Influence of the functionalization agent and crystalline phase of MnO2 Janus nanomaterials on the stability of aqueous nanofluids and its catalytic activity to promote asphaltene oxidation

Amphiphilic nanomaterials interact with water/oil interfaces, catalyzing reactions in the In-Situ Combustion (ISC) process. This work aims to compare the surface modification of different crystalline phases of MnO2 in the two most relevant processes involved in ISC: transportation and catalysis, by evaluating the stability of nano fluids and their catalytic activity regarding the oxidation of asphaltenes. alpha-, beta-, gamma-, and delta-MnO2 crystalline phases of manganese dioxide were synthesized by a hydrothermal method and later functionalized either with (APTES) (3-Aminopropyl)triethoxysilane) or citric acid (CA) through a Pickering Emulsion route. The physicochemical properties of these nanomaterials were studied using TEM, IR spectroscopy, XRD, DSC, static contact angle, Z-potential and the results suggest a Janus character upon a suitable functionalization for all cases. Citric acid functionalized nanomaterials showed higher stability to promote aqueous suspensions due to the hydrophilic nature of the organic agent and the possibility of interaction through H-bonds with water molecules. Nevertheless, they show a lower catalytic activity regarding the oxidation of asphaltenes when compared to the materials functionalized with APTES. Therefore, chemical functionality must be considered in both transportation and combustion stages of in-situ combustion process to fabricate a suitable nanocatalyst.