Synthesis of BiOI/Mordenite Composites for Photocatalytic Treatment of Organic Pollutants Present in Agro-Industrial Wastewater.

Recently, bismuth oxyiodide (BiOI) is an attractive semiconductor to use in heterogeneous photocatalysis processes. Unfortunately, BiOI individually shows limited photocatalytic efficiency, instability, and a quick recombination of electron/holes. Considering the practical application of this semiconductor, some studies show that synthetic zeolites provide good support for this photocatalyst. This support material permits a better photocatalytic efficiency because it prevents the quick recombination of photogenerated pairs. However, the optimal conditions (time and temperature) to obtain composites (BiOI/ synthetic zeolite) with high photocatalytic efficiency using a coprecipitation-solvothermal growth method have not yet been reported. In this study, a response surface methodology (RSM) based on a central composite design (CCD) was applied to optimize the synthesis conditions of BiOI/mordenite composites. For this purpose, eleven BiOI/mordenite composites were synthesized using a combined coprecipitation-solvothermal method under different time and temperature conditions. The photocatalytic activities of the synthesized composites were evaluated after 20 min of photocatalytic oxidation of caffeic acid, a typical organic pollutant found in agro-industrial wastewater. Moreover, BiOI/mordenite composites with the highest and lowest photocatalytic activity were physically and chemically characterized using nitrogen adsorption isotherms, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and diffuse reflectance spectroscopy (DRS). The optimal synthesis conditions prove to be 187 °C and 9 h. In addition, the changes applied to the experimental conditions led to surface property modifications that influenced the photocatalytic degradation efficiency of the BiOI/mordenite composite toward caffeic acid photodegradation.

A facile synthesis of CuBi2O4 hierarchical dumbbell-shaped nanorod cluster: a promising photocatalyst for the degradation of caffeic acid.

The present study reports on the synthesis of Cu-bismuth oxide (CuBi2O4)-based nanorods by using a simple co-precipitation method for the photocatalytic degradation of caffeic acid (CA). The incorporation of Cu metal ions during the synthesis of CuBi2O4 nanorods might be advantageous to avoid the aggregation and control the leach out of metal ions. The calculated bandgap values of ~ 1.04, 1.02, and 0.94 eV were observed for CuBi2O4 with different amounts of Cu 1.0, 0.50, and 0.25 g, respectively. Varying the quantity of Cu metal ions easily tuned the bandgap value within the CuBi2O4-based nanorods. However, a further decrease in the bandgap value increased the recombination rate, and the less photocatalyst performance was observed. The CA degradation could be explained based on the species distribution. The CA pKa was mainly located between pKa1 and pKa2 of 4.43 and 8.6, respectively. The Cu within the CuBi2O4-based nanorods changed the electronic properties and the antibacterial ability. Therefore, the synthesized CuBi2O4-based nanorod cluster might be a promising material for the photocatalytic degradation of CA.

A novel bimetallic (Fe/Bi)-povidone-iodine micro-flowers composite for photocatalytic and antibacterial applications.

The present work describes the synthesis of polyvinylpyrrolidone (PVP) assisted Fe-BiOI based Fe/Bi-povidone­iodine (Fe/Bi-P-I) micro-flowers based composite and its photocatalytic and antibacterial applications. The Fe/Bi-P-I micro-flowers-based composite material was synthesized using a simple co-precipitation method. The prepared Fe/Bi-P-I micro-flowers-based composite materials were characterized using various characterization techniques and tested against photocatalytic degradation of rhodamine B (RhB) dye and antibacterial analysis. The PVP or povidone­iodine provides more exposure of reactive sites and oxygen vacancies, which leads to a high separation rate of photoinduced charge carriers, and migration, thereby 100% of photodegradation efficiency at 1 mg/L initial concentration of RhB dye towards the synthesized P-Fe-BiOI based micro-flowers composite. Interestingly, Povidone-Iodine in Fe/Bi-P-I micro-flowers-based composite might be advantageous for antimicrobial activity against both gram-negative (E. coli), and gram-positive (S. aureus) bacterial strains. Therefore, the prepared Fe/Bi-P-I micro-flowers-based composite improved both photocatalytic degradation of organic pollutants as well as high antimicrobial activity. The method of synthesizing the Bi/Fe-P-I micro flower composite in the present study is novel, facile, and economically viable.

Bimetal (Fe/Zn) doped BiOI photocatalyst: An effective photodegradation of tetracycline and bacteria.

