Fabrication of CeO2 nanoparticles decorated three-dimensional flower-like BiOI composites to build p-n heterojunction with highly enhanced visible-light photocatalytic performance

Enhancing the adsorption-photocatalytic efficiency of BiOBr for Congo red degradation by tuning the surface charge and bandgap via an Y3+-I- co-doping strategy

Metal-ion doping and halogen substitution have been largely applied to tune the bandgap of bismuth oxybromide (BiOBr) to upgrade its photodegradation capacity. In this work, the adsorption capacity and photocatalytic behavior of solvothermally synthesized BiOBr photocatalysts can be optimized via the synergistic effect of Y3+- and I--doping. After an adsorption reaction in the dark and exposure for another 80 min to visible light, pure BiOBr can remove 46.5% of Congo red (CR) from water with an initial CR concentration of 50 mg L-1. Meanwhile, Bi0.8Y0.20OBr0.97I0.03, the co-doped catalyst, displays total degradation rates exceeding 98% and 92% with CR dosages of 50 and 100 mg L-1, respectively, demonstrating a doubled degradation capacity. With the co-doping solution, the negative charges on the catalysts reduce, more oxygen vacancies are generated, the bandgap remarkably narrows, and the photoabsorption range broadens for derivation of photoinduced electron-hole pairs. The mechanism for optimized photodegradation behavior and dramatically increased adsorption capacity are discussed based on analyses of the structural evolution, surface properties including the chemical state and surface charge, electrochemical performance and the yield/type of photogenerated species. Density functional theory (DFT) simulations were conducted to investigate the structural state, density of states (DOS) and electrostatic potential.

Photocatalytic Co-Reduction of N2 and CO2 with CeO2 Catalyst for Urea Synthesis

The effective conversion of carbon dioxide (CO2 ) and nitrogen (N2 ) into urea by photocatalytic reaction under mild conditions is considered to be a more environmentally friendly and promising alternative strategies. However, the weak adsorption and activation ability of inert gas on photocatalysts has become the main challenge that hinder the advancement of this technique. Herein, we have successfully established mesoporous CeO2-x nanorods with adjustable oxygen vacancy concentration by heat treatment in Ar/H2 (90 % : 10 %) atmosphere, enhancing the targeted adsorption and activation of N2 and CO2 by introducing oxygen vacancies. Particularly, CeO2 -500 (CeO2 nanorods heated treatment at 500 °C) revealed high photocatalytic activity toward the C-N coupling reaction for urea synthesis with a remarkable urea yield rate of 15.5 μg/h. Besides, both aberration corrected transmission electron microscopy (AC-TEM) and Fourier transform infrared (FT-IR) spectroscopy were used to research the atomic surface structure of CeO2 -500 at high resolution and to monitor the key intermediate precursors generated. The reaction mechanism of photocatalytic C-N coupling was studied in detail by combining Density Functional Theory (DFT) with specific experiments. We hope this work provides important inspiration and guiding significance towards highly efficient photocatalytic synthesis of urea.

Fabrication of a P-Si/ZnO heterojunction based on galvanic cell driven and the complete degradation of RhB via fast charge transfer

Semiconductor heterojunctions can significantly enhance photocatalytic degradation efficiency by facilitating rapid interfacial charge transfer. This article is based on the galvanic-cell driven principle; porous silicon (P-Si) was prepared by the carbon-catalytic etching method, and ZnO was loaded on its surface via electroless chemical deposition technology to form a P-Si/ZnO heterojunction, which was applied to the degradation of Rhodamine B (RhB). At a deposition temperature of 90 °C, a flawless 1D hexagonal prism structure of ZnO was formed, allowing the P-Si/ZnO heterojunction to completely degrade RhB within 2 hours with a degradation rate of 100%. Compared with a single P-Si material, the degradation performance is improved by 1.7 times. The formation of the built-in electric field and the rapid charge transfer at the heterojunction interface realized the complete degradation of RhB organic pollutants. After 20 cycles of use, the photocatalytic degradation rate remains above 70%, demonstrating excellent stability and recyclability.

