demonstrated excellent recyclability and reusability without significant loss of catalytic activities. Furthermore, leaching of metal ions was not detected during catalytic reaction confirming high stability and low environmental impact of the as-synthesised hybrid nano-biomaterial. We believe that our result will help to synthesize easily separable hybrid nano-biomaterial as heterogeneous catalyst through cost effective and eco-benign synthetic route for development of environmental sustainable nanotechnology. Keywords: Metal nanoparticle, Magnetic properties, Supported catalyst, Photocatalytic reduction, Hydrogenation reaction, Suzuki coupling reaction, and Green chemistry *

Address for communication: Dr. Sujoy K. Das, Email: [email protected]; [email protected]. Tel: +914424437133. Fax: +914424910846.

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Introduction Catalytic applications of noble metal nanoparticles (MNPs) have received significant interest owing to their large specific surface areas and large number of exposed metal atoms, which greatly enhance the catalytic and physicochemical properties of MNPs.1,2 Among various MNPs, gold and palladium nanoparticles have attracted considerable attention in reduction of nitro compounds, oxidation of alcohols, photocatalytic degradation of dyes, catalytic conversion or decomposition of organic pollutants, electrochemical reduction of CO2, coupling reaction for CC bond formation, and many more.3-7 Therefore, the utilization of Au and PdNPs for environmental remediation and large scale production of agrochemicals, pharmaceuticals, polymers, etc. have received significant attention in recent years.8-10 However, catalytic activities of the MNPs is largely hampered due to aggregation/agglomeration of the MNPs in the reaction medium.11 Additionally, separation and recycling of the MNPs from the reaction medium remains a major challenge. Moreover, accumulation of free MNPs and subsequent leaching of metal ions into the environment raises secondary pollution problem and causes harmful effect on the living organisms.12,13 From sustainable point of view, significant efforts have been devoted in recent years on the

designing and synthesis of solid supported MNPs as recyclable

heterogeneous catalyst.14-16 However, recycling of the supported catalyst is still tedious as the separation process requires centrifugation or filtration. Iron oxide nanoparticles in this regard have aroused considerable interest as supportive material to address the above issues because of their high saturation magnetization and low coercivity.17,18 Furthermore, the unique combination of magnetic and plasmonic properties may provide a novel hybrid nano-biomaterial for diverse catalytic applications. Despite several attempts have been made for immobilization of MNPs on iron oxide nanoparticles,19-22 development of an eco-friendly approach for the preparation of monodisperse and stable MNPs on the surface of magnetic support is a significant challenge. Since iron oxide nanoparticles are poor in functional groups, the ordinary impregnation often results in formation of polydisperse MNPs on the surface of magnetic nanoparticles.23 The chemical functionalization of the magnetic nanoparticle with appropriate ligands or molecules becomes an important prerequisite to improve the conjugation, loading efficiency, stability and eventually improve the catalytic performance of the MNPs.24-26 Unfortunately, the functionalization of magnetic nanoparticles and subsequent conjugation of MNPs involve complicated synthesis process, which requires harsh reaction conditions, toxic chemicals and longer reaction time triggering environmental and safety issues.27 Very often the preparation process damages the magnetic structure, which reduces the magnetic response.28 Therefore, the current research focus has been


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converged on the designing and facile synthesis of magnetically supported stable MNPs to address the present challenges. In this study, we report an eco-friendly synthesis process for preparation of Au and PdNPs on the surface of magnetic nanoparticles (Figure 1) as a reusable heterogeneous catalyst. Initially, biogenic magnetic nanoparticles were prepared using Shewanella algae at ambient condition. In the next step the as-synthesized magnetic nanoparticle was encapsulated by chitosan (Fe3O4@Ch) for immobilization of MNPs. Being a potent natural biomaterial with macro-chelating ligand and surface-rich hydroxylic groups along with tunable molecular structure, encapsulation of iron oxide nanoparticles with chitosan could provide uniform distribution of MNPs on the surface of the nanostructure.29-31 In the final step, Fe3O4@Ch was decorated with Au and PdNPs through in situ reduction of metal ions by microwave irradiation to form magnetically separable hybrid nano-biomaterial (Fe3O4@Ch-MNPs, M=Au and Pd). The characterization, mechanism of formation and catalytic efficiency of the synthesized Fe3O4@ChMNPs in photocatalytic reduction of methylene blue, hydrogenation of p-nitrophenol and Suzuki coupling reaction has been demonstrated.

Materials and methods Materials. Chloroauric acid (purity≥ 99.99%), palladium chloride (purity≥ 99.9%), pnitrophenol, iodoacetophenene, phenylboronic acid, and glutaraldehyde were purchased from Sigma-Aldrich, India. Chitosan (MW ~300 kDa) with 90% degree of deacetylation was purchased from Panvo Organics, Chennai. Ferric chloride, light liquid paraffin, and other chemicals were purchased from Merck, India. The microbiological media were procured from Hi-media, India.

Microorganism. Shewanella algae (MTCC10455) was purchased from Institute of Microbial Technology, Chandigarh, India. The organism was cultured in nutrient agar (1% yeast extract, 1% peptone, 0.5% sodium chloride and 1.5% agar powder) slants and nutrient broth (1% yeast extract, 0.5% sodium chloride and 1% peptone) as necessary. The viability of the organism was maintained in nutrient agar slant through sub-culturing at 30 days intervals.

Methods Biosynthesis of Magnetic Nanoparticle. The biogenic synthesis of magnetic nanoparticle was carried out following incubation of magnetite precursor, akaganeite (FeOOH) with S. algae under anaerobic condition at 33 °C for 3 days. Lactate (10 mM) was served as the electron donor


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in this reaction. The colour of the solution changed to black from initial brown and attracted by the external magnet indicating formation of magnetic nanoparticles. On completion of reaction, the biogenic magnetite nanoparticles were washed with double distilled water three times to remove the attached bacterial cells and dried in a hot air oven at 60 C. A control experiment was carried out under similar condition by incubating magnetite precursor, akaganeite (FeOOH) with lactate, however, without addition of S. algae. The as-synthesised magnetic nanoparticles were calcined at 300 °C for 2 h and used for rest of the experiments.

