Cerium(IV) oxide nanocomposites: Catalytic properties and industrial application

Nanomaterials Aspects for Photocatalysis as Potential for the Inactivation of COVID-19 Virus

Coronavirus disease-2019 is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and is the most difficult recent global outbreak. Semiconducting materials can be used as effective photocatalysts in photoactive technology by generating various reactive oxidative species (ROS), including superoxide (•O2−) and hydroxyl (•OH) radicals, either by degradation of proteins, DNA, and RNA or by inhibition of cell development through terminating the cellular membrane. This review emphasizes the capability of photocatalysis as a reliable, economical, and fast-preferred method with high chemical and thermal stability for the deactivation and degradation of SARS-CoV-2. The light-generated holes present in the valence band (VB) have strong oxidizing properties, which result in the oxidation of surface proteins and their inactivation under light illumination. In addition, this review discusses the most recent photocatalytic systems, including metals, metal oxides, carbonaceous nanomaterials, and 2-dimensional advanced structures, for efficient SARS-CoV-2 inactivation using different photocatalytic experimental parameters. Finally, this review article summarizes the limitations of these photocatalytic approaches and provides recommendations for preserving the antiviral properties of photocatalysts, large-scale treatment, green sustainable treatment, and reducing the overall expenditure for applications.

Insights from a Bibliometrics-Based Analysis of Publishing and Research Trends on Cerium Oxide from 1990 to 2020

The purpose of this study is to evaluate the literature for research trends on cerium oxide from 1990 to 2020 and identify gaps in knowledge in the emerging application(s) of CeONP. Bibliometric methods were used to identify themes in database searches from PubMed, Scopus and Web of Science Core Collection using SWIFT-Review, VOSviewer and SciMAT software programs. A systematic review was completed on published cerium oxide literature extracted from the Scopus database (n = 17,115), identifying themes relevant to its industrial, environmental and biomedical applications. A total of 172 publications were included in the systematic analysis and categorized into four time periods with research themes identified; "doping additives" (n = 5, 1990-1997), "catalysts" (n = 32, 1998-2005), "reactive oxygen species" (n = 66, 2006-2013) and "pathology" (n = 69, 2014-2020). China and the USA showed the highest number of citations and publications for cerium oxide research from 1990 to 2020. Longitudinal analysis showed CeONP has been extensively used for various applications due to its catalytic properties. In conclusion, this study showed the trend in research in CeONP over the past three decades with advancements in nanoparticle engineering like doping, and more recently surface modification or functionalization to further enhanced its antioxidant abilities. As a result of recent nanoparticle engineering developments, research into CeONP biological effects have highlighted its therapeutic potential for a range of human pathologies such as Alzheimer's disease. Whilst research over the past three decades show the versatility of cerium oxide in industrial and environmental applications, there are still research opportunities to investigate the potential beneficial effects of CeONP in its application(s) on human health.

Confinement chemistry of FeOx centers for activating molecular oxygen under ambient conditions

Activating molecular oxygen under mild conditions is highly important for developing advanced green technologies and for understanding the origin and running of life as well, which still remains a challenge. In this work, we report on the confinement chemistry for activating molecular oxygen over oxides under mild conditions by presenting the synthesis and characterization of FeO_x species confined to the pores of support CeO₂ nanospheres. Active catalytic materials are obtained by a controllable three-step method via the formation of porous CeO₂ nanospheres that have an average diameter of 120 nm and exhibit a large surface area of 168 m² g^-1 and a pore size of 18.7 nm, confining FeO_x in intimate contact with ultra-small Pt particles in pores. The optimized PtO_y-FeO_x/CeO₂-H catalyst showed an excellent performance in the preferential oxidation of CO reactions, as featured by 100% CO conversion at room temperature with almost no attenuation in a prolonged operation, which could not be accessible without pore-confined FeO_x centers. Mechanical studies prove that the reaction progresses via abnormal non-competitive adsorption associated with synergistic roles from uniform loading, stabilization of divalent Fe species, surface oxygen activation on CeO₂ supports, and the reduced H₂ spillover effect on Pt⁰, making the CO species adsorbed on Pt^δ+ easier to be desorbed. The methodology demonstrated here may inspire one to explore more advanced catalysts with high activity at room temperature essential for a wide range of applications.