BiOI@CeO2@Ti3C2 MXene composite S-scheme photocatalyst with excellent bacteriostatic properties

As an influential antifouling material, photocatalytic materials have drawn attention increasingly over recent years owing to their potential bacteriostatic property in the domain of marine antifouling. Herein, a flower-like BiOI@CeO2@Ti3C2 S-scheme photocatalyst was contrived and prepared by hydrothermal method. The innovative combination of Ti3C2 and narrow band gap semiconductor BiOI was implemented to modify CeO2 and the photocatalytic bacteriostatic mechanism of BiOI@CeO2@Ti3C2 was elucidated. Schottky junction was formed between CeO2 and Ti3C2, and a p-n junction was formed between CeO2 and BiOI. By photoelectrochemical characterization, BCT-10 exhibits the best photoelectrochemical performance of which photogenerated carrier transport can be performed more readily at 10 % CeO2@Ti3C2 addition. 99.76 % and 99.89 % of photocatalytic bacteriostatic efficiency of BCT-10 against Escherichia coli and Staphylococcus aureus were implemented respectively, which were 2.98 and 3.07 times higher than that of pure CeO2. The ternary heterojunction can suppress photogenerated electron-hole complexes more effectively and enhance the photocatalytic bacteriostatic effect of CeO2, which also provided a new concept to the further broadened application of CeO2 in the marine bacteriostatic and antifouling field.

A sandwiched photoelectrochemical biosensing platform for detecting Cytokeratin-19 fragments based on Ag2S-sensitized BiOI/Bi2S3 heterostructure amplified by sulfur and nitrogen co-doped carbon quantum dots

A sandwiched photoelectrochemical (PEC) immunosensor based on BiOI/Bi₂S₃/Ag₂S was designed for the quantitative detection of cytokeratin-19 fragments (CYFRA21-1) in serum. In this work, due to the intervention of the narrow band gap Bi₂S₃, the absorption of the light source by the BiOI/Bi₂S₃ heterostructure has been significantly enhanced. Meanwhile, the matched band structure of BiOI, Bi₂S₃ and Ag₂S promoted the rapid transfer of electrons between the conduction bands and effectively inhibited the recombination of electron-hole pairs, thus enhanced the photoelectric signals. Sulfur and nitrogen co-doped carbon quantum dots (S,N-CQDs) with up-conversion luminescence properties provided more light energy for the base materials. On the other hand, S,N-CQDs were combined with Ab₂ through polydopamine (PDA), as secondary antibody labels, further enhanced the sensitivity of the sensor. Herein, the linear range of the sensor was from 0.001 to 100 ng mL^-1 and the detection limit was 1.72 pg mL^-1. In addition, the sensor provides a feasible way for the detection of tumor markers due to its excellent selectivity, repeatability and good stability.

A critical review on relationship of CeO2-based photocatalyst towards mechanistic degradation of organic pollutant

Nanostructured photocatalysts commonly offered opportunities to solve issues scrutinized with the environmental challenges caused by steep population growth and rapid urbanization. This photocatalyst is a controllable characteristic, which can provide humans with a clean and sustainable ecosystem. Over the last decades, one of the current thriving research focuses on visible-light-driven CeO₂-based photocatalysts due to their superior characteristics, including unique fluorite-type structure, rigid framework, and facile reducing oxidizing properties of cerium's tetravalent (Ce⁴⁺) and trivalent (Ce³⁺) valence states. Notwithstanding, owing to its inherent wide energy gap, the solar energy utilization efficiency is low, which limits its application in wastewater treatment. Numerous modifications of CeO₂ have been employed to enhance photodegradation performances, such as metals and non-metals doping, adding support materials, and coupling with another semiconductor. Besides, all these doping will form a different heterojunction and show a different way of electron-hole migration. Compared to conventional heterojunction, advanced heterojunction types such as p-n heterojunction, Z-scheme, Schottky junction, and surface plasmon resonance effect exhibit superior performance for degradation owing to their excellent charge carrier separation, and the reaction occurs at a relatively higher redox potential. This review attends to providing deep insights on heterojunction mechanisms and the latest progress on photodegradation of various contaminants in wastewater using CeO₂-based photocatalysts. Hence, making the CeO₂ photocatalyst more foresee and promising to further development and research.