Encapsulation of Chitosan on Magnetic Nanoparticles. Chitosan encapsulated magnetic nanoparticles (Fe3O4@Ch) was prepared by water-in-oil emulsion method.32 Initially 0.1% (w/v) magnetic nanoparticle solution was added into 1% (w/v) chitosan solution (dynamic viscosity: 33.15 mPa.s at 30 ºC) and sonicated for 30 min followed by incubation for 1 h at 30 °C under stirring. The chitosan-magnetic solution was added drop wise into light liquid paraffin containing Span-80 and stirred at 1800 rpm to form water-in-oil emulsion. Subsequently, glutaraldehyde solution to a final concentration of 1% was added into the suspension and continuously stirred for another 5 h. The obtained material was then separated from the emulsion by centrifugation and washed with double distilled water and ethanol repeatedly to remove residual paraffin oil and Span-80. Finally, the collected material was dried by lyophilisation to get Fe3O4@Ch powder.

Synthesis of Gold and Palladium Nanoparticles Decorated Fe3O4@Ch. The gold and palladium nanoparticles decorated Fe3O4@Ch were synthesized by microwave mediated in situ reduction of Au(III) and Pd(II) ions. In brief, 2 mL aqueous solution of gold and palladium (2 mM) were taken separately in screw cap vials and 50 mg of as-prepared Fe3O4@Ch powder was added followed by incubation for 1 h at 30 °C under stirring. The Au and PdNPs were then synthesized by microwave reduction (100 W) of bound Au(III) and Pd(II) ions for a period of 60 min and 240 min, respectively. The Au and PdNPs decorated Fe3O4@Ch were subsequently collected by centrifugation (20,000 g for 20 min) and washed with double distilled water several times to remove unreacted metal ions. Finally, the prepared materials were dried in a hot air oven at 50 °C. Here after the Au and PdNPs decorated Fe3O4@Ch were designated as Fe3O4@ChAuNPs and Fe3O4@Ch-PdNPs, respectively throughout the text. Characterization of Fe3O4, Fe3O4@Ch, Fe3O4@Ch-MNPs (M: Au and Pd). The morphology and chemical composition of all synthesized materials were characterized by several spectroscopic and microscopic techniques. The UV-vis spectra of dispersed solution of Fe3O4 ACS Paragon Plus Environment

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nanoparticles, Fe3O4@Ch, Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs were recorded on JASCO V650 UV-vis spectrophotometer. The crystal structure was recorded on Philips X-ray diffractometer at 080 with a Cu Kα source (λ= 1.54 Å), while thermal stability was measured by TGA (Philips) from 25 to 800 °C with heating rate of 10 °C/min. The morphology of the samples was studied by optical (Olympus microscope) and field emission scanning electron microscopy (FESEM; JEOL JSM 6700F) equipped with energy dispersive X-ray analysis (EDAX). The Fourier transform infrared spectra were recorded on FTIR spectrometer (PerkinElmer) from 4000500 cm-1 at a resolution of 1 cm-1. The chemical composition and oxidation state of surface element was determined by XPS analysis in Omicron Multiprobe (Omicron NanoTechnology, U.K.) spectrometer. The magnetic properties were examined by vibrating sample magnetometer (VSM, Lakeshore 7410) at room temperature with high purity nickel sphere as a standard reference, whereas the magnetic hysteresis loop was obtained using external magnetic field.

Photocatalytic Reduction of Dye. The photocatalytic activity of the as-prepared Fe3O4@ChAuNPs and Fe3O4@Ch-PdNPs for the reduction of methylene blue (MB) solution was studied under various conditions as described below. Briefly, 2 mg of hybrid nano-biomaterial was added into 20 mL of MB (20 mg/L) solution taken in a 100 mL reagent bottle and incubated in dark for 30 min with shaking to ensure the complete adsorption of MB. The dye solution was irradiated by sunlight, microwave (2.45 MHz, 100 W), visible (mercury vapour lamp, 400 W) and UV light (10 W, 285 nm) for different time intervals in presence of 2.9 mM of NaBH4. The samples were then withdrawn at regular intervals and the concentration of dye was measured spectrophotometrically by recording the absorbance at 665 nm.

Catalytic Hydrogenation and Suzuki Coupling Reaction. The catalytic activity of the synthesized Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs in hydrogenation reaction of pnitrophenol (p-NP) was evaluated using UV-vis spectrophotometer under stirring condition. Typically, 100 µL of 3×10-3 M p-NP was added into 2.8 mL of aqueous solution containing 5 ± 0.1 mg of the Fe3O4@Ch-MNPs (M: Au and Pd) taken in a quartz cuvette. The freshly prepared 100 µL of 0.3 M sodium borohydride (NaBH4) was added into the reaction mixture and the conversion of p-NP to p-amino phenol (p-AM) was monitored by measuring the absorbance value at 400 nm on UV-vis spectrophotometer. The experiment was performed in triplicates and repeated at different temperatures (2060 °C) under identical conditions. The control experiments were carried out under identical conditions as described above using Fe3O4@Ch and Fe3O4 nanoparticles. ACS Paragon Plus Environment

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The Suzuki coupling reaction of p-idoacetophenone and phenylboronic acid was studied with Fe3O4@Ch-MNPs (M: Au and Pd) in aqueous phase and oxic condition. In brief, a mixture of phenylboronic acid (182.9 mg, 1.5 mmol), 4-idoacetophenone (246 mg, 1 mmol) and double distilled water (3 mL) was taken in a round bottom flask. Potassium carbonate (276.5 mg, 2 mmol) was added to this mixture under stirring. The reaction was initiated following addition of 8 ± 0.5 mg of the hybrid nano-biomaterial and incubated under refluxing condition for 5 h. At the end of the reaction, the product was extracted with dichloromethane (DCM) and subsequently analysed by TLC and 1H NMR (400 MHz Bruker Avance- III Spectrometer). The coupling reaction was also performed under different reaction conditions like sunlight exposure, microwave irradiation, and in the laboratory at different temperature (3550 °C). The experiment on sunlight was conducted in a natural atmospheric environment in CLRI, Chennai, India on sunny days between 11 AM to 4 PM in October 2015 with average amount of solar radiation 5.12 kWh/m2, whereas the microwave irradiation was performed in a conventional microwave oven (2.45 MHz) at a power of 100 W for various time intervals. In all catalytic reactions the concentration of Au and Pd in the hybrid nano-biomaterial was 5.8 and 2.6 weight percentage, respectively and catalytic reaction were repeated minimum five times.

Recovery and Recyclability of Hybrid Fe3O4@Ch-MNPs (M: Au and Pd). The recovery and recyclability of the hybrid nano-biomaterial were executed to minimise the accumulation of the catalyst in the environment and reduce the production cost of the catalyst. After completion of first cycle, Fe3O4@Ch-MNPs was separated using a strong neodymium magnet, washed with DCM and finally dried in a hot air oven. The dried catalysts were used in successive cycle of catalysis reaction adopting similar procedure as described above.

