Elsevier

Carbohydrate Polymers

Volume 206, 15 February 2019, Pages 238-244
Carbohydrate Polymers

Eco-friendly modification of a regenerated cellulose based film by silicon, carbon and N-doped carbon quantum dots

https://doi.org/10.1016/j.carbpol.2018.10.074Get rights and content

Highlights

  • Cellulosic film modification by non-toxic nanodots (SiDs, CDs and N-CDs).

  • Easy and environmentally friendly film modification by dip-coating process.

  • Nanodots modify film optical, electrical and mechanical characteristics.

  • N-CDs/cellulosic film shows fluorescent, electrical and optical improvement.

Abstract

Modification of a regenerated cellulose thin film by inclusion of different non-toxic nanodots (silicon-dots (SiDs), carbon-dots (CDs)) or nitrogen-doped carbon dots (N-CDs)) by aqueous nanodots solution immersion was performed. Nanodots presence into the cellulosic structure was evidenced by confocal microscopy images at different depth and changes in film mechanical, electrical and optical parameters. Our results reveal that the inclusion of the different nanodots in the cellulosic support increases, indifferent percentages, the mechanical resistance and electrical conductivity of modified films, but they hardly affect light transmittance. Particularly, modification with N-CDs largely favored film conductivity due to the presence of the higher number of charged functional groups (Csingle bondNH2 and Odouble bondCsingle bondNH2) groups) on N-CDs surface, allowin gus the attainment of a flexible, fluorescent and transparent high conductive eco-friendly film. In fact, the non-toxic character of both support-film and nanodots, endorses the use of these new nano-engineering films in biomedical applications.

Introduction

Regenerated cellulose (RC) is a natural polymer widely studied due to its numerous properties such as renewable sources, biodegradability, transparency, flexibility, low cost and versatility, since it can be rather easily modified, which made of RC a key material for different applications (Garrison, Murawsky, & Quirino, 2016; Klemm et al., 2011; Lin & Dufresne, 2014; Moon, Martini, Nairn, Simonsen, & Youngblood, 2011). Two of these characteristics, its inherent biocompatibility and high transparency, make of RC an important chemical resource for technological applications such as electronic components, consumer products and aerospace in near future (Dutta et al., 2017; Mohanty, Misra, & Drzal, 2005; Pérez-Madrigal, Edo, & Alemán, 2016; Wang, Lu, & Zhang, 2016). In fact, new applications based on some of those properties of RC are nowadays being explored and developed to create cellulosic materials with added value, such as processing of cellulose-based materials with ionic liquids (Colburn, Wanninayake, Kim, & Bhattacharyya, 2018; Habibi, Lucia, & Rojas, 2010; Tsioptsias, Stefopoulos, Kokkinomalis, Papadopoulou, & Panayiotou, 2008; Wang, Gurau, & Rogers, 2012).

Functionalization of RC-films with CdSe/ZnS or CdS quantum dots, for improving their optical properties, has been performed by procedures involving chemical reactions (Abitbol et al., 2017; Wang et al., 2016). However, RC film modification by most simple methods (without chemical reaction), such as its immersion in aqueous solutions of the modifying agents for the attainment of hybrids cellulosic nanocomposites with improved properties, can be of interest. In this context, it has already been demonstrated in different papers that the high elastic and hydrophilic character of RC films allows the inclusion of different kinds of nanoparticles (lipid-NPs or Ag-NPs) or other modifying elements such as hydroxyapatite or dendrimers, for the attainment of hybrids cellulosic nanocomposites with improved properties (Algarra, Campos et al., 2014; Benavente et al., 2017; Sarkar et al., 2018; Vázquez et al., 2011).

In fact, our group has already studied the incorporation of fluorescent CdSe quantum dots (CdSe-QDs) coated by a thiol DAB dendrimer into a RC film (Algarra et al., 2013; Campos et al., 2016), being the reduction in the toxicity of the CdSe-QDs the main reason for dendrimer coverage (Barman et al., 2018), although it might also favour the link of the QDs with the cellulose chains to ensure their permanence into the structure of the RC film even in adverse conditions, that it, in contact with aqueous solutions in the case electrochemical applications. However, the presence of heavy atoms in the modifying agents limits the ecological benefits of the RC support, reducing the field of applicability of the nano-engineering cellulosic films. In fact, the stability of modified RC-based films using less toxic QDs such as silicon derivatives (SiDs), both bare and functionalized with PAMAM-OH dendrimer, has already been confirmed, and used for chemical sensing respectively (Campos, Abellan et al., 2015, 2016; Vázquez, Algarra, & Benavente, 2015).

