Controllable Crystal Growth and Improved Photocatalytic Activity of Porous Bi2O3-Bi2S3 Composite Sheets

Porous Bi₂O₃-Bi₂S₃ composite sheets were constructed through a combinational methodology of chemical bath deposition and hydrothermal reaction. The Na₂S precursor concentration in the hydrothermal solution was varied to understand the correlation between the vulcanization degree and structure evolution of the porous Bi₂O₃-Bi₂S₃ composite sheets. The control of the etching rate of the Bi₂O₃ sheet template and the regrowth rate of Bi₂S₃ crystallites via suitable sulfide precursor concentration during the hydrothermal reaction utilizes the formation of porous Bi₂O₃-Bi₂S₃ sheets. Due to the presence of Bi₂S₃ crystallites and porous structure in the Bi₂O₃-Bi₂S₃ composites, the improved visible-light absorption ability and separation efficiency of photogenerated charge carriers are achieved. Furthermore, the as-synthesized Bi₂O₃-Bi₂S₃ composite sheets obtained from vulcanization with a 0.01M Na₂S precursor display highly enhanced photocatalytic degradation toward methyl orange (MO) dyes compared with the pristine Bi₂O₃ and Bi₂S₃. The porous Bi₂O₃-Bi₂S₃ sheet system shows high surface active sites, fast transfer, high-efficiency separation of photoinduced charge carriers, and enhanced redox capacity concerning their constituent counterparts. This study affords a promising approach to constructing Bi₂O₃-based Z-scheme composites with a suitable microstructure and Bi₂O₃/Bi₂S₃ phase ratio for photoactive device applications.

Solar-induced efficient propylparaben photodegradation by nitrogen vacancy engineered reticulate g-C3N4: Morphology, activity and mechanism

Propylparaben (PrP) has attracted extensive concerns due to its wide occurrence in wastewater and potential health risk. Herein, nitrogen vacancy engineered reticulate g-C₃N₄ (Nv-RCN) was successfully synthesized for the photodegradation of PrP. Nv-RCN exhibited larger specific surface area, greater light absorption ability, higher transfer and separation efficiency of charge carriers in comparison with bulk g-C₃N₄ (CN). According to the characterization results and DFT calculation, nitrogen vacancy could capture electrons and facilitate oxygen adsorption. The Nv-RCN exhibited an outstanding PrP removal efficiency of 94.3 %, and the corresponding apparent rate constant of Nv-RCN was 3.37 times higher than that of CN. High O₂ concentration (8 mg/L) and low pH value (pH = 3) promoted PrP photodegradation based on Box-Behnken Design. The O₂^- was the major radical during PCOP of Nv-RCN, and could oxidize PrP by decarbonylation and dealkylation. This study provided new insights to the improvement of photodegradation performance of g-C₃N₄ for parabens removal and related environmental remediation.

The degradation of paraben preservatives: Recent progress and sustainable approaches toward photocatalysis

Parabens are a class of compounds primarily used as antimicrobial preservatives in pharmaceutical products, cosmetics, and foodstuff. Their widely used field leads to increasing concentrations detected in various environmental matrices like water, soil, and sludges, even detected in human tissue, blood, and milk. Treatment techniques, including chemical advanced oxidation, biological degradation, and physical adsorption processes, have been widely used to complete mineralization or to degrade parabens into less complicated byproducts. All kinds of processes were reviewed to give a completed picture of parabens removal. In light of these treatment techniques, advanced photocatalysis, which is emerging rapidly and widely as an economical, efficient, and environmentally-friendly technique, has received considerable attention. TiO₂-based and non-TiO₂-based photocatalysts play an essential role in parabens degradation. The effect of experimental parameters, such as the concentration of targeted parabens, concentration of photocatalyst, reaction time, and initial solution pH, even the presence of radical scavengers, are surveyed and compared from the literature. Some representative parabens such as methylparaben, propylparaben, and benzylparaben have been successfully studied the reaction pathways and their intermediates in their degradation process. As reported in the literature, the degradation of parabens involves the production of highly reactive species, mainly hydroxyl radicals. These reactive radicals would attack the paraben preservatives, break, and finally mineralize them into simpler inorganic and nontoxic molecules. Concluding perspectives on the challenges and opportunities for photocatalysis toward parabens remediation are also intensively highlighted.

