Integration of oxygen vacancy rich-TiO2 with BiOI and Ag6Si2O7: Ternary p-n-n photocatalysts with greatly increased performances for degradation of organic contaminants

Visible-light-driven photocatalytic degradation of ofloxacin by BiOBr nanocomposite modified with oxygen vacancies and N-doped CQDs: Enhanced photodegradation performance and mechanism

The rapid recombination of photogenerated carriers and weak light absorption capacity are two major challenges for bismuth-based photocatalysts. Here, N-CQDs/BiO_1-xBr micro-flower photocatalysts with the visible-light activity were fabricated through the ethylene glycol solvothermal method for the first time, and oxygen vacancies (OVs) and N-doped carbon quantum dots (N-CQDs) were simultaneously introduced on the surface of BiOBr. OVs were introduced to form defective BiOBr (BiO_1-xBr). N-CQDs and BiO_1-xBr formed a strong binding effect. Then, the composition, morphology, crystal structure and photoelectric property of photocatalysts were studied, and the mechanism and pathway of ofloxacin (OFL) photodegradation were studied. N-CQDs/BiO_1-xBr-4 was a micro-flower composed of nanosheets with a thickness of about 60 nm, this structure produced multiple light reflections. Photoelectrochemical analysis confirmed that the synergistic effect of OVs and N-CQDs significantly promoted the electron-hole separation (3 times vs BiOBr) and enhanced the light absorption range (Eg = 2.96 eV vs 3.24 eV). Meanwhile, the removal rate of OFL by N-CQDs/BiO_1-xBr-4 was 6 times higher than that by BiOBr (K_obs of N-CQDs/BiO_1-xBr-4 was 32 times higher than that of BiOBr). Electron spin resonances analysis and radical quenching experiments showed that ·O₂^- and h⁺ played dominant roles in the OFL photodegradation system, and their contribution rates were 89.84% and 70.31%, respectively. There were main degradation pathways for OFL, including oxidation, dealkylation, hydroxylation and decarboxylation. This study explored the synergistic and complementary effects between OVs and N-CQDs, and provided a promising strategy for the photodegradation of toxic antibiotics by visible-light-driven photocatalysts.

Novel strategies for 2,8-dichlorodibenzo-p-dioxin degradation using ternary Au-modified iron doped TiO2 catalysts under UV-vis light illumination

Polychlorinated dibenzo-p-dioxins (PCDDs), characterized by their extreme toxicity, high persistency and bioaccumulation, regard as one of the most concerned environmental pollutants on the priority list. In this study, microwave-hydrothermal and photoreduction methods were adopted for fabrication of ternary Au@Fe/TiO₂ composites for removal of 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD) under UV-Vis light irradiation. The acquired materials were characterized and analyzed by XRD, TEM, XPS, UV-Vis DRS, PL, etc. As a result, the 1%Au@1%Fe/TiO₂ exhibited much higher photocatalytic activity that 96.3% of 2,8-DCDD was removed within 160 min with respect to that of Fe/TiO₂ (3.0 times) and TiO₂ (5.5 times). It revealed the active substances might be produced, which were verified by ESR analysis. In a comparison, the 1%Au@1%Fe/TiO₂ also exhibited high activity in that 97.2% of 2,8-DCDD was removed within 240 min under an anoxic atmosphere. The 1%Au@1%Fe/TiO₂ systems were all pH-dependent that 2,8-DCDD could be fully degraded in neutral conditions. The results of repeatability on 1%Au@1%Fe/TiO₂ showed that the sample was high stability. Fe doping improved the charge separation of TiO₂ and Au modification improved the activity via SPR effect and Mott-Schottky barrier. The degradation mechanisms and pathways were proposed and discussed in detail. The current work develops a new approach on photocatalytic oxidation and reductive dechlorination of dioxins and may open a new opportunity to extend the application range of TiO₂ catalysts.

Synthesis of MFeO3/SBA-15 (M = La or Bi) for peroxymonosulfate activation towards enhanced photocatalytic activity

MFeO3/SBA-15 was synthesized by a simple sol–gel method and was used to activate peroxymonosulfate for the degradation of doxycycline hydrochloride.