Photocatalytic oxidation degradation of inhibitory fatty acids for aged Chlorella vulgaris cultivation medium recycling

The medium used for Chlorella vulgaris cultivation exerted obvious inhibitory effects on the growth of C. vulgaris after several culture-harvest cycles. The accumulated fatty acids secreted by C. vulgaris during their growth process were expected to be the cell inhibition components. In this work, the ultraviolet-driven photocatalytic oxidation technique was applied for the degradation of microalgae cell growth inhibition components in the aged cultivation medium, and the reaction parameters were optimized. The results indicated that the photocatalytic oxidation processes using 0.5 g/L [Formula: see text] NPs as the catalyst under the aeration condition showed as high as 74.61 ± 4.60% FA degradation efficiency after 20 min illumination, and the contents of -COOH, [Formula: see text] (α) and -COO-R functional groups in the aged C. vulgaris medium were significantly reduced. In addition, the modification of the photocatalyst further improved the ability of the degradation of FA. When the modified [Formula: see text]/AC and [Formula: see text]/Ag catalysts were applied, the FA degradation rates reached as high as 92.46 ± 0.37% and 93.91 ± 1.37%, respectively. In the recycled medium treated with [Formula: see text]/AC, the cell density in the stable phase reached 96.33 ± 1.83% of that in the fresh medium as the control. In summary, the photocatalytic oxidation with the modified [Formula: see text]/AC catalyst was proposed as the efficient strategy to realize the recycling of the aged C. vulgaris cultivation medium via the degradation of the FA as the cell growth inhibitors.

Selective laser welding in liquid: A strategy for preparation of high-antibacterial activity nanozyme against Staphylococcus aureus

Nanozyme was considered as one of the most promising substitutes for antibiotics, due to the selective catalysis for pathogens. In this work, a high-antibacterial activity SOD-like nanozyme based on hybrid Ag/CeO₂ nanocomposite was facilely prepared by using an innovative approach of selective laser welding in liquid. This prepared nanozyme displayed a high antimicrobial effect against Staphylococcus aureus under visible light illumination, the sterilization rate as high as 82.4%, which was 2.93 and 2.99 times higher than those of pure Ag and pure CeO₂, respectively. The enhanced antibacterial activity was attributed to the anchoring of Ag nanospheres on the surface of CeO₂ nanosheets, which induced the reduction of CeO₂ bandgap and boosted the visible light harvesting. Therefore, the charge carriers can be effectively stimulated to produce abundant reactive oxygen species on the Ag/CeO₂ nanocomposite via a SOD-like route. This work demonstrated a facile strategy for the preparation of high-antibacterial activity nanozyme, giving it great potential for scalable application in the biomedical and pharmaceutical industry.

Ingestion and effects of cerium oxide nanoparticles on Spodoptera frugiperda (Lepidoptera: Noctuidae)

The objective of this study was to evaluate the biological and nutritional characteristics of Spodoptera frugiperda (Lepidoptera: Noctuidae), an arthropod pest widely distributed in agricultural regions, after exposure to nano-CeO₂ via an artificial diet and to investigate the presence of cerium in the body of this insect through X-ray fluorescence mapping. Nano-CeO₂, micro-CeO₂, and Ce(NO₃)₃ were incorporated into the diet (0.1, 1, 10, and 100 mg of Ce L^-1). Cerium was detected in caterpillars fed with diets containing nano-CeO₂ (1, 10 and 100 mg of Ce L^-1), micro-CeO₂ and Ce(NO₃)₃, and in feces of caterpillars from the first generation fed diets with nano-CeO₂ at 100 mg of Ce L^-1 as well. The results indicate that nano-CeO₂ caused negative effects on S. frugiperda. After it was consumed by the caterpillars, the nano-CeO₂ reduced up to 4.8% of the pupal weight and 60% of egg viability. Unlike what occurred with micro-CeO₂ and Ce(NO₃)₃, nano-CeO₂ negatively affected nutritional parameters of this insect, as consumption rate two times higher, increase of up to 80.8% of relative metabolic rate, reduction of up to 42.3% efficiency of conversion of ingested and 47.2% of digested food, and increase of up to 1.7% of metabolic cost and 8.7% of apparent digestibility. Cerium caused 6.8-16.9% pupal weight reduction in second generation specimens, even without the caterpillars having contact with the cerium via artificial diet. The results show the importance of new ecotoxicological studies with nano-CeO₂ for S. frugiperda in semi-field and field conditions to confirm the toxicity.