Leaching of Metal Ions from Hybrid Fe3O4@Ch-MNPs (M: Au and Pd). The leaching of metal ions from the synthesized hybrid nano-biomaterial were analysed to understand the mechanism of catalysis reaction and stability of the Fe3O4@Ch-MNPs. The concentration of Au(III) and Pd(II) ions in the solution after catalysis reaction was measured using atomic absorption spectrometer (Analytic Jena, Nova 350) with appropriate standard solution.

Results and Discussion Synthesis and Characterization of Biogenic Magnetic Nanoparticles. The extracellular biogenic magnetite nanoparticles was synthesized upon interaction of iron oxyhydroxides


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(FeOOH), as magnetite precursor (akaganeite), with a dissimilatory metal-reducing bacterium, S. algae, under the anaerobic condition which is described graphically in Figure 1A.33 After 3 days of incubation the brown solution of akaganeite turned black and attracted by external magnetic bar (Figure 2A) indicating biosynthesis of magnetic nanoparticles by S. algae (Figure 2B). The formation and morphology of Fe3O4 nanoparticles was confirmed by FESEM image (Figure 2C), which clearly depicted synthesis of ~35 nm spherical magnetic nanoparticles. The extracellular synthesis of magnetite by S. algae did not require any harsh chemical and addition of exogenous electron carrier such as humic acids.33 The chemical composition of the biogenic magnetic nanoparticles was further investigated by XPS analysis. The survey spectrum showed core level Fe 2p peak along with C 1s, N 1s, and O 1s peaks as shown in Figure 2D. The high resolution Fe 2p peak had binding energies at 725.0 and 711.5 eV (inset Figure 2D) attributing to 2p1/2 and 2p3/2 of Fe, confirming the formation of Fe3O4 nanoparticles.34 The analysis of core level C 1s, N 1s, and O 1s peaks (Supporting information Figure S1) revealed association of proteins with Fe3O4 nanoparticles. Therefore, the in situ conjugation of protein molecules with Fe3O4 resulted in formation of stable biogenic magnetic nanoparticles. The crystalline nature of the as-synthesized magnetic nanoparticles was investigated by XRD analysis (Supporting Information Figure S2), which showed diffraction pattern at 2θ values of 30, 35.4, 43, 53.4, 56.9 and 62.5° corresponded to [220], [311], [400], [422], [511] and [440] planes of cubic Fe3O4 lattice, respectively. As per JCPDF data sheet (file no. 65-3107), these peaks indicated formation of pure cubic spinel structure of Fe3O4.35 Further, the biogenic magnetic nanoparticles were calcined at 300 C and the XRD pattern demonstrated that calcination process did not affect crystal structure of the magnetic nanoparticles, except the intensity of the peaks raised due to increase in crystallinity. Moreover, removal of bound proteins from the nanoparticles surface might also be responsible for higher peak intensity. The size Fe3O4 nanoparticle was also calculated using Scherrer equation (see Supporting Information), which demonstrated that size of Fe3O4 nanoparticle increased slightly from 25.6 nm to 29 nm after calcination process. The rest of the work was carried out with calcined magnetic nanoparticles. Synthesis and Characterization of Hybrid Fe3O4@Ch-MNPs (M: Au and Pd). The chitosan encapsulated magnetic nanoparticles (Fe3O4@Ch) were initially prepared by water-in-oil emulsion method, followed by formation of metal nanoparticles on the surface of Fe3O4@Ch to prepare Fe3O4@Ch-MNPs (Figure 1B). The encapsulation of Fe3O4 nanoparticles by chitosan was investigated by FTIR spectra. The IR spectrum (Figure 3) of chitosan showed characteristic absorption bands at 3401 cm-1 due to –NH and/or –OH stretching vibrations and at 2963 and 2852 cm-1 corresponded to –CH stretching vibration of copolymer of chitosan.36-38 The


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absorption bands at 1643, 1552 and 1265 cm-1 attributed to amide I (C=O stretching vibration), amide II (NH bending and CN stretching) and amide III (N–H bending and the C–N stretching) band, respectively. The peak assigned to CH2OH of C-6 position of the sugar moiety of chitosan appeared at 1402 cm-1, while the band at 1092 cm-1 accounted to O-H bending. 38,39 The peak at 1151 and 803 cm-1 corresponded to COC antisymmetric stretching and glycoside linkage of saccharide structure, respectively.37 Similarly, the FTIR spectrum of calcined Fe3O4 nanoparticles demonstrated peaks respectively at 3401, 1631, 1422, 1395, 1115, 1058 and 596 cm-1 due to the asymmetric and symmetric stretching vibration of surface bound residual protein molecules and FeO stretching vibration of Fe3O4,40 respectively. The IR spectrum of Fe3O4@Ch revealed characteristic bands of both chitosan (CH, CO, CN, NH and OH stretching and deformation vibrations) and magnetite. However, in comparison to pure chitosan and magnetite clear shifting of the absorption spectra were recorded in Fe3O4@Ch. The NH, OH and –CH stretching vibrations of chitosan molecule were shifted to 3431, 2927 and 2860 cm-1, respectively due to the binding of Fe3O4 nanoparticles with chitosan. Furthermore, amide II and III band shifted to 1564 and 1260 cm-1, respectively, whereas the absorption band for OH bending appeared at 1065 cm-1 suggesting conjugation of Fe3O4 nanoparticles with chitosan through binding with amine and hydroxyl groups. The cross-linking of amine group with glutaraldehyde in the formation of Fe3O4@Ch might also be responsible for shifting of amide band. In addition, the FeO stretching vibration shifted to 604 cm-1 and –COO- stretching vibration of surface proteins of magnetic nanoparticles disappeared. At the same time the absorption band at 1401 cm-1 was noticed due to CH2OH of chitosan in Fe3O4@Ch. The alterations of absorption bands therefore, supported the encapsulation of magnetic nanoparticles with chitosan forming Fe3O4@Ch. The FESEM image (Figure 4C) further revealed the size of the as-prepared Fe3O4@Ch was ~4 µm. The decoration of Au and PdNPs on the surface of Fe3O4@Ch and subsequent formation of Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs was carried out through microwave assisted reduction of surface bound metal ions.41 In this synthesis process, the chitosan acted not only as linker between magnetite and MNPs, but also stabilized both the MNPs and magnetite preventing their aggregation. Furthermore, the formation of Fe3O4@Ch-AuNPs and Fe3O4@ChPdNPs did not require any reducing agent, organic solvent and high temperature and thereby favours eco-friendly green synthesis process. The formation of Au and PdNPs on Fe3O4@Ch surface was observed with subsequent colour change of the material as shown in Figure 4A. The UV-vis spectra of the prepared Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs showed absorption peaks at 525 and 305 nm (Figure 4B)42,43 respectively, due to Surface Plasmon Resonance of Au and PdNPs; however, such characteristic peak was absent in chitosan, magnetic nanoparticles ACS Paragon Plus Environment

