Implementation of ZnO-functionalized macroporous cellular geopolymer foams: influence of porosity on radiative and photocatalytic properties

This work is part of a context of development of efficient photocatalytic materials for solar photoconversion in order to produce reactive species for degradation. Cellular foams, perfectly suited candidates, are the main subject of this work. Geopolymer foams were developed using two shaping methods, namely a replication method and a direct foaming method using a pore-forming agent. Macroporous cellular foams with a wide range of porous characteristics and porosities ranging from 0.06 to 0.9 were thus developed. The radiative properties were calculated by an experimental approach coupled with modeling. The absorption and diffusion coefficients, which depend on the porous characteristics, vary from 2 to more than 12 m 2 /Kg depending on the porosity of the foams. The absorption capacity is directly correlated to the average porosity of macroporous cellular foams, which promotes the diffusion of radiation within the cellular structure. The photoconversion process via the evaluation of the photocatalytic efficiency was then studied for the different foams. It appears that the photocatalytic efficiency is correlated to the porous characteristics of the foams. The photocatalytic efficiency of geopolymer foams consisting of closed or partially connected pores varies slightly. On the other hand, beyond the porosity threshold of 0.5, the photocatalytic efficiency of reticulated cellular foams consisting of an open porous network increases significantly depending on the porosity. A cellular geopolymer foam with a porosity equal to 0.89 gives an efficiency of 0.7%. This value is of the order of magnitude of those obtained in the literature for reticulated foams with high porosity. It also appears that catalytic performances are correlated with the radiative properties and in particular with the absorption coefficient of the foams. This original study establishes a correlation between porosity and photocatalytic performance highlighting the importance of porous properties. It seems essential to move towards the shaping of reticulated alveolar foams with high porosity consisting of open pores and millimeter sizes. • Macroporous cellular foams are elaborated with a wide range of porosity (0.06 to 0.9) • Absorption capacity is directly correlated to the porosity • Photocatalytic efficiency is increased with porosity and alveolar properties • move towards the shaping of reticulated alveolar foams with high porosity consisting of open pores and millimeter sizes