Tetracycline (TC) is one of the most commonly used broad-spectrum antibiotics to treat the bacterial infection. TC antibiotics enter into the environment because of partial metabolism in the humans and animals, thereby increasing the environmental toxicity. Therefore, it is highly needed to treat TC antibiotics from the water system. In this aspect, the present work focus on the synthesis of Fe and Zn (bimetal) incorporated with different concentrations into the bismuth-oxy-iodide (Fe/Zn-BiOI) based photocatalyst materials. The synthesized Fe/Zn-BiOI was tested against photocatalytic degradation of TC antibiotics and bacteria. The band gap value of the synthesized Fe/Zn-BiOI was calculated ~2.19 eV. The incorporation of the Fe and Zn metals within the BiOI aided advantages that increased the reactive sites, oxygen defects, photon adsorption, production of hydroxyl radicals, and decrease the recombination rate, thereby high photo-degradation ability. The maximum degradation of ~83% was observed using Fe/Zn-BiOI-1-1 at 10 mg/L of TC antibiotics concentration. Moreover, ~98% of degradation was observed at pH~10 of the TC antibiotics. The photo-activity against bacteria of the Fe/Zn-BiOI was also determined. The data suggested that the synthesized Fe/Zn-BiOI based photocatalyst materials effectively inhibited the bacterial strains. Therefore, Fe/Zn-BiOI based photocatalyst materials might be promising materials that effectively degrade TC antibiotics as well as bacteria.

Strategic Doping Approach of the Fe-BiOI Microstructure: An Improved Photodegradation Efficiency of Tetracycline.

The present study describes the strategic doping of Fe metal ions into a BiOI microstructure using ex situ and in situ processes to synthesize a Fe-BiOI microstructure and their effect on photocatalytic degradation of tetracycline (TC). The data suggested that in situ Fe-BiOI (Fe-BiOI-In) has superior performance compared to ex situ Fe-BiOI (Fe-BiOI-Ex) due to the uniform dispersion of Fe within the Fe-BiOI material. Calculated bandgaps ∼1.8, ∼1.5, and 2.4 eV were observed for BiOI (without Fe), Fe-BiOI-In, and Fe-BiOI-Ex, respectively. Interestingly, Fe incorporation within BiOI might decrease the bandgap in Fe-BiOI-In due to the uniform distribution of metal ions, whereas increasing the bandgap in Fe-BiOI-Ex attributed to nonuniform distribution or agglomeration of metal ions. The uniform dispersion of Fe within Fe-BiOI modulates electronic properties as well as increases the exposure of Fe ions with TC, thereby higher degradation efficiency of TC. The in situ Fe-BiOI material shows 67 and 100% degradation of TC at 10 and 1 mg/L, respectively. The TC degradation was also found to be pH-dependent; when increasing the pH value up to 10, 94% degradation was achieved at 10 mg/L within 60 min of solar irradiation. The analysis was also performed over BiOI, which proves that Fe has a profound effect on TC degradation as Fe(II) tends to trigger oxidation-reduction by utilizing the chelate formation tendency of TC. Therefore, the prepared Fe-BiOI-In has the potential ability to degrade pharmaceutical compounds, especially, TC from wastewater.

A Facile Synthetic Method to Obtain Bismuth Oxyiodide Microspheres Highly Functional for the Photocatalytic Processes of Water Depuration.

Bismuth oxyhalide (BiOI) is a promising material for sunlight-driven-environmental photocatalysis. Given that the physical structure of this kind of materials is highly related to its photocatalytic performance, it is necessary to standardize the synthetic methods in order to obtain the most functional architectures and, thus, the highest photocatalytic efficiency. Here, we report a reliable route to obtain BiOI microspheres via the solvothermal process, using Bi(NO3)3 and potassium iodide (KI) as precursors, and ethylene glycol as a template. The synthesis is standardized in a 150 mL autoclave, at 126 °C for 18 h. This results in 2-3 µm-sized mesoporous microspheres, with a relevant specific surface area (61.3 m2/g). Shortening the reaction times in the synthesis results in amorphous structures, while higher temperatures lead to a slight increase in the porosity of the microspheres, with no effect in the photocatalytic performance. The materials are photo-active under UV-A/visible light irradiation for the degradation of the antibiotic ciprofloxacin in water. This method has demonstrated to be effective in interlaboratory tests, obtaining similar BiOI microspheres in Mexican and Chilean research groups.

Solvothermal Synthesis and Photocatalytic Activity of BiOBr Microspheres with Hierarchical Morphologies.

BiOBr microspheres with hierarchical morphologies (BiOBr-MicSphe) has potential application in heterogeneous photocatalysis for decontamination of water and air. For this reason, the synthesis, characterization an evaluation of photocatalytic activity of these materials become important. In this article, BiOBr-MicSphe were synthesized using different ranges of reaction temperature (120-200 °C) and reaction time (12 h - 24 h). Samples grown at 145 °C and 18 h showed the higher photocatalytic activity on gallic acid degradation. Morphological properties, chemical composition and structural analysis revealed that sample with higher photocatalytic activity exhibited a microspherical morphology with pure BiOBr tetragonal phase. Besides, adsorption-desorption analysis showed a smaller pore diameter for sample grown at 145 °C and 18 hrs. The results showed that the reaction temperature has a strong influence on the different properties of the material, affecting the photocatalytic activity.