The promoted tetracycline visible-light-driven photocatalytic degradation efficiency of g-C3N4/FeWO4 Z-scheme heterojunction with peroxymonosulfate assisting and mechanism

Exquisitely designed TiO2 quantum dot/Bi2O2CO3 nano-sheet S-scheme heterojunction towards boosted photo-catalytic removal

The development of novel semiconductor photo-catalysts for the efficient degradation of antibiotics poses a considerable challenge in the context of ever-increasing environmental pollution. Herein, an S-scheme photo-catalyst consisting of TiO2 quantum dots (QDs, size ∼4-6 nm) anchored on Bi2O2CO3 nano-sheets was synthesised via a facile hydrothermal protocol. TiO2/Bi2O2CO3 (TB) nano-composite exhibits enhanced photo-catalytic removal of tetracycline, achieving ∼0.0158 min-1 photo-degradation rates using visible light, which is 3- and 53-fold greater than that of pristine TiO2 and Bi2O2CO3, respectively. The theoretical calculations substantiate that the built-in electric field in the TB nano-composite is conducive to the separation and transfer of photo-excited carriers. Notably, the generated superoxide radicals rather than hydroxyl were identified as the responsible species for tetracycline degradation. In addition, the corresponding degradation pathway and eco-toxicity analysis were also elucidated. In conclusion, this work contributes valuable insights and presents a feasible approach for the fabrication of S-scheme photo-catalysts (TiO2 QDs and bismuth-based nano-materials), thereby enabling the efficient removal of water pollutants.

CuS/Bi2O3 composites activating PMS under visible light for efficient degradation of antibiotic tetracycline

CuS/Bi2O3 composite photocatalyst was prepared by calcination and in situ precipitation, and peroxymonosulfate (PMS) was applied to the degradation of tetracycline (TC) wastewater under visible light. The microscopic morphology, chemical composition, and optical properties of the composites were investigated by characterization means of XRD, FTIR, SEM, XPS, and UV-Vis DRS. The results showed that the introduction of CuS increased the specific surface area of Bi2O3 and increased the visible absorption boundary of Bi2O3 from 455 to 524 nm, which effectively inhibited the complexation of photogenerated electron-hole pairs. The experimental results showed that the introduction of PMS strengthened the removal of TC from the composites, and 95% of TC could be removed under visible light irradiation, and the reaction rate was 8.22 times higher than that of the unspiked PMS, indicating that the BC-15+vis/PMS catalytic system could degrade the pollutants efficiently. The radical capture experiments showed that several radicals, including ·OH, SO4·-, ·O2-, h+, and 1O2, were present in the catalytic system as the main active species to degrade TC, and the mechanism of photocatalytic activation of PMS by Z-type heterostructures of CuS/Bi2O3 composites was proposed. The present study showed that BC-15 has excellent degradation performance and stability, which provides new ideas for the treatment of antibiotic wastewater.

The synergistic degradation of pollutants in water by photocatalysis and PMS activation

In recent years, the synergistic degradation of water pollutants through advanced oxidation technology has emerged as a prominent research area due to its integration of various advanced oxidation technologies. The combined utilization of peroxymonosulfate (PMS) activation technology and photocatalysis demonstrates mild and nontoxic characteristics, enabling the degradation of water pollutants across a wide pH range. Moreover, this approach reduces the efficiency of electron hole recombination, broadens the catalyst's light response range, facilitates electron transfer of PMS, and ultimately improves its photocatalytic performance. The paper reviews the current research status of photocatalytic technology and PMS activation technology, respectively, while highlighting the advancements achieved through the integration of photocatalytic synergetic PMS activation technology for water pollutant degradation. Furthermore, this review delves into the mechanisms involving both free radicals and nonradicals in the reaction process and presents a promising prospect for future development in water treatment technology. PRACTITIONER POINTS: Degradation of water pollutants by photocatalysis and PMS synergistic action has emerged. Synergism can enhance the generation of free radicals. This technology can provide theoretical support for actual wastewater treatment.

Efficient Photocatalytic Degradation of Tetracycline on the MnFe2O4/BGA Composite under Visible Light

In this work, the MnFe₂O₄/BGA (boron-doped graphene aerogel) composite prepared via the solvothermal method is applied as a photocatalyst to the degradation of tetracycline in the presence of peroxymonosulfate. The composite's phase composition, morphology, valence state of elements, defect and pore structure were analyzed by XRD, SEM/TEM, XPS, Raman scattering and N₂ adsorption-desorption isotherms, respectively. Under the radiation of visible light, the experimental parameters, including the ratio of BGA to MnFe₂O₄, the dosages of MnFe₂O₄/BGA and PMS, and the initial pH and tetracycline concentration were optimized in line with the degradation of tetracycline. Under the optimized conditions, the degradation rate of tetracycline reached 92.15% within 60 min, whereas the degradation rate constant on MnFe₂O₄/BGA remained 4.1 × 10^-2 min^-1, which was 1.93 and 1.56 times of those on BGA and MnFe₂O₄, respectively. The largely enhanced photocatalytic activity of the MnFe₂O₄/BGA composite over MnFe₂O₄ and BGA could be ascribed to the formation of type I heterojunction on the interfaces of BGA and MnFe₂O₄, which leads to the efficient transfer and separation of photogenerated charge carriers. Transient photocurrent response and electrochemical impedance spectroscopy tests offered solid support to this assumption. In line with the active species trapping experiments, SO₄^•- and O₂^•- radicals are confirmed to play crucial roles in the rapid and efficient degradation of tetracycline, and accordingly, a photodegradation mechanism for the degradation of tetracycline on MnFe₂O₄/BGA is proposed.

Fabrication of g-C3N4@Bi2MoO6@AgI floating sponge for photocatalytic inactivation of Microcystis aeruginosa under visible light

In this work, a floating photocatalyst was constructed by loading g-C₃N₄@Bi₂MoO₆@AgI (GBA) nanocomposite on a modified polyurethane sponge via a simple dip-coating method and applied for the inactivation of Microcystis aeruginosa under visible light. GBA ternary photocatalyst was fabricated successfully and the morphology, structure, chemical state, and optical properties were characterized systematically. The floating catalyst achieved near 100% removal efficiency of algae cells under 6 h visible light irradiation and also could be retrieved and used at least three times repeatedly. The influences of various conditions on photocatalytic performance such as loading content of nanoparticles, algae density, and concentration of natural organic matters were also studied, which revealed that the GBA floating catalyst exhibited excellent photocatalytic performance of algae removal under different conditions. Furthermore, the physiological characteristics of algae cells during the photocatalytic process, including cell morphology, membrane permeability, Zeta potential, photosynthetic system, antioxidant system, and the metabolic activity were investigated. Results confirmed that the algae cells were severely damaged during the photocatalytic inactivation and the normal physiological functions were significantly affected, which resulted in the death of algae cells at last. Finally, a possible photocatalytic inactivation mechanism of algae cells was proposed. In summary, GBA floating catalyst can effectively inactivate Microcystis aeruginosa under visible light, which confirmed the high efficiency of the novel photocatalytic algae removal technology. Meanwhile, the recyclable floating material also makes the practical application in eutrophic waters of the algae removal technology possible.