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In this work, the development of a composite material with geopolymer and a high content of rice husks without heat treatment was investigated to create and characterize a low-cost composite made with agro-industrial wastes. The ratio used was about 12/88 wt./% of sol–gel and metakaolin related to rice husks. This kind of composite geopolymer was designed as both a construction material for load or aesthetic finishing. X-ray diffraction studies reveal that the composite has an amorphous phase and a crystalline one, which is typical of geopolymeric materials. The scanning electron microscopy showed that the geopolymeric matrix completely wrapped the rice husks. The composite material has a compressive strength close to some mortars with a value of about 110 kg/cm2 (10.8 MPa). Laser scanning confocal microscopy reveals that there is a difference of emission in the visible spectrum between the inner and outer sides of the rice husks, which corroborates that they have a different chemical composition. Differential scanning calorimetry analysis confirmed that the composite material has combined characteristics of its raw materials. X-ray diffraction studies show that metakaolin with sol–gel solutions had temperature-dependent interactions besides that, after the dehydroxylation, the composite material is mostly amorphous. The material of high content of rice husk bound by geopolymer could be applicable in various areas of the construction industry and finishing.

Photocatalytic semiconductors require maintaining stability and pursuing higher efficiencies. The studied systems were silicon nanowires (SiNWs), silicon nanowires with cobalt oxide nanoparticles (SiNWs-CoONPs), and silicon nanowires with copper nanoparticles (SiNWs-CuNPs). SiNWs were synthesized by metal-assisted chemical etching (MACE) from silicon wafers keeping the remaining silver nanoparticles for all three sample types. The nanowires were about 23–30 µm in length. CoONPs and CuNPs were deposited on SiNWs by the autocatalytic reduction processes (electroless). There were many factors in the process that affect the resulting structures and degradation efficiencies. This work shows the degradation of methyl orange (MO) together with the chemisorption of methylene blue (MB), and rhodamine 6G (Rh6G) by direct illumination with visible radiation. The MO degradation kinetics were in the sequence SiNWs-CuNPs (88.9%) > SiNWs (85.3%) > SiNWs-CoONPs (49.3%), with the SiNWs-CuNPs having slightly faster kinetics. However, SiNWs-CoONPs have slow degradation kinetics. The chemisorptions of MB and Rh6G were SiNWs-CuNPs (87.2%; 86.88%) > SiNWs (86%; 87%) > SiNWs-CoONPs (17.3%; 12%), showing dye desorptions together with lower chemisorption capacities. This work shows iridescence in optical microscopy images by the visible light interference caused by the spaces between the nanowire bundles.