Hollow porous BiOCl microspheres assembled with single layer of nanocrystals: spray solution combustion synthesis and the enhanced photocatalytic properties

The hollow porous microspheres assembled with BiOCl nanocrystals were successfully synthesized via a facile spray solution combustion synthesis method. The microstructure, morphology, absorbance, optical properties of the samples were investigated in detail. The results show that hollow porous BiOCl microspheres have narrow band gaps (2.66-2.71 eV), and the degradation rate of rhodamine B (RhB) can reach 98% under visible light irradiation for 60 min. Furthermore, the mechanism of the photocatalytic degradation of RhB was proposed through the experiment of trapping active species. This excellent photocatalytic property can be ascribed to the larger specific surface area and the special microstructure.

Photocatalytic mechanism and performance of a novel wool flake-BiFeO3nanosheet-TiO2core-shell-structured composite photocatalyst

In this study, BiFeO₃(BFO) nanosheets ground from BFO particles were first incorporated with wool flakes to construct sandwich-like wool-BFO composites using the vibration-assisted ball milling technique in freezing conditions. The wool-BFO composites were then loaded with a thick layer of TiO₂nanoparticles to prepare the core-shell-structured wool-BFO-TiO₂composites using a hydrothermal synthesis process. The microstructure of the core-shell wool-BFO-TiO₂composites and its photocatalytic applications were systematically examined using a series of characterization methods. Trapping experiments and electron spin resonance spectra were also employed to judge the active radical species like superoxide radicals (·O₂^-), singlet oxygen (¹O₂), holes (h⁺), and hydroxyl radicals (·OH) using benzoquinone, furfuryl alcohol, ethylenediamine tetraacetic acid, and tert-butanol as the scavengers, respectively. The photodegradation performance of the wool-BFO-TiO₂composites was measured using more resistant methyl orange (MO) dye as the pollutant model. In comparison with the wool-TiO₂or wool-BFO composites, the superior photocatalytic properties of the wool-BFO-TiO₂composites under visible light irradiation were attributed to the presence of mesopores and macropores, the large specific surface area and intimate interface between wool-BFO composites and TiO₂nanoparticles, the coexistence of Fe³⁺, Fe²⁺, Bi³⁺, Bi^(3-x)+, Ti⁴⁺, and Ti³⁺species, and the strong visible light harvesting, thus leading to the fast separation of photogenerated electron-hole pairs. The wool-BFO-TiO₂composites could be used for the repeated photodegradation of organic pollutants and be recycled easily using a magnet. The active radical species of the wool-BFO-TiO₂composites were ·O₂^-and¹O₂rather than ·OH and h⁺, which were involved in the photodegradation of MO dye under visible light irradiation.

Phase transformation and room temperature stabilization of various Bi2O3 nano-polymorphs: effect of oxygen-vacancy defects and reduced surface energy due to adsorbed carbon species

We report the grain growth from the nanoscale to microscale and a transformation sequence from Bi →β-Bi₂O₃→γ-Bi₂O₃→α-Bi₂O₃ with the increase of annealing temperature. The room temperature (RT) stabilization of β-Bi₂O₃ nanoparticles (NPs) was attributed to the effect of reduced surface energy due to adsorbed carbon species, and oxygen vacancy defects may have played a significant role in the RT stabilization of γ-Bi₂O₃ NPs. An enhanced red emission band was evident from all the samples attributed to oxygen-vacancy defects formed during the growth process in contrast with the observed white emission band from the air annealed Bi ingots. Based on our experimental findings, the air annealing induced oxidation of Bi NPs and transformation mechanism within various Bi₂O₃ nano-polymorphs are presented. The outcome of this study suggests that oxygen vacancy defects at the nanoscale play a significant role in both structural stabilization and phase transformation within various Bi₂O₃ nano-polymorphs, which is significant from theoretical consideration.

Microwave synthesis of iodine-doped bismuth oxychloride microspheres for the visible light photocatalytic removal of toxic hydroxyl-contained intermediates of parabens: catalyst synthesis, characterization, and mechanism insight

The iodine-doped bismuth oxychloride (I-doped BiOCl) microspheres are synthesized as the visible light photocatalysts for the photocatalytic removal of three toxic hydroxyl-contained intermediates of parabens. With the aid of the unique heating mode of microwave method, the I-doped BiOCl photocatalysts with tunable iodine contents and dispersed energy bands, instead of a mixture of BiOI and BiOCl or solid solution, are synthesized under the controllable conditions. Due to the stretched architectures, high specific surface area, and effective separation of photogenerated carriers, they exhibit high activity to the photocatalytic degradation of methyl 2,4-dihydroxybenzoate (MDB), methyl 3,4-dihydroxybenzoate (MDHB), and ethyl 2,4-dihydroxybenzoate (EDB). As a typical result, it is indicated that though MDB as the most difficult intermediate of parabens to be degraded, a 91.2% removal ratio can still be achieved over the I-doped BiOCl with an energy band of 2.79 eV within 60 min. In addition, it is also confirmed that these photocatalysts remain stable throughout the photocatalytic reaction and can be reused, and more importantly, the photogenerated h⁺ and •O₂^- are the key reactive species, while •OH plays a negligible role in the photocatalytic reaction. Resorcinol was identified as the main photodegraded intermediate. These results demonstrate that this photocatalytic system not only exhibit a high efficiency but also avoid the consequent secondary pollutions due to the no formation of complex hydroxyl derivatives.