Facile Vacuum Annealing-Induced Modification of TiO2 with an Enhanced Photocatalytic Performance

In this work, the photocatalytic performance enhancement of hydrothermally prepared TiO₂ was achieved by facile vacuum annealing treatment. Calcination of TiO₂ powder in air (CA-TiO₂) maintained its white color, while gray powder was obtained when the annealing was performed under vacuum (CV-TiO₂). Fourier transform infrared, total organic carbon, X-ray photoelectron spectroscopy, and electron paramagnetic resonance analyses proved that vacuum annealing transformed ethanol adsorbed on the surface of TiO₂ into carbon-related species accompanied by the formation of surface oxygen vacancies (Vo). The residual carbon-related species on the surface of CV-TiO₂ favored its adsorption of organic dyes. Compared with TiO₂ and CA-TiO₂, CV-TiO₂ exhibited an improved charge carrier separation with surface Vo as trapping sites for electrons. Vacuum annealing-induced improvement of crystallinity, enhancement of adsorption capacity, and formation of surface Vo contributed to the excellent photocatalytic activity of CV-TiO₂, which was superior to that of commercial TiO₂ (P25, Degussa). Obviously, vacuum annealing-triggered decomposition of ethanol played an important role in the modification of TiO₂. In the presence of ethanol, vacuum annealing was also suitable for the introduction of Vo into P25. Therefore, the current work offers an easy approach for the modification of TiO₂ to enhance its photocatalytic performance by facile vacuum annealing in the presence of ethanol.

Ultrahigh Charge Separation Achieved by Selective Growth of Bi4O5I2 Nanoplates on Electron-Accumulating Facets of Bi5O7I Nanobelts

Ultrahigh charge separation was observed in Bi₄O₅I₂/Bi₅O₇I two-dimensional (2D)/one-dimensional (1D) hierarchical structures (HSs) constructed by selective growth of 2D monocrystalline Bi₄O₅I₂ nanoplates on the electron-accumulating (100) facet of 1D monocrystalline Bi₅O₇I nanobelts. In addition to the presence of type-II heterojunction between Bi₄O₅I₂ and Bi₅O₇I elementary entities in 2D/1D HSs, the type-II (100)/(001) surface heterojunction in Bi₅O₇I nanobelt substrates was also confirmed by means of density functional theory (DFT) calculations and selective photoreduction/oxidation deposition experiments. The synergistic effect of two kinds of heterojunctions in Bi₄O₅I₂/Bi₅O₇I 2D/1D HSs endowed them with ultrahigh charge carrier separation and transfer characteristics. In contrast with the control sample (BB40-C) constructed by growing Bi₄O₅I₂ nanoplates on whole four sides of Bi₅O₇I nanobelts, Bi₄O₅I₂/Bi₅O₇I 2D/1D HSs demonstrated significantly enhanced charge transfer between Bi₅O₇I nanobelt substrates and Bi₄O₅I₂ nanoplates, owing to respective electron and hole accumulations on (100) and (001) facets of Bi₅O₇I substrates caused by (100)/(001) surface heterojunction. The enhanced separation behavior was successfully verified by steady/transient-state photoluminescence, electrochemical techniques, and photocatalytic degradation experiments. Based on the above effective charge separation of Bi₄O₅I₂/Bi₅O₇I 2D/1D HSs as well as the routine advantages for 2D/1D HSs, such as the excellent charge transport in monocrystalline elementary entities, much higher specific surface area, and enhanced light absorption by multiple reflections, the optimal BB40 HSs demonstrated ultrahigh photocatalytic performance than the control samples, whose apparent rates for Rhodamine B [or tetracycline hydrochloride (TC)] degradation were 7.1 (2.9 for TC), 10.3 (4.7 for TC), and 2.2 (1.7 for TC) times those of pristine Bi₅O₇I nanobelts, Bi₄O₅I₂ nanoplates, and BB40-C, respectively. It is hoped that this crystal facet selection during the heterostructure construction in this work could provide a new strategy or some enlightenment for the exploration of highly active 2D/1D HSs or other-dimensional heterostructure nanomaterials applied in the fields of photocatalysts, solar cells, sensors, and others.