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and Fe3O4@Ch. The metal ions treated Fe3O4@Ch without exposure to microwave irradiation did not exhibit any SPR band of Au and PdNPs even after incubation for 24 h. This clearly demonstrated that reduction of Au(III) and Pd(II) ions to respective Au and PdNPs was assisted by microwave irradiation. The size and shape of the prepared Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs were determined by optical and FESEM images. The optical microscopic images of the as-prepared Fe3O4@Ch-MNPs are shown in Supporting Information Figure S3A-B, revealing homogenous distribution of monodisperse and spherical Fe3O4@Ch-MNPs with size ranges from 27 µm. Further, the morphology and shape of Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs was investigated by FESEM attached with EDXA. The low resolution FESEM images demonstrated average diameter of Fe3O4@Ch-AuNPs (Figure 4D) and Fe3O4@Ch-PdNPs (Figure 4G) were 4.21 ± 0.51 and 4.08 ± 0.4 µm, respectively. The high resolution FESEM images (Figure 4D-G, inset) of individual material clearly indicated the spherical shape of the hybrid nano-biomaterial. The formations of metal nanoparticles on the surface of Fe3O4@Ch-MNPs are clearly visible with further increasing the magnification of the images (Figure 4E, H). The elemental composition of the hybrid nano-biomaterial was confirmed by EDXA spectra. The area-profile analysis of Fe3O4@Ch-MNPs as shown in Figure 4F-I clearly depicted the appearance of Au and Pd peaks along with Fe, C, N, and O peaks. The metal peaks confirmed the formation of Au and PdNPs on the surface of Fe3O4@Ch, whereas Fe, C, N, and O signals originated from Fe3O4 and chitosan of Fe3O4@Ch-MNPs, respectively. The quantitative elemental analysis of the material counted 5.6 and 2.6% (w/w) of Au and Pd, respectively in Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs. The FTIR spectra of Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs (Figure 3) were recorded in order to understand the formation and stabilization of the MNPs on the surface of the nanobiomaterial. The initial incubation of positively charged metal ions with Fe3O4@Ch caused rapid binding of metal ions (Au and Pd) on the electronegative (32.6 mV ζ potential value) surface and void of Fe3O4@Ch through hydroxyl and amine groups of chitosan, resulting shifting of – NH/OH stretching band to 3124 cm-1. The intensities of amide II were reduced and appeared at 1560 cm-1, whereas amide III band disappeared in Fe3O4@Ch-MNPs resulting from binding of metal ions through amine group of chitosan.36 The spectra of the hybrid materials also revealed characteristic band of magnetite at 604 cm-1. The formation of Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs was further optimized by varying the microwave irradiation time and the kinetics of the reduction of metal ions to MNPs was monitored spectrophotometrically. The broad SPR band of AuNPs appeared at 505 nm with minimum exposure of 30 min and sharp peak appeared at 525 nm after exposure for 60 min indicating nucleation and growth of AuNPs ACS Paragon Plus Environment

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on the Fe3O4@Ch (Supporting Information Figure S4A). However, further increase in exposure time beyond 85 min caused broadening of SPR band attributing to the melting of AuNPs. In the same manner the process of Fe3O4@Ch-PdNPs preparation was optimized at 240 min for microwave irradiation of Pd(II) bound Fe3O4@Ch (Supporting Information Figure S4B). The result showed that microwave reduction of Au+3 ions required lesser time than that of Pd+2 ions. According to HSAB (hard soft acid base) principle44 Au+3 is softer than Pd+2 as Au has higher atomic radius and more polarisable than Pd. Therefore, it is easy to reduce the more labile Au+3 ions than relatively hard Pd+2 ions. The oxidation state of Au and Pd in the synthesized hybrid nano-biomaterial was further investigated by XPS analysis. The survey spectra showed core level Au 4f and Pd 3d peaks in addition to Fe 2p, C 1s, N 1s, and O 1s peaks as shown in Figure 5A. The Au 4f spectrum (Figure 5B) in Fe3O4@Ch-AuNPs was composed of doublet peaks at binding energy of 84.1 and 87.8 eV corresponded to 4f7/2 and 4f5/2 peaks of Au(0) respectively,43 whereas the related Pd 3d spectrum in Fe3O4@Ch-PdNPs (Figure 5C) was composed of doublet peaks corresponding to 3d5/2 and 3d3/2 peaks of Pd(0) and appeared at 335.2 eV and 340.4 eV, respectively.45 It is therefore, clear that all the bounded metal ions (Au(III) and Pd(II)) on Fe3O4@Ch were reduced to metallic nanoparticles. The signature of Fe 2p peak in the spectra appeared from magnetic nanoparticles, while C 1s, N 1s, and O 1s peaks were originated from chitosan of the Fe3O4@ChMNPs. Based on the obtained results a possible chemical structure of the Fe3O4@Ch-MNPs is schematically presented in Figure 1B. Further confirmation of Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs was carried out by XRD analysis. The X-ray diffraction pattern of chitosan, magnetite, Fe3O4@Ch, Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs are presented in Figure 6A. Chitosan had a broad peak at 21° attributing to the amorphous characteristic, whereas the calcined iron oxide nanoparticles showed diffraction pattern at 2θ values of 30.2, 34.7, 43.5, 53.7, 57.2 and 62.8° corresponded to [220], [311], [400], [422], [511] and [440] planes of cubic Fe3O4 lattice, respectively. The XRD pattern of Fe3O4@Ch demonstrated strong diffraction peaks at 30.2, 35.5, 43.2, 53.6, 57.1 and 62.7° corresponded to [220], [311], [400], [422], [511] and [440] planes of cubic Fe3O4 lattice and a weak diffraction peak of amorphous chitosan at 21°. The intensity of diffraction peak of chitosan was reduced in Fe3O4@Ch due to binding of Fe3O4 with chitosan through NH2/OH group causing disordered of 3D crystal structure of chitosan.46 The final Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs exhibited additional peaks for face-centered cubic structure of Au and PdNPs along with strong diffraction pattern of Fe3O4 and a weak peak of chitosan. The diffraction peaks of [111], [200], [220] and [311] planes of AuNPs appeared at 39.3, 45.9, 62.1 and 76.8°, respectively (JCPDS no. 04-0784). On the other hand the diffraction peaks for PdNPs were ACS Paragon Plus Environment