Sonochemical and sonocatalytic destruction of methylparaben using raw, modified and SDS-intercalated particles of a natural clay mineral

The first part of the study is about the degradation of a common PPCP-methylparaben by high-frequency ultrasound to highlight the operation parameters, the reaction sites, the oxidation byproducts and the role of OH radicals. The second part covers the catalytic effect of a highly abundant and cost-effective clay mineral-sepiolite, and investigates the role of surface modification and SDS-composites of the clay in improving the efficiency of the degradation reactions. It was found that the compound (C₀ = 10 mg L^-1) was readily and totally decomposed by 30-min sonication at neutral pH, producing phenolic and aliphatic intermediates, but with insignificant mineralization. The major reaction site was the bubble-liquid interface, where the reactions were governed by OH radical attack. Modification of the sepiolite surface by pre-sonication in an ultrasonic bath improved the rate of reaction and the degree of TOC decay. Further modification by the synthesis of 20-min sonicated (200 kHz bath) SDS-intercalates of the clay was found to yield significant enhancement in the rate of target compound decomposition and the fraction of TOC decay, provided that the reaction was operated at acidic pH.

Bi5O7NO3 and Ag/Bi5O7NO3 composites: one-step solution combustion synthesis, characterization and photocatalytic properties

In the present study, Bi₅O₇NO₃ and Ag/Bi₅O₇NO₃ composites, as novel efficient photocatalysts, were synthesized via a one-step solution combustion synthesis (SCS) using bismuth nitrate (Bi(NO₃)₃·5H₂O) as an oxidant, tartaric acid (C₄H₆O₆) as a fuel, and silver nitrate (AgNO₃) as an Ag source.

β-Bi2O3 reduction by laser irradiation in a liquid environment

This study reports the structural and stoichiometric modifications of bismuth oxide nanoparticles in the β phase (β-Bi₂O₃) by UV pulsed laser irradiation in water or ethanol solutions.

Facile Aqueous-Phase Synthesis of the PtAu/Bi2O3 Hybrid Catalyst for Efficient Electro-Oxidation of Ethanol

In this work, we present a facile aqueous-phase synthesis of a hybrid catalyst consisting of PtAu alloy supported on Bi₂O₃ microspheres. Multistep reduction of HAuCl₄ and K₂PtCl₄ salts on Bi₂O₃ and subsequent annealing lead to the formation of this hybrid catalyst. To the best of our knowledge, this is the first report of using Bi₂O₃ as a catalyst support in fuel cell applications. The material was characterized by powder X-ray diffraction and various microscopic techniques. This composite showed remarkable activity as well as stability toward the electro-oxidation of ethanol in comparison to commercially available Pt/C. The order of the reactivity was found to be commercial Pt/C (50.4 mA/m²mg_Pt^-1) < Pt/Bi₂O₃(10) (108 mA/m²mg_Pt^-1) < PtAu/Bi₂O₃(10) (459 mA/m²mg_Pt^-1). The enhancement in the activity can be explained through cooperative effects, namely, ligand effects of gold and Bi₂O₃ support, which helps in removing carbon monoxide molecules to avoid the poisoning of the Pt active sites.

A {110} facet predominated Bi6O6(OH)3(NO3)3·1.5H2O photocatalyst: selective hydrothermal synthesis and its superior photocatalytic activity for degradation of phenol

A Bi₆O₆(OH)₃(NO₃)₃·1.5H₂O photocatalyst with predominant {110} facets but a low BET surface area was selectively prepared. It exhibits high photocatalytic activities for degradation of phenol.

l-Asparagine-assisted synthesis of flower-like β-Bi2O3 and its photocatalytic performance for the degradation of 4-phenylphenol under visible-light irradiation

By introducing l-asparagine as a ligand, a flower-like precursor of Bi₂O₃ was prepared by a simple reflux process under atmospheric pressure. β-Bi₂O₃ was then conveniently obtained by decomposing the precursor and stabilized in a temperature range from room temperature to 420 °C due to the surface-coordination effects of CO₃²⁻ derived from l-asparagine.