Optimizing the CO2 reduction to produce CH3OH using flexible NiMoO4 coatings as a photocatalyst

Abstract

In this work, the CO2 photoreduction to generate renewable methanol was investigated. NiMoO4 was selected as a photocatalyst due to its visible light absorption and good electrical conductivity. The photocatalyst was deposited on glass fibers using a one-step microwave-hydrothermal method, which resulted in a homogeneous coating that favored a higher surface exposure and an easy application in photocatalytic reactors compared to slurry systems. The operation parameters of the CO2 photoreduction were modeled and optimized for CH3OH production using a central composite design centered on the faces. In the design of experiments, the factors: (i) temperature, (ii) light filter (blue and yellow), and (iii) NaHCO3 concentration were selected to maximize the CH3OH production. The selected factors significantly affected the rate of CH3OH production. The regression analysis showed consistency between experimental results and predictive values (Raj2 = 0.82). The optimal values proposed were 50 °C, and 1 M NaHCO3, using a yellow-light filter, which promoted the CH3OH production of 3365 μmol/(g-h) under visible light with an apparent quantum yield (AQY) of 17.9%. These results were associated with a synergistic effect of better CO2 solubility, easier desorption of the products, and more efficient light absorption on the NiMoO4 coating. The optimized results were corroborated by an L9 orthogonal design, which confirms the optimal point in the proposed factors. Additionally, the stability of the NiMoO4 coating was demonstrated after five cycles of consecutive evaluation.