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appeared at 39.3, 45.6, 64.7, and 79.6° assigning to the [111], [200], [220], and [331] planes, respectively, of face-centered cubic structure of metallic Pd crystal (JCPDS no. 46-1043). These results therefore, clearly demonstrated the fabrication of crystalline Au and PdNPs on the Fe3O4@Ch surface. The magnetic property of Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs was analysed by VSM measurement at room temperature and Figure 6B displayed ‘S’-shaped magnetic hysteresis loop of the samples demonstrating superparamagnetic behavior.47,48 The saturation magnetization value of Fe3O4@Ch-AuNPs was found at 23.1 emu/g, whereas the coercivity and retentivity values were 0.076 kOe and 2.5 emu/g, respectively. In case of Fe3O4@Ch-PdNPs, saturation magnetization, coercivity and retentivity values were observed, respectively at 30.3 emu/g, 0.064 kOe and 3.8 emu/g. Since the coercivity of Fe3O4@Ch-MNPs (Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs) and Fe3O4 nanoparticles (0.052 kOe) was almost same and very close to zero, the superparamagnetic property of Fe3O4 remained same in [email protected] The low saturation magnetization of Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs compared to the Fe3O4 nanoparticles (52.2 emu/g) was attributed to the encapsulation of Fe3O4 nanoparticles by chitosan. However, the magnetism of Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs was sufficient enough for magnetic separation of the hybrid nano-biomaterial from aqueous solution using external magnetic field leading to easy recycling and reuse. The thermal stability of the synthesized Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs was studied by TGA. The thermogram of chitosan, magnetite, Fe3O4@Ch and Fe3O4@Ch-MNPs showed the decomposition temperature of the samples (Figure 6C). The TGA curve of calcined Fe3O4 nanoparticle demonstrated only 3.6% weight loss throughout the entire temperature range might be due to the removal of absorbed water and/or some residual organic molecules. On the other hand, pure chitosan showed three stages of decomposition. The initial weight loss below 100 °C was quite small (8%), which was associated with the evaporation of both adsorbed and bound water. The residual acetic acid was also removed in this stage.50,51 The second stage contributed about 41.9% of weight loss at the range of 180–270 °C due to the degradation and deacetylation of chitosan.52 The third stage, which started at 450 °C and ended at 800 °C demonstrated complete degradation of chitosan. The Fe3O4@Ch, Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs demonstrated very similar thermogram patterns. Though the initial stage of water evaporation (7%) was same as that of chitosan, visible distinctions were observed in the second and third stages of weight loss. The Fe3O4@Ch, Fe3O4@Ch-AuNPs and Fe3O4@ChPdNPs started decomposition at 180, 196 and 220 °C, respectively and 32, 30 and ~27% of weight loss were recorded at this stage. The final stage of decomposition started at 290 and 300 °C in both Fe3O4@Ch and Fe3O4@Ch-MNPs (Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs) and ACS Paragon Plus Environment

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48.3, and 43.5 and 42.7% of weight loss were witnessed in Fe3O4@Ch, Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs respectively, which evidently demonstrated good thermal stability of the hybrid material. Compared to Fe3O4@Ch, the weight loss was less in Fe3O4@Ch-MNPs, suggesting incorporation of MNPs further stabilized the material. TGA data thus showed that the as-prepared Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs had enough thermal stability and very much suitable for catalytic reactions. Photocatalytic Reduction of Dye. Treatment of wastewater containing aromatic hydrocarbons especially organic dyes has been a major concern for environmental sustainability and remains a technical challenge. The catalytic performance of Fe3O4@Ch-MNPs in reduction of methylene blue (MB) to leucomethylene blue (LMB) (Figure 7A) was therefore, studied as a model dye pollutant. Figure 7D showed disappearance of dye color following treatment with Fe3O4@ChAuNPs in presence of NaBH4. The addition of Fe3O4@Ch-MNPs to the dye solution caused gradual decrease in absorption intensity of MB with time as measured by UV-vis spectra. The absorbance of MB at 665 nm became nearly zero within 9 min (Figure 7E) indicating complete reduction of MB to LMB by Fe3O4@Ch-AuNPs. On the other hand, Fe3O4@Ch-PdNPs took only 6 min (Figure 7F) to complete the reduction of MB. The control experiment performed both with Fe3O4 and Fe3O4@Ch did not exhibit reduction of absorption intensity of MB even after treatment for 5 h (Figure 7B-C). In case of Fe3O4@Ch, the absorbance reduced slightly due to absorption of MB on Fe3O4@Ch surface. The photocatalytic performance of Fe3O4@ChMNPs was further optimized at different reaction conditions (Table 1) such as microwave, UV, visible and sunlight exposure. Very likely, the reaction was facilitated upon irradiation with UV light (Figure 7G) and reduction process was accomplished just within 1 min. The rate of the reaction was calculated using pseudo-second order rate kinetics. The apparent rate constant (kapp) was calculated from the slop of linear regression of ln A (absorbance at 665 nm) as function of reaction time (Figure 7H). Finally the normalised rate constant (knor) was determined by dividing the kapp values with concentration of metal present in the hybrid nano-biomaterial. It was observed from the estimated knor value (Figure 7I) that Fe3O4@Ch-PdNPs has higher photocatalytic activity than Fe3O4@Ch-AuNPs in all reaction conditions. The catalytic degradation of MB has been reported under irradiation with UV and visible lights; 53 however, only limited study has been conducted on reduction of MB. Zhu et al.56 reported that reduction of MB using Fe3O4@Ch@silver core–shell nanostructures is completed within 10 min with a rate constant of 0.34/min, while Kim et al.57 demonstrated the complete reduction of MB by Pt decorated SiOx nanowire in 40 min. Interestingly in the present study, Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs took just 1 min under UV light to complete the reduction of MB to LMB with


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kapp of 4.0/min and 5.0/min. The knor values were found to be 1.14 × 102 and 1.72 × 102 mmol-1.s1

, respectively demonstrating superior catalytic activity of the synthesized Fe3O4@Ch-AuNPs

and Fe3O4@Ch-PdNPs in reduction of MB. In consistent with the obtained results, the photocatalytic activity of Fe3O4@Ch-MNPs is proposed to occur through the following steps; MB initially adsorbed on the surface of the hybrid nano-biomaterial and then reduced to LMB by Au or PdNPs through electron transfer process. The reduced dye desorbed from the Fe 3O4@ChMNPs to create a free space for further reduction to continue. In contrast, Fe3O4 and Fe3O4@Ch unable to decolorized MB due to the absence of MNPs.

