Photophysical and Photocatalytic Properties of BiSnSbO₆ under Visible Light Irradiation

Solar photocatalysis application in UWWTP outlets - simulations based on predictive models in flat-plate reactors and pollutant degradation studies with in silico toxicity assessment

The application of the solar photocatalysis for the degradation of residual pollutants found in surface water was demonstrated. Semi-pilot scale flat-plate cascade reactor (FPCR) was used to study the degradation of model organic pollutants: enrofloxacin (ENRO), 17β-estradiol (E2) and 1H-benzotriazole (1H-BT) over TiO2 thin-film supported on glass fibers. A modular panel with full-spectra solar lamps with appropriate UVB and UVA irradiation levels was used as a simulation of sunlight. Pollutant degradation in FPCR was estimated using predictive models; intrinsic reaction rate constants (ki) for ENRO, E2 and 1H-BT independent of the reactor size, flow rate and irradiation conditions were determined: 9.60, 3.35 and 0.37 109 s-1 W-0.5 m1.5, respectively. Main degradation products (DPs), formed upon hydroxylation, ring opening and oxidation, were identified using LC-QTOF-MS. The ecotoxicological impact was assessed via T.E.S.T. and ECOSAR open-source tools showing the formation of less harmful DPs after sufficient reaction time. Pollutant degradation was simulated at four locations of interest, i.e. exhausts from urban wastewater treatment plants (UWWTPs) in Zagreb, Croatia (45°N), Krakow, Poland (50°N), Sevilla, Spain (37°N) and Ioannina, Greece (39.6°N). Results have proved that a simple flat-plate system with supported photocatalysts can be easily scaled up and incorporated at the outlet of UWWTP for the reduction of pollutant load and related toxicity. The exhaust canal in Zagreb with the estimated length of a photocatalytic layer of 122 m for the > 90% degradation of all target pollutants was discussed as the best installation site among studied locations. ENVIRONMENTAL IMPLICATION: A multi-disciplinary approach to the tentative application of TiO2 solar photocatalysis outdoors to reduce pollutant loads and toxicity in surface waters was demonstrated. Possible application at four selected locations in Europe, as an additional step in water treatment after urban wastewater treatment plants (UWWTPs) was discussed. Target pollutants were studied under environmentally relevant conditions (sunlight levels, water matrix, simulation of process on a real scale at selected geographical location), at both higher and low concentrations.

Antimicrobial properties of heterojunction BiSnSbO6-ZnO composites in wastewater treatment

BiSnSbO6-ZnO composite photocatalytic material with type II heterojunction structure was synthesized by a simple solid-phase sintering method, it was characterized by XRD, UV-vis, and PT methods. The photocatalytic antibacterial experiments were carried out under LED light irradiation. The experimental results showed that the photocatalytic antibacterial properties of BiSnSbO6-ZnO composites against bacteria and fungi were significantly stronger than those of single BiSnSbO6 and ZnO. Under light conditions, the antibacterial efficiencies of 500 mg/L BiSnSbO6-ZnO composites against E. coli, S. aureus, and P. aeruginosa reached 99.63%, 100%, and 100% for 6 h, 4 h, and 4 h, respectively. The best antibacterial concentration of BiSnSbO6-ZnO composite against the eukaryotic microorganism Candida albicans was 250 mg/L, and the antibacterial efficiency reached the highest 63.8% at 6 h. Antibacterial experiments were carried out on domestic livestock and poultry wastewater, which showed that the BiSnSbO6-ZnO composite photocatalytic material has broad-spectrum antibacterial activity against bacteria, and the antibacterial effect has species differences. Through the MTT experiment, it is proved that the prepared BiSnSbO6-ZnO composite photocatalytic material has no toxicity at the experimental concentration. According to the free radical scavenging experiment and SEM observation of the morphological changes of the bacteria after light treatment, the prepared BiSnSbO6-ZnO composite photocatalytic material can generate active species OH, h+, and e- through light irradiation to achieve the purpose of sterilization, where e- play a major role, indicating that the BiSnSbO6-ZnO composite photocatalytic material has broad application prospects in the actual antibacterial field.

Preparation and Property Characterization of In2YSbO7/BiSnSbO6 Heterojunction Photocatalyst toward Photocatalytic Degradation of Indigo Carmine within Dye Wastewater under Visible-Light Irradiation

