Effect of sulfate ions on the crystallization and photocatalytic activity of TiO2/diatomite composite photocatalyst

Protecting against micropollutants in water storage tanks using in-situ TiO2 coated quartz optical fibers

Photocatalyst-coated optical fibers (P-OFs) using UV-A LEDs offer a highly promising solution for the degradation of micropollutants within municipal, reuse, industrial or home distribution systems, by integrating P-OFs into water storage tanks. P-OFs have photocatalysts attached to bundles of optical fibers, enabling their direct deployment within tanks. This eliminates the necessity for photocatalyst slurries, which would require additional membrane or separation systems. However, a current limitation of P-OFs is light management, specifically light oversaturation of the coated photocatalysts and short light transmission distances along fibers. This study overcomes this limitation and reveals strategies to improve the light dissipation uniformity along P-OFs, and demonstrates the performance of P-OFs on degrading a model micropollutant, carbamazepine (CBZ). Key tunable variables of fibers and light emission conditions, including photocatalyst coating patchiness (p), minimum light incident angles (θm), radiant flux launched to fibers (Φi), and fiber diameters (D), were modeled to establish their relationships with the light dissipation uniformity in TiO2-coated quartz optical fibers (TiO2-QOFs). We then validated modeling insights by conducting experiments to examine how these variables influence the generation of evanescent waves which are localized energy on fiber surfaces, leading to either photocatalyst activation or the recapture of unused light back into fibers. We observed substantial enhancements in evanescent waves generation by decreasing p and increasing θm, resulting in uniform light dissipation which reduces light oversaturation and improves light transmission distances. Moreover, these optimizations led to a remarkable three-fold improvement in CBZ degradation rates and a 65% reduction in energy consumption. Such improvement substantially reduces the capital and operational cost and enhances practicality of energy-efficient photocatalysis without additional chemical oxidants for micropollutant degradation in water storage tanks.

Application of diatomite for gallic acid removal from molasses wastewater

In this study, diatomite was refined by a simple purification method consisting of calcination combined with acid washing. Optimal purification conditions were the focus, including the influence of conditions on diatomite morphology, structure, and specific surface area. The results showed that the optimal conditions were a 550 °C carbonization temperature and 25 wt% HCl. This purified diatomite was then employed to adsorb gallic acid (GA) from molasses wastewater in a series of adsorption experiments, which illustrated that (ḭ) GA adsorption fitted a pseudo-second-order model and the Freundlich equation better with GA adsorption by purified diatomite; (ḭḭ) the adsorption process was physical, nonspontaneous, and endothermic; (ḭḭḭ) the maximum GA adsorption capacity by purified diatomite was 19.852 mg g^-1. This study reported the examination of a promising material for sugar mill wastewater pretreatment.

Environmental factors affecting degradation of perfluorooctanoic acid (PFOA) by In2O3 nanoparticles

Nanophotocatalysts have shown great potential for degrading poly- and perfluorinated substances (PFAS). In light of the fact that most of these catalysts were studied in pure water, this study was designed to elucidate effects from common environmental factors on decomposing and defluorinating perfluorooctanoic acid (PFOA) by In₂O₃ nanoparticles. Results from this work demonstrated that among the seven parameters, pH, sulfate, chloride, H₂O₂, In₂O₃ dose, NOM and O₂, the first four had statistically significant negative effects on PFOA degradation. Since PFOA is a strong acid, the best condition leading to the highest PFOA removal was identified for two pH ranges. When pH was between 4 and 8, the optimal condition was: pH = 4.2; sulfate = 5.00 mg/L; chloride = 20.43 mg/L; H₂O₂ = 0 mmol/L. Under this condition, PFOA decomposition and defluorination were 55.22 and 23.56%, respectively. When pH was between 2 and 6, the optimal condition was: pH = 2; sulfate = 5.00 mg/L; chloride = 27.31 mg/L; H₂O₂ = 0 mmol/L. With this condition, the modeled PFOA decomposition was 97.59% with a defluorination of approximately 100%. These predicted results were all confirmed by experimental data. Thus, In₂O₃ nanoparticles can be used for degrading PFOA in aqueous solutions. This approach works best when the target contaminated water contains low concentrations of NOM, sulfate and chloride and at a low pH.

Oxide-Clay Mineral as Photoactive Material for Dye Discoloration

Titanium and zirconium oxides (TiO2 and ZrO2, respectively) were obtained from alkoxides hydrolyses, and then deposited into palygorskite clay mineral (Pal) to obtain new materials for photocatalytic applications. The obtained materials were characterized by structural, morphological, and textural techniques. X-ray diffraction (XRD) results confirmed the characteristic peaks of oxides and clay transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of the modified palygorskite with both oxides showed that the clay was successfully modified by the proposed method. The increase in the specific surface area of the clay occurred when TiO2 and ZrO2 were deposited on the surface. The photocatalytic activity of these materials was investigated using the Remazol Blue anion dye under UV light. The evaluated systems presented high photocatalytic activity, reaching approximately 98% of dye discoloration under light. Thus, TiO2–Pal and ZrO2–TiO2–Pal are promising clay mineral-based photocatalysts.

SnO2/Diatomite Composite Prepared by Solvothermal Reaction for Low-Cost Photocatalysts

Abundant contaminants in wastewater have a negative effect on the natural environment and ecology. Developing highly efficient photocatalysts is a practical strategy to solve the pollution issue. In order to prevent the agglomeration of SnO2 nanoparticles and improve the photocatalytic efficiency, porous diatomite is adopted as a low-cost template to load monodispersed SnO2 nanoparticles by solvothermal reaction and sintering method. Through adjusting the mass of reactants, monodispersed SnO2 nanoparticles (~15 nm) generated on diatomite template achieved the maximum specific surface area of 23.53 m2·g−1. When served as a photocatalyst for degrading rhodamine B (Rh B) and methylene blue (MB), the composite presents an excellent photocatalytic activity close to pure SnO2, and achieves the fast degradation of Rh B and MB dye in 60 min. The degradation process is in well agreement with the first-order kinetic equation. The superior photocatalytic performance of SnO2/diatomite composite is attributed to the physical adsorption of dye molecules on the pores of diatomite, and the superior photocatalytic activity of monodispersed SnO2 nanoparticles. Due to the low-cost of diatomite and the easy preparation of SnO2 nanoparticles, the SnO2/diatomite composite has a promising application prospect, even better than pure SnO2 photocatalyst.

Influence of fluorine on the synthesis of anatase TiO2 for photocatalytic partial oxidation: are exposed facets the main actors?

The influence of fluorine on TiO₂ exposed facets and on the physico-chemical properties was evaluated and a synergetic effect of the presence of fluorine and the facets' distribution was observed.