Synthesis of a Flaky CeO2 with Nanocrystals Used for Polishing

It is important to adapt the morphology of CeO2 to different applications. A novel flaky CeO2 with nanocrystals was successfully synthesized using the ordinal precipitation method and calcination. The size of the flaky CeO2 was about 10 μm, and the nanocrystals were about 100 nm. Under the action of the precipitant NH4HCO3, Ce3+ nucleated in large quantities. The nanosized crystals gathered into flakes driven by the surface energy. As the calcination temperature increased, the grains grew slowly by mass transfer due to the slow diffusion of reactants. By adding AlOOH to the starting material, the Al3+ doped into the CeO2 increased the content of Ce3+ in the CeO2, which improved the chemical activity of the CeO2. When the starting material's Al:Ce ratio was 5:1, the Ce3+ increased to 31.11% in the CeO2, which provided good application potential in the polishing field. After polishing by the slurry of flaky CeO2 for 1 h, the SiC surface roughness reduced from 464 nm to 11 nm.

In Situ Construction of Near-Infrared Response Hybrid Up-Conversion Photocatalyst for Degrading Organic Dyes and Antibiotics

Unique nonlinear optical properties for converting low-energy incident light into high-energy radiation enable up-conversion materials to be employed in photocatalytic systems. An efficient near-infrared (NIR) response photocatalyst was successfully fabricated through a facile two-step method to load BiOBr on the Nd3+, Er3+@NaYF4 (NE@NYF) up-conversion material. The NE@NYF can transform NIR into visible and UV light and promote charge-energy transfer in the semiconductor. Consequently, the as-obtained photocatalysts exhibit excellent photodegradation performance for rhodamine B dye (RhB) and tetracycline (TC) organic pollutants. About 98.9% of the RhB was decomposed within 60 min with the 20% NE@NYF-B sample, outperforming the pristine BiOBr (61.9%). In addition, the 20% NE@NYF-B composite could decompose approximately 72.7% of the organic carbon during a 10 h reaction, which was almost two-fold more than that of BiOBr. Meanwhile, a possible charge transfer mechanism is proposed based on the recombination of electron-hole pairs and reactive oxygen species. This work provides a rational hybrid structure photocatalyst for improving photocatalytic performance in the broadband spectrum and provides a new strategy for NIR light utilization.

Green synthesis of cerium oxide nanoparticles using zucchini peel extract for cytotoxic and photocatalytic properties

The aim of this study is the green synthesis of cerium oxide nanoparticles (CeO₂-NPs) using a natural capping agent and its application in water and wastewater treatment. This study presents the biosynthesis of CeO₂-NPs by the exertion of a green method using zucchini (Cucurbita pepo) extract as a capping agent. Synthesized CeO₂-NPs were distinguished through TGA/DTA, FT-IR, XRD, FESEM/TEM and EDX/PSA, and DRS procedures. According to the XRD pattern of NPs, the crystallinity structure was a face-centered cubic (fcc) with an Fm3m space group and the size was estimated at 30 nm. The spherical morphology of NPs was confirmed through FESEM/TEM images. In the following, the photocatalytic property of NPs was investigated by the decolorization of methylene blue (MB) dye within UV-A light. Also, the cytotoxicity of NPs on the CT26 cell line was evaluated through the MTT test, and no toxicity was observed in the results, which indicates their biocompatibility.

Solar light-based advanced oxidation processes for degradation of methylene blue dye using novel Zn-modified CeO2@biochar

