Insight into visible light-driven photocatalytic degradation of diesel oil by doped TiO2-PS floating composites

Floating photocatalysts as promising materials for environmental detoxification and energy production: A review

The oxygenation process of the catalyst surface, the incident-light harvesting capability, and facile recycling of utilized photocatalysts play key role in the outstanding photocatalytic performances. The typical existing photocatalysts in powder form have many drawbacks, such as difficult separation from the treated water, insufficient surface oxygenation, poor active surface area, low incident-light harvesting ability, and secondary pollution of the environment. A great number of scientific works introduced novel and fresh ideas related to designing floating photocatalytic systems by immobilizing highly active photocatalysts onto a floatable substrate. Thanks to direct contact with the illuminated light and oxygen molecules in the interface of water/air, the photocatalytic performance is maximized through production of more reactive species, employed in the photocatalytic reactions. Furthermore, facile recovering of the utilized photocatalysts for next processes avoids secondary pollution as well as diminishes the process's price. This review highlights the performance of developed floating photocatalysts for diverse applications. Furthermore, different floating substrates and possible mechanisms in floating photocatalysts are briefly mentioned. In addition, several emerging self-floating photocatalytic systems are taken attention and discussed. Specially, coupling photo-thermal and photocatalytic effects seems to be a good strategy for introducing a new class of floating photocatalyst to utilize the free, abundant, and green sunlight energy for the aims of water desalination and purification. Despite of a large number of attempts about the floating photocatalysts, there are still plenty of rooms for more in-depth research to be carried out for attaining the required characteristics of the large scale utilizations of these materials.

Deep remediation of oil spill based on the dispersion and photocatalytic degradation of biosurfactant-modified TiO2

The employment of dispersant was an effective method to treat marine oil spill pollution. However, conventional dispersants only showed a single oil dispersion. Here, by modifying TiO₂ nanoparticles with biosurfactant-Rhamnolipids (Rha), a highly efficient particulate dispersant with photocatalytic activity was developed. Rha-TiO₂ showed both excellent oil spill dispersion and facilitated photodegradation for oil simultaneously. The oil droplets dispersed by Rha-TiO₂ in seawater exhibited long time stability, which indicated the synergistic emulsification interactions between TiO₂ and Rha in artificial sea water (ASW). The dispersion mechanism of Rha-TiO₂ was analyzed, we found the TiO₂ nanoparticles alone weren't effectively emulsified oil in high salinity ASW, but the addition of a small amount of Rha could modify the surface wettability of TiO₂ nanoparticles to form the stable emulsion. In addition, the addition of a small amount of Rha could reduce the surface tension of the oil-water interface, which contribute to increasing the content of TiO₂ nanoparticles at the oil-water interface, form a steric rigid layer around the oil droplets to prevent droplet coalescence and facilitate the further photocatalytic degradation of oil. In short, the Rha-TiO₂ nanoparticles could effective disperse oil in ASW, meanwhile the TiO₂ also played the role of photocatalytic degradation of oil pollution. Hence, this study developed a novel photocatalytic particulate dispersant to remediate marine oil spill and delivered a new feasible solution for practical oil spill treatment in the future.

Transparent floatable magnetic alginate sphere used as photocatalysts carrier for improving photocatalytic efficiency and recycling convenience

Practical application of powder photocatalysts is far from satisfying due to their low photon utilization, inconvenient recovery and potential environmental risk. In this study, an easily recoverable, environmentally friendly and highly transparent floatable magnetic photocatalyst carrier was prepared based on biopolymer alginate and Fe₃O₄ particles. Further, three different types of photocatalysts were chosen as model semiconductor photocatalysts and loaded on the shell of the carriers. The freeze process facilitated the formation of internal cavities that enhanced floating ability and transparency of the spheres. Meanwhile, the excellent floating performance offered massive reaction sites for pollutants reacting with photocatalysts, O₂ and photons on the air/water interface. Photodegradation results showed all three floatable hybrid photocatalysts exhibited enhanced photocatalytic efficiencies compared to the virgin photocatalysts. In short, the carrier can integrate excellent floating ability, environmental friendliness and full recycling with good stability, and it can greatly improve the photocatalytic efficiency of various powder semiconductor photocatalysts.

Application of Fe2O3/ZrO2 loaded polyhedron ball on photocatalytic degradation of diesel pollutants in seawater under visible light

Fe₂O₃/ZrO₂ nanocomposite photocatalyst was successfully prepared by coprecipitation method for the degradation of diesel pollutants in seawater under visible light. The effects of doping ratio, calcination temperature, photocatalyst dosage, initial diesel concentration, H₂O₂ concentration, and reaction time on the photocatalytic removal efficiency were investigated. Moreover, the optimal conditions for Fe₂O₃/ZrO₂ nanocomposite photocatalyst to degrade marine diesel pollution were determined. The removal efficiency of diesel by nanocomposite photocatalyst could reach 97.03%. A photocatalyst-loaded polypropylene polyhedral ball was prepared, and the removal efficiency of diesel by photocatalyst-loaded polypropylene polyhedral ball decreased from 99.35 to 68.84% after four recycling cycles.

BiOI-on-SiO2 microspheres: A floating photocatalyst for degradation of diesel oil and dye wastewater

The powder-based photocatalytic material is often difficult on wide application and then loaded on a matrix for separating conveniently from the liquid. Submerged photocatalysts may not take advantage of the light energy adequately. Thus, this boundedness may reduce their utilization and potentially cause the secondary pollution on the environment. In this paper, the micron-sized silica sphere is used as a floating substrate, and the visible-light-driven photocatalytic material iodine oxygen bismuth is prepared onto the hollow silica microspheres. The composite spheres as the visible-light-driven photocatalytic material have been characterized by XPS, XRD, SEM, EDX, PL, etc. It confirmed that BiOI combined on the SiO₂ microsphere (mSiO₂) by Bi-O-Si. The photogenerated electrons of the composite have a low probability of recombination and have a narrow band energy (1.82 eV). The composite was used to photodegrade diesel-containing wastewater and rhodamine B, and the superoxide group (·O₂^-) was found to be the main degradation active factor. And by GC-MS test, it is known that the superoxide group (·O₂^-) can degrade long-chain alkanes into short chains or form branches. Detailed studies on the acute exposure experiments of Vibrio qinghaiensis sp.-Q67 and zebrafish embryos showed that the composites can effectively reduce the toxicity of BiOI and mSiO₂.