Cerium-Bismuth Oxides/Oxynitrates with Low Toxicity for the Removal and Degradation of Organophosphates and Bisphenols

Nanoscale cerium-bismuth oxides/oxynitrates were prepared by a scalable low-temperature method at ambient pressure using water as the sole solvent. Solid solutions were formed up to a 1:1 Ce/Bi molar ratio, while at higher doping levels, bismuth oxynitrate photocatalysts with a pronounced layered structure were formed. Bismuth caused significant changes in the structure and surface properties of nanoceria, such as the formation of defects, oxygen-containing surface groups, and Lewis and Brønsted acid sites. The prepared bifunctional adsorbents/photocatalysts were efficient in the removal of toxic organophosphate (methyl paraoxon) from water by reactive adsorption followed by photocatalytic decomposition of the parent compound and its degradation product (p-nitrophenol). Bi-doped ceria also effectively adsorbed and photodegraded the endocrine disruptors bisphenols A and S and outperformed pure ceria and the P25 photocatalyst in terms of efficiency, durability, and long-term stability. The very low toxicity of Bi-nanoceria to mammalian cells, aquatic organisms, and bacteria has been demonstrated by comprehensive in vivo/in vitro testing, which, in addition to its simple "green" synthesis, high activity, and durability, makes Bi-doped ceria promising for safe use in abatement of toxic chemicals.

Facile one-step strategy for the formation of BiOIO3/[Bi6O6(OH)3](NO3)3·1.5H2O heterojunction to enhancing photocatalytic activity

The heterojunction photocatalyst, BiOIO₃/[Bi₆O₆(OH)₃](NO₃)₃·1.5H₂O (BiOIO₃/BBN), was successfully synthesized by a simple one-step hydrothermal method. The results showed that under UV light irradiation, the formation of a heterojunction could greatly enhance the photocatalytic efficiency of the prepared catalyst for bisphenol A (BPA). The BiOIO₃/BBN heterostructure had the best reaction rate constant, which was 81.82 times, 1.52 times, and 43.40 times improvement of TiO₂, BiOIO₃, and BBN respectively. Through the free radical capture experiments and electron spin resonance spectroscopy, it was conducted that ¹O₂, h⁺, e^-, •OH and •O₂^- were reactive species in the process of photocatalytic degradation of BPA. The photocatalytic mechanism was further investigated and confirmed that the BiOIO₃/BBN heterojunction could improve the separation and transfer of photo-generated carriers, thereby greatly enhancing the catalytic efficiency. The degradation products of BPA were detected by HPLC-MS, and the degradation reaction pathway was deduced.

Self-assembled ultrathin closely bonded 2D/2D heterojunction for enhanced visible-light-induced photocatalytic oxidation and reaction mechanism insights

Two-dimensional (2D) layered heterojunctions with a staggered band structure and unique interface properties exhibit promising application prospects in photocatalytic pollutant removal, water splitting, and CO₂ reduction. Ultrathin 2D/2D heterojunctions with a large specific surface area and a short migration path of the photogenerated charge always illustrate a better photocatalytic performance than non-ultrathin 2D heterojunction photocatalysts. In this study, a novel ultrathin 2D/2D heterojunction of the Bi₂O₂(OH)(NO₃)/BiOBr nanosheet composite (ultrathin BION/BiOBr) was in situ self-assembled though a cetyltrimethylammonium bromide assisted one-step hydrothermal method. Benefiting from the advantage of the unique ultrathin heterojunction structure, the ultrathin 2D/2D BION/BiOBr heterojunctions exhibit a greatly improved photocatalytic removal effect for multiple pollutants compared to the nanocrystal BION/BiOBr, pure BION. As a representative, the ultrathin 2D/2D Br-modified BION/BiOBr heterojunction shows an enhanced tetracycline degradation rate of 76%, which corresponded to a higher photodegradation rate constant of 0.01116 min^-1 when compared to pure BION (17%, 0.00161 min^-1) and nanocrystal BION/BiOBr (24%, 0.00223 min^-1) under visible-light irradiation for 2 h. A series of characterization and density functional theory calculations demonstrate the enhanced separation and migration efficiency of the photogenerated electrons and holes over the ultrathin heterojunction, facilitating the formation of oxidizing groups for the organic pollutant removal. The possible mechanism of the TC photodegradation and the possible photodegradation pathway are also investigated in detail. This work provides a feasible method for constructing ultrathin 2D/2D heterojunction materials for environmental purification.

Simultaneous formation of Bi2O2(OH)(NO3)/BiOBr ultrathin hierarchical microspheres for effectively promoting visible-light-driven photocatalytic activity in environmental remediation

As a two-dimensional nanomaterial, bismuth oxybromide (BiOBr) have attracted tremendous interest in the area of visible-light photocatalysis since it can provide the internal electric field (IEF) through z-axis through its unique electronic band structure. However, the insufficient active sites and rapid recombination rate of charged carriers hamper the efficiency of the photocatalysis. To address these two major obstacles, an enticing strategy of constructing heterojunction was established by introducing Bi₂O₂(OH)(NO₃) (BiON) in BiOBr with the same precursor. Through a facile one-pot hydrothermal synthesis, two Sillén-type layered photocatalysts, with intimately constructed ultrathin heterostructure, was synthesized by the co-precipitation method. In this work, the formation of Bismuth-based heterojunction for charge separation is established by the excessive bismuth nitrate, which subsequently participates with the in situ growth of ultrathin hierarchical microspheres. By attenuating the thickness of BiOBr from 20 nm to 8 nm with the aid of BiON, the photogenerated charges could migrate to the active sites through shorter charge diffusion pathway. Also, the BiOBr and BiON act as an active bridge to promote the separation of electron-hole pairs, which also brings out more active sites due to its increased specific surface area. BiON/BiOBr ultrathin hierarchical microspheres exhibited enhanced visible-light photocatalytic activity for decontaminating several types of pollutants. Besides, the activity of as-prepared BiON/BiOBr was further evaluated by inhibiting the growth of kanamycin-resistant bacteria strains. This study presents a novel strategy to incorporate the crystalline bismuth hydrate nitrate into BiOBr to form ultrathin hierarchical microspheres with high surface area for environmental remediation.

Synthesis and formation mechanism of self-assembled 3D flower-like Bi/γ-Fe2O3 composite particles

The self-assembled 3D flower-like Bi/γ-Fe₂O₃ composite particles consist of a Bi nanosphere core and a γ-Fe₂O₃ nanopetal shell.