Functional Supported ZnO/Bi₂MoO₆ Heterojunction Photocatalysts with 3D-Printed Fractal Polymer Substrates and Produced by Innovative Plasma-Based Immobilization Methods

Abstract

Inorganic photocatalysts became an essential and powerful tool for the remediation of polluted water. However, important limitations of photocatalysts in their colloidal form, especially nanosized, remain. For instance, their separation from water after use and recovery, which can be particularly demanding, time- and energy-wise. Considering such aspects, supported catalysts bear significant advantages. However, efforts still have to be made to develop processes that allow the permanent and efficient immobilization of inorganic photocatalysts in sustainable conditions, in order to maintain the advantages of supported catalysts over colloidal ones. Herein, we report the use of an aqueous-phase plasma-aided grafting (APPAG) process to produce functional and efficient hybrid photocatalysts. More specifically, based on cold plasma discharge (CPD), ZnO/Bi2MoO6 heterojunctions were permanently immobilized on polymer supports generated by 3D-printing, with fractal-inspired designs. Three different approaches of the APPAG process have been successfully used for the immobilization of the inorganic phase, that is core–shell-assisted direct grafting, indirect grafting and in situ complexation-assisted precipitation (ISCAP). Noticeably, the latter technique has never been reported before to our knowledge. These three immobilization routes rely on different strategies and yield to distinct morphological specificities, but all allow using mild synthesis conditions and producing stable, active, permanently immobilized coatings of photocatalysts. Regarding the preparation of the organic supports, two sorts of additive manufacturing (AM) technologies were employed, namely fused-deposition modeling (FDM) and liquid crystal diode (LCD)-based SLA (stereolithography). The use of fractal geometries combined with AM permits the production of supports with relatively high surface areas, in a single processing step. Overall, the three plasma-based immobilization methods revealed to be efficient and the performance of the different hybrid photocatalysts have later been assessed through the photodegradation of Rhodamine B dye under simulated sunlight irradiation and visible light only, with promising results.

Phosphor-Enhanced, Visible-Light-Storing g-C3N4/Ag3PO4/SrAl2O4:Eu2+,Dy3+ Photocatalyst Immobilized on Fractal 3D-Printed Supports

“…The resin supports were manufactured using a Photon-s LCD-based SLA 3D-printer (AnyCubic) and transparent photosensitive resin. Prior to printing, a CAD model was designed, partially based on previous works, using fractal geometry. , During the conception (cf. Scheme ), a structure made of fracahedron units (for fractal tetrahedron) of rank 3 slightly overlapped was designed first.…”

“…We believe this process is more adapted to photocatalysis specifically because the resulting thin coating can be optimally activated by light, and the catalytic phase is easily available for mass transfer during photocatalytic operations. In previous works, we developed a plasma immobilization process labeled aqueous-phase plasma-aided grafting, − in which cold plasma discharge was used to activate a polymer substrate and subsequently bind an inorganic colloidal catalyst onto its surface. Several subtechniques were explored, among which direct grafting was found to be very effective.…”

“…In recent years, the specific topic of fractal geometry applied to AM emerged, offering interesting prospects in a range of fields of material science. − We saw an opportunity in AM to produce polymer supports for catalysts, with hierarchical designs and high surface area. This was made possible through the use of fractal-inspired geometry. − …”

Hydrophilicity and Hydrophobicity Control of Plasma‐Treated Surfaces via Fractal Parameters

“…Complex nanomaterials and nanocomposites based on hierarchical surface structures are currently under extensive investigation. This is because such materials can be applied in a very broad range of contexts, [1][2][3] from sensors, [4][5][6] photocatalysts, [7] bio-electronic interface devices, [8] water repelling and self-cleaning materials, [9] various nanoelectronics devices [10,11] to even space technology applications such as photon-active diamond films for space propulsion [12,13] and nanostructured emitters for plasma propulsion systems [14,15] that are critical for miniaturized space assets. [16,17] It is not uncommon for the nanocomposites of this type to feature very complex surface, internal and interfacial structures that may in some instances form a fractal-like morphology.…”

3D Printed Materials in Water Treatment Applications

“…[ 77 ] Similarly, fractal 3D‐printed PLA and resin support utilizing creative and efficient plasma‐based techniques with immobilized ZnO/Bi 2 MoO 6 heterojunction were synthesized for photodegradation of Rhodamine B. [ 78 ] Similarly, the ZnO nanoparticles coated PLA fractal structures were prepared by core‐shell synthesis and plasma grafting. The prepared catalyst has shown 63% Rhodamine B degradation efficiency in 5.5 h. [ 79 ] Dip‐coated and inkjet‐printed nanosheets of ZnO with side‐by‐side alignment on glass plates resulted in thin, translucent, and aligned ZnO surfaces with exposed high‐energy facets.…”