The present research aimed to evaluate the photocatalytic activity of reduced graphene oxide and manganese ferrite nanocomposite supported on eucalyptus wood ash waste (WA) from industrial boilers, for the decolorization of methylene blue (MB) solutions, using sunlight as an irradiation source. For this, the photocatalyst named MnFe₂O₄-G@WA was synthesized by a solvothermal method and characterized by analyzes of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, Brunauer–Emmett–Teller and zeta potential. Firstly, the photocatalyst was evaluated for photocatalytic decolorization of MB under different reaction conditions. Then, the influence of pH, photocatalyst dose and H₂O₂ was evaluated. MnFe₂O₄-G@WA showed 94% of efficiency for photocatalytic decolorization of MB under operating conditions of solar irradiation, 0.25 g/L of catalyst, 300 mg/L of H₂O₂. The proposed degradation reaction mechanism suggested that the photodegradation of MB was through a synergistic mechanism of photocatalysis and photo-Fenton reactions, with the combined action of the three materials used. The data adjusted to the first order kinetics from the Langmuir–Hinshelwood model. In addition, MnFe₂O₄-G@WA showed high stability, maintaining its efficiency above 90% after 5 cycles. The results indicated that the nanophotocatalyst is a potential technology for the decolorization of MB solutions.

The main objective of this study was to synthesize a nanocomposite using graphene and manganese ferrite nanoparticles (MnFe2O4-G) and to evaluate its antibacterial activity for water treatment purposes. Its morphological characteristics were evaluated by instrumental techniques, such as scanning electron microscopy and transmission electron microscopy. The characterization results indicated that the nanocomposite presented nanoparticles of approximately 25 nm well dispersed in transparent and large (14 μm) graphene nanosheets. The antibacterial activity was evaluated in a batch experiment using a concentration of 40 μg mL-1 of nanocomposite (MnFe2O4-G, bare MnFe2O4 nanoparticles or graphene oxide), 1x105 CFU mL-1 of Escherichia coli, and 8 h of contact time at room temperature. The highest antibacterial capacity was observed for the hybrid nanocomposite (91.91%), due to the synergic effect of graphene and MnFe2O4 nanoparticles. Various mechanisms were proposed to explain the effective antibacterial activity of MnFe2O4-G, such as wrapping, oxidative stress, sharp-edge cutting effect, among others. The results showed that MnFe2O4-G is a potential alternative in water treatment processes as an antibacterial agent.

This study aimed to evaluate the technical and environmental feasibility of producing concrete paver blocks and pervious concrete paver blocks by incorporating marble waste to evaluate its filler effect within the cementitious matrix. The methodology included the characterization of marble waste, the production of test specimens with the control (0%), 10%, 20%, and 30% of cement replacement, and the execution of performance tests, supplemented by statistical analyses. The results indicated that marble waste replacement significantly impacted the properties. In terms of pervious concrete paver block permeability, the highest rates were observed in the control and 30% treatments. For water absorption, concrete paver blocks showed higher values at a maximum of 20%, while pervious concrete paver blocks maintained statistically analogous values for 10% and 20%. Regarding compressive strength, the concrete paver block formulation with 10% marble waste was statistically compatible with the control. It is concluded that the incorporation of marble waste into concrete and pervious concrete paver blocks is environmentally advantageous as it valorizes an industrial waste. However, mix design optimization is essential, given that excessive replacement (above 10%) resulted in a reduction in compressive strength.

In developing countries, the use of recycled aggregates can be an opportunity to combine economic, environmental, and sustainability benefits. Therefore, this research investigates an industrial internal recycling approach by reinserting residues from concrete-based tiles produced by a company in the south of Brazil into the production of new concrete tiles, using them as recycled aggregate in the partial replacement of natural aggregates and cement, simultaneously. The methodology comprised recycled aggregate preparation, material characterisation, production of concrete specimens using different replacement contents of natural aggregate and cement, and flexural strength testing to determine the optimum replacement content. The feasibility of the partial replacement of natural aggregates and cement with recycled aggregates was demonstrated, as an 87% increase in flexural strength was achieved for specimens containing 30% cement replacement and 25% natural aggregate replacement compared with the control. This improvement was attributed to the micro-filler effect of the superfine fractions, which optimised particle packing and matrix densification. In addition, the process prevented the emission of 55.1 kg carbon dioxide per ton produced. These findings demonstrate that industrial internal recycling can simultaneously improve technical performance while reducing environmental impacts and promoting resource efficiency in the construction industry.