Chiral nematic cellulose–gold nanoparticle composites from mesoporous photonic celluloseChem. Commun.

About

Authors
Maik Schlesinger, Michael Giese, Lina K. Blusch, Wadood Y. Hamad, Mark J. MacLachlan
Year
2015
DOI
10.1039/C4CC07596J
Subject
Chemistry (all) / Ceramics and Composites / Electronic, Optical and Magnetic Materials / Materials Chemistry / Metals and Alloys / Surfaces, Coatings and Films / Catalysis

Similar

Thermo-Plastic Materials

Authors:
Cellulose Nitrate
1947

Cellulose

Authors:
Carl G. Schwalbe
1910

Cellulose Ester Melt-Coating Compositions

Authors:
C. J. Malm, M. Salo, H. F. Vivian
1947

Polymers derived from cellulose

Authors:
C.V. Horie
1987

Text

This journal is©The Royal Society of Chemistry 2014 Chem. Commun.

Cite this:DOI: 10.1039/c4cc07596j

Chiral nematic cellulose–gold nanoparticle composites from mesoporous photonic cellulose†

Maik Schlesinger,a Michael Giese,a Lina K. Blusch,a Wadood Y. Hamadb and

Mark J. MacLachlan*a

Gold nanoparticles (NPs) have been loaded into mesoporous photonic cellulose (MPC) films. The NPs show a low polydispersity and a nanoparticle-based plasmonic chiroptical activity with potential for novel sensing materials.

Metal nanoparticles (NPs) are intriguing materials with many potential applications.1 By scaling metals from bulk to nanometer dimensions, light can induce collective electron charge oscillations, known as localized surface plasmon resonances (SPRs), in the NPs.2 The frequency and intensity of the resonance are strongly dependent on the NP size and local environment. Metal

NPs have gained attention for catalysis, antimicrobials and sensors.3 Au NPs are particularly interesting for biosensing,4 electronics,5 diagnostics6 and therapeutics.7

Many applications for Au NPs require that they are monodisperse and attached to a substrate. Elegant ways to prepare monodisperse Au NPs have been reported,8 and Au NPs have been dispersed on various substrates.9 In addition, Au NPs with optical activity can be prepared by adsorption of chiral molecules or by adopting an intrinsically chiral arrangement, offering applications in biology, nanotechnology and catalysis.10 However, the origin of the chiroptical activity is complex and still a hot topic, but progress has been made through detailed experimental and theoretical studies by extension of available model systems.11

In terms of stabilization of metal NPs in a chiral environment, we prepared Ag and Au NPs on chiral nematic silica substrates via in situ deposition, and showed that there is a chiral response of the

SPR that may be useful for sensing.12 Another attractive substrate for supporting NPs is cellulose, and numerous cellulose–NP hybrid materials are known.13 The use of cellulose nanocrystals (CNCs), isolated from plant biomass,14 provides additional advantages.

CNCs form films with helicoidal (chiral nematic) structures that are attractive for constructing chiral plasmonic materials.

Querejeta-Ferna´ndez et al. recently co-assembled pre-formed

Au nanorods and CNCs to give thin films that show chiral responses.15 To date, no examples of Au NPs inside a chiral nematic cellulose host have been reported. Here we describe novel mesoporous chiral cellulose–Au NP composites prepared by in situ reduction of metal ions within a mesoporous chiral nematic CNC film. These new composite materials are attractive for sensing applications owing to the narrow polydispersity of the NPs, the chirality of the structures, and the mesoporosity of the films.

We recently reported a co-templating process where CNCs and a urea/formaldehyde (UF) resin co-assemble into a chiral nematic composite. Removal of the UF resin by alkaline treatment followed by washing with ethanol and drying from supercritical CO2 (SC–CO2) yields mesoporous photonic cellulose (MPC).16 This flexible material, solely composed of CNCs, has a chiral nematic arrangement of mesopores as well as a surface composed of D-glucose units that could transfer molecular chirality to guests.

In a first step, MPC films were prepared as described above.16 After soaking MPC in an aqueous solution of HAuCl4 (5 mM: Au-5, 10 mM: Au-10, 100 mM: Au-100) for 1 h to ensure full swelling of thematerial, Au NPs were obtained by reduction with an aqueous NaBH4 solution (Fig. 1). Samples were characterized using UV/Vis- and circular dichroism (CD) spectroscopy, electron microscopy, energy dispersive X-ray spectroscopy (EDX), powder

X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and

N2 adsorption techniques.

Successful formation of Au NPs in MPC (MPC–Au) can be easily seen as the films have a dark blue color after drying under ambient conditions (Fig. S1, ESI†). Films prepared with the different precursor concentrations all appeared similar.

TGA of the samples was performed under air to investigate their loading and thermal stability (Fig. S2, ESI†). The films show a twostep weight loss with an onset temperature ofB265 1C and a weight loss of B45% during the first step (heating rate: 10 1C min1), which is similar to unloaded MPC.16 A slight difference between a Department of Chemistry, University of British Columbia, 2036 Main Mall,

Vancouver, BC, V6T 1Z1, Canada. E-mail: mmaclach@chem.ubc.ca b FPInnovations, 2665 East Mall, Vancouver, BC, V6T 1Z4, Canada † Electronic supplementary information (ESI) available: Experimental procedures; SEM, TEM, N2 adsorption, UV/Vis, CD & EDX spectra, tables with analytical data. See DOI: 10.1039/c4cc07596j

Received 26th September 2014,

Accepted 11th November 2014

DOI: 10.1039/c4cc07596j www.rsc.org/chemcomm

ChemComm

COMMUNICATION

Pu bl ish ed o n 20

N ov em be r 2 01 4.

D ow nl oa de d by

L au re nt ia n

U ni ve rs ity o n 23 /1 1/ 20 14 2 0: 19 :0 1.

View Article Online

View Journal

Chem. Commun. This journal is©The Royal Society of Chemistry 2014 the films with different loading is observed during the second weight loss step (burning of char), which is completed at 465 1C (MPC–Au-5), 490 1C (MPC–Au-10) and 508 1C (MPC–Au-100), respectively. Thus, compared to unloaded MPC, the second step of cellulose decomposition is accelerated by the presence of Au

NPs, in accordance with metal NPs incorporated in nanoporous cellulose gels.13a Finally, a total weight loss of 99.8 wt% (MPC–Au-5), 98.7 wt% (MPC–Au-10) and 98.1 wt% (MPC–Au-100) was obtained.

Thus, assuming no oxidation of the Au NPs, the loading of MPC with Au NPs is determined to be 0.2 (MPC–Au-5), 1.3 (MPC–Au-10) and 1.9 (MPC–Au-100) wt%.

N2 adsorption measurements were performed to determine the influence of the loading on the porosity of MPC. Unloaded

MPC shows a type IV isotherm, characteristic of mesopores, with a Barrett–Joyner–Halenda (BJH) pore size of 13.7 nm, average pore volume of 0.47 cm3 g1, and a Brunauer–Emmett–Teller (BET) surface area of 138 m2 g1 (Fig. S3 and Table S1, ESI†).