Since carbon materials based on carbon dots (CDs) are also biocompatible and non-toxic nanomaterials, they might be considered as a metal free alternative for innovative valorization of RC-films. In fact, functionalization of cellulosic films by CDs and sulphur or nitrogen doped carbon dots (S-CDs and N-CDs, respectively) has already been indicated (Zheng & Yan, 2015). CDs are fluorescent spherical nanoparticles (<10 nm) with a carbonaceous core containing multiple oxygen species, such as hydroxyl, carboxyl and aldehyde groups (Guo et al., 2017; Zhang & Yu, 2016).

To improve the quantum yield (QY) of the CDs, and for surface passivation reason, they are usually doped with heteroatoms, such as N, P or B; The N-doped CDs (N-CDs) seem to be the most efficient approach to get QY increase (Campos, Algarra et al., 2015; Shen et al., 2017; Liu et al., 2018; Travlou et al., 2018). In this context, the inclusion of CDs into the structure of the RC films should reduce the anisotropy of the modified cellulosic material, while their modification using carbon nanoparticles doped with nitrogen atoms (N-CDs) should improve the photo-physical properties and biocompatibility of the films compared with other doped carbon dots (Sun, Yang, Wang, & Wang, 2018). Since carbon dots (CDs) are non-toxic nanomaterials, they might be considered as a metal free alternative for innovative valorization of RC-films.

On the other hand, the coating effect of carbon dots to enhance luminescent properties of different matrix has been described. Particularly, CDs dispersed on carboxymethyl cellulose films were developed for sunlight (You, Zhang, Liu, & Lei, 2016), while N-CDs were loaded in bacterial cellulose, obtaining a nanocomposite able to be used as a chemical sensor for Fe3+ ions (Lv et al., 2017). Cellulose nanofibrils and polymer films (PVA matrix) were surface functionalized by using covalent process to enhance the quantum yield of fluorescence (Junka, Guo, Ilari, Laine, & Rojas, 2014; Li et al., 2015), while other researchers, using different CDs precursors, obtained tuneable luminescent polymer matrix-based polydimethylsiloxane (PDMS) (Bhunia, Nandi, Shikler, & Jelinek, 2016). Poly(methyl methacrylate) nanocomposites coated by CDs were used to obtain white light emitting system when loaded with lanthanides (Chen & Feng, 2015).

This work reports the possibility of inclusion of different types of nano-dots into the structure of a RC-film by simple dip coating method, and their effects on different characteristic membrane materials. Our results show that the modified films are transparent and luminescent (in visible region), with improved electrical conductivity and higher mechanical strength that the support film. Moreover, since the nanodots used for film modification have not any metal atom, they can be considered eco-friendly materials, and be used as platforms for technological and bioengineering systems.

Section snippets

Materials

Silicon quantum dots (SiDs), carbon and nitrogen-doped carbon dots (CDs and N-CDs) were prepared according to the methodology described in previous papers (Campos, Abellan et al., 2015; Campos, Algarra et al., 2015; Algarra, Vázquez et al., 2014) by hydrothermal approach. Briefly, to obtain SiDs, APTES (3-Aminopropyl)triethoxysilane, 99%) was heat at 200 °C for 3 h, while CDs were obtained from lactose, following the same procedure (at 80 °C) but using H2SO4 as oxidant agent for 24 h. N-CDs

Results and discussion

Fig. 1A shows the TEM image of the well dispersed N-CDs nanoparticles obtained upon solvothermal treatment at 100 °C, where their spherical morphology is clearly observed; for comparison reasons, TEM images of SiDs and CDs are given as Supplementary Information (Fig. 3S and Table 3S). Fig. 1B shows a comparison of the average size of the different nanodots used in this work: SiDs (∼14 nm), CDs (∼7 nm) and N-CDs (∼ 40 nm). The significant higher size exhibited by the N-CDs when compared with the

Conclusions

This study presents a simple and environmentally friendly way of functionalizing regenerated cellulose films by the inclusion of different nanodots (SiDs, CDs and nitrogen-doped carbon dots or N-CDs). The modification increases (in different percentages) the mechanical resistance and electrical conductivity of the films depending on the selected nanodot, and it also affects characteristic optical parameters (refractive index and extinction coefficient), but hardly modified the high transparency

Acknowledgements

One of the authors (M.A.) thanks to the project CTQ2015-68951-C3-3-R (MINECO, Spain) and to ARDITI-Agência Regional para o Desenvolvimento da Investigação Tecnologia e Inovação is also acknowledged through the project M1420-01-0145-FEDER-000005-CQM+ (Madeira 14-20 Program). We also thank to the Supercomputing and Bioinnovation Center and Junta de Andalucía (PAI group FQM 258) for financial support.

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