Catalytic Hydrogenation and Suzuki Coupling Reaction of Fe3O4@Ch-MNPs. Nitrophenols have been listed among the top 100 harmful organic pollutants according to EPA. Because of large solubility and high stability, nitrophenols remain in waterbody for prolong time triggering detrimental effects on agricultural plants, animals and human beings. The catalytic reduction of nitrophenol to aminophenol is considered as most convenient approach to convert organic waste to value added intermediate chemical as aminophenol is important intermediate for synthesizing analgesic antipyretic drugs, agrochemicals, corrosion inhibitors, dyes, etc.58,59 The catalytic hydrogenation performance of the hybrid nano-biomaterial was quantitatively evaluated in the reduction of p-NP to p-AP in presence of an excess NaBH4. Upon addition of Fe3O4@Ch-MNPs to the reaction medium of p-NP and NaBH4, the absorption intensity at 400 nm decreased successively with time along with simultaneous appearance of a new peak at 300 nm corresponding to p-AP (Figure 8A).42,60 The reaction was completed within 314 min depending upon the MNPs on the hybrid nano-biomaterial and reaction temperature. The control experiments performed with the addition of Fe3O4@Ch and Fe3O4 nanoparticles showed that the bright yellow solution of p-NP remained almost same. The maximum absorption peak did not exhibit any change in case of Fe3O4 nanoparticles, however, when Fe3O4@Ch was used as catalyst, the maximum absorption peak was reduced slightly due to the adsorption of p-NP on Fe3O4@Ch surface. This clearly indicated that the reduction of p-NP to p-AP was catalysed by Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs only. The time and temperature dependent absorption spectrum of p-NP reductions are presented in Figure 8BC. It is reported that in most of the catalytic reaction a certain amount of time is required upon addition of the catalyst, referred as an induction time ‘tind’, to initiate the hydrogenation reaction.60-62 However, in the present system reaction started immediately after addition of the Fe3O4@Ch-MNPs. This suggested that perhaps p-NP adsorbed on the surface of Fe3O4@Ch-MNPs instantly favouring the hydrogenation reaction. The catalysis reaction followed pseudo-first-order rate kinetics and the apparent rate constant (kapp) was determined from the slop of linear regression of ln A (absorbance at 400 nm) ACS Paragon Plus Environment

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vs. time (Figure 8D-E).62 Results showed that the average kapp value increased with temperature suggesting temperature dependent reduction process. It was also noted that Fe3O4@Ch-PdNPs exhibited higher catalytic activity than the Fe3O4@Ch-AuNPs in all temperature range. To further compare the catalytic efficiency of the Fe3O4@Ch-MNPs with other metal nanomaterials, as reported in the literatures, normalized rate constant (knor) values were measured at different temperature (Figure 8F) by dividing kapp values with the amounts of Au and Pd present in the hybrid nano-biomaterial. It was observed that the knor value of Fe3O4@Ch-PdNPs is higher than Fe3O4@Ch-AuNPs; moreover, catalytic activities of both Fe3O4@Ch-AuNPs and Fe3O4@ChPdNPs are higher than those of the chemically synthesized metal nanomaterials (Supporting Information Table S2). The Suzuki coupling is another important reaction catalysed by MNPs in CC bond formation. Unfortunately, most of the reactions are carrying out in highly flammable organic solvents and at high temperature raising environmental concern.63-66 In this context, coupling reaction in aqueous medium and oxic condition using recyclable and reusable catalyst has significant importance for the development of sustainable chemistry and economy of concern. Therefore, the catalytic behaviour of Fe3O4@Ch-MNPs in the CC bond formation of phenylboronic acid and p-iodoacetophenone in aqueous solution was explored under various conditions. We are delighted to observed a complete conversion of iodobenzene into biphenyl (Supporting Information Figure S5), when the reaction was carried out using Fe3O4@Ch-PdNPs under refluxing condition just for few hours (Table 2, entry 1). The coupling reaction was further optimized by changing the reaction conditions like exposure in sunlight, microwave irradiation, and in normal laboratory. The results showed that under sunlight exposure 98% yield (TON=50256 and TOF=5584) was achieved within 9 h (Table 2, entry 3), whereas under microwave irradiation (52 C, 2.45 MHz frequency, and 100 watt) 98% yield (TON=50256 and TOF=50256) was achieved just within 1 h of reaction (Table 2, entry 8) using Fe3O4@ChPdNPs. Similarly, when the same reaction was carried out in the normal laboratory condition 98% yield (TON= 50256 and TOF=16752) was recorded after 3 h (Table 2, entry 11), and 90% yield (TON= 46153 and TOF=61538) achieved just within 45 min (Table 2, entry 13). Although few report are available in the literature for enhancement of efficacy of coupling reaction by artificial light irradiation using palladium based catalyst,67-69 to the best of our knowledge there is hardly any report, if any, to perform Suzuki coupling reaction under normal laboratory condition in aqueous solution. On the other hand, Fe3O4@Ch-AuNPs demonstrated less activity and ~3% yield (TON= 1276 and TOF=142) (Table 2, entry 2) was observed under reflux condition and 1% yield (TON= 425 and TOF=47) was obtained under microwave irradiation for 9 h (Table 2, entry 15). We also performed the coupling reaction with less reactive 4-chloroacetophenon ACS Paragon Plus Environment

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under similar working conditions as in iodoacetophenone and observed that the catalyst did not exhibit any catalytic conversion.70,71 As a control experiment, Fe3O4@Ch-MNPs was replaced either with Fe3O4@Ch or Fe3O4 nanoparticles, giving rise to no product. Finally, the catalytic activity of Fe3O4@Ch-PdNPs was compared with the reported values and it was observed that Fe3O4@Ch-PdNPs exhibited higher or similar TON and TOF compared to those chemically synthesized PdNPs (Supporting Information Table S3).42,72,73 Furthermore, most of the catalytic reactions of chemically synthesized PdNPs were performed in organic solvents, anoxic condition and at high temperature, however, the catalytic reaction using Fe3O4@Ch-PdNPs occurred in aqueous solution at normal laboratory condition. Moreover, there was no black precipitation of Pd after completion of the reaction supporting high stability and activity of the Fe3O4@ChPdNPs. The leaching of metal ions from the hybrid nano-biomaterial was also measured by AAS analysis and results demonstrated absence of metal ions in the solution, which confirmed high electronic stabilization of Au and PdNPs on the hybrid nano-biomaterial. Immobilization of MNPs on solid support especially on magnetic nanoparticles often reduces its catalytic efficiency,67,74 however, such adverse effect was not observed in the Fe3O4@Ch-MNPs. In the proposed hybrid nano-biomaterial the Fe3O4, chitosan and MNPs acted independently; Fe3O4 favored easy magnetic separation of the catalyst, whereas MNPs catalysing the reaction and chitosan provide stability to both Fe3O4 and MNPs. Overall the high stability of as-synthesized Fe3O4@Ch-MNPs not only provide catalytic efficiency, but easy recovery and prevention of leaching of metal ions also protect the environment from toxic effect of nanoparticles.