Herein, a novel nanocomposite, namely, Zn-modified CeO₂@biochar (Zn/CeO₂@BC), is synthesized via facile one-step sol-precipitation to study its photocatalytic activity towards the removal of methylene blue dye. Firstly, Zn/Ce(OH)₄@biochar was precipitated by adding sodium hydroxide to cerium salt precursor; then, the composite was calcined in a muffle furnace to convert Ce(OH)₄ into CeO₂. The crystallite structure, topographical and morphological properties, chemical compositions, and specific surface area of the synthesized nanocomposite are characterized by XRD, SEM, TEM, XPS, EDS, and BET analysis. The nearly spherical Zn/CeO₂@BC nanocomposite has an average particle size of 27.05 nm and a specific surface area of 141.59 m²/g. All the tests showed the agglomeration of Zn nanoparticles over the CeO₂@biochar matrix. The synthesized nanocomposite showed remarkable photocatalytic activity towards removing methylene blue, an organic dye commonly found in industrial effluents. The kinetics and mechanism of Fenton-activated dye degradation were studied. The nanocomposite exhibited the highest degradation efficiency of 98.24% under direct solar irradiation of 90 min, at an optimum dosage of 0.2 g l^-1 catalyst and 10 ppm dye concentration, in the presence of 25% (V/V) 0.2 ml (4 µl/ml) hydrogen peroxide. The hydroxyl radical generated from H₂O₂ during the photo-Fenton reaction process was attributed to the nanocomposite's improved photodegradation performance. The degradation process followed pseudo-first-order kinetics having a rate constant (k) value of 0.0274 min^-1.

Coffee-waste templated CeOx/TiO2 nanostructured materials for selective photocatalytic oxidations

An environmentally friendly solvent-free approach was tested using spent coffee as a biomass sacrificial template for the preparation of TiO₂ modified with CeO_x. The use of coffee as a template pursues the preparation of a nanostructured heterojunction without the need for a solvent. Two variables were optimized in the synthesis process, i.e. calcination temperature and proportion of CeO_x. Firstly, bare coffee-template titania was prepared to explore the effect of the calcination temperature, within 500-650 °C. The anatase phase was obtained up to 600 °C. Higher temperatures, i.e. 650 °C, led to the appearance of rutile (10%) and efficient removal of the sacrificial agent (0.6% residue). The maximum photocatalytic activity in terms of conversion, in the oxidation of benzyl alcohol, was achieved employing the bare coffee-template TiO₂ at 650 °C, and it was found comparable to the benchmarked P25. The incorporation of ceria in the solvent-free approach considerably improved photocatalytic benzaldehyde production. No changes in the XRD pattern of TiO₂ were appreciated in the presence of ceria due to the low amount added, within 1.5-6.0%, confirmed by XPS as superficial Ce³⁺/Ce⁴⁺. The UV-visible absorption spectra were considerably redshifted in the presence of Ce, reducing the bandgap values of bare titania. An optimum amount of ceria in the structure within 3-0% was found. In this case, the selectivity towards benzaldehyde was ca. 75%, 3 times higher than the selectivity value registered for the benchmarked P25 or the bare prepared TiO₂.

Recent Advances in the Design and Photocatalytic Enhanced Performance of Gold Plasmonic Nanostructures Decorated with Non-Titania Based Semiconductor Hetero-Nanoarchitectures

Plasmonic photocatalysts combining metallic nanoparticles and semiconductors have been aimed as versatile alternatives to drive light-assisted catalytic chemical reactions beyond the ultraviolet (UV) regions, and overcome one of the major drawbacks of the most exploited photocatalysts (TiO2 or ZnO). The strong size and morphology dependence of metallic nanostructures to tune their visible to near-infrared (vis-NIR) light harvesting capabilities has been combined with the design of a wide variety of architectures for the semiconductor supports to promote the selective activity of specific crystallographic facets. The search for efficient heterojunctions has been subjected to numerous studies, especially those involving gold nanostructures and titania semiconductors. In the present review, we paid special attention to the most recent advances in the design of gold-semiconductor hetero-nanostructures including emerging metal oxides such as cerium oxide or copper oxide (CeO2 or Cu2O) or metal chalcogenides such as copper sulfide or cadmium sulfides (CuS or CdS). These alternative hybrid materials were thoroughly built in past years to target research fields of strong impact, such as solar energy conversion, water splitting, environmental chemistry, or nanomedicine. Herein, we evaluate the influence of tuning the morphologies of the plasmonic gold nanostructures or the semiconductor interacting structures, and how these variations in geometry, either individual or combined, have a significant influence on the final photocatalytic performance.

