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This paper aims to create visible light driven ternary photocatalysts using zinc oxide (ZnO), cerium (IV) oxide (CeO2), and carbon xerogel (CX) as constituent materials. The use of CeO2is based on the creation of direct-Z-scheme heterojunctions with the ZnO and the consequent diminishing of charge recombination, whereas the carbon xerogel inclusion is predicted to minimize bandgap energy, decrease electron-hole recombination, and boost specific surface area. Furthermore, the choice of the black-wattle tannin as a carbonaceous precursor was targeted at the development of an environmentally friendly and affordable composite. The existence of the hexagonal phase of zinc oxide and cubic structure of the cerium (IV) oxide in the ternary material was confirmed by X-ray diffractometry and X-ray photoelectron spectroscopy, with the latter also suggesting chemical bonding between the ZnO and the CX due to the creation of zinc oxycarbide complexes. The inclusion of the carbon xerogel provokes a significant modification in the morphology of the ternary material, resulting in an increased surface area and smaller particle aggregates. The CX/ZnO–CeO2ternary composite obtains the highest photocatalytic efficiency among all the materials studied, degrading 100% of 4-chlorophenol under simulated sunlight and 68% under visible radiation, after 5 h. The increased photocatalytic activity can be attributed to the formation of direct Z-scheme heterojunctions between the semiconductors, higher visible light response, and higher specific surface area, as evidenced by the results obtained by active radical scavenging, chronoamperometry, diffuse reflectance spectroscopy, and N2adsorption–desorption isotherms.

This study investigates the feasibility of employing a fluidized bed reactor for the degradation of 4-chlorophenol (4CP), considering multiple operational parameters (type of radiation, fresh inlet flow rate and recycle flow rate). The selection of the ZnO/g-C3N4/carbon xerogel as photocatalyst, a choice motivated by the improved charge transfer and increased catalyst activity under visible radiation provided by the presence of carbon xerogel and g-C3N4, was previously determined through tests conducted in a jacketed batch reactor under visible radiation, in which the ternary material efficiency was compared to their constituting counterpart materials. The semiconductors constituting the unary, binary, and ternary materials were chosen based on considerations of availability, sustainability, and abundance in nature. The use of the proposed fluidized bed reactor brings advantages in scalability, distribution of irradiated light and overall costs when compared to commonly used batch reactors, whereas the investigation of the flow parameters involved in such process is of great importance to understand and optimize the efficiency of the pollutant degradation process. Regarding the ternary photocatalyst, X-ray diffractometry (XRD) revealed the presence of zinc oxide's hexagonal crystalline structure. Moreover, additional characterization using Raman spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS) confirmed the presence not only of ZnO but also of carbon xerogel and g-C3N4in the composite. From the photodegradation experiments, it was determined that the optimal fresh inlet flow rate to achieve the best degradation, as well as the recycle flow rate for this purpose, were 0.07 and 25 L h−1, respectively. Mathematical simulations described that the model that best fits the system's behavior considers the specific reaction rate as dependent on the concentration of the catalyst in the medium.

The development of a novel TiO2/KNbO3/g-C3N4photocatalyst for the degradation of sulfamerazine under artificial sunlight was investigated in this study, aiming to obtain a highly effective material through the formation of Z-scheme heterojunctions between the proposed semiconductors. The characterizations confirmed the formation of the intended heterojunctions in the ternary composite photocatalyst, as the presence of TiO2, KNbO3,and g-C3N4was successfully verified. Furthermore, the coupling between the semiconductors in the form of the ternary photocatalyst led to structural, morphological, and optical modifications of the TiO2base matrix, such as a higher specific surface area and larger visible light absorption. The optimized ternary material (TiO2-5% KNbO3-0.25% g-C3N4) exhibited the highest reaction degradation capacity for the sulfamerazine (SFMZ) in both solar (86.5% degradation) and visible light (60% degradation) tests, confirming a significant enhancement over the pure TiO2, which achieved 48% degradation under solar light and 10% degradation under visible light. This result was mainly attributed to the formation of Z-scheme heterojunctions between the semiconductors, which enhanced the charge-transport efficiency during photonic excitation. Lastly, the degradation pathway proposed using mass spectroscopy analysis indicated the formation of mainly less toxic intermediates, as estimated through quantitative structure-activity relationship (QSAR) predictions.

This work proposed the study of a new lignin/cellulose carbon xerogel/ZnO/Bi2O3/Bi° composite photocatalyst for the degradation of bisphenol-A under sunlight. The reasoning behind the application of each component is based on the formation of multiple heterojunctions (p-n heterojunction between semiconductors, metal-semiconductor heterojunction, and carbon-semiconductor heterojunction) to hinder the recombination of photogenerated charges during the photocatalytic process. The lignin/cellulose carbon xerogel was employed as both a solid electron mediator and a reducing agent, promoting the reduction of the bismuth oxide into metallic bismuth. The results obtained from the characterization tests confirm the formation of all the intended phases in the hybrid photocatalyst. Furthermore, the inclusion of the carbon xerogel led to morphological modifications such as the formation of plate-like particles and the increase of specific surface area. The efficient formation of the heterojunctions between the composing phases of the hybrid composite led to an enhanced photocatalytic activity for the degradation of the bisphenol-A (BPA) molecule, under both simulated sunlight and visible light. The optimized composite achieved 84% degradation of the BPA under simulated sunlight and 27% under visible light irradiation, which is a great improvement in comparison to the pure ZnO, which obtained 55% degradation under simulated sunlight and 19% degradation under visible light. The enhanced photocatalytic activity of the lignin/cellulose carbon xerogel/ZnO/Bi2O3/Bi° composite was further verified by chronoamperometry tests, which evidenced its greater photocurrent generation capabilities.