Recovery and Recyclability of Fe3O4@Ch-MNPs. The recyclability and reuse of the catalysts in successive reactions are another important aspect for cost effective application of nanomaterial and preventing their accumulation in waste. Considering this critical and significant issue, Fe3O4@Ch-MNPs was separated from the reaction medium using an external magnet, washed with dichloromethane, dried and finally reused for next cycle of the hydrogenation and coupling reaction. It was worth to note that during multiple cycle of hydrogenation reaction (Supporting Information Figure S6A), the conversion of p-NP was still as high as 95% in the fifth cycle of the reaction and did not exhibit significant loss of catalytic activity even after tenth repetitive cycles; the conversion efficiency remained above 87%. Similarly in the coupling reaction using Fe3O4@Ch-PdNPs, 96% conversion was achieved in the second cycle and dropped to 70% in fifth cycles of the reaction (Supporting Information Figure S6B). Therefore, the overall conversion was calculated to be 85%, which demonstrated good catalytic activity and well recycling potential of the Fe3O4@Ch-PdNPs. The high catalytic ACS Paragon Plus Environment

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activity and recyclability of the synthesized hybrid nano-biomaterial is attributed to the synergistic effect of magnetic nanoparticles, chitosan and metal nanoparticles. The plenty of functional groups of chitosan favoured binding of aromatic compounds like p-NP, phenylboronic acid, p-iodoacetophenone and dye on Fe3O4@Ch-MNPs providing excellent contact of these aromatic compounds with the hybrid nano-biomaterial.75 Moreover, chitosan provide electronic stabilization of MNPs, thereby prevented aggregation and leaching of Au and PdNPs. The uniform distribution of MNPs (Au and Pd) on the surface favoured the catalytic reactions, whereas the magnetic behaviour facilitated their easy separation using external magnetic field leading to recycling and reuse. The proposed Fe3O4@Ch-MNPs thus, provides a promising opportunity for the preparation of highly efficient, stable and recyclable metal nanocatalyst.

Conclusion. In summary, a novel eco-friendly synthetic route has been developed for the preparation of MNPs decorated magnetically separable hybrid nano-biomaterial (Fe3O4@ChMNPs, M=Au and Pd) as heterogeneous catalyst. In the process of hybrid nano-biomaterial preparation, the spherical magnetic nanoparticles (~35 nm) were initially biosynthesized using S. algae and then functionalized with chitosan (Fe3O4@Ch, ~4 µm) to decorate with Au and Pd NPs. Chitosan played dual role in decoration of stable Au and Pd NPs by in situ microwave reduction of metal ions and preventing leaching of the metal ions from the MNPs. Both Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs exhibited superparamagnetic properties with saturation magnetization value of 23.1 and 30.3 emu/g, respectively and coercivity of 0.076 and 0.064 kOe, respectively. More importantly, Fe3O4@Ch-MNPs exhibited very good thermal and electronic stability and excellent catalytic activities (>99% conversion) in photocatalytic reduction of dye, hydrogenation, and Suzuki coupling reactions in aqueous solution at ambient temperature. The catalytic efficiency varied with the type of MNPs, and Fe3O4@Ch-PdNPs exhibited superior catalytic activity in all chemical reactions compared to other metal nanocatalysts. Furthermore, the prepared hybrid nano-biomaterial could be recovered easily with external magnetic field and reused multiple times without significant loss in catalytic activities. We believe that our result will help to synthesize easily separable hybrid nano-biomaterial as heterogeneous catalyst through cost effective and eco-benign synthetic route to reduce the environmental burden of toxic chemicals and improve the environmental sustainability.

ACKNOWLEDGEMENTS SK Das acknowledges Department of Science and Technology and Council of Scientific and Industrial Research, Government of India for providing financial support under Fast Track Research Scheme (SR/FT/LS-80/2012) and STRAIT programme, respectively. T. Parandhaman ACS Paragon Plus Environment

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gratefully acknowledges UGC for Rajiv Gandhi National Fellowship. We also acknowledge Central Sophisticated Instrumentation Facility (CSIL) of CLRI for TGA and Zeta potential analysis.


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Legend of Figures

Figure 1: Schematic representation of synthesis of biogenic magnetic nanoparticles (A), encapsulation of magnetic nanoparticle with chitosan and formation of metal nanoparticles on the chitosan encapsulated magnetic nanoparticles (B) to form hybrid metal nano-biomaterial (Fe3O4@Ch-MNPs).

Figure 2: Experimental set up and biosynthesis of Fe3O4 nanoparticles (A) by S. algae; FESEM images of S. algae (B) and biosynthesized Fe3O4 nanoparticles (C); XPS survey spectra (D) of biosynthesized Fe3O4 nanoparticles. The inset picture of Figure D shows high resolution core level Fe 2p spectrum of Fe3O4 nanoparticles.

Figure 3: FTIR spectra of chitosan, Fe3O4, Fe3O4@Ch, Fe3O4@Ch-AuNPs and Fe3O4@ChPdNPs.

Figure 4: Colour image (A) of Fe3O4@Ch, Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs; UV-vis spectra (B) of chitosan, Fe3O4, Fe3O4@Ch, Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs; FESEM image of Fe3O4@Ch (C), Fe3O4@Ch-AuNPs (D), and Fe3O4@Ch-PdNPs (G); High resolution FESEM image of Fe3O4@Ch-AuNPs (E) and Fe3O4@Ch-PdNPs (H) depicting formation of Au and PdNP on the surface of material; EDXA spectrum of Fe3O4@Ch-AuNPs (F) and Fe3O4@ChPdNPs (I). The inset picture of Figure (DG) showed high resolution FESEM image of single Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs.

Figure 5: XPS survey spectra of (A) Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs, and core level high resolution Au 4f (B) and Pd 3d (C) spectra of Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs, respectively.

Figure 6: XRD (A) of chitosan, Fe3O4, Fe3O4@Ch, Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs; VSM analysis (B) of the synthesized Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs; and TGA (C) of chitosan, Fe3O4, Fe3O4@Ch, Fe3O4@Ch-AuNPs and Fe3O4@Ch-PdNPs. ACS Paragon Plus Environment

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Figure 7: Catalytic activity of Fe3O4@Ch-MNPs in reduction of methylene blue to leucomethylene blue (A); colour image (B) and corresponding UV-vis spectrum (C) of methylene blue following treatment with Fe3O4 NPs; colour image (D) and time dependent UVvis spectra (E) of methylene blue following treatment with Fe3O4@Ch-AuNPs; UV-vis spectra (F-G) of methylene blue following treatment with Fe3O4@Ch-PdNPs in laboratory condition and with UV irradiation; plot of ln A665 (absorbance at 665 nm) against the reaction time for MB reduction by Fe3O4@Ch-PdNPs (H), and estimated knor values (I) at different temperature.