Recent Advances in MnOx/CeO2-Based Ternary Composites for Selective Catalytic Reduction of NOx by NH3: A Review

Recently, manganese oxides (MnOx)/cerium(IV) oxide (CeO2) composites have attracted widespread attention for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with ammonia (NH3), which exhibit outstanding catalytic performance owing to unique features, such as a large oxygen storage capacity, excellent low-temperature activity, and strong mechanical strength. The intimate contact between the components can effectively accelerate the charge transfer to enhance the electron–hole separation efficiency. Nevertheless, MnOx/CeO2 still reveals some deficiencies in the practical application process because of poor thermal stability, and a low reduction efficiency. Constructing MnOx/CeO2 with other semiconductors is the most effective strategy to further improve catalytic performance. In this article, we discuss progress in the field of MnOx/CeO2-based ternary composites with an emphasis on the SCR of NOx by NH3. Recent progress in their fabrication and application, including suitable examples from the relevant literature, are analyzed and summarized. In addition, the interaction mechanisms between MnOx/CeO2 catalysts and NOx pollutants are comprehensively dissected. Finally, the review provides basic insights into prospects and challenges for the advancement of MnOx/CeO2-based ternary catalysts.

Efficient hydrogen generation of vector Z-scheme CaTiO3/Cu/TiO2 photocatalyst assisted by cocatalyst Cu nanoparticles

Herein, the CaTiO₃/Cu/TiO₂ all-solid-state Z-scheme heterojunction is successfully designed via Cu nanoparticles situating at the interface between CaTiO₃ and TiO₂ with a new synthesis route. Interestingly, TiO₂ nanosheets are generated in-situ on the surface of CaTiO₃ in the second step hydrothermal reaction. The lifetimes of photoexcited carriers, photoluminescence emission spectra and transient photocurrent response tests have confirmed that the efficient Z-scheme charge transmission path of the CaTiO₃/Cu/TiO₂ is beneficial to facilitate the separation of photogenerated carriers and reduce their recombination efficiency. As expected, the hydrogen generation rate of CaTiO₃/Cu/TiO₂ is increased to 23.550 mmol g^-1h^-1 with the appropriate amount of copper loading, which is about 981 times and 93 times higher than that of pristine CaTiO₃ (0.024 mmol g^-1h^-1) and CaTiO₃/TiO₂ (0.253 mmol g^-1h^-1), respectively. Furthermore, the CaTiO₃/Cu/TiO₂ sample shows good stability in cycle experiments. Particularly, experimental results show that the non-noble metal Cu nanoparticles can be an effective electron mediator. And these merits strongly demonstrate that the CaTiO₃/Cu/TiO₂ composites have potential application in photocatalytic field. This study can provide fundamental guidance for designing rationally efficient non-noble metal vector Z-scheme system photocatalysts with outstanding photocatalytic H₂ generation performance.

Defect Engineering Enhances the Charge Separation of CeO2 Nanorods toward Photocatalytic Methyl Blue Oxidation

Defect-rich photocatalytic materials with excellent charge transfer properties are very popular. Herein, Sm-doped CeO₂ nanorods were annealed in a N₂ atmosphere to obtain the defective Sm-doped CeO₂ photocatalysts (Vo–Sm–CeO₂). The morphology and structure of Vo–Sm–CeO₂ were systematically characterized. The Vo–Sm–CeO₂ nanorods demonstrated an excellent photodegradation performance of methyl blue under visible light irradiation compared to CeO₂ nanorods and Sm–CeO₂. Reactive oxygen species including OH, ·O₂⁻, and h⁺ were confirmed to play a pivotal role in the removal of pollutants via electron spin resonance spectroscopy. Doping Sm enhances the conductivity of CeO₂ nanorods, benefiting photogenerated electrons being removed from the surface reactive sites, resulting in the superior performance.

Design and performance of a novel direct Z-scheme NiGa2O4/CeO2 nanocomposite with enhanced sonocatalytic activity

