Hybrid nanomaterials have been produced using a combination of core−shell synthesis, 3D printing, and plasma grafting. Metal oxides, that is, ZnO and TiO 2 , as well as iron-based metal organic frameworks (Fe-MOF) nanoparticles were grafted permanently onto the surface of 3D-printed fractal substrates via cold plasma discharge (CPD). The aim is to produce supported photocatalysts for the degradation of organic pollutants in water. Herein, different plasma grafting strategies are developed, namely direct (using core−shell prefunctionalization) and indirect grafting. Noticeably, the latter, using poly(vinylphosphonic acid) as an intermediate layer for self-assembly grafting, potentially opens the way for the functionalization of any polymeric surface by inorganic nanocompounds. This study mainly aims at giving insight into the plasma immobilization process, but also demonstrating the potential it offers in the domain of supported catalysis. The activity of the different hybrid materials has been assessed by monitoring the photodegradation of Rhodamine B dye (ZnO and TiO 2 ) and the removal of Ciprofloxacin antibiotic (Fe-MOF). Also, the reusability of the hybrid photocatalysts has been demonstrated. Independently, it was found that modifying the surface of the metal oxide nanoparticles with organic coupling agentsaiming at their plasma-grafting immobilization on polymer supportsallowed enhancing their photodegradation efficiency up to 20%. Finally, a resin fractal support has been printed by liquid crystal diode-based SLA (stereolithography) and later surface-functionalized by Fe-MOF nanoparticles. This provides evidence to the possibility of using laser-based 3D printing technologies to produce supports with high surface area for the immobilization of catalysts by plasma grafting.

The present paper partly aims at exploring the potential of fractal geometry for concrete applications in the field of materials science. It is more specifically a study about the conception of hybrid polymer-based materials with photocatalytic activity. The concept behind this work is to investigate the use of polymer fractal structures manufactured by 3D-printing technology, as a highly ordered substrate with an important surface area to immobilize catalyst nanoparticles, by means of plasma grafting technology. Two types of fractal units, fractal pyramids (fracmids) and fractal cones (fracones), have been described and the former has been extensively characterized on a geometrical aspect. Various complex superstructures have also been described using fractal units as building blocks. 3D structures based on the aforementioned theoretical models have been designed using computer-aided design (CAD). On the basis of CAD models, several structures have been 3D-printed with PLA using fused deposition modeling. PLA substrates have been successfully coated with nanoparticles of ZnO using a combination of core–shell synthesis and plasma grafting. Finally, the photocatalytic activity of a hybrid material has been assessed with a positive outcome, showing the relevance of the concept developed in this study.

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.

The combination of a phosphor with semiconductor photocatalysts can provide photoactivity in the dark. Indeed, the phosphor acts as a “light battery”, harvesting photons during irradiation and later re-emitting light that can be used by the catalytic phase when in conditions of total darkness. This allows for continued activity of the composite catalyst, even in conditions of unstable light stimulation. In this study, we assess the use of a heterojunction, namely graphitic-C3N4/Ag3PO4, that enables efficient photoactivity specifically under visible light stimulation, in combination with a phosphor that exhibits green–blue phosphorescence (510 nm), that is SrAl2O4:Eu2+,Dy3+. Our findings showed that this combination was particularly interesting, noticeably displaying significant photoactivity in darkness, after short periods of activation by visible light. After finding the right combination and optimal ratios for maximum efficiency, the resulting catalyst composite was immobilized on resin supports with a fractal surface, printed by LCD-SLA 3D printing. The immobilization was effectuated via an aqueous-phase plasma-aided grafting (APPAG) process, using cold plasma discharge (CPD) and using vinylphosphonic acid (VPA) as a coupling agent. Whereas the colloidal photocatalyst displayed a serious problem of partial physical separation between the catalytic phase, g-C3N4/Ag3PO4, and the phosphor, the immobilization of the composite catalyst on polymer supports allowed solving this issue. Photodegradation assessments confirmed that the hybrid supported phosphor-enhanced catalyst was active, notably in dark conditions, as well as fairly photostable. This study offers new prospects for the fabrication of polymer-based panels for water purification, with round-the-clock activity and that are, in addition, extremely easy to recover and reuse, by comparison with colloidal catalysts.

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