Abstract
Nanocellulose is known to act as a platform for the in-situ formation of metal oxide nanoparticles, where the multiple components of the resultant hybrids act synergistically toward specific applications. However, typical mineralization reactions require hydrothermal conditions or addition of further reducing agents. Herein, we demonstrate that carboxylated cellulose nanofibril-based films can spontaneously grow functional metal oxide nanoparticles during the adsorption of heavy metal ions from water, without the need of any further chemicals or temperature. Despite the apparent universality of this behavior with different metal ions, this work focuses on studying the in-situ formation of copper oxide nanoparticles on TOCNF films as well as the resultant hybrid films with improved functionality toward dye removal from water and antimicrobial activity. Using a combination of cutting-edge techniques (e.g., in-situ SAXS and QCMD) to systematically follow the nanoparticle formation on the nanocellulosic films in real time, we suggest a plausible mechanism of assembly. Our results confirm that carboxylated cellulose nanofibril films act as universal substrate for the formation of metal oxide nanoparticles, and thus hybrid nanomaterials, during metal ion adsorption processes. This phenomenon enables the upcycling of nanocellulosic materials through multistage applications, thus increasing its sustainability and efficiency in terms of an optimal use of resources.
Highlights
We have observed in our previous works[23−25] that carboxylated nanocellulose films (TOCNFs) can in situ grow metal oxide aggregates during the adsorption of metal ions from aqueous solutions at room temperature, which suggests a preformation of NPS that had coalesced and aggregated
We mechanistically study the ability of TOCNF films to spontaneously grow metal oxide nanoparticles (MO-NPS) during metal ion adsorption processes
We systematically demonstrate the capacity of carboxylated cellulose nanofibril films to spontaneously form MO-NPS occurring in situ during the adsorption of metal ions from aqueous solution, without the use of any chemical or temperature increase
Summary
Biopolymers are promising building blocks for the preparation of high-performance hybrid materials, especially in terms of efficiency, sustainability, and environmental-friendliness.[1,2] In this context, nanocellulose (NC) has currently been considered as one of the nanomaterials for the future because of the renewability and abundance of its source as well as the fascinating features that NC possesses, such as excellent mechanical properties, low density, and ease of processability into bulk materials.[3−7] NC offers a versatile surface chemistry that allows to tailor specific properties, for instance, to promote the growth of different nanoparticles (NPS), such as metal−organic frameworks (MOFs),[8] metal (oxide) nanoparticles,[9−14] silica nanoparticles,[15] or carbon nanomaterials.[16]. The size of the intermediate nanoclusters was approximated from the QCMD data by utilizing the conventional Sauerbrey model and the model proposed by Tellechea et al.[27] In the Sauerbrey method, it is assumed that the ion adsorption results in the formation of a homogeneous film on the sensor where the thickness (Sauerbrey thickness) of the film can be calculated by dividing the Sauerbrey mass (ΔmSauerbrey) by the density of the material. This Sauerbrey thickness can be correlated to the size of the small nanoclusters formed in the cellulose due to the ion adsorption.
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