Chemical versus physical grafting of photoluminescent amino-functional carbon dots onto transparent nematic nanocellulose gels and aerogels

Abstract

Self-assembly (Jiang and Hsieh 2016 ; Kobayashi et al. 2014 ; Saito et al. 2011 ) of individualized cellulosic nanofibers ( i -CNF) in aqueous colloidal dispersion state is an interesting phenomenon. It is currently intensively explored since it gives access to a new family of fully bio-based free-standing gels (Saito et al. 2011 ) and aerogels (Kobayashi et al. 2014 ) that feature intriguing properties. Anisotropic i -CNF aerogels have been demonstrated to bear a great potential for high-performance thermal insulation (Kobayashi et al. 2014 ; Plappert et al. 2017 ), nanoparticle filtration (Toivonen et al. 2015 ), or as templates for nanostructuration (Korhonen et al. 2011 ; Li and Huang 2016 ; Olsson et al. 2010 ; Zhu et al. 2018 ). Their large specific surface, high light transmittance and low apparent density—the latter effectuating low scattering and refractive indexes—literally invite to use these materials also for optical applications. This includes (bio)-sensing (Lim et al. 2015 ) and true volumetric 3D displays (Downing et al. 1996 ). All of these applications rely on a largely homogeneous dispersion of photoluminescent nanoparticles ( pl -NP) within the aerogel matrix and their specific response towards light. For sensing applications, a specific response is triggered depending on the presence and concentration of a certain target compound. Respective nanostructured porous i -CNF/ pl -NP hybrid materials greatly differ from their non-porous counterparts like cellulose/ pl -NP hybrid films (Abitbol and Gray 2008 ; Zeng and Yan 2015 ) or cellulose/ pl -NP hybrid fibers (Kulpinski et al. 2012 ) in terms of properties and target applications. Preservation of scaffold nanomorphology and optical properties as well as of nanoscale size and count of accessible functional groups on the surface of the pl -NP for inter-particulate bonding is a major challenge along the preparation process of i -CNF/ pl -NP hybrid aerogels. However, it is essential to all applications relying on both the large accessible surface of the scaffold and the nanosized scale of the functional nanoparticles.