Figure 8: UV-vis spectrum (A) of catalytic reduction of p-NP to p-AP by Fe3O4@Ch-MNPs; time-dependent absorption spectra of reduction p-NP by Fe3O4@Ch-AuNPs (B) and Fe3O4@ChPdNPs (C), respectively; Plot of ln A400 (absorbance at 400 nm) against the reaction time for pNP reduction by Fe3O4@Ch-AuNPs (D) and Fe3O4@Ch-PdNPs (E), respectively; and normalized (F) rate constant (knor) estimated at different temperature.


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(A)

S. algae/ 33 C Biosynthesis FeOOH

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300 C/ 2h Calcination Protein coated magnetite

(B)

h Microemulsion

Microwave reduction

Figure 1


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Before reaction

After reaction

A

Magnetic separation

B N2

N2

N2

C

D

C Figure 2


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Figure 3


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B

A

D

C

F

E

G

H

I

Figure 4


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A

B

C

Figure 5


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A

B

C

Figure 6


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A

B

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C

e

D

G

F

E

I

H

Figure 7


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A

B

D

C

E

F

Figure 8


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Table 1: Optimization of catalytic reduction of methylene blue to leucomethylene blue by Fe3O4@Ch-MNPsa: M=Au and PdNPs Entry Time (min) Reaction condition Temperature (°C) Conversion (%) 1

9

Laboratory/ H2O/ 32 ± 1 99 Fe3O4@Ch-AuNPs 2 9 Microwave/ H2O/ 52 ± 1 99 Fe3O4@Ch-AuNPs 3 6 Visible light/ H2O/ 33 ± 1 100 Fe3O4@Ch-AuNPs 4 4 Sunlight/ H2O/ 35 ± 1 100 Fe3O4@Ch-AuNPs 5 1 UV light/ H2O/ 32 ± 4 100 Fe3O4@Ch-PdNPs 6 6 Laboratory/ H2O/ 32 ± 3 99 Fe3O4@Ch-PdNPs 7 6 Microwave/ H2O/ 52 ± 2 100 Fe3O4@Ch-PdNPs 8 3 Visible light/ H2O/ 33 ± 2 100 Fe3O4@Ch-PdNPs 9 2 Sunlight/ H2O/ 35 ± 2 100 Fe3O4@Ch-PdNPs 10 1 UV light/ H2O/ 32 ± 2 100 Fe3O4@Ch-PdNPs a Conditions: Methylene blue (10 mL, 20 mg/L), NaBH4 (2.9mM), Fe3O4@Ch-MNPs (2 ± 0.5 mg, containing 2.6% Pd in Fe3O4@Ch-PdNPs and 5.8% Au in Fe3O4@Ch-AuNPs), pH 7.2.


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Table 2: Optimization of the Suzuki coupling reaction using Fe3O4@Ch-MNPsa: M=Au and PdNPs

Entry 1

Time (min) 540

Reaction condition

Temperature (°C) 100

Conversion (%) 99

TON

TOF

Refluxing/ H2O/ 50769 5641 Fe3O4@Ch-PdNPs 2 540 Refluxing / H2O/ 100 3 1276 142 Fe3O4@Ch-AuNPs 3 540 Sunlight/ H2O/ 37 ± 4 98 50256 5584 Fe3O4@Ch-PdNPs 4 300 Sunlight/ H2O/ 37 ± 3 73 37435 7487 Fe3O4@Ch-PdNPs 5 540 Microwave/ H2O/ 52 ± 1 98 50256 5584 Fe3O4@Ch-PdNPs 6 300 Microwave/ H2O/ 52 ± 1 98 50256 10051 Fe3O4@Ch-PdNPs 7 180 Microwave/ H2O/ 52 ± 1 98 50256 16752 Fe3O4@Ch-PdNPs 8 60 Microwave/ H2O/ 52 ± 1 98 50256 50256 Fe3O4@Ch-PdNPs 9 1080 Lab condition/ H2O/ 35 ± 2 77 39487 2193 Fe3O4@Ch-PdNPs 10 300 Lab condition/ H2O/ 50 ± 2 98 50256 10051 Fe3O4@Ch-PdNPs 11 180 Lab condition/ H2O/ 50 ± 2 98 50256 16752 Fe3O4@Ch-PdNPs 12 60 Lab condition/ H2O/ 50 ± 2 97 49743 49743 Fe3O4@Ch-PdNPs 13 45 Lab condition/ H2O/ 50 ± 2 90 46153 61538 Fe3O4@Ch-PdNPs 14 30 Lab condition/ H2O/ 50 ± 2 55 28205 56410 Fe3O4@Ch-PdNPs 15 540 Microwave/ H2O/ 52 ± 1 1 425 47 Fe3O4@Ch-AuNPs a Conditions: Phenylboronic acid (183 mg, 1.5 mmol), p-Iodoacetophenone (246.5 mg, 1 mmol), K2CO3 (276.5 mg, 2 mmol), Fe3O4@Ch-MNPs (8 ± 0.5 mg, containing 2.6% Pd in Fe3O4@ChPdNPs and 5.8% Au in Fe3O4@Ch-AuNPs), H2O, and under aerobic condition.


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Table of Content (TOC) Metal Nanoparticle Loaded Magnetic-Chitosan Microsphere: Water Dispersible and Easily Separable Hybrid Metal Nano-Biomaterial for Catalytic Applications Thanusu Parandhaman,a,c Nagaraju Pentela,b,c Baskaran Ramalingam,a Debasis Samanta,b,c and Sujoy K. Das*,a,c a

Biological Materials Laboratory, bPolymer Science Division, Council of Scientific and Industrial Research (CSIR)-Central Leather Research Institute (CLRI), Chennai-600020, India, cAcademic of Scientific and Innovative Research (AcSIR), New Delhi-110001, India.

Magnetically separable hybrid metal nano-biomaterial (Fe3O4@Ch-MNPs: M=Au and Pd) demonstrated excellent catalytic activities in reduction of dye and organic solvent free hydrogenation and Suzuki coupling reactions.


Metal Nanoparticle Loaded Magnetic-Chitosan Microsphere: Water

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