In₂YSbO₇ and In₂YSbO₇/BiSnSbO₆ heterojunction photocatalyst were prepared by a solvothermal method for the first time. The structural characteristics of In₂YSbO₇ had been represented. The outcomes showed that In₂YSbO₇ crystallized well and possessed pyrochlore constitution, a stable cubic crystal system and space group Fd3m. The lattice parameter of In₂YSbO₇ was discovered to be a = 11.102698 Å and the band gap energy of In₂YSbO₇ was discovered to be 2.68 eV, separately. After visible-light irradiation of 120 minutes (VLGI-120M), the removal rate (ROR) of indigo carmine (IC) reached 99.42% with In₂YSbO₇/BiSnSbO₆ heterojunction (IBH) as a photocatalyst. The ROR of total organic carbon (TOC) reached 93.10% with IBH as a photocatalyst after VLGI-120M. Additionally, the dynamics constant k which was taken from the dynamic curve toward (DCT) IC density and VLGI time with IBH as a catalyst reached 0.02950 min^-1. The dynamics constant k which came from the DCT TOC density and VLGI time with IBH as a photocatalyst reached 0.01783 min^-1. The photocatalytic degradation of IC in dye wastewater (DW) with IBH as a photocatalyst under VLGI was in accordance with the first-order kinetic curves. IBH was used to degrade IC in DW for three cycles of experiments under VLGI, and the ROR of IC reached 98.74%, 96.89% and 94.88%, respectively, after VLGI-120M, indicating that IBH had high stability. Compared with superoxide anions or holes, hydroxyl radicals possessed the largest oxidative ability for removing IC in DW, as demonstrated by experiments with the addition of trapping agents. Lastly, the probable degradation mechanism and degradation pathway of IC were revealed in detail. The results showed that a visible-light-responsive heterojunction photocatalyst which possessed high catalytic activity and a photocatalytic reaction system which could effectively remove IC in DW were obtained. This work provided a fresh scientific research idea for improving the performance of a single catalyst.

Preparation, Property Characterization of Gd2YSbO7/ZnBiNbO5 Heterojunction Photocatalyst for Photocatalytic Degradation of Benzotriazole under Visible Light Irradiation

The Gd2YSbO7/ZnBiNbO5 heterojunction photocatalyst was synthesized for the first time by the facile in situ precipitation method. The structural properties of a Gd2YSbO7/ZnBiNbO5 heterojunction photocatalyst were characterized by X-ray diffractometer, scanning electron microscope-X ray energy dispersive spectra, X-ray photoelectron spectrograph and UV-Vis diffuse reflectance spectrophotometer. The band gap energy (BGE) of Gd2YSbO7 or ZnBiNbO5 was found to be 2.396 eV or 2.696 eV, respectively. The photocatalytic property of Gd2YSbO7 or ZnBiNbO5 or Gd2YSbO7/ZnBiNbO5 heterojunction photocatalyst (GZHP) was reported. After a visible-light irradiation of 145 minutes (VLI-145 min), the removal rate (RER) of benzotriazole reached 99.05%, 82.45%, 78.23% or 47.30% with Gd2YSbO7/ZnBiNbO5 heterojunction (GZH), Gd2YSbO7, ZnBiNbO5 or N-doped TiO2 (NTO) as photocatalyst. In addition, the kinetic constant k, derived from the dynamic curve toward benzotriazole concentration and visible light irradiation time with GZH as a photocatalyst, reached 0.0213 min−1. Compared with Gd2YSbO7 or ZnBiNbO5 or NTO, GZHP showed maximal photocatalytic activity (PHA) for the photocatalytic degradation of benzotriazole under visible-light irradiation. The RER of total organic carbon during the photocatalytic degradation of benzotriazole reached 90.18%, 74.35%, 70.73% or 42.15% with GZH as a photocatalyst or with Gd2YSbO7, ZnBiNbO5 or NTO as a photocatalyst after VLI-145 min. Moreover, the kinetic constant k, which came from the dynamic curve toward total organic carbon concentration and visible light irradiation time with GZH as a photocatalyst, reached 0.0110 min−1. Based on above results, GZHP showed the maximal mineralization percentage ratio when GZHP degraded benzotriazole. The results showed that hydroxyl radicals was the main oxidation radical during the degradation of benzotriazole. The photocatalytic degradation of benzotriazole with GZH as a photocatalyst conformed to the first-order reaction kinetics. Our research aimed to improve the photocatalytic properties of the single photocatalyst.

Structure and photocatalytic performance of rice husk-like Ba-doped GaOOH under light irradiation

The effects of Ba-doping on the structure and photocatalytic performance of GaOOH were investigated for the first time in this paper. XRD, SEM, TEM, XPS, UPS, FT-IR, UV-Vis DRS, PL, BET and EPR characterizations were carried out to analyze the properties of Ba-doped GaOOH. The results showed that GaOOH crystallized well with the orthorhombic crystal system with space group Pbnm. The lattice parameters of GaOOH were found to be a = 4.509526 Å, b = 9.771034 Å and c = 2.969284 Å. The transition in the structural morphology of GaOOH before and after Ba-doping was observed in SEM pictures in which the morphology of GaOOH varied from wood-like to rice husk-like. At the same time, the specific surface area of 4 wt% Ba-doped GaOOH (21.5854 m² g⁻¹) was 3.42 times that of pure GaOOH (6.3047 m² g⁻¹). Ba-doping caused a red shift of the band gap according to UV-Vis DRS results. The enhanced defect states caused by Ba-doping was confirmed by PL results, which decreased the recombination rate of photogenerated electrons and photogenerated holes. Compared with pure GaOOH, when GaOOH with different Ba content was used as photocatalyst, the removal rate of enrofloxacin was increased by more than 20% only by illumination for 60 min. In addition, Ba-doped GaOOH had excellent stability and could be reused, which could reduce costs and increase the potential of its practical application.

The effects of Ba-doping on the structure and photocatalytic performance of GaOOH were investigated for the first time. Compared with pure GaOOH, when GaOOH with different Ba content was used, the removal rate of enrofloxacin was increased by more than 20% in 60 min.