A CeO2 Semiconductor as a Photocatalytic and Photoelectrocatalytic Material for the Remediation of Pollutants in Industrial Wastewater: A Review

The direct discharge of industrial wastewater into the environment results in serious contamination. Photocatalytic treatment with the application of sunlight and its enhancement by coupling with electrocatalytic degradation offers an inexpensive and green technology enabling the total removal of refractory pollutants such as surfactants, pharmaceuticals, pesticides, textile dyes, and heavy metals, from industrial wastewater. Among metal oxide—semiconductors, cerium dioxide (CeO2) is one of the photocatalysts most commonly applied in pollutant degradation. CeO2 exhibits promising photocatalytic activity. Nonetheless, the position of conduction bands (CB) and valence bands (VB) in CeO2 limits its application as an efficient photocatalyst utilizing solar energy. Its photocatalytic activity in wastewater treatment can be improved by various modification techniques, including changes in morphology, doping with metal cation dopants and non-metal dopants, coupling with other semiconductors, and combining it with carbon supporting materials. This paper presents a general overview of CeO2 application as a single or composite photocatalyst in the treatment of various pollutants. The photocatalytic characteristics of CeO2 and its composites are described. The main photocatalytic reactions with the participation of CeO2 under UV and VIS irradiation are presented. This review summarizes the existing knowledge, with a particular focus on the main experimental conditions employed in the photocatalytic and photoelectrocatalytic degradation of various pollutants with the application of CeO2 as a single and composite photocatalyst.

Bio-inspired construction of melanin-like polydopamine-coated CeO2 as a high-performance visible-light-driven photocatalyst for hydrogen production

In recent years, cerium oxide has been the most widely studied photocatalyst due to its unique properties.

NIR light-activated upconversion semiconductor photocatalysts

Harvesting of near infrared (NIR) light in the abundant and environmentally friendly solar spectrum is particularly significant to enhance the utilization rate of the cleanest energy on earth. Appreciating the unique nonlinear optical properties of upconversion materials for converting low-energy incident light into high-energy radiation, they become the most promising candidates for fabricating NIR light-active photocatalytic systems by integrating with semiconductors. The present review summarizes recent NIR light-active photocatalytic systems based on a sequence of NaYF₄-based, fluoride-based, oxide-based and Ln³⁺ ion-doped semiconductor-based photocatalysts for degradation of organic molecules. In addition, we provide an in-depth analysis of various photocatalytic mechanisms and enhancement effects for efficient photo-redox performance of different upconversion semiconductor photocatalysts. We envision that this review can inspire multidisciplinary research interest in rational design and fabrication of efficient full-spectrum active (UV-visible-NIR) photocatalytic systems and their wider applications in solar energy conversion.

Large enhanced photocatalytic activity of g-C3N4 by fabrication of a nanocomposite with introducing upconversion nanocrystal and Ag nanoparticles

A novel heterostructured nanocomposite UCNPs@SiO2@Ag/g-C3N4 was developed for the first time to substantially boost the solar-light driven photocatalytic activity of g-C3N4. Its photocatalytic properties and photocatalytic mechanism were investigated. The as-synthesized photocatalyst with excellent improvement in the solar absorption and separation efficiency of photoinduced electron-hole pairs exhibited optimum solar-induced photocatalytic activity in dye degradation and hydrogen production. The experimental results showed that the rates of degradation of Rhodamine B (RhB) and hydrogen evolution were about 10 and 12 times higher than that of pristine g-C3N4, respectively. The excellent photocatalytic activity was attributed to the synergetic effect of upconversion nanoparticles (UCNPs) and Ag nanoparticles (NPs) on the modification of the photocatalytic properties of g-C3N4, resulting in a broad light response range for g-C3N4 as well as the fast separation and slow recombination of photoinduced electron-hole pairs. This study provides new insight into the fabrication of g-C3N4-based nanocomposite photocatalysts with high catalytic efficiency through the artful assembly of UCNPs, Ag NPs and g-C3N4 into a hetero-composite nanostructure. The prominent improvement in photocatalytic activity enables the potential application of g-C3N4 in the photocatalytic degradation of organic pollutants and hydrogen production utilizing solar energy.