Preparation and characterization of 3D graphene oxide nanostructures embedded with nanocomplexes of chitosan- gum Arabic biopolymers

Development of nanoscale-based carbonaceous materials have gained popularity due to their techno-functional, flexibility and charming properties. The prosperous oxidation of pristine graphite results in the formation of expanded lamellar structures, full of oxygenated functional groups in their surface, named graphene oxide (GO). The attractiveness of GO due to possessing a flat structure, high surface area, diversity of functional groups, simplicity and low-cost synthesis method from graphite, motivated the scientists to define tremendous research topics to identify the potential of its application in different fields [1,2]. Also, the needs for specializing GO applications in order to meet predetermined requirements as well as modifying its properties, caused researchers to incorporate different polymers/biopolymers onto the GO surface [3] through covalent/noncovalent bonding with its functional groups; which creates new physicochemical features depending on the weight ratios of GO to polymer, polymer characteristics and synthesis procedure [4].

Accordingly, different polymers/biopolymers have been used to modify GO properties such as chitosan [1,[5], [6], [7]], polyethyleneimine [8,9], polyethylene glycol [10,11], poly(vinyl alcohol) [12,13], gum Arabic [[14], [15], [16]], welan gum [17,18], poly(amidoamine) [19], zeolitic imidazolate frameworks [20], poly(methyl methacrylate) [21], and poly(acrylamide) [22,23]. It has been declared that inclusion of polymers onto GO nanosheets gives rise to modifications toward aggregation prevention [24], improved sorption properties [25], enhanced stability [26,27], improved mechanical and barrier properties [28,29], modification of dispersion behavior and morphology [30], modification of dielectric and thermal properties [27,31,32], and changes in optical properties [7,33,34].

Nanotechnology has opened the door to a whole new world in all fields of science in terms of bringing singular physicochemical properties such as magic surface area. As an example, nanoparticles have received a broad attention during the last decade. In the viewpoint of separation and extraction, nanoparticles could effectively act toward adsorbing analytes of interest through their high surface area and reactivity [[35], [36], [37]].

Several groups of NPs are used in order to functionalize GO including noble and non-noble metal NPs such as Pt, Au and Cu; metal oxide/sulfide NPs such as Fe₃O₄, MnO₂ and SnS₂; quantum dots and polymeric/biopolymeric NPs such as polyaniline-poly(4-styrenesulfonate, poly(N-isopropylacrylamid-polyethylene oxide and starch [[38], [39], [40]]. The aims of embedding NPs onto GO sheets can be summarized in three categories of improving structural stability, technological performance and process facilities. In this regard, NPs on GO can play several roles such as inducing a magnetic field, preventing the restacking of sheets, increasing the surface area, and improvement in the catalytic activity and selective/non-selective adsorption of analytes [6,40,41]. When the aim of embedding NPs is improving the technological performance of GO toward selective adsorption of an analyte, polymeric/biopolymeric NPs can be a promising candidate due to the presence of functional groups on their surfaces. The research topic on the using of biopolymeric NPs for GO functionalization is scarce. As an example, Chen et al. [40] conducted a research toward functionalization of GO by starch NPs to adsorb dyes.

The term “Ionic Gelation” (IG) comes from the process in which a complexation occurs between two polymers of polyanions and polycations, resulted in forming structures of micro or nano size, depending on the factors such as pH and the weight ratios of applied polymers [42,43]. IG has gained significant ground in the food and pharmaceutical industry. Chitosan (CS) and gum Arabic (GA) could interact together through this mechanism by their amine and carboxyl groups, respectively. CS, a biodegradable amine rich marine polysaccharide is a popular biopolymer due to its nontoxicity, biocompatibility and low cost production method through deacetylation of chitin [44]. The protonation of CS amine groups in acidic aqueous medium causes its dispersion and solubilization, making it very reactive when exposed to negatively charged molecules [45]. GA, a complex-structure exudate polysaccharide is well known for its biodegradability, biocompatibility and water solubility [46]. Possessing high –COOH density of GA brings about its tendency to bond with polycations, and formation of complexes with nano/microsized structures based on the weight ratios of polyanion to polycation and also pH [5].

To the best of our knowledge, no report has been published about green decoration of GO nanosheets by nanoparticles of CS/GA. The aims of the present study were categorized in three stages: (1) preparing nanoparticles of CS/GA by IG followed by determining the optimum weight rations and pH; (2) synthesis of GO from pristine graphite by improved Hummers’ method; (3) fabricating 3D nanostructure of GO decorated with nanoparticles of CS/GA followed by its characterizing via field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy. The surface area and pore characteristics of 3D GO were assessed via Brunauer-Emmett-Teller (BET) and Barrett–Joyner–Halenda (BJH) methods, respectively.