A novel direct Z-scheme NiGa₂O₄/CeO₂ nanocomposite was designed and prepared via simple sol-hydrothermal and calcination methods, and its sonocatalytic activity was tested by studying the degradation of a model antimicrobial agent, malachite green (MG), under ultrasonic irradiation. Near complete (96.2%) degradation of MG (at 10 mg/L) could be achieved by the NiGa₂O₄/CeO₂ nanocomposite (at 1.0 g/L) after ultrasonic irradiation (40 kHz, 300 W) for 60 min at 25 °C. Under the same conditions, only 51.2 and 72.0% of the MG degraded in the presence of NiGa₂O₄ and CeO₂ (at 1.0 g/L), respectively. These results demonstrate that the direct Z-scheme NiGa₂O₄/CeO₂ nanocomposite has excellent sonocatalytic activity, which is attributed to the matching band-gaps between NiGa₂O₄ and CeO₂. The sonocatalytic activity of NiGa₂O₄/CeO₂ nanocomposite decreased by 17% after four cycles of reuse, which is indicative of relatively good reusability. Scavenging experiments revealed that sonocatalytic degradation of MG results from the combined action of hydroxyl radicals (OH) and holes (h⁺), with the latter having a greater contribution. The pathways and mechanism of MG degradation were proposed based on the degradation intermediates detected. The results demonstrate that the prepared direct Z-scheme NiGa₂O₄/CeO₂ nanocomposite worked as designed and exhibited high and stable sonocatalytic activity during MG degradation, and could thus serve as a promising candidate in sonocatalytic treatment of other organic pollutants in wastewaters. The findings also provide new insights on the mechanism of sonocatalytic degradation and the design of efficient Z-scheme sonocatalysts.

Room-temperature synthesized In-BiOBr1-xIx nanosheets with visible-light-driven superior photocatalytic activity: Degradation of dye/non-dye organic pollutants for environmental remediation

Photocatalysis is extensively investigated as a green, efficient and promising technique for environmental remediation. In this study, a series of template free In-doped BiOBr_xI_1-x photocatalysts have been successfully prepared at room temperature and characterized by various methods. Complete degradation of negatively charged methyl Orange, positively charged Rhodamine B and Methylene Blue organic dyes, and neutral and colorless non-dye organic compound of furfural was attained. The flat band potential offered the possibility of reduction of dissolved O₂ to O₂^.- in the conduction band while the trapping experiment identified the (O₂^.-)is the main radical species followed by h⁺ for the photodegradation. In-BiOBrI-0.4 had an excellent photocatalytic degradation activity which could be due to the synergetic effect between metal ion doping and solid solution formation. It further promotes visible light-harvesting ability and photoinduced charge carrier separation efficiency. The order of the reaction rate was determined and the mechanism was proposed. This work can lay a base for the design of effective photocatalyst toward environmental remediation.

Quaternary CZTS nanoparticle decorated CeO2 as a noble metal free p–n heterojunction photocatalyst for efficient hydrogen evolution

Practical implementation of photocatalytic hydrogen production has been required for the invention of efficient visible light absorption and low cost photocatalyst materials.

Fabrication of a Z-scheme AgBr/Bi4O5Br2 nanocomposite and its high efficiency in photocatalytic N2 fixation and dye degradation

Z-scheme AgBr/Bi₄O₅Br₂ nanocomposite was synthesized via a simple ion-exchange method and firstly applied in photocatalytic N₂ fixation under simulated sunlight.

Photocatalytic degradation of bisphenol A over a ZnFe2O4/TiO2 nanocomposite under visible light

A ZnFe₂O₄-TiO₂ nanocomposite combining p-type ZnFe₂O₄ and n-type TiO₂ was successfully fabricated. The ZnFe₂O₄-TiO₂ nanocomposite greatly enhanced the bisphenol A (BPA) photodegradation under visible light irradiation at 465 ± 40 nm. Loading TiO₂ with 1 wt% of ZnFe₂O₄ produced high photocurrent and low charge transfer resistance. The photodegradation rate of BPA by ZnFe₂O₄-TiO₂, which was highly dependent on the water chemistry including pH, anions, and humic acid, was 20.8-21.4 times higher than that of commercial TiO₂ photocatalysts. Chloride and sulfate ions enhanced BPA photodegradation mostly due to the production of more radical species; whereas nitrate, dihydrogen phosphate, and bicarbonate ions decreased the photodegradation rate of BPA due to the scavenge of hydroxyl radicals. The photoactivity and recyclability of ZnFe₂O₄-TiO₂ in lake water was also assessed. A near complete BPA removal from lake water was observed under visible light irradiation. Furthermore, >90% of photocatalytic activity toward BPA degradation was achieved in 5 cycles of continuous addition of BPA to the lake water. The BPA degradation intermediates were identified by HPLC/MS/MS and possible reaction pathways were proposed. Results clearly demonstrate the excellent visible-light-sensitive photocatalytic degradation of BPA over ZnFe₂O₄-TiO₂ composite which has a great application potential for the decomposition of emerging contaminants in impaired waters.